Solar Energy and Technology / Encyclopedia [2] 3110475774, 9783110475777

Table of contents :
Preface
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z

Citation preview

Goran Mijic Solar Energy and Technology Volume 2

Also of interest Solar Energy and Technology Volume 1: English-German Dictionary / Deutsch-Englisch Wörterbuch Mijic, 2016 ISBN 978-3-11-047575-3, e-ISBN 978-3-11-047717-7

Green Energy Efficient Processes for Functional Materials Lublow, 2018 ISBN 978-3-11-049690-1, e-ISBN 978-3-11-049694-9

Power-to-Gas Renewable Hydrogen Economy for the Energy Transition Boudellal, 2018

ISBN 978-3-11-055881-4, e-ISBN 978-3-11-055981-1

Solar Cells and Energy Materials Oku, 2017 ISBN 978-3-11-029848-2, e-ISBN 978-3-11-029850-5

Organic and Hybrid Solar Cells An Introduction Schmidt-Mende, Weickert, 2016 ISBN 978-3-11-028318-1, e-ISBN 978-3-11-028320-4

Goran Mijic

Solar Energy and Technology Volume 2: Encyclopedia

Author Dr. Goran Mijic Sandy, UT USA

ISBN 978-3-11-047577-7 e-ISBN (PDF) 978-3-11-047721-4 e-ISBN (EPUB) 978-3-11-047592-0 Library of Congress Control Number: 2018950594 Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at http://dnb.dnb.de. © 2018 Walter de Gruyter GmbH, Berlin/Boston Typesetting: Integra Software Services Pvt. Ltd Printing and binding: CPI books GmbH, Leck Cover image: Peng-guang Chen / Hemera / thinkstock www.degruyter.com

To my wife Amira, my daughter Lara, and my mother Brana: The light in my life

Preface The Sun is an immense, constant, inexhaustible source of energy. The amount of energy the Sun sends down to the Earth over a 24-h day averages 164 W/m2. After a sudden burst of radiation from the Sun, particles are accelerated to nearly the speed of light and released into the Sun’s atmosphere. It takes approximately 8 minutes and 20 seconds for moving particles without mass called photons to travel across the vacuum of space from the Sun to the Earth. Photon is both wave and particle. These packets of energy act as waves when traveling through space. When a photon hits a solar panel, it acts as a particle, giving up its energy to an electron. The photosensitive semiconductor material, such as silicon, absorbs the energy of the photons, which is strong enough to knock electrons out of the silicon atoms. The minimum photon energy required to induce photoconductivity and generate mobile electrons and holes is 1.1 eV. With this amount of energy, the excited electrons from the p-type layer are able to cross the p–n junction barrier and enter the n-type layer, starting a current flow. The electrons flow outside of the solar cell to the load and return through the back contact to the p-type semiconductor layer, occupying the vacant positions (holes) and thus closing the circuit. The solar cell output in direct sun is between 3 and 6 A and around 0.5 V. Although humans had been aware of and used, to some extent, the tremendous potential of solar energy dating back to as far as seventh century BC, it was only after the invention of the first silicon photovoltaic cell in 1954 that the science and industry embarked on a rapid solar journey, which is characterized by an ever-accelerating pace of new technologies. Over the past five decades, three generations of solar cells have been developed, competing in today’s global market for best performance, quality, and price: 1. conventional monocrystalline and polycrystalline silicon solar cells; 2. thin-film polymer solar cells; and 3. multijunction solar cells. Solar panels are mainly deployed in three sectors: residential (on home rooftops), commercial (on companies’ rooftops), and utility scale (in solar power plants). In recent years, solar companies and countries have been in a race to maximize energy density, which is the amount of energy that can be produced by a solar module per unit area – Watts per square meter or foot (W/m2 or W/ft2). Nanotechnology plays an important role in the development of miniature structures, such as carbon nanotubes (fullerene, C60), quantum dots, nanowires, nanopillar, nanocrystals, nanofibers, nanoporous filters, nanoparticulate metal oxides, dispersion nanoparticles, nanopin film, and polymer nanocomposites. The tendency in photovoltaic nanoindustry to design and build structures on a very small scale, from 1 to 100 nm, has the capability to significantly increase the energy conversion efficiency. The more efficient the solar panel, the more electricity (W/m2 or W/ft2) can be generated from the same aperture surface of a solar array, which is of vital importance in densely populated urban areas with limited space for solar installation. The rapid development of a wide variety of solar technologies, new semiconductor materials, and solar infrastructure has brought a flood of new words and technical https://doi.org/10.1515/9783110477214-201

VIII 

 Preface

terms. Newly coined words, expressions, and acronyms from the solar field are appearing at an astonishing speed. Due to their novelty and their use as modern technical buzzwords, they often have a vague and ambivalent meaning for users. The goal of this volume is to provide precise definitions of solar terms and ensure the correct usage of neologisms, helping them become widely accepted into the mainstream language. Volume 2 intends to cover all main aspects of solar energy and technology. It serves as a reference for quick learning of particular topics. Students, solar novices, researchers, and solar practitioners of all kinds may use the solar encyclopedia to quickly understand the basics of a specific concept. After reading a brief but thorough entry, users can follow the trace of cross-references to widen the semantic scope of a term and further explore the topic. The development of solar energy and technology holds promise for a brighter future. Together with other renewable energy sources, such as wind and hydro, solar technology promotes the generation of carbon-free sustainable energy. We can manage our development, construction, businesses, and civilization in such a way that we do not deplete the Earth’s natural resources and permanently damage our environment for today’s and future generations. Sustainability maintains or improves the quality of life and supports a long-term ecological balance. The search for life on distant planets is an important endeavor. However, it is more urgent to save the life on the only habitable planet we know so far – the Earth. According to the latest U.S. Energy Information Administration’s International Energy Outlook 2017, global energy consumption is expected to increase by 28% by 2040. In order to prevent the emission of millions of additional tons of harmful pollution (greenhouse gases) into the atmosphere, potentially leading to unexpected weather patterns and climate changes, a serious paradigm shift is necessary: solar and other renewable energies must grow significantly faster than fossil fuels. This encyclopedia is my contribution to rethinking the future and focusing all our attention and solar surfaces toward the sun. In conversation with his friends Henry Ford and Harvey Firestone in 1931, Thomas Edison said: “I’d put my money on the sun and solar energy. What a source of power! I hope we don’t have to wait till oil and coal run out before we tackle that.” Volume 2 fosters the adoption and spreading of solar economy, infrastructure, and culture. Solar, wind, and other types of sustainable power generation can meet the majority of our energy demand. Solar power gives nations as well as individuals an opportunity to gain more control over their energy supply or even complete energy independence. It is a quiet but powerful way to defuse international conflicts that are all too often associated with the control of oil and other fossil fuels and arbitrary price fluctuations. Solar energy is a peaceful, clean, environmentally friendly power source that is freely available to everyone on the planet. So, why not use it? Sandy, UT, USA June 2018

Goran Mijic

Encyclopedia

12-V system 

12-V system

 3

An off-grid system that uses →direct current (DC) from photovoltaic (PV) panels with a voltage of about 12 V to power camping appliances that can be operated at the same voltage, such as lights, water pump, fan, TV, coffee maker, or microwave oven. Small PV systems on an RV or a boat use small battery banks that are wired to provide a constant 12-V power source for electrical equipment.

2D nanoscale electrodes Advanced nanomaterial, such as graphene nanosheets and nanoparticle–nanowire hybrids, that has 2D architecture and is utilized for solar energy conversion and storage. 3D architecture

Visualization technology that allows a user to design a future small- or large-scale solar system in three dimensions with the help of realistic drawings that can be easily modified and looked at from different directions. 3D architecture software gives the user a general view of the entire structure as well as a more detailed view of complex areas, such as wiring or mounting components. A row of solar modules can cast shade on adjacent rows of solar panels. A shadow visualization across different seasons can help calculate an appropriate distance between the rows of solar modules, thus avoiding energy losses due to shading. 3D architecture is also helpful when integrating solar panels into existing as well as new building design.

3D nanoscale electrodes Advanced nanomaterial, such →carbon nanotubes, that has 3D architecture and is used for solar energy conversion and high-performance energy storage. 3-phase current

See →three-phase current.

A abrasion

A wearing away of a surface, such as a protective cover glass of a solar panel, as a result of applied friction.

abrasion resistance

The ability of a surface to resist →abrasion and keep the material’s original structure and look.

4 

 abrasion strength

abrasion strength

See →abrasive hardness.

abrasion-proof coating

See →abrasion-resistant coating.

abrasion-resistant coating

A coating that is applied to the top protective glass sheet of a solar panel or a solar reflector to resist the deterioration of the surface material caused by scratching, rubbing, or other types of mechanical wear. The improved scratch resistance allows more aggressive cleaning methods and provides a good protection against wind-blown sand and other debris.

abrasive hardness

A measure of the wearing qualities of a surface material subjected to →abrasion by scratching or other mechanical impact.

ABS

Abbreviation for acrylonitrile butadiene styrene. See →ABS plastic.

ABS plastic

(Acrylonitrile butadiene styrene) Low-cost engineering plastic, which is a part of thermoplastic polymers family. Due to its light weight and resistance to impact, sun, and moisture, it is commonly used for the manufacturing of outdoor →solar lighting systems, such as →garden lights or →solar-powered LED lights, junction and other electronic boxes and enclosures, and solar panel mounting brackets.

absence detector

See →presence detector.

absolute humidity

Water vapor amount present in a given volume of air.

absolute permittivity

Measure of the resistance that is encountered when forming an electric field in a medium.

absolute zero

The lowest possible temperature at which the fundamental particles have minimal vibrational motion.

absorbance

Solar energy ratio for measuring the efficiency of a solar cell or module. It is a proportion of solar radiation a surface absorbs.

absorbed glass mat

(AGM) A fiberglass mat, sandwiched between the battery cell plates, in which the electrolyte is held. AGM batteries utilize absorbent glass mats instead of liquid electrolyte that is used in traditional flooded batteries. See →absorbed glass mat battery.

absorbed glass mat battery

Absorbed glass mat (AGM) battery is a type of a sealed leadacid (SLA) rechargeable battery that uses absorbent glass mats instead of liquid electrolyte. Unlike the liquid electrolyte surrounding the electrodes, a very fine fiberglass mat

absorbed light 

 5

Positive plate Positive grid

Plate block Negative plate Negative grid Positive plate with fiberglass separator

Absorbed Glass Mat Battery

is saturated with the sulfuric acid, encapsulated, and sandwiched between the positive and negative battery plates. Even though the battery acid is immobilized by the fiberglass mat, it is still available to the plates. As a result, the battery is spill-proof and at the same time also still highly reactive due to the close proximity between acid and plates. This configuration improves both the discharge and recharge efficiency. AGM batteries can charge up to five times faster than flooded battery systems. They are more resistant to cold weather and vibration and enable high cranking. Disadvantages of AGM batteries include higher manufacturing costs and environmental hazards. absorbed light

The amount of light that is neither reflected from the cell surface nor transmitted through the semiconductor material and lost. Only the absorbed photons lead to the generation of charge carriers, →electrons and →holes.

absorbent glass mat

(AGM) A fiberglass mat, sandwiched between the battery cell plates, in which the electrolyte is held. AGM batteries utilize absorbent glass mats instead of liquid electrolyte that is used in traditional flooded batteries. See →absorbed glass mat battery.

absorber

Also known as solar collector plate or collector plate. A dark-coated plate in a solar collector that actively absorbs

6 

 absorber area

the solar radiation and converts it into heat. The collected heat is then transferred to the fluid (water or glycol heat transfer fluid) running through the copper tubes of the thermal collector. The quality of an absorber is measured by the absorption–emission ratio. A good ratio would be 10 and higher, for example, 0.90% absorption–0.10% emission, which can be achieved through the application of →selective surface coatings to the surface of an absorber. absorber area

Dark-coated area of a solar collector that actively absorbs the solar radiation and converts it into heat.

absorber body

Body of a solar collector absorber that actively absorbs the solar radiation and converts it into heat.

absorber coating

Most absorbers of solar collectors are painted with flat black paint. Black paint has high solar absorptance, but its infrared emittance is also high, resulting in higher thermal losses. To mitigate this thermal deficiency, special coatings have been developed in past years with high solar absorptance and low thermal emittance features called →selective surface coatings.

absorber layer

Layer of a solar collector absorber that actively absorbs the solar radiation and converts it into heat.

absorber pipe

See →absorber tube.

absorber plate

See →absorber.

absorber tube

Also known as absorber pipe or called heat collection element (HCE). A long metal tube that runs the length of a →concentrating parabolic trough or →linear Fresnel reflector (LFR). The →heat transfer fluid is heated in the parabolic trough absorber tubes and then circulated to a heat exchanger, converting water into steam that powers a steam turbine. In order to achieve a maximum absorption of solar radiation, the metal tube is coated with special materials, such as black chrome or cermet. To minimize heat losses, the metal tube is covered with glass, creating a vacuum effect in the empty space between glass and metal. This →Dewar tubelike insulation keeps thermal losses at 10%. The LFR tube consists of numerous small boiler tubes through which water flows. The heated water evaporates in the tubes, generating superheated steam, reaching a high temperature of about 270 °C (518 °F).

absorbing 

 7

absorbing

See →absorption.

absorptance

The ratio of solar radiation absorbed by a surface to that incident on the surface.

absorption

A process by which photons of light are absorbed as they enter the aperture area of a solar module.

absorption capacity

Capacity of an aperture area of a solar module to absorb solar radiation.

absorption charge

See →absorption charge stage.

absorption charge stage

The second stage in a three-stage lead-acid battery charge cycle to which the charge controller automatically switches when the battery has reached 80% state of charge. At this stage, the battery is charged at a slowly diminishing rate to prevent overheating. The controller holds the voltage at a constant level and decreases the current until the battery has reached between 95% and 98% state of charge, depending on the charger brand, when it switches to →float charge stage.

absorption charging

See →absorption charge stage.

absorption chiller

A cooling device that can use hot water heated by solar thermal collectors to cool air and thereby provide air conditioning for a residential or commercial building.

absorption coefficient

Solar energy ratio for measuring the efficiency of a solar cell or module. It is a proportion of solar radiation a surface absorbs.

absorption cooling

See →solar absorption system.

absorption depth

Indicates how deep an electromagnetic wave can penetrate into a material.

absorption factor

See →absorption coefficient.

absorption glass mat

(AGM) A fiberglass mat, sandwiched between the battery cell plates, in which the electrolyte is held. AGM batteries utilize absorbent glass mats instead of liquid electrolyte that is used in traditional flooded batteries. See →absorbed glass mat battery.

absorption loss

The part of electromagnetic radiation incident on a PV surface that is not absorbed by the semiconductor material. The maximum solar cell efficiency was around 30% in

8 

 absorption of electromagnetic radiation

2017. About 70% of radiant energy is lost due to various causes. A little bit less than half of solar radiation is lost as heat and around 18% of the photons pass straight through the PV cell and vanish. One part is reflected off the solar cell surface and there are also losses due to manufacturing impurities in the semiconductor and the resistance at the junction between metallic contacts and the silicon semiconductor. absorption of electromagnetic radiation

A process by which photons of light are absorbed by atoms of the semiconductor material and converted into other forms of energy, such as electricity or heat. The interaction between the photons of light and the semiconductor promotes →valence band electrons to excited states in which they are able to bridge the →band gap and jump to the →conduction band. As a result, electron–hole pairs are created that are responsible for the flow of current in the semiconductor.

absorption of light

See →absorption of electromagnetic radiation.

absorption rate

The rate at which radiant energy is absorbed by a surface.

absorption refrigerator

See →absorption chiller.

absorption stage

See →absorption charge stage.

absorptivity

See →absorptance.

AC

Abbreviation for →alternating current.

AC disconnect

A safety component that disconnects the inverter from the electrical grid.

AC grid stability

A prerequisite for a stable electricity grid is a continuous balance between energy production and consumption. With a higher penetration of renewable energy resources, such as solar systems or wind turbines, the stability of the grid is seriously challenged. For an AC electrical grid to remain stable, the frequency and phase of all energy generation units must remain synchronous within narrow limits. Voltage control, load shedding, energy storage, and the use of synchronous condensers are some of the methods for improving the grid stability.

AC inverter and battery power allowance

A small amount of power needed to keep an AC inverter and batteries running. The AC inverter and battery power

AC inverter power allowance 

 9

allowance should be included in →total daily power budget estimate, as this power is also drawn from a battery bank just like the regular load (all household appliances connected to the circuit). AC inverter power allowance

See →AC inverter and battery power allowance.

acceptance angle

The angular range over which the sun’s rays optimally fall onto a solar panel or solar concentrator enabling high throughput (>90%).

acceptor

Dopant material with fewer electrons in the outer shell that enables the atom to accept a free electron from another atom.

acceptor doping

Doping of the semiconductor substrate with →acceptor atoms (→boron) that are likely to accept free electrons when incorporated into a balanced silicon crystal structure, creating a →p-type semiconductor layer in a solar cell.

acceptor level

An intermediate energy level near the bottom of the energy →band gap and close to the →valence band, which may accept →electrons from the →valence band. At absolute zero temperature, this level is filled with electrons from acceptor impurities that are bound to their atoms. When photons of light fall onto the semiconductor material, valence electrons become excited and jump to the acceptor energy level.

E

Acceptor level

Acceptor Level

10 

 accumulated energy

accumulated energy

Stored energy for later use, for example, in a battery, an elevated water reservoir, aquifer, cavern, borehole, or compressed air.

accumulated power

See →accumulated energy.

accumulator

A rechargeable battery that can be discharged and recharged numerous times, as opposed to disposable batteries. The following rechargeable battery types are used for solar battery banks: →lead acid battery (→flooded-cell battery and →sealed lead-acid battery), lithium-ion battery, →redox flow battery, and →nickel–cadmium battery.

accuracy error

A difference between a specific measurement and the true value of the quantity being measured.

acid cleaning

See →acid rinsing.

acid rinsing

Also known as acid cleaning. A phase in a solar cell manufacturing process preceded by the texturing phase in which wafers are cleaned with acids, such as hydrogen fluoride vapor and hydrogen chloride, to remove any unwanted particle remains caused during the texturing process.

acid stratification

Acid stratification occurs when a battery is not in use for a long period of time. In a static lead-acid battery, the sulfuric acid electrolyte tends to accumulate at the bottom of the cell, resulting in increased →sulfation, reduced capacity, and shortened battery life. The stratification can be corrected and an even distribution of acid electrolyte in various layers of battery cells restored by periodic →equalization, a process of a controlled 5%–10% overcharging of the batteries.

ACR

Abbreviation for →active cavity radiometer.

ACRIM

Abbreviation for →active cavity radiometer irradiance monitor.

ACRIMSat

Abbreviation for →active cavity radiometer irradiance monitor satellite.

Acrylate®

See →acrylic glass.

acrylic

See →acrylic glass.

acrylic glass

Also known as an Acrylate® and Plexiglas®. Acrylic glass (polymethyl methacrylate, PMMA) is a synthetic polymer

acrylonitrile 

 11

of methyl methacrylate that is frequently used as a replacement for glass. This transparent and rigid thermoplastic finds an application in the solar industry as a top surface material for greenhouse glazing and photovoltaic modules due to its glasslike qualities. The PMMA acrylic film exhibits good solar energy and light transmittance, heat resistance, and glare control. As PMMA sheets are two-thirds lighter than glass, they are easier to transport and they reduce the weight impact of solar modules on the roof structure. They are also more impact resistant than all types of glass, withstanding high winds, hail, and vandalism. Another important advantage of PMMA is cost-effectiveness, as they are cheaper to produce than glass. The biggest shortcoming of the PMMA film is its sensitivity to high temperatures. This may pose a problem in warmer climates, as PV panels are exposed to high temperatures all the time. In spite of this disadvantage, the PMMA experiences a widespread use and growth in the thin-film flexible solar cell market. The PMMA is also used as a templating agent for the growth of →perovskite photovoltaic cells. The PMMA template offers a better control of the sensitive perovskite crystallization process. The acrylic glass can also be employed as a binder material in the solar cell →screen printing.  acrylonitrile

A toxic, colorless, volatile, flammable liquid compound CH2=CH.CN, synthesized from propylene and ammonia. Acrylonitrile is used in the manufacture of acrylic fibers and resins, rubber, and thermoplastics.

acrylonitrile butadiene styrene

(ABS) See →ABS plastic.

activated shelf life

The period of time that a charged battery can be stored at a specific temperature and still perform according to its intended use and specification before it becomes unusable.

activated stand life

See →activated shelf life.

activation energy

Minimum energy required to liberate a free electron and penetrate the cell barrier.

activation voltage

Minimum voltage required to liberate a free electron and penetrate the cell barrier.

12 

 active area of the solar cell

active area of the solar cell

See →aperture.

active cavity radiometer ACR, device for measuring →total solar irradiance. active cavity radiometer ACRIM, device for measuring →total solar irradiance. irradiance monitor Active Cavity Radiometer ACRIMSat, research satellite with ACRIM – device for measuring →total solar irradiance. Irradiance Monitor Satellite active region

See →active solar region.

active solar cooling

A cooling process in which photovoltaic panels convert solar energy into electricity to power a cooling unit. During the summer, cooling accounts for more than half of the energy use in an average household in warmer and moderate climates. Solar cooling systems offer a possibility of cutting over 50% of the electric bill by using free and environmental friendly solar energy in summer months. Many modern air conditioning systems are equipped with a special port that enables an easy connection with a solar system.

active solar energy system

A system that utilizes electrical devices, such as →inverters or →tracking systems, to generate electricity from sunlight. Unlike →passive solar energy systems that are able to heat and cool buildings without the use of electrical equipment, active solar energy systems employ electrical devices, such as sensors, controls, and motor-driven systems, such as pumps and fans, to transfer the collected solar energy across the building or to remove unwanted heat from the house. See also →active solar heating.

active solar energy use

See →active solar energy system and →active solar heating.

active solar energy utilization

See →active solar energy system and →active solar heating.

active solar gain

Utilizes photovoltaic modules to generate electricity, as opposed to passive solar gain that uses south-facing windows and walls to convert sunlight to heat and spread it throughout the building.

active solar heater

See →active solar heating system.

active solar heating 

 13

active solar heating

In contrast to the more natural →passive solar heating, the active solar heating techniques use moving parts, electrical devices, and motor-driven systems. Both active as well as passive solar heating systems collect and store solar radiation, but the difference is in distribution, since the active system utilizes mechanical equipment to circulate the fluid throughout the building. The active heating process can be described as follows: the sun’s energy captured by solar collectors heats a fluid, either liquid or air. The mechanical equipment, pumps or fans, is then used to transfer the fluid through a system of pipes or air ducts directly to the interior space of a building or to a heat storage tank. It is a more complex and involved process with higher upfront costs, but it produces much more heat and offers a higher level of control with the help of sensors than a passive solar heating method. Depending on the climate and the size of the system, at least a half of the heating costs, and often way more than that, can be covered by an active solar heating system.

active solar heating system

Unlike →passive solar heating system, active solar heating system is any solar water or air heating system that employs pumps, fans, controls, and other electrical equipment to circulate heated air or water from the collectors to a storage tank or further throughout the house. There are two types of active solar water-heating systems: an →open-loop system and a →closed-loop system.

active solar region

A bright active region in the outer layers of the Sun where →solar activity, such as violent →solar flare eruptions, occurs.

active solar retrofit

The integration of →photovoltaic or →solar thermal systems into existing structures, for example, house or yard.

active solar waterheating system

See →active solar heating system.

active system

See →active solar heating system.

actual yield

Actual power output on the AC side of a photovoltaic system; generated electricity that is ready to be used by loads, such as household appliances or lights.

14 

 adhesion layer

adhesion layer

An additional layer in the range of 10 nm that is added to thin films to improve adhesion in thin-film manufacturing technology. As the poor adhesion, related to surface uncleanliness due to dirt and debris, is recognized as the main issue in the thin-film production, the adhesion layer is deposited immediately before the structural film deposition to ensure cleanliness and thus enhance adhesion.

adhesive

A material for holding materials together by bonding their surfaces. See also →solar adhesive.

adiabat

Process without heat transfer.

adiabatic

Referring to a process in which volume, pressure, and temperature can change without heat entering or leaving the system.

adjustable mirror

Flat-plate, parabolic, or dish mirrors that have an adjustable tilt mechanism guided by a →solar tracking system, which tracks the sun as it traverses the sky.

adjustable mount

See →adjustable mounting system.

adjustable mounting system

Unlike a →fixed mounting system, an adjustable mounting system has a rotating bearing or bracket for manual adjustment of the tilt angle. The bracket usually has several locking tilt angle settings for adjusting the tilt of the PV panels according to the season.

adjustable rack mount

An adjustable rack mount is an adaptable PV mounting structure whose tilt angle can be manually adjusted, often with help of telescoping legs, to optimize the solar power output. Telescoping legs are either limited to four seasonal angle settings or they are freely adjustable to any desired angle.

adjustable set point

A desired value, a minimum and maximum voltage or temperature value, that is maintained by an automatic control system. A battery controller cuts the electric current when the battery reaches a set voltage value (is fully charged) to prevent overcharge and turns it on when a low-voltage set point is reached (the battery is discharged). Similarly, in solar water-heating systems such as →batch collectors, the temperature set points of a hot water controller prevent the storage tank from overheating and the solar tube-type collectors from freezing.

adsorption 

 15

adsorption

See →adsorption process.

adsorption cooling

See →solar desiccant system.

adsorption process

Adhesion of atoms, ions, or molecules to the solid surface. There are two major types of adsorption: physical and chemical adsorption. While in a physical adsorption or physisorption no chemical bond between the adsorbate and the adsorbent is created, a chemical bond between the adsorbate (gas or liquid) and the adsorbent (solid surface) is formed in a chemical adsorption or chemisorption.

AEC

Abbreviation for →atomic energy commission.

aerosol

Aerosols are miniature particles suspended in the atmosphere. Natural aerosols form fog and clouds through the condensation of vapor species, whereas artificial, humanmade aerosols, coming primarily from the burning of tropical and subtropical rain forests as well as of coal and oil (sulfate aerosols), are responsible for the formation of dust, smoke, haze, and perturbed (polluted) clouds. Human-made aerosols have a big impact on climate and the Earth’s energy budget. By scattering the sunlight, they reduce visibility and the amount of solar radiation reaching the Earth’s surface. When comparing unperturbed and perturbed clouds, it has been noticed that natural unperturbed aerosols, tiny water droplets, are several times larger than human-made, perturbed aerosols. The clean air clouds, consisting of bigger droplets, allow light to a large extent to pass through, whereas the polluted, more dense clouds, consisting of smaller water droplets with higher concentration, reflect and scatter sunlight back into space. Accordingly, in opposition to →greenhouse gases that warm the atmosphere and are responsible for →global warming, most human-made aerosols exert a cooling influence on Earth’s climate by blocking a significant part of the sun’s radiant energy.

aerosol optical depth

See →aerosol optical thickness.

aerosol optical thickness (AOT) Also known as aerosol optical depth. The degree to which natural and human-made →aerosols, such as fog, clouds, urban haze, smoke particles, and desert dust, block the transmission of light by absorption or scattering of light. It can be defined as the extinction of the solar beam

16 

 AES

per unit path length by aerosol particles. The AOT coefficient calculates the amount of direct solar radiation that is prevented from reaching the ground by dust and haze. The lowest value of the AOD range is 0.01, which stands for an exceptionally clean atmosphere, whereas the highest value 0.4 represents an extremely hazy atmosphere. AES

Abbreviation for Atmospheric Environment Service. See today’s name →Meteorological Service of Canada.

AFC

Abbreviation for →alkaline fuel cell.

afflux

A flow toward an area or a point.

aggregation

A nonequilibrium process in which a number of particles come together to form a cluster. The state of aggregation of a material depends on the material’s temperature.

aging

See →degradation.

AGM

Abbreviation for →absorption glass mat.

AGM battery

See →absorbed glass mat battery.

Ah

Abbreviation for →ampere-hour.

AIC

Abbreviation for →amperage interrupt capability.

air circulation

In →HVAC systems, the warm or cool air is circulated through duct work into different rooms of a home or a building. In →solar air heating systems, the warm air is circulated with the help of a fan through a solar air collector and then further through a network of ducts around the home.

air collector

See →solar air collector.

air conditioner

See →heating, ventilation, and air conditioning.

air conditioning

The process of controlling the ambient air temperature and humidity in a room or a building.

air conditioning with geothermal energy

The use of →geothermal energy to cool the building during summer. The heat from the interior of a building is moved through a system of underground or underwater pipes into the ground for cooling. See →geothermal heat pump.

air cushion tank

See →expansion vessel.

air density

The mass per unit volume of air. The density of the air depends on altitude and temperature. As altitude and temperature increase, air density decreases.

air heater 

 17

air heater

See →air collector.

air inlet

Opening(s) at the bottom of a →solar kiln through which air is drawn in. Together with an air outlet at the top, the air inlet allows air circulation around the stacked firewood inside the solar kiln, speeding up the drying process.

air leakage

Also known as infiltration. The air that escapes uncontrollably through cracks, joints, closed doors and windows, and other openings in the fabric of the building, causing heat loss. The accidental flow of air in and out of a building is caused by air pressure, wind, and differences in the indoor and outdoor temperatures. Air leakage is measured by the volume of air that escapes the building in a given length of time, for example, per hour per square meter of envelope area.

air leakage testing

See →airtightness testing.

air mass

Describes the length of a path a solar beam travels through the Earth’s atmosphere. When the sun is low in the sky, in the morning or in the evening (e.g., at a low 30° angle), the sun ray needs to travel through twice as much air mass as it would at solar noon (at a 90° angle) when it passes through the least amount of air mass. In the solar energy field, the air mass is the ratio of the actual solar beam path (in our example at the 30° angle, air mass of 2) compared to the optimal path, when the sun is directly overhead, at the zenith (90° angle to the horizontal surface, air mass of 1), and produces the highest amount of energy.

air mass 1.5

(AM1.5) In contrast to →air mass one (AM1), when the sun is directly overhead at noon, air mass 1.5 (AM1.5) expresses the sunbeam path through the earth’s atmosphere that is one and a half as long as the optimal, shortest AM1 path, because the sun is lower in the sky during the day – around 41.8° above the horizon or 48.2° of the solar zenith. In the midlatitudes of the continental USA or Europe, AM1.5 takes place sometime before 9 am and after 3 pm solar time in the summer. As the position of the sun constantly changes during the day, the air mass or atmospheric thickness value will be less or more than 1.5. AM1.5 is used as an overall yearly average value for midlatitudes for solar panel measurements. The AM1.5 standard represents the typical conditions under which a photovoltaic

18 

 air mass coefficient

cell is used when the sunbeam travels through one and a half “typical” Earth atmospheres, where a typical Earth atmosphere stands for air mass one (AM1) or the shortest sun path to the Earth’s surface. To determine a power conversion efficiency of new photovoltaic cell appliances, air mass 1.5 or normal irradiance conditions are simulated in a →solar test center for the purpose of measuring the I–V response of PV cells.

Zenith

Sun

ζ=4

Sun

8.2

°

AM0

5

h1

h

1.

AM1

AM1.5 Atmosphere

Earth

Air Mass: AM0, AM1, and AM1.5

air mass coefficient

The angle between the actual sunbeam path and the vector pointing straight upward to the →zenith of the sky – 90° angle to the horizontal surface. The air mass coefficient formula expresses the cosine of solar zenith angle: AM = 1/cos(θz).

air mass one

(AM1) The shortest possible solar beam path through the atmosphere, when the sun is directly overhead, at the zenith (90° angle to the horizontal surface). The higher the sun in the sky, the smaller the air mass.

air mass ratio

See →air mass.

air mass two

(AM2) In contrast to →air mass one (AM1), when the sun is directly overhead at noon, air mass two (AM2) expresses the sunbeam path through the earth’s atmosphere that is twice as long as the optimal, shortest AM1 path, because the sun is low in the sky – 30° above the horizon – in the morning or in the evening. The lower the sun in the sky, the larger the air mass.

air mass zero 

 19

air mass zero

(AM0) The extraterrestrial solar spectrum outside the earth’s atmosphere, where there is no air. The zero atmosphere AM0 is often measured from satellites at the top of the atmosphere, space shuttle missions, or rocket soundings.

air outlet

Opening(s) at the top of a →solar kiln through which air is released. Together with an air inlet at the bottom, the air outlet allows the air circulation around the stacked firewood inside the solar kiln, speeding up the drying process.

air permeability testing

See →airtightness testing.

air pollution

The presence of foreign or toxic substances in the air in concentrations that pose a threat to the health and welfare of humans, animals, and the environment.

air pollution control

All techniques and measures employed to limit and preferably eliminate the emission of harmful substances into the atmosphere. The air pollution control utilizes a wide variety of air measuring devices and continuous emission monitoring systems (CEMS) to constantly monitor the levels of pollutants, such as carbon monoxide, sulfur dioxide, ozone, nitrogen dioxide, and lead. Several attempts have been made, for example, by the →EPA and other organizations, to enact regulations that would control the emission levels of greenhouse gases, such as →carbon dioxide, →chlorofluorocarbons, →methane, and →nitrous oxide.

air pollution protection

See →air pollution control.

air pressure

Also known as atmospheric pressure. The force with which the weight of all the air above our heads presses down onto Earth’s surface. In addition, the collisions between molecules contribute to air pressure. Warm air molecules possess more energy than cold air molecules. As they vibrate energetically and bump into each other, they occupy more space and exert more pressure on their surroundings. In contrast, cold air molecules move slowly and occupy less space, which results in reduced air pressure. See also →atmospheric pressure.

air tightness

See →airtightness.

20 

 air-based solar heating

air-based solar heating

Captures the sun’s energy and uses the air to transfer heat from the solar collector to the interior of a house or a commercial building. Solar collectors can be integrated into a south-facing wall or on the roof. The heated air can be transported directly to the interior space or distributed through a network of ducts around the home with fans.

airlock

Two airtight doors with small space or passage between to reduce heat loss in a building.

air-source heat pump

A device for heating or cooling your home by transferring heat from outside to the inside of a building and vice versa (e.g., air-conditioning system).

airtightness

Also known as air tightness. The resistance of the building envelope, including the area of walls and roof, to infiltration or →air leakage. With tight barriers that do not permit the passage of air, an air-tight building reduces the air leakage and heat loss to the minimum. The airtightness of a building is measured by an airtightness test.

airtightness testing

Also known as air permeability testing or air leakage testing. A testing technique that measures the level of unintentional air flow through cracks and openings in the building envelope. The air permeability or leakage is measured by the volume of air that escapes the building in a given length of time, for example, per hour per square meter of envelope area.

albedo

Also known as Earth’s natural reflectivity or ground-reflected radiation. Albedo is reflection coefficient, a percentage of the light (solar radiation) falling on different objects and surfaces on the Earth that is reflected back into space. The total reflectivity of the Earth’s atmosphere is 31%. The largest part of solar radiation is blocked and reflected back toward space by clouds. One part is reflected off the white Earth’s surfaces, such as snow, ice, or white roofs, and one part is scattered back into space by dust and air molecules in lower and upper layers of the atmosphere. Albedo is an important part of the planet’s climate control because it protects the life on Earth from the Sun’s harmful radiation and the phenomenon of →global warming. The less sunlight is reflected back into space, the more solar radiation is trapped as heat in the lowest layer of the atmosphere

Grass 25%–30%

Forests 10%–20%

Snow 80%–95%

Concrete dry 17%–27%

Albedo values (% reflected)

Asphalt (black top) 5%–10%

Dark colored roof 8%–18%

Light-colored roof 35%–50%

albedo   21

22 

 ALCVD

and the more difficult the life on Earth becomes. One of the biggest global challenges in the upcoming years will be the melting of snow and ice in the polar regions. As the icecap melts, the reflectivity decreases and proportionately the global temperature increases. ALCVD

Abbreviation for atomic layer chemical vapor deposition. See →atomic layer deposition.

ALD

Abbreviation for →atomic layer deposition.

ALE

Abbreviation for atomic layer epitaxy. See →atomic layer deposition.

alignment of a solar array

Optimum alignment of a solar photovoltaic array to the sun throughout the whole year is achieved by positioning the panels to face the optimal south and finding the best year-round →tilt angle, which is 30° for photovoltaic modules on average.

alignment of a solar system

See →alignment of a solar array.

alignment of photovoltaic panels

See →alignment of solar modules.

alignment of solar modules

Optimum alignment of solar photovoltaic modules to the sun throughout the whole year is achieved by positioning the panels to face the optimal south and finding the best year-round →tilt angle. The average optimal inclination for PV modules is 30° measured from the horizontal; however, the latitude of a specific location must be taken into account, because the position of the sun in the sky varies by geographic location. Thus, a year-around tilt angle in a northern state, such as Alaska, will be significantly different than a tilt angle in one of the southern states, for example, Arizona.

alignment of solar thermal collectors

Optimum alignment of solar thermal collectors to the sun throughout the whole year is achieved by positioning the collectors to face the optimal south and finding the best year-round →tilt angle, which is 45° for thermal collectors on average.

aliphatic hydrocarbon

A carbon-based compound that consists of carbon and hydrogen combined together in straight chains, branched trains, or nonaromatic rings. Aliphatic hydrocarbon is present in materials for inhibiting the corrosion of metal components.

alkali silicate gel 

 23

alkali silicate gel

An amorphous material that can be used as a fire protection layer in a multipane glass of a solar panel.

alkaline fuel cell

(AFC) One of the first fuel cell technologies developed by the British engineer Francis Thomas Bacon. The AFC uses a solution of potassium hydroxide as the electrolyte. Power is produced by a redox reaction between hydrogen and oxygen. The oxidation of hydrogen occurs at the anode, forming water, heat, and electricity.

alkane

An organic solvent (saturated hydrocarbon) with only single bonds between atoms, such as hexanes, cyclohexanes, octanes, used in the manufacture of dopant ink.

alkyl-based alcohol

An organic solvent, such as ethanol or propanol, used in the manufacture of dopant ink.

alligator clamp

See →alligator clip.

alligator clip

A metal clip resembling the jaws of an alligator that is used to attach solar panels to the mounting frame. In addition to their securing function, they may also be used to ground PV modules.

allowed band

See →energy band.

alloy

A mixture of two or more elements that has metallic properties.

almucantar

A circle on the celestial sphere parallel to the horizon.

alternating current

(AC) An electric current that reverses the direction of electron flow at regular intervals, 60 times per second (USA, 60 Hz) and 50 times per second (Europe and many other countries, 50 Hz). As solar panels generate →direct current (DC), an →inverter is needed in every →grid-tie system to convert DC into alternating current in order to power household appliances.

alternative energy

A different kind of energy than the one in widespread use, purchased from a utility company and generated from fossil fuels. Alternative energy comes from renewable, environmentally sound sources such as solar, wind, hydrogen, wave, or geothermal energy.

alternative energy resource

See →alternative energy source.

24 

 alternative energy source

alternative energy source

An environmentally sound source of energy, such as solar, wind, hydrogen, wave, or geothermal energy. Any energy source other than a →fossil fuel.

alternator

An electric device that generates →alternating current (AC).

altitude angle

See →solar altitude angle.

aluminum

(Al) A light silvery-white metal that is one of the most abundant elements in the earth’s crust. Due to its lightweight and corrosion-resistant features, aluminum is a preferred material for →solar module frames and other outdoor solar mounting equipment.

aluminum alloy

A chemical compound in which alloying elements, such as copper, zinc, magnesium, silicon, manganese and lithium, are added to pure aluminum to enhance its properties. Aluminum alloys are used for →solar module frames, mounting rails, and other outdoor mounting components that require a lightweight but sturdy, weather- and corrosion-resistant material.

aluminum contact

See →aluminum electrode.

aluminum electrode

Also known as aluminum contact. Usually a rear, cathodic contact consisting of pure aluminum or an aluminum alloy, such as an aluminum/silicon (Al–Si) or calcium/aluminum (Ca–Al) cathode in silicon or polymer solar cells. In →thin-film solar cells, the organic, photoactive semiconductor material is sandwiched between the negative aluminum electrode and the transparent positive indium tin oxide (ITO) electrode. In contrast to transparent electrodes, the opaque aluminum electrode on the bottom enhances light trapping in thin-film solar cells by reflecting some of the incoming light back into the photovoltaic cell. The reflective aluminum electrode covers the entire back side of the cell. The rear aluminum electrode is typically manufactured by a screen printing method. The aluminum contact sample is then immersed in a plating bath to provide high wear and corrosion resistance.

aluminum frame

A frame made of aluminum that provides a strong support structure for the →photovoltaic laminate. The aluminum frame needs to be lightweight to reduce the weight impact

aluminum rail 

 25

of solar modules on the roof structure. In addition, it is critical that the aluminum frame is anodized to provide a robust finish resistant to corrosion, wear, and harsh outdoor weather conditions. aluminum rail

A key piece of solar panel roof-mounting hardware onto which PV modules are mounted with the help of →mid clamps and →end clamps. Aluminum rail needs to be anodized to resist corrosion and harsh weather conditions, such as rain and snow; lightweight to decrease the load on the roof; and sturdy to withstand strong winds.

AM0

Abbreviation for →air mass zero.

AM1

Abbreviation for →air mass one.

AM1.5

Abbreviation for →air mass 1.5.

AM2

Abbreviation for →air mass two.

amber light

Also known as solar amber light. Solar-powered LED light that casts an amber glow on walkways, steps, driveways, gardens, and ponds.

ambient

Relating to the immediate surroundings.

ambient conditions

Conditions of the immediate surroundings.

ambient temperature

The prevailing temperature of the surrounding environment. An increase in ambient temperature can have a negative effect on the output of solar modules. As the ambient temperature heats the panel to a temperature of 25 °C (77 °F) and above, it potentially reduces the power yield by 10%–25% based on the proportional voltage drop due to resistance.

ambient air temperature See →ambient temperature. American Society of Heating, Refrigerating, and Air-Conditioning Engineers

(ASHRAE) An international association with more than 57,000 members from over 132 nations devoted to the advancement of →heating, ventilation, and air conditioning (HVAC) and refrigeration to serve the public and promote a sustainable world. The ASHRAE handbooks and guidelines are regarded as standards for heating, air conditioning, and refrigeration.

American Solar Energy Society

(ASES) A national nonprofit organization of solar advocates, enthusiasts, and professionals based in Boulder, Colorado.

26 

 American Wire Gauge

American Wire Gauge

(AWG) American standard for wire diameter. The higher the number, the smaller the wire diameter and correspondingly the thinner the wire.

AMM

Abbreviation for →analog multimeter.

ammeter

Instrument for measuring the electric current in a circuit.

amorphous

Noncrystalline. The literal meaning of the word “amorphous” is defined as shapeless. Unlike crystalline silicon cells, the a-Si material does not have an orderly structure on a molecular level.

amorphous cell

See →amorphous silicon solar cell.

amorphous metal

Metallic material with noncrystalline structure.

amorphous microstructure

Noncrystalline microstructure.

amorphous module

Solar module with noncrystalline structure. See →amorphous silicon solar cell.

amorphous panel

Solar panel with noncrystalline structure. See →amorphous silicon solar cell.

amorphous semiconductor

Noncrystalline semiconductor material.

amorphous silicon

(a-Si) Also known as thin-film silicon. Silicon with noncrystalline structure. It is used as a semiconductor material in the production of →amorphous silicon thin-film solar cells. The material is deposited on a substrate by applying the →chemical vapor deposition (CVD) process and a silane gas (SiH4) precursor. This process is cheaper than the crystalline silicone manufacturing method, as the entire complex and expensive process of crystal growth and sawing of crystalline rods into wafers can be skipped. See also →amorphous silicon solar cell.

amorphous silicon cell

See →amorphous silicon solar cell.

amorphous silicon semiconductor

(a-Si) Silicon semiconductor with noncrystalline structure that is used in the production of →amorphous silicon thinfilm solar cells.

amorphous silicon solar (a-Si solar cell) Also known as thin-film solar cell. A type of cell thin-film solar cell with noncrystalline structure. It is pro

amorphous silicon solar module 

 27

duced by vapor-depositing several layers of doped silicon (about 1 μm thick) on a substrate. As it can be deposited at very low temperatures (as low as 75 °C), it can also be applied to the surface of a plastic substrate. a-Si semiconductor layers are much thinner than the ones of conventional crystalline silicon solar cells. Less semiconductor material used during the manufacturing process translates into lower production costs. Even though a-Si cells are less expensive than other cells on the market, they are considerably less efficient than the conventional crystalline silicon or polycrystalline solar cells. This means that a-Si cells require a much larger surface than traditional silicon cells to generate the same amount of energy. This is why homeowners hardly ever install amorphous solar panels, and they are mostly used in large-scale commercial projects. Another disadvantage of amorphous cells is the fact that their lifespan is shorter than the one of crystalline cells. The efficiency of a-Si modules is better in cloudy weather than under clear sky conditions because the light is richer in blue illumination under diffuse light conditions and a-Si has a higher spectral response to blue light. Other advantages include resistance to heat, lightweight, flexibility, and good uniformity over large areas. Light

Transparent conductive oxide layer p layer i layer n layer

Glass

Rear contact

Amorphous Silicon Solar Cell

amorphous silicon solar Also known as thin-film solar module. Silicon solar module module with noncrystalline structure. See →amorphous silicon solar cell.

28 

 amorphous silicon solar panel

amorphous silicon solar Silicon solar panel with noncrystalline structure. See panel →amorphous silicon solar cell. amorphous silicon thin-film solar cell

Silicon thin-film solar cell with noncrystalline structure. See →amorphous silicon solar cell.

amorphous silicon thin-film solar module

Silicon thin-film solar module with noncrystalline structure. See →amorphous silicon solar cell.

amorphous silicon thin-film solar panel

Silicon thin-film solar panel with noncrystalline structure. See →amorphous silicon solar cell.

amorphous solar cell

See →amorphous silicon solar cell.

amorphous solar module

Solar module with noncrystalline structure. See →amorphous silicon solar cell.

amorphous solar panel

Solar panel with noncrystalline structure. See →amorphous silicon solar cell.

amortisation

UK See →amortization.

amortization

An act of repaying a debt or returning invested funds over a period of time. In solar investments, it is crucial to be able to amortize the costs of a solar system over its useful life, which is typically 25 years for crystalline solar panels. For instance, if a PV system amortizes its cost in 10 years, it pays back the invested funds from the energy yield and will continue generating free electricity for a household for 15 more years. To roughly calculate the payback period for a photovoltaic system, the following formula can be used: payback period = total system cost (initial investment)/ value of electricity generated/annual electricity usage.

amortization period

The period of time it takes for a solar system to pay back its initial cost.

amortization time

See →amortization period.

Amp

Abbreviation for →ampere.

ampacity

Word coined by blending “ampere capacity” into a single word. It designates the amount of current (in amperes) a conductor can carry without exceeding its temperature rating, which is specified by the →National Electrical Code (NEC) in the United States. Going beyond the indicated maximum current value might lead to degradation, damage, or even wire melting, as ampacity ratings rest on the thermal limits of the insulation.

amperage 

 29

amperage

Current intensity.

amperage interrupt capability

(AIC) The maximum fault current (in amperes) that a protective device, such as a fuse or circuit breaker, can safely interrupt without causing damage to equipment or people.

ampere

(A, Amp) SI unit of electric current that expresses the rate at which electrons (charge) are flowing in a circuit. Ampere is equal to volts divided by resistance: A = V/R or A = V/Ω.

ampere interrupting capacity

See →amperage interrupt capability.

ampere meter

Instrument for measuring the electric current in a circuit.

ampere-hour

(Ah) Is equal to the flow of electrical current of one ampere for one hour. It is used to measure the electrical quantity, for example, the capacity of a battery.

ampere-hour meter

Instrument for measuring the electric current over time.

amp-hour

See →ampere-hour.

amps clamp

Measuring instrument with a clamp that measures the electric current in a circuit.

amps interrupting capacity

See →amperage interrupt capability.

anaerobic digester

A sealed tank in which bacteria act upon organic matter without oxygen, breaking down waste and gathering the biogas released in the process. Solar collectors can be added to anaerobic digester to reduce thermal losses in the digester, in particular in cold winter days, as well as to increase the temperature of the biomass slurry to accelerate the degradation process.

anaerobic digestion

A chemical process in which bacteria break down organic materials, such as manure, in the absence of oxygen.

analog meter

A meter that uses a dial hand to indicate a value.

analog multimeter

(AMM) A →multimeter that uses a dial hand as opposed to a digital multimeter with a digital display.

analog voltmeter

(AVM) A →voltmeter that uses a dial hand as opposed to a digital voltmeter with a digital display.

ancillary services

All services that assist the transmission of electricity from generating sources to the customer and manage the

30 

 anemometer

complex renewable energy smart meter infrastructure and grid stability. These services typically include: load following, scheduling and dispatch, system protection, system monitoring, reactive power and voltage control, loss compensation, energy imbalance, and harmonic cancellation. anemometer

An instrument for measuring the speed of the wind.

angle calculator

See →angle finder.

angle finder

A device, usually an application, which helps find the sun’s angle and calculate the best seasonal or monthly angle for solar panels.

angle of incidence

See →solar angle of incidence.

angle of inclination

Angle between the horizontal and the solar panel.

angle of insolation

See →solar angle of incidence.

angle of installation

An optimal angle of installation of solar panels can be determined by finding an optimal south position as well as the optimal tilt angle, taking into account the latitude of a specific location.

angle-dependent deposition

A technique for manufacturing nanostructures, for example, inclined columns, helices, and zigzag shapes, to optimize the optical →anisotropy, porosity, and crystallographic orientation of thin films.

angstrom

See →Ångström.

Ångström

(Å) Unit of length equal to 10−8 cm, approximately the size of an atom. It is used to measure the wavelength of electromagnetic radiation or distances between atoms.

anion

Negative →ion. When an atom gains one or more electrons, it becomes a negative ion (anion), carrying a negative charge as a result of the chemical reaction.

anisotropic

Referring to anisotropic material whose properties vary with different crystallographic orientations.

anisotropic etch1

See →anisotropic etching.

anisotropic etch2

Type of chemical used for anisotropic etching.

anisotropic etching

Orientation-dependent etching along crystallographic planes. Compared to curved edges of →isotropic etching,

anisotropic etching profile 

 31

the anisotropic etching can create specific orientations, for example, straight vertical wall edges or angled wall edges with less or no undercutting of the masked layer. It is suitable for etching complex shapes. Mask edge positioning and mask patterns control the final etched shape. To anisotropic etching, appropriate anisotropic wet etchants must be applied, such as potassium hydroxide (KOH) that is used for etching →crystalline silicon (c-Si). Etch rates can be better controlled in anisotropic etching, resulting in smaller and more specific etch patterns. Unlike the uniform etch rate in →isotropic etching, which is the same for all directions, the etch rate in the anisotropic etching is different for different directions in the material. Dry anisotropic etching

Wet anisotropic etching

Anisotropic Etching

anisotropic etching profile

The anisotropic etching profile is a profile that exhibits geometrically straight walls of the etch groove.

anisotropic material

Material whose properties vary with different crystallographic orientations.

anisotropy

Measure of directionality of the etch. It displays different etch rates in different directions. Unlike the etch rate in →isotropic etching that is the same in all directions, lateral etch rate is usually different than vertical etch rate in →anisotropic etching.

annealing

A heat treatment of semiconductor wafers in a high-temperature furnace to eliminate the produced crystal damage, relieve internal stresses in silicon, refine the structure, and activate →dopants.

32 

 annual current requirement

annual current requirement

See →annual electricity requirement.

annual electrical demand See →annual electricity requirement. annual electricity consumption

The size of a new photovoltaic system to be installed depends on the average electricity consumption of a household. The straightforward way to determine the annual electricity consumption in an existing building is to look at your electric utility bills. The electric bill usually displays your average kWh electricity usage by month, and in some areas even by year. The new PV system should be sized to meet the annual electricity requirement of a given home.

annual electricity requirement

Average annual amount of electricity needed to power a home. This information is crucial when sizing a new photovoltaic system to be installed. This information can be easily obtained from past electric utility bills; however, it gets more complicated in new houses that are being built with no previous average electricity consumption information. In such cases, an annual electricity requirement for the new building should be estimated by performing an electrical →load analysis with help from →load analysis worksheets. A load analysis worksheet should list all the electronic devices that consume electricity and will be used in the new house. For a more accurate estimate, a seasonal electrical energy consumption in watt-hours for each electrical appliance can be applied. As measuring each device individually with a power meter might be a time-consuming and challenging endeavor, PV system designers typically use wattage from rating labels of electronic devices. Some devices do not specify wattage, but only voltage and amps. By multiplying amps by volts, the power consumption of an appliance in wattage may still be calculated.

annual energy consumption

See →annual electricity consumption.

annual energy output

It is important to know how much electricity (how many watts) a photovoltaic array can generate per year. A solar array must be sized so that it is able to supply the total electrical load of the house and meet the →annual electricity requirement.

annual energy yield

See →annual energy output.

annual power requirement 

 33

annual power requirement

See →annual electricity requirement.

annual solar irradiance

The amount of sunlight a surface receives per year. PV system designers use maps with average annual energy values to calculate an accurate →annual energy output of a future solar array.

annual solar savings

An estimate showing how much energy one home with a solar array can save per year when compared with a nonsolar house and its yearly average cost of electricity.

anode

The positive electrode in a battery.

anode rod

An easily corroded metallic rod deliberately placed inside a water storage tank to attract corrosive elements and reduce the corrosion of the protected material. The anode rod must be replaced when it is severely corroded; otherwise, the water tank and its components will start to corrode.

anodic bonding

A method for graphene production in which graphite is first pressed onto a glass substrate with the help of an electrostatic field and then cleaved off to leave few layers of graphene on the substrate.

antifreeze

A liquid, such as a →glycol–water mixture, that is used in solar water-heating systems to prevent heat transfer fluid in pipes from freezing.

antifreeze solution

See →antifreeze.

antireflection coating

(ARC) A thin coating on solar cells that reduces the reflection and improves light transmission. Silicon nitride (SiN) is a preferred antireflection coating material, which is usually deposited on a semiconductor surface using →plasma-enhanced chemical vapor deposition (PECVD) process.

anti-reflection coating

See →antireflection coating.

antireflection glass

A glass with antireflection coating that reduces the reflection of incident light and increases the transmittance of the glass.

antireflection layer

A layer that reduces the reflection and improves light transmission.

anti-reflection layer

See →antireflection layer.

34 

 antireflective coating

antireflective coating

See →antireflection coating.

anti-reflective coating

See →antireflection coating.

antireflective tempered solar glass

A glass that reduces the reflection and improves light transmission.

antiscratch film

See →antiscratch layer.

antiscratch layer

An antiscratch film deposited on the outermost side of the solar module in order to prevent the panel from being damaged due to external contact.

AOT

Abbreviation for →aerosol optical thickness.

aperture

See →aperture area.

aperture area

A glass-covered surface area on a solar collector or a photovoltaic module that absorbs solar radiation.

aperture area of a solar array

See →aperture area of a solar system.

aperture area of a solar collector

The area of a solar thermal collector that absorbs solar radiation. The aperture area is usually larger than the absorber area.

aperture area of a solar module

A glass-covered surface area on a solar module that absorbs solar radiation.

aperture area of a solar panel

A glass-covered surface area on a solar collector or a photovoltaic module that absorbs solar radiation.

aperture area of a solar system

The total of all glass-covered surface areas of a solar system through which the incident solar radiation is admitted and transmitted to the absorbers.

aperture efficiency

A proportion of solar radiation that the aperture area of a solar collector absorbs.

aperture loss

A proportion of solar radiation that is admitted within the aperture area of a solar collector but then it never reaches the absorber due to the blockage or falling between the cracks. In photovoltaic modules, the aperture loss is the proportion of solar energy that is lost in the aperture area due to the patterning and shadow effects. The aperture loss, which counts as one of the major contributors to a drastic degradation of the performance in an organic PV module, can be reduced by manufacturing the main active layers without any patterns.

aperture surface 

 35

aperture surface

Glass-covered surface area on a solar collector that absorbs the solar radiation.

apparent solar time

Apparent solar time is time based on the Sun’s actual daily motion across the sky, in opposition to the man-made mean solar time or clock time. According to this “natural,” local apparent time, which can be roughly measured by a sundial, the sun always crosses the true north-south meridian at noon. When the sun is at its highest point in the sky, the noon in local solar time (LST) takes place. However, the Sun’s motion across the sky is not a uniform, circular movement because the Earth moves around the Sun in an elliptical orbit. That is the reason why apparent solar time, which is defined by the position of the sun, differs from the agreed upon →local mean time (LT) or clock time, which is based on man-made adjustments, such as time zones and daylight savings.

approach temperature

The minimum temperature difference between hot stream and cold stream in a heat exchanger.

aquifer

Porous rock layers, gravel or sand that are filled with water, acting as a water reservoir due to their impermeable top and bottom layer.

aquifer storage facility

See →aquifer thermal energy storage.

aquifer storage system

See →aquifer thermal energy storage.

aquifer thermal energy storage

(ATES) A large-scale thermal energy storage system that uses →aquifers to store heat or cold between seasons. For instance, during summer, the abundant excess thermal energy from solar thermal plants is stored in the aquifer for later use. The accumulated thermal energy provides heat for domestic hot water and space heating for a building, apartment complex, or an entire district over winter.

ARC

Abbreviation for →antireflection coating.

architecture

See →solar architecture.

ARDE

Abbreviation for →aspect ratio-dependent etch.

argon

(Ar) A noble gas with atomic number 18. As argon is an inert gas that undergoes almost no chemical reactions, it is often utilized in chemical processes that require a nonreactive atmosphere. Argon acts as a preferred sputtering gas

36 

 argon ion

in various sputter deposition processes because it does not react with the target material. In the →magnetron sputtering process, which takes place in a vacuum chamber, the sputtering gas argon bombards the target source material, sputtering off the material particles in a highly charged, magnetic plasma environment and depositing them onto the substrate. In hermetically sealed windows that consist of two or three glass sheets, argon is used as an insulator, filling the space between the panes. argon ion

Ions that are generated by the collision of inert, electrically neutral argon gas atoms with high-energy target material electrons, when a negative charge is applied to a target source material in the →magnetron sputtering process.

argon ion laser

A type of laser used for wafer testing.

argon ion-beam etching

Etching technology for the production of thin-film semiconductors.

argon plasma

→Plasma that is generated by ionizing the chemically inert sputtering gas argon (Ar). It is a hot, gaslike cloud consisting of roughly half gas ions and half electrons. When a negative charge is applied to a target source material in the →magnetron sputtering process, the inert, electrically neutral argon gas atoms become positively charged ions attracted to the negatively charged target material. The energetic ions of argon plasma collide with the target material (cathode), causing the atoms to be dislodged from the surface of the target material and condense on the surface of the substrate (anode) as a thin semiconductor layer. The argon gas usually requires relatively low energy to generate plasma, allowing a low-temperature deposition of amorphous materials on sensitive substrates.

array

Photovoltaic array. Group of solar panels connected together to form a unified power production system.

array current

The electrical current output generated by a photovoltaic array in full sun.

array DC disconnect

See →DC disconnect.

array operating voltage

See →solar array operating voltage.

arsenic 

 37

arsenic

Toxic semimetal that is utilized in the manufacture of semiconductors. Arsenic atoms are commonly used for n-type doping, generating the flow of electrons along the →conduction band. Arsenic has five electrons in the outmost energy level, which is incongruent with the geometry of the silicon lattice with four outer electrons. As the fifth arsenic electron has nothing to bond to, it moves freely from one silicon atom to another, carrying negative charge along the conduction band. It takes a small amount of arsenic impurity atoms to start a current flow across the silicon crystal.

arsine

A flammable, colorless, and highly toxic gas used in the semiconductor manufacturing. In the solar industry, arsine is utilized as a doping gas during the production process of polycrystalline silicon and gallium arsenide solar cells. The inhalation exposure to arsine can cause major health risks, as the gas is known as a highly toxic and carcinogenic chemical.

artificial aerosols

See →human-made aerosols.

asbestos

Fibrous silicate, such as asbestos actinolite, asbestos grunerite (amosite), asbestos anthophyllite, chrysotile, crocidolite, and asbestos tremolite. This silica compound, which is naturally found in rocks and soil, was used in buildings as a fire-resistant and insulating material. The use of asbestos is slowly being phased out because the inhalation of asbestos fibers can lead to serious illnesses, such as lung cancer and asbestosis.

ASES

Abbreviation for →American Solar Energy Society.

ASHRAE

Abbreviation for →American Society of Heating, Refrigerating, and Air-Conditioning Engineers.

a-Si

Abbreviation for amorphous silicon. This silicon type with noncrystalline structure is used as a semiconductor material in the production of →amorphous silicon thin-film solar cells.

a-Si solar cells on stainless steel foil

Lightweight, flexible thin-film solar cells made of an →amorphous silicon (a-Si) alloy that is deposited on stainless steel foil. As amorphous silicon triple-junction cells on thin stainless steel have an optimal band gap for AM0 solar radiation, they are utilized for space and stratospheric applications.

38 

 a-Si:H

a-Si:H

Abbreviation for →hydrogenated amorphous silicon.

aspect angle

Direction a solar module faces, for example, south or south west. Calculating the best aspect angle and positioning the panels to face the optimal south is the key for capturing as much solar energy as possible.

aspect ratio

The ratio of depth to width of an →etched trench.

aspect ratio-dependent etch

(ARDE) The etch phenomenon by which smaller features etch slower than those with larger dimensions.

assembly of a photovoltaic system

See →installation of a solar system.

assembly of a PV system See →installation of a solar system. assembly of a solar system

See →installation of a solar system.

astronomically controlled tracking

See →astronomically controlled tracking system.

astronomically controlled tracking system

Also known as an astronomically guided tracking system. A single- or dual-axis tracking system that uses an astronomical control mechanism to follow precisely the course of the sun in a certain location at a given time of the year. The accurate calculation of the position of the sun in a specific location and at a specific time is based on an astronomical algorithm that compares the latitude and longitude with the UTC time. The astronomically controlled tracking system allows optimal alignment of PV panels, achieving maximum solar output, without sun sensors.

astronomically guided tracking

See →astronomically controlled tracking system.

astronomically guided tracking system

See →astronomically controlled tracking system.

ATES

Abbreviation for →aquifer thermal energy storage.

at-home charging

See →residential electric vehicle charging infrastructure.

atmosphere

The layer of gases that surrounds the Earth or another planet.

atmospheric attenuation The reduction in the intensity and quantity of solar radiation as it passes through various weather conditions on its

atmospheric attenuation of solar radiation 

 39

way from the mirror surface of a →heliostat to the central receiver in a →concentrated solar power plant (CSP plant). The distance between a heliostat and the receiver (boiler) at the top of a →solar power tower, which is located at the center of the field, plays an important role in the amount of atmospheric attenuation. atmospheric attenuation See →solar attenuation. of solar radiation Atmospheric Environment Service

(AES) See today’s name →Meteorological Service of Canada.

atmospheric pressure

Also known as air pressure. The pressure or force per unit area exerted by the weight of the air above that area. Pressure decreases with increasing altitude as there is less air. In contrast, the pressure is greater at lower altitudes because the total weight of the air is larger and more air is pushing down. See also →air pressure.

atmospheric turbidity

The measure of relative clarity of the atmosphere. It is a key parameter for evaluating the air pollution, atmospheric aerosol load, and the attenuation of the solar radiation that reaches the Earth’s surface under a cloudless sky. An increased atmospheric turbidity leads to increased scattering of solar rays and a diminished intensity of →direct solar radiation, thus resulting in a decreased power output of the solar plant. The measurement of →diffuse solar radiation and atmospheric turbidity provide crucial information to designers of solar thermal or photovoltaic systems. A shadow ring and a measuring instrument called →pyranometer are used for the measurement of the diffuse solar radiation. Using this information, solar designers are able to better predict the availability of solar energy in a particular location.

atmospheric turbidity coefficient

The ratio of the turbidity of the atmosphere, including the scattering of light by small particles (water droplets, ice crystallites, and dust particles) and the absorption of light by water vapor, to a dry and clean atmosphere. The turbidity scale ranges from the lowest turbidity value of 0, which represents a perfectly clear sky, over a good medium turbidity value of 0.04 to the highest turbidity value of 1, which represents the perfectly opaque sky.

40 

 atmospheric turbidity factor

atmospheric turbidity factor

See →atmospheric turbidity coefficient.

atomic electron shell

See →electron shell.

atomic energy

See →nuclear energy2.

Atomic Energy Commission

(AEC) A US federal agency established after the World War II in 1946 in order to control the destructive power of atomic energy on a world level and foster the development of peaceful applications of atomic energy. The AEC was dissolved in 1974 and succeeded by the Energy Research and Development Administration and the U. Nuclear Regulatory Commission.

atomic energy level

See →energy level.

atomic layer chemical vapor deposition

(ALCVD) See →atomic layer deposition.

atomic layer deposition

(ALD) Also known as atomic layer epitaxy (ALE) or atomic layer chemical vapor deposition (ALCVD). A type of →chemical vapor deposition that is capable of producing highly uniform ultrathin films for semiconductor devices. This thin-film deposition nanotechnology method enables a full control over thickness, complex structures, and chemical features of a film on the atomic scale. The process is performed at relatively low temperatures, which is suitable for sensitive polymer-coated thin films. Unlike chemical vapor deposition, the ALD method splits the CVD process into two separate chemical reactions to achieve a better control of film growth. In that way, two precursor materials are kept separate during the reaction, allowing a precisely controlled deposition. First, precursor gas 1 is introduced into the reaction chamber, generating a monolayer of gas on the substrate surface. After the first monolayer has been deposited on the wafer, the remaining gas is removed from the chamber. In the next step, precursor gas 2 is introduced into the reaction chamber, reacting with precursor 1 and creating another monolayer on top of the first one. Any leftover precursor gas 2 is removed from the chamber. The process starts all over again with precursor 1, and this alternating layer-by-layer growth continues until a desired thickness is achieved. The thickness of the semiconductor layer is accurately controlled by the number of deposition cycles.

atomic layer epitaxy  

 41

One of the major disadvantages of the ALD method is the relatively slow deposition rate, compared to the conventional chemical vapor deposition. atomic layer epitaxy

(ALE) See →atomic layer deposition.

atomic nucleus

The central part of the atom, consisting of →protons and →neutrons.

attenuation

Weakening in force/intensity or thickness/density. See also →solar attenuation.

aureole

A ring-shaped zone of enhanced brightness surrounding the Sun due to the scattering of sunlight by aerosol particles.

autarkic

Energy-independent, self-sufficient in energy.

autarkic energy system

An independent, stand-alone power system that does not rely on the electrical grid.

automated battery control system

See →automatic battery management system.

automatic battery management system

Also known as an automated battery control system. A system that monitors charging and discharging processes for optimal performance of a rechargeable battery. Depending on the product, the automatic battery management system can monitor state of charge, state of health, current, voltage, and temperature, to ensure optimal and safe operation and the long life of a battery.

automatic disconnection Device for automatic disconnection from the public grid. device automatic equalization charge

An automatic periodic battery maintenance process. See →equalization charge.

automatic weather data acquisition

A weather data acquisition system developed by ASEA, Sweden, which uses automatic public telephone networks and the digital data communication (DIDAC) equipment to transmit weather data.

autonomous power generating system

Off-grid, stand-alone photovoltaic power generating system.

autonomous power system

See →autonomous power generating system.

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 autonomous system

autonomous system

See →autonomous power generating system.

autumnal equinox

See →fall equinox.

auxiliary system

A backup power system that provides a secondary source of energy, such as battery bank, wind turbine, or gas generator, when the primary source of energy, such as solar power, fails or does not provide enough electricity during extended periods of cloudy weather.

availability

Is often mentioned as a major argument against solar energy. The Sun is not available 24 hours a day, 365 days a year as other →fossil-fuel energy sources, but rather shines only half the day and with diminished intensity in the early morning, late afternoon, winter, and on cloudy days. Solar advocates offset the availability disadvantage by installing a →battery bank and/or wind turbine as a secondary energy source to fill in the solar inactivity gap. Another comfortable solution is a →grid-tie system, where the utility grid acts as a large storage system from which the connected solar user buys the electricity when needed (overnight) and to which he also sells the produced surplus energy back during the day. The →satellite power system (SPS) concept of producing solar power in space and beaming it to Earth promises to overcome the availability shortcoming.

availability factor

The availability factor of a photovoltaic array is the percentage of time, usually measured in hours per year, that the system is available to provide electrical power to a load or to the grid. Reduced power generation during winter months and on cloudy days should be taken into account as well as the fact that no electricity is produced at night.

average monthly temperature

The average of the mean monthly maximum and minimum temperatures. The average value is based on the statistical values collected in a computing system over a long period of time in a given region.

average wind speed

The average speed of the wind regardless of direction over a period of time, such as a day or a month, based on the hourly data from automated stations measured and recorded over the course of many years.

AVM

Abbreviation for →analog voltmeter.

avoided cost 

 43

avoided cost

The electricity production cost a utility avoids as a result of the qualifying renewable facilities.

away-from-home charging infrastructure

See →workplace electric vehicle charging infrastructure.

AWG

Abbreviation for →American Wire Gauge.

awning

Awnings prevent the solar heat from entering the house through windows. A house design including awnings is considered an effective →passive cooling technique.

azimuth

Measure of orientation. In the solar technology, the azimuth angle indicates the deviation of solar collectors from the optimal south.

azimuth angle

Indicates the deviation of solar collectors from the optimal south. In the solar technology, the optimal south often acts as a reference point with a value of 0°, whereas in other fields, azimuth is usually measured in degrees clockwise from north.

azimuth direction angle

See →azimuth angle.

B

back contact

See →rear contact.

back contact cell

See →back contact solar cell.

back contact layer

See →rear contact.

back contact solar cell

Also known as a rear contact solar cell. A solar cell with a unique crystalline-silicon photovoltaic architecture that moves front contact grids to the back of the device. The placement of interleaved positive and negative contacts on the rear surface eliminates shading losses, resulting in a higher energy conversion efficiency.

back layer

The very bottom layer of a solar cell that acts as an electrical contact. See →back contact.

back pad

See →rear contact pad.

back reflector

See →back surface reflector.

44 

 back sheet

back sheet

See →backsheet.

back surface field

(BSF) Higher doped region at the rear surface of a solar cell.

back surface reflector

(BSR) A special, usually randomized metallic or silver layer added to the base of a thin-film solar cell to achieve high-reflectance performance. The reflector on the back of the cell reflects incident light and traps it inside the cell for possible absorption. Using a rugged surface as a reflector on the rear of the cell results in irregular bouncing of reflected light in different directions, increasing the amount of light trapping and absorption inside the cell.

backsheet

Also known as a back sheet. The protective film on the back of the solar module, which acts as an electrical insulator. The backsheet is typically made of the following composites: →Tedlar Polyester Tedlar (TPT) and →Tedlar sheet (polyvinyl fluoride). The main function of the backsheet is to protect solar cells and electrical contacts from harsh weather conditions, humidity and water vapor, and mechanical stresses.

backstop resource

See →backup power system.

backup

See →backup power system.

backup energy system

See →backup power system.

backup generator

A generator that is used in case of electrical power outage or when additional power is needed to supplement the solar system. A battery bank, gas generator, or a flywheel functions as backup generators in the event of an emergency.

back-up generator

See →backup generator.

backup heating

See →solar backup heating system.

backup heating system

See →solar backup heating system.

backup power supply

See →backup power system.

backup power system

An emergency power system that provides a secondary source of energy, such as battery bank or gas generator, when the primary source of energy, such as solar power or power grid, fails or does not provide enough electricity during extended periods of cloudy weather.

back-up system

See →backup power system.

backward vortex 

backward vortex

See →vortex shedding.

bad heat conductivity

See →low thermal conductivity.

 45

bad thermal conductivity See →low thermal conductivity. balance of system

(BoS) Encompasses all components and costs with the exception of the photovoltaic modules themselves. It includes a battery bank, mounting structure, inverters, controllers, wiring, safety equipment, meters, maximum power point trackers (MPPT), GPS PV trackers, design, installation, operation, maintenance, and other related costs.

balance of system components

BoS components encompass all components with the exception of the photovoltaic modules themselves. It includes a battery bank, mounting structure, inverters, controllers, wiring, safety equipment, meters, maximum power point trackers (MPPT), GPS PV trackers, and other related components.

balance of system costs

BoS costs encompass all costs with the exception of the photovoltaic modules themselves.

balance of system performance

BoS performance encompasses the performance of all components with the exception of the photovoltaic modules themselves.

balancing area

A geographical area, in which a balancing area authority ensures that the electricity supply meets demand.

balancing of electricity

See →load balancing.

ball screw

Component of a wafer dicing machine responsible for high-precision linear motion.

ballast load

In nonpenetrating, flat-roof installations, heavy ballasts, such as concrete blocks, which are placed on the structure to keep the solar system in place. As ballasted systems add a lot of additional weight to the roof, a detailed analysis and evaluation of the roof structure by a structural engineer is required.

ballasted mounting

Installation of mounting systems on flat roofs or on the ground with help of heavy ballasts, usually concrete blocks, that are placed on the structure to keep the photovoltaic array in place. Ballasted mounting does not require

46 

 ballasted mounting system

ground or roof penetration. This is the reason why it is still a preferred method for many PV installers, even though roofing and solar associations recommend the →mechanically attached mounting. Many solar owners tend to avoid drilling numerous holes in their roofs for a mounting structure at all costs, as these potentially lead to roof leaks. In addition, the installation costs can be significantly reduced when a roofer does not need to be hired to install numerous impermeable flashings on the roof. On the other side, heavy concrete blocks can put too much weight on the roof. Therefore, the ballasted mounting requires a structural engineer to carefully evaluate if a specific roof structure can carry not only the mounting structure and panels but also the additional weight of the heavy concrete blocks. Another disadvantage of ballasted mounts is the blocking of drainage pathways, resulting in an accumulation of standing water on the roof. This can speed up roof degradation and increase the potential for water leakage.

Ballasted Mounting

ballasted mounting system

A ground- or roof-mounting system that uses heavy ballasts, usually concrete blocks, that are placed on the structure to keep the photovoltaic array in place.

ballasted racking

See →ballasted mounting.

ballasted racking system See →ballasted mounting system. band

See →energy band.

band gap 

band gap

 47

Energy range between the highest →valence band and the lowest →conduction band. It is the distance between the valence band and the conduction band. It embodies the minimum energy that is needed to excite an electron to a higher energy excited state, in which it would have enough momentum to jump from the valence band into the conduction band. In →conductors, as the valence and conduction bands overlap, they typically do not even have a band gap. →Semiconductors have a narrow band between the valence and the conduction bands, and the energy of 1.1 electron volt (eV) is required to bridge the gap. When the electrons in the valence band are hit by photons of light, they can easily cross it, starting a current flow. On the other hand, →insulators have a wide band gap, representing the energy of over 4 eV, which separates the two bands. The band gap is too wide to be easily crossed. In most cases, it prevents the electrons from the valence band from jumping across the “forbidden” gap into the conduction band.

Overlap

Electron energy

Conduction band

Band gap

Valence band

Metal

Semiconductor

Band Gap

Insulator

48 

 band gap energy

band gap energy

The minimum amount of energy (e.g., thermal phonon energy or photon energy of light) required to excite an electron to jump from the →valence band to the →conduction band. Silicon semiconductor material has a band gap energy of 1.1 electron volts (eV).

band structure

See →electronic band structure.

bandgap

See →band gap.

BAPV

Abbreviation for →building-applied photovoltaics.

barometer

Instrument that measures atmospheric pressure.

barometric pressure

The pressure or force per unit area exerted by the weight of the air above that area, measured by a barometer.

barometric pressure sensor

A sensor that measures pressure fluctuations in the atmosphere.

barrier energy

Minimum energy required to liberate a free electron and penetrate the cell barrier.

barrier layer

See →diffusion barrier layer.

base

The balk material of the silicon semiconductor that is associated with the p-type absorber layer between the →p–n junction and the →rear contact.

base doping

Doping of base p-type silicon layer that influences →open-circuit voltage (Voc) and base resistivity, and hence the performance of a solar cell.

base load

The minimum amount of electric power a utility company must consistently supply over 24 h to meet consumer power demand.

base load plant

See →base load power plant.

base load power plant

Power plant that can consistently generate the required energy throughout the year.

base metal

See →base metal layer.

base metal layer

A conductive layer at the back of the solar cell. Electrons flowing out of the cell and supplying electrical appliances return to the PV cell through the rear base metal layer, closing the circuit.

base power

Reliable electricity generated and provided consistently by a utility company at a large scale.

base voltage 

 49

base voltage

See →nominal voltage.

baseline usage

Is a household’s rate of electricity consumption without heating and air conditioning. It accounts for an essential portion of the energy a household uses, like lighting, cooking, and refrigeration.

batch collector

Also known as an integral collector storage (ICS) system or bread-box collector. A batch collector is a solar water-heating system that heats water either in a single enclosed tank or in a series of bigger enclosed tubes. The storage tank is usually made of steel, whereas the tubes are usually made of copper. In order to better absorb the sun’s thermal energy, tanks or tubes are painted black or/and with a selective coating and function as a solar absorber. Regardless of which collector option is used, a single tank or a series of tubes, they are placed in an insulated box that has glazing on the top side facing the sun to reduce heat loss. This is in particular important at night and in colder winter days. However, batch collectors should not be used in regions with temperatures below the freezing point, as the water in tanks/tubes might freeze and crack the tank/pipes open. In spite of this restriction, batch collectors are still widely used in warmer climates due to their high efficiency. As they are typically mounted on a house’s roof, they do not require a pump and are usually plumbed in-line with the domestic water and the existing water heater. In particular, when mounting a single tank on the roof, a reinforcement of existing roof structure should be considered due to the heavy weight of the tank.

battens

Long and narrow strips of squared wood or metal used to support solar modules. In addition to their decorative and shading function, various cross batten structures can also be utilized as support structures for solar panels, creating →solar car ports or →solar canopies.

battery

A collection of two or more electrochemical cells connected together to store and provide electricity when needed. This energy storage unit converts the chemical energy into electricity to power household appliances. They can be rechargeable or nonrechargeable. The standard battery voltages used for off-grid PV power systems are 12, 24, and 48 VDC.

50 

 battery available capacity

battery available capacity

See →battery capacity.

battery backup

Backup power supply, if the power grid fails.

battery bank

Also known as a battery pack. A group of batteries connected together to store and produce electricity for electrical devices. The batteries can be connected in parallel, where voltage remains the same, but the capacity of each battery is added together; or they can be connected in series, where the capacity across batteries remains the same, but the voltage of each battery is added together. Deep-cycle lead-acid batteries are commonly used in off-grid PV power systems, because they can be deeply discharged (up to 80% of its capacity) and recharged several hundred times over. Small PV systems on an RV or boat use small battery banks that are wired to provide constant 12 V power source for electrical equipment. In stand-alone PV power systems for an entire house, the batteries are connected to provide 24, 48, or even 110 V DC electricity. An inverter is used to convert direct current (DC) to grid-compatible alternating current (AC) to run household appliances.

battery cables

Battery cables are used to interconnect individual batteries in a battery bank. For this purpose, large high-quality cables made of fine-strand copper conductors are required.

battery capacity

Is measured in ampere-hours (Ah). A total amount of electrical current (ampere-hours) that can be drawn from a fully charged battery.

battery cell

A basic unit of a battery that stores electricity and releases it upon need to supply external electrical devices. Each battery cell consists of the following three main parts: electrodes/ plates, separators, and electrolyte. For instance, a lead-acid battery cell has two electrodes and two sets of eight overlapping plates. Negative plates are made of sponge lead and positive plates are covered with a paste of lead dioxide. Porous separators separate the positive and negative plates to prevent short circuits. The plates are soaked in an electrolyte, consisting of 65% water and 35% sulfuric acid (H2SO4). A battery typically has many cells. A lead-acid battery has six single cells (2 V per cell) that are connected together in series to produce a battery of about 12 V.

battery charge level 

 51

When the battery, for example, a lead-acid battery, is being discharged, the cell converts chemical energy into electrical energy. The negative electrode/plate (anode) covered with lead is being oxidized, releasing two electrons. Two electrons are flowing from negative to positive terminal, supplying on its way the external load with electricity, and re-entering the battery through the positive electrode. The positive electrode/plate (cathode) covered with lead dioxide is being reduced in the process. Lead (Pb) loses two electrons and lead dioxide (PbO2) receives those same two electrons. During the discharge process, both electrodes become coated with lead sulfate; the sulfuric acid (H2SO4) electrolyte is used up and water is produced. When the lead-acid battery is being recharged, the cell is converting electrical energy into chemical energy, and the chemical reactions are reversed. The electrons are flowing in the opposite direction, from positive to negative terminal. Now, the positive electrode/plate (cathode) covered with lead dioxide (PbO2) is being oxidized, losing two electrons, whereas the negative electrode/plate (anode) covered with lead (Pb) is being reduced, gaining those same two electrons. During the recharge process, the lead sulfate coating on the electrodes is removed, the lead and lead dioxide regenerated, the water is used up, and the sulfuric acid (H2SO4) is produced. The battery is recharged and ready to be used again. battery charge level

Available amount of energy in a battery, expressed as a percentage of fully charged. The percentage of remaining battery charge is also often displayed on the status bar.

battery charge regulator A control system that protects the battery from overcharge and overdischarge. battery charger

A device for charging batteries by converting utility AC power into direct current (DC) power stored in batteries. Unlike conventional battery charger, a →solar charger converts solar energy into DC that is directly stored in batteries.

battery charging cycle

See →charging cycle.

battery control system

A control system that monitors charging and discharging processes for optimal performance of a rechargeable battery.

52 

 battery cycle life

battery cycle life

The number of charge/recharge cycles that a battery can undergo before it starts to reduce noticeably its performance and its capacity falls below 80% of its rated capacity.

battery desulfation

See →desulfation.

battery disposal

Environmentally conscious removal and disposal of all batteries in accordance with the current federal and state laws and regulations of a country. Most batteries contain toxic chemicals, such as lead, lead dioxide, or a sulfuric acid solution electrolyte, so that the improper disposal can be harmful to the environment, affecting the health of humans, animals, and plants.

battery energy capacity

See →battery capacity.

battery energy storage

Provides a number of benefits to both homeowners and public utility services. To homeowners, the battery energy storage provides a backup power that can supply steady electricity during outages. It increases photovoltaic self-consumption by saving excess solar energy during the day and delivering it in the evening and night when the sun is not shining. Finally, it enables load shifting by allowing homeowners to charge their batteries during →off-peak time when utilities sell electricity at lower rates and use the stored cheap energy during the hours of high electricity demand and high electricity rates (→peak hours). To public utilities, the battery energy storage provides grid stabilization, →spinning and nonspinning reserve, increased power quality, →load balancing, and deferred generation, transmission, and distribution investments. Through the widespread deployment of home batteries as reserve services for grid, utilities can defer conventional utility investments and build less power plants, transmission and distribution lines.

battery hydrometer

An instrument for measuring the state of charge of a battery.

battery life

Is a measure of battery longevity. When the capacity of a battery falls under 80% of its rated capacity, it is considered the end of battery life. After that threshold, the battery deteriorates rapidly and shows poor performance. The battery life can be measured in three ways:

battery life cycle 

 53

1. In years. Regardless whether the battery is used or not, it will deteriorate over time. The temperature and time affect the calendar life of a battery. 2. In milliampere hours (mAh) or ampere hours (Ah) as specified by the manufacturer. 3. In cycles that are defined as the number of charge/ recharge cycles that a battery can undergo before it starts to noticeably reduce its performance and its capacity falls below 80% of its rated capacity. The battery life can be prolonged by proper charge management. When electrical usage and battery charge level are carefully monitored, ensuring that batteries are not deeply discharged (under 50%), the battery bank of a PV system will certainly last longer. battery life cycle

Lifetime of a battery.

battery management system

(BMS) A system that monitors charging and discharging processes for optimal performance of a rechargeable battery. Depending on the model, the automatic battery management system can monitor state of charge, state of health, current, voltage, and temperature, to ensure optimal and safe operation and the long life of a battery.

battery on float charge

When the battery has reached between 95% and 98%, depending on the charger brand, it switches to float charge stage. At this stage, the voltage and current decrease to ensure the safe charging at a measured rate. The float charge brings the battery to a 100% state of charge and maintains it in the fully charged condition.

battery pack

See the →battery bank.

battery performance

Rechargeable battery performance.

battery plate

Positive and negative plates are major components of a battery. These thin, flat metal plates, typically made of lead or lead compound, are the electrodes of a battery consisting of a grid and active material. The plates are immersed in the electrolyte of the battery.

battery power allowance A small amount of power needed to keep batteries running. battery self-discharge

Energy loss by an inactive battery sitting on the shelf.

battery shelf life

The period of time that a device can be stored and still perform according to its intended use and specification. It

54 

 battery state of charge

determines when a device should be taken off the shelf in a store and declared unfit for sale, for example, when the battery drops under 80% of its original capacity. battery state of charge

See →state of charge.

battery sulfation

See →sulfation.

beam

Column of light. Beam is a bundle of rays consisting of parallel, converging, or diverging rays. 

beam bending

Changing of a beam shape as a result of a bending moment.

beam generator

See →diffractive beam splitter.

beam irradiation

When solar radiation reaches a photovoltaic cell directly from the Sun without any obstacles, for example, clouds or pollution, we talk about a beam irradiation, →direct solar radiation, →direct beam radiation, →beam solar radiation, or →beam radiation. The best solar energy yield is achieved on a clear day, when solar radiation travels on a straight line from the sun to a PV surface.

beam path

The trajectory of a light beam from a light source, such as the Sun or a laser, to a light-absorbing surface, for example, a solar panel, a window, a cloud, or a target material.

beam radiation1

See →direct normal irradiance.

beam radiation2

When solar radiation reaches a photovoltaic cell directly from the Sun without any obstacles, for example, clouds or pollution, we talk about a beam radiation, →direct solar radiation, →direct beam radiation, →beam solar radiation, or →beam irradiation. The best solar energy yield is achieved on a clear day, when solar radiation travels on a straight line from the sun to a PV surface.

beam solar radiation

See →beam radiation.

beam splitter

See →diffractive beam splitter.

bench test for solar modules

A test carried out on solar modules prior to their release or installation to ensure they are in perfect condition and work as designed. A bench test can include performance testing, reliability testing, and failure testing. For instance, a solar simulator with a powerful halogen lamp can be employed to illuminate the photovoltaic module under test. A ventilator with a temperature regulator helps

benzene 

 55

evaluate the effects of temperature on PV panels. A variable electrical load is applied to the output of the photovoltaic module to assess the electrical resilience of solar panels. benzene

(C6H6) An organic chemical compound that is composed of six carbon atoms and six hydrogen atoms. It is a colorless volatile flammable toxic liquid hydrocarbon that is used in the production of polymer thin films.

beyond the meter services

Services, such as home automation systems, energy management systems, demand response programs, data analysis, or auditing and security, that utilities offer to their customers in search for additional source of revenue.

BGP

See →boron glass powder.

biaxial tracker

See →dual-axis tracking system.

biaxial tracking

See →dual-axis tracking system.

biaxial tracking system

See →dual-axis tracking system.

bidirectional inverter 

An inverter that can convert DC to AC or AC to DC.

bidirectional meter

A meter that measures electricity flow in two directions. Similarly to a traditional →electricity meter, it reads how much electricity flows into your home from the utility company. In addition to measuring the consumed energy, it also measures the electricity fed into the public electrical grid.

bidirectional reflectance A ratio of reflected solar radiation to incident radiation. When the sunlight hits an opaque surface, one part of radiation is absorbed, whereas the other part bounces off in irregular manner, depending on the surface properties that are in most cases not as geometrical as a mirror. bifacial photovoltaic cell See →bifacial solar cell. bifacial photovoltaic module

Absorbs solar radiation from both sides of the PV module (see the figure on page 56). The front side of the module including monocrystalline silicon and amorphous silicon semiconductor layers absorbs direct and diffuse solar radiation, whereas the back side with an a-Si layer captures diffuse solar radiation from the sky and the reflected light from surrounding surfaces.

56 

 bifacial photovoltaic panel

Bifacial Module

Monofacial Module

Glass

Glass

White/black backsheet

Transparent backsheet Roof

Roof

Bifacial Photovoltaic Module

bifacial photovoltaic panel

See →bifacial photovoltaic module.

bifacial PV cell

See →bifacial solar cell.

bifacial PV module

See →bifacial photovoltaic module.

bifacial PV panel

See →bifacial photovoltaic module.

bifacial solar cell

Captures sunlight from both sides of the solar cell. A single-crystal silicon wafer is sandwiched between two thin amorphous noncrystalline silicon layers. The monocrystalline silicon layer absorbs →direct solar radiation, whereas amorphous silicon layers work best in cloudy weather and better capture diffuse solar radiation and reflected light. As they absorb multiple parts of solar spectrum, bifacial solar cells have a higher absorption rate and therefore higher performance than single-sided modules.

bifacial solar module

See →bifacial photovoltaic module.

bifacial solar panel

See →bifacial photovoltaic module.

bimodal inverter

See →multimodal inverter.

binding energy

The energy required to free an electron from a molecule, an atom, or a nucleus.

biofuel

A fuel, such as ethanol, methanol, or biodiesel, made from different types of vegetation – organic matter called biomass.

biomass

Plant-derived materials, including wood, vegetation, grains, or agricultural waste. Biomass is used as a fuel or energy source.

biomimetic photovoltaic cell 

 57

biomimetic photovoltaic cell

See →biomimetic solar cell.

biomimetic photovoltaics

Photovoltaic technology mimicking natural systems, such as leaves.

biomimetic PV cell

Biomimetic photovoltaic cell. See →biomimetic solar cell.

biomimetic solar cell

Solar cell mimicking natural systems, such as leaves.

biomimetic solar technology

Solar technology mimicking natural systems, such as leaves.

biomimetics

A method of mimicking natural systems.

biosolar house

Energy-efficient house.

bipolar battery

Also known as layer cells and stacked wafer cells. A battery consisting of a plurality of cells that are designed according to the following configuration: a separator, such as fibrous boron nitride, is sandwiched between the negative electrode (a lithium alloy) and the positive electrode (iron sulfide). The electrodes are electrically insulated from one another by a separator element. The cells are grouped and electrically connected in series to generate higher voltage output. Electrodes are shared by two series-coupled electrochemical cells in such a way that one side of the electrode acts as an anode for one cell and the other side acts as a cathode for the adjacent cell.

bipolar plate

A conductive plate that connects and separates the individual fuel cells in series, forming a fuel cell stack. The bipolar plate has a multifunctional character, as it acts as an anode in one cell and a cathode in the next cell.

BIPV

Abbreviation for →building-integrated photovoltaics.

BIPV system

A system that uses →building-integrated photovoltaics.

bird lobby

A group of people who try to raise awareness about endangered bird species and influence a government or public officials to adopt their protective action recommendations. Regarding the solar energy generation, the bird lobby claims that solar farms, in particular →concentrated solar power plants, threaten birds. For instance, according to a federal biologists’ study, around 6,000 birds a year are killed by flying through a concentrated beam of sunlight

58 

 bituminous sand

at the Mojave Desert Ivanpah solar plant. The bird lobby seeks ways to protect birds from solar power plants and deadly concentrated rays. bituminous sand

A bitumen-send mix that is used in tank foundation to provide a firm layer and a weather protection, preventing corrosion of the tank bottom.

bivalent hot water cylinder

See →bivalent hot water storage tank.

bivalent hot water storage tank

Also known as a bivalent hot water cylinder. A tall, upright-standing hot water cylinder that allows →thermal stratification – keeping heavier cold water at the bottom and lighter warm/hot water at the top of the tank. Bivalent tanks have two heat exchangers.

bivalent solar hot water cylinder

See →bivalent solar hot water storage tank.

bivalent solar hot water storage tank

Also known as a bivalent solar hot water cylinder. A storage tank with two heat exchangers: a solar heat exchanger that transfers warm water from a solar thermal collector to the bottom of the cylinder, where the heavier, cold water gathers, and a backup heat exchanger at the top of the cylinder that is applied when the solar hot water resource is insufficient, for example, on cold winter days.

black body

Also known as blackbody. A theoretically ideal absorber that absorbs all the electromagnetic radiation that falls on it. The black body is also an ideal radiator, emitting the maximum amount of energy according to its temperature.

black body radiation

The energy emitted by a blackbody.

black monocrystalline solar cell

A high-efficiency solar cell made of monocrystalline semiconductor material. The monocrystalline solar cell tends to have a black hue. In addition to their high conductivity due to the purity of the monocrystalline semiconductor material, black surfaces naturally absorb more light than their blue polycrystalline counterparts.

black silicon

A nanostructured silicon that appears black due to the low reflection of visible wavelengths. The nanostructuring of silicon surfaces reduces optical front-surface reflection in solar modules, which results in an increased amount of

black silicon solar cell 

 59

absorbed photons in solar cells. An increased number of photons in the solar cell lead directly to a higher number of generated charge carriers, electrons and holes, and thus the higher power output of the →photovoltaic cell. A Harvard team created the material by combining a gaseous sulfur compound with a silicon wafer in a vacuum. After that, they bombarded the silicon wafer surface with a femtosecond laser to restructure it on the nanoscale. black silicon solar cell

A solar cell with a nanostructured surface that reduces the amount of optical reflectance, thus increasing the absorption of visible and infrared light in the semiconductor material. The nanostructured silicon surface consists of an array of microscopic rods, spikes, or cones of variable sizes and spaces on a nanometer scale. The surface morphologies of black silicon solar cells are examined by →scanning electron microscopy (SEM). The cones or rods can have a base diameter of 100–150 nm and height of 800–1000 nm. The nanostructured silicon can absorb solar radiation over a wider spectrum than traditional silicon. It is able to capture light from low-frequency visible light through near- and short-wave infrared wavelengths that would usually be transmitted through the normal semiconductor material and lost. Even though this nanotechnology holds promising potentials and a significant route toward higher efficiency PV devices, it is not without issues. Solar researchers are looking for a better integration of black silicon into PV cells, as the increased charge carrier recombination at the nanostructured silicon surface still seems to be an obstacle to higher conversion efficiencies.

black water

Waste water that gets flushed down the toilet. It is more challenging to process and recycle black water than →gray water.

blackbody

See →black body.

blazed grating

Also known as echelette grating. A type of diffraction grating, either transmissive or reflective, which through its profile can redirect the incident light into only one specific diffraction order to achieve the maximum efficiency.

60 

 blemished solar cell

blemished solar cell

A new solar cell with a minor defect (e.g. scratch or similar cosmetic imperfection) preventing it from being sold as new merchandise. However, the cell is functional and the slight defect does not affect the cell’s performance.

blemished solar module See →blemished solar panel. blemished solar panel

A new solar panel with a minor defect (e.g. scratch on the frame or similar cosmetic imperfection) preventing it from being sold as new merchandise. However, the panel is functional and the slight defect does not affect the panel’s performance.

blocking diode

A diode that prevents the reverse current from flowing backward through a module. It functions like a one-way valve, allowing electricity to flow only one way. Blocking diodes are installed on the output end of a PV panel, usually in a junction box, to prevent undesired discharging by reverse flow of electrical current from the battery bank to the PV array, for example, in the dark or under cloudy conditions, when no current is generated by the PV modules.

block-type thermal power plant

US (BTTP) A thermal power plant generating both electrical and heat energy.

block-type thermal power station

UK (BTTP) A thermal power station generating both electrical and heat energy.

BMS

Abbreviation for →battery management system.

BMUB

Abbreviation for Bundesministerium für Umwelt, Naturschutz, Bau und Reaktorsicherheit. See →Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety.

BNetzA

Abbreviation for Bundesnetzagentur. See →Federal Network Agency.

boat

See →evaporation boat.

boiler drain cock

See →boiler drain valve.

boiler drain valve

Also known as a boiler drain cock. In a solar water-heating system, a valve that allows water from a solar storage tank to be drained.

bolometer

Instrument for measuring electromagnetic radiation.

bonding 

 61

bonding

See →chemical bond.

borane

Any of the compounds of boron and hydrogen, for example, trihydridoboron (BH3).

BORCAL

Abbreviation for →Broadband Outdoor Radiometer CALibration.

borehole

A hole drilled in the bedrock to transport excess heat from solar thermal collectors into the ground in summer and extract that thermal energy in winter when needed for domestic hot water and space heating in buildings.

borehole thermal energy (BTES) A type of →seasonal thermal energy storage in storage which the generated heat is transferred from solar thermal collectors into underground boreholes. Unlike →CTES and →ATES that use natural underground caverns and →aquifers for thermal storage, boreholes need to be drilled to depths of 50 m (164 ft) or more. After drilling, polyethylene probes are inserted into underground holes, forming a closed-loop system that is connected with a →heat exchanger above ground, regulating temperature in a building or a district →solar thermal heating plant. The main advantage of the BTES technology is that it is not limited to sites with natural underground aquifers and caverns but it can be installed into any bedrock that allows drilling. Another important advantage is that the BTES system can be customized to the required size. Correspondingly, while a small-scale BTES system for a residential building will require only a few boreholes, a large-scale district heating BTES system can consist of over 100 boreholes. boron

(B) Semimetal that is frequently used as a p-type dopant for silicon semiconductors in photovoltaic cells. Boron is a chemical element with atomic number 5 that has three electrons in its outer shell. When added to a silicon semiconductor, a boron atom creates a hole in the silicon crystal lattice because it has one electron less (three valence electrons) than the surrounding silicon atoms (four valence electrons), which is not enough to fill all four bonds. A hole gladly accepts an electron from a neighboring silicon atom, compensating for the boron’s electron deficiency. At the same time, it leaves a hole behind in the neighboring silicon atom, which is instantly filled up by another

62 

 boron etch-stop

electron from another neighboring atom, and so on and so forth. Holes are uninterruptedly created and filled. This chain reaction in which electrons are moving in one direction across the silicon crystal lattice and holes in the opposite direction produces electrical current. In this process, silicon atoms donating electrons to fill the vacancies in the neighboring atoms become positively charged, producing a p-type layer and improving remarkably the conductivity of the silicon semiconductor. boron etch-stop

A boron-doped film (membrane) that stops the etching process at the exact depth of an →etched trench.

boron glass powder

(BGP) A chemically resistant powder with a low thermal expansion coefficient. The BGP can be manufactured as rod, tube, or plate and utilized at high temperatures.

boron-containing glass powder

See →boron glass powder.

boron-doped diffusion paste

A p-type doping paste for solar cells that can uniformly diffuse →boron onto the silicon surface.

borosilicate glass

A strong and heat-resistant glass consisting of →silica and boron oxide. In →evacuated tube solar collectors, twinglass vacuum tubes are typically made from strong borosilicate glass.

BoS

Abbreviation for →balance of system.

BOS performance

See →balance of system performance.

BOS product

See →balance of system components.

Bosch process

See →deep reactive ion etching.

boule

Single crystal ingot, wafer production using the →Czochralski process.

bound dopant species

Dopant species that are chemically bonded to other atoms. They can be blended into a suspension including silicon oxide-based nanoparticles or silicon nanoparticles. Bound dopant species may be an →n-type dopant or a →p-type dopant atom, such as a →boron or →phosphorous atom. They are included into the →dopant ink and deposited onto a substrate by →inkjet printing, →screen printing, →spin coating, blading, →etching, →slot-die coating, and →gravure printing.

bound state 

 63

bound state

See →valence state.

box cooker

Also known as a solar box cooker or solar oven. See →solar oven.

bread-box collector

Also known as an integral collector storage (ICS) system or batch collector. Bread-box collector is a solar water-heating system that heats water either in a single enclosed tank or in a series of bigger enclosed tubes. The storage tank is usually made of steel, whereas the tubes are usually made of copper. In order to better absorb the sun’s thermal energy, tanks or tubes are painted black or/and with a selective coating and function as a solar absorber. Regardless of which collector option is used, a single tank or a series of tubes, they are placed in an insulated box that has glazing on the top side facing the sun to reduce heat loss. This is in particular important at night and in colder winter days. However, bread-box collectors should not be used in regions with temperatures below the freezing point, as the water in tanks/tubes might freeze and crack the tank/pipes open. In spite of this restriction, bread-box collectors are still widely used in warmer climates due to their high efficiency. As they are typically mounted on a house’s roof, they do not require a pump and are usually plumbed in-line with the domestic water and the existing water heater. In particular, when mounting a single tank on the roof, a reinforcement of existing roof structure should be considered due to the heavy weight of the tank.

breaker panel

See →distribution panel.

Bridgman method

Method for growing single crystals from melt.

Bridgman technique

See →Bridgman method.

Bridgman–Stockbarger method

See →Bridgman method.

Bridgman–Stockbarger technique

See →Bridgman method.

bright sunshine

Solar radiation strong enough to cast distinct shadows and be recorded by a →Campbell–Stokes sunshine recorder. The recorded data of a the Campbell–Stokes sunshine recorder are used for calculating the mean daily, monthly, or annual

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 British thermal unit

total hours of bright sunshine for a given location. The Campbell–Stokes sunshine recorder is able to record the duration of bright sunshine during the day and to disregard weak sunlight below the Campbell–Stokes recorder threshold, which occurs during “visible” daylight hours after sunrise and before sunset as well as during cloudy hours. The lower threshold for bright sunshine is between 70 W/m2 (very dry air) and 280 W/m2 (very humid air). British thermal unit

(BTU, Btu) British thermal unit is used for solar thermal measurements. It is the amount of heat required to raise the temperature of 1 lb (0.45 kg) of water by 1 °F (0.55 °C).

Broadband Outdoor Radiometer CALibration

(BORCAL) The method developed by the →NREL for the annual →calibration of →pyranometers and →pyrheliometers based on the summation technique.

broadband solar irradiance

The solar radiation arriving at the Earth’s surface that includes all the different wavelengths of electromagnetic radiation. The total broadband flux is obtained by summing flux over all wavelengths. However, the scope is limited to the spectral range of available measuring instruments. While →pyranometers and →pyrheliometers are able to measure broadband solar irradiance (ultraviolet, visible light, and infrared) from approximately 0.3 to 3 μm, other wavelengths must remain outside of the measuring range. The present solar cells are limited to a range of approximately 0.3–1 μm.

brownfield

See →disturbed area.

BSF

Abbreviation for →back surface field.

BSR

Abbreviation for →back surface reflector.

BSW

Abbreviation for Bundesverband Solarwirtschaft. See →German Solar Industry Association.

BTES

Abbreviation for →borehole thermal energy storage.

BTTP

Abbreviation for →block-type thermal power plant.

Btu

Abbreviation for →British thermal unit.

bubble cover

See →solar pool cover.

Buckminsterfullerene

See →fullerene.

buffer storage 

 65

buffer storage

A temporary storage of generated photovoltaic or solar thermal energy.

buffer storage unit

In solar–thermal systems, a water tank for the storage of heat energy acts as a buffer storage unit. In photovoltaic systems, batteries for the storage of generated electric current fulfill that function.

building envelope

Also known as building skin. The imaginary assembly of planes, including walls, floors, roofs, fenestrations, and doors, which indicates the maximum volume of a building with regard to zoning. Different climate types require different building envelops. To successfully match the building skin to the local climate and take advantage of →passive solar building design strategies, it is important to select suitable building materials and apply appropriate insulation and building techniques.

building skin

Colloquial expression for →building envelope.

building thermography

Thermal infrared (IR) imaging for buildings that makes heat energy visible.

building-applied photovoltaics

(BAPV) Unlike building-integrated photovoltaics, which entirely integrate PV cells into the original building construction by replacing materials of the building envelope with photovoltaics, building-applied photovoltaics add solar panels to an existing building structure in a postconstruction step. See also →building-integrated photovoltaics.

building-integrated photovoltaics

(BIPV) Use of photovoltaics, for example, →solar roof, →solar façade, →solar canopy, or →solar windows, in place of conventional materials of the building envelope. When a new house is built, →solar shingles and →solar tiles are integrated into the roof, →solar façade clads the walls, →solar canopy provides shade from the sun and shelter from rain, and →solar windows and →solar skylights protect an interior from direct solar radiation, while simultaneously generating electricity from PV panels. Building-integrated photovoltaics provide a thermal insulation, offer a unique external design, and generate energy for households or businesses.

building-integrated PV

(BIPV) See →building-integrated photovoltaics.

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 building-integrated solar system

building-integrated solar A solar system that is not installed onto the roof with help system of a roof-mounting structure, but it is integrated into the roof, the walls, or the glass façade of a building. Solar panels fulfill a dual function: not only do they produce electrical energy, but they also serve as an outer layer of the building, performing the waterproofing function. In doing that, they replace traditional cladding materials, for example, roofing material or conventional glass windows. The building-integrated solar systems eliminate the need for bulky mounting structures of conventional PV arrays, while offering simultaneously a more robust and sturdier structure able to withstand heavy rain, high winds, and hail. Their flat profile ensures a low-wind drag, thanks to their more aerodynamic shape. They also provide a more refined, aesthetically pleasing design than traditional roof-mounted PV systems, as the solar structural part is architecturally better united with the whole building. bulk charge

See →bulk charge stage.

bulk charge stage

The first stage in a three-stage lead-acid battery charge cycle in which the charge controller allows maximum charging to 80% of the battery capacity.

bulk charging

See →bulk charge stage.

bulk stage

See →bulk charge stage.

Bull’s eye effect

The etch phenomenon by which edges of wafer have a higher etch rate than the central regions.

bunded pallet

Also known as spill containment pallet. A secondary containment item designed for transport of old batteries, chemicals, and damaged solar panels containing hazardous materials, such as →cadmium telluride.

buoyancy

Tendency of less dense objects to float or rise in a fluid (water or air), for example, upward movement of hot air in a chimney or building.

buoyancy ventilation

See →stack ventilation.

bus bar

See →busbar1.

bus ribbon

See →bus wire.

bus wire 

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bus wire

Also known as bus ribbon. A flat wire that is used to connect the strings of solar cells (tab wires) together and steer the current to the junction box of a PV module. In order to channel current with minimal losses, this conductive wire is typically made of copper, the metal with very high electrical conductivity. The copper ribbon is coated in solder that serves as a protection against oxidation and a suitable surface for a strong solder bond between tab and bus wires. The bus wire is at least two times wider and often ticker than the tab wires, to which it is connected, because it needs to be able to conduct the higher amount of current collected from the solar cell strings.

busbar cost

Average power generation costs up to the point of the power plant busbar.

busbar1

Metallic strip that conducts electricity along a silicon solar cell. A net of numerous miniature conductive lines called →fingers are connected with two busbars on each silicon solar wafer. The fingers collect the electricity generated within the photoactive silicon semiconductor and transport it to two busbars. Then the busbars conduct the electricity to the next cell and further through the module’s circuit. There are two types of busbars: busbars of constant width and tapered busbars. The latter are tapered at the ends of a PV cell and have lower resistive losses than busbars of constant width. The commonly used materials for busbars are copper and aluminum.

Fingers

Busbars

Busbar

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 busbar

busbar2

In a power plant, a main bar or conductor that functions as a starting point of the electric transmission system, connecting two or more circuits.

bussing

Connecting several strings of solar cells (tab wires) together with →bus wires to steer the current to the junction box of a PV module.

button cell

Nonrechargeable single-cell battery.

butyrate

See →cellulose acetate butyrate.

buy-back agreement

See →buy-back contract.

buy-back contract

A contract between a utility company and a customer in which the utility agrees to buy back all excess electricity produced by the PV system owner at a stated price.

bypass diode

Solar cell protection that eliminates hot spots in case of partial module shading or broken cells. Bypass diodes are installed across solar cells in a photovoltaic module, usually at the end of each group of cells. They are also installed across photovoltaic modules in a PV array and can be typically found in →PV junction boxes. They prevent damage from overvoltage due to high-resistance conditions (hot spots) by diverting the current past shaded or broken cell/module.

bypass valve

In an →active solar heating system, a valve that is attached to a bypass line to control the flow of fluid when parts of the system need to be bypassed for the purpose of repair.

bypassdiode

See →bypass diode.

C CAB

Abbreviation for →cellulose acetate butyrate.

cable diameter

See →cable thickness.

cable duct

A rigid duct that holds cables that interconnect solar components and route power from the solar source to loads. The cable housing can be manufactured from different materials, such as galvanized or stainless steel, aluminum, or various types of plastics. The cable duct provides wire

cable layout 

 69

management and cable protection from impact damage and adverse weather conditions. cable layout

A detailed layout of the entire system including all PV components and cable connections. The cable layout diagram is a crucial help for →solar installers, giving them a clearer understanding on the relationship between connections and showing them how to wire components together into a functioning circuit.

cable losses

Power losses in electric cables depend on the cable thickness, length, and current strength (cable material). Therefore, it is essential to calculate the correct cable thickness to match the electrical load being run through the cables. Cable lengths should be kept as short as possible, as longer cables increase voltage drop and energy losses due to resistive heating in the cable. Finally, high-quality copper or aluminum conductor materials should be used with a thick weather-, abrasion-, and UV-resistant jacket.

cable route

Cable routes connecting different components of a photovoltaic system should be as short as possible to reduce power losses within the PV system.

cable sizing

Careful selection and calculation of cable type, thickness, length, and insulation.

cable sizing calculator

A device, typically an application, for calculating the correct size of cables for a solar system.

cable thickness

The wire thickness must be carefully calculated to match the electrical load being run through the cables to enable a smooth current flow, preventing the voltage drop in the line. Using a wire that is too thin will result in a high resistance, conductor heating, significant energy losses, and in case of an extreme wire size mismatch even a fire. The high resistance can be decreased by using thicker gauge wires, which can better handle bigger currents, enabling a smoother electron flow through the wire. On the other side, using cables that are too thick may result in increased costs that go way beyond what is necessary. Therefore, the correct wire size will meet the least electrical resistance, minimize energy losses, and keep your costs down.

cable tray

See →cable duct.

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 cables

cables

There are four types of cables that are used for connecting different components of a solar system: →photovoltaic wires, controller cables, inverter cables, and battery cables. Photovoltaic wires or solar cables are used for interconnecting solar modules. Controller cables connect the controller with the battery bank. In general, they can have the same wire thickness as solar cables, since these wires carry no more current than the solar module wires. Inverter cables connect an inverter with batteries and household appliances in a →stand-alone solar power system. Inverters require the largest cables in a solar system to ensure the full current flow to the appliances. Sizing of these wires depends on the battery voltage and needs to be individually calculated. Battery cables are used to interconnect individual batteries in a battery bank. For this purpose, large high-quality cables made of fine-strand copper conductors are required.

cadmium

(Cd) Dense, heavy metal, hazardous due to its toxicity. This chemical element with atomic number 48 is used in the manufacture of →cadmium telluride thin-film solar cells and certain types of batteries.

cadmium sulfide

(CdS) A semiconductor material used in combination with other materials for manufacturing of certain types of →thin-film solar cells. The cadmium sulfide is always an →n-type semiconductor, for instance an n-doped layer in a →cadmium telluride thin-film solar cell or →CIGS thin-film solar cell.

cadmium telluride

(CdTe) A polycrystalline semiconductor material of II–VI group with an energy band gap of 1.56 eV used in the manufacture of →cadmium telluride thin-film solar cells.

cadmium telluride thinfilm solar cell

Type of thin-film solar cell that uses cadmium telluride as a semiconductor material. Cadmium telluride is commonly used in the production of thin-film PV cells because it can absorb a broad spectrum of the solar radiation. The major disadvantage of cadmium telluride is its toxicity. It is hazardous for humans and animals and can damage the environment if not disposed of properly. Therefore, extreme caution is required during the manufacturing process as well as during the recycling at the end of the product life.

cadmium telluride thin-film solar module 

 71

Sunlight

Glass Transparent conductive oxide (TCO) n-layer (CdS) p-layer (CdTe) Aluminium (back contact)

Cadmium Telluride Thin-film Solar Cell

cadmium telluride thinfilm solar module

A solar module that uses cadmium telluride as a semiconductor material. Cadmium telluride is an efficient light-absorbing, thin film material that is employed as a p-type absorber together with a much thinner layer of n-type →cadmium sulfide (CdS) in a CdTe solar module. Conversion efficiency of over 22% has been achieved with laboratory cells and over 18% with commercial fullsized modules. Compared to the 100 times thicker crystalline silicon semiconductor layer, only a thin layer of CdTe, which is 1–8 μm thick, is required to absorb solar radiation and convert it into electricity. The minimal material usage of 2 g/m2 significantly reduces the costs of a solar panel. In addition, CdTe also has the lowest production cost per watt. Compared to other production methods, cadmium telluride is easy to deposit and can be manufactured at a relatively high speed by using one of the following deposition methods: →physical vapor deposition, →sputter deposition, vapor transport deposition, or close space sublimation. Cadmium telluride is a stable chemical compound that does not degrade over time. This means that the power output of a solar module will remain relatively constant during the lifetime of the device. Silicon solar cell semiconductor materials are sensitive to temperature. When they heat up to a cell temperature higher than 25°C (77°F), the power output will decrease. Cadmium telluride is not susceptible to this decrease in performance due to high temperatures. That is why it is a preferred material

72 

 cadmium telluride thin-film solar panel

in hot climates. The largest solar farms in the hottest regions of the United States (California and New Mexico) Topaz, Agua Caliente, and Macho Springs use CdTe solar modules. Another important advantage of CdTe solar modules is the fact that they absorb diffuse radiation better than silicon modules. While the power output of the traditional silicon modules will be significantly reduced on cloudy days, the performance of the CdTe solar panels will be not as affected, as they make a better use of diffuse radiation. The major disadvantage of cadmium telluride solar modules is the toxicity of cadmium, which has a negative impact on the environment. cadmium telluride thinfilm solar panel

See →cadmium telluride thin-film solar module.

CAES

Abbreviation for →compressed air energy storage.

CAES plant

Compressed air energy storage plant. See →compressed air energy storage.

CAES station

Compressed air energy storage station. See →compressed air energy storage.

CAES system

Compressed air energy storage system. See →compressed air energy storage.

CAES technology

Compressed air energy storage technology. See →compressed air energy storage.

CAIBE

Abbreviation for →chemically assisted ion-beam etching.

calibration

The process of checking the accuracy of a measuring instrument and adjusting it to conform to a reliable standard. As the instruments for measuring solar irradiance, such as →pyranometers and →pyrheliometers, are inclined to deviate from the standard, their measuring results need to be periodically compared against those of the accepted reference instrument and corrected.

California Energy Commission

(CEC) A main energy policy and planning agency in California that provides access to data on energy production, consumption, research, conservation, and use. One of the major responsibilities of the commission is to promote energy efficiency and conservation by setting the appliance and building energy efficiency standards.

calorie 

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The commission is also committed to forecasting future energy needs and developing renewable energy resources. calorie

(cal) A unit of heat equal to the amount of energy required to raise the temperature of 1 g of water by 1 °C. It is also often referred to as 4.1868 J.

calorimeter

Instrument for measuring quantity of heat.

calory

(cal) See →calorie.

Campbell–Stokes recorder

See →Campbell–Stokes sunshine recorder.

Campbell–Stokes sunshine recorder

A meteorological instrument that records the amount of →bright sunshine on a given day. The duration of bright sunshine is determined by concentrating the light through a glass sphere onto a paper graph, where it creates a burnt track. As the day is divided into hours and minutes on the paper graph placed behind the glass sphere, one can calculate the mean daily total hours of bright sunshine for a given location by adding all burnt traces at the end of the day. During cloudy minutes and hours, the trace will be interrupted and those time intervals are not included into the calculation.

camping solar cooker

See →portable solar cooker.

Canadian Standards Association

(CSA) See →CSA Group.

capacitance

The property of a body to store an electrical charge.

capacitor

Component for temporary storing of electrical charges. It is made up of two conductive metal plates separated by an insulating dielectric. When an electrical current is fed into the plates, it creates an electric field across the dielectric, causing the plates to store a charge. Typically installed behind PV modules in a conventional PV array, capacitors are added to the system with a goal to smooth current spikes and maintain voltage stability. They ensure maximum power point voltage transfer and an optimal operation of the system. The major disadvantages of capacitors that are integrated in a PV system are: — the lifetime of a capacitor is much shorter than that of the rest of the PV equipment; — the electrolyte in electrolytic capacitors is likely to dry out at high temperatures.

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 capacity

capacity

See →battery capacity.

capacity demand response

A US electricity management program in which customers give the →system operator the right to call upon them to reduce demand during the hours of high energy demand, so-called →peak hours.

capacity factor

The ratio of the actual output of a power generation unit, for example, a PV solar array or a power plant, to its rated (nameplate) capacity over a period of time. If a PV system with a maximum (rated) power output of 300 MW generates power at an average of 250 MW, the system’s capacity factor can be calculated by the following formula: 250 MW/300 MW = 0.83. This means that 83% of the array’s capacity is actually utilized.

capacity rating

Also known as rated capacity. See →rated power.

capital costs

The costs associated with the initial costs of equipment, land, and installation of a solar system.

captive electrolyte

Immobilized electrolyte used in →sealed lead-acid batteries.

captive electrolyte battery

A rechargeable →sealed lead-acid battery with an immobilized electrolyte.

car sharing

See →electric car sharing.

carbon bisulfide

See →carbon disulfide.

carbon capture and sequestration

A low-fossil-fuel economy (LFFE) technology that captures CO2 emissions from industries, such as a coal electricity plant, and injects them into repositories located deep underground or beyond the bottom of the sea. The CO2 stored or sequestered in underground rock formations can potentially be reused later on.

carbon consumption

An indicator of carbon pollution and unsustainable energy use. It is usually calculated per person, city, region, or country. See also →carbon footprint.

carbon credit

See →carbon credit certificate.

carbon credit certificate

Also known as carbon credit. A tradable permit representing the right to emit one tone of carbon dioxide. The practice of issuing carbon credit certificates to countries serves the purpose of reducing →greenhouse effect emissions on an industrial scale and mitigating →global warming.

carbon dioxide 

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carbon dioxide

(CO2) A gas that is produced and emitted into the atmosphere, when fossil fuels, such as oil, gas, and coal, are burned. CO2 traps heat in Earth’s atmosphere, contributing significantly to →global warming and →climate change. The amount of this dangerous gas has increased 30% in Earth’s atmosphere since preindustrial times and the disturbing evidence shows that CO2 levels keep climbing, surpassing 400 parts per million (ppm) threshold in September 2016. CO2 is the major greenhouse gas and number one pollutant, which accounts for 72% of all →greenhouse gases (disregarding water vapor). It is a long-lived greenhouse gas that stays in the air for more than a century, once emitted into the atmosphere. Even though human-made CO2 additions contain 3.2% of all greenhouse gas concentrations, most of the anthropogenic pollution and climate change seems to be due to CO2.

carbon dioxide emissions

Also known as CO2 emissions. The release of carbon dioxide gas into the atmosphere. The CO2 emission is naturally produced by breathing, decomposition of plants, and ocean releases. The point of concern is, however, human-made CO2 emissions that upset natural balance of the carbon cycle and can be reduced by globally coordinated actions. The human CO2 emissions are produced by burning fossil fuels, such as oil, gas, and coal. The worldwide emissions of carbon dioxide keep climbing, contributing significantly to →global warming and →climate change. The largest sources of anthropogenic carbon dioxide emissions are: 1. power plants/electricity and heat generation, which accounted for 42% of global CO2 emissions in 2013; 2. transportation vehicles (cars, airplanes, ships, and trains), which were responsible for almost one quarter (23%) of CO2 emissions around the world in 2013; 3. industrial processes, for example, cement manufacturing, which accounted for 19% of CO2 emissions in 2013; 4. deforestation and agricultural activities; and 5. residential activities, such as fuel combustion in households, which accounted for 6% of global CO2 emissions in 2013.

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 carbon dioxide removal

carbon dioxide removal

(CDR) Also known as carbon geoengineering. A removal of carbon dioxide from the atmosphere with help of various technologies, such as carbon capture and sequestration in repositories located deep underground, tree planting, biochar or burying biomass in the soil, removing of CO2 by chemical engineering, and ocean fertilization.

Carbon Disclosure Project

(CDP) The association in the United Kingdom for climate protection.

carbon disulfide

(CS2) Also known as carbon bisulfide. A clear, colorless, toxic, highly volatile and flammable liquid with a strong disagreeable odor. In the manufacture of organic photovoltaic devices, a blend of carbon disulfide and acetone is used to deposit a donor–acceptor polymer semiconductor thin film.

carbon footprint

The total amount of carbon dioxide and other greenhouse gases emitted into the atmosphere throughout a particular period of time by the activities of a person or company, expressed as grams of CO2.

carbon geoengineering

See →carbon dioxide removal.

carbon lattice

A symmetrical structure consisting of carbon atoms that form two-dimensional crystals in a nanostructured →graphene semiconductor.

carbon management

Includes all technologies, such as carbon measurements or →carbon capture and sequestration, and all other government measures and activities leading to the reduction of CO2 emissions into the atmosphere.

carbon nanotubes

(CNT) Cylinders of carbon atoms (fullerene, C60) in the form of connected hexagonal structures, like a chicken wire, with remarkable features: light, sturdy, conducting, and semiconducting. As these cylindrical carbon molecules exhibit good electrical properties, they find wide application as semiconductor materials for →thin-film solar cells. The manufacturing of carbon nanotubes includes a variety of synthesis technologies, such as arc discharge, →laser ablation, and some types of →chemical vapor deposition (CVD). Miniaturization of semiconductor nanocarbon components allows various types of carbon structures, such as a flat sheet of graphite, partially rolled sheet of graphite, completely rolled-up sheet of graphite or →single-walled

carbon neutrality 

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carbon nanotube (SWCNT), →double-walled carbon nanotube (DWCNT), and →multiwalled carbon nanotube (MWCNT). The electric resistivity can be decreased by adding carbon nanotubes to semiconductor materials. For instance, the addition of carbon nanotubes to polymer composites can significantly increase polymer conductivity and hence the efficiency of a thin-film photovoltaic cell. carbon neutrality

Also known as climate neutrality or CO2 neutrality. An environment or activity that does not emit carbon dioxide and other greenhouse gases into the atmosphere. Net zero carbon emissions can also be achieved by balancing a measured amount of carbon released with an equal amount sequestered or offset.

carbon nitride

A compound of carbon and nitrogen. Polymeric carbon nitride (C3N4) layers are often used in thin-film polymer solar cells. A graphitic carbon nitride compound (g-C3N4) increases photoconductivity of PV cells by impeding photo-induced electron interception to the redox couple and injecting electrons into the conduction band of the semiconductor. The employment of graphitic carbon nitride in quantum dot sensitized solar cells can lead to up to 70% improvement in power conversion efficiency.

carbon offset

See →carbon offsetting.

carbon offset program

See →carbon offsetting.

carbon offsetting

A program in which a company or an organization mitigates or offsets its emission of greenhouse gases, for example, →carbon dioxide (CO2), →methane (CH4), →hydrofluorocarbons (HFCs) and other pollutants, through the funding of projects that reduce overall carbon emissions. Some carbon offset programs use a certification evaluation system, in which a certificate represents the reduction of one metric ton (2,205 lbs.) of CO2 emissions.

carbon payback

See →carbon payback period.

carbon payback period

Period of time, expressed in days or months, a PV system needs to produce clean energy to compensate for its imbedded carbon footprint (amount of energy required to produce and transport them).

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 carbon-fiber reinforced plastic

carbon-fiber reinforced plastic

(CFRP) Also known as carbon-fiber reinforced polymer. A very strong and light composite material that is made of carbon fiber and plastic. The CFRP is used in the manufacture of lightweight →solar-powered vehicles and →electric vehicles. The carbon-fiber reinforced plastic can reduce the weight of a vehicle by about 50% and thus energy consumption by as much as 35%. At the same time, the CFRP material improves the safety of passengers because it is stronger than conventional materials used in automobile construction. The major disadvantage of the carbon-fiber reinforced plastic is the high cost of high-grade CFRP.

carbon-fiber reinforced polymer

(CFRP) See →carbon-fiber reinforced plastic.

carrier

See →charge carrier.

carrier concentration

Also known as carrier density. The concentration of charge carriers, electrons and holes, in a doped semiconductor layer (conduction or valency band) or in an intrinsic, undoped, chemically pure semiconductor. While the valence band is full of electrons, the conduction band is generally empty or partially filled. The conduction band has the potential to accept the electrons from the valence band under certain conditions, when the valency electrons gain enough energy from sunlight to bridge the →band gap and jump into the conduction band.

carrier density

See →carrier concentration.

carrier layer

See →charge carrier layer.

carrier lifetime

See →minority carrier lifetime.

carrier mobility

A measure of velocity at which a charge carrier, an →electron or a →hole, moves through the →semiconductor. It is a ratio of velocity to the electric field applied to a semiconductor in which the carriers collide with impurities and lattice vibrations. An increase in doping concentration results in a decreased carrier mobility because the free carriers collide with the dopant atoms more frequently.

carrier multiplication

(CM) The technique by which an energetic photon absorbed in the semiconductor is utilized to generate multiple electron–hole pairs before it relaxes. In contrast to the traditional PV cell method, in which one photon of light can only

carrier recombination 

 79

excite one electron and the excess absorbed photon energy above the energy gap is lost as heat, the CM concept allows one photon to excite multiple electrons across the band bap of the semiconductor and thus improve the conversion efficiency of a solar cell. carrier recombination

See →recombination.

carrier slide

Component of a wafer dicing machine.

carsharing

See →electric car sharing.

cascade cell

See →cascade photovoltaic cell.

cascade photovoltaic cell

Also known as multijunction photovoltaic cell, consists of two or more superimposed subcells that are made of different semiconductor materials and thus absorb different parts of solar spectrum.

cathode

The negative electrode in a battery.

cathodic corrosion protection

Corrosion protection of exposed metal surfaces.

cathodic etching

See →cathodic etching.

cathodic protection

See →cathodic corrosion protection.

cation

Positive →ion. When an atom loses one or more electrons, it becomes a positive ion (cation), carrying a positive charge as a result of the chemical reaction.

cavern thermal energy storage

(CTES) A type of →seasonal thermal energy storage in which the generated heat is transferred from solar thermal collectors into an underground cavern, such as a deserted mine or oil store. These natural underground sites are suitable for utility-scale thermal energy storage due to their large storage capacity and ability to maintain heat for a long period of time.

CB

Abbreviation for →cellulose butyrate.

CBD

Abbreviation for →chemical bath deposition.

CCD

Abbreviation for →cell color deviations.

CCPP

Abbreviation for combined cycle power plant. See →combined gas and steam power plant.

CCS1

Abbreviation for →combined charging system.

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 CCS2

CCS2

Abbreviation for →carbon capture and sequestration.

CDD

Abbreviation for →cooling degree day.

CDP

Abbreviation for →carbon disclosure project.

CDR

Abbreviation for →carbon dioxide removal.

CdTe

Abbreviation for cadmium telluride. Semiconductor material for manufacturing thin film →cadmium telluride solar cells.

CdTe cell

See →cadmium telluride thin-film solar cell.

CdTe module

See →cadmium telluride thin-film solar module.

CdTe solar cell

See →cadmium telluride thin-film solar cell.

CdTe solar module

See →cadmium telluride thin-film solar module.

CdTe solar panel

See →cadmium telluride thin-film solar module.

CdTe thin-film cell

See →cadmium telluride thin-film solar cell.

CdTe thin-film module

See →cadmium telluride thin-film solar module.

CdTe thin-film solar cell

Cadmium telluride thin-film solar cell is a type of thin-film solar cell that uses cadmium telluride as a semiconductor material. Cadmium telluride is commonly used in the production of thin-film PV cells because it can absorb a broad spectrum of the solar radiation. The major disadvantage of cadmium telluride is its toxicity. It is hazardous for humans and animals and it can damage the environment if not disposed of properly. Therefore, extreme caution is required during the manufacturing process as well as during the recycling at the end of the product life.

CdTe thin-film solar module

Cadmium telluride thin-film solar module.

CdTe thin-film solar panel

Cadmium telluride thin-film solar panel.

CEA

See →cost-effectiveness analysis.

CEC

Abbreviation for →California Energy Commission.

CEE

Abbreviation for →cloud enhancement event.

ceiling light diffuser

A component of a →sun tube. A light panel at the bottom end of a sun tube that is fitted into the ceiling to spread the daylight brought in from outside throughout a room.

celestial sphere 

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Compared to direct light coming through windows, the diffuser generates a soft lighting known as a white glow. celestial sphere

An imaginary sphere of enormous radius formed by the sky. The observer’s position is the center of the celestial sphere and only one half of the sphere is visible to him or her at any time, whereas the other half remains hidden below the horizon. Degrees are used to measure objects on the celestial sphere, for example, the angular distance between the celestial equator that acts as a reference point and a celestial object.

cell architecture

See →solar cell architecture.

cell barrier

See →cell junction and →depletion zone.

cell color deviations

(CCD) Color deviations in solar cells that quality assurance auditors identify during color testing, which is typically a part of a routine solar cell inspection procedure. With solar cell testing equipment, testers inspect and measure deviations from a reference solar cell color. In addition, the testing procedure usually focuses on identifying differing cell colors within a photovoltaic module and deviating cell colors between two PV modules.

cell efficiency

The ratio of output power (electricity) that a photovoltaic cell generates under optimal conditions (full solar radiation averaging 1,000 W/m2 [1 kW/m2]) divided by the input power, the total amount of solar energy falling on the PV cell. The cell efficiency is usually expressed in percentages. For instance, the efficiency record for the silicon solar cell in 2016 was 24%.

cell junction

Also known as p–n junction, cell barrier, depletion zone, or space charge. Intersection between positively doped and negatively doped semiconductor layers in a →solar cell. See also →depletion zone.

cell temperature

See →solar cell temperature.

cell temperature sensor

See →solar cell temperature sensor.

cell voltage

See →solar cell voltage.

cell1

See →photovoltaic cell.

cell2

See →battery cell.

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 cells with interleaved contacts

cells with interleaved contacts

Photovoltaic cells with interleaved contacts of opposite polarity on the back surface of the PV cell. In contrast to traditional PV cell with front-side metal grids and the entire surface or latticelike metallized back contacts, the cells with interleaved positive and negative contacts on the rear surface eliminate shading losses, resulting in a higher energy conversion efficiency.

cellulose acetate butyrate

(CAB) Also known as butyrate. An amorphous, transparent thermoplastic used for collector glazing due to its ability to withstand extreme outdoor operating conditions. Acting as a replacement for heavy and expensive glass, cellulose acetate butyrate is weatherproof and resistant to ultraviolet (UV) rays. This tough material produced from cellulose has an extremely high impact strength.

cellulose butyrate

(CB) A tough, transparent thermoplastic used as additives in coatings applications for solar collectors.

Celsius

(°C) Unit of temperature, scale for measuring temperature. Water freezes at 0 °C and boils at 100 °C.

Celsius scale

A temperature scale used by most European countries.

central inverter

An inverter that converts DC solar power generated by the entire solar array into grid-compatible alternating current at one central point.

central inverter station

Facility where the central inverter converts the generated solar power from direct current to grid-compatible alternating current.

central receiver

In a →concentrating solar power plant (CSP), the central receiver is a boiler at the top of the →solar power tower that is heated by reflected sunlight from numerous sun-tracking mirrors, called heliostats. The receiver captures the focused sunlight and transfers the large amounts of concentrated energy into →heat transfer fluid, such as →molten salt. In the process, high temperatures of over 540  °C (1,004 °F) are achieved, producing higher conversion efficiency rates than small-scale systems.

central receiver system

A large-scale concentrating solar power system consisting of a large field of numerous sun-tracking mirrors, called heliostats, that focus sun’s rays on a single focal point, the →central receiver (boiler) at the top of a →solar power

central rotation mechanism 

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tower, which is located at the center of the field. The concentrated energy heats the →heat transfer fluid, such as →molten salt, in the central receiver to high temperatures of over 540 °C (1,004 °F). The heated fluid is either stored in a →molten salt storage system (also called →solar storage tank) for later use or it is transported to a →heat exchanger that converts heat fluid to water and then water to steam, driving the steam turbine and generating electricity. central rotation mechanism

A mechanism for rotating the entire solar house.

ceramic layer

A layer made of ceramic material that is used as a barrier layer in →thin-film photovoltaic cells to provide electrical isolation between the substrate and the device, blocking the diffusion of metallic impurities during the high-temperature deposition process.

ceramic powder

Ceramic precursor powder used for the manufacture of ceramic substrates in thin single-crystal silicon solar cells.

CFC

Abbreviation for →chlorofluorocarbon.

CFL

Abbreviation for →compact fluorescent light.

CFRP

Abbreviation for →carbon-fiber reinforced plastic.

changing of places

The type of →diffusion in which dopant atoms are exchanged with the silicon atoms in the crystal lattice.

characteristic curve

Also known as characteristic diagram and characteristic line. A graph showing the relation between two changing but interdependent values. For instance, a current–voltage characteristic curve helps visualize the behavior and changes in a semiconductor diode – variation of current with applied voltage in a number of different situations.

characteristic diagram

See →characteristic curve.

characteristic line

See →characteristic curve.

characteristic value

A value that indicates dimensions, average consumption or degree of utilization, a solar day at a particular location, or any other value that is important for evaluating the size and capacity needed for a future solar energy system.

charge

Adding electrical current to a battery for storage.

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 charge carrier

charge carrier

A mobile particle, for example, an →electron or →hole, which carries an electric charge in a semiconductor.

charge carrier layer

A doped layer in a solar cell that encourages the movement of mobile particles, →electrons and →holes, along the →conduction band and →valency band, carrying electric charges in a semiconductor and thus producing direct current (DC) electricity. Doping or the intentional introduction of impurities into a pure semiconductor enhances conductivity so that electrons can effortlessly be excited into the empty or partially filled conduction band under certain conditions. When the electrons gain enough energy from sunlight, they become excited and are able to bridge the →band gap, a small gap between the valence and the conduction band. The conduction band that is generally empty or partially filled gladly accepts the electrons from the valence band that is full of electrons. The charge carrier layer transports photo-generated carriers or DC current to an external circuit, coming back to the cell through the counter electrode at the bottom of the cell and closing the circle by occupying the empty holes in the valency band. See also →photovoltaic cell.

charge carrier separation Also known as charge separation. A photo-induced process in which two different charge carrier types, →electron and →holes, are driven toward the two different terminals of the semiconductor absorber. Negative charge carriers or electrons are attracted to the n-type side and positive charge carriers called holes to the p-type side of the →p–n junction. The separation and collection of charge carriers at the opposing contacts are attributed to an electric field or gradients of quasi-Fermi energies. In addition to the drift of carriers caused by the electric field, there is another separation type in which charge carriers move from zones of higher carrier concentration to zones of lower carrier concentration. New nanotechnologies, such as plasmonic nanostructuring, can enhance the charge separation in the semiconductor and thus increase the performance of the solar cell. charge control

Battery protection from overcharge and overdischarge.

charge controller 

charge controller

Solar panel

 85

A device that regulates the flow of electric current into a battery bank and protects the batteries from overcharge and overdischarge. It is usually installed between a photovoltaic system and a battery bank. The charge controller cuts the electric current when the battery reaches a set voltage value (is fully charged) to prevent excessive overcharge and turns it on when a low-voltage set point is reached (the battery is discharged). Both overcharging and discharging damage the lead plates of a lead-acid battery, significantly reducing its lifespan. Besides the protection, most charge controllers also monitor system performance and provide information about state of charge. Off-grid interactive inverters typically use charge controllers. Controller SOLAR CHARGE CONTROLLER

888 V

Loads

+

Battery

Charge Controller

charge cycle

See →charging cycle.

charge equalization

A periodic battery maintenance process, in which deep-cycle lead-acid batteries are deliberately overcharged (5%–10% of the specified charge level) to remove lead sulfates from plates and ensure that all cells are restored to an equal state of charge.

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 charge factor

charge factor

A fraction of the total battery capacity representing the time it takes to fully charge a battery at a constant current without doing damage to the battery. C/2 designates a charge factor of 2 h.

charge migration

See →charge transfer.

charge rate

The rate at which a battery is charged relative to the capacity of the battery when it is fully charged.

charge recombination

A process by which free electrons and holes come together in a semiconductor. There is a constant movement of electrons between the →conduction and the →valence bands. When a free electron loses energy, it jumps from the conduction band into the valence band and occupies the vacant position (hole). Electron and hole recombine, eliminating the electron–hole pair. The newly freed electrons then start the electron–hole pair generation process anew. There are three types of recombination: radiative, nonradiative, and Auger recombination. In a radiative recombination process, the energy of recombination leads to the emission of a photon of light. In the nonradiative recombination process, the energy is transferred to one or more phonons. Finally, in the Auger recombination process, the energy of recombination is passed on in the form of kinetic energy to another electron. Recombination occurs at the front surface of the solar cell, in the bulk of the cell, junction region, or between interfaces.

charge regulator

See →charge controller.

charge resumption set point

(CRSP) A minimum set voltage value at which a charge controller turns on and resumes charging of a rechargeable battery.

charge separation

See →charge carrier separation.

charge termination set point

(CTSP) A maximum set voltage value at which a charge controller cuts the electric current to prevent overcharging in a rechargeable battery.

charge transfer

In a solar cell, a process by which electrical charge is transferred from one location, for example, dopant region with small amounts of →phosphorus or →boron, to the next, for example, the host region consisting of silicon atoms.

charging 

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charging

In a →rechargeable battery, the process of receiving electrical current from a power generation source and converting it into chemical energy for storage.

charging capacity

The largest amount of energy that can be stored in a battery. Charging capacity is typically calculated as the charging current multiplied by time. When the battery reaches the charge threshold, the charging process is automatically terminated.

charging controller

See →charge controller.

charging cycle

One charge—discharge cycle of a rechargeable battery.

charging infrastructure for electric vehicles

Various systems for charging electric vehicles (eVs) that can be divided into residential, workplace, and public charging infrastructure. The residential charging infrastructure facilitates overnight charging at home, including →Level 1 charging and →Level 2 charging. The workplace charging infrastructure facilitates charging of employees’ vehicles during business hours, including →Level 1 charging and →Level 2 charging. The public charging infrastructure facilitates public charging at →electric vehicle charging stations at any time.

charging pump

In a solar water-heating system, a pump designed to fill and pressurize a closed solar loop with →heat transfer fluid.

charging station

A home or public station for charging →electric vehicles (eV). See →Level 2 charging station.

check valve

In an →active solar heating system, a valve that allows flow of fluid in one direction only to prevent →thermosimphon flow of →heat transfer fluid after the pump is turned off.

chemical adsorption

See →chemisorption.

chemical bath deposition (CBD) A method for depositing thin semiconductor layers on substrates immersed in dilute solutions encompassing metal ions and a source of hydroxide, sulfide or selenide ions. chemical bond

Attraction between atoms, ions, or groups of atoms that holds them together in a molecule or crystal, forming chemical compounds, electrical continuity, and conductivity.

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 chemical deposition

chemical deposition

Deposition of semiconductor thin-film coatings on a substrate by using chemical processes. See also →chemical vapor deposition.

chemical dry etching

Also known as vapor phase etching or plasma dry etching. A type of dry etching in which a chemical reaction between etchant gases and the semiconductor surface to be etched takes place. Instead of the use of liquid chemicals as in a →wet etching process, the chemical dry etching uses plasma to generate gas radicals that attack the silicon surface. First, a →photoresist mask is deposited on the wafer using a →photolithographic process to protect the parts of the wafer that should not be etched and define contact holes at the same time. Then, the masked wafers are placed on a holder in a vacuum chamber in which the reaction process is carried out. After that, the etching gas is introduced into the vacuum reaction chamber. The reaction gas must be suitable for the semiconductor surface layer, for example, tetrafluoromethane (CF4) will favorably react with silicon dioxide (SiO2). In the plasma, the neutral atoms and molecules (radicals) are excited to a high-energy level, when they begin to react with the atoms on the unmasked silicon wafer surface. Finally, the SiO2 atoms are removed from the wafer surface that is not covered by the photoresist mask, producing the conducting channels. A volatile byproduct generated during the etching process – a gas containing fluorine, silicon, and oxygen – is evacuated from the chamber with help of a vacuum pump.

chemical dry etching process

See →chemical dry etching.

chemical energy

Energy that is released during a chemical reaction or absorbed during the formation of a new chemical compound. The chemical energy is in a dormant state, when, for instance, a battery sits on a shelf. It is a standing reserve that cannot be seen. It only becomes visible when the chemical energy is released in a chemical reaction, in a process known as →electrolysis, when the battery is connected to a load.

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chemical etching

In wafer production, the process of using chemicals to selectively etch away materials that are not protected by masks. The reaction between the chemical →etchant and the material being etched away takes place in →wet etching as well as in →dry etching processes.

chemical polishing

A process of creating a smooth surface by chemical action. The main advantage of chemical polishing is the removal of material in places that are inaccessible when using mechanical processes.

chemical reaction

A chemical change that occurs as a result of the interaction between two or more chemicals that have combined to form a new chemical compound. The number of electrons in an outmost energy level of an atom gives an indication as to how the atom will react. The typical chemical reactions are: combination, displacement, decomposition, →reduction–oxidation reaction, and combustion.

chemical resistance

A property of a material or surface to resist chemical degradation when exposed to highly reactive substances, such as acids and bases.

chemical solution deposition

(CSD) See →chemical bath deposition.

chemical texturing

The process of immersion of silicon wafers into a chemical bath to create a textured surface capable of reducing the amount of reflected light of solar panels, which is considered lost energy. A dilute solution of sodium hydroxide with isopropanol or potassium hydroxide is typically used in a chemical texturing process as a wetting agent. The solution is heated to a certain temperature until tiny microscopic pyramids are created on the surface of the silicon wafer. This low-reflectance surface reflects only one-third of solar radiation that a nontextured, flat silicon surface would reflect.

chemical vapor deposition

(CVD) A method of depositing conductive thin-film coatings on a substrate in the manufacture of photovoltaic semiconductors by using chemical processes. It is a type of vapor transfer process, in which a source material in form of a volatile precursor mixture, a high-temperature gas, is introduced into a reaction chamber containing a heated substrate to be coated. At elevated temperatures

90 

 chemical vapor deposition process

Pressure sensor Heat source

Gas out Substrate Quartz tube

Gas in

Heat source

Chemical Vapor Deposition (CVD)

in the range of 450  °C–1,050  °C (842  °F–1,922  °F) in a CVD reactor, the gas is activated, breaking apart the molecular bonds. The freed atoms recombine and settle on the surface of the substrate. They undergo chemical reactions with the heated substrate to form the desired thin film. The major advantage of the CVD process is that it is less expensive than the traditional silicon wafer production process of growing single crystals (silicon ingots) from melt. See also →physical vapor deposition. chemical vapor deposition process

A semiconductor surface engineering process in which the vapor phase is generated from a chemical reaction in a vacuum environment. See also →chemical vapor deposition.

chemical wet etching

See →chemical wet etching process and →chemically textured cell.

chemical wet etching process

Etching technology for production of thin-film semiconductors. See →chemically textured cell.

chemically textured cell

A solar cell whose silicon surface is textured with inverted pyramid or normal micropyramid patterns through chemical etching via alkaline solution. The textured low-reflectance surface can trap a greater amount of light than a flat, nontextured surface, significantly enhancing the performance of solar modules.

chemically assisted ion-beam etching 

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chemically assisted ion-beam etching

(CAIBE) A type of →dry etching that combines features of chemical →wet etching and physical →dry etching.

chemical–mechanical planarization

(CMP) See →chemical–mechanical polishing.

chemical–mechanical polishing

(CMP) Also known as chemical–mechanical planarization. A technique of creating a smooth surface by chemical and mechanical action. For instance, the surface roughness of stainless steel substrate in hydrogenated amorphous silicon thin-film photovoltaic cells can be considerably improved by combining chemical corrosion with mechanical abrasion.

chemisorption

Also known as chemical adsorption. A type of adsorption in which a chemical bond between the adsorbate (gas or liquid) and the adsorbent (solid surface) is formed. In a thin-film growth process, chemisorption is the accumulation of gas molecules to form a thin layer on the solid surface.

chimney effect

Upward movement of hot air in a chimney or building due to its lower density than the surrounding cool air.

Chinese Renewable Energy Industries Association

(CREIA) A Chinese association that was established in 2000, with the goal of promoting the adoption of advanced renewable technologies and fostering the rapid industrialization of the Chinese renewable energy sector. The CREIA provides a platform for members from industry and enterprises, academics, and individual experts to exchange ideas and voice their concerns.

chipping

One of the major defects that occurs during the mechanical wafer dicing process. The mechanical load causes edge chipping on the back and front side of the wafer, which can affect the functionality of solar cells. The amount of the wafer’s edge chipping depends on the quality and width of the cutting blade as well as on the intensity of vibration during the cutting process. As chipping defects can lead to PV cell failures, further polishing and processing to turn rough textures into usable wafers is required. Laser scribing is becoming an increasingly popular method to process semiconductor wafers, in particular in →thin-film photovoltaic industry, due to superior precision, clean process, and lower costs.

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 chiral sculptured thin films

chiral sculptured thin films

Nanoengineered microstructure of thin films that is characterized by helicoidal columns. The chiral STF nanomorphology is tailored to generate favorable optical responses upon excitation with incoming light.

chlorofluorocarbon

(CFC) Is a man-made compound composed of carbon, fluorine, and chlorine. This industrial chemical was invented in the early 1930s and was widely used as propellants for aerosols, refrigeration coolants (also known as Freon by DuPont), and industrial cleansers. After chlorofluorocarbon was identified as a major cause of ozone depletion in the stratosphere, the phase-out of CFCs under the guidance of the 1987 Montreal protocol gained ground throughout the industrial world with some encouraging results showing that the levels of CFC gases in the atmosphere are slowly but steadily declining.

CHP

Abbreviation for →combined heat and power.

chromium

(Cr) A lustrous, hard metal with a high resistance to corrosion. It is used in chromium electroplating and the manufacture of stainless steel.

CIGS

Abbreviation for copper indium gallium (de)selenide. Semiconductor material for manufacturing thin-film →copper indium gallium selenide solar cells.

CIGS solar cell

See →copper indium gallium selenide thin-film solar cell.

CIGS solar module

See →copper indium gallium selenide thin-film solar module.

CIGS solar panel

See →copper indium gallium selenide thin-film solar module.

CIGS thin-film solar cell

See →copper indium gallium selenide thin-film solar cell.

CIGS thin-film solar module

See →copper indium gallium selenide thin-film solar module.

CIGS thin-film solar panel

See →copper indium gallium selenide thin-film solar module.

CIGS2 solar cells on stainless steel foil

Lightweight, flexible thin-film solar cells made of CIGS2 that is deposited on stainless steel foil. As CIGS2 heterojunction cells on thin stainless steel have an optimal band gap for extraterrestrial →AM0 solar radiation, they are used for space and stratospheric applications.

circuit

See →electric circuit.

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circuit breaker

A circuit protection component that shuts off the flow of electricity when it senses overcurrent or a short circuit.

circuit network

See →circuit.

circuit protection

In order to protect a circuit from overcurrent or a short circuit, circuit protection devices such as fuses or circuit breakers should be installed in any PV circuit network, in a low-voltage as well as in a high-voltage network. In a very small low-voltage circuit, a fuse would be sufficient, but bigger DC and AC circuits must have circuit breakers or other protection equipment installed in accordance with the applicable national guidelines.

circuit protection device A safety device protecting the electrical circuit by shutting off the flow of electricity in the event of overcurrent or a short circuit. circular heliostat field

A heliostat field design in which heliostats are arranged in an orderly circular pattern around a →solar power tower, which is located at the center of the field. The optimal configuration of heliostats around the →solar power tower is analyzed and calculated by computer-supported mathematical methods, ensuring the best optical efficiency and flux distribution on the central receiver. Various optical losses, such as shadowing, blocking, spillage, →atmospheric attenuation, and →cosine effect can be avoided by a fine-tuned circular design of heliostat layouts.

circulates around

The wind flowing or circulating around solar panels on the roof.

circumsolar radiation

The part or amount of solar radiation not coming from the sun’s disk but from the circumsolar region or aureole in the immediate vicinity of the sun. This diffuse radiation is caused by scattering of sunlight by water vapor, cloud, or aerosol particles. The circumsolar radiation is typically measured by an instrument called a →pyrheliometer.

circumsolar ratio

(CSR) A ratio between the circumsolar radiation and the sum of the circumsolar and solar disc radiations. It focuses on the →circumsolar radiation, determining the part of the →direct normal irradiance that does not come from the sun’s disc.

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 CIS

CIS

Abbreviation for the semiconductor compound material →copper indium selenide.

CIS cell

See →CIS thin-film solar cell.

CIS solar cell

See →CIS thin-film solar cell.

CIS thin-film cell

See →CIS thin-film solar cell.

CIS thin-film module

See →CIS thin-film solar module.

CIS thin-film solar cell

A thin-film solar cell made of the compound semiconductor material CIS, which consists of copper, indium, and selenide. A CIS cell typically has a complex heterojunction structure that consists of different semiconductor materials with different band gaps. For instance, copper, indium, and selenide (CuInSe2) layer is combined with cadmium sulfide (CdS) to capture a wider range of the solar spectrum and thus increase power output of the cell.

CIS thin-film solar module

A type of solar module that is composed of →CIS thin-film solar cells. Compared to monocrystalline and polycrystalline modules that are hundreds of micrometers thick, CIS modules require significantly less material due to the very thin layers of copper, indium, and selenide semiconductor material that are deposited on the substrate. In addition, a more cost-effective manufacturing process can be applied in CIS processing. Although the conversion efficiency of CIS modules is still lower than that of conventional silicon crystalline modules, they have made a significant progress in the recent years, reaching over 20% efficiency. CIS solar panels have higher sensitivity for low-irradiation conditions and longer wavelengths, making them more suitable for northern countries, where the sun rests lower in the horizon and there are more cloudy days per year, or for rooftops with an east/west orientation.

CIS thin-film solar panel See →CIS thin-film solar module. citizen-funded photovoltaic array

See →citizen-funded solar system.

citizen-funded photovoltaic system

See →citizen-funded solar system.

citizen-funded PV array

See →citizen-funded solar system.

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citizen-funded PV system See →citizen-funded solar system. citizen-funded solar array See →citizen-funded solar system. citizen-funded solar system

A solar system that is funded by investments, donations, and solar fund contributions from citizens. A typical citizen-based solar fund accepts tax-deductible donations, ranging from as low as 1$ to 1,000$ or above. The major part of funds usually comes from citizens’ investments. Some solar funds allow crowdfunding with low minimum investments amounts. The raised money is then used to build a new photovoltaic array or solar field that will be jointly owned by investors and/or a given solar community. The citizen-funded solar system is a bottom-up model of financing solar projects that has arisen in past years from the wish of citizens to be active at the local and global level and do more to use solar energy resources and curb global warming.

cladding

The application of one material over another to provide a protective layer over a surface, shielding it against environmental conditions.

clamp

See →mounting clamp.

clamp assembly

Also known as clamp system. A structure for mounting solar panels to the purlins of carports, canopies, or other similar rain shelters. Depending on the design, a clamp assembly can include mounting brackets, clamps, clamping structures, structural arms, and other fasteners.

clamp mount

See →mounting clamp.

clamp system

See →clamp assembly.

clamping arm

A clamping device that provides support for mounting solar panels on poles or other vertical structures.

clamp-on ammeter

Measuring instrument with a clamp that measures the electric current in a circuit.

clean air

Air free from pollution and →greenhouse gas emission.

clean air act

Act  on  the  prevention of harmful effects on the  environment caused by air pollution, noise, vibration, and similar phenomena.

clean electricity

See →clean energy.

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 clean energy

clean energy

Energy produced without creating air pollution and toxic byproducts, for example, solar, wind, hydro, and geothermal energy.

clean energy economy

Economy that relies on clean energy resources, such as solar, wind, hydro, and geothermal, as opposed to an economy that is powered by coal, oil, and gas (the fossil fuels).

clean energy innovation Innovation that adds new clean energy solutions to the existing clean energy portfolio, such as nanotechnology, ocean tides, waves, or hydrogen. clean energy resources

All resources that produce clean energy, for example, solar, wind, hydro, and geothermal.

clean power

See →clean energy.

clean technology

Also known as cleantech or clean-tech. Any technology that supports a sustainable business approach that aims at minimizing or eliminating negative effects on the environment and making more efficient and responsible use of natural resources. A cleantech business model includes a wide range of different industry sectors and categories, such as →clean energy, →smart grid, →energy storage, transportation, recycling, materials and equipment innovation, →sustainable building and many others.

cleantech

See →clean technology.

clean-tech

See →clean technology.

clear plastic

See →clear plastic cover.

clear plastic cover

A plastic cover made of transparent polyethylene material. Clear polyethylene plastic films are used as cover in greenhouses for growing a variety of vegetables, fruits, flowers, or other plants under controlled, protected conditions. The transparent cover allows a penetration of the maximum light and heat transmission. The heated soil gives off longwave infrared radiation that is trapped in the greenhouse, keeping the interior and plants warm during cold winter days. Clear plastic films are also a preferred cover for swimming pools. As transparent polyethylene material does not absorb much sunlight, it lets it pass through, heating the water below the cover. Just like in the greenhouse, heat is

Clear Sky model 

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trapped underneath the cover. Solar pool cover reduces heat loss from evaporation at night, cutting swimming pool heating costs by up to 50%. Clear Sky model

Algorithm for calculating solar radiation.

cleavage of lateral (CLEFT) A process for producing single-crystal thin films epitaxial film for transfer on amorphous substrates. In this process, single‐crystal gallium arsenide (GaAs) films are grown by →vapor phase epitaxy (VPE) on reusable GaAs substrates. After the upper surface of the grown GaAs film is bonded to the GaAs substrate, it is cleaved from the substrate and integrated into a cell. The same substrate can be reused for growth of several single-crystal GaAs films, thus lowering the overall manufacturing costs. cleavage of lateral epitaxial films for transfer

See →cleavage of lateral epitaxial film for transfer.

CLEFT

Abbreviation for →cleavage of lateral epitaxial film for transfer.

CLFR

Abbreviation for →compact linear Fresnel reflector.

climate

General weather pattern expected in a geographic region on the basis of the gathering of meteorological data, such as temperature, humidity, wind, and precipitation, over a long period of time.

climate bond

See →green bond.

climate change

A long-term change in the climate of a region, including main changes in temperature, precipitation, or wind patterns, measured over a long period of time.

climate change migrant

See →climate change refugee.

climate change refugee

Person forced to leave his or her country because of the impacts of climate change.

climate engineering

Also known as carbon engineering. See →carbon dioxide removal.

climate migrant

See →climate change refugee.

Climate Monitoring and Diagnostics Laboratory

(CMDL) See →Global Monitoring Division.

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climate neutrality

Also known as carbon neutrality or CO2 neutrality. An environment or activity that does not emit carbon dioxide and other greenhouse gases into the atmosphere. Net zero carbon emissions can also be achieved by balancing a measured amount of carbon released with an equal amount sequestered or offset.

climate parameter

See →meteorological variable.

climate protection

All measures and actions that address climate disturbances, reduce carbon emissions, increase the use of clean, sustainable energy, and in general promote the protection of climate and ozone layer.

climate protection measures

See →climate protection.

climate refugee

See →climate change refugee.

climatic cycle

A cycle that takes place any time when the daily load exceeds the typical power supply from the photovoltaic array due to changes in the weather. In contrast to a regular and repetitive daily charge and discharge cycle in battery operation in a PV system, the climatic cycle is dependent on variable climatic conditions.

clipping

Also known as inverter saturation. Clipping occurs when DC power from a PV array feeding an inverter exceeds the maximum input level of the inverter (maximum rated power) and the excess power is “clipped” and lost.

clipping loss

Loss of power due to →clipping. When DC power from PV modules is too large for an inverter to handle, the excess power is “clipped” or regulated by the inverter.

cloaking effect

Cloaking of solar cell contacts that results in enhancing efficiency of photovoltaic cells. A polymer cloak is often used to bend the path of light around the metallic contact fingers and guide it toward the PV cell.

cloaking film

See →cloaking layer.

cloaking layer

Also known as a cloaking film. A layer of polymer in the optical invisibility cloak that is used to hide metallic contacts in solar cells, increasing efficiency by up to 10%.

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close-coupled solar hot water system

Also known as a close-coupled system. A hot water system in which a storage tank is mounted together with solar collectors on a roof in order to reduce electricity consumption and hence greenhouse gases emissions. The system does not require an electric pump as it applies the natural thermosiphon principle. The tank is mounted above the solar panels, so that the water heated in the panels – hot, less dense, and lighter water – rises from the solar collectors into the storage tank, whereas cooler, denser, and heavier water from the tank sinks down to the bottom of the collector.

close-coupled system

See →close-coupled solar hot water system.

closed-loop system

Also known as an indirect circulation system. The closedloop system is a subsystem of an active →solar water-heating system. In this closed system, →heat transfer fluid (HTF) is kept separate from the household water. The antifreeze solar fluid (HTF) circulates in a sealed loop through the solar collectors, heating the fluid and a heat exchanger that transfers the heat to domestic water stored in the tank. Closed-loop systems with antifreeze heat transfer fluid provide good freeze protection for solar collectors in regions with temperatures below freezing. See also →openloop system.

closed-loop tracking

A solar tracking technology that relies on optical sensors to measure incident sunlight and thereby orient heliostats or panels toward the sun’s movement across the sky.

cloud amount

See →cloud cover.

cloud cover

Also known as cloud cover or cloudiness. The fraction of the sky dome covered by clouds. It is usually expressed in oktas or eighths (1/8–8/8), ranging from 0 oktas (completely clear sky) to 8 oktas (completely cloudy sky). Four oktas or 4/8 means that the four-eighths of the total area of the sky dome (half of the sky) are obscured by clouds.

cloud coverage

See →cloud cover.

cloud enhancement

Also known as cloud enhancement event (CEE). The increased solar irradiance above the clear-sky ceiling due to multiple diffusion of short-wave radiation by partial cloud

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 cloud enhancement event

cover. In addition to the direct solar radiation, the ground beneath the scattered clouds also receives the reflected sunlight from thin, broken clouds. This increased irradiance can affect the performance of photovoltaic modules by causing them to temporarily produce more power than they would normally do if the sky was clear. cloud enhancement event

(CEE) See →cloud enhancement.

cloud monitoring

See →cloud-based monitoring.

cloud type

The type of clouds in the sky dome, ranging from the lowest clouds (stratus, cumulus, stratocumulus) over midlevel clouds (altocumulus, altostratus) to the highest clouds (cirrocumulus, cirrus, cirrostratus) in the atmosphere.

cloud-based monitoring A process in which critical data, such as solar power yield or solar module temperature, are routinely acquired and analyzed by using a cloud-based monitoring platform for the purpose of better data evaluation and further processing. cloudiness

See →cloud cover.

CM

Abbreviation for →carrier multiplication.

CMDL

Abbreviation for Climate Monitoring and Diagnostics Laboratory. See →Global Monitoring Division.

CMP

Abbreviation for →chemical–mechanical polishing.

CNT

Abbreviation for →carbon nanotubes.

CO2

Abbreviation for →carbon dioxide.

CO2 emission-free electricity

Also known as emission-free electricity. Electrical energy that is generated without emitting carbon dioxide (CO2) into the Earth’s atmosphere. The most common types of emission-free electricity are solar, wind, hydro, geothermal, and nuclear.

CO2 emission-free city

Also known as an emission free city. A city that uses largescale →solar power plants, low-scale →solar arrays, →emission-free transport, and takes other necessary measures to reduce CO2 emissions to a zero-emission level, at which no harmful pollutants are emitted into the atmosphere.

CO2 emission-free energy Also known as emission-free energy. Energy, such as electrical energy or thermal energy, which is generated without

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releasing carbon dioxide into the atmosphere, causing global warming. The most common types of emission-free energy are solar, wind, hydro, geothermal, and nuclear energy. CO2 emission-free power See →CO2 emission-free energy. CO2 emission-free power US Also known as a carbon dioxide (CO2) emission-free plant power station. A power plant that produces electrical energy without emitting CO2 into the Earth’s atmosphere, which is the main cause of →global warming. The most common types of emission-free power plants are solar, wind, hydro, geothermal, and nuclear. Although nuclear and hydroelectric power plants do not release harmful greenhouse gases into the atmosphere, they have other environmental problems, such as hazardous nuclear waste and changing of natural habitats, which can have devastating consequences for some species. CO2 emission-free power UK See →CO2 emission-free power plant. station CO2 emission-free transport

See →emission-free transport.

CO2 emissions

See →carbon dioxide emissions.

CO2 neutrality

See →carbon neutrality.

CO2 offset

The reduction of CO2 emissions by making environmental friendly choices in our everyday activities, such as turning off the lights when leaving a room, using public transportation instead of cars, or funding solar projects that reduce overall CO2 emissions.

coal

Is a black sedimentary rock found in the earth’s crust in so-called coal beds formed from plant debris millions of years ago. This major fossil fuel is frequently burned to make electricity. Around 38% of the world’s total electricity production depends on coal. When burned, coal emits the largest amounts of carbon dioxide (CO2) into the atmosphere of all fossil fuels, more than diesel, gasoline, propane, and natural gas. There are two opposing tendencies regarding the use of coal around the world today. On the one side, Greenpeace helps communities worldwide break free from coal and other fossil fuels and supports their shift toward renewable

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 coalescence

energies, such as solar, wind, and hydropower. On the other side, numerous “clean coal technologies” have been developed with the goal of utilizing coal in an environmentally acceptable way. coalescence

In the context of →thin-film growth, after the →nucleation process, when it is chemically favorable for two nuclei to come together and stay permanently at a location, they undergo coalescence with another, forming a continuous film.

coastdown

The gradual decrease of the reactor power level as the fuel in the core is depleted.

coat thickness

See →coating thickness.

coater

See →coating machine.

coating

Layer that is applied to the surface of a substrate. The following types of coating are frequently used in solar manufacturing: semiconductor coating, →antireflection coating, weather-resistant coating, and impact- and wear-resistant coating.

coating inspection

A solar cell inspection at different stages of the coating process to ensure high quality and compliance with the specification. The coating inspection can include the evaluation of the surface to be coated, cleanliness, environmental conditions, layer thickness, gauge-based testing, and visual inspection.

coating machine

Also known as coater. A machine designed for coating and printing of organic, perovskite, and other flexible photovoltaic cells. One of the commonly applied technologies is →roll-to-roll coating. The coater is typically used for the deposition of following semiconductor materials: →copper indium gallium selenide (CIGS), →copper zinc tin sulfide (CZTS), →cadmium telluride (CdTe), →cadmium sulfide (CdS), →perovskite, →copper indium selenide, →gallium arsenide (GaAs), and →dye-sensitized cell (DSC). Coating machines range from small and compact coaters with a narrow web for slow printing to large machines for wide web printing with high printing speed.

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coating material

Material deposited on a thin-film photovoltaic cell. A rapid growth of thin-film and multijunction solar cell industry in recent years has resulted in a wide range of coating materials, such as →amorphous silicon (a-Si), →copper indium gallium selenide (CIGS), →copper zinc tin sulfide (CZTS), →cadmium telluride (CdTe), →cadmium sulfide (CdS), →perovskite, →copper indium selenide, →gallium arsenide (GaAs), and →dye-sensitized cell (DSC).

coating process

A process for depositing thin films of semiconductor materials on the surface of a substrate.

coating technique

See →coating process.

coating technology

See →coating process.

coating thickness

Also known as coat thickness. Thickness of a layer deposited on the substrate of a solar cell. The thickness is one of the most important features for the surface coating because optical and electric properties of a photovoltaic cell semiconductor films are directly affected by it. As semiconductor structures are nowadays mostly designed on a very small scale, from 1 to 100 nm, the inspection of film thickness at different stages of the coating process belongs to a regular solar cell inspection procedure. The measurement of film thickness is conducted with a coating thickness gauge.

coefficient of performance

(COP) The COP of a heat pump or air conditioning system is the ratio of the heating or cooling output to the operating energy input.

COGAS power plant

Abbreviation for →combined gas and steam power plant.

cogeneration

See →combined heat and power.

coherent light

In a →laser cutting machine, a beam of →photons of light that have the same frequency. It is a special kind of “in-phase” light that does not spread and diffuse. As waves are identical and in phase, they generate a beam of coherent light, which is characteristic for lasers in general.

cold air mass

A large body of cold air with consistent temperature and humidity. As the air mass moves from one region to another, it inevitably changes, adopting the temperature and humidity properties of the region it is in.

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collection point for recycling

Any designated place at which discarded solar panels and other photovoltaic waste are collected at a designated time.

collector

See →solar collector.

collector circuit

See →solar collector loop.

collector fluid

The working fluid, such as water, glycol →heat transfer fluid, or air, which is directly heated in solar collectors and then transported to the hot-water tank or circulated throughout the house. In →concentrating parabolic troughs and →concentrated solar power plants, the heat transfer fluid is heated by concentrated sun’s rays in black absorber tubes or a central receiver container and transported to a heat exchanger, converting water to steam that drives the steam turbine, generating electricity.

collector glazing

The glazing on the top side of the collector box facing the sun. A tempered glass is often used as a glazing material to provide a good protection against the elements. A patterned surface of the cover glass is a better solution than a smooth glass surface, as it reduces reflection and thereby increases the absorption of sunlight. In addition to the protective function, glazing traps heat inside the collector box, increasing the temperature and thus the thermal energy output of the collector.

collector loop

See →solar collector loop.

collector plate

See →absorber.

collector pump

A pump that is used in active solar thermal systems for the control of working fluids, such as water and →heat transfer fluid. Unlike →passive solar water-heating systems that do not require pumps and other electrical control equipment for their operation, →active solar heating systems use pumps to circulate fluids through the collectors and into the house. To make the system more sustainable, the collector pump can be powered by a →photovoltaic module.

collector system

Also known as a solar collector system. A system consisting of many solar collectors that convert the sunlight into thermal energy.

collision gas

See →reaction gas.

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colloid

A mixture consisting of tiny particles of one substance that are dispersed throughout another substance but are not dissolved. Some of the examples of colloids include gels, sols, and emulsions.

colloidal solution

Also known as a colloidal suspension. A solution in which a substance is equally suspended throughout a liquid, never settling as in other solutions but remaining in a state of a permanent suspension.

colloidal suspension

See →colloidal solution.

color check

See →color testing.

color inspection

See →color testing.

color testing

A part of the solar cell inspection in which quality assurance auditors test solar cells for possible color deviations. With solar cell testing equipment, testers inspect and measure deviations from a reference solar cell color. In addition, the testing procedure usually focuses on identifying differing cell colors within a solar module and deviating cell colors between two modules.

colored photovoltaic cell A solar cell whose antireflection coating is modified in such a way to produce different colors. Solar cells typically come in two standard colors: dark blue and black. The appearance of solar cells can be altered by varying the thickness of the silicon nitride (SiN) antireflection coating (ARC). In this way, a palette of different colors, orange, red, or green, and adjustable transparencies can be obtained. The colored photovoltaic (PV) cells are less efficient than their black counterparts according to the rule: the darker the color of the cell, the more energy efficient the PV cell. One of the major advantages of colored solar cells is their aesthetical appeal that makes them suitable for →building-integrated photovoltaics. colored photovoltaic glass See →colored solar glass. colored photovoltaic module

A solar module that consists of →colored photovoltaic cells. Although they are less efficient than their conventional black counterparts, their aesthetical appeal makes them suitable for →building-integrated photovoltaics. Besides their primary function of generating electricity, these panels

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 colored photovoltaic panel

Colored Photovoltaic Module

fulfill an additional function by becoming an integral part of the aesthetics of the building. They replace the outer building envelope skin or surface, while enhancing the design of the edifice. Colored PV modules give architects and designers a freedom of choice to match the color of the existing façade or to emphasize one part of the building – balcony, awing, or glazed wall – by using a different color. colored photovoltaic panel

See →colored photovoltaic module.

colored photovoltaics

Photovoltaic technology based on →dye-sensitized solar cell technology that utilizes special →colored solar glass or →colored photovoltaic cells to produce solar modules that can be aesthetically and functionally integrated into building structures.

colored PV cell

See →colored photovoltaic cell.

colored PV glass

Colored photovoltaic glass. See →colored solar glass.

colored PV module

See →colored photovoltaic module.

colored PV panel

Colored photovoltaic panel. See →colored photovoltaic module.

colored solar cell

See →colored photovoltaic cell.

colored solar glass

A special semitransparent, colored glass that can generate energy and provide shading for the interior of a building. In addition, it enhances the aesthetical appeal of the building by turning a conventional glass wall into an ornamental façade. Colored solar glass is produced by depositing a special, thin coating on the glass surface or by applying the →dye-sensitized solar cell technology. See also →colored photovoltaic cell.

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colored solar module

See →colored photovoltaic module.

colored solar panel

See →colored photovoltaic module.

combi system

See →combisystem.

combined air-solar collector

See →solar air collector.

Combined Charging System

(CCS) A system that combines single-phase AC charging with rapid three-phase DC charging to quickly feed high-voltage direct current to the eV battery pack. The Combined Charging System commonly uses the standard →J1772™ combo connector to rapidly deliver 400–600 VDC and fill up an 80-mi or 129-km battery pack in around 30 min.

combined collector

See →combined solar collector.

combined cycle plant

See →combined gas and steam power plant.

combined cycle power plant

US (CCPP) See →combined gas and steam power plant.

combined cycle power station

UK See →combined gas and steam power plant.

combined gas and steam (COGAS power plant) A type of power plant that combines power plant a gas and a steam turbine to generate more electrical power from the same fuel. A gas turbine generator produces electricity, while the steam turbine utilizes the waste heat from the gas turbine to make steam and generate extra electricity. combined gas and steam UK See →combined gas and steam power plant. power station combined heat and power

(CHP) Also known as cogeneration. Simultaneous generation of electrical and heat energy from a single fuel source. Electricity and heat are usually produced in separate power generation plants, in separate processes. In a joined process, a CHP plant is capable of capturing “waste heat” from electricity generation that would otherwise be discarded, adding greenhouse gases to the Earth’s atmosphere. The waste heat is recycled; for example, the excess steam is utilized to produce heat. Small combined heat and power systems use →Stirling engines in residential houses, as they are safer and more efficient than steam engines.

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 combined heat and power plant

Traditional system Power plant

CHP system

Electricity

CHP Boiler

~50% Efficiency

Heat

~75% Efficiency

Combined Heat and Power (CHP)

combined heat and power plant

US (CHP plant) A plant generating both electrical and heat energy from a single fuel source.

combined heat and power station

UK (CHP station) A station generating both electrical and heat energy from a single fuel source.

combined solar collector Also known as photovoltaic (PV)-thermal system, hybrid PV/T system, and photovoltaic thermal hybrid solar collector. A high-efficiency PV module that converts sunlight into electricity and heat. As PV panels get hotter, they suffer from a drop in efficiency. When the temperature of the module rises over 25 °C (77 °F), it potentially reduces the power yield by 10–25% based on the proportional voltage drop due to resistance. The combined solar collector takes advantage of this shortcoming by removing waste heat from the PV panel. The PV cells first convert the incoming solar radiation into electricity, then the solar thermal collector placed behind the PV module kicks in, capturing the excess heat that is otherwise lost to the surrounding environment. The benefit of adding a solar thermal collector to the PV module is twofold: on the one hand, it cools off the panel keeping PV cells at an optimal operating temperature around 25 °C (77 °F) and thereby improving their efficiency; on the other hand, the solar thermal collector absorbs the surplus heat and utilizes it by producing hot water for domestic use or hot air that is circulated around the home, warming the building. The major hybrid PV/T systems are: PV/T liquid system, PV/T air system, PV/T a liquid and air system, and PV/T concentrator system (CPVT).

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combined solar system

A solar system that combines two or more technologies, for instance, a photovoltaic and solar–thermal technology. Other examples include a solar heating installation that provides space heating as well as domestic hot water or a combined solar and heat pump system.

combiner box

A waterproof, electrical housing in which the output of several PV strings is joined. The combiner box comprises →overcurrent protection devices, disconnect, and the bus bars and terminals for combining the inputs.

Solar modules + –

+ – Combiner box

+ –

+ –

+ –

+ –

To inverter or charge controller

Overcurrent protection: three 10 A fuses

Combiner Box

combisystem

A domestic hot water storage system that combines two systems into one, namely, the portable hot water system and the space heating system. Instead of using two separate storage tanks for each system, the combisystem utilizes one hot water storage tank for both separate water circulation systems. Although there is a wide variety of combination models, in a simple embodiment, both systems can be merged by adding an additional heat exchanger for the space heating loop to the existing portable hot water tank. Another commonly used combisystem is →tank-in-tank hot water storage system.

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 commercial solar power plant

commercial solar power plant

US Also known as a commercial solar power station UK. A large-scale power plant that can take two forms: →solar thermal power plant or →photovoltaic power plant.

commercial solar power station

UK See →commercial solar power plant.

commercial solar system A large-scale installation for utility companies, busiinstallation ness, government, schools, and other public organizations. A commercial solar system installation can include a ground installation, such as a →photovoltaic power plant, a roof installation, or a carport installation, covering parking lots of large companies with solar modules. committed scheduling

To maintain reliable operation of the grid, ancillary services, assisting the transmission of electricity from generating sources to the customer, need to schedule solar resources in advance. Every owner of a solar generator that participates in committed scheduling must commit their solar generating resource within agreed upon timeframe.

common enclosure

According to the 2011NEC, Proposal 4-183 and Proposal 4-184, whenever they are part of the same photovoltaic system, the AC and DC conductors can be contained in the same junction box or enclosure only if they are properly separated by a partition and identified by separate color coding, marking tape, tagging, or other approved means.

comms interface

A communication interface that is often connected via network to the inverter(s) and other monitoring devices to gather data for solar monitoring.

communication interface A device that communicates over Ethernet (local network infrastructure) with the inverter cabinet, subarray string monitoring boxes, energy meters, and other measuring devices to monitor different segments of the →photovoltaic power plant. commutator

A device that reverses the direction of electric current flow in an electric motor.

compact fluorescent light

See →compact fluorescent light bulb.

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compact fluorescent light bulb

(CFL) An energy-efficient light bulb made of glass tubes filled with mercury vapor and phosphor coating. When an electric current is driven through the tube, the high-speed electrons collide with the mercury atoms, generating the ultraviolet (UV) light. The invisible short-wave UV light strikes then a phosphor powder in the coating, which in turn emits visible, specific fluorescent white light. CFLs use far less electric power than a traditional →incandescent light bulb. CFL bulbs last at least 8 times longer than incandescent light bulbs. In the past, →LED lamps have surpassed CFL bulbs in efficiency and performance features.

compact linear Fresnel reflector

(CLFR) The compact linear Fresnel reflector technology is an extension of the conventional →linear Fresnel reflector technology. Unlike the conventional linear Fresnel reflector concept, which uses a single →absorber tube located at the focal line of the mirrors, the CLFR concept utilizes several absorber tubes in the system. Individual reflectors can direct reflected solar radiation to at least two absorbers. See also →linear Fresnel reflector.

compass

An instrument with a magnetic needle that can be used for finding the optimal south position. When planning a new solar project, it is crucial to find an optimal position for solar panels. For every location, there is an optimal orientation for each month that will ensure the maximum insolation and correspondingly the maximum power output. The ideal orientation is found by calculating the best →aspect angle and positioning the panels to face the optimal south.

compensation area

An area for which compensation and offset measures are required under nature conservation laws of a given country. If, for instance, a large solar park installation encroaches on productive agricultural land or the environment, the solar company in charge of the solar project might be obliged to reforest a wasteland area of similar acreage, create a habitat for birds, or complete another environmentally supportive compensatory project.

compensation zone

See →compensation zone.

compensator

A flexible tube that connects solar collectors to solar loop piping.

composite

See →composite material.

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composite material

Also known as composite. A material made by combining two or more diverse materials in such a way that the individual constituents or materials can still be identified in the final form. However, the properties of the final composite product are considerably different from either constituent.

compound parabolic collector

See →compound parabolic concentrator.

compound parabolic concentrator

(CPC) Also known as compound parabolic collector or Winston collector, named after his inventor Roland Winston. A trough-shaped solar collector that concentrates solar radiation onto the absorber positioned at the bottom of the trough. With help of two parabolic sides, it gathers the sunlight from multiple directions and concentrates it onto a common focal line. This is why this completely stationary solar device does not require an expensive →solar tracking system. As the CPC collects both direct and indirect sunlight, it works well not only on bright sunny days with a clear sky but also on cloudy days and in hazy conditions.

compound semiconductor

Also known as a semiconductor compound. A type of semiconductor that is not composed of just one element, for example, silicon, but of two or more species in a variety of proportions. The elements of group III and V of the Periodic Table are often combined to generate compound semiconductors, for example, →gallium arsenide (GaAs), →gallium nitride (GaN), or indium phosphide (InP). Other semiconductor compounds, such as →cadmium telluride (CdTe) or zinc selenide (ZnSe), are composed of groups II and VI. It is also possible to combine different elements from the same group, for instance, silicon and carbide from group IV, to generate the →silicon carbide (SiC) compound. Compared to the rigid crystalline structure of the pure silicon, compound semiconductors are characterized by low crystal quality. Due to numerous defects in the crystal, the cost of making the crystal is relatively high. In addition, defects and impurities negatively affect optoelectronic properties. Compound semiconductors are commonly employed in thin-film semiconductors because they are more tolerant to impurities and defects as well as to lower optoelectronic quality resulting from the same.

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compressed air energy storage

(CAES) Involves the technique of compressing air with a gas-fired generator. When there is a surplus power in a PV system during the day, it is fed/sold back to the grid. This excess power can be stored in the CAES system by compressing air into large high-pressure tanks or ideally into an underground cavern, such as a salt dome or deserted mine, usually during the hours of low consumption (offpeak time). The stored compressed air becomes a potential energy just like the power stored in a battery. During periods of high-electricity demand (peak hours), the compressed air is released, becoming kinetic energy and driving an air turbine generating electricity. The major disadvantage of the compressed-air energy storage is its dependence on underground caverns as well as on gasfired generators that cannot be considered environmentally friendly.

compressed air energy storage plant

US CAES plant. See →compressed air energy storage.

compressed air energy storage station

UK CAES station. See →compressed air energy storage.

compressed air energy storage system

CAES system. See →compressed air energy storage.

compressed air energy storage technology

CAES technology. See →compressed air energy storage.

compressed air storage power plant

US CAES plant. See →compressed air energy storage.

compressed air storage power station

UK CAES station. See →compressed air energy storage.

concave mirror

A mirror that curves inward. It reflects parallel sun’s rays inward toward a focus. A →dish or a →concentrating parabolic trough are two different types of concave mirrors whose inner surface acts as a reflecting surface, focusing sunlight to a single point or a narrow line.

concentrated load

A load that acts on a small area of a supporting structure, in opposition to a →uniform distributed load (UDL). A concentrated force applied over a small area of the solar installation disturbs the stability of both the mounting structure and the roof.

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concentrated photovoltaic system

Photovoltaic system that uses lenses or mirrors to concentrate sunlight onto highly efficient, multijunction solar cells.

concentrated photovoltaics

(CPV) Photovoltaic technology that uses lenses or mirrors to concentrate sunlight onto highly efficient solar cells.

concentrated solar plant US CSP plant. See →concentrated solar power plant. concentrated solar power plant

CSP plant. A large-scale system that consists of mirrored reflectors concentrating solar energy onto a →receiver or receivers. The receiver converts the absorbed solar radiation into heat that is stored in a working fluid (→heat transfer fluid or gas) and sent to a thermal engine for electric power generation. The four main types of concentrated solar power plants are: →central receiver system, →Dish–Stirling power plant, →parabolic trough power plant, and →linear Fresnel reflector system. The →heliostats of a central receiver system and the dish collectors in a Dish–Stirling power plant utilize a →dual-axis tracking system to follow the motion of the sun across the sky and concentrate the light beams onto a →focal point, at which the receiver is located. On the other hand, the →parabolic troughs and linear Fresnel reflectors use a →single-axis tracking system to concentrate the sunrays along a narrow →focal line, where the →absorber tube is positioned. A CSP plant can be twice as efficient as a →photovoltaic power plant. However, they also have higher investment and operation costs than photovoltaic systems and are not as affected by falling solar prices as photovoltaic devices. While photovoltaic panels can generate a decent power output even on cloudy days under diffuse light conditions, the CSP plants, which operate at high working temperatures, respond only to direct solar radiation. As they require intensive, direct sunlight, not all locations are appropriate for CSP plants. To operate CSP plants economically, their installation should be considered only within the Sun Belt region between the 35th northern and 35th southern latitudes. The CSP plants produce clean energy without creating air pollution, thus contributing to the recovery of a healthy climate balance.

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Receiver Powerlines

Steam condenser

Stream generator

Tower

Turbine Generator

Thermal energy storage tanks

Heliostats

Concentrated Solar Power Plant

concentrated solar power station

UK (CSP station) See →concentrated solar power plant.

concentrated solar power technology

CSP technology. A technology that uses mirrors or lenses to concentrate solar radiation onto a →receiver at the top of a →solar power tower, a single →focal point, or an →absorber tube of a →concentrating parabolic trough, a narrow →focal line, to heat a fluid or make vapor-activating turbines that produce electricity.

concentrated solar thermal energy

Solar thermal energy generated by the CSP technology.

concentrated solar thermal system

A system that uses mirrors or lenses to concentrate sunlight onto a →central receiver or an →absorber tube to heat a fluid or make vapor-activating turbines that produce electricity. In a nutshell, the working principles of a concentrated solar thermal system are a) concentration and b) conversion. Just like a magnifying glass, large reflective surfaces concentrate the rays of the sun onto a small area, either a single →focal point in a →dish collector or a →central receiver system or a narrow →focal line in a →concentrating parabolic trough or a →linear Fresnel

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reflector (LFR), increasing the energy hundreds of times. The energy collected in →heat transfer fluid, reaching high temperatures between 300 °C and 1,000 °C (572 °F –1832  °F) is converted first into hot water and then into steam to drive turbine generators, producing electricity. concentrated solar thermal technology

See →concentrated solar power technology and →concentrated solar thermal system.

concentrating collector

See →concentrating solar collector.

concentrating optic

An optical element, for example, a thin layer made of glass or acrylic material, which traps and redirects the sun’s rays to the focal point. At the focal point, a high efficiency →photovoltaic cell absorbs the concentrated solar energy, which has a higher intensity and temperature than the one originally received by the concentrating optic.

concentrating parabolic trough

Concentrating parabolic troughs or U-shaped large mirrors focus the sun rays onto a black tube running the length of the trough. They are usually oriented on a north-south horizontal axis. The concentrated sunlight heats a →heat transfer fluid in the black absorber tubes, usually synthetic oil, reaching a temperature of about 400 °C (752 °F). The oil is then circulated through the insulated pipe system to a heat exchanger converting water to steam. Finally, the steam turbine generates electricity. In order to postpone the generation of electricity, the heat from the thermal oil can be transferred to molten salt that is utilized as storage medium. Later, when sun is not shining and electricity is needed, the stored heat can be taken from the tanks of molten salt and used for vapor production and consequently power generation.

concentrating parabolic trough collector

Consists of  a long parabolic mirror that concentrates the sun rays onto a black absorber tube running the length of the trough.

concentrating photovoltaic module

See →concentrator solar module.

concentrating photovoltaic panel

See →concentrator solar module.

concentrating photovoltaics

(CPV) Photovoltaic technology that uses lenses or mirrors to concentrate sunlight onto highly efficient solar cells. Unlike →flat-plate photovoltaics that work well with both

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direct and diffuse solar radiation, the concentrating photovoltaics respond only to direct sunlight. concentrating PV module See →concentrator solar module. concentrating PV panel

See →concentrator solar module.

concentrating reflector

A reflector, such as a mirror or polished metal surface, which reflects and concentrates the solar rays onto an →absorber tube at a focal line in →concentrating parabolic troughs and →linear Fresnel reflector systems or a →receiver at a focal point in →central receiver systems and →Dish– Stirling systems.

concentrating solar collector

Also known as concentrating collector or focusing collector. A solar device that uses mirrored surfaces to collect solar radiation and concentrate it onto an absorber that is known as a →receiver. As the gathered sunlight falling on relatively large mirror surface is focused onto a very small area, solar energy is enhanced hundreds of times, reaching a high temperature of around 1,000 °C (1,832 °F) or more. This dramatic rise in temperature results in a higher conversion efficiency, compared to conventional →solar collectors. There are four major types of concentrating solar collectors: →parabolic trough solar collector, →linear Fresnel reflector, →dish collector, and →heliostat in →central receiver systems. The parabolic trough solar collector and linear Fresnel reflector concentrate solar energy along the narrow focal line, where an →absorber tube is mounted, typically several meters (yards) directly above the mirrored collector surface. The dish collector and heliostats concentrate the incoming Sun’s beams onto a single focal point, at which a thermal →receiver is located. The receiver absorbs the heat and transfers it to the →heat transfer fluid that is used as a working fluid for electricity generation.

concentrating solar power plant

US CSP plant. See →concentrated solar power plant.

concentrating solar power station

UK CSP station. See →concentrated solar power plant.

concentrating solar power technology

CSP technology. See →concentrated solar power technology and →concentrated solar thermal system.

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concentrating solar thermal system

See →concentrated solar thermal system.

concentrating solar thermal technology

See →concentrated solar power technology and →concentrated solar thermal system.

concentration ratio

The ratio of the radiant flux incident on the effective area of the →aperture to that on the absorber.

concentrator

A photovoltaic device that uses Fresnel lenses or mirrors to gather and focus sunlight onto a receiver, a boiler, or a solar cell with a small aperture area (some even not bigger than a few square inches), increasing insolation at the focal point hundreds of times. Some concentrators are static, such as →parabolic troughs, whereas others, for example, dish concentrators, are guided by →solar tracking systems following constantly the course of the sun. Most solar concentrators work well only with direct solar radiation and perform poorly on cloudy days with scattered radiation. Therefore, concentrators are an ideal option for regions with clear-sky and many sunny days per year, such as zone 2 in the USA, including six southwestern states (Arizona, California, Colorado, Nevada, New Mexico, and Utah).

concentrator cell

See →concentrator solar cell.

concentrator lens

Lens that concentrates incident solar radiation onto a small, special solar cell, intensifying solar energy numerous times.

concentrator optics

The scientific study of light behavior in large reflectors that concentrate the incident solar energy onto a small receiver.

concentrator photovoltaics

(CPV) photovoltaic technology that uses lenses or mirrors to concentrate sunlight onto highly efficient solar cells.

concentrator solar cell

Also known as a concentrator cell. A solar cell that uses optics, such as Fresnel lenses, to focus sunlight onto a small absorbing surface, consisting of high-efficiency →multijunction photovoltaic cells.

concentrator solar module

Also known as a concentrator solar panel or concentrating photovoltaic (CPV) module. A type of CPV that uses lowcost polymer optics, such as polymethyl methacrylate, to focus sunlight onto small absorbing surfaces, consisting of high-efficiency →multijunction photovoltaic cells. In spite of the added optical layer, concentrator solar modules can

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still be as thin as traditional solar panels, requiring no special coatings, metal enclosures, or heat sinks. By means of added lenses, the Sun’s radiation can be magnified 10 or more times, resulting in record power conversion efficiencies of up to 40%. concrete pylon

A pillarlike concrete structure used to support a large frame with →solar panels or →heliostat mirrors.

conductance

See →electrical conductance.

conducting path

A path along which photo-generated electric charge carriers such as electrons and holes flow. The solar cell material producing electricity is →semiconductor, which is half insulator half conductor. Under certain conditions, when the sunlight hits the solar cell, the semiconductor insulator turns into a conductor generating lots of charged particles that are free to move along the given path.

conducting polymers

Also known as intrinsically conducting polymers (ICPs). Organic polymers that conduct electric current. Conducting polymers, which can be engineered to conduct electricity just like metals, have found a wide application as semiconductor materials in the manufacture of →thin-film photovoltaic modules, →multijunction photovoltaic cells and →dye-sensitized solar cells (DSSCs). The major advantage of conducting polymers is the fact that their electrical properties can be easily fine-tuned. By selecting suitable polymer compounds and adjusting the polymer side chains, the polymer engineering on a nanometer scale offers a great flexibility in tuning nanostructures to enhance intrinsic properties, such as band gap, exciton diffusion lengths, energy levels, and mobility. Conducting polymers are polyacetylene (PA), polyaniline (PANI), polypyrrole (PPy), poly(p-phenylenevinylene) (PPV), poly(3,4-ethylene dioxythiophene) (PEDOT), polyfuran (PF), polyvinylidene fluoride (PVDF), and other polythiophene (PTh) derivatives.

conduction

The movement of heat or energy through a substance.

conduction band

An energy band consisting of electron orbitals, mostly the outermost shells of the atoms in a semiconductor. Unlike →valence band that is full of electrons, the conduction band is generally empty at absolute zero temperature, but it has the potential to accept the electrons from the valence

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band under certain conditions. When the electrons gain enough energy from sunlight, for example, thermal phonon energy or photon energy of light, they become excited and are able to bridge the →band gap, a small gap between the valence and the conduction band. After they jump from the valence band to the conduction band, the electrons start moving freely through the conduction band, proceeding from one silicon atom to another in a chain-reaction manner, since they are not tied to any atom. This free movement of electrons through the conduction band initiates the flow of photovoltaic DC electric current through the circuit. conduction efficiency

The fraction of the temperature difference between the temperature at the inlet of the duct and ambient temperatures, which remains at the outlet of the duct.

conduction electron

An electron that gains a sufficient amount of energy by external influences, such as thermal excitation or illumination, to break loose from its atom and jump into the conduction band, where it is free to move in the host semiconductor, generating electric current.

conduction level

See →conduction band.

conductive layer

A layer on the surface of a substrate consisting of semiconductor materials that transfer electrical current.

conductivity

The ability of a material to conduct heat or electricity. See →thermal conductivity and →electrical conductivity.

conductor connector

A multipin (2, 3, or 6 pins) connector whose male side is snapped-mounted into the female side, creating secure connections.

conductor line

A main electrical line to which a number of solar panels are electrically connected.

conductor1

A material that allows the free flow of electrons. Good electrical conductors, in which electrons can move unobstructed, are copper, silver, gold, brass, and aluminum. Most metals are good conductors. In photovoltaic (PV) systems, the commonly used materials for conducting lines, busbars, and PV wires are copper and aluminum.

conductor2

Conductive path on a semiconductor substrate.

conduit

A tube or trough for routing and protecting electrical cables.

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cone-shaped Fresnel reflector

A Fresnel-type reflector in the shape of a cone. This reflector has a greater light gathering efficiency than an equivalent reflector without Fresnel structures. In addition, a curved Fresnel structure is more efficient than a flat Fresnel-type reflector.

conjugated polymers

Organic polymers with conjugated double bonds in the main chain that can conduct electricity. In contrast to the majority of polymers that are insulators, having no mobile charges and the lowest electronic excitations, conjugated polymers are semiconductors or conductors that interact with light and are capable of producing excitation energies necessary for generation of current flow. Polyacetylene is the simplest conjugated polymer.

connection accessories

Accessory parts, such as →photovoltaic connectors, →photovoltaic cables, →junction boxes, or modular terminal blocks, which are used to interconnect photovoltaic components.

connection cable

The interconnection cable used for linking solar modules, controller, batteries, and DC/AC inverter together.

connection cable set

See →PV cable set.

connection point

See →grid connection point.

conservation of energy

See →energy conservation.

console

An instrument panel with controls and displays in a solar or energy management system.

constant current

The capacity of a system to vary the voltage across an electronic circuit to maintain a constant electric current.

constant-speed wind turbine

A controlled wind turbine operating at fixed rotor revolutions per minute (RPM) regardless of wind speeds.

consumption meter

Measures the energy coming from the public power grid.

contact cell structure

See →metal contact structure.

contact finger

Contact fingers are tiny silver conductive lines that are connected with two →busbars on each silicon solar wafer. A grid of numerous contact fingers collect the electricity generated within the photoactive silicon semiconductor and transport it to the two busbars, which then conduct the electricity further through the module’s circuit.

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contact pad

See →rear contact pad.

contact point

A positive or negative contact point of a photovoltaic cell. During solar cell testing, the black lead of the →multimeter needs to be connected to the negative contact point of the photovoltaic module and the multimeter’s red lead must be connected to the positive contact point of the module.

contact resistance

Is a resistance between metallic contacts and the silicon semiconductor, as opposed to the intrinsic resistance. A heavier doping under the contacts region reduces contact resistance losses and enables a smoother current flow across the metal-semiconductor interface.

contacts

See →electrical contacts.

contamination

A doping method in which impurities are introduced in a controlled manner into the surface of a silicon wafer in low-level quantities.

contingency reserve

Also known as operating reserve. Reserve services that are used to provide electrical energy in an emergency situation, when a generator or transmission line breaks down. As power supplied must always be equal to power being consumed, the purpose of the contingency reserve, and the duty of a system operator, is to maintain the system reliability in case of an emergency by continuously balancing supply and demand. Contingency reserves consist of →spinning reserves, →nonspinning reserves, and supplemental reserves.

continuous solar simulator

See →steady-state solar simulator.

contour inspection

An optical inspection of a photovoltaic module that is concerned with testing contour and symmetrical deviations of solar cells.

control unit

See →controller.

controller

A device that manages the communication between two solar systems, for instance, between the →photovoltaic array and the →battery bank or between the array of →solar thermal collectors and the →hot water storage tank. Accordingly, the →charge controller regulates the flow of generated electric current into a battery bank and

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protects the batteries from overcharge and overdischarge. The →solar thermal controller regulates the transport of the generated heat to the hot water storage tank. controller cables

Controller cables connect the controller with the battery bank. In general, they can have the same wire thickness as solar cables, since these wires carry no more current than the solar module wires.

convection

The transfer of heat through liquids and gases. The warmer water or air rises and the cooler water or air comes down. For centuries, house owners have taken advantage of this natural law by inducing vertical flow of air through the house. Opening one north-facing window in the basement and one window on the top floor on the sunny side of the house will generate a cool breeze through the house. Cool air is being sucked in, and as warm air rises to the ceiling, it will exit the house through the open top floor window. This old →passive cooling technique is also known as chimney effect, cross ventilation, or simply natural ventilation.

conventional energy

See →conventional energy sources.

conventional energy sources

Energy sources that include oil, natural gas, coal, nitrogen, uranium and water power. They are mostly nonrenewable sources of energy with the exception of water.

conventional photovoltaic cell

See →conventional solar cell.

conventional PV cell

See →conventional solar cell.

conventional solar cell

Also known as traditional solar cell. Crystalline silicon solar cells, including →monocrystalline silicon solar cells and →polycrystalline silicon solar cells, are considered conventional solar cells as they account for ~80% of the entire photovoltaic market share.

conversion

The transformation of solar radiation into electrical energy (→photovoltaics) or heat (→solar thermal system).

conversion area

Also known as an →aperture area. A photoelectric or heat-absorbing area of a solar panel that converts solar radiation into electricity or heat.

conversion coefficient

A ratio of the amount of generated energy (solar output) to the value of the absorbed light energy.

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conversion efficiency

See →conversion efficiency of solar cells.

conversion efficiency factors

The following factors affect the conversion efficiency of solar cells: wavelength, temperature, I–V characteristics, reflection, orientation, and shading. The major task of the solar research is to find new semiconductors or a better combination of different semiconductor materials in →multijunction solar cells that are able to absorb more different parts of solar spectrum: ultraviolet, visible, and infrared wavelengths. The temperature is the second factor affecting the conversion efficiency. As semiconductor materials are sensitive to temperature, solar cell power output will decrease when they heat up and the temperature of the PV cells is higher than 25°C (77°F). Although electrical current increases to some extent with temperature, the overall power decreases due to a significant voltage drop. The high temperature can be decreased by installing the mounts with PV modules a few inches off the roof to allow a natural airflow to cool the panels. I–V characteristics are another important factor exploring the relationship between the current and voltage under different conditions of light intensity and temperature. The MPPT algorithm searches for the best current and voltage values for any given irradiance/heat condition, ensuring the best power yield at any time. Energy losses from reflection in a silicon solar cell are estimated 30%. They can be mitigated by using antireflection coatings and textured surfaces. An optimum orientation of solar panels to the sun and the absence of shading maximize the power output of the solar array.

conversion efficiency of photovoltaic cells

See →conversion efficiency of solar cells.

conversion efficiency of PV cells

See →conversion efficiency of solar cells.

conversion efficiency of solar cells

The percentage of incident solar radiation (sunlight) that is converted into electrical power by a solar cell.

conversion of solar energy

A process of transformation of solar radiation into electrical energy. The conversion process is regulated by four

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subprocesses: →light absorption, →charge carrier separation, →charge transfer, and →charge recombination. converter

An electrical device that converts a direct current (DC) voltage into another DC voltage to optimize power. See also →DC to DC converter.

Cook/Mayne method

A rigorous and logical application of statistical methods to extreme wind loads for use in structural design.

cooling agent

Water or air that is circulated around solar modules for cooling photovoltaic cells and thus enhancing the performance of PV modules.

cooling battery system

A thermal management system that keeps temperatures of the cells in a →battery pack within its optimum operating temperature range in order to enhance performance and extend the life cycle of the battery pack. The performance of an →electric vehicle (eV) greatly dependents on the performance of the battery pack.

cooling degree day

(CDD) Unit of measurement for cooling energy requirements that is calculated based on the difference between room and outdoor temperature.

cooling load

The amount of heat energy per unit time that must be removed from a building by a HVAC system or the amount of conditioned air that is necessary to maintain occupant comfort. See also →heating load.

cooling system

Any cooling system, such as →evaporative cooler, →heatpump, or →air conditioner, that generates cool air.

cooling with geothermal See →geothermal heat pump and →air conditioning with energy geothermal energy. Coordinated Universal Time

(UTC, Universal Time Coordinated) World standard for time that replaced Greenwich Mean Time (GMT).

COP

Abbreviation for →coefficient of performance.

coplanar contact

Wraparound connections between the front and back surfaces of GaAs/Ge coplanar contact solar cells.

copper

(Cu) Reddish-brown transition metal that has a high amount of electrical and thermal conductivity. It is used for manufacturing thin film →copper indium gallium selenide solar cells.

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 copper film

copper film

A thin layer of copper that is used in a thin-film heterojunction semiconductor. In addition to copper film, the heterojunction solar cell also includes different semiconductor materials with different energy band gaps, such as indium gallium (di)selenide.

copper indium (di) selenide

(CIS) Semiconductor material for manufacturing thin-film solar cells.

copper indium gallium (di)selenide

(CIGS) Semiconductor material for manufacturing thinfilm →copper indium gallium selenide solar cells.

copper indium gallium selenide

(CIGS) Semiconductor material for manufacturing thinfilm →copper indium gallium selenide solar cells.

copper indium gallium selenide solar cell

A thin-film solar cell made of the compound semiconductor material copper indium gallium selenide (CIGS). This second-generation solar cell is characterized by light weight, flexibility, thin profile, low material consumption, and a less expensive production process when compared to the expensive silicon wafer manufacturing method. The CIGS solar cell is the most efficient type of thin-film solar cells, achieving the record efficiency of almost 23%. It is more efficient than its main thin-film competitors →amorphous silicon solar cell and →cadmium telluride thin-film solar cell. Polycrystalline CIGS cells slightly surpassed the efficiency of polycrystalline silicon cells. The architecture of the CIGS cell is rather complex. The →heterojunction design consists of numerous layers that are deposited on a glass, plastic, stainless steel, or aluminum substrate. The first layer is a back-contact, usually made of the nontransparent material molybdenum (Mo). The second layer consists of the Cu(In,Ga)Se2 p-type layer that serves as a major absorber of photons of light. A thin n-type buffer film, such as →cadmium sulfide (CdS), is deposited between the CIGS film and an n-type transparent window layer, usually consisting of heavily doped zinc oxide (ZnO). One of the major advantages of the CIGS is that its band gap is tunable, ranging from 1.0 to 2.4 eV and achieving high optical absorption efficiency. The CIGS solar cell is manufactured by one of the following methods: →evaporation (PVD), →sputtering, →electrochemical deposition, nanoparticle printing, and →ion beam deposition.

copper indium selenide 

Sunlight

 127

Transparent conductive oxide ( TCO) Cds CIGS

Mo Glass metal foil, plastics

Copper Indium Gallium Selenide (CIGS) Solar Cell

copper indium selenide

(CIS) A compound semiconductor material for manufacturing thin-film solar cells. CIS is composed of copper, indium, and selenide.

copper indium selenide solar cell

See →CIS solar cell.

copper soldering area

See →copper soldering pad.

copper soldering pad

A thin layer, a few microns thick, deposited on the metal rear contact by plasma deposition or sputtering to form a reliable soldered metal region.

copper soldering surface See →copper soldering pad. copper zinc tin sulfide

(CZTS) Semiconductor material for manufacturing thinfilm →copper zinc tin sulfide solar cells.

copper zinc tin sulfide solar cell

Also known as CZTS solar cell or copper zinc tin sulfide thin-film solar cell. A type of thin-film solar cell made of a semiconductor compound material copper zinc tin sulfide. CZTS solar cell was designed with the goal of replacing rare and expensive thin-film materials, such as →indium and →tellurium, as well as highly toxic →cadmium in CdTe or →cadmium telluride thin-film solar cells and CIGS or →copper indium gallium selenide solar cells. The CZTS solar

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 copper zinc tin sulfide thin-film solar cell

cell uses nontoxic and cost-effective, earth-abundant elements. However, its optoelectrical properties and conversion efficiency are still far below CdTe and CIGS solar cells to be considered for commercial manufacture. copper zinc tin sulfide thin-film solar cell

CZTS thin-film solar cell. See →copper zinc tin sulfide solar cell.

copper, indium, and selenium

CIS, semiconductor material for manufacturing thin-film →copper indium selenide solar cells.

copper, indium, gallium, See →copper indium gallium selenide. and selenium copper, indium, gallium, See →copper indium gallium selenide solar cell. and selenium solar cell corner bracket

A piece of metal that is fastened to the four corners of a framed photovoltaic module to provide support and additional strength to PV panels. Hinges are often attached to corner brackets to connect adjacent modules together on the roof with the help of bolts.

corner mounting bracket A bracket providing support for the four corners of a framed photovoltaic module. The PV module is mounted on the four brackets with glue. The prefabricated height of corner mounting brackets allows enough air circulation underneath PV surfaces, ensuring an optimal ventilation and cooling of solar modules in hot summer months. corona

The outmost layers of the sun consisting of variable structures of rarefied gases with a low density and a temperature of a million degrees Kelvin.

coronal mass ejection

A process by which large bursts of plasma are ejected from the Sun, sending streams of electrically charged particles toward the Earth.

corpuscle

A very small distinct particle that is the basic constituent of matter, such as electron, proton, or atom.

corrosion

See →galvanic corrosion.

corrosion inhibitor

Also known as rust inhibitor. A substance that, when applied to a metal, inhibits the formation of rust. After the installation, it is recommended to do a vigilant quality control and spray corrosion inhibitor onto places where

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installers have scraped off the coating on the frame or ground lugs during installation. cosine correction

See →cosine response.

cosine effect

See →cosine loss.

cosine emission law

See →Lambert’s cosine law.

cosine factor

The product of the direction of the incident rays of light and the normal of the heliostat mirror surface.

cosine loss

Also known as cosine effect. The reduction of the projected →heliostat area exposed to the sun’s rays caused by the heliostat tilt angle. Cosine loss is one of the main type of losses that affect the optical efficiency of a heliostat field in a →concentrated solar power plant (CSP plant). Cosine losses depend on the field location and landscape, how much each heliostat’s mirror surface area is exposed to the sun, the configuration of the heliostats, and the design of the central →solar power tower.

cosine response

Also known as directional response or cosine correction. The angle of the incident solar radiation that affects the proper operation of a →pyranometer. A pyranometer must have a cosine response that is as close as possible to the ideal cosine value, which is 0° angle of incidence. About 0° angle of incidence occurs when the sun is at zenith or directly above the pyranometer’s sensor. The optimal incident radiation of 1,000 W/m2 is received when the sunbeam is perpendicular to the sensor. If the pyranometer is tilted, it will measure 500 W/m2 at a 60° angle or 0 W/ m2 at a 90° →solar zenith angle.

cost effectiveness

Relationship between the invested money and the desired outcome.

cost per watt

Also known as price per watt or dollar per watt. A metric used to calculate or express the cost of a solar system. In many countries, cost per watt has become standard, which is in particular useful for comparing different solar systems available on the market. Price per watt is calculated by dividing the total cost of the future PV system by the number of watts in the system. In 2017, the standard solar system installation costs in the USA were around $3.17/W for an average PV system size of 5 kW (5,000 W).

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 cost-effective solar energy

cost-effective solar energy

Measured over the lifetime of a given solar array (25 years), solar energy is cost-effective, if it is good value for the amount of money invested and costs less than grid electricity.

cost-effective solar power

See →cost-effective solar energy.

cost-effectiveness analysis

(CEA) An economic analysis comparing the invested money and the desired outcome.

cost-effectiveness ratio

The cost-effectiveness ratio could be described as follows: The higher the power output from solar panels and the lower the investment and maintenance costs, the higher the overall cost-effectiveness of a solar system.

cost-performance index

(CPI) See →cost–performance ratio.

cost-performance ratio

Also known as price–performance ratio or cost–performance index (CPI). A ratio that measures the effectiveness of a project by dividing earned value or product’s performance by actual costs. As many other high-tech products, solar panels have gone through different cost–performance phases, which are to certain extent predictable, according to Raymond Kurzweil, an American inventor, computer scientist, and visionary. The first solar panels in the seventies were extremely expensive, but had low performance. Over time, the cost of solar modules has steadily improved as well as solar module efficiency. We can say that solar modules today are in the middle of the scale with a medium or affordable cost and good performance. It is expected that solar panels will reach the most desirable cost–performance ratio in the upcoming years: low cost and high performance.

costs of generating electricity

Costs for generating one kilowatt-hour of electricity. They typically include the invested funds, the financing charges, and the →operation and maintenance costs.

Coulomb

The SI unit of electric charge. It equals the quantity of electricity passing through the cross section of conductor in 1 s by a current of 1 A. The formula can be expressed as follows: 1 C = 1 A ×1 s.

Coulomb force

Also known as electrostatic force. The electrostatic force between two or more charged bodies. The force is repulsive, if both bodies are positively or negatively charged, or it is attractive, if both bodies are of opposite charge, for example, negative/positive or positive/negative.

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counter-flow heat exchanger

The most common kind of liquid–liquid heat exchanger in which two working fluids flow in opposite directions. The hot working fluid, which gives off heat, enters at one end of the heat exchanger flow path and the cold fluid, which absorbs the transferred heat, enters at the other, opposite end of the flow path. They are the most efficient type of heat exchangers because they generate a more uniform temperature difference between the fluids and they transfer more heat than comparable →parallel-flow heat exchangers.

Covenants, Conditions, and Restrictions

(CC&R) A set of rules established by a homeowners’ association for a neighborhood or condo building that must be followed by homeowners.

cover glass

A special, chemically strengthened glass that is used as a top layer of a solar panel to protect →semiconductor materials and wiring from impact and elements. The cover glass is sealed on an aluminum frame with a →solar adhesive or other appropriate silicon sealants. The proper sealing of the panel keeps moisture away from the cells, prolonging the life of the module.

cover layer

See →top layer.

cover plate

One or two sheets of glass that cover the solar collector box, protecting the →absorber from physical damage and direct exposure to weather. The glass is transparent to incoming solar radiation and opaque to the infrared radiation, keeping the collected heat inside the box.

coverage ratio

See →ground coverage ratio.

CP

Abbreviation for →coefficient of performance.

CPC

Abbreviation for →compound parabolic concentrator.

CPI

Abbreviation for cost–performance index. See →cost–performance ratio.

CPV

Abbreviation for →concentrating photovoltaics.

C-rate

Also known as charge/discharge rate. C-rate is the rate at which electrical current is withdrawn from a battery relative to the capacity of the battery when it is fully charged. It is typically expressed in amperes or time. Some batteries display C-rates on their labels. A 1C rate indicates that the continuous discharge current will discharge the entire

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battery in 1 h; 2C will discharge in 30 min; and C/2 in 2 h. To find the discharge rate of a battery, the C-rate number should be multiplied by the capacity of the battery. In case of 5C rate and a capacity of 100 A, the formula would look as follows: 5 × 100 A = 500 A. In other words, up to 500 A can be continuously drawn from the battery without harming the battery plates. CREIA

Abbreviation for →Chinese Renewable Energy Industries Association.

critical wavelength

The wavelength at which the integral of the spectral absorbance curve reaches 90% of the integral over the ultraviolet (UV) spectrum from 290 to 400 nm.

Croatian Solar Energy Association

(HSSE) A Croatian association that comprises freely and voluntarily associated professional organizations, legal representatives, and entrepreneurs who are engaged in the field of solar and other renewable energies. The HSSE promotes the adoption of advanced solar and renewable technologies; helps shape public opinion through continuous education and mass media outreach, including print, radio, TV, and internet; gathers and shares scientific, research, technical, professional, and practical information; helps create a legislation platform that will accelerate and intensify the use of solar and other renewable energy sources; and fosters innovation and creativity in the field of solar and other renewable energies in the Republic of Croatia.

crocodile clamp

See →alligator clip.

crocodile clip

See →alligator clip.

cross ventilation

Cross ventilation is a →passive cooling technique for reducing the heat in the house during the summer. It is a natural way to cool a home by regulating airflow through the building with a help of an optimal arrangement of windows and vents. This natural ventilation technique reduces the use of air conditioners, which in turn results in decreased energy consumption, lower energy bill, and less carbon emissions. It also removes stale, stagnant indoor air and replaces it with fresh air from outside. See also →convection.

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crossflow

The flow of two fluids perpendicular to each other, for instance, in a →cross-flow heat exchanger or a →cross-flow turbine.

cross-flow heat exchanger

A heat exchanger through which two fluids flow perpendicular to each other. A cross-flow heat exchanger is used in cooling and ventilation applications where thermal energy is exchanged from one airstream to another.

cross-flow turbine

A turbine where the water flows across the rotor, across the turbine blades, hitting them at right angles. These impulse turbines are mostly used on small and microhydropower sites with typical power outputs from 5 up to 100 kW.

cross-section

See →cross-sectional view.

cross-sectional illustration

See →cross-sectional view.

cross-sectional view

Sliced view of a component displaying the interior structure and hidden parts in a device.

CRSP

Abbreviation for →charge resumption set point.

crucible

Is a container that is loaded with the target material to be melted in a →Czochralski method or evaporated and deposited onto the substrate in a PVD →evaporation process.

crystal breeding

See →crystal growing from the melt.

crystal breeding process See →crystal growing from the melt. crystal disk

See →silicon wafer.

crystal growing

See →crystal growing from the melt.

crystal growing from the melt

Production of artificial crystals from the melt. The process starts with the melting of high-purity silicon (99.9%) in a →crucible. The bath of highly purified molten silicon as well as a very clean environment in a crucible is necessary prerequisites for the manufacture of a silicon ingot in a controlled →Czochralski crystal growth process. A small seed crystal, which is mounted on a rod, is dipped into the silicon bath. A large single silicon crystal is grown by slowly pulling the rod out of the melt. The control of the speed of rotation and temperature in the crucible allows the optimization of the semiconductor product.

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 crystal growing system

crystal growing system

See →crystal growing from the melt.

crystal growth

See →crystal growth process.

crystal growth process

Process for production of artificial crystals. See also →crystal pulling process.

crystal lattice

See →crystal lattice structure.

crystal lattice structure

A symmetrical structure consisting of atoms, ions, or molecules that form a silicon crystal.

crystal nucleus

Small single crystal from which a large crystal is grown.

crystal orientation

See →crystallographic orientation.

crystal pulling

See →crystal pulling process.

crystal pulling process

A process for production of artificial crystals in which a single silicon crystal is pulled from the melt in the →Czochralski method. It is the first step in the larger →solar wafer manufacturing process that begins with the dipping of a silicon seed crystal into molten silicon called melt. As the seed crystal is rotated and slowly pulled upward, the molten silicon atoms attach to the seed crystal, creating a compact cylindrical crystal structure around the seed known as an →ingot.

crystal structure

A symmetrical structure consisting of atoms, ions, or molecules.

crystal wafer

See →silicon wafer.

crystalline material

A type of semiconductor material with a crystalline structure, such as →monocrystalline silicon or →polycrystalline silicon.

crystalline semiconductor

Semiconductor material, such as crystalline silicon, which is made of a single crystal. The single silicon crystal is grown using the →Czochralski method.

crystalline silicon

A semiconductor material from which a majority of silicon solar cells are made. The material is made either from a single crystal, in which case it is referred to as →monocrystalline silicon, or it is fabricated from multiple small single crystals of different shapes and sizes, 1 mm and larger, in which case we are talking about a →polycrystalline silicon. Monocrystalline silicon is more expensive silicon type than polycrystalline due to its complex manufacturing process.

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crystalline silicon photovoltaics

A first-generation photovoltaic technology that produces solar modules made of →crystalline silicon solar cells. Crystalline silicon photovoltaics is the most widely used photovoltaic technology that accounts for ~80% of the photovoltaic market’s total sales.

crystalline silicon solar cell

A conventional solar cell that is made of a crystalline silicon semiconductor wafer. The crystalline silicon solar cell converts the sunlight into electric energy by the →photovoltaic effect. There are two main types of crystalline silicon solar cells: →monocrystalline silicon solar cell and →polycrystalline silicon solar cell. The monocrystalline silicon solar cell is made from a wafer that consists of a single silicon crystal, whereas the polycrystalline silicon solar cell is made from a wafer that consists of multiple small silicon crystals, also known as →crystallites. See also →solar cell.

crystalline silicon solar module

A conventional solar module that is made of →crystalline silicon solar cells. There are two main types of crystalline silicon solar modules: →monocrystalline silicon solar module and →polycrystalline silicon solar module.

crystalline silicon solar panel

See →crystalline silicon solar module.

crystalline solar cell

See →crystalline silicon solar cell.

crystalline structure

A symmetrical structure consisting of atoms, ions, or molecules.

crystalline substrate

A crystalline base onto which a crystalline or noncrystalline (amorphous) layer is deposited. The deposited overlayers or films mimic the crystallographic orientation of the substrate.

crystallisation

UK Formation/growth of crystals.

crystallites

Also known as grains. Small single crystals of different sizes (1 mm and larger) and orientations, of which polycrystalline silicon materials are made. In a controlled polycrystalline manufacturing process, a silicon ingot is cooled down for a couple of days. As it cools and hardens, it crystallizes into multiple smaller individual crystals with a jumbled structure. These individual crystals called crystallites give polycrystalline wafers a specific speckled texture – many nuances of blue color with numerous irregular frostlike multicrystal patterns.

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crystallization

US Formation/growth of crystals.

crystallographic orientation

The orientation of the crystal lattice regarding some reference frame. Crystallographic orientation can be random, when grains are oriented randomly with respect to each other, or preferred, when grains have a preferred orientation. The preferred crystallographic orientation, which is also known as crystallographic texture, directly influences the optical, electrical, mechanical, and thermal properties of semiconductor materials. Therefore, the strict control of crystallographic orientations becomes more and more important in nanoengineering of semiconductor materials and solar cell manufacturing in general.

crystallographic texture A material has a crystallographic texture if there is a preferred →crystallographic orientation within a polycrystalline material. crystal-pulling method

See →crystal-pulling process and →Czochralski method.

crystal-pulling process

Crystal growth process for producing single crystals for the semiconductor and photovoltaic industry. See →Czochralski method.

CSA

Abbreviation for →Canadian Standards Association. See →CSA Group.

CSA Group

Formerly known as Canadian Standards Association (CSA), CSA Group is a not-for-profit organization that develops standards and provides evaluation, testing, and certification for photovoltaic panels and equipment.

CSD

Abbreviation for chemical solution deposition. See →chemical bath deposition.

CSP

Abbreviation for →concentrating solar power.

CSP plant

See →concentrating solar power plant.

CSR

Abbreviation for →circumsolar ratio.

CTES

Abbreviation for →cavern thermal energy storage.

CTSP

Abbreviation for →charge termination set point.

curing

A process by which a chemical reaction takes place, resulting in adhesive bonding, for example, between →EVA sheets and other solar panel components, such as solar cells and the front cover (glass).

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current

(I) The flow of an electric charge, such as the flow of negative charge (electrons) in a conductor between two points. Electric current is measured in amps (amperes) by a device called →ammeter. According to Ohm’s law, current is equal volts (potential difference) divided by resistance: I = V/R.

current at maximum power

(Imp) The current at which the maximum amount of power is generated by a PV module. Pmax (maximum power point) of a photovoltaic module is the product of the greatest voltage value (Vmp) and the greatest current value (Imp), Pmax = Vmp × Imp. Based on this equation form of Ohm’s law, we can calculate the current at maximum power: Imp = Pmax/Vmp.

current clamp

Measuring instrument with a clamp that measures the electric current in a circuit.

current flow

Flow of electrons through an electrical conductor.

current intensity

Also known as current strength. Stands simply for current. The traditional symbol for current is I, representing the intensity of current (ıntensité de courant) or the amount of electric current crossing a given area per unit time.

current meter

A device, such as an →ammeter, for measuring the intensity of an electric current.

current strength

See →current intensity.

current measurement

Measuring the flow of electrical charge across a specific surface area at the rate of one coulomb per second. Current is measured in amperes, which equals 1 C/s.

current–voltage characteristic

See →current–voltage curve.

current–voltage curve

I–V curve or current–voltage characteristic. A graphic representation of a relationship between current and voltage illustrating the operating characteristics of a solar cell, module, or array within an electrical circuit. As current times voltage equals power, I–V curve provides information crucial to determining the power output and the conversion efficiency of a cell, panel, or solar system. Moreover, it helps to maximize the solar power output by customizing the system to achieve the →maximum power point (MPP) operation.

 current–voltage curve

PMPP

ISC

IMPP

MPP

Cell voltage (V)

VMPP

Cell power (W)

Cell current (A)

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VOC

Current-Voltage Curve

MPP is an ideal power output point on the graph between the maximum current point that is short circuit current (ISC) and the maximum voltage point that is open-circuit voltage (VOC). Short circuit current (ISC) is the maximum current produced by a solar cell when its terminals are short-circuited, which means connected to each other. As there is no connection to an external load, there is no resistance in a circuit and the voltage is zero. On the other side, open-circuit voltage (VOC) is the maximum voltage produced by a solar cell, when there is a break in a circuit. As there is no connection between terminals, the resistance is extremely high and no current is flowing (current value is zero). However, under normal operating conditions, when the PV system is connected to an external load (electrical household appliances, batteries, inverters), the actual maximal current and voltage values will be different than the above-described ISC and VOC extremes (ideal values). The ratio showing the relation between the actual maximum power from a PV cell to the ideal maximum power (product of ISC and VOC) is called fill factor (FF). The ratio can be mathematically expressed as: FF = VMPPIMPP/VOCISC . The larger the area of the rectangle IMPP × VMPP, the closer it comes to its ideal rectangle with area ISC × VOC. Therefore, MPP of a photovoltaic module is the product of the greatest voltage value (VMPP) and the greatest current value (IMPP), MPP = VMPP × IMPP. The efficiency of a photovoltaic module is usually calculated by this MMP equation that is derived from

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the →Ohm’s law power equation: P = V × I. There can only be one MPP, or one point on the I–V curve (current–voltage curve), for a certain PV module (PV product) estimated with an optimal load under optimal illumination, temperature, and other conditions. curtain

Prevents the solar heat from entering the house through windows. The use of curtains is considered an effective →passive cooling technique.

curvature

The measure of how much a curve deviates from a straight line.

curve factor

The fill factor of an ideal photovoltaic cell without resistance losses.

curved concentrator oven See →solar parabolic cooker. curved mirror

A mirror that curves inward or outward. The inward-curving mirrors or surfaces, known as →concave mirrors, are used in the →concentrating solar collector technology to concentrate incoming solar radiation at the focal point of the →dish or a focal line of a →concentrating parabolic trough, thus increasing the solar energy numerous times.

curved surface

Curved mirror surface in a →parabolic through collector.

cutoff voltage

A set voltage value at which the →charge controller cuts the electric current to protect the batteries. The high cutoff voltage value disconnects the photovoltaic system from the battery bank to prevent overcharging and the low cutoff voltage value automatically disconnects the load (all electrical devices connected to the circuit) from the battery bank to prevent excessive discharging. Both cutoff voltage set point values protect the batteries from damage and prolong their life.

cut-off voltage

See →cutoff voltage.

cutoff wavelength

The maximum wavelength above or below which a particular mode ceases to propagate and exist. Two types of cutoff wavelength are of importance in the solar energy field: ultraviolet (UV) cutoff wavelength and infrared (IR) cutoff wavelength. UV cutoff wavelength is the shortest wavelength at which the absorption of solar energy begins, resulting in emitted photoelectrons in a semiconductor

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 cut-off wavelength

material. IR cutoff wavelength is the longest wavelength at which the absorption of solar energy ends. Wavelengths longer than 1,100 nm pass by silicon atoms without triggering the emission of photoelectrons in the silicon semiconductor. cut-off wavelength

See →cutoff wavelength.

cutting blade

Component of a →wafer dicing machine. A blade usually made of diamonds embedded into the binder for cutting hard materials such as →silicon.

cutting disk

See →cutting blade.

CVD

Abbreviation for →chemical vapor deposition.

cycle

One complete discharge and charge cycle a battery performs during its operation. Battery life is often estimated by the number of discharge–charge cycles a battery can complete before it reaches the end of its usable life.

cycle durability

See →cycle stability.

cycle life

The number of discharge–charge cycles a battery can perform before it reaches the end of its usable life, which is typically 80% of its original capacity.

cycle per second

Shows how many times the direction of the electric current is reversed in an AC circuit per second.

cycle stability

Also known as cycle durability. Stability or durability is one of the key features of a rechargeable battery that refers to the number of discharge–charge cycles of the battery. The more discharge–charge cycles a battery can run through before it reaches the end of its usable life, the more stable and durable it is.

cycling batteries

A regular discharging and recharging of flooded batteries to ensure a long life.

cyclosilane

A saturated hydrosilicon compound with a cyclic structure that can be utilized for forming a silicon film on the surface of a substrate.

cyclotron

See →particle accelerator.

cyclotron resonance

High-density plasma etching. See →electron cyclotron resonance (ECR).

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cylindrical ingot

In solar wafer manufacturing, the typical shape of a single-crystal →ingot that is pulled out of the melt.

cylindrical parabolic mirror

A parabolic mirror in the shape of a cylinder that focusses the reflected solar beams onto a receiver unit, an →absorber tube, running along the focal line.

Czochralski crystalgrowth process

See →Czochralski method.

Czochralski crystalpulling method

See →Czochralski method.

Czochralski crystalpulling process

See →Czochralski method.

Czochralski growth

See →Czochralski method.

Czochralski method

Crystal growth process for producing single crystals for the semiconductor and photovoltaic industry. In the first phase of the Czochralski process, high-purity silicon is melted in an oven and the molted silicon is doped with small amounts of →boron or →phosphorus, a few parts per million, changing the electronic properties of the silicon into p-type or n-type. A silicon seed crystal is dipped into molten silicon called melt. As the seed crystal is rotated and slowly pulled upward, the molten silicon atoms attach to the seed crystal, creating a compact cylindrical crystal structure around the seed known as an ingot. The ingot withdrawn is exceptionally pure, as impurities tend to remain in the liquid. The cooled ingot is trimmed into a quadratic shape and sliced with a diamond saw into →wafers that are then made into solar cells.

Czochralski process

See →Czochralski method.

Czochralski silicon

(Cz-Si) Monocrystalline silicon fabricated using the Czochralski crystal growth process. Due to single crystal wafers’ good resistance to thermal stress, the majority of the commercially grown silicon today is Czochralski silicon.

Czochralski technique

See →Czochralski method.

CZTS solar cell

See →copper zinc tin sulfide solar cell.

CZTS thin-film solar cell

Copper zinc tin sulfide thin-film solar cell. See →copper zinc tin sulfide solar cell.

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Seed holder Seed

Single crystal silicon

Heater Si

Crucible susceptor Crucible

Silicon melt

Crucible shaft

Czochralski Method

D

daily cycle

In a photovoltaic system, a process that is repeated again and again every day in battery operation. During the day, batteries are charged, and in the evening, batteries are discharged by the nighttime load.

dangling bonds

A chemical bond that is not connected to another atom of the silicon lattice but extends to the surrounding exterior at the surface of the silicon crystal. When a silicon atom, which has four valence electrons, is not able to join with four other surrounding silicon atoms to establish the octet-stability with eight electrons in the outer valence

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shell, it is referred to as a free radical. If a free radical is unable to form covalent bonds and is present in a solid environment, it is called a dangling bond. These unsaturated, broken bonds at the semiconductor surface are highly chemically reactive toward other substances. dark sky

In weather forecast maps, a darkness line represents dark sky. It shows when the sky will be dark (black), excluding light pollution, dust, clouds, or snow.

DAS

Abbreviation for →dendrite arm spacing.

DAST

Abbreviation for →dual-axis solar tracker.

data communication

Transmission of data to and from computers and components of a certain data-communication system, for example, Global Forecast System data in solar forecasting.

data logger

An electronic instrument that records data over a period of time. Data loggers can be utilized for collecting and storing temperature, relative humidity, solar radiation, or solar output data of a solar system. The stored data are used for evaluation, comparison, and further processing.

data monitoring

A process in which critical data, such as solar power yield, temperature of solar panels or weather data are routinely collected and stored for the purpose of better data evaluation and further processing. With help of data monitoring, the actual data can be compared against previously achieved values across different periods, resulting in a more accurate assessment of the earning power of the system. See also →monitoring platform and →solar system monitoring.

data monitoring system

A system for →data monitoring.

data-communication system

Includes the exchange of data among different computers, networks, and communication systems, for example, Global Forecast System data in solar forecasting.

dawn

The time of day immediately before sunrise, when sunlight begins to appear in the sky.

daylight coefficient

Also known as daylight factor. The ratio between the luminance levels and patterns of the sky and the actual daylight illuminance in the interior of a room due to the light from that sky.

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daylight control

See →daylight management.

daylight factor

See →daylight coefficient.

daylight management

Also known as daylight control. The best daylight management is achieved when daylighting techniques are incorporated into the home design during the construction of the building. The major challenge of solar architects is that while they need to allow the maximum amount of ambient daylight into the interior of the building, they must ensure that tenants are protected from direct ultraviolet (UV) radiation, glare, and excessive solar heat gain at the same time. The goals of an effective daylight management include the control of glare and excessive brightness with special windows, interior solar shades, and automated shading systems, the preservation of outdoor views, the reduction of electric light use, and the mitigation of solar heat gain.

daylight pipe

See →sun tube.

daylight quotient

The ratio of the illumination inside a building, calculated from a point on the horizontal measuring plane, to the illumination outside the building (horizontal illumination intensity) when the sky is obscured. DQ = (Ei/Eo) ×100%.

daylighting

The use of windows, skylights, or →sun tubes to illuminate the interior of a building by natural light. When UV rays are appropriately controlled, natural daylight promotes human health and makes the use of artificial light during the day superfluous, reducing the energy bill as well as the unnecessary heating of the house.

daylighting device

Any device that brings natural light into the interior of a building, such as window, →sun tube, →skylight, →skylight dome, or pitched skylight.

daylighting system

See →daylighting device.

days of autonomy

Also known as days of storage. The number of days without solar irradiation, for example, in fall or winter, when an autonomous off-grid solar system relies solely on its battery bank to provide power supply for a household.

days of storage

See →days of autonomy.

DBG

Abbreviation for →direct band gap.

DBS 

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DBS

Abbreviation for →drainback system.

DBT

Abbreviation for →dry-bulb temperature.

DBU

Abbreviation for Deutsche Bundesstiftung Umwelt. See →German Federal Foundation for the Environment.

DC

Abbreviation for →direct current.

DC cable

Direct current cable.

DC circuit breaker

See →photovoltaic DC circuit breaker.

DC combiner box

A DC box that is installed between a photovoltaic array and an →inverter in a →grid-tie system or a →charge controller in an →off-grid photovoltaic system or →backup power system. The DC combiner box connects PV modules into a system by bringing the output of several photovoltaic strings together. A string can include one or more (up to 24) modules. The combiner box fulfills several important functions, such as combining the strings into parallel, transition to conduit, overcurrent protection, and monitoring of the solar system.

DC daily power budget

The average amount of watts your appliances use each day in a direct current (DC) system. When planning a DC system, for example, for an RV or a small or medium boat, calculating a DC daily power budget helps us estimate how many batteries will be needed in the future DC battery bank to cover all our power needs. Let us take a brief look at a simplified version of a daily power budget creation. We take the average power consumption of each appliance we will use from their power labels in watts. If only voltage and current values are indicated on the label, we can get power in watts by multiplying voltage (V) by current (I) in amps. To get an accurate evaluation, the power budget needs to be expressed in watt-hours (Wh). Therefore, the approximate number of hours an appliance will be used daily is estimated und then multiplied by labeled power value in watts. Finally, the watt-hours (Wh) of all appliances needed, for example, in an RV (lights, pumps, TV, radio, and laptop), are summed up, giving us a good idea how much power will be drawn from our battery bank every day. Equipped with the information about the total storage capacity, we know how many deep cycle batteries we need to purchase for our DC storage system.

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 DC disconnect

DC disconnect

An important, recommended and in some countries, for example, USA, required piece of safety equipment that is installed between a power source, for example, →photovoltaic array, and an →inverter in a →grid-tie system or a →charge controller in an →off-grid photovoltaic system or →backup power system. The main function of this box with a manual disconnect handle is to interrupt the DC current from a PV array before reaching the inverter or charge controller in case of an emergency (fire) or when the inverter needs to be removed for service.

DC fast-charging station See →DC fast-charging station for electric vehicles. DC fast-charging station Also known as a level 3 charging station. A public chargfor electric vehicles ing station that uses a special J1772™ combo connector to allow ultra-fast charging of →electric vehicles. This is the fastest type of charging electric vehicles capable of delivering 400–600 VDC and filling up an 80-mi or 129-km battery pack in around 30 min. The regular J1772™ connector of level 2 stations is expanded by two large DC pins at the bottom, allowing CCS to bypass the on-board charger and feed power directly to the eV battery pack. The batteries must be specially engineered to accept a fast charge. Audi, BMW, Daimler, Ford, General Motors, Porsche, and Volkswagen were among the first car brands to adopt the J1772™ fast DC charging standard. Fast charging only works to 70% state-of-charge, while the rest of charging occurs at a slower rate. Some electric car makers discourage all too frequent rapid charging, as they believe that ultrafast charging might cause overheating and an accelerated degradation in lithium-ion batteries, reducing driving range and the lifetime of batteries in general. DC plug-in connector

See →photovoltaic plug-in connector.

DC power optimizer

See →DC to DC power optimizer.

DC pump

A water pump powered by direct current (DC) from a →solar array or a →battery bank. For small-scale irrigation purposes, pumps with a DC motor, such as pond pumps or circulating pumps, are usually sufficient. The variable speed motors of DC pumps can be directly connected to photovoltaic panel(s).

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DC-to-DC converter

Is a power optimizer that functions as an interface between the solar module and the load. To maximize the energy output of a solar system, direct current (DC)-to-DC converter converts one level of DC voltage, such as photovoltaic panel voltage, into another level of DC voltage, such as load voltage. It adjusts the PV voltage by constantly searching for a →maximum power point (MPP) and by stepping the PV output voltage up or down to match the load voltage.

DC-to-DC power optimizer

A power optimizer connected to each solar module to maximize the energy output of a solar system.

DC/DC converter

See →DC-to-DC converter.

DC/DC power optimizer

See →DC-to-DC power optimizer.

DCS

Abbreviation for →distributed control system.

dead load

Also known as dead weight. Fixed, permanent load or the weight of the structure itself. When calculating the weight impact of solar panels and support structures on a roof, it is important to differentiate between dead load and live load. The structural engineer or solar technician needs to take both into account, dead load or the weight of PV panels and racking systems as well as live load or movable external load on the PV panels and structure, such as potential snow or wind load.

dead weight

See →dead load.

deadweight

See →dead load.

deburring machine

See →trimming machine.

deburring tool

See →trimming machine.

decalin

(decahydronaphthalene) An industrial solvent, a clear colorless liquid used in a thermochemical storage system of a →concentrated solar power plant.

DECC

Abbreviation for →Department of Energy and Climate Change.

December solstice

See →winter solstice.

decentralised solar energy

Electrical energy that is generated close to the point where it will be used by a small-scale solar energy producer

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 decentralised solar power

(homeowner) as opposed to a centralized, large-scale electricity production by a utility company. The decentralized solar energy production is mainly driven by the wish to reduce CO2 and other greenhouse gas emissions as well as to liberate the electricity markets. In addition, a large amount of losses in power distribution and transmission lines as well as conversion losses can be avoided by decentralized on-site energy generation. decentralised solar power

See →decentralised solar energy.

decentralized energy

Electrical energy that is generated on-site by a small-scale energy producer, such as a solar system owner, as opposed to a centralized, large-scale electricity production by a utility company.

decentralized generation An autonomous, small-scale power generation system, plant such as a solar array, which can be built in residential areas. A decentralized solar power plant does not generate harmful emissions and decreases transmission and conversion loses. deciduous trees

Provide shade in the summer and are considered an effective →passive cooling technique preventing the solar heat from entering the house. It is less efficient to plant trees, in particular every green trees, on the south side of the house, since they block the sun in the winter, when a maximum solar gain is desired. For the purpose of sun control, the best place to plant trees is east and west of the house. During the summer months they will shade east-facing walls and windows from 7 to 11 in the morning and west-facing walls and windows from 3 to 7 in the afternoon.

declination

The angular distance, measured in degrees, north or south of the celestial equator. Being an equivalent of geographic latitude, declination is used to determine a position on a celestial sphere in the equatorial coordinate system. A declination in the northern hemisphere is positive, whereas a declination in the southern hemisphere is negative. At the spring and fall equinoxes, when the Sun is perpendicular to equator and the Earth’s axis is tilted neither toward nor away from the Sun, the declination angle equals 0°. Apart from the two equinoxes, when the Earth’s equatorial plane

declination angle 

 149

passes through the center of the Sun, the Earth is always tilted either toward or away from the Sun for the rest of the year. One half of the year, after the →spring equinox, the Earth gradually tilts toward the Sun every day, reaching its maximum declination angle of +23.5° north of the equator on the longest day of the year, which is known as →summer solstice, when the sun is at its highest point in the sky at noon. The other half of the year, after the →fall equinox, the Earth gradually tilts away from the Sun every day, reaching its maximum declination angle of –23.5° south of the equator on the shortest day of the year, which is known as →winter solstice, when the sun is at its lowest point in the sky at noon. declination angle

Angle of declination, north or south of the celestial equator in the equatorial coordinate system.

decrease of performance The decrease of solar module performance can occur as a result of long-term factors, such as →delamination, →shading or cracked cells, or short-term factors, such as overcast sky or snow. deep discharge

A discharge of a battery to at least 20% of its full charge.

deep discharge protection

A module that protects certain types of lead-acid batteries from excessive discharging that can damage the batteries. When the battery reaches a low voltage set point, typically 20% of its full charge, the deep discharge protection automatically disconnects the load (all electrical devices connected to the circuit) from the battery to prevent the further discharging.

deep discharge recovery Some batteries, such as →AGM batteries, require additional measures to revitalize a deeply discharged battery. deep discharge state

A battery is in a deep discharge state, when the →state of charge (SOC) drops to 20% or less of its full capacity, which can damage the lead plates and the battery.

deep discharge voltage

A critically low-voltage point when a →deep discharge protection mechanism is activated, automatically disconnecting the load from the battery.

deep eaves

Deep eaves prevent the solar heat from entering the house directly through windows and indirectly through walls.

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 deep reactive ion etching

Although they are an efficient device for shading southfacing windows in the summer, they are less useful for east and west exposures. A house design that includes deep eaves is considered an effective →passive cooling technique. deep reactive ion etching

(DRIE) Also known as Bosch process, named after the German company that invented and patented this method. A plasma-assisted →dry etching technology for producing deep, high aspect ratio (~30:1) structures (etched trenches) in silicon wafers. The DRIE process consists of two major production cycles: 1. passivation or polymerization cycle and 2. etching cycle. In the passivation or polymerization cycle, a thin polymer film is deposited on the side walls and bottom of an etched trench. During the passivation cycle, the octafluorocyclobutane (C4F8) gas is used in the reaction chamber. The passivation cycle is followed by the etching cycle in which the sulfur hexafluoride (SF6) gas is introduced into the chamber. The directional ion bombardment attacks and is able to penetrate the horizontal polymer structures at the bottom of the trench, whereas the vertical

Photoresist mask C4F8

Polymer (nCF2)

Silicon

1. Passivation or polymerization cycle

SF6

2. Etching cycle

Deep Reactive Ion Etching

deep-cycle 

 151

sidewall structures remain intact, protected by the etch-resistant polymer layer. After the polymer film is removed from the bottom of the trench, the high-energy ions react with the silicon atoms and etch away a thin layer of the semiconductor material. After that, the system switches to the passivation cycle again. The passivation and etching cycles are successively repeated numerous times until the desired trench depth is reached. The technique of successive switching between passivation and etching cycles results in high anisotropy with a high aspect ratio. As the DRIE process allows a good control over the trench depth and shape, it is a preferred method when deeper, uniform, and precisely etched trenches are required. deep-cycle

See →deep-cycle lead-acid battery.

deep-cycle battery

See →deep-cycle lead-acid battery.

deep-cycle lead-acid battery

Is an energy storage device with ticker plates that can be deeply discharged (up to 80% of its capacity) and recharged several hundred times over. This battery type has less instant energy, but greater long-term power supply. Deep-cycle lead-acid batteries are commonly used in off-grid PV power systems due to a high number of discharge cycles. Even though they can be discharged up to 20%, it is not recommended to discharge batteries below 50% for longer life.

deflected radiation

A type of scattered radiation in which light rays are deflected in different direction from a straight path by dust or cloud particles.

deflector

A plate for deflecting a flow of air, water, or heat. See →solar panel wind deflector.

degradation

A decrease in the efficiency of a solar module or solar system over time. While degradation rates for an entire solar system are more difficult to calculate due to numerous factors, solar module degradation rates, based on strict testing procedures, have become a standard that manufacturers are expected to include in their solar product warranties and documentation. The main causes of PV module degradation are temperature, ultraviolet (UV) exposure, environmental causes, such as pollution or soiling, and mechanical damages, such as lamination defects, humidity on the contacts, or wiring degradation.

152 

 degradation factor

A study of the →National Renewable Energy Lab (NREL) from 2012 showed a mean solar panel degradation rate of 0.8% per year. Banks often assume a mean degradation rate of 0.5% per year for crystalline solar modules, whereas →polycrystalline silicon solar modules exhibit smaller degradation rates than →monocrystalline silicon solar modules. On the other hand, thin-film →amorphous silicon solar modules (a-Si), whose degradation rates have significantly improved during the last decade, still show higher degradation rates than →crystalline silicon solar modules. While degradation rates of crystalline panels are constant over the entire module life, thin-film a-Si modules exhibit higher degradation rates in the first 6 months of operation, after which the degradation stabilizes and remains at a slower rate. degradation factor

See →photovoltaic module degradation rate and →degradation.

degradation of performance

See →degradation.

degradation rate

See →photovoltaic module degradation rate.

degraded land

The land that has temporarily or permanently lost its natural productivity due to adverse human impact, for example, deforestation or soil pollution, or due to natural causes. Strongly acidic soils, abandoned land, and wasteland are suitable for solar farms, as they do not encroach on productive agricultural land and the environment.

degree day

Unit of measurement for heating energy requirements that is calculated based on the difference between room and outdoor temperature.

degree-day

See →degree day.

dehumidification chamber

A chamber in a →solar kiln in which hot air is circulated to dry stacked wood.

delamination

The process of reduction in bond strength and detachment of the laminated components. A solar module consists of several layers that must be hermetically sealed together by applying heat, vacuum, and pressure in an encapsulation process. If the encapsulation process is not conducted in a

demand for electric power 

 153

professional →solar panel laminator or it has been rushed, it can lead to delamination. Delamination is also caused by using inferior materials, such as cheap polymer, →EVA, or glass materials. Another cause of delamination is an unclean environment during the production process, including the use of not perfectly clean plastics or glass. Delamination is a huge problem, as it allows air and moisture to penetrate inside the solar panel, leading to corrosion and imminent failure. Depending on the size of the affected areas, the power output of solar modules will decrease. Hot cells also speed up the process of delamination. demand for electric power

See →annual electricity requirement.

demand for electricity

See →annual electricity requirement.

demand response

A type of US →smart grid program, which engages customers in →smart energy management by offering time-based rates or other forms of financial incentives. In this platform, the customers contribute to balancing electricity supply and demand by reducing or shifting their electricity usage during the hours of high-energy demand, so-called →peak hours.

demand response management

The management of supply and demand of electrical energy by a grid operator.

demand side management

(DSM) Also known as energy demand management. A program of utility companies that manages energy demand by encouraging consumers to modify their electricity consumption patterns. Instead of building new power plants to meet the increased power demand, DSM programs motivate consumers with the help of incentives and favorable →offpeak rates to reduce their energy consumption overall and/ or to shift their loads, their typical electricity consumption patterns, from →peak hours to →off-peak hours.

DENA

Abbreviation for Deutsche Energie-Agentur. See →German Energy Agency.

dendrite

A spike-shaped single-crystal seed that is used during the →dendritic web growth. As two dendrites are slowly withdrawn from the melt, a web of single-crystal silicon forms between them. It solidifies into a compact, flat, wafershaped crystal structure as the silicon cools.

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 dendrite arm spacing

dendrite arm spacing

(DAS) In the production of metallic alloys, the distance between the protruding adjacent secondary arms of a →dendrite.

dendritic solar cell

Also known as a →dendritic web solar cell. A type of solar cell that is fabricated by applying a →dendritic web growth technique.

dendritic web growth

See →dendritic web growth technique.

dendritic web growth technique

A method for growing long, thin sheets of polycrystalline silicon that are slowly withdrawn from molten silicon as in →Czochralski method. What differentiates dendritic web technique from the Czochralski method with silicon →ingots is the thin silicon sheet that forms between two silicon dendrites as it is slowly pulled upward from the melt and cooled, creating a compact, flat, wafer-shaped crystal structure.

dendritic web solar cell

See →dendritic solar cell.

dendritic web technique See →dendritic web growth technique. Department of Energy

(DOE, United States Department of Energy) Is a Cabinet-level department of the United States’ government that manages the US nuclear infrastructure and administers the country’s energy policy.

Department of Energy and Climate Change

(DECC) British Department of Energy that is committed to providing environmental friendly, affordable energy and promoting international action to mitigate climate change.

depletion layer

See →depletion zone.

depletion region

See →depletion zone.

depletion zone

Also known as cell barrier. A region in a P–N junction diode that has no charge carriers, neither electrons nor holes. It acts as a barrier opposing the flow of electrons from the negatively doped semiconductor layer and holes from the positively doped semiconductor layer (see the figure on page 155).

depositing

See →deposition and →deposition method.

deposition

A process by which a substance changes from a gaseous to a solid state without first becoming a liquid. In a solar cell manufacturing process, thin films of various semiconductor materials are deposited onto a substrate by going directly from a gaseous state to a solid state in a vacuum chamber.

deposition method  Depletion zone

 155

Free electron Hole

P-type

N-type

P

Nagative ion

–

+

–

+

–

+

–

+

–

+

–

+

Depletion Zone

N

Positive ion

deposition method

There are two major deposition methods used in manufacturing of thin-film solar cells: →chemical deposition and →physical deposition.

deposition process

See →deposition method.

deposition rate

The rate at which a semiconductor material is deposited onto a substrate in a →physical vapor deposition (PVD) or →chemical vapor deposition (CVD) process for manufacturing of thin-film semiconductor devices. The deposition rate corresponds to the epitaxial growth rate, which is typically expressed in layer thickness per unit time, microns/ minute (µm/min). The factors that influence the deposition rate include the temperature of the substrate, type of semiconductor material, gas composition, gas flow rate, and chamber pressure.

deposition region

A region on the substrate designated and prepared for the deposition of the semiconductor material.

deposition technique

See →deposition method.

depreciation

The reduction in value of a solar facility over time, usually the estimated useful life of the system.

depth of discharge

(DOD) The degree to which a battery is discharged relative to its total capacity. When the battery is completely charged,

156 

 DER

its DOD is 0%; when the battery is fully discharged, its DOD is 100%. For optimal battery health and a long battery life, the depth of discharge should never exceed 50%. DER

Abbreviation for →distributed energy resources.

DESERTEC project

A large-scale solar project to power Europe with North Africa’s desert sun.

desertification

A process by which fertile land becomes desert. The land degradation process can be attributed to natural forces, including drought and climate changes, and inappropriate human activities, such as deforestation, overcropping, and overgrazing. Solar energy can be employed to prevent and combat desertification. In Africa, →SODIS bottles, →PET bottles, and →solar cookers are used to boil water or cook food, reducing the need to cut down trees for water disinfection or cooking. In China, water is extracted from seawater by utilizing →solar-powered desalination plants and used for irrigation of arid areas, reforestation, and other methods that fight desertification.

desiccant

A hygroscopic substance that attracts water and is used as a drying agent. Solid desiccants include materials such as silica gel, calcium chloride, or sodium chloride, whereas liquid desiccants include lithium bromide and lithium chloride.

desiccant cooling

See →solar desiccant system.

design load

Calculation of heating or cooling loads for winter or summer design conditions.

design month

The month in which the lowest daily mean insolation was recorded. When the load is constant throughout the year, this worst-case scenario serves as a yardstick for sizing a new →off-grid photovoltaic (PV) system. If the PV array can meet the load in the least sunny month, the owner of a stand-alone solar system can be rest assured that their electricity needs will be covered throughout the year.

design reference year

See →typical meteorological year.

design temperature

The highest or the lowest temperature to which a building may be subjected in the warmest summer or the coldest winter weather scenario. The design temperature is used for estimating or predicting a building’s heating or cooling requirements.

design temperature difference 

 157

design temperature difference

(DTD) The difference between the indoor design temperature or the optimal AC room temperature and the average coldest outdoor temperature for a given location.

designated illumination area

The area of the photovoltaic cell or module that actively absorbs the incident light. During the testing and measurement of a PV module performance, the designated illumination area is calculated by subtracting the nonabsorbing areas, such as the masked area, including →busbars, →fingers, and →interconnections, as well as the aluminum frame, from the total surface area of the PV device.

desorption

Phenomenon in which atoms or molecules leave the surface of a solid.

desulfation

A method for removing lead-sulfate crystals from the plates of a →lead-acid battery. For instance, the pulse conditioning claims to break up crystals that clog the plates and revive the battery by applying short bursts of high voltage. Even though several desulfation techniques are offered on the market today, such as pulse conditioning, there is insufficient scientific evidence and practical value to support these reconditioning methods.

device for cooling of solar modules

See →water-cooled solar panel.

dew point

Also known as a saturation point. The temperature at which air becomes completely saturated and water vapor starts to condense as drops on the surface.

dew point temperature

See →dew point.

Dewar tube

A vessel, such as a vacuum flask, which consists of two tubes, an outer and inner tube. The smaller inner tube is nested within the larger, outer tube and separated from it by a vacuum, which acts as an efficient insulator, reducing the thermal loss. The Dewar tube double-wall design is utilized in →evacuated-tube collectors and →absorber tubes for →concentrating parabolic troughs or →linear Fresnel reflectors (LFR).

Dewar tube collector

A solar–thermal collector that uses a Dewar tube design to reduce the thermal loss in the water-heating system. The inner tube that absorbs the solar irradiation is nested within the outer tube and separated from it by a vacuum, which functions as an efficient insulator.

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 DGS

DGS

Abbreviation for Deutsche Gesellschaft für Sonnenenergie. See →German Solar Energy Society.

DHI

Abbreviation for →diffuse horizontal irradiance.

dial plate

The plate of a sundial marked out with hour lines, onto which a gnomon (shadow stick) casts the shadow, indicating the time of day.

diamond blade

Also known as a diamond saw. A dicing blade made of diamonds embedded into the binder for cutting hard materials such as silicon. In the →Czochralski method, the cooled silicon →ingot is sliced with a diamond blade into →solar wafers.

diamond saw

See →diamond blade.

diamond wire saw

A machine for cutting mono- or polycrystalline silicon wafers. The main component of the machine is a diamond wire that slices large silicon bricks into individual wafers.

DIBD

Abbreviation for →direct ion-beam deposition.

diborane

(B2H6) The chemical compound consisting of →boron and →hydrogen that is used as dopant gas in solar cell manufacturing. The gaseous compound adds doped, impurity layers to the silicon wafer by a →diffusion process to increase the conductivity of the semiconductor.

DIBS

Abbreviation for →dual ion-beam deposition.

dichroic mirror

Also known as dichroic reflector. A mirror coated with a special film that selectively reflects solar radiation according to its wavelength. Dichroic mirror allows short-wave visible light to be concentrated onto a target point while letting long-wave infrared radiation (heat) escape through the backside of the mirror.

dichroic reflector

See →dichroic mirror.

dicing

See →wafer dicing.

dicing blade

Also known as a dicing saw. The major component of a →wafer dicing machine responsible for cutting silicon wafers. The blade is typically made of abrasive grit and diamonds that are embedded into the binder. Diamonds are suitable for cutting hard materials such as silicon.

dicing saw 

 159

A blade with a low diamond concentration is used when a precise cut and better surface finish are required. The major disadvantages of mechanical sawing are: 1. the mechanical load, causing chipping and damage to semiconductor wafers 2. the necessity of further polishing and processing to turn rough textures into usable wafers 3. a relatively large kerf width 4. the time-consuming dicing process that can take several hours to complete 5. the production of unhealthy tiny particles of silica during the sawing process. As the wafer material is getting thinner, dicing blades become unsuitable to saw thin wafers in the range of 100 μm or less. In this area, mechanical sawing is replaced by laser dicing processes, such as →laser ablation and →stealth dicing. dicing saw

See →dicing blade.

die

A block of semiconductor material. See also →graphite die.

dielectric

Also known as dielectric material. Nonconducting material; an insulator.

dielectric absorption

The retention of electric polarization of a dielectric material after the electric field is removed.

dielectric capacitor

A dielectric capacitor consists of an electrically insulating material, such as polymer, inserted between two metal plates. The dielectric insulator keeps the conducting plates from coming in contact, while increasing its capacitance by reducing the electric field strength.

dielectric constant

A measure of how easily a material can become polarized by imposition of an electric field on a dielectric material. See also →relative permittivity.

dielectric dispersion

The phenomenon by which the variation of electric permittivity of a dielectric material is dependent on the frequency of the applied electric field.

dielectric displacement

Also known as dielectric strain, dielectric stress, or dielectric flux density. The amount of charge displaced by an electric field within a given material. It is the sum of the

160 

 dielectric dissipation factor

strength of an applied electric field multiplied by the permittivity of the dielectric material. Dielectric displacement is often expressed in coulombs per square meter (C/m2). dielectric dissipation factor

The measure of the loss of photoelectric current or electric current through scattering in a dissipative system.

dielectric film

See →dielectric layer.

dielectric fluid

A dielectric material in liquid state used for transformer cooling.

dielectric flux density

See →dielectric displacement.

dielectric hysteresis

The phenomenon by which dielectric materials experience the changes in orientation of electron orbits due to the rapid reversals of the polarity of the line voltage, resulting often in a loss of energy.

dielectric layer

A thin-film layer made of dielectric material, such as SiN:H, which is deposited by the →plasma enhanced chemical vapor deposition (PECVD) method.

dielectric loss

The dissipation and loss of energy in a dielectric material in the form of heat as a result of alternating electric field.

dielectric loss factor

Also known as dielectric loss index. The degree to which electrical current is dissipated and lost as heat in a dielectric material due to conduction, slow polarization currents, and other forms of energy dissipation. This measure of energy loss is commonly expressed by the following formula: ε″ = ε′ tanδ.

dielectric loss index

See also →dielectric loss factor.

dielectric material

A material that is a poor conductor of electric current. Insulators, such as ceramic, porcelain, air, plastic, and mica, are common dielectric materials. Dielectric material can be polarized by an applied electric field.

dielectric medium

See →dielectric material.

dielectric passivation

See →dielectric surface passivation.

dielectric permittivity

The measure of how much resistance is encountered in a semiconductor material under the influence of an electric field. It is the ratio of the electric displacement in the material to the applied field strength.

dielectric polarisation 

 161

dielectric polarisation

UK The process of charge separation that occurs in dielectric, insulating materials when an external electric field is applied to it. Due to the presence of the electric field, the positive charges align with the electric field and the negative charges align against it.

dielectric polarization

US A process in which positive and negative charges are displaced in opposite directions in a dielectric material due to the presence of an electric field.

dielectric relaxation

The tendency of majority and minority carriers moving in a semiconductor electrical field to return to electrical neutrality and achieve an equilibrium of a dipolar system.

dielectric resonator antenna

(DRA) An antenna consisting of high-dielectric materials mounted on a grounded dielectric substrate. The major advantages of a dielectric resonator antenna are small size, light weight, low cost, low loss, and ease of excitation. The transparent dielectric resonator antenna is placed on top of a photovoltaic cell, acting as a radiating element as well as a focusing lens for an underlying solar cell. The concentrating effect of the DRA improves the power output of the solar cell.

dielectric resonator oscillator

(DRO) A microwave oscillator that utilizes a dielectric resonator to achieve frequency stability.

dielectric strain

See →dielectric displacement.

dielectric strength

The maximum voltage or electric field strength that a dielectric material (insulator) of specified thickness can withstand without breaking down. The higher the dielectric strength of a dielectric material the better its quality.

dielectric stress

See →dielectric displacement.

dielectric surface passivation

Also known as dielectric passivation. A process of coating the front surface of a photovoltaic cell with a dielectric layer, such as SiN:H, in order to reduce the density of silicon surface states, which could act as recombination centers for light-induced charge carriers. Hence, dielectric surface passivation results in the reduction of the chemical reactivity of the surface.

dielectricity

A phenomenon by which dielectric materials, such as semiconductors, conduct electricity only under certain circumstances, for example, when a direct current voltage is

162 

 diesel generator

applied to it, creating an electric field and dividing electric charge into positive and negative charges that form at both ends of the material. diesel generator

Besides →battery banks, diesel generators are also used as backup power systems for a →photovoltaic array. It is deployed, when the primary source of energy, such as solar power or power grid, fails or does not provide enough electricity.

differential pressure

The difference in pressure between two points of measurement in a system, for instance, the difference between →upstream pressure and →downstream pressure. The change in pressure of liquids and gases is usually measured with differential pressure.

diffraction

The bending of light waves around a barrier or the spreading out of waves when they pass through a narrow opening. The aperture must be very narrow for diffraction of light to occur.

diffraction grating

See →optical diffraction grating.

diffraction loss

A portion of incoming solar radiation that is lost due to diffraction at the edges of the Fresnel lenses used in concentrating photovoltaics (CPV). In CPV systems, Fresnel lenses concentrate sunlight onto highly efficient PV cells or on the entrance apertures of secondary optical elements. As a Fresnel lens is made of several prism rings, usually the conical prism surfaces, a fraction of solar radiation might spill outside the target area due to light diffraction by Fresnel lenses. According to Hornung and Nitz, “the diffraction loss is approximately proportional to the lens radius divided by the target area radius.”

diffractive beam splitter Also known as a beam splitter or beam generator. An optical element for splitting an input beam of light into two or more separate output beams. diffuse horizontal irradiance

(DHI) The amount of solar radiation received by a planar surface, for example, a solar panel, which does not arrive on a direct path from the sun like →direct normal irradiance but is scattered or diffused by clouds, pollution, or dust and comes equally from all directions. The DHI is usually measured by an instrument called a →pyranometer.

Ground-reflected

Diffuse Horizontal Irradiance

Direct beam

Scattered

Diffuse

diffuse horizontal irradiance   163

164 

 diffuse insolation

→Amorphous silicon solar cells, →dye-sensitized solar cells, and →luminescent solar concentrators are responsive to diffuse light and perform well under scattered radiation. diffuse insolation

See →diffuse solar radiation.

diffuse irradiance

See →diffuse solar radiation.

diffuse radiation

See →diffuse solar radiation.

diffuse reflection

A reflection off of a rough surface, for example, clothing, paper, or a polycrystalline material. Unlike regular, →specular reflection, in which incident and reflected angles are equal, in diffuse reflection, beams of light are reflected at multiple diverse angles and scattered in different directions because they strike the uneven surface at different heights.

diffuse sky radiation

See →diffuse horizontal irradiance and →diffuse solar radiation.

diffuse solar radiation

When solar radiation passes through clouds, pollution, or dust in the atmosphere before reaching a photovoltaic cell, we talk about diffuse solar radiation, diffuse radiation, diffuse sky radiation, diffuse irradiance, or diffuse insolation. The mentioned obstacles (clouds, pollution, or dust) will scatter radiation and decrease the solar transmission. On overcast days, photons are scattered by clouds and humidity (water droplets, molecules, and particles) causing solar radiation to come from many different directions at the same time and to reach a solar absorber surface in a lesser degree of intensity than a →direct solar radiation. Therefore, the larger the percentage of diffuse solar radiation, the smaller the amount of solar radiation energy that reaches a photovoltaic surface. See antonym →direct solar radiation.

diffuser

See →ceiling light diffuser.

diffusion

Process in which →dopants scatter across the silicon lattice and occupy adjacent vacant lattice sites of silicon atoms.

diffusion annealing

The heat treatment in the semiconductor manufacturing process in which silicon wafers are thermally treated to repair the damage done to the crystal structure during the →ion implantation process. During the thermal annealing, the dopant atoms, such as →phosphorus and →boron, diffuse into substitutional positions in the silicon crystal

diffusion area 

 165

lattice. After the annealing process, the dopant ions are incorporated into the crystal structure. They are now electrically activated and turned into charge carriers: a p-type dopant produces a →hole, whereas an n-type dopant generates an →electron. diffusion area

See →diffusion barrier layer.

diffusion barrier

See →diffusion barrier layer.

diffusion barrier layer

A thin layer that inhibits the movement of electrons between negative and positive semiconductor regions.

diffusion capacitance

The →capacitance associated with the excess carriers in the quasi-neutral region. Diffusion capacitance forms in a →p–n junction diode under forward bias. See also →junction capacitance.

diffusion coefficient

Also known as diffusivity. A value that expresses how fast the molar flux can diffuse through the surface of the semiconductor per unit concentration gradient. The diffusion coefficient is commonly expressed in length2/ time (m2/s). The higher the diffusion coefficient, the faster the impurities will diffuse in the semiconductor solid. The analysis of the diffusion coefficient can lead to significant improvements in the power output of a PV cell. The diffusion mobility of the excess minority charge carriers (electrons and holes) across the silicon semiconductor depends on several factors, such as irradiation energy, temperature, frequency modulation, the concentration of impurities, and the atmosphere of annealing.

diffusion current

Current in a semiconductor near the depletion zone of a p–n junction that is caused by concentration difference of charge carriers.

diffusion depth

A process of profiling dopant species to a desired depth in wafers by diffusion. In the diffusion process, wafers are heated and held at a specific temperature for a determined period of time until desired diffusion depth and dopant profile are achieved.

diffusion furnace

A furnace that is used for doping silicon wafers. In a diffusion furnace, the →dopant is inserted into the semiconductor material by a diffusion process, in which the reaction

166 

 diffusion layer

of gases with silicon wafers takes place at temperatures between 700 °C and 1,400 °C. diffusion layer

See →diffusion barrier layer.

diffusion length

The average distance an electron or a hole travels in a semiconductor between generation and recombination with another hole or electron.

diffusion mask

A mask that is deposited on the surface of a semiconductor substrate to block the diffusion of a material into the substrate. For instance, an alumina-silicate glass mask prevents the diffusion of →gallium and →indium.

diffusion path

The progression of structural modifications formed during isothermal diffusion in multiphase, multicomponent diffusion systems.

diffusion potential

The potential difference across a depletion region, which is created by free charge carriers diffusing across a semiconductor junction. The diffusion potential equals the negative sum of the potentials drops across the charge regions of the →p–n junction: UD = EC(p) – EC(n)/q.

diffusion process

Process in which dopants scatter across the silicon lattice and occupy adjacent vacant lattice sites of silicon atoms.

diffusion profile

A profile consisting of different regions with higher, lower, and transition dopant concentrations.

diffusion rate

Rate at which the given dopant species diffuse in the semiconductor solid.

diffusion region

A region that is formed by diffusing dopant species, such as →phosphorus or →arsenic, into a semiconductor substrate, such as →silicon or →germanium, by one of the following diffusion methods: →ion implantation, gaseous phase diffusion, or solid phase diffusion.

diffusion source

Source of dopant atoms commonly employed in semiconductor deposition processes, for instance dopant →diborane or →phosphine gas.

diffusion technique

See →diffusion process.

diffusion technology

See →diffusion process.

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diffusion time

Electrical feature of a solar cell that describes how fast the impurities – the excess minority charge carriers (electrons and holes) – diffuse through the surface of the semiconductor solid. The faster the impurities diffuse in the semiconductor solid, the higher the mobility of charge carriers and thus the higher the solar power output.

diffusion velocity

Speed at which an atom, molecule, or compound moves from an area of high concentration toward a low-concentration region. Diffusion velocity depends on temperature and time.

diffusion voltage

In a →diffusion process, an electrical charge expressed in volts that is built up based on the differences in mobilities of the diffusing particles.

diffusion zone

See →diffusion-inhibiting layer.

diffusion-inhibiting layer

A thin layer that inhibits the movement of electrons between negative and positive semiconductor regions.

diffusivity

See →diffusion coefficient.

digital angle measuring device

See →digital angle measuring tool.

digital angle measuring instrument

See →digital angle measuring tool.

digital angle measuring tool

Also known as a digital angle measuring device. Angle measuring instrument with a digital display gauge used for measuring sloping roof angles and finding an optimal angle or tilt for →ground mounting systems.

digital multimeter

(DMM) A →multimeter that uses a digital display as opposed to an analog multimeter with a dial hand.

digital protractor

An instrument with an LCD display for measuring angles. The digital display gauge measures angles in degrees. This high-precision device is usually equipped with measuring rulers and a lock angle feature.

Digital Surface Model

(DSM) A topographic model that provides a 3D representation of the earth’s surface. DSM is a useful tool for planning solar projects as it provides unbiased, empirical information to homeowners, solar investors, or solar designers about the potential of their available photovoltaic surfaces.

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 digital voltmeter

The DSM visualizes terrain features, buildings, trees, power lines, and other potential shading obstacles in a specific location. digital voltmeter

(DVM) A →voltmeter that uses a digital display as opposed to an analog voltmeter with a dial hand.

dimethylbenzene

See →xylene.

dimmer

A switch that allows users to gradually increase or decrease the intensity of an electric light. Dimming lights in the house reduces the wattage of lightbulbs, resulting in energy savings and a reduced environmental footprint.

diode

A two-terminal semiconductor device that allows electric current to flow only in one direction. Two types of diodes find a broad application in photovoltaic arrays: →blocking diode and →bypass diode.

dioxygen

An odorless and colorless gas with the formula O2. Dioxygen consists of two oxygen atoms and accounts for 21% of the Earth’s atmosphere.

direct band gap

(DBG) A band gap in which the electrons in the conduction band and holes in the valence band have nearly the same momentum. The maximum energy level of the →conduction band is in alignment with the minimum energy level of the →valence band, allowing a direct recombination. The probability of recombination is high, as excited electrons are at the maximum level of the conduction band and can easily hop across the narrow band gap to the valence band without any change in momentum. This is why semiconductor materials with a DBG, such as →gallium arsenide (GaAs) and indium arsenide (InAs), are more efficient than materials with an →indirect band gap, such as →silicon (Si) or →germanium (Ge).

direct band gap semiconductor

A semiconductor with a →direct band gap. The III–V materials, such as →gallium arsenide (GaAs), indium arsenide (InAs), and indium phosphide (InP) are examples of direct band gap semiconductors. Due to the direct band gap, these materials exhibit better optoelectronic properties and a higher solar energy absorption coefficient than the →indirect band gap semiconductors, such as →silicon (Si) or →germanium (Ge).

direct beam radiation 

direct beam radiation

 169

See →direct solar radiation.

direct circulation system See →open-loop system. direct conversion

See →direct energy conversion.

direct current

(DC) An electric current that always flows in one direction. Photovoltaic modules produce direct current electricity. This type of current can be stored in a battery, but it must be converted to alternating current (AC) to run household appliances.

direct current voltage

(VDC) Type of voltage or electric current that flows only in one direction and cannot travel very far until it begins to lose energy. Graphically illustrated, a DC current looks like a straight line, steady stream of electrons flowing only in one direction, as opposed to a sinusoidal AC waveform.

direct daylighting

A percentage of natural light that reaches a certain location directly from the Sun, without any obstruction or diffusion.

direct energy conversion Direct conversion of solar energy into electricity through photovoltaic cells without an intermediate process by means of a →photovoltaic effect. direct evaporation

Direct evaporation of water into the air that is circulated to the space being cooled.

direct gain

The heat from the sun that is absorbed and retained in a specially designed interior space. See →direct-gain building.

direct insolation

See →direct solar radiation.

direct ion-beam deposition

(DIBD) A method for forming thin semiconductor films directly on a substrate. In a controlled vacuum chamber environment, a low-energy ion beam is employed to direct an energetic vapor flux toward a substrate. The main advantage of the DIBD is that it allows the precise control of deposition parameters, which in turn has a direct impact on the physical and optical properties of the films.

direct mount

A photovoltaic (PV) mounting technique, in which PV modules are directly secured to the roof without a bulky mounting structure.

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direct normal insolation Direct insolation on a planar surface, for example, a solar panel, which is perpendicular (normal) to the Sun. direct normal irradiance (DNI) Also known as beam radiation. The amount of solar radiation received by a planar surface, for example, a solar panel, which is perpendicular or “normal” to the Sun. The DNI is typically measured by an instrument called a →pyrheliometer. direct radiant cooling

See →direct radiative cooling.

direct radiation

See →direct solar radiation.

direct radiational cooling See →direct radiative cooling. direct radiative cooling

Also known as direct radiant cooling or direct radiational cooling. A cooling technique by which a building’s roof structure, a massive ceiling slab or other type of masonry, cools the building by radiation to the night sky. The ceiling slab absorbs heat from interior rooms during the day, acting as a heat sink and radiates it away at night.

direct roof integration

A photovoltaic (PV) mounting technique, in which PV modules, for example, solar roof tiles, are integrated into the roof surface to seamlessly blend in with conventional roof tiles and the rest of the roof and building.

direct solar dryer

An apparatus for drying food in which the fruit, vegetables, and herbs to be dehydrated are exposed to direct sunlight. Some direct solar dryers have a glass or plastic transparent top surface and some can be rotated to follow the sun in the course of the day. In closed systems, the solar radiation is transmitted through the glass, absorbed by the interior surface, and converted to long-wave thermal radiation. The lid prevents heat from escaping the box, increasing the temperature within the drying chamber. The air is drawn in through an inlet or vent holes at the bottom of the box and allowed to exit through an outlet or vent holes at the top. Following the principles of natural convection, the hot air continuously moves upward, circulating around food pieces and removing efficiently moisture from food. See also →solar dryer.

direct solar evaporation

The generation of the superheated steam in the collector, reaching temperatures of over 500 °C (932 °F), for steam turbines by means of direct solar evaporation of water.

direct solar gain 

 171

direct solar gain

See →direct gain.

direct solar radiation

When solar radiation reaches a photovoltaic cell directly from the sun without any obstacles, for example, clouds or pollution, we talk about a direct solar radiation, →direct beam radiation, →beam solar radiation, →beam radiation, or →beam irradiation. The best solar energy yield is achieved on a clear day, when solar radiation travels on a straight line from the sun to a PV surface. See also the antonym →diffuse solar radiation.

direct solar steam

(DSS) Steam that is directly generated within the absorber tubes that are heated by concentrated solar radiation. The generated steam is directed to a steam turbine, powering a generator that produces electrical current.

direct solar steam generation

See →direct steam generation.

direct solar transmission The amount of incident solar radiation that passes directly through a body, for example, a solar module or a window. See also →transmittance. direct steam

See →direct solar steam.

direct steam generation

(DSG) Also known as direct solar steam generation. A process in which solar radiation is concentrated on an →absorber tube that runs the length of a →concentrating parabolic trough or →linear Fresnel reflector (LFR). Inside the tube, the direct steam generation method uses water as the direct working fluid instead of →heat transfer fluid. Water is vaporized and transferred to steam turbine that drives the generator, producing electricity. In order to store the collected energy for a later use on an overcast day or at night, hot steam can heat salt that absorbs energy at a high temperature of 305 °C (581 °F), changing from a solid to a liquid state. Later in the evening, when electrical energy is needed, the molten salt is cooled down, reverting to its solid form and releasing the stored energy in the process.

direct sunlight

Sunlight falling directly on a solar module.

direct tunneling

A process in silicon solar cells in which electrons from the silicon conduction band are directly transported (without changing energy) through the ultrathin oxide layer – into the conduction band of metal.

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 direct ultraviolet radiation

direct ultraviolet radiation

Shortwave radiation that reaches the Earth’s surface directly from the sun without being absorbed by stratospheric ozone.

direct UV radiation

See →direct ultraviolet radiation.

direct-coupled photovoltaic system

Also known as a direct-coupled solar system. The simplest type of an independent solar power system that is neither connected to an electrical grid nor does it have batteries. The DC power generated by solar panels is directly connected to a DC load that can only be operated during the day when the sun is shining. Due to such special conditions, a limited number of appliances, such as water pumps and ventilation fans, can be used in a direct-coupled photovoltaic system.

direct-coupled PV system

See →direct-coupled photovoltaic system.

direct-coupled solar system

See →direct-coupled photovoltaic system.

direct-coupled system

See →direct-coupled photovoltaic system.

direct-gain building

A →passive building with most of its windows facing south. An energy-efficient solar design allows windows to admit the maximum amount of winter sunshine into the house, whereas deep eaves and roof overhangs protect windows from the blazing sun of the summer months. During a winter day, the direct sunshine heats thermal mass, such as solid floors made of stone or concrete. The stone floor slabs radiate the stored heat into the space during the night, when the outside temperature drops.

directional response

See →cosine response.

directional solidification The controlled process of solidification that starts at the bottom of the casting and works its way to the top. Directional solidification is used as a purification method in the manufacturing of polycrystalline silicon for photovoltaic cells. The method allows most of the impurities and defects found in the molten silicon to be removed in a vertical way where the solid materials at the bottom of the crystallization crucible push the impurity contents to the surface. directional solidification See →directional solidification system. principle

directional solidification system 

 173

directional solidification (DSS) A system that is used to purify polycrystalline silicon system by directional solidification in order to obtain high-quality photovoltaic grade silicon. Silicon can be melted and directionally solidified in the same or in two separate crucibles, a melting and a solidification crucible. The principle of directional solidification is the same: as silicon is vertically solidifying from a molten silicon solution from the bottom of the mold to the top, undesirable impurity content remains in the molten solution and is pushed to the top of the crucible by the solid materials below. directional solidification Also known as DSS furnace. Furnace in which silicon feedsystem furnace stock is melted into silicon ingots using the method of controlled solidification of molten silicon. dirt repellent

A coating that repels dirt and dust, keeping sensitive electronic components clean and in good operating condition.

dirt-repellent coating

See →dirt-repellent surface.

dirt-repellent surface

Also known as dirt-repellent coating or dirt-resistant coating. A special surface texture that prevents dust and dirt from becoming engrained in the coated surface. By preventing contaminants to stick to a surface, a dirt repellent allows an easy removal of dirt from components, thus preserving functionality of sensitive electronic parts.

dirt-resistant coating

See →dirt-repellent surface.

dirty power plant

US A power plant that generates high levels of pollution, in particular of carbon dioxide emissions, in the atmosphere. The dirty power plant par excellence is a coal-fired power plant, which is more carbon intensive than other fossil fuel power plants. Old oil or gas-fired plants also produce high levels of pollution.

dirty power station

UK See →dirty power plant.

dirty silicon

Low-grade silicon hundreds of times less pure than conventional pure silicon. Scientists experiment with different material combinations, for instance, a glass/silicon synthesis, by replacing 50%–90% of the silicon with glass. The use of a suitable alternative material to replace a significant part of silicon promises to cut the cost of solar cells. As fewer production steps are required, the dirty silicon

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 dirty water inlet

manufacturing process is less energy intensive and thus less expensive than traditional Czochralski crystal growth and pure silicon wafer production process. In some methods, the impurities are left in the semiconductor material; however, they are manipulated in a way that reduces their impact on the solar cell efficiency. dirty water inlet

Dirty water inlet in a solar distillation unit.

discharge

Process of withdrawing electrical energy from a battery.

discharge chamber

In an →ion beam source, a chamber in which ions are produced by subjecting atoms of a noble gas, typically →argon, to an RF field. Gas atoms are ionized by dynamic electron bombardment and a plasma is established.

discharge current

See →maximum continuous discharge current.

discharge factor

A fraction of the total battery capacity representing the time it takes to discharge a battery at a constant current without doing damage to the battery. C/2 designates a discharge factor of 2 h.

discharge rate

The rate at which current is withdrawn from a battery relative to the capacity of the battery. See →C-rate.

discharge voltage

The voltage of a battery during discharge.

discharging

In a →rechargeable battery, the process of conversion of chemical energy into electrical energy and supplying current to any load.

discoloration

See →EVA discoloration.

discoloration of solar cells

A solar cell degradation process by which the transparent encapsulant →ethylene vinyl acetate (EVA) turns yellow, orange, or brown. The discoloration is caused by a chemical reaction – the oxidation of EVA – in which acetic acid is produced. The discoloration is not only an aesthetic issue but also a performance issue. The solar modules with some yellow or brown cells reflect a portion of light. As less photons are absorbed by the semiconductor material and converted into electrical energy, the panel’s efficiency can be reduced between 10% and 50%, depending on the severity of the discoloration.

disconnect 

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disconnect

Is an electronic control module that monitors the voltage in a system at all times. When a high or low voltage is detected, this safety switch automatically disconnects and reconnects different components in a photovoltaic array to prevent damage and to prolong life of the PV equipment (e.g., deep cycle batteries). See →high-voltage disconnect and →low-voltage disconnect.

disconnect switch

Safety switch that disconnects different components in a PV array. There are three types of disconnect switches: →AC disconnect, →DC disconnect, and →string disconnect.

Solar strings

Solar modules

Solar inverter String disconnects DC disconnect

AC disconnect

Disconnect Switch Types

disconnection device

Device for automatic disconnection from the public grid.

dish

See →dish collector.

dish collector

A type of →concentrating solar collector in the shape of a parabolic dish with mirrors that collect and focus the sun’s rays onto a thermal →receiver, reaching a high temperature of around 1,000 °C (1,832 °F). See →Dish–Stirling system.

dish concentrator

Solar parabolic dish with mirrors that focuses the sun’s rays onto a receiver.

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 dish farm

dish farm

See →Dish–Stirling power plant.

dish reflector

Solar parabolic dish with mirrors.

dish system

See →Dish–Stirling system.

Dish–Stirling power plant

US Also known as Dish farm or solar Stirling power plant. A power plant that consists of numerous individual →Dish– Stirling system units (see the figure on page 177). The external-combustion →Stirling engine, which runs on heat generated by concentrating solar collectors and not on polluting fossil fuels like internal-combustion engines, is a viable choice for an environmental friendly power plant. In addition, the Stirling engine converts thermal energy into electricity more efficiently than a steam engine. Stirling engines are also safer than internal combustion and steam engines, as they are not susceptible to explosions.

Dish–Stirling power station

UK See →Dish–Stirling power plant.

Dish–Stirling system

A system that uses a solar parabolic dish and Stirling engine to produce energy. The parabolic dish consisting of numerous mirrors tracks the sun on two axes and focuses its rays onto a single receiver fixed at the focal point in front of the reflector. The heat gathered by the receiver heats the working gas, for example, helium, which drives the →Stirling engine. Finally, the Stirling engine powers the generator that produces electricity. Dish–Stirling efficiency rate lies between 31% and 34%.

dispatching

See →economic dispatch.

dispersed generation

A power generation concept in which smaller power plants, such as →solar arrays and →solar farms, are built along the existing grid, close to the end-user.

dispersed generation plant

A decentralized generation plant, such as a solar farm, which can be sized between 1 and 30 MW.

dispersed power plant

See →dispersed generation plant.

disposal

See →recycling and →photovoltaic recycling.

dissipation

Loss of different forms of energy, such as photoelectric current, electric current, or heat, through scattering or spreading widely without accomplishing useful work. See also →energy dissipation and →heat dissipation.

Power grid

Dish-Stirling Power Plant

Energy storage

Solar tracking system

Receiver

Generator Stirling engine

Parabolic solar dish concentrator

Solar radiation

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 dissipation factor

dissipation factor

The energy loss factor that is opposite of the storage factor.

distributed control system

(DCS) A digital automated control system that is employed in a large-scale solar power plant, such as a →solar thermal power plant or →photovoltaic power plant, to control different industrial processes, optimize operations, and maximize efficiency and productivity. Unlike a centralized control system, every section of the plant, for instance, solar field, solar tracking, inverters, or switchyard, has its own autonomous controller. Even though the controllers work autonomously, they are connected via network to the central monitoring station run by an operator, overviewing information sharing across different systems.

distributed energy

Energy generated from many small energy sources, for example, from small solar power plants, as opposed to a large centralized utility power plant.

distributed energy resources

(DER) Energy resources that are equally spread out over one geographical region and can be found wherever there is sun. The fossil energy resources in contrast are concentrated in few locations. Although every roof can be easily converted into an energy resource, fossil fuel resources are rare and require costly installations such as mines, oil wells, thermos-electric power plants, and refineries.

distributed generating plant

See →distributed solar collector system.

distributed generation

See →distributed power generation.

distributed generation system

Generates energy from many small energy sources, for example, from small solar power plants, as opposed to a large centralized utility power plant. The following advantages make distributed energy systems worth pursuing: — Since the energy is generated onsite where it is used, the losses through transmission are minimal. — Distributed systems are less vulnerable to major power outages due to natural disasters or human-caused system failures. — It is cheap, easy to install, and PV plant owners can profit from their own energy generation. — Unattractive space, such as roofs, can be utilized, whereas transmission lines and their complex structures can be reduced and their corridors aesthetically improved.

distributed power 

 179

distributed power

See →distributed energy.

distributed power generation

Energy is generated onsite or near the point of use. An example would be a flexible, decentralized solar power generation system as opposed to a large centralized utility power plant.

distributed solar collector system

Generates energy onsite or near the point of use, for example, a flexible, decentralized solar power generation system as opposed to a large centralized power plant.

distributed solar energy Energy generated onsite or near the point of use. distributed solar power

Power generated onsite or near the point of use.

distributed system

See →distributed generation system.

distribution grid

See →electric power distribution.

distribution panel

Also known as panelboard, breaker panel, or load center. A metal box in which electrical current from the main feeder line from the public electricity grid is distributed to the different branch lines or subsidiary circuits of the building. Each branch circuit is protected from overcurrent through the employment of circuit breakers or fuses. In the solar energy context, the distribution panel plays a key role as a junction between the public utility grid, different solar system parts, such as →inverter, →controller, and →battery bank, and loads. In →smart homes, →smart energy management system software can be connected to the distribution panel to provide better control of energy consumption.

distribution system operator

(DSO) See →system operator and →grid operator.

disturbed area

Also known as brownfield. An area where vegetation and topsoil have been removed or “disturbed,” for instance, by coal mining or industrial pollution. Permanently disturbed, abandoned, or underutilized areas are classified as suitable for solar power plant installations.

diurnal

An adjective meaning daily or the daily cycle.

diurnal curve

A curve on a graph that represents values measured throughout the 24-h cycle. For instance, when the collected 24-h data are plotted on the graph with two curves that

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 diurnal cycle

are placed side by side, different daily patterns of solar short-wave and terrestrial long-wave infrared radiation can be observed. diurnal cycle

Patterns within 24 h that reoccur each day, such as the daily rise and fall of temperatures, as a result of the rotation of the Earth around its own axis.

diurnal cycle of the solar irradiance

See →diurnal solar cycle.

diurnal pattern

Any pattern within 24 hours that reoccurs every day, such as a humidity, temperature, or solar irradiance pattern. The observations and research of diurnal weather patterns are critical, because the interaction between solar and earth-emitted terrestrial radiation in a given geographic region produces specific climate patterns that affect the output of →solar collectors and →photovoltaic modules.

diurnal rhythm

The basic temperature patterns or rhythms that repeat cyclically throughout the 24-h timeframe, affecting the performance of →solar collectors and →photovoltaic modules.

diurnal solar cycle

Daily cycle of the sun based on the intensity of →solar radiation. The traditional daily solar cycle begins with the sunrise with minimum solar irradiance due to the minimum sun altitude. The lowest temperature occurs at sunrise as the ground and air cool down overnight. The maximum intensity of the sun or maximum solar irradiance occurs at noon, when the sun is at the zenith. Sunset occurs when the zenith angle is 90° and the sun starts disappearing below the horizon. Solar irradiance is at the minimum but the temperature is still relatively high, compared to the cold sunrise, due to the intensive earth-emitted terrestrial radiation. The ground and atmosphere keep cooling down during the night, which closes the diurnal solar cycle or the four traditional parts of the day.

diurnal temperature range

(DTR) See →diurnal temperature variation.

diurnal temperature variation

The variation in temperature from the daytime high to the nighttime low over the course of one day. The peak daily temperature does not occur at noon but between 3 and 5 pm as air keeps absorbing the increasing earth-emitted terrestrial

diversification of energy supply 

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radiation after noon in addition to solar radiation. Correspondingly, the minimum daily temperature occurs after midnight, early morning just before sunrise, because the heat of the day slowly dissipates and the atmosphere gradually cools down over the course of the night. diversification of energy supply

A utility company technique that mixes a wide variety of small energy-generation sources, such as solar, wind, hydro, geothermal, tidal power, or biomass, to reduce the reliance on conventional →fossil fuels. As some of the renewable energy sources are not available 24 h per day, such as solar and wind, the utility company can overcome the availability shortcoming and still achieve energy supply stability by relying on many diverse energy-generation sources. Due to the rapid switching among numerous small energy providers, this method requires the development and employment of energy management systems with a high level of complexity. The energy management systems must be able to process the extremely high volume of data involved and respond within minutes or even seconds when the power demand rapidly increases during peak hours.

DIY

Abbreviation for →do it yourself.

DMM

Abbreviation for →digital multimeter.

DNI

Abbreviation for →direct normal irradiance.

do it yourself

(DIY) The practice of building or repairing something for oneself without the aid of experts or companies. In the solar field, numerous DIY kits and books about home-built solar panels are available on the market. Many solar hobbyists decide to build their own solar module from scratch by soldering all solar cells together, encapsulating all cells and electrical wiring in glass, and attaching protective and strengthening frames to the laminates of the photovoltaic (PV) module. There is an entire online market for building PV modules with slightly damaged but still functional solar cells, which are significantly cheaper than the brand new solar cells. Other solar enthusiasts purchase solar panels and other components of the solar array, but they install the system themselves instead of hiring professionals to cut high installation costs.

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 DOD

DOD

Abbreviation for →depth of discharge.

DOE

Abbreviation for →Department of Energy.

do-it-yourselfer

A person who builds or repairs something for themselves without the aid of experts or companies. See also →solar do-it-yourselfer.

dollar per watt

See →cost per watt.

domestic hot water

The hot water used for indoor household purposes, such as bathing and washing dishes and clothes.

domestic hot water storage tank

See →hot water storage tank.

donor

An atom or a molecule, such as →phosphorus, which easily gives its extra electron away. See also →n-type dopant.

donor atom

Atom that easily gives its extra electron away.

donor electron

An electron of a donor atom, for example, the fifth electron of phosphorus atom, which is weakly bound to the phosphorus atom and can easily jump into the conduction band by thermal excitation or illumination.

Si

Si

Si Free electron

Si

P

Si

Silicon atom Shared electrons Phosphorus atom

Si

Si

Si

Donor Electron

donor level

An intermediate energy level near the top of the energy →band gap and close to the →conduction band, which may donate →donor electrons to the →conduction band. At absolute zero temperature, this level is filled with electrons from donor impurities that are bound to their atoms.

donor–acceptor principle 

E

 183

Donor level

Donor Level

When photons of light fall onto the semiconductor material, these donor electrons become excited and jump into the conduction band, generating electric current. donor–acceptor principle Interaction between electron →donors and electron →acceptors, transferring particles and energy in a dynamic electric field of a solar cell. The forces of attraction and repulsion controlled by precisely calculated doping techniques initiate with the help of solar radiation the flow of negative and positive charge carriers, →electrons and →holes, across n-type and p-type semiconductor layers. dopant

A chemical element, also known as impurity, added in a small, controlled amount (one atom in millions) to a pure semiconductor in order to modify its electrical properties.

dopant activation

Activation of the movement of free electrons in a solar cell by intentional incorporation of impurities, so-called dopant atoms, into a pure semiconductor.

dopant atom

Impurity atom. An atom with an odd number of electrons in its outer shell that initiates a flow of electrons in a solar cell and thereby generates electric current. A dopant atom, for example, phosphorus, is inserted into a pure semiconductor, silicon, in order to modify its electrical properties. During the silicon cell production, the n-type dopant atom, phosphorus, is typically added by diffusion of phosphine gas. This so-called impurity disturbs the octet-stability in the semiconductor silicon lattice, in which each silicon atom is surrounded by four other silicon atoms and has

184 

 dopant concentration

eight electrons in the outer valence shell. The intentional incorporation of a dopant atom, phosphorus in this case with five electrons in the outer orbital, will create a disturbance in the pure semiconductor silicon lattice order. When solar energy is applied, or in other words, the sunlight falls on a solar cell, the fifth “extra” electron gets excited and leaves its valence band. Silicon atoms pass this extra electron to their neighboring silicon atoms in order to achieve their “octet-rule” stability. This means that the odd number electron changes energy levels and moves from a valence to a conduction band. The movement of free electrons through the conduction band and further through the wire begins, and hence, the energy is generated. dopant concentration

See →doping concentration.

dopant diffusion

A process in which the impurity migrates among vacant positions in the silicon or germanium crystal lattice. This so-called substitutional diffusion takes place due to the presence of the neighboring point-defects. The introduced dopants move across the symmetrical host lattice by occupying adjacent vacant lattice sites of silicon atoms.

dopant gas

A gas that is used during the silicon cell production to add doped layers to the silicon wafer, increasing the conductivity of the semiconductor. The →n-type dopant atom, →phosphorus, is typically added by diffusion of phosphine gas (PH3), whereas the →p-type dopant atom, →boron, is added by diffusion of diborane gas (B2H6). As phosphine and diborane gases present health hazards, when inhaled or when they get in contact with skin, it is crucial to ensure that workers are protected from exposure to these dangerous chemicals in semiconductor manufacturing facilities.

dopant ink

Ink used for doping of silicon wafers. Compared to dopant →vapor phase deposition methods, which include the use of expensive high-temperature furnaces and vacuum chambers, the utilization of liquid deposition in a faster mass production process with an →inkjet printer considerably reduces solar cell manufacturing costs.

dopant ink composition

A dopant ink composition can consist of a →matrix precursor, one or more →dopant species, and a solvent.

dopant ions 

 185

dopant ions

Charged dopants that are implanted into a semiconductor by being accelerated in an electric field to high energies and shot into the wafer in a low-temperature process. The most common dopant ions are →phosphorus and →boron.

dopant material

An impurity added to a pure semiconductor in order to modify its electrical properties.

dopant precursor

A precursor that consists of →p-type or →n-type dopants that generate positively or negatively doped layers in a →semiconductor.

dopant profile

See →doping profile.

dopant species

Also known as impurity species. The atoms of the third and the fifth group of the periodic table, which are implanted into silicon by an →ion implantation method to produce positively or negatively doped layers in the →semiconductor. The p-type dopant atoms →boron, →indium, and →gallium are used to generate →holes in the positively doped region called →valence band, whereas the n-type dopant atoms →phosphorus, →arsenic, and antimony are used to generate electrons in the negatively doped region known as →conduction band.

doped

Referring to →doping process.

doped emitter layer

A top layer of the semiconductor that is negatively doped with →phosphorus atoms to increase the conductivity of pure silicon semiconductor, initiate the flow of negative charge carriers (electrons), as well as to determine the flow direction of the same. See also →n-doped semiconductor layer.

doped emitter region

See →doped emitter layer.

doped layer

See →doped semiconductor layer.

doped region

See →doped semiconductor layer.

doped semiconductor

A semiconductor that has undergone a doping process, incorporating impurity atoms into the silicon wafer to define the electrical properties of the semiconductor. After the doping procedure, the semiconductor takes shape of a photovoltaic cell diode that consists of an →n-doped semiconductor layer and a →p-doped semiconductor layer.

186 

 doped semiconductor layer

doped semiconductor layer

A semiconductor region that is positively or negatively doped in a controlled manner to modify the electrical properties of the pure silicon semiconductor. A semiconductor region that is positively doped is known as a →p-doped semiconductor layer and a semiconductor region that is negatively doped is known as an →n-doped semiconductor layer.

doped semiconductor material

See →doped semiconductor.

doped silicon

See →doped semiconductor.

doping

Intentional and controlled incorporation of impurities into a pure semiconductor, in order to change its electrical characteristics.

doping atom

Impurity atom. See →dopant atom.

doping compensation

The addition of donor impurities, →n-type dopants, to compensate for the effects of an already doped p-type semiconductor; or the addition of acceptor impurities, →p-type dopants, to compensate for the effects of an already doped n-type semiconductor.

doping concentration

The concentration of →dopant with respect to the →intrinsic semiconductor, for example, pure, undoped silicon. As doping concentrations are rather small, they are often expressed in molar ppm or parts per million, which represent the atomic percentage of the dopant. For instance, 0.3 parts per million Boron (0.3 ppm B) is required to increase silicon conductivity from 4.4 × 10−4 to 100 S/m. Electron concentration follows exactly doping concentration. The higher the doping concentration, the higher the number of electrons and holes and the conductivity in the semiconductor. However, an increase in doping concentration results in a decreased carrier mobility because the free carriers collide with the dopant atoms more frequently. Even though the total conductivity in the semiconductor will still be increased, a portion of conductivity will be lost due to the decreased carrier mobility. n+ or p+ signifies high doping concentration in an n-type or a p-type semiconductor, whereas n- or p- signifies low doping concentration in an n-type or a p-type semiconductor.

doping concentration difference 

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doping concentration difference

The difference between the concentration of donor impurities or n-type dopants and acceptor impurities or p-type dopants.

doping density

→Doping efficiency is directly proportional to doping density. The higher the doping density, the higher the doping efficiency, which in turn results in higher conductivity. See also →doping concentration.

doping efficiency

The ratio of the number of free charge carriers, electrons and holes, to the number of →dopants. It shows the efficiency of charge transfer between the dopant and the host molecule.

doping gas

See →dopant gas.

doping gradient

Also known as impurity gradient. An increase or a decrease in a →doping concentration introduced in a semiconductor material.

doping level

The number of doping atoms added to the →intrinsic semiconductor, for example, pure, undoped silicon.

doping method

See →doping process.

doping process

A process in which boron and phosphorous atoms are deliberately incorporated into the silicon crystal lattice to initiate current flow in a semiconductor. These so-called impurity atoms or →dopant atoms have an odd number of electrons in their outer shells, one less electron (→boron) or one more electron (→phosphorus) than silicon, which creates a disturbance in the pure semiconductor silicon lattice order. When the sunlight falls on a solar cell, the fifth “extra” electron in the outer shell of phosphorus gets excited and starts moving along the conduction band, generating electricity.

doping profile

The point-to-point concentration throughout a semiconductor material of a doped atom introduced into the semiconductor.

doping technique

See →doping process.

doping tube

A movable tube that can be elevated and lowered down into a →crucible to add the melted →dopant to the →melt. The tube is a component of a pull-up device that pulls a doped silicon single crystal from a melt by →Czochralski method.

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 doping uniformity

doping uniformity

A consistent special distribution of →dopants over the whole surface of the →semiconductor – the front and back side of the →wafer.

double meander absorber

Also known as a serpentine absorber. A copper piping system in a solar collector that is designed as a double meander. The double meander absorber allows the easy hydraulic interconnection of the collectors, as supply and return to the collectors can be easily connected on one side. This design provides a homogenous flow through the collector and an optimized heat transfer. In addition, the serpentine absorber permits the modular extension of the collector arrays and the application of a →drainback system.

double-glass module

See →double-glass photovoltaic module.

double-glass panel

See →double-glass photovoltaic module.

double-glass photovoltaic module

Also known as a glass-on-glass solar panel or frameless solar panel. A photovoltaic (PV) module without an aluminum frame. Solar cells are sandwiched between two sheets of glass, one on top and one on the back of the cells. As there is no frame to hold the glass sheets in place, the glass layers must be thicker to ensure the structural strength of the entire panel. Frameless PV modules have a clear aesthetic advantage over →framed photovoltaic modules because they can be easier and seamlessly integrated into an architectural structure, such as a roof, windows or skylights. On the other hand, the frameless solar panels are more difficult to install than the framed PV modules as they require a more complicated mounting system.

double-glass photovoltaic panel

See →double-glass photovoltaic module.

double-glass PV module

See →double-glass photovoltaic module.

double-glass PV panel

See →double-glass photovoltaic module.

double-glass solar module

See →double-glass photovoltaic module.

double-glass solar panel See →double-glass photovoltaic module. double-pitched roof

A roof with two slopes that meet at a central ridge.

double-sided photovoltaic cell 

double-sided photovoltaic cell

See →bifacial solar cell.

double-sided photovoltaic module

See →bifacial photovoltaic module.

double-sided photovoltaic panel

See →bifacial photovoltaic module.

double-sided PV cell

See →bifacial solar cell.

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double-sided PV module See →bifacial photovoltaic module. double-sided PV panel

See →bifacial photovoltaic module.

double-sided solar cell

See →bifacial solar cell.

double-sided solar module

See →bifacial photovoltaic module.

double-sided solar panel See →bifacial photovoltaic module. double-walled carbon nanotube

(DWCNT) A carbon nanostructure consisting of two rolled-up layers or concentric tubes of graphene. In this crystalline nanoarchitecture, a →single-walled carbon nanotube (SWCNT) is nested within another, larger SWCNT.

downconversion

A process by which a transparent layer, such as graphene-quantum dot film, converts short-wave ultraviolet (UV) light to visible light that can be absorbed by the silicon solar cell underneath. While the transparent QD layer can pass visible light to the photoactive silicon layer, it can also convert high UV energies down to lower visible light energies that can be captured by the silicon semiconductor and converted into electrical current. Downconversion can considerably expand the absorbing range of semiconductor materials, covering larger parts of the electromagnetic spectrum. In addition to the conventional visible light harvesting, the downconversion method allows capturing of UV light, increasing significantly the efficiency of the solar cell.

downstream pressure

The pressure at the outlet of the pipe or duct.

downtime

Percentage of time, often expressed in hours per year, when a photovoltaic system is not available to provide electrical power to the load or to the grid.

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 downtime period

downtime period

Period of time, when a PV system is not available to provide electricity to the load or to the grid.

DRA

Abbreviation for →dielectric resonator antenna.

drain cock

See →drain valve.

drain down system

See →draindown system.

drain valve

Also known as a drain cock. A valve for draining →heat-transfer fluid from the →solar collector loop. In a solar water-heating system, a valve that allows water from solar collectors, piping system, and storage tank to be drained.

drainback solar waterheating system

A system in which a pump moves a heat transfer fluid, such as demineralized or distilled water, through the →solar collectors and circulates it through a →heat exchanger. Heat transfer fluid, which is contained in an unpressurized, closed loop and pumped through the collectors, is separated from the water for the final consumption that is heated by the heat exchanger. When the pump is turned off, the water drains from the collectors and outdoor piping to a storage tank to prevent water pipes from freezing.

drain-back solar waterheating system

See →drainback solar water-heating system.

drainback system

(DBS) A component of a solar water-heating system that ensures the automatic draining of the collectors and outdoor piping when the pump is turned off, thus protecting the collectors from freezing.

drain-back system

See →drainback system.

drainback tank

Component of a drainback solar hot water system.

drain-back tank

See →drainback tank.

drainback solar hot water system

A →closed-loop, →active solar heating system that uses a pump to circulate →heat transfer fluid in a sealed loop through the solar collectors and a heat exchanger that transfers the heat to domestic water stored in the tank. When the pump is turned off, the heat transfer fluid drains from the collectors and outdoor piping to a storage tank, protecting the collectors from freezing.

drain-back solar hot water system 

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drain-back solar hot water system

See →drainback solar hot water system.

draindown system

An open-loop system in which water from the solar collectors and piping system is drained to a storage tank when the pump is turned off to prevent water pipes from freezing.

DRIE

Abbreviation for →deep reactive ion etching.

DRO

Abbreviation of →dielectric resonator oscillator.

DRY

Abbreviation for →design reference year.

dry cell

See →dry-cell battery.

dry etching

Etching technology for the production of wafers in which the semiconductor material is removed or etched away by using plasmas or etchant gasses. The process usually begins by creating →etch masks to protect the parts of the wafer that should not be etched and define contact holes. A polymer coating known as a →photoresist is typically applied to the wafer as a mask using a →photolithographic process, projecting geometric patterns onto the wafer. After the desired mask patterns are deposited onto the surface, plasma or an ion beam is applied to etch any portions of a thin-film semiconductor that are not protected by the photoresist mask. The unmasked material is removed through a chemical reaction and/or a physical interaction between etching gas molecules and the exposed semiconductor film, producing the conducting channels. Based on the reaction type, there are three kinds of dry etching: →physical dry etching, →chemical dry etching, and →reactive ion etching. The dry etching process and equipment are more expensive than the →wet etching option. However, when fine geometries for conducting channels are needed, for example, straight vertical wall edges or angled wall edges with less or no undercutting of the masked layer, the dry etching is the preferred method. The dry etching produces a lower →etch bias than →wet etching and as such, it can better handle complex patterned structures. As it is not dependent on temperature like wet etching, the dry etching

192 

 dry etching process

Before dry etching

Photo resist

After dry etching

Photo resist Photo resist

Etchinig ions

Silicon dioxide

Photo resist

Silicon dioxide

Dry Etching

process is reproducible and automatable. The etching can be stopped and started at any time, offering a better control over the etching process. The dry etching allows both isotropic and anisotropic etch profiles. Compared to wet etching, it uses smaller amounts of chemicals and disposes of dangerous acids and solvents. On the negative side, special attention needs be given to some toxic and corrosive gases in dry etching. dry etching process

Ion-beam etching, sputter etching, or vapor deposition.

dry-bulb temperature

(DBT) The ambient air temperature measured by a regular thermometer that is not affected by the moisture of the air.

dry-cell battery

Also known as absorbed glass mat (AGM) battery; it is a type of a sealed lead-acid (SLA) rechargeable battery that uses absorbent glass mats instead of liquid electrolyte. Unlike the liquid electrolyte surrounding the electrodes, a very fine fiberglass mat is saturated with the sulfuric acid, encapsulated, and sandwiched between the positive and negative battery plates. Even though the battery acid is immobilized by the fiberglass mat, it is still available to the plates. As a result, the battery is spill-proof, whereas it is still highly reactive due to the close proximity between acid and plates. This configuration improves both the discharge and recharge efficiency. Dry-cell batteries can charge up to five times faster than flooded battery systems. They are more resistant to cold weather

drying chamber 

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and vibration and enable high cranking. Disadvantages of dry-cell batteries include higher manufacturing costs and environmental hazards. drying chamber

A chamber in a →solar kiln in which hot air is circulated to dry stacked wood.

DSC

Abbreviation for dye-sensitized cell. See →dye-sensitized solar cell.

DSG

Abbreviation for →direct steam generation.

DSM

Abbreviation for →demand side management.

DSM2

Abbreviation for →Digital Surface Model.

DSS furnace

See →directional solidification system furnace.

DSS1

Abbreviation for →direct solar steam.

DSS2

Abbreviation for →directional solidification system.

DSSC

Abbreviation for →dye-sensitized solar cell.

DTD

Abbreviation for →design temperature difference.

DTR

Abbreviation for diurnal temperature range. See →diurnal temperature variation.

dual ion-beam deposition

See →dual ion-beam sputtering.

dual ion-beam sputtering

(DIBS) A method for growing different types of thin films at room temperature. The first Ar+ ion beam bombards the target surface in a vacuum chamber, ejecting atoms and molecules from the target semiconductor material. The sputtered material particles are condensing on the substrates to form the thin film. A second ion gun is added to support the deposition by bombarding the growing film. This assistance of the thermal deposition process imparts additional energy to the material particles. The accelerated particles impact the substrate with more force, generating a thin film with a higher density, which in turn results in a more durable coating and material savings. In addition to high density, the DIBS generates good stoichiometry and improves film-substrate adhesion. It is a process that allows manufacturers a detailed control of film composition – microstructural, optical, and electrical properties of thin deposited layers.

1

194 

 dual-axis solar tracker

dual-axis solar tracker

(DAST) A type of a solar tracker with two rotational axes that allow the solar modules to have the optimal tilt angle and point directly toward the solar disk at all times. See also →dual-axis tracking system.

dual-axis tracker

See →dual-axis solar tracker.

dual-axis tracking

See →dual-axis tracking system.

dual-axis tracking array

A photovoltaic array that relies on the →dual-axis tracking system to find the optimum angle for solar modules at any time of day.

dual-axis tracking collector

A collector that uses a solar tracker with two rotational axes, allowing the reflector surfaces to have the optimal tilt angle and point directly toward the solar disk at all times.

dual-axis tracking system

A tracking system that rotates the frame with solar panels on two axes. The frame with PV panels is moved via an electronically controlled motor. The two-axis system enables the array to follow the sun horizontally and

Dual-axis Tracking System

dual-junction solar cell 

 195

vertically. In addition to the horizontal movement following the sun (azimuth angle) from east to west like →single-axis tracking systems, the dual-axis trackers also follow the sun vertically, ensuring the optimum altitude (tilt) angle, also known as seasonal angle, toward the sun. The dual-axis tracking system allows panels to be perfectly perpendicular, at a right azimuth and seasonal angle, to the sun at any time of day. Pointing directly at the sun at all times ensures the maximum power output of a solar system. This is particularly important in →concentrating photovoltaics because they do not absorb diffuse solar radiation. As they are responsive only to direct sunlight, the →concentrating collectors often use dual-axis solar trackers. Compared to a fixed solar array, a PV array with a dual-axis tracking system can increase the energy output by 30%. Compared to a →single-axis tracking system, a dual-axis tracking system can increase the energy output by 5%–6%. dual-junction solar cell

See →tandem junction solar cell.

duct ground heat storage model

A model that proposes a large number of uniformly placed ground heat exchangers for the heat transfer with the ground. The heat carrier fluid is circulated in a channel system inserted in a borehole and a conductive heat transfer is envisaged between the heat carrier fluid and the ground.

duct mastic

See →duct sealant.

duct sealant

A material used to seal leaking HVAC air ducts in forced air heating and cooling systems. Properly sealed ducts make a home safer and more energy efficient.

dusk

The time of day immediately following sunset, which can be described as the transition from day to night.

dusk-to-down sensor

A photosensor that detects light, turning on and off →solar garden lights, →solar street lights, and other →solar lighting systems. During the day, the solar cells capture the sun’s energy and store it in a battery. As it gets darker at the end of the day, the amount of light falling onto the sensor

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 duty cycle

decreases, reaching a threshold when the photosensor will let the current flow and turn the light on. The LED lights shine throughout the night until the photosensor switches them off at dawn. duty cycle1

The cycle of operation of an appliance. The ratio between the active (operating) time and the inactive (resting) time of an appliance or system that works intermittently rather than continuously.

duty cycle2

The amount of time a device can be run safely and according to its specified output.

duty ratio

The ratio between the active (operating) time and the inactive (resting) time of an appliance or system that works intermittently rather than continuously.

DVM

Abbreviation for →digital voltmeter.

DWCNT

Abbreviation for →double-walled carbon nanotube.

dye cell

(DSC) Also known as Grätzel cell. See →dye-sensitized solar cell.

dye-sensitized cell

(DSC) Also known as Grätzel cell. See →dye-sensitized solar cell.

dye-sensitized photovoltaic cell

(DSSC) Also known as Grätzel cell. See →dye-sensitized solar cell.

dye-sensitized photovoltaic module

See →dye-sensitized solar module.

dye-sensitized PV cell

(DSSC) Also known as Grätzel cell. See →dye-sensitized solar cell.

dye-sensitized PV module

See →dye-sensitized solar module.

dye-sensitized solar cell (DSSC) is a third-generation photovoltaic cell that was invented by Professor Michael Grätzel and Dr Brian O’Regan in 1991. Hence, it is commonly known as Grätzel cell. This electrochemical solar cell consists of a transparent conducting glass functioning as a minus electrode facing the sun, dye-sensitized titanium dioxide as a nanostructured semiconductor layer, iodide electrolyte, and an opposite electrode coated with platinum catalyst.

dye-sensitized solar cell 

 197

Anode TiO2

e– e–

Dye

e– –

I3

3I

–

e– e– Cathode

Dye-Sensitized Solar Cell

DSSC energy production process is often compared to photosynthesis, where the sunlight absorbing dyes function like chlorophyll in green leaves. When photons of light (incident light, but also artificial light) fall onto a thin layer of dye material, they kick electrons into a higher energy state. The photoexcited electrons leave their usual orbit and continue moving through the n-type TiO2 conduction band with nanopores toward the external circuit. They come back to the cell through the counter electrode (platinum catalyst), continue their journey through the liquid electrolyte (iodide) or solid-state electrolyte (polymer), and finally close the circle by occupying the empty holes and supplying electrons to the dye. This rather simple energy production process that uses the inexpensive semiconductor material →titanium dioxide (TiO2) promises low-cost manufacturing. Another

198 

 dye-sensitized solar module

advantage is the fact that DSSC can generate energy in a wide range of light conditions regardless of the cell’s position/angle to the sun: indoors and outdoors, in diffuse light on cloudy and foggy days, in shaded locations, early in the morning, or late in the afternoon. The rising temperature during the day does not affect the cell performance. Average DSSC efficiencies vary between 10% and 15%, but some DSSC drawbacks still hinder a major breakthrough of this technology: platinum is a rare and expensive metal and electrolyte could potentially leak. dye-sensitized solar module

A solar module that consists of many →dye-sensitized solar cells that are interconnected in series. The photoexcited electrons from the thin, light-absorbing dye film leave their usual orbit and continue moving through the n-type titanium dioxide (TiO2) conduction band, whereas the holes are transferred to a liquid electrolyte (iodide) or a solid-state electrolyte (polymer), depending on the model.

dynamic pressure

Pressure resulting from a fluid in motion, for instance, the volume of air following through a HVAC duct cross-section at certain velocity.

dynamo

A machine that generates →direct current.

E earth

UK Also known as ground in the USA. A connection between an electric circuit (photovoltaic equipment) and the earth, which acts as a return path for current, conducting unwanted electrical charges away from the circuit to the ground. Grounding wires and rods are used as a safety measure to protect persons from electrical shocks and prevent the PV equipment damage due to lightning or electrostatic buildup.

earth house

See →earth-sheltered home.

earth rod

A rod driven into the ground, with which earth cables are connected, providing a conducting path to the earth for all unwanted electrical charges from the circuit and PV equipment.

earth sheltering 

 199

earth sheltering

See →earth-sheltered home.

Earth System Research Laboratory

(ESRL) The research laboratory within the →National Oceanic and Atmospheric Administration (NOAA) with the mission to conduct sustained observations and research related to atmospheric mechanisms that drive the Earth’s climate, assure the continuing health and restoration of atmospheric resources, improve predictions through expanded climate and weather products, and advance national research capabilities.

Earth’s natural reflectivity

See →albedo.

earth-friendly

Not harmful to the Earth.

earthing

See →grounding.

earthing rod

See →earth rod.

earth-sheltered home

Also known as an earth house or earth sheltering. A house built partially or mostly underground to provide a weather-resistant and energy-efficient dwelling. The earth surrounding the house protects it from rain, wind, scorching sun, and other extreme weather conditions. The soil also acts as a thermal mass that remains cooler than the outside air in summer and warmer in winter, reducing significantly heating and cooling needs. The optimal location for an earth-sheltered home is a well-drained hillside facing south.

earthship

Passive solar building type built with used tires filled with tamped earth.

e-beam evaporation

See →electron beam physical vapor deposition.

e-beam irradiation

See →electron-beam irradiation.

e-beam lithography

See →electron-beam lithography.

e-bicycle

See →electric bicycle.

e-bicycle charging station

See →electric bicycle charging station.

e-bike

See →electric bicycle.

e-bike charging station

See →electric bicycle charging station.

EBPVD

Abbreviation for →electron beam physical vapor deposition.

200 

 EC

EC

Abbreviation for →Environment Canada.

e-car

See →electric vehicle.

ECCC

Abbreviation for →Environment and Climate Change Canada.

echelette grating

See →blazed grating.

ECMWF

Abbreviation for →European Center for Medium Range Weather Forecasting.

eco investment

Ecological, sustainable investment.

eco power plant

US A power plant that takes into account ethical and environmental issues in their operations by generating and delivering pollution-free →green energy to their customers.

eco power station

UK See →eco power plant.

eco-conscious

Showing concern for the environment; making decisions and acting to protect the immediate as well as global environment.

eco-consciousness

The state of being →eco-conscious, taking an interest in environmental issues and acting to preserve the environment.

Ecodesk

A web-based resource platform for sharing sustainability information, analysis, strategies, and models with ecologically minded individuals and companies.

eco-electricity

See →eco-energy.

eco-energy

Also known as renewable energy. Energy generated from solar, wind, or other renewable energy resources.

ecofreak

A person that is devoted to the cause of protection and preservation of the natural environment.

eco-freak

See →ecofreak.

eco-friendly

See →environmentally friendly.

ecological engineering

See →environmental engineering.

ecological footprint

Indicates how much surface area of the Earth a person needs to maintain his or her lifestyle.

ecological footprint reduction

Reduction of surface area of the Earth a person needs to maintain his or her lifestyle.

ecological investment 

 201

ecological investment

See →sustainable investment.

economic dispatch

A process of managing electricity generation and transmission facilities to meet the load and maintain the system reliability from minute to minute by continuously balancing supply and demand at the lowest cost. For instance, a system operator turns on (dispatches) the cheapest generation facility first and when the capacity constraint of the facility is reached, he switches to the second-cheapest generation facility, and so on and so forth.

eco-power

See →eco-energy.

ecoscience

See →environmental engineering.

ECR

Abbreviation for →electron cyclotron resonance.

EDAC

Abbreviation for →electron-donor–acceptor complex.

edge grinding

Also known as edge profiling. A step in a wafer manufacturing process following wafer cutting in which edges of a wafer are grinded. Silicon is a hard but very fragile material in its crystalline form. When the edges are not properly rounded off, silicon wafer will flake during further processing operations. Apart from damaging the wafer, the edge flaking can contaminate the processing equipment or nearby wafers with chipped fragments.  

edge profiling

See →edge grinding.

edge-defined film-fed growth

(EFG) A method for producing crystalline or polycrystalline silicon sheets for photovoltaic cells. Unlike growing large silicon boules as in →Czochralski method, the EFG grows silicon wafers in a sheet form from the start and thus eliminates the cutting process and the cutting-related costs. With help of a →graphite die, silicon is drawn from a melt by capillary action, solidifying under a carefully adjusted temperature into a long, thin silicon sheet.

EED

Abbreviation for →Energy Efficiency Directive.

EEED

Abbreviation for →European Energy Efficiency Directive.

EEG

Abbreviation for Erneuerbare-Energien-Gesetz. →German Renewable Energy Sources Act.

EEG clearing agency

An agency that answers interpretation questions regarding the Renewable Energy Law.

See

202 

 EEG clearing office

EEG clearing office

See →EEG clearing agency.

EER

Abbreviation for →energy efficiency ratio.

efficiency

The ratio of generated electricity (energy output) to available energy (solar energy input). See →conversion efficiency.

efficiency gain

For the most part, efficiency gains are measured by energy →conversion efficiency of solar devices. The biggest incremental gains in solar cell efficiency in recent years have been achieved by improving luminescence and electrical properties in semiconductor materials. The combination of different semiconductor materials in a →multijunction photovoltaic cell, which is capable of absorbing a wider range of the solar spectrum, has ensured additional efficiency gains. The optimization of solar module encapsulation materials and electrical contacts is essential to mitigate the negative effects of solar panel degradation.

efficiency loss

Energy loss in solar modules that is caused by →soiling, →reflection, heating, or →recombination within PV cells. Dust and dirt on PV panels as well as reflection of incident solar radiation from a glass surface of a PV module affect the power output of a solar array. A large portion of energy losses in solar modules can be attributed to heating. When the temperature of the module rises over 25 °C (77 °F), it potentially reduces the power yield by 10%–25% based on the proportional voltage drop due to resistance. Finally, the recombination or the imperfection of transport of excess charge carriers within a solar cell accounts for another part of power losses. In →solar thermal collectors, poorly insulated enclosures containing absorber plate and liquid tubes, contribute to heat losses, resulting in a reduced solar output.

efficiency calculation

A type of photovoltaic panel testing that focuses on measuring the output energy and calculating the efficiency of a PV module.

efficient energy system

Any system designed to generate energy or reduce energy usage by means of efficient technologies or processes.

EFG

Abbreviation for →edge-defined film-fed growth.

EL

Abbreviation for →electroluminescence.

electric aircraft 

 203

electric aircraft

See →solar-powered airplane.

electric bicycle

Also known as an electric bike, e-bicycle, or e-bike. A bicycle which is powered by an electric motor instead of a gasoline-powered engine. The e-bike utilizes different types of rechargeable batteries whose range varies depending on the model and the rider’s riding style and can be between 25 and 96 km/h (16 and 60 mph). Although there is a wide variety of different e-bike models on the market, most of them have the same features and parts like traditional bicycles. The added electric parts include the electric motor, the drivetrain, and the battery. The role of electric power is not to replace the rider’s pedal-power but to assist it when needed. For instance, when pedaling uphill becomes more difficult, the integrated sensor detects constant elevated pressure upon the pedals and starts the electric motor, supporting riders and enhancing their power. Besides this pedal assist mode, the rider can also switch between pedal only mode that allows a regular bicycle ride and electric only mode, in which the bike is ridden like a moped that is powered by the electrical motor all the time. Electric bike batteries require a small amount of energy. They can be recharged at home with a 250-W solar panel, at a solar e-bicycle charging station, or simply from the electric mains. E-bikes are a clean, environmental friendly alternative to gasoline-powered vehicles that helps urban congested and densely populated centers decrease the emission of problematic →greenhouse gases and thus reduce their →carbon footprint.

electric bike

See →electric bicycle.

electric bike charging station

See →electric bicycle charging station.

electric capacitance

The property of a body to store an electrical charge.

electric car

See →electric vehicle.

electric car sharing

A type of electric car rental for local users that is mainly designed for shorter time (a few hours) and shorter distance trips. The major objective of car sharing programs is to decrease personal car ownership, dependence on fossil fuels, and the emission of greenhouse gases in densely

204 

 electric charge

populated and polluted city centers. An easy access to electric cars within walking or cycling distance is crucial for the success of a car sharing program. Electric cars are usually available in several car sharing vehicle zones around the city center. The vehicles can be picked up in reserved parking areas and sometimes, depending on the program, dropped off in almost any parking lot within the designated car sharing zone. The next objective would be to charge electric car sharing vehicles with solar energy. This can be achieved by turning reserved parking areas into solar carports or solar electric vehicle (EV) charging stations. electric charge

An elementary property of matter to exert an attractive or repulsive force, when it has a surplus of electrons or protons. An atom has no net electric charge, when the number of electrons equals the number of protons. We say that such atom is in a normal/neutral state. However, whenever an atom has more electrons than protons or more protons than electrons, it becomes electrically charged. Accordingly, a matter can be positively or negatively charged. See also →positive electric charge and →negative electric charge.

electric circuit

The complete path an electric current takes, starting at the source (solar panel), where energy is generated, flowing to the load (all electrical devices drawing power from the circuit when turned on, such as refrigerator, TV, or lights) and back to the source (solar panel) again.

electric current

(I) The flow of an electric charge, such as the flow of negative charge (electrons) in a conductor between two points. Electric current is measured in amps (amperes) by a device called →ammeter. According to →Ohm’s law, current is equal →Volts (potential difference) divided by →resistance: I = V/R.

electric demand

The amount of electrical power that is being consumed at a given time, expressed in kilowatts or kilovolt amperes.

electric field

The electric field equals the electric force per unit of electric charge: E = F/q. It is the force that occupies the space around an electric charge and acts upon other electric charges or objects.

electric flux 

 205

electric flux

The flow of the lines of force that make up an electric field through a given surface. The electric flux (f) is the product of the number of electric field lines (E) and the surface area (A) perpendicular to the field: f = EA.

electric grid

See →electrical grid.

electric hysteresis

Difference between the switch-on and off temperature.

electric isolation barrier The barrier inhibits the electric contact between n- und p-layers of a solar cell. electric meter

See →electricity meter.

electric mobility charging infrastructure

A network of different types of charging devices and systems for electric vehicles (eVs). It includes residential charging infrastructure, workplace charging infrastructure, and public charging infrastructure. The residential charging infrastructure facilitates overnight charging at home, including →Level 1 charging and →Level 2 charging. The workplace charging infrastructure facilitates charging of employees’ vehicles during business hours, including →Level 1 charging and →Level 2 charging. The public charging infrastructure facilitates public charging at →electric vehicle charging stations at any time. The development of a wide-spread public and private charging infrastructure is one of the key prerequisites that lead to a decreased demand for fossil fuels and reduced carbon dioxide emissions. It encourages the adoption of electrical vehicles, increases the number of electric miles driven, and maintains electric grid reliability.

electric polarizability

The ability of a dielectric material to allow an externally applied electric field to generate separated positive and negative electric charges in the material. See also →dielectric constant.

electric potential

An electric pressure, electric tension, or electromotive force present in electric current. SI unit for electric potential is volt. See also →voltage.

electric power

Amount of energy produced or consumed per unit time. It is measured in watts (W). Solar modules are rated by the amount of electric power they generate. For instance, a solar panel is rated at 600 W. Power is equal to voltage (V) multiplied by current (I): P = V × I.

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electric power distribution

The transfer of electrical energy from a substation to various end users, such as individual consumers or businesses. This is the final stage in electricity delivery, in which electric power is stepped down by a transformer to a lower voltage before reaching our homes.

electric power distribution system

A network of power lines that run along streets, carrying low-voltage electricity to residential and commercial customers.

Electric Power Research Institute

(EPRI) An independent, nonprofit organization that collaborates with numerous electric power companies in the United States. EPRI conducts research and development in the area of electricity generation, delivery, and use for the benefit of the public in the USA and internationally.

electric power transformation substation

A fenced electrical facility, at which the high-voltage electricity from high-voltage power lines is converted to lower voltages and delivered through low-voltage electric distribution lines to various end users, including residential, commercial, and industrial consumers.

electric power transmission

The transport of electric energy through power lines from a generating site, such as an industrial-scale →solar power plant, to a substation. At the substation, the high-voltage electricity is converted to lower voltages and delivered through low-voltage electric distribution lines to various end users, including residential, commercial, and industrial consumers. The use of →superconducting transmission lines (SCTL) promises to lower total electrical losses during transmission, opening doors to a sustainable power transmission technology.

electric utility company

An electrical energy provider that generates, manages, and delivers electricity to individual households and commercial enterprises.

electric vehicle

(eV) A vehicle that is powered by one or more electric motors instead of the conventional internal combustion engine. Unlike gasoline-powered vehicles, electric vehicles utilize electricity stored in a battery pack to power electric motors. If the battery electricity comes from solar or other renewable resources, the carbon footprint is reduced to zero. Electrical vehicles burn no gasoline and generate no harmful tailpipe emissions. Beside the major role they play

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in reducing greenhouse gas emissions, eVs are quieter and cheaper to operate than vehicles that are fueled by gasoline. Electric vehicles include electric cars, electric bikes, electric motorcycles and scooters, electric trolleybuses, battery electric buses, electric streetcars or trams, electric trucks, and electric locomotives. Two major disadvantages hindering the widespread use of electrical vehicles are high upfront cost and short driving range. electric vehicle charging station

Also known as an EV charging station or electric vehicle supply equipment (EVSE). A station that provides electricity for the recharging of electric vehicles. The charging station converts household electricity to electric energy that can be stored in an EV’s battery. The car battery does the charging. A charging station has roofs that are covered with solar panels and is hence powered by solar energy is called →solar electric vehicle charging station. There are three main types of EV charging stations: Level 1, Level 2, and DC fast-charging station. Level 1 is an overnight charging model that converts general-purpose alternating current (AC) into direct current (DC) used by electric cars by utilizing an on-board converter in the electric vehicle. In Level 1 charging, the 120 V charger cord, which comes with all electric vehicles, is merely plugged into a standard household outlet. Level 1 is the simplest but also the slowest type of EV charging. It takes up to 16 h to charge an 80-mi or 129-km battery pack. The major advantage of slow charging is an extended battery life, as the slow charging rate cannot damage the batteries. Level 2 charging is a home or public electric vehicle charging model that uses a 240-V outlet to allow fast charging. Depending on the type of electric vehicle, Level 2 stations can charge an eV battery pack several times faster than the regular Level 1 charging. It takes up to 3.5 h to fill up an 80-mi or 129-km battery pack. The larger the battery pack, the more time it takes to charge it. The majority of today’s electric vehicles, such as Chevy Volt, Nissan LEAF, Tesla Model S, or new Prius, use the J1772™ connector for Level 2 charging at 240 V.

electric vehicle supply equipment

(EVSE) See →electric vehicle charging station.

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 electric voltage

electric voltage

The amount of strength or electric potential in electric current. See also →voltage.

electrical box

See →electrical enclosure.

electrical bushing

See →roof bushing.

electrical circuit

See →electric circuit.

electrical circuitry

See →electric circuit.

electrical conductance

Indicates the ease with which electricity flows through a material. It is measured in Siemens (S). The precious metals silver and gold have the highest electrical conductance values of any element.

electrical conductivity

The ability of a material to conduct electricity. It is a measure of how readily a material transmits an electrical current. Electrical conductivity is the reciprocal of the resistivity.

electrical conductor

A material that allows the free flow of electrons. Good electrical conductors, in which electrons can move unobstructed, are copper, silver, gold, brass, and aluminum. Most metals are good conductors. In photovoltaic systems, the commonly used materials for conducting lines, busbars and PV wires, are copper and aluminum.

electrical consumption worksheet

See →load analysis worksheet.

electrical contacts

Electrodes on the front and rear sides of solar cells that collect electrical current generated within the photoactive silicon semiconductor, when sunlight strikes solar cells, and transport it to the next cell and further through the module’s circuit. The contact on the front of the PV cell is usually made in the form of a grid, consisting of a net of numerous miniature, parallel conductive lines called →fingers, and two busbars that intersects the fingers at a right angle on each silicon solar wafer. The electrical current, which is generated in the semiconductor layer and carried out of the solar cell through a front electrical contact, is transported to the next PV cell via back contact. The negative tabbing wire from the front contact (busbar) of the first cell is soldered to the positive pad at the bottom of the second cell, and the negative tab from the top of the second cell is soldered to the positive back of the third cell, and so on.

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electrical current

See →electric current.

electrical enclosure

Also known as an electrical box or electrical housing. A rigid ABS plastic, stainless steel, or aluminum enclosure in which wires are connected in different ways, fulfilling various functions in photovoltaic (PV) installations. Ranging from small boxes to large cabinets, electrical enclosures can be divided into four groups: junction, combiner, recombiner, and subcombiner boxes. These different types of electrical boxes interconnect solar panels into a unified electrical system. The pyramidlike cabling pathway guides generated solar energy from numerous individual modules – small junction boxes – to larger combiner and recombiner boxes, ending its journey in a single subcombiner box on top of the horizontal pyramid. Junction boxes are enclosures on the back of a PV module that house electrical connections and diodes. It is an input/output interface connecting the module to other PV modules. In a different configuration, junction boxes can be installed at the end of the rows of solar modules, connecting a group of solar panels to the combiner boxes. The combiner, recombiner, and subcombiner boxes fulfill the same function at different levels: they combine the output of several PV strings and channel it into a single conductor pair. At the end of the cabling path, there is only one conductor pair, feeding all generated PV energy into the inverter that converts solar DC current into grid-compatible alternating current (AC).

electrical energy

Unlike power that is an instantaneous measure of produced power in watts, energy is a power generation or consumption over time. It is measured in watt-hours (Wh). It applies the formula energy = power × time, which calculates the amount of energy a device, for example, a solar panel, will produce over a certain period of time, for instance, over 6 hours a day. It helps estimate overall solar module output.

electrical generation

See →electricity generation.

electrical generation facility

A utility-scale facility for the generation of electric power.

electrical generator

A device that turns mechanical energy into electrical energy.

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electrical grid

Integrated network of electricity suppliers and consumers connected by high-voltage transmission and distribution lines that serve the public power supply. A power grid typically consists of a high-voltage transmission grid (50–380 kV), a medium-voltage distribution grid (10–30 kV), and a low-voltage distribution grid (120, 230, or 400 V), to which a solar array is connected.

electrical housing

See →electrical enclosure.

electrical insulator

Also known as nonconductor, a material such as plastic that does not conduct electricity well and has the task to stop the flow of electric current in unwanted places. Conducting photovoltaic copper wire is insulated with polyethylene coating.

electrical load

Also known as load. Any electrical device (e.g., refrigerator, TV, or lights) in an electrical circuit that draws power from that circuit when turned on.

electrical metallic tubing (EMT) A tubing through which wires and cables used in PV installations are run. The EMT tubing is usually manufactured from galvanized steel to provide a long-lasting exterior protection from impact damage and adverse weather conditions. electrical meter

See →electricity meter.

electrical mobility charging infrastructure

See →electric mobility charging infrastructure.

electrical overload

See →power overload.

electrical resistance

Electrical resistance measures how much a material (a conductor) restricts the flow of electricity. SI unit for resistance is ohm (Ω).

electrical storage appliance

An appliance for storing electrical energy. See →rechargeable battery.

electrical stress

Electrical stress in a cable caused by defects, such as ruptured insulation, causing voltage to leave the conductor in search for ground (earth). This can create hot spots, significantly diminishing the transmission performance and potentially causing a cable failure. In order to avoid the

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negative effects of the electrical stress on the cable, the ruptured cable needs to be replaced at the earliest convenience. electrical supply meter

Measures the energy that is generated by a solar system and fed into the public power grid.

electrical voltage

See →voltage.

electric-bicycle charging Also known as e-bicycle charging station or e-bike chargstation ing station. A filling station for charging electric bicycles. Even though some e-bicycle stations offer power coming from the regular electric mains for recharging e-bike batteries, most of contemporary e-bike stations use solar power. As a rather small amount of energy is required to charge an electric bike battery, several solar panels suffice to power a large number of e-bicycles during the day. electric-bicycle station

See →electric-bicycle charging station.

electricity

The flow of electrons through a conductor.

electricity consumer

A person who purchases electrical energy from the local electric company. When a house owner acquires a solar system and connects it to the power grid, he or she assumes the role of both the electricity consumer and the electricity provider, selling the surplus energy to the utility company.

electricity consumption

The amount of electrical energy consumed by an individual or organization over a period of time.

electricity demand

See →annual electricity requirement.

electricity demand response

A type of US →smart grid program, which engages customers in →smart energy management by offering timebased rates or other forms of financial incentives. In this platform, the customers contribute to balancing electricity supply and demand by reducing or shifting their electricity usage during the hours of high-energy demand, so-called →peak hours.

electricity generation

Electricity generated by converting other forms of energy, such as solar, wind, hydro power, or fossil fuels, into electrical energy. The generated electricity is typically measured in →kilowatts (kW), →megawatts (MW), →gigawatts (GW), and →terawatts (TW).

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 electricity generation from renewable sources

electricity generation from renewable sources

Energy generation from natural energy resources, such as solar, wind, hydropower, tidal and wave, biomass, geothermal, and other nonfossil-fuel energy sources that are constantly present or can replenish themselves over short periods of time. The two major benefits of the clean energy generation are that it reduces the depletion of Earth’s natural resources and emits no harmful →greenhouse gases into the atmosphere, thus reducing the carbon footprint to zero.

electricity management

The management of supply and demand of electrical energy at the large utility scale by a grid operator or at the small scale by a household or business owner. The major task of a grid operator is to ensure a constant balance between supply and demand of electric power, regulating the inconsistency in the output frequency and maintaining scheduled frequency. Homeowners and business owners can reduce their electricity consumption by installing a solar array, sealing all gaps and openings in the building envelope, using an →energy management and information system and various other energy saving techniques.

electricity meter

Also known as a power meter. An instrument that measures the amount of electrical energy in kilowatt-hours (kWh) that is used by a resident or a company. Unlike smart →two-way meters that are becoming standard in solar homes, a conventional electricity meter measures only the energy coming from the electric utility company to a house.

electricity price

The price of 1 kWh of electricity is established by levelized →costs of generating electricity as well as by electricity demand and supply that varies minute by minute. The general trend shows that the cost of electricity from solar energy sources has dropped in recent years primarily due to constant improvements in energy →conversion efficiency and a decrease in installation costs. With the current median price of five cents per kilowatt hour in the USA, solar electricity is becoming one of the cheapest energy sources that is able to compete with low coal, natural gas, and wind prices. The average price of solar energy is expected to fall to four cents per kilowatt hour in the upcoming years.

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electricity price increase

See →future increase in electricity prices.

electricity production

See →electricity generation.

electricity production costs

See →costs of generating electricity.

electricity production from renewable sources

See →electricity generation from renewable sources.

electricity provider

Utility company that generates, manages, and delivers electricity to individual households and commercial enterprises. An electricity consumer, who owns a →grid-connected photovoltaic system, can simultaneously function as an electricity provider, selling the surplus energy to the local utility company.

electricity rate

Cost per unit of electricity. The price of electricity depends on the time of use. Customers can take advantage of favorable kilowatt hour (kWh) electricity rate during the hours of low-energy consumption (off-peak time). During the hours of high-energy demand or peak hours, utilities sell electricity at higher rates than during off-peak time.

electricity shortage

See →energy shortage.

electricity surplus

See →power surplus.

electricity transmission grid

See →electricity transmission network.

electricity transmission network

The network that consists of high-voltage and low-voltage lines transmitting electricity from power plants, such as →large-scale photovoltaic installations or →large-scale solar thermal systems, to various end users, such as individual consumers or businesses.

electricity user

See →electricity consumer.

electrochemical accumulator cell

See →battery cell.

electrochemical cell

See →battery cell.

electrochemical deposition

Deposition method based on the common process for producing metallic coatings is used in thin-film solar cell production, where small amounts of a semiconductor material are applied to the substrate.

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electrode

Electrodes are electric conductors, such as positive and negative terminals in a battery, anode and cathode, through which an electrical current enters or leaves the electrolyte or gas.

electrode layer

In a solar cell, the top transparent layer that is commonly made of transparent conductive oxide (TCO) material, which is characterized by highest electrical conductivity and transparency with a solar energy transmittance value of over 80%. Optical transmittance decreases with the increase in thickness of the electrode layer, resulting in less incident solar radiation reaching the semiconductor.

electrodeposition

A process for producing metallic coatings, electroplating.

electroluminescence

The emission of light by a material, for example, silicon semiconductor, resulting from application of an electrical current to the semiconductor. When current is fed into a silicon cell, a →recombination of the →electron–hole pairs occurs. The excited electrons release energy, in the form of photons, producing the emission of light. Although the radiative recombination emission is relatively low and invisible, it can be sensed by highly sensitive detectors, such as →shortwave infrared cameras. An →electroluminescence inspection tests the uniformity of solar cells and is able to find hidden defects in semiconductors before solar modules are moved to the next manufacturing stage or even delivered to customers.

electroluminescence imaging

Capture, storage, and manipulation of →electroluminescence (EL) radiation. When electric current is applied to a solar cell, a →recombination of the →electron–hole pairs takes place. The excited charge carriers release low radiative energy that can only be detected by a highly sensitive camera, for example, a →shortwave infrared camera or Si-CCDs camera. The camera takes an image of the emitted photons and stores it in the computer. During a solar cell testing, high-resolution images allow an inspector to detect hidden defects in crystalline and thin film solar cells, which under normal circumstances are invisible to the human eye. Depending on the sensitivity level of the camera, the electroluminescence imaging can identify the following issues: physical defects, microcracks, bad finger contacts, broken contacts, electrical shunts, grain boundaries, and crystallization faults.

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electroluminescence inspection

A type of solar cell inspection that utilizes short-wave infrared (SWIR) cameras to detect physical defects and cracks inside the wafer. The short-wave infrared wavelengths beyond 1.1 µm make silicon transparent, allowing the camera to identify hidden issues in different types of solar cells, ranging from mono and polycrystalline over thin-film ribbon to CIS and CIGS PV cells. The SWIR imaging can also reveal voids in →silicon ingots before slicing them into wafers. The SWIR camera can be scanned across a module of solar cells to test the uniformity of solar cells and detect weak areas and problematic cells.

electroluminescence measurement

A measurement of the PV module characteristics that is based on →electroluminescence imaging. Images as well as various maps and data extracted from images help inspect individual cell parameters, allowing measurements for different purposes. Compared to the measurement of solar cell current-voltage characteristic or →I-V curve, electroluminescence imaging makes some invisible phenomena transparent and measurable, such as micro cracks in a polycrystalline silicon solar cell or defect fingers in a monocrystalline silicon solar cell.

electrolysis

A process of producing chemical changes in a liquid by passing an electric current through the electrolyte containing ions.

electrolyte

A liquid that can conduct electricity. In a battery, the electrolyte transfers electrical current, positively and negatively charged ions, between the positive and negative electrodes. In rechargeable lead-acid batteries, the electrodes consist of lead (Pb)/lead dioxide (PbO2) and the electrolyte is sulfuric acid (H2SO4).

electrolyte stratification See →acid stratification. electrolytic bath

See →galvanization.

electrolytic cell

A cell containing an electrolyte and two electrodes. When an electric charge is passed through the electrolyte, an electrochemical reaction, →reduction–oxidation reaction, takes place between the positive and negative electrodes.

electrolytic deposition

A process for producing metallic coatings, electroplating.

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 electrolytic process

electrolytic process

A process that uses the electric current to separate and deposit metals from solution. The electrolytic process is commonly employed for producing corrosion protection layers for various outdoor solar applications.

electromagnetic

Describes electric and magnetic forces.

Electromagnetic Compatibility Directive

(EMC Directive) A legal act of the European Union that ensures that electrical and electronic equipment does not generate or is not affected by electromagnetic disturbance.

electromagnetic interference

(EMI) Also known as radio-frequency interference (RFI). A disturbance in which one electromagnetic field interferes with another, resulting in diminished performance of electrical equipment.

electromagnetic radiation

(EMR) Consists of waves of electric and magnetic fields traveling at right angles to each other at the speed of light in a bundle of light energy called a photon.

electromagnetic spectrum

The complete range of electromagnetic radiation. The spectrum spans from very short gamma rays, over X-rays, ultraviolet radiation, visible light, infrared radiation, microwaves, to very long radio waves.

electromagnetism

Study of the electromagnetic field produced by an interaction between electricity and magnetism.

electromobility

Also known as e-mobility. The utilization of vehicles that are powered by electricity as a means of transportation. The e-mobility comprises full electric vehicles, hybrid electric vehicles, and hydrogen fuel cell vehicles. Fostering the development and adoption of electrical vehicles and an EV infrastructure leads directly to a decreased demand for fossil fuels and reduced carbon dioxide emissions.

electromobility act

See →electromobility law.

electromobility law

(EmoG) German act for promoting →electromobility.

electromobility regulation

See →electromobility law.

electron

A particle with a negative electric charge. Electrons orbit around the nucleus and under normal circumstances, they do not leave their stable orbiting positions in the electron

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 217

shell (cloud). However, if there are excess electrons on some of the atoms introduced into a semiconductor layer of a PV module (e.g., n-type silicon, doped with phosphorus) and a lack of electrons on the neighboring atoms, electrons will leave their usual orbits and start moving from one atom to another. This movement of electrons through an electrical conductor is called electrical current. electron acceptor

An atom or a molecule, such as →boron, which easily accepts an extra electron from another chemical entity in an oxidation–reduction reaction. By accepting the electrons, the acceptor is reduced in the process. See also →p-type dopant.

electron affinity

In chemistry, the affinity of an atom or a molecule to gain an electron and form a negative ion. In physics, it is associated with the amount of energy required to move an electron from the vacuum level to the bottom of the conduction band or from the bottom of the conduction band into a vacuum. The electron affinity of a silicon crystal surface is 4.05 eV.

electron beam

A stream of electrons generated from an →electron gun and focused by electric and magnetic fields onto the target material. The energized and accelerated electrons bombard the material and vaporize it in a vacuum chamber. Electron beams are used in →electron beam physical vapor deposition (EBPVD).

electron beam generator

See →electron gun.

electron beam gun

See →electron gun.

electron beam irradiation test

A testing and validation process in which the radiation hardness of solar cells is tested. In a radiation test, solar cells are exposed to electron-beam irradiation to measure and test their performance and resistance to radiation.

electron beam lithography

Also known as e-beam lithography. A →maskless lithography method in which a beam of electrons directly writes precise patterns down to sub-10 nm onto a photosensitive surface of the wafer, usually a →photoresist coating.

electron beam micromachine

A device for fine processing of materials by means of a focused electron beam.

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 electron beam physical vapor deposition

electron beam physical vapor deposition

(EBPVD) Also known as e-beam evaporation. A type of →physical vapor deposition (PVD) process for manufacturing thin-film semiconductor devices. In this PVD process, a high-energy beam of electrons is aimed at the target material, usually an ingot. The intense beam heats up the material to such a high-temperature point, so that it evaporates into the gaseous phase. The dislodged atoms of the evaporated material are transported by diffusion to the substrate in the vacuum chamber. Under high-vacuum conditions with a low thermal energy of less than 1 eV, the evaporated particles traverse the chamber relatively unobstructed with a minimal number of impacts with the remaining gases. Finally, the evaporated atoms uniformly coat the substrate, which is positioned above the target material, with a thin layer of the conductive material. Compared to other deposition methods, the electron beam physical vapor deposition method offers a number of advantages, such as high deposition rates and high material utilization efficiency. Another major advantage includes the ability to precisely control thin-film patterns, thickness, and morphology.

electron binding energy Also known as ionization energy or ionization potential. The amount of energy required to remove a →valence electron from an atom or a molecule. electron conduction

The conduction of electrons in the →conduction band of a semiconductor, where they are free to move under the influence of an electric field, generating electric current.

electron cyclotron resonance

(ECR) A type of →dry etching for etching substrates, such as semiconductor wafers. This high-density plasma system employs microwaves to generate plasma and a magnetic field to control the flow of ions toward the substrate.

electron donor

An atom or a molecule, such as →phosphorus, which easily gives its extra electron away in an oxidation–reduction reaction. See also →n-type dopant.

electron excitation

Occurs when the electron absorbs a photon of light and is promoted from its ground state to its excited state. The excited electron gains enough energy to jump up from the →valence band into the →conduction band.

electron gun 

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electron gun

A device that generates a stream of electrons that are focused onto the target material to be evaporated and deposited on a substrate. Electron guns are used in →electron beam physical vapor deposition (EBPVD).

electron hole

See →electron–hole pair.

electron impact ionization

See →electron impact ionization.

electron ionisation

UK See →electron ionization.

electron ionization

US Formerly known as electron impact ionization. The most commonly used method of →ionization in which an atom or a molecule is ionized by electron impact to generate a positive ion.

electron irradiation

See →electron-beam irradiation.

electron mobility

A measure of velocity at which an electron moves through the semiconductor. It is a ratio of velocity to the electric field applied to a semiconductor in which the electrons collide with impurities and lattice vibrations. An increase in doping concentration results in a decreased electron mobility because the free carriers collide with the dopant atoms more frequently.

electron oscillation

Vibration of electrons at certain frequencies while orbiting an atom’s nucleus in a fuzzy, electron cloud. An interaction between positive and negative energy states produces what appears to be an oscillation. The frequency of electron oscillation increases with energy.

electron shell

Orbital in which negatively charged electrons are spinning around the positively charged nucleus of an atom.

electron transfer

The transfer of an electron from its ground state to its higher, excited energy state, after the electron has absorbed a photon of light.

electron volt

(eV) The amount of energy that an electron gains when passing through an electric potential difference of one volt.

electron-beam lithography

Method for nanostructuring of thin-film layers in the semiconductor industry.

electron-beam processing

See →electron-beam irradiation.

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 electron-beam irradiation

electron-beam irradiation

Also known as electron-beam radiation or e-beam irradiation. The bombardment of a material with high-energy electrons, resulting in the penetration of the target material and ejecting electrons from their orbits.

electron-beam radiation

See →electron-beam irradiation.

electron-donor–acceptor (EDAC) Also known as donor–acceptor principle. A complex complex that consists of a combination of electron donors, such as polymers, and electron acceptors, such as fullerenes (C60). A blend of polymers as electron donors and carbon nanotubes (C60) as electron acceptors can boost charge mobility in polymeric photovoltaics. By carefully controlling the amount and morphology of →donors and →acceptors, photovoltaic properties and power output in →organic solar cells can be considerably enhanced. electron-hole pair

The compound word that merges →electron and →hole with a dash into one term, viewing them as an inseparable complex whole. This whole is rather a quasiunit, describing a process responsible for perpetual generation and recombination of electrons and holes in a semiconductor and thus for photovoltaic energy generation. When the light with →photon energies greater than the →band gap falls onto the semiconductor material, an electron becomes excited, gaining enough energy to jump up from the →valence band into the →conduction band. The dislodged electron leaves behind a vacant position or →hole in the valence band. While an electron is generated in the conduction band, a hole is created in the valence band, thus generating simultaneously an electron–hole pair in the semiconductor. When the electron occupies the vacant position (hole) again, we say that electron and hole recombine, eliminating the electron–hole pair. The newly freed electrons then start the electron–hole pair generation process anew.

electron–hole pair generation

See →electron–hole pair.

electronic band structure

Also known as a band structure. In quantum physics, behavior of electrons in a semiconductor solid with regard to the variety of energy levels they have, such as energy bands, including →valency band or the highest occupied band and →conduction band or the lowest unoccupied

electronic circuit 

 221

band. Both bands are separated by a band gap, which is characterized as an energy range between the highest valence band and the lowest conduction band. electronic circuit

Circuits are used in numerous solar applications, such as →inverters, →charge controllers, →portable solar chargers, and →solar lighting systems. A solar circuit, which is powered by a solar panel, usually consists of the following basic parts: resistors, capacitors, transistors, diodes, solid core wires, batteries, and a board. Circuit components can be connected in series or in parallel.

electronic ink

Material for producing solar cells.

electronic networking

See →electronic circuit.

electronic waste

Also known as e-waste. Electrical and electronic devices, such as inverters, controllers, batteries, and photovoltaic modules, which are no longer in use because they are damaged, obsolete, or discarded. As long as the e-waste product is not hazardous, such as a cadmium telluride solar panel, reusing or recycling is the best practice for discarded equipment. The generation of electronic waste can be reduced through regular maintenance.

electronvolt

See →electron volt.

electroplating

A process for producing metallic coatings.

electrostatic energy

Electrostatic energy is defined as the potential energy of a system of separated electric charges.

electrostatic field

An electric field generated by electric charges at rest.

electrostatic force

See →Coulomb force.

elementary particle

Also known as a fundamental particle. The smallest known, most basic constituents of matter, for example, quarks and neutrinos, which do not consist of smaller components.

elevation

Solar elevation angle. The angle between the horizon and a line drawn through the center of the sun. Solar elevation angle is used to measure the vertical position of the sun, the height of the sun in the sky.

embodied energy

Is the amount of energy required to produce and deliver a solar object, for example, a solar panel or a photovoltaic inverter, to the PV array site.

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 EMC Directive

EMC Directive

Abbreviation for →Electromagnetic Compatibility Directive.

EMCS

Abbreviation for energy management and control system. See →energy management and information system.

emergency backup generator

See →backup generator.

emergency backup system

See →backup power system.

emergency generator

See →backup generator.

emergency power generator

See →backup generator.

emergency power supply

See →backup power system.

emergency power system

See →backup power system.

emergency power unit

See →backup power system.

emergency shutdown

See →emergency shut-off.

emergency shut-off

A safety shut-off system that is integrated into a photovoltaic system to provide protection for persons accessing the solar array in case of an emergency. As photovoltaic panels can generate lethal DC voltages of up to 600 V, they can be dangerous for technicians or homeowners accessing the roof. The emergency shut-off allows emergency personnel to switch off the electricity generation from PV modules, providing a safe working environment.

EMI

See →electromagnetic interference.

EMIS

Abbreviation for →energy management and information system.

emission credits

See →carbon credit certificate.

emission reduction

See →greenhouse gas emission reduction.

emission-free city

Also known as an emission free city. A city that uses largescale →solar power plants, low-scale →solar arrays, →emission-free transport, and takes other necessary measures to reduce CO2 emissions to a zero-emission level, at which no harmful pollutants are emitted into the atmosphere.

emission-free electricity 

 223

emission-free electricity See →CO2 emission-free electricity. emission-free energy

See →CO2 emission-free energy.

emission-free power

See →CO2 emission-free electricity.

emission-free power plant

US Also known as a CO2 emission-free power station. A power plant that produces electrical energy without emitting carbon dioxide (CO2) into the Earth’s atmosphere, which is the main cause of →global warming. The most common types of emission-free power plants are solar, wind, hydro, geothermal, and nuclear. Although nuclear and hydroelectric power plants do not release harmful greenhouse gases into the atmosphere, they have other environmental problems, such as hazardous nuclear waste and changing of natural habitats, which can have devastating consequences for some species.

emission-free power station

UK See →emission-free power plant.

emission-free transport

A transport that is based on the use of →zero-emission vehicles, such as hydrogen-powered fuel cell vehicles or battery-powered →electric vehicles. The main goal of an emission-free transport is CO2 reduction and, in the long run, completes decarbonization of the transportation sector, leading eventually to clean air free from harmful emissions.

emissions

All substances, especially pollutants, discharged into the air during combustion.

emissions compliance

A legal requirement for cars, trucks, engines, and business units to comply with the emission standards of a given country.

emissivity

The ratio of the amount of infrared radiation emitted by a body to the amount emitted by an ideal →blackbody at the same temperature. See also →thermal emittance.

emittance

See also →emissivity and →thermal emittance.

emitter

High-conductivity region in semiconductor devices. This term, which comes from transistor technology, is sometimes used to describe the top n-type layer of a silicon semiconductor between the →antireflection coating and the →p–n junction.

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emitter layer

A top layer of the semiconductor that is negatively doped with →phosphorus atoms to increase the conductivity of pure silicon semiconductor, initiate the flow of negative charge carriers (electrons) as well as to determine the flow direction of the same. See also →n-doped semiconductor layer.

emitter region

See →emitter layer.

e-mobility

See →electromobility.

empty space diffusion

The type of →diffusion in which dopant atoms fill empty places in the crystal lattice.

EMR

Abbreviation for →electromagnetic radiation.

EMS

Abbreviation for energy management software. See →energy management and information system.

EMT

Abbreviation for →electrical metallic tubing.

encapsulant

Material used to laminate solar cells to the front cover (glass) and backsheet (→Tedlar sheet). To achieve this, the encapsulant material must possess good bonding characteristics. In addition, it needs to be transparent, tough, durable, and resistant to harsh weather conditions. The most common material used for solar module encapsulation is EVA, which refers to →ethylene vinyl acetate.

encapsulated DC/DC converter

Power optimizer connected to each solar module to maximize the energy output of a solar system.

encapsulating glass

Glass used for solar module encapsulation.

encapsulation

A solar panel manufacturing technology in which solar cell strings are laminated to the front cover (glass layer) and backsheet (→Tedlar sheet) to provide hermetic sealing, electrical insulation, and good protection against harsh weather conditions. The encapsulation process is conducted in a →solar panel laminator, in which different solar module layers are heated to 150 °C (302 °F). The two EVA →ethylene vinyl acetate films, which are placed between the solar cell strings and the front glass and backsheet layers, melt into a gel and bond all layers together into a compact unity – a solar panel. The pressure and vacuum are applied to eliminate all air bubbles from the module, producing waterproof panels.

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encapsulation material

Material used for solar module encapsulation. See also →encapsulant.

encapsulation technology

Technology for solar module encapsulation. See also →encapsulation.

end clamp

A piece of solar panel mounting hardware that secures framed PV modules to mounting rails. In comparison to middle clamps that are installed between PV modules and secure two modules at the same time, end clamps hold the edges of the first and last PV modules of a string to the rail system. End clamps are usually made of anodized aluminum, which is resistant to corrosion. Two main types of end clamps are adjustable and nonadjustable end clamps.

end-of-charge voltage

Adjustable end-of-charge voltage in →electric vehicles (eV). By lowering the voltage at the end of charging, manufacturers avoid full charge to extend the service life.

energetic self-reliance

The ability to generate one’s own energy and supply one’s own needs, rather than relying on foreign energy supplies.

energy

Capacity to perform work. There are different types of energy: nuclear energy that is generated by two major nuclear processes: fission and fusion, chemical energy that is generated by diesel or gasoline combustion, or thermal energy that is generated by burning charcoal, wood, or gas. These types of energy are derived from the fossil fuels, such as coal, natural gas, and crude oil, and have a negative impact on the human health and the environment. Unlike these problematic energies, the radiant energy obtained from sunlight established itself as a leading →clean energy by converting solar radiation (electromagnetic energy) with help of photovoltaic technology into electricity or heat. According to the energy flow and its various conversion steps, the following forms of energy can be distinguished: →primary energy, →secondary energy, →final energy, and →useful energy.

energy amortization period

The period of time it takes for a solar system to pay back its initial cost. See also →amortization.

energy amortization time

See →energy amortization period.

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 energy audit

energy audit

An inspection of a house, typically performed by a qualified energy auditor, identifying how much energy a homeowner uses and what needs to be done to lower the energy bill.

energy auditor

Is a trained specialist who performs a house energy audit with the goal of finding ways to save energy. For instance, after identifying all thin walls, holes, and cracks in the house through which energy escapes, the energy auditor makes suggestions for fixing and retrofitting the house, based on the cost of the improvements, annual cost savings, return of investment, and other items of their analysis.

energy balance

A method of analysis based on the ratio of input of energy into system to output of energy from system. →Solar critics point out that the solar panel manufacturing process consumes a large amount of electricity, having potentially a negative energy balance. The energy balance analysis seeks to achieve the best possible use of energy. The amount of →useful energy delivered from a solar device should have a positive balance in relation to the amount of energy used to produce the given solar device and/or the amount of →primary energy (solar radiation source). The best possible use of energy includes a reduction of energy costs of PV device production by finding less energy-intensive manufacturing processes, for instance, the ones that use lower temperatures to process semiconductor material or the ones that require less silicon material. It also conducts a statistical analysis of percentage of lost solar radiation energy input due to →reflection, heating (module temperature over 25 °C [77 °F]), →recombination within PV cells and other energy loss factors. The actual measured values are compared against existing standard values of each specific type of energy loss with the goal to improve the overall efficiency and energy output of a PV module or other solar product.

energy band

Also known as band. An energy level consisting of electron orbitals, mostly the outermost shells of the atoms in a semiconductor. Two main energy bands are the conduction band, which is generally empty at absolute zero temperature and the valence band, which is full of electrons that are firmly kept in their orbits by the nuclear forces of atoms. When the electrons gain enough energy from

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sunlight, for example, thermal phonon energy or photon energy of light, they can bridge the →band gap and jump from the valence band into the conduction band. energy band gap

See →band gap.

energy bottleneck

An increased demand for power that many industrial plants and commercial facilities experience during daily peak periods. To avoid operation or service interruptions in the hours with the highest loads, industrial and commercial facilities can install solar PV arrays on their warehouse rooftops. By feeding electricity into the grid, solar systems provide a load relief to local utility companies, helping them indirectly meet the peak load and provide electricity when it is most needed.

energy carrier

Energy carrier is defined by ISO 13600 as a “substance or a phenomenon that can be used to produce mechanical work or heat or to operate chemical or physical processes.” Energy carriers include electric current, heat, and solid, liquid, and gaseous fuels.

energy conservation

Saving energy by reducing the amount of energy consumed or by skipping a work or operation altogether. For instance, when we open windows on the opposite sides of our home in summer and use natural ventilation to cool the house, we conserve energy by reducing the work of air conditioners. Another method to reduce the electricity consumption of an air conditioner and heating system is to turn up the thermostat two or three degrees in summer and down in winter. See also →convection.

energy conservation law

See →energy conservation regulation.

energy conservation regulation

A country- or statewide regulation that seeks to minimize the consumption of energy and resources as well as the damage to the natural environment. The positive effect of the regulation on energy conservation includes raising the awareness of businesses and public agencies about the ways to conserve the energy. Depending on the type, some regulations might even require that companies develop energy conservation management, imposing restrictions on the technical systems for heating, hot water supply, ventilation, or building envelope. Energy conservation

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regulation may also become burdensome to some companies by being too strict, increasing the costs of operation and reducing competitiveness. On the other side, conservation regulations that help companies save money on electric bills and foster economic growth find widespread acceptance. energy consumption

The amount of energy consumed by an individual or organization over a period of time. In the solar energy context, two energy consumption types are of main interest: electricity consumption and hot water consumption.

energy contribution potential

Recombination taking place at the front surface of a photovoltaic cell in the so-called emitter region, which is an n-type silicon region. As high recombination rates at the surface of the PV cell have a negative effect on current and voltage, resulting in current and voltage losses, the top surfaces are usually passivated with silicon dioxide (SiO2) to reduce the impact of surface recombination.

energy conversion

The transformation of one form of energy into another, for example, solar energy into electrical or thermal energy.

energy conversion efficiency

See →conversion efficiency of solar cells.

energy converter

Any device that transforms one form of energy into another. For instance, a →heat exchanger is a type of energy converter that transforms heat energy into electrical energy.

energy deficit

In the context of the Earth’s energy balance, energy deficit is an insufficiency of incoming →insolation that a region in the polar latitudes between 35N and the →North Pole and between 35S and the →South Pole has, as opposed to an →energy surplus in tropical regions.

energy degradation

A process by which energy becomes unavailable to perform useful work. An example would be the energy degradation in hot water lines. It is the portion of thermal energy that is lost to the surroundings of hot water pipes and that never reaches the customer.

energy demand

The amount of energy required to heat all heated spaces in a building and provide electricity for lighting and all household appliances over a period of one year.

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energy demand management

See →demand side management.

energy density

Energy density is the key feature of rechargeable batteries, indicating how much energy a battery can store per unit of volume. It is measured in watt-hours per kilogram (Wh/ kg). See also →high energy density and →storage density.

energy dispersal

Also known as →entropy. Spreading out of thermal energy through →conduction, →convection, and →radiation. The heat can easily be lost and converted into unusable forms, as energy always changes from hot to cold and never the other way around, according to the second law of thermodynamics. When building a →passive solar house, the knowledge of energy dispersal and building materials can help a homeowner minimize their heat losses. When retrofitting an old building, →thermal imaging can detect window cracks, broken seals around the edge of chimneys, loose insulation, leaky air ducts, and other hidden places where warm air is escaping from a building.

energy dissipation

A process by which energy is lost through its conversion into heat. During the conversion of light into electricity in traditional crystalline silicon solar cells, a large amount of energy, in particular the energy coming from photons of blue and ultraviolet light, is lost as heat due to the very short relaxation time of hot electrons.

energy distribution

The process by which energy, electricity or heat, generated by a utility company or purchased by the same from renewable sources, such as solar and wind, is delivered through a transmission grid or a heat distribution network to customers.

energy efficiency

Using less energy to complete the same amount of work. For instance, if we replace an old energy-guzzling fridge with a new Energy Star certified refrigerator, the new appliance will complete the same work, but consume less energy in the process, leading to a lower energy bill and less greenhouse gas emissions.

Energy Efficiency Directive

(EED) Directive 2012/27/EU of the European Parliament and of the Council of 25 October 2012 on energy efficiency. The directive establishes a framework of binding energy

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 energy efficiency measures

efficiency measures for all EU countries to reach their 20% energy efficiency target by 2020. An update to the EED from November 2016 proposes a new 30% energy efficiency target for 2030. energy efficiency measures

Measures that a country, a city, or a company introduces to improve their energy efficiency. Energy efficiency measures can include measures to improve energy efficiency in buildings, to improve the energy performance of products and devices, or to increase the use of smart home and →energy management systems.

energy efficiency ratio

(EER) A rating system for measuring the efficiency of a →Heating, Ventilation, and Air Conditioning system. The ratio, which can be expressed as Btu/Wh, indicates how much heat is added or removed, measured in British thermal units (Btu) per hour, for each watt of energy used.

energy equation

All the energy inputs and outputs that occur within a specified area, such as region, country, or continent.

energy flux

The rate of transfer of energy per unit area.

energy flux density

See →energy flux.

energy gap

See →band gap.

energy generation

Energy generated by converting other forms of energy, such as solar, wind, hydro power, or fossil fuels, into electrical or thermal energy.

energy imbalance

Difference between an hourly scheduled amount and an hourly actually delivered amount of electrical energy to a load within an ancillary service area.

energy imbalance service

An →ancillary service that manages deviations between an hourly scheduled amount and an hourly actually delivered amount of electrical energy to a load within an ancillary service area.

energy independence

At the macrolevel, one of the sustainable ways for a nation to gain energy independence is to lower their electricity and gas consumption and support solar and other renewable energies with its laws. Energy independence makes a country safer, as it does not rely on foreign imports of oil and natural gas and it is not tied to constant supply and price fluctuations.

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At the microlevel, one of the simplest ways for home owners to gain energy independence is to install solar modules on their property. Generating electricity with solar energy at home is a convenient way to gain more control over energy supply, as the power generating system is always accessible and requires a minimal amount of maintenance and upgrades. Any excess electricity produced during the day is fed back into the grid at a favorable, low feed-in tariff and used at night or on cloudy days. energy input

The amount of energy that enters a system, for instance the amount of direct current (DC) generated by PV modules entering a →solar inverter.

energy investment tax credit

Federal tax break that usually covers 30% of solar-installation cost.

energy label

A label attached to an appliance, such as →HVAC, refrigerator, or lighting, displaying the energy efficiency of a given device, based on a certain classification type. For instance, according to the European Union (EU) energy label classification system, products are labeled on a scale of A+++ (green, the most energy efficient) to G (red, the least energy efficient).

energy level

Also known as energy state. A constant value of energy that a quantum mechanical system, for example, an electron, can have. Two energy levels (stationary states of constant energy) that might be assumed by electrons in a PV cell are: →ground state and →excited state. At nighttime, electrons are in the ground state, which is described as the lowest energy level of electrons in a semiconductor material of a solar panel at absolute zero temperature. As the sun is rising in the morning and the light with →photon energies greater than the →band gap falls onto the semiconductor material, electrons become excited and are raised from the lower energy level to a higher energy level, at which they gain enough energy to jump up from the →valence band into the →conduction band.

energy loss

See →power loss.

energy loss coefficient

A coefficient used to calculate the energy (heat) losses of a →solar collector or a solar–thermal piping system to the environment.

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energy management

The management of supply and demand of electrical and thermal energy at the large utility scale by a grid operator or at the small scale by a household or business owner. The major task of a grid operator is to ensure a constant balance between supply and demand of electric power, regulating the inconsistency in the output frequency and maintaining scheduled frequency. Homeowners and business owners can reduce their electricity and heat consumption by installing a solar array, sealing all gaps and openings in the building envelope, using an →energy management and information system and various other energy saving techniques.

energy management and control system

(EMCS) See →energy management and information system.

energy management and information system

(EMIS) A system that monitors, analyzes, and manages energy consumption at home or at a commercial or industrial facility. The EMIS can typically be customized by users and companies to meet their specific needs. Depending on the size of the building and the number of monitored appliances, the EMIS can include different types of metering devices and energy tracking and analytical tools. The EMIS software can be connected to existing breaker panels, sensors, and controller hardware in the building or the EMIS metering modules can be attached to the appliances that should be monitored. The collected and graphically displayed information provides insight into energy consumption, identifying the electricity guzzlers and showing where to save. The energy management and information system helps homeowners and companies cut energy waste and costs, detect equipment faults, and operate their buildings and businesses more efficiently. See also the related term →smart energy management system.

energy management software

(EMS) See →energy management and information system.

energy management system

See →energy management and information system.

energy market

A physical and virtual space in which the commodity energy, for example, electricity or heat, is bought or sold. Energy markets consist of physical elements, such as the

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natural resources, institutions, infrastructure, and market participants (e.g., solar producers and electricity company), and financial elements that comprise the purchasing and selling of financial products derived from the physical energy. energy meter1

See →electricity meter.

energy meter2

See →heat meter.

energy mix

The specific arrangement of various primary energy sources, renewable or nonrenewable, which a country or a region uses to meet its energy needs. The energy mix of a country depends on the energy resources available to the country as well as the level of development. Coal burning accounts for 80% of the electricity production in China, whereas it represents 33% of the generated electricity in the USA. In spite of a different energy mix from country to country, fossil fuels still account for over 80% of the global energy mix. The goal of many governments around the world is to reduce the share of fossil fuels in favor of a more diversified renewable energy generation mix, consisting of solar, wind, hydro, geothermal, and biomass.

energy output

The amount of energy that exits a system, for instance, the amount of alternating current (AC) coming out of a →solar inverter.

energy payback period

See →energy payback time.

energy payback time

The period of time it takes for a solar system to generate as much energy as was needed for manufacturing of the system.

energy pile

Also known as a geothermal pile. A U-shaped, W-shaped, or spiral-shaped metal or plastic pipe buried into the subsoil to absorb and release thermal energy. Fluid, for example air, water, or refrigerant, is circulated by pumps through the underground loop system, which acts as a heat exchanger, extracting heat from the building into ground in summer and absorbing geothermal heat from subsurface and transporting it into the building in winter. The energy pile is a cost-effective way to heat and cool a building. It requires a minimum amount of electricity used by pumps, which can also be powered by a photovoltaic module.

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energy policy

A set of plans and actions a government takes to address issues related to the production, distribution, and consumption of diverse sources of energy. With the help of various programs, such as tax credit or energy conservation incentives, the government can steer energy development in a certain direction; for instance, increasing renewable energy production.

energy price

See →electricity price.

energy rating

An assessment based on testing or/and statistics of how much energy an appliance will use over a year. Energy rating is usually expressed in kilowatt hours per year (kWh/year).

energy rating system

A rating system that shows how energy efficient an appliance is. Often expressed in kilowatt hours per year (kWh/ year) or stars, a device with a good energy rating consumes less electricity than one with a low rating. An energy rating system allows buyers to compare side by side the energy efficiency of similar appliances.

energy related product

(ErP) A product that does not use energy but has an impact on energy consumption during use, such as a window.

Energy Related Products (ErP directive) The European Union’s directive that proDirective vides an EU-wide framework for improving the environmental performance of →energy-using products as well as →energy related products. In November 2009, the ErP directive replaced the Eco-Design Directive (EuP). energy requirement

See →energy demand.

energy resource

See →energy source.

energy saving regulation

A regulation that sets energy saving standards for residential and commercial buildings. This includes, for instance, thermal insulation standards that must be observed during the refurbishment of an existing building or during the construction of a new building. Other regulations target efficiency improvements for commercial air conditioners, rooftop units, refrigeration, and electric motors. The agencies, such as the US →Department of Energy (DOE), develop and enforce energy saving regulations.

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energy savings

The reduction of energy consumption by switching to energy-saving appliances and avoiding the activities that require the use of electricity. Replacing existing incandescent bulbs with →LED bulbs or old household appliances, such as refrigerators, washers, and dryers, and central air conditioners, with energy-efficient →Energy Star appliances saves energy and reduces →greenhouse gas emissions. The line-drying of laundry outside instead of using a dryer is a behavioral change that contributes to the conservation of energy.

energy savings measures

See →energy saving regulation.

energy self-sufficient

The ability to generate one’s own energy and supply one’s own needs, rather than relying on foreign energy supplies.

energy self-sufficient region

See →energy independence.

energy self-supply

See →energy independence.

energy service

The task to be performed using energy, such as lighting or heating.

energy service provider

(ESP) A vendor that provides energy to a retail or end-use customer from conventional or →renewable energy sources.

energy shortage

Also known as electricity shortage or power shortage. A condition that occurs in an electrical network when all energy generation sources of the utility company are unable to produce enough electricity to supply all of their customers. Power shortages can be eliminated or at least reduced by integrating more solar energy resources via smart grid into the electrical network.

energy source

Energy sources are divided into nonrenewable energy sources, such as →fossil fuels and →nuclear energy, and renewable energy sources, such as solar, wind, hydropower, and geothermal.

energy standard of a building

A standard for new or retrofitted buildings that encourages sustainable building designs, materials, and solar technologies to maximize the energy efficiency of a commercial building or a residential house. This energy standard is

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 energy standard of a house

usually measured by the energy consumed for heating and cooling per each square meter or square foot of building surface over a period of one year: kWh/m2/year or kWh/ ft2/year. For instance, savings from added insulation to a home or building are expressed by kilowatt-hours which would be consumed for heating or cooling or by metric tons of CO2 emissions that will be avoided annually. energy standard of a house

See →energy standard of a building.

Energy Star appliance

An appliance with an Energy Star label that indicates that the device has met rigorous energy efficiency standards set by the US →Department of Energy and →Environmental Protection Agency.

energy state

See →energy level.

energy storage

The process of storing excess energy, electricity or heat, until it is needed, at night or on hazy and cloudy days.

energy storage system

A system for storing excess solar energy, electricity or heat, collected and generated during the day. As solar energy is a →variable energy resource dependent on five to eight full sun hours per day, it is vital to ensure the stability of the energy supply for further development and growth of the solar energy. Energy storage systems can be divided into two main categories: 1. →large-scale solar energy storage systems, such as →seasonal thermal energy storage systems or →pumped hydroelectric energy storage systems, which store energy for large industrial/residential complexes or entire districts, and 2. small-scale →home energy storage systems, such as →battery banks or →hot water storage tanks, which store energy only for one residential unit.

energy supply

Energy forms, such as electricity, natural gas, or fuel oil, made available by an energy provider and requested by a customer.

energy surplus

In the context of the Earth’s energy balance, energy surplus is an excess of incoming →insolation that a region in the tropical latitudes between 35N and 35S has, as opposed to an →energy deficit in polar regions.

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energy systems integration

(ESI) A holistic approach of tackling energy crisis by bringing together various energy systems and infrastructures and optimizing their cooperation. By data and information networks, the energy generation from numerous photovoltaic and solar–thermal systems is coordinated with the public utilities’ energy demand, scheduling, and dispatch. The operation of other infrastructure systems, such as energy smart meter infrastructure, electric transmission systems, and large-scale energy storage facilities, also needs to be harmonized with power generation and delivery systems. The integration and convergence of different systems and subsystems into a large interconnected and interdependent system has the goal to increase reliability, reduce costs, maximize efficiency of each sub-system, reduce carbon dioxide emissions, and minimize environmental impacts.

energy transformation

The change of energy from one form to another, for instance, from thermal energy or heat into mechanical energy in a steam engine.

energy transition

A significant structural change in an energy system, for example, a shift away from fossil fuels, such as coal, natural gas, and crude oil, toward a system that uses renewable energy sources, for instance, solar and wind energy.

energy transmission

The transport of electric or thermal energy through power lines or pipeline from a generating site, such as an industrial-scale →solar power plant or →solar thermal heating plant, to various end users. As a fast movement of energy from one region to another is required by →smart energy management systems in a new environment interwoven with numerous distributed energy resources, the future of solar energy will also depend on the development of more efficient transmission lines with less energy losses over long distances. See also →superconducting transmission lines (SCTL).

energy transmission network

An electricity transmission network or a piping system network through which electric or thermal energy is transported from generating sources, such as an industrial-scale →solar power plant or →solar thermal heating plant, to various customers.

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energy turn

See →energy turnaround.

energy turnaround1

A shift in direction from fossil fuels and nuclear to renewable energy sources, such as solar and wind.

energy turnaround2

See →yield factor.

energy yield

See →solar energy yield.

energy-efficient

Using as little energy as possible for the same amount of work.

energy-efficient building

A building that combines various techniques to reduce energy consumption, such as a →passive solar building design with most of its windows facing south, →shading2, and other energy-efficient solar design features; →energy management and information systems, showing homeowners where to save; and the use of solar thermal and photovoltaic systems.

energy-efficient building design

See →energy-efficient building design.

energy-efficient building materials

The employment of energy-efficient roof, walls, and glazing materials can significantly reduce energy consumption in a new building. Although energy-efficient materials can cost 20%–30% more than traditional building materials, they can save money in the long run, as they lead to lowered costs of heating and cooling. In addition, a reduced energy consumption translates directly into less →greenhouse gas emissions.

energy-efficient building standard

A building standard, also known as a passive house, which focuses on conserving energy through thick insulation, airtightness, ventilation, the choice of energy-efficient materials, and solar radiation and thermal control, including the essential part of a passive house: architecture of high-performance windows.

energy-efficient light bulb

→light emitting diode (LED) and →compact fluorescent light (CFL) bulbs are energy-efficient light bulbs that use far less electric power than a traditional →incandescent light bulb, which is slowly being phased out by various efficiency regulations. Although they cost more upfront than traditional incandescent bulbs, LEDs and CFLs can save money during their lifetime, because they use less energy.

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In addition to high-energy efficiency, LEDs are an environmentally conscious solution because they have no toxic elements, have a long lifespan, which translates into less CO2 emissions, and have a better quality of light distribution. energy-efficient lighting

See →energy-efficient light bulb.

energy-efficient technology

Any technology that reduces the amount of energy required to do useful work or provide products and services.

energy-isolating device

A manually operated device, such as a →disconnect switch or →emergency shut-off, which stops the transmission or release of energy.

energy-performance label

A label that shows how energy efficient a building or an appliance is.

energy-saving house

See →passive house.

energy-to-weight ratio

The capacity and a long-lasting performance of a battery are typically measured with help of an energy-to-weight ratio, which is expressed in watt-hours per kilogram (Wh/kg). The higher the energy density per kilogram, the better the performance and capacity of a battery. A battery with a high-energy density can store a large amount of energy and supply it to an electrical load for longer than a battery with a low-energy density.

energy-using product

A product that produces, uses, transfers, or measures energy, such as a computer, monitor, TV, and various household appliances.

engineering, procurement, and construction

(EPC) The contracting agreement and management of a large project, such as a solar array installation.

engraved cylinder

See →engraved roller.

engraved drum

See →engraved roller.

engraved roll

See →engraved roller.

engraved roller

An engraved cylinder that is employed in gravure printing. Engraved roller is associated with the contact technology in which the application of the ink to substrate is carried out through physical contact between the master and the substrate.

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entropy

A measure of the molecular disorder within an isolated system or the amount of energy that has been converted to unusable forms.

environment

The surroundings of a human being including all natural and living things.

Environment and Climate Change Canada

(ECCC) The former name was Environment Canada (EC). The Canadian Department of the Environment with the mandate to protect the environment, conserve Canada’s renewable resources, provide weather and meteorological information to all of Canada, and coordinate environmental policies and programs for the federal government.

Environment Canada

(EC) The former name for the Canadian Department of the Environment. See today’s department →Environment and Climate Change Canada.

environmental engineering

The application of science and technology to improve people’s health and protect humans, animals, and plants from the effects of adverse environmental effects, such as pollution, degradation of soil, or global warming.

environmental impact

Possible negative impact that the activities of people, industry, and services have on the environment.

environmental impact analysis

See →environmental impact assessment.

environmental impact assessment

Also known environmental impact analysis. An analysis of the possible environmental consequences, positive or negative, of a proposed legislation or a project, such as a solar installation or a large-scale construction.

Environmental Management System

EMS, set of processes and practices that enable an organization to reduce its environmental footprint.

environmental migrant

See →environmental refugee.

environmental protection

All policies, procedures, and activities aimed at protecting and conserving the natural environment from pollution and destruction, improving the health of humans, animals, and plants.

Environmental Protection Agency

(EPA) A United States agency for environmental protection with numerous offices, labs, and research centers across the country. The EPA’s mission is to protect human health

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and the environment. To accomplish this mission, the EPA sponsors and conducts research and also develops and enforces environmental regulations. environmental refugee

Person forced to leave his or her country because of the impacts of climate change.

environmental science

See →environmental engineering.

environmentally friendly Also known as eco-friendly, environment-friendly, earthfriendly, or nature-friendly. Not harmful to the environment and nature. environmentally friendly Also known as environmentally friendly power transmisenergy transmission sion. Energy transmission that utilizes specially designed devices and components that pose a smaller risk to environment. For instance, the use of biodegradable ester fluids in transformers instead of conventional transformer oils significantly reduces environmental risk. environmentally friendly A house that employs different environmentally friendly house technologies, such as →passive solar building design, →passive cooling techniques, and the integration of photovoltaic and solar thermal systems, in order to minimize CO2 emissions and other negative impacts of the house on the environment. environmentally friendly See →environmentally friendly energy transmission. power transmission environmentallyconscious

See →environmentally friendly.

environmentally-friendly See →environmentally friendly. environmentally-sound

See →environmentally friendly.

EPA

Abbreviation for →Environmental Protection Agency.

EPC

Abbreviation for →engineering, procurement, and construction.

epitaxial film

A crystalline overlayer that is deposited on a crystalline substrate, displaying the same lattice structure and crystallographic orientation as the underlying crystalline substrate.

epitaxial growth

See →epitaxial growth process.

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 epitaxial growth process

Epitaxial Growth

epitaxial growth process

Growth of crystalline silicon layers on a silicon substrate in such a way that the structure and crystallographic orientation of the substrate are precisely replicated in the epitaxial layer. There are two types of epitaxial growth: →homoepitaxy, in which growth layers and substrate consist of the same material, and →heteroepitaxy, in which growth layers and substrate consist of different materials.

epitaxial growth rate

See →deposition rate.

epitaxial layer

See →epitaxial film.

epitaxial layer structure

See →epitaxial structure.

epitaxial process

See →epitaxial growth process.

epitaxial silicon solar cell

A solar cell whose silicon semiconductor wafer is produced by growing a crystalline silicon thin film on a crystalline silicon substrate. An epitaxially grown thin film reproduces the structure and crystallographic orientation of the underlying substrate.

epitaxial silicon wafer

A semiconductor wafer that is manufactured by growing a crystalline silicon thin film on a crystalline silicon substrate. The epitaxial film replicates the morphology and crystallographic orientation of the underlying substrate.

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The →molecular beam epitaxy (MBE) or various types of →chemical vapor deposition, for example, →CVD, →APCVD, or →MOCVD, are used for growing →epitaxial layers on the surface of a crystalline silicon substrate. epitaxial solar cell

See →epitaxial silicon solar cell.

epitaxial structure

A structure of the →epitaxial film that has the same lattice configuration as the underlying crystalline substrate. The crystalline substrate acts as a template or a →seed crystal from which epitaxial layers are grown.

epitaxial wafer

See →epitaxial silicon wafer.

epitaxy

The growth of a crystalline silicon layer on a crystalline silicon substrate in such a manner that the layer has the same structure and crystallographic orientation as the underlying crystalline substrate.

epitaxy reactor

A reactor in which an →epitaxial growth process takes place. See also →metal-organic chemical vapor deposition.

epoxy foam

Also known as expanding foam. A solid foam that expands over time as it dries and hardens. Epoxy foam is used for sealing energy-wasting cracks or gaps in old and new building structures. Expanding foam has many advantages, including providing waterproofing, air barrier, sound insulation, and an added degree of structural support.

EPRI

Abbreviation for →Electric Power Research Institute.

EQE

Abbreviation for →external quantum efficiency.

equalization

See →equalizing charge.

equalization charge

See →equalizing charge.

equalization process

See →equalizing charge.

equalizing charge

A periodic battery maintenance process, in which deep-cycle lead-acid batteries are deliberately overcharged (5%–10% of the specified charge level) to remove lead sulfates from plates and ensure that all cells are restored to an equal state of charge. The batteries will last longer if they are equalized at least every three months.

equalizing process

See →equalizing charge.

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equalizing 

Periodic overcharging of batteries to remove lead sulfates from plates and ensure a better charge performance.

equation of time

The difference between →apparent solar time, as measured by a sundial, and →local mean time or standard time, as displayed on a watch.

equator

Imaginary line that divides the earth into the northern and southern hemispheres.

equilibration

In the energy management field, the act of balancing between numerous supply and demand variables with the goal of bringing a highly complex system with different tendencies into the state of equilibrium.

equinox

The time of the year when the sun is directly above the equator and daytime and nighttime are nearly of equal length, 12 h each. It occurs twice a year, usually on March 20 or 21 and September 22 or 23. Accordingly, they are two kinds of equinoxes: spring equinox and fall equinox. Summer solstice Equinox

Winter solstice W

S

N

E

Equinox

erg

Unit of work in the CGS (centimeter–gram–second) system. A →joule is 10,000,000 ergs.

ERP

Abbreviation for →energy related product.

ESEER 

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ESEER

Abbreviation for →European seasonal energy efficiency ratio.

ESI

Abbreviation for →energy systems integration.

ESP

Abbreviation for →energy service provider.

ESRL

Abbreviation for →Earth System Research Laboratory.

estival solstice

See →summer solstice.

ESTTP

Abbreviation for →European Solar Thermal Technology Platform.

etch bath

See →etching solution.

etch bias

The difference between the width of the →etched trench and the width of the →etch mask. We say that →isotropic etching as an uncontrolled uniform etching in all directions has a large bias, because there is a significant difference between the etched lateral line and the mask, resulting in overetching and undercutting of the mask.

etch chamber

See →etching chamber.

etch chemical

See →etchant.

etch depth

The depth of the etched trench is typically controlled by the etching time. The control of etched depth and stability of the high-precision shape with minimal edge defects are critical to wafer performance. In general, →wet etching offers a small amount of control over fine edges and the depth of a groove because it is mostly based on →isotropic etching. By contrast, →dry etching offers a better control over the depth of a conducting channel since the etching process can be instantly stopped and started at any time. See also →etch-stop.

etch directionality

Measure of comparative etch rates in different directions, for example, vertical versus horizontal.

etch factor

The ratio of etched depth of lateral etching (undercutting). An etch ratio of 4:2 means that there are 2 units of sideways etch for every four unites of downward etch. The thicker the material that is etched, the longer it takes for the →etchant to dissolve the material.

etch gas

See →etching gas.

etch groove

See →etched trench.

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 etch mask

etch mask

A mask that protects the selected areas of a wafer from liquid or gaseous etching chemicals. In addition to its masking function, this protective film defines the patterns along which the material is etched away, forming conducting channels. The preferred masking materials are: photoresist, silicon dioxide (SiO2), silicon nitride (Si3N4, more durable mask), black-wax, and chromium (Cr). Etch mask

Anisotropic

Isotropic

Etch Mask

etch moat

A U-shaped groove in a material created by the etching process.

etch patterns

Patterns that are created in semiconductor materials by selective etching. Etch patterns are typically formed by masking the material with help of →photoresist or other →etch masks, defining the borders of the unwanted material. The channels in the mask are etched away and then filled with conductive materials.

etch pit

See →etched trench.

etch polish

The process of wetting silicon wafers from below with the etching solution to etch-polish them.

etch profile

See →etching profile.

etch rate

A rate at which a layer of material is removed during an etching process. In other words, it is a rate of dissolution of solid materials. Etch rates depend on →etchant, treated material, and the type of etching. Changing one of the parameters, such as temperature of etchant or concentration of etchant (increasing or decreasing the amount of certain chemical elements within the etching solution), will have a direct impact on the etch rate. In

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→isotropic etching, etch rate is the same in all directions, whereas in →anisotropic etching, the etch rate depends upon orientation to crystalline planes and is different in horizontal and vertical direction. Measuring and monitoring the etch rate is crucial for precise material removal, as the depth of the etched trench is often controlled by the etching time. It is usually measured in →angstroms per minute (Å/m) or →micrometer per minute (µm/m). etch ratio

See →etch factor.

etch reactor

A type of reactor in which a plasma etching process takes place. The etching gas is introduced into a heated reaction chamber to produce chemical reactions with the semiconductor surface and remove the unmasked silicon material in the process. See →plasma etch reactor.

etch resist

The material that is used in a wafer →etching process and acts as an →etch mask, protecting the selected areas of a wafer from liquid or gaseous etching chemicals. The →photoresist serves as the etch resist, defining the surface layer circuitry of the wafer or the borders of the unwanted material that should be etched away.

etch selectivity

A ratio of etch rates of different materials, for example, the masking material or the substrate material.

etch uniformity

A measure of the process repeatability in wafer etching.

etchant

A chemical in either liquid or gaseous state used to remove materials from unmasked areas of a →wafer. Carefully chosen chemicals are selected to etch different materials. The following liquid etchants are applied to →silicon (Si) during a wet etching process: potassium hydroxide (KOH), ethylenediamine pyrocatechol (EDP), nitric acid (HNO3) + hydrofluoric acid (HF), and tetramethylammonium hydroxide (TMAH). The liquid etchants, hydrofluoric acid (HF) and buffered oxide etch (BOE), are applied to →silicon dioxide (SiO2) during a wet etching process. The phosphoric acid (H3PO4) is applied to →silicon nitride (Si3N4) and hydrogen peroxide–ammonia (H2O2–NH3) to →gallium arsenide (GaAs). The following gaseous etchants are applied to silicon (Si) during a dry etching process: tetrafluoromethane (CF4), sulfur hexafluoride (SF6), nitrogen trifluoride (NF3), chlorine

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 etchant gas

gas (Cl2), dichlorodifluoromethane (CCl2F2). The following gaseous etchants are applied to silicon dioxide (SiO2) during a dry etching process: tetrafluoromethane (CF4), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3). etchant gas

See →etching gas.

etched depth

See →etch depth.

etched trench

A groove in a semiconductor material created by the etching process. The control over the groove depth and shape is one of the crucial factors for cell performance. The etched shape is controlled by the orientation of mask edge and the details of the mask pattern. The following trench profiles are known: V-grooves, square trenches, rectangular trenches, moats, pyramidal pits, and pyramidal cavities.

etcher

A person who etches designs into various materials.

etching

A process of selective physical or chemical removal of material along the well-defined patterns formed on the semiconductor surface in the fabrication of photovoltaic wafers. The two main types of etching are →wet etching and →dry etching.

etching agent

See →etchant.

etching bath

See →etching solution.

etching chamber

Also known as etch chamber. A reaction chamber of an etch reactor in which a plasma etching process takes place.

etching depth

See →etch depth.

etching directionality

See →etch directionality.

etching factor

See →etch factor.

etching fluid

See →etching solution.

etching gas

Also known as etchant gas or etch gas. Gas used for etching a silicon semiconductor wafer surface, creating channels that are then filled with conductive materials. Instead of the use of liquid chemicals as in a →wet etching process, the chemical dry etching process uses plasma to generate gas radicals that attack the silicon surface. First, a →photoresist mask is deposited on the wafer using a →photolithographic process to protect the parts of the wafer that should

etching ground 

 249

not be etched and define contact holes. After that, the etching gas is introduced into the reaction chamber, reacting with the semiconductor surface and removing the unmasked silicon material. The following gaseous etchants are applied to silicon (Si) during a dry etching process: tetrafluoromethane (CF4), sulfur hexafluoride (SF6), nitrogen trifluoride (NF3), chlorine gas (Cl2), and dichlorodifluoromethane (CCl2F2). The following gaseous etchants are applied to silicon dioxide (SiO2) during a dry etching process: tetrafluoromethane (CF4), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3). etching ground

See →etch-resistant layer.

etching machine

Equipment for the removal of silicon layers from unmasked areas of a wafer by means of wet etching. A typical etching machine includes processes, such as etching, neutralization, rinsing baths, and drying.

etching mask

See →etch mask.

etching profile

Also known as etch profile. The outline of the →etched trench created during the →etching process. Two main etching profile types are: isotropic etching profile and anisotropic etching profile. The isotropic etching profile does not display geometrically straight walls but a U-shaped profile with horizontal undercutting of the masked layer, which is a result of isotropic uniform etching in all directions. By contrast, the anisotropic etching profile is a profile that exhibits geometrically straight walls of the etch groove. The usual sidewall shapes are: rectangular-shaped, positive sloping, and negative sloping.

etching ratio

See →etch factor.

etching resist

See →etch resist.

etching solution

Also known as an etch bath or →etchant. An acid solution that dissolves the unwanted material from unmasked areas of a →wafer. The wafer covered with →etch masks is immersed into the etching solution that etches the semiconductor material in a uniform manner until the preferred channel structure is developed.

etching technique

Two major etching techniques are →wet etching and →dry etching.

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 etching time

etching time

The time it takes an →etchant to eat away the material. It is important to know the →etch rate for a certain material in order to control the depth of an →etched trench with etching time.

etching-ground

See →etch-resistant layer.

etch-mask

See →etch mask.

etch-resistant layer

A film that is resistant to liquid or gaseous etching chemicals and as such is used as an →etch mask in a wafer →etching process.

etch-resistant material

See →etch resist.

etch-stop

A system that enables termination of the etching process at a controllable depth.

ethyl acetate

(CH3COOC2H5) A colorless liquid made from acetic acid and ethanol. Ethyl acetate is employed as an antisolvent in fabrication of perovskite solar cells to optimize morphology of perovskite thin films. During spin coating, ethyl acetate is added to the film, acting as a moisture absorber that protects perovskite intermediate phases from airborne water and encourages rapid crystal formation of the perovskite film.

ethyl acetate species

→Ethyl acetate species can be used as a solvent in dopant ink compositions for the manufacture of solar cells.

ethylene glycol

An organic compound that is often used as an →antifreeze or →heat transfer fluid in →heat transfer systems. Due to its toxicity, ethylene glycol should only be utilized in a →closed-loop system.

ethylene vinyl acetate

(EVA) is a copolymer consisting of ethylene and vinyl acetate. This elastic yet tough material with excellent transparency and bonding properties is a major encapsulation material used in the manufacture of photovoltaic crystalline silicon, thin-film, and BIPV modules.

ethylene vinyl acetate film

Also known as EVA film. A film consisting of ethylene and vinyl acetate that is used to encapsulate solar cells. It is installed between the glass cover and the photovoltaic cells in a solar module. The EVA layer shows the following advantages: resistivity, thermal stability, durability, transparency, lasting adhesive bonding to PV glass, and flame retardancy.

ethylene vinyl acetate sheet 

 251

ethylene vinyl acetate sheet

See →ethylene vinyl acetate film.

ETR

Abbreviation for →extraterrestrial radiation.

EU energy label

See →European Union energy label.

EU energy market

A unified energy market of the European Union (EU) that is bound by EU law and energy policies, seeking to reduce fossil fuel production, lessen their dependence on energy supplies from foreign countries, and support and promote sustainable energy generation.

EUP

Abbreviation for →energy-using product.

European Center for Medium Range Weather Forecasting

(ECMWF) An intergovernmental organization that acts as a research institute and weather prediction service, specializing in numerical weather predictions. The ECMWF, based in Reading, United Kingdom, is renowned for its accurate medium-range weather forecasts that the center delivers to its 34 member states around the clock. In addition to numerical weather forecasts, the ECMWF also provides air quality and ocean circulation analysis as well as atmospheric and climate monitoring.

European Energy Efficiency Directive

(EEED) Seeks solutions for higher energy independence and efficiency in the EU.

European seasonal energy efficiency ratio

(ESEER) A measure of the cooling efficiency of →air conditioners in Europe. See also →seasonal energy efficiency ratio.

European Solar Thermal Technology Platform

(ESTTP) A platform established by the European solar thermal industry and research centers in June 2005 with the goal to foster research and accelerate the development of solar thermal technology across Europe.

European Union energy label

Also known as EU energy label. A label affixed to an appliance, such as →HVAC, refrigerator, or lighting, displaying how the device ranks according to the EU Energy Label system, which classifies products on a scale of A+++ (green, the most energy efficient) to G (red, the least energy efficient).

EUVL

See →extreme ultraviolet lithography.

eV

Abbreviation for →electron volt and →electric vehicle.

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 EV charging station

EV charging station

See →electric vehicle charging station.

EVA

Abbreviation for →ethylene vinyl acetate.

EVA discoloration

The optical degradation of the encapsulant →ethylene vinyl acetate (EVA), resulting in power loss and a reduced aesthetic appeal of the affected solar cell. See also →discoloration of solar cells.

EVA film

See →ethylene vinyl acetate film.

EVA layer

See →ethylene vinyl acetate film.

EVA sheet

See →ethylene vinyl acetate film.

evacuated chamber

See →vacuum chamber.

evacuated tube collector See →evacuated-tube collector. evacuated-tube collector Also known as a solar thermal tube collector or tube collector. A solar water-heating system that heats water or another heat-transfer liquid in transparent glass tubes. Similar to thermos bottle, each glass tube has another thinner glass tube within, containing →heat transfer fluid. Although the composition and mechanism of the inner tube that absorbs the solar irradiation varies widely from one model to another, they all share the same function, and that is the absorption and transfer of the heat to the manifold to which they are connected. The manifold (heat exchanger) circulates then the heated fluid throughout the system. The inner tube is separated from the outer tube by a vacuum that functions as an efficient insulator. It reduces the thermal loss and helps the inner tube maintain the collected heat. This means that even though there are low winter temperatures outside and the outer tube is relatively cool, the liquid in the inner tube will still be able to reach and maintain high temperatures. That is why the evacuated tube collectors are a far better option in colder climates than →flat-plate collectors or →batch collectors. However, due to their more advanced and complex technology, they are more expensive than flat-plate or batch collectors.

evacuated-tube collector system 

 253

Hot water OUT

Heat transfer

Solar radiation

Copper manifold (heat exchanger)

Cold water IN

Individual evacuated tube Heat pipe Absorber plate

Evacuated-tube Collector

evacuated-tube collector See →evacuated-tube collector. system evacuated-tube solar collector

See →evacuated-tube collector.

evaporant

Target material to be evaporated and deposited onto the substrate in a PVD →evaporation process.

evaporation boat

In a PVD →thermal evaporation process, a thin sheet metal piece with a recess into which the target material to be evaporated and deposited is placed. Evaporation boats are made up of materials that are able to withstand high temperatures, for example, tungsten, molybdenum, molybdenum-lanthanum (ML), molybdenum-yttrium oxide (MY), or tantalum. After being heated up to a high-temperature point, the material first melts in the boat and then evaporates into a gaseous phase.

evaporation1

The changing of a liquid into a vapor. The evaporation of water begins at 0 °C and 32 °F. As the temperature increases,

254 

 evaporation2

so does the motion of the atoms or molecules in a liquid and thus the rate of evaporation. The excited particles change from a slow movement within a structure to a rapid free movement (zooming) in all directions, leading to a faster separation process and thus the more dynamic evaporation. evaporation2

A type of →physical vapor deposition (PVD) process for manufacturing of thin-film semiconductor devices. PVD by evaporation begins with the placement of thoroughly cleaned substrates and target material into a vacuum chamber. A vacuum pump generates a vacuum in the reaction chamber with pressures of less than 10−5 Torr. The material is then heated to its vaporization point. The vacuum allows the created vapor stream to traverse relatively unobstructed to its target objects, the substrates, and to condense on the surface of the substrates as a thin semiconductor layer. The major methods of PVD by evaporation include →thermal evaporation, →electron beam physical vapor deposition, and →resistive evaporation. The evaporation causes less damage to substrate surface than →sputtering, whose high-energy particle bombardment might damage the substrate. Another advantage of the evaporation method is high purity of the film. This is why it is generally used in the deposition of Schottky contacts on a wafer. Evaporation has higher deposition rates than sputtering and evaporation equipment is less expensive than the more complex sputtering equipment.

evaporative cooler

A device that filters outside air through a pad soaked with water, cools it down through the water evaporation process, and finally distributes the cooled air through duct work into different rooms of a building. Solar energy can be used to power evaporative coolers.

evaporative cooling

A process in which outside air is passed through a pad soaked with water, cooled through the water evaporation process, and distributed through duct work into different rooms of a building.

evapotranspiration

Is a natural process, a part of the water cycle, that includes the evaporation from the land surface and transpiration from plants.

EVSE

Abbreviation for electric vehicle supply equipment. See →electric vehicle charging station.

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e-waste

See →electronic waste.

excess electricity

When the household appliances are not in use, the surplus electricity generated by solar panels is fed into the grid.

excess energy

Surplus energy generated by a photovoltaic or solar– thermal system that is either fed into the utility grid or stored in one of the →energy storage systems.

excited electron

An electron is excited, if it has a higher energy level than the zero-point energy in the →ground state. When the light with →photon energies greater than the →band gap falls onto the semiconductor material, an electron becomes excited and is raised to a higher energy level, gaining enough energy to jump up from the →valence band into the →conduction band.

excited energy level

See →excited state.

excited particle

See →excited electron.

excited state

A higher energy level to which an electron is raised when the photons of light fall onto the semiconductor material of a solar cell.

exciton

A mobile, electrically neutral entity, a quasiparticle, which stands for the concentration of energy in a semiconductor initiated by an excited electron that is bound to an associated, positive hole.

exciton binding energy

The energy required to free an electron from a molecule, atom, or nucleus.

expandability

One of the major and beloved features of photovoltaic and solar thermal technology that allows solar systems to be expended at any time. The modular nature of solar system components gives the opportunity to users to always add new solar panels to the existing system without any difficulty and hence meet the new power requirements, for instance, when two additional persons move into the house.

expanding foam

See →epoxy foam.

expansion tank

See →expansion vessel.

expansion vessel

Also known as an expansion tank. In heating systems and domestic hot water systems, a vessel used to collect the

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 export meter

increased volume of →heat transfer fluid that tend to expand when heated, filling any available space in a →closed-loop system. By accommodating the fluid expansion in the pressurized closed-loop system, the expansion tank acts as a control mechanism that keeps critical pressure limits under control. export meter

A meter that measures the amount of solar-generated electricity exported to the public electricity grid. See also →smart meter.

exterior roller shade

Prevents the solar heat from entering the house directly through windows and indirectly through walls. A house design that includes exterior roller shades is considered an effective →passive cooling technique.

exterior shutter

Prevents the solar heat from entering the house through windows. The use of exterior shutters is considered an effective →passive cooling technique.

exterior sunshade

Passive cooling.

external quantum efficiency

(EQE) A type of →quantum efficiency, indicating the ratio of the number of charge carriers generated by the solar cell to the number of all the photons incident on a solar cell, including the outcome of optical losses such as transmission and reflection. See also →internal quantum efficiency (IQE).

external shading devices

Include →awnings, →overhangs, →horizontal shading fins, →vertical shading fins, →light shelves, →exterior roller shades, and →deciduous trees. External shading devices prevent the solar heat from entering the house directly through windows and indirectly through walls. A house design that includes external shading systems is considered an effective →passive cooling technique.

external shading systems

See →external shading devices.

external sun protection

See →external shading devices and →passive cooling.

extraterrestrial radiation

(ETR) Also known as top-of-atmosphere irradiance. The amount of solar radiation expressed in Watts per square meter (W/m2) at the top of the Earth’s atmosphere. The average solar radiation outside the earth’s atmosphere is 1,367 W/m2.

extreme ultraviolet lithography  

 257

extreme ultraviolet lithography

(EUVL) Also known as extreme UV lithography. A lithography technique that focuses light through lenses to transfer a pattern to a →substrate. The ultraviolet light source, such as super-charged xenon gas, is used to cast light onto the substrate, carving precise patterns on the →silicon wafer. The EUVL is characterized by the highest pattern transfer resolution in optical lithography.

extreme UV lithography

(EUVL) See →extreme ultraviolet lithography.

extrinsic conduction

Also known as extrinsic conductivity. A low-temperature conduction in semiconductor materials caused by extra electrons from impurity atoms, such as →phosphorus, rather than by heat.

extrinsic conductivity

See →extrinsic conduction.

extrinsic semiconductor A type of semiconductor that has been doped with a small amount of →impurities in form of →n-type dopants and →p-type dopants, with the goal to increase the electrical conductivity of the semiconductor material.

F

facade greening

A passive cooling technique for reducing heat inside and outside of a building by growing climbing plants, such as ivy.

facade integration

Integration of photovoltaic modules into the façade of a building. See →solar façade.

facade-mounted PV plant See →solar façade and →building-integrated photovoltaics. facade-mounted PV system

See →solar façade and →building-integrated photovoltaics.

FACTS

Abbreviation for →flexible alternating current transmission system.

Fahrenheit

(°F) Unit of temperature, the English scale for measuring temperature. Water freezes at 32 °F and boils at 212 °F.

fail-safe

A mechanism designed to automatically switch to a safe mode in the event of a breakdown or malfunction.

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 failure monitoring

failure monitoring

Photovoltaic →monitoring platforms usually include the automatic detection of performance failures and troubleshooting. When the monitoring system detects a problem, it immediately sends a warning message.

fall equinox

Also known as autumnal equinox or September equinox, occurs once a year, usually on September 22 or 23. It is the time of the year when the sun is directly above the equator and daytime and nighttime are nearly of equal length, 12 h each. The September equinox marks the beginning of fall and the end of summer.

fast charging

Rapid charging of electric vehicles by means of a DC fast-charging station with a J1772™ combo connector, which is capable of delivering 400–600 VDC and filling up an 80-mi or 129-km battery pack in around 30 min. The car batteries must be specially engineered to accept a fast charge. Fast charging only works to 70% state-of-charge, while the rest of charging occurs at a slower rate. Some electric car makers discourage all too frequent rapid charging, as they believe that ultrafast charging might cause overheating and an accelerated degradation in lithium-ion batteries, reducing driving range and the lifetime of batteries in general.

fast ion conductor

See →solid electrolyte.

fast-charging station

See →DC fast-charging station for electric vehicles.

fault current

Any irregular electric current, for example, →short circuit.

fault detection and diagnosis

(FDD) A method used for an early detection and diagnosis of errors in an electrical system while the appliance is still operating. As the system is still functioning, the FDD can prevent faults from progressing to failures and reduce invisible performance losses, for instance, power losses in a faulty HVAC system. See also →fault detection and diagnosis tool.

fault detection and diagnosis tool

A software tool that monitors a system, for example, an →HVAC system, detects and diagnoses faults, and localizes where these occurred. The software typically functions on the principal of detection of a deviation from optimal system performance. As deviations are often associated with HVAC power losses, the tool makes a diagnosis, pinpointing

F-CHART 

 259

one or more root causes of problems. Fault localization is an important part of the fault and diagnosis process because it can be a challenging task to localize an error in highly complex systems, such as a →smart grid. F-CHART

PV system analysis software.

FDD

Abbreviation for →fault detection and diagnosis.

Federal Energy Regulatory Commission

(FERC) An independent US agency that monitors, investigates, and regulates the interstate transmission of electricity, natural gas, and oil, as well as wholesale electricity prices.

Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety

(BMUB) Bundesministerium für Umwelt, Naturschutz, Bau und Reaktorsicherheit. A ministry of the Federal Republic of Germany in charge of national environmental policy, environmental education, climate protection, and other environmental and sustainability promotional programs.

Federal Network Agency (BNetzA) Bundesnetzagentur. The German regulatory agency for electricity and gas, telecommunications, post, and rail. feed-in agreement

See →feed-in contract.

feed-in compensation

Compensation for electricity fed into the public electrical grid.

feed-in contract

A contract between the utility company and the solar energy producer that guarantees the compensation for electricity fed into the utility grid. It is typically a long-term contract covering a period of 15–20 years, during which the utility company is obliged to purchase solar power from PV owners at favorable feed-in rates, which are based on the cost of solar power generation.

feed-in management

A computer-supported remote control of →feed-in power coming from small-scale residential and utility-scale photovoltaic power plants by system operators. The goal is to remove bottlenecks, improve grid stability, and feed in the maximum amount of energy into the grid from PV plants by means of an intelligent feed-in power management.

feed-in meter

An instrument that measures the energy that is generated by a solar system and fed into the public power grid.

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 feed-in permit

feed-in permit

A permit issued by the local utility company, allowing solar energy producers to sign a long-term contract that guarantees the compensation for electricity fed into the utility grid.

feed-in power

Power fed into the electricity grid from residential photovoltaic systems.

feed-in power quantity

See →quantity regulation.

feed-in rate

A favorable rate above the retail price paid to solar energy producers by a utility company with the goal of encouraging the deployment of solar and other renewable energy sources.

feed-in tariff

(FIT) Also known as a green tariff. Compensation for electricity fed into the public electrical grid. A favorable feed-in rate is typically guaranteed to solar energy producers by the local utility company, which signs a long-term contract with them. The FIT is usually based on the costs of generating 1 kWh of solar electricity. The costs of generation typically include the funds invested into solar power plant, the financing charges, and the →operation and maintenance costs. The favorable tariff above the market rate was introduced in some countries to promote the deployment of solar energy and other renewable energy resources. In Germany and many other European countries, Australia, and in the US states of California, Hawaii, Oregon, and Vermont, grid operators are obliged to give priority to renewable energy sources when purchasing electricity. Accordingly, they cannot refuse to buy and pay compensation for electricity generated from solar producers. FITs have proved effective in spurring the rapid solar energy growth, the reduction of →greenhouse gases, job creation, and economic growth. The fixed feed-in rates can potentially lead to more stable electricity rates. On the flip side, as the number of solar power producers who adopt the FIT policy increases, the FIT is reduced and the cost of electricity to customers tends to rise.

feeding into the power grid

Solar owners, whose solar system is connected to the public electrical grid, are able to feed any excess power they produce into the power grid.

feedstock

Any bulk raw material converted to another form of fuel or an energy product.

femtosecond optics

See →femtosecond spectroscopy.

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 261

femtosecond spectroscopy

A spectroscopic method that utilizes ultrashort pulse lasers for the study of dynamical chemical processes on femtosecond time scales.

FERC

Abbreviation for →Federal Energy Regulatory Commission.

Fermi level

Fermi level is the highest energy level occupied by electrons in a semiconductor material at absolute zero temperature. This energy level can be located in the band gap between the highest →valence band and the lowest →conduction band. At 0 K all states below the Fermi level in the valence band are filled, and all above the Fermi level in the conduction band are empty. In the Fermi energy state at absolute zero, no electrons will have enough energy to bridge the →band gap. The Fermi energy level has a 50% probability of being occupied by an electron at any time. When electrons gain enough energy from sunlight, for example, thermal phonon energy or photon energy of light, they become excited and are able to bridge the band gap. After they jump from the valence band to the conduction band, the electrons start moving freely through the conduction band, proceeding from one silicon atom to another in a chain-reaction manner, since they are not tied to any atom. This free movement of electrons through the conduction band initiates the flow of photovoltaic DC electric current through the circuit.

FIB

Abbreviation for →focused ion beam.

Forbidden gap

Fermi level

EC

EC

EF Eg

Eg EF

EV

EV n-type

p-type

Fermi Level

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 FIB device

FIB device

See →focused ion-beam device.

fiber nickel cadmium battery

See →fiber-nickel-cadmium battery.

fiber optics

The technology that uses thin flexible fibers of glass or plastic to transmit light pulses to another location, as opposed to the use of copper wires to transmit electrical pulses over long distances.

fiberglass

Also known as glass-reinforced plastic (GRP) or fiberglass-reinforced plastic. A material composed of plastic reinforced by fine glass fibers. Fiberglass is commonly used as an insulation material, a thermal and sound barrier, in storage tanks, walls, and roofing, where it is installed between ceiling rafters.

fiberglass-reinforced composite

See →fiberglass.

fiberglass-reinforced plastic

See →fiberglass.

fiber–nickel–cadmium battery

(FNC) A long-lasting, low-maintenance battery type that does not require water additions or special ventilation.

fiber-optic

Relating to →fiber optics.

fiber-optic solar energy transmission

The transport of concentrated solar energy through highquality optical fibers. Broad-band solar radiation can be directly converted into coherent and narrow-band laser radiation by means of →solar-powered laser technology. The concentrated solar flux is strong enough to pump a solar laser. The technology of the fiber-optic solar energy transmission is still in an early stage of development. While in first prototype models solar energy can be transmitted by the optical fiber to a nearby storage tank or interior spaces of a building, the long-term objective is to eventually transport solar energy over long distances to a desirable place, for instance, from the hot Sahara Desert to cold weather regions of Northern Europe (→DESERTEC project), to carry out a useful work.

fiber-optic solar lighting

The type of lighting that utilizes a plastic or glass fiber to transmit light from a light source through optical fibers to another location, such as interiors of a building.

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fiber-optic solar lighting A system that collects sunlight by solar collectors and system guides it through optical fibers into interior spaces of a building that need to be lit. fiber-optical

Relating to →fiber optics.

field installation

Mounting of a solar–thermal or photovoltaic system on the proposed site.

field mounting

See →field installation.

fill factor

The ratio showing the relation between the actual maximum power from a PV cell to the ideal maximum power, which is a product of VOC and ISC. See →I–V curve.

filled band

In semiconductor physics, the lower valence band is filled with electrons, while the upper conduction band is empty or partially filled at zero Kelvin. By thermal excitation, electrons gain enough energy, for example, 1.1 eV in narrow band gaps, to bridge the “forbidden” energy gap and jump from the valence into the conduction band.

filling factor

See →fill factor.

film growth

The growth of a crystalline silicon layer on a silicon crystal substrate using the →chemical vapor deposition (CVD) or →molecular beam epitaxy (MBE) method.

final energy

The energy supplied to the end user for consumption, for instance, electricity from the wall outlet or hot water.

Fingers

Busbars

Fingers

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 finger

finger

Fingers are tiny silver conductive lines that are connected with two →busbars on each silicon solar wafer (see the figure on page 263). A grid of numerous fingers collect the electricity generated within the photoactive silicon semiconductor and transport it to the two busbars, which then conduct the electricity further through the module’s circuit.

fire-protection-equipped A solar module made of special materials and/or a fire-prosolar module tection layer to prevent fire risks. first-generation photovoltaic cell

Also known as a conventional or traditional solar cell. The type of photovoltaic cell, such as →monocrystalline silicon solar cell or →polycrystalline silicon solar cell, which is mainly based on silicon wafer manufacturing technology. Due to their high performance and quality, they account for the majority of all the photovoltaic modules seen in residential →roof-mounted solar arrays and ground-mounted solar arrays. Monocrystalline solar modules are durable and have a long lifespan. Their high efficiency of 22% still outperforms the majority of commercial nonsilicon solar modules. The major disadvantages of first-generation photovoltaic cells are the expensive manufacturing process, low performance at high temperatures, and rigid and bulky solar panels. See also →second-generation photovoltaic cell and →third-generation photovoltaic cell.

first-generation photovoltaics

Silicon wafer-based PV technology. A method for converting solar radiation into electricity by using →first-generation photovoltaic cells.

first-generation PV cell

See →first-generation photovoltaic cell.

first-generation solar cell

See →first-generation photovoltaic cell.

FIT

Abbreviation for →feed-in tariff.

fixed at latitude tilt

Means that the mounting structure is fixed at a year-round tilt angle that is equal to the latitude of a specific location.

fixed mount

See →fixed mounting system.

fixed mounting system

A mounting system fixed in place at an optimal year-round tilt angle.

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fixed rack mount

A fixed rack mount is a rigid, nonadjustable PV mounting structure that is oriented to the south and whose tilt angle is fixed in an optimal year-round position.

fixed-tilt array

See →fixed-tilt solar system.

fixed-tilt solar system

A solar system whose modules are fixed in place at an optimal year-round tilt angle.

flare

See →solar flare.

flasher

See →solar flasher.

flash-to-roof mounting

See →mechanically attached mounting.

flash-to-roof mounting system

See →mechanically attached mounting system.

flash-to-roof racking

See →mechanically attached mounting.

flash-to-roof racking system

See →mechanically attached mounting system.

flat glass

Flat transparent, pattern glass that is used as front glass in crystalline solar modules.

flat jumper

A type of flexible cable designed to be run under window sills, through door frames and other tight spots, when drilling through walls is not recommended.

flat photovoltaic module

See →flat-plate photovoltaic module.

flat photovoltaic panel

See →flat-plate photovoltaic module.

flat plate collector

See →flat-plate collector.

flat PV module

See →flat-plate photovoltaic module.

flat PV panel

See →flat-plate photovoltaic module.

flat roof installation

See →flat roof mounting.

flat roof mount

See →flat roof mounting system.

flat roof mounting

Installation of photovoltaic modules or solar thermal collectors on a flat roof. While many types of →solar thermal collectors can be mounted horizontally on flat roofs, photovoltaic modules require a fixed or flexible tilting structure for an optimum inclined position to the sun. See →flat roof mounting system.

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 flat roof mounting system

flat roof mounting system

Also known as flat roof mount. A support structure, typically an aluminum frame, for mounting and positioning photovoltaic (PV) modules or solar thermal collectors on a flat roof. There are two major types of flat roof mounting systems: fixed and adjustable. A fixed flat roof mount is a rigid, nonadjustable PV mounting structure whose tilt angle is fixed in an optimal year-round position, based on the site’s latitude. An adjustable flat roof mount is an adaptable PV mounting structure whose tilt angle can be manually adjusted each season to optimize the solar power output. More precise day-to-day adjustments to the sun can be achieved by adding a →solar tracker to the system. Flat roof mounting systems should be lightweight to avoid putting an additional ballast on the roof; however, they also need to be stable and wind resistant to prevent lifting of PV modules at high winds. These opposing forces have led to a dilemma in recent years that home owners and PV technicians face on a daily basis: installation with or without roof penetration. Although the application of mechanically attached mounting systems is a suggested practice by roofing and solar associations, ballasted mounting systems in which heavy ballasts, usually concrete blocks, are placed on the structure to weigh down the solar modules, are still a preferred method for many PV installers for two reasons. First, many solar owners tend to avoid drilling numerous holes in their roofs for a mounting structure at all costs, as these potentially lead to roof leaks. Secondly, the installation costs can be significantly reduced when a roofer does not need to be hired to install numerous impermeable flashings. On the other side, it is easier to conduct a routine roof inspection and maintenance in the properly installed mechanically attached mounting systems than in the ballasted mounting systems, which require a disassembling of a large portion of the PV system to find and repair a leak. Both systems require a structural engineer to evaluate the load capacity of the roof before the installation; however, the engineer must conduct more careful calculations in ballasted racking systems to ensure that the

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Flat-roof Mounting System

roof structure can carry not only the mounting structure and panels but also the additional weight of heavy concrete blocks. Another disadvantage of ballasted mounts is the blockage of drainage pathways, resulting in an accumulation of standing water on the roof. This can speed up roof degradation and increase the potential for water leakage. flat roof mounting triangle

A support structure, typically an aluminum frame in the shape of a triangle, upon which →photovoltaic modules are mounted. The base triangle can be a fixed flat roof mount with an optimal year-round tilt position or an adjustable flat roof mount with three seasonal tilt configurations: one for winter, one for spring and fall, and one for summer.

flat roof photovoltaic system

A photovoltaic system that is mounted on a flat roof.

flat roof PV system

See →flat roof photovoltaic system.

flat roof racking

See →flat roof mounting.

flat roof racking system

See →flat roof mounting system.

flat roof solar system

See →flat roof photovoltaic system.

flat roof stand

See →flat roof mounting system.

flat silicon substrate

A substrate without any roughening of the surface. The flat surface of a wafer reflects the incident light at the same angle as it hits the surface, causing significant optical losses that can be as high as 30%. To reduce reflection losses, the flat surface is textured by adding pyramids or other corrugated shapes that help trap light inside the cell and increase the probability of absorption.

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flat solar module

See →flat-plate photovoltaic module.

flat solar panel

See →flat-plate solar panel.

flat substrate

See →flat silicon substrate.

flat wire

See →tabbing wire.

flat-panel collector

See →flat-plate collector.

flat-panel solar collector See →flat-plate collector. flat-plate array

See →flat-plate photovoltaic array.

flat-plate collector

Is a solar water-heating system that heats water in enclosed copper tubes fitted to the heat-absorbing plate. The absorbing plate is usually a metal with high thermal conductivity covering the entire aperture area of the collector. It is painted black to increase absorptivity. The major function of the absorbing plate is to absorb the maximum amount of incoming solar radiation and to transfer the absorbed heat to the tubes containing water or another →heat transfer fluid. As copper tubes are much smaller in size (0.5″) than the ones used in →batch collectors (3–4″), they do not hold

Solar radiation Glazing

Hot water OUT

Cold water IN

Glazing frame Foam or aluminium insulation Heat absorbing riser tube Heat absorbing backplate

Manifold

Flat-Plate Collector

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much water. Therefore, hot water should be constantly circulated through the piping and stored in hot water storage cylinder. The pipe grid consists of tiny copper pipes that are welded to two copper manifolds: one at top and one at bottom. Copper heat absorbing fins are installed between pipes and connected to them to enable an effective thermal transfer. The pipe grid is placed in an insulated box that has glazing on the top side facing the sun to reduce heat loss. A tempered glass is usually used as a glazing material to provide a good protection against the elements. A patterned surface of the cover glass is a better solution than smooth glass surface, as it reduces reflection and thereby increases the absorption of sunlight. All components are held together by a light but solid aluminum frame shielding the box against strong wind. Flat-plate collectors are the most common collector type today as they are less expensive (but also less efficient) than →evacuated-tube collectors. Their flat form is aesthetically appealing and they perform equally well in both warmer and colder climates. In regions with temperatures below freezing, water will not freeze, as the operating range of the flat-plate collector allows even temperatures below 0 °F. flat-plate collector system

See →flat-plate collector.

flat-plate module

See →flat-plate photovoltaic module.

flat-plate panel

See →flat-plate solar panel.

flat-plate photovoltaic array

Group of nonconcentrating →flat-plate photovoltaic modules connected together to form a unified power production system.

flat-plate photovoltaic module

The most common nonconcentrating photovoltaic (PV) flat module that absorbs direct as well as diffuse light. Unlike concentrating modules that are only responsive to direct solar radiation and perform poorly with scattered radiation, the flat-plate PV modules work well not only on sunny days with clear-sky but also on cloudy days with diffuse solar radiation. The flat-plate PV modules can be mounted on a →fixed-tilt solar system or on a →single-axis or →dual-axis tracking system.

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 flat-plate photovoltaic panel

flat-plate photovoltaic panel

See →flat-plate photovoltaic module.

flat-plate photovoltaic system

See →flat-plate photovoltaic array.

flat-plate photovoltaics

As opposed to →concentrating photovoltaics that respond only to direct solar radiation, the flat-plate photovoltaics are a photovoltaic technology that converts both direct and diffuse solar radiation into electricity.

flat-plate PV

See →flat-plate photovoltaics.

flat-plate PV array

See →flat-plate photovoltaic array.

flat-plate PV module

See →flat-plate photovoltaic module.

flat-plate PV panel

See →flat-plate photovoltaic module.

flat-plate PV system

See →flat-plate photovoltaic array.

flat-plate solar collector See →flat-plate collector. flat-plate solar module

See →flat-plate photovoltaic module.

flat-plate solar panel

Any kind of nonconcentrating flat solar device, →flat-plate solar module or →flat-plate collector, which collects the solar radiation and uses it to generate electricity or to heat water.

flat-plate Stirling engine

A solar device that combines a flat-plate solar collector with a →Stirling engine to generate mechanical energy. The solar collector consists of a dark-coated plate, an air box, and a glass cover. The dark-coated plate of a solar collector is installed at the bottom of the solar box. It actively absorbs the solar radiation and converts it into heat. The heated air that is trapped under the insulated glass expands, pushing a piston that drives a flywheel. A displacer moves the air from the hot side to the cold side of the box. The cooling reduces the pressure in the cold side and causes the air to contract, pulling the piston up in the original position. A repeated cycle of expansion and contraction of air begins, creating flywheel momentum and continuous propulsion. The Stirling engine can power a generator that produces electrical power or conduct a different kind of mechanical work.

flat-plate system

Any kind of nonconcentrating flat solar system →flat-plate photovoltaic system or →flat-plate collector system.

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flexible AC transmission See →flexible alternating current transmission system. system flexible alternating current transmission system

(FACTS) Also known as flexible AC transmission system. According to the definition of the →Institute of Electrical and Electronics Engineers (IEEE), the FACTS are systems that incorporate power electronics-based and other static controllers to enhance controllability and increase power transfer capability. The FACTS systems optimize transmission quality and allow rapid voltage regulation and damping of active power oscillations. In general, the flexible AC transmission systems increase the reliability and stability of an AC network.

flexible film

A bendable thin photovoltaic layer that is affixed to a →flexible substrate by using the →chemical vapor deposition technology.

flexible layer

See →flexible film.

flexible metal conduit

(FMC) A conduit through which wires and cables used in PV installations are run. The flexible metal conduit is usually made of a high-strength aluminum alloy strip that protects electrical wiring in solar systems.

flexible photovoltaic module

See →flexible thin-film solar module.

flexible photovoltaic panel

See →flexible thin-film solar module.

flexible PV module

See →flexible thin-film solar module.

flexible PV panel

See →flexible thin-film solar module.

flexible solar module

See →flexible thin-film solar module.

flexible solar panel

See →flexible thin-film solar module.

flexible substrate

A bendable →substrate that is made of plastic, for example, low-cost polyethylene. Flexible substrates are used for the production of →thin-film solar modules.

flexible sun tube

Sun tube made of flexible material that transports daylight into interior spaces of a building to provide natural illumination. As flexible sun tubes can be bent around attic obstructions, they are suitable for installations where

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 flexible swimming pool heating system

straight runs of tubing are not possible. Due to the flexing in the tubing, the light is sometimes subject to intensive bending, resulting in illumination losses and slightly less light performance when compared to →rigid sun tubes. flexible swimming pool heating system

A system that uses flexible, unglazed solar thermal systems, such as →swimming pool absorbers or →solar pool covers, for heating swimming pool water.

flexible thin-film solar cell

A solar cell, in which thin semiconductor layers are affixed to a →flexible substrate. The semiconductor material is typically deposited on plastic substrates by using →chemical vapor deposition process.

flexible thin-film solar module

A module that consists of flexible thin-film solar cells. Flexible solar modules are lightweight, easy to install, bendable, and portable (see the figure on page 273). Unlike →rigid photovoltaic modules that are inflexible, heavy, bulky, and often require a support structure in form of a →mounting system, flexible thin-film solar modules can be easily affixed or even simply glued to the roof without screws and leak-causing roof penetrations. As they are light in weight and do not require a heavy mounting system, they do not add a significant additional weight to the roof. Flexible modules are more aerodynamic than rigid PV modules, having the same wind uplift performance as the roof itself. On curved roofs, the flexible modules can bend to accommodate the shape of the roof. Their flexibility and light weight make them an ideal portable PV device that can be attached to a backpack, an RV, or trailer roof. During a camping trip, flexible panels can cover a tent or be rolled out on the ground to heat water for a swimming pool.

flexo printing

See →flexographic printing.

flexographic printing

A roll-to-roll method for printing flexible →organic photovoltaic cells (OPV cells) with the help of a rotary printing mechanism. The printing appliance consists of an ink tray, a fountain roller, an anilox roller, a doctor blade, a printing plate roller, an impression roller, and a roll of thin-film substrate. The flexographic printing process begins with

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Flexible Thin-film Solar Module

a fountain roller being immersed into an ink bath, carrying the ink on its surface and transferring it to the ceramic anilox roller. The ink fills thousands of tiny engraved cavities on the anilox cylinder surface. While the anilox roller is rotating, the doctor blade wipes off the surplus of ink and transfers the right amount of ink to the relief on the printing plate roller. The raised areas of the relief form an ink pattern that is transferred to the rotating thin-film substrate. The film is then run through a dryer, drying the ink before further processing. The features of printed films can

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 float charge

be optimized by increasing or decreasing pressure on the film by the impression roller, changing the printing speed, or adjusting other printing parameters, such as the ink formula. The main advantages of flexographic printing are high-throughput, scalability, and an inexpensive process. All manufacturing phases are conducted under ambient conditions without costly and time-consuming vacuum or evaporation procedures. float charge

See →float charge stage.

float charge stage

When the battery has reached between 95% and 98%, depending on the charger brand, it switches to float charge stage. At this stage, the voltage and current decrease to ensure the safe charging at a measured rate. The float charge brings the battery to a 100% state of charge and maintains it in the fully charged condition.

float glass

A type of extra smooth and clear plate glass produced by floating molten glass onto a surface of molten tin. In solar industry, float glass is often used because of its engineered chemical composition that allows maximum transmission of light into the photovoltaic cells. Transmittance can be augmented by reducing the iron content of the glass. Float glass finds wide applications as cover glass for photovoltaic modules and solar collectors as well as substrate for solar mirrors.

float life

The number of years or hours a battery can operate at manufacturer’s specified capacity in a float charge mode before it reaches the end of its usable life. The float life depends on the ambient temperature at which the battery is charged. In general, the higher the temperature (above 20  °C/68  °F), the lower the expected lifetime of a battery due to the increased corrosion. See also →cycle life.

float stage

See →float charge stage.

float voltage

The reduced voltage, 2.25 V–2.27 V/cell for most →flooded-cell batteries, for maintaining the full charge of battery. Once fully charged, the battery is maintained at lower voltage in order to reduce the possibility of overcharging.

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floating platform

A platform floating on a body of water onto which the rows of solar panels are mounted. It is usually made of individual floating high-density polyethylene modules that are recyclable and resistant to corrosion and UV rays.

floating solar energy island

See →floating solar installation.

floating solar farm

See →floating solar installation.

floating solar installation

Also known as a floating solar energy island, floating solar power plant, or floating solar farm. A solar power generation installation that floats on the water surface of a reservoir, lake, irrigation canals, or coastal areas. The main component of the floating solar farm is a floating platform onto which the rows of solar panels are mounted. The floating platform is usually made of individual floating high-density polyethylene modules that are recyclable and resistant to corrosion and UV rays. The floating platforms need to be properly anchored to the concrete blocks at the bottom of the reservoir, lake, or sea by cables to stay in a static position and avoid hitting the shore and cause other damage during high winds and storms. The floating solar farm conserves valuable agricultural land, keeps water from evaporating, and controls algae growth. The body of water surrounding the floating photovoltaic modules cools the panels and hence increases the power output. The main disadvantage of a floating solar installation is the fact that it is more expensive than a traditional →ground-mounted solar array. While solar floating installations might not attract too much attention in industrial canals, water reservoirs in desert areas or abandoned quarry lakes, their application in natural environments might spark controversy when they destroy the balance of an ecosystem or the natural beauty of a lake and coastal region.

floating solar island

See →floating solar installation.

floating solar power plant

See →floating solar installation.

floating zone melting process

See →float-zone process.

floating zone melting technique

See →float-zone process.

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 floating zone method

floating zone method

See →float-zone process.

floating zone process

See →float-zone process.

float-zone method

See →float-zone process.

float-zone process

Also known as float-zone method, floating zone process, floating zone method, or zone melting. A type of high-quality single-crystal growth in solar cell manufacturing. In this method, a high-purity polycrystalline rod is placed atop a monocrystalline seed. As a radiofrequency heating coil is slowly raised along the polycrystalline rod, a narrow, molten zone is created between the polycrystalline rod and the single-crystal seed rod. Because the impurities tend to stay in the melt, the narrow zone purifies the polycrystalline material by carrying the impurities with the melt to the end of the rod. This end is then cut off and discarded. As the RF coil is pulled upward, the molten silicon solidifies into a single crystal, creating the same crystal orientation as the seed crystal. The result is an ultrapure single crystal with a minimal amount of contamination, since the entire process is carried out in a vacuum chamber or in inert gases. This controlled environment ensures low concentrations of impurities, such as carbon and oxygen, which are present in high concentrations in the →Czochralski process due to a large amount of the melt in the crucible. This is why the float-zone method is considered a viable alternative to Czochralski method for the growth of ultrapure silicon crystals. The major disadvantage of the floatzone process is the diameter of the single crystal, which is at present limited to 150 mm.

float-zone silicon

High-purity silicon obtained by a single-crystal growth method known as →float-zone process.

flooded battery

See →flooded-cell battery.

flooded-cell battery

Also known as wet cell battery or liquid electrolyte battery. A type of the rechargeable lead-acid battery with plates immersed in a liquid electrolyte. Deep cycle flooded leadacid batteries are the most commonly used battery type for →off-grid photovoltaic systems. They are not suitable for →grid-connected photovoltaic systems where they act as a backup power system because when flooded batteries sit around without any activity for a long time, their

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 277

performance diminishes. Flooded batteries require cycling, a regular discharging and recharging to ensure a long life. If they are promptly recharged after every deep discharging, they can last approximately 7–10 years. Wet cell batteries should be kept in a warm, but good ventilated space and routinely maintained in good operating condition by a periodical refilling of evaporated electrolyte, venting, and →equalization. All this is easier accomplished in an independent off-grid solar power system. floor heating

See →underfloor heating.

Florida room

See →sunroom.

flow

Movement of fluid.

flow battery

Also called redox flow battery, is a rechargeable battery where energy is stored in the liquid electrolyte instead of solid plates. The liquid electrolyte is pumped past a membrane held between two electrodes generating a current flow. As it wears over time, the electrically conducting solution is replaced by fresh electrolyte that is stored in an external tank. By storing the electrolyte in an external tank, the storage capacity of a flow battery can be increased.

flow charging

A first phase in a battery charging process in which the storage battery is subjected to constant flow charging until the voltage value of the battery reaches a first preset voltage value, switching to the next charging phase.

flow coefficient

Also known as a flow rate coefficient. A measure of the ease in which a fluid flows through a device. The volume of water, measured in gallons in the USA, at standard temperature of 60 °F (16 °C), which will flow per minute through a valve with a pressure drop of 1 psi.

flow controller

See →flow-rate controller.

flow meter

See →flow sensor.

flow rate

The velocity at which fluid moves.

flow rate coefficient

See →flow coefficient.

flow regulator

See →flow-rate controller.

flow sensor

Also known as a flow meter. A sensor that measures flow volume and flow rate in the return to the →solar collectors.

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 flow-rate controller

flow-rate controller

Also known as a flow-rate regulator. A regulator that controls the flow of →heat transfer fluid in solar collectors. The flow rate is increasing with increasing temperature. By regulating the flow rate, the controller can increase the performance of a solar thermal system.

flow-rate regulator

See →flow-rate controller.

fluid deposition technique

A method for depositing the liquid photoactive semiconductor material, such as →solar ink, onto the substrate of a photovoltaic cell. Common fluid deposition techniques include →inkjet printing, →screen printing, →spin coating, blading, →etching, →slot-die coating, and →gravure printing.

fluid dielectric

Also known as liquid dielectric. A dielectric material in liquid state that forms a barrier between the tool and workpiece. It is used for cooling the machining area.

fluorescent light

Uses thin glass tubes filled with noble gases and a small amount of mercury vapor. When an electric current is driven through the tube, the high-speed electrons collide with the mercury atoms, elevating them to an excited state and consequently generating ultraviolet (UV) light. The invisible short-wave UV light strikes a phosphor powder, with which the inside of the tube is coated. Finally, the “excited” phosphor electrons in the coating emit visible, specific fluorescent white light.

flux calorimeter

See →heat meter.

flux pen

A flux application device for rework and touch-up soldering. A must-have tool for a DIY solar panel assembly.

flux1

See →energy flux and →radiant flux.

flux2

A chemical cleaning agent that consists to a significant extent of rosin or synthetic resin. The rosin flux facilitates soldering by ensuring a strong bond between solder ribbons and metal connectors. Apart from the bonding enhancement, it also removes oxides from treated surfaces, thereby improving electrical conductivity in solder joints.

flyback diode

See →freewheeling diode.

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 279

flywheel

Is a device that stores excess energy in the form of rotational kinetic energy. An electric motor accelerates the flywheel to a high velocity and preserves the energy in the system as rotational energy. When electrical power is needed during hours of peak energy demand, the rotational energy is converted into electricity by the same motor that now functions as generator.

FMC

Abbreviation for →flexible metal conduit.

FNC

Abbreviation for →fiber-nickel-cadmium battery.

focal length

The distance between the center of a lens and the focal point of the lens where all light rays converge. Finding an optimal focal length is of crucial importance in DIY solar cooking with Fresnel lenses. In professional solar cookers, the focal length, usually expressed in centimeters, millimeters, or inches, is specified in the technical documentation of a product.

focal line

A narrow line running the length of a →parabolic trough or →linear Fresnel reflector, along which focused light rays meet. The rays of light reflected from large mirrored surfaces are concentrated onto the small focal line to increase the intensity of solar radiation. Theoretically, the maximum possible degree of concentration is 215-fold. Along this area of enhanced solar energy, an →absorber tube is mounted, typically several meters (yards) directly above the mirrored collector surface. The →single-axis tracking system follows the sun’s trajectory throughout the day, ensuring that the absorber tube always remains in the focal line of the parabolic trough or Fresnel reflector mirrors.

focal point

A point at which focused beams of light meet. The rays of light reflected from large mirrored surfaces of a dish collector or →heliostats are concentrated onto the small focal point to increase the intensity of solar radiation. Theoretically, the maximum possible degree of concentration is 46,200-fold. A thermal →receiver is mounted at the focal point of the parabolic dish, typically several meters (yards) directly above the mirrored collector surface, or at the center of the heliostat field. The →dual-axis tracking

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 focal width

system follows the sun’s trajectory throughout the day, ensuring that the receiver always remains at the focal point of the reflecting mirrors. focal width

The length of a horizontal or vertical line that runs through the focus of the parabola, touching the parabola on each end.

focused ion beam

(FIB) In the semiconductor manufacturing, a method that directs a beam of accelerated high-energy ions at the source material to pulverize it. The ejected material particles are then deposited onto a solar cell substrate in a controlled vacuum chamber environment. The FIB technique is also used for etching of semiconductor films by means of beams of charged particles, ions, in a high-vacuum system.

focused ion-beam device

Also known as a FIB device. A device that is made up of a vacuum chamber with a vacuum system, a liquid metal ion source (LMIS), an ion-beam column, a sample stage, detectors, and a gas delivery system. A FIB device uses a beam of ions instead of electrons to pulverize source material and deposit it onto a substrate or to etch or mill a semiconductor film.

focused ion-beam instrument

See →focused ion-beam device.

focused ion-beam microscope

A scanning electron microscope (SEM) into which a focused ion-beam column is incorporated. The focused ion-beam microscope is used for nanotomography and nanofabrication applications.

focusing collector

See →concentrating solar collector.

focusing solar collector

See →concentrating solar collector.

foldable parabolic mirror A parabolic mirror, made of aluminum-coated cardboard or other lightweight material, can be folded up after cooking, allowing compact storage for camping. Depending on the design, this portable solar cooker can consist of between 8 and 24 small reflective panels. The black cooking vessel positioned at the focal point can reach a maximum temperature of 140°C (284°F). forced hot air heating system

See →forced-air central heating system.

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forced-air central heating system

A heating system that uses a furnace to heat the air and distribute it through duct work into different rooms of your home.

forced-air heating system

See →forced-air central heating system.

fossil energy

Heat energy released by burning fossil fuels, such as coal, natural gas, and crude oil.

fossil fuel epoch

See →fossil fuel era.

fossil fuel era

Also known as fossil fuel epoch. An era that roughly starts with the arrival of the Industrial Revolution in the mid-1700s and whose end is uncertain but foreseeable in the course of the twenty-first century due to the overwhelming scientific evidence for human-caused →global warming, such as accelerated melting of Arctic and Antarctic ice cover and the poleward migration of plant and animal species across the globe. At the beginning of the twenty-first century, the fossil fuel epoch defined by oil cartels and coal corporations faced a transformation in the way humans generate energy, as renewable energy installations started to outnumber new installations of fossil-fuel-based energy systems for the first time in the modern history. According to many experts, the solar and renewable energy era has already begun in many countries around the world and it is expected to expand and gain momentum in the years to come. The joint efforts to decarbonize the atmosphere seem to be the only reasonable course of action to avert extreme weather and looming global climate catastrophe.

fossil fuels

Are carbon-rich fuels, such as coal, natural gas, oil shale, and crude oil, that have been formed over millions of years from the remnants of long-dead living things: terrestrial as well as oceanic plants and animals and other organic materials.

fossil-fuel electricity

Electricity generated by burning fossil fuels, such as coal, natural gas, or petroleum.

fossil-fuel energy

A form of nonrenewable energy that is produced by burning fossil fuels, such as coal, natural gas, or petroleum.

fossil-fuel energy sources

See →fossil fuels.

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 fossil-fuel exit

fossil-fuel exit

Also known as fossil-fuel phase-out. A transition away from the extraction and use of fossil fuels, such as coal, oil, and gas, which are harmful to the environment. The ultimate goal is to keep fossil fuels in the ground and to replace them with renewable sources of energy, such as solar and wind.

fossil-fuel phase-out

See →fossil-fuel exit.

fossil-fuel power

See →fossil-fuel energy.

framed photovoltaic module

A solar module whose photovoltaic (PV) laminates are glued into a lightweight aluminum frame that provides mechanical strength to the entire panel and protection during transport. Framed photovoltaic modules are easier and faster to install than →frameless photovoltaic modules. It is critical to properly seal the PV laminates into the aluminum frame to prevent rain and moisture from reaching the solar cells and electrical contacts, which can cause damage. Specially engineered →solar adhesives are employed to make a strong bond between the two surfaces. For proper bonding and sealing, it is recommended to use a solar panel framing machine instead of manually attaching the frame.

framed photovoltaic panel

See →framed photovoltaic module.

framed PV module

See →framed photovoltaic module.

framed PV panel

See →framed photovoltaic module.

framed solar module

See →framed photovoltaic module.

framed solar panel

See →framed photovoltaic module.

frameless laminate

See →frameless photovoltaic laminate.

frameless photovoltaic laminate

Also known as light-permeable module. A frameless, transparent or semitransparent thin-film photovoltaic panel that is suitable for →building-integrated photovoltaics.

frameless photovoltaic module

Also known as a glass-on-glass solar panel. A photovoltaic module without an aluminum frame. Solar cells are sandwiched between two sheets of glass, one on top and one on the back of the cells. As there is no frame to hold the glass sheets in place, the glass layers must be thicker to ensure the structural strength of the entire panel. Frameless PV

frameless PV laminate 

 283

modules have a clear aesthetic advantage over →framed photovoltaic modules because they can be easier and seamlessly integrated into an architectural structure, such as a roof, windows or skylights. On the other hand, the frameless solar panels are more difficult to install than the framed PV modules as they require a more complicated mounting system. frameless PV laminate

See →frameless photovoltaic laminate.

frameless PV module

See →frameless photovoltaic module.

frameless solar laminate A frameless, transparent or semitransparent thin-film solar panel that is suitable for →building-integrated photovoltaics. frameless solar module

See →frameless photovoltaic module.

frameless solar panel

See →frameless photovoltaic module.

frameless thin-film photovoltaic module

Also known as frameless thin-film solar module. A thinfilm photovoltaic module without an aluminum frame. The frameless glass-on-glass laminate consists of a thinfilm solar cell sandwiched between glasses. As there is no frame to hold the glass sheets in place, the glass layers must be thicker to ensure the structural strength of the entire panel. Frameless thin-film PV modules have a clear aesthetic advantage over →framed photovoltaic modules because they can be easier and seamlessly integrated into an architectural structure, such as a roof, windows, or skylights. On the other hand, the frameless solar panels are more difficult to install than the framed PV modules as they require a more complicated mounting system. As thin-film solar cells are less susceptible to heat-related efficiency losses than traditional crystalline silicon solar cells, they have an energy-output advantage in warmer climates and show excellent performance in the Sun Belt region states between the 35th northern and 35th southern latitudes.

frameless thin-film PV module

See →frameless thin-film photovoltaic module.

frameless thin-film solar module

See →frameless thin-film photovoltaic module.

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 frameless thin-film solar panel

frameless thin-film solar panel

See →frameless thin-film photovoltaic module.

framing process

A process in which frames are attached to the PV laminates of the solar module to provide strength to the entire panel and protection during transport. The process also includes the junction box installation that facilitates connection between PV panels.

Frank van der Merwe growth mode

See →layer-by-layer growth.

free electron

In contrast to a loose →valence electron that is still attached to the atom in the outmost valence shell, a free electron is a valence electron that has escaped from its parent atom and can move freely along the →conduction band, acting as a →charge carrier. See also →n-type dopant and → phosphorus.

free of shadow

One of the most important criteria in solar planning and installation is that the proposed solar site is free of shadow during →peak sun hours in any season. The locations free of shadow with optimal sun exposure can achieve maximum power generation.

free-standing installation

See →ground-mounted solar array.

freewheeling diode

Also known as a flyback diode. Freewheeling diodes are utilized across inductive components, such as coils, to prevent damage to circuits when the power is switched off.

frequency

(f) number of oscillations, vibrations, or waves per unit of time. The frequency of electrical current is measured in cycles per second. One hertz equals one cycle per second: 1 Hz = 1/s. It shows how many times the direction of electric current is reversed in an AC circuit per second. In Europe and other countries, the direction of electron flow is switched 50 and in the USA 60 times per second. Accordingly, electrical devices in Europe and other countries use 50 Hz and in the USA 60 Hz as the AC frequency.

frequency conversion control system

Also known as a frequency converter. A power conversion system that operates motors optimally at their load point, providing electrical energy savings.

frequency convertor

See →frequency conversion control system.

frequency regulation 

 285

frequency regulation

The ability of network operators and ancillary services to regulate the inconsistency in the output frequency and maintain scheduled frequency. Frequency regulation is a type of power management that has the task to ensure a constant balance between supply and demand of electric power. If demand (the load) is greater than supply (power production), the grid frequency decreases. On the other side, when supply exceeds demand, the grid frequency increases. The system operators bring balance to the grid by adding and subtracting generation assets, electricity storage, and other frequency regulation techniques.

fresh water drain

A component of a solar distillation device. A chute into which fresh water is collected.

fresh water reservoir

See →fresh water storage tank.

fresh water storage cylinder

See →fresh water storage tank.

fresh water storage tank A reservoir for domestic hot-water storage. Water can be heated with a →solar collector system or a ground-source heat pump. fresh water tank

See →fresh water storage tank.

fresh water trough

A component of a →solar water distiller.

Fresnel collector

A type of →concentrating solar collector that employs a →Fresnel lens to concentrate sunrays onto an absorber surface, increasing the intensity of solar energy multiple times.

Fresnel collector system Fresnel lens or reflector that focuses a large area of sunlight onto a smaller absorbing surface, increasing the solar energy supplied to the →receiver numerous times. Fresnel CSP system

A concentrating solar power (CSP) system that uses linear Fresnel reflectors to focus the sun’s rays onto elevated →receivers or →absorber tubes through which water flows. By concentrating the Sun’s beams along a narrow focal line, solar energy can be increased by approximately 30 times its normal intensity, heating water to the boiling point. The boiling water evaporates in the tubes, generating superheated steam, which reaches a temperature of 270 °C (518 °F). The saturated steam is then transported to a steam turbine, driving a generator that converts kinetic energy into electricity.

286 

 Fresnel lens

Fresnel lens

Is an optical device consisting of a number of concentric rings (grooves) that are cut into the lens surface at slightly different angles to concentrate light onto a small area called focal point. Directing the beams of light to the same point creates a short focal length, reducing significantly the active solar-cell surface and thus saving the material. In addition, the insolation at the focal point is increased hundreds of times, making solar equipment with Fresnel lenses more efficient than conventional silicon PV modules. Therefore, Fresnel lenses find application in various solar devices, such as solar ovens, concentrators, collectors, and reflectors. Light rays

Fresnel lens

Solar cell

Fresnel Lens

Fresnel mirror

Two plane mirrors that are inclined to each other in such a way that they mimic the optical characteristics of a parabolic or dish mirror. By dividing a curved mirror into linear mirror segments, an analogous optical effect – concentrating light rays onto a focal line/absorber tube – can be achieved as in a conventional →parabolic trough. Several long parallel lines of shallow curvature or flat mirrors replace the curved parabolic trough mirror. Similarly, a paraboloid mirror can be divided into circular inclined mirrors to replace a parabolic dish. See also →linear Fresnel reflector.

Fresnel mirror collector

See →Fresnel mirror.

Fresnel reflector  

Fresnel reflector

 287

See →linear Fresnel reflector and →compact linear Fresnel reflector.

Fresnel reflector system See →linear Fresnel reflector and →compact linear Fresnel reflector. front

The boundary between an area of warm and an area of cold air.

front contact

Also known as top contact. The electrical contact layer located at the front of a →solar cell. It is made of a net of numerous miniature metallic conductive lines called →fingers that are connected with two →busbars on each silicon solar wafer. The electrical current generated in the semiconductor layer is carried out of the solar cell through the front electrical contact to an external load and is returned back into the PV cell via →back contact, closing the electric circuit.

front contact layer

See →front contact.

front grid contact

The contact on the front of the PV cell is usually made in the form of a grid, consisting of a net of numerous miniature, parallel conductive lines called →fingers and two busbars that intersects the fingers at a right angle on each silicon solar wafer. The electrical current, which is generated in the semiconductor layer and carried out of the solar cell through a front electrical contact, is transported to the next PV cell via back contact. The grid contacts are typically made of silver or nickel.

front print check

See →front print inspection.

front print inspection

Also known as front print check. An optical solar cell inspection method that examines the front side of a photovoltaic cell for printing defects and deviations. The front print inspection occurs during PV cell production in order to detect defects early in the process and correct them before they become bigger and more expensive.

front surface texture

See →surface texture.

fuel

Any material, such as coal, oil, or natural gas, which can be burned to generate energy.

fuel cell

A device that converts chemical energy from hydrogen-rich fuels into electricity. As the fuel is directly converted by

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 full sine wave inverter

electrochemical means without a combustion process, pollutant gases are not emitted into the atmosphere, making fuel cells a sustainable energy generation process. full sine wave inverter

Full sine wave inverter, also called pure sine wave inverter or simply sine wave inverter, is a power inverter that produces a sine wave curve. The conversion of direct current from solar panels to alternating current that is needed for most household appliances can be graphically illustrated in the following manner: a straight line, steady stream of electrons flowing in one direction only, representing the direct current (DC), is converted into a sinusoidal AC waveform that goes from 0 volt to a positive peak of around 120 volts, and then, when the direction of electron flow is switched, it plunges to a negative peak of around 120 volts. The cycle is repeated 50 (in Europe) or 60 (in the USA) times per second. Although full sine wave inverters are a bit more expensive than modified sine wave inverters, they are more efficient, reliable, universal, and overall of better quality than modified sine wave power inverters. As they do not struggle with rough waveforms, interference, and increased heating, full sine wave inverters use 20 to 30% less power than modified sine wave inverters. They produce high-quality AC power that closely matches utility supplied electricity and in some brands even surpassing it. Full sine wave inverters are universal nowadays, as all household appliances run on them without any problems. In particular sensitive electronical devices that have a hard time with square and modified sine wave inverters (digital clocks, LED TVs, audio equipment, and laser printers) run better on full sine wave inverters. Full sine wave inverters will not cause overheating of electric motors and overall will not reduce electric noise. Fans do not produce a humming sound, and LED lights, microwave ovens, and audio amplifiers do not pick up a buzzing sound. Due to smoother running on full sine wave inverters, the lifespan of equipment will be extended. Taking into consideration all of the aforementioned advantages and as the price of full sine wave inverters keeps falling, they have become the first choice for an average household today.

full solar eclipse

See →total solar eclipse.

full sun 

 289

full sun

The amount of solar power strength received at the surface of the earth at noon on a clear day (about 1,000 W/m2).

full sun hours

See →peak sun hours.

fullerene

Also known as →buckminsterfullerene. Spherical molecule consisting of 60 carbon atoms and exhibiting a symmetrical and stable structure. Together with polymers as electron donors, fullerenes are used as efficient electron acceptors in an →electron-donor–acceptor complex, drastically enhancing photovoltaic properties of →organic photovoltaic cells.

Fullerene

full-load operation

See →full-load operational range.

full-load operational range

An operational range in which a solar system works under optimal solar radiation and alignment conditions, generating the maximum amount of power. As a continuous fullload operation is achieved only in a PV testing laboratory, solar systems operate largely in a partial-load operational range.

fully integrated photovoltaic roof

See →fully integrated photovoltaic roof system.

290 

 fully integrated photovoltaic roof system

fully integrated photovoltaic roof system

A photovoltaic system, in which PV modules, for example, solar roof tiles, are completely integrated into the roof surface to seamlessly blend in with conventional roof tiles and the rest of the roof and building. The major challenge for solar installers is to ensure the absolute watertightness of the roof-integrated PV system. The lack of cooling airflow under the tiles is another drawback of this system, as it leads to the overheating of solar cells, reducing their efficiency.

fully integrated photovoltaic system

Any photovoltaic system whose solar modules or solar cells are fully integrated into a building structure without the use of a mounting or any other external structure. See also →roof-integrated photovoltaic system.

fundamental particle

See →elementary particle.

furnace annealing

See →wafer annealing.

fuse

A safety device protecting electrical equipment from short circuits. The key component of the fuse is a thin metal wire that melts, interrupting the flow of electrical current when too much electricity passes through the circuit.

fuse switch

Also known as a fuse-switch disconnector. A switch combined with a fuse is a disconnect switch that isolates a system from a circuit. Fuse switches are typically installed in environments where high-fault levels are present. Their main function is to protect solar electrical equipment against overload and short circuit.

fuse-switch disconnector

See →fuse switch.

future electricity price increase

See →future increase in electricity prices.

future expansion capabilities

Solar technology is modular by nature, which means that individual house owners and companies can effortlessly expend their solar systems according to their actual electricity needs at any time. When the energy demand of a home changes, for example, two additional persons move into the household, the home owner is able to add new solar modules to the existing system and so meet the new power requirements.

future increase in electricity prices 

future increase in electricity prices

 291

Regardless whether the adoption of renewable energies, such as solar and wind, are increasing or depressing energy prices, the research and analysis indicate that electricity prices will continue to increase in the future. Taking into account these trends and long-term projections, an investment in solar energy pays off and promises high returns.

G gain

A solar power output; the amount of energy produced by a →photovoltaic system.

gallium

(Ga) A rare posttransition metal utilized in the manufacture of the following solar cells: →copper indium gallium selenide thin-film solar cells (CIGS), →gallium arsenide (GaAs) →gallium nitride, and →indium gallium nitride. Gallium is a p-type dopant atom that is implanted in small quantities into a silicon semiconductor to generate charge carriers →holes in the positively doped region called →valence band.

gallium arsenide

(GaAs) Is known as one of the most efficient solar photoactive materials. This III–V type semiconductor owes its favorable optoelectronic properties to the fact that it has a →direct band gap. Due to their wide band gap, gallium arsenide solar cells can be operated at higher temperatures. Gallium arsenide is used for the production of →gallium arsenide nanowires. Although gallium arsenide has higher electrical conductivity than silicon, the production costs of gallium arsenide still significantly exceed those of silicon, so that the application of GaAs solar cells is mostly reserved for expensive space solar energy devices. In recent years, continuous efforts have been made in innovation and improvement to reduce the costs of the GaAs production, for instance, by making extremely thin layers of gallium arsenide, which promise to replace silicon in manufacturing of thin-film photovoltaic modules.

gallium arsenide nanowire

Gallium arsenide (GaAs) nanowires are known as one of the most efficient solar photoactive materials.

292 

 gallium indium phosphide

gallium indium phosphide

(GaInP2) is often used as a top layer in triple-junction solar cells. The top film with a high band gap captures highenergy photons while allowing the lower-energy photons to pass through.

gallium nitride

(GaN) A compound semiconductor material that is utilized as an absorber layer in multijunction solar cells. The gallium nitride has a →direct and →wide band gap, which allows this semiconductor to be operated at high temperatures. The band gap energy of gallium nitride is 3.4 electron volts (eV). Due to its resistance to cosmic radiation, chemical stability, and hardness, the GaN semiconductor is often used in space. The optical properties of gallium nitride show potential for the use as a blue and ultraviolet (UV) n-type semiconductor. The gallium nitride manufacturing uses the following →vapor phase epitaxy methods to grow GaN crystals: →molecular beam epitaxy (MBE), halide vapor phase epitaxy (HVPE), and →metal-organic chemical vapor deposition (MOCVD).

gallium nitride crystal

Gallium nitride crystals can be grown by using various →vapor phase epitaxy methods, such as →MBE, →HVPE, and →MOCVD, in the following two structures: the hexagonal Wurtzite crystal structure and cubic Zinc-blende crystal structure.

gallium nitride semiconductor

A III–V semiconductor made of gallium nitride (GaN) compound material with a →wide band gap of 3.4 electron volts (eV). Compared to the narrow silicon band gap of 1.1 eV, the wide band gap allows gallium nitride semiconductors to be operated at much higher voltages and temperatures than conventional semiconductors, such as →silicon (Si) and →gallium arsenide (GaAs).

gallium nitride substrate

In a →molecular beam epitaxy process, the substrate acts as a template on which crystalline GaN thin films are grown, layer by layer, replicating the structure and crystallographic orientation of the underlying substrate. The substrate is heated to appropriate temperatures and rotated in an ultrahigh vacuum (UHV) growth chamber to obtain uniform thin film structures.

gallium nitride template See →gallium nitride substrate.

gallons per minute 

 293

gallons per minute

(GPM) US unit of flow rate in hydroelectric power systems.

galvanic anode

See →sacrificial anode.

galvanic corrosion

An electrochemical process that occurs when two different metal types, for example, stainless steel and aluminum, are brought into electrical contact in a humid, corrosive environment. When exposed to water that acts as an electrolyte, the aluminum (→anode) deteriorates, losing electrons to the stainless steel that functions as a →cathode next to the aluminum. The more dissimilar the metals or the greater the humidity, the greater the rate and extent of corrosion. In photovoltaic (PV) systems, corrosion can lead to serious structural failures in →rack mounts and to operational failures in metallic contacts. In order to mitigate the risk of an aggressive galvanic corrosion, the following guidelines should be considered during the installation of mounting structures: The rule of a thumb for PV installers is to avoid combining metals that are dissimilar in the Galvanic Series Table. Instead, metals that are galvanically compatible should be joined. If dissimilar metals are still used, they should be insulated, for example, by using a gasket. In coastal regions or other constantly wet areas with high humidity levels, the anodized aluminum should be applied. The corrosion of electrical contacts in solar modules and other electrical components of a PV system leads to a higher contact resistance, resulting in excessive heating and increased power losses. Also here, the negative effects of the galvanic corrosion can be avoided by carefully matching metallic contacts with help of the Galvanic Series Table. Ideally, PV electricians should use the same type of connector, coming from the same manufacturer, for the entire photovoltaic system.

galvanisation

UK See →galvanization.

galvanization

US Also known as electrolytic bath. A process for producing metallic coatings, electroplating.

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 gas and steam turbine

gas and steam turbine

See →combined gas and steam turbine.

gasket

See →sealing gasket.

gassing

Emitting destructive gasses during lead-acid battery charging. Excessive charging leads to electrolysis, generating oxygen and hydrogen gas and causing in turn water loss and corrosion of grids of positive battery plates. When the concentration of hydrogen reaches 4% in a battery, the risk of an explosion increases.

gassing current

The current at which the →gassing process begins.

gassing voltage

The voltage at which the →gassing process begins. It often acts as a voltage threshold that is set in order to prevent destructive gas generation in a lead-acid battery. As long as the charging voltage is kept below the 2.30 V limit, the battery will not be damaged.

GCR

Abbreviation for →ground coverage ratio.

gel

A jellylike substance used as an immobilized electrolyte in →gel batteries.

gel battery

A rechargeable →sealed lead-acid battery with an immobilized electrolyte. The electrolyte is immobilized by gelling the liquid sulfuric acid with help of a silicon dioxide addition. Unlike the liquid electrolyte in a flooded battery, the gelled electrolyte has solid pastelike consistency, resulting in a spill-proof battery. The gelled batteries do not require water additions and the water loss through gassing is not an issue. They are easily transported, as they demonstrate a good resistance to shock and vibration. Due to these features, they are commonly used in mobile installations, such as planes, boats, submarines, power wheelchairs, and cars. Since they are sensitive to temperature extremes, the application in excessively hot places should be avoided.

gelled electrolyte battery See →gel battery. gel-type battery

See →gel battery.

general liability coverage (GLC) See →general liability insurance.

general liability insurance  

 295

general liability insurance

(GLI) An insurance that protects an individual or/and their solar business against claims of injury or damage made by others against them or their employees.

generator

A device that turns mechanical energy into electrical energy.

geodetic north

See →true north.

geodetic south

See →true south.

geoengineering

Also known as climate or carbon engineering. See →carbon dioxide removal.

geographic information system

(GIS) Also known as a geographical information system. A computer-based system that stores, analyzes, manipulates, and manages geographic information. A specialized solar GIS tool helps users visualize solar, meteorological, and geographic data on interactive maps. The GIS data are utilized to calculate the solar energy potential of a specific roof or open ground area.

geographical information system

See →geographic information system.

geometric fill factor

(GFF) Also known as a total geometric fill factor. The ratio between the photoactive (PV) surface and the total surface of a solar module. Interconnections and currentcollecting electrodes cause resistance losses, reducing the overall efficiency of the PV panel. The geometric fill factor is expressed as a percentage. While the GFF for OPV in a standard printing manufacturing process ranges between 50% and 75%, the laser scribing manufacturing process can achieve a geometric fill factor of over 90%.

geospatial information system

See →geographic information system.

geothermal

Relates to the harvesting energy from the Earth’s heat.

geothermal energy

Energy harvested from the heat of the Earth, originating either from the very surface of the Earth’s crust or from the molten core of the Earth. Geothermal energy is an environmental friendly energy source that, unlike oil, gas, and coal, has no →greenhouse gases emissions.

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 geothermal heat pump

geothermal heat pump

Also known as groundwater heat pump. A central heating and cooling system that makes use of the heat of the earth or the subterranean water to heat or cool a building. While the air temperature on the surface considerably vary from month to month, season to season, the earth’s temperature in the upper 10 ft below surface remains fairly constant ranging from 45 °F (7 °C) to 75 °F (21 °C) throughout the entire year. One can access this constant energy source by circulating water or refrigerant through a closed or open loop system. During the summer, the heat from the interior of a building is moved through a system of underground or underwater pipes into the ground, cooling the building. Here, the subterranean geothermal loop functions as a heat sink. However, during the winter, the water or refrigerant are heated in the same underground piping loop and pumped up into the house, warming the building. Although the installation of a geothermal heating and cooling system may be a complex and costly endeavor, the system can potentially reduce heating and cooling costs by 60%. Horizontal geothermal ground loops, which are buried at 4–6 ft below the surface, are usually less costly to install than vertical ground loops, for which 100–400 ft deep holes must be drilled in the ground.

Geothermal cooling system

Cooled air

Very hot air temperature

Thermostat

Warm air

Cooler ground temperature

Geothermal Heat Pump

geothermal power 

geothermal power

 297

See →geothermal energy.

geothermal power plant US Also known as a geothermal power station (UK). A power plant that uses the heat – hot water or steam reserves – from the interior of Earth to drive turbines, generating electrical energy. Hot underground rock can also be fractured and filled with cold water. After the heated water is returned to the surface, it is converted into steam that powers stream turbines, generating electricity. Geothermal power plants are environmental friendly because they do not emit carbon dioxide (CO2) into the atmosphere. Unlike solar power plants, which are considered variable energy resources due to their dependence on weather conditions and natural geographical features, geothermal power stations provide electricity 24 h a day. geothermal power station

UK See →geothermal power plant.

geothermal probe

A U-shaped metal or plastic pipe buried into the subsoil to absorb and release thermal energy. See also →energy pile.

German Energy Agency

(DENA) Deutsche Energie-Agentur. DENA is a Germany-based company with an international outreach that was founded in fall 2000. The agency promotes energy efficiency, renewable energy sources, and intelligent energy systems.

German Federal Foundation for the Environment

(DBU) Deutsche Bundesstiftung Umwelt. The DBU is a German federal agency that was founded in 1991, with a goal to promote innovative environmental projects and sustainability-focused practices in small- and medium-sized businesses.

German Renewable Energy Sources Act

(EEG) Erneuerbare-Energien-Gesetz. A legal framework, consisting of various laws and financial incentives, such as the famous →feed-in tariff (FIT), for an expansion of renewable energies in Germany. The goal of the EEG platform was to enable young technologies, such as solar and wind, to stand on their own feet and protect the environment at the same time. This law, which was originally introduced on April 1, 2000, has been a powerful funding instrument, which is largely responsible for creating a favorable solar infrastructure in the past 17 years. In 2016, solar energy accounted for around 6% of Germany’s electricity.

298 

 German Solar Energy Society

German Solar Energy Society

(DGS) Deutsche Gesellschaft für Sonnenenergie. The DGS is a German society with around 2,500 members that is active on a national level. The primary mission of the society is the change in the energy industry toward a sustainable economy model by the far-reaching introduction of renewable energies.

German Solar Industry Association

(BSW) Bundesverband Solarwirtschaft. Association representing the interests of numerous member companies from the solar industry.

germanium

(Ge) Material used in solar cell production due to its semiconductor properties. Germanium is one of the purest materials used in the semiconductor industry with a purity percentage as high as 99.9%. This lustrous and solid rare semimetal appears under atomic number 32 in Group IV (carbon group) of the periodic table. It has four valence electrons in the outer shell that readily bond with nearby atoms.

germanium crystal

A single Germanium crystal is produced by applying a Czochralski crystal-growth method. According to the Czochralski process, a seed crystal is dipped into molten Germanium called melt and then slowly pulled upward, creating a compact cylindrical crystal structure around the seed known as an ingot. Impurities, donor or acceptor atoms, are incorporated in the melt, changing dramatically the electrical properties of the intrinsic semiconductor material. Similar to Silicon, Germanium has four valence electrons, forming a crystal lattice with a highly symmetrical structure. Dopant atoms, for example, arsenic atoms, with their “fifth” extra electron in their outer shells disturb the stability in the Germanium crystal, causing the movement of electrons across the lattice and thus the generation of electric current. When sunlight hits the semiconductor, the fifth electron gets excited and leaves its valence band. Germanium atoms pass this extra electron to their neighboring Germanium atoms in order to achieve their “octetrule” stability.

getter

Coating on the top of the tube in an evacuated tube solar collector that removes any remaining gases from the evacuated chamber.

getter material 

 299

getter material

Material that removes any remaining gases from the evacuated chamber and keeps the vacuum stable.

getter metal

A type of getter material that has an affinity for certain nonnoble gases. The getter metals or metal alloys are used in getter pumps to gather the residual nonnoble gases, such as →water vapor and →hydrogen, and remove them from the vacuum vessel.

getter pump

A pump that comprises getter materials with an affinity for certain nonnoble gases. The main function of the getter pump is to remove the residual nonnoble gases, such as →water vapor and →hydrogen, from the vacuum vessel.

GFCI

Abbreviation for →ground fault circuit interrupter.

GFF

Abbreviation for →geometric fill factor.

GFP

Abbreviation for →ground-fault protection.

GFPE

Abbreviation for →ground-fault protection of equipment.

GFS

Abbreviation for →Global Forecast System.

GFS data

See →Global Forecast System data.

GHI

Abbreviation for →global horizontal irradiance.

gigawatt

(GW) SI unit of power that is equivalent to 1,000 MW, 1,000,000 kW, or 1,000,000,000 W.

gigawatt hour

(GWh) Measure of electricity generated by large-scale solar plants or used in a region or country over a period of time, 1 GW for 1 h.

GIS

Abbreviation for →geographic information system.

glare

The sensation produced by brightness within the visual field caused by direct or reflected sunlight.

glass cover

See →glazing.

glass cover plate

See →glazing.

glass house

UK See →greenhouse.

glass sheet

See →glazing.

glass substrate

A metal-coated glass board on which a thin p-type silicon semiconductor film is deposited. The metal (aluminum) layer isolates glass from the silicon layer. The glass substrate

300 

 glasshouse

is used to reduce material cost. In order to prevent softening of glass and minimize the release of impurities from the substrate (interaction of metal with silicon), a lowtemperature process needs to be utilized when depositing silicon on the glass substrate. The temperature of the substrate must be kept below 300 °C (572 °F). glasshouse

See →greenhouse.

glass-on-glass photovoltaic module

See →frameless photovoltaic module.

glass-on-glass solar module

See →frameless photovoltaic module.

glass-on-glass solar panel

See →frameless photovoltaic module.

glass-reinforced plastic

(GRP) See →fiberglass.

glazing

A single or multiple layers of glass or plastic covering a →solar panel. It protects a →photovoltaic module from harsh environmental conditions. In addition to the protective function, glazing traps heat inside the box of a →solar thermal collector, increasing the temperature and thus the thermal energy output of the collector. A patterned surface of the cover glass is a better solution than smooth glass surface, as it reduces reflection and thereby increases the absorption of sunlight.

glazing sheet

See →glazing.

GLC

Abbreviation for →general liability coverage.

GLI

Abbreviation for →general liability insurance.

global change

See →global climate change.

global climate change

A long-term change in the Earth’s climate, including the increase in the average atmospheric temperature on Earth. Many scientists prefer the term “global climate change” over “global warming,” as the phenomenon of global warming is not evident in some regions of Earth. Although the planet as a whole is warming, some regions might still have the same or even cooler average temperature.

global footprint

Indicates how much surface area of the Earth a person needs to maintain his or her lifestyle.

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Global Forecast System

(GFS) is a global, computer-based model for weather prediction run by →National Oceanic and Atmospheric Administration (NOAA).

Global Forecast System data

Weather datasets provided by the →NOAA server. On the basis of this data, weather forecasts can be made up to about 180 h (7.5 days) in advance.

global heating

See →global warming.

global horizontal irradiance

(GHI) Also known as global horizontal radiation. The total amount of solar radiation received by a planar surface, for example, a solar panel. The GHI comprises both →direct normal irradiance (DNI) and →diffuse horizontal irradiance (DHI). It is typically measured by an instrument called a →pyranometer. When a direct measurement is not possible, the global horizontal irradiance (GHI) can be calculated from direct normal irradiance (DNI) and diffuse horizontal irradiance (DHI) by applying the following formula: GHI = DHI + DNI * cos (Z), where Z is the →solar zenith angle.

global horizontal radiation

See →global horizontal irradiance.

global insolation

The total insolation on a planar surface, for example, a solar panel, which includes both →direct normal insolation and →diffuse insolation.

Global Monitoring Division

(GMD) Formerly Climate Monitoring and Diagnostics Laboratory (CMDL). A division of the →Earth System Research Laboratory (ESRL) within →NOAA that conducts sustained observations and research related to atmospheric mechanisms that drive the Earth’s climate.

global radiation

See →global solar radiation.

global solar exposure

The sum of →direct solar radiation and →diffuse solar radiation received by a horizontal surface.

global solar irradiance

See →global solar radiation.

global solar radiation

Also known as total insolation. The global solar radiation is the sum of →direct solar radiation and →diffuse solar radiation. On a sunny day without clouds, the global solar radiation mostly consists of the direct solar radiation, whereas on an overcast day, it mostly consists of the diffuse solar radiation.

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global warming

A gradual increase in the Earth’s atmospheric and oceanic temperatures due to rising levels of heat-trapping →greenhouse gases, such as →carbon dioxide, →methane, →chlorofluorocarbons, and other pollutants. The average global temperature on Earth has risen by about 0.8°C (1.4°F) since 1880. If global temperatures continue to rise, the consequences could be far-reaching and long-lasting: the loss of polar ice caps, sea level rise, and extreme weather, including longer, more intense heat waves, followed by droughts, and high-speed winds and severe rain/snow storms, followed by floods and general devastation. Many scientists prefer the term “global climate change” over “global warming,” as the phenomenon of global warming is not evident in some regions of Earth. Although the planet as a whole is warming, some regions might still have the same or even cooler average temperature.

glycol

Ethylene and propylene glycol is used as an antifreeze in →glycol–water mixtures for solar water-heating systems.

glycol–water mixture

Is a →heat transfer fluid with a 50/50 or 60/40 glycol-to-water ratio. Glycol–water mixture is an antifreeze that is frequently used in solar water-heating systems to transfer heat from solar collectors to heat exchangers.

GMD

See →Global Monitoring Division.

gnomon

A shadow stick or arm that casts a shadow onto the dial plate of a sundial, indicating the time of day.

GNR

Abbreviation for →graphene nanoribbon.

GO

Abbreviation for →graphene oxide.

gold electrode

An electrode made of gold that is used in photovoltaic cells due to its high electrical conductivity and resistance to corrosion. While golden electrodes were frequently employed in the early days of solar technology, they have become less competitive in the last two decades because of the trend to produce increasingly cheaper solar modules that replace gold with less expensive electrode materials. As gold can be operated at very high temperatures, it will remain the optimal material for contacts in solar cells that are used

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in extremely hot climates and space stations. The development of very thin nanocoating techniques might lead to a return of gold electrode employment in commercial solar cells. gold nanoparticles

Gold nanoparticles are incorporated into an organic solar cell to increase photovoltaic (PV) cell efficiency. The tuning of size, concentration, and architecture of gold nanoparticles improves photoabsorption in the organic PV cell and leads to a higher power output compared to a regular →organic PV cell.

good heat conductivity

See →high thermal conductivity.

good thermal conductivity

See →high thermal conductivity.

GPM

Abbreviation for →gallons per minute.

GPS solar tracker

Uses the Global Positioning System (GPS) to follow the sun.

GQD solar cell

Abbreviation for →graphene-quantum dot solar cell.

granulated rubber mat

An isolating mat manufactured from a mixture of highgrade, recycled rubber granules and a polyurethane elastomer. Granulated rubber mat can be used as a protective mat on roofs during the installation of solar systems on roofs. In a →ballasted mounting system, the mat can be laid under ballast, usually concrete blocks, for protection of flat roofs.

graphene

A nanostructured, two-dimensional carbon material with an extremely high electrical conductivity due to the high electron velocity. See also →graphene material.

graphene electrode

A graphene-based transparent electrode in thin-film solar cells. Due to its high optical transparency of 90%–100%, excellent electrical conductivity, and outstanding mechanical properties, graphene is increasingly used as a replacement for traditional electrode materials, such as →indium tin oxide (ITO). Although ITO has excellent transparency and conductivity, the indium resource is very scarce, which makes ITO material increasingly expensive. Graphene in contrast is an abundant material that is less expensive, more mechanically flexible, and less biologically harmful than ITO. In addition, graphene also possesses better chemical and mechanical stability than indium tin oxide.

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 graphene growth

graphene growth

Graphene is a high-quality material whose thin layers can be epitaxially grown on a →silicon carbide (SiC) substrate by thermal decomposition.

graphene layer

A superthin layer of graphene that is deposited onto a solar cell to enhance its energy conversion performance. A single, one-atom thick layer consists of carbon atoms that are bonded together in a repeating geometric pattern of hexagons (honeycomb). As the graphene layer is highly transparent (90%–100%), hard, light, flexible, and highly conductive, it is a suitable material for nanoengineered thin-film solar cells and perovskite solar cells.

graphene material

The two-dimensional material with unique physical and electrical properties, such as hardness, lightweight, transparency, conductivity, and flexibility. The optical transparency of graphene lies in the range between 90% and 100%. Another important property of graphene is tunability, allowing manufacturers to engineer the material in different ways, adapting its light-absorption features to capture different ranges of electromagnetic radiation. As graphene is made of carbon – an inexpensive and abundant raw material – its employment in solar industry can significantly reduce the manufacturing costs of thin-film and perovskite solar cells.

graphene nanoribbon

(GNR) A graphene ribbon with a diameter in the range of nanometers. Graphene nanoribbons are narrow strips of graphene manufactured by one of the state-of-the-art nanopatterning methods. For instance, one of the techniques produces graphene oxide nanoribbons that can be utilized as hole extraction layers in different solar cell types, replacing traditional electrode materials such as →indium tin oxide (ITO).

graphene oxide

(GO) A compound material that is deposited as a two-nanometer thick →p-doped semiconductor layer, transporting →holes. The application of graphene oxide in combination with other light-absorbing materials can dramatically increase the performance of a solar cell. Graphene oxide can be used as a hole transporting medium in a →perovskite photovoltaic cell.

graphene production

See →manufacturing of graphene.

graphene ribbon 

graphene ribbon

See →graphene nanoribbon.

graphene sheet

See →graphene layer.

graphene surface

See →graphene layer.

graphene-based Ga/As solar cell

See →graphene–gallium arsenide solar cell.

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graphene-based polymer See →graphene–polymer solar cell. solar cell graphene-based silicon solar cell

See →graphene–silicon solar cell.

graphene–Ga/As solar cell

See →graphene–gallium arsenide solar cell.

graphene–gallium arsenide solar cell

Also known as a graphene–Ga/As solar cell. A solar cell that incorporates graphene to increase the power conversion efficiency of one of the most efficient semiconductor materials gallium arsenide. Graphene has been chosen as a replacement for the →indium tin oxide (ITO) electrode material because of its excellent properties, such as high electrical conductivity, optical transparency, flexibility, and mechanical and chemical stability. An ultrathin graphene film, as small as a single atom layer of carbon hexagons, can be deposited by the →chemical vapor deposition (CVD) or other methods onto a gallium arsenide (GaAs) substrate. Due to its direct band gap of 1.42 eV, gallium arsenide has a superb electron mobility and radiation resistance, which makes it suitable for high-temperature applications.

graphene–organic solar cell

See →graphene–polymer solar cell.

graphene–perovskite solar cell

A solar cell that integrates graphene, graphene oxide, or other graphene-derived nanomaterials into the structure of a →perovskite photovoltaic cell to increase the power conversion efficiency of the cell. For instance, in one of the numerous possible designs, the TiO2 layer is doped with graphene flakes and graphene oxide (GO) is inserted as an interlayer between the perovskite and hole-transport layers, leading to an improved chargecarrier mobility.

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 graphene–polymer solar cell

graphene–polymer solar cell

Also known as a graphene-organic solar cell. A solar cell consisting of a graphene electrode deposited on top of a polymer semiconductor layer. The transparent graphene film increasingly replaces the indium tin oxide (ITO) electrode, because ITO material has become more expensive due to the limited availability of the rare posttransition metal Indium. In contrast, graphene is an abundant and inexpensive material that can significantly reduce production costs. Made of carbon atoms, the simple structure of graphene ensures an uncomplicated manufacturing process. In addition, graphene is light, flexible, mechanically strong, and chemically stable, which are all vital features for thin-film photovoltaic cells. Other important properties of graphene suitable for the manufacture of thin-film multijunction solar cells are tunability and adaptability. When different solar cell layers with different band gaps are stacked on top of each other, nanoengineering makes it possible for each of the materials to be tuned up to be responsive to specific parts of the solar spectrum.

graphene-QD solar cell

See →graphene-quantum dot solar cell.

graphene-quantum dot solar cell

Also known as graphene-QD solar cell or GQD solar cell. A solar cell consisting of a combination of graphene and quantum dot layers. The layered structure ensures an effective electron transmission from the quantum dots to the graphene while suppressing the recombination of charges. When deposited on top of a silicon solar cell, graphene quantum dots can considerably expand the absorbing range of semiconductor materials, covering larger parts of the electromagnetic or solar light spectrum and thus increasing the efficiency of the solar cell. Silicon semiconductor is not responsive to ultraviolet (UV) light. Quantum dots as small flakes of graphene are able to convert shortwave UV light to visible light that can be absorbed by the silicon solar cell. While the transparent QD layer can pass visible light to the photoactive silicon semiconductor layer, it can also convert high UV energies down to lower visible light energies. This process is known as downconversion and it can significantly boost the power output of a solar module.

graphene–silicon solar cell 

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graphene–silicon solar cell

A solar cell consisting of a combination of graphene and silicon semiconductor materials. An integration of graphene with traditional silicon technologies can potentially increase the efficiency of solar cells in the future.

graphite

Graphite is a substance made of pure carbon and it is abundant across the Earth. This black mineral efficiently absorbs and retains solar radiation.

graphite anode

An anode made of graphite, which is the most widely used material for lithium-ion battery anodes. Graphite anode can be derived from both natural and synthetic sources.

graphite die

Also known as die and shaper. A graphite die mold that defines the cross-section of the resulting silicon crystal sheet in an →edge-defined film-fed growth (EFG) process. With help of a graphite die slot, silicon is drawn from a melt by capillary action, solidifying under a carefully adjusted temperature into a long, thin silicon sheet.

graphite nanofluid

Recent research has shown that graphite nanofluid might be the →heat transfer fluid of the future due to its excellent heat transfer performance. Graphite is a substance made of pure carbon and it is abundant across the Earth. This black mineral efficiently absorbs and retains solar radiation. When added to oil, a thermal conductivity increase of around 40% was observed in comparison to basefluids. Therefore, the graphite-containing nanofluids might soon find a widespread application as a new heat transfer fluid in transparent absorber tubes of →concentrating parabolic troughs.

graphite oxide

Formerly known as graphitic acid or graphitic oxide. A  graphene-based chemical compound that is not found in nature. It can be synthesized by applying mechanical or thermal exfoliation, →chemical vapor deposition (CVD), and →epitaxial growth. Graphene oxide and graphene oxide mixed with titanium oxide (TiO2) can be used to manufacture →dye-sensitized solar cells. Graphite oxide demonstrates a relatively high light-capturing capacity.

graphitic acid

See →graphite oxide.

graphitic carbon nitride

(g-C3N4) A chemical compound often used in the PV industry due to its good light harvesting features. The g-C3N4 increases photoconductivity of photovoltaic cells by impeding

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 graphitic oxide

photo-induced electron interception to the redox couple and injecting electrons into the conduction band of the semiconductor. The employment of graphitic carbon nitride in quantum dot sensitized solar cells can lead to up to 70% improvement in power conversion efficiency. graphitic oxide

See →graphite oxide.

grating pattern

In optical lithography, a pattern that is replicated on a surface, for instance, to create a diffracting, antireflection layer for a solar cell.

grating structure

A thin-film structure consisting of a large number of microscopic rods, spikes, or cones on a nanometer scale. The texturing of silicon surfaces for photovoltaic cell applications can significantly enhance light trapping and thus the energy conversion and power output of a solar cell.

grating1

Also known as diffraction grating. A set of equally spaced parallel lines or bars on a reflective surface for the purpose of splitting light into spectra.

grating2

A framework of parallel bars and crossbars preventing animals, insects, and debris like leaves from entering an enclosed space, such as →solar kiln, but admitting air necessary for ventilation purposes.

Grätzel cell

Is a third-generation photovoltaic cell that was invented by Prof. Michael Grätzel and Dr Brian O’Regan in 1991. It is also commonly known as a dye-sensitized solar cell (DSSC). This electrochemical solar cell consists of a transparent conducting glass functioning as a minus electrode facing the sun, dye-sensitized titanium dioxide as a nanostructured semiconductor layer, iodide electrolyte, and an opposite electrode coated with platinum catalyst. DSSC energy production process is often compared to photosynthesis, where the sunlight absorbing dyes function like chlorophyll in green leaves. When photons of light (incident light, but also artificial light) fall onto a thin layer of dye material, they kick electrons into a higher energy state. The photoexcited electrons leave their usual orbit and continue moving through the TiO2 conduction band with nanopores toward the external circuit. They come back to the cell through the counter electrode (platinum catalyst), continue their journey through the liquid

gravity water system 

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electrolyte (Iodide), and finally close the circle by occupying the empty holes and supplying electrons to the dye. This rather simple energy production process that uses the inexpensive semiconductor material →titanium dioxide (TiO2) promises low-cost manufacturing. Another advantage is the fact that DSSC can generate energy in a wide range of light conditions regardless of the cell’s position/ angle to the sun: indoors and outdoors, in diffuse light on cloudy and foggy days, in shaded locations, early in the morning, or late in the afternoon. The rising temperature during the day does not affect the cell performance. Average DSSC efficiencies vary between 10% and 15%, but some DSSC drawbacks still hinder a major breakthrough of this technology: platinum is a rare and expensive metal and electrolyte could potentially leak. gravity water system

See →gravity-fed system.

gravity-fed solar pool heater

See →gravity-fed system.

gravity-fed solar shower See →gravity-fed system. gravity-fed solar water heater

See →gravity-fed system.

gravity-fed system

A system, in which a water storage tank is placed high above the point of use, for example, in an attic or on a hill above the house, and uses gravity to provide sufficient pressure to run water through the pipes to the home’s taps or showers. A few examples of gravity-fed solar water systems include: →gravity-fed solar water heater, →gravity-fed solar shower, and →gravity-fed solar pool heater.

gravure printing

A method for printing flexible →organic photovoltaic cells (OPV cells) with the help of a rotary printing mechanism. The printing appliance consists of an ink tray, a doctor blade, a gravure cylinder, an impression cylinder, and a roll of thinfilm substrate. The gravure printing process begins with a gravure cylinder being immersed into an ink bath, filling tiny engraved cavities on the cylinder surface. While the gravure cylinder is rotating and carrying ink on its surface, the doctor blade wipes off the surplus of ink, forming a clean ink pattern that is transferred to the flexible thin-film substrate. The features of printed films can be optimized by

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 gray water

increasing or decreasing pressure on the film by the impression cylinder, changing the printing speed, or adjusting other printing parameters, such as the ink formula. gray water

Waste water from dishwasher, washing machines, baths, or sinks. This relatively clean water is easier to process and reuse than →black water.

green antenna

Antenna that collects unused blue photons that are then turned into energy.

green architecture

See →sustainable architecture.

green area

Also known as green space. An area that has a lot of grass, plants, or trees, keeping balance between the natural environment and highly urbanized areas. Green area fulfills the ecological, aesthetic, and public health needs of an expanding urban population.

green bond

Also known as a climate bond. A financial instrument in the form of tax-exempt bonds issued by a federally qualified organization for a sustainable investment, such as a development of disturbed areas that are abandoned and permanently damaged by coal mining or another form of industrial pollution.

green bond expert

An expert in →green bonds and sustainable investment.

green building

See →sustainable building.

green certificate

Also known as Renewable Energy Certificate (REC); is a financial instrument that is created to keep track of energy generated from renewable resources. One certificate typically represents 1,000 kWh of renewable energy and it is issued to customers who deliver clean energy to the grid. It is a system of renewable energy credits, also known as green certificates or green tags, that are earned by customers and can be sold or traded to a utility company or an agency, or at least claimed later when needed.

green chemistry

See →sustainable chemistry.

green electricity

Electricity generated from solar, wind, or other renewable energy resources.

green electricity provider

A provider that delivers green electricity from a pollutionfree, renewable source, such as solar, wind, or hydropower.

green energy 

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When purchasing energy, many environmentally conscious electric utility companies give preference to green electricity providers in order to reduce the negative environmental impacts of fossil fuel extraction, transportation, and consumption. green energy

Energy generated from solar, wind, or other renewable energy resources.

green façade

See →façade greening.

green investment

Sustainable investment.

green job

Is a job that benefits the environment or conserves natural resources.

green job creation

Creation of jobs that take into account the benefits for the environment or conservation of natural resources.

green power

See →green energy.

green power generation

Power generation from solar, wind, or other renewable energy resources.

green project bond

A type of sustainable investment. See →green bond.

green roof

Also known as a live roof. A type of a passive cooling and heating system in which a roof is covered with living plants, such as grass, flowers, and other vegetation, to provide an insulation of a building against heat gain or heat loss. The roof covered with vegetation reduces heat during hot summer days by reflecting sunlight and optimizes energy conservation by providing a better insulation in cold winter days than traditional roofs. Flat roofs are suitable for a green roof installation. However, it is critical to ensure that the trusses of the existing roof can support the heavy weight, because even a design with shallow growing beds adds significant stress on the structure. The first step of a roof retrofit project is the installation of a waterproof membrane over the existing roof. After that, a drainage layer ensures that the excess water is not retained on the roof but funneled off it. The next layer consists of a specially designed soil substitution medium into which vegetation is planted.

green space

See →green area.

green tag

See →green certificate.

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 green tariff

green tariff

See →feed-in tariff.

green wall

See →vertical garden.

greenhouse

US Also known as solar greenhouse, glasshouse, or glass house in the United Kingdom. A structure made of glass panels or polyethylene plastic films for growing a variety of vegetables, fruits, flowers, or other plants under controlled, protected conditions. The glass or polyethylene roof and walls allow visible light and shortwave infrared radiation to pass through without letting long-wave infrared radiation escape, which is accomplished through the use of the special glass coating. The heated soil gives off longwave infrared radiation that is trapped in the glasshouse, keeping the interior and plants warm during cold winter days. While the trapped heat is beneficial in winter and fall, it becomes a problem in hot summer months. Therefore, it is common to frequently cycle the air in a greenhouse in the summer. The application of solar fans is an economical way to exhaust hot air from a greenhouse. For larger glass houses, a number of fans can be employed. In order to ensure proper circulation of air, the fans should be installed in such a way that some fans blow fresh air in, whereas the others blow hot air out on the opposite side of the glasshouse.

greenhouse effect

Is a global heating effect that occurs when the heat from the sun is trapped by the heat-absorbing →greenhouse gases in the Earth’s atmosphere. Just as infrared radiation is trapped by the glass roof and walls in an actual greenhouse, greenhouse gases trap long-wave infrared radiation in the Earth’s atmosphere, contributing to increased global warming. Sunlight reaches the Earth as shortwave radiation in the form of visible and ultraviolet light. One part of solar radiation is absorbed by the Earth, whereas the rest is reflected at longer wavelengths in the form of infrared radiation to the outer space, because the Earth is cooler than the Sun. The greenhouse gases trap some of the reflected infrared rays and reradiate them back to the Earth’s surface, creating a greenhouse effect and making the entire planet warmer. Some naturally occurring greenhouse

greenhouse gas emission allowance 

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gases, such as water vapor that is a part of the water cycle, are beneficial, because they keep the average Earth’s surface temperature at 14.5  °C (58  °F), ensuring a comfortable environment for humans, animals, and plants. Without them, the Earth would be a cold and challenging place to live for all living creatures with average temperatures of around 0 °F (or −18 °C). However, the greenhouse gases produced from human activity, such as carbon dioxide or methane, add an extra burden to the earth’s fragile atmosphere. The more greenhouse gas there is, the bigger the blanket trapping the heat (infrared radiation) before it can naturally escape the atmosphere, and consequently, the warmer the planet Earth. greenhouse gas emission allowance

The right to emit one ton of carbon dioxide (CO2) or its equivalent in other greenhouse gases. The allowance can be used to compensate firms or individuals affected by climate change policy.

greenhouse gas emissions

The release of greenhouse gases, such as →carbon dioxide, →methane, →ozone, nitrous oxide, and →chlorofluorocarbons, into the Earth’s atmosphere, which leads to →global warming and →climate change. See also →carbon dioxide emissions.

greenhouse gases

Heat-trapping gases. The greenhouse gases warm the atmosphere by absorbing heat from the sun that is radiated by Earth. They release only part of that heat to outer space and trap a large part in Earth’s atmosphere contributing to the →greenhouse effect. The major greenhouse gas and number one pollutant is →carbon dioxide whose emission values have risen steadily since the onset of the Industrial Revolution. CO2 enters the atmosphere when fossil fuels, such as oil, gas, and coal, are burned or plants decompose. Additional major contributors to increasing global CO2 emissions are transportation, fertilization, landfills, crop burning, just to name a few. Even though water vapor is the biggest contributor to the greenhouse effect, humans are not directly responsible for its emissions, because it occurs naturally in the atmosphere. However, as global temperatures rise caused by man-made emissions of CO2 and other greenhouse gases,

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 greenhouse gas emission reduction

the amount of water vapor in the atmosphere rises proportionally. The global warming triggers more evaporation from the surface of the oceans and lakes. Other important greenhouse gases are →methane, →ozone, nitrous oxide, and →chlorofluorocarbons. The greenhouse gases are responsible for the temperature increase over the past 150 years (1.53 °F [0.85 °C]) from 1880 to 2012, and some hottest temperatures on the record for the Earth over the past decade. greenhouse gas emission reduction

The reduction of overall emissions of carbon dioxide and other greenhouse gases (GHG) into the Earth’s atmosphere. The GHG emissions can be reduced by switching from fossil fuel power generation to renewable energy production. As the electricity and heat generation accounts for 42% of global CO2 emissions, one of the major goals and challenges of many nations around the world is to decarbonize their electric power supply. Regional electric companies should purchase more electricity from local renewable energy sources, such as solar and wind. As they rely more and more on →renewable energy sources and numerous →distributed generation systems, the further optimization of the →smart grid technology is the key to dealing with an increasingly complex system and improving grid reliability. The second largest source of human-made carbon dioxide emissions is transportation, which accounted for almost one quarter (23%) of global CO2 emissions in 2013. One way of coping with this problem is to increase fuel efficiency and switch to →zero-emission vehicles, such as hydrogenpowered fuel cell vehicles or battery-powered →electric vehicles. Another strategy to mitigate emissions from transport is to decrease oversea, international, and interregional transportation by relying more on local products and supply. Passing stricter laws and regulations that address emissions from various transportation vehicles, such as cars, trucks, trains, ships, and airplanes, is another way to tackle transport emissions. More and more cities around the world introduce →low-emission zones in which the most polluting vehicles are restricted or discouraged from access and use. Reducing greenhouse gas emissions from deforestation, agriculture, and industry are further sectors that deserve our full attention.

grid 

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grid

See →electrical grid.

grid compatibility

The ability of power quality characteristics of a solar system to work in harmony with the electrical grid.

grid compatibility test

A test that evaluates whether the electrical properties of a solar power generation system are compatible with the ones of the electrical grid. A grid compatibility test is carried out by the authorized local utility company after the request for grid connection has been approved.

grid connection point

The point at which a solar system is connected to the public electrical grid. Grid system operators test and verify the grid compatibility of the solar system. On the utility side, they make sure that their connection point is suitable in terms of the voltage, frequency, and other →National Electrical Code (NEC) safety requirements in order to be able to warrant an optimized, reliable, and secure operating system. It must be able to absorb the generated energy when the solar system is operating at its maximum capacity. Accordingly, smaller PV systems can be connected directly to a low-voltage power grid. However, larger solar arrays must be connected to a medium- or high-voltage utility grid through distribution or substation transformers to step up the inverter output voltage to the public electrical grid. →Grid-connected photovoltaic systems typically use a →smart grid system with a bidirectional connection, which allows electricity flow in two directions. In addition to the conventional electricity that flows into one’s home from the utility company, solar owners are also able to feed any excess power they produce into the power grid.

grid coupling

A device used to connect a photovoltaic array directly to the grid.

grid failover system

A solar system configuration that relies fully on the public utility energy supply and uses the solar power only as a backup-system during a power outage. A household takes power from the grid and switches to solar generated electricity stored in a battery bank only when there is a power failure.

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 grid fallback system

grid fallback system

A solar system that primarily supplies electricity to a home. Home owners who use the grid fallback system do not sell electricity to a utility company and, in general, rely less on a public grid. This system is the most environment-friendly way to power a house with solar panels. It is a preferred option for smaller households, in particular in areas with unreliable public grid that experience frequent power outages. The electricity generated by PV panels is stored in a battery bank and is used via a DC–AC inverter and the house distribution panel to run all household appliances. When the batteries are depleted, the power is taken/purchased from the public grid to power the house. Once the PV modules recharge the batteries, the system switches back to solar power again.

grid lines

Metallic contacts on the surface of the photovoltaic cell, such as →busbars and →fingers. The shape and design of grid lines is important because they should provide the path of least resistance for electric current flowing through the cells toward →junction boxes. For instance, →tapered busbars have lower resistive losses than busbars of constant width.

grid management

See →grid management system.

grid management software

A software that analyzes, manages, and optimizes a complex network of numerous interconnected electrical systems. Local utility companies use a grid management software to conduct proactive fault detection and prevention; monitor and control voltage levels and energy use; and regulate and configure smart grid devices, for instance smart meters, thermostats, and other appliances.

grid management system

An all-embracing system that constantly coordinates and manages energy generation and consumption with the goal to achieve a balance between supply and demand of electric power. The integration of numerous small-scale residential solar systems into the grid results in a more intricate relationship between solar owners and utility companies, requiring a development of a complex energy management infrastructure with computer-supported load following, scheduling, dispatch, and other ancillary services. Only an intelligent, highly automated and flexible energy management structure can manage the ever-increasing complexity of the grid and ensure grid stability. The grid management

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system encompasses a number of different software and hardware systems, such as advanced distribution management systems (ADMS), outage management systems (OMS), energy management systems (EMS), geographic information systems (GIS), electric-vehicle charging infrastructure, and smart solar inverters. grid operator

An entity responsible for the delivery of electricity over the electrical network to all customers. The major task of a grid operator is power management, ensuring a constant balance between supply and demand of electric power. In the upcoming era of an increased complexity of the →smart grid with countless small renewable energy generation sources, the grid operator will continue to face increasingly complex planning processes and rely more and more on automated systems. The ultimate goal is a complete automation of the grid. In Germany and many other European countries, Australia, and in the US states of California, Hawaii, Oregon, and Vermont, grid operators are obliged to give priority to renewable energy sources when purchasing electricity. Accordingly, they cannot refuse to buy and pay compensation for electricity generated by solar producers.

grid service provider

See →energy service provider.

grid stability

The major goal of utility companies is to achieve a balance between supply and demand of electric power. To ensure power supply at a frequency of 60 Hz in the USA, Venezuela, Western Japan, and Taiwan and 50 Hz in Europe, Argentina, China, India, and Eastern Japan, →ancillary services must constantly coordinate energy generation and consumption. It is relatively easy to plan generation of electricity, but it is difficult to predict future energy consumption. The process of predicting solar and wind energy production is more challenging, as the energy supply is weather dependent, relying on sunshine and wind. Statistical and machine learning models are often used to forecast the annual power production of a future photovoltaic installation.

grid-connected inverter

See →grid-tie inverter.

grid-connected photovoltaic system

See →grid-tie system.

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 grid-connected PV system

grid-connected PV system

Grid-connected photovoltaic system. See →grid-tie system.

grid-connected solar energy

Generated solar energy that is fed back into the grid.

grid-connected solar power

See →grid-connected solar energy.

grid-connected solar power plant

See →grid-tie system.

grid-connected solar power system

See →grid-tie system.

grid-connected solar system

See →grid-tie system.

grid-connected system

See →grid-tie system.

grid-connected system with battery backup

See →grid-tie system with battery backup.

grid-connected system without battery backup

See →grid-tie system without battery backup.

grid-interactive system

See →grid-tie system.

grids

In an →ion beam source, a set of electrically biased grids in which source ions are accelerated to the required energy.

grid-tie inverter

Also known as →synchronous inverter. Converts the generated solar power from direct current to grid-compatible alternating current. It enables the owner to connect his or her PV system to the grid. Two types of inverters that are commonly used in →grid-tie solar systems are: →threephase solar inverter and →single-phase solar inverter.

grid-tie system

(GTS) A solar PV system that is connected to a utility’s electrical grid. Apart from a PV array consisting of numerous interconnected solar panels, this system requires a →twoway electricity meter and a →grid-tie inverter that converts the solar generated DC power into an AC power output that is compatible with the utility power. After the two-way electricity meter and grid-tied inverter are installed, the excess power can be fed into the utility grid and stored for later use.

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During the day, the PV system will power the home appliances and send any surplus energy to the grid. The two-way electricity meter tracks all energy units deposited into the utility’s “bank” simply by running backward. In the evening or at night, when solar irradiation is not available, the energy will be drawn from the grid as usual. There are two types of grid-tie systems: grid-tie system without battery backup and grid-tie system with battery backup The grid-connected solar system without a battery bank is simpler, cheaper, and easier to install and maintain; however, when there is a power outage, the system will shut off. Even though the sun shines outside, the power from the solar system is cut for safety reasons. To mitigate this disadvantage, a battery bank can be added to the PV system. When the grid experiences a power outage, a special inverter switches to battery power that continues to power household appliances without interruption. The grid-tie solar system with battery backup is more complicated to install and maintain than a grid-tie system without batteries, and the costs might reach surprising heights if a larger battery bank is required that can provide uninterruptible power supply for several hours after grid failure. In conclusion, the advantages of a grid-tie system are threefold: it enables one to generate their own energy and reduce their utility bill, save any surplus energy in the utility’s virtual “energy storage bank” for later use, and reduce the carbon footprint and negative impact on the environment. grid-tie system with battery backup

The grid-connected solar PV system with battery backup is more complicated to install and maintain than a grid-tie system without batteries, and the costs might reach surprising heights if a larger battery bank is required that can provide uninterruptible power supply for several hours after grid failure. When the grid experiences a power outage, a special inverter switches to battery power that continues to power household appliances without interruption.

grid-tie system without battery backup

The grid-connected solar PV system without a battery bank is simpler, cheaper, and easier to install and maintain; however, when there is a power outage, the system will shut off. Even though the sun shines outside, the power from the solar system is cut for safety reasons.

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 grid-tied inverter

grid-tied inverter

See →grid-tie inverter.

grid-tied photovoltaic system

See →grid-tie system.

grid-tied PV system

See →grid-tie system.

grid-tied solar energy

Generated solar energy that is fed back into the grid.

grid-tied solar power

See →grid-tied solar energy.

grid-tied solar power plant

See →grid-tie system.

grid-tied solar system

See →grid-tie system.

grid-tied system

See →grid-tie system.

gross collector area

See →gross collector surface.

gross collector surface

The total size of the collector surface, including framing and structural support.

ground

See →earth and →grounding.

ground coverage ratio

(GCR) The ratio of the entire land occupied by the solar array to →solar aperture – all solar panel surfaces capable of absorbing solar radiation. The GCR is calculated by dividing the aperture area by the roof area or the area of land on which the PV array is installed. The higher the ground coverage ratio, the higher the power generation output per unit of land. For instance, the arrays with smaller separation distance between the PV rows (without negative shading effect) have a higher ground coverage ratio than the arrays with greater separation distance between the PV rows.

ground fault

An accidental contact to earth that occurs when current takes an alternative path to the ground from the intended – through the personnel or equipment, posing a hazard of electric shock and fire. A ground fault usually occurs as a result of damaged wiring, insulation failures, and defective or old appliances.

ground fault circuit interrupter 

(GFCI) An appliance that monitors the electric current in a circuit and shuts off the power in the event of a →ground fault to protect people against electric shock. Compared to the →ground-fault protection of equipment (GFPE), the ground-fault circuit interrupter has a lower trip point than the GFPE.

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ground fault protection

Provides protection for personnel and equipment from the effects of →ground faults.

ground fault protection of equipment

(GFPE) A device that protects equipment from damaging line-to-ground fault currents by disconnecting the circuit when a current to ground exceeds the safe values. Compared to the →ground-fault circuit interrupter (GFCI), the GFPE has a higher trip point than the GFCI.

ground mount

See →ground mounting system.

ground mounting

Mounting of a photovoltaic system on the ground, as opposed to →roof mounting.

ground-mounting structure

See →ground-mounting system.

ground-mounting system

A support structure for a →ground-mounted solar array, a frame upon which photovoltaic modules are mounted. See also →rack mount.

ground rod

See →earth rod.

ground source heat pump

Also known as geothermal heat pump. Is a central heating and cooling system that makes use of the heat of the earth or the subterranean water to heat or cool a building. While the air temperature on the surface considerably vary from month to month, season to season, the earth’s temperature in the upper 10 ft below surface remains fairly constant ranging from 45 °F (7 °C) to 75 °F (21 °C) throughout the entire year. One can access this constant energy source by circulating water or refrigerant through a closed- or open-loop system. During the summer, the heat from the interior of a building is moved through a system of underground or underwater pipes into the ground, cooling the building. Here, the subterranean geothermal loop functions as a heat sink. However, during the winter, the water or refrigerant are heated in the same underground piping loop and pumped up into the house, warming the building. Although the installation of a geothermal heating and cooling system may be a complex and costly endeavor, the system can potentially reduce heating and cooling costs by 60%. Horizontal geothermal ground loops, which are buried at 4–6 ft below the surface, are usually less costly to install than vertical ground loops, for which 100–400 feet deep holes must be drilled in the ground.

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 ground state

ground state

The lowest energy level of electrons in a semiconductor material at absolute zero temperature. When they gain enough energy from sunlight, for example, thermal phonon energy or photon energy of light, the electrons can be raised from the ground state to a higher energy state, in which they become excited and jump from the →valence band into the →conduction band.

grounding

Solar PV systems require equipment grounding for safety. All exposed metal parts (metal frames, junction boxes, inverters, charge controllers, batteries) must be connected to ground. The negative terminal on the battery must be grounded. If the proper electrical ground is missing, an →earth rod should be driven into the soil.

grounding connection

A connection between an electric circuit (photovoltaic equipment) and the earth.

grounding rod

See →earth rod.

grounding wire

The wire that carries extra electric current out of the solar panels to the grounding rods.

ground-installed system

See →ground-mounted solar array.

ground-mounted photovoltaic power plant

See →ground-mounted solar array.

ground-mounted photovoltaic system

See →ground-mounted solar array.

ground-mounted power plant

See →ground-mounted solar array.

ground-mounted solar array

A solar array that is mounted on a support structure on the ground. A ground-mounted solar array can be installed on a →fixed or an →adjustable mounting system. The major benefit of an adjustable mounting system is that the tilt angle of the photovoltaic (PV) frame can be changed every month or every season to capture the maximum sunlight. The maximum power output is achieved when photovoltaic panels are perpendicular, at right angles, to the sun. A →solar tracking system will find the best angle for your solar panels at any time, but due to its more complex technology

ground-mounted solar  

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and moving parts, it is prone to failure at some point. It is also much more expensive than an adjustable mounting system. A ground-mounted solar array should be installed in a suitable unshaded area as close as possible to the house to avoid power loses. The modules of a PV system that is more than 15 m (50 ft) away from the house would need to be wired in series (see →series connection) to increase the voltage. Compared to a →roof-mounted solar array, there are three main advantages of a ground-mounted PV system: 1. It is easier to clean the panels in the summer and to remove snow from the modules in winter. 2. It is easier to make seasonal or monthly adjustments to the ideal tilt angle. 3. It is easier to make repairs, system updates, or a modular expansion of the system on the ground. ground-mounted solar power plant

See →ground-mounted solar array.

ground-mounted solar power system

See →ground-mounted solar array.

ground-mounted solar system

See →ground-mounted solar array.

ground-reflected radiation

See →albedo.

groundwater heat pump See →geothermal heat pump. growth of graphene on SiC

A method for graphene production in which the graphene layer is grown directly on an SiC substrate surface. This →epitaxial growth technique permits the growth of numerous graphene layers in a high controllable process. While silicon evaporates from the SiC substrate, the carbon rearranges itself in a hexagonal structure. The graphene islands start forming at different locations on the crystal, growing together into an imperfect whole. Due to its defects or grain boundaries, the graphene product has poor purity. In spite of the limited purity of graphene, the main benefit of this method is the fact that it is suitable for commercial production.

GRP

Abbreviation for glass-reinforced plastic. See →fiberglass.

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GTS

Abbreviation for →grid-tie system.

g-value

Total solar energy transmittance. See →solar heat gain coefficient.

H

hard coating

Impact- and scratch-resistant coating that also provides external protection for solar modules against weathering and abrasion.

hardware costs

Include all solar equipment, such as photovoltaic modules, inverters, mounting systems, performance monitoring systems, batteries, and other components. Hardware costs account for around 40% of the total installation cost today, while the share of →soft costs, such as system design, permitting, inspections, installation, and interconnection, has risen to 60%.

hardware damage

The major causes for hardware damage are harsh environmental conditions, such as high wind, snow, humidity, and extreme temperatures. It is important to be aware of the wind zone in which a solar installation is built. Solar structures in zone 3, which includes all coastal regions of Alaska and many coastal regions of Florida, Louisiana, and North Carolina, must be built to withstand 110 mph winds. Excessive snow loads and ice can also lead to structural damage and PV failures. In addition, the damage is often caused by homeowners trying to knock off the ice and snow of solar panels. In snow-rich regions, additional support rails should be added to the mounting system to increase the structural capacity to carry the snow load. Damage and failure from corrosion can be substantial, in particular in regions with high humidity. A galvanized aluminum mounting system and stainless steel hardware should be used in coastal regions. Dissimilar metals in contact, for example, aluminum and copper, and their use for grounding, conduit, or mounting systems should be avoided at all costs, as they cause accelerated corrosion. During installation, installers should avoid scraping the coating on the frame or ground lugs, as this also leads to a progressive corrosion.

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harmonic content

The number of frequencies in the electric current waveform that exceed the nominal frequency (50 or 60 Hz) in a circuit, leading to energy loss and overheating of the load.

harmonic distortion

When the normal, linear electric current waveform is distorted by →nonlinear loads in an AC circuit we talk about harmonic distortion.

harmonics

See →harmonic distortion.

harvested power

See →solar energy output.

hay box cooking

See →heat-retention cooking.

HCE

Abbreviation for →heat collection element.

HCPV

Abbreviation for high-concentration photovoltaics. See →high-concentration photovoltaic system.

HCPV module

See →high-concentration photovoltaic module.

HCPV system

See →high-concentration photovoltaic system.

HDD

Abbreviation for →heating degree day.

HDPE1

See →high-density polyethylene.

HDPE2

See →high-density plasma etching.

heat

See →heat energy.

heat capacity

The amount of heat that must be added to or removed from a body to increase or decrease its temperature for 1 K (1 °C).

heat carrier

A medium, such as →heat transfer fluid, which transfers heat from →solar collectors to a →heat exchanger.

heat carrier fluid

Also known as heat transfer fluid. Liquid that carries thermal energy or heat from a heat-generating unit, such as →solar collector, to a →heat exchanger.

heat chimney

See →solar chimney.

heat collection element

(HCE) See →absorber tube.

heat conductance

Thermal conductance. See →heat conductivity.

heat conducting paste

A thermally conductive paste specially designed to transfer heat between components, for instance, between the surface and the sensor to ensure adequate thermal contact and hence accurate reading of solar fluid temperatures.

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 heat conduction

heat conduction

Heat transport; heat transfer.

heat conductivity

Thermal or heat conductivity is the ability of a material to conduct heat. It is defined as the rate at which heat is transferred per unit time through a unit area from a warmer surface of a given material to its colder surface. It is measured in watts per square meter kelvin (W/m2K).

heat consumption

The amount of thermal energy consumed by an individual or organization over a period of time. The annual heat consumption is typically expressed in kilowatt hours per year (kWh/a).

heat demand

The amount of thermal energy required to provide hot water for a household and/or heat all heated spaces in a building over a period of one year. Heat demand is commonly expressed in kilowatt hours per annum (kWh/a).

heat dissipation

A cooling process in which heat is transferred to the colder objects and the surrounding environment. For instance, in solar thermal technology, a heat dissipation occurs, when the →cover plate of a →flat-plate collector is not sealed properly, giving off the collected heat to the colder surrounding environment.

heat dump

An appliance, such as pool, fin, or heat pipe heat sink, utilized to remove unwanted excess heat from a solar loop or a high-efficiency solar cell.

heat energy

Also known as thermal energy or heat. A form of energy stored in a body by virtue of its temperature. The atoms and molecules are more excited and move faster in a hot body than in a cold body. Accordingly, the heat is the total amount of atomic and molecular motion in a body.

heat engine

A device that converts thermal energy into useful, mechanical work, for instance, a →Stirling engine.

heat exchanger

A device that transfers the heat from a solar thermal collector to water for domestic usage. In a solar water-heating system, the solar collector absorbs the solar radiation and converts it into a heat transfer fluid, which is then circulated through a copper piping system to a heat exchanger, transferring heat from heat transfer fluid to the domestic water.

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heat flux

The amount of thermal energy flowing through a given surface per time unit.

heat from the earth

Thermal energy of the Earth, originating either from the very surface of the Earth’s crust or from the molten core of the Earth.

heat gain

The amount of heat that is transferred into or produced inside a building space, resulting from solar radiation, cracks and openings in the building envelope, or the heat given off by electrical household appliances, people, and other sources.

heat gain prevention

To prevent heat from entering the building in the summer, the following strategies can be used: 1. Sealing all gaps and openings in the building envelope 2. Keeping direct sunlight off walls, windows, and roofs with →deciduous trees around the house, →facade greening, →awnings, →horizontal shading fins, →vertical shading fins, →light shelves, →deep eaves, →exterior roller shades, →interior roller shades, →low-E windows and curtains 3. Painting exterior walls and doors a light color to reflect solar radiation 4. Inspecting attic insulation and vents, and installing a solar attic fan to ensure proper ventilation of the attic space 5. Avoiding activities that generate heat in a home, such as cooking, doing laundry, or running the dishwasher.

heat generation

Thermal energy generated by converting other forms of energy, such as solar, wind, hydro power, or fossil fuels, into heat.

heat gun

A handheld electrical tool that generates a stream of hot air for heating and melting →EVA films, which bond different solar panel layers together, such as front glass, solar cell strings, and rear Tedlar layer. The heat gun is a must-have tool for a DIY solar panel assembly. A word of caution: a DIY solar panel encapsulation with a heat gun is not without problems, as multiple bulges of different sizes can appear. Although there are some heat gun techniques to remove bulges, the process can take several hours to complete with larger modules. In order to produce waterproof panels, it

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 heat gun

heat gun

is critical to achieve a good vacuum and eliminate all air from the module. Therefore, it might be a good idea to use a →solar panel laminator to properly seal the solar module.

heat insulation

See →thermal insulation.

heat insulation ordinance

See →heat insulation regulation.

heat insulation regulation

Also known as heat insulation ordinance. A thermal insulation standard, such as the one legally adopted in 2000 by the member states of the European Union, which establishes rules and regulations for residential and commercial buildings to reduce heat loss and provide energy saving.

heat loss

The amount of heat that is lost from a building space, solar thermal collector, or a photovoltaic module. See also →heat transfer coefficient.

heat loss prevention

The crucial step to reduce heat loss in a small-scale home solar collector system or a large utility-scale solar thermal piping system is to insulate all pipes and fittings. The common materials used for pipe insulation include: polyethylene, fiberglass wrap, glass wool, mineral wool, rubber foam, cellular glass, and aerogel. In addition, a proper insulation of a solar collector box, →hot water storage tank, or a →molten salt storage system can further minimize heat losses in a solar thermal system.

heat meter

Also known as an energy meter or flux calorimeter. An instrument for measuring thermal energy in solar thermal systems and conventional heating or cooling systems. The heat meter typically consists of three main components: a flow sensor or meter, a matched pair of temperature sensors, and a calculator. A flow sensor measures flow volume and flow rate in the return to the →solar collectors. Two temperature sensors – one in the inlet pipe and one in the outlet pipe – measure flow and return temperatures. Based on the flow and temperature data, the calculator calculates the energy generated by the solar thermal system.

heat mirror

Also known as hot mirror. A thin, transparent film that is inserted between double glazing in a window. The film has a special nanoscale coating that reflects infrared radiation or heat back to its source, while allowing visible light to pass.

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heat pipe

A heat-transfer system consisting of a hollow tube that absorbs heat energy by the process of water evaporation at one end and gives off latent heat by condensation of the water vapor at the other, cooler end of the pipe.

heat pipe principle

A heat pipe is a sealed, hollow metal tube whose inside walls are coated with capillary wick structure, holding a small amount of working fluid. This sealed vessel, which consists of an evaporator and a condenser, acts as a closedloop system. When the heat is applied on one side of the pipe, it causes fluid evaporation. Vapor transfers heat by moving to the other, cooler section of the pipe. As water vapor condenses and changes from its gaseous form into liquid again, it releases heat at the cooler end of the pipe. The working fluid is returned from condenser to evaporator via capillary action through the wick structure and the evaporation–condensation cycle begins anew.

heat pipe vacuum tube

See →evacuated tube solar collector.

heat proofing

The padding that provides thermal insulation for roof, walls, and ductwork.

heat pump

Also known as geothermal heat pump. Is a central heating and cooling system that makes use of the heat of the earth or the subterranean water to heat or cool a building. While the air temperature on the surface considerably vary from month to month, season to season, the earth’s temperature in the upper 10 ft below surface remains fairly constant ranging from 45 °F (7 °C) to 75 °F (21 °C) throughout the entire year. One can access this constant energy source by circulating water or refrigerant through a closed- or open-loop system. During the summer, the heat from the interior of a building is moved through a system of underground or underwater pipes into the ground, cooling the building. Here, the subterranean geothermal loop functions as a heat sink. However, during the winter, the water or refrigerant are heated in the same underground piping loop and pumped up into the house, warming the building. Although the installation of a geothermal heating and cooling system may be a complex and costly endeavor, the system can potentially reduce heating and cooling costs by 60%. Horizontal geothermal ground loops, which are

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 heat recovery

by 60%. Horizontal geothermal ground loops, which are buried at 4–6 ft below the surface, are usually less costly to install than vertical ground loops, for which 100–400 ft deep holes must be drilled in the ground. heat recovery

The collection and reuse of heat from various equipment that would otherwise be wasted. See also →waste heat recovery.

heat requirement

Heat demand for space heating and domestic hot water heating in buildings. Various methods are used for calculation of energy requirements for space heating systems and domestic hot water systems.

heat retention solar oven

A solar oven that utilizes solar energy to perform →heat-retention cooking. The sunlight entering the solar oven box through a window heats the oven’s black metal container that retains heat well. The stored heat is then used to slow cook food in an insulated vessel that prevents the heat loss to the surrounding air. The major limitation of the heat retention solar oven is the fact that it does not work on a cloudy day when there is not enough solar energy to reach safe minimum cooking temperatures.

heat sink

A device that absorbs excessive heat and removes it from a high-temperature element, such as a solar cell. Heat sinks are an essential component of →high-concentration photovoltaic systems, because excessive PV cell temperatures can significantly reduce the power output of the cell or even damage the solar cell. Fin or heat pipe heat sinks are utilized to passively remove unwanted heat from the high-efficiency solar cell in →high-concentration photovoltaic systems.

heat stack

See →solar chimney.

heat storage

Process of storing heat for later use in thermal energy storage systems, such as →hot water storage tank, →thermosiphon system, and →molten salt storage system.

heat storage system

See →thermal energy storage system.

heat storage tank

See →thermal storage tank.

heat storage unit

See →thermal storage tank.

heat transfer

The movement of heat from on object to another of different temperature. According to the first law of thermodynamics,

heat transfer coefficient 

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The movement of heat from on object to another of different temperature. According to the first law of thermodynamics, energy can only be changed from one form to another, but it cannot be created or used up, as the total amount of energy in the universe is always the same. The second law of thermodynamics complements the first law by explaining the direction of energy change: it is always a movement from hot to cold, unless a new energy is added to generate heat. The fast-moving atoms and molecules of a warm object flow to the slow-moving atoms and molecules of a cold object and never the other way around. It is a one-way movement. The atoms and molecules will keep colliding with each other until they reach a thermal equilibrium. This collision of atoms and molecules of different temperatures is called heat transfer. For instance, hot water in your water heater tank will gradually get colder, resulting from heat flow through walls under the influence of colder air surrounding the water heater. The opposite process, →heat gain, is only possible by reheating water with help of solar power or by burning fossil fuels: gas, oil, or electricity. The heat can be transferred in three different ways: 1. →Conduction, in which heat travels through a substance through direct contact, 2. →Convection, in which heat moves through fluid (liquid and gases), or 3. →Radiation, in which heat is propagated through electromagnetic waves. heat transfer coefficient

Also known as K-value. The heat transfer coefficient (h) is equal to the amount of heat (q) transferred through a surface area (A) in a unit of time (Δt), when the difference in temperature between the solid surface (e.g., wall) and the surrounding fluid area (e.g., air) is 1° (ΔT): h = ΔQ/A ⋅ ΔT ⋅ Δt Although a number of different formulas are used, the heat transfer coefficient is typically measured in watts per square meter kelvin W/m2 ⋅ K.

heat transfer fluid

(HTF) Also known as solar fluid. The most common heat transfer fluids are water, glycol–water mixtures, and thermal oil. While water and glycol–water mixtures are frequently used in solar water-heating systems to transfer heat from

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 heat transfer liquid

solar collectors through a heat exchanger to storage tanks, thermal oil is more used in linear solar thermal systems such as →concentrating parabolic troughs. The concentrated sunlight heats a heat transfer fluid in the black absorber tubes, usually synthetic oil, reaching a temperature of about 400 °C (752 °F). The oil is then circulated through the insulated pipe system to a heat exchanger, converting water to steam. Finally, the steam turbine generates electricity. Recent research has shown that →graphite nanofluids might be the heat transfer fluid of the future due to its excellent heat transfer performance. heat transfer liquid

See →heat transfer fluid.

heat transfer medium

See →heat transfer fluid.

heat transfer system

A system that uses an indirect heating medium, such as →heat transfer fluid, and a →closed-loop system to transfer heat from one place (→solar collectors) to another (→hot water storage tank). It typically consists of pumps, pipes, storage tanks, heat exchangers, and heating and/or cooling sources.

heat transmission

Transmission of heat energy by conduction, convection, or radiation, through different materials and substances, for instance, when solar radiation passes through a window pane or through water in a pool.

heat trap

Valves or loops preventing the heat loss through the water inlet and the water outlet piping of the water heater.

heating

Heating of air and water inside a building. As heating accounts for roughly a third of the total →primary energy consumption in developed countries, replacing conventional heating systems with solar heating systems would directly lead to a significant reduction in greenhouse gas emissions.

heating degree day

(HDD) Unit of measurement for heating energy requirements that is calculated based on the difference between room and outdoor temperature.

heating demand

The amount of thermal energy required to be injected into all heated spaces of a building over a period of 1 year.

heating energy

Energy required for heating a building.

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heating energy demand

The amount of energy required to heat all heated spaces in a building over a period of 1 year. The annual heating requirement can be calculated by the following formula: KWh/m2*a – kilowatt hour per square meter per year.

heating energy requirement

See →heating energy demand.

heating load

The amount of heat per unit time that must be added inside a building space to maintain occupant comfort. See also →cooling load.

heating requirement

See →heating demand.

heating, ventilation, and (HVAC) Produces a warm, cool, or dehumidified air in one air conditioning central area and distributes it through duct work into different rooms of a home or a building. heat-retention cooking

Also known as hay box cooking. Cooking of food by using stored heat instead of traditional fuels, such as firewood or gas. A →solar cooker can be utilized to heat food to cooking temperature. After that, the food is placed into an insulated container in which it continues to cook until it is done. The insulation must be good to prevent the heat loss to the surrounding air and the pot must be made of a material that retains heat well. The main advantage of heat-retention cooking is that it uses less energy than the electric stove and many other cooking devices.

heat-sensitive substrate See →temperature-sensitive substrate. heat-trapping gases

Also known as greenhouse gases. Gases, such as →water vapor, →carbon dioxide (CO2), or →methane, which trap heat in the atmosphere, resulting in the rise in temperature of the Earth – the phenomenon called →global warming.

heavy doping

Controlled incorporation of high concentration of impurities (→dopant atoms) into a pure semiconductor in order to change its electrical properties. Heavy doping has a direct effect on the energy band structure of →silicon, causing band gap narrowing and qualitative changes in the optical and electrical properties of a semiconductor.

heliochronometry

Telling time on the basis of the sun.

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 helioelectric power plant

helioelectric power plant

Any power plant that uses the power of the sun or concentrated sunlight to generate the high-temperature heat needed to produce electricity. The helioelectric power plant consists of a large field of sun-tracking mirrors known as →heliostats, which reflect and focus the sun’s beams onto a receiver on the top of a tower. The collected thermal energy, reaching a temperature as high as 1,000 °C (1832 °F), is converted first into hot water and then into steam to drive turbine generators, producing electricity.

heliograph

See →sunshine recorder.

heliostat

A type of →concentrating solar collector covered with mirrors that tracks the sun throughout the day and reflects the Sun’s rays onto a single →receiver on the →solar power tower in →concentrated solar power (CSP) facilities.

heliostat field

Large solar installation including numerous heliostats that focus the sunlight onto a single receiver on the tower.

heliostat field design

An optimal configuration of a heliostat field or different groups of heliostats around a tower is of vital importance for →concentrated solar power plants (CSP plants) with a →central receiver system. Computer-supported optical analysis tools are used to calculate the best layout for hundreds of heliostats. The optimization of the heliostat field design through calculation and tuning of optical parameters of all individual heliostats ensures the best optical efficiency and flux distribution on the central receiver (boiler) at the top of a →solar power tower, which is located at the center of the field. Different optical losses, such as shadowing, blocking, spillage, →atmospheric attenuation, and cosine effect can be avoided by a fine-tuned design of heliostat layouts.

heliostat field layout

See →heliostat field design.

heliotrope

Rotating solar house.

heliotropic device

Any device or system that tracks the movements of the sun across the sky. →Solar tracking system, →heliostats, and →heliotrope are some examples of heliotropic systems.

heliotropic system

See →heliotropic device.

HEMS

Abbreviation for →home energy management system.

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Hertz

(Hz) The SI unit of frequency in →alternating current (AC). The frequency of electrical current is measured in cycles per second. One hertz equals one cycle per second: 1 Hz = 1/s. It shows how many times the direction of electric current is reversed in an AC circuit per second. In Europe and other countries, the direction of electron flow is switched 50 and in the USA 60 times per second. Accordingly, electrical devices in Europe and other countries use 50 Hz and in the USA 60 Hz as the AC frequency.

HET

Abbreviation for →heterogeneous electron transfer.

heteroepitaxy

Epitaxial growth, in which thin layers consist of different materials than the substrate (crystal). As the substrate acts as a seed or a template for the growth, the growing epitaxial films follow the same grain structure and crystallographic orientation as the underlying silicon substrate.

heterogeneous electron transfer

(HET) A movement of an electron between a chemical species and a solid-state electrode.

heterojunction

An interface between an n-layer and a p-layer in a solar cell that consists of different semiconductor materials, for example, in a →p–i–n solar cell.

heterojunction photovoltaic cell

See →heterojunction solar cell.

heterojunction PV cell

See →heterojunction solar cell.

heterojunction solar cell A solar cell whose interface consists of different semiconductor materials, for example, →p–i–n solar cell, →CIS solar cell, or →silicon heterojunction solar cell. The use of different nanostructured layers significantly increases the spectral response, electrical carrier mobility, and thus the power output of solar cells. heterojunction technology

(HJT) See →silicon heterojunction technology.

hibernal solstice

See →winter solstice.

high-absorption capacity

The use of special materials with high-absorption capacity increases solar output. In solar thermal technology, the use of →selective surface coating boosts the absorption capacity of the solar collector →absorber, converting larger amounts of short-wave solar radiation into heat, while

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 high cell voltage

thermal emittance levels low. In photovoltaic technology, the application of special semiconductor materials enables high-absorption capacity. For instance, the combination of different semiconductor materials in a →multijunction photovoltaic cell is capable of absorbing a wider range of the solar spectrum than a single-material semiconductor. high cell voltage

In rechargeable battery technology, high cell voltage allows manufacturers to produce batteries with fewer cells, achieving a higher energy-to-weight ratio. For instance, one high-voltage cell can replace three regular cells. A high energy-to-weight ratio is especially important in the development of efficient →electric vehicles, allowing for better power output and performance. →High energy density increases the range of an electric vehicle.

high-concentration photovoltaic array

See →high-concentration photovoltaic system.

high-concentration photovoltaic cell

Also known as high-concentration solar cell. While in →low concentration photovoltaic systems (LCPV) the concentrating optical devices focus magnified solar energy on single-junction silicon PV cells, high-concentration photovoltaic (HCPV) systems employ multijunction solar cells as solar radiation absorbers. III–V multijunction solar cells specially designed for HCPV systems have reached an energy conversion efficiency of 45%.

high-concentration photovoltaic module

Also known as a HCPV module. A photovoltaic module that uses optical magnification devices, such as Fresnel lenses or dish reflectors, to focus sunlight onto specially engineered III–V multijunction solar cells, increasing solar energy between 150 and 1,000 times. Due to a highconcentration magnification ratio and very high temperatures that they produce, HCPV modules require thermal management, such as heat sinks to avoid thermal damage.

high-concentration photovoltaic panel

See →high-concentration photovoltaic module.

high-concentration photovoltaic system

(HCPV system) Photovoltaic system that uses Fresnel lenses or dish reflectors to concentrate sunlight onto multijunction solar cells. Highly efficient multijunction solar cells with a conversion efficiency of 45% are specially

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designed for high current density, as the HCPV system has a concentration magnification ratio between 150× and 1,000×. The HCPV systems are significantly more efficient than low-concentration photovoltaic systems (LCPVs); however, they are also more expensive to manufacture, install, and maintain. They also require expensive tracking systems and cooling mechanisms, such as heat sinks, to avoid thermal damage. Heat sinks are an essential component of HCPV systems, because excessive PV cell temperatures can significantly reduce solar power output. Fin or heat pipe heat sinks can be used to passively remove unwanted heat from high-efficiency solar cells. Compared to LCPV systems that can capture both the direct and diffuse parts of the solar electromagnetic spectrum, HCPV systems can only absorb direct sunlight. This means that on foggy or cloudy days, they generate little or no electrical power. Therefore, HCPV systems are more suited in southern Sun Belt regions between the 35th northern and 35th southern latitudes than in northern regions with frequent cloudy weather and diffuse light conditions. high-concentration photovoltaic technology

(HCPV technology) Photovoltaic technology that uses lenses or mirrors to concentrate sunlight onto highly efficient solar cells. Compared to the low-concentration photovoltaic (LCPV) technology that can capture both the direct and diffuse parts of the solar electromagnetic spectrum, high-concentration photovoltaics can only harvest direct solar radiation.

high-concentration photovoltaics

See →high-concentration photovoltaic technology.

high-concentration PV array

See →high-concentration photovoltaic system.

high-concentration PV cell

See →high-concentration photovoltaic cell.

high-concentration PV module

See →high-concentration photovoltaic module.

high-concentration PV panel

See →high-concentration photovoltaic module.

high-concentration PV system

See →high-concentration photovoltaic system.

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 high-concentration solar cell

high-concentration solar See →high-concentration photovoltaic cell. cell high electric density

See →high energy density.

high electrical conductivity

Also known as high specific conductance. The ability of certain materials, such as copper, to conduct a large amount of electrical current. Electric current is able to flow through the material with little resistance.

high energy density

Energy density is the key feature of rechargeable batteries. The capacity and a long-lasting performance of a battery are typically measured with help of an energy-to-weight ratio, which is expressed in watt-hours per kilogram (Wh/kg). The higher the energy density per kilogram, the better the performance and capacity of a battery. A battery with a high energy density can store a large amount of energy and supply it to an electrical load for longer than a battery with a low energy density.

high energy density storage

See →high energy density.

high input voltage inverter

See →string inverter.

high power density

Power density is an important feature of rechargeable batteries, indicating how quickly a battery can store and deliver energy per unit of volume. It is measured in watts per kilogram (W/kg). The higher the power density per kilogram, the more rapidly a battery is charged and discharged. This is especially important when a quick surge of power is required to crank a car engine. In addition, the spread of electric vehicles in the future will depend to a significant extent on the improvement of fast charging battery technology.

high-pressure depletion

(HPD) Also known as high-pressure depletion regime. A technique used for deposition of thin-film semiconductor layers, such as hydrogenated amorphous silicon (a-Si:H) or →hydrogenated microcrystalline silicon (μc-Si:H), which is characterized by a high growth rate. To boost the deposition rate, the flow rate of the precursor gas and plasma power in the →reactor are increased, transitioning from a low-pressure to a high-pressure depletion regime.

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high-pressure depletion regime

See →high-pressure depletion.

high-purity quartz sand

(HPQS) Quartz sand with a purity quotient of around or greater than 99.99% silica or →silicon dioxide (Si02). Quartz send is produced by crashing quartz rocks to sand and then purifying it into high-purity quartz sand. Refining and processing of raw quartz into HPQS is essential for solar manufacturing, as silicon photovoltaic cells cannot be produced without high-purity quartz sand.

high-quality plastic

A special type of plastic that is employed in solar modules and solar garden lights due to its hardness, weather resistance, and durability.

high specific conductance

See →high electrical conductivity.

high thermal conductivity

Property of some materials to transfer heat well. Materials with high thermal conductivity are commonly used in microelectronics. See →high thermal conductivity materials.

high thermal conductivity materials

High conductivity materials conduct heat well and are commonly used in microelectronics, for example, as heat sinks. Materials with high thermal conductivity are: →graphene, diamond, silicon nitride, copper, and rock salt.

high thermal mass

See →high thermal mass materials.

high thermal mass materials

Materials with high thermal mass, such as concrete or water, are able to effectively absorb and store solar heat during the day. After the sunset, they reradiate the heat to interior spaces.

high voltage

(HV) An electrical potential at voltages high enough to damage the equipment or cause injury. →National Electrical Code (NEC) defines HV as more than 600 V, nominal.

high-voltage disconnect

Is an electronic module, an automatic disconnect switch, which protects the batteries from overcharging. Usually a part of a charge controller, the HV disconnect constantly monitors battery voltage. When a high battery voltage is detected, the switch automatically disconnects the load (all electrical devices connected to the circuit) from the battery bank to prevent overcharging.

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 high wind load

high wind load

The high intensity of the pressure or force that wind exerts on the surface of a structure, for example, a →solar array.

high-capacity battery

A rechargeable battery that can store a large amount of energy. The higher the capacity of a battery, the longer it can last per charge.

high-density plasma etching

(HDPE) A type of →dry etching in which high-density plasma is employed for etching semiconductor wafers. An energy source is often used for generating plasma and another energy source for accelerating ions toward the substrate. The HDPE utilizes a source of electromagnetic radiation, such as microwaves, to produce plasma in a separate chamber. The flow direction of the ions is controlled by magnetic fields, providing the uniformity of the ion flux at the substrate.

high-density polyethylene

(HDPE) Also known as polyethylene high-density (PEHD). A  petroleum thermoplastic with a high strength-to-density ratio, which is commonly used for the manufacture of geothermal heat transfer piping systems. HDPE has found wide application in buried piping systems due to its resistance to humidity, impact and chemicals as well as its superior tensile strength.

highly concentrated photovoltaic

(HCPV) photovoltaic technology that uses lenses or mirrors to concentrate sunlight onto highly efficient solar cells.

highly transparent plastic layer

A specially engineered polymeric thin film employed as a top cover in a solar module, allowing a maximum amount of light to pass through and reach photovoltaic cells.

high-pressure test

A proof, leak, and burst pressure test up to 200,000 psi with liquid for checking the integrity of pressure vessels such as pipelines, tanks, and boilers.

high-purity silicon

A type of silicon semiconductor material with a high-purity level of 99.99% that is required for a successful manufacture of crystalline silicon solar cells. Silicon is commonly purified by a method that encompasses reduction and/or thermal decomposition of an exceptionally pure vaporizable compound of silicon such as trichlorosilane.

high-tech glass window

Window that consists of two or three glass sheets hermetically sealed with space between the panes. The space between the panes can be filled by an inert gas, such as argon or krypton, or a vacuum technique can be applied to

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increase insulation. The specially designed glass coating is added to block heat and glare but to let sunlight in. high-temperature collector

A solar collector, such as →flat-plate collector and →evacuated-tube collector, designed and constructed for operating at temperatures above 180 °F or 82 °C.

high-voltage breakdown

Failure that occurs when the electric field in a system becomes high enough to cause large outbursts of electrons.

high-voltage direct current power transmission

HVDC power transmission.

high-voltage direct current transmission technology

HVDC transmission technology.

high-voltage line

See →high-voltage power line.

high-voltage lines

See →primary circuit.

high-voltage photovoltaic cell

See →high-voltage solar cell.

high-voltage photovoltaic module

See →high-voltage solar module.

high-voltage photovoltaic panel

See →high-voltage solar module.

high-voltage power lines

Also known as high-voltage transmission lines. A set of wires that carry electrical energy at high voltage from the power plant to substations that deliver electricity to customers.

high-voltage PV cell

See →high-voltage solar cell.

high-voltage PV module

See →high-voltage solar module.

high-voltage PV panel

See →high-voltage solar module.

high-voltage solar cell

Also known as a high-voltage photovoltaic cell. A solar cell with high voltage and low current, which can achieve up to 10% higher conversion efficiency than a traditional silicon cell. Due to their high voltage, these solar cells reduce electrical resistance losses. The cells can be connected in parallel, minimizing undesirable current mismatch effects.

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 high-voltage solar module

high-voltage solar module

Also known as a high-voltage photovoltaic module. A solar module consisting of →high-voltage solar cells that are specifically designed for high-voltage systems. According to →National Electrical Code (NEC), a high-voltage system is a circuit with over 600V. Due to high voltage, modules should be installed behind the fence and operated by public utilities. High-voltage solar modules can be up to 10% more efficient than regular silicon solar modules. Because of their significantly higher efficiency, the installation costs of high-voltage solar modules are proportionally reduced.

high-voltage solar panel See →high-voltage solar module. high-voltage strength

→National Electrical Code (NEC) defines high voltage as an electrical potential with more than 600 V, nominal.

high-voltage transmission lines

See →high-voltage power lines.

HJT

Abbreviation for heterojunction technology. See →silicon heterojunction technology.

HOE

Abbreviation for →holographic optical element.

hole

The vacant position that would normally be occupied by an electron in semiconductors. When an electron is promoted from the →valence band into the →conduction band, it leaves behind a hole. Even though they are not physical particles, they behave as particles with the same characteristics as electrons. Unlike electrons that move along the conduction band, holes move from atom to atom along the valence band in the opposite direction, carrying positive charge. Together with electrons they are responsible for electric current generation in semiconductor materials.

hole conduction

Although only electrons are commonly associated with current flow, it is critical to also view →holes as equally important electrical charge carriers in a →semiconductor. Just as electrons carry negative electrical charge, holes carry positive electrical charge in the →valence band and without them current conduction would not be possible.

hole mobility

A measure of velocity at which a charge carrier →hole moves through the semiconductor.

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hologram

A three-dimensional image formed by the interference between two parts of a split laser beam.

hologram foil

See →holographic foil.

hologram layer

See →holographic foil.

holographic bifacial solar module

See →holographic double-sided solar module.

holographic diffraction grating

A type of →diffraction grating that can either consists of a large number of replicated, parallel grooves or of grooves of unequal distribution on a reflective surface in order to optimize system performance. A holographic diffraction grating is manufactured using a photolithographic process.

holographic double-sided solar module

A solar panel that captures sunlight from both sides of the module.

holographic film

See →holographic foil.

holographic foil

Also known as holographic film or hologram foil. A thin film embossed with a hologram. Holographic elements responsible for bending, redirecting, and concentration of light are printed on a glass or foil using lasers. While this technology is still in an embryonic phase, holographic foils promise to replace expensive →Fresnel lenses. Although the holographic optical element is only a few millimeters away from the photovoltaic cell, it still achieves a decent 20- to 30-times light concentration. One of the major hopes of this new technology is the bending of light waves by using the principle of →diffraction. It enables a splitting and selection of different ranges of electromagnetic waves to increase the solar output. Thus, the separated visible wavelengths of light are concentrated on a PV cell, while the infrared wavelengths are directed at a solar thermal →absorber. The absorption of heat eliminates the overheating problem, known as the major issue of conventional solar panels. Compared to a standard solar cell efficiency of around 20%, this method promises a record conversion efficiency of over 28%. Another important advantage of the holographic foil method is material savings. The technology also utilizes

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 holographic optical element

the second most abundant element on Earth silicon, but, due to the strong concentration of light, it requires only a fraction of silicon semiconductor material that a conventional solar cell uses. holographic optical element

(HOE) A type of solar concentrator that uses a thin film printed on a glass with a specific holographic structure that is engineered to bend, redirect, and concentrate light beams in such a way that it increases the performance of solar cells multiple times. In comparison to traditional refractive and reflective optics, the HOE is much thinner and made of a lightweight film. Compared to the expensive →Fresnel lenses production, the HOE manufacturing is rather inexpensive because it uses the low-cost, high-output laser printing process.

holographic structure

The configuration of holographic lenses with different symmetries, for example, spherical and cylindrical, in holographic concentration technology.

home automation

A house that uses a computer system to control interconnected home appliances, such as washer/dryers, lighting, ventilation, heating, and air conditioning, in order to save energy. The automation system relies on system management software, appliance controllers, motion and temperature sensors, and cameras.

home energy audit

See →energy audit.

home energy management system

(HEMS) A computer-based system that monitors, analyzes, and manages energy consumption at home. By tracking electricity consumption in real time, detecting equipment faults, and analyzing interactions and trends, homeowners can better control their energy usage, reducing their electricity costs as well as CO2 emissions harmful to environment at the same time. See also →smart energy management system.

home energy storage system

Unlike →large-scale solar energy storage systems that store energy for entire districts, the storage of energy in a home energy storage system is limited to one residential house. This small-scale energy storage system includes devices such as →hot water storage tanks or →battery banks.

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home photovoltaic system

See →homemade solar power system.

home PV system

See →homemade solar power system.

home solar system

See →homemade solar power system.

homemade electricity

Also known as homemade energy or homemade power. Electricity generated in your own home by means of a →solar array or a →wind turbine system.

homemade energy

See →homemade electricity.

homemade power

See →homemade electricity.

homemade solar energy See →homemade solar power system. system homemade solar power system

Also known as a homemade solar energy system or homemade solar system. A solar power system that is designed and built by a do-it-yourselfer or a handyman without the aid of experts or companies. Even though there are numerous do-it-yourself kits and books available on the market on the topic of the design and installation of photovoltaic (PV) systems, the homeowner must have a certain level of technical skill and especially a good working knowledge of electricity and wiring. Generally, it is not recommended to put together a solar array from different components bought on sale. The interconnecting and mismatching of PV cells or modules that have dissimilar properties can lead to serious energy losses or even system failures. The best practice is to wire solar modules and batteries of the same make and model with identical properties. An equally serious problem a DIY enthusiast might encounter is a mismatch between solar modules and the battery bank. The charging of 12-V deep-cycle batteries with 24-V solar modules without an appropriate power controller, which should limit the excessive current, can damage the batteries. It is also important to use only plug-in connectors from the same manufacturer for a solar array. Using incompatible plug-in connectors from different manufacturers leads to overheating due to increased electrical resistance, resulting in energy losses, failures, and damage to the PV system.

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 homoepitaxy

homoepitaxy

Epitaxial growth, in which thin layers consist of the same material as the substrate (crystal). As the substrate acts as a seed or a template for the growth, the growing epitaxial films follow the same grain structure and crystallographic orientation as the underlying silicon substrate.

homojunction

An interface between an n-layer and a p-layer in a solar cell that consists of a single semiconductor material, for example, in a p–n solar cell.

homojunction solar cell

Solar cell whose interface consists of a single semiconductor material, for example, p–n solar cell.

horizontal axis

An imaginary horizontal line around which a solar tracker rotates solar modules horizontally with respect to the ground, following the east-to-west movement of the sun across the sky.

horizontal irradiation

Irradiation on horizontal surfaces.

horizontal plane

A flat surface, such as a solar module, parallel to the horizon. In various solar irradiance estimation methods, the radiation on a tilted plane is measured and compared against the radiation on a horizontal plane. Daily measurements performed on tilted and horizontal planes are used to calculate a monthly mean value.

horizontal single-axis tracker

(HSAT) A type of a single-axis tracker that rotates solar panels from east to west on an axis that is horizontal with respect to the ground. Electric motors and maximum light detection controllers or computer-navigated devices control the motion of solar modules that are mounted on horizontal steel tubes throughout the day. Solar module rows need to be spaced apart to avoid the self-shading effect and energy losses during rotation. →Large-scale solar power plants typically use horizontal single-axis trackers.

hot electron

Highly excited electron.

hot mirror

See →heat mirror.

hot point effect

See →hot spot effect.

hot spot

See →hot spot effect.

hot spot effect

Overheating as a result of damaged cells or partial shading of a solar panel. Shaded or cracked cells function as a

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resistive load in a PV module causing a large dissipation of power in the bad cells, which in turn results in overheating and often in melting of the cells. The hot spots in case of partial module shading or broken cells can be eliminated and our healthy cells protected by installing →bypass diodes in solar modules. hot spot heating

See →hot spot effect.

hot water

Artificially heated water, for example, by →solar collectors, for domestic use, such as food preparation and washing, space heating, and pool or spa heating.

hot water circulation

A closed circuit consisting of a hot water storage tank, a piping system, and pumps that circulate domestic hot water across the house to all faucets, dish washer, washing machine, and space heating system.

hot water cylinder

See →hot water storage tank.

hot water solar boiler

See →solar hot water storage tank.

hot water storage tank

An insulated vessel for storing hot water for domestic use, space heating, and pool or spa heating. The temperature of the water in the tank is usually regulated by a thermal controller and a pump, which are automatically turned on when a temperature set point is reached. The hot water that is stored in hot water storage tanks can be generated by →solar collectors.

hot water tank

See →hot water storage tank.

hour angle

The difference between local solar time and solar noon, which is the reference point: zero. The hour angle, which is expressed in degrees, increases by 15° every hour. In the afternoon, the hour angle is positive in the westward direction, whereas it is negative in the morning in the eastward direction.

house energy plant

A concept in which a single energy generation plant, for example, powered by a solar array, provides power supply for all household appliances and home equipment. In contrast, in a decentralized energy generation model at a house level, many devices are powered straight by their own integrated or nonintegrated photovoltaic cells.

house wrap

See →weather-resistant barrier.

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 housewrap

housewrap

See →weather-resistant barrier.

HPD

Abbreviation for →high-pressure depletion.

HPQS

Abbreviation for →high-purity quartz sand.

HRES

Abbreviation for →hybrid renewable energy system.

HSAT

Abbreviation for →horizontal single-axis tracker.

HSSE

Abbreviation for →Croatian Solar Energy Association.

HTF

Abbreviation for →heat transfer fluid.

human-made aerosols

Unlike →natural aerosols that form fog and clouds through the condensation of vapor species, artificial, human-made aerosols, come primarily from the burning of tropical and subtropical rain forests as well as of coal and oil (sulfate aerosols). They are responsible for the formation of dust, smoke, haze, and perturbed (polluted) clouds.

humidity

Also known as atmospheric moisture. The amount of water vapor in the air. See also →relative humidity.

HVAC

Abbreviation for →heating, ventilation, and air conditioning.

hybrid collector

Collector that converts solar radiation into electrical and thermal energy.

hybrid cooling system

A system that combines two cooling technologies, for instance, air cooled condensers, cooling towers, surface condensers, or air-cooled heat exchangers, in a single operating system.

hybrid installation

See →hybrid mounting.

hybrid inverter

An inverter that is commonly used in →off-grid photovoltaic (PV) systems, combining inverter and battery storage technologies in one system. Similar to a standard PV inverter, the hybrid inverter converts DC energy generated by solar panels into AC electricity and the voltage to the same voltage as you receive from the public grid. In addition, it works together with a →battery bank, in which it stores any surplus energy. In the evening or on cloudy days when the solar source is not available, the hybrid inverter draws upon the stored energy to ensure an uninterruptable power supply, in particular in remote regions far away from the utility grid.

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hybrid material

A semiconductor material mix that combines →organic and →inorganic semiconductor materials to increase the conversion efficiency of a →solar cell. The organic materials, such as conjugated polymers or pentacene, are employed as →donors, absorbing the photons of light, generating →excitons (e.g., pentacene is able to produce efficient spin-triplet excitons), and transferring them to an inorganic semiconductor. The inorganic material, usually silicon, acts as an →acceptor that harvests electrons and passes them along the conduction band, creating a steady current flow.

hybrid mounting

Also known as minimally attached mounting. A solar system mounting technique that combines two installation technologies: →ballasted mounting and →mechanically attached mounting to keep the number of roof penetrations to a minimum.

hybrid photovoltaic cell

Combines a photovoltaic (PV) cell with conjugated polymer films to achieve a higher total conversion efficiency. By pairing organic and inorganic semiconductor materials, hybrid PV cells are able to capture a larger portion of the solar spectrum than conventional silicon solar cells. The heterojunction organic–inorganic hybrid complex simultaneously harnesses sunlight and heat. The inorganic semiconductor materials can be processed as nanoparticles of different sizes, making a band gap tuning possible. By changing the size of the nanoparticles, the band gap is tuned to achieve the highest electron mobility within the photoactive layer. The result is the maximum energy yield from the sunlight. The part of the solar radiation that is not absorbed by the PV cell is captured by the second organic polymer film that warms up, converting unused light into heat. Finally, a sheet of pyroelectric film and a thermoelectric device, which are placed under the polymer layer, convert heat into electricity. The complex technology makes hybrid PV cells more expensive than conventional silicon PV cells; however, a significantly higher power output might compensate for the pricey investment.

hybrid photovoltaic module

A high-efficiency module consisting of photovoltaic cells with an additional organic conjugated polymer layer responsible for capturing the unused heat. This combination

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 hybrid photovoltaic panel

of photovoltaic and thermal conversion technology, which is able to harvest both sunlight and heat, is an ideal choice for crowded civic environments where maximum power output in minimum space is desired. hybrid photovoltaic panel

See →hybrid photovoltaic module.

hybrid photovoltaic system

A solar power generation system that consists of a photovoltaic system and at least one other power generation device, for example, a diesel generator or wind turbine. See →photovoltaic diesel hybrid system, →solar–wind hybrid power system, and →solar–wind–diesel hybrid system.

hybrid power plant

US A power plant that combines two or more technologies, for instance, solar, wind, and diesel, with the aim of providing a stable energy supply, in particular in remote isolated regions, far away from power lines.

hybrid power station

GB See →hybrid power plant.

hybrid power system

See →hybrid solar system.

hybrid PV cell

See →hybrid photovoltaic cell.

hybrid PV module

See →hybrid photovoltaic module.

hybrid PV panel

See →hybrid photovoltaic module.

hybrid PV system

See →hybrid photovoltaic system.

hybrid PV/T system

Stands for a hybrid photovoltaic and thermal system. See →combined solar collector.

hybrid renewable energy system

(HRES) Any power generation system that relies on renewable energy sources, such as solar, wind, or hydro, to produce electricity. A hybrid renewable energy system combines two or more renewable technologies with the aim of providing a stable energy supply, in particular in isolated far-off regions that cannot rely on the electrical network. Some renewable energy sources, such as solar and wind energy, are considered variable, intermittent energy resources, because their energy production fluctuates all the time. The limited power production of each individual system is overcome by merging solar and wind generation into one hybrid system, which can provide a more stable power supply throughout the year.

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hybrid solar cell

See →hybrid photovoltaic cell.

hybrid solar module

See →hybrid photovoltaic module.

hybrid solar panel

See →hybrid photovoltaic module.

hybrid solar system

See →hybrid photovoltaic system.

hybrid system

See →hybrid photovoltaic system.

hybrid technology

A technology that combines two or more technologies with the aim of providing a stable energy supply for a household, in particular in →off-grid photovoltaic systems that cannot rely on the electrical network. Different systems complement and enhance one another. In a →solar–wind– diesel hybrid system, the →wind turbine system will supply the most energy on an overcast day, when the energy output from PV modules drops to minimum. Similarly, the solar system will take over on a calm day without wind, when the blades of the wind turbine are not turning. The diesel generator, acting as a backup system, will kick in when both other systems are not available.

hydroelectric

Relating to the generation of electricity by harnessing the power of moving water.

hydroelectricity

Electricity generated by harnessing the power of moving water.

hydrogen

This gas is the lightest and most abundant element in the universe. The electrolysis process is used for hydrogen production by passing an electrical current through water and splitting water molecules into hydrogen and oxygen. If the solar energy is used to produce hydrogen gas, then such hydrogen can be classified as a sustainable solar fuel.

hydrogen fuel

An emissions-free alternative fuel when used in a →hydrogen fuel cell to generate electricity or burned with oxygen to form nonpolluting water vapor.

hydrogen fuel cell

Hydrogen fuel cells generate electricity without pollution. Unlike power sources that use fossil fuels, the hydrogen fuel cells convert the chemical energy from hydrogen directly into electrical energy without heat/energy losses that occur in the combustion process. Hydrogen is a preferred fuel cell energy source because it ensures a quiet

352 

 hydrogenated amorphous silicon

and simple, but nevertheless efficient and sustainable energy generation process. The hydrogen fuel cell method reverses the electrolysis process by providing a continuous supply of hydrogen gas to one electrode (anode) and oxygen to the other (cathode). Since they are chemically attracted to each other, the hydrogen and oxygen combine and produce electricity as the chemical reactions unfold. hydrogenated amorphous silicon

(a-Si:H) Amorphous silicon semiconductor containing 10% hydrogen. The addition of hydrogen to an amorphous silicon eliminates the electronic defects of the pure amorphous silicon through the passivation of the silicon dangling bonds. The reduction of the dangling bond density results in an increased photoconductivity and thus an improved absorption coefficient in the amorphous silicon solar cell. As the hydrogen incorporation allows the doping of the thin film semiconductor material, the added impurities boost electric current flow in the semiconductor.

hydrogenated microcrystalline silicon

(μc-Si:H) A semiconductor silicon material that is used for the manufacturing of thin-film solar cells. It is a popular material because it makes the processing of complex microstructures at law temperatures possible. The low-temperature process on large areas with little material consumption allows a deposition of a thin semiconductor layer in the micrometer range on substrates. μc-Si:H has good optoelectrical characteristics with an extended spectral response to the near infrared (IR) region. Hydrogenated microcrystalline silicone is often deposited on top of the conventional →hydrogenated amorphous silicon (a-Si:H) solar cell to form a tandem or multijunction cell with high-conversion performance.

hydrogenated microcrystalline silicon solar cell

Also known as a μc-Si:H solar cell. A solar cell that is made of →hydrogenated microcrystalline silicon.

hydrolysis

Old Greek, hydor “water,” lysis “separation, loosening, decomposition”; splitting of a chemical bond by reacting with water.

hydrometer

A device for measuring the specific gravity of liquids, which is the ratio of the density of the liquid to the density of water. The composition of the →heat transfer fluid in a solar–thermal system is typically measured with the help of a hydrometer.

hydronic 

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hydronic

Relating to a heating system that transfers heat by circulating hot water or heat transfer fluid (glycol) through a closed system of pipes, for example, underfloor heating system.

hydronic cooling system

The use of water (hydro) or →heat transfer fluid to cool a building. In a hydronic cooling system, radiation to the night sky cools water or heat transfer fluid, which then cools the building by circulating the cooled liquid through the hydronic piping system.

hydronic heating system

The hydronic heating system transfers heat by circulating hot water or heat transfer fluid (glycol) through a closed system of pipes, e.g. underfloor heating system. See also →hydronic system.

hydronic system

The use of water (hydro) or →heat transfer fluid and electronics (pumps and sensors) to heat or cool a building.

hydrophobic

See →water-repellent.

hydrophobic coating

See →water-repellent coating.

hydrophobic layer

See →water-repellent coating.

hydrosilicon

A compound that contains at least one hydrogen atom bonded to a silicon atom.

hydrostatic pressure test

A procedure for checking the integrity of pressure vessels, such as pipelines, tanks, and boilers. The vessel is filled with a liquid, such as water or →heat transfer fluid, and subjected to the specified test pressure. After the pressure supply is turned off, the pressure within the vessel is monitored for a pressure loss.

hydrostatic test

See →hydrostatic pressure test.

hydrotesting

See →hydrostatic pressure test.

hydrotesting new piping systems

After construction and before placing a utility-scale solar– thermal pipeline in service, →hydrostatic pressure tests are utilized by licensed professionals to ensure the integrity of the pipeline.

hysteresis

Difference between the switch-on and off temperature.

hysteresis brake

Locking the turbine once the batteries are fully charged.

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 I/H converter

I

I/H converter

Current to hydraulic pressure converter.

I/P converter

Current to hydraulic pressure converter.

IAD

Abbreviation for →ion-assisted deposition.

IBAD

Abbreviation for ion beam assisted deposition. See →ionassisted deposition.

IBC

Abbreviation for →integrated backside contact.

IBD

Abbreviation for →ion beam deposition.

IBE

Abbreviation for →ion beam etching.

IBG

Abbreviation for →indirect band gap.

IBSD

Abbreviation for →ion beam sputter deposition.

ICP

Abbreviation for intrinsically conducting polymers. See →conducting polymers.

idle power

The energy in an AC circuit that does not perform work. See also →standby power.

IEA

Abbreviation for →International Energy Agency.

IECC

Abbreviation for →International Energy Conservation Code.

IEEE

Abbreviation for →Institute of Electrical and Electronics Engineers.

IES

Abbreviation for →integrated energy system.

IFEU

Abbreviation for Institut für Energie- und Umweltforschung Heidelberg. See →Institute for Energy and Environmental Research Heidelberg.

III–V semiconductor

A compound semiconductor consisting of elements from groups III (e.g., gallium, indium) and V (e.g., arsenic, nitrogen) of the Periodic Table. One frequently used III–V semiconductor is the two-element compound →gallium arsenide (GaAs), which is known as one of the most efficient solar photoactive materials. The three-element compounds →indium gallium arsenide (InGaAs) and →indium gallium nitride (InGaN) are further examples of efficient III–V semiconductors.

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illuminance

The amount of visible light – solar radiation in the visible region of the solar spectrum – falling onto a given surface area.

immobilized electrolyte

Also known as captive electrolyte, immobilized electrolyte is an electrolyte used in →sealed batteries. The electrolyte is immobilized by turning the liquid sulfuric acid into a gel form or by absorbing the electrolyte into fine fiberglass mats that are sandwiched between the positive and negative battery plates.

impact pressure

The difference between total pressure (pitot pressure) and static pressure.

import meter

A meter that measures the amount of electrical energy imported from the public electricity grid. See also →smart meter.

IMPP

Abbreviation for →maximum power point current.

impressed current anode

An anode powered by current from an external DC source to control corrosion of a buried or submerged structure.

impurity

Intentional incorporation of impurities into a pure semiconductor, in order to change its electrical characteristics.

impurity atom

See →dopant atom.

impurity concentration

See →doping concentration.

impurity conduction

A process in which a donor electron, such as a →phosphorus donor electron, moves from one silicon atom to another across the host crystal lattice and hence generates electric current in a photovoltaic cell. During the growth of a silicon crystal, impurities and imperfections are incorporated into the silicon crystal structure in a controlled manner to initiate the liberation and movement of the fifth phosphorus electron from the outer valence shell upon the absorption of →phonons of heat or →photons of light.

impurity gas

Also known as →dopant gas. A gas that contains a silicon dopant, for instance, diborane (B2H6). It is typically introduced into a reactor chamber, where it is first ionized and then deposited onto a silicon substrate to define the electrical properties of semiconductor layers. See also →dopant gas.

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impurity gradient

Also known as doping gradient. The rate of change of a →doping density introduced in a semiconductor material.

impurity semiconductor

See →doped semiconductor.

impurity species

See →dopant species.

inaccuracy error

A difference between a specific measurement and the true value of the quantity being measured.

incandescent bulb

See →incandescent light bulb.

incandescent light

See →incandescent light bulb.

incandescent light bulb

A light bulb that generates light by heating a tungsten filament to high temperatures until it emits visible light.

incidence

The falling of light rays on a surface, while moving in a straight line.

incidence angle

Angle between the solar beam and the perpendicular (90°, straight on) line to the surface. It is the angle at which the sun’s rays hit solar cells. The closer the solar ray to the 90° angle is, the greater the solar radiation and correspondingly the energy yield of a solar power system.

incident angle

Also known as angle of incidence. See →incidence angle.

incident light

Light that falls onto the surface of a solar module, as opposed to the reflected light.

incident photon to converted electron

(IPCE) See →quantum efficiency.

incident photon-tocurrent efficiency

(IPCE) See →quantum efficiency.

incident radiation

Incoming radiation. See →incident solar radiation.

incident solar radiation

See →insolation and →solar irradiance.

incidental irradiation

See →incident solar radiation.

inclination

See →inclination angle.

inclination angle

Angle between the horizontal and the solar panel. Straight up has an inclination angle of 90°.

increase in electricity prices

An argument that is often raised against promotion of solar energy is that generous sponsorship of renewable energies is driving electricity prices up. The counterargument of

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solar dealers usually states that if the price of electricity is constantly increasing, the payback on solar project investments is a lot shorter due to the generated savings. independent power producer

Also known as a nonutility generator (NUG). A person, company, or other legal entity that is permitted to produce electricity for sale to electric utilities. Over the past three decades, many countries have made significant efforts to decrease the amount of harmful →greenhouse gases as well as their dependence on foreign energy by promoting the local energy production. Favorable →feed-in tariffs and a variety of incentive mechanisms have been created to encourage the deployment of solar energy and other renewable energy resources. With this help, nonutility power producers can sign a long-term power purchase agreement (typically covering the period between 10 and 25 years) that includes a long-term price guarantee, but they also must fulfill certain operating, efficiency, and ownership standards established by their responsible regulatory agencies and authorities.

independent power system

A stand-alone solar power system that is not connected to an electrical grid. See also →off-grid photovoltaic system.

independent system operator

(ISO) A US organization in charge of maintaining the system reliability by continuously balancing supply (electricity generation) and demand (the load).

index of refraction

The ratio of the velocity of light in one medium to the velocity of light in a second medium.

indirect band gap

(IBG) A band gap in which the electrons in the conduction band and holes in the valence band have different momentums. The maximum energy level of the →conduction band is not in alignment with the minimum energy level of the →valence band. Due to this momentum mismatch, hindering the electron mobility, the probability of radiative recombination is relatively low, compared to the perfectly aligned →direct band gap. The electron must pass through an intermediate state, in which an interaction with a third particle with momentum, a →phonon, takes place. Vibrations of the atoms in the crystal or phonons are required to raise the electrons into the conduction band. This indirect band edge recombination results in a lower light absorption.

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 indirect band gap semiconductor

This is why semiconductor materials with an →indirect band gap, such as →silicon (Si) and →germanium (Ge), are less efficient than materials with a direct band gap, such as →gallium arsenide (GaAs) and indium arsenide (InAs). indirect band gap semiconductor

A semiconductor with an →indirect band gap. The materials, such as →silicon (Si) and →germanium (Ge), are examples of indirect band gap semiconductors. Due to the indirect band gap, these materials exhibit less favorable optoelectronic properties and a lower solar energy absorption coefficient than the →direct band gap semiconductors, such as →gallium arsenide (GaAs), indium arsenide (InAs), and indium phosphide (InP).

indirect circulation system

See →closed-loop system.

indirect lighting

A lighting system that directs the indoor light upward toward the ceiling and upper parts of walls, where it is reflected back down into the room.

indirect radiant cooling

See →indirect radiative cooling.

indirect radiation

See →indirect solar radiation.

indirect radiational cooling

See →indirect radiative cooling.

indirect radiative cooling

Also known as indirect radiant cooling or indirect radiational cooling. A type of radiative cooling that uses water (hydro) or →heat transfer fluid to cool a building. Radiation to the night sky cools water or heat transfer fluid, which then cools the building by circulating the cooled liquid through the hydronic piping system.

indirect solar dryer

Compared to the food that is directly heated by the sun in →direct solar dryers, the food to be dehydrated in indirect solar dryers is not directly exposed to the sunlight. Although there are a wide variety of indirect solar dryer designs, they all share the same, simple food-drying principle that is based on hot-air circulation in an enclosed space. The air is drawn in through an inlet or vent holes at the bottom of the box; it is absorbed and heated by the black surface. Finally, the heat is allowed to exit through an outlet or vent holes at the top. Following the principles of natural

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convection, the hot air continuously moves upward, circulating around food pieces and removing efficiently moisture from food. To ensure uniform drying and better control of hot-air circulation, specially arranged racks and solar-powered fans can be added inside the dryer. See also →solar dryer. indirect solar radiation

Indirect solar radiation include →diffuse solar radiation and →reflected solar radiation.

indirect solar system

A closed solar collector loop system that employs antifreeze solar fluid to transport thermal energy from →solar collectors to a →heat exchanger that transfers the heat to domestic water stored in the tank.

indium

(In) Very rare posttransition metal that is used for manufacturing thin-film →copper indium gallium selenide solar cells. Indium atoms are commonly utilized for →p-type doping, generating →holes in a →valence band.

indium gallium arsenide (InGaAs) A III–V compound semiconductor material that consists of the group III elements indium and gallium and the group V element arsenic. Indium gallium arsenide is used as a thin layer in triple-junction solar cells to improve PV cell efficiency by capturing a wider range of the electromagnetic spectrum. By engineering the GaInAs band gap in such a way that it matches the →germanium (Ge) substrate, the extra energy of solar radiation can be unlocked and converted into electricity. indium gallium nitride

(InGaN) A III–V compound semiconductor material that combines gallium nitride (GaN) and indium nitride (InN). Indium and gallium are both the elements of group III and nitrogen is the element of group V of the Periodic Table. In the field of photovoltaics, the application of the InGaN semiconductor is still in a development phase. Although the semiconductor material is not yet ready for the market, the easy tunability of its band gap to capture wider ranges of solar spectrum promises a future application in →multijunction solar cells. In addition, GaN has a →wide band gap, which allows the semiconductor to be operated at high voltage and high temperatures. One of the methods that a group of scientists at the Arizona State University and the Georgia Institute of

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 indium oxide

Technology are currently working on is known as a metal modulated epitaxy method. It is a variation of the epitaxial growth process in which a thin layer of semiconductor material is deposited on top of the substrate in such a way that it precisely replicates the structure and crystallographic orientation of the substrate template. Again, other research methods focus on finding a way to integrate InGaN nanostructures into →multijunction solar cells in order to improve the light trapping efficiency of the InGaN semiconductor. indium oxide

(In2O3) Is a chemical compound that is usually doped with tin oxide to make →indium tin oxide (ITO). The ITO material is deployed in production of transparent thin films for solar cells and →low-e window panes.

indium phosphide

(InP) A member of the III–V family of semiconductors composed of →indium and →phosphorus. Similar to gallium arsenide (GaAs), indium phosphide is characterized by high mobility of charge carriers, →electrons and →holes. The main disadvantage of indium phosphide is the fact that Indium (In) is a very rare posttransition metal and therefore even more expensive than gallium arsenide. Gallium indium phosphide (GaInP2) is often used as a top layer in triple-junction solar cells. The top film with a high band gap captures high-energy photons while allowing the lower-energy photons to pass through.

indium tin oxide

(ITO) A type of →transparent conductive oxide (TCO) consisting of indium, tin, and oxygen. This material is characterized by highest electrical conductivity and transparency with a solar energy transmittance value of over 80%. This is why it is widely used in the production of →transparent conducting films (TCFs) for inorganic and organic photovoltaic cells and →low-e window panes. It is usually deposited by →electron beam physical vapor deposition or →sputtering. As indium is a rare and therefore expensive posttransition metal, it is increasingly being replaced in low-cost applications such as thin-film modules by alternative materials, for example, aluminum-doped zinc oxide (AZO), indium-doped cadmium oxide, →carbon nanotubes, and →graphene.

inductive transformer

See →rectifier.

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inductively coupled plasma

(ICP) Used in high-density plasma etching method.

industrial hangar

See →industrial roof.

industrial roof

The roofs of municipal governments, commercial, and industrial buildings are large surfaces that are suitable for solar installations. Big industrial warehouses and hangars are good candidates for solar systems because their roofs are often flat and unused. →Flat roof photovoltaic systems with special →flat roof mounting systems are specially designed for industrial flat roof buildings. The major advantage of an industrial rooftop solar installation is that the electricity is generated in close proximity to loads. If the roof surface is big enough, the rooftop PV panels will be able to meet the electricity needs of the warehouse below.

infiltration1

See →air leakage.

infiltration2

Heat loss due to outside air entering the house through cracks in the walls, ceilings, windows, and doors.

infrared

Referring to →infrared radiation (heat).

infrared camera

See →thermal imaging camera.

infrared cutoff wavelength

Also known as IR cutoff wavelength. The longest wavelength at which the absorption of solar energy ends. Wavelengths longer than 1,100 nm pass by silicon atoms without triggering the emission of photoelectrons in the semiconductor.

infrared light

See →infrared radiation.

infrared radiation

A type of electromagnetic radiation with the wavelengths in the range from 0.75 to 1,000 μm. It is a long-wave radiation that lies between the visible and microwave portions of the electromagnetic spectrum. Although it is invisible to humans, people feel and experience it as heat. After absorbing incoming solar →shortwave radiation, the Earth re-emits one part of the absorbed energy as longwave infrared radiation (heat).

infrared reflector

See →infrared reflector layer.

infrared reflector layer

In a →combined solar collector, which is also known as a photovoltaic-thermal system, an infrared reflector layer

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 infrared thermography

that reflects all reradiated infrared energy back into the system. Copper is a common metal used in the manufacture of infrared reflector coating. In a hybrid PV/T system, the copper film must be separated from the silicon layer in order to avoid a diffusion problem, resulting in recombinationactive defects. infrared thermography

(IRT) Thermal infrared (IR) imaging for buildings that makes heat energy visible. This mapping of temperature differences on walls and roofs with a special camera shows the heat loss in a building.

ingot

Mono- or polycrystalline silicon block for wafer fabrication.

ingot grinder

See →ingot grinding machine.

ingot grinding machine

Also known as an ingot grinder. A grinding machine for removing defects and refining irregularities on the surface of a silicon →ingot.

ingot manufacturing

There are two major types of ingots: →monocrystalline silicon ingot and →polycrystalline silicon ingot. The monocrystalline silicon ingot is produced using the →Czochralski crystal growth process, in which a cylindrical single crystal is pulled from the melt. The polycrystalline silicon ingot is manufactured by a process of melting polysilicon directly into cube-shaped ingots.

ingot production

See →ingot manufacturing.

inhibitor

Agent that slows down or prevents a chemical reaction.

injection molding

A manufacturing process for mass production of solar components, such as plastic junction boxes or polymerbased Fresnel lenses, by heating the molding material and injecting the molten plastic into a matrix shaped like the end product. The high-speed fabrication process based on injection molding promises to reduce manufacturing and material costs in solar industry, as many metal and glass solar components are likely to be replaced by less expensive polymer-based solar components. For instance, polymer-based solar mounting systems offer properties, such as corrosion resistance, light weight, and design flexibility, which are superior to their metallic counterparts.

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injection molding machine

A machine that uses an →injection molding process to manufacture solar components in high volumes and at high speed.

ink jetting

See →inkjet printing.

inkjet nozzle

A component of an inkjet printer. A miniature nozzle from which droplets of photovoltaic ink are sprayed onto polymer or other substrates of a solar cell.

ink-jet nozzle

See →inkjet nozzle.

inkjet printhead

A component of an inkjet printer that consists of numerous tiny nozzles spraying solar ink onto substrates and creating conductive layers on solar cells.

ink-jet printhead

See →inkjet printhead.

inkjet printing

Also known as solar cell printing. In the solar field, inject printing uses an inkjet printer to deposit the photoactive semiconductor material onto a flexible substrate of a

Ink supply

Piezoelectric transducer Nozzle

Ink droplets Printed pattern Flexible substrate

Inkjet Printing

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 ink-jet printing

thin-film solar cell. Basically, the inject printing applies the same method that is used for printing polymer banknotes. This printing method is suitable for manufacturing thin-film →copper indium gallium selenide (CIGS) solar cells or →organic photovoltaic cells (OPV). ink-jet printing

See →inkjet printing.

ink-jet solar cell

See →inkjet solar cell.

inkjet solar cell

A solar cell that is produced with the help of an inkjet printer that deposits the photoactive semiconductor material onto a flexible substrate. Inkjet solar cell printing applies the same method that is used for printing polymer banknotes. Common commercial printers can be tuned up to use the solar ink for manufacturing thin-film →copper indium gallium selenide (CIGS) solar cells or →organic photovoltaic cells (OPV). In comparison to the complex and expensive production process for silicon solar cells that includes vacuum-sealed chambers and toxic chemicals, the inkjet printing method offers a cheaper and cleaner solution. As it is capable of printing precise conducting patterns on the substrate, it uses less material than screen printing. Similarly, the material is also not wasted in the spray dust of a vapor deposition process; instead, it is applied with the accuracy of one micrometer. The solar ink usually consists of metal salts or polymer fullerene blends that are rather inexpensive compared to the costly silicon semiconductor material. The extremely thin inkjet-deposited conducting layer, compared to a 200-μm thick silicon layer on conventional PV cells, further reduces the volume of the needed material and minimizes the production costs at the same time. The major disadvantages associated with inkjet solar cells are low efficiency, stability, and film morphology.

inkjet printer

Also known as a solar cell printer. An inkjet printer is a printing device that uses a high-speed printing process, in which droplets of ink are sprayed from numerous tiny nozzles following the computer-navigated patterns onto polymer or other substrates. For thin-film solar cell fabrication, inject printers use a so-called →solar ink. In contrast to screen printing, an inkjet printer does not apply

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pressure to a silicon wafer, as there is no direct contact. As a result, less wafers are broken or damaged, thereby reducing the waste during the production process. ink-jet printer

See →inkjet printer.

inorganic electronics

Conventional electronics.

inorganic semiconductor See →inorganic semiconductor material. inorganic semiconductor A semiconductor material manufactured from a noncarmaterial bon-based material such as silicon, gallium, or arsenide. The manufacturing process of inorganic semiconductors is more complex and therefore costlier than the one of organic polymer semiconductors. Another disadvantage of inorganic semiconductor material is that it is inflexible. On the positive side, it still has higher electrical performance and better degradation rate than organic semiconductors. input voltage

The voltage that is required for the inverter to run smoothly and supply enough source energy for the alternating current (AC) as well as for direct current (DC) loads. The required input voltage is determined by carrying out a →load analysis, including all the electronic devices that need to be powered. Depending on the system design, the input voltage could be 24 or 48 VDC, or even in the range between 200 and 400 VDC.

in-roof installation

A photovoltaic installation system, in which PV modules, for example, solar roof tiles, are directly integrated into the roof surface to seamlessly blend in with conventional roof tiles and the rest of the roof and building. The major challenge for solar installers is to ensure the absolute water tightness of the roof-integrated solar system. The lack of cooling airflow under the tiles is another drawback of this system, as it leads to the overheating of solar cells, reducing their efficiency. See also →roof-integrated photovoltaic system.

in-roof mounting

See →in-roof installation.

in-roof system

See →in-roof installation.

insolation

The total amount of solar radiation incident on a unit surface over a given period of time. The typical unit of insolation is →watt-hour per square meter (Wh/m2). See also →solar irradiance and →solar irradiation.

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installation area

Area available on the roof or in the front, side, or back yard for rooftop or ground-mounted solar installation.

installation costs

The costs that include labor and the electronics required to wire a photovoltaic array into an existing electrical system. Permits and inspection fees are often added to the installation costs. As the solar system cost is often expressed in cost per watt, the installation costs can also be calculated in price per watt. After subtracting the costs of solar panels, balance of system components, the federal and state solar tax credit, and operational costs from the total, the remainder will show the installation costs in dollars per watt of energy. However, solar companies usually offer a bulk price – the total cost of an installed system. In 2017, the installation costs for a standard solar system in the USA were around $3.17/W for an average PV system size of 5 kW (5,000 watts).

installation of a photovoltaic system

See →installation of a solar system.

installation of a PV system

See →installation of a solar system.

installation of a solar system

Assembly and connection of all components of a solar system, such as solar panels, controller, inverter, and batteries. As one works with electricity, hazardous chemicals, and heavy, fragile objects, it is important to observe safety precautions during the installation. When working with batteries and electrical connections, solar installers should wear appropriate protective clothing, gloves, and eye protection. When installing solar panels on roofs, special equipment must be used for safe lifting and handling of solar modules. The installers must use appropriate ladders, safety harnesses, and scaffolding. Wiring of solar components into a working solar array is one of the most challenging parts of the solar installation. When it comes to wiring, it is recommended to leave it to a professional installer. If you decide to do it yourself, bear in mind that advanced electrical skills and a readable wiring diagram are required to safely and successfully complete the installation.

installation surface

See →installation area.

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installed capacity

See →rated power.

installed height

The height of the →solar collectors from surrounding grade level.

instantaneous heating system

See →tankless heater.

instantaneous water heater

See →tankless heater.

Institute for Energy and Environmental Research Heidelberg

Institut für Energie- und Umweltforschung Heidelberg (IFEU). A Heidelberg-based nonprofit organization for environmental research. The research institute was founded in 1978 and it has more than 70 employees today, mostly scientists in the fields of natural sciences, engineering, and social sciences.

Institute of Electrical and Electronics Engineers

(IEEE) The world’s largest technical professional society with headquarters in New York, advancing innovation and technological excellence for the benefit of humanity. The IEEE promotes the development of national and international standards and publishes a number of journals and magazines in electrical and electronic engineering, power and energy, and numerous other allied technologies.

insulant

Insulating material.

insulating barrier

A thin electrically insulating barrier layer placed between a solar cell front contact and a semiconductor (substrate) or between a semiconductor (substrate) and a solar cell back contact in order to reduce the impact of surface recombination and achieve stable current–voltage behavior.

insulating material

See →insulation material.

insulation

See →insulation material.

insulation material

Thermal insulation. Materials that prevent or decrease heat loss or heat gain by providing a barrier between inside and outside temperatures of a building or a box (→batch collector).

insulation of hot water storage tank

Wrapping of insulation material, such as foamed polyurethane, polyethylene, or polypropylene, around a →hot water storage tank to minimize heat loss and increase performance. Insulating an old hot water storage tank can reduce standby heat losses by 25%–45%.

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 insulator

insulator

Electrical insulator. Also known as nonconductor, a material such as plastic that does not conduct electricity well and has the task to stop the flow of electric current in unwanted places. Conducting photovoltaic copper wire is insulated with polyethylene coating. Insulators have a large →band gap that is greater than 4 eV. Under normal circumstances, →valence electrons will not have enough energy to bridge the large band gap and will remain separated from the →conduction band.

insurance

See →solar insurance.

integral collector storage See →integral collector storage system. integral collector storage system

(ICS system) Also known as a batch collector or bread-box collector. ICS system is a solar water-heating system that heats water either in a single enclosed tank or in a series of bigger enclosed tubes. The storage tank is usually made of steel, whereas the tubes are usually made of copper. In order to better absorb the sun’s thermal energy, tanks or tubes are painted black or/and with a selective coating and function as a solar absorber. Regardless of which collector option is used, a single tank or a series of tubes, they are placed in an insulated box that has glazing on the top side facing the sun to reduce heat loss. This is in particular important at night and in colder winter days. However, ICS systems should not be used in regions with temperatures below the freezing point, as the water in tanks/tubes might freeze and crack the tank/pipes open. In spite of this restriction, ICS systems are still widely used in warmer climates due to their high efficiency. As they are typically mounted on a house’s roof, they do not require a pump and are usually plumbed in-line with the domestic water and the existing water heater. In particular, when mounting a single tank on the roof, a reinforcement of existing roof structure should be considered due to the heavy weight of the tank.

integrated backside contact

(IBC) A contact cell structure that moves front contact grids to the back of the device. The placement of interleaved positive and negative contacts on the rear surface eliminates shading losses, resulting in a higher energy conversion efficiency.

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integrated energy system

(IES) According to the US Department of Energy, a system that combines “on-site power or distributed generation technologies with thermally activated technologies to provide cooling, heating, humidity control, energy storage and/or other process functions using thermal energy normally wasted in the production of electricity/power.”

integrated resource planning

(IRP) A utility company planning that considers supply– and-demand resources in order to provide reliable and least-cost electricity to all customers over a specified period of time.

integrated solar combined cycle power plant

US A type of power plant that combines a conventional natural gas-fired combined cycle (NGCC) power plant with a →concentrated solar power plant (CSP plant) to reduce usage of polluting coal and oil as well as the cost of electricity. Steam generated from a CSP plant is fed into the water-steam cycle of the NGCC plant, thus adding the “clean” and cheap power to the steam turbine.

integrated solar combined cycle power station

UK See →integrated solar combined cycle power plant.

intelligent charging electronics

See →intelligent charging system.

intelligent charging infrastructure

A basic structure for vehicle-to-grid (V2G) sustainable energy management that facilitates continuous exchange of information between →electric vehicles (eVs), →charging stations, →smart grid, and the network operator’s control center.

intelligent charging system

A system that monitors charging and discharging processes for optimal performance of a rechargeable battery. The intelligent charging system reduces charging time; protects the battery against overcharge, overdischarge, short circuit/ over current, and temperature; and increases the length of battery life. The system’s controller senses when the batteries are fully charged and turns the charge off to prevent excessive overcharge and battery damage. Depending on the model, the intelligent charging system can monitor →state of charge, →state of health, current, voltage, temperature, and other operating conditions of a rechargeable battery. It can accurately estimate the charging time of the battery in accordance with the health of the battery.

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 intelligent electricity meter

intelligent electricity meter

See →solar electricity meter and →two-way meter.

intelligent energy consumption

A sustainable energy consumption that relies on intelligent energy tools, such as wireless smart energy sensors and →smart energy management systems, to optimize energy consumption in a building and reduce pollution at the same time. Smart energy sensors monitor the electricity usage of all electrical appliances and send the collected information to the energy management system, which evaluates the received data and finds different ways to reduce overall energy consumption.

intelligent energy meter

See →solar electricity meter and →two-way meter.

intelligent energy usage

See →intelligent energy consumption.

intelligent grid

See →smart grid.

intelligent monitoring platform

A web- or cloud-based monitoring platform for acquisition and analysis of critical photovoltaic data, such as solar power yield or solar module temperature. The key advantages of an intelligent monitoring platform include: a realtime monitoring of complex and often large solar systems, the visualization of solar panels and graphical representation of the solar panel behavior, multisite monitoring, fault detection and troubleshooting, advanced configuration of data to be collected, ability to analyze and rearrange the stored data, and access to data from various remote devices, such as computer, smartphone, or tablet, from any location.

intelligent power consumption

See →intelligent energy consumption.

intelligent power usage

See →intelligent energy consumption.

intentional impurity

Intentional incorporation of impurities into a pure semiconductor, in order to change its electrical characteristics.

inter-lattice diffusion

The type of →diffusion in which dopant atoms move in-between the silicon atoms in the crystal lattice.

interactive inverter

See →utility-interactive inverter.

interarray cable

A type of submarine high-voltage cable that connects an offshore solar installation, such as a floating solar power plant, to the substation on shore.

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intercalation

Insertion of molecules between layers, for example, in a graphite lattice.

interconnect wire

See →tabbing wire.

interconnect1

To connect an independent electricity generating system, such as a photovoltaic array, to the utility grid.

interconnect2

See →interconnection1.

interconnect3

See →interconnection2.

interconnection agreement

A legal agreement between the homeowner or small commercial customer and the local utility company, allowing the homeowner or commercial customer to connect their solar electrical generating system to the public utility grid. In many districts, the agreement includes the →net energy metering program that provides a compensation for any excess electricity the residential or commercial customer exports to the grid.

interconnection1

The connection between an independent electricity generating system, such as a photovoltaic array, and the utility grid. Both the PV system and the utility system are linked in such a way to allow a two-way power transfer – a mutual exchange of electricity. Each side can act as a supplier as well as a buyer of electrical power.

interconnection2

A conductor, such as →tabbing wire or →bus wire, which is used to interconnect solar cells within a solar module. The tabbing wire is applied to electrically connect adjacent cells in series by soldering →tabbing ribbons to →rear contact pads. The bus wire is used to connect strings of solar cells together and steer the current to the junction box of a PV module.

interface

A point where two different systems or energies meet and interact. For instance, the inverter is an interface between a photovoltaic array and the utility grid, between direct current (DC) and alternating current (AC). It converts DC energy generated by solar panels into AC electricity and synchronizes the power output with the utility voltage and frequency.

interferometer

An instrument for measuring the spectral distribution of irradiance. It merges two or more beams of light, generating an interference pattern that is used to determine wavelengths of light, wave velocities, and other measurements.

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 interferometry

interferometry

A measurement technique that uses the phenomenon of interference of waves to make measurements of wavelength, wave velocity, and distance with great accuracy.

Intergovernmental Panel on Climate Change

(IPCC) An international scientific body established by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) in 1988. The main goal of the IPCC is to provide an objective, unbiased view on different aspects of climate change and its potential impact on environment and society. The organization does not conduct research of its own, but it collects scientific information from 130 countries, analyzes and evaluates the received climate data and policies, and synthesizes the findings into assessment reports every 5–7 years.

interior roller shade

Prevents the solar heat from entering the house through windows. A house design that includes interior roller shades is considered an effective →passive cooling technique.

interior shutter

Prevents the solar heat from entering the house through windows. The use of interior shutters is considered an effective →passive cooling technique.

interior sun protection

See →passive cooling.

interior sunshade

See →passive cooling.

intermittent energy source

An energy source that does not provide electricity 24 h a day. Solar and wind energy are considered intermittent and variable energy resources, because their energy production fluctuates all the time, depending directly on weather conditions and natural geographical features.

internal consumption

See →internal power consumption.

internal electric field

Electric field formed within the doped semiconductor layers due to optically or thermally stimulated charge carriers. Due to the presence of the electric field, the positive charges align with the electric field and the negative charges align against it.

internal energy consumption

See →internal power consumption.

internal power consumption

1. Energy consumed to run the system itself. 2. The electricity used for internal energy consumption as opposed to the electricity sold to the power grid.

internal quantum efficiency 

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internal quantum efficiency

(IQE) A type of →quantum efficiency, indicating the ratio of the number of charge carriers generated by the solar cell to the number of all the photons absorbed by the cell, excluding the outcome of optical losses such as transmission and reflection. See also →external quantum efficiency (EQE).

internal shading devices

Include →window blinds, →interior shutters, and →curtains. Internal shading devices prevent the solar heat from entering the house through windows. A house design that includes internal shading systems is considered an effective →passive cooling technique.

internal shading systems See →internal shading devices. internal sun protection

See →passive cooling.

International Energy Agency

(IEA) An autonomous international organization with a mandate to promote reliable, affordable, and clean energy for its 29 member nations and beyond. The IEA was founded in November 1974 during an oil crisis caused by the OPEC embargo of 1973 in order to ensure energy security for its member countries. The agency is also committed to the promotion of renewable energy policies and environmental protection.

International Energy Conservation Code

(IECC) The International Energy Conservation Code is designed to promote the energy efficiency in residential and commercial buildings. It establishes minimum regulations and requirements for energy-efficient buildings that 47 US states that have adopted and must abide by it.

International Solar Energy Society

(ISES) An international, UN-accredited organization devoted to the research, advancement, and promotion of solar and other renewable forms of energy. ISES has more than 57,000 members from over 110 countries and sections in over 50 countries. The ultimate goal of the association is to achieve 100% renewable energy for all.

intertie

See →interconnection.

intrinsic carrier concentration

See →intrinsic carrier density.

intrinsic carrier density

The concentration of charge carriers, electrons and holes, in an undoped, chemically pure semiconductor.

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 intrinsic conduction

intrinsic conduction

Also known as intrinsic conductivity. Conduction in semiconductor materials caused by heat or radiant energy rather than by impurities and structural defects.

intrinsic conductivity

See →intrinsic conduction.

intrinsic layer

An undoped, chemically pure semiconductor layer with the properties of the material itself.

intrinsic semiconductor

Also known as i-type semiconductor. An undoped, chemically pure semiconductor with the properties of the material itself. The most common intrinsic semiconductor materials are →Silicon (Si) and →Germanium (Ge) from Group IV of the Periodic Table. They are characterized by an electron–hole balance – an equal number of negative carriers (electrons) in the conduction band and positive carriers (holes) in the valence band. As this charge balance (n=p) has poor conductivity, a small amount of →impurities in form of →n-type dopants and →p-type dopants are added to an intrinsic semiconductor to increase the electrical conductivity of the material.

intrinsically conducting polymers

(ICP) See →conducting polymers.

inversion

See →temperature inversion.

inverted metamorphic cell

See →inverted metamorphic multijunction cell and inverted solar cell.

inverted metamorphic multijunction cell

A metamorphic multijunction solar cell grown upside down on a gallium arsenide (GaAs) substrate. After pro cessing

Bo tto m Mi Ce dd ll le Ce ll To pC ell

Top Cell

Middle Cell Bottom Cell

GaAs Substrate

Inverted Metamorphic Multi-junction Cell

Support Sub.

inverted OPV cell 

 375

all multijunction layers, the whole stack is removed from the growth substrate, flipped over, and transported to the device substrate. See also →inverted solar cell and →metamorphic multijunction solar cell. inverted OPV cell

Inverted organic photovoltaic cell. See →inverted solar cell.

inverted photovoltaic cell

See →inverted solar cell.

inverted polymer fullerene solar cell

See →inverted solar cell.

inverted pyramid

See →inverted pyramid texture.

inverted pyramid texture

Solar cell surface texture, consisting of inverted pyramid patterns that reduce the surface reflectance and thus improve the performance of solar cells. The inverted pyramid texture reduces reflectance more efficiently than its counterpart →random pyramid texture.

inverted pyramid texturing

Solar cell surface texturing technique that uses a →photolithographic process to produce inverted pyramid patterns, reducing the surface reflectance and thus improving the performance of solar cells.

inverted solar cell

A →solar cell with an inverted semiconductor layer structure. The conventional →polymer solar cell design has an n–p structure, in which the top layer is a negative electrode and the transparent bottom layer over the substrate is a positive electrode. In an inverted solar cell design, the positive and negative electrodes are reversed, displaying a p–n structure. This layer architecture puts a p electrode on top, whereas the transparent bottom layer over the substrate consists of an n electrode. The inversion switches the direction of the electric charge flow in the cell. The major benefit of the inverted PV cell design is that it enables manufacturers to use a more efficient →cathode. Negative electrodes in conventional polymer solar cells have a short lifetime because they are made of a reactive metal that easily corrodes by oxidation. The inversion of the layer structure allows the producers to replace the metal with other corrosion-resistant materials, such as →indium tin oxide (ITO)/polymer compounds, which ensure a longer

376 

 inverter

lifetime of organic PV cells. The deposition process of an indium tin oxide layer is also less energy intensive than the conventional metal layer deposition. inverter

Converts the generated solar power from direct current to grid-compatible alternating current. It is used in →offgrid as well as in →grid-tie solar systems. There are two major types of inverters: string or →central inverters and →microinverters. While a central or string inverter converts DC solar power generated by the entire solar array into AC power at one central point, microinverters are attached to the back of each individual PV panel to convert DC output from each module into AC power.

inverter cables

Inverter cables connect an inverter with batteries and household appliances in a →stand-alone solar power system. Inverters require the largest cables in a solar system to ensure the full current flow to the appliances. Sizing of these wires depends on the battery voltage and needs to be individually calculated.

inverter efficiency

The percentage of the DC power that is successfully converted into usable AC power.

inverter saturation

Also known as clipping. Occurs when DC power from a PV array feeding an inverter exceeds the maximum input level of the inverter (maximum rated power) and the excess power is “clipped” and lost.

inverter station

Converts the generated solar power from direct current to grid-compatible alternating current.

inverter surge capacity

See →surge capacity.

investment tax credit

(ITC) See →solar investment tax credit.

invisibility cloak

Guides sunlight around objects such as contact fingers that cast a shadow on the solar panel.

invisible light

Also known as nonvisible light. Wavelengths of the →electromagnetic spectrum that are too short or too long to affect the retina and be visible to the human eye. The types of invisible light are: →ultraviolet (UV) light, →infrared (IR) light, radio waves, →X-rays, microwaves, and gamma rays. Certain new generation photovoltaic cells can capture parts of UV and IR radiation and convert it into electricity.

iodine 

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iodine

A nonmetallic chemical element that can improve the photon-to-electron conversion efficiency of a solar cell when added in a small, controlled amount to a polymer semiconductor film. The Nobel Prize winners Alan J. Heeger, Alan MacDiarmid, and Hideki Shirakawa realized in the late 1990s that polymer materials, traditionally known as insulators, can be tweaked to act as semiconductors. They doped conjugated polymers with iodine, improving optical and electronic properties of polymers to such an extent that they were able to transfer electrons. This invention resulted in a paradigm shift in the solar industry, introducing the era of →organic photovoltaic cells. Iodine also promotes the mobility of the nc-TiO2 layers in a →dye-sensitized solar cell (DSSC).

ion

An atom or a molecule with a positive or negative electrical charge. An atom itself is neutral, having an equal number of protons and electrons. An atom becomes an electrically charged ion by gaining or losing electrons. When an atom loses one or more electrons, it becomes a positive ion (cation), carrying a positive charge as a result of the chemical reaction. On the opposite side, when an atom gains one or more electrons, it becomes a negative ion (anion), carrying a negative charge as a result. Therefore, the number of electrons is always different from the number of protons in an ion, resulting in a positive or negative charge.

ion-assisted deposition

(IAD) Also known as ion beam-assisted deposition. A thin-film deposition technology that combines the standard thermal with the →ion beam deposition technique. In the standard thermal deposition process, the target material is electrically heated to high temperatures until it is released in evaporating plume. The dislodged material particles move up and settle on the surface of the substrate to form the desired thin film. The IAD method adds the →ion beam source and directs its high-energy ions at the substrate. The ion beam assists the thermal deposition process by imparting additional energy to the material particles. The accelerated particles impact the substrate with more force, generating a thin film with a higher density, which in turn results in a more durable coating and material savings.

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 ion beam

ion beam

A beam of charged particles, ions, directed toward desired target.

ion beam-assisted deposition

(IBAD) See →ion-assisted deposition.

ion beam deposition

(IBD) A technology for depositing of semiconductor films by means of beams of charged particles, ions, in a high-vacuum system. The IBD applies an →ion beam source to direct a beam of accelerated high-energy ions at the target material. The ion beam bombards and sputters the target material, ejecting atoms and molecules from the semiconductor solid. The ejected material particles are then deposited onto the substrate which is tilted toward the target material holder. The structure and composition of the deposited film depends on the target material as well as on the amount and type of ion bombardment. Various parameters, such as the intensity of the energy of ion beams, can be adjusted during the manufacturing process, which will significantly influence optical, mechanical, and electrical properties of the film.

Rotatable manipulator

Substrate

Deposition ion source

Thin layer coating Thickness monitor

View port

Target holder Ar/Ar+

Rotatable target assembly

Ar/Ar+

Pressure gauge Assisted ion source

Ion Beam Deposition – Ion Assisted Deposition

ion beam etching 

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ion beam etching

(IBE) Also known as ion beam milling. A technology for etching of semiconductor films by means of beams of charged particles, ions, in a high-vacuum system. In this →dry etching process, the ion beam is directed in a highly controlled manner at the wafer to be patterned. After the desired mask patterns are deposited onto the photosensitive surface of the wafer covered with →photoresist, the ion beam is applied to etch any portions of the thin-film semiconductor that are not protected by the photoresist mask. The high-energy ions bombard the substrate, removing material from the etch target by physical sputtering. Compared to chemical etching processes, which can produce defects due to contamination and undercutting of films, the ion beam etching offers an anisotropic etching profile, exhibiting geometrically straight walls of the etch groove. Other advantages include an excellent uniformity of patterns, high purity, high repeatability, and a good control of the etching process that allows stopping of etching at a specific point. The IBE is able to render high-precision etching of nanometer-sized features.

ion beam etching system

A device that uses an →ion beam etching technology to remove material from the etch target by physical sputtering.

ion beam lithography

A →maskless lithography method in which a focused beam of ions scans across the substrate surface and writes precise patterns onto an electron-sensitive resist coating. The main advantages of ion-beam lithography are that no expensive hard mask is required, the ion beam is computer-controlled, fine ultrathin pattern structures, highly sensitive resist, and high resolution.

ion beam milling

See →ion beam etching.

ion beam source

A part of the ion beam apparatus that generates an ion beam. The ion beam source consists of three parts: a discharge chamber, the grids, and a neutralizer. Ions are produced in the discharge chamber in which atoms of a noble gas, typically Argon, are subjected to an RF field. Gas atoms are ionized by dynamic electron bombardment and a plasma is established. In a set of electrically

380 

 ion beam sputter deposition

biased grids, source ions are accelerated to achieve high energies. The role of the neutralizer is to balance the charge of the ions in the beam. ion beam sputter deposition

(IBSD) A process in which high-energy ions strike and penetrate the target semiconductor surface in a vacuum chamber, ejecting atoms and molecules from the solid target material. The ejected material particles are then deposited onto the substrate that is tilted toward the target material holder.

ion beam sputtering

A process in which high-energy ions strike and penetrate the target semiconductor surface in a vacuum chamber, ejecting atoms and molecules from the solid target material.

ion beam technology

A technology for etching or depositing of semiconductor films by means of beams of charged particles, ions, in a high-vacuum system.

ion bombardment

A process in which large numbers of accelerated high-energy ions bombard the target semiconductor surface, causing ejection or sputtering of atoms and molecules and thus the removal of target material. The optical, mechanical, and electrical properties of the deposited film depend not only on the target material but also on the amount and type of ion bombardment. Therefore, by altering various parameters of ion bombardment, such as energy intensity and speed, the structure and composition of the film can be greatly controlled.

ion current

The flow of charged particles, ions, constitutes an electric current.

ion etching

A type of →dry etching by means of accelerated high-energy ions that are directed in a precisely controlled manner at the target material.

ion exchange

A process in which ions of different substances are exchanged, for instance, between a solution and an insoluble solid.

ion implantation

The main technology for incorporating doping, impurity atoms into a semiconductor wafer to define the electrical properties of semiconductor layers, n-type and p-type regions, and thus to form a PV cell diode.

ion implanter 

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In the low-temperature ion implantation process, dopant ions are accelerated in an electric field to high energies and shot into the wafer. The doping process delivers a precise amount of dopant but it also creates damage to the wafer surface. The thermal process called →annealing is deployed to repair damage and homogenize the structure by removing any non-uniformity. After a thermal annealing process, the dopants are incorporated into the crystal structure. The dopant ions are now electrically activated and turned into charge carriers: a p-type dopant produces a →hole, whereas an n-type dopant generates an →electron. ion implanter

A device that uses the beams of electrically accelerated ions to incorporate impurity atoms into a semiconductor wafer, thus defining the electrical properties of semiconductor layers, n-type and p-type regions. The quality of an ion implanter is measured by the ability of the device to achieve a good ion implantation uniformity.

ion milling

See →ion etching.

ion source

See →ion beam source.

ionic conduction

Also known as ionic conductivity. A process in which positively or negatively charged ions carry the current. Ionic conductivity can only take place if defects are present in the crystal. Most of the →recombination in silicon occurs via defects. By doping silicon, extrinsic defects or vacancies in the crystal lattice are produced. Defects act as the charge carriers, allowing the movement of ions in an electric field. Ions migrate through defects in the crystal by hopping from an occupied site to a vacant site.

ionic conductivity

See →ionic conduction.

ionic current

The flow of ions that are either positively or negatively charged, as opposed to the flow of electrons that are always negatively charged.

ionisation

UK See →ionization.

ionisation energy

UK See →ionization energy.

ionisation energy of acceptor

UK See →ionization energy of acceptor.

382 

 ionisation energy of donor

ionisation energy of donor UK See →ionization energy of donor. ionisation potential

UK See →ionization energy.

ionization

The formation of →ions as a result of a chemical process in which an atom or a molecule obtains a positive charge by losing one or more electrons or a negative charge by gaining one or more electrons.

ionization energy

US Also known as ionization potential. The minimum amount of energy required to remove a →valence electron from an atom to form a cation. Ionization energy is a measure of the strength of chemical bonds. The higher the ionization energy, the more difficult it is to remove the valence electron. The ionization energy increases from left to right across a period and decreases from top to bottom in a group in the Periodic Table.

ionization energy of acceptor

US →Ionization energy that is measured from the →valence band edge.

ionization energy of donor

US →Ionization energy that is measured from the →conduction band edge.

ionization potential

US See →ionization energy.

ionized reaction gas

A noble gas, such as argon (Ar), krypton (Kr), or xenon (Xe), which is introduced into the process chamber and ionized by colliding with electrons generated by plasma discharging. When the ionized reaction gas strikes the sputtering target, atoms and molecules are ejected from the target material, transferred via plasma and deposited on the substrate, forming a thin semiconductor film.

IPCC

Abbreviation for →Intergovernmental Panel on Climate Change.

IPCE

Abbreviation for incident photon-to-current efficiency. See →quantum efficiency.

IPP

Abbreviation for →independent power producer.

IQE

Abbreviation for →internal quantum efficiency.

IR cutoff wavelength

See →infrared cutoff wavelength.

IRP

Abbreviation for →integrated resource planning.

irradiance

See →solar irradiance.

irradiance sensor 

 383

irradiance sensor

See →pyranometer.

irradiation

See →solar irradiation.

irradiation intensity

The power of the solar radiation, measured in watts, falling on an area of 1 m2. Intensity of solar radiation is measured by a →pyranometer or →solar power meter. When assessing overall energy and efficiency of a solar system or window surfaces, it is crucial to measure the irradiation intensity on a specific site. The information about how many watts per square meter or BTUs a site is really receiving will give a more precise estimate of the amount of solar energy passing through solar panel or windows surfaces.

IRT

Abbreviation for →infrared thermography.

ISC

Abbreviation for →short-circuit current.

ISCC power plant

US See →integrated solar combined cycle power plant.

ISCC power station

UK Integrated solar combined cycle power station. See →integrated solar combined cycle power plant.

ISES

Abbreviation for →International Solar Energy Society.

island growth

Also known as a Volmer–Weber growth mode. Island growth is an uneven growth of thin films in which atoms are more strongly bound to each other than to the substrate. The slow diffusion rate leads to random clustering of atoms, forming three-dimensional islands of various sizes Volmer-Weber deposition method

Island Growth (Volmer-Weber)

384 

 ISO

and a rough surface. As the islands grow during the deposition process, they connect with each other, creating a thin layer. See also →layer-by-layer growth and →mixed growth. ISO

Abbreviation for →independent system operator.

isolation barrier

The barrier inhibits the electric contact between n- and p-layers of a solar cell.

isolation switch

See →safety shut-off.

isolation valve

A type of valve that isolates a device, such as an expansion tank, from fluid flow. The isolation valve is typically turned off for system maintenance or repair or for safety reasons.

isotope

Atom sorts with equal atomic number, but different mass number.

isotropic etch

See →isotropic etching.

isotropic etching

Uniform etching in all directions with the same →etch rate. In the isotropic etching technique, the selected chemical etches the semiconductor layer vertically, horizontally, and diagonally, undercutting the protected layer. The isotropic etching offers a small amount of control over the etching process, resulting in a large →etch bias. Isotropic etching is mostly used in →wet etching and in fabrication where a higher etch bias can be tolerated. For a higher level of

Isotropic Etching

isotropic etching profile 

 385

control, finer geometries, and smaller lateral undercutting of the masked layer, the →anisotropic etching is a preferred method. isotropic etching profile

The isotropic etching profile does not display geometrically straight walls but a U-shaped profile with horizontal undercutting of the masked layer, which is a result of isotropic uniform etching in all directions.

isotropic material

A material, such as metal or glass, whose properties, for instance, mechanical and thermal properties, are uniform in all directions.

isotropy

Old Greek, isos “equal” tropos “way”; equal properties in all orientations.

ISPRA

Abbreviation for Istituto Superiore per la Protezione e la Ricerca Ambientale. See →Italian National Institute for Environmental Protection and Research.

ISPRA guidelines

Guidelines for the evaluation of solar photovoltaic power plants, published by the Italian research institute →ISPRA.

Italian National Institute for Environmental Protection and Research

(ISPRA - Istituto Superiore per la Protezione e la Ricerca Ambientale) A governmental research institute established in 2008 in order to foster environmental protection, environmental stewardship, and research.

ITC

Abbreviation for investment tax credit. See →solar investment tax credit.

ITO

See →indium tin oxide.

i-type semiconductor

See →intrinsic semiconductor.

I–V curve

Current–voltage curve or current–voltage characteristic. A graphic representation of a relationship between current and voltage illustrating the operating characteristics of a solar cell, module, or array within an electrical circuit. As current times voltage equals power, I–V curve provides information crucial for determining the power output and the conversion efficiency of a cell, panel, or solar system. Moreover, it helps to maximize the solar power output by customizing the system to achieve the →maximum power point (MPP) operation.

386 

  I–V curve

MPP is an ideal power output point on the graph between the maximum current point that is short-circuit current (ISC) and the maximum voltage point that is open-circuit voltage (VOC). Short-circuit current (ISC) is the maximum current produced by a solar cell when its terminals are short-circuited, which means connected to each other. As there is no connection to an external load, there is no resistance in a circuit and the voltage is zero. On the other side, open-circuit voltage (VOC) is the maximum voltage produced by a solar cell, when there is a break in a circuit. As there is no connection between terminals, the resistance is extremely high and no current is flowing (current value is zero). However, under normal operating conditions, when the PV system is connected to an external load (electrical household appliances, batteries, inverters), the actual maximal current and voltage values will be different than the above described VOC and ISC extremes (ideal values). The ratio showing the relation between the actual maximum power from a PV cell to the ideal maximum power (product of VOC and ISC) is called fill factor (FF). The ratio can be mathematically expressed as: FF = VMPPIMPP/VOCISC . The larger the area of the rectangle VMPP × IMPP , the closer it comes to its ideal rectangle with area VOC × ISC . Therefore, MPP of a photovoltaic (PV) module is the product of the greatest voltage value (VMPP) and the greatest current value (IMPP), MPP = VMPP × IMPP. The efficiency of a photovoltaic module is usually calculated by this MMP equation that is derived from the →Ohm’s law power equation: P = V × I. Along with other ratings, some PV manufacturers also include MPP value into their product data sheets. According to their rating, there is only one MPP on the →I–V curve (current–voltage curve) for a certain PV module (PV product) estimated with an optimal load under optimal illumination, temperature, and other conditions. However, as in a real-life scenario, load, illumination, and temperature conditions constantly vary during the day in an operating solar array, an MPP tracking controller tracks the optimal power point on the I–V curve and adjust values to ensure the maximum power output (wattage) of the PV array.

J1772™ combo connector 

J

 387

J1772™ combo connector

A standard connector for ultrafast charging of electric vehicles. The regular →J1772™ connector of →Level 2 stations is expanded by two large DC pins at the bottom, allowing carbon capture and sequestration (CCS) to bypass the onboard charger and feed power directly to the eV battery pack. The batteries must be specially engineered to accept a fast charge. Audi, BMW, Daimler, Ford, General Motors, Porsche, and Volkswagen were among the first car brands to adopt the J1772™ fast DC charging standard.

J1772™ connector

A standard connector with five pins that the majority of today’s electric vehicles, such as Chevy Volt, Nissan LEAF, Tesla Model S, or new Prius, use for →Level 2 charging at 240 V.

Japan Photovoltaic Energy Association

(JPEA) A Japanese photovoltaic association with a mission to contribute to the prosperity of Japanese economy and the improvement of the national life depending on the promotion and utilization of solar technologies.

J-Box

See →junction box.

Joule

(J) Unit of energy, work, or amount of heat.

JPEA

Abbreviation for →Japan Photovoltaic Energy Association.

j-tube

A waterproof tube used for the mechanical protection of subsea power cables between the sea floor and the offshore solar or wind platform. J-tube consists of three parts: 1. tube water section, in which the annulus is filled with water; 2. tube air section above the sea level, in which the annulus is filled with air; and 3. above the hang off with exposed phases.

junction

Also known as p–n junction. Intersection between positively doped and negatively doped semiconductor layers in a solar cell.

388 

 junction box

junction box

Also known as solar junction box, module junction box, and J-Box. A protective enclosure on the back of a photovoltaic (PV) module that houses electrical connections and diodes. It is an input/output interface connecting the module to other PV modules. It includes PV module protection devices such as bypass diodes and/or blocking diodes. A bypass diode eliminates hot spots in case of partial module shading or broken cells. It prevents damage from overvoltage due to high resistance conditions (hot spots) by diverting the current past the shaded or broken module. A blocking diode prevents the reverse current from flowing backward through a module. It functions like a one-way valve, allowing electricity to flow only one way. They prevent undesired discharging by reverse flow of electrical current from the battery bank to the PV array, for example, in the dark or under cloudy conditions, when no current is generated by the PV modules. In a different configuration, junction boxes can be installed at the end of the rows of solar modules, connecting a group of solar panels to the →DC combiner box. Good junction boxes are waterproof and are able to regulate heat.

junction built-in potential

See →junction built-in voltage.

junction built-in voltage Built-in voltage at the p–n junction intersection that prevents penetration of electrons into the p-layer and holes into the n-layer in a semiconductor. When the voltage surpasses the built-in voltage threshold of the p–n junction, the electrical current can flow through the p–n junction. junction capacitance

The →capacitance associated with the charge variation in the →depletion zone. Junction capacitance forms in a →p–n junction diode under reverse bias. See also →diffusion capacitance.

junction diode

See →p–n junction diode.

junction voltage

See →junction built-in voltage.

June solstice

See →summer solstice.

Kelvin 

K

 389

Kelvin

(K) Unit for thermodynamic temperature.

kerf

The width of a cut made by a silicon wafer dicing saw. The groove width or kerf is proportional to the thickness of the blade.

kerf loss

The amount of material lost during a wafer-cutting process. The kerf loss depends on the width of the cutting blade, the intensity of vibration during cutting, and the amount of edge chipping of materials.

kilowatt

(kW) SI unit of power that is equivalent to 1,000 W. Kilowatt is used for solar electric power measurements.

kilowatt-hour

(kWh) 1 kWh = 3.6 MJ. Measure of electricity generated by a solar system or used in a household over a period of time, 1 kW for 1 h. Utility companies measure the electrical energy consumption/production and sell/buy electricity in kilowatt-hours.

kilowatt-hour meter

See →electricity meter.

kilowatt-peak

(kWp) Measurement unit for the capacity (nominal output) of solar cells and solar modules. It refers to peak power, a maximum energy output generated by a photovoltaic system under optimal conditions – full solar radiation averaging 1,000 W/m2 (1 kW/m2).

kilowatt-peak output

Optimum power output achieved under →standard test conditions, which presume a solar radiation of 1,000 W/m2, 25  °C (77  °F) module temperature, and 1.5 air mass.

kinetic energy

The energy a body has because of its movement.

K-value

A measure of the thermal conductivity of a material. See →heat transfer coefficient.

Kyoto Protocol

International environmental agreement that commits industrialized countries to reduce →greenhouse gas emissions.

390 

 Lambert’s cosine law

L

Lambert’s cosine law

Also known as cosine emission law or Lambert’s emission law. The law for optical absorption stating that radiant intensity is directly proportional to the cosine of the zenith angle – angle between the direction of the incident light and the surface normal.

Lambert’s emission law

See →Lambert’s cosine law.

Lambertian back reflector

See →Lambertian rear reflector.

Lambertian rear reflector

Also known as a Lambertian rear reflector. A reflector on the back of a solar cell that reflects incident light with the goal of trapping it inside the cell for possible absorption. Using a rugged surface as a reflector on the rear of the cell results in irregular bouncing of reflected light in different directions, increasing the amount of light trapping and absorption inside the cell.

laminate

See →photovoltaic laminate.

lamination

A manufacturing process in which different solar module layers or low-E window sheets are bonded together in a compact unity – solar panel or →low-E window – by applying heat, pressure, vacuum, and adhesives.

laminator

See →solar panel laminator.

lan

Abbreviation for solar radiation unit “langley.”

landscape layout configuration

A layout configuration in which solar panels are mounted horizontally. See also →layout configuration.

langley

(lan, ly) Solar radiation unit.

Langmuir waves

See →plasma oscillation.

large-scale photovoltaic installation

A ground-mounted large scale →photovoltaic power plant. See →solar farm.

large-scale solar energy During the day and sunny weather, solar panels work storage just fine providing necessary energy for households and industry. However, since there are, for instance, only five full sun hours available per day in one particular region for solar power generation, an energy storage system

large-scale solar installation 

 391

would ensure the stability of the energy supply. Just like uninterruptible power supplies from conventional nuclear or coal-fired power plants, the solar storage system must provide energy at night as well as on hazy and cloudy days. There are numerous solutions for storing solar energy on a large scale: →pumped hydroelectric energy storage (PHES), →compressed air energy storage (CAES), →molten salt storage, →methanol tanks, →net energy metering, →batteries, →supercapacitors, →hydrogen fuel cells, →flow batteries, or →mechanical flywheels. large-scale solar installation

See →large-scale solar power plant.

large-scale solar plant

See →large-scale solar power plant.

large-scale solar power plant

There are two types of large-scale solar power plants: →large-scale photovoltaic installation and →large-scale solar thermal system. The first type consists of a large number of ground-mounted solar modules and the second one of a large number of concentrating reflectors, solar dishes, parabolic troughs, or linear Fresnel reflectors and various types of absorbers such as →central receiver or →absorber tube, in accordance to the solar thermal technology type. The common denominator for all large-scale solar power plants is the utility-scale electricity production in the megawatt range that can supply electrical power to hundreds or thousands of homes and businesses.

large-scale solar thermal installation

See →large-scale solar thermal system.

large-scale solar thermal system

The large-scale solar thermal systems use high-temperature collectors (>250 °C, >482 °F) that concentrate sunlight with the help of mirrors and lenses onto a large receiver at the top of a →solar power tower or onto a black tube or smaller receiver in the middle of the parabolic trough or solar dish. Unlike small-scale solar thermal systems that are used to heat water for domestic use, the large-scale solar thermal systems are typically utilized for electric power generation. The concentrated solar energy heats →heat transfer fluid reaching a high temperature that is then used to produce steam to run turbines, generating electricity. Three main types of large-scale solar thermal

392 

 laser

systems include: →central receiver system with a solar power tower, →concentrating parabolic trough, →linear Fresnel reflector system, and →solar dish. laser

A device that generates a concentrated beam of light through optical amplification based on the simulated emission of photons.

laser ablation

Removal of material from a solid surface with a laser beam in order to cut, groove, or scribe silicon substrates. The laser ablation process can be described as follows: The energy from the pulsed laser beam is converted into internal energy of the target material, leading to excessive heat, melting, evaporation, and plasma formation and expansion, which in turn results in the elimination of material.

laser ablation cutting

See →laser ablation dicing.

laser ablation dicing

A wafer-cutting process in which laser energy is focused onto a minute area, subliming and vaporizing the solid along the dicing path.

laser beam

A narrow, intense beam of light emitted by a laser, which is employed in →laser beam cutting of silicon wafers.

laser beam ablation

See →laser ablation.

laser beam cutting

A cutting technique that uses a laser beam to cut a semiconductor wafer into a desired shape.

laser cutter

See →laser cutting machine.

laser cutting

A cutting technique that uses a laser to cut a semiconductor wafer into a desired shape.

laser cutting machine

A machine that utilizes a laser to cut semiconductor materials into desired →solar wafer shapes.

laser dicing

See →laser cutting.

laser dicing process

A process in which a laser beam is used to cut a semiconductor wafer into a desired shape. Two main laser dicing processes are →laser ablation and →stealth dicing.

laser scribing

Is a PV scribing method that uses a laser beam to cut scribe patterns in a semiconductor material in order to create a grid of conductive channels and interconnections in a solar cell. Although the →mechanical scribing method

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might still work fine with some softer semiconductor materials, laser scribing is becoming an increasingly popular method to process semiconductor layers, in particular in →thin-film photovoltaic industry, due to superior precision, clean process, and lower costs. The pulsed laser produces precise cuts, straight lines, and boundaries without damage, resulting in higher quality, less short circuits, and less material usage. Compared to the mechanical scribing with a diamond stylus that can create imperfect conductive channels and cause chipping of the layers, the focused laser beam is able to control the cutting depth with great accuracy (within ±5 μm) and produce microchannels with sharp edges that are so desired in the thin-film photovoltaic semiconductor processing. Finally, the channels are cleaned with the help of a laser ablation process removing excess materials (debris) from the surface. laser scribing machine

A machine that uses a laser beam to scribe patterns in a semiconductor material in order to create a grid of conductive channels and interconnections in a solar cell.

laser structuring

Creating geometrical microstructures with a very precise function in component surfaces. The main advantages of a laser structuring process include highly reproducible results, flexibility in the design, and texturing of complex forms. The high-precision structuring with a laser can reduce energy losses and improve the photoelectrical efficiency of thin-film photovoltaic cells.

laser-induced graphene

(LIG) In photovoltaic production, a →graphene material that is incorporated into an electronic device, such as a →thin-film photovoltaic cell, by means of a laser.

LAT

Abbreviation for →local apparent time.

latent heat

The thermal energy absorbed by or released from a material during a phase change from a solid to a liquid (melting), from a liquid to a gas (vaporization), or from a liquid to a solid (fusion), without change of temperature.

latent heat storage

→Thermal energy storage systems use →phase change materials (PCMs), for example, various salt mixtures, to store →latent heat (form of thermal energy) in an insulating container. During a phase change, for example, melting, heat is

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 lateral wind load

added to the storage material (salt), whereas during solidifying heat is released from salt. Therefore, when energy is needed after the sunset, the molten salt is pumped into a steam generator that boils water, powering a turbine that in turn generates electrical power. lateral wind load

Horizontal pressure or force of the wind that can make a solar structure tilt or overturn.

latitude

An imaginary horizontal line that circles the Earth and runs parallel to the equator. Latitude lines are used for measuring distance and locating places north or south of the equator.

lattice

See →lattice structure.

lattice structure

A symmetrical structure consisting of atoms or molecules that form a silicon crystal in a semiconductor.

layer cells

See →bipolar battery.

layer formation

Solidification of coating made of millions of individual splats on the surface of the substrate immediately after the deposition process.

layer growth

Vapor phase epitaxy of silicon layers.

layer thickness

The thickness of a semiconductor layer is an important factor affecting cost-effectiveness of solar cell production. →Thin-film solar cells have not become a viable alternative to standard bulk →silicon solar cells because of their quality and better performance. In spite of the fact that the conventional crystalline silicon solar cells still show better performance characteristics and durability, the reduced layer thickness of a thin-film wafer, which is only several micrometers thick, compared to conventional silicon wafer with a thickness of approx. 150 μm, generates significant savings in material, resulting in low-cost thin-film fabrication.

layer-by-layer growth

Also known as a Frank van der Merwe growth mode or layered growth. A uniform layer-by-layer growth of smooth thin films in which atoms form a strong bond to the substrate. The layered growth creates high-quality, well-oriented crystalline thin films with perfectly flat two-dimensional layers of materials. See also →island growth and →mixed growth.

layered growth

See →layer-by-layer growth.

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Frank-van der Merwe deposition method

Layer-by-layer Growth

layer-plus-island growth

See →mixed growth.

layout configuration

Configuration of solar panels in a →photovoltaic system with regard to their horizontal or vertical orientation. There are two standard layout configurations for solar systems: landscape and portrait. On →ground-mounted solar arrays, both configurations work equally well, as they achieve approximately the same solar yield. The main criterion in the choice of a PV configuration is how many solar panels can be fitted within the available surface. The shading effect of neighboring panels should also be taken into consideration. If more horizontally mounted PV modules than vertically mounted PV modules can be fitted on the available surface, then the priority should be given to a landscape layout configuration. However, on →roof-mounted solar arrays, a portrait configuration is generally preferred due to lower hardware and installation costs as well as due to a better structural stability. In most cases, rails must run perpendicular to the rafters and the narrow width of each module. A landscape configuration requires more rows on a rooftop and more rows translate into more material and installation. Additional rails, mounting clamps, and standoffs are required, which increase the time needed to complete the installation.

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 LCB

LCB

Abbreviation for →linear current booster.

LCC

See →life-cycle cost.

LCCA

See →life-cycle cost analysis.

LCE

See →low carbon economy.

LCOE

Abbreviation for →levelized cost of energy.

LCPV cell

See →low concentration photovoltaic cell.

LCPV system

See →low concentration photovoltaic system.

LCPV1

Abbreviation for →low concentration photovoltaics.

LCPV2

Abbreviation for low concentration photovoltaics. See →low concentration photovoltaic system.

lead

A posttransition, heavy toxic, dense metal that is commonly used in accumulator batteries.

lead-acid battery

See →lead-acid battery.

lead selenide

(PbSe) A semiconductor material with cubic crystal structure that is used for the manufacturing of lead-selenide quantum dots in thin-film nanocrystal photovoltaic (PV) cells. Lead selenide semiconductor has a narrow →band gap of 0.27 eV at room temperature. As temperature increases so does the energy gap of lead selenide. Thin films consisting of PbSe nanorods are incorporated into →heterojunction solar cells to expend spectral response of PV cells and convert a wider range of irradiation wavelengths into electricity.

lead-acid battery

Is a battery type that is commonly used in large photovoltaic battery banks. A lead-acid battery has six single cells (2 V per cell) that are connected together in series to produce a battery of about 12 V. Each cell consists of the following three main parts: electrodes/ plates, separators, and electrolyte. One cell has two electrodes and two sets of eight overlapping plates. Negative plates are made up of sponge lead and positive plates are covered with a paste of lead dioxide. Porous separators separate the positive and negative plates to prevent short circuits. The plates are soaked in an electrolyte, consisting of 65% water and 35% sulfuric acid (H2SO4).

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When a lead-acid battery is being discharged, it converts chemical energy into electrical energy. The negative electrode/plate (anode) covered with lead is being oxidized, releasing two electrons. Two electrons are flowing from negative to positive terminal, supplying on its way the external load with electricity, and reentering the battery through the positive electrode. The positive electrode/ plate (cathode) covered with lead dioxide is being reduced in the process. Lead (Pb) loses two electrons and lead dioxide (PbO2) receives those same two electrons. During the discharge process, both electrodes become coated with lead sulfate; the sulfuric acid (H2SO4) electrolyte is used up and water is produced. When the lead-acid battery is being recharged, it is converting electrical energy into chemical energy, and the chemical reactions are reversed. The electrons are flowing in the opposite direction, from positive to negative terminal. Now, the positive electrode/plate (cathode) covered with lead dioxide (PbO2) is being oxidized, losing two electrons, whereas the negative electrode/plate (anode) covered with lead (Pb) is being reduced, gaining those same two electrons. During the recharge process, the lead sulfate coating on the electrodes is removed, the lead and lead dioxide regenerated, the water is used up, and the sulfuric acid (H2SO4) is produced. The battery is recharged and ready to be used again. lead-acid battery charging

There are three stages in lead-acid battery charging: bulk, absorption, and float. At the first →bulk charge stage, the charge controller allows maximum charging to 80% of the battery capacity. At the →absorption charge stage, the controller holds the voltage at a constant level and decreases the current until the battery has reached between 95% and 98% state of charge, depending on the charger brand, when it switches to →float charge stage. In this last phase, the voltage and current decrease until the battery is fully charged.

leak current

See →leakage current.

leak detection

A technique such as a →hydrostatic pressure test, which tests whether there is a leak in a system, such as a pipeline, a tank, or a boiler.

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 leakage current

leakage current

Current that flows beyond the limit of the intended path.

leaking electricity

See →leakage current.

leasing roof area

See →leasing roof space.

leasing roof area for photovoltaic systems

See →leasing roof space for photovoltaic systems.

leasing roof area for PV systems

See →leasing roof space for photovoltaic systems.

leasing roof space

Renting out of unused roof space to a company by a homeowner for the purpose of having a free solar system installation on their roof. In this way, a homeowner who is unable to purchase a solar energy system and shoulder other high upfront costs can start buying green electricity. The company that leases a roof surface usually offers the homeowner, a lessor, a relatively favorable electricity rate that is slightly lower than the one offered by the local utility provider. The major disadvantage of roof space leasing is the fact that leasing reduces the economic returns for homeowners and makes money for the solar system owner, not the homeowner.

leasing roof space for photovoltaic systems

A business practice in which a solar company leases an unused roof surface from a homeowner for a fixed period of time, for example, 20 years. An important term of the lease is the mutual agreement between the lessor and the lessee according to which the homeowner agrees to purchase electricity produced by the newly installed solar panels for the agreed-upon period of time. Under ideal circumstances, both sides can potentially benefit from this agreement: homeowners by purchasing electricity at a favorable long-term rate, which is typically slightly lower than the one of their local utility company or a solar company as a lessee, which can build solar projects without the added costs of land ownership. Leasing seems to be a preferred option for building owners who tend to move more frequently and like to maintain their flexibility. The major drawback of leasing is that building owners have no control over the installed solar equipment, no tax benefits, and they are tied to solar leases or →power purchasing agreements (PPAs) that usually last 20 years.

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leasing roof space for PV systems

See →leasing roof space for photovoltaic systems.

leasing roof surface

See →leasing roof space.

leasing roof surface for photovoltaic systems

See →leasing roof space for photovoltaic systems.

leasing roof surface for PV systems

See →leasing roof space for photovoltaic systems.

LED

Abbreviation for →light-emitting diode.

LED solar light

See →solar LED light.

lens

In the solar energy context, a piece of glass or other transparent material ground to a curved shape to concentrate light rays in such a way that they increase the amount of solar energy falling onto solar cells.

lens mount

A mounting system holding a magnifying lens above the corresponding solar cell.

LEV

Abbreviation for →low emission vehicle.

Level 1 charging

Level 1 is an overnight charging model that converts general-purpose alternating current (AC) into direct current (DC) used by electric cars by utilizing an onboard converter in the electric vehicle. In Level 1 charging, the 120 V charger cord, which comes with all electric vehicles, is merely plugged into a standard household outlet. Level 1 is the simplest but also the slowest type of EV charging. It takes up to 16 h to charge an 80 mile or 129 km battery pack. The major advantage of slow charging is an extended battery life, as the slow charging rate cannot damage the batteries. See also →Level 2 charging station and →DC fast-charging station for electric vehicles.

Level 2 charging

The type of fast charging of electric vehicles at 240 V with the help of a →Level 2 charging station with a →J1772™ connector.

Level 2 charging station A home or public electric vehicle charging station that uses a 240 V outlet to allow fast charging. Depending on the type of electric vehicle, Level 2 stations can charge an eV battery pack several times faster than the regular Level 1 charging. It takes up to 3.5 h to fill up an 80 mile or 129 km

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 Level 3 charging station

battery pack. The larger the battery pack, the more time it takes to charge it. The majority of today’s electric vehicles, such as Chevy Volt, Nissan LEAF, Tesla Model S, or new Prius, use the J1772™ connector for Level 2 charging at 240 V. See also →Level 1 charging and →DC fast-charging station for electric vehicles. Level 3 charging station

See →DC fast-charging station for electric vehicles.

levelized cost of electricity

(LCOE) See →levelized cost of energy.

levelized cost of energy

(LCOE) The cost of energy of a solar system over its lifetime. The LCOE is calculated by the following formula: LCOE = Total Life-Cycle Cost/Total Lifetime Energy Production. This commercial assessment tool takes into account all the expected life-cycle costs, such as financing, design, incentives, construction, fuel, operation and maintenance, taxes, and insurance, and divides them by the expected total lifetime energy production. The LCOE is a useful comparison tool that estimates the cost of energy delivered by different power-generating technologies. When different projects utilizing different technologies are placed side by side with LCOE values, the project designer can opt for the project with the lowest LCOE, which translates into the solar system with the lowest cost of energy and the highest return on investment.

levelized cost of energy calculator

The LCOE calculator is an assessment tool that calculates the cost of energy of a solar system over its lifetime. The LCOE result is typically expressed in cents per kilowatt-hour (kWh). See also →levelized cost of energy.

LEZ

Abbreviation for →low-emission zone.

LFFE

Abbreviation of low-fossil-fuel economy. See →low carbon economy.

LFMC

Abbreviation for →liquid-tight flexible metal conduit.

LFP battery

Abbreviation for →lithium iron phosphate battery.

LFR

Abbreviation for →linear Fresnel reflector.

LIB

Abbreviation for →lithium-ion battery.

LID

Abbreviation for →light-induced degradation.

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LID effect

See →light-induced degradation.

life cycle

Life cycle of a product refers to its lifetime, encompassing different phases in the life of a product, such as acquisition, operation, maintenance, and disposal.

life cycle of a photovoltaic array

See →life cycle of a photovoltaic system.

life cycle of a photovoltaic module

Refers to the lifetime of a PV module, encompassing different phases in the life of the PV device, such as acquisition, operation, maintenance, and disposal.

life cycle of a photovoltaic panel

See →life cycle of a photovoltaic module.

life cycle of a photovoltaic system

Refers to the lifetime of a PV system, encompassing different phases in the life of the PV array, such as acquisition, operation, maintenance, and disposal.

life cycle of a PV array

See →life cycle of a photovoltaic system.

life cycle of a PV module See →life cycle of a photovoltaic module. life cycle of a PV panel

See →life cycle of a photovoltaic module.

life cycle of a PV system See →life cycle of a photovoltaic system. life cycle of a solar array See →life cycle of a photovoltaic system. life cycle of a solar module See →life cycle of a photovoltaic module. life cycle of a solar panel See →life cycle of a photovoltaic module. life cycle of a solar system See →life cycle of a photovoltaic system. life-cycle cost

(LCC) Is the total cost of a system over its useful life – from cradle to grave. See also →life-cycle cost analysis.

life-cycle cost analysis

(LCCA) Is an effective planning and analysis tool that helps house owners and companies examine the feasibility of their proposed solar projects. The total life-cycle cost includes upfront cost (cost of all PV equipment) as well as all maintenance and operation costs (e.g., replacement of batteries). The other important parameter for an LCC analysis is the needed anticipated annual output in kWh. This information can be extracted and calculated from your utility bill that shows your average daily kWh usage. As the

402 

 life-cycle cost assessment

standard warranted life span of PV panels is 25 years, the required annual output is multiplied by 25 years. The total life-cycle cost per kilowatt hour can be expressed by the following formula: CostkWh = total lifecycle cost including upfront and maintenance costs/total kWh used over the lifetime of the PV system. In order to compute an accurate LCC, this simplified formula should be accompanied by other formulas, such as the one that takes into account long-term trends in electricity prices (average electricity inflation rate). The life-cycle cost analysis is typically a comparative analysis, juxtaposing solar electricity cost and regular utility electricity cost. Various solar versus utility costs and projections are placed side by side in a comparison chart showing the more cost-effective option in the long run between the competing alternatives. life-cycle cost assessment

See →life-cycle cost analysis.

LIG

Abbreviation for →laser-induced graphene.

light

Electromagnetic radiation in the wavelength range between 400 nm (violet) and 700 nm (red) that is visible to the human eye.

light absorption

The amount of incident →visible light radiation that falls on a surface and is absorbed by it.

light control

Also known as lighting control. The regulation of the intensity and quality of light in a given space. It also includes the automation of lighting, allowing homeowners to schedule their lights to turn on and off at specific times.

light diffuser

See →ceiling light diffuser.

light intensity

The rate at which radiant energy spreads over a surface of a given area. The intensity of light equals energy per unit time per unit area and it is often measured in watts per square meter (W/m2). The intensity of solar radiation falling on a PV module, multiplied by the area of the module, indicates how much power or energy per unit time is available in a given location. The intensity varies with the distance of a solar module from the source of light.

light pipe 

 403

light pipe

See →sun tube.

light reflection

The amount of incident →visible light radiation that falls on a surface and bounces off it in the form of visible light.

light sail

Provides power supply for a space station.

light scattering

The deflection of light rays in different, random directions as a result of the passage of light or other electromagnetic radiation through a medium, such as clouds and dust particles.

light sensor

Also known as a photodetector or photosensor, which is an electronic device that detects light. There are several different types of light sensors, such as photocell or photoresistors, photodiodes, and phototransistors. →Solar garden lights, →solar street lights, and other →solar lighting systems rely on integrated light sensors to turn the light on and off. During the day, the solar cells capture the sun’s energy and store it in a battery. As it gets darker at the end of the day, the amount of light falling onto the sensor decreases, reaching a threshold when the photosensor will let the current flow and turn the light on. The LED lights shine throughout the night until the photosensor switches them off at dawn.

light shelf

Is a horizontal overhang that reflects the sunlight deep into the interior of a building, thereby reducing lighting energy. Light shelves can either be installed internally or externally; however, a combination of internal and external light shelves seems to give best results. Apart from increasing daylighting, it reduces glare, improves the equal distribution of light, and prevents the solar heat from entering the building directly through windows. They are usually installed on high south-facing windows of official buildings. A building design that includes light shelves is considered an effective →passive cooling technique.

light source

A natural or artificial source of visible electromagnetic radiation in the range of 400–700 nm.

light spectrum

The portion of the electromagnetic spectrum, approximately between 400 nm (violet) and 700 nm (red), which is visible to humans.

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 light transmission

light transmission

The amount of incident solar radiation that passes through a body, for example, a solar module or a window. The control of light transmission in a solar cell is an important factor to be considered in order to reduce optical and energy losses within a semiconductor. See also →transmittance.

light trapping1

The trapping of the incoming light within a semiconductor to increase the efficiency of solar cells. Significant quantities of solar energy are lost in the semiconductor because a large number of incoming photons are reflected from the cell or transmitted through it. The conventional techniques used for trapping light inside the semiconductor are the →surface texturing and adding of an →antireflection coating. By etching random pyramid or inverted pyramid patterns onto the surface of solar cells, the angle at which light penetrates the PV cell will be modified. Instead of photons of light being reflected away from the PV surface, they are potentially redirected onto the surface with help of the texture, trapped by →total internal reflection, and absorbed by the semiconductor material. Although these methods work well with conventional crystalline silicon solar cells, they find less application in →thin-film solar cell technology. Antireflection coatings can successfully minimize the amount of light reflected from the cell; however, they cannot capture light that is transmitted through the semiconductor material and lost. Various light-trapping surfaces, which should boost solar cell efficiency, are developed for thin-film solar cells. →Nanoantenna technology tries to capture incoming light with a top layer consisting of nanoantennas and trap it against the surface, thus preventing both reflection and transmission energy losses. Bendable organic solar cells employ a light-scattering layer for trapping light in the semiconductor. The efficient light-scattering layer is made up of quasiperiodic discrete silica nanoparticles deposited onto flexible polymer substrates. Similarly, in →plasmonic photovoltaic cells, metallic nanoparticles are responsible for light trapping. Through scattering of light across the surface of the semiconductor and expending the path length of light, the absorption of photons is significantly increased in a solar cell.

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light trapping2

A method for enhancing light absorption in →thin-film solar cells. The conventional techniques used for trapping light inside the semiconductor are the →surface texturing and adding of an →antireflection coating. By etching random pyramid or inverted pyramid patterns onto the surface of solar cells, the angle at which light penetrates the PV cell will be modified. Instead of photons of light being reflected away from the PV surface, they are potentially redirected onto the surface with the help of the texture, trapped by →total internal reflection, and absorbed by the semiconductor material.

light tube

See →sun tube.

light tunnel

See →sun tube.

light-activated nanoparticles

See →quantum dots.

light-emitting diode

(LED) A semiconductor device that emits photons of visible light when current flows through it. LEDs are a more energy-efficient source of electrical lighting than →incandescent or →compact fluorescent light (CFL) sources. They also last 25 times longer than incandescent and 10 times longer than CFL light bulbs.

light-guide solar concentrator

An optical system that traps incident light within the guide layer where either a dye-sensitized concentrator or micro-optic concentrator is installed, focusing the light onto a high-efficiency solar cell.

light-guiding element

An optical element that concentrates or redirects incident light collected on the surface by optical microstructures onto a focal point or focal line where high-efficiency photovoltaic cell is installed.

light-induced defects

Defects that occur as a result of the exposure of hydrogenated amorphous silicon semiconductor (a-Si:H) films to sunlight. This light-induced instability in solar cells made from hydrogenated amorphous silicon can be traced to the disordered nature of amorphous silicon. The light exposure triggers an increase in the recombination current, which in turn leads to an escalation in the density of dangling bond defects, resulting in a reduced PV cell power output. This light-induced degradation

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 light-induced degradation

of solar cell efficiency, from which the hydrogenated amorphous silicon suffers, is also known as a Staebler–Wronski effect. The increase in defects considerably reduces photoconductivity and the charge carrier lifetime. light-induced degradation

Degradation of the solar cell performance that occurs as a result of the exposure of boron-doped silicon crystalline semiconductor to sunlight. During the growth of the silicon crystal in the →Czochralski process, the impurities, such as oxygen atoms, tend to accumulate in the melt together with dopant boron atoms. When the silicon solar cell is exposed to light, the oxygen and boron atoms form boron–oxygen defects under the influence of increased recombination current. The defects affect the electrical properties and conversion efficiency of the solar cell and might also lead to a degradation in lifetime of the silicon wafer.

lighting control

See →light control.

lighting control system

Also known as smart lighting. A network-based system supported by lighting management software that allows the control of the intensity and quality of a single light or different groups of light bulbs indoors or outdoors as well as the scheduling and automation of lighting. The use of dimmers at home allows homeowners to control the intensity of the electric light. Dimming lights in the house reduces the wattage of lightbulbs, resulting in energy savings and a reduced environmental footprint. Presence of detectors, which provide automatic control of lighting by detecting body heat and movement of tenants, can also reduce energy consumption. When a person is detected by sensors in a room, lights are automatically turned on; when the tenant leaves the room, the detector automatically switches off the lighting. The smart lighting system includes the automation of lighting by means of timers, allowing homeowners to schedule their lights to turn on and off at specific times.

lightning arrester

An external lightning protection device for channeling a lightning strike to the ground to prevent damage to equipment. One terminal of the arrester is wired to the photovoltaic equipment and the other terminal is wired to an →earth rod.

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lightning protection

A set of devices applied to a solar power system to protect structure, people, and electrical equipment from the damaging effects of lightning strikes. An internal lightning protection includes surge protection devices (SPDs), such as →surge arresters, which are used on electrical systems to provide a discharge path to earth and to shut off the flow of electricity in the event of overcurrent caused by lightning. An external lightning protection includes →lightning arresters and →earth rods, conveying the lightning current safely to the ground.

light-permeable module

See →photovoltaic laminate.

lightweight photovoltaic module

See →lightweight solar module.

lightweight photovoltaic See →lightweight solar module. panel lightweight PV module

See →lightweight solar module.

lightweight PV panel

See →lightweight solar module.

lightweight solar module

Also known as a lightweight solar panel, lightweight photovoltaic (PV) module, and lightweight PV panel. A module that consists of flexible or semiflexible →thin-film solar cells that are laminated into a thin plastic sheet. These thin PV modules weigh much less, occupy less space, and are less bulky than conventional rigid PV modules, which makes them suitable for the incorporation into building structures, such as rooftops and facades. Due to their lightweight, flexibility, and aerodynamic profile, they are also ideal for motorhomes, boats, or other vehicles. They are commonly installed on some delicate rooftop structures, such as carports, canopies, or tents, which cannot support the weight of conventional solar panels. Lightweight solar panels cost much less to install because they do not require the complex installation of a support structure, a →ground-mounting system or a →roof-mounting system. On the other side, conventional photovoltaic (PV) modules are more rugged than lightweight PV panels. Even though lightweight PV cells are laminated into special composite materials, the tempered glass of rigid modules is more durable, providing a better protection against the elements and scratches.

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 lightweight solar panel

lightweight solar panel

See →lightweight solar module.

line extension

Extension of a utility line to a property to bring the electricity to a new customer. When planning a new photovoltaic (PV) system, the utility line extension costs should be considered. In general, →off-grid photovoltaic systems are more expensive than →grid-connected photovoltaic systems; however, if you live in a remote area over a mile away from the closest power lines, an off-grid PV system might be a better option.

line load

The amount of electric current that is drawn from a circuit.

line loss

A loss of electric energy due to the transmission of current across power lines. The voltage drops and the waste of electrical energy occurs due to conductor heating by the current when PV cables are too long or PV cable size is too small. Line losses in a low-voltage system can be significant over long distances and they should not exceed 3%. Therefore, the solar array should be installed as close as possible to the house in order to keep the cable runs as short as possible. The wire thickness must be calculated to match the load being run through the cables to enable a smooth current flow, preventing the voltage drop in the line. The correct wire size and careful selection of the cable type (e.g., UV-protected PV cable is a better choice) will meet less resistance and minimize energy losses.

Line of Balance

(LOB) A management control process applied to large solar-thermal projects that consists of blocks of repetitive work activities, such as mounting of →parabolic mirrors and →absorber tubes as well as the installation of pipelines. LOB collects, evaluates, and presents information relating to time, cost, and accomplishment and presents it against a specific plan.

Line of Balance method

Method for planning and monitoring of requests.

linear current booster

(LCB) Is an electric device that optimizes the current coming out of PV panels to match the water pump power needs. The power adjusted by an LCB boosts the speed of the motor and improves the overall performance of the pump.

linear Fresnel reflector 

linear Fresnel reflector

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(LFR) A type of →concentrating solar collector that consists of numerous reflector stripes that are tilted in such a way to reflect and concentrate the Sun’s rays onto a linear receiver called →absorber tube. The absorber system is typically mounted several meters (yards) directly above the mirrored collector surface. It consists of a series of boiler tubes through which water flows. By concentrating the Sun’s beams along a narrow focal line, solar energy can be increased by approximately 30 times its normal intensity, heating water to the boiling point. The boiling water evaporates in the tubes, generating superheated steam, which reaches a temperature of 270  °C (518  °F). The saturated steam is then transported to a steam turbine, driving a generator that converts kinetic energy into electricity. The LFR technology is very similar to the →concentrating parabolic trough technology with the exception that the LFR system uses cost-effective flat mirrors or reflectors instead of large curved parabolic mirrors, which are more expensive to manufacture. The flat mirrors apply the

flector Secondary reflector ator) (reconcentrator)

be Absorber tube (receiver)

Sun rays ra

Primary reflector

Linear Fresnel Reflector

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 linear load

→single-axis tracking technology to follow the Sun’s trajectory and focus solar radiation onto the absorber tube. The major disadvantage of the linear Fresnel reflector technology is the fact that the concentrating collectors respond only to direct sunlight. While they demonstrate a much higher conversion efficiency than the conventional →flat-plate collectors under clear sky conditions, they perform poorly in →diffuse solar radiation under cloudy conditions. See also →compact linear Fresnel reflector. linear load

A load in which the voltage sine wave is shaped like the current sine wave, which means that voltage is applied across a constant impedance resulting in current. In other words, the load resistance is constant and it does not change with the applied voltage.

line-commutated converter

An inverter that is connected to an electrical grid and relies on the power line voltage for DC to AC conversions.

line-focus solar collector See →line-focusing solar concentrator. line-focusing concentrator

See →line-focusing solar concentrator.

line-focusing solar concentrator

A system that concentrates the rays of sunlight along the narrow focal line, where an →absorber tube is mounted, typically several meters (yards) directly above a parabolic trough or a flat mirrored collector surface in an LFR system. The →single-axis tracking technology is typically used to follow the Sun’s trajectory and focus solar radiation onto the focal line or absorber tube. The line-focusing solar concentrators are: →parabolic trough solar collector, →linear Fresnel reflector (LFR), and →compact linear Fresnel reflector (CLFR). See also →point-focusing solar concentrator.

line-focusing solar system

See →line-focusing solar concentrator.

line-tied system

See →grid-tie system.

liquid battery

See →flooded-cell battery.

liquid dielectric

See →fluid dielectric.

liquid electrolyte battery See →flooded-cell battery. liquid etching

See →wet etching.

liquid fuel cell 

 411

liquid fuel cell

Liquid fuel cells use liquid fuels, such as methanol, ethanol, or butane, instead of gaseous fuels such as hydrogen. Liquid methanol in particular demonstrates numerous advantages over traditional hydrogen that is widely used for powering fuel cells. The advantages are: higher efficiency and low maintenance costs due to direct conversion of liquid fluid into electric current in comparison to more complex combustion engines; easier storage – pressureless liquid storage tanks are safer and hold more energy for the equivalent volume than high-pressure gas tanks; and safer and more convenient transport.

liquid nanocrystal solar cell

A solar cell made of cadmium selenide nanocrystals that are 4 nm in size. Due to their miniature size, the nanocrystals can be suspended in a liquid solution and used as a solar ink. With the help of a roll-to-roll coating machine, the nanocrystal PV ink can be printed onto various surfaces, for instance glass, like a newspaper. As nanocrystals allow a relatively low-temperature process, liquid solar cells can be printed onto thin, flexible plastic substrates without the risk of melting. The main disadvantage of liquid nanocrystal solar cell is the toxicity of cadmium selenide, which is considered a heavy pollutant. Scientists are searching for a replacement of cadmium selenide, which would open the door for a commercial use of liquid nanocrystal solar cell technology.

liquid phase epitaxy

(LPE) A method used in the photovoltaic industry for the growth of crystalline thin films from the melt on solid substrates. In one of the LPE methods, thin films are grown in a horizontal plane by immersing a substrate in a melt for a predetermined period of time. The substrate is then removed from the melt and tilted at an angle to drain the melt from the wafer. The LPE method allows the growth of epitaxial layers at relatively low temperatures.

liquid photovoltaic cell

See →liquid solar cell.

liquid PV cell

See →liquid solar cell.

liquid silicon

Also known as silicon ink or Si ink. A nanotechnology-based semiconductor material in the liquid state. There are three types of liquid silicon: intrinsic silicon ink, n-type

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 liquid solar cell

doped silicon ink, and p-type doped silicon ink. Industry standard screen printers can be used to deposit ink onto various surfaces. The use of commercial screen printers and solar ink significantly reduces production costs, while speeding up the manufacturing process. The solar cell with the phosphorus back surface field from liquid silicon has reached an efficiency of around 21%, whereas the cell with the boron emitter from liquid silicon has reached an efficiency of around 22%. liquid solar cell

A solar cell whose tiny material particles at the nanoscale can be suspended in a liquid solution, creating a photovoltaic ink that can be printed on glass or plastic surfaces using the roll-to-roll processing.

liquid-based solar collector

See →Liquid-based solar heating system.

liquid-based solar heating system

A system that heats a liquid (typically water, but also an antifreeze solution or synthetic oil) in the tubes of a liquid-based collector and pumps it then to a storage tank or distributes it through a heat exchanger and radiators/air ducts across the house. In case of concentrating collectors, the heated fluid is transferred to a molten salt storage tank or to a heat exchanger converting water to steam, which in turn activates turbines that produce electricity. There are several types of liquid-based solar collectors: →batch collectors, →flat-plate collectors, →unglazed flat-plate collectors, →evacuated-tube collectors, and →concentrating solar collectors.

liquid-based solar system

See →Liquid-based solar heating system.

liquid-phase exfoliation (LPE) A method for graphene production in which graphite is exfoliated in liquid environments exploiting ultrasounds. The graphite is first dispersed in an organic solvent. Then a graphene layer is detached from the crystal. Finally, in the purification process, exfoliated flakes are separated from the large un-exfoliated flakes. liquid-tight flexible metal conduit

(LFMC) A conduit through which wires and cables used in PV installations are run. The flexible metal conduit is made of a zinc-coated galvanized low carbon steel strip, over which a weather-resistant polyvinyl chloride (PVC) jacket is applied.

Lithium 

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Lithium

(Li) Soft, silvery-white alkali metal. The lightest of all metals is used in rechargeable lithium-ion batteries. Lithium has become a high-demand metal with growing interest in clean-energy technologies, such as solar system battery banks and electric vehicles, which rely on the lithium-ion battery industry.

lithium anode

See →lithium-ion battery anode.

lithium cathode

See →lithium-ion battery cathode.

lithium iron phosphate battery

(LiFePO4) Also known as an LFP battery. A type of lithium-ion battery that utilizes lithium iron phosphate (LiFePO4) as cathode material. Compared to other rechargeable battery types, the lithium iron phosphate battery stands out with its good low-resistance electrochemical performance, allowing charging and discharging at high speeds.

lithium polymer battery

(LiPo, LIP, Li-Poly, LiPoly) See →lithium-ion polymer battery.

lithium-ion battery

(LIB) A rechargeable battery type in which lithium ions move from the positive electrode (cathode) to the negative electrode (anode) during charge and from the negative electrode (anode) to the positive electrode (cathode) during discharge. Compared to other rechargeable batteries, the lithium-ion battery is characterized by lightweight and a high energy density. LIBs can pack in more energy, 150 Wh of electricity in 1 kg (2.2 lbs) of battery, than many other rechargeable batteries. For instance, a lead-acid battery can only store 25 Wh/kg (2.2 lbs). Two main disadvantages of lithium-ion batteries include their sensitivity to high temperatures and a relatively high degradation rate regardless of the frequency of the charge–discharge cycling.

lithium-ion battery anode

Negative electrode in a lithium-ion battery cell. The electrodes of a lithium-ion battery are typically made of lightweight lithium and carbon.

lithium-ion battery cathode

Positive electrode in a lithium-ion battery cell. The electrodes of a lithium-ion battery are typically made of lightweight lithium and carbon.

lithium-ion ironphosphate battery

See →lithium iron phosphate battery.

414 

 lithium-ion polymer battery

lithium-ion polymer battery

(LiPo, LIP, Li-Poly, LiPoly) A rechargeable battery that replaces a conventional liquid electrolyte with a solid-state polymer electrolyte to achieve a higher energy density and lower weight.

lithography

The transfer of a pattern from one surface onto another, for example, from a →photolithographic mask onto a →wafer.

live load

Moving load as opposed to a fixed, permanent load. When calculating the weight impact of solar panels and support structures on a roof, it is important to differentiate between dead load and live load. The structural engineer or solar technician needs to take both into account, dead load or the weight of PV panels and tracking systems as well as live load or movable external load on the PV panels and structure, such as potential snow or wind load.

live roof

See →green roof.

living wall

See →vertical garden.

LMP

Abbreviation for →locational marginal price.

LMST

Abbreviation for →local mean solar time.

LMT

Abbreviation for →local mean time.

load

See →electrical load.

load analysis

An analysis that calculates the energy requirements of a household by taking into account all the loads. The average power consumption analysis is typically calculated in watt-hours (Wh) by using itemized →load analysis worksheets, listing all the electronic devices that need to be powered in the facility.

load analysis worksheet

Also known as load sizing worksheet. A worksheet listing all the electronic devices that consume electricity and will be used in a new building. When sizing a new photovoltaic (PV) system, PV installers use load analysis worksheets if no electric utility bills with average electricity consumption data are available.

load balancing

Power management with the task to ensure a constant balance between supply and demand of electric power.

load center

See →distribution panel.

load circuit 

 415

load circuit

The wiring that connects the load to the energy source, creating a closed circle and flow of energy.

load current

The amount of current required to power an electrical appliance (expressed in amps).

load forecast

Forecast of energy demand (load) that is based on all devices attached to the output of a circuit.

load forecast system

A system that uses a →load forecast.

load impedance

See →load resistance.

load leveling

See →load balancing.

load matching

See →load balancing.

load relief

Solar PV arrays can provide a load relief to utility companies, in particular at times of peak demand, in the hours with the highest loads.

load resistance

Resistance of the device connected to the output of a circuit.

load shifting

One of the major Demand Side Management (DSM) programs that motivates consumers with the help of favorable →off-peak rates to shift their loads, their typical electricity consumption patterns, from →peak hours to →off-peak hours.

load sizing worksheet

See →load analysis worksheet.

load voltage

The voltage required to power an electrical appliance connected to the output of a circuit.

load-bearing capacity

The capacity of a roof structure to support the superimposed roof loads. In addition to the downward weight impact of the roof cladding (tiles or shingles), the weight of solar modules, the rack, as well as potential snow loads and wind uplift force should be included into the roof’s load-bearing capacity calculations.

load-bearing wall

A wall capable of supporting superimposed loads: the weight of a →roof-mounted solar array in addition to the weight of the roof itself, consisting of a roof structure and cladding.

LOB

Abbreviation for →Line of Balance.

local apparent time

(LAT) See →apparent solar time.

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 local mean solar time

local mean solar time

(LMST) See →local mean time.

local mean time

(LMT) Also known as local time. A type of solar time that is based on the average length of a solar day or 24 h. A wristwatch or mobile phone displays local mean time. It averages out the variations in the position of the actual Sun by synchronizing many sundial clocks or local apparent times of a region to a single agreed-upon time standard within a time zone that includes daylight savings and other manmade time adjustments.

local solar time

(LST) See →solar time.

local standard time

The official local time kept in a region, country, or time zone.

local time

See →local mean time.

location factor

A vital factor during the site survey at the beginning of a solar project, determining the amount of sunlight that strikes the available surface at a specific location. A careful assessment conducted by a trained evaluator, including all the collected location data, determines whether a proposed site is suitable for a photovoltaic or solar-thermal installation or not.

locational marginal price (LMP) A wholesale electricity price at a particular location at a given time. This volatile hourly varying price is based on the level of energy demand at a specific location (load), power generation costs from different types of generators (supply), transmission, and other operational constraints. For instance, the locational marginal price is usually higher in dense populated metropolitan areas with high demand for electric power and higher levels of transmission congestion. locational marginal pricing

See →locational marginal price.

longitude

An imaginary vertical line drawn on Earth’s surface between the North and South Poles. Longitudinal lines are used for measuring distance and locating places east or west of the prime (Greenwich) meridian.

long-term heat storage tank

Also known as a →seasonal heat storage tank. A storage vessel that uses an alternative storage medium that is more efficient than water, for example, →molten salt. The longterm heat storage tanks are able to retain heat for a longer

longwave 

 417

period of time, up to several weeks or months, by storing both →sensible heat and →latent heat during process. longwave

Referring to →longwave radiation.

longwave radiation

Also known as outgoing longwave radiation (OLR). After absorbing incoming solar shortwave radiation, the Earth reemits one part of the absorbed energy as longwave radiation. Contrary to the sun’s powerful →shortwave radiation, the much cooler Earth gives off longwave radiation in the form of infrared rays to space. The terrestrial radiation, also known as heat, contains much less energy than solar shortwave radiation, but enough to warm our planet’s surface. A large part of this thermal energy leaving the Earth is kept in the atmosphere by natural greenhouse gases such as water vapor, keeping the Earth’s surface at comfortable 14.5  °C (58  °F). However, the greenhouse gases produced from human activity, such as carbon dioxide or methane, add an extra burden to the earth’s fragile atmosphere. The more greenhouse gas there is, the bigger the blanket trapping the heat (infrared radiation) before it can naturally escape the atmosphere, and consequently, the warmer the planet Earth.

longwave solar radiation

See →longwave radiation.

longwave thermal radiation

See →longwave radiation.

loss of pressure

An event that occurs when pressure in a water distribution system drops below normal, which is defined as a pressure of less than 20 pounds per square inch (psi). A pressure loss can be caused by a water main break, loss of power, or an equipment failure. A pressure drop affects the heat performance in a closed thermal system.

low carbon city

A city that takes various measures, such as energy conservation, →large-scale solar energy storage systems, →passive solar building design, →smart meters, →smart grid, →smart energy management system, →emission-free transport, →solar street lights, →solar roadway, and →electric vehicles to reduce its →greenhouse gases emissions and →carbon footprint.

low carbon economy

(LCE) Also known as low-fossil-fuel economy (LFFE), an economy based on the use of sustainable and low-carbon alternative energies, such as solar and wind, to run their

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 low concentration photovoltaic cell

businesses. In addition, the low carbon economy gives preference to investments in green technologies, fosters →emission-free transport, non-CO2 agriculture, and takes other necessary measures to reduce CO2 emissions to a zero-emission level, at which no harmful pollutants are emitted into the atmosphere. With regard to heavy industries, the LCE applies innovative technologies, such as CCS, to decrease the amount of emissions from industries. The CCS technology can capture CO2 emissions from industries, such as a coal electricity plant, and inject them into repositories located deep underground or beyond the bottom of the sea. The CO2 stored or sequestered in underground rock formations can potentially be reused later on. low concentration photovoltaic cell

Also known as low concentration solar cell. A conventional, single junction silicon photovoltaic cell that is integrated into a →low concentration photovoltaic system, which uses concentrating optics to focus sunlight onto the cell.

low concentration photovoltaic module

(LCPV) A photovoltaic module to which side mirrors or other optical concentration devices are added to magnify solar energy multiple times and hence achieve higher power output.

low concentration photovoltaic system

(LCPV system) A photovoltaic system that has a concentration magnification ratio of less than 10×. This type of photovoltaic system employs various optical devices, such as side mirrors, prism-based concentrators, compound parabolic concentrators, and V-troughs to focus sunlight onto regular, single-junction silicon photovoltaic cells that are located at the base of the system, increasing solar energy multiple times. Having a concentration ratio of less than 10×, the LCPV system is less efficient than a high concentration photovoltaic system (HCPV system) with a ratio between 150× and 1,000×. In spite of lower efficiency, the LCPV systems are easier to finance and install. They do not require bulky and expensive tracking and cooling mechanisms and can be installed in a stationary condition. In contrast to high concentration photovoltaics that can only absorb direct solar radiation, the LCPV can capture both the direct and diffuse parts of the solar electromagnetic spectrum. As the LCPV systems can utilize one part of

low concentration photovoltaic technology 

 419

diffuse radiation, they are also suitable for →building-integrated photovoltaics and installation in northern regions with frequent cloudy weather conditions. low concentration See →low concentration photovoltaics. photovoltaic technology low concentration photovoltaics

(LCPV) A photovoltaic technology that employs side mirrors, prism-based concentrators, compound parabolic concentrators, and V-troughs to achieve a concentration magnification ratio between 2× and 10×. Compared to high-concentration photovoltaics that can only harvest direct solar radiation, the LCPV can capture both the direct and diffuse parts of the solar electromagnetic spectrum.

low concentration PV cell

See →low concentration photovoltaic cell.

low concentration PV module

See →low concentration photovoltaic module.

low concentration PV technology

See →low concentration photovoltaics.

low concentration solar cell

See →low concentration photovoltaic cell.

low concentration solar module

See →low concentration photovoltaic module.

low concentration solar system

See →low concentration photovoltaic system.

low concentration system

See →low concentration photovoltaic system.

low electrical conductivity

A slow flow of electrons through a material. Some materials have high thermal conductivity and low electrical conductivity, for instance, diamond, boron nitride, and silicon carbide. The electric resistivity can be decreased by adding →carbon nanotubes to semiconductor materials. For example, the addition of carbon nanotubes to polymer composites can significantly increase polymer conductivity and hence the efficiency of a thin-film photovoltaic cell.

420 

 low emission vehicle

low emission vehicle

(LEV) A light duty passenger vehicle that emits low levels of motor vehicle emissions, such as unburned hydrocarbons and particulates, into the atmosphere, meeting strict emissions regulations in a given country or state. Low emission vehicles are divided into the following subcategories: 1. ultralow emissions vehicles (ULEV) with 50% less CO2 emission than an average new car; 2. super ultralow emissions vehicles (SULEV) with 90% less CO2 emission than an average new car; 3. partial zero-emission vehicles (PZEV) that meet SULEV tailpipe-emission standards have a 15 year/150,000 mile warranty, and zero evaporative emissions; and 4. Zero-emission vehicles (ZEV) that emit no harmful →greenhouse gases into the atmosphere.

low emissivity

See →low thermal emissivity.

low energy density

Energy density is the key feature of rechargeable batteries, indicating how much energy a battery can store per unit of volume. It is usually measured in watt-hours per kilogram (Wh/kg). The higher the energy density per kilogram the better the performance and capacity of a battery. Therefore, a battery with a low energy density can store less energy and accordingly power an electrical load over a shorter period of time than a battery with a high energy density.

low heat conductivity

See →low thermal conductivity.

low light

See →low light incidence.

low light incidence

Areas with low light incidence and intensity, for instance an area between trees, should be avoided for photovoltaic installation. Even though thin-film solar modules can still generate some energy under low light conditions characterized by reflection and light scattering, it is a general rule to install solar panels in areas that are free of shading obstacles.

low power density

Power density is an important feature of rechargeable batteries, indicating how quickly a battery can store and deliver energy per unit of volume. It is measured in watts per kilogram (W/kg). The lower the power density per kilogram the more slowly a battery is charged and discharged. Therefore, low power density batteries are suitable for devices that do not require fast charging and discharging or rapid bursts of energy.

low-temperature solar collector 

low-temperature solar collector

 421

A stationary, nonconcentrating →solar collector for supply of heat between 40  °C and 100  °C (104  °F and 212  °F). The typical application of low-temperature solar collectors comprises solar water heating and space heating and cooling. The most commonly used types of low temperature solar collectors are →flat-plate collectors, →evacuated-tube collectors, →batch collectors, and →thermosiphon systems. The installation of low-temperature solar collectors includes piping, primary and secondary water circuit, →heat exchanger, →hot water storage tank, and expansion vessel.

low thermal conductivity Property of some materials to transfer heat at a lower rate. Materials with low thermal conductivity are commonly used as insulators. See →low thermal conductivity materials. low thermal conductivity Low conductivity materials transfer heat at a lower rate materials and are commonly used as insulators. Materials with low thermal conductivity are polystyrene, aluminum oxide (alumina), and zirconium dioxide (zirconia). low thermal emissivity

Refers to the ability of certain materials to emit low levels of radiant energy (heat).

low thermal mass

See →low thermal mass materials.

low thermal mass materials

Materials with low thermal mass, such as drywall or timber, have low heat storage capacity.

low visibility

Weak market presence.

low voltage cutoff

(LVC) See →low voltage disconnect.

low voltage directive

(LVD) (2014/35/EU) A European Union directive that ensures that domestic and professional electrical equipment within certain voltage limits provides a high level of protection for European citizens.

low voltage disconnect

(LVD) Is an electronic module, an automatic disconnect switch, which protects the batteries from overdischarging. Usually a part of a charge controller, the LVD, constantly monitors battery voltage. When a low battery voltage is detected, the LVD automatically disconnects the load (all electrical devices connected to the circuit) from the battery bank to prevent excessive discharging.

422 

 low voltage disconnect hysteresis

low voltage disconnect hysteresis

LVD hysteresis. The voltage difference between the low voltage disconnect set point and the load reconnect voltage. The LVD hysteresis range should not be too small because it would result in a constant on and off switching of the load, leading to instability and the possible failure of the controller or connected appliances. Therefore, solar inverters must be fitted with LVD, turning off the device when battery voltage falls to 11.5 V and back on when it reaches 12.5+ V.

low voltage distribution

The low-voltage power lines that carry electricity from the distribution transformer to various end-users, such as individual consumers or businesses.

low voltage distribution grid

See →low voltage distribution network.

low voltage distribution losses

Losses connected with the introduction of solar photovoltaic (PV) systems at the low voltage side of the distribution network. A new model in which electricity flows in two directions at lower voltage levels, from the electric utility grid to a house as well as from a home’s PV system to the grid, poses new challenges to low-voltage distribution networks. Nodes next to solar array installations are especially affected, causing grid voltage fluctuations, overvoltage, undervoltage, power losses, and unbalanced lines.

low voltage distribution network

Also known as a secondary network. A network consisting of low-voltage power lines carrying electricity that is stepped down from higher voltage by the distribution transformers and delivered to each building in the city or countryside.

low voltage ride-through (LVRT) Power supply management during grid voltage dips. In some countries, for instance in Germany, the gridcode regulations require that a renewable power generation system, such as a →solar array, →solar power plant, or a →wind farm, must remain connected to the grid when the voltage drops occur as a result of a mismatch between the produced active power and the active power delivered to the grid. low voltage warning

Warning that alerts the user that the battery is approaching a voltage that will not be sufficient for a normal and safe operation.

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low voltage1

An electrical potential at voltages not large enough for a normal and safe operation.

low voltage2

12 or 24 V direct current (DC).

low-carbon energy

Also known as low-carbon power. Energy that comes from alternative energy sources that should replace polluting fossil fuels, such as solar, wind, hydro, biomass, and marine energy.

low-carbon power

See →low-carbon energy.

low-E coating

See →low-E window.

low-E glass

Special, energy-efficient glass with microscopically thin coating that is used in →low-E windows.

low-E window

(low-emissivity window) An energy-efficient window that prevents the solar heat from entering the house by using a special coating on window glazing. Low-E glass coating

Summer heat or long wavelength (IR) reflected out Winter heat reflected back inside

Visible light or short wavelength passes through glazing UV light reflected out

Low-E Window

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 low-emission zone

blocks and reflects ultraviolet and infrared light, while admitting visible light. Since the coating is microscopically thin, it is virtually invisible to the human eye. The use of sun protection glass is considered an effective →passive cooling technique. low-emission zone

(LEZ) A geographically defined zone where the most polluting vehicles are restricted or discouraged from access and use. The goal of the LEZ access restriction is to improve the air quality in densely populated areas, such as city centers, where the number of inhabitants exposed to harmful pollution and road traffic noise levels is high. Low-emission zones are an effective measure to reduce emissions of nitrogen dioxide (NO2) and particulate matter (PM) from vehicle exhausts. The reduction of harmful emissions has also an indirect impact on →ozone levels, mitigating ozone depletion and →global warming.

low-emissivity coating

A special tin oxide coating that ensures low thermal emissivity of the window. See also →low-E window.

low-emissivity glass

Special, energy-efficient glass with microscopically thin coating that is used in →low-E windows.

low-emissivity window

Window with a special tin oxide coating that ensures low thermal emissivity. See also →low-E window.

low-energy architecture

An energy-efficient, sustainable architecture that focuses on the design and development of →low-energy buildings and →zero-energy buildings. Low-energy architecture promotes energy savings for homeowners, optimizes the quality and comfort of living, reduces carbon emissions, and mitigates climate change. To achieve these goals, the low-energy architecture relies on the extreme external and internal insulation of the building envelope, including thick walls, triple-glazed windows, special insulation materials, and efficient ventilation that circulates fresh air from the outside across the building. In addition to these passive solar building design technologies, the low-energy architecture seeks to incorporate active solar technologies that generate electricity from sunlight. It looks at a building as a dynamic place of energy exchange between the indoor and outdoor environment.

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low-energy building

A building that uses less energy (electricity and heat) than a conventional building. The low-energy consumption is typically achieved by a →passive solar building design, →passive cooling techniques, and the integration of photovoltaic and solar thermal systems.

low-energy home

See →low-energy building.

low-energy house

See →low-energy building.

low-flow solar hot water A solar hot water heating system that employs a reduced heating system flow rate to increase the system’s efficiency. Due to the low flow rate, smaller diameter tubing can be used, reducing material and installation costs. Correspondingly, thinner tubes require significantly lower amount of →heat transfer fluid per square meter or square foot in the →closed-loop system. The reduced volume of heat transfer fluid in the system results in faster heating and increased tank stratification. low-flow system

See →low-flow solar hot water heating system.

low-fossil-fuel economy

(LFFE) See →low carbon economy.

low-grade silicon

See →dirty silicon.

low-iron glass

A type of low-iron, transparent plate glass that is characterized by high transmission and low reflectivity of solar radiation. →Silica is the material that is mainly used in the manufacture of low-iron glass. Low-iron tempered glass is widely employed in solar industry due to its high strength and longevity.

low-iron tempered glass See →low-iron glass. low-light performance

The low light performance of photovoltaic (PV) cells is an important feature for the overall efficiency of solar panels, in particular in northern regions where the sun rests lower in the horizon. In the early morning and the late evening hours and on cloudy days with low light intensity, a PV cell with a low shunt resistance experiences significant power losses, as the amount of current flowing through the shunt resistance increases. Therefore, the right choice of the panel type plays an important role in northern countries or on rooftops with an east/west orientation. Some types of solar modules, such as thin-film copper indium and

426 

 low-temperature solar collector

selenide (CIS) PV modules, have higher sensitivity for low irradiation conditions and longer wavelengths, achieving higher power output than traditional silicon solar panels. low-temperature solar collector

A type of solar collector without glazing or insulation that is operated at temperatures below 110°F or 43°C. They are commonly made of special UV-resistant black plastic or rubber and used for heating outdoor swimming pools.

low VOC product

A product with a low content of volatile organic compound (VOC) – at or below 150 g/L. The low VOC product is associated with high indoor air quality, low odor, and lasting performance.

LPE1

See →liquid phase epitaxy.

LPE2

Abbreviation for →liquid-phase exfoliation.

LSC

Abbreviation for →luminescent solar concentrator.

LSC technology

Luminescent solar concentrator technology.

LST

Abbreviation for local solar time. See →solar time.

luminescence

Cold body radiation. The emission of light that occurs at low temperatures.

luminescent solar concentrator

(LSC) Consists of three main elements: a sheet of glass/ plastic, luminescent dyes, and photovoltaic (PV) cells. The glass/plastic is coated with a thin film of fluorescent dyes that absorb the incoming solar radiation and then reemit it. The emitted light does not leave the sheet and scatter outside in all directions, but is instead trapped in the glass plate by total internal reflection. Through this internal reflection, the light is guided along a staircase pattern to the edges of the glass or plastic sheet, on which PV cells absorbing the energy are mounted. Two layers of LSCs are stacked one over another to absorb a broader range of solar spectrum and thereby provide a higher solar energy yield. Luminescent solar concentrators are more efficient than traditional solar panels because large areas of PV panels are replaced by cheaper fluorescent dye surfaces that require fewer PV cells for the same amount of produced energy.

luminosity 

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In addition, luminescent solar concentrators can collect both direct and diffuse solar radiation. That makes the installation of an expensive →solar tracking system superfluous. LSC collects not only direct sunlight but also indirect sunlight, generating significant energy on foggy or cloudy days likewise. These properties make LSC a good candidate for →solar facades and other vertical PV structures (→building-integrated photovoltaics). luminosity

The amount of light given out by an object, such as a lamp.

lux

(lx) The word is derived from Latin word lūx, which means light. The SI unit of illuminance, the amount of light produced by an object. It is equal to 1 lumen per square meter.

LVC

See →low voltage cutoff.

LVD1

Abbreviation for →low voltage disconnect.

LVD2

Abbreviation for →low voltage directive.

LVRT

Abbreviation for →low voltage ride-through.

ly

Abbreviation for solar radiation unit “langley”.

M

macrogrid

See →electrical grid.

macroclimate

The prevailing climate of a large area, such as a region or a country.

magnesium anode

A magnesium rod deliberately placed inside a water storage tank to attract corrosive elements and reduce the corrosion of the protected material.

magnetic declination

Is the angle between magnetic north and true north.

magnetic declination chart

See →magnetic declination map.

magnetic declination map

Shows whether and how much magnetic south or north deviate from true south and north.

magnetic declination table

See →magnetic declination map.

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 magnetic field

magnetic field

A field of force generated by moving electric charges – electrons traveling along the conduction band of a semiconductor or orbiting the atomic nucleus.

magnetic iron ore

Also known as magnetite. A hard gray-black iron oxide mineral that is strongly attracted by magnets. It is a source of iron.

magnetic nanoparticles

(MNP) A type of nanoparticle whose features are controlled by the application of magnetic fields. The conversion efficiency of solar cells can be increased by up to 10% by adding magnetic nanoparticles to the substrate.

magnetic protractor

An angle-measuring device with a magnetic base and back.

magnetic storm

See →solar storm.

magnetite

Magnetic iron ore.

magnetron sputtering

Is an advanced version of the conventional →sputtering process in which the target material (cathode) is bombarded by energetic ions or electrons of argon plasma, causing the atoms to be dislodged from the surface of the target material and condense on the surface of the substrate (anode) as a thin semiconductor layer. The traditional sputtering method proved slow and the high-energy bombardment might cause overheating of the substrate and damage to the deposited semiconductor layer. The magnetron sputtering method overcomes these limitations by superimposing magnets on the negatively charged electrode (cathode). The magnetic field traps electrons over the target plate and creates a dense plasma in the confined target region, leading to increased ion bombardment of the target and, correspondingly, to faster deposition rates. As the plasma is restricted to a region near the target plate, it causes less damage to the thin film being deposited on the substrate.

mains frequency

UK See →utility frequency.

mains power

UK See →utility power.

mains voltage

UK See →utility voltage.

mains voltage fluctuation

Systematic or random changes in the magnitude of the supply voltage. These variations of voltage and frequency usually range from 0.1% to 10% of the nominal supply voltage.

maintenance  

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maintenance

See →solar system maintenance.

maintenance costs

An important part of the expected PV life-cycle costs. As the cost of energy is measured over the lifetime of a given solar array (25 years), a cost-effectiveness analysis must include maintenance costs. Compared to other power generation technologies with many movable parts and complex technologies, the maintenance costs of a PV system are relatively low. They include cleaning of panels, an annual inspection, and insurance and property taxes.

maintenance engineer

See →maintenance technician.

maintenance technician

A person in charge of maintaining the day-to-day operations of large solar power plants. He or she must be a trained person who is able to troubleshoot and repair electrical and mechanical solar equipment according to safety regulations.

maintenance-free battery

A battery type referring to →sealed lead-acid batteries, →gel battery and →Absorbent Glass Mat (AGM) battery. These low-maintenance batteries got their somewhat controversial name “maintenance free” from the fact that, unlike →flooded lead-acid batteries, they do not require a periodical refilling of evaporated electrolyte and →equalization.

majority carrier

See →majority charge carrier.

majority charge carrier

Dominant charge carrier that is mainly responsible for current flow in a semiconductor. In the n-layer of the semiconductor, which is doped with →phosphorus, the electrons are in excess, moving freely from one atom to another and carrying negative charge along the conduction band. As the number of electrons is higher than the number of holes in this layer, the electrons are the majority charge carriers and the holes are the minority carriers. In the p-layer, which is doped with →boron, the electron–hole ratio is reversed. The holes are in excess, carrying positive charge along the valence band. As the number of holes is higher than the number of electrons in this layer, the holes are the majority charge carriers and the electrons are the minority carriers.

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 Manufacturer’s Certification Statement

Manufacturer’s Certification Statement

A signed statement from the manufacturer certifying that the product or component qualifies for the Renewable Energy tax credit at the federal, state, and local levels.

manufacturing of graphene

Also known as graphene production. Graphene is manufactured using one of the following methods: 1. micromechanical exfoliation in which graphene is cleaved off an existing graphite crystal, yielding high quality layers in the order of millimeters; 2. growth of graphene on SiC, in which the graphene layer is grown directly on a substrate surface; 3. anodic bonding, in which graphite is first pressed onto a glass substrate with the help of an electrostatic field and then cleaved off to leave few layers of graphene on the substrate; 4. photoexfoliation, in which short laser pulses are used to detach intact graphene monolayers from a graphite surface; and 5. liquid-phase exfoliation, in which graphite is exfoliated in liquid environments exploiting ultrasounds.

March equinox

See →spring equinox.

mask

In a photolithographic process, a glass or quartz plate that contains data about the structures to be printed. See also →photomask.

masked area

The area of a photovoltaic (PV) cell or module that includes →busbars, →fingers, and →interconnections. During the testing and measurement of a PV module performance, the masked area and the aluminum frame are subtracted from the total surface area of the PV device, as they do not absorb solar radiation.

maskless lithography

A dynamic, photolithographic method that does not utilize a permanent, fixed photomask to generate patterns. In contrast, pattern information is stored digitally and can be easily modified from one run to another. The programmable photomask reduces manufacturing costs because the production of expensive masks is not required and new mask designs can be generated significantly faster. The main types of maskless lithography are →electron beam lithography, direct laser writing, and →ion-beam lithography.

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mass flow rate

The amount of mass (substance/fluid) passing by a single point per unit of time. The formula for mass flow rate is m = ρ v A, where p stands for density, v for velocity, and A for the area of the cross section.

master combiner box

See →subcombiner box.

matched pair of temperature sensors

In a heat meter system, two temperature sensors – one in the inlet pipe and the other in the outlet pipe – measure flow and return temperatures.

matrix precursor

A compound that is used as a source material in various deposition processes, such as →CVD, →PVD, or →ALD.

maximum continuous AC power

The maximum continuous output AC power that a →solar inverter can deliver.

maximum continuous discharge current

The maximum current at which a battery can be constantly discharged without doing damage to the battery.

maximum input DC current

The maximum input direct current (DC) from a photovoltaic array that can be fed into an inverter. When DC power feeding an inverter exceeds the maximum input level of the inverter (maximum rated power), the excess power is “clipped” and lost.

maximum light detection controller

A type of tracker controller that operates according to a principal of maximum light detection, directing solar panels toward the brightest point in the sky over the course of the day.

maximum light detection technology

See →maximum light detection tracking system.

maximum light detection tracker

See →maximum light detection tracking system.

maximum light detection tracking system

(MLD®) A type of tracking system that uses a maximum light detection (MLD) sensor and controller to continuously direct solar panels toward the brightest point in the sky over the course of the day. The MLD sensor detects intensity and angle of the incident solar flux at all times. Based on the received current light conditions information, the system moves the solar panel platform into a most favorable position where it will receive the maximum sunlight and gain optimum energy yield. Depending on the

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latitude, solar systems that use the MLD tracking technology can produce over 30% more electricity than traditional →static solar systems. The MLD tracking technology works on sunny as well as on cloudy and rainy days. maximum light detection See →maximum light detection tracking system. tracking technology maximum operating DC voltage

The maximum DC input voltage value threshold that should not be exceeded to prevent permanent damage to the inverter.

maximum output

See →maximum power output.

maximum output current Maximum output current that a →solar inverter can deliver. maximum output voltage (Vmax) See →maximum power point voltage. maximum power output

Also known as PMAX or maximum power point (MPP). Maximum power output or MPP of a photovoltaic module is the product of the greatest voltage value (VMPP) and the greatest current value (IMPP), MPP = VMPP × IMPP. The efficiency of a photovoltaic module is usually calculated by this MMP equation that is derived from the →Ohm’s law power equation: P = V × I. There can only be one MPP, or one point on the →I–V curve (current–voltage curve), for a certain PV module (PV product) estimated with an optimal load under optimal illumination, temperature, and other conditions.

Maximum Power Point

(MPP) Maximum power point of a photovoltaic (PV) module is the product of the greatest voltage value (VMPP , →Maximum Power Point voltage) and the greatest current value (IMPP , →Maximum Power Point current), MPP = VMPP × IMPP. The efficiency of a PV module is usually calculated by this MMP equation that is derived from the →Ohm’s law power equation: P = V × I. Along with other ratings, some PV manufacturers also include MPP value into their product data sheets. According to their rating, there is only one MPP on the →I–V curve (current–voltage curve) for a certain PV module (PV product) estimated with an optimal load under optimal illumination, temperature, and other conditions. However, as in a real-life scenario load, illumination, and temperature conditions constantly vary during the day in an

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operating solar array, an MPP tracking controller tracks the optimal power point on the I–V curve and adjust values to ensure the maximum power output (wattage) of the PV array. Maximum Power Point current

Is one of the two important parameters that a Maximum Power Point Tracking algorithm of an inverter continually tracks to ensure Maximum Power Point (MPP) value, and hence maximum PV system output. MPP is the sum of the greatest voltage value (VMPP, →Maximum Power Point voltage) and the greatest current value (IMPP, Maximum Power Point current), MPP = VMPP × IMPP.

Maximum Power Point tracker

Is a digital tool that optimizes the power gain from solar panels by finding a →Maximum Power Point (MPP) and ensuring the optimal system operation. MPP tracker matches the voltage of the solar array to the voltage of the battery bank or utility grid. See also →Maximum Power Point Tracking and →Maximum Power Point.

Maximum Power Point Tracking

(MPPT) Is a function used by most grid-tie system inverters and charge controllers of battery-based systems to ensure that a solar system operates at its →maximum power point (MPP) and yields the maximum power output (wattage). This regulation algorithm constantly tracks the voltage and current of a solar system with the goal of finding an optimal combination: a maximum power point voltage (VMPP) and maximum power point current (IMPP). According to the Ohm’s law equation, VMPP × IMPP will result in MPP, and hence achieve an MPP operation of a PV array. As illumination and cell temperature conditions constantly change during the day, a DC power output of solar modules varies as well. The MPPT closely monitors these changes and adjusts the voltage of the PV panels to the optimal voltage (VMPP) for a given battery bank or utility grid. For instance, if the MPP tracker receives 16.5 V from the solar panels, it will convert it down to 12 V, exactly matching the voltage of the panels to one of the batteries. Also, as load in a circuit constantly changes, the MPPT regulates the impedance of the load ensuring the maximum power gain. MPPT can improve the annual power yield by 15–20%.

Maximum Power Point Tracking charge controller

See →Maximum Power Point Tracking solar charge controller.

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 Maximum Power Point Tracking controller

Maximum Power Point Tracking controller

See →Maximum Power Point Tracking solar charge controller.

Maximum Power Point Tracking inverter

An inverter that uses an MPPT regulation algorithm ensuring that a solar system operates at its optimal power point and yields the maximum power output (wattage).

Maximum Power Point Tracking solar charge controller

A controller that uses an MPPT regulation algorithm ensuring that a solar system operates at its optimal power point and yields the maximum power output (wattage).

Maximum Power Point voltage

Is one of the two important parameters that an MPPT algorithm of an inverter continually tracks to ensure Maximum Power Point (MPP) value, and hence maximum PV system output. MPP is the sum of the greatest voltage value (VMPP, Maximum Power Point voltage) and the greatest current value (IMPP, →Maximum Power Point current), MPP = VMPP x IMPP. MPP voltage represents the greatest voltage value at which PV panels can safely be operated.

Maximum Power Temperature Coefficient

The percentage of power output drops for every degree Celsius increase in the PV panel temperature. As semiconductor materials are sensitive to temperature, solar cell power output will decrease when they heat up and the temperature of the PV cells is higher than 25°C. This power output efficiency reduction due to high temperatures can be calculated by the temperature coefficient formula: percentage per degree Celsius (% per °C). Each PV manufacturer provides Maximum Power Temperature Coefficient info in the technical data sheets for their products. That means, if the temperature coefficient of a solar panel is –0.38%, the module would lose –3.80% of energy yield when the temperature reaches 35°C (10 degrees higher than 25°C).

maximum power tracking

See →Maximum Power Point Tracking.

maximum series fuse rating

The value that prescribes the largest size of overcurrent protection devices (OCPD), such as fuses, which can be applied. Every solar module has a series fuse rating listed in its specifications, which is used for protecting the module.

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maximum voltage

Also known as an open circuit voltage (VOC). The maximum voltage from a PV cell that occurs when no current is flowing through the device and the net current is zero.

MBE

Abbreviation for →molecular beam epitaxy.

MC

Abbreviation for micromechanical cleavage. See →micromechanical exfoliation.

MC4 cable

A cable with a male or female →MC4 connector.

MC4 connector

A type of interlocking →photovoltaic connector that is usually found on new solar modules since 2011. The interlocking mechanism with male and female connectors makes wiring simpler and faster. While older PV panels with junction boxes required a professional electrician to connect wires to appropriate terminals, MC4 connectors can safely and legally be connected by anybody without the use of special tools. The male connector simply snaps into the female connector, providing a permanent connection. As MC4 connectors are designed for one-time, longterm connection, they require a special →MC4 disconnect tool to be disassembled. MC4 connectors are suitable for 4 and 6 mm solar cables, making a reliable contact. They have an ingress protection IP67, which means when they are properly locked, they can withstand water and dust penetration. They are also resistant to ultraviolet (UV) radiation. It is important to use only plug-in connectors from the same manufacturer for a solar array. Using incompatible plug-in connectors from different manufacturers leads to overheating due to increased electrical resistance, resulting in energy losses, failures, and damage to the PV system.

MC4 disconnect tool

A special tool used to disconnect a male →MC4 connector from a female MC4 connector.

MC4 unlock tool

See →MC4 disconnect tool.

MCPV

Abbreviation for medium concentration photovoltaics. See →medium concentration photovoltaic system.

MCPV system

Abbreviation for →medium concentration photovoltaic system.

MCS

Abbreviation for →Microgeneration Certification Scheme.

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 mean solar day

mean solar day

See →mean solar time.

mean solar time

Also known as mean solar day. Compared to local apparent solar time that is based on the Sun’s actual daily motion across the sky and roughly measured by a sundial, mean solar time is man-made clock time. The Sun’s motion across the sky is not a uniform, circular movement because the Earth moves around the Sun in an elliptical orbit. That is the reason why apparent solar time, which is defined by the position of the sun, differs from the agreed-upon →local mean time (LT) or clock time, which is based on man-made adjustments, such as time zones and daylight savings.

measurement uncertainty

When making an estimate for a new solar system, the first thing to check is whether enough solar resource is available at a proposed site. The expected annual energy production is calculated by looking at the publicly available solar resource maps and annual →global horizontal irradiance (GHI) data for a given region. The generally measured data may not be completely reliable for a specific project due to the greater spatial diversity of sites in certain regions. In order to avoid financial risks, many solar developers and planners resort to on-site measurements. The site-specific measurements certainly increase the precision of the solar resource assessment; however, measurements are never perfect. According to Heisenberg’s uncertainty principle, one cannot measure or know all aspects of a quantum system at the same time. Different measuring devices will show different results; even the results of the most precise sensor will deviate to a larger or smaller extent from the results of another sensor. Instruments in use today are subject to a great amount of uncertainty. Nevertheless, an on‐site measurement can reduce the overall uncertainty from around 9% to 5% or even less. To lower the risk, it is advisable to include this 5% accounting for measurement uncertainty into the solar resource assessment. In conclusion, the lowest possible measurement uncertainty for a given site is achieved by taking into account both long-term satellite-derived irradiance data and short-term on-site irradiance measurement data.

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measuring clamp

Measuring instrument with a clamp that measures the electric current in a circuit.

mechanical cutting

See →mechanical sawing of wafers.

mechanical flywheel

Is a device that stores excess energy in the form of rotational kinetic energy. An electric motor accelerates the flywheel to a high velocity and preserves the energy in the system as rotational energy. When electrical power is needed during hours of peak energy demand, the rotational energy is converted into electricity by the same motor that now functions as generator.

mechanical sawing

See →mechanical sawing of wafers.

mechanical sawing of wafers

A type of wafer dicing that utilizes a machine called a dicing blade. Mechanical sawing is a traditional method for cutting hard materials such as silicon. The major disadvantages of mechanical sawing are: 1. the mechanical load, causing chipping and damage to semiconductor wafers; 2. the necessity of further polishing and processing to turn rough textures into usable wafers; 3. a relatively large kerf width; 4. the time-consuming dicing process that can take several hours to complete; and 5. the production of unhealthy tiny particles of silica during the sawing process. As the wafer material is getting thinner, dicing blades become unsuitable to saw thin wafers in the range of 100 μm or less. In this area, mechanical sawing is replaced by laser dicing processes, such as →laser ablation and →stealth dicing.

mechanical scribing

Is a PV scribing method that uses a diamond-tipped stylus to cut scribe patterns in a semiconductor material in order to create a grid of conductive channels and interconnections in a solar cell. Although the mechanical scribing method might still work fine with some softer semiconductor materials, →laser scribing is becoming an increasingly popular method to process semiconductor layers, in particular in →thin-film photovoltaic industry, due to superior precision, clean process, and lower costs.

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 mechanical strength

mechanical strength

The ability of a material, for example, solar panel glass, to withstand an applied force, for example, wind. Solar modules in zone 3, which includes all coastal regions of Alaska and many coastal regions of Florida, Louisiana, and North Carolina, must be built to withstand 110 mph winds.

mechanical texturing

A texturing method based on mechanical etching to reduce the amount of reflected light of solar panels, which is considered lost energy. The micromachining or engraving of the uniform pyramid patterns into the solar wafer surface with a depth in the range between 3 and 50 μm can reduce two-thirds of lost reflected light, compared to the flat, nontextured PV wafer surface.

mechanically attached mounting

A method in which a mounting structure is mechanically attached to the ground or roof. Although many solar owners tend to avoid drilling numerous holes in their roofs for a mounting structure at all costs, as these potentially lead to roof leaks, roofing and solar associations strongly recommend the mechanically attached mounting over →ballasted mounting, in which an additional weight of heavy concrete blocks is placed on the roof. Impermeable flashings, waterproof standoffs, and heavy duty rails keep roof penetrations to a minimum. A properly done solar installation with these special parts should prevent leakages. It is also easier to conduct a routine roof inspection and maintenance in the properly installed mechanically attached mounting systems than in the ballasted mounting systems, which require a disassembling of a large portion of the PV system to find and repair a leak.

mechanically attached mounting system

A ground- or roof-mounting system that is mechanically attached to the ground or the roof.

mechanically attached racking

See →mechanically attached mounting.

mechanically attached racking system

See →mechanically attached mounting system.

mechanically textured cell

A solar cell whose silicon surface is textured with inverted pyramid or normal micropyramid patterns through mechanical grooving to minimize the amount of reflected light and thus enhance the performance of solar modules.

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medium concentration photovoltaic system

(MCPV system) A photovoltaic system that has a concentration magnification ratio between 10× and 150×. This type of photovoltaic system employs various optical devices, such as side mirrors, prism-based concentrators, compound parabolic concentrators, and V-troughs to focus sunlight onto photovoltaic cells that are located at the base of the system, increasing solar energy multiple times.

medium concentration photovoltaics

See →medium concentration photovoltaic system.

MEG

Abbreviation for →multiple exciton generation.

megawatt

(MW) SI unit of power that is equivalent to 1,000 kW or 1,000,000 W. Megawatts are used to measure the output of larger solar system installations, such as solar PV plants or solar farms. For instance, Topaz solar farm in San Luis Obispo County, California, is a 550 MW photovoltaic power plant.

megawatt alternating current

(MWAC or MWAC) Power rating that uses the AC power output to the grid as a measurement unit for the system capacity. As there are some evident inverter and transformer power losses between the solar panels and the AC output to the grid, some countries prefer to rate the capacity of PV power plants in converted megawatt alternating current (MWAC). The converted megawatt AC power output, which will actually be fed into the utility grid, is always lower (15–20%) than the megawatt peak (MWp) DC output. Therefore, MWAC provides a more realistic account of the solar plant capacity. In general, the European standard is to express the capacity of solar farms in MWp, while the North American practice tends to give preference to MWAC rating. See also →megawatt peak.

megawatt hour

(MWh) Measure of electricity generated by a large-scale solar plant or used in a region over a period of time, 1 MW for 1 h.

megawatt peak

(MWp) Measurement unit for the capacity (nominal output) of solar power generating plants. It refers to peak power, a maximum energy output generated by a photovoltaic system under optimal →standard test conditions (STC).

megawatt peak output

(MWp) See →megawatt peak.

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 melt

melt

A silicon slurry that is produced by melting silicon rocks at high temperatures (around 1,371  °C [2,500  °F]) in a special container called →crucible. Dopant atoms, such as →boron or →phosphorus, are usually added to the melt in a highly controlled manner to dope the →silicon and thus change its electrical properties. A single silicon crystal is pulled from the melt in the →Czochralski method.

melting

A physical process of changing phase from solid to liquid.

melting point

The temperature at which a given solid becomes liquid at a specific pressure. The melting point of the most important photovoltaic semiconductor material →silicon at ambient pressure of 0.1 MPa is 1,414  °C (2,577  °F). As pressure has a significant effect on the melting temperature of silicon, the following rule needs to be considered during the manufacturing process: the melting point is lowered with an increase in pressure. For instance, an increase in pressure to 10 GPa will reduce the melting point of silicon to 1,000 °C (1,832 °F).

melting process

A process in silicon →solar wafer manufacturing in which silicon rocks, some of which are doped with a small amount of →boron, are melted at high temperatures (around 1,371 °C [2,500 °F]) in a →crucible into a silicon slurry, called melt. A single silicon crystal is pulled from the melt in the →Czochralski method.

membrane

A thin film in a battery that functions as a separator between anode and cathode to prevent short-circuiting, while allowing the transport of ions through its porous thin layer at the same time.

membrane expansion vessel

(MEV) An →expansion vessel with a membrane that separates →heat transfer fluid in a closed-loop system from pressurized air in the expansion tank. As the heat transfer fluid is heated in solar collectors, it expands to fill any available space in the closed-loop system, exerting pressure on the membrane. The membrane allows the expanding water to enter the expansion vessel and to collect all the extra fluid, ensuring a balanced system pressure. The rubber membrane prevents any water contact with the steel shell, inhibiting internal corrosion.

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MEMS

Abbreviation for →microelectromechanical system.

mesh screen

See →wire mesh.

mesoclimate

The climate of a specific site at an intermediate geographic scale of approximately hundreds of meters (yards). A particular site, such as a city park, airport, hill, or river bank, might have a different climate than the general climate of the region. It is important to include these regional specifics into a →solar resource assessment by conducting on-site solar irradiance measurements.

metal contact fingers

See →metal contacts.

metal contact structure

Also known as contact cell structure. Structure of metal contacts in a photovoltaic cell. The light absorption and solar cell performance can be increased by up to 10% with different metal contact designs. One design proposes a decrease in the width of metal →busbars and →fingers on the front surface. Another contact structure buries metal electrodes inside the silicon semiconductor to reduce shading by the electrodes. The third design moves front contact grids to the back of the device. The placement of interleaved positive and negative contacts on the rear surface eliminates shading losses, resulting in a higher energy conversion efficiency.

metal contacts

Also known as metallic contacts. Front and rear contacts of a photovoltaic cell are electrical paths that guide generated electric current outside of the cell and back into the cell. The →fingers collect the electricity generated within the photoactive silicon semiconductor and transport it to the two →busbars at the front surface. The busbars then conduct the electricity to the next cell and further through the module’s circuit. The energy comes back to the cell through the positive connection (+) at the bottom of the cell (e.g., aluminum layer).

metal electrode

A form of metal, metal grid or metal plate, which is used to take an electric current to or from a solar cell. In a polymer solar cell, the transparent →indium-tin-oxide (ITO) film is commonly used as the electron-collecting electrode (cathode), while a low-cost metal, such as aluminum, forms the hole-collecting electrode (anode).

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 metal grid lines

metal grid lines

See →metal contacts.

metal layer

A thin, metal layer that is used as a transparent and conductive electrode in organic and amorphous silicon solar cells.

metal mirror

A mirror made of polished metal, including silver, copper, or aluminum, for various solar applications, such as a →solar concentrator or →solar cooker.

metal oxide

A metallic compound that is composed of metal and oxygen. Metal oxide, such as crystalline indium tin oxide (c-ITO), is used as a thin transparent electrode in perovskite solar cells. Metal oxide is characterized by outstanding mechanical properties, thermal stability, and chemical robustness.

metal oxide varistor

(MOV) See →metal-oxide varistor.

metal oxide-laser induced graphene

(MO-LIG) A process for integrating metallic nanoparticles into laser-induced graphene. The method uses a combination of inexpensive polymers and metal salts that are subjected to the laser scriber, which produces metallic nanoparticles that are uniformly distributed across the →graphene.

metal plate

In a flat-plate solar collector, a dark-coated plate made of metal that actively absorbs solar radiation and converts it into heat. The collected heat is then transferred to the fluid (water or glycol heat transfer fluid) running through the copper tubes of the thermal collector that are soldered or welded onto the metal plate. Thin, flat metal plates are positive and negative electrodes – the major components of a battery.

metallisation

UK See →metalization.

metallization

US A process for producing metallic coatings, electroplating.

metallic contacts

See →metal contacts.

metal-organic chemical vapor deposition

(MOCVD) A type of →chemical vapor deposition process that utilizes metal-organic compounds (e.g., metal alkyls, metal carbonyls, or metal alkoxides) as source materials

metal-organic chemical vapor phase epitaxy 

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to produce single crystal or polycrystalline thin films on wafer substrates. The MOCVD is a preferred method, when complex multilayer semiconductor structures for solar cells need to be deposited. It is especially suitable for the growth of very thin layers of III–V compound semiconductors, such as →gallium nitride (GaN) or →gallium arsenide (GaAs). The deposition process takes place in a reactor chamber into which vaporized chemicals are introduced together with other gases. The chemicals break up and chemically react with the atoms of the heated semiconductor wafer, producing the epitaxial growth. In other words, a very thin layer of atoms, reproducing the morphology and crystallographic orientation of the underlying wafer, diffuse onto the surface of the semiconductor substrate. The MOCVD offers a good control over the compound composition as well as the thickness of the deposited layer. Properties of the film can be modified at an almost atomic scale, depositing the desired atoms on the substrate, layer by layer, until the exact thickness is achieved. metal-organic chemical vapor phase epitaxy

(MOVPE) See →metal-organic chemical vapor deposition.

metal-oxide varistor

(MOV) Also known as movistor. An electronic component that is used in power circuits to protect sensitive equipment from various overvoltage conditions, such as lightning strikes or other power-line disturbances.

metal–semiconductor contact

There are two types of metal–semiconductor contacts: 1. nonrectifying, low-resistance →ohmic contacts, which are formed when a metal is in contact with the heavily doped silicon semiconductor; and 2. rectifying, high-resistance →Schottky diodes, in which a high barrier is formed when a metal is in contact with the lightly doped silicon semiconductor.

metal–semiconductor junction

Also known as M–S junction. A junction created between a metal and an n-type semiconductor. There are two kinds of metal–semiconductor junctions: 1. the nonrectifying metal–semiconductor junction that is also known as

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 metamorphic multijunction photovoltaic cell

→ohmic contact; and 2. the rectifying metal–semiconductor junction that is also known as →Schottky diode. metamorphic multijunction photovoltaic cell

See →metamorphic multijunction solar cell.

metamorphic multijunction solar cell

Also known as metamorphic multijunction photovoltaic cell. An ultralight, highly efficient, and flexible photovoltaic cell that consists of a concentrator and two or more superimposed subcells. The subcells are deliberately made of various semiconductor materials, having different tandem →p–n junctions, different semiconducting →band gaps and hence absorbing specific parts of the solar electromagnetic spectrum. For instance, in a lattice-matched, metamorphic triple-junction solar cell (GaInP/GaInAs/Ge), the top cell gallium indium phosphide (GaInP) with a high band gap captures high-energy photons, absorbing blue light. The middle cell gallium indium arsenide (GaInAs) with a somewhat lower band gap than the top cell harvests the lower-energy, middle-wavelength photons (green light) that were not captured by the top layer. Finally, the bottom germanium (Ge) cell absorbs long wavelength photons or infrared light that passed through and were not absorbed by the top layers. With this stacking technique, the key portions of the solar spectrum can be harvested, increasing solar cell efficiency to over 40%.

metamorphic solar cell

See →metamorphic multijunction solar cell.

Meteorological Service of Canada

(MSC) Also known as Service météorologique du Canada (SMC). A Canada-wide observation network that gathers and provides meteorological and environmental data and warnings to public around the clock, seven days a week.

meteorological variable

Also known as a climate parameter. A value that constantly changes, such as temperature, pressure, and humidity, and is of crucial importance for meteorological measurements in →solar forecasting.

meteorology

The study of the weather and atmosphere.

metered flow

Metered flow of fluid.

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methane

(CH4) Is a colorless, odorless, inflammable gas, which is a main component of natural gas. It is the second largest pollutant released in the Earth’s atmosphere after carbon dioxide. It is a dangerous competitor though, because although the CO2 volume in the atmosphere is much larger than the volume of methane, methane is 25 times more powerful than carbon dioxide (CO2) at absorbing longwave infrared radiation – atmospheric heat. Methane is produced by the following natural and man-made processes and activities: decomposition of plant and animal matter; decaying waste in landfills; rice cultivation; livestock waste; oil, gas, and coal production; transportation, and emissions from homes. Even though methane is hard to capture, different new technologies are being developed to capture methane before it is released into the atmosphere. The captured methane is then recycled and reused as a fuel for generating electricity and/or heat. Another way to control methane emissions is the development of better filtration equipment.

methanol

(CH3OH) Also known as wood alcohol. It is a light, colorless, and flammable liquid with a very high energy density. Since methanol can be generated from solar energy, it is considered a sustainable →solar fuel. George A. Olah considers methanol as the number one energy storage medium of the future. See →methanol economy. When there is a surplus power in a PV system during the day, it is fed/sold back to the grid. During the hours of low consumption (off-peak time), the utility can convert this excess power to liquid methanol and store it in large methanol tanks. During periods of high electricity demand (peak hours), the process is reversed and the liquid methanol is converted back to electricity.

methanol economy

According to the methanol advocate, Nobel Prize winner George A. Olah, methanol should play a bigger role as a clean energy resource and storage or transportation medium in the future sustainable economy. Methanol is stable and does not degrade or lose its strength over time. It is a high-octane fuel that can be safely stored in large methanol storage tanks. Methanol can be obtained from sustainable resources such as solar and wind energy, biomass (algae or other types of vegetation), and by converting

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 methanol storage tank

carbon dioxide from industrial exhausts into liquid methanol. Methanol operation practices are also sustainable because emissions from methanol conversion processes, for example, from electricity to methanol and from methanol to electricity, are low. Therefore, the proposal to use methanol as an alternative to diminishing fossil fuels for efficient energy storage on a large scale and for transportation deserves further consideration. methanol storage tank

A tank in which liquid methanol is stored for electricity production upon need. As methanol is extremely flammable, the storage tank must be fabricated according to the recognized safety standards.

methylbenzene

See →toluene.

metrology

The scientific study and practice of measurement.

metrology for lithography

Measuring of structures on the wafer, such as the width of a printed resist structure, pattern height, pattern sidewall angle, or the overlay between two printed patterns.

METSTAT

A program that uses meteorological data and weather variables to estimate hourly values of direct normal, diffuse horizontal, and global horizontal solar radiation. METSTAT employs statistical algorithms to generate a nominal value of solar irradiance.

MEV

Abbreviation for →membrane expansion vessel.

micro-ablation

A type of →micro-processing by means of laser-based vaporization of materials. Ultrashort laser pulses penetrate into the irradiated material in a highly controlled manner, generating a very thin molten layer that soon starts to vaporize, removing material. Micro-ablation offers accuracy on a micron scale.

micro-grid

Decentralized small-scale energy system including power generation and storage. Micro-grids can operate either as part of the →macro-grid or as an independent off-grid power system.

micro-hydro

See →micro-hydrosystem.

micro-hydropower system

See →micro-hydrosystem.

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micro-processing

Processing of silicon and other semiconductor materials in solar cell production by lasers and other micro-structuring devices. The tendency in photovoltaic industry to design and build miniature structures requires processing on a very small scale from 1 to 100 μm. Micro-ablation is a type of micro-processing by means of laser-based vaporization of materials. Ultra-short laser pulses penetrate into the irradiated material in a highly controlled manner, generating a very thin molten layer that soon starts to vaporize, removing material.

micro-solar cell

A small solar cell with the size of as little as 600 μm on each side. The micro-solar cell consists of multiple semiconductor layers that are stacked on top of each other. Each layer is made of a different semiconductor material, allowing the thin-film solar cell to capture different portions of the electromagnetic spectrum and hence achieve a high energy conversion efficiency between 25% and 35%. Concentrating lenses, such as →Fresnel lenses, can be added to the system, to focus sunlight onto microscale photovoltaic cells, increasing the amount of generated energy. The miniature size allows micro-solar cells to dissipate heat and remain cool without the use of any energy-wasting cooling tools.

microchipping

See →micro-chipping.

micro-chipping

Defects that occur during the wafer dicing process within the range between 1 and 5 μm. As the edge chipping defects on the front and back sides of the wafers can lead to PV cell failures, further polishing and processing to turn rough textures into usable wafers is required. Compared to the mechanical scribing and dicing with a diamond stylus and saw that can cause chipping of the layers, the focused laser beam is rapidly becoming the preferred choice of many manufacturers because it can control the cutting depth with great accuracy – within ±5 μm. A detection of micro-chipping defects at an early stage of the manufacturing process can save a company a lot of time and money.

microclimate

The distinctive climate of a small area, such as the interior of a building or a backyard. Surrounding buildings, hills, or trees can create a district microclimate in your backyard that is different from the climate of the neighboring sites.

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 microclimate analysis

Therefore, a careful microclimate analysis can help in assessing the feasibility of installing a photovoltaic/thermal panel system or building a sustainable house on a particular site. microclimate analysis

An analysis of various factors that influence a specific site climate, such as solar radiation, temperature, humidity, and wind, over a period of a year. Homeowners should consider a detailed microclimate analysis when designing a sustainable building or a solar system.

micro-crack detection

The process of an early detection of micro-crack defects in solar cells is an important part of solar cell inspection.

microcracks

See →micro-cracks.

micro-cracks

Microscopic cracks in solar cells that are hardly visible to human eyes. Micro-cracks typically occur during the manufacturing, shipping, or installation of solar modules. As they are directly exposed to harsh weather conditions, they can grow over time and lead to energy conversion losses or even to failures. Even if only one cell has micro-cracks, it can affect the power output of the entire PV module, as the cells are connected in series. Micro-cracks are identified as one of the most common issues with PV modules. Therefore, special caution should be exercised during the manufacturing, shipping, or installation of solar panels.

microcrystalline

(Material) composed of microscopic crystals.

microcrystalline absorber

In a thin-film solar cell, a semiconductor absorber layer composed of microscopic silicon crystals.

microcrystalline silicon

(μc-Si) A type of thin-film semiconductor material with small grains of crystalline silicon on a micron scale. See also →nanocrystalline silicon.

microcrystalline solar cell

A solar cell made of →microcrystalline silicon.

microelectromechanical system

(MEMS) A miniaturized mechanical and electromechanical system consisting of miniature mechanical parts and electronic circuits. MEMS devices, which have physical dimensions in the range of 20 μm to a few millimeters, include miniaturized structures, sensors, actuators, and microelectronics. New polymer-based thin-film PV cell

micro-electro-mechanical system 

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technologies that combine micro- and nano-manufacturing methods rely to a great extent on MEMS components and architecture. micro-electromechanical system

See →microelectromechanical system.

microelectronic system

Miniaturized electronic system.

microelectronics

A branch of electronics that deals with the study of microchips and microcircuits. Photovoltaic technology and microelectronics share the same basic technology, as photovoltaic cells are made of the same types of semiconductor materials, for example, silicon, as microelectronic devices. Therefore, a close, continuous cooperation between solar and microelectronics industries sharing intellectual property and new manufacturing technologies is crucial for a rapid development of both sectors.

micro-Fresnel lenses

See →microlenses.

Microgeneration Certification Scheme

(MCS) Is a nationally recognized certification program for solar and other renewable energy equipment manufacturers and installers that sets standards for good quality solar products and installations. The program is supported by the →Department of Energy and Climate Change (DECC) and it helps users find MCS certified products or an MCS certified installation company.

microgrid

See →micro-grid.

microgroove

A small, narrow groove scribed into the surface of the substrate, which is filled with metal for contacts.

micro-hydrosystem

A small-scale hydroelectric power system that generates up to 100 kW of electricity by harnessing the kinetic energy of moving water. There are two major types of harnessing the natural flow of water for homeowners who have a stream flowing through their property. A turbine with an underwater generator can be directly submerged into the stream (on the bed of the creek, river, or canal) to produce electricity. A portion of the stream’s water is diverted into a pipeline transporting the flowing water downhill to a turbine.

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 microinverter

The power of the moving water spins the blades of the turbine, creating the rotational energy that is in turn converted into electrical power by a generator. microinverter

See →micro-inverter.

micro-inverter

Converts the generated solar power from direct current (DC) into grid-compatible alternating current (AC). In contrast to a central or string inverter that converts DC solar power generated by the entire solar array into AC power at one central point, micro-inverters are attached to the back of each individual PV panel and convert DC output from each module into AC power. Compared to central inverters, the major advantage of micro-inverters is that in case of a single panel failure, for example, due to shading, snow, or cracked cells, the operation of the entire solar system will not be negatively affected. The failed module is isolated from the rest of the system that continues its operation without interruption. Another important advantage of micro-inverters is that they utilize →Maximum Power Point Tracking (MPPT) power optimization for each individual panel. When the MPPT algorithm searches for the optimum power for each PV module, it increases the energy output of the entire system. Micro-inverters are safer than conventional string inverters because they do not require high-voltage DC power lines. The major disadvantage of micro-inverters is a significantly higher upfront investment as they cost more per watt than central inverters.

microlenses

Also known as micro-Fresnel lenses, focus the incident light by refraction directly on the →photovoltaic cell.

microlithography

Lithography that involves the patterning and printing of very small structures on the order of micrometers in semiconductor manufacturing.

microloading

The etch phenomenon by which concentrated features, equally wide trenches located nearby, etch slower than less concentrated features.

micromechanical

Referring to →micromechanics of materials.

micromechanical cleavage 

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micromechanical cleavage

(MC) See →micromechanical exfoliation.

micromechanical exfoliation

Also known as micromechanical cleavage. A method for graphene production in which graphene is cleaved off an existing graphite crystal, yielding high quality layers in the order of millimeters. Due to the very high quality and purity of generated graphene, the exfoliation method is ideal for laboratory research. However, it is not suitable for commercial production because of the poor controllability and the size of the obtained flakes.

micromechanics

See →micromechanics of materials.

micromechanics of materials

Also known as micromechanics. A systematic study of mechanical, electrical, and thermodynamical behaviors of materials at a micrometer scale (µm). The analysis of crystal lattice structures, crystallographic orientations, and dynamics of composite materials gives solar scientists an opportunity to control and tune microscale structures in order to improve photoelectric properties of semiconductor materials and hence the power output of thin-film solar cells.

micrometer

(µm) Also known as micron. One-millionth of a meter, 0.000001 m.

micromorph

In the solar context, the neologism micromorph first appeared in 1995 and was constructed by merging the words MICROcrystalline and aMORPHous. See also →micromorph solar cell.

micromorph cell

See →micromorph solar cell.

micromorph solar cell

A thin-film tandem solar cell consisting of two different solar-absorbing layers: amorphous silicon (a-Si:H) and microcrystalline silicon (µc-Si). The multijunction structure, in which the amorphous silicon layer is stacked on top of the microcrystalline silicon layer, is able to absorb a wider range of the electromagnetic spectrum than a single-junction solar cell. The solar spectrum is shared between the thinner top amorphous silicon film (0.2–0.3 µm), which is responsible for absorbing the visible blue light, and the thicker bottom microcrystalline silicon film (1.5–2 µm), which captures the red and near-infrared light.

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 micron

The energy band gaps of µc-Si (1.1 eV) and a-Si:H (1.7 eV) are ideally matched, allowing a high photovoltaic conversion efficiency of over 30%. As the micromorph solar cell is a thin-film cell, whose combined µc-Si and a-Si:H absorber layers are only a few microns and even less thick, its deployment results in significant material savings. Compared to the conventional, expensive silicon solar production process, the micromorph tandem cells can be manufactured at very low costs. micron

See →micrometer.

micro-optical device

See →micro-optical system.

micro-optical system

Also known as micro-optics. An optical system that is in the range between a few micrometers and a millimeter. A micro-optical system allows the control of →photons of light with micron and submicron scale structures and components.

micro-optics

See →micro-optical system.

microporous separator

See →thin-film membrane.

micro-precision sieve

A precision mesh or screen for a high precision →screen printing process used in solar cell manufacturing.

microstructure

The surface structure of materials, such as thin polymer films, on a microscopic scale. The role of the microstructure in the photovoltaic performance of a solar cell is vital, as the optical properties of solar-absorbing semiconductor materials depend on the microstructure of the thin films. The modification and tuning of microstructures to make them antireflective or more responsive to certain desired wavelengths of the electromagnetic spectrum can considerably increase the energy conversion efficiency of a solar cell.

microstructure material

A careful selection of solar-absorbing materials, mostly composites with a complex microstructure (e.g., dielectric-air composite or metal-dielectric composite), can significantly enhance the power output of a solar cell.

microwatt

(µW) Unit of power, one-millionth of a watt, 0.000001 W.

mid-clamp

See →middle clamp.

middle clamp 

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middle clamp

Also known as a mid-clamp. A piece of solar panel mounting hardware that holds framed photovoltaic (PV) modules to mounting rails. As they are installed between the PV modules, middle clamps can simultaneously secure two modules to the rail system. Mid-clamps are usually made of anodized aluminum, which is resistant to corrosion. Two main types of middle clamps are adjustable and nonadjustable middle clamps.

Mie scattering

The scattering of light by particles in the atmosphere that are about the same size or larger than the wavelength of the light. Mie scattering occurs when incoming solar radiation encounters larger particles in the atmosphere, such as cloud droplets or dust, on its way to the Earth’s surface. The scattering of radiation in all directions produces whitecolored light, accounting for the white color of the clouds.

milliamp

(mA) One-thousandth of an ampere, 0.001 A.

milliwatt

(mW) Unit of power, one-thousandth of a watt, 0.001 W.

Minergie

Building standard for energy-efficient buildings in Switzerland.

mini-solar power station Usually a small portable power station consisting of several →solar panels, a →battery bank, a →charge controller, and an →inverter. A solar-powered ministation is an environmentally friendly replacement for gasoline emergency generators. In addition to providing backup power during outages, the mini solar power generator can also be used for recreational purposes in RVs, boats, trailers, summer houses, cottages, and cabins. miniaturization

Tendency to design and build structures on a very small scale, from 1 to 100 nm. Some solar components, materials, and structures are constructed at a scale below 100 nm, such as →carbon nanotubes (fullerene, C60), →quantum dots, →nanowires, →nanopillar, →nanocrystals, nanofibers, nonoporous filters, nanoparticulate metal oxides, dispersion nanoparticles, nanopin film, polymer nanocomposites.

minimal output

See →minimal output current.

minimal output current

The minimal output AC power that a →solar inverter can deliver.

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 minimally attached mounting

minimally attached mounting

See →hybrid mounting.

minimum AC power

See →minimal output current.

minimum operating DC voltage

The minimum DC input voltage value threshold that must be met for the inverter to operate.

minority carrier

See →minority charge carrier.

minority carrier injection

Injection of minority carriers into the semiconductor material on the two sides of a →p–n junction, when the junction is forward biased.

minority carrier lifetime

The average time a →minority carrier prevails in the opposite-doped layer of the semiconductor before →recombination. For instance, the lifetime measures how long an electron stays around in a p-doped layer before occupying a vacant hole, or how long a hole exists in an n-doped layer before being occupied by an electron. The minority carrier lifetime depends on material quality, doping concentration, and illumination level.

minority charge carrier

Subordinate charge carrier that is responsible for the lesser part of current flow in a semiconductor than a major carrier. In the n-layer of the semiconductor, which is doped with →phosphorus, the holes are in the minority. As the number of holes is smaller than the number of electrons in this layer, the holes are the minority charge carriers and the electrons are the majority carriers. In the p-layer, which is doped with →boron, the electron–hole ratio is reversed. As the number of electrons is smaller than the number of holes in this layer, the electrons are the minority charge carriers and the holes are the majority carriers.

minutes of sunshine

Unit of →bright sunshine duration. Many statistical models use minutes of sunshine to calculate their hourly or daily solar irradiance estimates. The →Campbell–Stokes sunshine recorder or a meteorological station with an electronic sensor record the actual amount of solar radiation reaching the Earth on a given day. By adding all burnt traces on a Campbell–Stokes card at the end of the day, one can calculate total minutes of sunshine for a given location.

mirror coating 

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mirror coating

See →mirror film.

mirror film

Thin film consisting of a silver layer and multiple protective plastic layers.

mixed growth

Also known as a Stranski–Krastanov growth mode is a combination of Frank van der Merwe and Volmer–Weber growth modes. The process starts with a strained layerby-layer growth to match the substrate structure and to reduce the interface energy. After a few two-dimensional layers, the strain is relaxed, changing into the relaxed, three-dimensional island growth mode. The transition from layered to island growth takes place at a critical film thickness which is determined by the physical and chemical properties of the deposited layer and substrate. See also →layer-by-layer growth and →island growth.

mixing valve

The thermostatic mixing valve (TMV) for →solar thermal systems. See →thermostatic mixing valve.

MLD

Abbreviation for maximum light detection. See →Maximum Light Detection tracking system.

MLD technology

Maximum Light Detection technology. See →Maximum Light Detection tracking system.

MLD tracking

Maximum Light Detection tracking. See →Maximum Light Detection tracking system.

MLD tracking system

See →Maximum Light Detection tracking system.

MLD tracking technology

Maximum Light Detection tracking technology. See →Maximum Light Detection tracking system.

MNP

Abbreviation for →magnetic nanoparticles.

mobile photovoltaic generator

See →portable solar generator.

mobile photovoltaic system

See →mobile solar system.

mobile PV generator

See →portable solar generator.

mobile PV system

See →mobile solar system.

mobile solar light

See →mobile solar light tower.

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 mobile solar light tower

mobile solar light tower

Also known as a portable solar light tower. A transportable solar-powered lighting system that can be moved from one place to another. It consists of a trailer onto which →solar modules are mounted, a →battery bank, a →charge controller, and a light tower either with two or four LED light fixtures. The tower’s expendable and retractable pole is made of anodized aluminum, which is resistant to corrosion. The mobile solar light tower is designed for various outdoor lighting applications, such as nighttime constructions and utility repairs, security or emergency situations, sport and political events, and disaster recovery. It is environmentally friendly as it does not produce carbon emissions, fumes, light pollution, and noise.

mobile solar system

Also known as a mobile photovoltaic (PV) system. A transportable solar system that can be moved from one place to another. Mobile PV systems are designed to operate independent of utility connections. They are often utilized on boats, recreational vehicles, for camping, and other various outdoor activities. They are also used as mobile power stations on trailers for special field projects, powering remote construction job equipment, land surveyor equipment, remote radar equipment, solar testing equipment, portable kitchens, and many other electrical appliances. Mobile PV systems vary from manufacturer to manufacturer, but they usually comprise the following components in different configurations: a set of →photovoltaic modules, a →solar generator, a →solar inverter, a →charge controller, a →battery bank, and →MC4 connectors. Depending on the power demand, the system can be customized, including the appropriate size solar generator and a set of PV modules, ranging from as low as two PV panels to as many as 24 panels and more.

MOCVD

Abbreviation for →metal-organic chemical vapor deposition.

moderate climate zone

See →temperate climate zone.

modified sine wave

Waveform of voltage output produced by a power inverter. It has a shape of a square with one or two additional square steps.

modified sine wave inverter 

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modified sine wave inverter

Also known as quasi-sine wave inverter. This is a power inverter that produces a square waveform with one or two extra square steps. Since the voltage waveform is in the shape of a square rather than a sine, it should be actually called a modified “square” inverter. Nevertheless, it is a better solution than a →square wave inverter, as it can be used for most appliances, but it has a lower performance and efficiency than →pure sine wave inverters. Although the modified sine inverter is compatible with most household electrical devices, it is not completely problem free. Sensitive electronics with a silicon-controlled rectifier (SCR), such as audio equipment, laser printers, and photocopiers, but also fluorescent lights, ceiling fans, microwave ovens, and digital clocks perform poorly with modified sine inverters. The modified sine inverter will probably not damage the mentioned devices, but they might pick up a buzz, make annoying humming noises, show other strange behavior (e.g., clocks might run faster), or not work at all. Modified AC sine wave inverters are less expensive than pure sine wave inverters; however, they use 20–30% more energy than pure sine wave inverters. The reduced efficiency goes back to waveform problems causing enhanced radio interference and increased heating of motors, thereby shortening the motor’s life.

modular

Referring to the →modular structure of photovoltaic components.

modular structure

Solar technology is essentially modular. A solar array consists of standardized components – solar modules, and solar modules themselves consist of smaller uniform building blocks – solar cells. The modular structure gives the manufacturer the flexibility to easily change the size of a solar panel by combining solar cells according to the desired design. The users, individual house owners and companies, can also profit from the flexibility of a modular structure because it allows them to combine solar panels into a desired PV system according to their electricity needs and budget. The major advantage of a modular system is that it can be effortlessly expanded at any time.

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 modularity

modularity

The ability of a solar system consisting of numerous independent PV modules to combine their standardized units in a desired way. When the energy demand in a household changes, for example, two additional persons move into the house, the homeowner is able to add new solar modules to the existing system without any difficulty and so meet the new power requirements. Modularity gives the opportunity to users to always recombine their PV components into a desired system according to their actual needs.

module

A photovoltaic module that converts solar radiation into electrical current. See →photovoltaic module.

module cabling

Includes all connectors and tools required for interconnecting two or more photovoltaic modules, for example, →MC4 connector, →Y-type MC4 branch connector, →MC4 disconnect tool, →DC disconnect, and →junction box.

module degradation rate See →photovoltaic module degradation rate. module derate factor

A factor that reduces the amount of power a PV system can generate. The typical derate factors responsible for diminished PV power output of solar modules are: →soiling (dust and dirt on PV panels), DC and AC wiring inefficiencies, diodes and connections, →shading, inverter and transformer losses, mismatch, and age (degradation loss factor).

module efficiency

The percentage of incident solar radiation (sunlight) that is converted into electrical power by a solar module.

module frame

See →solar module frame.

module junction box

Also known as solar junction box, junction box, and J-Box. A protective enclosure on the back of a photovoltaic (PV) module that houses electrical connections and diodes. It is an input/output interface connecting the module to other PV modules. It includes PV module protection devices such as bypass diodes and/or blocking diodes. A bypass diode eliminates hot spots in case of partial module shading or broken cells. It prevents damage from overvoltage due to high resistance conditions (hot spots) by diverting the current past the shaded or broken module.

module mount 

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A blocking diode prevents the reverse current from flowing backward through a module. It functions like a one-way valve, allowing electricity to flow only one way. They prevent undesired discharging by reverse flow of electrical current from the battery bank to the PV array, for example, in the dark or under cloudy conditions, when no current is generated by the PV modules. Good junction boxes are waterproof and able to regulate heat. module mount

Mounting plate or similar structure for mounting individual solar modules on a pole, to a roof, or other structures.

module nameplate

See →PV module nameplate.

module performance

See →solar module performance.

module temperature

See →solar module temperature.

molecular beam epitaxy

(MBE) A type of →physical vapor deposition (PVD) process for manufacturing of thin-film semiconductor devices. The MBE process begins with the loading of a substrate into an ultrahigh vacuum (UHV) growth chamber, where it is heated at high temperatures of around 500 °C (932 °F) to ensure an absolutely clean surface of the substrate free of all contaminants. Then, different beams of atoms or molecules are fired at the heated substrate from “guns” called effusion cells. Finally, the molecules, a small amount of source material emitted by the molecular beams, collect and condense on the substrate, forming one extremely thin layer at a time. The growth of crystalline thin films, layer by layer, by applying an MBE method allows a high degree of control with regard to thickness, composition, transition sharpness, and morphology. This is why the method is celebrated as the most precise and flexible technique for growing epitaxial layers on the surface of a substrate. The major disadvantage of the MBE process is a low deposition (growth) rate: approximately one monolayer (lattice plane) per second, a few microns per hour.

MO-LIG

Abbreviation for →metal oxide-laser-induced graphene.

molten bath

A molten bath of silicon that is produced by melting silicon rocks at high temperatures (around 1,371 °C [2,500 °F]) in a →crucible into a silicon slurry. In the →Czochralski method,

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 molten particles

a single silicon crystal is pulled from the molten bath, which is also known as melt. In the string ribbon technology, two wires are drawn through a silicon melt, forming a polycrystalline silicon ribbon between the wires, as the film of molten silicon solidifies in the process. molten particles

Particles that are created when powder material is injected into hot plasma and melted at very high temperatures in a vacuum environment. As the microstructure of a film is directly influenced by deposition parameters, the precise control of molten particle temperature, size, and velocity is vital for the optimization of coating.

molten salt

Molten salt has the ability to store energy and is therefore used for heat storage in →large-scale solar thermal systems.

molten salt mixture

Usually a combination of sodium and potassium nitrate.

molten salt storage

See →molten salt storage system.

molten salt storage system

A large-scale storage system that uses molten salt as a medium for storing excess thermal energy for later use. Nontoxic, environmentally friendly molten salt mixtures, such as sodium nitrate, potassium nitrate, and calcium nitrate, are typically applied in the process. Molten salt is suitable for the storage process for multiple reasons. Compared to some other storage mediums, it is a low-cost storage solution. It can be pumped and stored in tanks just like water. Molten salt is capable of storing thermal energy that is collected in CSP plants during the day for up to a week, if properly stored in an insulated tank at atmospheric pressure at 566°C (1,050°F). Later, in the evening, at night, or on cloudy days, when the sun is not shining and electricity is needed, the stored heat can be taken from the tanks of molten salt and used for vapor production and consequently for power generation.

molten salt storage technology

An economical and environmentally sound technology that utilizes molten salt as a medium for storing thermal energy for later use in →large-scale solar thermal systems. The heated fluid from solar power towers or parabolic troughs is transferred to a molten salt storage tank where it is kept under special conditions until electricity is needed,

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molten silicon 

at night or on overcast days. A solar thermal power plant, which employs the molted salt storage technology, is capable of supplying their customers with electricity 24/7. molten silicon

See →melt.

momentum

The quantity of motion that an object has. It is often expressed in equation p = mv, where p is the product of the mass (m) and velocity (v) of an object.

monitoring

See →solar system monitoring.

monitoring platform

A system that enables the homeowner or →solar plant operator to monitor how much energy a PV system generates and consumes. It usually also provides a fault detection and troubleshooting feature. When the monitoring system detects a problem, it immediately sends a warning message. Other levels of monitoring, such as weather data, wind speed, battery bank status, or temperature of solar panels, can be included in a monitoring platform. Today’s monitoring systems are mostly web-based, allowing the user to check his PV system remotely from his computer, smartphone, or tablet from any location. Remote data viewing is enhanced by PV visualization tools, including interactive graphs, charts, and tables. For instance, the display/simulation of all PV system modules on a map can visualize and pinpoint, with the help of a color code, individual PV modules with diminished power output due to shading, broken cells, or some other issue.

monitoring portal

See →monitoring platform.

monitoring system

See →monitoring platform.

monocrystal structure

A semiconductor material structure that is created from a single continuous crystal structure.

monocrystalline

Referring to the material consisting of a single crystal.

monocrystalline Czochralski silicon

(Cz-Si) Monocrystalline silicon produced →Czochralski crystal growth process.

monocrystalline hybrid solar module

Also known as a monocrystalline hybrid solar panel. A solar module that combines monocrystalline photovoltaic cells with thin-film layers to maximize solar panel power output.

by

the

462 

 monocrystalline hybrid solar panel

monocrystalline hybrid solar panel

See →monocrystalline hybrid solar module.

monocrystalline ingot

See →monocrystalline silicon ingot.

monocrystalline silicon

Also known as single-crystal silicon or mono-Si. Key semiconductor material used in solar cell production. It is made of pure single crystal silicon using the →Czochralski process. This excellent semiconductor material is made from the highest quality silicon and it can be identified by its dark black color. Monocrystalline silicon has a high electrical conductivity that is only superseded by a few materials, such as gallium arsenide; however, the production costs of gallium arsenide significantly exceed those of silicon. Due to its abundance and affordable prices, silicon remains the material of choice for solar cells. Solar modules made of monocrystalline silicon material are space-efficient because they yield a high power output, while occupying less space than many other PV panels made of different semiconductor materials with lower electrical conductivity, such as →amorphous silicon or →polycrystalline silicon.

monocrystalline silicon block

See →monocrystalline silicon ingot.

monocrystalline silicon cell

See →monocrystalline silicon solar cell.

monocrystalline silicon ingot

In silicon wafer manufacturing, single crystal silicon ingot that is produced using the →Czochralski crystal growth process. The cooled ingot is trimmed into a quadratic shape and sliced with a diamond saw into →solar wafers that are then made into solar cells.

monocrystalline silicon material

Semiconductor material consisting of pure single crystal silicon.

monocrystalline silicon module

See →monocrystalline silicon solar module.

monocrystalline silicon panel

See →monocrystalline silicon solar module.

monocrystalline silicon photovoltaic module

See →monocrystalline silicon solar module.

monocrystalline silicon photovoltaic panel 

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monocrystalline silicon photovoltaic panel

See →monocrystalline silicon solar module.

monocrystalline silicon PV module

See →monocrystalline silicon solar module.

monocrystalline silicon PV panel

See →monocrystalline silicon solar module.

monocrystalline silicon solar cell

Also known as single-crystal solar cell. A type of silicon solar cell made from a wafer that consists of a single silicon crystal (see the figure on page 464). A large single crystal silicon cylinder called boule is grown in an oven and pulled out of a molten mass of silicon and boron by the →Czochralski process. The cooled boule is trimmed into a quadratic shape and sliced with a diamond saw into wafers that are then processed into monocrystalline silicon solar cells. Due to this complex and costly manufacturing process, the monocrystalline solar cell is one of the most expensive solar cell types to purchase. On the other side, it achieves purity levels of as high as 99.999%. This high-purity semiconductor silicon material translates into the most efficient solar conversion technology available on the market. The best efficiency levels to date are between 20% and 22%, whereas efficiencies of 25% have been achieved in the lab. As they are made of pure single crystal silicon, monocrystalline solar cells have a uniform look, a consistent black or dark blue color. See also polycrystalline silicon solar cell.

monocrystalline silicon solar module

A module that consists of monocrystalline solar cells that are made from a single silicon crystal using the Czochralski method. According to Czochralski process, a silicon seed crystal is dipped into the molten silicon with added dopant boron called melt. As the seed crystal is rotated and slowly pulled upward in an oven, the molten silicon atoms attach to the seed crystal, creating a compact cylindrical crystal structure around the seed known as an ingot. The cooled ingot is trimmed into a quadratic shape and sliced with a diamond saw into wafers that are then made into monocrystalline silicon solar cells. Monocrystalline silicon technology is the oldest, most efficient, reliable, and durable traditional solar technology.

Metal back contacts

N-doped silicon P-n junction P-doped silicon

Anti-reflective coating

Glass

Monocrystalline Silicon Solar Cell

Metal front contacts

464   monocrystalline silicon solar module

monocrystalline silicon solar panel 

 465

It was invented in 1955 and has reached efficiency levels between 20% and 22%, whereas efficiencies of 28% have been achieved in the lab. Monocrystalline panels are typically around 2–3% more efficient than their major competitor polycrystalline panels. As they generate more energy per square meter than other solar technologies, monocrystalline modules require the least amount of space and are an attractive option for urban areas with limited roof or backyard space. Monocrystalline panels are durable and have a long life span. Even though manufacturers typically offer a warranty of 25 years for monocrystalline panels, they can last longer, as their degradation rate is between 0.25% and 0.50%. Monocrystalline silicon modules handle the heat slightly better than polycrystalline modules and their materials are not hazardous to the environment. As they are made of pure single crystal silicon, monocrystalline solar modules have a uniform look, a consistent black or dark blue color. The major disadvantages of monocrystalline silicon modules are high initial costs and fragility. Due to their complex and costly manufacturing process, the monocrystalline solar panels are the most expensive conventional modules on the market. Although they are protected by a safety glass, they can be broken by falling objects. monocrystalline silicon solar panel

See →monocrystalline silicon solar module.

monocrystalline solar cell

See →monocrystalline silicon solar cell.

monocrystalline solar module

See →monocrystalline silicon solar module.

monocrystalline solar panel

See →monocrystalline silicon solar module.

monocrystalline solar wafer

A wafer made of pure single crystal silicon that is manufactured by the application of the →Czochralski process.

monocrystalline wafer

See →monocrystalline solar wafer.

monolayer

A layer one molecule or atom thick.

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 monolayer graphene

monolayer graphene

A very thin, one molecule thick layer of semiconductor graphene material, which is deposited by chemical vapor deposition (CVD) onto a silicon substrate.

monolithic

Referring to solar modules that are produced as a single structure.

monolithic module assembly

An assembly process in which the cells in a module are encapsulated and electrically connected in a single step.

mono-pitched roof

A roof having a single slope.

mono-Si

Abbreviation for →monocrystalline silicon.

mordant

See →etchant.

motion sensor control

A device that provides automatic control of lighting, heating, and ventilation by detecting movement of tenants. When a person is detected by sensors in a room, lights are automatically turned on; when the tenant leaves the room, the detector automatically switches off the lighting. In addition to reducing energy consumption indoors, motion sensor control is also employed in outdoor security lighting.

motorhome solar module

See →solar module for motorhome.

mount

See →mounting system.

mounting area

See →mounting surface.

mounting brackets

Brackets that support the rail in a →roof-mounting system. Rails are secured to mounting brackets and brackets on the other end are either secured to →standoffs or they are directly screwed into a conduit penetration flashing or into the roof batten with the help of rubber washers for a weather proof seal. Mounting brackets are made of anodized aluminum, which is resistant to corrosion. Two types of brackets that are commonly used in solar installations are Z and U brackets, named after their shape.

mounting clamp

A clamp for mounting framed solar panels. There are two main types of mounting clamps: middle clamps and end clamps. Middle clamps are installed between the PV modules, securing two modules to the rail system at the same time. End clamps hold the edges of the first and last

mounting control 

 467

PV modules of a string to the rail system. Mounting clamps are made of anodized aluminum, which is resistant to corrosion. mounting control

Quality inspection that ensures that the mounting of solar panels or concentrating reflectors in a photovoltaic and solar-thermal system is carried out according to specifications and in compliance with the relevant installation standards.

mounting device

See →mounting system.

mounting frame

See →mounting system.

mounting hardware

Hardware for mounting solar panels. It includes →aluminum rails, →mounting clamps, →mounting brackets, →standoffs, bolts, washers, and nuts.

mounting material

High-quality aluminum and stainless steel are typically used for the manufacture of →mounting systems.

mounting rack

See →mounting system.

mounting structure

See →mounting system.

mounting structure for building facades

A special aluminum or stainless steel mounting structure to which solar panels are mounted, creating a solar wall that is placed in front of the existing façade. The solar wall structure converts solar radiation into electricity and heat, provides protection against weather (heavy rain, high winds, and hail), and fulfills a decorative function. See also →solar wall and →photovoltaic façade.

mounting surface

The surface for the mounting of →photovoltaic modules or →solar thermal collectors. Depending on the roof profile and terrain of the ground, the following types of mounting surfaces are differentiated: flat mounting surfaces, sloping mounting surfaces, and adjustable mounting surfaces.

mounting system

A support structure, a frame upon which →photovoltaic modules are mounted. Two major types of mounting systems are →ground-mounting system and →roof-mounting system. With regard to fastening, several systems are available: rail system, clamp system, and a combined rail and clamp system. See also →rack mount.

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 mounting triangle

mounting triangle

A support structure, typically an aluminum frame in the shape of a triangle, upon which →photovoltaic modules are mounted. Mounting triangles are mostly used on flat roofs and on solid ground.

MOV

Abbreviation for →metal-oxide varistor.

movistor

(MOV) See →metal-oxide varistor.

MOVPE

Abbreviation for metal-organic vapor phase epitaxy. See →metal-organic chemical vapour deposition.

MPP

Abbreviation for →Maximum Power Point.

MPP tracker

See →Maximum Power Point tracker.

MPP tracking

See →Maximum Power Point tracking.

MPP voltage

See →Maximum Power Point voltage.

MPPT

Abbreviation for →Maximum Power Point Tracking.

MPPT charge controller

Maximum Power Point Tracking charge controller protects the battery from overcharge and overdischarge.

MPPT solar charge controller

See →MPPT charge controller.

M–S junction

See →metal–semiconductor junction.

MSC

Abbreviation for →Meteorological Service of Canada.

multi-MPPT inverter

See →multistring inverter.

multicell battery

A battery with more than one cell, which are connected together internally in series, in which the stored chemical energy is converted into electrical energy, providing power for various household appliances.

multicrystalline

See →polycrystalline.

multicrystalline microstructure

See →polycrystalline microstructure.

multicrystalline photovoltaic cell

See →polycrystalline photovoltaic cell.

multicrystalline photovoltaic module

See →polycrystalline photovoltaic module.

multicrystalline photovoltaic panel

See →polycrystalline photovoltaic panel.

multicrystalline PV cell 

multicrystalline PV cell

See →polycrystalline PV cell.

multicrystalline PV module

See →polycrystalline PV module.

multicrystalline PV panel See →polycrystalline PV panel. multicrystalline semiconductor

See →polycrystalline semiconductor.

multicrystalline silicon

See →polycrystalline silicon.

multicrystalline silicon block

See →polycrystalline silicon block.

multicrystalline silicon cell

See →polycrystalline silicon cell.

multicrystalline silicon ingot

See →polycrystalline silicon ingot.

multicrystalline silicon module

See →polycrystalline silicon module.

multicrystalline silicon panel

See →polycrystalline silicon panel.

multicrystalline silicon solar cell

See →polycrystalline silicon solar cell.

multicrystalline silicon solar module

See →polycrystalline silicon solar module.

multicrystalline silicon solar panel

See →polycrystalline silicon solar panel.

multicrystalline silicon wafer

See →polycrystalline silicon wafer.

multicrystalline solar cell

See →polycrystalline solar cell.

multicrystalline solar module

See →polycrystalline solar module.

multicrystalline solar panel

See →polycrystalline solar panel.

multicrystalline solar wafer

See →polycrystalline solar wafer.

 469

470 

 multicrystalline structure

multicrystalline structure

See →polycrystalline structure.

multicrystalline thin-film See →polycrystalline thin film. multicrystalline thinfilm solar cell

See →polycrystalline thin-film solar cell.

multicrystalline thinfilm solar module

See →polycrystalline thin-film solar module.

multicrystalline thinfilm solar panel

See →polycrystalline thin-film solar panel.

multicrystalline thinfilm technology

See →polycrystalline thin-film technology.

multicrystalline wafer

See →polycrystalline wafer.

multifunction inverter

See →multimodal inverter.

multijunction cell

See →multijunction photovoltaic cell.

multijunction device

See →multijunction photovoltaic cell.

multijunction photovoltaic cell

See →multijunction photovoltaic cell.

multijunction photovoltaic cell

A PV cell that consists of two or more superimposed subcells that are made of different semiconductor materials and thus absorb different parts of solar spectrum (see the figure on page 471). Although the technology of stacked solar cells with different band gaps has reached the staggering conversion efficiency results of 45%, the manufacturing process is still somewhat too complex and expensive due to the matching and alignment challenges among different subcells.

multijunction PV cell

See →multijunction photovoltaic cell.

multijunction solar cell

See →multijunction photovoltaic cell.

multilayer antireflection coating

An antireflection coating (ARC) technique in which dielectric nanoparticles are coated as multilayers to reduce the reflection and improve light transmission.

multilayer coating

See →multilayer antireflection coating.

multilayer photovoltaic cell

See →multilayer solar cell.

multilayer PV cell 

 471

Air-reflection coating Top contact

InGaP 1.9 eV

Top cell junction 1 Tunnel junction

GaAs 1.4 eV

Middle cell junction 2 Tunnel junction

GalnNAs (Sb) 1.0 eV

Bottom cell junction 3

GaAs substrate

Bottom contact

Multijunction Photovoltaic Cell

multilayer PV cell

See →multilayer solar cell.

multilayer solar cell

A solar cell that consists of different thin-film semiconductor layers each of which is optimized to capture a specific range of the electromagnetic spectrum. By changing the particle size in organic as well as in inorganic semiconductors, solar scientists can tune band gaps in such a way that the energy band gaps of different layers allow harvesting of different wavelengths of solar spectrum. High level of controllability of nanostructures increases the photoresponse and carrier mobility of semiconductor materials, resulting in harvesting of a wider range of the solar spectrum in →thin-film solar cells. The ultimate goal of a synthesis of numerous nanostructured multispectral absorber layers in a multilayer solar cell is to capture the complete range of electromagnetic (solar) radiation.

472 

 multilayer solar cell technology

multilayer solar cell technology

The third-generation photovoltaics that use →multijunction photovoltaic cells. Although third-generation technology is based on the second-generation thin-film technology, the major difference is that each thin semiconductor layer in multijunction photovoltaic cells consists of diverse semiconductor materials with different →p–n junctions. Each layer is nanostructured in a different way to respond to different ranges of the solar spectrum. The use of multispectral thin-film absorber layers achieves greater overall conversion efficiency than the plain thin-film photovoltaic cell.

multimeter

An instrument used to measure voltage, current, resistance, and other electrical properties.

multimodal inverter

Also known as bimodal or multifunction inverter. A hybrid inverter that can operate as either a →grid-tie inverter or a →stand-alone inverter. Similarly to a stand-alone inverter, it is wired to a battery bank that receives the DC power from the PV array. Once the batteries are fully charged, the inverter converts the solar-generated energy into AC power to supply the loads connected to the home’s electrical system. Finally, the excess power beyond storage and consumption by the connected load is sent to the public utility grid, “turning back” your two-way electricity meter and earning credits toward your energy bill. Modern multimodal inverters are modular and scalable, allowing owners to expend their PV arrays with additional modules and increase the size of their battery bank.

multipane glass

An energy-efficient glass consisting of two or three window panes. A multipane glass reduces energy consumption and costs, while minimizing outside noise. The added panes as well as the sealed air gaps between them add additional layers of insulation in a window system. In summer, these added thermal control layers decrease the amount of heat entering the house, whereas in winter, double or triple glazing prevents heat from escaping the building.

multiple exciton generation

(MEG) The formation of more than one electron per absorbed photon. This process occurs for instance in →nanocrystalline semiconductors.

multiple solar cell 

 473

multiple solar cell

See →multiple junction solar cell.

multiple junction solar cell

Consists of two or more superimposed subcells that are made of different semiconductor materials and thus absorb different parts of solar spectrum.

multistage controller

A type of controller that allows multistage lead-acid battery charging. It regulates different voltages and current levels as the battery is being charged, going from the bulk over the absorption to the float charging stage.

multistring inverter

Also known as a multi-MPPT inverter, a multistring photovoltaic (PV) inverter or a multistring PV inverter. A string inverter that has two or more →string inputs, each with its own →Maximum Power Point Tracker (MPPT), to optimize the conversion of different DC inputs into grid-compatible alternating current (AC). In contrast, a single-string inverter converts DC solar power generated by a single string of PV panels into AC. A number of solar panels, usually facing the same direction, are connected to a single-string inverter at one central point. This centralized method works fine as long as none of the panels on the string are shaded and all PV modules face the same direction. However, even if only one PV module is shaded for a portion of the day, the power output of all modules on the same string is reduced to the level of the shaded panel. If PV modules are oriented in different directions, for instance, one roof area covered with panels facing north and another facing south, it is advisable to connect each roof area’s modules in a separate string. Each string is wired into its own Maximum Power Point Tracker (MPPT) that is connected into one multistring inverter.

multistring photovoltaic See →multistring inverter. inverter multistring PV inverter

See →multistring inverter.

multitester

See →multimeter.

multiwalled carbon nanotube

(MWCNT) A carbon nanotube that consists of multiple nanotubes of different dimensions that are concentrically nested within each other. Multiwalled carbon nanotubes have excellent optical and electrical properties. Their extended spectral response includes large parts of →infrared

474 

 MWAC

(IR) and →ultraviolet (UV) range of the electromagnetic spectrums. By varying the size of nanoparticles, each MWCNT layer can be engineered in a slightly different way to allow the capturing of different wavelengths of solar radiation. This is why the MWCNT films are often used in →heterojunction solar cells. MWAC

Abbreviation for →megawatt alternating current.

MWAC

Abbreviation for →megawatt alternating current.

MWCNT

Abbreviation for →multiwalled carbon nanotube.

MWp

Abbreviation for →megawatt peak.

N

n– region

Region that is characterized by low doping concentration in an n-type semiconductor.

n+ region

Region that is characterized by high doping concentration in an n-type semiconductor.

NABCEP

See →North American Board of Certified Energy Practitioners.

nacelle

A housing for a propeller-type wind turbine.

nadir

Arab., naẓīr “opposite,” the lowest point diametrically opposite the zenith.

nameplate capacity

See →rated power.

nameplate output

See →rated power.

nano

Latin, nanus “dwarf,” SI unit prefix meaning one-billionth of a meter, 10−9, 0.000 000 001.

nanoantenna

Or nantenna is an emerging technology that theoretically can provide an ultrahigh efficiency (up to 85%) by tapping into wider ranges of the solar spectrum than the conventional photovoltaic cell technology. Nanoantennas use tiny nanoscale optical antennas coupled with the high-speed diodes to convert the electromagnetic waves into direct current electricity. This technology uses the antenna principle; however, unlike an antenna receiving radiowaves, the optical rectennas (nantennas) need to be of much smaller

nanocarbon 

 475

size, at a nanoscale, in order to be able to capture smaller electromagnetic light waves. The goal is to customize the size of nantennas and to use arrays of nantennas to absorb solar radiation at high-energy wavelengths between 0.4 and 1.6 μm for maximum efficiency. The light induces electron movement creating an alternating current flow in the nanoantenna circuit. The alternating current must be then rectified, converted into direct current, which is done with high-speed electronic diodes. The ultimate goal is to capture the entire solar spectrum, including ultraviolet light, visible light, and infrared light. It is proposed that even the infrared radiated from the earth’s surface at night could be harvested. However, nanoantenna research is still in its early stages, and some concrete fabrication challenges would need to be solved, before it can be effectively put into practice. nanocarbon

A carbon material, such as →graphene, →fullerene, or →graphite, whose crystallite size is smaller than a millionth of a meter or a micrometer (μm). Nanocrystalline materials usually have a grain size of a few nanometers. Nanocarbon is measured and engineered on the →nanoscale.

nanocarbon architecture

See →nanocarbon structures.

nanocarbon structure

Also known as nanocarbon architecture. Miniaturization of semiconductor nanocarbon components allows various types of carbon structures, such as a flat sheet of graphite, partially rolled sheet of graphite, completely rolled-up sheet of graphite or →single-walled carbon nanotube (SWCNT), →double-walled carbon nanotube (DWCNT), and →multiwalled carbon nanotube (MWCNT).

nanocoating

See →nanocoating.

nanoengineer

A solar engineer that has knowledge and experience in nanostructures, optics and plasmonics research, nanomanufacturing, and nanotechnology in general.

nanophotovoltaics

See →nanophotovoltaics.

nanosolar cell

A solar cell that consists of multiple nanoengineered thinfilm layers that can absorb 60% more ultraviolet (UV) and infrared (IR) rays than the traditional silicon solar cell. The following are the various types of nanosolar cells: →organic cells, hybrid cells, →dye-sensitized solar cell (DSSC), →quantum dot photovoltaic cells, and →nanowire

476 

 nanocoating

solar cells. In contrast to the regular silicon PV cells that do not work under cloudy conditions, nanosolar cells can generate energy on cloudy days. By varying the size of nanoparticles, nanocrystalline structure can be tuned in such a way that the energy band gaps of different layers allow harvesting of different wavelengths of solar spectrum. The stacked architecture of solar cells has the potential to significantly improve the conversion efficiency of PV cells. The enhanced optical absorption range directly results in a higher power output. The generated energy carriers, electrons and holes, travel over a short path, reducing recombination losses. nanocoating

A fine, thin film of polymeric substances is used as a protective layer on solar panels against corrosion, ultraviolet (UV) radiation, extreme heat, and other severe weather conditions. Nanocoating is also any semiconductor thin layer on a substrate, measured on the nanoscale. It is capable of absorbing 60% more UV and IR rays than the traditional silicon solar cell.

nanocomposite

See →nanocomposite materials.

nanocomposite coating

A coating with a nanocomposite structure that is composed of one or more nanoscale phases in coating matrices.

nanocomposite materials

Materials with a nanocomposite structure that are characterized by outstanding mechanical properties, thermal stability, and oxidation resistance.

nanocomposite solar cell

A solar cell that uses cost-efficient nanoengineered composite films to replace more expensive, widely used traditional semiconductor materials, such as monocrystalline or polycrystalline silicon.

nanocrystal

A crystalline particle with a diameter in the range of nanometers in at least one dimension.

nanocrystal semiconductor

A semiconductor material consisting of individual crystals with a diameter in the range of nanometers. The optoelectronic features of nanocrystal semiconductors can be optimized by changing their size. The scientists can tune the nanocrystal size in such a way to adept it to a certain target range of the solar light spectrum and absorb the maximum amount of solar radiation within that range. This type of nanoscale engineering promises to create highly reactive

nanocrystal solar cell 

 477

semiconductor nanocrystals that can absorb more incoming light than conventional semiconductors. However, the problematic flow of electrons across different layers of individual nanocrystals must still be improved before nanocrystals can be manufactured as a stand-alone semiconductor. Today, nanocrystal semiconductors are commonly used in combination with other semiconductor materials, such as amorphous silicon, in so-called →multiple junction solar cells. nanocrystal solar cell

Also known as a quantum dot solar cell. A solar cell that utilizes →nanocrystal semiconductor materials. Although nc solar cells are still in the embryonic stage, they promise to double the conversion efficiency of photovoltaic cells. Small nanoscale crystals are able to capture and convert photons of blue and ultraviolet light, which are lost as heat in traditional silicon semiconductors. By reducing the size of crystalline particles, the scientists can engineer the band gap in such a way to prevent short-lived hot electrons from escaping the cell. Instead, this energy is converted into the current flow, maximizing the power output. Silicon nanocrystals can generate two or three electrons per photon of light. Today, nanocrystals are typically used as thin-film layers in combination with other semiconductor materials in →multiple junction solar cells. As the multiple junction solar cells require a complex and expensive manufacturing process, the scientists work on creating a stand-alone nanocrystal solar cell. In contrast to multiple junction solar cells, nanocrystals are easy and cheap to make. However, the flow of electrons across different layers of individual nanocrystals is still problematic and it might take some time before this technology is ready for commercial application. See also →quantum dot photovoltaic cell.

nanocrystalline coating

See →nanocrystalline coating material.

nanocrystalline coating material

A polycrystalline material for the manufacture of semiconductor thin films, whose crystallite size is smaller than a millionth of a meter or micrometer (μm). Nanocrystalline materials usually have a grain size of a few nanometers. Due to their small size, the majority of the microstructure consists of interfaces or grain boundaries. Accordingly, most atoms reside in grain boundaries.

478 

 nanocrystalline material

Common technologies used to manufacture nanocrystalline materials include →physical vapor deposition (PVD), →metal-organic chemical vapor deposition (MOCVD), →plasma-enhanced chemical vapor deposition (PECVD), or →sol–gel process. The major advantage of nanocrystalline processing is the fact that it mostly occurs under ambient conditions, reducing the production costs. It is vital to keep the interfaces extremely clean during processing. nanocrystalline material

See →nanocrystalline coating material.

nanocrystalline silicon

(nc-Si) Also known as microcrystalline silicon (μc-Si). A type of thin-film semiconductor material with small grains of crystalline silicon, about 20 nm in size. Nc-Si thin-film layers can be manufactured using →plasma-enhanced chemical vapor deposition (PECVD). Electronic properties of nanocrystalline silicon are similar to those of →crystalline silicon (c-Si) because they both have about the same band gap: ~1.1 eV. nc-Si can effectively replace c-Si and many producers opt for the nc-Si alternative, as the manufacturing costs of nanocrystalline silicon are much lower than those of crystalline silicon. The major difference between nc-Si and c-Si is the fact that hot electrons in an nc-Si semiconductor do not return as quickly to the initial nonexcited state as in a c-Si semiconductor. A longer relaxation time in nanocrystalline semiconductors results in a higher conversion efficiency, as the hot electrons are trapped before they escape the solar cell. A large amount of energy, in particular the energy coming from photons of blue and ultraviolet light, will not be lost as heat as it occurs in traditional crystalline silicon due to the very short relaxation time of hot electrons. In addition, a single photon can excite multiple electrons in nanocrystalline silicon semiconductors. Compared to →amorphous silicon (a-Si), nc-Si also shows higher electrical conductivity than a-Si. The band of a thin nanocrystalline silicon layer can be engineered in such a way to harness a specific range of the electromagnetic spectrum, for instance, the ultraviolet range that is not absorbed by amorphous silicon semiconductors. That is why nanocrystalline silicon is often combined with amorphous silicon into a →tandem junction solar cell to capture different parts of solar spectrum and thus maximize the solar output. See also →nanocrystal semiconductor.

nanocrystalline silicon solar cell 

 479

nanocrystalline silicon solar cell

A solar cell made of →nanocrystalline silicon.

nanoelectromechanical system

(NEMS) A miniaturized mechanical and electromechanical system consisting of miniature mechanical parts and electronic circuits at or below 100 nm.

nanoelectronics

In the solar field, the branch of electronics that investigates the mobility of charge carriers, electrons and holes, in nanostructured semiconductor materials. A close examination of different properties and behavior of materials at the nanoscale as well as the manipulation of nanoparticle sizes lead to the production of thin-film solar cells that are able to trap more light and achieve higher energy conversion efficiency.

nanoengineering

The branch of solar technology that is concerned with the planning, design, and construction of solar nanostructures.

nanoflake

An ultrathin crystalline →nanostructure at the scale of 1–100 nm in at least one dimension. Due to their unique nanostructure and shorter distances to travel within the solar cell, nanoflakes promise to capture and convert more solar energy than conventional →crystalline silicon solar cells. High surface-to-volume ratios and high levels of photoresponse have the potential to convert up to 30% of the solar radiation into electrical energy. According to Prof. Aagesen, who discovered the nanoflake structure, his company SunFlake plans to reduce the solar cell production costs by growing nanowire solar cells onto a low-grade silicon substrate. The technology is still in a prototype phase and it might take some time before a final design is ready for production.

nanoflake solar cell

→Nanowire →solar cells grown directly on top of the →silicon solar cell. The unique →nanostructure with favorable optoelectronic features promises the conversion efficiency of up to 30% of solar energy directed at a semiconductor surface. See also →nanoflake.

nanographene ribbon

Graphene ribbon with a diameter in the range of nanometers.

nanographene ribbon

See →graphene nanoribbon.

480 

 nanograting

nanograting

A symmetric and asymmetric grating structures on a nanoscale. The regular, symmetric nanogrates, rods, or cones on a semiconductor surface with a base diameter of 100–150 nm and height of 800–1,000 nm can significantly increase optical absorption in the semiconductor material and thus the power output of a PV cell. The asymmetric grating structures show higher light-trapping efficiency than symmetric structures, as the light rays entering the cell are bent and redirected in specific directions to prevent them from escaping the solar cell and keep them in the photoactive absorber.

nanolithography

Lithography that involves the patterning and printing of ultrasmall structures under 100 nm in semiconductor manufacturing.

nanomanufacturing

Manufacturing of materials, such as →polymers, →silicon, or →gallium arsenide, at a nanoscale to improve their mechanical, optical, electrical, and chemical properties.

nanomaterials

Also known as nanostructured materials. Materials, such as →polymers, →silicon, or →gallium arsenide, manufactured at a nanoscale, typically between 1 and 100 nm in at least one dimension. Their engineered structure with a reduced grain size and altered band gap gives them unique properties, such as increased strength, chemical reactivity, or high electrical conductivity. The building blocks of nanomaterials are →nanoparticles, such as →fullerenes, →carbon nanotubes, →quantum dots, quantum wires, quantum films, and →nanowires.

nanomechanics

See →nanomechanics of materials.

nanomechanics of materials

Also known as nanomechanics. A systematic study of mechanical, electrical, and thermodynamical behaviors of materials at a nanometer scale. The analysis of crystal lattice structures, crystallographic orientations, and dynamics of composite materials gives →solar scientists an opportunity to control and tune nanoscale structures, for example, →nanowires and →quantum dots, in order to improve photoelectric properties of semiconductor materials and hence the power output of thin-film solar cells.

nanomesh 

 481

nanomesh

An inorganic nanostructured two-dimensional material in the form of a mesh with law thermal conductivity.

nanometer

One-billionth of a meter, 10−9, 0.000000001 m.

nanometer scale

See →nanometer.

nanometer-sized crystalline solid

A polycrystalline material with a crystallite or grain size of a few nanometers.

nanoparticle

A microscopic particle with a diameter in the range of nanometers, usually between 1 and 100 nm in at least one dimension.

nanophase material

A polycrystalline material with a grain size of a few nanometers.

nanophotovoltaics

Also known as nanoscale solar technology. A branch of photovoltaics that utilizes nanoparticles in the manufacture of photovoltaic cells. In contrast to the expensive, high-temperature PV cell manufacturing process, nanophotovoltaics use a low-temperature process that significantly reduces the production costs. In addition, nanophotovoltaics require less material, further reducing the price of panels. Correspondingly, nanosolar panels are much thinner and lighter than the regular, bulky solar modules, occupying less space and reducing installation costs. On the other side, in spite of the promising optoelectrical characteristics, the performance of nanophotovoltaics is still lagging behind the traditional →monocrystalline silicon solar cells.

nanopowder

Powdered materials that consist of ultrafine particles at a nanoscale, usually between 1 and 100 nm. An example of these powder nanoclusters are →zinc oxide nanoparticles used in industrial coatings for the protection of plastic materials against UV radiation and corrosion.

nanoribbon

A nanostructure in the shape of a ribbon with a diameter in the range of nanometers. See →graphene nanoribbon.

nanoscale

See →nanometer.

nanoscale solar technology

See →nanophotovoltaics.

nanosilicon

See →nanocrystalline silicon.

482 

 nanostructure

nanostructure

A structure at a nanoscale between 1 and 100 nm in at least one dimension. It is a structure of intermediate size between a nano- and a microdimension. The two main types of nanostructure used for the manufacture of semiconductor materials are: →nanocrystal and →nanotube. Nanocrystals are ultrathin crystals with a diameter in the range of nanometers, such as →quantum dots, →nanowires, or →nanoflakes. Nanotubes commonly refer to →carbon nanotubes, a semiconductor material known for its high electrical and thermal conductivity.

nanostructured material

See →nanomaterial.

nanostructured photovoltaic cell

See →nanostructured solar cell.

nanostructured PV cell

See →nanostructured solar cell.

nanostructured solar cell

Also known as a nanostructured photovoltaic cell or nanostructured PV cell. A solar cell in which the surface of the active semiconductor regions, where electrons and holes are generated, is nanostructured. Up to 10% of the incoming sunlight can be lost due to reflection when the light is reflected away from the surface of the solar cell instead of being absorbed by it. Because of the reflection loss, the photons of light never get a chance to be converted into energy. The basic idea behind nanostructured solar cell is to boost the efficiency of PV cells by improving the absorption of sunlight with the help of nanostructures. Carrier/excitons separation, charge extraction, and recombination are all influenced by the nanostructures. First, the efficiency is increased by taking advantage of nanostructured absorber materials, such as →nanowires, →nanorods, and →quantum dot structures. Nanostructured ultrathin films allow smaller amounts of lower-grade solar semiconductors to be used. Second, high optical absorption and high carrier collection efficiency are achieved by novel nanostructured solar cell geometries, including nanostructured device patterning and coating.

nanostructured solid

A nanoengineered, polycrystalline material with a grain size of a few nanometers.

nanostructuring 

 483

nanostructuring

A type of nanotechnology that produces different nanostructures on semiconductor surfaces to improve energy conversion efficiency of solar cells. The creation of light-trapping nanostructured surfaces with optical concentration increases the number of absorbed photons in the semiconductor material and thus the power output of a PV cell.

nanotechnology

The engineering of materials on an atomic or molecular scale, which is about 1–100 nm, to build nanostructured semiconductor materials, such as →polymers, →silicon, or →gallium arsenide. It also includes numerous structures and techniques that are even smaller than 100 nm, such as →carbon nanotubes (fullerene, C60), →quantum dots, →nanowires, →nanopillar, →nanocrystals, nanofibers, nonoporous filters, nanoparticulate metal oxides, dispersion nanoparticles, nanopin film, polymer nanocomposites.

nanotopography

Mapping of a wafer surface in the range of nanometers to improve light-trapping features of a solar cell.

nanotube

A tube-like structure at a nanoscale with a diameter size between 1 and 100 nm or smaller. In the context of solar energy, nanotubes commonly refer to →carbon nanotubes, a semiconductor material known for its lightness, sturdiness, and high electrical and thermal conductivity.

Nanotube

nanowatt

(nW) unit of power.

nanowire

A fabricated, extremely thin columnar structure with a diameter in the range of nanometers.

484 

 nanowire photovoltaic cell

nanowire photovoltaic cell

See →nonowire solar cell.

nanowire PV cell

See →nonowire solar cell.

nanowire solar cell

Also known as nanowire photovoltaic cell or nanowire PV cell. A solar cell made of semiconductor nanowires that enhance broadband optical absorption and reduce radial carrier collection distances. Nanowire PV cells are able to absorb more light, more wavelengths of the solar spectrum, than regular solar cells. They generate more electrons per photon, whereas the produced energy carriers, electrons and holes, travel over a short path, hence reducing recombination losses.

nantenna

See →nanoantenna.

narrow band gap

Semiconductors, such as →silicon (1.1 eV) and →gallium arsenide (1.4 eV), have a narrow band gap of less than 2 eV between the →valence band and the →conduction band. Compared to insulators (e.g., plastic) with a wide band gap of over 4 eV, which requires a considerable amount of energy to cross the forbidden gap, narrow band gaps demonstrate a high electron mobility. This means that electrons require a relatively low amount of energy, for example, 1.1 eV, to bridge the gap and jump from the valence into the conduction band.

NaS battery

See →sodium-sulfur battery.

NASA

Abbreviation for →National Aeronautics and Space Administration.

National Aeronautics and (NASA) Is a U.S. government agency in charge of science Space Administration and technology research related to airplanes and space. National Climatic Data Center

(NCDC) American archive of weather data.

National Electrical Code

(NEC) U.S. standard regulating the safe installation of electrical equipment, including all solar electrical devices and systems.

National Electrical Manufacturers Association

(NEMA) The association of electrical equipment and medical imaging manufacturers that sets technical standards for electrical products that are in the best interests of the industry and users.

National Fire Protection Association 

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National Fire Protection Association

(NFPA) A US organization that creates electrical and building standards and codes to minimize the danger of fire.

National Oceanic and Atmospheric Administration

(NOAA) A US scientific agency responsible for monitoring the oceans and the atmosphere.

National Renewable Energy Laboratory

(NREL) Is the U.S. Department of Energy’s (DOE) research institute for renewable energies and energy efficiency, located in Golden, Colorado.

National Solar Radiation Data Base

(NSRDB) Provides information on meteorological and solar radiation.

natural aerosols

Aerosols that form fog and clouds through the condensation of vapor species. See also →human-made aerosols.

natural air cooling

See →natural draft.

natural cooling

See →natural draft.

natural draft

US The natural upward movement of warm air in vertical, closed structures, such as a multistory building or a chimney, caused by the temperature and pressure difference between the hot air within the structure and cool outdoor air. Natural draft is an environmental-friendly cooling technique that does not utilize fans or other electromechanical devices.

natural draft cooling tower

US A cooling tower that utilizes buoyancy or natural draft to cool hot industrial water and hence remove waste heat from the system. The warm water from a plant, usually an oil refinery, a chemical or a power plant, is pumped to the natural draft cooling tower and is distributed through a cooling fill material. The air, which is circulated inside the cooling tower by natural convection, gets in touch with water, causing a certain volume of water to evaporate. The evaporation process removes the heat and the colder water, which is gathered in a collection basin, is pumped back to the system to cool down the heated equipment and condensers. Natural draft cooling towers are environmentally friendly as they do not use fans or other electromechanical devices. Other advantages include low energy consumption, low maintenance, high longevity, minimal noise, and operational safety.

natural draught

UK See →natural draft.

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 natural draught cooling tower

natural draught cooling tower

UK See →natural draft cooling tower.

natural gas

A fossil fuel found alongside coal deposits.

natural heat sink

A natural substance that absorbs excessive heat. For instance, ground with a temperature that is lower than the above-ground air temperature can be used as a natural heat sink in summer. Hot air from the interior of a building is circulated through the tubes that are buried in the ground. Due to the temperature difference, the air exiting the underground tube is cold enough to cool the building.

natural ventilation

See →convection.

nature-friendly

See →environmentally friendly.

NCDC

Abbreviation for →National Climatic Data Center.

n-doped region

See →n-doped semiconductor layer.

n-doped semiconductor layer

A negatively doped region of a semiconductor that regulates the movement of electrons in the →conduction band. The flow of electric charge in a →solar cell resembles a counterflow heat exchanger in which two working fluids (hot and cold) flow through two different pipes in opposite directions. The chemical process called →doping determines the flow direction in a PV cell. The semiconductor layer doped with n-type dopants, such as →phosphorus atoms, regulates the flow of →electrons along the conduction band only in one direction, while the semiconductor layer doped with p-type dopants, such as →boron atoms, allows the flow of holes only in the opposite direction. In a nutshell, every solar cell acts as a →p–n junction diode or an electrical one-way valve that passes current in only one direction. The interplay of this bidirectional movement driven by the attraction between the opposite positive and negative charges produces a current flow in a photovoltaic cell.

n-doping

A chemical process in which a semiconductor layer is doped with n-type dopants such as →phosphorus to increase the conductivity of pure silicon semiconductor and determine the flow direction of electrons.

near-field communication

(NFC) Contactless communication between electronic devices.

NEC 

NEC

Abbreviation for →National Electrical Code.

negative carriers

See →negative charge carrier.

negative charge

See →negative electric charge.

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negative charge carriers Free →electrons that carry negative charge with them while moving from one silicon atom to another along the →conduction band in the semiconductor. negative contact finger

Negative metal contact fingers are connected to n-type diffusion regions of the solar cell.

negative declination

A declination south of the celestial equator is known as a negative or southerly declination.

negative declination angle

An angle between the celestial equator (0°) and south celestial pole (–90°).

negative electric charge An →electric charge that has more electrons than protons. In semiconductors, →electrons are negative charge carriers that move along a →conduction band. In an →n-type semiconductor, electrons move from left to right through the silicon crystal lattice, carrying negative charge. See also →positive charge. negative electrode

Also called a cathode – a negative terminal of a battery. A terminal through which an electrical current leaves a battery or electrolytic cell during discharge. In an electrochemical cell, positively charged ions (cations) migrate toward the negative electrode.

negative photoresist

A type of →photoresist that undergoes polymerization and becomes very difficult to dissolve in the photoresist developer solution, when exposed to UV light. Hence, UV light is pointed at the material that should remain intact, in form of isolated lines or islands. The unexposed portion of the photoresist is washed away by the developer solution.

negative plate

A battery plate that is connected to the negative terminal.

negative temperature coefficient

(NTC) A decrease in electrical resistance as a result of an increase in temperature. Some semiconductor materials, such as silicon, germanium, and carbon, have a negative temperature coefficient of resistance.

negative terminal

See →negative electrode.

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 NEMA

NEMA

Abbreviation for →National Electrical Manufacturers Association.

NEMS

Abbreviation for →nanoelectromechanical system.

net collector area

See →net collector surface.

net collector surface

The glass-covered area of a collector, also known as an aperture area, through which solar radiation passes and is absorbed by the semiconductor surface. Net collector surface excludes framing and structural support of a collector.

net energy metering

Also known as net metering. Solar consumer compensation for any excess electricity they export to the grid. Usually, two types of net metering programs are offered depending on the country’s or state’s jurisdiction. According to one program, if you generate more energy than you use, any surplus energy is fed into the electric grid and your →two-way electricity meter runs backward. You make a deposit into your “solar account,” as you would into a bank account, earning credits toward your energy bill, and you have the ability to withdraw the electricity from the power grid when needed, for instance, at night or in winter. According to the other program, utility companies are required to purchase all excess energy produced by households at a fair rate. This is the case in Germany and in some of the US states. For all PV owners without their own storage banks, the net metering system functions as a giant virtual energy storage and the utility as an energy storage manager accepting surplus energy and distributing it where needed, often in far-away regions.

net metering

See →net energy metering.

net metering system

See →net energy metering.

network operator

See →grid operator and →system operator.

net zero building

See →zero-energy building.

net zero-energy building (NZEB) See →zero-energy building. neutralizer

The role of the neutralizer in an →ion beam source is to balance the charge of the ions in the beam.

neutron

A subatomic particle without an electric charge, found in the →nucleus of an →atom.

NFC 

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NFC

Abbreviation for →near-field communication.

NFPA

Abbreviation for →National Fire Protection Association.

NiCad

See →nickel–cadmium battery.

NiCad battery

See →nickel–cadmium battery.

NiCd battery

See →nickel–cadmium battery.

nickel

(Ni) Silvery-white, hard, and ductile metal that is one of the most abundant minerals on earth. Nickel is commonly used in the solar storage industry. It is an important metal for the manufacture of batteries.

nickel-based batteries

Batteries that are made of nickel and another material. Nickel-based batteries that are frequently used in the solar industry include →nickel–cadmium battery (NiCd), →nickel–metal hydride battery (NiMH), and nickel–iron battery (NiFe).

nickel–cadmium battery Also known as NiCd battery or NiCad battery. A rechargeable battery containing the chemicals nickel (Ni) and cadmium (Cd), whereas anode is usually made of nickel hydroxide (Ni(OH)2) and cathode of cadmium hydroxide (Cd(OH)2). A potassium hydroxide (KOH) solution is typically used for the electrolyte. A NiCad battery has higher storage densities than a lead-acid battery. Unlike a lead-acid battery whose voltage gradually drops off as it is emptied, a nickel–cadmium battery maintains a stable voltage of 1.2 V per cell up until it is almost fully depleted. As NiCad batteries contain cadmium, a highly toxic metal that acts as a human carcinogen, they must be properly recycled. Toxic substances must be destroyed or transported to hazardous waste drop-off facilities. Due to the negative impact on the environment, high initial cost, and complicated maintenance, the nickel– cadmium batteries are not the best choice for a sustainable solar power system. nickel–iron battery

(NiFe) A long-lasting rechargeable battery with a life span of 2,000–3,000 cycles that is used for storage of solar-generated energy in off-grid and renewable energy solar systems. The nickel–iron battery is more environmentally friendly than →nickel–cadmium battery as its anode

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 nickel–metal hydride battery

is made of iron, which is less toxic than the hazardous substance cadmium. The NiFe battery has high tolerance against high temperatures and it is resilient to overcharge and overdischarge. The major disadvantage of NiFe batteries is their poor performance at low temperatures. nickel–metal hydride battery

(NiMH) Also known as a NiMH battery. A rechargeable battery that is used for storage of solar-generated energy in →solar garden lights and other outdoor →solar lighting systems. The nickel–metal hydride battery is more environmentally friendly than →nickel–cadmium battery as its anode consists of a hydrogen-absorbing alloy. NiMH battery has a high energy density, which is at least twice as much as that of a →lead-acid battery and 40% higher than that of a nickel–cadmium battery.

NiFe battery

See →nickel–iron battery.

night cooling

A natural, passive cooling technique in which windows are kept open at night in summer to remove warm air out of the building and cool walls for the next day. The cold walls will retain nighttime coolness during the day, reducing ventilation and air-conditioning usage.

night flushing

See →night cooling.

night-purge ventilation

See →night cooling.

NiMH battery

See →nickel–metal hydride battery.

NIP

Abbreviation for →normal incident pyrheliometer.

nitride

(N) A compound consisting of nitrogen and a more electropositive element, such as →silicon, →phosphorus, or →boron. →Silicon nitride film is commonly used in the manufacture of →polycrystalline silicon solar cells. →Indium gallium nitride (InGaN) is a further example of an efficient nitride semiconductor compound.

nitrous oxide

(N2O) Also known as laughing gas. This is a man-made compound composed of two nitrogen atoms and one oxygen atom. It is an industrial byproduct of nitrogen-intensive agriculture that is identified as one of the heat-trapping →greenhouse gases (pollutants), contributing to →global warming and →climate change.

n-layer 

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n-layer

Thin top silicon semiconductor layer of a solar cell that is doped with →phosphorus atoms. See →n-type semiconductor.

NLTC

Abbreviation for no-load tap changer. See →off-load tap changer.

NMR spectroscopy

See →nuclear magnetic resonance spectroscopy.

NOAA

Abbreviation for →National Oceanic and Atmospheric Administration.

NOCT

See →nominal operating cell temperature.

no-load tap changer

(NLTC) See →off-load tap changer.

nominal capacity

See →rated power.

nominal operating cell temperature

(NOCT) Temperature of the solar cells under →standard operating conditions (SOC) that are determined as follows: a solar radiation of 800 W/m2, 20 °C ambient temperature, and 1 m/s wind speed with PV cells operating in an open circuit condition. The nominal operating cell temperature (NOCT) replicates the working environment of a PV module more closely than standard test conditions (STC) which are set in an ideal laboratory setting and therefore fairly removed from a real-world experience. Therefore, the STC rating is always higher than the NOCT rating.

nominal operating point A point on the →I–V curve graph at which the current and voltage lines meet, representing the maximum power generation of a PV module or array when connected to a load or a battery bank. nominal power

The maximum amount of continuous power that a solar panel or an inverter, based on their specification, can supply to the connected devices (load) in a house.

nominal rating

See →nominal power.

nominal voltage

Also known as rated voltage. This is a rated value, indicating the available input or output voltage of a battery, PV module, or other PV component. This is a rounded, general voltage value that is derived from testing equipment under optimal standard conditions and it is listed on a solar panel’s or battery’s specification sheet (i.e., a 12,

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 nonabrasive

24, or 48 V battery, module, or system). These numbers may not coincide with actual voltage values during real use, but they come pretty close. The actual voltage of a 12 V PV module can be a few volts higher or lower. In the bright sunshine, the output can reach 14 V or even 18 V, or it can drop to 10 V under certain circumstances. Regardless of these variations, the nominal voltage helps users better plan and size a PV system for their home, or match their battery bank size to PV panels. nonabrasive

Not abrasive; containing no abrasive ingredients.

nonconcentrating solar collector

See →stationary solar collector.

nonconducting material

Also known as an insulator. Material that does not conduct electricity or heat.

nonconductor

Electrical insulator. Also known as nonconductor, a material such as plastic that does not conduct electricity well and has the task to stop the flow of electric current in unwanted places. Conducting photovoltaic copper wire is insulated with polyethylene coating.

noncrystalline semiconductor

Also known as amorphous semiconductor. A semiconductor that consists of noncrystalline materials, such as amorphous silicon. Noncrystalline semiconductors do not have an orderly structure on a molecular level.

nondoped layer

See →undoped layer.

nonlinear load

See →nonlinear load.

nonlinear load

A load in which the load impedance is not constant but it changes with the applied voltage. It leads to →harmonic distortion with nonlinear current waveforms. The nonlinear loads are found in rectifiers and switching power supplies and they can affect the electrical circuit as well as the connected appliances.

nonrechargeable battery

Also known as primary battery. A type of battery that is not rechargeable and is discarded after use.

nonrenewable

Not able to be restored.

nonrenewable

See →nonrenewable.

nonrenewable energy 

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nonrenewable energy

Energy generated from finite natural resources that cannot be restored when they are used up, for example, fossil fuels, such as coal, petroleum, and natural gas.

non-renewable energy

See →nonrenewable energy.

nonrenewable energy source

Energy source that cannot be restored when it is used up, for example, fossil fuels, such as coal, petroleum, and natural gas.

non-renewable energy source

See →nonrenewable energy source.

nonrenewable fuels

Fuels such as coal, petroleum, and natural gas that cannot be restored when they are used up.

non-renewable fuels

See →nonrenewable fuels.

nonrenewable resource

Is a finite natural resource that cannot be restored when it is used up, for example, fossil fuels, such as coal, petroleum, and natural gas.

non-renewable resource See →nonrenewable resource. nonspinning reserve

Any back-up energy generation capacity which is held in reserve and can be brought online and made available to grid within 10 min to meet sudden high electricity demands and maintain system frequency stability.

nontoxic material

Material that is not destructive to environment or human health.

nonuniform heat distribution

See →nonuniform temperature distribution.

nonuniform temperature Nonuniform temperature and heat distribution on the distribution →receiver pipe, absorbing focused beams of solar energy from concentrating solar collectors, such as →parabolic trough solar collector, →dish collector, and →linear Fresnel reflector. Nonuniform temperature distribution leads to heat loss and a diminished performance of the solar thermal system. Therefore, during the installation of the system, it is imperative to ensure uniform heat flux and temperature distribution on the receiver all day long by carefully calculating the best angle for solar collectors. nonutility generator

(NUG) See →independent power producer.

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 nonutility-scale photovoltaic system

nonutility-scale photovoltaic system

See →nonutility-scale solar system.

nonutility-scale PV system

See →nonutility-scale solar system.

nonutility-scale solar system

Unlike the utility-scale photovoltaic and solar thermal systems that are typically utilized for large-scale electric power generation, a nonutility-scale solar system is a small-scale solar system whose main aim is to provide electricity or heat for domestic use in a single household.

nonutility-scale system

See →nonutility-scale solar system.

nonvisible light

See →invisible light.

normal incident pyrheliometer

(NIP) An instrument for measuring →direct normal irradiance (DNI) from the sun.

normal operating cell temperature

(NOCT) See →nominal operating cell temperature.

normal operating temperature

See →nominal operating cell temperature.

normal operation

The expected day-to-day operation and power output of a solar device under certain regular conditions.

normal radiation

Radiation that strikes a flat surface facing the sun. For instance, a solar panel, which is perpendicular or “normal” to the Sun, absorbs normal radiation. Normal radiation does not only include the direct beam solar irradiance (DNI) from the sun but also all radiation that strikes the →aperture facing the sun.

North American Board of Certified Energy Practitioners

(NABCEP) A board of experienced renewable energy professionals who are voluntarily committed to create and implement high-quality credentialing and certification programs for clean energy practitioners, such as photovoltaic and solar-thermal installers. The major goals of NABCEP certification programs are to promote renewable energy, increase the competence and safety of workers, and improve the overall quality of renewable energy services and products.

North Pole

Also known as Geographic North Pole or true north. The northernmost point on the Earth’s surface at latitude 90°

nowcasting 

 495

north, where the Earth’s imaginary axis of rotation intersects the Earth’s surface and all lines of longitude meet. nowcasting

Current solar forecast, 3–4 h.

NREL

Abbreviation for →National Renewable Energy Laboratory.

NSRDB

Abbreviation for →National Solar Radiation Data Base.

NTC

Abbreviation for →negative temperature coefficient.

n-type

See →n-type semiconductor.

n-type diffusion region

Is an n-type region in which excess electrons move along the conduction band and eventually diffuse across the junction into the p-type region of the semiconductor.

n-type dopant

A chemical element from Group V of the periodic table, for example, →phosphorus, which is added in a small, controlled quantity to a silicon semiconductor, in order to change its electrical properties. The dopant incorporates more electrons than are needed for the perfect structure of the silicon crystal. Phosphorus with five electrons in the outer orbital will create a disturbance in the pure semiconductor silicon lattice order, known as an octet stability. In the octet stability, each silicon atom is surrounded by four other silicon atoms and has eight electrons in the outer valence shell. The phosphorus atom, so-called impurity, donates its fifth “extra” electron to the neighboring silicon atom. Once released, the free electron starts migrating through the silicon crystal lattice, producing an electrically conductive →n-type semiconductor.

n-type doping

Doping of a silicon semiconductor with a chemical element from Group V of the periodic table, for example, →phosphorus, to induce a negative charge and produce an electrically conductive →n-type semiconductor under given conditions.

n-type semiconductor

A semiconductor in which electrons are the dominant charge carrier. n-Type semiconductor is created by doping an →intrinsic semiconductor with a chemical element from Group V of the periodic table, for example, →phosphorus. This n-type dopant, also called impurity, has five electrons in its outer shell, creating an imbalance in a silicon crystal structure dominated by a symmetric four-electrons-in-thevalence-shell pattern. To fulfill the bonding requirements,

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 n-type silicon

E

Donor level

N-type Semiconductor

phosphorus atoms donate their “extra” electrons to the silicon atoms, increasing considerably the electrical conductivity of the pure semiconductor and starting an electron flow along the conduction band that we call electricity. As electrons are negative charge carriers, the doped material is referred to as an n-type (negative type) semiconductor. n-type silicon

Silicon doped with a chemical element from Group V of the periodic table, for example, →phosphorus. Phosphorus has one more electron in its outer shell (five electrons) than does silicon (four electrons), creating an imbalance in a symmetric silicon crystal structure and giving the silicon lattice a negative charge. When the photons of sunlight hit the photosensitive negatively doped silicon layer, the fifth “extra” phosphorus electron bonds with its silicon neighbor atoms. It moves along the conduction band from one silicon atom to another, producing the electrical current.

nuclear energy1

Energy generated by splitting of the nuclei of uranium atoms.

nuclear energy2

Electricity produced by a nuclear power plant.

nuclear exit

Exit from nuclear power.

nuclear magnetic resonance spectroscopy

Also known as NMR spectroscopy. A type of spectroscopy or an analytical chemistry technique used to determine the molecular structure of the observed sample.

nuclear power exit

Nuclear power phase-out.

nuclear power phase-out 

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nuclear power phase-out

Exit from nuclear power.

nucleation

The first phase of the thin-film formation process in which small particles, such as ions, atoms, or molecules, from a liquid or a vapor become arranged in a pattern and condense onto the substrate. The newly formed crystal layer is a base upon which additional layers are deposited, as the crystal continues to grow. In other words, nucleation is an initial stage in a phase transformation process in which a substance, gas in →chemical vapor deposition (CVD), is converted into small nanosized liquid droplets that condense onto the substrate, forming a crystalline solid capable of growing.

nucleus

See →atomic nucleus.

NUG

Abbreviation for nonutility generator. See →independent power producer.

numerical weather forecast

See →numerical weather prediction.

numerical weather forecast model

A model that uses the →numerical weather prediction to make a weather forecast.

numerical weather prediction

(NWP) A method of weather forecasting that employs multiple numerical algorithms to generate a more reliable forecast. Numerous weather observations, based on satellite data and ground measurement data, are collected and processed by supercomputers that make predictions on solar irradiance and atmospheric variables, such as temperature, pressure, wind, and rainfall. At the end of the process, a human data analysis specialist is still required to evaluate and interpret the interaction between different variables to predict what the weather will be like.

NWP

Abbreviation for →numerical weather prediction.

NZEB

Abbreviation for net zero-energy building. See →zero-energy building.

O O&M

Abbreviation for →operations and maintenance.

O&M costs

Abbreviation for →operations and maintenance costs.

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 OAD

OAD

Abbreviation for →oblique angle deposition.

oblique angle deposition

(OAD) A method for producing nanostructures, for example, inclined columns, helices, and zigzag shapes, to enhance the optical anisotropy and porosity of thin films. The OAD generates directional columnar structures through the self-shadowing effect during film growth. The oblique angle deposition allows the strict control over porosity, →anisotropy and crystallographic orientation of thin films. The OAD refers to a particular geometry in the deposition reactor rather than a particular deposition technique. Physical vapor deposition (PVD), plasma- and laser-assisted deposition of thin films can all apply oblique angle deposition technique.

OC

Abbreviation for →open circuit.

occupancy detector

See →presence detector.

OECD

Abbreviation for →Organisation for Economic Co-operation and Development.

off-circuit tap changer

See →off-load tap changer.

off-grid

Not connected to a utility power grid.

off-grid building

See →off-grid house.

off-grid heating

Off-grid heating is a combination of a well-insulated home, →passive solar heating, and solar thermal collector system. The proper insulation wraps the entire house in a weatherproof blanket that can significantly reduce the heating demand. The passive solar heating techniques include the admission of the sun’s heat through the large south-facing windows in winter, →Trombe wall, →sunroom, and →transparent thermal insulation. With the exception of northern areas with short daylight hours, an appropriately sized solar thermal collector system can efficiently heat the off-grid house. The water heated by solar collectors can provide not only domestic hot water but also radiant space heating. The same hot water that is stored in a →hot water storage tank and comes out of a hot water tap can also be directly run through the hot water pipes underneath the floor, heating the interior of an energy-efficient house.

off-grid heating system

See →off-grid heating.

off-grid home 

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off-grid home

See →off-grid house.

off-grid house

An autonomous house that is not connected to the utility grid and relies on its own solar thermal heating system and home-made electricity production. When planning an off-grid house, it is vital to carefully calculate the energy requirement of the house. It is better to have some extra panels and batteries installed to cover for a potential increase in energy usage in a household or an exceptionally cold winter with less sunny days. To be on the safe side, an off-grid house should have an additional source of energy supply, such as a wind turbine or a backup generator.

off-grid inverter

An inverter used for an →off-grid photovoltaic system. Photovoltaic modules generate direct current (DC) electricity that is stored in a →battery bank. In order to power AC household appliances in an off-grid home, an appropriate off-grid inverter is required to convert DC to AC electricity. While a →modified sine wave inverter is suitable for simple appliances, including older TVs, incandescent lights, and motors with brushes, modern electric devices, such as high-definition TVs, digital clocks, laser printers, or gaming consoles, require →pure sine wave inverters.

off-grid photovoltaic

See →off-grid photovoltaic system.

off-grid photovoltaic system

Also known as stand-alone solar power system is a photovoltaic (PV) power system that is not connected to an electrical grid. An off-grid PV power system usually consists of several solar panels, batteries, an inverter, a charge regulator, and a mounting system. The solar panels produce power, which is stored in a battery bank. Upon need, the stored DC electricity is converted with help of the inverter into AC power and distributed across the home to power house appliances. In northern, less sunny regions it is advisable to have a generator as a backup power besides the battery bank. Off-grid systems work at low voltages and a homeowner can choose between 12, 24, and 48 V systems. When choosing a new system, a user can consider the following guidelines: The lower the voltage, the safer the system, but the higher the power losses. The higher the voltage, the less safe the system, with a possibility of electrocution, but the lower the power losses.

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 off-grid power supply

Apart from green enthusiasts who would always choose a stand-alone solar power system, the off-grid PV power system is a preferred option among users who are subject to frequent power fluctuations or outages or who live in the boonies and the closest power lines are one or more miles away from their property. To bring power lines to their home site might cost a fortune; therefore, the installation of an off-grid solar power system is a cost-effective alternative. off-grid power supply

See →off-grid photovoltaic system.

off-grid power supply system

See →off-grid photovoltaic system.

off-grid power system

See →off-grid photovoltaic system.

off-grid PV system

See →off-grid photovoltaic system.

off-grid solar energy system

See →off-grid photovoltaic system.

off-grid solar system

See →off-grid photovoltaic system.

off-grid system

See →off-grid photovoltaic system.

off-load tap changer

Also known as no-load tap changer or off-circuit tap changer. A →tap changer in which tap changing occurs while transformer is in an off-load or no-load mode. An off-load tap changer is mostly used with solar power generation facilities.

off-load voltage

The amount of voltage being present between the positive and negative poles, if no loads are connected to the voltage source, for example, photovoltaic panels.

off-peak energy

Electricity that is sold by utilities at lower rates during the hours of low energy consumption, usually evening and night hours. With a favorable tariff, utility companies attempt to attract users and fill in the low power demand gap, as their power plants produce energy 24 h.

off-peak hours

See →off-peak time.

off-peak kilowatt hour

A favorable kilowatt hour (kWh) electricity rate during the hours of low energy consumption (off-peak time).

off-peak time

The hours of low energy consumption, usually evening and night hours, when utilities sell electricity at lower rates than during the hours of high electricity demand (peak hours).

off-the-grid 

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off-the-grid

(OTG) Not connected to an electrical grid.

ohm

(Ω) Unit of electrical resistance. The resistance of 1 Ω exists between two points in a DC circuit when a potential difference of 1 V generates a current of 1 A. Accordingly, ohm (Ω) is equal to volts (V) divided by amps (A): Ω = V/A.

ohmic

Referring to the unit of electrical resistance →ohm.

ohmic contact

Is a nonrectifying metal–semiconductor junction of low resistance that allows current to flow both ways roughly equally.

ohmic drop

Voltage or potential drop as a result of current (I) flowing through resistance (R) in a circuit.

ohmic loss

Loss of electric energy in a power circuit arising from resistance (load, heat) and current flow.

ohmic load

A resistive load in which resistance remains constant, as the electrical current and the voltage are in phase or in step with each other. If voltage rises or falls, the current also rises or falls with it.

ohmic resistance

A measure of electrical resistance – how much a material, such as a copper wire, or an electrical device (load) opposes the flow of an electric current. It is measured in ohms (Ω).

ohmmeter

An instrument for measuring electrical resistance.

Ohm’s law

The Ohm’s law explains the relationship between potential difference, electric current, and resistance. With help of Ohm’s law equation V = I x R, the voltage can be calculated when the other two values are known. The voltage (V), or potential difference between two points, equals the current (flow of electrons) between those two points (I) times the total resistance of all electrical appliances (load) between those two points (R). The formula can be rearranged, and for instance, when voltage (V) and current (I) are known, resistance (R) can be calculated in the following manner: R = V/I. In the third rearrangement of the equation, the current can be calculated with the following formula: I = V/R, whereas current (I) is equal to voltage (V) divided by resistance (R).

oil

A black liquid →fossil fuel found in the earth’s crust, in deposits that were formed from oceanic animals and plant debris millions of years ago. It is used to make gasoline, kerosene, diesel, and most plastics.

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 oil sand

oil sand

Also known as tar sand. A naturally occurring mixture of sand, water, clay, and bitumen. The oil-rich bitumen must be treated before it can be used by refineries to produce gasoline or diesel.

oil-repellent agent

See →oil-resistant agent.

oil-repellent coating

See →oil-resistant coating.

oil-resistant

A chemical property that has a strong aversion to oil.

oil-resistant agent

A chemical substance that has a strong aversion to oil.

oil-resistant coating

Also known as oil-repellent coating. A coating made of special materials that repels oils to protect electrical equipment from oils. The hydrophobic layer typically consists of two main elements: an active molecule with oil-repelling characteristics and a binder. After the hydrophobic coating is sprayed on the desired electronic surface and the robust, rubbery texture is formed, oil is repelled and rolls off the coating without touching the underlying electrical contacts.

okta

The unit of measurement of the cloud cover. It is expressed as eighths (1/8 – 8/8), ranging from 0 okta (completely clear sky) to 8 oktas (completely cloudy sky); 4 octas or 4/8 means that the four-eighths of the total area of the sky dome (half of the sky) are obscured by clouds.

OLR

Abbreviation for outgoing longwave radiation. See →longwave radiation.

OLTC

Abbreviation for →on-load tap changer.

OMCVD

Abbreviation for organo-metallic  chemical vapor deposition. See →metal-organic chemical vapor deposition.

OMVPE

Abbreviation for organo-metallic vapor phase epitaxy. See →metal-organic chemical vapor deposition.

on the AC side

Refers to the current or power output on the AC side of a photovoltaic system.

on the DC side

Refers to the current or power output on the DC side of a photovoltaic system.

on-demand heater

See →tankless heater.

one-axis tracker

See →single-axis tracking system.

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one-axis tracking

See →single-axis tracking system.

one-axis tracking system

See →single-axis tracking system.

one-way diode

A device that allows electric current to flow only in one direction.

one-way valve

Also known as nonreturn valve. A valve that permits liquids or gases to flow in only one direction. Various nonreturn mechanisms, such as ball, diaphragm, swing check, or stop check nonreturn valves, are used to close the valve by fluid pressure, preventing return flow.

on-grid

Connected to the power grid run by your local electrical utility.

on-grid photovoltaic system

See →on-grid solar system.

on-grid PV system

See →on-grid solar system.

on-grid solar system

A solar system that is connected to a utility power grid.

on-grid system

See →on-grid solar system.

on-load tap changer

(OLTC) A →tap changer in which tap changing occurs while transformer is in an ON-load mode. An on-load tap changer is mostly used with non-solar power generation facilities.

on-roof installation

The installation of a solar system on the roof. Two conventional on-roof installation methods are: →ballasted mounting without roof penetration and →mechanically attached mounting with roof penetration. Sometimes, a third hybrid installation method is used, which combines ballasted and attached mounting technologies to keep the number of roof penetrations to a minimum. See also →roof-mounted solar array.

on-roof installation system

See →roof-mounted solar array.

on-roof mounting

See →on-roof installation.

on-roof mounting system

See →roof-mounted solar array.

on-roof system

See →roof-mounted solar array.

504 

 on-site renewable energy generation

on-site renewable energy generation

The generation of energy close to the point where it is used by a small-scale solar energy producer (homeowner) or a large-scale solar energy producer (corporation). Many companies, such as FedEx Corporation, Kohl’s, and Staples, have installed hundreds or thousands of solar panels on the roofs of their corporate facilities, producing often 100% of their own electricity on-site. Besides photovoltaics, the on-site generation includes the following types of renewable energy: →solar water heating, →combined heat and power, →wind power, biomass heating, and ground source →heat pumps. The on-site renewable energy generation is driven by the following factors: desire to reduce the costs of energy, to earn additional income by feeding excess energy back into the grid, to reduce fossil fuel use, and to reduce carbon dioxide and other →greenhouse gas emissions.

open circuit

(OC) An electrical circuit that is not complete, for example, because a wire in a circuit is frayed. Due to the broken path, there is no current flow. As no load is applied, voltage is at its maximum.

open circuit voltage

See →open-circuit voltage.

open land installation

See →ground-mounted solar array.

open land mounting

See →ground-mounted solar array.

open-circuit voltage

(VOC) Is the maximum voltage produced by a solar cell when there is a break in a circuit. As there is no connection between terminals, the resistance is extremely high and no current is flowing. The current value is zero.

open-loop system

A direct circulation system in which water is heated in the solar thermal collectors and circulated directly into the home and storage tank by using pumps. The open-loop system works well in warmer climates where freezing is not a concern. However, in regions with temperatures below freezing, it is recommended to use →closed-loop systems with antifreeze →heat transfer fluid.

operating and maintenance costs

See →operations and maintenance costs.

operating costs

See →operations and maintenance costs.

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operating lifetime

Also known as service life. The length of time a solar device is expected to function according to the manufacturer’s specification that guarantees that the power output of the device will not fall under 80% of the nominal power. The same PV product life span of 25 years is usually warranted by most manufacturers, even though different types of solar modules have different degradation rates. The degradation rate for crystalline silicon solar modules is about 0.5% per year, whereas thin-film solar modules, such as a-Si and copper indium gallium selenide (CIGS), degrade faster than their mono- and polycrystalline counterparts. Taking into account nearly 2,000 degradation rates of different modules, a study of the →National Renewable Energy Lab (NREL) from 2012 showed a mean solar panel degradation rate of 0.8%/year, which supports the 25-year operating lifetime rule in PV warranties.

operating point

A point on the →I–V curve graph at which the current and voltage lines meet, representing the power generation of a PV module or array when connected to a load or a battery bank.

operating pressure

Also known as working pressure. Optimal preset-limit pressure, expressed in →Pascals (psi), at which a closed-loop solar-thermal system, such as →evacuated-tube collector, can operate without failure. If pressure levels exceed the preset operating pressure threshold in hot summer months, the →temperature and pressure relief valve and →thermostatic mixing valve are automatically activated, discharging the excess heat and adding cool water to prevent overheating and cracking of the evacuated glass tubes.

operating reserve

See →contingency reserve.

operating temperature

The temperature range within which a solar module can properly operate according to its specification. The operating temperature plays an important role in conversion efficiency of a PV module. Conventional silicon solar modules are typically rated at 25 °C (77 °F) under 1 kW/m2. When the temperature of the module rises over 25 °C (77 °F), it potentially reduces the power yield by 10–25% based on the proportional voltage drop due to resistance. See also →nominal operating cell temperature.

operational costs

See →operations and maintenance costs.

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 operational verification

operational verification

An operational test of solar equipment in its normal, daily mode of operation after being installed in a solar system.

operations and maintenance

(O&M) Operations and maintenance of solar systems comprises cleaning, bill management, inventory and management of facility’s assets, scheduled maintenance services, which include scheduled replacement of parts that are out of compliance, and unscheduled maintenance, which includes repairs as they occur. A proper operations and maintenance management ensures the operation of a solar facility at peak efficiency, the extended life of solar equipment, and the reduction of costs related to interruptions and major repairs.

operations and maintenance costs

Also known as O&M costs. The costs associated with maintaining and operating a solar system over its useful life (25 years). They exclude the initial costs of equipment, land, and installation of a solar system. Compared to other power generation technologies with many movable parts and complex technologies, the operating costs of a conventional PV system are relatively low. They include cleaning of panels, an annual inspection, and insurance and property taxes. Inverter is the component that is most frequently associated with failures. Other possible areas of failures are cracked panels and corroded electrical contacts. Therefore, a routine inspection and servicing of solar equipment help prevent breakdowns and reduce power losses.

OPL

Abbreviation for →optical path length.

optical absorption

A process by which photons of light, as they enter the aperture area of a solar module, are absorbed by the electrons in solar cells.

optical depth

See →aerosol optical thickness.

optical diffraction grating

Also known as diffraction grating. An optical component consisting of a surface with a large number of equidistant, parallel lines or grooves. The purpose of the diffraction grating is to diffract light into its component wavelengths, several beams traveling in different directions. Two main types of diffraction grating are ruled and holographic diffraction grating. Ruled diffraction grating consists of

optical invisibility cloak 

 507

grooves on a reflective surface that are parallel with the next. In addition to the replicated, parallel structure, holographic diffraction grating may also be produced by forming grooves of unequal distribution on a reflective surface in order to optimize system performance. optical invisibility cloak

Guides sunlight around objects such as contact fingers that cast a shadow on the solar panel.

optical lens

An optical device that focuses a Sun’s beam to generate a controlled optical result, intensifying solar energy multiple times. Optical lenses appear either as a single component or as part of a larger array of lenses in a concentrating photovoltaic (CPV) system.

optical lithography

See →photolithography.

optical loss

A portion of incoming solar radiation that is lost due to reflection from the front or rear surface (top and bottom electrodes) of a solar cell or transmission of light through the semitransparent semiconductor material of organic solar cells. Optical losses in a polymer thin-film solar cell can be reduced by random surface texturing, geometric engineering of the cell structures, meticulous choice of the electrode and interface materials, and/or the use of optical spacers.

optical nanoantenna

A device that allows control over the propagation and manipulation of light waves by converting optical radiation to localized energy and vice versa. Nanoantennas, which operate at nanometer wavelengths, have found a wide application in optoelectronic devices, such as photovoltaic (PV) cells. Optical nanoantennas are used to artificially enhance the absorption cross-section or →quantum yield of PV cells. The advantages of optical nanoantennas include polarization, tunability, and rapid time response.

optical path

See →optical path length.

optical path length

(OPL) The product of the physical distance the light travels through a medium between two points A and B and the refractive index of the medium. The light absorption in a semiconductor material can be improved by enhancing the flow of photons through expending the optical path length and concentrating the incident field.

508 

 optical rectenna

optical rectenna

Is also called nanoantenna or nantenna. It is an emerging technology that theoretically can provide an ultrahigh efficiency (up to 85%) by tapping into wider ranges of the solar spectrum than the conventional photovoltaic cell technology. Optical rectennas use tiny nanoscale optical antennas coupled with the high-speed diodes to convert the electromagnetic waves into direct current electricity. This technology uses the antenna principle; however, unlike an antenna receiving radio waves, the optical rectennas (nantennas) need to be of much smaller size, at a nanoscale, in order to be able to capture smaller electromagnetic light waves. The goal is to customize the size of rectennas and to use arrays of rectennas to absorb solar radiation at high energy wavelengths between 0.4 and 1.6 μm for maximum efficiency. The light induces electron movement creating an alternating current flow in the optical rectenna circuit. The alternating current must be then rectified, converted into direct current, which is done with high-speed electronic diodes. The ultimate goal is to capture the entire solar spectrum, including ultraviolet light, visible light, and infrared light. It is proposed that even the infrared radiated from the earth’s surface at night could be harvested. However, optical rectenna research is still in its early stages, and some concrete fabrication challenges would need to be solved, before it can be effectively put into practice.

optical spectrometer

See →spectrometer.

optical thickness

See →aerosol optical thickness.

optical time-domain reflectometer

Optical measuring instrument.

optimal orientation of a solar power system

Optimum alignment of a solar power system to the sun maximizes the energy yield. When solar trackers are not used, →tilt-correction frames and mounts can be deployed to achieve the optimal tilt and orientation of PV panels.

optimal power flow

See →economic dispatch.

optimal power transmission

See →optimal energy transmission.

optimum alignment

Optimum alignment of a solar array to the sun maximizes the energy yield.

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optimum alignment of a solar array

See →optimal orientation of a solar power system.

optimum alignment of a solar system

See →optimal orientation of a solar power system.

optimum alignment of solar collectors

Optimum alignment of solar collectors to the sun.

optimum alignment of solar modules

See →optimum alignment of solar panels.

optimum alignment of solar panels

Optimum alignment of solar panels to the sun maximizes the energy yield. When solar trackers are not used, tilt-correction frames and mounts can be deployed to achieve the optimal tilt and orientation of PV panels.

optimum orientation

Optimum alignment of solar panels to the sun.

optimum tilt angle

Optimal inclination of a solar panel towards the sun measured from the horizontal.

optimum voltage

Optimum voltage that is maintained by an MPPT charge controller in a solar module despite variations in input voltage, for instance, varying light conditions, such as cloudy weather, morning, noon, summer, or winter.

optimum voltage distribution

A type of voltage distribution in which the voltage of the first and last multiplier stages, V1 and VN, respectively, have equal amplitudes.

optoelectronic device

A device, such as →radiometer, →spectrometer, →spectrophotometer, and →spectroradiometer, which converts electrical signals into photon signals and vice versa.

optoelectronics

A field of electronics concerned with electronic devices that emit, sense, transmit, and modulate light in various wavelength ranges, such as infrared, visible, and ultraviolet.

OPV

Abbreviation for →organic photovoltaics.

OPV cell

See →organic photovoltaic cell.

organic

In the context of solar manufacturing, organic refers to a semiconductor material that contains the element carbon. Organic semiconductors are used to produce polymer photovoltaic cells, also known as plastic PV cells.

510 

 organic electronics

organic electronics

Flexible, lightweight and low cost electronics.

organic material

See →organic semiconductor material.

organic photovoltaic cell (OPV cell) Also known as a plastic photovoltaic cell or organic solar cell. OPV cell is a polymer photovoltaic cell that is made of semiconductor materials from organic chemistry. Organic semiconductors are carbon-rich compounds whose structure can be tuned to receive a particular range of visible light. Two thin organic semiconductor layers are sandwiched between two electrodes: the donor material (D) and the acceptor material (A). The organic layers absorb the sun and create excitons at the interface between p- and n-type organic layers (D and A). The dissociation process begins, in which excited electrons leave their valence bands and move to the higher conduction bands, through the organic acceptor material toward the negative electrode, whereas the holes move through the donor material in the opposite direction and gather at the lower positive electrode. The electrons continue their flow from the negative electrode through the external path (powering desired devices) to the positive electrode, where they occupy the holes again, closing the energy circuit. The same exciton process starts all over again, generating electricity with help of photoactive semiconductors. The major advantage of organic solar cells is the cheap polymer semiconductor replacing the expensive silicon material. Also, the deposited polymer thin film is 1,000 times thinner than silicon semiconductor layer resulting in additional material cost reduction. The organic solar cells are lightweight and flexible compared to the heavy and rigid silicon solar panels. That makes the installation easier and cheaper. In addition, these features open up a wide variety of application possibilities. As there are no size or shape restrictions, flexible solar cells can be easily incorporated into various irregular designs such as roofs, building facades, cars, unmanned aerial vehicles (UAVs), backpacks, or clothing. The OPV cell manufacturing expenses are smaller than the ones for silicon solar cells, since one of the cheaper low-temperature processes can be used, such as high throughput →inject printing or →roll-to-roll (R2R) method.

organic photovoltaics 

 511

Polymer blend I/V

Hole conductor

Cathode

Transparent anode

Light

Flexible substrate

Organic Photovoltaic Cell

Two major disadvantages of organic solar cells are their low efficiency and short lifetime, as plastic material degrades over time. See also →polymer solar cell. organic photovoltaics

(OPV) Polymer solar cells that are made of materials from organic chemistry.

organic polymer

Low-cost semiconductor material deposited as a thin film on a rigid or flexible substrate.

organic PV cell

See →organic photovoltaic cell.

organic semiconductor

See →organic semiconductor material.

organic semiconductor material

Semiconductor material that contains carbon-rich, nonmetallic compounds, for example, polyphenylene vinylene, polyfluorene, polythiophene, and carbon fullerenes. Two main types of organic semiconductor materials are small-molecule organic semiconductor and long-chain polymeric organic semiconductor. In the past two decades, electroconductive polymers have become a major competitor to inorganic semiconductor materials, such as silicon

512 

 organic solar cell

and gallium arsenide, due to their mechanical strength, simplified manufacturing process, reduced cost, and increased flexibility. The physicochemical parameters of an organic semiconductor are modifiable, as band gaps can be tuned to capture a specific range of the electromagnetic spectrum of the solar radiation. Controlling the band gap of the electroactive polymer finds broad application in →multijunction photovoltaic cell technology. In spite of significant improvements in recent years, organic semiconductor material is still less efficient than conventional silicon semiconductor; however, it maintains relatively low costs. organic solar cell

See →organic photovoltaic cell.

organic solvents

Carbon-based substances that are capable of dissolving or dispersing one or more substances. Organic solvents contain at least one carbon atom in their molecular structure, have low molecular weight, and exist in liquid form at room temperature.

Organisation for Economic Co-operation and Development

(OECD) An international organization of 35 nations that work together to promote economic growth, sustainable development, and social well-being of its members as well as of all people around the world. The OECD focuses on issues such as improving health, battling diseases, safety of chemical products, re-establishing healthy public finances, and many others.

organoborane

See →organoboron compound.

organoborane polymer

An electron-deficient type of polymer that is combined with an electron-rich, thiophene polymer to create an organic semiconductor for plastic thin-film solar cells. The carbon-based, molecular →p–n junction allows the absorption of photons of light and the movement of electrons from the negative electrode to the positive electrode, generating electricity.

organoboron compound

Also known as organoborane. An organic compound or a molecule that encompasses one or more carbon-to-boron bonds (C–B).

organometallic chemical (OMCVD) See →metal-organic chemical vapor deposition. vapor deposition

organo-metallic chemical vapor deposition  

 513

organometallic chemical vapor deposition 

(OMCVD) See →metal-organic chemical vapor deposition.

organometallic vapor phase epitaxy 

(OMVPE) See →metal-organic chemical vapor deposition.

organometallic vapor phase epitaxy 

(OMVPE) See →metal-organic chemical vapor deposition.

organophosphine

(Ph3) Any organic phosphine. A colorless, odorless, and toxic gas utilized in the manufacture of solar cells for the incorporation of →phosphorus into silicon crystals.

organophosphorus

An organic compound containing phosphorus that can be used in the manufacture of dopant photovoltaic ink.

orientation

Position of a building, roof, or solar panel in relation to the sun. When planning a new solar project, it is crucial to find an optimal position for solar panels. For every location, there is an optimal orientation for each month that will ensure the maximum insolation and correspondingly the maximum power output. The ideal orientation is found by calculating the best →aspect angle and positioning the panels to face the optimal south as well as the best →tilt angle, which would be the optimal inclination of a solar panel toward the sun measured from the horizontal. See also →layout configuration.

orientation of a photovoltaic system

Position of photovoltaic panels in relation to the sun. See →orientation and →layout configuration.

orientation of a solar power system

Position of solar panels in relation to the sun. See →orientation and →layout configuration.

OTG

Abbreviation for →off-the-grid.

outgas

To produce gases, typically hydrogen sulfide (H2S) gas, during the battery charging process.

outgassing

See →gassing.

outgoing longwave radiation

(OLR) See →longwave radiation.

overall power requirement

See →total electricity requirement.

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 overcast conditions

overcast conditions

In cloudy and overcast conditions, traditional silicon photovoltaic modules generate 10–25% of their rated capacity. Although →thin-film photovoltaic modules are less efficient than monocrystalline or polycrystalline silicon modules, they can outperform conventional PV panels in hazy and overcast weather conditions. The efficiency of amorphous silicon (a-Si) modules is better in cloudy weather than under clear sky conditions because the light is richer in blue illumination under diffuse light conditions and a-Si has a higher spectral response to blue light. Also, CIS (copper indium selenide) solar panels have higher sensitivity for low irradiation conditions and longer wavelengths, making them more suitable for northern countries, where the sun rests lower in the horizon and there are more cloudy days per year, or for rooftops with an east/ west orientation.

overcharge

To force excessive current into a fully charged battery.

overcharge protection

An electronic control module, such as →high voltage disconnect, which protects the batteries from overcharging by monitoring the voltage in a system at all times. When a high voltage is detected, the safety switch automatically disconnects the load to prevent damage.

overcurrent

An electrical current that exceeds the specified amperage capacity in a circuit, leading to conductor overheating and possible equipment failures. The common causes of overcurrent are overload, loose connection, short circuit, surge power, or ground fault.

overcurrent protection

Protection against excessive currents exceeding the acceptable rating of conductors or equipment.

overcurrent protection devices

(OCPD) Circuit protection devices such as fuses or circuit breakers should be installed in any PV circuit network in order to protect a circuit from harmful overcurrent. The overcurrent protection devices are commonly installed in various types of electrical enclosures, such as combiner, recombiner, and subcombiner boxes.

overdischarge

Excessive discharge of a rechargeable battery that may result in permanent damage. Therefore, it is advisable to use a charge controller in a photovoltaic array to protect the batteries from both overdischarge and overcharge.

overhang 

overhang

 515

Overhangs prevent the solar heat from entering the house directly through windows and indirectly through walls. Whereas they are an efficient device for shading southfacing windows in the summer, they are less useful for east and west exposures. A house design that includes overhangs is considered an effective →passive cooling technique.

overheated photovoltaic See →overheated solar module. module overheated PV module

See →overheated solar module.

overheated solar module Also known as an overheated photovoltaic module. A solar panel whose performance is negatively affected by temperature increases. With increased heat comes decreased energy output. When the temperature of the module rises over 25 °C (77 °F), it potentially reduces the power yield by 10–25% based on the proportional voltage drop due to resistance. High temperature can be decreased by installing the mounts with PV modules a few inches off the roof to allow a natural airflow to cool the panels. overheated solar panel

See →overheated solar module.

overload

See →power overload.

overload protection

A protection by means of safety devices, such as fuses and circuit breakers, against overcurrent that can possibly lead to overheating, damage of equipment, short circuit, and fire. Overload protection devices are designed to stop the flow of current, when it overloads the circuit.

overnight charging

See →Level 1 charging station.

overvoltage

A voltage that exceeds the normal operating voltage in an electrical system. It may be caused by lightning surges, sudden reduction in heavy loads, switching surges, or equipment failure.

overvoltage protection

A circuit that protects an electrical system from damage due to excessive voltage, which may be caused by lightning surges, sudden reduction in heavy loads, switching surges, equipment failure, and many others. Electrical devices, such as fuses, surge protectors, varistors, surge arresters, or lightning arresters, provide protection against overvoltage.

516 

 own electricity

own electricity

See →energy independence.

own power

See →energy independence.

oxidation

Is a chemical reaction that is characterized by the loss of electrons, gain of oxygen, and loss of hydrogen. The opposite reaction →reduction is the other half of the oxidation reaction because they always occur together and complement each other. See also →reduction–oxidation reaction.

oxidation–reduction reaction

Also known as redox reaction. This is a chemical reaction in which there is a simultaneous transfer of electrons between chemical species (atoms, molecules, or ions). The redox reaction involves two half-reactions: oxidation and reduction. Oxidation is a chemical reaction that is characterized by the loss of electrons, gain of oxygen, and loss of hydrogen. The opposite reaction “reduction” is characterized by the gain of electrons, loss of oxygen, and gain of hydrogen. Oxidation and reduction always occur together and complement each other. The same electrons that are lost in the oxidation reaction are gained in the reduction reaction. The easily remembered acronyms for these opposing chemical reactions are: LEO standing for “loss of electron is oxidation” and GER standing for “gain of electron is reduction.” For instance, when a lead-acid battery is being discharged, it is converting chemical energy into electrical energy. It is a spontaneous redox reaction producing new electrons and thus generating the electricity to supply external electrical devices. The negative electrode/plate (anode) covered with lead is being oxidized, releasing two electrons. Two electrons are flowing from negative to positive terminal, supplying on its way the external load with electricity, and reentering the battery through the positive electrode. The positive electrode/plate (cathode) covered with lead dioxide is being reduced in the process. Lead (Pb) loses two electrons and lead dioxide (PbO2) receives those same two electrons. During the discharge process, both electrodes become coated with lead sulfate, the sulfuric acid (H2SO4) electrolyte is used up, and water is produced. When the lead-acid battery is being recharged, it is converting electrical energy into chemical energy, and the

oxide 

 517

chemical reactions are reversed. The electrons are flowing in the opposite direction, from positive to negative terminal. Now, the positive electrode/plate (cathode) covered with lead dioxide (PbO2) is being oxidized, losing two electrons, whereas the negative electrode/plate (anode) covered with lead (Pb) is being reduced, gaining those same two electrons. During the recharge process, the lead sulfate coating on the electrodes is removed, the lead and lead dioxide regenerated, the water is used up, and the sulfuric acid (H2SO4) is produced. The battery is recharged and ready to be used again. oxide

A compound formed between a chemical element and oxide.

oxide layer

A thin layer of oxide that is deposited on the surface of a wafer. The thinner the surface oxide layer the better the electrical conductivity of the silicon nanowires.

oxygen

A colorless, tasteless, odorless, reactive gas that makes up 21% of the atmosphere. People, animals, and plants need oxygen to live.

ozone

(O3) Trioxygen. A gas molecule consisting of three oxygen atoms. Ozone occurs naturally in the middle layer of the atmosphere, the stratosphere, right above the troposphere and below the mesosphere. This “good” ozone in the stratosphere protects life on Earth by absorbing the harmful ultraviolet (UV) radiation coming from the sun. However, when in the troposphere, which is a natural habitat of all living things, the sunlight hits other pollutants, such as carbon monoxide coming from vehicle exhaust and other emissions or volatile organic compounds (VOCs) coming from industrial processes, it triggers the chemical reactions creating ozone. This “bad” ozone near the Earth’s surface is harmful to humans, animals, and plants when it reaches unhealthy levels. That is why ozone is considered the third most important greenhouse gas after carbon dioxide (CO2) and methane (CH4). Serious efforts have been made by many cities and communities to reduce ground-level ozone by encouraging the following practices: Conserving energy at home and at work, buying ENERGY STAR-labeled home or office appliances, carpooling, using public transportation, biking, and many others.

518 

 ozone hole

ozone hole

A large area of the ozone layer in the stratosphere over Antarctica and a smaller one over the Arctic that is depleted of ozone. Seasonal thinning of the ozone layer over Antarctica occurs every year between September and December, when ~50% of ozone is destroyed. The annual depletion of ozone is caused by certain man-made chemicals, chlorofluorocarbons (CFCs), nitrogen oxides (NO2), and other pollutants. Less ozone in the stratosphere means that more harmful ultraviolet (UV) rays will pass through and reach the Earth’s surface. The increased levels of UV radiation trigger a whole series of serious negative effects on all living creatures and the entire environment, ranging from increased sunburns, eye cataracts, skin cancers, over decreased yields of crops and seafood, to increased smog and acid rain, just to name a few. The ozone hole can be reduced by phasing out of ozone-destroying chemicals, such as chlorofluorocarbons (CFCs) and nitrogen oxides (NO2).

ozone layer

Is a layer in the stratosphere encompassing the region between about 10 and 50 km (about 6 and 31 miles) above the surface. The ozone layer functions as a protective shield around the Earth against the harmful ultraviolet (UV) radiation coming from the sun. In the past 50 years, the ozone shield has been gradually depleted by certain man-made chemicals, predominantly chlorofluorocarbons (CFCs) and nitrogen oxides (NO2). The result is the thinning of the ozone layer that has reached some alarming dimensions in the region above Antarctica. The area of the deteriorated ozone layer is called ozone hole. The ozone hole can be reduced by phasing out of ozone-destroying chemicals, such as chlorofluorocarbons (CFCs) and nitrogen oxides (NO2).

ozone pollution

Ozone is not a straightforward pollutant, since it is not directly emitted into the atmosphere like carbon dioxide (CO2) and methane (CH4). However, when the sunlight hits other pollutants, such as carbon monoxide coming from vehicle exhaust and other emissions or volatile organic compounds (VOCs) coming from industrial processes, it triggers the chemical reactions creating ozone. This “bad” ozone near the Earth’s surface in the troposphere is harmful to humans, animals, and plants when it reaches unhealthy levels.

p– region 

P

 519

p– region

Region that is characterized by low doping concentration in a p-type semiconductor.

p/n junction

See →p–n junction.

p+ region

Region that is characterized by high doping concentration in a p-type semiconductor.

packing density

Also known as packing factor. The ratio of the total area of the PV cells to the total area of the PV module. The packing density has a direct impact on the power output of the PV module. When assembled into a panel, round solar cells or monocrystalline square cells with missing corners have more waste gaps between wafers than square cells. Polycrystalline square cells can be efficiently assembled together with the minimum space left between them. Accordingly, the round solar cells have a small packing density, whereas the square solar cells are characterized by a high packing density. The higher the packing density the larger the surface area of a solar module that actively absorbs the solar radiation, and thus the higher the power output of the solar module. The packing density or factor can also refer to the ratio of the total area of the photovoltaic array (module area) to the total land area.

packing factor

See →packing density.

panel

See →solar panel.

panelboard

See →distribution panel.

paper photovoltaic cell

Highly flexible photovoltaic cells that are easy and cheap to produce; however, they demonstrated a very low energy conversion efficiency. See also →photovoltaic printing.

paper photovoltaic module

Highly flexible solar module consisting of →paper photovoltaic cells.

paper photovoltaic panel

Highly flexible solar panel consisting of →paper photovoltaic cells.

520 

 paper photovoltaic technology

paper photovoltaic technology

Photovoltaic printing, highly flexible photovoltaic cells that are easy and cheap to produce; however, they demonstrated a very low energy conversion efficiency.

paper photovoltaics

See →paper photovoltaic technology.

paper PV cell

See →paper photovoltaic cell.

paper PV module

Highly flexible photovoltaic module consisting of →paper photovoltaic cells.

paper PV panel

Highly flexible photovoltaic panel consisting of →paper photovoltaic cells.

paper PV technology

Photovoltaic printing, highly flexible photovoltaic cells that are easy and cheap to produce; however, they demonstrated a very low energy conversion efficiency.

paper solar cell

Highly flexible solar cells that are easy and cheap to produce; however, they demonstrated a very low energy conversion efficiency. See also →photovoltaic printing.

paper solar module

Highly flexible solar module consisting of →paper photovoltaic cells.

paper solar panel

Highly flexible solar panel consisting of →paper photovoltaic cells.

paper solar technology

Photovoltaic printing, highly flexible solar cells that are easy and cheap to produce; however, they demonstrated a very low energy conversion efficiency.

parabolic cooker

Solar cooker with a parabolic mirror that concentrates sunlight onto a cooking pot.

parabolic dish

Solar parabolic dish with mirrors that collects and focuses the sun’s rays onto a →receiver. See →Dish–Stirling system.

parabolic dish collector

See →parabolic dish.

parabolic mirror

A curved, concave mirror that has a shape of a parabola. It is used in →concentrating parabolic troughs or →parabolic cookers to collect and focus the sun’s rays onto a target point.

parabolic reflector

See →parabolic mirror.

parabolic solar cooker

A →solar cooker that uses a →parabolic mirror or parabolic mirrors to focus the sun’s rays onto a cooking pot.

Parabolic Trough

parabolic solar cooker 

 521

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 parabolic solar stove

parabolic solar stove

A type of solar cooker consisting of a parabolic reflector that concentrates sunlight onto the cookware positioned at the focal point. As parabolic solar stoves can quickly reach a high temperature of 450  °F (232  °C), they are suitable for rapid cooking, such as grilling, frying, boiling, and steaming.

parabolic trough

U-shaped large mirrors that focus the sun’s rays onto a black absorber tube running the length of the trough (see the figure on page 521).

parabolic trough collector

(PTC) See →parabolic trough solar collector.

parabolic trough concentrator

(PTC) See →parabolic trough solar collector.

parabolic trough power plant

US Parabolic troughs or U-shaped large mirrors focus the sun’s rays onto a black tube running the length of the trough. They are usually oriented on a north–south horizontal axis. The concentrated sunlight heats a →heat transfer fluid in the black absorber tubes, usually synthetic oil, reaching a temperature of about 400 °C (752 °F). The oil is then circulated through the insulated pipe system to a heat exchanger converting water to steam. Finally, the steam turbine generates electricity. In order to postpone the generation of electricity, the heat from the thermal oil can be transferred to molten salt that is utilized as storage medium. Later, when sun is not shining and electricity is needed, the stored heat can be taken from the tanks of molten salt and used for vapor production and consequently power generation. Power lines

Steam condenser Thermal storage tanks Receiver tube

Generator Turbine

Parabolic Trough Power Plant

Parabolic trough

parabolic trough power station 

 523

parabolic trough power station

UK See →parabolic trough power plant.

parabolic trough reflector

See →parabolic mirror.

parabolic trough solar collector

Also known as a parabolic trough concentrator (PTC). A type of →concentrating solar collector that consists of a long parabolic mirror that concentrates the sun rays onto a black absorber tube running the length of the trough.

paraffin

A waxy, white, or colorless substance used as an energy storage medium for solar applications. Excess energy generated by solar panels can be stored in water tanks containing paraffin. As paraffin is warmed up by hot water, it stores the thermal energy. The stored energy is released by running cold water through the system. The thermal energy storage capacity of paraffin can be increased by addition of nanomagnetite particles.

paraffin wax

See →paraffin.

parallel circuit

A circuit in which components are connected side by side. See also →parallel connection.

parallel connection

One of the two main connection types for solar panels or batteries is parallel connection, in which components are connected side by side (+ to + to + on one side and – to – to – on the other side). When batteries are connected in parallel, the voltage remains the same, but the capacity of each battery is added together.

parallel connection of solar cells

If solar cells are connected in parallel, the voltage remains the same across cells, but the capacity is added together.

parallel to the roof

A conventional on-roof installation technique for placing solar panels parallel to the roof. In order to properly align panels with the roof, tools like →angle finder or →protractor are used as well as a PV-mounting system consisting of →aluminum rails, →mounting clamps, →mounting brackets, and →standoffs.

parallel wiring

A circuit in which components are connected side by side. See →parallel connection.

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 parallel-flow heat exchanger

parallel-flow heat exchanger

A type of liquid–liquid heat exchanger in which both working fluids flow in the same direction. The major drawback of a parallel-flow heat exchanger is that the large temperature difference at the ends leads to large thermal stresses. See also →counter-flow heat exchanger.

parasitic resistance

Resistive forces in a PV cell, such as →series resistance and →shunt resistance, which oppose the free flow of electrons through the semiconductor and dissipate electric current across internal resistances. The series and shunt resistances can significantly reduce the →fill factor and thus the power output of a →solar cell.

partial load

See →partial-load operational range.

partial shading

See →partial shading of a solar module and →partial shading of photovoltaic system.

partial shading of photovoltaic module

See →partial shading of a solar module.

partial shading of photovoltaic panel

See →partial shading of a solar module.

partial shading of photovoltaic system

Shading of one or more solar panels of a photovoltaic array, as opposed to →total shading.

partial shading of PV module

See →partial shading of a solar module.

partial shading of PV system

See →partial shading of photovoltaic system.

partial shading of solar array

See →partial shading of photovoltaic system.

partial shading of solar module

Shading of one or more solar cells of a solar module, as opposed to →total shading.

partial shading of solar panel

See →partial shading of a solar module.

partial shading of solar system

See →partial shading of photovoltaic system.

partial solar eclipse

A phenomenon in which the solar disk is only partially obscured by the passage of the Moon.

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partial zero-emission vehicle

(PZEV) Motor vehicles that meet SULEV tailpipe-emissions standards, have a 15 year/150,000 mile warranty, and zero evaporative emissions.

partial-load operation

See →partial-load operational range.

partial-load operational range

An operational range in which a solar system works at low or partial load conditions. As a continuous full-load operation is achieved only in a PV testing laboratory under optimal solar radiation and alignment conditions, solar systems operate largely in the partial-load operational range.

particle

A tiny speck of matter, for example, an →electron, →atom, or →molecule.

particle accelerator

Also known as a cyclotron. A device in which charged particles or source ions are accelerated by an electric field to very high speeds and energies. The energized and accelerated ions are used to bombard the target material in a vacuum chamber.

particle bombardment

The subjecting of a target material to bombardment by high-energy particles, such as ions, atoms, or neutrals. Particle bombardment is used in the →ion beam etching process in which high energy ions bombard the target semiconductor surface in a vacuum chamber, ejecting atoms and molecules and thus removing material from the substrate following the mask template. In an →ion beam deposition process, the particle bombardment is employed to sputter the target material and then deposit the ejected material particles onto the heated substrate.

Pascal

(Pa) Unit of pressure that equals 1 N/m2.

passage

Flow of fluid.

passivated contact

A contact that is coated with a thin oxide layer, for example, silicon dioxide (SiO2), to increase the efficiency solar cells. The passivation of contacts significantly reduces the surface recombination at the metal–semiconductor interface, while maintaining a good electrical contact.

passivation

A process of coating the front surface of a photovoltaic cell with a thin oxide layer, typically silicon dioxide (SiO2), in order to reduce the chemical reactivity of the surface. As

526 

 passivation layer

a dynamic surface →recombination leads to current and voltage losses, the passivation has become an integral part of the semiconductor manufacturing process. passivation layer

Protective coating against corrosion obtained by chemical passivation.

passive

Passive heating and cooling techniques use the processes of natural cooling and heating without moving parts, motor-driven systems, or electrical devices.

passive building

Energy-efficient building standard that keeps the house warm in winter and cool in summer without electrical devices. See →passive solar building design.

passive cooling

Includes all techniques that prevent a house from gaining heat and enhance heat loss. Passive cooling uses the processes of natural cooling without moving parts, motor-driven systems, or electrical devices. →deep eaves, →awnings, →vertical fins, →light shelves, and →deciduous trees shade windows and house walls from the blazing sun as it climbs higher in the sky in the summer. Thick walls and good thermal insulation is another passive cooling technique that reduces the heat gain in the house. Also, well-insulated, thick walls can be cooled at night by the circulation of the cold air from outside. The cold walls will retain nighttime coolness during the day, reducing air-conditioning usage. Heat can also be removed from the interior of the building by a cross-ventilation system. It is a natural way to cool a home by regulating airflow through the building with a help of an optimal arrangement of windows and vents. This natural ventilation technique reduces the use of air conditioners, which in turn results in decreased energy consumption, lower energy bill, and less carbon emissions. Another efficient way to reduce heat gain is the control of internal heat-emitting sources such as appliances and lights. To name just a few techniques: replacing traditional incandescent bulbs with LED light bulbs that emit much less heat, relocating some of the appliances to basement, garage, or storage room, and turning off unused appliances such as flat-screen TV or desktop computer will all lower the heat gain in the house.

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passive cooling strategies

See →passive cooling techniques and →passive cooling.

passive cooling techniques

Include all strategies aimed at minimizing heat gain (e.g., →deep eaves, →awnings, →vertical fins, →light shelves, →sun protection glass, →deciduous trees) and maximizing heat loss (e.g., →cross ventilation, →solar chimneys, →draft).

passive home

See →passive house.

passive house

An energy-efficient building standard that focuses on conserving energy through thick insulation, airtightness, ventilation, the choice of energy-efficient materials, and solar radiation and thermal control, including the essential part of a passive house: the architecture of high-performance windows. The passive house design, which was originally invented in Germany in the 1980s, can reduce energy consumption by up to 80%.

passive house design

See →passive solar building design.

passive solar building

See →passive solar house.

passive solar building design

Passive solar building design is an energy-efficient building technique that keeps the house warm in winter and

Summer

Winter Solar thermal collectors

Roof windows vent warm air in summer

Summer

Winter

Thermal-mass back wall stores the sun’s heat Radiant heat

Solar hot water storage tank Thermal-mass floor stores the suns’s heat

Passive Solar Building Design

528 

 passive solar building design

cool in summer. It is called passive because the heating and cooling take place in a natural way, without moving parts, motor-driven systems, or electrical devices. A house is designed to make the most of the sun’s heat by admitting it through large south-facing windows in winter and keeping it in with good insulation. Solid floors made of stone, concrete, brick, or ceramic tile absorb and store the solar energy during the day, and radiate the heat during the night, when the outside temperature drops. Deep eaves, awnings, and deciduous trees shade windows and house walls from the blazing sun as it climbs higher in the sky in the summer. Well-insulated, thick walls are cooled at night by circulating the cold outside air through the house by an efficient ventilation system. The cold walls will retain nighttime coolness during the day, reducing air-conditioning usage. passive solar cooling

See →passive cooling.

passive solar design

See →passive solar building design.

passive solar element

An element of the building, such as a south-facing →Trombe wall, which collects, stores, and distributes solar energy into interior spaces of the house, reducing heating costs and greenhouse gas emissions at the same time.

passive solar energy

See →passive solar energy system and →passive solar heating.

passive solar energy system

Unlike →active solar energy systems employing electrical devices and motor-driven systems, passive solar energy systems are able to heat and cool buildings without the use of electrical equipment.

passive solar energy use

The use of solar energy without electrical equipment. See →passive solar heating, →passive solar cooling, and →passive solar building design.

passive solar energy utilization

See →passive solar energy use.

passive solar gain

Uses south-facing windows and walls, for example, →Trombe wall, to convert sunlight to heat and spread the absorbed thermal energy throughout the building, as opposed to active solar gain that utilizes photovoltaic modules to generate electricity. See also →solar heat gain.

passive solar greenhouse

Use of the sun instead of an artificial heat source.

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passive solar heat

Solar heat generated without the use of electrical equipment.

passive solar heating

Passive solar heating techniques use the processes of natural heating without moving parts, motor-driven systems or electrical devices. These heating techniques have been around for thousands of years. The old Greek, Roman, and Anasazi cultures built their houses facing south to maximize the solar gain in winter months and constructed overhangs to minimize the heat in summer months. The insulation, thickness of walls, size of windows, material used, and type of roofs all play a significant role in effectiveness of a passive solar heating system. Modern examples illustrating a passive solar heating structure would be →Trombe wall, →sunroom, →transparent thermal insulation, or greenhouse.

passive solar heating system

See →passive solar heating.

passive solar home

See →passive solar house.

passive solar house

Energy-efficient building standard that keeps the house warm in winter and cool in summer without electrical devices. See →passive solar building design.

passive solar retrofit

The integration of 1) passive cooling installations, such as →deep eaves, →awnings, →vertical fins, →light shelves, →sun protection glass, →deciduous trees, or 2) passive heating installations, such as →Trombe wall, →sunroom, or greenhouse, into existing structures, for example, house or yard.

passive solar tracker

A tracker that uses heating and cooling of refrigerant-like liquid/gas elements and reflective mirrors to track the motion of the sun across the sky during the day. Passive trackers are less accurate than motor-powered and computer-navigated active trackers.

passive solar water heating system

Passive solar water heating systems, such as →integral collector storage systems and →thermosiphon system, do not employ a controller, a pump, a heat exchanger, and other electrical equipment to circulate water through the system. Instead, they use the principle of natural →convection to transport the heated water from the collectors to the

530 

 passive stack ventilation

storage tank. The storage tank is typically mounted on a house’s roof above the solar collectors, so that warm, lighter water can naturally rise from the collectors into the tank and cooler water can sink down to the bottom of the collector. See also →active solar heating system. passive stack ventilation See →stack ventilation. passive system

See →passive solar energy system.

patterning

A photolithographic method in which geometric patterns are generated on a physical or digital photomask, which are then projected onto a photosensitive surface of the wafer, usually a →photoresist coating.

payback formula

A formula that is used to calculate the payback period for a photovoltaic system. According to a simple payback formula, the payback period equals total system cost (initial investment) divided by the value of electricity generated and by the annual electricity usage.

payback period

The period of time it takes for a solar system to pay back its initial cost.

payback time

See →payback period.

PC

Abbreviation for →polycarbonate.

PCE

Abbreviation for →power conversion efficiency.

PCM

Abbreviation for →phase-change material.

PCS

Abbreviation for →power-conditioning system.

PCSC

Abbreviation for →point-contact solar cell.

p-doped region

See →p-doped semiconductor layer.

p-doped semiconductor layer

A positively doped region of a semiconductor that regulates the movement of holes in the →valence band. The flow of electric charge in a →solar cell resembles a counterflow heat exchanger in which two working fluids (hot and cold) flow through two different pipes in opposite directions. The chemical process called →doping determines the flow direction. The semiconductor layer doped with p-type dopants, such as →boron atoms, regulates the flow of →holes along the valence band only in one direction, while the semiconductor layer doped with n-type dopants,

p-doping 

 531

such as →phosphorus atoms, allows the flow of electrons only in the opposite direction. In a nutshell, every solar cell acts as a →p–n junction diode or an electrical one-way valve that passes current in only one direction. The interplay of this bidirectional movement driven by the attraction between the opposite positive and negative charges produces a current flow in a photovoltaic cell. p-doping

A chemical process in which a semiconductor layer is doped with p-type dopants, such as →boron to increase the conductivity of pure silicon semiconductor and determine the flow direction of →holes.

peak consumption

See →peak load.

peak demand

See →peak load.

peak demand-load

See →peak load.

peak electrical demand

See →peak load.

peak hours

The hours of high energy demand when utilities sell electricity at higher rates than during the hours of low energy consumption (off-peak time).

peak kilowatt

One thousand peak watts (1,000 Wp).

peak kilowatt-hour

The most expensive kilowatt-hour (kWh) electricity rate during the hours of high energy demand (peak hours).

peak load

The maximum amount of electrical power demanded by utility customers (commercial and residential sector) usually between late in the morning and early evenings. Solar systems can help a local utility company meet the peak load and provide inexpensive electricity when it is most needed and most valuable to the electrical grid.

peak load-demand

See →peak load.

peak megawatt

One million peak watts (1,000,000 MWp).

peak output

Stands for a maximum energy output generated by a photovoltaic system under optimal conditions – full solar radiation averaging 1,000 W/m2 (1 kW/m2) and 25°C.

peak period

See →peak hours.

peak power

The maximum amount of electricity that a solar panel can generate under optimal standard test conditions – full solar

532 

 peak power current

radiation. Peak power of a solar module is determined by measuring current and voltage while varying the resistive load. peak power current

The current (amperage) generated by a solar panel operating at the maximum power point on the →I–V curve and consequently producing the maximum power output.

peak power point

Maximum operating point that is a product of the greatest voltage value (VMPP, →Maximum Power Point voltage) and the greatest current value (IMPP, →Maximum Power Point current) on the →I–V curve for a photovoltaic cell or module.

peak power rating

The maximum amount of electricity that a solar panel or an inverter can generate under optimal standard test conditions – full solar radiation. Each manufacturer’s data sheet specifies the “rated” amount of power (kWp – kilowatt-peak) a PV device will generate.

peak power tracker

Is an algorithm/microprocessor that tracks the peak power point of a solar module to maximize PV module performance. It also serves to control battery float voltage, thereby protecting the battery from high voltage and improving battery life. This DC/DC converter steps the higher PV module voltage down to the charging voltage of the battery.

peak power tracking

Monitors the peak power point (optimal voltage and current) to maximize photovoltaic module performance and to step the higher PV module voltage down to the charging voltage of the battery.

peak sun

Peak sun is equivalent to 1,000 W/m2.

peak sun hours

(PSH) Also known as full sun hours or even perfect sun hours. Refers to the average daily solar insolation, a number of hours of full sunlight (1,000 W/m2 or 1 kW/m2) that a solar system receives per day. The full sun hours can be calculated by dividing the total amount of solar radiation on a given day by the amount of energy in a full sun hour. In that way, one can estimate the amount of energy expected per square meter at one’s location. Whereas the rainy Seattle in Washington has a year-round average of 3.57 full sun hours, the sunny Phoenix in Arizona has 6.58

peak time 

 533

full sun hours available per day. Peak sun hours for a specific region are measured in kW/m2/day and can be found in solar maps and tables. peak time

See →peak hour.

peak watt

Also known as watt peak (Wp). Measurement unit for the capacity (nominal output) of solar cells and solar modules. It stands for peak power, a maximum energy output generated by a photovoltaic system under optimal conditions – full solar radiation averaging 1,000 W/m2 (1 kW/m2) and 25°C. Each manufacturer’s data sheet specifies the “rated” amount of power a PV device will generate.

peaker

See →peaking power plant.

peaking power plant

Also known as a peak-load power plant or peaker. A power plant that only operates during times of high demand. Solar energy as a peaking resource can potentially replace gas-fired peaker plants.

peak-load power plant

See →peaking power plant.

PEC

Abbreviation for →photoelectrochemical cell.

PECVD

Abbreviation for →plasma-enhanced chemical vapor deposition.

PEDOT:PSS

The conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) commonly utilized as an anode in thin-film →organic photovoltaic cells.

pedotransfer function

A mathematical model that allows estimating soil hydraulic properties from soil data.

peel-and-stick photovoltaic cell

See →peel-and-stick solar cell.

peel-and-stick photovoltaic laminate

See →peel-and-stick solar module.

peel-and-stick photovoltaic module

See →peel-and-stick solar module.

peel-and-stick photovoltaic panel

See →peel-and-stick solar module.

peel-and-stick PV cell

See →peel-and-stick solar cell.

534 

 peel-and-stick PV laminate

peel-and-stick PV laminate

See →peel-and-stick solar module.

peel-and-stick PV module

See →peel-and-stick solar module.

peel-and-stick PV panel

See →peel-and-stick solar module.

peel-and-stick solar cell

A flexible, lightweight solar cell that literally acts as a sticker: A protective sheet is peeled away from the adhesive backing that can be stuck onto various surfaces, such as shingles, metal, or glass. Due to the ease of installation, the “peel-and-stick” technology promises to take →building-integrated photovoltaics to the next level.

peel-and-stick solar laminate

See →peel-and-stick solar module.

peel-and-stick solar module

A flexible, lightweight solar module that can be adhered per “peel-and-stick” application to various surfaces, such as shingles, metal, or glass. The major advantage of this panel technology is the ease of installation that can combine the uncomplicated “peel-and-stick” application with the simplified →plug-and-play PV system installation technology. Another important cost-saving factor is the fact that peel-and-stick solar panels eliminate the need for expensive PV-mounting systems.

peel-and-stick solar panel

See →peel-and-stick solar module.

PEHD

Abbreviation for polyethylene high-density. See →highdensity polyethylene (HDPE).

pellicle interferometer

A membrane interferometer that uses an imaging method for a simultaneous measuring of microfluidic pressure and flow rate.

Pelton turbine

Is an impulse turbine driven by high-velocity jets of water. It is used in micro-hydrosystems to tap the kinetic energy of falling water and convert it into electricity.

Pelton wheel

See →Pelton turbine.

penetration depth

Indicates how deep an electromagnetic wave can penetrate into a material.

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 535

percent possible sunshine

The ratio of actual →bright sunshine to the total possible bright sunshine per day in a given geographic region, expressed as a percent. For instance, on a mainly sunny day with some afternoon clouds, the ratio can be expressed as 75% of possible sunshine.

perfect sun hours

(PSH) See →peak sun hours.

performance ratio

(PR) Also known as quality factor. The ratio between →actual yield, which refers to the actual power output on the AC side of a photovoltaic system, and →target yield, which refers to the maximal power output on the DC side of the photovoltaic system, under optimal standard test conditions as specified by the PV manufacturer.

performance warranty

A contract between the manufacturer and the customer in which the manufacturer guarantees a specific power output and performance of a solar product over the course of time, for example, usually 25 years for a silicon photovoltaic module. For each year of the lifetime of a solar module, the performance warranty gives the product user a defined power output value, allowing them to calculate their solar yields in advance.

permanent magnet alternator

(PMA) An alternator in wind turbines that utilizes moving permanent magnets instead of electromagnets to induce electric current in coils of wire. The PMA is a preferable alternative to the traditional induction motor.

permanent shading

Permanent shading is caused by physical obstacles, such as trees, neighboring houses, vents, chimneys, and equipment, casting an enduring shadow on the panels. The permanent shading can be divided into partial and total shading. As the name suggests, partial shading exists when only one part of the solar system is shaded, while the other part can still generate electricity or heat. In case of total shading, either the obstacles such as trees or shrubs should be removed, and if that is not an option, the entire solar installation should be moved to another site. See also →temporary shading.

permittivity

The measure of how much resistance is encountered in a material under the influence of an electric field. It is the ratio of the electric displacement in the material to the applied field strength. Permittivity is usually expressed in farads per meter (F/m).

536 

 perovskite

perovskite

A natural mineral composed of calcium, titanium, and oxygen (CaTiO3) and named after a Russian mineralogist Lev Aleksevich von Perovski.

perovskite cell

See →perovskite photovoltaic cell.

perovskite crystal

A CaTiO3 crystal displays a cubic structure with a calcium atom in the center, titanium atoms at the corners, and oxygen atoms at the midpoints of the edges.

perovskite photovoltaic cell

A photovoltaic cell that includes a perovskite material with a cubic crystal structure. Perovskite structure comprises a large family of compounds that have the same type of crystal structure as perovskite (CaTiO3). The perovskite material is characterized by a high level of light absorption, electrical conductivity, and long operation lifetime. Recent hybridization and continuous research efforts, such as the development of multijunction perovskite-based solar cells, have elevated perovskite PV cells from a low-performance to a high-performance technology over the past 7 years. In 2016, the energy conversion efficiency of perovskite solar cells reached 22%. As high-performance perovskite cells can be made from low-cost polycrystalline halide perovskites (CH3NH3 PbI3) and a very thin film of semiconductor material of approximately 400 nm suffices to be deposited onto a substrate, perovskite PV cells promise to become a low-cost, industry-scalable solar technology in years to come. Due to the extremely thin light-absorbing layer, perovskite solar cells can also be incorporated into windows.

perovskite PV cell

See →perovskite photovoltaic cell.

perovskite solar cell

(PSC) See →perovskite photovoltaic cell.

perovskite structure

Any compound that has the same type of crystal structure as the perovskite mineral calcium titanium oxide (CaTiO3). The chemical formula is often written as ABX3, where “A” and “B” are →cations and “X” is an →anion.

perovskite superconductor

Superconductor that includes a perovskite material, CaTiO3.

perpendicular lines

Two or more lines that are at right angles or 90° to each other.

personal electric vehicle 

 537

personal electric vehicle

A small, low-speed electric vehicle for one, two, or four persons, usually powered by several 12 V batteries located under the seat. Personal electric vehicles are typically used as golf course carts, hotel or apartment complex maintenance crew transportation, or neighborhood or recreational transportation with an electric driving range of 25–50 miles. Personal electric vehicle is an emission-free transportation whose batteries can be charged by solar panels.

PET

Abbreviation for →polyethylene terephthalate.

PET bottle

Bottle made of polyethylene terephthalate that is used for →solar water pasteurization. See also →SODIS bottle.

PET substrate

A →substrate made of →polyethylene terephthalate material upon which other →organic photovoltaic cell layers are deposited.

PETE

Abbreviation for →photon-enhanced thermionic emission or →polyethylene terephthalate.

phantom load

See →standby power.

phase change

A change from one state, for example, solid, liquid, or gas, to another without a change in chemical composition.

phase transformation

Transformation from the liquid or gaseous phase to the solid phase. An important part of thin-film growth process in which a substance, gas in →chemical vapor deposition (CVD), is converted into small nanosized liquid droplets that condense onto the substrate, forming a crystalline solid capable of growing. Therefore, the phase transformation includes two processes: →nucleation and growth.

phase velocity of a wave The rate at which the phase of an electromagnetic wave propagates in space. phase-change material

(PCM) A material that absorbs and releases thermal energy during the process of melting and solidifying. Phase change materials, such as salt mixtures or paraffin waxes, are capable of storing large amounts of thermal energy in relatively small volumes. Due to their favorable characteristics, various types of salt mixtures have found a broad application in large-scale concentrated solar power (CSP) plants as an ideal heat storage medium. See also →molten salt.

538 

 PHES

PHES

Abbreviation for →pumped hydroelectric energy storage.

phonon

A quantum of sound or vibrational elastic energy in a crystal lattice or solid.

phonon polariton

A coupled state between a →phonon and a →photon.

phosphine

(PH3) n-Type dopant for silicon semiconductor manufacture. During the silicon cell production, the n-type dopant atom, phosphorus, is typically added by diffusion of phosphine gas. As phosphine is a flammable and extremely toxic gas, accidental releases can pose a serious health hazard to employees working in a photovoltaic plant and even to persons living near a PV plant.

phosphorous compound UK See →phosphorus compound. phosphorus

(P) Nonmetallic chemical element with atomic number 15 that has five electrons in its outer shell. Phosphorus often acts as an →n-type dopant atom that is inserted into a pure semiconductor, silicon, in order to modify its electrical properties. During the silicon cell production, phosphorus is typically added by diffusion of phosphine gas. This so-called impurity disturbs the octet stability in the semiconductor silicon lattice, in which each silicon atom is surrounded by four other silicon atoms and has eight electrons in the outer valence shell. The intentional incorporation of a dopant atom, phosphorus in this case with five electrons in the outer orbital, will create a disturbance in the pure semiconductor silicon lattice order, leading to the free movement of the liberated fifth electrons across the crystal lattice and thus production of electric current.

phosphorus compound

US Phosphorus compounds, such as →indium and →phosphorus, are used as semiconductor materials in the manufacture of solar cells.

phosphorus-doped diffusion paste

An n-type doping paste for solar cells that can uniformly diffuse →phosphorus onto the silicon surface.

photoactive absorber layer

The thickest silicon layer of a solar cell, also known as a base layer, in which the absorption of photons of light occurs, raising electrons to a higher energy state. The minimum photon energy required to induce photoconductivity and generate mobile electrons and holes is 1.1 eV. With this amount of energy, the excited electrons are

photoactive layer 

 539

able to bridge the →band gap and start the electric current flow along the →conduction band and further through an outside circuit. This p-type semiconductor layer is doped with →boron atoms, which have a lack of electrons, creating holes in the →valence band that carry a positive charge. photoactive layer

See →photoactive absorber layer.

photoactive material

A photosensitive semiconductor material, such as →silicon, which is responsive to light and able to absorb a certain range of electromagnetic radiation, converting photons to electrons and thus generating a current flow.

photocatalytic water splitting

A process of hydrogen generation by means of water splitting over semiconductor photocatalysts. The splitting of water into its integral parts hydrogen and oxygen by using solar energy is a clean and environmentally friendly way to produce hydrogen.

photochemical effect

A chemical reaction produced by ultraviolet (UV), visible light, or infrared (IR) radiation.

photocurrent

An electric current (stream of electrons) produced by a →photoelectric or a →photovoltaic effect.

photodetector

See →photosensor.

photoelectric

Relating to the ejection of electrons from a semiconductor surface and an increased electrical conductivity caused by light.

photoelectric cell

A device that produces an electric current by the action of light. See also →solar cell.

photoelectric effect

A phenomenon in which a high-frequency light (e.g., ultraviolet light) falling on a surface (semiconductor material) can cause electrons to be ejected and thus a current to flow.

photoelectric emission

See →photoemission.

photoelectrochemical cell

(PEC) A solar cell type that directly utilizes the electrical current generated within a cell to produce hydrogen by splitting water into →hydrogen (H2) and →oxygen (O2) gases.

photoelectrons

An electron ejected from a solid surface by an incident photon of light.

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 photoemission

photoemission

Also known as photoelectric emission. The emission of electrons from atoms or molecules of a solid surface when photons of light hit them.

photoemitter

Radiation-emitting semiconductor.

photoemitter film

See →photoemitter layer.

photoemitter layer

Also known as a photoemitter film. A thin layer of photoemitter that is formed by deposition of radiation-emitting semiconductor materials on a substrate. The photoemitter film is a porous flexible element with low density between 5% and 20% of its constituent material in bulk form.

photoexfoliation

A method for graphene production in which short laser pulses are used to detach intact graphene monolayers from a graphite surface. Tuning the laser energy density allows for a precise patterning of graphene.

photogalvanic cell

A cell that converts the energy obtained from the sun directly into electrical energy. See →solar cell.

photolithographic mask A template that consists of a transparent substrate on which layout patterns are written. In a typical photolithographic process, the photolithographic mask is positioned between a source of light and a semiconductor wafer. When the light illuminates the mask, it projects the geometric patterns onto a photosensitive surface of the wafer, usually a →photoresist coating. After the patterns are written in the photoresist layer, the desired template is etched into the substrate material by applying a →wet etching or a →dry etching method. photolithographic method

Two major photolithographic methods are mask-based lithography and →maskless lithography. In a mask-based or deposition-through-mask method, the substrate is coated with a photoresist layer. The ultraviolet light is projected through a patterned photomask onto the photoresist film, forming a mask pattern. The area without the pattern is etched by applying a →wet etching or a →dry etching method. One major disadvantage of the mask-based method is the inflexibility of the fixed master photomask. In contrast, in maskless photolithography, no permanent, fixed mask is needed as pattern information is stored

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digitally and can be easily modified from one run to another. The programmable photomask reduces manufacturing costs because the production of expensive masks is not required and new mask designs can be generated significantly faster. photolithographic process

In a photolithographic process, a source of light illuminates the photolithographic mask, projecting the geometric patterns onto a photosensitive surface of the wafer, usually a →photoresist coating. After the patterns are written in the photoresist layer, the desired template is etched into the substrate material by applying a →wet etching or a →dry etching method.

photolithographic texturing

The use of →photolithography to produce patterns on a silicon wafer material. The surface texturing, for example, the fabrication of inverted pyramidal structures on silicon, reduces the loss of solar energy through reflection and increases the amount of solar radiation that will reach the silicon absorber and be converted into electricity.

photolithography

Also known as optical lithography. In a semiconductor production, a photographic method by which geometric patterns are transferred from a photomask onto a substrate.

photoluminescence

Luminescence induced by the absorption of photons, causing an excitation of a substance to a higher energy state, and then by reradiation of photons or a return to a lower energy state.

photolysis

A chemical decomposition induced by radiation.

photomask

A mask used in →photolithography. See also →photolithographic mask.

photometer

Instrument for measuring the intensity of the light.

photon

Fundamental particle of light or electromagnetic radiation.

photon energy

The energy of a →photon which equals Planck’s constant times the frequency of the radiation: E = hf. The photon’s energy is defined by the photon’s wavelength. The shorter the wavelength, the higher its frequency, and thus the greater the energy of a photon. The minimum photon energy required to induce photoconductivity in a semiconductor and generate mobile electrons and holes is 1.1 eV.

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 photon enhanced thermionic emission

photon enhanced thermionic emission

(PETE) A solar-energy conversion method that includes both a photovoltaic process harvesting photon energy and a thermal process harvesting heat energy. This combined method, in which both light and heat generate electric current, promises to increase the conversion efficiency to above 50%.

photon flux

The number of photons hitting the surface of a solar cell per second per square meter. The photon flux is expressed by the following formula: Φ = no. of photons/s m2. This formula helps calculate photon flux and hence determine the power potential of a light source. In the analysis of photovoltaic cells, the photon flux calculation determines how many electrons can be generated for current flow.

photopolymerisation

UK See →photopolymerization.

photopolymerization

US →Polymerization brought about visible light or ultraviolet photons.

photo-polymerization

UK See →photopolymerization.

photoresist

A photosensitive, etchant-resistant polymer material that is frequently used in wafer →etching processes. When exposed to light, a template defined by a →photolithographic mask is written on the photoresist coating. The illuminated photoresist patterns solidify, forming an →etch mask resistant to the acid solution. The photoresist mask protects parts of the wafer material that should not be removed and defines at the same time the patterns of conduction paths that should be etched away.

photosensitive film

A semiconductor layer capable of absorbing incident light particles called photons. The energy of the absorbed light, so-called photon energy, knocks electrons loose, allowing them to flow freely along the →conduction band and further to an external load.

photosensitizer

Material that functions as a photochemical catalyst.

photosensor

Also known as a photodetector or light sensor. An electronic device, such as photodiode or photocell, which detects and measures light and other electromagnetic energy.

photothermic

Relating to the generation of heat by light.

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photovoltaic

(PV) Is a compound adjective consisting of two words “photo” that means light and “voltaic” denoting electric. Accordingly, photovoltaic refers to the conversion of light into electricity by using photovoltaic cells.

photovoltaic 3D printer

A special type of printer that 3D prints semiconductor materials onto a lightweight, flexible plastic film by using a liquid →solar ink. 3D printing can reduce production costs up to 50%.

photovoltaic accessories

Extra parts that make a photovoltaic (PV) system more efficient or help a PV installer or homeowner cope with a wide range of different wiring, measurement, or maintenance scenarios. Accessory parts include →photovoltaic connectors, →photovoltaic cables, data loggers, →DC combiner boxes, radiation sensors, just to name a few.

photovoltaic adhesive

See →solar adhesive.

photovoltaic appliance

See →photovoltaic device.

photovoltaic array

See →photovoltaic system.

photovoltaic awning

See →solar awning.

photovoltaic battery

Power storage for a photovoltaic system.

photovoltaic buoy

A buoy whose electrical equipment is powered by photovoltaic panels. The sun’s energy is collected by solar panels and stored in batteries during the day. At night, the navigational light is automatically turned on, showing ships and boats where they can go and warn them of danger.

photovoltaic cable

See →solar cable.

photovoltaic calculator

See →solar calculator2.

photovoltaic canopy

See →solar canopy.

photovoltaic capacity

The total amount of cumulative installed photovoltaic systems, usually expressed in gigawatts (GW), or generated photovoltaic energy over a period of time, usually expressed in gigawatts or terawatts per hour (GWh or TWh) in a specific region. For instance, in 2016, the installed global photovoltaic capacity was around 303 GW, which is equal to generating 375 TWh of solar power each year.

photovoltaic carport

See →solar carport.

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 photovoltaic cell

photovoltaic cell

Is the basic building block of a photovoltaic module that converts the sunlight into electric energy. It works on the principle of →photovoltaic effect that was first observed by French physicist Edmond Becquerel in 1839. When the sunlight strikes the photovoltaic cell, the photons eject a phosphorus valence electron from its orbital and elevate it to the conduction band of the semiconductor. What happens next is similar to the process that takes place in a game of billiards: when the white ball hits a color ball, it starts a chain reaction, passing on its energy to all other colored balls in its way. The phosphorus extra electron is passed on from one silicon atom to another throughout the crystal lattice, generating electric current. The →fingers collect the electricity generated within the photoactive silicon semiconductor and transport it to the two →busbars. The busbars then conduct the electricity to the next cell and further through the module’s circuit. This electromotive force present on the top of the cell is negative (–), driving the electrons through a load (e.g., garden lights) in the external circuit. After doing the work, powering garden lights, electric current comes back to the cell through the positive connection (+) at the bottom of the cell (e.g., aluminum layer). When the sunlight knocks loose electrons and initiates their movement in the top n-layer, it leaves empty spaces (holes) behind that gather in the p-layer at the bottom part of the cell. The electrons reentering the cell through the bottom connection occupy the holes, closing the energy circuit. The same exciton process starts all over again, generating electricity with the help of photoactive semiconductors. The type of electric current generated through this process is called direct current (DC), flowing only in one direction and typically producing the electric potential of around 0.5 V. The DC energy can be stored directly in a battery bank or converted into alternating current (AC) and used for powering electrical equipment in a building. A typical silicon PV cell consists of the following parts: a substrate, n-doped silicon semiconductor layer, p-doped silicon semiconductor layer, depletion layer, conductive lines (busbars and contact fingers), back contact, and glass cover.

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Depending on the semiconductor materials used, there are the following types of photovoltaic cells: →crystalline silicon solar cell (monocrystalline, polycrystalline), →thin-film solar cell (amorphous silicon, tandem amorphous silicon, copper indium gallium selenide [CIGS], and cadmium telluride), inorganic chemical compound cell (gallium arsenide), and organic chemical compound cell (dye-sensitized, organic polymer). photovoltaic cell efficiency

The ratio of output power (electricity) that a photovoltaic (PV) cell generates under optimal conditions (full solar radiation averaging 1,000 W/m2 [1 kW/m2]) divided by the input power, the total amount of solar energy falling on the PV cell. The cell efficiency is usually expressed in percentages. For instance, the efficiency record for the silicon solar cell in 2016 was 24%.

photovoltaic concentrator

See →photovoltaic concentrator system.

photovoltaic concentrator cell

A specially engineered photovoltaic cell that is capable of absorbing higher illumination levels, which is achieved by magnifying the intensity of solar electromagnetic radiation multiple times by means of an optical concentrator device, such as a Fresnel lens.

photovoltaic concentrator system

A photovoltaic system that uses an optical concentrator, such as Fresnel lenses or reflectors, to focus sunlight onto solar cells. Higher illumination levels magnify solar energy multiple times, resulting in higher power conversion efficiencies. The efficiency can be additionally improved by placing all the grid lines on the rear surface of the cell. Photovoltaic concentrator systems are usually mounted on →dual-axis tracking system to follow the motion of the sun across the sky at all times during that day. As concentrating optical devices are only able to absorb direct sunlight and are hardly responsive to the diffuse portion of the solar spectrum, photovoltaic concentrator systems are best suited to southern Sun Belt regions between the 35th northern and 35th southern latitudes.

photovoltaic See →photovoltaic concentrator system. concentrator technology

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photovoltaic connector

A connector that links two solar modules or other photovoltaic (PV) components together. The PV connector interlocking system typically consists of a male connector (plug) and a female connector (socket). Since 2011, →MC4 connector has become a standard PV connector in the solar market for simple and safe interconnections of PV applications, while MC3 and Tyco connectors have largely become obsolete.

photovoltaic conversion

A conversion of incident solar radiation or photons of light into two forms of energy: electricity and heat.

photovoltaic conversion efficiency

The percentage of incident solar radiation (sunlight) that is converted into electrical power by a photovoltaic cell.

photovoltaic converter

See →solar energy converter.

photovoltaic current

See →solar current.

photovoltaic data logger

Also known as a PV data logger or solar data logger. A device for measuring various parameters on-site at a solar facility, including solar irradiance, temperature, solar energy yield, electricity, and voltage. Usually, the PV data logger is equipped with a processor that sends collected data via network system to a computer. →Solar engineers, →solar architects, →solar plant operators, and →solar installers use photovoltaic data loggers to collect, measure, and monitor various data that are vital for maximum power conversion efficiency and optimal operation of the solar power plant.

photovoltaic DC circuit breaker

Also known as a solar DC circuit breaker or PV DC circuit breaker. A circuit protection component that shuts off the flow of electricity when it senses overcurrent or a short circuit. The DC circuit breaker safeguards both sides of the →charge controller, protecting wiring from potential fires in the event of unexpected controller failure. The PV DC circuit breaker can also be used as an integrated disconnect switch for various solar applications.

photovoltaic design software

See →solar design software.

photovoltaic development

Also known as solar development. In last 10 years, the photovoltaic (PV) industry has experienced rapid growth and development with 30–50% annual increasing rates.

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photovoltaic device

Also known as PV device. A device that absorbs light and converts incident photons into electrons of direct current electricity. Semiconductor materials for manufacturing PV devices include: →crystalline silicon (c-Si), →amorphous silicon (a-Si), →germanium, →copper indium gallium selenide (CIGS), →copper zinc tin sulfide (CZTS), →cadmium telluride (CdTe), →cadmium sulfide (CdS), and →gallium arsenide (GaAs).

photovoltaic device with holographic structure

A photovoltaic device that uses a thin film printed on a glass with a specific holographic structure that is engineered to bend, redirect, and concentrate light beams in such a way that it increases the performance of solar cells multiple times. In comparison to traditional refractive and reflective optics, the holographic optical element is much thinner and made of a lightweight film. Compared to the expensive →Fresnel lenses production, the holographic optical element manufacturing is rather inexpensive because it uses the low-cost, high-output laser printing process.

photovoltaic diesel hybrid system

A hybrid system that consists of a photovoltaic system and a diesel power generation device. The hybrid power plants are mostly designed as stand-alone off-grid systems for remote areas far away from grid lines. Different systems complement each other, with the preference given to the nonpolluting, environmentally friendly photovoltaic power plant. On sunny days, solar panels provide continuous uninterruptable power supply. On cloudy and overcast days with little or no solar radiation or in evening hours, the diesel generator automatically turns on, compensating for the minimal solar energy production.

photovoltaic effect

The generation of voltage across the PN junction in a semiconductor due to the absorption of solar radiation. The French scientist, Edmond Becquerel, observed in 1839 that certain materials would create an electric current when exposed to sunlight. He coined the term “photovoltaic effect” which would become a key principle of a solar cell. When the energy from photons strikes an N-type semiconductor consisting of two different materials, such as phosphorus and silicon, it causes the motion of electrons.

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 photovoltaic efficiency

The energized phosphorus extra electron escapes its valence shell, bonds with the neighboring silicon atom, which in turn easily passes the extra electron further from one silicon atom to another throughout the crystal lattice. This movement of free electrons through the conduction band is actually the process of electric current generation. photovoltaic efficiency

The percentage of incident solar radiation that is converted into electrical energy by a photovoltaic cell.

photovoltaic electricity meter

See →solar electricity meter.

photovoltaic energy

Energy generated by a direct conversion of solar radiation into electric current.

photovoltaic energy forecast

Predicts future energy output based on weather forecast, satellite data, and ground measurement data.

photovoltaic façade

A photovoltaic facade fulfills multiple functions. It provides a good thermal insulation, interior illumination similar to glass facades, visual contact to the exterior, protection of the interior from direct solar radiation, protection against weather (heavy rain, high winds, and hail), while simultaneously generating electricity from photovoltaic panels. With regard to the structure, there are two main types of photovoltaic (PV) facades: the ones that are integrated into the external walls of a building and the ones that are attached to the walls of a building. PV panels can be directly integrated into a glass façade. →Frameless photovoltaic modules are in particular suitable for wall-integrated PV systems since they do not expose mounting components. They replace traditional wall cladding materials and offer an aesthetically pleasing design at the same time. On the other side, photovoltaic systems that are fixed to the building walls use aluminum- or stainless steel-mounting systems and substructures. Regarding the light permeability and color, photovoltaic facades can be divided into several groups: dark solar facades, facades with colored solar panels, transparent, and semitransparent solar facades. Due to their vertical position, photovoltaic facades are particularly efficient during the winter months, when the sun is low in the sky. To optimize the solar yield, architects

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should take into consideration the following obstacles when designing photovoltaic facades: canopies, hanging roofs, high trees, neighboring buildings, and structures. See also →building-integrated photovoltaics. photovoltaic facade system

See →photovoltaic façade.

photovoltaic forum

A virtual or physical place in which solar workers, users, or enthusiasts discuss photovoltaic applications and exchange various ideas and techniques from the photovoltaic field.

photovoltaic fuse

See →solar fuse.

photovoltaic generator

A total of all electrically interconnected photovoltaic modules that act as an integrated power supply system.

photovoltaic glass

Also known as PV glass. A special type of glass into which PV cells are integrated. The transparent PV cells are usually inserted between two sheets of glass. The PV glass is typically semitransparent, blocking harmful ultraviolet (UV) radiation in the interior of the building and hence reducing air-conditioning demand. The color, thickness, semitransparency degrees, and shape can often be tailored to fit the specific architectural design, blending in with the rest of the building or creating an accent glass wall or roof.

photovoltaic glass module

A solar module made of a special →photovoltaic glass with incorporated PV cells that convert solar energy into electricity.

photovoltaic hybrid system

A PV power generation system that consists of a PV system and at least one other power generation device, for example, a diesel generator or wind turbine. See →photovoltaic diesel hybrid system, →solar-wind hybrid power system, →solar-wind-diesel hybrid system.

photovoltaic industry

See →solar industry.

photovoltaic ink

Is a special ink type that is able to convert sunlight into electricity. This photoactive ink is applied with a commercial inkjet printer to a plastic substrate. The printer deposits an exceptionally thin layer of solar ink, thereby reducing significantly the volume of required semiconductor material in the production process. The photovoltaic (PV)

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 photovoltaic installation

ink usually consists of copper indium gallium selenide (CIGS), metal salts, and various polymer fullerene blends that are rather inexpensive compared to the costly silicon semiconductor material. The more expensive versions are silicon and nanowire ink. Even though they are costlier than the above-mentioned PV inks, they are also more efficient and can squeeze more electricity out of the sunlight. In particular the nanowire ink that is made of gallium arsenide (GaAs) nanowires is known as one of the most efficient solar materials. Different formulas and fullerene blends can be tuned up in ink solutions to absorb a wider range of irradiation wavelengths. Various ink types are created and applied in layers on one substrate, whereas each layer absorbs a different wavelength of the solar radiation. That way, a much higher efficiency of a PV cell is achieved. photovoltaic installation

See →solar installation.

photovoltaic installer

See →solar installer.

photovoltaic inverter

Converts the generated solar power from direct current to grid-compatible alternating current.

photovoltaic investment Federal tax break that usually covers 30% of solar instaltax credit lation cost. photovoltaic junction box

Also known as solar junction box, module junction box, and J-Box. A protective enclosure on the back of a photovoltaic (PV) module that houses electrical connections and diodes. It is an input/output interface connecting the module to other PV modules. It includes PV module protection devices such as bypass diodes and/or blocking diodes. A bypass diode eliminates hot spots in case of partial module shading or broken cells. It prevents damage from overvoltage due to high resistance conditions (hot spots) by diverting the current past the shaded or broken module. A blocking diode prevents the reverse current from flowing backward through a module. It functions like a one-way valve, allowing electricity to flow only one way. They prevent undesired discharging by reverse flow of electrical current from the battery bank to the PV array, for

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 551

example, in the dark or under cloudy conditions, when no current is generated by the PV modules. Good junction boxes are waterproof and able to regulate heat. photovoltaic kit

See →solar set.

photovoltaic laminate

An encapsulated solar module without an aluminum frame. A flexible →frameless photovoltaic laminate is also often referred to as a photovoltaic laminate.

photovoltaic lamination

See →solar panel lamination.

photovoltaic leasing

See →solar leasing.

photovoltaic long-term forecasting

Solar forecasting for a month, or a year.

photovoltaic manufacturer

See →solar manufacturer.

photovoltaic manufacturing

See →solar manufacturing.

photovoltaic market

See →solar market.

photovoltaic market segment

See →solar market segment.

photovoltaic market share

The percentage of the total electricity generation market that the photovoltaic (PV) power generation industry has over a specified period of time. For instance, in 2016, the PV share of total electrical generation was 1.3% worldwide, 1.4% in the United States, 3.4% in Europe, and 6.9% in Germany.

photovoltaic marketing

See →solar marketing.

photovoltaic material

See →solar material.

photovoltaic meter

See →solar power meter.

photovoltaic micro-grid

See →solar micro-grid.

photovoltaic miniappliance

Also known as a solar mini-appliance. A low-voltage mini-appliance, such as a mini-refrigerator or a portable cooler, which is powered by solar energy and used in recreational vehicles (RVs) and boats.

photovoltaic module

See →solar module.

552 

 photovoltaic module degradation rate

photovoltaic module degradation rate

The rate at which PV power output of a solar module is reduced over time. In order to be able to calculate →levelized cost of energy and accurately predict power supply over the course of time, a PV module degradation rate should be taken into account. The ability to quantify degradation rate is vital to PV system designers and investors for accurate predictions of return on investment (ROI). As this information might motivate the stakeholders to choose one PV system over another, manufacturers include the degradation rate into their product data sheet. This indication is also used to support their standard 25-year warranty. A 20% loss of power after 25 years is tolerable for conventional crystalline modules, whereas manufacturers try to achieve a –0.8% degradation rate per year.

photovoltaic module efficiency

See →solar module efficiency.

photovoltaic module test lab

See →solar test center.

photovoltaic module test laboratory

See →solar test center.

photovoltaic module tester

See →solar module tester.

photovoltaic module testing

See →solar testing.

photovoltaic module testing device

See →solar module testing device.

photovoltaic module testing equipment

See →solar module testing device.

photovoltaic module testing lab

See →solar test center.

photovoltaic module testing laboratory

See →solar test center.

photovoltaic monitor

See →solar energy monitoring system.

photovoltaic monitoring See →solar system monitoring. photovoltaic mount

See →mounting system.

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Photovoltaic-mounting system

See →mounting system.

photovoltaic operator

See →solar plant operator.

photovoltaic panel

Converts the sunlight into electric energy. Synonym term for →photovoltaic module. It can also mean a collection of PV modules.

photovoltaic panel test lab

See →solar test center.

photovoltaic panel test laboratory

See →solar test center.

photovoltaic panel testing

See →solar testing.

photovoltaic panel testing lab

See →solar test center.

photovoltaic panel testing laboratory

See →solar test center.

photovoltaic paradox

PV modules require sunlight to produce electricity, but they suffer from a drop in efficiency as they get hotter. When the temperature of the module rises over 25 °C (77 °F), it potentially reduces the power yield by 10–25% based on the proportional voltage drop due to resistance.

photovoltaic park

See →photovoltaic power plant.

photovoltaic park system

See →photovoltaic power plant.

photovoltaic peak watt

Stands for peak power, a maximum energy output generated by a photovoltaic system under optimal conditions – full solar radiation averaging 1,000 W/m2 (1 kW/m2) and 25 °C.

photovoltaic plant

See →photovoltaic power plant.

photovoltaic plug

See →photovoltaic plug-in connector.

photovoltaic plug-in connector

Also known as a DC plug-in connector or photovoltaic plug. A connector for wiring solar modules and inverters. The interlocking mechanism, typically consisting of a male connector (plug) and a female connector (socket), can safely and legally be connected by anybody without the use of special tools.

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 photovoltaic power

It is important to use only plug-in connectors from the same manufacturer for a solar array. Using incompatible plug-in connectors from different manufacturers leads to overheating due to increased electrical resistance, resulting in energy losses, failures, and damage to the PV system. See also →MC4 connector. photovoltaic power

Power generated by a direct conversion of solar radiation into electric current.

photovoltaic power forecast

Predicts future energy output based on weather forecast, satellite data, and ground measurement data.

photovoltaic power meter

See →solar power meter.

photovoltaic power plant

Also known as a photovoltaic (PV) power station, solar farm, solar park, or solar power plant. A ground-mounted large-scale solar plant for utility-scale electricity production from solar power. It is an on-grid PV system that consists of →solar modules, →ground-mounting system, →inverter, step-up transformer, and switchgear. The inverter converts the generated solar power from direct current into alternating current (AC). The transformer steps up AC output voltage from the inverter to the utility system. Finally, the switchgear connects the PV power plant to the public utility grid. Apart from these basic components, the PV plant often includes a →solar tracking system, →monitoring platform, and technical support. Besides large, concentrating solar thermal plants, multimegawatt PV plants are the second largest solar power plants. However, compared to traditional power plants, PV power plants cover a significant area of land. One MW crystalline silicon PV power plant without solar trackers requires around 1 ha or 2.47 acres of land in sunny regions. The ratio 1 ha/1 MW will be significantly higher for a thin-film solar power plant or for a crystalline silicon power plant in northern regions. The measurement unit for the capacity (nominal output) of large-scale solar power-generating plants is often megawatt peak (MWp). It refers to peak power, a maximum energy DC output generated by a PV system under optimal →standard test conditions (STC). As there are some evident inverter and transformer power losses

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between the solar panels and the AC output to the grid, some countries prefer to rate the capacity of PV power plants in converted megawatt alternating current (MWAC). The converted MWAC power output, which will actually be fed into the utility grid, is always lower (15–20 %) than the MWp DC output. Therefore, MWAC provides a more realistic account of the solar plant capacity. In general, the European standard is to express the capacity of solar farms in MWp, while the North American practice tends to give preference to MWAC rating. See also →megawatt peak. photovoltaic power station

UK See →photovoltaic power plant.

photovoltaic power supply

The energy that is generated by a PV array and either supplied to electronic appliances or fed into the public power grid. Before being used by the loads or fed into the grid, the generated DC energy needs to be converted with help of an inverter into grid-compatible alternating current.

photovoltaic principle

See →photovoltaic process.

photovoltaic printer

A special type of printer that 3D prints semiconductor materials onto a lightweight, flexible plastic film by using a liquid →solar ink. 3D printing can reduce production costs up to 50%. See also →inject printer.

photovoltaic printing

Photovoltaic printing stands for the printing of solar cells. The process requires a printer that produces photovoltaic cells in a similar way newspapers or banknotes are manufactured. The machine deposits a thin layer of solar ink made of →copper indium gallium selenide (CIGS) or some other material onto a substrate, usually a sheet of plastic or some similar flexible material. These paper-thin cells that are called →thin-film solar cells are very light and can be attached to different surfaces, ranging from rooftops over curtains, windows, and backpacks to smartphones. The photovoltaic printing method has high initial costs due to the expensive printer, but after the somewhat high upfront investment the manufacturing is easier, faster, highly scalable, and much cheaper than in the traditional solar panel alternative. The four major types of photovoltaic printing are: →gravure printing, →flexographic printing, →screen printing, and →inkjet printing.

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 photovoltaic process

photovoltaic process

Is a process by which solar energy is directly converted into electrical energy. The light photons eject a valence electron from its orbital and elevate it to the conduction band generating electric current.

photovoltaic producer

See →solar manufacturer.

photovoltaic provider

See →solar provider.

photovoltaic recycling

Around 90% by weight of a polyvoltaic (PV) panel is recyclable, as they consist of easily recyclable materials such as glass, metals, and plastics. Various methods, such as crushing, shredding, processing of intact silicon wafers into new solar cells, and separation of solids from liquids, are used to process materials in order to turn them into new products. The recycling of old PV modules is a prerogative for a healthy long-term sustainable development, in particular because an exponential growth of PV installations is expected in the upcoming years. The European Union made the PV recycling mandatory by including PV panels into the Waste Electrical and Electronic Equipment (WEEE) Directive in 2012. Likewise, there is an effort in other countries outside Europe to make PV manufacturers and sellers responsible for collecting and recycling solar products at the end of life.

photovoltaic ribbon

See →tabbing wire.

photovoltaic roof

See →solar roof.

photovoltaic roof system See →solar roof. photovoltaic sealant

See →solar adhesive.

photovoltaic set

See →solar set.

photovoltaic shade structure

Also known as photovoltaic (PV) shading structure. A customized, vertical or horizontal aluminum or stainless steel structure of different shapes and sizes to which solar panels are mounted, creating a solar wall, overhang, or canopy, which is attached to a building or placed in front of it. The opaque PV shade structure is used in front of a brick or concrete façade, and the semitransparent or transparent PV shade structure is used in front of a glass façade. The PV shade structures are also often installed in parking

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lots, playgrounds, patios, school yards, bus stops, parks, campuses, and open areas adjacent to buildings. They fulfill multiple functions: they convert solar radiation into electricity and heat, provide protection against weather (direct sunlight, heavy rain, high winds, and hail), and fulfill a decorative function. The parking lot shade structure, which is better known as a solar carport, can also provide electricity for recharging electric cars. photovoltaic shading structure

See →photovoltaic shade structure.

photovoltaic shading system

See →photovoltaic shade structure.

photovoltaic shingle

→Building-integrated photovoltaics. Photovoltaic shingle is a durable roofing material with integrated photovoltaic cells that can be incorporated easily into a roof than balky, complex solar panel →roof-mounting systems. Like regular photovoltaic panels, PV shingles harness the sun’s energy and convert it into electricity. They also provide a good thermal insulation as well as weather protection designed to withstand heavy rain, high winds, and hail, similarly to conventional asphalt shingles. Although more expensive than solar panels, they are more aesthetically appealing than photovoltaic modules. They offer a unique high-tech external design by using patterns and colors that effectively blend in with the rest of the roof. Since photovoltaic shingle is relatively a new product, available since 2005, there are mainly two types of photovoltaic shingles that are offered on the market: →thin-film photovoltaic shingle and →silicon-based photovoltaic shingle. Thin-film photovoltaic shingles utilize →CIGS (copper indium gallium selenide) solar cells to turn sunlight into electricity. Due to their flexibility and lightweight, they replicate actual shingles in size and design. In addition, since they deliver a good thermal insulation and durability as asphalt shingles do, they can replace roofing material and be stapled directly to the roofing cloth like regular shingles. Silicon-based photovoltaic shingles, also known as →photovoltaic tiles, have higher power output than thin-film photovoltaic shingles. Even though they are more energy efficient than thin-film photovoltaic

558 

 photovoltaic short-term forecasting

shingles, silicon-based photovoltaic shingles cost more and are associated with certain design constraints. As the name suggests, they are made of thin silicon strips that are implanted into glass or other materials and work like conventional →silicon solar modules. photovoltaic short-term forecasting

Solar forecasting for 7 days.

photovoltaic simulation software

See →solar simulation software.

photovoltaic skylight

See →solar skylight.

photovoltaic software

See →solar simulation software.

photovoltaic solar airconditioning system

In a photovoltaic (PV) solar air-conditioning system, PV modules capture and convert solar energy into electricity that is then used to power the air conditioner. If the air conditioner is not operating, the electric current is routed through the breaker box to power other electrical appliances in the house. The excess power is fed into the utility grid. See also →solar thermal air-conditioning system.

photovoltaic solar panel See →solar module. photovoltaic stand-alone Also known as off-grid system is a photovoltaic (PV) power system system that is not connected to an electrical grid. An off-grid PV power system usually consists of several solar panels, batteries, an inverter, a charge regulator, and a mounting system. The solar panels produce power, which is stored in a battery bank. Upon need, the stored DC electricity is converted with help of the inverter into AC power and distributed across the home to power house appliances. In northern, less sunny regions it is advisable to have a generator as a backup power besides the battery bank. Stand-alone systems work at low voltages and a homeowner can choose between 12, 24, and 48 V systems. When choosing a new system, a user can consider the following guidelines: The lower the voltage, the safer the system, but the higher the power losses. The higher the voltage, the less safe the system, with a possibility of electrocution, but the lower the power losses. Apart from green enthusiasts who would always choose an off-grid system, the stand-alone solar system is

photovoltaic storage 

 559

a preferred option among users who are subject to frequent power fluctuations or outages or who live in the boonies and the closest power lines are one or more miles away from their property. To bring power lines to their home site might cost a fortune; therefore, the installation of an offgrid solar power system is a cost-effective alternative. photovoltaic storage

See →solar energy storage.

photovoltaic subsidy

Financial incentives offered by a government to homeowners to install residential photovoltaic (PV) systems. Federal and state subsidy programs typically involve cash rebates for installing a PV system and a →net energy metering program. Some countries offer a battery storage subsidy for households willing to add a battery bank to their PV system.

photovoltaic surface

Surface covered with solar panels.

photovoltaic surfboard

See →solar surfboard.

photovoltaic system

Also known as a photovoltaic (PV) array or solar system. A group of solar panels connected together to form a unified power production system. Other components that are usually included in a PV system are: inverter, controller, meter, tracker, battery bank, and mounting system. The size of a photovoltaic system can range from a small 5 kW residential photovoltaic array with 12–20 monocrystalline silicon solar modules to a large-scale multimegawatt →photovoltaic power plant with thousands and hundreds of thousands of solar modules. They are three main types of photovoltaic systems: →offgrid photovoltaic system, →grid-tie system with battery backup, and →grid-tie system without battery backup.

photovoltaic system efficiency

The ratio of the useful energy output (energy converted into electricity for human consumption) to the energy input (the amount of solar radiation incident on the →photovoltaic modules). The photovoltaic (PV) system efficiency is expressed in percentages. For instance, a PV system is 22% efficient if 22% of the available solar energy is converted into electrical energy, whereas the rest is lost as heat and due to other factors. The following formula can be used to calculate the PV system efficiency: E = energy output/energy input × aperture area.

560 

 photovoltaic system monitoring

photovoltaic system monitoring

See →solar system monitoring.

photovoltaic technology Technology of converting solar radiation into electricity. photovoltaic test center

US See →solar test center.

photovoltaic test centre

UK See →solar test center.

photovoltaic testing

See →solar testing.

photovoltaic thermal hybrid solar collector

See →combined solar collector.

photovoltaic thermography

The use of an infrared camera and thermal infrared (IR) imaging technique to detect defects in photovoltaic devices and systems. During the inspection and testing of individual modules or the entire solar installations, photovoltaic thermography helps detect and visualize hot spots – places of high resistance and overheating as a result of damaged cells or partial shading – and other defects on photovoltaic surfaces.

photovoltaic tile

→Building-integrated photovoltaics. Photovoltaic tile is a durable roofing material with integrated photovoltaic cells that can be incorporated easily into a roof than balky, complex solar panel →roof-mounting systems. Like regular photovoltaic panels, photovoltaic tiles harness the sun’s energy and convert it into electricity. They also provide a good thermal insulation as well as weather protection designed to withstand heavy rain, high winds, and hail, similarly to conventional roof tiles and shingles. Although more expensive than solar panels, they are more aesthetically appealing than photovoltaic modules. They offer a unique high-tech external design by using patterns and colors that effectively blend in with the rest of the roof. Photovoltaic tiles have higher power output than →thinfilm solar shingles. Even though they are more energy efficient than thin-film solar shingles, silicon-based photovoltaic tiles cost more and are associated with certain design constraints. As the name suggests, they are made of thin silicon strips that are implanted into glass or other materials and work like conventional →silicon solar modules.

photovoltaic tracker 

 561

photovoltaic tracker

Also known as solar tracker. See →solar tracking system.

photovoltaic tracking

Enables solar panels to constantly follow the course of the sun.

photovoltaic trailer

See →solar trailer.

photovoltaic waste management

See →solar waste management.

photovoltaic window

See →solar window.

photovoltaic wire

A single-conductor copper wire used for interconnecting solar modules. The photovoltaic (PV) wire has a thick protective insulation that makes the cable heat, moisture and sunlight resistant. This is why the PV wire is suitable for surface or underground wiring in wet or dry locations. In spite of thick, double-jacket insulation, the PV wire uses stranded conductors that are flexible enough for various wiring scenarios. PV wires typically have 90 °C wet rating and up to 150 °C dry rating.

photovoltaics

A method for converting solar radiation into electricity by using solar cells.

photovoltaic-thermal system

(PV/T) See →combined solar collector.

phthalocyanine photovoltaic cell

See →phthalocyanine solar cell.

phthalocyanine PV cell

Phthalocyanine photovoltaic cell. See →phthalocyanine solar cell.

phthalocyanine solar cell

A type of →organic solar cell that uses phthalocyanines as one of the main components – active semiconductor material – in the manufacture of thin-film heterojunction photovoltaic cells. The active layer consisting of copper phthalocyanine (CuPc) and →buckminsterfullerene (C60) is deposited by evaporation onto an ITO-conductive glass electrode coated with a conducting polymer →PEDOT:PSS.

physical adsorption

See →physisorption.

physical deposition

Deposition of semiconductor thin-film coatings on a substrate by using physical forces. See →physical vapor deposition.

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 physical dry etching

physical dry etching

A type of →dry etching in which high-energy ion beams are used to etch away the semiconductor material from the substrate. As no chemical reaction takes place in this etching method, the material is physically removed from the substrate. The unmasked surface to be etched is bombarded with ions, electrons, or photons. The high energy particles knock out the atoms from the surface of the target material, causing the vaporization of the material and producing the desired conducting channels. The following disadvantages of the physical dry etching method are to be considered: low etch rates, low selectivity among different materials, damages to the etching surface caused by the high energy bombardment, and redeposition of the dislodged particles on mask edges, generating unwanted ridges. See also →dry etching.

physical dry etching process

See →physical dry etching.

physical etching

See →physical dry etching.

physical vapor deposition

(PVD) A method of depositing conductive thin-film coatings on a substrate in the manufacture of photovoltaic semiconductors by using physical forces – thermodynamic and mechanical processes. The entire process takes place in vacuum chambers and at lower temperatures in the range of 250 °C to 500 °C (482 °F to 932 °F) than in the →chemical vapor deposition process. It is a type of vapor transfer process in which a raw material, a pure solid precursor, is gasified by being bombarded with a beam of electrons or ions. The dislodged, vaporized atoms are then transported into a PVD reactor containing a substrate to be coated. Finally, the freed atoms move and settle on the surface of the substrate to form the desired thin film. In the PVD process, a coating is deposited over the entire surface rather than in certain areas. Different methods of physical vapor deposition include →evaporation, →sputtering, →pulsed laser deposition, and →molecular beam epitaxy (MBE). The major advantage of the physical vapor deposition process is that it is less expensive than the traditional silicon wafer production process of growing single crystals (silicon ingots) from melt.

physical vapor deposition process 

 563

Substrate and film growth

Sputtering gas

Ar+

Sputtering target

Physical Vapor Deposition

physical vapor deposition process

A semiconductor surface engineering process in which the vapor phase is generated by condensation from a liquid or solid source in a vacuum environment. See →physical vapor deposition.

physical-chemical dry etching

A type of etching that combines physical and chemical →dry etching.

PhysikalischMeteorologisches Observatorium Davos/World Radiation Center

(PMOD/WRC) A center for research in radiation measurements and instrumentation located in Davos, Switzerland. The main activities of the center include the establishment and maintenance of international standards for measurement of solar radiation in the visible range, infrared radiation, atmospheric optical depth, and ultraviolet radiation. The PMOD/WRC develops and tests radiometric instruments and also serves as an international calibration center for meteorological radiation measurement instruments.

physisorption

Also known as physical adsorption. A type of adsorption in which no chemical bond between the adsorbate (gas or liquid) and the adsorbent (solid surface) is formed. The physical bonding of gas molecules to the surface is weak, as only a minimal perturbation of electronic states of the adsorbate and the adsorbent is recorded.

PI

Abbreviation for →polyimide.

564 

 picowatt

picowatt

(pW) Unit of power between nanowatt and femtowatt. The picowatt equals one-trillionth of a watt, 10−12 W.

PID

Abbreviation for →potential induced degradation.

PID effect

See →potential induced degradation.

piezoelectric crystal

A crystal, such as →quartz, that can generate electricity when subjected to a mechanical stress. The crystal, which can shrink or expand, is commonly placed between two metal plates. When the crystal is compressed, the mechanical energy triggers the generation of electrical charge in the crystalline material. The piezoelectric effect can be reversed in such a way that electrical energy is converted into mechanical energy.

piezoelectric effect

See →piezoelectricity.

piezoelectric materials

Are materials such as crystals and ceramics that can generate electrical charge when subjected to a mechanical stress or vibrations. The artificial piezoelectric material lead zirconate titanate is more efficient than the natural piezoelectric material →quartz, producing higher voltage for the same amount of pressure.

piezoelectricity

Also known as piezoelectric effect. Electrical charge generated in certain materials, such as →quartz or ceramics, when subjected to pressure or vibrations. In the solar field, devices that use the piezoelectricity include pressure →sensors, →transducers, and hybrid solar cells. Recent research claims that piezoelectricity could improve solar cell efficiency by capturing energy from vibrations. City noise as well as the road vibrations caused by vehicles can potentially be converted into electricity. Future solar roads might combine solar cells with piezosensitive films to generate both solar and piezoelectricity at the same time.

PIM

Abbreviation for →powder injection molding.

p–i–n

See →p–i–n junction.

pin diode

See →p–i–n diode.

p–i–n diode

A diode with an intrinsic or undoped semiconductor layer sandwiched between a positively doped semiconductor region (p-type layer) and negatively doped semiconductor

pin junction 

 565

region (n-type layer). This diode structure is commonly used with amorphous →thin-film silicon solar cells. pin junction

See →p–i–n junction.

p–i–n junction

A junction with a three-layered structure: positive/intrinsic/negative. In this structure, a wide intrinsic or undoped semiconductor layer is sandwiched between p-type and n-type semiconductor layers. This junction structure is commonly used with amorphous →thin-film silicon solar cells.

p–i–n solar cell

A type of the thin-film amorphous silicon heterojunction solar cell that uses a →p–i–n junction structure consisting of three differently doped regions. Light

Transparent conductive oxide layer p layer i layer n layer

Glass

Rear contact

p-i-n Solar Cell

pitch angle

In plasma physics, the angle between the velocity vector of a charged particle and the ambient magnetic field vector.

pitched roof

A roof having a single slope or a double slope on both sides of a central ridge.

pitched roof PV installation

An installation method for mounting solar panels on a pitched roof with a single or a double slope. In order to properly align panels with the roof, tools like →angle finder or →protractor are used as well as a PV-mounting system consisting of →aluminum rails, →mounting clamps, →mounting brackets, and →standoffs.

566 

 pitched roof PV mounting

pitched roof PV mounting

See →pitched roof PV installation.

pivoting mechanism

A mechanism of a solar tracker that operates the →azimuth axis, providing horizontal rotation of solar modules. As the major solar energy improvement goes back to tracking the azimuth, the pivoting mechanism is a crucial component of a →dual-axis tracking system.

Planck constant

See →Planck’s constant.

Planck law

See →Planck’s law.

Planck’s constant

Also known as the Planck constant. The ratio of the amount of energy in one photon of electromagnetic radiation to its frequency. Planck constant is explained with the following equation: E = h × f, where E stands for the energy of the photon (J), h for Planck’s constant (6.626 ×10–34 J/s), and f for frequency (Hz).

Planck’s law

Also known as the Planck law. A law that states that the energy of electromagnetic radiation is emitted, propagated, or absorbed in invisible, discrete quanta (packages) of energy which are proportional to the frequency of the radiation.

plasma

A thin ionized gas, produced at very high temperatures, in which electrons become unbound and free from their atoms. A lightning bolt, solar corona, or a flame are some examples of plasma. The wide application of plasma in solar semiconductor manufacturing goes back to the low cost and environmentally friendly clean plasma process, which is safe for operators. It is easy to use and material integrity is maintained.

plasma acceleration

A process that utilizes high temperature ionized →plasma to intensify the kinetic energy of charged particles, such as electrons, protons, and ions, relying on electric fields generated by radio waves.

plasma cloud

A cloud of electrically charged particles propagating from the sun to the earth.

plasma coating

See →plasma-enhanced chemical vapor deposition.

plasma component

See →plasma equipment.

plasma deposition

See →plasma-enhanced chemical vapor deposition.

plasma dry etching 

 567

plasma dry etching

See →chemical dry etching.

plasma-enhanced chemical vapor deposition

(PECVD) A type of dry etching. A method of depositing conductive thin-film coatings on a substrate for manufacturing photovoltaic semiconductors. It is a type of vapor transfer process in which a high temperature gas is introduced into a reaction chamber containing a heated substrate to be coated. In a CVD reactor, plasma is able to activate the gas silane at lower temperatures than in a conventional CVD process, breaking apart its molecular bonds into its constituent elements: silicon and hydrogen atoms. The freed atoms recombine and settle on the surface of the substrate to form the desired thin film.

plasma equipment

An apparatus for semiconductor processing, typically consisting of several modules, such as power supply, vacuum system, pump, matching network, reactor chamber, power monitor, and power controller.

plasma etch reactor

An appliance for etching a solar semiconductor wafer. It consists of a reactor chamber with a grounded upper electrode and a lower electrode which is connected to high frequency and low frequency power supply. The reactor chamber can also be equipped with magnets in order to generate a high magnetic field and thus a sufficiently dense plasma. The magnetic field confines the plasma and prevents the loss of charged ion species to the reactor walls. The etching gas, such as tetrafluoromethane (CF4), nitrogen trifluoride (NF3), or chlorine gas (Cl2), is introduced into the heated reaction chamber to produce chemical reactions with the semiconductor surface and remove the unmasked silicon material in the process.

plasma etcher

An apparatus for etching of semiconductor wafers. See →plasma etch reactor.

plasma etching

See →chemical dry etching.

plasma etching apparatus

See →plasma etch reactor.

plasma etching device

An apparatus for etching of semiconductor wafers. See →plasma etch reactor.

plasma etching machine See →plasma etching device.

568 

 plasma flame

plasma flame

In a plasma spraying process, a stream of working plasma gas made luminous by heat. The feed stock in powder form that is fed into the plasma flame is rapidly melted at high temperatures and sprayed onto the target surface.

plasma gas

All gases or gaseous mixtures that are heated to high temperatures at which a significant number of atoms or molecules are ionized. Usually generated by radio frequency (RF), plasma is used as a working gas that undergoes a chemical reaction with the target material. The target material exposed to the plasma receives energetic ion bombardment, causing the atoms to be dislodged from the surface of the target material. The vaporized particles traverse in a plasma cloud through the vacuum chamber and condense on the surface of the substrate as a thin semiconductor layer.

plasma gas nozzle

A main component of a plasma spray gun, through which high temperature plasma gas is flowing, constricting the arc. A high frequency arc is generated between the plasma gas nozzle (anode) and the electrode (cathode).

plasma generation

The generation of a plume of hot plasma gas by radio frequency (RF) or direct current (DC) discharge between two electrodes.

plasma generator

A device capable of exciting electrons to a uniform energy level at which hot →plasma gas is generated. There are three main types of plasma generators: radio frequency (RF) discharge, direct current (DC) discharge, and microwave discharge plasma generator. The RF discharge generator is most widely used in semiconductor manufacturing.

plasma gun

See →plasma spray gun.

plasma jet

See →plasma particle jet.

plasma oscillation

Also known as Langmuir waves. It is the oscillation of charged particles, electrons, and positive ions in a plasma. Under typical circumstances, there are equal number of electrons and positive ions in a volume within a plasma. The plasma is assumed to be in a state of dynamic equilibrium, where the charged particles are not moving but oscillating to and fro. The oscillation can be described as a process of random motion that is averaged out.

plasma particle jet 

 569

plasma particle jet

A stream of hot ionized plasma with very high energy and temperature.

plasma plume

A gaseous blend of atoms, molecules, clusters, free electrons, and ions. See also →plume.

plasma processing

Physical and chemical surface modification method.

plasma reactor

An appliance in which standard →plasma-enhanced chemical vapor deposition (PECVD), →very high frequency (VHF), or →high pressure depletion (HPD) deposition of thin-film semiconductor layers, such as a-Si:H or μc-Si:H, is performed. With the participation of a lowtemperature plasma, heat and mass transfer processes are carried out.

plasma spray coating

A technique of coating of surfaces by a →plasma spraying process with the help of a →plasma spray gun.

plasma spray gun

A coating apparatus that generates high temperatures to melt coating material in powder form, making it suitable for surface coatings. The main components of a plasma spray gun are a nozzle (anode) and the electrode (cathode), between which a high frequency arc is created. Working gases, usually mixtures of argon, nitrogen, hydrogen, and helium, flowing between the anode and cathode are ionized to become a plasma plume, reaching very high temperatures of over 6,600 °C (12,000 °F). The feed stock in powder form (e.g., →zirconia) is fed into the plasma

Powder injection

Spray stream of molten particles Cathode Plasma gas

Anode Nozzle

Plasma Spray Gun

Coating

570 

 plasma spray process

flame through an external powder port mounted near the anode nozzle exit. After powder is injected into the gas stream, it is rapidly melted at high temperatures and sprayed onto the target surface. plasma spray process

See →plasma spraying.

plasma spraying

A process by which doped silicon powder is injected into a stream of high temperature ionized plasma gas to become molten. The heated and accelerated high-velocity particles are sprayed onto a substrate to form a silicon coating upon cooling.

plasma spraying process See →plasma spraying. plasma technology

A sputtering technology that involves the bombardment of the target material (cathode) with energetic ions or electrons of argon plasma, causing the atoms to be dislodged from the surface of the target material and condense on the surface of the substrate (anode) as a thin semiconductor layer. Plasma has a double function in the process, which is conducted in a vacuum reactor chamber. High energy plasma vaporizes the target material and also serves as a medium for the transfer of vaporized particles from the source to a substrate. There are several common plasma vapor deposition methods, such as →ion-beam sputter deposition, →ion-assisted deposition, →reactive ion etching, and →magnetron sputtering.

plasma treatment

See →plasma technology.

plasmon

A quasiparticle defined as a quantum of the collective excitation of free electrons in a piece of conducting material. It is a quantum of plasma oscillation, commonly observed in metals.

plasmon polariton

A coupled state between a →plasmon and a →photon.

plasmonic effect

An effect that occurs when photons of light hit a metal, exciting free electrons at the metal surface and causing a →surface plasmon polariton.

plasmonic energy

Energy transported from the metal to the semiconductor to encourage the charge separation in the nanostructured plasmonic semiconductor by direct electron transfer.

plasmonic graphene 

 571

plasmonic graphene

Transparent conductor material with enhanced light trapping and scattering features for →thin-film solar cells. Compared to the regular →graphene, the plasmonic graphene demonstrates higher electrical conductivity, which in turn results in a higher solar power output.

plasmonic nanoparticle

Particles at the nanoscale whose size, shape, and composition can be engineered in such a way that they respond to certain incident electromagnetic wavelengths, ranging from the ultraviolet (UV) through the visible to the near-infrared areas. The light absorption in the semiconductor material can be improved by enhancing the flow of photons through expending the optical path length and concentrating the incident field. By tuning plasmonic nanoparticles to match favorable regions of the electromagnetic spectrum, the free conduction electrons in the metal nanoparticle are excited into oscillation due to robust coupling with incoming photons. The →miniaturization and tunability of plasmonic nanoparticles are some of the major advantages of this type of nanoparticles, making them one of the most promising new solar materials capable of trapping more light within the cell and thus achieving a high energy conversion efficiency.

plasmonic nanostructure

A structure in which the constituent materials are joined together by the collective excitation of free electrons and their oscillation under the influence of incoming photons of light. Nanostructuring technologies offer new ways to better control and design complex plasmonic nanostructures able to significantly increase the light absorption capacity of the solar cell. Precise plasmonic nanostructures take advantage of the oscillations of free surface electrons in a coupled state between plasmons and photons.

plasmonic photovoltaic cell

A type of thin-film photovoltaic cell that uses plasmons for converting light into electricity.

plasmonic photovoltaic device

A photovoltaic cell that uses plasmonic nanostructures to increase the photoresponse and carrier mobility of semiconductor materials and capture a wider range of the solar spectrum in →thin-film solar cells. High level of controllability of plasmonic nanostructures allows the tuning of various absorber layers in a different way to harvest specific ranges of the electromagnetic spectrum. The ultimate

572 

 plasmonic photovoltaics

goal of a synthesis of numerous nanostructured multispectral absorber layers in a →multijunction photovoltaic cell is to capture the complete range of electromagnetic (solar) radiation. plasmonic photovoltaics

A branch of optoelectronics that is concerned with the light absorption and scattering in →plasmonic photovoltaic cells. Plasmonic photovoltaics closely examines the interaction of plasmons and photons in a plasmonic thin-film solar cell. Another main area of interest is the research of charge carrier transfer and collection. The further important focus of the plasmonic investigation is the design of →plasmonic nanostructures, which can significantly improve the power output of thin-film solar devices.

plasmonic PV cell

See →plasmonic photovoltaic cell.

plasmonic PV device

See →plasmonic photovoltaic device.

plasmonic solar cell

See →plasmonic photovoltaic cell.

plasmonic structure

Typically metallic nanostructures carefully engineered at nanoscale to generate excitation of free electrons in metal nanoparticles or at metal/dielectric interfaces. The application of plasmonic structures, such as nanoparticle plasmons and →surface plasmon polariton, can significantly enhance the efficiency of solar cells. Plasmonic light trapping techniques are based on diffraction on photonic nanostructures and scattering using plasmonic structures.

plasmonics

Study and application of plasmons.

plasmons

Short-lived high-energy states, waves of electrons. Plasmons are quasiparticles of plasma oscillation.

plastic composite film

A film that consists of two or more materials, one of which is always plastic, for instance, perovskite–polymer composite film that is employed in hybrid heterojunction solar cells. By adjusting the content of polymer doping, the optical characteristics of the perovskite films can be tuned in such a way to achieve higher energy conversion efficiency.

plastic composite material

See →plastic composite film.

plastic film

See →polymer film.

plastic layer 

 573

plastic layer

See →polymer film.

plastic photovoltaic module

See →plastic solar module.

plastic photovoltaic panel

See →plastic solar module.

plastic solar cell

See →organic photovoltaic cell.

plastic solar module

Also known as a plastic solar panel. A solar module made of single or multiple polymeric semiconductor films for converting solar energy into electricity. In multiple plastic semiconductor films, solar cells of different material compositions are encapsulated into polymeric sheets to capture maximum possible ranges of the solar electromagnetic radiation spectrum. Lightweight plastic solar modules replace heavy and bulky glass modules and allow the application of a cost-effective manufacturing process.

plastic solar panel

See →plastic solar module.

plate

See →battery plate.

plate glass

Flat, transparent, thick, and polished glass cast in plates that is commonly used as front glass in photovoltaic modules and solar collectors. Two main types of plate glass are →float glass and →rolled glass.

plate heat exchanger

A heat exchanger that consists of a series of parallel plates for transferring heat between hot and cold fluids.

p-layer

Thick lower silicon semiconductor layer of a solar cell that is doped with →boron atoms. See →p-type semiconductor.

PLD

See →pulsed laser deposition.

Plexiglas®

See →acrylic glass.

plug load energy

Energy used by all electrical devices that are usually plugged into a power system.

plug loads

All electrical devices that are usually plugged into a power system. An analysis of a →plug load energy in a system, for example, all loads, such as computers, printers, TVs, and kitchen appliances, that are typically plugged into AC outlets of an office can lead to plug load reduction solutions.

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 plug-and-play PV system

plug-and-play PV system

A photovoltaic (PV) system with simplified installation, inspection, and electronic permitting processes. One of the key advantages of this system is the ease of installation. Homeowners are able to install the PV system without special training because it uses pre-fabricated wiring and touch-safe connectors that easily plug the system into a PV-ready circuit that includes a PV-ready socket and an inverter that is able to interface with the utility grid and use standard data transfer protocols. The system simplifies the inspection process by applying an electronic safety self-test that ensures safety and code compliance. Finally, the plug-and-play PV system simplifies jurisdiction and utility approval by transmitting crucial data to local jurisdiction and utility company that remotely approves and issues a permit. This ambitious system requires a high level of standardization and cooperation between system manufacturers on one side and jurisdiction and utilities on the other. Its goal is to install and commission a PV array within several hours, a process that usually takes in a best-case scenario at least several days and in reality often several weeks or even months.

plug-in connector

See →photovoltaic plug-in connector.

plume

Also called vapor plume or plasma plume. Plasma-like substance that is composed of energetic fragments, usually a blend of atoms, molecules, clusters, free electrons, and ions.

plus-energy building

A building that generates more energy from solar and other renewable energy sources than it uses. The surplus energy can be used to charge electric vehicles or it can be fed into the public electricity grid.

plus-energy house

See →plus-energy building.

PMA1

Abbreviation for →permanent magnet alternator.

PMA2

Abbreviation for →polymethyl acrylate.

PMAX

See →maximum power output.

PMMA

Abbreviation for polymethyl methacrylate. See →acrylic glass.

PMOD/WRC 

 575

PMOD/WRC

Abbreviation for →Physikalisch-Meteorologisches Observatorium Davos / World Radiation Center.

pn diode

See →p–n junction diode.

p–n diode

See →p–n junction diode.

pn junction

See →p–n junction.

p–n junction

Intersection between positively doped and negatively doped semiconductor layers in a solar cell.

p–n junction diode

A semiconductor diode that passes current in only one direction. When a positively doped semiconductor layer and a negatively doped semiconductor layer are placed side by side, a depletion zone forms in-between that acts like a barrier opposing the flow of electrons from one region to another. The terminals of the diode are attached to the n- and p-layers. When the sun hits the photosensitive semiconductor material, a higher voltage is applied and some electrons/holes will be able to overcome the depletion zone barrier, jumping to the other region. As the current can flow in only one direction, the diode acts like an electrical one-way valve. All photovoltaic cells are junction diodes. Depletion zone

Free electron Hole

P-type

P

Nagative ion

N-type –

+

–

+

–

+

–

+

–

+

–

+

p-n Junction Diode

N

Positive ion

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 pocket plate

pocket plate

Plate of a nickel–cadmium battery in which electrochemical active mass is held in perforated nickel–steel pockets.

pocket plate electrode

See →pocket plate.

point focus solar cell

CPV, photovoltaic technology that uses lenses or mirrors to concentrate sunlight onto highly efficient solar cells.

point-contact cell

See →point-contact solar cell.

point-contact solar cell

(PCSC) A high-efficiency silicon solar cell suitable for concentrator applications. The major components of the cell include a texturized top surface, an array of small point contacts on the back of the cell, and a backside mirror. The texturized top surface reduces the reflection of incident light and thus prevents light energy losses. Moving all the front contact grids to the rear of the cell simplifies interconnection and eliminates shading losses. Rear-surface mirror diminishes backlight absorption and causes light trapping. Of all the above-mentioned energy-efficient factors, the light trapping that takes place between the texturized top surface and the reflective rear surface boosts the cell efficiency the most.

point-focus solar concentrator

See →point-focusing solar concentrator.

point-focusing concentrator

See →point-focusing solar concentrator.

point-focusing solar collector

See →point-focusing solar concentrator.

point-focusing solar concentrator

A system that concentrates the incoming Sun’s beams, which are reflected from a mirrored surface of a parabolic dish or from a series of sun-tracking mirrors called heliostats, onto a single focal point, increasing the intensity of solar energy. At the focal point, a central →receiver is located. The central receiver can be a boiler in a CSP system or a system of tubes that is integrated into a Stirling engine in a →Dish–Stirling system. The point-focusing concentrators are →heliostats in →concentrated solar power plants, →dish collectors, and →Fresnel collectors. See also →line-focusing solar concentrator.

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polar climate zone

A zone that lies within the Arctic and Antarctic Circles and is characterized by short mild summers and a long, extremely cold winters. Building a house on a south-facing hillside provides wind protection and increases heat retention.

polarimeter

An instrument for measuring the amount of polarization of light. The polarimeter is equipped with a polarization filter, which filters out all disorderly waves, vibrating in all directions, from the regular light and passes through only orderly waves that vibrate in one direction. Polarized light is inclined at only one angle defined by the filter’s grating.

polarisation

UK See →polarization.

polariton

A coupled state between an elementary excitation and a →photon.

polarizability

A distortion of an electron cloud or the measure of the change in an atomic or molecular electron distribution under the influence of an applied electric field.

polarization

US The property of electromagnetic waves that consist of electric and magnetic fields oscillating perpendicular to the direction of propagation.

polarization division

See →polarization separation.

polarization separation

Also known as polarization division. A process in which electric and magnetic fields oscillate in different directions in electromagnetic waves. The electric and magnetic field vectors point perpendicular to the direction of wave travel.

pole mount

See →pole mount system.

pole mount system

A support structure for a ground-mounted solar array consisting of a pole and a frame upon which photovoltaic modules are mounted.

pole mounting

Mounting of a solar array on a pole.

pole-mounted photovoltaic system

See →pole-mounted solar system.

pole-mounted PV system

See →pole-mounted solar system.

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 pole-mounted solar system

pole-mounted solar system

A solar system that is mounted on a support structure consisting of a pole and a frame. A single pole can carry a frame with up to 24 solar panels; if another pole or two are added, a lead-bearing capacity is even higher. Due to a heavy weight it needs to support, a solid concrete foundation and a large sturdy pole are required to withstand strong wind. A pole mount system is a preferred option for solar installations on the ground because the multiple PV modules attached to a single frame can be simultaneously tilted for →seasonal adjustments to capture the maximum amount of sun’s energy. More precise day-to-day adjustments to the sun can be achieved by adding a solar tracker to the system. A pole mount is ideal for a →solar tracking system since the whole structure can be pivoted and controlled from one central point.

polished metal mirror

See →polished metal surface.

polished metal surface

A reflective material that is used as a mirror in →parabolic troughs and →solar cookers to concentrate the reflected sunlight along the focal line, intensifying solar radiation energy numerous times.

pollution

Dumping of toxic or harmful substances into the environment – water, soil, or air.

pollution control measures

Control measures that prevent the environmental pollution generated by industry, transportation, agriculture, oil production, and consumers. Measures against the dumping of pollutants into the ocean, uncontrolled disposal of hazardous waste, or uncontrolled agricultural burning are some examples of pollution control.

polyacetylene

(C2H2)n The simplest →conjugated polymer that contains acetylene repeat units of H−C≡C−H.

polycarbonate

(PC) Polycarbonates are a family of thermoplastic polymers characterized by robustness, durability, and high impact and fracture resistance. At the beginning, polycarbonate was used as a cost-efficient glass replacement, but over the years improved polycarbonate materials outperformed traditional glass properties in many respects. Polycarbonate is used in the manufacture of unbreakable windows and glazing structures. PC demonstrates better light transmission than glass, from 80% up to 92%

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of natural light. Polycarbonates can be engineered to admit more natural daylight while blocking ultraviolet (UV) radiation and infrared radiation (IR) that create heat. Today’s polycarbonates are six times lighter than glass and they allow a high degree of manufacturing flexibility in color and design. That is why polycarbonate sheets find a wide application in architectural roofing, skylights, greenhouses, canopies, carports, overpass covers, sports buildings, and many other outdoor glazing structures. polycarbonate panel

A transparent, durable, and shatter-resistant plastic sheet used in the manufacture of various outdoor glazing structures. Other desirable properties include lightweight and an overall engineering flexibility that allows tailoring-specific solar transmission properties, such as anti-UV and anti-IR layers, and a wide variety of designs.

polycarbonate sheet

See →polycarbonate panel.

polycrystal structure

A structure consisting of numerous small individual silicon crystals with irregular sizes and patterns.

polycrystalline

Referring to silicon material that consists of many small crystals.

polycrystalline ingot

See →polycrystalline silicon ingot.

polycrystalline material

See →polycrystalline semiconductor material.

polycrystalline microstructure

Microstructure of polycrystalline semiconductor materials with complex microstructural morphology and crystallographic orientation. A detailed knowledge of the microstructure, crystallographic orientation, grain size, and grain boundaries between numerous crystals that block the flow of electrons can lead to improvement of the polycrystalline semiconductor efficiency.

polycrystalline semiconductor

See →polycrystalline semiconductor material.

polycrystalline semiconductor material

Blue semiconductor material that is rougher than monocrystalline silicon because it consists of many small individual silicon crystals with irregular sizes and patterns. The grain boundaries between numerous crystals block the flow of electrons, reducing the electricity yield of the silicon cell. This is why polycrystalline cells are slightly

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 polycrystalline silicon

less efficient (around 2%) than monocrystalline silicon cells. The contemporary research is trying to compensate for this drawback and increase the polycrystalline semiconductor efficiency through various new methods, such as increasing the grain size or the neutralization of shallow acceptors at silicon gain boundaries using hydrogen. More knowledge about the structure and crystallographic orientations of individual grains holds promise for greater electronic quality of polycrystalline semiconductor materials. polycrystalline silicon

Also known as multicrystalline silicon or polysilicon. One of the key materials used in solar cell production that is made up of many small individual silicon crystals. See also →polycrystalline semiconductor material.

polycrystalline silicon block

See →polycrystalline silicon ingot.

polycrystalline silicon brick

Also known as multicrystalline silicon brick. A wafer-size brick consisting of multiple silicon crystals. The polycrystalline bricks are produced by direct casting of silicon into polycrystalline ingots that are cut up into wafer-size bricks. The bricks are then sliced with a wire saw into thin →silicon wafers.

polycrystalline silicon cell

See →polycrystalline silicon solar cell.

polycrystalline silicon ingot

Is typically a large rectangular- or square-shaped polycrystalline silicon block, for example, with dimensions of 1 m × 1 m (3 × 3 ft.) or larger. Other polycrystalline ingot shapes include rods and billets. Silicon feedstock is melted at high temperatures (1,415 °C and above) in a →directional solidification system furnace into a square mold. The large square silicon ingot takes a couple of days to cool down, whereupon it is sliced into wafer-size bricks.

polycrystalline silicon photovoltaic cell

See →polycrystalline silicon solar cell.

polycrystalline silicon photovoltaic panel

See →polycrystalline silicon solar module.

polycrystalline silicon PV cell

See →polycrystalline silicon solar cell.

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polycrystalline silicon PV panel

See →polycrystalline silicon solar module.

polycrystalline silicon solar cell

Also known as multicrystalline silicon solar cell or polysilicon solar cell. A type of silicon solar cell made from a wafer that consists of multiple small silicon crystals, also known as →crystallites. Polycrystalline cell production process is less complex than the one of monocrystalline silicon cells. Instead of being grown into a single crystal by the Czochralski method, silicon rocks are melted at high temperatures (1,415 °C and above) in a →directional solidification system furnace into a square mold. The square ingot takes a couple of days to cool down. As it cools and hardens, it crystallizes into multiple smaller individual crystals with a frost-like structure. The silicon ingot is sliced with a diamond saw into wafers that are then processed into polycrystalline silicon solar cells. The percentage of silicon material that is wasted during the cutting process is much smaller than in the monocrystalline cell production. The grain boundaries between numerous individual crystals block the flow of electrons, reducing the electricity yield of the silicon cell. This is why polycrystalline cells are slightly less efficient (around 2%) than monocrystalline silicon cells. On the other side, polycrystalline manufacturing costs are slightly lower than that of monocrystalline cells due to its less complex production process. When compared against amorphous solar cells, a similar relationship, now with polycrystalline technology being on top, can be observed. As the polycrystalline production process is more complex than the one of amorphous solar cells, they are more expensive than amorphous PV cells. However, they are proportionally more efficient than amorphous solar cells.

polycrystalline silicon solar module

A module that consists of →polycrystalline solar cells that are made from multiple small silicon crystals, also known as →crystallites. As they are made up of multiple individual crystals, polycrystalline solar panels have a specific jumbled texture – many nuances of blue color with numerous irregular frost-like multicrystal patterns.

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Although they are slightly less efficient (around 2%) than their monocrystalline counterparts, their lower costs due to a less complicated manufacturing process and less wasted material compensate for the lower power output. Their market share has surpassed the one of monocrystalline panels and continues to grow. The degradation rate of polycrystalline solar panels is very low. Even though they have a shorter real-life expectancy than monocrystalline panels, the same product life span of 25 years is warranted by most manufacturers for both PV panel types. polycrystalline silicon solar panel

See →polycrystalline silicon solar module.

polycrystalline silicon wafer

Also known as multicrystalline silicon wafer. A wafer made of multiple small silicon crystals that are produced by direct casting of silicon into polycrystalline ingots. The ingots are cut up into wafer-size bricks that are then sliced with a wire saw into thin silicon wafers. The wafers are subsequently processed into →polycrystalline silicon solar cells.

polycrystalline solar cell See →polycrystalline silicon solar cell. polycrystalline solar panel

See →polycrystalline silicon solar panel.

polycrystalline thin film A thin-film coating consisting of →polycrystalline semiconductor material. polycrystalline thin-film A thin-film solar cell made of →polycrystalline semiconducsolar cell tor material. polycrystalline wafer

See →polycrystalline silicon wafer.

polyethylene

A →thermoplastic material often used in manufacture of semi-transparent, UV-resistant plastic films for greenhouse covering and transparent cover sheets for solar modules. Polyethylene is also utilized as a transparent encapsulant material for solar cells. Polyethylene coating acts as an electrical insulator around the conducting photovoltaic copper wire.

polyethylene high density

(PEHD) See →high-density polyethylene (HDPE).

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polyethylene terephthalate

(PET, PETE) A →thermoplastic material often used in manufacture of →PET substrates for flexible →organic solar cells.

polyethylene terephthalate substrate

A substrate for flexible →organic solar cells made of the thermoplastic material polyethylene terephthalate (PET).

polyimide

(PI) A type of polymer, originally developed by DuPont, which contains repeating imide groups. Due to its resistance to high temperature, radiation, wear, and corrosion, it is often used for heat-resistant substrates or coatings in solar panel manufacturing.

polyimide substrate

A flexible substrate made of polyimide onto which semiconductor materials, such as →copper indium gallium selenide (CIGS), are deposited. In comparison to other polymer materials, polyimide allows higher deposition temperatures, resulting in higher efficiencies. Other advantages of polyimide substrate include flexibility, transparency, high electrical insulating properties, toughness, and smoothness.

polymer

A substance made from a long chain of molecules that are composed of a large number of repeating subunits.

polymer composite material

Solid polymer composite material used as substitute for liquid electrolytes in →solid-state batteries.

polymer film

Also known as a plastic film. An organic photovoltaic film made of polymer materials or a hybrid organic–inorganic blend. Apart from polymer films with semiconductor characteristics, plastic films are also used in the manufacture of →backsheets, as encapsulant films in the encapsulation process, and as protective layers on solar panels and windows.

polymer layer

See →polymer film.

polymer solar cell

(PSC) Also known as organic solar cell and plastic solar cell. A type of solar cell that uses semiconducting polymers instead of traditional inorganic semiconductor materials, such as silicon, gallium, or arsenide, to generate electricity. The Nobel Prize winners Alan J. Heeger, Alan MacDiarmid, and Hideki Shirakawa realized in the late 1990s that polymer materials, traditionally known as insulators, can be tweaked to act as semiconductors.

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 polymer solar module

They doped conjugated polymers with iodine, improving optical and electronic properties of polymers to such an extent that they were able to transfer electrons. They opened a new chapter in the solar cell history, which was characterized by low conversion efficiency of first plastic photovoltaic cells that could not compete with the superior conversion performance of monocrystalline silicon solar cells in spite of their inexpensive material and production process. Over the years, the efficiency of polymer solar cells has gradually improved. The big leap forward occurred in recent years when scientists came to the conclusion that low exciton diffusion lengths and poor electron mobilities in polymer solar cells can be significantly improved by nanoscale morphology. See also →organic photovoltaic cell. polymer solar module

See →plastic solar module.

polymer solar panel

See →plastic solar module.

polymer substrate

A flexible substrate made of polymer onto which semiconductor materials, such as →cadmium telluride (CdTe), a-Si: H, polycrystalline Cu(In,Ga)Se2, or other heterojunction semiconductor layers can be deposited. During the deposition of semiconductor thin films, polymer substrates require much lower substrate temperatures than traditional substrates, resulting in lower efficiencies.

polymeric substrate

See →polymer substrate.

polymerisation

UK See →polymerization.

polymerization

US A reaction in which many small molecules called monomers are synthesized into a covalently bonded chain to form a polymer.

polymethyl acrylate

(PMA) A polymer of methyl acrylate, used in the form of nanofiber membranes in a polymer matrix in quasisolidstate electrolytes for →dye-sensitized solar cells (DSSCs).

polymethyl methacrylate (PMMA) See →acrylic glass. polymethylmethacrylate

(PMMA) See →acrylic glass.

poly-Si

Abbreviation for →polycrystalline silicon.

polysilicon

See →polycrystalline silicon.

polysilicon feedstock  

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polysilicon feedstock

Chunks of hyperpure silicon that are directly melted into multicrystalline silicon ingots.

polysilicon layer

Polycrystalline silicon layer.

polysilicon solar cell

See →polycrystalline silicon solar cell.

polysiloxane

Also known as silicone or silicone polymer. A polymer that consists of alternating silicon and oxygen atoms and is commonly used in polymer manufacturing. Silicones exhibit the following properties: corrosion, abrasion, and chemical resistance, flexibility, and law surface energy. In solar industry, the polysiloxanes are utilized as weather and corrosion-resistant coatings, sealants, and insulation.

polystyrene

A synthetic polymer that is often used as a common building insulation material. Recently, potential health risks are associated with polystyrene that is regarded as a possible carcinogen that can also disrupt hormones or affect reproduction in humans. As the brominated flame retardant HBCD used in polystyrene insulation is considered hazardous to both human health and the environment, scientists and manufacturers search more and more for alternative insulation materials that can replace polystyrene.

polyvinyl chloride

(PVC) A plastic used for wire insulation and cable jacketing.

polyvinyl fluoride

(PVF) Also known as Tedlar®. The formula of polyvinyl fluoride is (C2H3F)n. A transparent polymer material that is typically used as a protective layer, for example, a backsheet or a top protective coating, in solar modules due to its extraordinary characteristics: mechanical strength, resistance to harsh weather conditions, and low permeability of moisture and air.

pool collector

See →solar swimming pool heater.

PoP

Abbreviation for →print-on-print.

portable solar battery charger

See →portable solar charger.

portable solar charger

A solar-powered charger capable of collecting and storing solar energy in order to supply electricity to a wide range of portable electronic devices, such as cell phones, MP3 players, fitness trackers, cameras, and other low-power

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 portable solar cooker

devices. The solar charger typically consists of a solar panel and a chemical or lithium-ion rechargeable battery. USB port and cable are commonly used to connect the charger with a cell phone or another portable device. The main advantages of a portable solar charger are the generation of clean, sustainable energy and the freedom of movement. As they do not need to be connected to the utility power outlet to recharge the batteries, portable solar chargers charge cell phones or cameras on the go, while using renewable solar energy that is constantly replenished in a natural way and virtually inexhaustible. The main disadvantages of portable solar chargers are that they do not work in the evening and at night and that their performance is minimal on cloudy days. portable solar cooker

Also known as a camping solar cooker. A lightweight solar cooker that can usually be folded up for easy storage and transport. The foldable construction is designed for camping, boating and other outdoors activities, allowing carbon-free cooking without the use of fire, gas, or electricity.

portable solar generator A type of →solar generator, often mounted on plastic or bicycle wheels, which can be moved from one place to another. As portable solar generators are designed to be used off-grid, they are equipped with numerous power outlets, such as 12 V AC, USB, and Anderson Powerpole connectors, to provide power to various electric devices ranging from lights over fans and power tools to sensitive electronics, for example, cellphones, laptops, digital cameras, and TVs. portable solar light

See →mobile solar light tower.

portable solar light tower

See →mobile solar light tower.

portable solar module

A solar module designed for camping trips, RVs, boats, and travel in general. The power generated by portable modules during the day is stored in a →portable solar recharger or a battery pack to power various electronic devices day or night, such as cellphones, laptops, digital cameras, GPS, iPads, and iPods. Portable solar modules are typically lightweight and foldable for easy transport and storage.

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In spite of the lightweight, they are made of rugged materials that are able to resist harsh weather conditions, such as rain, snow, wind, and extreme heat. portable solar panel

See →portable solar module.

portable solar shower

A simple, easily transportable shower system whose water is heated by sunlight. Portable solar shower consists of a water container – a tank or a PVC bag, a mounting bracket, a nozzle valve, and a hose with a shower head. The compact reservoir or flexible bag is mounted by means of a mounting bracket on a pole, tree, or a recreational vehicle (RV). The tank or bag is painted black to absorb heat and warm water faster. As the system is gravity fed, it does not require a pump or any other electrical equipment.

portable solar still

A plastic bag or →watercone for seawater distillation.

portrait layout configuration

A layout configuration in which solar panels are mounted vertically. See also →layout configuration.

positive carriers

See →positive charge carriers.

positive charge

See →positive electric charge.

positive charge carriers

→Holes that carry positive charge with them while moving from one place to another along the →valence band.

positive contact finger

Positive metal contact fingers are connected to p-type diffusion regions of the solar cell.

positive contact pad

A metal contact on the back side of a silicon crystalline solar cell that is connected to the positive electrode. A PV cell is serially connected to another PV cell by a →tabbing ribbon that electrically connects the negative contact pad to a positive contact pad of the other photovoltaic cell.

positive declination

A declination north of the celestial equator is known as a positive or northerly declination.

positive declination angle

An angle between the celestial equator (0°) and north celestial pole (+90°).

positive electric charge

An →electric charge that has more protons than electrons. In semiconductors, →holes are positive charge carriers that move along a →valence band. In a →p-type semiconductor, holes move from left to right through the silicon crystal lattice, carrying positive charge. See also →negative charge.

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 positive electrode

positive electrode

Also called an anode – a positive terminal of a battery. A terminal through which an electrical current enters a battery or electrolytic cell. In an electrochemical cell during discharge, electrons flow from the negative electrode, through the external circuit, to the positive electrode.

positive photoresist

A type of →photoresist that becomes easily soluble in the photoresist developer solution, when exposed to UV light. Hence, UV light is pointed at the material that should be removed. The exposed photoresist is then washed away by the developer solution, leaving only the unexposed portion of the photoresist. Positive photoresist is typically used for contacts.

positive plate

A battery plate that is connected to the positive terminal.

positive terminal

See →positive electrode.

positive-energy home

Home that produces more energy that it uses. See also →zero-energy home.

post-2012 Climate Agreement

A long-term plan that promotes a cooperative action at a global level for emission reductions with the goal to “stabilize greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system” (Bali Action Plan). The European Union proposed that a post-2012 climate agreement should include the following eight basic building blocks: 1. Limiting global warming to 2 °C above the preindustrial temperature. 2. Deeper mandatory absolute emission reductions by developed countries. 3. Fair and effective contributions by other countries, especially the rapidly emerging economies. 4. Strengthening and extending the global carbon market. 5. Increasing cooperation on research, development, and deployment of the clean technologies needed to reduce emissions. 6. Enhancing efforts to address adaptation to climate change. 7. Addressing emissions from international aviation and shipping. 8. Reducing emissions from deforestation, which is responsible for up to 20% of global CO2 emissions.

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potential induced degradation

(PID) Performance degradation in solar modules as a result of leakage current.

potential transformer

See →voltage transformer.

pounds per square inch

(Psi) A British and American unit of measure for pressure. Psi equals the pressure resulting from a force of 1 pound applied to an area of 1 in2.

powder feeder

In →plasma spray guns or other plasma powder thermal spray systems, a component that provides a constant flow of powder, for example, →zirconia, into the plasma flame, ensuring even distribution and uniformed surface coatings.

powder injection

Injection of powders, such as →zirconia, in plasma jets used in a plasma spray coating process. The quality of the particle beam and the final coating product depends on powder injection parameters such as gas flow, injection angle, and injector position. In internal injection, the powder injectors are placed inside the nozzle of the plasma torch, while in external injection they are positioned at a short distance downstream of the plasma torch exit.

powder injection molding

US (PIM) A mass manufacturing process in which high-precision parts with complex geometries are produced from powders in high volumes and at high speeds.

powder injection moulding UK (PIM) See →powder injection molding. powder supply

See →powder feeder.

power

The amount of work done divided by the total time it takes to do the work. See also →electric power.

power analysis

See →load analysis.

power conditioner

A device that converts DC power to AC power, regulates voltage, and protects grid interconnection.

power conditioning

Converting photovoltaic power generated by solar panels into a desired power output form that is safe and suitable for all types of loads (household appliances).

power-conditioning equipment

Electrical equipment that converts photovoltaic power generated by solar panels into a desired output form providing a safe and suitable power supply to all types of loads (household appliances). Examples of power conditioning devices are →converter, →inverter, →micro-inverter, →battery

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 power-conditioning system

charge regulator, →blocking diode, and →uninterruptible power supply (UPS). power-conditioning system

(PCS) See →power-conditioning equipment.

power control unit

See →solar power control unit.

power conversion efficiency

(PCE) The power conversion efficiency describes the general efficiency of a solar cell or solar module. The PCE is the ratio of power input to power output, for example, the percentage of incoming light energy that is converted into electrical energy.

power deficit

Energy shortage of more than 2% or 3% in a region or a country is considered a power deficit. Among other strategies, power deficit can be overcome by a better integration of residential small-scale solar photovoltaic systems into the utility grid and by developing intelligent, computer-supported feed-in power management, which allows grid operators to better distribute electricity across different regions.

power demand

See →annual electricity requirement.

power density

Power density is an important feature of rechargeable batteries, indicating how quickly a battery can store and deliver energy per unit of volume. It is measured in watts per kilogram (W/kg). High power density batteries are used for starting the car engine, as they need to deliver a quick surge of power for a few seconds. The improvement of the fast charging technology for eV batteries is one of the main goals of the electric vehicle industry, which will encourage the spread of this sustainable means of transportation.

power distribution

See →electric power distribution.

power factor

(PF) The ratio of real power in watts to apparent power in volt-amps in an AC circuit. Power factor is calculated by dividing the real power (watts) by the apparent power (volts × amps).

power flux

The rate of transfer of energy per unit area.

power generation

See →electricity generation.

power generation from renewable sources

See →electricity generation from renewable sources.

power grid 

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power grid

See →electrical grid.

power line

A cable used for electricity transmission, carrying electrical energy below the ground or above the ground, supported by poles or by metal pylons.

power loss

In general, low-voltage solar systems, for example, 12 or 24 V systems have higher power losses. The higher the voltage, the lower the power losses. A significant part of the energy losses comes from losses in electric cables. It is essential to use the correct cable thickness and keep cable lengths as short as possible. PV inverter losses account for another part of lost energy. The major portion of inverter losses, around 80%, come from a switching device and AC inductors, whereas →standby current, when the device is not in use, can also contribute to power loss. Power losses in solar modules can be caused by →soiling, →shading, heating, →reflection, and →recombination within PV cells. Dust and dirt on PV panels as well as complete or partial module →shading by trees or other structures affect the power output of a solar array. A large portion of energy losses in solar panels can be attributed to heating. When the temperature of the module rises over 25 °C (77 °F), it potentially reduces the power yield by 10–25% based on the proportional voltage drop due to resistance. Another part of energy losses is incurred by reflection. A portion of incident solar radiation is reflected by the glass surface of a solar panel and lost. Finally, the recombination or the imperfection of transport of excess charge carriers within a solar cell accounts for another part of power losses.

power loss in electric cables

See →cable losses.

power management

The management of supply and demand of electrical and thermal energy at the large utility scale by a grid operator or at the small scale by a household or business owner. The major task of a grid operator is to ensure a constant balance between supply and demand of electric power, regulating the inconsistency in the output frequency and maintaining scheduled frequency. Homeowners and business owners can reduce their electricity and heat consumption by

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 power management system

installing a solar array, sealing all gaps and openings in the building envelope, using an →energy management and information system and various other energy saving techniques. power management system

See →energy management and information system.

power meter

See →electricity meter.

power monitoring

A process in which critical data, such as solar power yield, are routinely monitored and stored for the purpose of better data evaluation and further processing. By measuring DC and AC power, currents, and voltages, solar owners and producers have a better overview of the overall performance and efficiency of their solar systems. In addition, by keeping track of how much electricity is being generated, the solar owner can also detect a system malfunction or a maintenance issue, such as the accumulated dirt on PV panels. When the solar power output goes down, a thorough inspection, an identification of the problem, and probably a repair or cleaning are needed. Some monitoring systems are able to locate and diagnose problems in the solar system.

power monitoring system

A monitoring platform consisting of a wide variety of monitoring devices, such as →voltmeters, →ammeters, and inverter displays, often connected to the Internet to provide real-time data about system performance. A reduced solar power yield is an indicator of a possible system malfunction or a maintenance issue due to the accumulated dirt on solar panels. Modern power monitoring systems include a fault detection and troubleshooting features. When the monitoring system detects a problem, it immediately sends a warning message, pointing to problematic modules with help of PV visualization tools.

power optimizer

DC to DC converter connected to each solar module to maximize the energy output of a solar system.

power optimizer for solar modules

See →power optimizer.

power output

See →solar energy output.

power overload 

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power overload

An overload of electricity which occurs when an excessive amount of current flows through the circuit, leading to excessive heat generation, fire risk, and damage to equipment. Excessive load, when too many electrical appliances are simultaneously working in a power system, is a common cause of energy overloads. When lightning strikes a building, it surges through the existing paths of electrical wiring to the ground, shorting out the circuits. If the power grid is not upgraded, a rapid expansion and connection of too many solar systems to the grid can cause congestion and surges. Around noon, when solar systems work at full capacity, the surge can become too large for an old grid to cope with. To deal with this problem, along with the expansion of PV systems, it is crucial to parallelly develop intelligent grid technology able to coordinate and rapidly move large quantities of electricity from one place to another, as well as large-scale energy storage facilities.

power production

See →electricity generation.

power production from renewable sources

See →electricity generation from renewable sources.

power purchase agreement

(PPA) A contract between the solar owner and the local utility company according to which the utility is obliged to purchase the electricity or thermal energy generated by the solar array from the system owner. Depending on the country’s or state’s renewable energy policy, a fixed rate is typically used, which is equal to or less than the current market rate.

power rating

Nominal power output, the maximum amount of continuous power that a solar panel or an inverter, based on their specification, can supply to the connected devices (load) in a house.

power regulator

An electrical device that regulates the current and voltage coming from solar panels to protect the batteries from overcharge and overdischarge. See also →charge controller.

power shortage

See →energy shortage.

power source

Also known as →energy source. Any substance, for example, coal, solar, wind, or natural gas, that can be converted into a suitable form of energy to supply heat or electricity.

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 power supply

power supply

The energy that is generated by a solar system and either supplied to electronic equipment or fed into the public power grid. Before being used by the loads or fed into the grid, the generated DC energy needs to be converted with help of an inverter into grid-compatible alternating current.

power supply container

Stand-alone photovoltaic power package consisting of solar modules and lead-acid batteries.

power supply control unit

(PSCU) An energy management system specifically designed for monitoring the surplus electricity level of lead-acid batteries and controlling supply and demand. PSCU reduces deterioration of the batteries, thus extending their life span. In addition, it reduces maintenance demands and replacement costs.

power surge

Is a sudden, fast rise in voltage causing a transient excessive current flow in a circuit that can damage electrical devices.

power surplus

Also known as electricity surplus. The quantity of power that exceeds its demand. As new solar, wind, and other renewable power sources are added to the electricity network, these new electricity producers generate more energy in some counties and regions that it is needed. If the surplus energy is continuously fed into the public grid, it leads to an overload of the electrical grid, excessive heat generation, fire risk, and damage to equipment. To avoid the overloading problem, communities or states with power surplus can sell their energy and distribute it where needed, often in far-away regions. Another way to deal with the problem of overloading the electricity grid is to develop large-scale energy storage systems that are able to store solar electricity over long periods of time. Such energy storage systems include →pumped hydroelectric energy storage (PHES), →compressed air energy storage (CAES), →molten salt storage, →net energy metering, →batteries, →supercapacitors, →hydrogen fuel cells, →flow batteries, or →mechanical flywheels. With the help of long-term energy storage systems, the power surplus that is generated and stored in hot summer months will be used in cold seasons to offset the winter power shortage, when the solar power supply is very humble. The longterm energy storage is one of the major challenges that the

power tolerance 

 595

solar technology needs to overcome in order to become a mainstream power source. power tolerance

A measure of how much electrical power a →photovoltaic module can generate above or below its →rated power, as specified in the product data sheet. The range of outperformance and underperformance is typically expressed as a +/– percentage in technical specifications, for example, ±5% or +5%/–5%. Most PV modules work in the range of ±3%, which means that a 100 W module can produce 97–103 W under real-world conditions.

power tower

See →solar power tower.

power transmission

See →energy transmission.

power transmission grid See →energy transmission network. power transmission network

See →energy transmission network.

power yield

See →solar energy output.

power-to-mass ratio

See →power-to-weight ratio.

power-to-weight ratio

Power-to-weight ratio is often used to evaluate the performance of a photovoltaic (PV) panel or a battery. It indicates how much energy a PV module or a battery can deliver or store per unit of volume. It is typically measured in watts per kilogram (W/kg). The goal of solar manufacturers is to produce lighter devices (solar panels and batteries) with higher energy density.

PPA

Abbreviation for →power purchase agreement.

PR

Abbreviation for →performance ratio.

precipitable water

The total water vapor contained in a vertical column of the atmosphere. It is measured in millimeters or inches as a depth of water that would be obtained if all the water vapor in a given column of air were condensed and precipitated over a location.

precise optical instrument

An optical instrument for making precise measurements for beams of light and detailed analysis of semiconductor material contents. As the miniaturization trend, such as →nanotechnology, in solar industry tends to design and build structures on smaller and smaller scale, precise

596 

 precision sieve

optical instruments play an increasingly important role in the observation of small-scale, dynamic chemical and electric processes. precision sieve

A precision mesh or screen for a high precision →screen printing process used in solar cell manufacturing.

precision spectral pyranometer

(PSP) An instrument for measuring →total solar radiation (the sum of →direct and →diffuse solar radiation) or defined wavelength bands. The pyranometer consists of an outer clear glass hemisphere or colored glass hemispheres (yellow, orange, red, or dark red) for transmitting specific bandwidths of the solar spectrum and a rectangular or circular multijunction Eppley wire-wound thermopile glued to the back of the sensor disk.

precursor

A compound that is used as a source material in various deposition processes, such as →CVD, →PVD, or →ALD. Liquid precursors are often used in →chemical vapor deposition (CVD) processes, whereas solid precursors are applied in →physical vapor deposition (PVD) methods. In a CVD process, for instance, the chemical reactions of precursor particles take place both in the gas phase and on the wafer.

pre-doped

→Silicon wafers are pre-doped with →boron, forming a →p-type semiconductor.

presence detector

Also known as occupancy detector or absence detector. A device that provides automatic control of lighting, heating and ventilation by detecting body heat and movement of tenants. If a person is detected by sensors in a room, the presence detector automatically switches on the lighting or heating system. When the tenant leaves the room and nobody is detected in the perimeter, the detector automatically switches off the systems, reducing energy consumption of the household as well as harmful →greenhouse gas emissions at the same time.

pressure drop

The amount of pressure that is permanently lost as a fluid, water, or gas passes through pipes (pipe walls), valves, fittings, and other appliances.

pressure drop in the solar circuit

In a solar collector or another solar-thermal circuit, the total pressure drop is determined by the sum of friction or major losses and local or minor losses. Friction or major

pressure gauge 

 597

losses occur in pipe flow due to the frictional resistance of the pipe walls exposed to the →heat transfer fluid. Pressure losses in components like valves, fittings, bends, and tees are known as local or minor losses. pressure gauge

A device for measuring fluid pressure.

pressure loss

See →pressure drop.

pressure sensor

A device that senses the mechanical pressure and converts it into an electric signal.

price of electricity

See →electricity price.

price per watt

See →cost per watt.

price-performance ratio

See →cost–performance ratio.

primary battery

A nonrechargeable battery that is discarded after use.

primary circuit

A circuit or high-voltage lines that transfer electric energy from a source, such as a →solar power plant, to the stepdown transformer and the →secondary circuit.

primary energy

Energy as it is found in the natural environment in the form of solar radiation, wind, rivers, tides, or crude oil. Sunlight as a primary energy source can be directly used for natural heating of the house without any electrical devices, as is the case in →passive solar heating technologies. However, in most cases, the primary energy is converted into the →secondary energy.

primary energy source

Energy sources as they appear in the natural environment. They are divided into non-renewable energy sources, such as →fossil fuels and →nuclear energy, and renewable energy sources, such as solar, wind, hydropower, and geothermal.

primary lines

High-voltage power lines that transfer electrical current from the power plant to substations in the city.

primary network

See →primary circuit.

printed solar cell

A photovoltaic (PV) cell that is printed to a flexible substrate by using a printing appliance, such as a roll-to-roll coating machine. Polymer thin-film PV cells consist of multiple layers, each of which has different functions: →semiconductors absorb solar radiation, whereas electrodes

598 

 printed solar cell on paper

conduct electric charges. The printing process allows a quick selection of different →solar inks and other parameters, such as rotation speed, pressure, or drying time, suitable for a specific thin film. The semiconductor material and electrodes can be rapidly put down onto a flexible plastic substrate roll, ensuring a high throughput. Various sizes and shapes of PV cells are possible, allowing a higher amount of design freedom. The most of the printing process phases can be completed under ambient conditions without costly and time-consuming vacuum or evaporation techniques, further reducing the manufacturing costs of this technology. printed solar cell on paper

A highly flexible photovoltaic cell that is easy and cheap to produce by means of photovoltaic printing; however, they demonstrated a very low energy conversion efficiency.

printed solar module on paper

A highly flexible photovoltaic module that is easy and cheap to produce by means of photovoltaic printing; however, they demonstrated a very low energy conversion efficiency.

printed solar panel on paper

See →printed solar module on paper.

printing paste

A conductive metal paste that is spread over the screen and forced through a mask into the mesh openings to form a grid of circuit lines on a silicon wafer.

print-on-print

(PoP) A method of printing the metallization grid onto the front side of a solar cell twice in order to reduce the →finger width. The first print prints screen fingers only, whereas the second print prints screen fingers and busbars. The decrease in finger width reduces shadowing, letting more sunlight through to the silicon semiconductor, which in turn improves solar cell efficiency.

process heat

Thermal energy, typically generated from fossil fuels, which is used in chemical and other industrial processes.

propylene glycol

A synthetic organic compound that is often used as an →antifreeze or →heat transfer fluid in →heat transfer systems. It is commonly mixed with water in 60/40 or 50/50 ratios.

protective coating

A protective nanocoating with hydrophobic and self-cleaning properties that provides an invisible protective shield

protective cover 

 599

around the solar module, allowing maximum solar power generation. Hydrophobic coating protects solar cells against water and moisture by letting water flow off the panel more easily during rain and in humid weather conditions. The self-cleaning coating keeps the module’s surface clean by repelling dust and dirt particles. The self-cleaning film reduces cleaning and maintenance costs. The ultimate goal of all protective coatings is to allow more incident light to pass through the surface and reach the solar energy-absorbing semiconductor, hence producing the maximum solar output. protective cover

See →protective coating.

protective layer

See →protective coating.

proton

A subatomic particle with a positive electric charge, found in the nucleus of an atom.

protractor

An instrument for measuring angles in on-roof and on-ground PV installations. If electrical tools for an obstacle analysis are not available, a protractor can be used to conduct an analysis of obstacles blocking the sun on the future PV site. A pencil is taped to the center of the protractor, so that it can be moved across the protractor, aiming at different angles of the sun as it moves across the sky in different seasons.

PSC1

Abbreviation for perovskite solar cell. See →perovskite photovoltaic cell.

PSC2

Abbreviation for →polymer solar cell.

PSCU

Abbreviation for →power supply control unit.

PSH

Abbreviation for pumped-storage hydroelectricity. See →pumped hydroelectric energy storage.

Psi

Abbreviation for →pounds per square inch.

PSP

Abbreviation for →precision spectral pyranometer.

PTC

Abbreviation for parabolic trough concentrator (PTC). See →parabolic trough solar collector.

p-type diffusion region

A p-type diffusion layer that is formed in a photovoltaic cell by doping the semiconductor substrate with →acceptor atom material, such as →boron.

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 p-type dopant

p-type dopant

Is a chemical element from Group III of the periodic table, for example, →boron, which is added in a small, controlled quantity to a silicon semiconductor, in order to change its electrical properties. The boron atom, so-called →impurity, gladly accepts an electron from its neighboring silicon atom since it has one electron less (three valence electrons) than the surrounding silicon atoms with four valence electrons. The silicon atom that donated an electron to the boron atom to fulfill the bonding requirements leaves a “hole” behind that will attract another silicon electron and so on and so forth. The hole starts migrating through the silicon crystal lattice, producing an electrically conductive →p-type semiconductor.

p-type doping

Doping of a silicon semiconductor with a chemical element from Group III of the periodic table, for example, boron, to induce a positive charge and produce an electrically conductive →p-type semiconductor under given conditions.

p-type semiconductor

A semiconductor in which holes are the dominant charge carrier. p-Type semiconductor is created by doping an →intrinsic semiconductor with a chemical element from Group III of the periodic table, for example →boron. This p-type dopant, also called impurity, has three electrons in its outer shell, creating an imbalance in a silicon crystal structure dominated by a symmetric four electrons in the

E

Acceptor level

P-type Semiconductor

public charging infrastructure 

 601

valence shell pattern. To fulfill the bonding requirements and compensate for their electron deficiency, boron atoms accept electrons from the neighboring silicon atoms, leaving holes behind them. As electrons move into holes, they considerably increase the electrical conductivity of the pure semiconductor, boosting the electron flow along the valence band. Since the number of holes that are positive charge carriers is higher than the number of electrons, the doped semiconductor material is referred to as a p-type (positive-type) semiconductor. public charging infrastructure

A network of public charging stations for electric vehicles (eVs). The development of a widespread public charging infrastructure is one of the key factors for a successful switch from gas to electric vehicles.

public grid

See →electrical grid.

Public Utilities Commission

(PUC) Each state in the United States has a public utilities commission that is in charge of regulating utility services and rates, so that the citizens receive utility service at reasonable and standardized rates

Public Utility Regulatory The Public Utility Regulatory Policies Act (PURPA) was Policies Act passed in 1978 to encourage the conservation of electrical energy and natural gas, development of hydroelectric potential, alternative energy sources and energy efficiency, and reasonable retail rates for electric consumers. It enables individuals and businesses to sell excess electrical power generated by photovoltaic modules to their local utilities. PUC

Abbreviation for →Public Utilities Commission.

pulse width modulated inverter

See →pulse width-modulated wave inverter.

pulse width modulated wave inverter

Also known as PWM inverter. A high-end inverter that produces a steady, high-quality output voltage irrespective of the load. In contrast to the output voltage fluctuations due to the changes in the load in conventional inverters, PWM inverters are able to adjust the output voltage to the connected load.

pulse width modulation

(PWM) See →pulse width modulated wave inverter.

pulsed laser

A laser that emits light in the form of optical pulses or short bursts of energy rather than in the form of a continuous beam.

602 

 pulsed laser deposition

pulsed laser deposition

(PLD) A type of →physical vapor deposition (PVD) process for manufacturing of thin-film semiconductor devices. In this PVD process, a pulsed laser beam is focused onto the target material to be deposited. The vaporized, ablated material forms a transient plasma plume, a gaseous blend of atoms, molecules, clusters, free electrons, and ions. Under high vacuum conditions, the plume expands rapidly away from the target material until it reaches the substrate, on which it condenses as a thin semiconductor layer. The pulsed laser deposition has the following advantages: 1. high deposition rates; 2. stoichiometric transfer of complex materials from target material to the film on a substrate; 3. good adhesion of the deposited film to the substrate; 4. control over the growth rate, film thickness, and crystallinity; 5. deposition of multilayer thin films without the need to interrupt the operation for each layer; 6. low substrate temperatures, ideal for deposition onto polymers; and 7. well-defined final structure (uniformity).

pulsed solar simulator

A type of →solar simulator that has a pulsed radiation source for generating electromagnetic radiation. The light source generates pulsed light beams that are directed at one or more mirrors and run through different optical filters that simulate various ranges of solar radiation, such as ultraviolet (UV), infrared, visible light, or near infrared. Pulsed solar simulators are suitable for testing applications that require a large area of illumination, such as big solar panels. They are more cost-efficient than →steadystate solar simulators.

pulse duration modulation

(PDM) See →pulse width modulated wave inverter.

pulverized spray material

In thermal spray coating, powder material, such as →zirconia, is pulverized after being fed into the plasma flame. The generated high-temperature zirconia particles are sprayed onto the target surface, forming evenly distributed thin-film coating.

pump

A device that regulates the flow of →heat transfer fluid from →solar collectors to the →heat exchanger and →storage tank in a →solar water heating system.

pumped hydrosystem

See →pumped hydroelectric energy storage.

pumped hydroelectric energy storage 

 603

pumped hydroelectric energy storage

(PHES) Also called pumped-storage hydroelectricity (PSH) or pumped hydrosystem. Pumped hydroelectric energy storage is one of the most promising large-scale solar energy storage systems. In consists of two reservoirs at different elevations and one reversible pump-turbine unit in between. When there is a surplus power in a PV system during the day, it is fed/sold back to the grid. This excess power is stored in the PHES system by pumping water from the lower reservoir into an elevated storage reservoir usually during the hours of low consumption (offpeak time). The stored water in the upper lake becomes a potential energy just like the power stored in a battery. During periods of high electricity demand (peak hours), the pump motor is switched to the generator mode and the stored water is released from the upper reservoir, becoming kinetic energy. The stream/current is run downhill through the turbine at the lower level as in a conventional hydropower plant generating electricity. The major drawback of the pumped hydroelectric energy storage is the fact that they don’t work well in some geographical regions, such as flat land and arid area because the upper reservoir needs to be at a considerably higher elevation than the lower reservoir and large volumes of water are required for both lakes.

pumped-storage hydroelectricity

(PSH) See →pumped hydroelectric energy storage.

pure lithium

For instance, →pure lithium anode in a solid-state battery.

pure lithium anode

A very pure lithium-metal foil placed along with a lithium salt in a solid-state electrolyte, providing a large electrochemical stability and allowing a dynamic charge transport.

pure sine wave inverter

Pure sine wave inverter, also known as full sine wave inverter or simply sine wave inverter, is a power inverter that produces a sine wave curve. The attribute “pure” is preferred by manufacturers and it refers probably more to a high-quality power output than to the actual sine wave, since in reality, the output voltage does not produce a “pure” sinusoidal waveform, just a less distorted one than the →modified sine wave inverters. The conversion of direct current from solar panels to alternating current that is needed for most household appliances can be graphically illustrated in the following manner: a straight line,

604 

 purified silicon

steady stream of electrons flowing in one direction only, representing the direct current (DC), is converted into a sinusoidal AC waveform that goes from 0 V to a positive peak of around 120 V, and then, when the direction of electron flow is switched, it plunges to a negative peak of around 120 V. The cycle is repeated 50 (in Europe) or 60 (in the United States) times per second. Although pure sine wave inverters are a bit more expensive than modified sine wave inverters, they are more efficient, reliable, universal, and overall of better quality than modified sine wave power inverters. As they do not struggle with rough waveforms, interference, and increased heating, pure sine wave inverters use 20–30% less power than modified sine wave inverters. They produce high-quality AC power that closely matches utility supplied electricity and in some brands even surpassing it. Pure sine wave inverters are universal nowadays, as all household appliances run on them without any problems. In particular sensitive electronical devices that have a hard time with square and modified sine wave inverters (digital clocks, LED TVs, audio equipment, and laser printers) run better on pure sine wave inverters. Pure sine wave inverters will not cause overheating of electric motors and overall will not reduce electric noise. Fans do not produce a humming sound, and LED lights, microwave ovens, and audio amplifiers do not pick up a buzzing sound. Due to smoother running on pure sine wave inverters, the life span of equipment will be extended. Taking into consideration all the above advantages, and as the price of pure sine wave inverters keeps falling, they have become the first choice for an average household today. purified silicon

Silicon semiconductor material with a high purity level of 99.99% that is required for a successful manufacture of crystalline silicon solar cells. Silicon is commonly purified by a method that encompasses reduction and/or thermal decomposition of an exceptionally pure vaporizable compound of silicon such as trichlorosilane.

purified silicon melt

The bath of highly purified molten silicon (99.9%) required for the manufacture of a silicon ingot in a controlled →Czochralski crystal growth process. Ultraclean silicon

purlin 

 605

material as well as a very clean environment in a →crucible are necessary prerequisites for a successful crystal growth from the silicon melt. purlin

A piece of timber that rests horizontally on the main rafters of a roof and supports the common rafters on which the roof covering is laid. A structure for mounting solar panels is often secured into the purlins of a roof, canopy or a car port. Steel or aluminum purlins are horizontal beams on which solar panel are mounted. They are a vital part of a ground-mounting structure. A clamp assembly holding solar panels in place is screwed into the wood or steel purlins.

PURPA

Abbreviation for →Public Utility Regulatory Policies Act.

PV

Abbreviation for →photovoltaic.

PV accessories

See →photovoltaic accessories.

PV adhesive

See →solar adhesive.

PV appliance

See →photovoltaic device.

PV array

See →photovoltaic array.

PV array disconnect

See →DC disconnect.

PV awning

See →solar awning.

PV battery

Power storage for a photovoltaic system.

PV buoy

See →photovoltaic buoy.

PV cable

See →photovoltaic cable.

PV cable set

A set of different cable types used for interconnecting various components of a photovoltaic system.

PV calculator

See →solar calculator2.

PV canopy

See →solar canopy.

PV capacity

See →photovoltaic capacity.

PV carport

See →solar carport.

PV cell

See →photovoltaic cell.

PV concentrator

See →photovoltaic concentrator.

PV concentrator cell

See →photovoltaic concentrator cell.

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 PV concentrator system

PV concentrator system

See →photovoltaic concentrator system.

PV concentrator technology

See →photovoltaic concentrator technology.

PV connector

See →photovoltaic connector.

PV contracting

See →photovoltaic contracting.

PV conversion

See →photovoltaic conversion.

PV conversion efficiency See →photovoltaic conversion efficiency. PV converter

Photovoltaic converter. See →solar energy converter.

PV current

See →photovoltaic current.

PV CYCLE

European leading PV recycling program.

PV data logger

See →photovoltaic data logger.

PV DC circuit breaker

See →photovoltaic DC circuit breaker.

PV design software

See →solar design software.

PV development

See →photovoltaic development.

PV device

See →photovoltaic device.

PV diesel hybrid system See →photovoltaic diesel hybrid system. PV disconnect

See →DC disconnect.

PV display model

See →photovoltaic display model.

PV effect

See →photovoltaic effect.

PV efficiency

See →solar module efficiency.

PV electricity meter

See →photovoltaic electricity meter.

PV energy

See →photovoltaic energy.

PV energy forecast

Predicts future energy output based on weather forecast, satellite data, and ground measurement data.

PV facade

→Building-integrated photovoltaics. A photovoltaic (PV) facade fulfills multiple functions. It provides a good thermal insulation, interior illumination similar to glass facades, visual contact to the exterior, protection of the interior from direct solar radiation, protection against weather (heavy rain, high winds, and hail), while simultaneously generating electricity from PV panels.

PV facade system 

 607

With regard to the structure, there are two main types of PV facades: the ones that are integrated into the external walls of a building and the ones that are attached to the walls of a building. PV panels can be directly integrated into a glass façade. →Frameless photovoltaic modules are in particular suitable for wall-integrated PV systems since they do not expose mounting components. They replace traditional wall cladding materials and offer an aesthetically pleasing design at the same time. On the other side, PV systems that are fixed to the building walls use aluminum- or stainless steel-mounting systems and substructures. Regarding the light permeability and color, PV facades can be divided into several groups: dark solar facades, facades with colored solar panels, transparent, and semitransparent solar facades. Due to their vertical position, PV facades are particularly efficient during the winter months, when the sun is low in the sky. To optimize the solar yield, architects should take into consideration the following obstacles when designing PV facades: canopies, hanging roofs, high trees, neighboring buildings, and structures. PV facade system

See →photovoltaic facade system.

PV F-CHART

PV system analysis software.

PV fuse

Photovoltaic fuse. See →solar fuse.

PV generator

See →photovoltaic generator.

PV glass

See →photovoltaic glass.

PV glass module

See →photovoltaic glass module.

PV hybrid system

See →photovoltaic hybrid system.

PV industry

Photovoltaic industry. See →solar industry.

PV ink

See →photovoltaic ink.

PV installation

See →photovoltaic installation.

PV installer

Photovoltaic installer. See →solar installer.

PV inverter

Photovoltaic inverter converts the generated solar power from direct current to grid-compatible alternating current.

PV junction box

See →photovoltaic junction box.

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 PV kit

PV kit

Photovoltaic kit. See →solar set.

PV laminate

See →photovoltaic laminate.

PV lamination

Photovoltaic lamination. See →solar panel lamination.

PV leasing

Photovoltaic leasing. See →solar leasing.

PV long-term forecasting Solar forecasting for a month or a year. PV manufacturer

Photovoltaic manufacturer. See →solar manufacturer.

PV manufacturing

Photovoltaic manufacturing. See →solar manufacturing.

PV market

Photovoltaic market. See →solar market.

PV market segment

Photovoltaic market segment. See →solar market segment.

PV market share

See →photovoltaic market share.

PV marketing

Photovoltaic marketing. See →solar marketing.

PV material

Photovoltaic material. See →solar material.

PV micro-grid

Photovoltaic micro-grid. See →solar micro-grid.

PV mini-appliance

See →photovoltaic mini-appliance.

PV module

See →solar module.

PV module degradation rate

See →photovoltaic module degradation rate.

PV module laminator

See →solar panel laminator.

PV module nameplate

A plate that is attached to a photovoltaic (PV) product. Besides the manufacturer’s name, model, and serial number, it typically includes performance ratings in watts, volts, amps, and frequency for the PV module.

PV module test lab

See →solar test center.

PV module test laboratory

See →solar test center.

PV module tester

See →solar module tester.

PV module testing

See →solar testing.

PV module testing device

See →solar module testing device.

PV module testing equipment

See →solar module testing device.

PV module testing lab 

 609

PV module testing lab

See →solar test center.

PV module testing laboratory

See →solar test center.

PV monitor

Photovoltaic monitor. See →solar energy monitoring system.

PV monitoring

Photovoltaic monitoring. See →solar system monitoring.

PV mount

See →mounting system.

PV-mounting system

See →mounting system.

PV operator

See →solar plant operator.

PV panel

See →photovoltaic panel.

PV panel laminator

Photovoltaic panel laminator. See →solar panel laminator.

PV panel test lab

Photovoltaic panel test lab. See →solar test center.

PV panel test laboratory Photovoltaic panel test laboratory. See →solar test center. PV panel testing

Photovoltaic panel testing. See →solar testing.

PV panel testing lab

Photovoltaic panel testing lab. See →solar test center.

PV panel testing laboratory

Photovoltaic panel testing laboratory. See →solar test center.

PV park

Photovoltaic park. See →photovoltaic power plant.

PV park system

Photovoltaic park system. See →photovoltaic power plant.

PV plant

See →photovoltaic plant.

PV plug

See →photovoltaic plug-in connector.

PV plug-in connector

See →photovoltaic plug-in connector.

PV power

See →photovoltaic power.

PV power forecast

Predicts future energy output based on weather forecast, satellite data, and ground measurement data.

PV power meter

See →solar power meter.

PV power station

Photovoltaic power station. See →photovoltaic power plant.

PV printing

See →photovoltaic printing.

PV producer

Photovoltaic producer. See →solar manufacturer.

PV production

See →photovoltaic production.

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 PV short-term forecasting

PV recycling

See →photovoltaic recycling.

PV ribbon

See →tabbing wire.

PV sealant

See →solar adhesive.

PV set

See →solar set.

PV shading system

See →photovoltaic shading system.

PV shingle

→Building-integrated photovoltaics. Photovoltaic (PV) shingle is a durable roofing material with integrated PV cells that can be incorporated easily into a roof than balky, complex solar panel →roof-mounting systems. Like regular PV panels, PV shingles harness the sun’s energy and convert it into electricity. They also provide a thermal insulation as well as weather protection designed to withstand heavy rain, high winds, and hail, similarly to conventional asphalt shingles. Although more expensive than solar panels, they are more aesthetically appealing than PV modules. They offer a unique high-tech external design by using patterns and colors that effectively blend in with the rest of the roof. Since PV shingle is a relatively a new product, available since 2005, there are mainly two types of PV shingles that are offered on the market: →thin-film photovoltaic shingle and →silicon-based photovoltaic shingle. Thin-film PV shingles utilize →CIGS (copper indium gallium selenide) solar cells to turn sunlight into electricity. Due to their flexibility and lightweight, they replicate actual shingles in size and design. In addition, since they deliver a good thermal insulation and durability as asphalt shingles do, they can replace roofing material and be stapled directly to the roofing cloth like regular shingles. Silicon-based PV shingles, also known as →photovoltaic tiles, have higher power output than thinfilm PV shingles. Even though they are more energy efficient than thin-film PV shingles, silicon-based PV shingles cost more and are associated with certain design constraints. As the name suggests, they are made of thin silicon strips that are implanted into glass or other materials and work like conventional →silicon solar modules.

PV short-term forecasting

Solar forecasting for 7 days.

PV skylight

See →solar skylight.

PV solar panel 

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PV solar panel

Photovoltaic solar panel. See →solar module.

PV storage

Photovoltaic storage. See →solar energy storage.

PV surfboard

Photovoltaic surfboard. See →solar surfboard.

PV system

See →photovoltaic system.

PV system monitoring

Photovoltaic system monitoring. See →solar system monitoring.

PV technology

Photovoltaic technology. Technology of converting solar radiation into electricity.

PV test center

US Photovoltaic test center. See →solar test center.

PV test centre

UK Photovoltaic test centre. See →solar test center.

PV testing

See →solar testing.

PV thermography

See →photovoltaic thermography.

PV tile

→Building-integrated photovoltaics. Photovoltaic (PV) tile is a durable roofing material with integrated PV cells that can be easier incorporated into a roof than balky, complex solar panel →roof-mounting systems. Like regular PV panels, PV tiles harness the sun’s energy and convert it into electricity. They also provide a good thermal insulation as well as weather protection designed to withstand heavy rain, high winds, and hail, similarly to conventional roof tiles and shingles. Although more expensive than solar panels, they are more aesthetically appealing than PV modules. They offer a unique high-tech external design by using patterns and colors that effectively blend in with the rest of the roof. Photovoltaic tiles have higher power output than →thin-film solar shingles. Even though they are more energy efficient than thin-film solar shingles, silicon-based photovoltaic tiles cost more and are associated with certain design constraints. As the name suggests, they are made of thin silicon strips that are implanted into glass or other materials and work like conventional →silicon solar modules.

PV tracker

See →photovoltaic tracker.

PV tracker designer

See →photovoltaic tracker designer.

PV tracking

Enables solar panels to constantly follow the course of the sun.

PV trailer

Photovoltaic trailer. See →solar trailer.

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 PV waste management

PV waste management

Photovoltaic waste management. See →solar waste management.

PV window

Photovoltaic window. See →solar window.

PV wire

See →photovoltaic wire.

PV/T

Stands for photovoltaic-thermal. See →combined solar collector.

PVC

Abbreviation for →polyvinyl chloride.

PVD

Abbreviation for →physical vapor deposition.

PVD coating plant

Physical vapor deposition coating plant.

PVD sputtering system

Physical vapor deposition sputtering system. See →sputtering process.

PVF

Abbreviation for →polyvinyl fluoride.

PVF film

See →Tedlar film.

PVF sheet

See →Tedlar sheet.

PV-thermal system

(PV/T) photovoltaic-thermal system. See →combined solar collector.

PWM

Abbreviation for →pulse width modulation.

PWM inverter

See →pulse width modulated wave inverter.

pylon

A tall, pillar-like structure used to support a frame with solar panels or to which solar panels are directly attached.

pyramid texture

See →random pyramid texture.

pyramid-based texture

See →random pyramid texture.

pyranometer

An instrument for measuring solar irradiance. The pyranometer measures direct as well as diffuse radiation.

pyrheliometer

An instrument for measuring the intensity of direct solar radiation. When a direct solar ray enters the case through a small window, it is directed onto a radiation-sensing element which converts the solar heat into a voltage that is then recorded by a voltmeter.

PZEV

Abbreviation for →partial zero-emission vehicle.

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Q QE

Abbreviation for →quantum efficiency.

QF

See →qualifying facility.

quad

A unit of energy equal to 1 quadrillion Btus or 293,071,000,000 kWh.

qualification test

A testing procedure applied to a specific solar module to determine its power ratings and overall performance for certification, labeling, compliance, and marketing purposes. Based on qualification tests, solar companies issue warranties on their solar products. By means of measured module performance data, companies guarantee their customers a specific power output and high performance usually over the course of 25 years. The testing procedure may include a number of particular qualification tests, such as thermal cycling, hot spots/shading, humidity/freeze, mechanical stress, ultraviolet (UV) light, hail, and electrical isolation.

qualifying facility

(QF) A small power production facility, such as solar, wind, or hydro, or a cogeneration facility that meets certain operating, efficiency, and ownership standards established by the US →Federal Energy Regulatory Commission (FERC).

quality assurance for photovoltaic modules

See →quality assurance for solar modules.

quality assurance for PV See →quality assurance for solar modules. modules quality assurance for solar cells

The quality assurance process starts already during wafer production. An early detection of microcrack and saw-mark defects in wafers is an important part of solar cell inspection. A detailed testing of electrical performance includes the measurement of the following solar cell parameters: →short-circuit current (Isc), →open-circuit voltage (Voc), →fill factor (ff), current density (Jsc), →maximum output power (Pmax), →maximum output voltage (Vmax), →maximum output current (Imax), →cell efficiency (η), and →shunt resistance. Quality assurance also covers surface, backside printing, and antireflection coating inspection.

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 quality assurance for solar modules

quality assurance for solar modules

Systematic testing and evaluation of different aspects of a solar module to ensure the desired level of quality of the solar product. Quality inspections are carried out at a solar module testing facility, assessing functionality, inherent structure, and real-world performance. The first level of a QA process includes a failure analysis, for example, electrical and hot spot tests, visual inspection, and IR imaging, which should catch and replace defective solar cells and components prior to delivery to the client. The second, more detailed level of a QA process comprises a series of various outdoor real-world testing, for example, insulation resistance test, hail impact test, snow load test, wind test, UV light test, panel breakage test, low temperatures test, and many other tests. The third level of quality assurance includes long-term monitoring that follows the behavior of solar panels over a longer period of time to record degradation rates and other important long-term data.

quality assurance for solar panels

See →quality assurance for solar modules.

quality factor

See →performance ratio.

quantity regulation

A regulatory instrument for the promotion of solar and other renewable energy sources that focuses on the regulation of the quantity of electricity in the market rather than on the price paid for it, as in →feed-in tariff (FIT).

quantum dot

Also known as a nanocrystal and light-activated nanoparticle. A nanoscale particle of semiconducting material such as silicon, cadmium selenide, cadmium sulfide or indium arsenide. It is also known as a nanocrystal that confines the motion of electrons, holes, or excitons (bound pairs of excited electrons and associated holes) in all three spatial directions. Due to reduction in grain size, having dimensions between 2 and 10 nm in diameter, quantum dots have a tunable band gap. By engineering and aligning the bands of the quantum dot layers, so that they include different sizes and combinations of quantum dots, a significantly higher absorption rate can be achieved. This way, hot electrons are trapped before they escape the photovoltaic (PV) cell and multiple, wider regions of the solar

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spectrum are harnessed and converted into energy. Due to the band alignment engineering with various compositions, quantum dots are suitable for multijunction solar cells. Compared to conventional silicon PV cells, in which a photon of light produces one electron, a single photon of light in silicon quantum dots cells is able to generate two electrons. In addition to the increased conversion efficiency, the use of quantum dots in semiconductors also leads to a low-cost fabrication. The manufacturing costs can be significantly reduced by suspending tiny quantum dots in an organic polymer solution, thus creating quantum dot inks for a cheaper and faster inkjet printing process, in which the semiconductor ink is printed onto a substrate. quantum dot photovoltaic cell

Also known as nanocrystal solar cell. A photovoltaic (PV) cell that is made up of quantum dot semiconductors, also called →semiconductor nanocrystals. Quantum dots are extremely small, roughly around 1–10 nm in size. Using quantum dots as the absorbing material gives quantum dots an advantage over other silicon or thin-film semiconductor materials, since less material is required. This will have a cheaper production costs as result. Another advantage of quantum dots against silicon and thin film is the fact that their quantum energy levels can be tuned to absorb a wide range of irradiation wavelengths. Even with the best technology, traditional solar cells can absorb still under one-third of the energy hitting them. They only harness the visible solar radiation, energy in the middle range. The entire infrared region of the solar spectrum (almost one half of total solar radiation reaching the earth’s surface) as well as the ultraviolet region are not absorbed. High energy electrons, so-called hot electrons, escape and get lost as heat before they can be converted into energy. By engineering and aligning the bands of the quantum dot layers, so that they include different sizes and combinations of quantum dots, a significantly higher absorption rate can be achieved. In this way, hot electrons will be trapped before they escape the PV cell and multiple regions of the solar spectrum harnessed and converted into energy. Due to the band alignment engineering with various compositions quantum dots are suitable for multijunction solar cells.

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 quantum dot PV cell

Expectations are high and some scientists claim that quantum dot PV cells would be able to absorb energy around the clock. However, it should be emphasized that the quantum dot technology is still in an early research phase and that some important practical solutions are still missing. See also →nanocrystal solar cell. quantum dot PV cell

See →quantum dot photovoltaic cell.

quantum dot solar cell

See →quantum dot photovoltaic cell.

quantum efficiency

(QE) Also known as incident photon-to-current efficiency (IPCE) or spectral sensitivity. A measure of how efficiently a solar cell converts the incident light into electrical energy at a given wavelength. It specifies the ratio of the number of charge carriers generated by the solar cell to the number of photons incident on a solar cell. There are two types of quantum efficiency: →external quantum efficiency (EQE) and →internal quantum efficiency (IQE).

quantum efficiency of solar cells

One of the key factors affecting energy conversion efficiency of →solar cells. See →quantum efficiency.

quantum leap

The abrupt change of a particle from one state to another, for example, a jump of an electron from the ground state to a higher energy excited state. See also →quantum-mechanical tunneling.

quantum system

A system that is made of particles and waves at the same time. It is impossible to predict the behavior of a microsystem. Nobody can tell which path an →electron or →photon will take because the uncertainty is at the core of a quantum system. All we can predict is probability. We cannot know all aspects of a quantum system at the same time. German physicist Werner Heisenberg postulated that if we precisely measure the position of a subatomic particle, we cannot measure its momentum and vice versa.

quantum tunneling

See →quantum-mechanical tunneling.

quantum vacuum

The lowest energetic state of a →quantum system. It is a state entirely devoid of quantum excitations, particles, or ordinary matter.

quantum yield

The ratio of the number of electrons released by a photocell divided by the number of incident or absorbed photons.

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quantum-mechanical tunneling

A quantum-mechanical phenomenon in which a particle passes through a potential barrier. For instance, when photons of light hit semiconductor materials, some of the electrons get excited into a high mobility state, in which they are able to cross the energy barrier and make a quantum leap. The electrons now have enough energy to jump from the →valence band into the →conduction band, tunneling through the barrier that they cannot surmount under normal circumstances.

quantum-mechanical tunnelling process

See →quantum-mechanical tunneling.

quartz

A hard, colorless, or white mineral that consists primarily of silica or →silicon dioxide (SiO2). Silicon as the crucial raw material for the manufacture of semiconductors for photovoltaic modules is refined from quartz.

quartz sand

An essential raw material for the manufacture of semiconductors for photovoltaic modules. Quartz sand is produced by crushing quartz rocks to sand and then purifying it into →high-purity quartz sand.

quartzite

A hard, granular rock consisting entirely of the mineral →quartz, which is in turn primarily made of pure →silicon dioxide (SiO2).

quasiparticle

A quantum of energy in a semiconductor crystal lattice that has particle-like properties, such as a position, mass, or energy. Examples of quasiparticles include electrons, holes, plasmons, and phonons. An electron quasiparticle describes an interacting many-body system consisting of a real electron and the nearby particles it affects. When an electron is excited into a higher state by the photons of light, it leaves an empty space, called hole, behind in its old state. Hole is a positive-charge quasiparticle that denotes the absence of an electron. Another example of quasiparticle is a plasmon that represents a collective excitation arising from the quantization of plasma oscillations. Phonon, on the other hand, represents a collective excitation arising from the quantization of mechanical oscillations – a sound wave moving through a solid material.

quasi-sine wave

Modified sine wave signal used by less expensive inverters. The signal is in the shape of a square with one or two extra square steps.

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 quasi-sine wave inverter

quasi-sine wave inverter Also known as modified sine wave inverter is a power inverter that produces a square waveform with one or two extra square steps. Since the voltage waveform is in the shape of a square rather than a sine, it should be actually called a modified “square” inverter. Nevertheless, it is a better solution than a →square wave inverter, as it can be used for most appliances, but it has a lower performance and efficiency than →pure sine wave inverters. Although the quasi-sine inverter is compatible with most household electrical devices, it is not completely free. Sensitive electronics with a silicon-controlled rectifier (SCR), such as audio equipment, laser printers, and photocopiers, but also fluorescent lights, ceiling fans, microwave ovens, and digital clocks perform poorly with quasi-sine wave inverters. The quasi-sine wave inverter will probably not damage the mentioned devices, but they might pick up a buzz, make annoying humming noises, show other strange behavior (e.g., clocks might run faster), or not work at all. Quasi-sine wave inverters are less expensive than pure sine wave inverters; however, they use 20–30% more energy than pure sine wave inverters. The reduced efficiency goes back to waveform problems causing enhanced radio interference and increased heating of motors, thereby shortening the motor’s life.

R R2R

Abbreviation for →roll-to-roll printing method.

raceway

A conduit or tubing through which electric conductors used in PV installations are run. The major function of raceways is to protect wires and cables from physical damage and adverse weather conditions, such as UV exposure, rain, and snow. Raceways are manufactured from different materials, ranging from plastics of any color to aluminum, galvanized steel, or stainless steel. The following tubing and conduits are often used in solar systems: →electrical metallic tubing (EMT), →rigid steel conduit (RSC), →flexible metal conduit (FMC), →liquid-tight flexible metal conduit (LFMC), or →polyvinyl chloride (PVC).

rack mount 

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A support structure, typically an aluminum frame, upon which →photovoltaic modules are mounted. A rack mount can be fixed or adjustable. A fixed rack mount is a rigid, nonadjustable PV-mounting structure whose tilt angle is fixed in an optimal year-round position, based on the site’s latitude. An adjustable rack mount is an adaptable PV-mounting structure whose tilt angle can be manually adjusted, often with help of telescoping legs, to optimize the solar power output. Telescoping legs are either limited to four seasonal angle settings or they are freely adjustable to any desired angle. A rack mount can be installed either on the ground or on a roof. This PV-mounting system, in particular if it is adjustable, can significantly improve the power output. However, when mounted on a roof, they prove to be less resistant to strong winds and also less esthetically pleasing than a →standoff-mounting system.

Rack Mount

rack mounting

Mounting of a photovoltaic system on →rack mounts.

racking system

See →rack mount.

rack-mounted photovoltaic system

A photovoltaic system that is mounted on →rack mounts.

rack-mounted PV system See →rack-mounted photovoltaic system. radiant cooling

See →radiative cooling.

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 radiant energy

radiant energy

The energy of electromagnetic waves that radiates outward in all directions from its source.

radiant flux

The amount of solar energy flowing through a given area or surface per time unit.

radiant heat

See →thermal radiation.

radiant heating system

In comparison to →HVAC and other forced-air heating systems that move warm air through ducts and circulate it throughout the house, radiant heating systems supply heat directly through floors or walls of a building. The space is heated primarily by radiation and less by →convection as in conventional air-conditioning systems. See also →solar underfloor heating and →wall heating.

radiation

See →solar radiation.

radiation entry

The incoming solar radiation entering a building through the transparent enclosures, such as windows or glass walls.

radiation intensity

See →solar radiation intensity.

radiation output

The amount of energy the Sun gives off. The Sun’s or solar radiation output depends on solar activity, which varies cyclically over time, going through different phases in an 11-year →solar cycle. At the beginning of a cycle with a few →sunspots, solar activity and output are low, marked by a minimal number of solar flares. Over the course of the cycle, the sun is gradually covered with more sunspots, moving closer to peak solar activity, so-called →solar maximum, which is characterized by a higher number of solar flares and thus a greater solar output.

radiation pressure

Force per unit area exerted upon matter or a surface by a stream of photons of light.

radiational cooling

See →radiative cooling.

radiative cooling

Also known as radiant or radiational cooling. The process by which a body, the surface of the earth or a roof structure, cools down by emission of infrared radiation. A building’s roof structure, a massive ceiling slab or a →roof pond, absorbs heat from interior rooms during the day, acting as a heat sink and radiates it away at night. This cooling of

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a house by radiation to the night sky is known as direct radiative cooling. In the indirect radiative cooling type, the radiation to the night sky cools water or heat transfer fluid, which then cools the building by circulating the cooled liquid through the hydronic piping system. radio frequency interference

(RFI) See →electromagnetic interference.

radiometer

An instrument that is used to measure the amount of electromagnetic energy in a particular wavelength range.

radiosonde

A small weather station that travels through the atmosphere, typically suspended below a balloon, and conducts pertinent meteorological measurements. A radio transmitter sends the information on atmospheric temperature, pressure and humidity collected by sensors to a receiver on the ground every second.

rafter finder

An electric tool for locating rafters for solar installations.

rafters

The sloping pieces of wood, such as beams, reaching from the ridge of the roof down to the eaves and supporting the covering of a roof. Rafters also provide the main support structure for a →roof-mounted solar array. One of the first steps in mounting a PV system on the roof is locating the rafters. As finding rafters is often a rather daunting task, a →rafter finder or a reliable stud finder will prevent making any unnecessary penetrations in the roofing.

Raman effect

Light scattering while passing through a transparent medium.

Raman scattering

See →Raman effect.

ramp

See →ramp output.

ramp output

An increase or reduction in generation output.

ramp rate

The rate, usually expressed in megawatts per minute (MW/ min), at which a power generator, for example, a photovoltaic power plant, increases or reduces its power output per minute. See also →solar variability.

random pyramid texture Solar cell surface texture consisting of random pyramid patterns that reduce the surface reflectance and thus improve the performance of solar cells.

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random pyramid texturing

Solar cell →surface texturing technique that uses a →photolithographic process to produce random pyramid patterns on the silicon substrate, reducing the surface reflectance and thus improving the performance of solar cells.

Rankine cycle

A thermodynamic cycle for vapor power plants, in which an operating fluid is constantly evaporated and condensed. In a concentrated solar power plant, mirrors are used to focus sunlight onto a receiver, a single focal point, at the top of a tower. The concentrated sunlight heats a →heat transfer fluid and makes vapor, activating turbines that produce electricity.

RAP

An abbreviation for reactive atom plasma or →reactive atom plasma processing.

rapid charging

See →fast charging.

RAPS

Abbreviation for →remote area power supply.

rate of change

(RoC) The rate of change of solar module or solar system performance over time. See also →photovoltaic module degradation rate.

rated battery capacity

Manufacturer’s rating measured in ampere-hours (Ah) indicating the maximum amount of power that can be withdrawn from a battery under normal condition at a specified standard rate.

rated capacity

See →rated power.

rated current

See →rated power.

rated module current

Nominal power output that a photovoltaic module can supply to the load according to its specification.

rated output

See →rated power.

rated power

Is the nominal power output, that is, the maximum amount of continuous power that a solar panel or an inverter, based on their specification, can supply to the connected devices (load) in a house.

rated temperature

Also known as STC rated temperature. A standard test conditions (STC) temperature used in solar testing facilities, providing optimal conditions for best solar energy output. The STC rated temperature for photovoltaic panels is 25 °C (77 °F). That means that a silicon monocrystalline

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photovoltaic module should be no hotter than 25  °C (77  °F) in order to generate its rated max power found in technical specifications. However, the temperature in southern geographical regions goes over 25 °C (77° F) in hot summer months, resulting in a reduced solar panel power output by 10–25%, based on the proportional voltage drop due to resistance. rated voltage

Also known as nominal voltage. This is a rated value, indicating the available input or output voltage of a battery, PV module, or other PV component. This is a rounded, general voltage value that is derived from testing equipment under optimal standard conditions and it is listed on a solar panel’s or battery’s specification sheet (i.e., a 12, 24, or 48 V battery, module, or system). These numbers may not coincide with actual voltage values during real use, but they come pretty close. The actual voltage of a 12 V PV module can be a few volts higher or lower. In the bright sunshine, the output can reach 14 V or even 18 V, or it can drop to 10 V under certain circumstances. Regardless of these variations, the rated voltage helps users better plan and size a PV system for their home, or match their battery bank size to PV panels.

Rayleigh scattering

The scattering of light by particles in the atmosphere that are much smaller than the wavelength of the light. The Rayleigh scattering of the shorter wavelengths of visible light (violet and blue) by atmospheric gases – the molecules of the air – accounts for the blue color of the sky. See also →Mie scattering.

reaction gas

Collision gas (argon, hydrogen, oxygen, dichlorosilane, or silane or a combination of two or more gases) that undergoes a chemical reaction with the target material to be deposited on a solar cell →substrate. Reaction gases are introduced into the →reactor chamber to generate plasma of the reaction gas and to deposit sputtered material particles on the surface of the substrate.

reactive atom plasma

(RAP) A very precise plasma chemical etching process. See →reactive atom plasma processing.

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 reactive atom plasma processing

reactive atom plasma processing

(RAP) An atmospheric plasma etching process that uses argon plasma to deposit, etch, polish, and clean substrate materials with minimal subsurface damage. The RAP is characterized by a nanometer level accuracy, while still achieving high material removal rates. In a reactor chamber, a chemically reactive gas is introduced into the heated plasma that atomizes the gas in such a way that it can react with the substrate material. The RAP as a form of a plasma-enhanced chemical etching at atmospheric pressure has found a wide application in various segments of precision optics, engineering, and machining.

reactive ion etching

(RIE) A type of →dry etching that integrates the →chemical dry etching method, such as the →plasma etching, and the →physical dry etching method, such as the →ion-beam milling etching, into a new physical–chemical dry etching technology. This plasma-assisted dry etching approach finds a wide application in wafer fabrication today because it can produce very fine recesses (conducting channels) with a high level of →anisotropy. The hybrid method, in which physical and chemical etching processes complement each other, is also much faster due to this optimization. First, a →photoresist mask is deposited on the wafer using a →photolithographic process to protect the parts of the wafer that should not be etched and define contact holes at the same time. Then, the masked wafers are placed on a holder, which also acts as a radio frequency-powered electrode, in a vacuum chamber in which the reaction process is carried out. The reactive gas is subjected to a strong electromagnetic field creating plasma. The particles are accelerated with high energy toward the substrate. The unmasked semiconductor material is bombarded by highly energetic chemically reactive ions, electrons, and photons. The tetrafluoromethane (CF4) or sulfur hexafluoride (SF6) gases are carefully selected to favorably react with silicon atoms from the semiconductor film. The high energy ions knock out the silicon atoms from the wafer surface that is not covered by the photoresist mask. Finally, the substrate is etched into the desired form, producing the designed conducting channels. A volatile byproduct generated during the etching process – a gas containing fluorine, silicon, and oxygen – is evacuated from the chamber with help of a vacuum pump.

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reactive ion-beam etching

(RIBE) A type of plasma-assisted dry etching technology for semiconductor processing. See →reactive ion etching.

reactive power

The amount of power in watts in an AC system when the current waveform is out of phase with the voltage waveform. Also known as “phantom power” because it is not known where it goes. See also →true power.

reactive sputter etching

(RSE) See →reactive ion etching.

reactive sputtering

A →sputtering process in which a gas, usually oxygen or nitrogen, is introduced into the argon plasma in a vacuum chamber. The reactive gas undergoes a chemical reaction with the target material cloud that is sputtered away to form a thin-film coating on the surface of the substrate. The major advantage of the reactive sputtering method is a good control of the thin-film composition, the deposited molecular compound, which can be achieved by regulating the amounts of the inert and reactive gases added to the plasma.

reactor

Also known as a reactor chamber. A heated chamber into which appropriate gases are introduced to produce chemical reactions. The atoms released in the reaction are deposited onto a →substrate.

reactor chamber

See →reactor.

real-time monitoring

Allows the home owner to monitor their system operation and view how much power is being produced at any time.

rear contact

Also known as back contact. The electrical contact layer located at the back of a →solar cell. It is made of a good conductor, typically metal, such as aluminum, copper, silver, Al–Ca–Mg, or other metallic compounds. The electrical current, which is generated in the semiconductor layer and carried out of the solar cell through a front electrical contact to an external load, is returned back into the PV cell via back contact, closing the electric circuit. Rear contacts are often passivated to increase the efficiency of solar cells. The coating of contacts with a thin oxide layer, for example, silicon dioxide (SiO2), significantly reduce the surface recombination at the metal–semiconductor interface, while maintaining a good electrical contact.

rear contact cell

See →back contact solar cell.

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 rear contact pad

rear contact pad

A metal contact on the back side of a silicon crystalline solar cell.

rear contact solar cell

See →back contact solar cell.

rear print check

See →rear print inspection.

rear print inspection

Also known as rear print check. An optical solar cell inspection method that examines the rear side of a photovoltaic (PV) cell for printing defects and deviations. The rear print inspection occurs during PV cell production in order to detect defects early in the process and correct them before they become bigger and more expensive.

rear reflector

See →Lambertian rear reflector.

rear ventilation

It is important to keep roof- or façade-mounted solar modules several inches away from the roof or façade for ventilation purposes. As photovoltaic (PV) modules are susceptible to the effect of the high temperature, only cool or moderately heated cells can achieve the maximum energy yield. The PV modules with poor or no rear ventilation will heat up, resulting in a reduced →solar power output.

REC

Abbreviation for →Renewable Energy Certificate.

receiver

Also known as solar receiver. A device that absorbs focused beams of solar energy from →concentrating solar collectors and converts them into heat. Depending on the applied concentrated solar power system, there are four different types of receivers. In →concentrating parabolic troughs, the receiver is a black absorber tube located along the focal line of the trough. The concentrated solar energy heats →heat transfer fluid flowing through the tube, reaching temperatures of 390 °C (735 °F) or higher. The hot oil is then used to boil water, which makes steam, driving the steam turbine that generates electricity. Similar to parabolic trough receiver, the →compact linear Fresnel reflector (CLFR) receiver tube runs the length of the collector mirrors. However, the CLFR absorber tube consists of numerous small boiler tubes through which water flows. The heated water evaporates in the tubes, generating superheated steam, reaching a high

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temperature of around 270 °C (518 °F). Also here, the hot steam is mostly used for electricity generation. In →Dish collectors, the receiver in a form of a system of tubes is often integrated into a →Stirling engine. The receiver, which is located at the focal point of the dish, absorbs the reflected and concentrated sun’s rays and transfers the heat to the working fluid, typically hydrogen or helium. The heated working gas expends in the tubes, drives the pistons in the cylinders of the Stirling engine, and thus generates electricity. The large-scale →central receiver system uses a single large central receiver that is installed at the focal point of a large field of numerous sun-tracking mirrors, called heliostats. The heliostats reflect solar radiation and concentrate it on the receiver at the top of a →solar power tower. The concentrated energy heats the →heat transfer fluid, such as →molten salt, in the central receiver (boiler) to high temperatures of over 540  °C (1,004  °F). The hot fluid is transported to the →heat exchanger, converted to steam, which, in turn, is used in a steam turbine generator to produce electricity. rechargeable

See →rechargeable battery.

rechargeable battery

Is a storage battery that can be discharged and recharged numerous times, as opposed to disposable batteries. The following rechargeable battery types are used for solar battery banks: →lead-acid battery (→flooded-cell  battery and →sealed lead-acid battery), lithium-ion battery, →redox flow battery, and →nickel– cadmium battery.

recombination

A process by which free electrons and holes come together in a semiconductor. There is a constant movement of electrons between the →conduction and the →valence bands. When a free electron loses energy, it jumps from the conduction band into the valence band and occupies the vacant position (hole). Electron and hole recombine, eliminating the electron–hole pair. The newly freed electrons then start the electron–hole pair generation process anew. There are three types of recombination: radiative, nonradiative, and Auger recombination. In a radiative recombination process, the energy of recombination leads to the

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 recombination lifetime

emission of a photon of light. In the nonradiative recombination process, the energy is transferred to one or more phonons. Finally, in the Auger recombination process, the energy of recombination is passed on in the form of kinetic energy to another electron. Recombination occurs at the front surface of the solar cell, in the bulk of the cell, junction region, or between interfaces. recombination lifetime

See →minority carrier lifetime.

recombination process

See →recombination.

recombiner

See →recombiner box.

recombiner box

Also known as a recombiner or solar recombiner. An electrical housing in which the output of several PV strings is brought together and converted into a single conductor pair. In medium and in particular in large-scale solar arrays, a number of recombiner boxes are required before reaching the master combiner box, called →subcombiner, which includes the →inverter.

recrystallization

A method for purifying solid compounds. It is a rearrangement at the amorphous–crystal interface during a thermally activated →Solid Phase Epitaxy (SPE) growth process, in which deformed grains of the crystal configuration are replaced by a new group of stress-free grains.

RECS

Abbreviation for →Renewable Energy Certificate System.

rectangular polycrystalline silicon block

A block that is manufactured by melting the raw polycrystalline silicon material in a →crucible, adding a small amount of dopant material →boron, and pouring the melt into a rectangular shape. After the block (ingot) is formed by controlled heating and cooling techniques, it is sawn into bars using a band saw. Finally, the bars are sliced into →silicon wafers using a →wire saw.

rectifier

Also known as inductive transformer. An electrical appliance with one or more diodes that converts alternating current (AC) into direct current (DC).

rectifier unit

See →rectifier.

recycling

The removal and reutilization of old or broken solar modules and other photovoltaic (PV) equipment that are

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no longer in use. Recycling reduces soil, water, and/ or air contamination by diverting PV waste from landfills and converting it into new materials and products. By doing that, it also reduces energy consumption by eliminating the need to produce materials from scratch. Some PV modules contain rare elements, for example, gallium and indium. The reuse of these materials to produce new solar modules or other industrial applications slows down the process of permanent depletion of these rare elements from the Earth’s crust. A special attention should be given to solar panels containing toxic materials such as →cadmium or lead. Toxic substances must be destroyed or transported to hazardous waste drop-off facilities. See also →photovoltaic recycling. recycling of old modules See →photovoltaic recycling and →recycling. recycling of old photovoltaic modules

See →photovoltaic recycling and →recycling.

recycling of old PV modules

See →photovoltaic recycling and →recycling.

recycling of old solar modules

See →photovoltaic recycling and →recycling.

redox

Abbreviation for →reduction-oxidation.

redox cell

See →reduction–oxidation cell.

redox chemistry

A branch of chemistry that is concerned with exchange of electrons or net electron flow during a chemical reaction. Reduction is gain of electrons and thus gaining of negative charge, whereas oxidation is loss of electrons and gaining of positive charge.

redox flow battery

Rechargeable battery where energy is stored in the liquid electrolyte instead of solid plates. The liquid electrolyte is pumped past a membrane held between two electrodes generating a current flow. As it wears over time, the electrically conducting solution is replaced by fresh electrolyte that is stored in an external tank. By storing the electrolyte in an external tank, the storage capacity of a flow battery can be increased.

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 redox potential

redox potential

The tendency of a chemical species to either acquire or lose electrons through the process of ionization. Redox potential is measured in volts (V).

redox reaction

See →reduction–oxidation reaction.

reduction

Is characterized by the gain of electrons, loss of oxygen, and gain of hydrogen. The opposite reaction →oxidation is the other half of the reduction reaction because they always occur together and complement each other. See also →reduction–oxidation reaction.

reduction of CO2 emissions

See →greenhouse gas emission reduction.

reduction–oxidation

See →reduction–oxidation reaction.

reduction–oxidation reaction

Also known as redox reaction. This is a chemical reaction in which there is a simultaneous transfer of electrons between chemical species (atoms, molecules, or ions). The redox reaction involves two half-reactions: oxidation and reduction. Oxidation is a chemical reaction that is characterized by the loss of electrons, gain of oxygen, and loss of hydrogen. The opposite reaction “reduction” is characterized by the gain of electrons, loss of oxygen, and gain of hydrogen. Oxidation and reduction always occur together and complement each other. The same electrons that are lost in the oxidation reaction are gained in the reduction reaction. The easily remembered acronyms for these opposing chemical reactions are: LEO standing for “loss of electron is oxidation” and GER standing for “gain of electron is reduction.” For instance, when a lead-acid battery is being discharged, it is converting chemical energy into electrical energy. It is a spontaneous redox reaction producing new electrons and thus generating the electricity to supply external electrical devices. The negative electrode/plate (anode) covered with lead is being oxidized, releasing two electrons. Two electrons are flowing from negative to positive terminal, supplying on its way the external load with electricity, and reentering the battery through the positive electrode. The positive electrode/plate (cathode) covered with lead dioxide is being reduced in the process. Lead (Pb) loses two electrons and lead dioxide (PbO2) receives those

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same two electrons. During the discharge process, both electrodes become coated with lead sulfate, the sulfuric acid (H2SO4) electrolyte is used up, and water is produced. When the lead-acid battery is being recharged, it is converting electrical energy into chemical energy, and the chemical reactions are reversed. The electrons are flowing in the opposite direction, from positive to negative terminal. Now, the positive electrode/plate (cathode) covered with lead dioxide (PbO2) is being oxidized, losing two electrons, whereas the negative electrode/plate (anode) covered with lead (Pb) is being reduced, gaining those same two electrons. During the recharge process, the lead sulfate coating on the electrodes is removed, the lead and lead dioxide regenerated, the water is used up, and the sulfuric acid (H2SO4) is produced. The battery is recharged and ready to be used again. reference meter

Measures the energy coming from the public power grid.

REFIT

Abbreviation for →renewable energy feed-in tariff.

reflectance

Also known as reflectivity, reflection factor, and reflection coefficient. The ratio of the amount of radiant energy reflected from a solar cell surface to the total amount of solar radiation incident on the surface. It is crucial to reduce optical reflectance in a solar cell, as it causes optical losses, which directly decrease the amount of generated electrons and thus the power output of a →photovoltaic cell.

reflected radiation

See →reflected solar radiation.

reflected solar radiation A type of indirect solar radiation. A part of incident solar radiation that is reflected from a surface, for instance from a solar panel, a window, or a cloud. reflection

The bouncing back of light or other electromagnetic radiation from a surface. There are two kinds of reflection: specular and diffuse reflection. Specular reflection, also known as regular reflection, is a reflection off of a smooth surface, for example, a mirror or calm water, in which the angle of incident light is equal to the angle of reflected light. Diffuse reflection is a reflection off of a rough surface, for example, clothing, paper, or a polycrystalline material.

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 reflection coefficient

Unlike regular, specular reflection, in which incident and reflected angles are equal, in diffuse reflection, beams of light are reflected at multiple diverse angles and scattered in different directions because they strike the uneven surface at different heights. reflection coefficient

See →reflectance and →albedo.

reflection factor

See →reflectance and →albedo.

reflection grating

A polished thin metal surface with many fine parallel grooves or slits that are used to reflect specific electromagnetic wavelengths.

reflection loss

Also known as reflective loss. The portion of incident radiation that is reflected away from a solar surface instead of being absorbed by it. The light is reflected from the front surface (top electrode) as well as from the rear surface (bottom electrode) of the solar cell. As a considerable amount of the incoming solar energy is lost due to reflection in both electrodes, solar scientists see the opportunity to improve the efficiency of organic photovoltaic cells by reducing reflective losses. A coating consisting of molybdenum, titanium, tungsten, zirconium, or other refractory metals reduces the reflection losses, while increasing the →refractive index and thus the absorption capacity of the cell.

reflective loss

See →reflection loss.

reflective metal layer

A reflective layer made of silver or aluminum in →concentrating solar collectors, acting as a mirror capable of reflecting and focusing solar radiation onto a receiver.

reflective surface

A surface that is capable of reflecting solar radiation – ultraviolet, visible, and infrared electromagnetic wavelengths. For instance, the employment of a white roof instead of a black roof can significantly reduce the transfer of thermal energy (heat) to the building. The white roof, which is also known as a cool roof, can reflect 75–85% of solar energy away, minimizing energy consumption and costs.

reflectivity

See →reflectance.

reflectometer

Instrument for measuring reflectance.

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reflector

A mirror or polished metal surface that reflects solar radiation, focusing the sun’s rays onto a very small area of an →absorber and thus increasing solar energy numerous times.

refraction

The bending of light rays at a particular point, where they enter a different medium, such as water, a lens, or the Earth’s atmosphere. In PV technology, the direction of light rays falling on a PV cell surface is often deliberately changed by a specially engineered surface texture to guide photons of light inside the semiconductor. The angles of refractions are precisely controlled to prevent light rays from escaping the solar cell and thus to keep them in the photoactive absorber.

refractive index

The ratio of the velocity of light in one medium to the velocity of light in a second medium.

refractometer

An optical device for measuring an index of refraction. The instrument measures the extent to which light is bent when it moves from the air through a substance, such as water or a →solar module.

refractor

A lens, a material, or a medium that bends light rays.

refractory metal

A very thin layer, around 1 nm thick, which acts as an antireflection coating in a thin-film amorphous silicon solar cell. The coating consisting of molybdenum, titanium, tungsten, zirconium, or other refractory metals reduces the reflection losses, while increasing the →refractive index and thus the absorption capacity of the cell. As photons of light strike the absorber surface, the refractory metal layer bends the light rays in such a way to keep the photons within the semiconductor.

refrigerant

Fluid, such as Freon, used for the generation of cold by a chemical reaction in air conditioners or heat pumps.

refrigerating machine

A machine for the removal of heat from the object needing to be cooled to a temperature below the ambient temperature.

regenerative energy

Energy, such as solar →primary energy, which naturally regenerates itself without human interaction. See also →renewable energy.

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 regenerative energy source

regenerative energy source

An energy source, such as solar or wind, which naturally renews itself without human interaction. See also →renewable energy resource.

regression analysis

A statistical method used to predict photovoltaic (PV) power output of a specific solar array or to forecast global solar irradiance in a geographical region. The method quantifies the value(s) of a dependent variable (e.g., kilowatt-hours that can be expected from a certain PV system) from a change in several independent, given variables, such as satellite data, various ground-based measurements, seasonal variation, shading, longitude, latitude, and orientation.

regular reflection

See →specular reflection.

regulator

See →solar thermal controller, →power regulator, and →charge controller.

reheating domestic water

Domestic water can be heated with help of solar power. Typically, the solar panels continuously heat up a domestic water tank until the reheat set point is reached. Apart from solar panels, a controller and a pump are often used to optimize the performance of these solar thermal systems.

relative density of liquids

The ratio of the density of the liquid to the density of water.

relative dielectric constant

See →relative permittivity.

relative humidity

The ratio of the measured amount of moisture in the air to the maximum amount of moisture that air can hold (saturation point) when water vapor starts to condense as drops on the surface. Relative humidity is expressed in percentage of saturation, for example, 40%. The →dew point temperature, when the air is maximally saturated with water, is identical with 100% relative humidity.

relative permittivity

The ratio of the permittivity of a substance (ε) to the permittivity of space or vacuum (ε0). The relative permittivity is expressed by the following formula: εr = ε/ε0.

remote area power supply

(RAPS) Is an off-grid stand-alone power system designed to provide electricity to remote areas far away from power lines, such as distant farms in Australia or isolated far-off villages in the Amazon region of South America. Due to

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the remoteness and isolation of these communities, RAPS usually relies on two or more power generation systems, so-called →hybrid solar systems, such as →solar-wind hybrid power system, →photovoltaic diesel hybrid system, or →solar-wind-diesel hybrid system. See also →stand-alone solar power system. remote sensing

The scanning of the Earth by satellites or aircraft to obtain various geophysical and meteorological data.

remote system

An off-grid →stand-alone solar power system.

renewable

See →renewable energy.

renewable energy

Energy that originates from carbon-neutral and regenerative sources. Unlike fossil fuels that cannot be restored once they have all been used up, renewable energy, such as solar, wind, and hydropower, is constantly replenished in a natural way and it is virtually inexhaustible.

Renewable Energy Act

Erneuerbare-Energien-Gesetz (EEG). See →German Renewable Energy Sources Act.

Renewable Energy Certificate

(REC) A financial instrument that is created to keep track of energy generated from renewable resources. One certificate typically represents 1,000 kWh of renewable energy and it is issued to customers who deliver clean energy to the grid. It is a system of renewable energy credits, also known as green certificates or green tags, which are earned by customers and can be sold or traded to a utility company or an agency, or at least claimed later when needed.

Renewable Energy Certificate System

(RECS) See →Renewable Energy Certificate.

renewable energy credit See →Renewable Energy Certificate. renewable energy epoch Epoch following the fossil fuel epoch. It is defined by the generation of energy from renewable energy sources, such as solar and wind. renewable energy era

Is the era following the fossil fuel era. It is defined by the generation of energy from renewable energy sources, such as solar and wind.

renewable energy feed-in rate

(REFIT) See →feed-in tariff.

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 renewable energy feed-in tariff

renewable energy feed-in tariff

(REFIT) See →feed-in tariff.

Renewable Energy Law

Erneuerbare-Energien-Gesetz (EEG). See →German Renewable Energy Sources Act.

renewable energy rebate Financial incentives for energy efficiency offered by a govprogram ernment in the form of federal and state subsidy programs to install residential photovoltaic systems. renewable energy resource

Natural energy resources, such as solar, wind, wave, or geothermal energy, which are constantly replenished and will never be depleted.

renewable energy source See →renewable energy resource. renewable energy standard

(RES) A standard that encourages public utility companies of a state or a country to obtain a certain amount of the electricity they produce or sell from renewable sources, such as solar, wind, hydro, geothermal, tidal power, or biomass. This standard amount of energy generated from renewable resources is typically expressed in percentages. For instance, the goal of the Washington state calls for at least 15% of its generated and delivered electricity to come from renewable sources by January 1, 2020.

renewable energy system

A system that uses renewable energy resources, such as solar and wind.

renewable energy technology

Any technology that is utilized to convert the renewable resources, such as solar, wind, hydro, or biomass, into electrical energy. Solar renewable energy technologies are: →photovoltaics, →solar thermal energy, →concentrated solar thermal systems, and →passive solar energy systems.

renewable fuel

Naturally renewable fuels, such as solar, wind, and hydro power, as opposed to →nonrenewable fuels that cannot be restored once they are used up.

renewable resource

See →renewable energy resource.

renewable technology

See →renewable energy technology.

renewables

See →renewable energy.

repowering

Replacement of an old power generation system with a new one.

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reradiation

Secondary radiation resulting from the previous absorption of primary radiation. An example is the reemission of electromagnetic radiation in the form of thermal energy or long-wavelength infrared radiation that was previously absorbed by the Earth’s surface.

reradiation loss

In →solar concentrator technology, thermal energy leaving the →receiver due to wind or colder environment. Reradiation thermal losses are proportional to the surface area of the receiver. The higher the concentration ratio, the smaller the →focal point or →focal line, which results in lower reradiation thermal losses. In high concentration systems, it is crucial to absorb as much energy as possible.

RES

Abbreviation for →renewable energy standard.

reserve capacity

Extra capacity that a utility power system must have to meet peak loads. At the level of a →stand-alone solar power system, additional energy reserve that a system needs to supply enough energy to the connected load. As the power output generated by a solar array varies from day to day due to the always diverse intensity of the sunlight, based on the season and sunny or overcast days, an additional energy reserve stored in a battery bank is a necessity for an uninterrupted electricity supply.

residential electric vehicle charging infrastructure

Also known as at-home charging. Residential charging infrastructure for electric vehicles that facilitates overnight charging at home, including →Level 1 charging and →Level 2 charging.

residential solar energy system

A small-scale solar energy system that is designed to generate enough electricity for a household. It is typically composed of →solar modules, a →rack mount, electrical wiring, an optional →battery bank, and an →inverter.

residential solar module A solar module designed for residential solar system installation. Two main types of the residential solar module are: →monocrystalline silicon solar module and →polycrystalline silicon solar module. In recent years, →thin-film photovoltaic modules have also gained in popularity in residential applications as their prices keep falling, while their conversion efficiency keeps improving.

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 residential solar system installation

residential solar system In densely populated urban areas, residential solar systems installation are usually mounted on roofs. However, if there is enough space in the backyard of a suburban or country house, a →ground-mounted solar array has proven to be a more practical option. A ground-mounted system is less expensive and it is easier to make seasonal or monthly adjustments to the ideal tilt angle on the ground. In addition, it is also easier to clean panels, make repairs, system updates, or a modular expansion of the system on the ground. residual value

The value of the solar system at the end of a project’s life, usually 25 years after the installation, which corresponds to the standard warranted life span of a photovoltaic (PV) module. In order to achieve the full potential value of their PV arrays and avoid the system’s degradation and reduced solar output, owners must constantly monitor and maintain their PV systems.

resilient photovoltaics

A type of photovoltaics that combine a photovoltaic generation system with another technology, such as a battery bank or a backup diesel generator, which allows the system to continue providing power during grid outages or when the sun is not shining.

resistance

(R) A measure of electrical resistance – how much a material, such as a copper wire, or an electrical device (load) opposes the flow of an electric current. It is measured in ohms (Ω).

resistance loss

Loss of electric energy in a power circuit arising from resistance (load, heat) and current flow.

resistant to abrasion

The ability of a surface to resist abrasion and keep the material’s original structure and look.

resistive evaporation

A type of →physical vapor deposition (PVD) process for manufacturing of thin-film semiconductor devices. In this PVD process, the target material is heated up in a resistive →evaporation boat or coil with a high current to such a high temperature point where it evaporates into the gaseous phase. The evaporated particles traverse through the vacuum chamber and condense on the surface of the substrate as a thin semiconductor layer.

resistive load

An Ohmic load in which resistance remains constant, as the electrical current and the voltage are in phase or in step

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with each other. If voltage rises or falls, the current also rises or falls with it. resistive voltage drop

Is the amount of electrical potential that is lost due to the cell resistance opposing the flow of electrical current.

resistor

An electrical component that limits the flow of electrons (electricity) in a circuit.

resistor layer

A thin-film layer that is deposited on top of the substrate surface by →sputtering in order to improve electrical properties of a →polycrystalline silicon solar cell.

resistor network

A voltage divider for power functions, which is a combination of several resistors configured into a pattern. By dividing the voltage that is applied to a circuit into smaller amounts, resistor networks can be used as a current-limiting protection for higher current solar modules.

Restriction of Hazardous (RoHS Directive) The EU directive on the restriction of Substances Directive the use of certain hazardous substances, such as lead, mercury, cadmium, hexavalent chromium, and some polybrominated flame retardants, in electrical and electronic equipment. A special attention should be given to solar panels containing toxic materials such as →cadmium. Toxic substances must be destroyed or transported to hazardous waste drop-off facilities. retrofit

See →solar retrofit.

return flow

Drainage of water or →heat transfer fluid in a sealed loop of the →solar collector system. When the pump is turned off, the water drains from the collectors and outdoor piping to a storage tank to prevent water pipes from freezing.

reverse current

Also known as leakage current. The amount of direct current (DC) that flows in a reverse direction, for instance, unwanted current flow from the battery bank to the solar array at night when the sun is not producing energy.

reverse current protection

An electrical component, such as a →charge controller or a →blocking diode, which prevents the reverse current from flowing backward through a photovoltaic (PV) array or, at a smaller, singular level, through a PV module. It functions like a one-way valve, allowing electricity to flow only one way. They prevent undesired discharging by reverse flow

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 reverse saturation current

of electrical current from the battery bank to the PV array, for example, in the dark or under cloudy conditions, when no current is generated by the PV modules. reverse saturation current

Also known as leakage current. Current that flows under reverse bias in a semiconductor.

R-factor

Also known as insulating or resistance factor. R-factor is a measure of a material’s resistance to heat transfer. It is the inverse of the →U-factor that is a measure of heat flow through a material. For example, the smaller the U-factor, the higher a window’s resistance to heat flow or the R-factor, and accordingly the more energy efficient the window.

RFI

Abbreviation for radio frequency interference. See →electromagnetic interference.

ribbon photovoltaic cell

See →ribbon polycrystalline photovoltaic cell.

ribbon polycrystalline photovoltaic cell

A PV cell that is made of polycrystalline wafers cut from a long silicon ribbon sheet. The ribbon is manufactured by attaching a silicon seed crystal to two heat-resistant wires that are pulled through the silicon melt. As the wires are slowly pulled upward, the molten silicon atoms attach to the seed crystal, creating a compact thin ribbon structure.

ribbon polycrystalline silicon wafer

A wafer that is cut from a long polycrystalline silicon ribbon sheet and used as a ground plate for polycrystalline photovoltaic cells. See also →ribbon polycrystalline photovoltaic cell.

RIBE

Abbreviation for →reactive ion-beam etching.

RIE

Abbreviation for →reactive ion etching.

rigid base material

Semiconductor base material that is not flexible.

rigid photovoltaic module

A photovoltaic (PV) module with a solid aluminum frame holding all solar components together. Unlike →flexible thin-film solar modules, rigid photovoltaic panels are inflexible, heavy, bulky, and often require a support structure, a →ground-mounting system or a →roof-mounting system. Their installation is also more complex and costly than that of flexible solar panels. On the other side, rigid photovoltaic panels are more rugged than flexible PV panels since they are typically covered with a tempered glass. The solid aluminum frame

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and tempered glass provide a good protection against the elements and scratches. Compared to flexible PV panels that do not allow air flow under the thin-film panels, rigid photovoltaic panels are mounted several inches away from the roof for ventilation purposes. The air flowing under the modules cools the rigid panels in hot summer months, increasing the power output. rigid photovoltaic panel

See →rigid photovoltaic module.

rigid photovoltaic system

A PV system which uses rigid modules that are fixed onto the roof or ground surface. Rigid modules are commonly mounted on →mounting structures.

rigid PV module

See →rigid photovoltaic module.

rigid PV panel

See →rigid photovoltaic module.

rigid PV system

See →rigid photovoltaic system.

rigid solar module

See →rigid photovoltaic module.

rigid solar panel

See →rigid photovoltaic module.

rigid solar system

See →rigid photovoltaic system.

rigid steel conduit

(RSC) A conduit through which wires and cables used in PV installations are run. The RSC conduit is usually manufactured from galvanized steel to provide a long-lasting exterior protection from physical damage and adverse weather conditions.

rigid substrate

An inflexible →substrate that is usually made of glass, plastic, or steel.

rigid sun tube

Sun tube made of rigid material that transports daylight into interior spaces of a building to provide natural illumination. Rigid sun tubes are suitable for installations when there is a straight, unhindered path from the roof to the ceiling. The straighter the tubing, the better the light performance. As the light is not as extensively bent as in →flexible sun tubes, the rigid sun tubes provide high reflectivity and better illumination of interior spaces than flexible sun tubes. See also →sun tube.

rigid swimming pool heating system

A system that uses rigid, glazed solar thermal systems, such as →evacuated-tube collectors or →flat-plate collectors, for heating swimming pool water.

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rigidly installed photovoltaic module

A stationary photovoltaic (PV) module that are fixed onto a static-mounting structure, in opposition to mobile PV modules that constantly follow the course of the sun with help of a →solar tracking system.

rigidly installed photovoltaic panel

See →rigidly installed photovoltaic module.

rigidly installed photovoltaic system

A photovoltaic (PV) system whose rigid modules are mounted on a non-adjustable PV-mounting structure. The tilt angle of the structure is often fixed in an optimal yearround position.

rigidly installed PV module

See →rigidly installed photovoltaic module.

rigidly installed PV panel See →rigidly installed photovoltaic module. rigidly installed solar module

See →rigidly installed photovoltaic module.

rigidly installed solar panel

See →rigidly installed photovoltaic module.

rigidly installed solar system

See →rigidly installed photovoltaic system.

RMS

Abbreviation for →root mean square.

RoC

Abbreviation for →rate of change.

RoHS conformity

The EU directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment.

RoHS Directive

Abbreviation for →Restriction of Hazardous Substances Directive.

rolled glass

A type of low-iron, plate glass manufactured by casting the plate between two rollers, one of which can carry a pattern. Float glass finds wide applications as cover glass for photovoltaic modules and solar collectors due to its high transmittance performance, which is slightly above 91%.

roll-to-roll coating

See →roll-to-roll printing.

roll-to-roll manufacturing

A method for manufacturing flexible →organic photovoltaic cells (OPV cells) with the help of a roll-to-roll printing and coating machine.

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roll-to-roll printing

Also known as roll-to-roll coating. A printing process that uses multiple rollers to optimize the ink intake, the formation of printing patterns (motifs), and the transfer of the same to the flexible thin-film substrate. The roll-to-roll printing process allows a good control of various process parameters, such as ink composition, layer thickness, rotation speed, pressure, angle, and drying time. As polymer thinfilm photovoltaic cells consist of multiple layers, a rapid selection of different parameters for each layer is needed. The main advantages of roll-to-roll printing are high-throughput, scalability, and an inexpensive process. All manufacturing phases are conducted under ambient conditions without costly and time-consuming vacuum or evaporation procedures. The major challenge for rollto-roll coating is to find materials that have required photoelectric properties and that are roll-printable at the same time.

roof alignment

Position of a roof in relation to the sun. A south-facing roof captures the most solar energy; however, some slight deviations toward west and east with a favorable roof tilt will still provide an excellent power output.

roof angle

See →roof pitch.

roof angle calculator

See →roof pitch calculator.

roof bushing

In roof mounting, depending on the design and manufacturer, a bushing can consist of an aluminum or bronze pipe and a rubber grommet. It is placed into a roof hole to create a water-tight seal around screws or solar cables passed through it.

roof gradient

See →roof pitch.

roof hook

Roof hooks are used to fasten the rails of a →mounting system to the rafters.

roof inclination

See →roof pitch.

roof installation

See →roof mounting.

roof integration

See →roof-integrated photovoltaic system.

roof integration system

See →roof-integrated photovoltaic system.

roof lease

Leasing roof surface for photovoltaic systems.

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 roof load

roof load

Besides the regular weight of the roof, the roof load also includes the weight of the entire photovoltaic (PV) array and the mounting structure in the context of a solar PV system installation. Solar modules and the racking system add approximately 2–4 pounds of extra weight per square foot or 10–20 kg/m2 to the existing roof load. In addition to the downward weight impact of the solar modules and the rack, potential snow loads and wind uplift force should also be included into the roof load bearing capacity calculations. The structural engineer or solar installer must ensure that the roof is structurally sound to carry the added weight of the solar system.

roof load-bearing capacity

The capacity of a roof structure to support the superimposed roof loads. In addition to the downward weight impact of the roof cladding (tiles or shingles), the weight of solar modules, the rack, as well as potential snow loads and wind uplift force should be included into the roof load-bearing capacity calculations.

roof mount

See →roof-mounting system.

roof mounting

Mounting of a photovoltaic system on the roof, as opposed to →ground mounting. Two main types of roof mounting are: →in-roof installation and →on-roof installation, including two conventional on-roof mounting methods: →ballasted mounting without roof penetration and →mechanically attached mounting with roof penetration. When installing a photovoltaic system on an existing roof, an on-roof installation with a few roof penetrations points might be a more practical option, as it reduces the potential for roof leaks. In spite of better water-tightness of the on-roof installation, an in-roof installation, which seamlessly blends in with the existing roof and the building, is still a preferred option for many PV owners who pay attention to design and an aesthetically pleasing exterior.

roof-mounting structure See →roof-mounting system. roof-mounting system

A support structure for a →roof-mounted solar array, a frame, upon which photovoltaic modules are mounted.

roof orientation

Position of a roof in relation to the sun. As the roof orientation affects the power output of a solar system, the south-facing

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roof that is tilted toward the sun and not shaded by trees or other buildings will result in the maximum energy yield. roof parallel

Parallel to the roof.

roof penetration

Mounting a solar array on the roof requires roof penetration. Some home owners are hesitant to drill numerous holes in their roofs, as they see them as potential trouble spots causing roof leaks. Impermeable flashings, waterproof standoffs, and heavy-duty rails keep roof penetrations to a minimum. A properly done solar installation with these special parts should prevent leakages. For standing-seam metal roofs, there are roof mounts available that do not require roof penetrations.

roof pitch

The measure of steepness of a roof. The roof pitch is an important factor in determining whether a roof is suitable for solar panels or not. To achieve a maximum solar yield, the best angle for photovoltaic (PV) modules is between 30° and 45°, while an optimum year-round angle for thermal systems is 45°. A mansard roof with steep roof surfaces is less suited for a PV installation, as a complex mounting structure would be necessary to get an optimal year-round tilt. If a roof has a favorable tilt angle that corresponds to your local latitude, thus receiving the maximum amount of sunlight over the course of the year, an additional frame for angle adjustment might not even be needed.

roof pitch calculator

Also known as a roof angle calculator. A tool, usually an application, which helps calculate how many degrees are in a roof pitch. By entering rise and run values into the available boxes of the application, one can calculate pitch, slope, angle, and rafter lengths.

roof plane

Shape of roof.

roof pond

Passive heating or cooling system that is installed on flat roofs. On sunny winter days, the open roof pond heats the house by transferring the heat accumulated in the water to the ceiling and rooms below. On summer days, the opposite process is applied; the roof pond is covered with insulation panels that prevent the heating of water during the day. The water remaining relatively cold throughout the day cools the ceiling and house in general by absorbing the

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 roof slope

heat from the rooms below, based on the principle of buoyancy according to which warm air rises up to the top. The absorbed heat from interior spaces during the day is radiated away at night. roof slope

See →roof pitch.

roof support

In the context of a solar photovoltaic (PV) system installation, a roof’s ability to support the roof skin and a solar array. Early in the PV project planning process, a thorough calculation and inspection of the construction of the roof is crucial. When designing a new house, the extra weight of the PV array must be included into the roof load bearing capacity calculations. However, when installing a PV system on an existing roof, it is recommended to engage a structural engineer, who should evaluate the condition and the ability of the roof to support the solar system. First, the specialist inspects the roof for rotted or damaged rafters that should be replaced. Then, he analyzes if the supporting structure of the roof is strong enough to carry the entire solar array plus the mounting structure. In addition to the examination of the downward weight impact of the solar modules and the racking system, the structural engineer or solar installer must also take into account potential snow loads and wind uplift force. Finally, he may also assess how many roof penetrations are needed, as many regulatory agencies suggest mounting structures to be bolted down into the center of the rafters, to prevent a potential negative impact of an upward force from wind. Most owners try to limit the number of roof penetrations as much as possible, as they regard them as a potential for roof leaks.

roof surface

An unused roof area suitable for a PV or solar collector installation. A solar potential of a specific roof surface can be quantified and estimated by means of a →solar potential analysis system or a site survey conducted by a trained evaluator.

roof tilt

See →roof pitch.

roof type

There are two major types of roofs that are suitable for the installation of solar panels: flat roofs and sloping roofs. Mansard roofs with numerous dormer windows and other

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exotic roofs with complex curved surfaces are less suited for a PV installation. An installation on a flat roof is usually easier and less expensive than an installation on a sloping roof. Typically, the solar system owner can choose between two installation methods: →ballasted mounting without roof penetration and mechanically attached mounting with roof penetration. The challenges that solar installers often face during the flat roof mounting include vents, exhaust fans, rooftop units, and other physical obstacles typically found on a flat roof. The proper management of roof drainage system, in particular in ballasted mounting, should be taken into consideration. The mechanically attached mounting is a recommended installation method on sloping roofs. In spite of higher costs of installation and roof penetration, a mechanically attached mounting system weighs way less than a ballasted system, which adds an additional load on the roof structure with heavy concrete blocks. Other advantages of an attached system include easier inspection and maintenance. roof-integrated photovoltaic system

A photovoltaic (PV) system, in which PV modules, for example, solar roof tiles, are directly integrated into the roof surface to seamlessly blend in with conventional roof tiles and the rest of the roof and building. If the roof-integrated solar panels do not have or have a poor rear ventilation, the PV panels will heat up more than the ones in a →roof-mounted solar array with standoffs and a mounting frame, resulting in a reduced →solar power output. The major advantage of a roof-integrated photovoltaic (PV) system is that it has a far better stability and wind resistance than a rack-mounted PV system. Another important advantage of the roof integrated PV systems is their aesthetical appeal. They provide a more refined design than the traditional, bulky roof-mounted PV systems, because the solar structure is architecturally better united with the entire building, acting as a part of the building shell.

roof-integrated photovoltaics

See →roof-integrated photovoltaic system.

roof-integrated PV system See →roof-integrated photovoltaic system. roof-integrated solar system

See →roof-integrated photovoltaic system.

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 roof-mounted photovoltaic array

roof-mounted photovoltaic array

See →roof-mounted solar array.

roof-mounted photovoltaic system

See →roof-mounted solar array.

roof-mounted PV array

See →roof-mounted solar array.

roof-mounted PV system See →roof-mounted solar array. roof-mounted solar array A solar array that is mounted on the roof. Although a roof-mounted solar array can be installed on a →fixed or an →adjustable mounting system, most of them end up on fixed mounts on account of difficult access to the roof. The challenging accessibility of many roofs makes seasonal or monthly adjustments to the ideal tilt angle a rather demanding affair. It is also more difficult to clean the panels in the summer, to remove snow from the modules in winter, and in general to make any kinds of repairs or updates on a roof-mounted solar array, as opposed to a →ground-mounted solar array. A ground-mounted solar array might be a less problematic option for the installation of your solar array, but in many urban areas with a limited or nonexisting space for a groundmounted solar system, a roof mount is the only choice. On the other hand, roofs are large, unutilized surfaces that many consider an ideal location for the production of solar energy. Two important things must be checked before installation: the structure and the orientation of the roof. A solar technician should evaluate whether the roof structure is strong enough to support the weight of the solar mount and panels plus snow loads and wind impact. They should also carefully inspect the orientation of the roof since not everyone has a perfectly oriented roof. PV modules are most effective when installed on a southfacing roof. Home owners without an optimal south-facing roof can construct an angled mounting system that will position the panels toward the south. roof-mounted solar system See →roof-mounted solar array. roof-mounted system

See →roof-mounted solar array.

roof-parallel

Parallel to the roof.

rooftop photovoltaic power plant 

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rooftop photovoltaic power plant

See →roof-mounted solar array.

rooftop PV power plant

See →roof-mounted solar array.

rooftop solar array

See →roof-mounted solar array.

rooftop solar collector

Is a solar collector, such as a flat-plate collector or an →evacuated-tube collector, mounted on the roof of a building.

rooftop solar power plant See →roof-mounted solar array. root mean square

(RMS) The effective value of alternating current, approximately 70% of the peak voltage. An effective value of 240 V RMS is drawn from the power outlets of a UK house and 117 V RMS from the wall sockets of a US home, whereas the peak voltage value is much higher: 339 V peak in the UK and 167 V in the United States.

rosin flux

See →flux.

rotary disc

See →rotating platform.

rotary screen printing

(RSP2) Also known as rotational screen printing. A printing process for front and rear side metallization of thinfilm photovoltaic cells. The RSP method uses the screen in shape of a cylinder with a squeegee on the inside to transfer ink onto a substrate. The squeegee forces solar ink through the open screen, printing front or back electrode patterns on a flexible thin-film substrate, which is rotating at the same speed as the rotating screen.

rotating house

A rotating solar house that tracks the sun over the course of the day.

rotating platform

Also known as a rotary disk. A large rotating main structure underneath which a rotating drive system is installed. The rotating disk is able to achieve 360° rotation, turning the entire house with a photovoltaic system toward the sun over the course of the day.

rotating shadowband pyranometer

(RSP1) See →rotating shadowband radiometer.

rotating shadowband radiometer

(RSR) An instrument for measuring the →direct solar radiation, →diffuse solar radiation, and →global solar radiation by periodically blocking the direct solar radiation with help of an added rotating →shadow band. The basic RSR head

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 rotating solar house

unit mechanism consists of a →pyranometer, →shadow band, and a motor powering the rotational movements of the shadow band. Rotating shadowband radiometers are utilized in solar energy resource assessment, solar power system monitoring, metering, and evaluation. rotating solar house

A solar house that tracks the sun over the course of the day.

rotation mechanism

Mechanism for rotating solar house.

rotational screen printing See →rotary screen printing. rotational speed

The rotational speed of a →solar tracking system which is adjusted to and follows the Earth’s rotational speed, but in a direction opposite to that of the planet Earth.

rotor

The rotating part of a →wind turbine, including the blades, which is attached to a single shaft.

round grinding

See →round grinding process.

round grinding process

A process in which the surface defects and irregularities of a silicon →boule are refined with the help of an ingot grinding machine.

RSC

Abbreviation for →rigid steel conduit.

RSE

Abbreviation for reactive sputter etching. See →reactive ion etching.

RSP1

Abbreviation for rotating shadowband pyranometer. See →rotating shadowband radiometer.

RSP2

Abbreviation for →rotary screen printing.

RSR

Abbreviation for →rotating shadowband radiometer.

ruled diffraction grating A type of →diffraction grating that consists of a large number of replicated, parallel grooves on a reflective surface. See also →holographic diffraction grating. rust inhibitor

See →rust inhibitor.

R-value

Stands for the thermal resistance value. It is the ability of an insulation material to resist heat flow. The higher the R-value, the greater the insulating efficiency. The factors that affect the R-value are the type of insulation, its thickness, and its density.

S/S 

S

 651

S/S

Abbreviation for →stainless steel.

SA/V ratio

Surface-area-to-volume ratio. See →surface-to-volume ratio.

sa/vol ratio

Surface-area-to-volume ratio. See →surface-to-volume ratio.

sacrificial anode

Also known as a galvanic anode. An easily corroded material deliberately attached to a metal object, such as a water-heating tank, to attract corrosive elements and reduce the corrosion of the protected material, for example, the water tank. This piece of metal must be replaced when it is severely corroded; otherwise, the water tank and its internal components will start to corrode. As they corrode easier than the materials they are protecting, zinc, aluminum, and magnesium are often used as sacrificial anodes in cathodic protection.

safe operating area

(SOA, SOAR) Area within which the device can operate without failure.

safety glass

A tempered or laminated glass that provides thermal insulation, reduces the possibility of cutting injuries when broken, and can resist wind forces and physical impact. Safety glass blocks heat and UV radiation from the sun and prevents them from entering the building, while still letting enough daylight through the glass.

safety shutdown

See →safety shut-off.

safety shut-off

A safety shut-off system that is integrated into a photovoltaic system to provide protection for persons accessing the solar array in case of an emergency. As photovoltaic panels can generate lethal DC voltages of up to 600  V, they can be dangerous for technicians or homeowners accessing the roof. The emergency shut-off allows emergency personnel to switch off the electricity generation from PV modules, providing a safe working environment.

saline lake

See →salt lake.

salt evaporation pond

See →solar salt evaporation pond.

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 salt lake

salt lake

Also known as a saline lake. As saltwater is able to capture and store a large amount of solar thermal energy, shallow salt lakes could act as large thermal storage reservoirs. At night or on cloudy days, when solar modules are not in operation, the local utility company can tap into the warm water layer at the bottom of the saline lake to extract thermal energy for heating or electric power generation.

satellite data

Environmental data, such as solar irradiance, temperature, pressure, or other variables, collected by sensors of geostationary and polar-orbiting meteorological space crafts and sent to ground stations for further processing. The processed data help monitor and predict weather and environmental events on a daily basis and in general provide a bigger picture of the Earth’s changing climate.

satellite power system

(SPS) Concept for solar power generation on satellites orbiting the Earth. A large solar array on each satellite would convert sunlight into electricity, which would be then turned into microwave energy. The microwaves would be beamed to a receiving antenna (rectenna) on Earth’s surface, which would convert microwaves back into electricity. Finally, the electricity would be transported through the usual transmission networks to the utility grid. The satellite power system concept promises significant energy yields because there are no clouds and solar energy losses due to the effects of reflection and absorption in the Earth’s atmosphere. As the Sun is available 24 h a day, 365 days a year, massive quantities of energy could be collected from this uninterruptible power supply.

satellite-based information

See →satellite-based information system.

satellite-based information system

Also known as a satellite-based information technology. A space-borne remote sensing information system that utilizes a wide range of sensors on different satellites to continuously monitor Earth-atmosphere system processes and parameters. The collected data about the current state of weather and climate are sent down to a weather station on the Earth where the large amount of information coming from different satellites is centralized and processed by super computers at high speed. A wireless module allows the sharing of data with other weather stations and other real-time weather data-processing systems.

satellite-based information technology 

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satellite-based information technology

See →satellite-based information system.

saturated air

Air that contains the maximum amount of water vapor it can hold at a given temperature and pressure. The relative humidity is 100% and any increase in moisture content would lead to condensation into tiny droplets and then gradually into larger drops of water.

saturated hydrocarbon

Hydrocarbon molecules that contain only single bonds.

saturation point

See →dew point.

SBSP

Abbreviation for space-based solar power. See →satellite power system.

scanning electron microscope

(SEM) A type of electron microscope that generates a three-dimensional image by moving a beam of focused electrons point by point across the examined object.

scanning tunneling microscope

(STM) A high-resolution microscope that utilizes an ultrafine tip of a tungsten needle to obtain images of the atoms on the surfaces of a material. High-resolution images on a scale of 1  nm or less are used in nanostructuring and nanotechnology in general to provide three-dimensional images of atomic topography. The reconstruction of the silicon surface allows scientists to map electron clouds and study and manipulate semiconductor nanostructures at an atomic level.

scattered radiation

A type of radiation that occurs when the sunbeam collides with small particles in the earth’s atmosphere, such as water vapor or dust molecules, and is redirected from its straight downward trajectory. The radiation that is reflected from particles scatter in all directions, producing →diffuse solar radiation with a diminished solar energy intensity.

scattering of light

An interaction of a sunbeam with small particles in the earth’s atmosphere, such as water vapor or dust molecules, causing the light to be redirected and scattered in all directions.

SCB

Abbreviation for string combiner box. See →DC combiner box.

SCCR

Abbreviation for →short-circuit current rating.

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 scheduling

scheduling

See →committed scheduling.

Schottky barrier

A potential energy barrier formed at the →metal–semiconductor junction or M–S junction, which exhibits rectifying characteristics. The rectifying metal–semiconductor junction has a large barrier height, which is defined by the combination of metal and semiconductor. Due to the large barrier, the metal–semiconductor contact generates higher resistance than the conventional →ohmic contact. The →n-type semiconductor acts as the cathode and the metal acts as the anode. As the Schottky barrier has a low forward voltage drop and very fast switching, it is suitable for use as a →diode.

Schottky diode

A semiconductor diode formed at the →metal–semiconductor junction or M–S junction. It is characterized by very fast switching and low forward voltage drop.

SCR

Abbreviation for →solar catenary reflector.

scratch hardness

See →scratch resistance.

scratch resistance

The ability of a surface to resist scratching or other mechanical impact and maintain the material’s original structure and look. A scratch-resistant surface is produced by adding a special coating to the top protective glass sheet of a solar panel or a solar reflector to resist the deterioration of the surface material caused by scratching, rubbing, or other types of mechanical wear. The improved scratch resistance allows more aggressive cleaning methods and provides good protection against wind-blown sand and other debris.

scratched surface

The physical damage of an encapsulation surface of a solar panel ranging from small to large scratches. Scratches can affect the performance of solar cells. While one portion of light is deflected or blocked to a certain extent due to scratches, the other portion of solar radiation still reaches the photovoltaic cells, although at a diminished rate. The surface of many solar panel models is protected by a special scratch-resistant coating today. If that is not the case, an additional thin protective film, capable of resisting scratching or other mechanical impact, can be added to the solar panel at any time.

scratch-resistant 

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scratch-resistant

See →scratch resistance.

screen printing

Screen printing is a printing process in which conductive lines are created on the front and back sides of a crystalline silicon solar cell. On the front side, a grid of numerous tiny conductive lines called “fingers” are connected with two larger silver contact lines called “busbars.” The fingers and busbars collect the electricity generated within the photoactive silicon semiconductor and transport it to the next cell and further through the circuit. On the back side of the solar cell, there are only large contact lines. In short, the printing process can be described as follows: a screen is placed onto a solar cell wafer along with a conductive paste. A squeegee spreads conductive silver paste over the screen and forces it through a stencil into the mesh openings. After that, the paste is dried in a furnace and then fired at high temperatures in order to bond the silver conductive lines to the silicon semiconductor. Screen printing method is still the industry standard – a mature technology that has been in use since the 1970s and that accounts for almost 90% of solar cell fabrication.

screen-printed silicon solar cell

See →screen-printed solar cell.

screen-printed solar cell

A solar cell that is created by the application of a screen printing method.

screen-printing metallization

Is another, more vivid name for the screen-printing process, in which a grid of metallic lines is created on the front and back sides of a crystalline silicon wafer.

screen-printing method

See →screen printing.

screen-printing paste

Is a conductive metal paste that is spread over the screen and forced through a mask into the mesh openings to form a grid of circuit lines on a silicon wafer.

screen-printing process

See →screen printing.

screen-printing silicon solar cell

See →screen-printed solar cell.

screen-printing solar cell See →screen-printed solar cell. screen-printing technology

See →screen printing.

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Scribing

Is a PV cutting method that uses a diamond-tipped stylus or a laser beam to cut scribe patterns in a semiconductor material in order to create a grid of conductive channels and interconnections in a solar cell. Two major scribing methods that are used in processing of semiconductor materials are: →mechanical scribing and →laser scribing.

scribing process

See →scribing.

SCTL

Abbreviation for →superconducting transmission lines.

sculptured nematic thin films

(SNTF) Nanoengineered microstructure of thin films that is characterized by zigzag, chevron, S-shape, and C-shape columns. The SNTF nanomorphology is tailored to generate favorable optical responses upon excitation with incoming light.

sculptured thin films

(STF) Nanosculptured microstructure of thin films whose columnar morphology is engineered to generate favorable optical responses upon excitation with incoming light. Two main types of sculptured thin films include sculptured nematic thin films (SNTFs), which are characterized by zigzag, chevron, S-shape, and C-shape columns, and chiral sculptured thin films, which are characterized by helicoidal columns.

seal bushing

See →roof bushing.

sealed battery

See →sealed lead-acid battery.

sealed lead-acid battery A type of rechargeable lead-acid battery with an immobilized electrolyte. The electrolyte is usually immobilized in two ways, either by turning the liquid sulfuric acid into gel or by absorbing the electrolyte into fine fiberglass mats that are sandwiched between the positive and negative battery plates. Accordingly, there are two main types of sealed leadacid batteries: →gel battery and →Absorbent Glass Mat (AGM) battery. Neither the gel nor the AGM battery leaks and the water loss through hydrogen gassing is not an issue since the hydrogen gases are retained within the battery. When the hydrogen pressure levels become dangerously high in the battery, a safety valve regulates the pressure by releasing the excess hydrogen. They are easily transported and do not require water additions.

sealing gasket 

 657

Due to the minimal electrolyte losses, the sealed batteries can sit around without any activity much longer than →flooded-cell batteries. This is why they are the first choice for backup power systems (battery banks) in →gridtied photovoltaic systems. However, all these favorable low-maintenance features come with a price. The sealed lead-acid batteries usually cost twice as much as conventional flooded lead-acid batteries and they require special charge controllers. As they are sensitive to temperature extremes, the application in excessively hot places should be avoided. sealing gasket

A piece of tape or other soft material that is put between aluminum frame edges and glass to prevent intrusion of water and dust into solar panels. As water and other particles can damage the appliance or shorten the life of the solar module, the proper front and back encapsulation with the help of sealing gaskets is an important part of a successful PV panel manufacturing process.

sealing sheet

An encapsulant sheet for solar cells that consists of a resin, for example, ethylene–vinyl acetate copolymer or polyethylene. The sealing sheets are laminated on both sides of a photovoltaic (PV) cell, facilitating the vacuum bonding and integration of the PV cell with the upper and lower protective materials.

seasonal adjustments

Refer to seasonal angle adjustments on →adjustable mounting systems. The best power output of a PV array is achieved when PV panels are perpendicular to the sun. As the position of the sun changes over the course of the year, the panels should be tilted accordingly. Four seasons require three different seasonal angles because spring and fall have the same angle, which is equal to the latitude of a given region. As the sun moves lower in the sky during the winter, the panels should be adjusted to the latitude angle plus approximately 15°. In the summer, when the sun hovers high in the sky, the angle of the array should be set at the latitude minus approximately 15°.

seasonal depth of discharge

Factor accounting for a gradual discharge of a battery over a period of reduced solar insolation, resulting in a smaller PV array.

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 seasonal energy efficiency ratio

seasonal energy efficiency ratio

(SEER) A measure of the cooling efficiency of →air conditioners in the USA. The ratio indicates the total electric energy input required to generate a specific cooling output. The SEER rating formula can be expressed as follows: SEER = Btu/(W·h). The Btu of cooling output during its usual annual usage is divided by the total electricity input in watt hours (W·h) during the same period. The higher the SEER, the more energy efficient is the cooling system and thus the greater the energy savings.

seasonal heat storage

See →seasonal thermal energy storage.

seasonal heat storage tank

Also known as a long-term heat storage tank. A large-scale vessel for the storage of heat for a longer period of time, up to several weeks or months. The long-term heat storage tank is typically part of a large-scale →solar thermal heating plant that provides heat for domestic hot water and space heating for an entire district over winter.

seasonal solar angle

See →seasonal adjustments.

seasonal thermal energy storage

(STES) Also known as seasonal heat storage. The storage of heat in the summer and fall for use in winter. This longterm storage of thermal energy provides heat for domestic hot water and space heating for an entire district. The thermal energy from →solar thermal power plants can be stored in large-scale →seasonal heat storage tanks above ground or in various underground thermal energy storage systems, such as →aquifers, →caverns, or →boreholes. The seasonal accumulation of solar heat is a vital part of future secure and sustainable energy supply, as the solar energy is a variable energy resource. As it is susceptible to solar fluctuations, such as cloudy days with a minimum solar input, it can have a negative impact on the stability of thermal energy supply. This is why the long-term storage of thermal energy will play a key role in the development of a reliable future solar energy infrastructure.

seawater still

Plastic bag for seawater distillation.

secondary battery

A →rechargeable battery.

secondary circuit

A circuit in a transformer that receives power from a primary circuit (high-voltage lines) and distributes it to different end-users, such as individual consumers or businesses.

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secondary energy

Energy that is generated by the transformation of →primary energy sources, such sunlight or crude oil. A photovoltaic cell generates secondary energy by converting solar radiation energy into electricity. It is the energy that is ready for transport or transmission.

secondary network

See →low-voltage distribution network.

second-generation photovoltaic cell

Is a →thin-film solar cell. A type of photovoltaic cell that is produced from thin-layers of semiconductor materials, such as →amorphous silicon (a-Si), and →cadmium telluride (CdTe), and →copper indium gallium selenide (CIGS), which are deposited on a →substrate, for example, plastic, glass, or metal. The second-generation solar cells, which are based on thin films only a few micrometers thick, employ only a tiny fraction of material that the traditional 150–200  μm thick silicon wafer of the first-generation solar cell uses. A low material consumption as well as a less costly production process than the expensive silicon wafer manufacturing method lead to the overall solar module price reduction. The disadvantages of the second-generation PV cells include lower performance than first-generation silicon PV cells and the use of a relatively scarce and expensive rare earth element →indium as well as the environmental unfriendly, highly toxic element →cadmium. See also →first-generation photovoltaic cell and →third-generation photovoltaic cell.

second-generation photovoltaics

A method for converting solar radiation into electricity by using →second-generation photovoltaic cells.

second-generation PV cell

See →second-generation photovoltaic cell.

second-generation solar cell

See →second-generation photovoltaic cell.

SED

Abbreviation for spectral energy distribution. See →spectral power distribution.

Seebeck generator

See →thermoelectric generator.

seed crystal

A small single crystal, which acts as a template, from which a large crystal is grown.

seed single crystal

See →seed crystal.

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 SEER

SEER

Abbreviation for →seasonal energy efficiency ratio.

SEG

Abbreviation for →selective epitaxial growth.

selective absorber

A solar collector absorber that uses a special coating with high solar absorptance and low thermal emittance features called →selective surface coating.

selective coating

See →selective surface coating.

selective epitaxial growth

(SEG) A process used during the formation of a thin semiconductor layer, for example, →hydrogenated microcrystalline silicon (μc-Si:H) film, in which the →plasma-enhanced chemical vapor deposition (PECVD) is stopped and held for 5–30 s, depending on the method. This is done a couple of times in order to decrease defect regions that occur due to collision with neighboring grains during the film growth, increasing the conversion efficiency of the semiconductor.

selective surface

A surface with a special coating that absorbs more energy than it emits.

selective surface coating

A special coating that increases the absorption capacity and thermal efficiency of a solar collector absorber. It is developed from a combination of different materials with good optical and thermal properties. As the quality of an absorber depends on the absorption–emission ratio, its performance can be improved by increasing solar absorptance values (absorption of shortwave ultraviolet, visible, and near-infrared rays) and by decreasing the longwave infrared emittance (thermal losses). In other words, the goal is to absorb most of the solar radiation and to lose/ emit as little as possible of the absorbed heat. A good high absorptance–low emittance ratio would be 0.90%–0.10%, total of 10% and higher. For instance, one of better selective surface coatings, black chrome, has a ratio of 9.7% with the solar absorptance of 0.87% and a thermal emittance of 0.09%. Other selective surfaces are black sulfide, nickel oxide, and copper treated with NaCIO2 and NaOH.

selectivity

A property of high-energy reactive particles to etch away only the unmasked material intended for removal, while leaving the material covered by the →etch masks intact. See also →chemical dry etching.

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selenium

(Se) Semimetal that has a certain amount of electric and thermal conductivity. This →semiconductor is used as material in the microelectronic industry, for example, in the production of photocells, specifically →copper, indium, gallium, and selenium solar cells.

self-discharge

Energy loss by an inactive battery sitting on the shelf.

self-discharge rate

Rate by which a battery self-discharges over a period of time naturally regardless of whether it is used or not. High temperatures and time affect the self-discharge rate.

self-generated power

Electricity completely generated by homeowners’ solar arrays without relying on external sources, such as grid-supply.

self-sufficiency

Energy independence.

self-sufficient

Energy self-sufficient, energy independent.

self-sufficient energy supply

The supply of an off-grid house with its own electrical energy and hot water. Depending on the location, solar, wind, or →microhydro systems offer themselves as options for building an entirely energy-autonomous, self-sufficient home.

self-sufficient solar house

(SSSH) An energy-efficient house whose entire energy demand for electricity, heating, domestic hot water, and cooking is supplied by solar energy. The energy autonomy is easier achieved when the need for energy is reduced by building an energy-efficient →passive solar house, reducing unnecessary loads or conserving energy at home, and using energy-efficient appliances. In addition to two traditional solar systems, a photovoltaic energy generation system and solar hot water system, an integration of a battery bank and a seasonal energy storage system, for example, a hydrogen-based system, can enhance the energy autonomy of the home. As the building generates as much energy as it consumes, it emits no harmful →greenhouse gases into the atmosphere.

SEM

Abbreviation for →scanning electron microscope.

semiconductor

A material, a basic component of a solar cell, that is responsible for electrical conductivity. The semiconductor material has features of both insulators and conductors. Normally, it functions as an insulator; however,

662 

 semiconductor compound

under certain circumstances, when exposed to sunlight, it conducts electric current. Its energy gap, which is less than 4 eV, is slightly narrower than the one of an insulator, allowing electrons to jump to the conduction band when they are hit by incoming photons of light. A silicon semiconductor, which is doped with boron or phosphorus atoms, has three or five electrons in its valence shell. When exposed to solar radiation from near infrared, visible light, or ultraviolet (UV) rays, the extra odd number electrons get excited, leave their orbits, and enter the conduction band, where they move freely from one silicon atom to another and further through an outside circuit, generating electricity. When an electron deserts a silicon atom, it leaves a hole behind, which is instantly filled up by another electron from a neighboring atom. Holes are uninterruptedly created and filled. With the increase of temperature, the electrical conductivity of semiconductors increases. Major semiconductor materials that are used in solar cell production include →crystalline silicon, →amorphous silicon, →gallium arsenide, →copper indium gallium selenide, →copper indium selenide, →cadmium telluride, →copper zinc tin sulfide, and →organic polymer. semiconductor compound

See →compound semiconductor.

semiconductor device

An electrical device that takes advantage of the photoelectric properties of semiconductor materials, such as →silicon, →germanium, →gallium arsenide, →copper indium gallium selenide, and →organic semiconductors.

semiconductor diode

A diode that is created by joining n-type and p-type semiconductor layers. The negatively doped semiconductor layer (cathode) has an excess of electrons, whereas the positively doped semiconductor layer (anode) has a lack of electrons and an excess of holes. The opposite anode and cathode layers or electron and holes attract each other. At a →p–n junction between the positively charged semiconductor region (p-type layer) and negatively charged semiconductor region (n-type layer), a depletion region forms, which is depleted of charge. Having neither electrons nor holes, it acts as a barrier opposing the flow of electrons.

semiconductor doping 

 663

The diode acts as a one-way valve, passing current only in one direction. When the light falls onto the solar cell, the photosensitive semiconductor material absorbs the energy of the photons, which is strong enough to knock electrons loose. The minimum photon energy required to induce photoconductivity and generate mobile electrons and holes is 1.1  eV. With this amount of energy, the excited electrons from the p-type layer are able to cross the p–n junction barrier and enter the n-type layer, starting a current flow. The electrons flow outside of the solar cell to the load and return through the back contact to the p-type semiconductor layer, occupying the vacant positions (holes) and thus closing the circuit. The solar cell output in direct sun is between 3 and 6 A and around 0.5 V. semiconductor doping

Intentional and controlled incorporation of impurities into a pure semiconductor, in order to change its electrical characteristics.

semiconductor electronics

The branch of electronics dedicated to the theory and practice of optoelectronic and electronic devices based on semiconductors. The major focus of semiconductor electronics is the p–n junction that is formed at the boundary between positively doped and negatively doped semiconductor layers in a solar cell. Semiconductor physicists closely investigate electron conductivity in the →n-type semiconductor region and hole conductivity in the →p-type semiconductor region.

semiconductor film

See →semiconductor layer.

semiconductor layer

A photoelectric conversion layer that is sandwiched between the rear metal contact and the top contact in a photovoltaic cell. The semiconductor layer consists of a top n-type semiconductor layer and a bottom p-type absorber semiconductor layer. The n-type semiconductor layer is doped with →phosphorus atoms, which have an excess of electrons that roam free along the →conduction band, producing negative charge carriers. The p-type semiconductor layer is doped with →boron atoms, which have a lack of electrons, creating holes in the →valence band that carry a positive charge. While a conventional silicon semiconductor layer is approx. 150  μm thick, a thin-film semiconductor layer is only several micrometers thick.

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 semiconductor materials

semiconductor materials

Semiconductor materials for manufacturing PV devices include: →crystalline silicon (c-Si), →amorphous silicon (a-Si), →germanium, →copper indium gallium selenide (CIGS), →copper zinc tin sulfide (CZTS), →cadmium telluride (CdTe), →cadmium sulfide (CdS), and →gallium arsenide (GaAs).

semiconductor nanocrystal

See →quantum dot photovoltaic cell.

semiconductor substrate

A monocrystalline or a polycrystalline substrate, in which →p–n junctions are formed. A polycrystalline semiconductor substrate can consist of a p-type semiconductor, an n-type emitter region, and a p–n junction.

semiconductor wafer

See →solar wafer.

semicrystalline

See →polycrystalline.

semiflexible solar collector

See →semiflexible solar module.

semiflexible solar module

A module that consists of semiflexible →thin-film solar cells. Semiflexible PV modules are lightweight, semibendable, and easy to install. They weigh much less and are less bulky than conventional →rigid photovoltaic modules, which makes them suitable for motorhomes, boats, or other vehicles. Unlike →flexible thin-film solar modules that can be rolled-up or folded, semiflexible solar modules can be bent up to about 30°, which is still flexible enough to accommodate the shape of a curved RV or boat roof. They can also be attached to boat canopies or tents. Commercial glue, double-sided tape, zippers, or Velcro may be used to mount or attach the semiflexible panels.

semiflexible solar panel See →semiflexible solar module. semiflexible substrate

A semibendable →substrate that is made of aluminum or plastic, for example, low-cost poly-ethylene.

semitransparent cell

See →semitransparent solar cell.

semitransparent photovoltaic cell

See →semitransparent solar cell.

semitransparent photovoltaic module

See →semitransparent solar module.

semitransparent PV cell 

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semitransparent PV cell

See →semitransparent solar cell.

semitransparent PV module

See →semitransparent solar module.

semitransparent solar cell

A solar cell that transmits visible light and generates electricity by using thin semitransparent semiconductor layers. The semitransparency of the semiconductor layers is achieved by depositing ultrathin semiconductor absorber films onto a transparent substrate. The semiconductor thin films can be fabricated from different materials, such as →cadmium telluride (CdTe), cadmium sulfide (CdS), →copper indium gallium selenide (CIGS), →perovskite (CaTiO3), or →amorphous silicon (a-Si). The cell has a transparent substrate or superstrate layer and both electrodes are also transparent. The top electrode is usually made of →transparent conductive oxide (TCO) and the back electrode of a metallic layer, such as Ag. As they transmit one part of visible light and utilize the other part to generate electrical current, semitransparent solar cells are suitable to be applied to →solar windows or →solar skylights.

semitransparent solar module

A photovoltaic module that consists of →semitransparent solar cells. Another type of semitransparent solar module is made of visible solar cells and a see-through glass or polymer →superstrate. As solar cells are encapsulated in a transparent superstrate, a spacing is left between the PV cells, allowing light to pass through and thus creating high visual transparency. Both types of semitransparent solar modules are often employed as →photovoltaic windows or →solar skylights, because they allow enough light into the interior of a building, while simultaneously generating electricity.

semitransparent solar panel

See →semitransparent solar module.

semitransparent solar skylight

A solar skylight that is made of →semitransparent solar modules.

semitransparent solar window

A solar window that is made of →semitransparent solar modules.

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 semitransparent thin-film solar cell

semitransparent thin-film solar cell

See →semitransparent solar cell.

sensible heat

Heat storage with no phase change where the changes in the temperature of the material depend on the amount of stored energy. For instance, when water is heated in a →hot water storage tank, its temperature rises as heat is added.

sensitizer

Material that functions as a photochemical catalyst.

sensor

A device that monitors and detects changes in ambient conditions or a system and responds to it. The following types of sensors are commonly deployed in →photovoltaic and →solar thermal systems: →solar power meter, →temperature sensor, →thermocouple, →pressure gauge, and →anemometer.

sensor-controlled tracking

See →sensor-controlled tracking system.

sensor-controlled tracking system

A tracking system that uses photosensors to direct the PV modules at the brightest point in the sky. While the application of this system in regions that receive a large amount of direct sunlight throughout the year is rather questionable due to some misalignment errors, the sensor-controlled tracking systems show better results and can achieve high energy yields in regions with a high annual percentage of diffuse radiation.

sensor-guided tracking

See →sensor-controlled tracking system.

sensor-guided tracking system

See →sensor-controlled tracking system.

SEP

Abbreviation for →solar electric propulsion.

separation energy

The energy required to free an electron from a molecule or atom or nucleus.

separator

The material separating the electrodes. Typically, a polymer, thin-film membrane that prevents contact between anode and cathode in a storage battery.

September equinox

See →fall equinox.

serial connection of solar cells

See →series connection of solar cells.

serial interconnection 

serial interconnection

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See →series connection.

serial interconnection of See →series connection of solar cells. solar cells series charge controller

Is a charge controller that is connected in series between the photovoltaic array and the battery bank with a task to disconnect the current flow from PV modules when the batteries are full.

series circuit

A circuit in which components are connected in series (one after the other) to increase voltage. See also →series connection.

series connection

One of the two main connection types for solar panels or batteries is series connection, in which components are connected consecutively (one after the other, + to − to + to − on one side and − to + to − to + on the other) to increase voltage. When batteries are connected in series, the capacity across batteries remains the same, but the voltage of each battery is added together.

series connection of solar cells

Individual solar cells of a silicon solar module are mostly connected in series, to increase the power and voltage. The negative tabbing wire from the front of the first cell is soldered to the positive pad on the bottom of the second cell, the negative tab from the top of the second cell is soldered to the positive back of the third cell, and so on.

series controller

See →series charge controller.

series regulator

See →series charge controller.

series resistance

Is a resistance to current flow in a solar cell that is associated with the cell materials and contacts. The contact resistance includes (a) the resistance between metallic contacts and the silicon semiconductor and (b) the resistance of the top and rear metallic contacts. As the series resistance has an effect on the solar cell output and might cause a decrease in maximum power point voltage, it is important to include it in measurements. With the help of collected data, engineers can reduce contact and material resistance losses. Through application of different materials and different types of contacts, they can enable a smoother current flow, which will automatically result in higher power output.

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 series string

series string

A group of solar panels or batteries connected in series.

series wiring

Wiring, in which components, for example, solar panels or batteries, are connected in series to increase voltage.

serpentine absorber

See →double meander absorber.

service life

See →operating lifetime.

service water

Water that does not meet safe drinking water quality standards. Service water can still be heated by solar panels and used for washing, space heating, and various industrial purposes.

service water storage tank

A tank in which service water is stored.

set point

A desired value, a minimum and maximum voltage or temperature value, that is maintained by an automatic control system. A battery controller cuts the electric current when the battery reaches a set voltage value (is fully charged) to prevent excessive overcharge and turns it on when a low-voltage set point is reached (the battery is discharged). Similarly, in solar water-heating systems such as →batch collectors, the temperature set points of a hot water controller prevent the storage tank from overheating and the solar tube-type collectors from freezing.

setpoint

See →set point.

setpoint setting

See →set point.

setpoint value

See →set point.

SEZ

Abbreviation for →solar energy zone.

SF

Abbreviation for →shade factor.

SFU

Abbreviation for →solar flux unit.

shade factor

(SF) Photovoltaic systems should ideally be installed on sites without any shading obstacles. However, if that is not possible, a shading assessment using SF procedure should be performed to evaluate to what extent a neighboring building, chimney, or trees would affect the power output of a future solar system. A shading-analysis tool can determine the total shading of a house throughout the year by using dynamic shading simulations. A sun path diagram with segments

shading coefficient 

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(squares) is applied displaying all visible objects (obstacles) on the horizon. The value of the SF is calculated by using the formula: SF = 1 − (sum of affected squares), where 1 stands for a clear sky without any shading or 100% insolation. If, for instance, the obtained result shows an SF value of 95%, this means that a solar owner must expect 5% less power output from future PV panels when compared to the ideal PV module position without shading obstacles. shading coefficient

See →shade factor.

shading coefficient calculation

See →shade factor.

shading disk

A disk mounted on an automated solar tracker arm to continuously follow the sun and cast a shadow on the pyranometer. By blocking the direct solar radiation on the measuring instrument, the shading disk allows the measurement of only diffuse solar radiation.

shading factor

See →shade factor.

shading factor calculation

See →shade factor.

shading system

A system that keeps a building cool during the warm summer months. It can include a →photovoltaic shading structure, →deep eaves, →awnings, →vertical fins, or →light shelves.

shading1

Shadows falling on solar modules can significantly impact the power output of a solar system. In older systems, the shading of a single cell can reduce the power output in the entire module. As the cells are connected in series, the shaded cell will impact the operation of the next cells in the line by blocking the free flow of electrons. The current drop leads to overheating, resulting in energy losses and potential equipment damage. Most modern PV modules have bypass diodes that prevent power losses and damage by diverting the current past the shaded cell and allowing the continuous flow of electricity. However, bypass diodes are not attached to each and every cell, but they are installed in parallel with a string of solar cells. Accordingly, one single shaded cell will still reduce the power output of the entire string, which often accounts for one-third of the module output.

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 shading

Two types of shading can be differentiated: temporary and permanent shading. Temporary shading is caused by the accumulation of dirt, snow, moss, or other particles on the surface of the panels and can be easily eliminated by regular cleaning of solar modules. The permanent shading is caused by physical obstacles, such as trees, neighboring houses, vents, chimneys, and equipment, casting an enduring shadow on the panels. The permanent shading can be divided into partial and total shading. As the name suggests, partial shading exists when only one part of the solar system is shaded, while the other part can still generate electricity or heat. In the case of total shading, either the obstacles, such as trees or shrubs, should be removed, or if that is not possible, the entire solar installation should be moved to another site. In order to avoid output losses due to permanent shading, a careful assessment should be conducted by a trained evaluator during the site survey at the beginning of the solar project. He will try to avoid shading at all cost by planning the future solar system installation in areas that are free of tree and building shade. If a partial shading is unavoidable, the assessor should be able to evaluate the impact of shading on your power output by using →solar calculator and other tools for obstacle analysis. shading2

One of the oldest passive cooling techniques that prevents a house from gaining heat and enhances heat loss. →Deciduous trees, →deep eaves, →awnings, →vertical fins, →light shelves, and →low-e window panes shade windows and house walls from the blazing sun in the summer.

shadow angle

During the design of a new solar installation, it is vital to carefully calculate shadows cast on the surface behind solar modules to ensure that a row of PV modules does not shade the adjacent row of solar panels. The challenging part of taking horizontal and vertical shadow angles is the fact that they always change with different dates, times, and location, as the sun constantly alters its position in the sky throughout the year. Some modern programs simulate the movement of shadow during the day, helping solar architects visualize the complex interaction between the position of the sun, the site’s latitude, the orientation and tilt of solar modules, and the shadow angle.

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shadow band

A rotating metal strip mounted on a pyranometer at such angle to cast a shadow on the pyranometer throughout the day. By blocking the direct solar radiation on the measuring instrument, the shading disk allows the measurement of only diffuse solar radiation.

shadow band pyranometer

See →rotating shadowband pyranometer.

shadowing

A shading effect in a photovoltaic or solar thermal power plant, in which one collector casts a shadow on a neighboring collector. Shadowing is likely to occur in the early morning and late afternoon hours at a specific location. As a shadowing effect can have a dramatic impact on energy production of a solar system, it is essential to optimize the design of the system by an in-depth analysis of the spacing between collectors, the type and height of collectors, the row length, the tilt angle, and the latitude.

shaft

A component of a wafer dicing machine consisting of a long, cylindrical bar, inside of which a rotating spindle is housed, to which a cutting blade is affixed. The rotating part of the shaft transmits kinetic power to the blade.

shallow-cycle

See →shallow-cycle battery.

shallow-cycle battery

A type of battery with small plates that is designed to be kept almost fully charged. Unlike a deep-cycle battery that can be discharged between 50% and 80% of the battery’s total capacity, the shallow-cycle battery will perform best when it is only partially discharged between 10% and 15%. On the other hand, it will not perform well if discharged more than 25% of its full capacity. The shallower the depth of discharge, the longer the battery life. However, it is recommended to deeply discharge the battery to 50%–80% from time to time to keep the plate material active.

shaped mirror

Unlike a plane, flat mirror, a shaped mirror is a curved mirror that bulges inward or outward. The inward-curving mirrors or surfaces, known as →concave mirrors, are used in the →concentrating solar collector technology to concentrate incoming solar radiation at the focal point of the →dish or a focal line of a →concentrating parabolic trough, thus increasing the solar energy numerous times.

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 shaper

shaper

See →graphite die.

shear wind load

Horizontal pressure or force of the wind that can make a vertical solar structure tilt or crack.

sheet glass

See →plate glass.

shelf life

See →shelf life of a battery.

shelf life of a battery

The period of time that a battery can be stored and still perform according to its intended use and specification. It determines when a battery should be taken off the shelf in a store and declared unfit for sale, for example, when it drops under 80% of its original capacity.

shell

See →electron shell.

SHGC

See →solar heat gain coefficient.

SHJT

Abbreviation for →silicon heterojunction technology.

Shockley–Queisser efficiency limit

Also known as Shockley–Queisser limit or SQ limit. A theoretical limit, calculated by William Shockley and HansJoachim Queisser in 1961, which postulates that the ultimate conversion efficiency of a →photovoltaic cell can never exceed 34% for a single optimized semiconductor →p–n junction with a →band gap of 1.34 eV.

Shockley–Queisser limit See →Shockley–Queisser efficiency limit. short circuit

An electrical circuit in which an electrical path of low resistance has been created by accidental connection of two points of different potential without any load. The lowresistance connection results in excessive current flow, producing high temperatures and possibly catching fire.

short-circuit current rating

(SCCR) A rating required on all components and assemblies that depicts the maximum short-circuit current that a component or assembly can withstand without causing fire or other safety hazard. This SCCR rating displays whether a home or business owner is in compliance with the National Electrical Code (NEC) rule # 110.10 or not.

short-circuit current

(ISC) Is the maximum current produced by a solar cell when its terminals are short circuited, which means connected to each other. As there is no connection to an external load, there is no resistance in a circuit and the voltage is zero.

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short-circuit protection

In order to protect a circuit from overcurrent or a →short circuit, circuit protection devices such as fuses or circuit breakers should be installed in any PV circuit network, in a low-voltage as well as in a high-voltage network.

short-term heat storage tank

A storage vessel that uses water as a storage medium and can retain stored heat only for a couple of days. See →hot water storage tank.

shortwave

Referring to →shortwave radiation.

shortwave infrared camera

Also known as a SWIR camera. A camera that operates in a shortwave infrared wavelength range between 0.9 and 1.7 μm and is used for solar cell inspection.

shortwave radiation

Solar radiant energy that enters the Earth’s atmosphere in the form of ultraviolet (UV) rays, visible light, and near-infrared light. The UV radiation includes the wavelengths between 0.1 and 0.4 μm of the electromagnetic spectrum; the visible light covers the wavelengths from 0.4 to 0.7 μm; and the near-infrared radiation spans from 0.7 to 5.0 μm. Shortwave radiation contains a lot of energy heating the Earth. The shorter the wavelength, the more energy it contains. That is why the UV radiation with the shortest wavelengths of the aforementioned three has the harmful effects on humans, animals, and plants. Solar radiation is often referred to as shortwave radiation.

shortwave solar radiation

See →shortwave radiation.

SHS

Abbreviation for →solar home system.

shunt charge controller

Is a charge controller that is connected in parallel between the photovoltaic (PV) array and the battery bank with a task to prevent overcharging by diverting the current flow from PV modules to a “shunt” load, for example, a water heater, when the batteries are full.

shunt controller

See →shunt charge controller.

shunt regulator

See →shunt charge controller.

shunt resistance

A type of parasitic resistance that reduces the →fill factor and thus the power output of a solar cell by dissipating electric current across internal resistances. Compared to the optimal infinite shunt resistance, the low shunt resistance

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 Si ink

leads to energy losses by providing an alternative path for the generated current. Instead of flowing through the PV cell →p–n junction, a portion of the current is diverted to the different path and lost through dissipation. The leakage of power due to low shunt resistance is caused by manufacturing flaws, such as crystal defects, and impurities near the junction. On cloudy days with low light intensity, a PV cell with a low shunt resistance experiences significant power losses, as the amount of current flowing through the shunt resistance increases. Si ink

See →silicon ink.

SI2

Abbreviation for →Solar Impulse 2.

Siemens process

A chemical purification process for making purified silicon for →photovoltaic cells. The →chemical vapor deposition process takes place in a vacuum chamber, in which thin U-shaped polysilicon rods are mounted on the purified graphite electrodes. The gaseous trichlorosilane (SiHCl3) is introduced into the reaction chamber, containing the heated silicon rods. At an elevated temperature of 1,150 °C, the gas decomposes and the pure silicon settles on the surface of the hot rods. Finally, high-purity polysilicon rods are broken up to form silicon chunks, which are packaged and used for further processing.

sieve

In a →metallization and →screen printing process, a mesh used in solar cell manufacturing for transferring conductive metal paste or solar ink onto a substrate.

SiHJT

Abbreviation for →silicon heterojunction technology.

silane

Also known as hydrosilicon or silicon hydride. A colorless flammable gas with an unpleasant odor that is typically used as a →precursor to silicon in the manufacture of semiconductors. Any of a class of covalently bonded compounds containing silicon and hydrogen. The simplest of these is silane SiH4, consisting of one silicon and four hydrogen atoms.

silane species

Deposition species (silane molecules) in a →chemical vapor deposition process.

silica

See →silicon dioxide.

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silica gel

A hygroscopic substance that attracts water and is used as a drying agent to reduce the humidity of air or gas.

silica sand

High-purity sand that is derived from →quartz and is almost entirely made of silica or →silicon dioxide (SiO2).

silicon

(Si) Key material used in solar cell production due to its semiconductor properties. After oxygen, silicon is the most common element on the planet making up 28% of the Earth’s crust, by weight. It is the main component of sand. In the Periodic Table, it appears under atomic number 14, between →carbon (C) and →germanium (Ge) in the vertical carbon group, and between →aluminum (Al) and →phosphorus (P) in the third period. It has a face-centered cubic lattice structure and four valence electrons in the outer shell that readily bond with nearby atoms. To achieve balance, the silicon atom shares four outer electrons with four other neighboring silicon atoms forming a uniform structure called a crystal. Silicon is typically doped by phosphorus or boron initiating the flow of electrons across the silicon crystal lattice.

silicon atom

A silicon atom has 14 electrons. Of these, four are valence electrons, occupying the third orbital or energy level, whereas eight electrons occupy the second energy level and two electrons occupy the first energy level. The complete electron configuration of the silicon atom is 1s22s22p63s23p2. By doping silicon with an element from group 15, such as phosphorus, arsenic, or antimony, an extra electron is introduced into the geometric silicon crystalline structure. Under the influence of thermal or photoexcitation, the energized extra electron is passed on from one silicon atom to another throughout the crystal lattice, creating an n-type semiconductor and generating electric current in the process. In addition, by doping silicon with an element from group 13, such as boron, aluminum, gallium, or indium, a hole is introduced into the geometric silicon crystalline structure. A hole gladly accepts an electron from a neighboring silicon atom, compensating for the boron’s electron deficiency and creating a p-type semiconductor. Holes are uninterruptedly created and filled. This chain reaction in which electrons are moving in one direction from n to p across the silicon crystal lattice and holes in the opposite direction from p to n produces electrical current in a solar cell.

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 silicon block

silicon block

Usually a polycrystalline silicon block for wafer fabrication. See →polycrystalline silicon ingot.

silicon brick

See →polycrystalline silicon brick.

silicon carbide

(SiC) A compound of silicon and carbon. The material is a semiconductor with numerous favorable characteristics, such as hardness, wide band gap of 3.2  eV, thermal stability, dielectric strength, and resistance to radiation and harsh environments. Due to these features, the silicon carbide is an attractive material for solar cells that are exposed to high temperatures and high solar radiation. SiC can be doped n-type by →phosphorus and p-type by →boron or →gallium. It is typically grown as a single crystal on a →silicon substrate by epitaxial growth or deposited on a substrate by →chemical vapor deposition (CVD) in a polycrystalline process.

silicon carbide semiconductor

A semiconductor made of →silicon carbide (SiC) compound material with a →wide band gap of 3.2 eV. Compared to the narrow silicon band gap of 1.1 eV, the wide band gap allows silicon carbide semiconductors to be operated at much higher voltages and temperatures than conventional semiconductors, such as →silicon (Si) and →gallium arsenide (GaAs).

silicon carbide solar cell

A solar cell consisting of silicon carbide (SiC) semiconductor material that is suitable for the application in harsh environments due to its resistance to high temperatures and high solar radiation.

silicon casting

A wafer-manufacturing technology in which liquid silicon is poured into a casting frame under which a colder substrate is moving, which leads to the growth of a thin silicon layer known as a silicon ribbon.

silicon cell

A photovoltaic cell made of silicon semiconductor material.

silicon compound

A compound consisting of silicon and one or more elements in a specific ratio. The most common silicon compound is silicon dioxide (SiO2), also known as silica. It is an abundant mineral found in rocks and sand. The pure silicon is obtained from silicon dioxide by melting silicon rocks at high temperatures (around 1,371 °C [2,500 °F]) in a →crucible into a silicon slurry (melt) and pulling a single silicon crystal from the melt in the →Czochralski method.

silicon crystal 

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Other silicon compounds that are commonly utilized in solar industry include silane, which is employed as a →precursor in a →chemical vapor deposition process, and silicon carbide (SiC), which is often used as a semiconductor material for solar cells. silicon crystal

See →crystalline silicon.

silicon cylinder

See →silicon ingot.

silicon dioxide

(SiO2) Also known as silica. A natural compound that consists of the two most abundant elements in the Earth’s crust: silicon (Si) and oxygen (O2). This oxide of silicon is found on every continent as sand or quartz. Silicon, as the vital raw material for the manufacture of semiconductors for photovoltaic modules, is produced from silicon dioxide.

silicon dioxide substrate

→Silicon dioxide can be used as a substrate for multiple →graphene films or III–V or II–IV semiconductor materials. Double or multilayer graphene is grown via →chemical vapor deposition (CVD) and then transferred onto silicon dioxide substrate. The use of silicon dioxide substrate as the base for multijunction solar cells allows high-voltage cell circuits with two or more superimposed subcells to be manufactured on a single wafer.

silicon dust

Dust created during silicon dicing that can cause damage to delicate mechanical structures. In semiconductor manufacturing facilities, employers must ensure that workers are protected from the inhalation of tiny crystalline silicon dust particles, which can cause a serious lung disease, called silicosis.

silicon etching

The removal of silicon layers from the surface of a wafer by means of etchant – a chemical in either liquid or gaseous state.

silicon heterojunction photovoltaic cell

See →silicon heterojunction solar cell.

silicon heterojunction photovoltaic module

A photovoltaic module that is composed of →silicon heterojunction solar cells.

silicon heterojunction photovoltaic panel

See →silicon heterojunction photovoltaic module.

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 silicon heterojunction PV cell

silicon heterojunction PV cell

See →silicon heterojunction solar cell.

silicon heterojunction PV module

See →silicon heterojunction photovoltaic module.

silicon heterojunction PV panel

See →silicon heterojunction photovoltaic module.

silicon heterojunction solar cell

A solar cell that consists of monocrystalline (c-Si) and amorphous silicon (a-Si) semiconductor layers. The monocrystalline layer in the center of the solar cell is covered on both sides by thin amorphous silicon layers to minimize the power loss due to recombination. In traditional crystalline solar cells, the recombination current at the metal/semiconductor interface is very high, resulting in a reduced solar cell power output. Amorphous silicon layers have wide band gaps that minimize recombination of electrons. By adding thin hydrogenated a-Si films on both sides of the n-type crystalline silicon wafer, the c-Si absorber material is electronically separated from extremely recombination-active metallic contacts. On the front and back of the silicon wafer, an antireflective transparent conductive oxide (TCO) film is deposited by physical vapor deposition (PVD). The result of this combination of conventional crystalline and thin-film technologies is a solar cell with a conversion efficiency above 20%.

silicon heterojunction solar module

See →silicon heterojunction photovoltaic module.

silicon heterojunction solar panel

See →silicon heterojunction photovoltaic module.

silicon heterojunction technology

(SHJT, SiHJT) A photovoltaic technology that combines the traditional crystalline silicon solar cell manufacturing method with amorphous silicon thin-film technology. See also →silicon heterojunction solar cell.

silicon ingot

A mono- or polycrystalline silicon block for wafer fabrication.

silicon ingot production

Production of artificial single silicon crystals called →ingots from the melt. The process starts with the melting of high-purity silicon (99.9%) in a →crucible. The bath of highly purified molten silicon as well as a very clean

silicon ink 

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environment in a crucible are necessary prerequisites for the manufacture of a silicon ingot in a controlled →Czochralski crystal growth process. A small seed crystal, which is mounted on a rod, is dipped into the silicon bath. A large single silicon crystal is grown by slowly pulling the rod out of the melt. The control of the speed of rotation and temperature in the crucible allows the optimization of the semiconductor product. silicon ink

A type of liquid solar ink based on nanotechnology. Using a solar industry standard screen printer, one production step is added to an existing photovoltaic cell production line: the doped silicon ink is deposited in a pattern configuration slightly wider than the subsequently deposited front metal contacts. The controlled deposition of silicon ink improves the absorption of high-energy, short-wavelength light, which in turn increases the conversion efficiency of photovoltaic cells.

silicon material

See →silicon.

silicon melt

Molten mass of silicon into which a seed crystal is immersed and then slowly pulled upward to create 1. a crystal silicon →ingot in the wafer production using the →Czochralski process or 2. a silicon ribbon in the production of →ribbon polycrystalline silicon wafers.

silicon nanowire

(SiNW) Quasi one-dimensional structures with a diameter of less than 100 nm that are employed in solar cells and sensors. The nanoscale diameter leads to a large surface-to-volume ratio that is capable of significantly improving the performance of photovoltaic cells, sensors, and batteries. Silicon nanowires can be produced by applying one of the top-down synthesis methods, such as →ion beam etching or →laser ablation, or one of the bottom-up synthesis methods, such as →molecular beam epitaxy or vapor liquid solid growth. The control of verticality and orientation in silicon nanowires is crucial for optimizing electron and hole mobilities in silicon nanowire-based solar cells.

silicon nanowire solar cell

A nanocrystalline thin-film solar cell that is based on →silicon nanowires. The proper alignment of nanowire structures is a key element of a successful SiNW manufacturing process, as the electrical performance of the cell significantly depends on the orientation of silicon nanowires.

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 silicon nitride

silicon nitride

(SiN) A chemical compound that is synthesized by combining silicon and nitrogen. Silicon nitride is a hard material that demonstrates great strength at high temperatures. Owing to these and other favorable properties, it is often used as an antireflective coating to reduce the reflection and improve light absorption in a solar cell. A →plasma-enhanced chemical vapor deposition (PECVD) process is commonly used to deposit a silicon nitride antireflective layer on the semiconductor surface. The color and appearance of solar cells can be altered by varying the thickness of the silicon nitride antireflection coating. Silicon nitride (Si3N4) is also a preferred masking material, offering a more durable protection against liquid or gaseous etching chemicals than other etch masks.

silicon oxide

A white or colorless crystalline compound, an oxide of silicon, for example, SiO2, which is found in the earth’s crust as quartz, sand, flint, cristobalite, tridymite, and other minerals. See also →silicon dioxide.

silicon photovoltaic concentrator cell

A conventional, single-junction silicon photovoltaic cell that is specially designed for →low-concentration PV systems (LCPV). This high-efficiency PV cell is integrated into an LCPV system, which uses concentrating optics to focus sunlight onto the cell.

silicon photovoltaics

See →crystalline silicon photovoltaics.

silicon powder

Yellow-brown powder composed of very small grains of silicon, with a high purity level of 99.99%. Silicon powder is used as a main raw material in →chemical vapor deposition (CVD) and →physical vapor deposition (PVD) processes for the manufacturing of →thin-film solar cells and →amorphous silicon solar cells.

silicon rod

See →silicon ingot.

silicon semiconductor

A type of semiconductor with a narrow →band gap on the order of 1–1.5 eV. This means that when sunlight falls on the silicon semiconductor, the minimum photon energy required to induce photoconductivity and generate mobile electrons and holes is 1.1 eV. By absorbing this amount of energy from incoming photons, the excited electrons in the →valence band are able to bridge the band gap and start the electric current flow along the →conduction band and further through an outside circuit.

silicon sensor 

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To increase the conductivity, the electronic properties of the silicon semiconductor are modified in a controlled manner by adding small amounts of dopant material, such as →phosphorus and →boron, to a pure semiconductor. silicon sensor

Also known as silicon detector or silicon irradiance sensor. A solar cell for measurement of solar irradiance. In spite of the utilization of a high-quality monocrystalline solar cell that is connected to a high accuracy shunt, the spectral response of the silicon sensor is not as exact as that of →thermopile instruments.

silicon solar cell

See →crystalline silicon solar cell.

silicon solar module

A solar panel that is composed of silicon solar cells. It is still the most common type of solar panel for residential applications. Two main types of the traditional crystalline silicon solar module are: →monocrystalline silicon solar module and →polycrystalline silicon solar module.

silicon solar panel

See →silicon solar module.

silicon substrate

A wafer made of →silicon that is doped with impurity, a small amount of p-type dopant →boron. The Si substrate acts as a base of a photovoltaic cell onto which other layers are deposited.

silicon wafer

A thin slice of semiconductor silicon material that acts as a main product or raw material for photovoltaic cells. Silicon wafers are sliced from a →monocrystalline or →polycrystalline silicon ingot using wire saws or laser cutting. Subsequently, they undergo multiple processing steps, such as coating, baking, and etching, before they are made into photovoltaic cells.

silicon wafer cutting machine

A machine for slicing the cooled monocrystalline or polycrystalline silicon blocks into →solar wafers. Wafer-cutting machines commonly utilize steel-wire or diamond-wire saws to slice silicon →ingots into wafers. Regarding the way and speed of processing, the following two saw types are differentiated: inner-diameter (ID) saws and parallel wire saws. While an ID saw can slice only a single wafer at a time, more efficient parallel wire saws are able to simultaneously cut the entire silicon ingot, producing hundreds of wafers at once. In the multiwire saw mass-production method, a several-kilometer-long

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wire is wetted with a type of paste, called slurry, a mixture of silicon carbide and polyethylene glycol. The ingot is slowly lowered into a web of parallel ultrathin wire saws, moving at the speed of up to 60  km/h (37  mi/h). The cutting process takes several hours to complete. In general, silicon wafers thicker than 100  μm are usually cut by diamond saws, whereas silicon wafers less than 100 μm thick are commonly cut by →laser ablation or →stealth dicing. As silicon and germanium are brittle materials that easily chip or even crack during a mechanical cutting process, many manufacturers prefer laser machines for the cutting of monocrystalline, polycrystalline, and thinfilm solar cells. The laser cutting machines allow a high-precision cutting, sharp edges, and a high speed of processing. silicon wafer dicing machine

See →silicon wafer cutting machine.

silicon wafer fabrication See →silicon wafer production. silicon wafer manufacturing

See →silicon wafer production.

silicon wafer production

In silicon wafer manufacturing, two major production processes can be distinguished: monocrystalline silicon manufacturing process and polycrystalline manufacturing process. In the first process, the single crystal silicon ingot is produced using the →Czochralski crystal growth process, whereas in the second one, the polycrystalline bricks are produced by direct casting of silicon into polycrystalline ingots. The cooled single crystal ingot is trimmed into a quadratic shape and the large polycrystalline brick is cut up into wafer-size bricks. In the next step, the wafer-size bricks are sliced with a diamond saw into →wafers that are then made into solar cells.

silicon wafer solar cell

Conventional silicon photovoltaic cell. See →crystalline silicon solar cell.

silicon/silicon dioxide substrate

A type of substrate commonly used as a base for multijunction solar cells.

silicon-based photovoltaic shingle

→Building-integrated photovoltaics. Silicon-based photovoltaic shingles have higher power output than →thin-film photovoltaic shingles. Although they are more energy efficient

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than thin-film photovoltaic shingles, silicon-based photovoltaic shingles cost more and are associated with certain design constraints. As the name suggests, they are made of thin silicon strips that are implanted into glass or other materials and work like conventional →silicon solar modules. In comparison with heavy solar panels, notably lighter silicon-based photovoltaic shingles can easier be incorporated into a roof than balky, more complex →roof mounting systems. silicon-based PV shingle See →silicon-based photovoltaic shingle. silicon-based solar shingle

→Building-integrated photovoltaics. Silicon-based solar shingles have higher power output than →thin-film solar shingles. Although they are more energy efficient than thin-film solar shingles, silicon-based solar shingles cost more and are associated with certain design constraints. As the name suggests, they are made of thin silicon strips that are implanted into glass or other materials and work like conventional →silicon solar modules. In comparison with heavy solar panels, notably lighter silicon-based solar shingles can easier be incorporated into a roof than balky, more complex →roof mounting systems.

silicone

See →polysiloxane.

silicone polymer

See →polysiloxane.

silicosis

Lung disease caused by exposure to tiny particles of silica. In semiconductor manufacturing facilities, employers must ensure that workers are protected from the inhalation of crystalline silicon dust particles.

siloxane

A compound whose molecules consist of chains of alternate silicon and oxygen atoms in either a linear or cyclic configuration.

silver contact

See →silver electrode.

silver electrode

Also known as silver contact. A transparent, semitransparent, or nontransparent electrode often made of nanoporous silver thin film that is in contact with semiconductor layer in a solar cell. Depending on the solar cell model, →organic photovoltaic cell, →inverted solar cell, or →crystalline silicon solar cell, the silver electrode can act as a top electrode (front contact) or bottom electrode

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(rear contact). In some fabrication methods, the top silver film can be spray-coated or screen-printed on the organic semiconductor layer. The silver electrodes formed on the PV cell are resistant to the effects of water, moisture, and other harsh weather conditions. Silver is also used as a low-cost electrode material for →perovskite photovoltaic cells. silver iodide

(AgI) A yellow, insoluble powdery material that darkens on exposure to light. AgI has a potential to be used as a material in quantum dots sensitized solar cells.

silver nanoparticle

Nanoparticles of silver, between 1 and 100  nm in size, which are often employed in photovoltaic materials, such as →solar ink, due to its favorable optical, electrical, and thermal properties.

silver/glass mirror

A solar thermal reflector consisting of a silver reflecting surface and the glass superstrate. The major function of the silvered mirror surface is to concentrate the incoming solar flux onto a receiver in order to multiply solar energy and attain high temperatures in absorber tubes. The glass superstrate acts as a protective barrier, light transmitter, and a structural support. The silver/glass mirrors are mostly used in large-scale solar thermal systems, such as →concentrating parabolic troughs, →linear Fresnel reflectors, →parabolic dishes, and →heliostats.

silvering

The technology of coating a surface with a thin film of silver to create a mirror capable of reflecting and focusing solar radiation onto a receiver.

silvering of glass

A process used in the manufacture of solar thermal reflectors in which a thin layer of silver is bonded to glass.

simulation program

See →solar simulation software.

sine wave

A sine wave or sinusoidal wave is a graphical representation of alternating current/voltage. The curve illustrates the repetitive oscillations of voltage from a positive peak to a negative over and over again, 60 times per second (60 Hz) in the USA, and 50 times (50 Hz) in Europe.

sine wave inverter

Sine wave inverter is a power inverter that produces a sine wave curve. The conversion of direct current from solar panels to alternating current (AC) that is needed for most household appliances can be graphically illustrated

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in the following manner: a straight line, steady stream of electrons flowing in one direction only, representing the direct current (DC), is converted into a sinusoidal AC waveform that goes from 0 V to a positive peak of around 120 V, and then, when the direction of electron flow is switched, it plunges to a negative peak of around 120 V. The cycle is repeated 50 (in Europe) or 60 (in the USA) times per second. Although pure sine wave inverters are a bit more expensive than modified sine wave inverters, they are more efficient, reliable, universal, and overall of better quality than modified sine wave power inverters. As they do not struggle with rough waveforms, interference, and increased heating, sine wave inverters use 20%–30% less power than modified sine wave inverters. They produce high-quality AC power that closely matches utility supplied electricity and in some brands even surpassing it. Sine wave inverters are universal nowadays, as all household appliances run on them without any problems. In particular sensitive electronical devices that have a hard time with square and modified sine wave inverters (digital clocks, LED TVs, audio equipment, and laser printers) run better on sine wave inverters. Sine wave inverters will not cause overheating of electric motors and overall will not reduce electric noise. Fans do not produce a humming sound, and LED lights, microwave ovens, and audio amplifiers do not pick up a buzzing sound. Due to smoother running on sine wave inverters, the lifespan of equipment will be extended. Taking into consideration all of the aforementioned advantages and as the price of sine wave inverters keeps falling, they have become the first choice for an average household today. single cell battery

A battery with one cell in which the stored chemical energy is converted into electrical energy, providing power for various devices.

single crystal

A semiconductor material structure that is created from a single continuous crystal structure.

single-crystal X-ray diffraction

A method that utilizes high-resolution microscopy and X-rays to analyze the internal lattice of crystalline substances, including structure of molecules, bonds in molecules, and similar. The use of X-ray diffraction allows

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a solar scientist to conduct a detailed study of the single-crystal material orientation, which is of crucial importance for the improvement of solar cell performance. single pitch roof

A roof having only a single slope on one side. If the slope side faces south, it is suitable for a →roof-mounted solar array. If it faces in a different direction, for instance, north, a position adjustment of the tilt angle with a →roof-mounting structure toward south might be necessary to improve →solar output.

single-axis tracker

See →single-axis tracking system.

single-axis tracking

See →single-axis tracking system.

single-axis tracking collector

A collector that uses a solar tracker with one rotational axis, allowing the reflector surfaces to have the optimal tilt angle and point toward the solar disk at all times.

single-axis tracking system

A tracking system that rotates the frame with solar panels on a single axis. The frame with PV panels is moved via an electronically controlled motor. It follows the movement of the sun across the sky from east to west. While the single-axis rotation mechanism tracks the azimuth angle of the sun from sunrise to sunset, the altitude (tilt) angle is either fixed in an optimal year-round position or limited to four seasonal angle settings that are manually adjusted. Compared to a fixed solar array, a PV array with a single-axis tracking system can increase the energy output by 15%–25%.

Single-axis Tracking System

single crystal

Referring to the material consisting of a single crystal.

single-crystal Czochralski silicon

See →monocrystalline Czochralski silicon.

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single-crystal silicon

See →monocrystalline silicon.

single-crystal silicon ingot

See →monocrystalline silicon ingot.

single-crystal silicon material

Semiconductor material consisting of pure single-crystal silicon.

single-crystal silicon solar module

See →monocrystalline silicon solar module.

single-crystal silicon solar panel

See →monocrystalline silicon solar module.

single-crystal solar cell

See →monocrystalline solar cell.

single-crystal solar wafer

See →monocrystalline solar wafer.

single-junction cell

See →single-junction solar cell.

single-junction photovoltaic cell

See →single-junction solar cell.

single-junction PV cell

See →single-junction solar cell.

single-junction solar cell

Also known as a single-junction photovoltaic cell. A simple, traditional solar cell with only one →p–n junction as opposed to a →multijunction solar cell that has more than one p–n junction.

single-layer antireflection coating

A single thin-film antireflection coating that can decrease the light loss by eliminating reflection at one wavelength, typically at the middle of the visible spectrum.

single-phase inverter

See →single-phase solar inverter.

single-phase solar inverter

A solar inverter for converting direct current (DC) from photovoltaic modules into alternating current (AC). Designed for use in →grid-tie solar systems, the inverter feeds the converted AC power into the public utility grid. The inverter is equipped with an automatic monitoring system that conducts a continuous performance analysis, fault detection, and troubleshooting. A single-phase solar inverter should be used for a single-phase connection. It might also work with a threephase connection, if the solar array is not too large. When a large amount of energy is pushed through a single phase

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with the single-phase solar inverter, the increased pressure might result in too much voltage and an abrupt shutdown by the monitoring system. Directing 5  kW of power into one phase is not an issue and can usually be handled by the single-phase inverter. However, for systems that are 6  kW or larger or if a lot of electricity needs to be transported through a small cable over long distances, it is recommended to employ a three-phase solar inverter, which will better distribute power over all three phases. single-pitched roof

See →single pitch roof.

single-stage controller

A →charge controller with a voltage regulation algorithm that limits the peak primary current as the battery nears full state-of-charge.

single-string inverter

Also known as a single-string photovoltaic inverter or a single-string PV inverter. An inverter that converts DC solar power generated by a single sting of PV panels into grid-compatible alternating current. A number of solar panels, usually facing the same direction, are connected to a single string inverter at one central point. This centralized method works fine as long as none of the panels in the string are shaded and all PV modules face the same direction. However, even if only one PV module is shaded for a portion of the day, the power output of all modules on the same string is reduced to the level of the shaded panel. If PV modules are oriented in different directions, for instance, one roof area covered with panels facing north and another facing south, it is advisable to connect each roof area’s modules in a separate string. Each string is wired into its own →Maximum Power Point Tracker (MPPT), which are connected into one multistring inverter. Multistring inverters have two or more string inputs, each with its own MPPT.

single-string photovoltaic inverter

See →single-string inverter.

single-string PV inverter See →single-string inverter. single-walled carbon nanotube

(SWCNT) A single graphene sheet that is rolled into a tube. In contrast to multiwalled carbon nanotubes, the cylindrical structure of the SWCNT has a single wall, as the name suggests. The crystalline hexagonal structure

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of the graphene sheet consists of a network of hexagonal rings with double and single carbon–carbon bonding. A single-walled carbon nanotube typically has a diameter in the order of a nanometer, while they can be up to several micrometers long. The major building block of this honeycomb crystal lattice architecture is the electric wire. The cylindrical carbon molecules exhibit excellent electrical properties. SiNW

Abbreviation for →silicon nanowire.

site assessment

See →site check for solar systems.

site check

See →site check for solar systems.

site check for photovoltaic systems

See →site check for solar systems.

site check for PV systems

See →site check for solar systems.

site check for solar systems

Also known as site survey, site evaluation, or site assessment. An evaluation of the site prior to the start of the solar project to check if a proposed location is a good fit for a solar installation. A careful assessment conducted by a trained solar site survey technician helps prevent unpleasant surprises during and after project implementation. A solar site evaluation typically includes a sun path analysis, shading analysis, orientation and tilt, and other site-specific considerations. The sun path or the path along which the sun moves across the sky in a specific location can be read from a →sun path diagram for any date of the year. The evaluator can use various professional devices to determine the average amount of sun that falls on a particular site over the course of a year. In order to avoid output losses due to permanent shading, the solar surveyor needs to make sure that the future solar energy site is free of tree and building shade. She or he uses cameras and other devices for obstacle analysis, taking multiple photographs from various positions. If a partial shading is unavoidable, the assessor should be able to evaluate the impact of shading on the power output by using →solar calculator. For ideal solar gain, the new photovoltaic array should be oriented toward true south and not magnetic

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 site evaluation

south in the Northern Hemisphere. The local surveyor usually consults the corresponding magnetic declination map or chart, which shows whether and how much magnetic south deviates from the true south on a given site. The tilt of solar panels is another parameter that should be carefully analyzed during the site survey. The solar technician needs to evaluate if optimal angles in the range between 25° and 35° are possible on a given roof. Other site-specific considerations include location-specific weather pattern quantification, roof condition, structural fitness of a building, or historic building issues. site evaluation

See →site check for solar systems.

site survey

See →site check for solar systems.

sizing

The process of estimating the size and capacity of a future solar system based on various calculations.

sky dome

The visible hemisphere of sky, from horizon to zenith in all directions.

sky radiation

Diffuse sky radiation. See →diffuse horizontal irradiance and →diffuse solar radiation.

skylight

A glazed opening in a roof to allow light in. See also →solar skylight.

skylight dome

A skylight in the shape of a dome. It is glazed with a transparent or translucent material to provide additional natural light to the space below. See also →solar skylight.

sliding frame

An adjustable component of a →wafer dicing machine for optimal control of the dicing process.

sloping roof

A roof with one, two, or four sloping sides.

slot nozzle

Also known as slotted nozzle. A narrow end fitted to a pipe to control the flow of solar ink in a coating process. Spray nozzles can usually be easily replaced to change deposition pattern, providing desired flexibility in the manufacturing process.

slot-die coating

A noncontact, large-area coating method that can deploy inks with a wide variety of viscosities. Slot-die coating is able to hold a fluid’s temperature and to deposit a homogeneous wet film with high cross-directional uniformity.

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The thickness of wet films is regulated by the flow rate of the ink, the coating width, and the speed, allowing a wide range of thicknesses from 20 nm to >150 μm to be deposited on flexible or rigid substrates. The main advantages of the slot-die coating process include high manufacturing speeds, high material utilization, and a good control of coating fluid supply. slotted nozzle

See →slot nozzle.

slurry

A semiliquid mixture of an insoluble substance suspended in water.

small-scale solar thermal system

The small-scale solar thermal systems use low- and medium-temperature collectors (