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Physics of Energy Sources
 1773614215, 9781773614212

Table of contents :
Cover
Half Title Page
Title Page
Copyright Page
About the Editor
How to Use the Book
Table of Contents
List of Figures
List of Tables
Acronyms
Preface
Synopsis
Introduction
Chapter 1 Introduction: Physics and Energy
1.1 Energy in Science and Physics
1.2 Physics
1.3 Definition of Energy and its Place in the Knowledge of Physics
Chapter 2 Energy Sources: Definition and Types
2.1 Nonrenewable Energy Sources and Advantages and
Disadvantages of Them
2.2 Renewable Energy Sources and Advantages and
Disadvantages of Them
Chapter 3 Fossil Fuels
3.1 The Carbon Cycle
3.2 Natural Gasses
3.3 Coal
3.4 Utilization of the Fossil Fuels
3.5 Internal Combustion Engine
Chapter 4 Solar Energy
4.1 The Source of the Solar Energy
4.2 Energy Source of the Sun
4.3 The Ways Solar Energy is Sustained
4.4 Alternative Technologies of the Conversion of Solar Energy
Chapter 5 Wind Energy
5.1 The Source of the Energy
Chapter 6 Hydropower
6.1 Water Cycle
6.2 History of The Use of Hydropower
6.3 Hydropower Potential
Chapter 7 Biomass
7.1 Source of The Energy of Biomass
7.2 Slagging and Fouling
Chapter 8 Geothermal Energy
8.1 The Concept of Geothermal Energy
8.2 Resources
8.3 Use of Geothermal Energy
8.4 Power Plant Components
Chapter 9 Nuclear Power
9.1 History of Nuclear Power
9.2 Atomic Structure
9.3 Radioactivity
Chapter 10 Energy Storage
10.1 Different Ways of Storing Energy
10.2 Classification Depending on Application
References
Index

Citation preview

PHYSICS OF ENERGY SOURCES

PHYSICS OF ENERGY SOURCES

Edited by:

Nelson Bolívar

ARCLER

P

r

e

s

s

www.arclerpress.com

Physics of Energy Sources Nelson Bolívar

Arcler Press 2010 Winston Park Drive, 2nd Floor Oakville, ON L6H 5R7 Canada www.arclerpress.com Tel: 001-289-291-7705         001-905-616-2116 Fax: 001-289-291-7601 Email: [email protected] e-book Edition 2019 ISBN: 978-1-77361-599-8 (e-book) This book contains information obtained from highly regarded resources. Reprinted material sources are indicated and copyright remains with the original owners. Copyright for images and other graphics remains with the original owners as indicated. A Wide variety of references are listed. Reasonable efforts have been made to publish reliable data. Authors or Editors or Publishers are not responsible for the accuracy of the information in the published chapters or consequences of their use. The publisher assumes no responsibility for any damage or grievance to the persons or property arising out of the use of any materials, instructions, methods or thoughts in the book. The authors or editors and the publisher have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission has not been obtained. If any copyright holder has not been acknowledged, please write to us so we may rectify.

Notice: Registered trademark of products or corporate names are used only for explanation and identification without intent of infringement. © 2019 Arcler Press ISBN: 978-1-77361-421-2 (Hardcover) Arcler Press publishes wide variety of books and eBooks. For more information about Arcler Press and its products, visit our website at www.arclerpress.com

ABOUT THE EDITOR

Nelson Bolivar has a PhD. in physics from the University of Lorraine in France finished in 2014. His expertise is in quantum systems and condensed matter. His interest includes spintronic devices and correspondences between general relativity and condensed matter. He is currently an associate professor at the Central University of Venezuela.

HOW TO USE THE BOOK

The readers will have the necessary idea about energy and its different forms by reading this book. They will also be able to learn about the energy sources that are being used. The readers will also be able to understand the techniques of the synthesization of the energy sources. Knowledge about the natural and economic effects of using different energy sources will also be available for the students through this book.

TABLE OF CONTENTS



List of Figures.................................................................................................xi



List of Tables................................................................................................ xvii

Acronyms..................................................................................................... xix Preface..................................................................................................... ....xxi Synopsis..................................................................................................... xxiii Introduction................................................................................................ xxv Chapter 1

Introduction: Physics and Energy............................................................... 1 1.1 Energy in Science and Physics.............................................................. 2 1.2 Physics................................................................................................. 4 1.3 Definition of Energy and its Place in the Knowledge of Physics............. 7

Chapter 2

Energy Sources: Definition and Types...................................................... 21 2.1 Nonrenewable Energy Sources and Advantages and Disadvantages of Them.................................................................... 26 2.2 Renewable Energy Sources and Advantages and Disadvantages of Them.................................................................... 28

Chapter 3

Fossil Fuels............................................................................................... 33 3.1 The Carbon Cycle............................................................................... 35 3.2 Natural Gasses.................................................................................... 45 3.3 Coal.................................................................................................... 47 3.4 Utilization of the Fossil Fuels.............................................................. 59 3.5 Internal Combustion Engine................................................................ 61

Chapter 4

Solar Energy............................................................................................. 67 4.1 The Source of the Solar Energy............................................................ 69 4.2 Energy Source of the Sun.................................................................... 73 4.3 The Ways Solar Energy is Sustained..................................................... 75 4.4 Alternative Technologies of the Conversion of Solar Energy................. 99

Chapter 5

Wind Energy........................................................................................... 105 5.1 The Source of the Energy................................................................... 106

Chapter 6

Hydropower........................................................................................... 129 6.1 Water Cycle...................................................................................... 130 6.2 History of The Use of Hydropower.................................................... 131 6.3 Hydropower Potential....................................................................... 134

Chapter 7

Biomass.................................................................................................. 155 7.1 Source of The Energy of Biomass....................................................... 156 7.2 Slagging and Fouling........................................................................ 190

Chapter 8

Geothermal Energy................................................................................ 193 8.1 The Concept of Geothermal Energy................................................... 195 8.2 Resources......................................................................................... 196 8.3 Use of Geothermal Energy................................................................ 198 8.4 Power Plant Components.................................................................. 203

Chapter 9

Nuclear Power....................................................................................... 205 9.1 History of Nuclear Power.................................................................. 207 9.2 Atomic Structure............................................................................... 211 9.3 Radioactivity..................................................................................... 212

Chapter 10 Energy Storage....................................................................................... 235 10.1 Different Ways of Storing Energy..................................................... 237 10.2 Classification Depending on Application........................................ 251 References.............................................................................................. 257 Index...................................................................................................... 261

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LIST OF FIGURES Figure 1.1: The branches and subbranches of science Figure 1.2: Branches of natural science Figure 1.3: Physical science and its subtopics Figure 1.4: Classification of physics depending on time period Figure 1.5: Classification of classical physics Figure 1.6: Classification of modern physics Figure 1.7: The study of thermodynamics Figure 1.8: Layout of a simplified open system Figure 1.9: An example of a closed system, a working internal combustion engine Figure 1.10: Basic forms of energy Figure 1.11: Energy and different forms of energy Figure 1.12: Earth’s gravitational field Figure 2.1: Different ways of classification of energy sources Figure 2.2: Classification of energy sources Figure 2.3: The structure of global energy absorption from primary sources Figure 2.4: Classification of energy sources depending on financial aspects Figure 2.5: Classification of energy sources depending on availability and financial aspects. Figure 2.6: Classification of energy sources depending on reusability Figure 2.7: Use of renewable energy source compared to total energy use Figure 2.8: Percentage of electricity generation from renewable sources Figure 2.9: Change in the geographic character of surrounding areas of the Three Gorges Reservoir of China Figure 3.1: Classification of hydrocarbon Figure 3.2: A basic carbon cycle

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Figure 3.3: A fractional distillation plant for separating different types of oils from crude oil Figure 3.4: Chemical structure of coal Figure 3.5: Peat Figure 3.6: Lignite Figure 3.7: Subbituminous coal Figure 3.8: Bituminous coal Figure 3.9: Anthracite Figure 3.10: Raw Graphite and its most refined form, pencil Figure 3.11: Molecular structure of graphite Figure 3.12: Different techniques of coal mining Figure 3.13: Different types of open surface mining Figure 3.14: An open-pit mining site Figure 3.15: A three-dimensional model of an underground mine. Figure 3.16: Room and pillar mining process Figure 3.17: World energy consumption by source Figure 3.18: A standard structure of an internal combustion engine Figure 3.19: Combustion cycle of a four-stroke engine (spark ignition engine) Figure 3.20: Combustion cycle of a four-stroke engine (Diesel engine) Figure 3.21: A two-stroke engine structure Figure 3.22: Brayton cycle Figure 3.23: Human sources of carbon dioxide Figure 4.1: The source of solar energy, The Sun Figure 4.2: The layers of the Sun Figure 4.3: A cutout of the sun showing the inner and outer layers. Figure 4.4: A natural way of sustaining solar energy, photosynthesis Figure 4.5: A satellite powered by solar power Figure 4.6: Multi-Si (left) and mono-Si (right) Figure 4.7: Atomic structure of a crystalline silicon Figure 4.8: A standalone PV system Figure 4.9: Grid PV system without any battery backup Figure 4.10: A Grid PV system xii

Figure 4.11: A standard layout of a hybrid power system Figure 4.12: A horizontal coordination system showing the measuring technique of the celestial sphere Figure 4.13: The Sun path on 0° latitude and 0° longitude Figure 4.14: The Sun path on 23.40° latitude and 84.80° longitude Figure 4.15: Different forms of system architectures used in different PV systems Figure 4.16: Different types of load profile Figure 4.17: A solar water heating system Figure 4.18: Classification of solar water heating system Figure 5.1: Windmill Figure 5.2: Modern wind turbine Figure 5.3: Global production of energy using wind power. Figure 5.4: Gansu wind farm, China Figure 5.5: An offshore wind farm Figure 5.6: Global wind flow pattern Figure 5.7: Classification of wind turbines Figure 5.8: Horizontal and vertical axes wind turbine Figure 5.9: Basic structural diagram of a wind turbine Figure 5.10: Detailed structure and mechanisms of a wind turbine Figure 5.11: A standard wind turbine blade. Figure 5.12: Diagram showing the aerodynamic effects on an airfoil-shaped blade Figure 5.13: Basic structure of a rotating or synchronous generator Figure 5.14: Different regions requiring speed controls Figure 5.15: Radial layout of wind farm turbines Figure 6.1: The water cycle Figure 6.2: The Hoover Dam Figure 6.3: A runoff river power plant; Chief Joseph Dam, USA Figure 6.4: A simplified diagram of a runoff river hydroelectric power station Figure 6.5: A hydroelectric power station with storage reservoir; Água Vermelha Dam of Brazil. xiii

Figure 6.6: A simplified diagram of a hydroelectric power station with storage reservoir Figure 6.7: A diagram of pumped-up storage hydroelectric power plant Figure 6.8: A pumped-up storage hydroelectric power plant; Bath County Pumped Storage Station, USA. Figure 6.9: A simplified diagram of a tidal power hydroelectric power plant. Figure 6.10: A tidal power hydroelectric power plant; Rance tidal power station, France. Figure 6.11: Classification of hydroelectric power generator depending on production capacity Figure 6.12: Diagram of a low-head hydroelectric power station Figure 6.13: A diagram of a medium-head power unit Figure 6.14: Mandatory components of a hydroelectric power station Figure 6.15: A diagram of a hydroelectric turbine Figure 6.16: Different types of blades used in hydroelectric turbines Figure 6.17: Classification of hydroelectric turbines Figure 6.18: A cutout of a generator used in a hydroelectric power plant Figure 6.19: A diagram of a standard hydroelectric power station showing most important components Figure 7.1: Different sources of biomass energy Figure 7.2: Sources and types of biomass materials for conversion into bioenergy Figure 7.3: Biomass waste-derived fuels Figure 7.4: Properties of gasoline, methanol separately and as mixed compound Figure 7.5: Flowchart of ethanol production process Figure 7.6: A continuous distillation setup Figure 7.7: Classification of synthetic ethanol production methods Figure 7.8: Production process of synthetic ethanol Figure 7.9: Chemical reaction of the production process of MTBE Figure 7.10: Chemical structure of fatty acid (propanoic acid) Figure 7.11: Chemical structure of glycerol Figure 7.12: Refining process of raw oil Figure 7.13: A basic and simplified diagram of methane production plant xiv

Figure 7.14: Principles of methane fermentation Figure 8.1: Temperature at different layers of the Earth Figure 8.2: Layers of the Earth Figure 8.3: Diagram of EGS technique Figure 8.4: Diagram of a dry stream power plant Figure 8.5: A dry stream power plant situated in California, USA Figure 8.6: Diagram of a flash stream power plant Figure 8.7: Diagram of a binary cycle power plant Figure 9.1: Global primary energy consumption by source Figure 9.2: Global electricity production of 2014 from all energy sources Figure 9.3: A cathode ray tube Figure 9.4: Model of an atom showing the structure of the nucleus and the circular pathway of the electrons Figure 9.5: Position of the radioactive elements in the periodic table Figure 9.6: Example of an alpha decay Figure 9.7: A standard nuclear fission reaction layout Figure 9.8: A chain fission reaction Figure 9.9: A nuclear reactor Figure 9.10: Classification of nuclear reactors depending on the type of reaction Figure 9.11: A standard light water reactor Figure 9.12: A reactor with pressurized water cooling system Figure 9.13: The pressure vessel of PWR reactor Figure 9.14: A diagram showing complete layout of pressurized water reactor Figure 9.15: A diagram of a boiling water reactor Figure 9.16: Supercritical water reactor scheme Figure 10.1: Two major classifications of energy storage Figure 10.2: Different types of natural storage of energy Figure 10.3: Chemical bonds in a glucose molecule Figure 10.4: Most frequent forms of energy used in energy storage Figure 10.5: Diagram of a standard primary battery Figure 10.6: A Pb acid cell Figure 10.7: A diagram of a Pb acid cell xv

Figure 10.8: A cutout diagram of a standard NiCd cell Figure 10.9: A standard Li-ion battery Figure 10.10: Diagram of a Li-ion battery Figure 10.11: Cutout of a zinc air battery Figure 10.12: An electrolytic cell Figure 10.13: Classification and types of supercapacitors

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LIST OF TABLES Table 3.1: Boiling point of different types of fuels Table 4.1: The elements present in the Sun Table 4.2: Perturbation of the voltage of a PV system to attain the MPP using P & O algorithm Table 5.1: The largest wind farms of the world Table 6.1: The largest hydroelectric power plants of the world Table: 9.1: Properties of the subatomic particles

ACRONYMS Ah Ampere-hour of the battery capacity BIPV Building-integrated photovoltaic BWEA British Wind Energy Association Cp Rotor energy conversion efficiency C/D Charge/discharge of the battery DC Direct current DOD Depth of discharge of the battery DOE Department of Energy DWIA Danish Wind Industry Association ECU European currency unit EDF Energy delivery factor EPRI Electric Power Research Institute EWEA European Wind Energy Association GW Gigawatts (109 watts) GWh Gigawatt hours HV High voltage HVDC High-voltage direct current (transmission) IEA International Energy Agency IEC International Electrotechnical Commission ISES International Solar Energy Society kW Kilowatts kWh Kilowatt hours LV Low voltage LVRT Low-voltage ride-through MW Megawatts MWa Megawatts accumulated MWe Megawatts electric

MWh Megawatt hours PV Photovoltaic QF Qualifying facility SOC State of charge of the battery SRC Specific rated capacity (kW/m2) THD Total harmonic distortion in quality of power THM Top head mass (nacelle + rotor) TPV Thermophotovoltaic TSR Tip speed ratio (of the rotor) TWh Trillion (1012) watt hours UCE Unit cost of energy Wp Watt peak

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PREFACE

Energy is the most critical property of matter. Energy is an essential property for the existence of every single molecule. The whole existence is functioning depending on energy. Without energy, life is entirely impossible. It is equally vital regardless the subject is a living entity or an object. The smallest particles known to humans are quark and leptons. Moreover, these particles exist due to the presence of energy. It is energy processes that combine these smallest particles and gradually build bigger particles such as electrons, neutrons, protons, atoms; so, it is the energy that is holding everything together. As energy is mandatory for the existence of every single cell and atom; every element requires energy to sustain. Moreover, the energy available comes from a variety of sources. If we consider the necessity of energy at a larger scale rather than subatomic level, we will find that the importance of energy is present in an equal manner. For every single action, any living or non-living entity take requires energy. Energy is available through different sources, and we are using a lot of these sources. However, using the energy available without accounting the probable effect on the whole system we exist in can cause huge problems. We are already suffering from several of those adverse impacts of unaccounted usage of energy available. So, it is critical to understand the impact of using a specific energy source before using it. Moreover, while developing the knowledge and technologies for using any source, it is also important to find the most appropriate and efficient technique of utilizing that source of energy for environmental and economic concerns. This book was written to help readers understand the basic concepts and knowledge related to the energy sources available and help them to understand the effects, advantages and disadvantages, potential outcomes in the future of using different sources of energy. Providing basic knowledge about the energy sources we use and how the energy is harnessed and prepared for use was another influence behind this book. If the readers can achieve the minimum knowledge about the available energy sources and the energy synthesizing and storing techniques by reading this book, then the purpose of this book will be fulfilled.

SYNOPSIS Physics and energy Science and physics, physics, energy, thermodynamics and thermodynamics systems, forms of energy, potential, and kinetic energy Energy sources Nonrenewable energy sources, renewable energy sources Fossil fuels Petroleum, natural gas, coal Solar energy Radioactive properties, blackbody radiation, PV effect, PV systems

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INTRODUCTION

Any organism needs energy to live. Energy is linked to all human activities: When we think or move, we use energy stored in our bodies and all the objects that surround us or we use need energy to function or have needed it to be built; energy illuminates and heats our homes, allows us to move around, feeds the tools with which we produce food and so on. All that produces energy is an “energy source.” The Sun is the Earth’s main source of energy. The Earth receives from the Sun an uninterrupted flow of energy that, in addition to feeding all vital processes, plants and animals it melts the ice and feeds the cycle of water between sea and atmosphere, produces the winds, growing plants that over millions of years have been transformed, along with the remains of animal organisms, into fossil fuels, oil, coal and natural gas. In general, all the energy available on our planet comes directly or indirectly from the Sun: hydroelectricity, wind power, the chemical energy of fossil fuels such as coal, oil and natural gas and biomasses. The energy of the tides comes from the gravitational fields of the Sun, Moon, and Earth. Geothermal energy and nuclear energy date back to the formation of the Earth. The many existing energy sources can be classified into different ways. They are said to be primary if they can be used directly, just as they are found in nature. Primary sources are coal, oil, natural gas, wood, nuclear fuels, like uranium, the Sun, wind, wind, tides, mountain lakes and rivers and the heat of the Earth that provides geothermal energy. Secondary sources of energy are derived from the transformation of primary energy sources: for example, petrol, which is derived from the processing of crude oil, and electricity obtained from the conversion of mechanical energy, chemical energy, or nuclear energy—renewable and nonrenewable sources Some sources are renewable, a type of energy that is provided continuously, being regenerated through chemical transformations or physical processes. In particular, the sun, wind, water, tides and earth’s heat are inexhaustible sources, always available. Biomasses, on the other hand, are able to regenerate in times

comparable with those of human life. In the case of wood, for example, it is possible to have fuel available at all times, in order to consume only a limited amount of fuel and take care to reforest. The so-called nonrenewable sources, on the other hand, have long regeneration times, meaning that once used up they are considered exhausted. These are those that have been formed over millions of years, such as fossil fuels or even at the time of the formation of the planet, such as uranium. The availability of these sources, however large, is limited and they constitute a sort of energy warehouse on Earth. Only around 13% of the world’s energy consumed is produced from renewable sources. All the rest comes from nonrenewable sources, mostly fossil fuels and from nuclear sources. The energy sources are measured mostly for their physical quantities and or heat content. Among the most well-known measures for physical quantities, we can mention the ton, used for crude oil and coal; the barrel, used for crude oil; the cubic meter, used for gas; the liter, for petrol and diesel. Comparing energy sources to each other using the different units of measurement for physical quantities is extremely complex, since same quantities of material do not generate same quantity of energy: One kilogram of oil does not produce the same energy produced by one kilogram of coal or one cubic meter of gas. If we want to compare different energy sources, it is convenient to use a common unit of measurement, in other words to express them in terms of energy or heat content. The official unit of measurement of energy is the Joule (J). Among the most common units of measurement for energy, we can then remember the kilowatts per hour used mainly for electricity. To measure the production of large power plants, terawatt/hour (TWh) is used, which corresponds to one billion kilowatt/hour. Each type of energy presents its advantages and disadvantages, so that there is no source that is present as convenient over the others in terms of viability. Some are cheap and plentiful but generate serious environmental impacts; others are clean and sustainable but not financially viable.

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CHAPTER 1

INTRODUCTION: PHYSICS AND ENERGY

CONTENTS 1.1 Energy in Science and Physics................................................................................... 2 1.2 Physics...................................................................................................................... 4 1.3 Definition of Energy and its Place in the Knowledge of Physics.................................. 7

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(The concept of energy and precisely which parts of physics discuss energy will be debated in this chapter. Several important concepts that are important for the understanding of energy and the classification of energy will also be discussed in this chapter)

1.1 ENERGY IN SCIENCE AND PHYSICS Energy is the factor that determines the ability of any living or non-living material to conduct any activity. To understand energy and its properties, comprehending several preliminary and basic concepts of science and physics is essential. Science is the most significant fuel of the initiation and development of human civilization. Science and the technologies are derived from the knowledge attained by scientific analysis of every single natural and environmental phenomenon. This knowledge has provided the structure of the present state of humanity. The word “Science” is originated from the Latin word “Scientia,” which is synonymous with “Knowledge” if translated back to English. According to one of the oldest and most popular dictionary, the Meristem Webster, the word science can be defined as below: “A department of systematized knowledge as an object of study” and “something (such as a sport or technique) that may be studied or learned like systematized knowledge”(Meristem-Webster,1928, https://www.merriamwebster.com/). The practice of science started from the first step of the human civilization, the invention of fire. Since then the knowledge acquired by the practice of science has increased immeasurably. So, to keep the education of science easily accessible, they have been divided and arranged into three major categories. They are as follows: •

• •

Formal science: This part of scientific discussion provides with statistical, mathematical, and logical explanations of all types of every single manifestation. Natural science: This branch of science holds the physical and chemical explanation and knowledge of the phenomena. Humanistic science: This sector of science discusses, justify, and evaluate human behavior and discuss the changes in it in altered conditions. The structure of the social build-up of human civilization is also discussed in this part of science.

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Figure 1.1: The branches and subbranches of science http://tx.english-ch.com/teacher/jacob/branchsciences3.jpg

Among these three branches, natural science can be further divided into two branches: • •

Physical science, and Biological science.

Figure 1.2: Branches of natural science

This classification is the result of the existence of life on the planet earth. There are living elements alongside the nonliving elements among all the materials included in the discussion area of natural science, and these elements behave in entirely different manners. And so, this classification is created by the physists for more comfortable and better understanding of the behavior of these different types of elements. Physical science is the discussion and knowledge of the elements of the universe which are of the nonliving type while biological science discusses and stores the knowledge of the living entities. The differentiation between the living and nonliving components has been conducted by determining the presence of nucleus in the cells containing DNA and RNA.

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Physical science can be further divided into three major subtopics. These subtopics are stated below: • • •

Physics, Chemistry, and Earth science.

Figure 1.3: Physical Science and its subtopics https://qph.ec.quoracdn.net/main-qimg-86cffb031b4e36841e024c9665787bcac

1.2 PHYSICS Physics is one of the oldest topics of academic knowledge. Several scientists and historians consider it to be the oldest of all academic disciplines. The word “Physics” is originated from ancient Greek word φυσική (phusis) which means “nature.” According to Meristem Webster, physics is “a science that deals with matter and energy and their interactions.” During the initial stage of the development of scientific knowledge, physics was considered to be a part of natural philosophy. Chemistry, biology, and several portions of mathematics were included in the practice of natural philosophy along with the discussion of physics. The oldest proof of the existence of the study of physics dates back to the earliest stage of human civilization. It has been found that the Sumerians and ancient Egyptian civilization existing before 3000 BC contained basic understandings of the astronomical physics. During the period of 650–480 BC, natural philosophy was developed by several philosophers and later on, the Islamic scholars

Introduction: Physics and Energy

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improved, modified, and expanded the ideas and statements provided by the Greek philosophers as well as proving them through scientific observations. The knowledge of astronomy, optics, and vision was vastly developed during this time. The concept of classical physics was developed utilizing this primary knowledge. This knowledge influenced modern physics also. It was the scientific revolution of the 17th century when these different parts of natural science were recognized as separate unique parts of science, and the era of classical physics began. Modern physics was the result of Max Plank’s work on quantum theory and Albert Einstein’s theory of relativity during the early 20th century. Physics can be classified into many different branches depending on the variable considered for the classification. Depending on the period, physics can be divided into two major parts: • •

Classical physics and Modern physics

Figure 1.4: Classification of physics depending on period



• • •

Classical physics: Classical physics is the study of traditional forces and the studies that were developed before the 20th century. Classical physics can be further divided into several branches, such as: Mechanics: It is the study of the physical effects on the subject bodies created by the static or non-static condition of the body. Acoustics: This part of physics discusses and studies the generation, transformation, and movement of sound waves. Optics: Optics is the physics of light. The generating process of light, the nature of light, properties of light, the importance and mechanism of light making vision possible, the reflectionabsorption and the difference in the behavior of light on different surfaces are the primary concerns that are discussed in this part

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of classical physics. Thermodynamics: This section of physics examines the energy existing in the universe, the transformation process, and effects of the energy. Electromagnetism: This part of physics discusses electromagnets and their properties.

Figure 1.5: Classification of classical physics



• • • • • • •

Modern physics: This branch of physics contains the studies that have been conducted from the beginning of the 20th century. Unlike classical physics, this department of physics is more concerned about the effect of different stimulations at the molecular level rather than the effects on the whole subject matter. Modern physics can be divided into the following major sectors: Atomic and Nuclear physics Quantum physics Solid state of physics Relativistic physics Condensed matter physics Plasma physics Low-temperature physics

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Figure 1.6: Classification of modern physics

1.3 DEFINITION OF ENERGY AND ITS PLACE IN THE KNOWLEDGE OF PHYSICS In English, the term energy means the strength and vitality required to perform any physical or mental activity. However, the definition of energy is different from the perspective of physics. In physics, energy is the capacity of a physical system to perform any action. Energy is considered to be a property of matter. The SI unit of energy is Joule. The measuring unit and dimensions of energy are the same as they are for work. Energy is one of the most complex and vast concepts of physics. It contains so much diversity that energy cannot be classified into a single part of science. Discussion of energy includes thermodynamics, mechanics, electromagnetism, optics, and acoustics along with the topics of modern physics such as atomic and nuclear physics, quantum physics, relativistic physics.

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1.3.1 Thermodynamics and Thermodynamic Systems Thermodynamics is the part of the physics that concerns about the generation and transformation of energy. The discussion of thermodynamics can be classified as stated in the figure below:

Figure 1.7: The study of thermodynamics http://nptel.ac.in/courses/112103016/module1/images/1.png

The concept of the thermodynamic system is an essential concern in understanding the nature of energy. A thermodynamic system is the entire amount of mass and energy that has been considered for any specific study concerning the understanding of thermodynamic effects. For example, if an engine is considered to understand and measure the thermodynamic activities of that engine, then the engine is a thermodynamic system. There are three types of thermodynamic systems that can be used to understand the nature of energy. They are: • Open system, • Closed system, and • Isolated system. Open system: An open system is a system where energy can transfer into the system from outside the system or can flow out of system smoothly and without any constraints. The previous example of an engine can be used to make this easily understandable. When an engine works, it creates heat, and the engine transmits a portion of the heat into the outer surrounding environment. The ability of the heat to move out of the engine and the continuously changing

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mass due to the change in the amount of fuel makes it an open system.

Figure 1.8: Layout of a simplified open system

http://www.‫עדי‬.com/wp-content/uploads/2014/06/%D7%9E%D7%A2%D7% A8%D7%9B%D7%AA-%D7%A4%D7%AA%D7%95%D7%97%D7%94. jpg Figure 1.9: An example of an open system, a working internal combustion engine





Closed system: In this type of system, the energy transfer with the surrounding environment by the considered system can continue without any disturbance, but the transmission of mass is entirely restricted. Change in the heat of a fluid or gas in a closed container is a prime example where the energy is transferred outward or absorbed from the environment, but the mass is static. Isolated system: This system is wholly cut off from the

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Physics of Energy Sources

surrounding environment to ensure the complete consistency of energy and mass of the system. The earth is an open system. And it is possible to exploit the energy sources only because of this open nature of the earth. As a result, the study of open system holds an essential position in the study of the energy sources.

1.3.2 The Laws of Thermodynamics The Zenith law: “If two systems are in thermal equilibrium with a third system, they are in a thermal equilibrium with each other.” Thermal equilibrium is a steady condition where there are two or more interconnected subjects at the same thermal stage, and so there is no heat transfer between the two. • The First law of thermodynamics: “When energy is transferred, as work, heat, or with matter, in or out of a system, the system’s internal energy changes in accordingly with the law of conservation of energy. Equivalently, perpetual motion machines of the first kind (machines that produce work without the input of energy) are impossible.” So, for an ideal gas, dQ = dU + dW •

Here, dQ = the amount of energy that is provided into or taken away from a closed system. dU = change in the internal energy of a system dW = the amount of work conducted by the system Again, marking the heat content of a system as H, the relation of the heat with internal energy U, pressure p, and volume V can be formed from the equation below: H = U + pV •

The Second law of thermodynamics: This law has been stated in different ways by different physicists. As per the German scientist Rudlof Calcius, “Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time” (“Über eine veränderte Form des zweiten Hauptsatzes der mechanischen Wärmetheorie, 1854”). He is considered to be the developer of the second law of thermodynamics.

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Lord Kelvin stated, “It is impossible, by means of inanimate material activity, to derive mechanical effect from any portion of matter by cooling it below the temperature of the coldest of the surrounding objects.” (On the Dynamical Theory of Heat, with numerical results deduced from Mr. Joule’s equivalent of a Thermal Unit, and M. Regnault’s Observations on Steam, 1851). However, the original statement is made by the French physicist Carnot, “The efficiency of a quasi-static or reversible cycle depends only on the temperatures of the two heat reservoirs, and is the same, whatever the working substance. An engine operated in this way is the most efficient possible heat engine using those two temperatures.” It is often expressed by the terms of efficiency, e = (T1 − T2)/T1; Here, T1 = the higher temperature and T2 = the lower temperature.

This law means that heat cannot transfer from warmer temperatures to the subjects with lower temperature without causing any external effects. This law also determines the direction of the flow of heat. The Third law of thermodynamics: This law discusses the absolute zero temperature. This law states, “The entropy of a perfect crystal at absolute zero is exactly equal to zero.” Here, absolute zero temperature is “zero Kelvin” or −273°C which is considered as the lowest possible temperature theoretically. •

Another statement of this law was provided by Gilbert N. Lewis and Marle Randall. They stated, “If the entropy of each element in some (perfect) crystalline state be taken as zero at the absolute zero of temperature, every substance has finite positive entropy; but at the absolute zero of temperature the entropy may become zero, and does so become in the case of perfect crystalline substances.” Consequence and expansion of the third law provided by Nernst is, “It is impossible for any process, no matter how idealized, to reduce the entropy of a system to its absolute-zero value in a finite number of operations” (The Third Law of Thermodynamics, 1947) This expression was practically demonstrated and proved by Masanes and Oppenheim in 2017. As per this expression, if the entropy change in a system is dS, where the achievement of energy by the environment is dQ and temperature of environment is T,

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dS = dQ/T. As per Ludwig Boltzmann, entropy can be defined as below: S = k·lnW where W is the number of possible ways of the energy to be distributed in the environment, and k is Boltzmann’s constant, k = 1.38·10−23 J/K. This law defines the absolute Zero temperature and proves that it is impossible to reach absolute zero temperature practically. Absolute zero is 0 K or −273°C. As temperature and volume are proportionally related, if the temperature of the object falls, the volume of the material will reduce too. And theoretically, at the absolute zero temperature, the volume of the subject particle will also be 0 which is impossible. These four laws help to understand the change of energy within its different forms.

1.3.3 Different Forms of Energy The conservation theory of energy proves that the total amount of energy in the universe is constant, while it changes from one form to another. Albert Einstein described the conservation of energy as below: “Energy cannot be created or destroyed; it can only be changed from one form to another.” The change in energy that can be experienced is the change of its appearance or form. These forms can be divided into two primary types. They are: Potential energy and Kinetic energy. • Potential energy: Potential energy is the type of energy that an object or a particle achieves because of its relative position compared to other objects of the frame. It is the energy a particle achieves or loses as the result of the work conducted by any force on the subject material that is enforced to make the position of the subject particle or material to change. This type of energy stays stored in the subject system or material. Potential energy is the result of conservative forces which is also known as internal stress. Potential energy is identified with Ep, and it can be calculated using the equation stated below: Ep = mgh

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Here, m = mass of the object g = the acceleration of free fall (9.8 m/s2) h = height of the position of the object

Figure 1.10: Basic forms of energy

Kinetic energy: Kinetic energy is the result of the existence of a motion of the subject matter. The amount of energy the subject material achieves due to the motion contained by the matter is identified as kinetic energy. It is achieved from the work that was done to provide the subject materials’ body mass enough push to reach from rest to its required velocity. The kinetic energy of an object is defined with Ek,, and it can be calculated with the equation stated below: Ek = (½) mv2 •

Here,

m = mass of the material. v = velocity of the material. The amount of total energy contained by any subject material can be calculated by adding potential and kinetic energy of that material. So, amount of energy = E = Ep + Ek.

This amount of total energy can be identified as “Mechanical energy.” Mechanical energy is the cumulative amount of energy present in a subject material. These two significant forms of energy play the role of characterizing a more diversified classification of the forms of energy. Energy is found in ten different forms which are divided into these two major types. The more elaborate forms of energy falling under these two primary types are described below:

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1.3.4 Various Types of Potential and Kinetic Energy Potential energy can be divided into several forms. They are as mentioned below: • Gravitational energy • Chemical energy • Nuclear energy and • Elastic energy or stored mechanical energy On the other hand, kinetic energy can be divided into the forms stated below: • Electric energy • Radiant energy • Thermal energy • Motion energy • Sound energy • The energy of light All these different forms of energy are described in short below as these various forms, and the interchange of these forms are the principal way energy is harnessed and becomes usable.

Figure 1.11: Energy and different forms of energy

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• Gravitational energy: Gravitational energy is one of the primary forms of potential energy. This energy is the result of the attraction of one element of the universe with another. In earth, gravitational energy is created due to the gravitational field of Earth. Earth pulls everything to itself within a specific range of area, and this area is known as the gravitational field. The amount of energy generated is depended on the position of the subject material within the gravitational field. The acceleration of the subject material that develops as the result of the gravitational pull is the determining factor of the gravitational energy. The gravitational energy is the highest while closer to the surface of the earth where the gravitational acceleration is static at 9.8 ms−2. The measurement of gravitational energy is conducted with the help of Newton’s law of gravitation. It states that “Every point mass attracts every single other point mass by a force pointing along the line intersecting both points. The force is proportional to the product of the two masses and inversely proportional to the square of the distance between them” (Philosophiæ Naturalis Principia Mathematica, 1687). According to this statement, F = G (m1m2/r2). Here,

F is the force between the masses; G is the gravitational constant (6.674 × 10−11 N · (m/kg)2); m1 is the first mass;

m2 is the second mass;

r is the distance between the centers of the masses. As potential energy Ep = F × r,

These equations can be merged and stated as mentioned below. Ep = G (m1m2/r)

Again, when one object within them is Earth, the mass of Earth is identified with M. And so, we can find that,

Gravitational potential energy, Ep = G (Mm/r) Here, G and M are constant. By simplifying the equation further, we can

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find Gravitational energy = mgh Here, m = mass of the subject particle g = gravitational acceleration h = distance or height of the particle. This equation indicates that the potential energy stored into a material or an object at a certain height above the zero point (where gravitational acceleration is 0) is equal to the work that is required to be done to live the object to its position. When the object is displaced from the higher position and is allowed to fall freely, the stored potential energy transforms into kinetic energy and accelerates.

Figure 1.12: Earth’s gravitational field

https://upload.wikimedia.org/wikipedia/commons/thumb/b/be/ Gravitational_field_Earth_lines_equipotentials.svg/372px-Gravitational_ field_Earth_lines_equipotentials.svg.png Chemical energy: Chemical energy is the amount of energy that is generated due to interatomic bonds of all the materials of the universe. Every single matter is created with extremely tiny atoms. The surrounding atoms of an atom are internally chemically bonded to each other. This bond is the storing mechanism of energy. Energy can be absorbed or released while creating or breaking these bonds. Chemical energy is one of the primary forms in which potential energy •

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is stored in different materials. It is the central mechanism of the fossil fuels containing energy and also the mechanism of achieving energy from those. The amount of chemical energy formed or absorbed by any compound is the difference of energy associated with the creating and breaking bonds. The energy stayed stored in the atoms of the subject material until it takes part in a chemical reaction. In most of the cases, the reactions are exothermic, and energy is released or absorbed in the form of heat. In several situations, energy changes into light and sound too. The most frequent process of energy being stored in the form of chemical energy is the photosynthesis process. Thus, it can be stated that all the living organisms depend on chemical energy stored by the plants for their survival. Chemical energy can be attained through six types of chemical reactions. They are as follows: • Combustion • Synthesis • Acid-base • Decomposition • Single displacement • Double displacement. Chemical energy can be stored in both natural and artificial processes. Plants storing energy into nutrition compound cells through photosynthesis and later the breaking process of the compounds through digestion of the living entities to generate necessary heat for survival can be considered natural techniques of storing and utilizing chemical energy. On the other hand, using batteries, explosives where energy is attained by artificially creating specific bonds and later changing them back to their previous forms can be considered as the artificial technique. •

Nuclear energy: This type of energy is also known as nuclear binding energy. This kind of energy is created by changing the format of an atom—more specifically changing the initial quantity of electrons within an atom. There is the necessity of a binding energy to keep an atom of any subject material functioning. The main reasons for the energy being free are the nuclear reactions and nuclear decay. The most significant example of the nuclear reaction is the Sun. The huge amount of energy created by the sun is the result of a constant nuclear reaction which changes an active hydrogen molecule into a helium molecule. As the nuclear

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reactions and decay are being used in nuclear power plants as a sole and individual source of energy, the whole concept will be discussed in the later part of this book. • Stored mechanical energy: This type of energy is also known as the elastic energy. Stored mechanical energy is one specific type of mechanical potential energy which is the result of the change in the physical form of the subject material. More specifically, if the subject material is stretched or compressed, or deformed, elastic energy generates. The mechanical energy that is required to change the regular shape gets stored as potential energy within the material and when the external simulation is taken off; it releases the energy and gets back to the original form. • Electric energy: Electric energy or electricity is the most frequently used form of energy. This energy is sourced from electric kinetic energy. Generally, this type of energy is achieved by using other forms of potential energy. Heat combustion or nuclear fusion is the primary source of electric energy. But in recent times, many other techniques have been adapted to achieve electricity. In modern times, electricity is the most critical and significant form of all the different forms of energy. • Radiant energy: Radiant energy is the kinetic energy that is the result of electromagnetic and gravitational radiation. This form of energy is most crucial in artificially absorbing solar energy as the energy received in the radiant form is synthesized and stored using solar panels. One of the most significant characteristics of this energy is that it does not need any external carrier to transport. • Thermal energy: Thermal energy is created due to the temperature difference between the observing system and the external environment. Thermal energy is often used as the synonym of heat. • Sound energy: Sound is the form of energy that is related to the vibration of the matters. The sound energy is not solely a form of kinetic energy. A sound wave contains both kinetic energy and potential energy. If the value of sound wave energy can be stated as W, then it can be stated that, W = W potential + W kinetic = (P2/2 ρ0c2) V + ((ρv2)/2) V Here,

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V is the volume of interest; P is the sound pressure; v is the particle velocity; ρ0 is the density of the medium without the presence of sound; ρ is the local density of the medium; c is the speed of sound. •

The energy of Light: Light is an electromagnetic radiation within a specific portion of the electromagnetic spectrum. The range of the spectrum visible to the human eye is known as visible light.

CHAPTER 2

ENERGY SOURCES: DEFINITION AND TYPES

CONTENTS 2.1 Nonrenewable Energy Sources and Advantages and Disadvantages of Them............ 26 2.2 Renewable Energy Sources and Advantages and Disadvantages of Them................. 28

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(In this chapter, different approaches of classifying energy sources and the classifications of the energy sources depending on those approaches have been discussed) It has been mentioned and discussed in the previous chapter that the total amount of energy in the whole universe is constant. The change in the energy that can be observed is only the change in the form of it. Energy converts from one type to another. Moreover, due to this variation in the form of energy, it is available from a range of sources. An energy source is an element or activity which delivers energy. According to Cambridge Dictionary, energy source can be defined as below: “Energy Sources are the Natural resources; something such as oil, coal or the sun, which can be used to provide power for light, heat, machines etc.” So, an energy source is that natural element which acts as a source of necessary energy that is required to maintain the systematic circulation of the natural phenomena. Although the energy sources are natural elements, it can be harnessed and sustained through both natural and artificial processes. Few of the most important natural techniques of sustaining energy are photosynthesis and digestion, whereas in the creation of battery, explosives are the most significant examples of the artificial ways of sustaining energy. The energy sources can be classified into different manners considering different characteristics.

Figure 2.1: Different ways of classification of energy sources

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The energy sources can be divided into two major types depending on the generation process of the sources: primary sources and secondary sources.

Figure 2.2: Classification of energy sources



Primary sources of the energy are those sources that do not attain the energy from other ones. Instead, they generate the energy by themselves from the mass of the storage material. The prime example of the primary source of energy is the Sun. Other examples include fossil fuels and nuclear fuels, wind, water and the heat of Earth. Simply, the natural sources of energy which can be directly used are known as the primary sources of energy.

Figure 2.3: The structure of global energy absorption from primary sources http://www.theenergycollective.com/sites/theenergycollective.com/files/imagepicker/305171/energymix2009.png

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Secondary energy sources are those sources that cannot be directly achieved by nature. This type of energy is achieved by transforming or processing the primary sources of energy. Secondary energy sources are not always artificial sources of energy. A prime example of secondary energy is gasoline (petrol or octane). These types of energy sources are developed by processing crude oil. Crude oil is the oil primarily achieved from the mines which contain several different types of oils. By processing the crude oil, these different oils can be separated and used in specific different mechanisms. Electric energy is another example of the secondary sources of energy. This type of energy is generated from different types of electricity production plants using different primary sources. Though these secondary sources are more expensive compared to the primary sources, their production can be controlled which makes them much more preferable to use. Depending on the usability and financial aspects of the energy generated from the sources, the sources can be divided into two ways: commercial sources and non-commercial sources.

Figure 2.4: Classification of energy sources depending on financial aspects

http://cdn.yourarticlelibrary.com/wp-content/uploads/2014/02/image_ thumb175.png The classification can also be conducted in the manner stated below:

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Figure 2.5: Classification of energy sources depending on availability and financial aspects. http://cdn.economicsdiscussion.net/wp-content/uploads/2014/12/clip_image0027.jpg

As conventional and non-conventional energy sources are the same as nonrenewable and renewable energy, they will be discussed in the next differentiation. Commercial sources of energy are simply the ones with a price. Those energy sources which require financial currency transferring for consumption and are present in a limited quantity are considered as the commercial sources. These sources contain economic value mainly because of the necessity of processing them. Moreover, in most of the cases, these sources have multiple adverse effects on the environment. The most frequently used commercial sources of energy are electricity, fossil fuels, and nuclear energy. On the other hand, non-commercial sources are the sources that have much less or no economic value. These sources are frequently available and generally do not need any conversion or processing. These types of energy sources are used mostly in the areas where a low output of energy is enough as these sources are not capable of producing energy at a high rate. The third type of classification of energy sources is the most important and significant one. This classification is conducted by depending on the availability of the energy sources. The sources can be divided into two primary forms. They are as follows: • Renewable sources • Nonrenewable sources Renewable sources are recyclable, i.e., these energy sources can be used over and over again. Moreover, this type of source is available in a considerable amount. On the other hand, nonrenewable energy sources can

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only be used once. And these sources are limited in nature. Moreover, these nonrenewable sources are extremely harmful to nature. The following diagram shows the major types of renewable and nonrenewable sources of energy.

Figure 2.6: Classification of energy sources depending on reusability

2.1 NONRENEWABLE ENERGY SOURCES AND ADVANTAGES AND DISADVANTAGES OF THEM Most of the nonrenewable energy sources are fossil fuel, which answers the reason behind the limited amount of the energy sources. Though it was the use of fossil fuels which initiated and made the improvement of human civilization possible and brought the civilization in its current position, it

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is hazardous to the environment. The reason behind the massive popularity of these fossil fuel sources is the convenience and low processing cost. As most of the cases, these sources can be extracted at a ready-to-be-used condition, they are comparatively cheap. Even the ones requiring processing are cheap to purify. However, the biggest drawback of these sources is the environmental effects. Using these fuels causes the emission of hazardous gas which is the major reason for global warming. Global warming is one of the biggest threats that all the living organisms on the planet Earth are currently facing. Another drawback of these sources is that they are limited in quantity. These sources take thousands of years to be created and are now being used up at an extremely fast rate. As per BBC, the oil left unused around the whole world will be entirely used up within 50 years. The natural gas will finish within 70 years, and the world will run out of coal within 250 years. As the significant part of the energy required by the whole planet Earth is currently generated using nonrenewable energy, it is alarming information. The wastage of energy while using these sources is another negative side of these sources. While using the fossil fuels, more than 60% of energy is wasted in the form of heat that gets released into the environment by the energy utilization system. Along with high wastage, the excess heat released in the environment also accelerates greenhouse effect. Another frequently used nonrenewable energy source is the nuclear energy. This energy is generated through controlled nuclear reactions. This source is comparatively better than the fossil fuels as they do not emit any pollution to nature. However, these reactions emit extreme radiations which are much more dangerous to the living entities of the planet. The system needs to be conducted in a completely isolated environment, and the smallest leakage can release a tremendous amount of radiation in the environment. A prime example of the danger is the Chernobyl project. Though it takes a small amount of radioactive material to produce a lot of energy, the complete setup, infrastructure, and storage of toxic radioactive residues of the process are extremely costly. Earth minerals are also used as a nonrenewable source of energy too. These metals are frequently available on the crust of the Earth. Though the use of nonrenewable sources is the cheapest option available, these sources pose several severe threats to the environment, and the limited quantity of the sources is a significant concern. As the number of nonrenewable sources of energy is quickly diminishing, the importance of more available and reusable energy sources is increasing fast.

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2.2 RENEWABLE ENERGY SOURCES AND ADVANTAGES AND DISADVANTAGES OF THEM The renewable energy sources are the direct opposite of the nonrenewable energy sources. They are vastly available in the environment and are reusable. As these sources can restore the used-up energy fast from other sources of energy, the amount of energy stored in these energy sources does not fluctuate significantly. As these sources can supply energy continuously without creating any concern about being all used up, these sources are also known as the infinite energy sources. These sources include solar energy, wind energy, tidal energy. The sunlight, wind, and water flow are continually occurring phenomena and are highly unlikely to get all used up. The energy harnessed from these sources always requires artificial approaches. Solar energy can be harnessed using solar panels and converted into electricity; the harnessed energy can also be stored in batteries by changing them and transferring the energy into the form of chemical energy. On the other hand, in the case of wind, tide, and waves, the kinetic energy of the airflow, water waves, and tides can be used to run turbines and generate electricity. As sunlight is available in most of the places on earth through the whole year, it is straightforward and convenient to use the solar radiations as a source of energy. The radiant energy can be absorbed using solar panels and can be stored for future use also. Airflow is another renewable source of energy. However, sufficient amount of energy can only be attained using this source in the places where the airflow is extremely higher and a vast amount of open space is available. Using the airflow, the rotors of the turbines can to rate and electricity can be generated using the rotation. On the other hand, wave and tidal energy are not as much frequently available compared to solar and wind energy sources. The necessary amount of energy can only be sustained from the hydroenergy sources where the wave and water flow are strong enough to move turbines and generate electricity. Geothermal energy is another source of energy with high level of potential output. The heat generated from the core of the Earth is sustained and used in this process. Geothermal energy is one of the most recently developed techniques of attaining energy. This technique can be utilized in the volcanic regions where the temperature of the surface is much higher

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than its surroundings. In this technique, cold water is pumped underground using water pumps. The heat of the earth vaporizes the water, and as the pressure of the steam is less than water, it flows back upward. The steam is then used to run turbines and electricity can be generated from the turbines.

Figure 2.7: Use of renewable energy source compared to total energy use https://upload.wikimedia.org/wikipedia/commons/thumb/6/6e/Ren2008. svg/1000px-Ren2008.svg.png

The use of renewable energy is relatively new, and less than 25% of the total energy that is being used worldwide is from renewable sources. The white area of the leftmost pie cart of the image above indicates the amount of renewable energy used compared to the total use of energy. However, the use of this type of energy is increasing rapidly in recent years. The main reason behind the rapid growth of the use of renewable energy sources is the diminishing nonrenewable and conventional energy sources. As the rapidly ending nonrenewable energy sources are being all used up and these nonrenewable sources are posing considerable threats to the environment endangering the life on Earth, the importance of environmentally friendly renewable sources is increasing every moment. Though the initial cost of the establishments required to harness the renewable sources is high compared to the conventional sources, these establishments are much more nature friendly, long lasting, and cost-efficient in the long run. Due to the potential capacity of generating much more energy compared to conventional sources from setups costing the same, the whole world is being more interested in using these renewable sources of energy.

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Renewable sources are environment friendly too. As these sources generally use natural phenomena to collect energy in the form of electricity, they hardly leave any carbon footprint. The establishment of the facilities and necessary equipment and other deliveries required in the facilities are the only cases where carbon footprint is created. These energy sources do not have any toxic residues; in fact, there is no residue or after effects to consider at all.

Figure 2.8: Percentage of electricity generation from renewable sources http://geocurrents.info/wp-content/uploads/2012/07/Renewable-Energy-byCounty-Map.jpg

The renewable sources are not at all free from drawbacks. Some of these sources can pose considerable threats to the ecology of the environment if not planned properly. For example, dams are built to generate electricity from water flow. These dams store a considerably high amount of water on its one side, causing extreme changes to the ecosystem of the whole area. For example, the image inserted below can be considered.

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Figure 2.9: Change in the geographic character of surrounding areas of the Three Gorges Reservoir of China https://upload.wikimedia.org/wikipedia/commons/a/a8/ThreeGorgesDamLandsat7.jpg

The image shows the corresponding geographical changes in the environment of the surrounding areas of the electricity generation plant using water flow. This caused flooding of a vast area, destroying agricultural fields and cultural sites and displacing more than 1.3 million people.

CHAPTER 3

FOSSIL FUELS

CONTENTS 3.1 The Carbon Cycle.................................................................................................... 35 3.2 Natural Gasses........................................................................................................ 45 3.3 Coal........................................................................................................................ 47 3.4 Utilization of the Fossil Fuels................................................................................... 59 3.5 Internal Combustion Engine..................................................................................... 61

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(Fossil fuels are the leading source of energy. In spite of having multiple adverse effects on the environment and being a limited rapidly diminishing source, the broad use of fossil fuels makes it the backbone of the industrialized civilization. Petroleum, natural gas, and coal are considered as fossil fuels. In this chapter, overall extraction, purification, refining, and energy extraction techniques of the fossil fuels will be discussed.) Fossil fuels are those hydrocarbons that are used as a source of energy. Generally, coal, oil, and natural gas are considered to be fossil fuels which formed from the remains of dead plants and animals. In ordinary senses, fossil fuel also includes the hydrocarbons generated from non-plant and nonanimal sources. Fossil fuels are the prime example of nonrenewable sources of energy. Fossil fuels are also known as the mineral fuels. The generation process of fossil fuels is extremely lengthy. Organic matters often get buried underground due to various natural causes or disasters. These organic matters gradually get deeper into the Earth’s core. Due to the higher temperature and pressure, the chemical bonds of the organic matters change. These changed hydrocarbons turn into different types of fuels depending on their carbon numbers and the complexity of the atoms. Fossil fuels are considered as the primary source of energy as they can be used directly. The energy is stored in the form of chemical energy within the bounds of the atoms of the compounds. Primarily, the solar energy was absorbed and stored in the body of the organic entities in the form of chemical energy. When they went through extremely high temperature and pressure, these bonds reformed and the chemical energy within the bonds became more sustained. When these fuels are burnt, the bonds reform and the chemical energy transforms into heat. There are three basic types of fossil fuels. They are listed below: • Petroleum or oil, • Natural gas, and • Coal. Petroleum and natural gas are organic compounds known as hydrocarbons where coal is formed with pure carbon.

Hydrocarbons Hydrocarbons are the organic chemical compounds whose main components

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are hydrogen and carbon atoms. Due to the chemical properties of carbon and its capability of creating different types of bonds with single or multiple atoms of another compound, there is a considerable variation of hydrocarbons in the environment. In fact, hydrocarbons are the most frequently found compounds. Hydrocarbons are the principal constituents of natural gas and oil. Hydrocarbons can be classified into a profoundly dividable classification. The general classification of the hydrocarbons is shown below:

Figure 3.1: Classification of hydrocarbon http://lh3.googleusercontent.com/-XFQ-6oc2unw/VgS3v3e283I/ AAAAAAAAAns/0lXJSmRXnWA/clip_image020_thumb2.jpg? imgmax=800

Almost all the organic materials used as fossil fuel are alkanes. Alkanes are the hydrocarbons where the carbons are connected by a single bond. The individual bonds of the carbons enable the alkanes to release the chemical energy efficiently and with the minimum presence of external influences.

3.1 THE CARBON CYCLE Carbon is the most available element in all the fossil fuels. It is critical to the existence of the life on this planet. The significance of carbon can be easily described with the help of carbon cycle. The carbon cycle is the biochemical cycle through which carbon keeps moving through the whole ecosystem of the Earth. It is one of the three fundamental cycles for preserving the ecosystem of the planet.

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Figure 3.2: A primary carbon cycle https://i.pinimg.com/736x/a3/89/49/a38949ae3d55df2e5f64eb570a67842a-carbon-cycle-th-grade-science.jpg

The principle portion of the cycle is the part backed by the living organisms. Plants absorb the carbon from the environment in the form of carbon dioxide and then create glucose through photosynthesis process. By this, carbon becomes a part of the plant body. When animals attain their nutrition from the plants, the carbon gets transferred from the plant body to the animal body. When the living organisms die, the body decays and the carbon compounds chemically react with the oxygen of the air and get rereleased into the atmosphere. Another way the carbon is released into the environment is when the living animal or plant body cells burn the compounds, providing nutrition to the cells. The mixture breaks down, contains the necessary energy and the carbon atoms react with the oxygen and gets rereleased to the environment in the form of carbon dioxide. The reaction is as stated below: C6H12O6 + 6O2 = 6CO2 + 6H2O

Glucose + oxygen = carbon dioxide + water Fossil fuels are the result of a disruption of this normal process. The generation process of fossil fuel begins if there is a situation where the stored carbon cannot react with the oxygen of the environment and is subjected to extreme heat and pressure. Different types of microscopic organisms cause the organic materials to decay and transform into an insoluble solid material identified with the generic name kerogen. Over a long period, these kerogens

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get more and deeper into the earth’s crust and reach a depth where the environment contains extreme temperature and pressure. Over a period of millions of years, the excessive heat and pressure breaks the smaller carbon bonds, recreates new bonds, and creates extremely long carbon chains. The final products of this long-time process are diverse. A major portion of the newly reformed carbon chains contained from five to twenty carbon atoms. The chains kept reforming and finally chains were containing one to more than twenty carbon atoms. Here, the hydrocarbons with chains containing up to four carbon atoms were in gas form. The hydrocarbons that had chains containing five or more than five carbons achieved a liquid form, and the hydrocarbons with chains containing up to twenty carbon atoms were liquid. These liquids are known as petroleum or crude oil. Chains containing carbon atoms higher than the mentioned amount were in solid- and jelly-like conditions and are considered as different forms of wax.

3.1.1 Petroleum Petroleum is a sophisticated form of hydrocarbon. Generally, this term is reserved for the alkane hydrocarbons of liquid form and is also known as crude oil. In real conditions, petroleum contains several gasses and a nearly solid form of hydrocarbon known as bitumen.

History of use The use of petroleum as a source of energy is an ancient practice, and it is one of the most significant practices that shaped the modern civilization into the present form. It has been an affair of profound importance in the industrialization of the whole world. The use of petroleum as a source of energy dates back to the civilization of ancient Sumerians, Assyrians, and Babylonians. They did not have any idea about the oil reserved under the surface. Instead, it was the small surface seeps from where they achieved oil. Ancient Egyptians started using liquid oil as medicine. Oil was also used in warfare too. It was used in various weapons to turn standard weapons into flammable ones. The extraction of oil from underground resources was conducted far later, during the nineteenth century. The rapid growth of the civilization required more efficient and better fuels as the conventional fuels available back at that time suddenly started becoming inadequate. By the mid-19th century, North America and European countries began extracting oil and coals from the mines and started using them as the primary source of fuel.

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It was the industrial revolution that created a huge demand for cheaper and more convenient source of lubricants and fuel as a better source of energy. As the source of energy in the production process back then were the muscles of animals and humans and flammable natural resources which were not even close to enough compared to the amount of energy required; it was a must to have a better source of energy to attain a sustainable growth of industrialization. It was the year of 1859 when the groundwork for the first petroleum industry began. It was the brainchild of Edwin L. Drake. Within a concise period, relatively cheaper oil was excised from underground sources and used after being processed. And after that, the usage of oil as a source of energy kept growing. At present, oil is one of the most used sources of energy around the globe.

Products of petroleum Gases While processing petroleum, a fair amount gas is obtained. This gas is redirected to the fuel system of the refineries. If the amount of gas achieved is relatively higher, then they are processed and used in both domestic and light industrial sectors.

Gasoline or Oil This is the most important output of the petroleum. Gasoline used to run motors is known as petrol and must contain three fundamental requirements. They are as follows: • • •

An even combustion pattern, Ability to work in cold weather, and Meet environmental requirements.

Octane rating Octane rating or octane number is a standard way of measuring the quality of fuel. It is essential for the fuel to burn without any premature detonation to ensure highest efficiency and fluency in the combustion process. A poor octane number of the fuel can create knocking. Knocking can reduce the power output and even cause severe damages to the power delivery process as well as harm the engine components. Knocking is the phenomenon of

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extra fuel being burnt off the combustion pattern, disrupting the combustion process and creating knocking sound in the engine. Some fuels have the tendency of knocking more than other fuels. The length of the carbon chain is the most significant influencing factor of the knocking present in an engine. The longer the chain, the lesser the knocking is. As the boiling point of the oils gets higher with longer carbon chain, extra oil cannot burn without sufficient heat and pressure, and so unwanted burning of fuel reduces. A scientific study during the 1920s showed that the highest amount of knocking was conducted by pure normal heptane. On the other hand, the lowest amount of knocking was done by pure isooctane. This study and observation achieved led the way to develop the octane scale. The octane rating is measured and marked with the corresponding difference in the amount of knocking made by the percentage of isooctane and heptane present in the fuel. For example, if a fuel provides the performance same as an equivalent fuel containing 80% isooctane and 20% pure heptane, the fuel is marked to have an octane ratio rating of 80%. There are two procedures for measuring knocking: • Research octane rating and • Motor octane rating. While research octane rating measures the performance of the oil at controlled and favorable conditions, motor octane rating is measured at a comparatively higher temperature and pressure, along with higher rev and more serious situation.

Diesel fuel Diesel fuel is obtained from petroleum after the gasoline or petrol is separated from the crude oil. Diesel is comparatively cheaper compared to gasoline as it requires less refining. The ignition point of diesel is much higher than petrol. There are several available standards for diesel oil. They are as follows: • Light middle distillates, • Middle distillates, and • Heavy distillates. While the light middle and middle distillates are best for the engines designed for generating higher and variable amount of energy, heavy distillates are for producing lower and constant amount of energy.

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One significant drawback of diesel fuel is the existence of sulfur at a relatively high amount. As the oxidation of sulfur creates polluting and hazardous gas which is harmful to the living entities of the planet, the use of diesel is highly regulated to reduce the amount of sulfur being released into the environment.

Fuel oil Furnace oil is the residue of crude oil after separating petrol and diesel. By conducting necessary processing steps, the crude oil can be used as fuel oil.

3.1.2 The Process of Extracting Oil There are approximately 600 established basins from where oil is extractable. And more or less the same procedure is followed to achieve oil from the sources. From the very beginning, drilling has been considered as the most efficient way of reaching the oil reserves under the surface and extracting the oil. On a course of about two hundred years, the technology associated with drilling and extracting oil has been improved hugely. The critical stages of the most famous technique of drilling and extracting oil are described below: • • • • • • • • •

Cable tooling The rotary drill The drill pipe The Derrick Casing Directional drilling Drilling offshore Well logging and drill-stem testing Well completion

Properties of Crude Oil Crude oils are complex mixtures of different hydrocarbons. Along with hydrocarbons, several additional elements are there such as compounds of sulfur, nitrogen, and oxygen. Traces of meager amount of vanadium, nickel, chlorine, sodium, and arsenic are there too. These elements ruin the purity of the oil as well as create the possibility of danger and hazards in the transportation system of the fuel. If these elements are present at a really low

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amount, then they can be overlooked. But the presence of impurities above a specific tolerance level requires proper treatment and precautions.

Saturated Hydrocarbons The shortest carbon chain found in a system is known as methane. It is expressed as CH4. Methane contains a carbon atom with four hydrogen atoms establishing single bonds with it. The next one is known as ethane. These two compounds of carbon describe a complete series of hydrocarbons known as the paraffin. The compounds form a chain-like formation with a standard chemical formula of CnH2n+2. These types of hydrocarbons are known as saturated hydrocarbons. The carbon molecule always creates bonds with four hydrogen molecules with each of its electron of the outer most shell being shared with a single hydrogen molecule. This type of single bonds produces a more stable compound leaving no electron vacant for sharing. Creating a bond concentrated in a single direction delivers the complete bond a higher strength. The hydrocarbon molecules of paraffin oil can be arranged in straight chains or branched chains. Generally, the singlechained compounds are more preferred as they are the most frequently available options. Paraffins contain closed ring-like structure too. When a hydrocarbon chain contains more than four carbon molecules, the molecules can align themselves in a closed chain. This type of structure is known as a cyclocompound. They are chemically named as naphthalene. These compounds provide much less heat if directly used as fuel. But processing this type of hydrocarbons can produce gasoline with higher quality having extremely high octane rating.

Unsaturated Hydrocarbons If two carbon molecules share more than one electron within themselves, they form an unsaturated bond. If the quantity of shared electrons is two, the bond is called a “double bond.” The bond is a “triple bond” if the shared amount of electron is three. These types of compounds are known as olefins. These compounds are much less stable compared to paraffin oils and have a tendency of generating different types of long chains. Sometimes, these carbons create a ring-like structure where the shared electron keeps moving within the atoms. These types of compounds are known as aromatics. The most straightforward aromatic is benzene, which contains double bonds within every single-carbon molecules and the adjacent

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molecules. Though these unsaturated hydrocarbons are efficient as fuels, their higher reactivity makes the use of these compounds as fuel dangerous.

Non-hydrocarbon contents Along with these compounds consisting of carbon and hydrogen, several hydrocarbons contain additional atoms of other molecules such as nitrogen, oxygen, or sulfur. Though the amount of these molecules present in a compound is extremely low, they are highly significant as they change the characteristics of the molecules completely. Some hydrocarbon chains present in the crude oil contains molecules of metals.

3.1.3 The Basic refining process of petroleum As the petroleum extracted from the mines is a mixture of different types of oils and hydrocarbons, it is crucial to separate and refine them before using accurately. Generally, three significant steps are present in a refinery or refining system: • • •

Separating the different types of oils containing specific types of hydrocarbon chains showing specific characteristics; Chemically altering the separated hydrocarbons to transform them into a different form of fuel with higher efficiency; and Eliminating the unwanted components and ensuring the purity of all different types of oils.

Fractional Distillation The first stage of separating the hydrocarbons from the complex mixture called crude oil is conducting fractional distillation. The diagram below shows a standard distillation system designed to separate different types of fuels from the complex crude oil.

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Figure 3.3: A fractional distillation plant for separating different types of oils from crude oil http://www.bbc.co.uk/staticarchive/d1fc03f39806642998b1bd6ea1dda2c8e2e2b674.gif

The distillation starts when the crude oil is heated and transported into a huge capsule-shaped boiler. The crude oil is pumped into the chamber at a steady rate to ensure a contestant percentage of crude oil present in the system. The lower part of the chamber heats the crude oil up to 650°C. As the temperature is more than the boiling point of most of the components of the crude oil, almost all of it is vaporized. But bitumen has a higher boiling point, and so it stays in the liquid form. The liquid bitumen is collected through a collecting tube situated at the lowest part of the boiler. As the oils become relatively lighter in vaporized form, they start traveling to the higher parts of the boiler. Several strays and side-stream systems are provided to the system. Those side streams are placed at specific heights to ensure the collection of the particular type of oil by a specific stream. Depending on the boiling point of the compounds, different oils leave the system using different side streams. The relative boiling point ranges of different oils are as stated below: Table 3.1: Boiling point of different types of fuels Name of the fuel Natural gas

Boiling point range Less than 20°C

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From 20°C to 70°C From 70°C to 120°C From 120°C to 170°C From 170°C to 270°C From 270°C to more than 450 °C

Due to this difference in the boiling point of the fuels, they gradually condense on the surface of the trays while traveling upward at separate temperatures and so can be easily collected separately using the collection trays and stream pipes. After this process, the fuels are put into specific cracking reactions to ensure the continuity of chemical structure within the entire amount of fuel. The cracking is conducted following the free radical theory of molecular transformation. Under extreme heat and pressure, the bonds of the carbon chains can be broken and reformed. Generally cracking is used to break the long chains of hydrocarbons, transforming them into smaller chains. Usually the complete process is conducted into a reactor which operates at a temperature ranging in between 480–550°C. Using catalytic compounds accelerates the production process. Generally, solid catalysts are used in modern cracking reactors to prevent pollution of the fuel.

Purification Before transporting the oils to make available for use, the oils are purified to ensure the lowest knocking and smoothest performance from the output machines. Most common impurities are several sulfur components and benzenes. Along with them, nitrogen compounds can also exist which can cause the fuel to provide reduced performance. Several purification processes can be followed to purify the oils. The most frequent type is the oxidization reactions to turn the unwanted elements into disulfides. The oils can be treated with clay to remove resin and resincreating materials which would absorb the materials causing the gluing. The most preferred technique is the use of zeolite, which is capable of absorbing water, carbon dioxide, hydrogen sulfide, and all other impurities without affecting the oil itself.

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3.2 NATURAL GASSES Natural gasses are short-chained hydrocarbon compounds which can be found in a gas form in normal temperature. These gases generally contain methane and ethane. Typically natural gas is available with petroleum in the mines. The gas can found in a dissolved condition along with natural petroleum. Also, the gas can stay as a separate layer over the petroleum storage. In most of the cases, the petroleum from the natural reservoirs is collected using the force of the natural gas layer present right above the layer of the petroleum. Though natural gas can be found along with oil, there can be independent reservoirs of natural gas.

3.2.1 History of the use of Natural Gas Compared to other types of fossil fuels, the use of natural gas is a relatively new concept. The first invention of natural gas as a source of energy was conducted during the time period of 6000 and 2000 BCE in the Middle East. Accidental ignition of the gas by lighting created fire and the constant flow of gas from the reservoirs directly below kept the fire alive. The ancient humans considered it as the eternal fire, and it was the begging of the religions which considered fire as one of the Gods and started worshipping fire. It was the beginning of 19th century when first success in synthesizing natural gas was achieved. But since the process was much more costly and sophisticated compared to the most widely used source of fuel of that time, coal; the technique was not used to ensure mass production of natural gas. It was the beginning of the 20th century when the technologies for developing long-distance pipelines were invented, and so the potential profitability of using gas became higher than coal. After the Second World War, a large number of long pipelines were established around the globe to make the use of natural gas efficient and affordable. A prime example is the 5470-km-long pipeline built across the Ural mountains named as the long Northern Lights pipeline.

3.2.2 The Generation Process of Natural Gas Natural gas is formed due to the same reason that causes the formation of petroleum. The only difference is the temperature and heat received by the organic materials and the kerogen creating hydrocarbons with shorter carbon chains.

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It has already been mentioned that the generation of petroleum takes place deep under the surface. Generally, the petroleum generation takes place within 750 to 5000 meters under the surface. At this depth, irregular production of gas occurs along with regular petroleum. But it is 2900 meters from the surface where the fossil fuel generation is solely primary wet gas. Wet gas is natural gasses with liquid vaporized hydrocarbons. When the depth reaches 5000 meters, it is known as post mature stage. At this level, oil cannot stay in the stable form, instead the carbon chains of the oil keep breaking into smaller pieces and natural gasses prevail at that stage. And so, when the depth is more than 5000 meters, the hydrocarbon fuels stored are entirely gas. Natural gas can be generated following inorganic formation process too.

3.2.3 Gas Reservoirs Gas reservoirs are of different types and forms depending on the geographic characteristics. This variation causes the necessity of unique and specialized approaches to achieve gas from different sources. Due to the uneven shape of the reservoirs and moisture of the soil surrounding them, 20% of the gas stays unachievable.

3.2.4 Natural gas as a premium fuel Before the 1960s, natural gas was considered as a cheap and undesirable source of fuel. Even in many refineries, the gas dissolved in the crude oil was separated using flaring, which just merely burnt the gas off. It was the global oil crisis of the 1970s which made natural gas an essential source of energy worldwide. One of the most frequent utilizations of natural gas is the LPG. LPG is the short form of liquefied petroleum gas which is actually a mixture of various short-chained hydrocarbons such as propane, butene, and butane. The gas is compressed and transformed into liquid form and stored in cylinder-shaped containers. The liquid can flow out through a valve and the drastic change in pressure causes the liquefied fuel to vaporize and come out in the form of gas. LPG is most frequently used in fulfilling household requirements of energy.

3.2.5 Molecular Properties of Natural gas Natural gas components are generally hydrocarbons in association with

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nonhydrocarbon compounds at a substantial amount. The most common nonhydrocarbon compound is the hydrogen sulfide. The most common hydrocarbon components present in the natural gasses are the ones with shorter carbon chain such as methane and ethane. Both have less than four carbon atoms in their individual carbon chain and are in a gaseous form under atmospheric conditions. Some other hydrocarbons available in the mixture are propane, butane, pentane, and hexane. Though pentane and hexane are liquid under environmental conditions, they are extracted in gaseous form from the natural gas reservoirs. After extraction, they gradually liquefy, and these liquid fuels are referred as natural gas liquids. These natural gas liquids can be separated from the gas while extracting from the reservoir or after the extraction is complete. Along with the hydrocarbons, the raw natural gas contains a considerable amount of other non-organic gases such as nitrogen, oxygen, carbon dioxide, hydrogen, helium, argon. An identifiable amount of water vapor can also be found from the extracted gas. While considering the physical properties, most of the organic hydrocarbon compounds existing in natural gas are colorless, odorless extremely flammable. But some of the non-hydrocarbon gasses contain distinguishable physical properties such as specific colors or odor.

3.3 COAL Coal is the oldest and most available form of fossil fuels among the ones discussed. It is black or deep brown-colored material. Technically it is a solid mineral of carbon. Coal is one of the most important influencing factors of shaping the modern civilization. The most frequent use of coal is in the electrical power plants where the heat generated from coal is used in creating electricity. Coal geologist James Morton Schopf proved that more than 50% of the fossil fuel created under the surface of the planet earth is coal. These coals are of different types and standards. There is a fundamental difference between coal and other different types of fossil fuels. While almost all the fossil fuels are generally pure hydrocarbons, coal is solely a crystal of carbon. There is only a really little amount of different compounds present, but no aliphatic hydrocarbons exist in coal.

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Figure 3.4: Chemical structure of coal http://www.scienceline.ucsb.edu/images/carbon.png

3.3.1 Classification Coals found in nature are divided into different ranks depending on the percentage of pure carbon present in the mineral. •

Peat: it is considered to be the primary or pre-development stage of coal. It is not considered to be actual coal but as the final stage of the coal development process. Peat is used as a source of energy in a few countries. Due to its high absorbability of hydrocarbons, it is also frequently used to absorb oil spills on both land and water.

Figure 3.5: Peat

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https://4.imimg.com/data4/MG/CU/MY-31953627/agarbatti-raw-material250x250.jpg



Lignite: Lignite is considered to be the lowest class of coal. This type of coal is brown colored and solely used in electricity or heat generation technologies. A compact and polished form of this type of coal is known as jet. It is generally used as an ornamental stone.

Figure 3.6: Lignite https://4.imimg.com/data4/YI/CV/MY-3127899/lignite-coal-250x250.jpg



Sub-bituminous coal: This type of coal is better than the lignite. This kind of coal is also used in power plants.

Figure 3.7: Sub-bituminous coal https://fthmb.tqn.com/yPnc-eAc2oV9R0GNciUzgEntCZ8=/400x0/filters: no_ upscale ()/coal_group-56a627ac3df78cf7728b9db6.jpg



Bituminous coal: This type of coal contains an extraordinarily high percentage of carbon and so is considered to be a coal type

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with a really high standard. Generally, this type of coal is black or deep brown in color. This type of coal is the most preferred one in the generation of electricity due to its high efficiency. This type of coal and sub-bituminous coal looks quite similar. The best way to differentiate them is to consider the glossiness of the coals. A higher percentage of carbon provides the bituminous coals with higher glossiness.

Figure 3.8: Bituminous coal https://qph.ec.quoracdn.net/main-qimg-c92d2a9960ebd3cc1b25915589774975





Steam Coal: This type of coal is mostly used in creating steam in the steam locomotives hence the naming. Sometimes this coal is also known as the sea-coal of the United States. Anthracite: This coal contains the highest quality possible. This type of coal is relatively harder in molecular strength and more compact in size. The carbon bonds are really dense, which is the reason behind the compact form. This type of coal is easily distinguishable for its nearly silverish glossy black appearance.

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Figure 3.9: Anthracite https://upload.wikimedia.org/wikipedia/commons/1/1c/Ibbenbueren_Anthracite. JPG



Graphite: This one is the hardest and the most stable form of coal. The carbon bonds are in its most stable form in this type of minerals. Due to highly stable form, it is not used in power generation. Graphite can be further divided into several forms: – Crystalline – Amorphous – Lump – Highly ordered pyrolytic – Graphite fiber or carbon fiber

Figure 3.10: Raw graphite and its most refined form, pencil

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https://www.thermofisher.com/blog/wp-content/uploads/sites/3/2016/05/istock_000019978938_graphitejpg-4.jpg

Figure 3.11: Molecular structure of graphite https://bam.files.bbci.co.uk/bam/live/content/zt4xfg8/small

3.3.2 Proximity Analysis of Coal Proximity analysis is the process of testing the quality and rank of coal using several tests. The tests available to analyze the proximity are as follows: • • • • •

Volatile matter content, Moisture content, Ash content, Fixed carbon content, and Calorific value of a coal.

Volatile Matter Content Volatile matter contents indicate the number of unwanted materials present in the coal. The sample is heated at over 950°C as at that temperature most of the unnecessary compounds and elements vaporize except the carbon. By measuring the pure carbon left and then by calculating the weight difference before and after burning, volatile matter content is determined. Higher ranked coals contain a lower value of volatile matter content and it is close to zero in graphite. Generally, coals with higher volatile matter value ignite easily and burn faster than the purer coals.

Moisture content This test determines the amount of moisture present in coal. The amount of moisture is measured by heating the sample of coal at 105–110 °C (221–

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230 °F) under specified conditions until a constant weight is obtained. The weight difference before and after heating indicates the amount of moisture present in the coal. The moisture content decreases with increasing rank of the coals. As moisture causes higher flammability of the coals, less moisture content is more desirable. Moreover, moisture creates unnecessary dead weight to the coal hampering the output as well as creating problems in storing and transportation.

Mineral content Several different types of minerals are contained with coal at different percentages. When coal is burnt, these minerals create the ash. The amount of ashes generated, and the characteristics of it can affect and influence the design of the whole system the coal is supposed to be used in. The amount of ash determines the type of ash managing system the whole setup needs. Failing to manage the ash properly would cause the whole system to fail as well as create an environmental disaster.

Fixed carbon content Fixed carbon is the amount of carbon that is going to generate heat after all the volatile matter and ash is separated. In other words, fixed carbon content indicates the amount of pure carbon present in coal. This can be calculated by subtracting the values of the previous three contents from the weight of the sample coal.

Calorific Value This value measures the amount of chemical energy stored in the carbon bonds that would be released by an oxidation reaction of the coal. In most of the cases, it is the caloric value that determines the rank of a coal.

3.3.3 Mining process of coal Mining indicates the extraction process of coal from the mines. During the long period of the usage of coal, there have been various types of mining techniques developed. But these systems can be classified into two major classes. They are as follows: • •

Surface mining and Underground mining

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Figure 3.12: Different techniques of coal mining

Surface mining Surface mining is the most ancient way of mining. This type of mining started back in the 16th century. In this process, the upper surface over the mine is removed and the coal layer is revealed for mining. Though there are different approaches for conducting surface mining, there are several basic steps that are uniform regardless of the approach. These steps are as mentioned below: • • • • •

Clearing the plants, trees, and vegetation of the surface above the mine Removing the uppermost layer of soil and transferring them elsewhere. The hard strata over the coal layer will have to be drilled to make deep enough holes. Explosives will have to be placed into the holes by precise calculation so that the explosion destroys the strata entirely. The blasted strata will then have to be removed. The coal layer

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will be exposed after the strata are completely cleaned off. • The coal layer will have to be measured and calculated. Depending on the calculation, the layer will have to be drilled and blasted using explosives to break the layer and make the coal of the mine attainable. As the success of the whole operation is depended on this stage, the calculation will have to be extremely precise. • The fragmented coal will have to be extracted and transported for refining plant. Surface mining divided into four major types. They are as follows: • • • •

Contour strip mining Area strip mining Open air mining Auger mining

Figure 3.13: Different types of open surface mining

These different approaches are based on the type of the surface the mining will have to be conducted on. Contour strip mining is the type of mining conducted at the hilly terrains. In this technique, the soil of the uppermost part of the hill is removed, and then the process is conducted along the hillside creating a bench-like structure around the hill. In the primary stages, the blasted soil and rocks were simply thrown off the mountains while at

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present they are carried down to chosen sites or to cover the places from where the coal is already have been extracted, reducing the pollution and natural changes at a minimum. Area mining is conducted in the flat areas. Here, a certain amount of area is marked for mining and the overburden is removed from the specified area creating a box-like shape. After all the coal is extracted from the box cut, another box of the same measurement is cut parallel to the first one. The overburden from the first box cut is simply dumped into the first cut to save space and reduce pollution and geographic change. Open-pit mining is the technique where several benches are created in the overburden soil and strata as well as the coal layer. This type of mining is conducted where there are layers of overburdens within the layer of coals, creating different layers of coal at the same place.

Figure 3.14: An open-pit mining site https://i.ytimg.com/vi/MY0r2xWPHXM/hqdefault.jpg

Auger mining is a similar approach to the contour strip method. The only difference is that the overburden soils are removed at an auger shape from the first contour. The potential achievement of coal increases up to 60% with this system. But there is a higher risk of pollution and accidents due to the extreme depth of the augers.

Underground mining Underground mining is the process of extracting the coals from the mines without removing the layer of soil and ground over the mine. In this type of mining, the working environment is under the surface of the earth. The

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natural geographical structure is kept unaltered in mining through this system. A standard diagram of underground mining setup is shown below:

Figure 3.15: A three-dimensional model of an underground mine https://en.wikipedia.org/wiki/Underground_mining_(hard_rock)#/media/File: Underground_3D_model.jpg

Underground mining facilities require several facilities as a must. These necessary facilities are as mentioned below: •



Ground support: Ground support is required to keep the ground above the mine intact when the coals are extracted, and no support is there for the surface to keep its original shape. Mechanical bolts, grouted bolts, and friction bolts are most frequently used ground support systems. Proper ventilation system: As the mines are situated under the ground and air circulation is absent at that place, it is extremely important to have a proper ventilation system. Generally, there are turbines or motors on the ground, and they send fresh air down into the mines through ventilation shafts where another set

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of motors pulls out the polluted air from the mine. Due to the extreme heat and presence of different types of gases, it is crucial that the air ventilation and circulation system stays functional all the time. • Transportation shafts are another important element for a coal mine. These shafts bring the extracted coals over the ground and also help the workers to travel from the surface to the different layers of the mine. Setting up all the essential facilities is known as the mine development stage. The extraction of coals while conducting the setting up process is often referred to as first mining while extracting the remaining coal from the mine is referred to as second mining. Modern mining technologies can be classified into four types: • Room and pillar, • Long wall, • Short wall, and • Thick seam Room and pillar system is the most frequently used mining technology among all the underground mining technologies. In this process, from the primary shaft, several parallel entries are conducted into the coal layer. Then connections among these parallel entries are created by creating new entries transverse to the primary entries at a specific distance. As a result, a grid-like pattern is formed having intact coal layers working as walls between two parallel entries. These layers of coals work as beams to hold the overhead strata and ground from falling down. This system can be further divided into two types: • •

Conventional systems and Continuous systems.

Figure 3.16: Room and pillar mining process

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https://wvcoalassociation.files.wordpress.com/2013/05/room__pillar1-copy. jpg

By proper calculation and providing supporting beams to hold the ground, the coals of the pillars can be extracted too. In longwall mining process, from the primary shaft, an entry is created through the boundary surface of the mines sidewall in a way that a long wall from 100 to 300 meter of thickness and 1 to 3 km in length is available for extraction. Coals are extracted in slices of blocks. The dimensions of the blocks are precalculated and depend on the thickness of the wall. There are two approaches to longwall mining. They are as mentioned below: • Retreating system and • Advancing system In the retreating system, the blocks are extracted from the boundary of the far end, and gradually mining continues back to the main tunnel. In the advancing system, development of the passage and extraction of the coal is conducted at the same time toward the boundary. Short wall mining system contains several similarities to the longwall system. In fact, the basic mechanism is identical to the longwall method. The only difference is that the length of the wall is much shorter compared to the longwall system. In this process, the length of the walls never exceeds 100 meters. Thick seem mining is conducted when the thickness of the wall is extremely high, and it is not possible to extract all the coal during a single attempt. In this case, the total thickness is divided into several layers while calculating and setting up the extraction mechanism and then the coal is extracted layer by layer. The extracted coal can be used directly, or they can be transformed into gas or liquid by following gasification and liquidation process, respectively.

3.4 UTILIZATION OF THE FOSSIL FUELS Fossil fuels are the most frequently used source of energy around the globe. The diagram below shows the breakdown of the total energy used depending on their sources.

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Figure 3.17: World energy consumption by source (2013) https://upload.wikimedia.org/wikipedia/commons/b/b6/Total_World_Energy_ Consumption_by_Source_2013.png

The diagram shows that nearly 80% of the energy used is sourced from fossil fuels. Generally, these fossil fuels transform the chemical energy stored in the bonds of their atoms into heat and later the heat is transferred into other forms of energy. This transformation in the form of energy is conducted using the combustion system. Combustion is the process of carbon being released from a compound in the presence of active oxygen ion. Usually, it is the atmospheric oxygen which initiates the combustion process. The basic combustion equation is as stated below: CxHy[g] + zO2[g] = xCO2[g] + (y/2) H2O[g] + energy

While the source of carbon is CH4, the equation will be as follows: CH4[g] + 2 O2[g] = CO2[g] + 2 H2O[g] + energy

In most of the cases, the bigger carbon chains are broken into smaller chains and the reaction stated above is the final combustion reaction. Combustion can be of two types. They are as listed below: • incomplete combustion and • Complete combustion. During an incomplete combustion, the carbon of the source hydrocarbon is not completely burnt, and so, carbon monoxide is generated. On the other hand, in a complete combustion, the total amount of carbon available is burnt.

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The combustion of oil and natural gas occurs at the same process. The liquid oil gets vaporized due to the extreme heat, and the reaction takes place in the gas form. But as coal is extracted in solid condition, the combustion process of coal is a little different. Fossil fuels are sued in a wide range of ways. But depending on the purpose and type of energy delivered, the types of energy conversion can be classified into two major types: •

Transforming the chemical energy into heat and finally in mechanical energy • Transforming the chemical energy into heat and finally in electricity. As a standard example of the first process, an internal combustion engine can be described. A special type of internal combustion engine is also used to generate electricity. It is known as the gas turbine.

3.5 INTERNAL COMBUSTION ENGINE Internal combustion engine is that type of heat engine where the fuel is burned in gaseous form, and the heat created from the fuel is utilized in generating mechanical energy. Heat generation occurs when the fuel is combusted in the presence of oxidizer (oxidizer is an element or compound with the capability of oxidizing any element. In the case of an internal combustion engine, it is generally air) in a chamber completely separated from the outer environment. This chamber is known as the combustion chamber. There are three types of internal combustion engines. They are as follows: • The spark ignition engine • The diesel engine and • The gas turbine Though engines are varied depending on their characteristics and work types, there is a standard structure of an internal combustion engine.

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Figure 3.18 A standard structure of an internal combustion engine https://patentimages.storage.googleapis.com/US8261548B2/US0826154820120911-D00000.png

Engine operating cycles There are two basic types of engines basing on the operating cycles. They are the two-stroke engine and the four-stroke engine. The combustion cycles of these two kinds of engines are as below:

Combustion cycle of four-stroke engine The cycle of this type engine is known as the four-stroke cycle. There are four strokes or stages of the cycle. They are as follows:

Figure 3.19: Combustion cycle of a four-stroke engine (spark ignition engine)

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http://philschatz.com/physics-book/resources/Figure_16_03_04.jpg Figure 3.20: Combustion cycle of a four-stroke engine (diesel engine) https://image.slidesharecdn.com/icenginefinalppt20150216105225150403072050-conversion-gate01/95/icengine-24-638.jpg? cb=1432553413



An intake cycle: In this stage, the piston of an engine comes down, and fuel enters the combustion chamber over the piston. • A compression stroke: The piston moves up, compressing the gaseous fuel and air of the combustion chamber. At the end of this stroke, controlled explosion or combustion is conducted (using the spark plug in a petrol engine), and the pressure increases rapidly. • A power stroke: Extreme heat and pressure are created due to the combustion; the piston comes down again at an extremely high speed. Combustion is technically the oxidation of the hydrocarbons of the fuel present in the combustion chamber. • An exhaust stroke: The piston moves upward, and the burnt exhaust gas leaves the combustion chamber. On the other hand, a two-stroke engine conducts the energy conversion in two stages. They are as follows: •

A compression stroke: The stage starts with the exhaust and inlet ports get closed. The cylinder moves upward and compresses the fuel and air of the combustion chamber. At the end of this stroke, combustion is initiated.

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A power of expansion stroke: The piston moves downward, and the exhaust port opens due to the decreased pressure. The inlet port opens when the exhaust gas flows out, and internal pressure falls due to the reduction of the amount of gas present in the chamber.

Figure 3.21: A two-stroke engine structure http://2.bp.blogspot.com/--gIgNmihpuM/UC3-E_R8fCI/AAAAAAAAAGQ/ aHzNE9iReEs/s1600/2+stroke. JPG

The extreme pressure and heat created by the combustion transforms into mechanical energy and moves the piston. The piston is built in a way that the movement of the piston rotates a driveshaft. This rotation of the driveshaft rotates the wheels of the vehicles the engine is installed in when the engine is connected to any type of automotive. In other cases, the shaft is connected with the working hand with a belt, and the rotation of the shaft makes the working mechanism of the system to work. By connecting this type of engine to an electromagnetic source, electricity can be generated at a limited amount. This type of electric source can be used in establishments requiring a comparatively lower amount of output. The gas turbine is different from the spark ignition and diesel engine. In this type of engine, gas is subjected to an isentropic compression and an isobaric combustion. In an isobaric combustion, the pressure of the system and the gas stays constant. But the temperature rises hugely and the high temperature generates the controlled explosion. This technique is known as the Brayton cycle. The below diagram shows the standard procedure of the Brayton cycle.

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Figure 3.22: The Brayton cycle http://www.nuclear-power.net/wp-content/uploads/2017/04/Brayton-cycle-example-calculation.png? c3bb24

The heat generated by the engine and the flow of the gas runs the turbine and generates electricity if the turbine is connected to an electrical circuit. There are different types of gas turbine engines in function at present. They are as follows: •









Jet engines: Jet engines are the gas turbines designed to produce thrust from the exhaust gas or by using a turbine to accelerate airflow. They are generally used in aircrafts and rockets. Turboprop engines: This type of engine is also used in aircrafts. These engines rotate the propellers of an aircraft using the gas flow which creates the necessary lift for the aircraft. These engines are generally used in small aircrafts. Aero-derivative gas turbine: These turbines are used in the production of electricity. These engines are more capable of adapting to sudden changes of voltage compared to the industrial sources of electricity as they are smaller and lighter in size. Axillary gas turbines: These turbines are used in axillary power units. This type of power unit is smaller than the conventional engines as well as more efficient and much less noisy. These engines use the rotation of the propellers of a small turbine to generate electricity. Industrial gas turbines for power generation: Industrial gas

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turbines use the mechanical power achieved from the chemical power of the fuels and generate electricity. These types of power generators can be used in big but mobile devices as well as in the power grid to generate necessary electricity.

Environmental impacts of Fossil Fuels Fossil fuels contain deep environmental impacts. The carbon footprint created by the fossil fuels is extremely hazardous for the entire planet. The diagram below shows the source of carbon dioxide generated from human sources.

Figure 3.23: Human sources of carbon dioxide https://whatsyourimpact.org/greenhouse-gases/carbon-dioxide-emissions

More than 87% of the carbon dioxide generated by humans is because of the use of fossil fuels. And this huge amount of carbon dioxide is accelerating the greenhouse effect every moment. The excessive heat received from the Sun is getting trapped by the huge amount of carbon dioxide gas storing on the upper layers of the atmosphere. Most of the heat radiating on the surface of the Earth that comes from the Sun is getting trapped into the atmosphere rather than being able to radiate into space. This excessive heat is destroying the temperature balance and the ecological balance of the planet. Due to the greenhouse effect, the average temperature of the Earth is going to increase up to 3°C within next twenty years. This increased temperature would cause the frozen ice of the polar areas to liquefy and increase the surface level of the seas. As a result, more nearly half of the world’s land would be permanently flooded. It is not only the use of fossil fuels, but the negative natural effects also start from the very first stage of the extraction process of the fossil fuels.

CHAPTER 4

SOLAR ENERGY

CONTENTS 4.1 The Source of the Solar Energy................................................................................. 69 4.2 Energy Source of the Sun......................................................................................... 73 4.3 The Ways Solar Energy is Sustained.......................................................................... 75 4.4 Alternative Technologies of the Conversion of Solar Energy...................................... 99

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(Energy irradiated by the Sun is known as the solar energy. Solar energy is the primary source of all the sources of energy available at the Earth. In this chapter, the source of solar energy, generation process of solar energy, concepts concerning the harnessing technologies, and the technologies developed for harnessing solar energy will be discussed) Solar energy is the energy that is achieved from the sun through radiant light and heat. This energy is the most significant source of renewable energy. Technically, all the energy that is available on the planet Earth is initially generated in the form of solar energy. Solar energy is being harnessed using both natural processes and with the help of modern technology. In natural techniques, plants harness the energy radiated by the sun and then stores it in the form of chemical energy through the process of photosynthesis. On the other hand, solar panels which convert the solar power into electricity are a well-established way of harnessing the solar energy. Solar energy is the result of nuclear reactions on the surface of sun where the hydrogen molecules are constantly converting into helium atoms releasing a single electron as well as generating an extreme amount of energy. As the nuclear reactions are also being used in the nuclear power plants to generate energy in the form of electricity, the concept of nuclear reactions will be discussed in some detail in the nuclear energy chapter of this book. Solar energy can also be considered as the initial source of the fossil fuels. Fossil fuels are the result of living organisms being treated with extreme temperature and pressure for thousands of years, and the energy that was stored in the bodies of the living organisms was actually achieved harnessing solar energy. Sun is the primary source of energy for the planet earth. Due to the constant nuclear reactions occurring on the surface of the Sun, it radiates an extremely high amount of energy. Though the Earth is 149.6 million km away from the Sun, the average power density on the upper surface of the atmosphere of the Earth is 1366 w/m2. This amount is more or less static and known as the solar constant. The radius of the Earth is measured to be as (2π × 107)m. And so, the total amount of radiation that reaches the atmosphere of the planet Earth can be calculated using the equation stated below. Total solar radiation reaching the surface of earth = 1366 × (4/π) × 1014 W = 1.73 × 1017 W.

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Though the atmosphere receives more or less the equal amount of radiation, the energy reaching the surface of the planet Earth varies hugely due to the curvature of the planet.

4.1 THE SOURCE OF THE SOLAR ENERGY The source of the solar energy is the Sun. In fact, it is the main source of all the energy that the planet Earth contains. The Sun is a star of the Milky Way galaxy. It is 1390000 km in diameter, and the mass of the star is 1.98930 kg. The temperature of the Sun is 5800 K on the surface and 15,600,000 K in its core. All the stars are classified using letters and numbers to indicate their comparative heat. The classes are O, B, A, F, G, K, M. O identifies the hottest stars while M identifies the coldest. The sun is marked as G2 which makes it one of the mid-ranged stars on the basis of temperature. The Sun is one of the largest stars of the Milky Way galaxy. It is in the top 10% of the stars while mass is considered and the average diameter of the stars of the Milky Way galaxy is less than half of the Sun’s.

Figure 4.1: The source of solar energy, the Sun. http://nineplanets.org/images/thesun.jpg

The Sun formed approximately 4.6 billion years ago due to a gravitational collapse of matter from a molecular cloud. The major portion of the cloud was centered and formed the sun, while the remaining portion created the rest of the solar system. It is currently at its middle age of its life-span. The Sun is the center of the solar system of which the Earth is in. The extreme heat is an indication that the Star is incompletely gaseous form. It is, in fact, a perfectly round geometrical object made out of hot plasma. The

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Sun contains 99.86% of the mass of the whole solar system. The sun mainly is formed by hydrogen and helium gas where hydrogen contains 74.9% of the mass and helium covers about 23.8% of the mass. The remaining 2% mass is much heavier elements; most prominent of them are oxygen, carbon, neon, and iron. The table below shows the components and their amount present in the Sun in percentage.

Table 4.1: The elements present in the Sun https://qph.ec.quoracdn.net/main-qimg-d10f3b06be315bf1f364b93a6048028b

All the elements of the Sun are in a gaseous state. Though the complete star is made out of gas, there is a drastic fluctuation in the temperature and pressure from the atmosphere to the core of the planet. Depending on these differences, the Sun can be divided into six layers. They are as mentioned below from the innermost to outer direction. • The core • The radioactive zone or radiative zone • The convection zone • The photosphere • The chromosphere • Transition region and • The corona These layers can be primarily divided into outer layers and inner layers. Inner layers are the layers under the surface of the sun where the outer layers are above the surface.

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Figure 4.2: Layers of the Sun

Figure 4.3: A cutout of the sun showing the inner and outer layers https://sites.google.com/a/ellingtonps.net/www-the-galaxy-net/_/ rsrc/1468741392413/layers-of-the-sun/Layers%20of%20the%20sun.jpg? height=400&width=400

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The innermost layer of the Sun is the core. The core contains up to 25% of the Sun’s total radius or solar radius. The temperature of the core reaches close to 15.7 million Kelvin while the density is generally 150 g/cm3 which is 150 times more than the density of water. The core layer rotates faster than the immediately upper layer known as the radiative layer. It is the core layer where the production of energy through nuclear reaction takes place, and hydrogen molecules turn into helium molecules releasing a huge amount of energy. The core is the only place where the energy production takes place. Radiation is entirely nonexistent at about 30% distance from the center of the sun. On every second, the nuclear reaction takes place 9.2 × 1037 times. During this time period, 3.7 × 1038 protons weighing nearly 6.2 × 1011 kg of hydrogen turn into helium. During this reaction about 7% of mass converts into energy. And so, the amount of energy created in the core of the Sun is about 3.846 × 1026 Watts per second. The upper layer of the core is the radiative zone. This zone is really dense, and the movement of energy is languid through this layer. The radiated energy takes more than 170,000 years to transfer past this layer. This layer rotates slower than the inner core of the sun. This is one of the thickest layers. It contains 45% of the suns inner radius. The next layer of the Sun situated on the radiative layer is the convective zone. This layer does not have a static rotation rate; rather, the rotating velocity frequently fluctuates. The sudden changes in the characteristics of the rotation as well as the difference within the rotation velocities create a thin transition layer within these two layers. This thin layer is known as the Tacholine. This thin layer is the reason behind the Sun’s magnetic field. As the name suggests, the energy starts being transporting through convection process through this layer. The comparatively cooler gases flow to the inner border of the layer, absorb heat from there and flow upward, transporting the energy to the surface of the Sun. The gases rapidly cool down when they get closer to the surface, or the photosphere and the density of the gases increase back. So again, the gases flow down to the border of the radiative layer and receive energy. In this process, the whole convective layer stays operational. The temperature on the upper boundary of this layer reduces down to 5700 K only, and the density also decreases nearly 3000000 times. The photosphere of the sun is considered to be the surface layer of the sun. This is considered as the surface as it is the most profound layer that reflects waves of the visible waveband and so is directly observable. This

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layer is about 400 km thick. This substantial thickness causes a variation in the temperature. While the temperature at the lower surface is close to 6500 K, it reduces to 4000 K at the upper surface. This difference in the temperature makes it look brighter in the center and gradually darker to the limbs. Granulation covers most of the photosphere. The thickness of this layer is not constant rather rapidly fluctuating. The next layer is the chromospheres and is a part of the Sun’s atmosphere. The layer starts at about 400 km above the surface and exists till the height of 2100 km. This layer has a significant difference compared to the layers below. While all the previous layers have a higher temperature on the lower surface and much lower temperature on the higher surface, it is entirely opposite in this layer. The temperature of the lower surface is about 4000 K which is identified as the temperature minimum. On the other hand, the upper surface has a temperature of 8000 K. Technically over the surface, the temperature rises with the distance gradually increasing from the surface toward the atmosphere of the Sun. The lower temperature or the temperature minimum allows the molecules of several elements to exist in a nonreactive form. Over the chromosphere, there is a thin layer having a thickness of only 100 km known as the transition layer. The naming indicates the extreme rise in the temperature within this small layer of space. Temperature rises from 8000 K to 500,000 K within the transition region. The next layer is the final layer of the Sun. This layer is called the corona. It starts at about 2100 km from the solar surface. The upper limit of corona fluctuates so frequently that it is nearly impossible to define the upper surface. The corona has a lowest temperature of 500,000 K which can rise above 106 K. The corona is generally invisible in naked eyes. But it can be seen during a solar eclipse.

4.2 ENERGY SOURCE OF THE SUN The energy that is created in the core of the sun is solely by nuclear reaction in which a hydrogen atom releases neutron and turns into a helium atom, creating a huge amount of energy. The energy is generated from the reduced mass of the hydrogen atom. This phenomenon can be described through Einstein’s statement about the transformation of mass into energy. His statement is as mentioned below: “If a body gives off energy ΔE in the form of radiation, its mass diminishes by ΔE/c2. Because whether the energy

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withdrawn from the body becomes radiation or else makes no difference, we might make a more general conclusion that the mass of a body is a measure of its energy content; If the energy changes by ΔE, the mass changes accordingly by ΔE/c2” (Einstein, 1946). According to the statement stated above, if the initial mass is m0 and the final mass is m1, then the change in the mass Δm = m1 − m0. And so, the energy emitted due to the change in the mass will be, ΔE = Δmc2.

Radiometric Properties Radiometry is a topic of optics. This discussion helps the measurement of light. As in most of the cases, solar energy is absorbed and converted into electricity, and the energy is received in the form of sunlight, it is vital to be able to measure the radiometric properties accurately. The amount of energy available in per unit time or the power of a source is important in solar science, not the total amount of energy. If the amount of power received is P, then P = A Ω Lecosθ Here,

A = total area of the surface Le = radiance

And (θ, φ) is the coordinate of the surface relative to the source. Again, Ω = θ φ sin θ

Blackbody Radiation If any component is heated, it starts glowing at a specific temperature. The glow is reddish initially and gradually becomes yellow. Heating the glowing object further causes it to emit electromagnetic radiation which is identified as thermal radiation. Thermal radiation is the carrier of the solar energy from the Sun’s atmosphere to the atmosphere of the Earth. A blackbody is an element that absorbs all the energy it receives regardless of the wavelength and the angle of the waves of the radiation. As it is not existent in the natural environment, all the elements that exist reflect a certain amount of energy that is radiated upon it. And it can be calculated using the standard properties of a blackbody.

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4.3 THE WAYS SOLAR ENERGY IS SUSTAINED Solar energy is the fundamental source of energy used by the whole solar system. On the Earth, all the energy that is being used primarily was received as the solar energy. Solar energy is harnessed using both natural and artificial ways.

Natural Phenomena Sustaining Solar Energy The most frequent way the solar energy is sustained is the photosynthesis of the living green plants. Plants are the only living entities with the capability of generating the nutrition necessary for the whole living entity of the planet. And to generate nutrition, it uses photosynthesis. Trees absorb carbon from the environment, necessary minerals from the soil with its roots, and then create hydrocarbons with the help of chlorophyll in the presence of sunlight using sun’s thermal radiation and creating new chemical bonds. So, in short, it absorbs the thermal radiation and stores it in the form of chemical energy.

Figure 4.4: A natural way of sustaining solar energy, photosynthesis

In this technique, carbon dioxide is transformed into oxygen in a process called carbon fixation. The energy absorbed from the solar radiation is used in the form of free electrons to split carbons from carbon dioxide, create new chemical bonds, and form carbohydrates. The general standardized equation of the photosynthesis process was first developed by Cornelius Van Neil. The equation is stated as below: CO2 + 2H2A + photons → [CH2O] + 2A + H2O

carbon dioxide + electron donor + light energy → carbohydrate + oxidized electron donor + water

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Here, the electron donor is generally an oxygen ion. And so, this equation can be stated as below: CO2 + 2H2O + photons → [CH2O] + O2 + H2O

Some plants do not use water as an electron donor; in those cases, arsenate is used. CO2 + (AsO3−3) + photons → (AsO3−4) + CO

Carbon dioxide + arsenite + light energy → arsenate + carbon monoxide Carbon monoxide can be used to develop other compounds in subsequent reactions. The more detailed light-dependent reactions, which transform the solar energy into chemical energy is as mentioned below: 2 H2O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+ + 3 ATP + O2

The drawback of this process is that the solar energy of all wavelengths cannot be used. Specific types of plants absorb and synthesize and store energy conveyed by different wavelengths.

Artificial Techniques for Sustaining Solar Energy The artificial way of synthesizing the solar energy is the PV technology. Photovoltaic technology is also known as the solar technology that uses solar panels to convert solar power into electricity. The symbolic name PV is derived from the process of the technology which turns photons (P) into electricity or voltage (V). Traditional solar panels are built using silicon. These panels are generally flat and really efficient. The next generation of solar panels is known as the second-generation solar cells. These cells are also known as the thin film solar cells, as they are built with non-silicon materials such as cadmium telluride. Due to the structure and characteristics, they can be used for operating multiple purposes. The most recent type of panels uses high-efficiency PV materials which provide higher efficiency with a lower amount of materials being required. Solar thermal energy is another technique of sustaining solar energy. While PV technique sustains the solar radiation, this process uses the laws of thermodynamics to attain and sustain the energy. Another artificial technique of storing solar energy is in the form of solar fuels. In this process, the energy is transferred into chemical energy and then utilized.

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4.3.1 Synthesizing Solar Energy Using Photovoltaic Effect Short history of development of Solar Cells Solar cells are generally considered to be a modern invention, but actually it is quite an ancient technique. It is the seventh-century BC where the first use of Sun’s energy with the help of magnifying glasses to create fire can be found. After this invention, ancient Greek and Roman civilizations improved this mechanism and started using more developed concentrating mirrors designed for generating fire from the Sun’s energy. The discovery of photovoltaic effect was achieved by Alexandre– Edmond Becquerel in 1839. After this, a French inventor Augustin Mouchot developed solar power steam engines using solar collector for the first time during the 1860s and 1870s. After the development of the idea of photoelectric effect by German physicist Heinrich Hertz in 1887, harnessing solar energy was considered as a possibility for the first time. The modern solar cell development started after 1953 in the Bell Laboratories in the United States. The first solar cell was developed in 1954 by three scientists working in Bell Laboratories named Daryl M. Chapin, Calvin S. Fuller, and Gerald L. Pearson. It was a silicon-based panel. After this, many other companies started their research in developing silicon-based solar panels to operate as the power source of the planned earth orbiting satellites. The Vanguard 1 was the first artificial satellite to have solar power harnessing system with solar cells. It was the fourth satellite made by humans.

Figure 4.5: A satellite powered by solar power

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https://userscontent2.emaze.com/images/aa10b89c-a38c-414e-b5504958d37a351c/b9263d03-e2b9-488a-9118-a24b4ad380e7.png

The research of the development of solar power using had a boost during the energy crisis of the 1970s. The first thin film solar cells were developed in 1980. It was based on copper sulfide–cadmium sulfide junction instead of silicones. That type of solar panels had 10% conversion efficiency compared to the conventional ones of that time. In 1985, the University of New South Wales in Australia showed another new type of solar panels with 20% efficiency. These cells were built with crystalline silicon. In 1991, École Polytechnique fédérale de Lausanne in Switzerland, dye-sanitized solar cell was developed by Michael Grätzel and his coworkers. It was the first of its kind at that time which was one kind of photoelectrochemical system having a semiconductor placed in between an electrode and a photoanode. The semiconductor was built based on molecular sensitizers. On the last decade of the 20th century and the first decade of the 21st century, there have been multiple worldwide investments in the development of this technology, and as a result, in 2012, the global energy production through solar energy passed 100 GWp with an annual growth of 40%. PV Effect

The most efficient way of synthesizing solar energy through PV effect is using solar cell. In a solar cell, the solar radiation is used to create a potential difference on the junction of two mediums created with different materials. This technique is quite similar to the photoelectric effect of generating electricity. In 1905, Einstein discovered that photoelectric effect could be defined by assuming the existence of photons in the light. Photons are considered to be really small but a well-defined energy carrier. The energy contained by these photons can be calculated by using the formula stated below: E=hv Here, E = energy contained by the photon, h = Planck’s constant, and v = velocity of the light. The PV technique can be divided into three distinct stages. They are as follows:

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The materials forming the junction absorb the photons and as a result, electric charge is generated. The junction receives photo-generated charge in a separated manner The charges generated from the photons are consumed by the charge.

4.3.2 Basic concepts required to understand PV technology Basic Concepts of Electrodynamics Though electricity and magnates are known concepts from a really distant past, the interrelation between them was invented not a long time ago. The relation between them is known as electromagnetism. The relation can be easily described by identifying their sources. Electricity is the result of the existence of charge in a system, and a system is blessed with a magnetic field when it contains unstable charge or current. So, if there is an object containing electric charge and it starts transferring to anywhere, it will show magnetic power. Moving charges can transform electricity into magnetic energy, and a magnetic field can initiate electricity. It was James Clerk Maxwell, who was the first to successfully establish the relation within electricity and magnetic energy using equations. He published his equations during the period 1861–1862. These equations are stated below: • • • • Here,

Gauss’ law for electricity: ∫ E dA = q/εo Gauss’ law for magnetism: ∫ B dA = 0 Faraday’s law of induction: ∫ E ds = dΦB/dt Ampere’s law: ∫ B ds = µ0i + (1/c2) d/dt (∫ E dA)

E = Electric field B = Magnetic field ρ = charge density μ0 = permeability

c = speed of light By using these equations, Maxwell established the existence of electromagnetic waves and calculated that the speed of the waves is exactly

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equal to the speed of light. And so, using this relationship, he described light as an electromagnetic wave.

Electromagnetic Waves Electromagnetic waves can be described using the formula stated below: E − (n2/c02) (d2E/d2t) = 0

where E = (d2/dx2) + (d2/dy2) + (d2/dz2) The angular frequency can be measured with the equation stated below: Ω = 2πv = 2π/T Here, T = 1/v is the time period in seconds. If the number of waves can be identified with kz and it can be calculated using wavelength λ, λ = 2π/kz = 2πc/nω = c/n v

The properties of electromagnetic waves can be stated as below: •

• •

The electric and magnetic vectors tend to be perpendicular to each other while being perpendicular to the vector expressing their propagation. Electromagnetic waves are transverse waves. The ratio of electric and magnetic waves of an electromagnetic wave is constant and depends on the material of the medium.

PV technology and its working mechanism Silicon materials are one of the most important materials in the PV technology. The major types of silicone materials used can be listed as below: Crystalline silicon (c-Si), used in traditional, conventional, wafer-based solar cells: • • •

Monocrystalline silicon (mono-Si) Multicrystalline silicon (multi-Si) Ribbon silicon (ribbon-Si), currently this type of silicone is not in use Not classified as crystalline silicon, used in thin film and other solar cell technologies: • •

Amorphous silicon (a-Si) Nanocrystalline silicon (NC-Si)

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Protocrystalline silicon (PC-Si) Other non-silicon materials, such as CdTe, CIGS Emerging photovoltaics Multi-junction solar cells (MJ) commonly used for solar panels on spacecraft for space-based solar power. They are also used in concentrator photovoltaics (CPV, HCPV), an emerging technology best suited for locations that receive much sunlight.

Crystalline Silicon Solar Cells This type of solar cells is built using the crystalline form of silicon. Crystalline silicon can be of two types. They are: • •

Multi-crystalline silicone: This type of crystalline silicon is a combination of several smaller crystalline silicones. Mono-crystalline silicone: This type of crystalline silicon is a single continuous crystal, most frequently used in making solar panels.

Figure 4.6: Multi-Si (left) and mono-Si (right) https://en.wikipedia.org/wiki/Crystalline_silicon#/media/File: Comparison_solar_cell_poly-Si_vs_mono-Si.png

The atoms are arranged in specific repetitive patterns in crystalline silicon. These patterns are completely different in different directions. The general density is about 2.3 g/cm3 and has a diamond structure. The atomic structure of crystalline silicon is shown in the image below:

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Figure 4.7: Atomic structure of a crystalline silicon http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/imgsol/sidia2.gif

Production of Silicon Wafers Silicon crystalline is used in the form of a wafer in the conventional solar cells. The production process of mono-crystalline silicon wafers is as below: Generally the wafer containing the lowest quality is known as the metallurgical silicon which is made from quartzite. The silicon dioxide present in the mineral is used to produce silicon wafers. The simplified overall reaction can be stated as below: SiO2 + 2C = Si + 2CO

The silicon achieved through this reaction can be dried off and turned into powder and is 98% to 99% pure. A higher graded wafer can be created from the powder of metallurgical silicon. The powder is put into a reactor and heated in the presence of hydrochloric acid. The reaction is as mentioned below: Si + 3 HCl = H2 + HSiCl3

Silicon found in this way is nearly 99.9999% pure.

PV Systems PV systems are the necessary physical setups of the PV panels by which they absorb the solar energy and transform it into electricity. There are several types of PV systems that can be used depending on the demand for power. From a small and simple setup to generate enough electricity for small electric motors to large power plants capable of

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producing multiple MW of electricity is possible to establish. Depending on the configuration, these systems can be of three types: • • •

Standalone system, Grid-connected system, and Hybrid system.

Standalone Systems This type of system is also known as the off-grid PV systems. These off-grid systems are the simplest and the smallest option of the three. This system is completely depended on solar power. Along with a PV module, the system contains a load only or a battery to utilize and store the generated energy. Controllers can be connected to disconnect the batteries when the batteries are fully charged as well as to have the desired amount of energy stored in the battery constantly. As the module can attain energy only during the daytime, the battery should be powerful enough to store enough energy which can be used during the night time. A slandered diagram for a standalone system is shown below:

Figure 4.8: A standalone PV system

The system contains solar panels which are most likely to be mounted on the roof of the establishment the system is meant to supply the power, or open space receiving enough sunlight. The photovoltaic modules produce necessary electricity in direct current (DC) form. One or multiple batteries can be connected to store the generated electricity. A charge controller is also attached to prevent the overcharging of the batteries. An inverter specially designed for a specific system is also required to transform the Dc current into Ac current. The system can also be designed without a battery. In that case, it is a simple DC PV system with a direct connection between the PV module and the machinery. This type of layout is mostly used for single machines which are meant to run on daytimes only.

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Grid-Connected Systems The grid-connected system is the most frequently used and the most popular PV system. It is most suitable for large-scale electricity production. This type of system is directly connected to the electricity grid. The system is connected to the grid through an inverter which plays the role of converting the DC current created by the PV module into AC electricity. The inverter is generally connected to the distribution board, and the voltage is strictly controlled to match exactly with the Ac current of the grid. As the electricity is directly supplied to the grid, there is no requirement for batteries to store the energy. In several new systems, energy storing capacity is also installed to store extra electricity produced.

Figure 4.9: Grid PV system without any battery backup https://www.researchgate.net/profile/Anne_Gerd_Imenes/publication/268487729/figure/fig21/AS:295302155259918@1447416928709/Figure-27-Main-components-in-a-grid-connected-PV-system-without-battery-reserves.png

Figure 4.10: A grid PV system power station

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https://inhabitat.com/wp-content/blogs.dir/1/files/2016/02/crescent-dunes-02. jpeg

Hybrid Systems A hybrid system is a compound structure of electricity production. These systems contain a grid PV system combined with an additional source of electricity such as oil or gas generator wind generator. As this system combines several different types of power sources, they require more sophisticated and controlled collection, transformation, and distribution system. These systems are much more complex than the previous two options. If the PV module is connected with a diesel or gas generator, the generator cannot be started before the energy generation through PV system reaches a specific level, and it should be turned off if the electricity generation from the PV system falls under the specific level. Otherwise, the lack of balance within the power from two sources would cause the PV system to fail. Batteries can be involved in this type of system where the generator works as a backup power source to maintain a continuous power delivery at a steady voltage.

Figure 4.11: A standard layout of a hybrid power system https://en.wikipedia.org/wiki/Solar_hybrid_power_systems#/media/File: Hybrid_Power_System.gif

This type of power system has been developed due to the fluctuating supply of solar energy. The generators work as a backup source to maintain the balance of the supplied power. Using batteries is recommended for optimum utilization of the sources. Though diesel generator is efficient in the context of cost, the most efficient type of grid system is a combination

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of solar PV system with wind turbines. This combination is beneficial for remote places where transporting diesel is a costly option. This type of systems can work without being connected to the main grid, supplying power to a specific area or establishments.

Necessary components for a PV system As the amount of electricity generated from a single cell is limited due to the size of the cell and the delivery is not constant due to many external influences as well as the variation in the amount of electromagnetic wave reaching the system, it is not possible to achieve enough electricity from a single cell. For this reason, multiple cells are connected in order to build a module known as the solar module or PV module. The main instrument for a PV system is the solar panels. But several other components are necessary for achieving a working setup. All these systems are known as the “balance of system” together. Different types of equipment are required depending on the type of the system. A grid system will require several different types of equipment compared to the ones needed in a standalone one. The most important types of equipment that are a must in a balance of system are as mentioned below: •







It is a must to have a mounting source so that the modules can be placed facing the sun. It is better if the mounting source contains revolving facility to have optimum angle within sunlight and the surface of the module regardless of the change of Sun’s position throughout the year. Energy storage is also essential equipment. As sunlight is not available during night and when the weather is not optimum, the storing facility will ensure continuous energy supply during those times when enough sunlight is not available. Batteries are used as the storing medium. A DC to DC converter is also important. The voltage of the generated electricity fluctuates, and a sudden change in the voltage can cause problems including the failure of the complete grid. And so, it is a must to maintain a static voltage all the times, and a DC–DC converter ensures that. The electricity generated is DC current. On the other hand, the grids generally contain AC current. It is essential to have inverters

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in the system to transform the DC current into AC currents. Many systems contain an inverter that has a converter combined with it to ensure the constant flow of electricity. High-end inverters also include a maximum power point tracker to track and keep the PV voltage and current independent and unaffected by the battery’s voltage and current. Another important equipment is the cables. Cables are the connecting medium of these different types of equipment as well as the grid or the electric machines with the whole system. It is essential to maintain the quality and standard of the cables to prevent any breakdowns. If the cable is not up to par, then a sudden surge of power can burn the cable and cause devastating disaster.

Location Issues Position of the sun It is extremely important to have detailed information about the position of the Sun in order to have maximum power possible. The movement of Sun and the changes in the comparative position of earth and sun can be projected using a sphere with an arbitrary radius. This specially designated sphere is known as the celestial sphere. Using this sphere, the position of all the celestial objects can be calculated. The results are found in angles, and using the horizontal coordinate system is the most convenient way. The position measuring process can be described using the diagram below.

Figure 4.12: A horizontal coordination system showing the measuring technique of the celestial sphere

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The position of the sun can be measured and expressed with two angles. In the diagram above, the elevation of the center of the sun or the solar disk is expressed with the letter (altitude). The elevation is an angular elevation. The range of the angular elevation can be expressed as −90° ≤ ≤ 90°. Here the negative value would indicate that the position of the object is below the horizon at the moment the measurement is conducted and so the celestial object is not visible. The azimuth A is the angle within the line of sight projected on the horizontal plane and due north. It is counted eastward, such that A = 0°, 90°, 180°, 270° correspond to due North, East, South, and West, respectively. Its angular range is A ∈ [0°, 360°]. In another standard of measurement, 0° is considered to be south, and then the measurement is conducted eastward. Meridian is the line connecting the geological North Pole and the South Pole of the earth.

Instead if using spherical coordinates, Cartesian coordinates can also be used. Cartesian coordinates would indicate the position in reference to X, Y, and Z axes. These two coordinating systems can be adjusted using the formulas stated below: X = cos cos A Y = cos sin A Z = sin cos cos 0 = sin In the celestial sphere, X2 + Y2 + Z2 = 1. The relative sun paths at different places on earth are inserted below to show the operation of this technique more easily.

Figure 4.13: The Sun path at 0° latitude and 0° longitude http://andrewmarsh.com/apps/releases/sunpath2d.html

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Figure 4.13: The Sun path at 23.40° latitude and 84.80° longitude http://andrewmarsh.com/apps/releases/sunpath2d.html

Irradiance on a PV module Measuring the irradiance on a solar module is extremely important in setting up the system. In determining the irradiance on a PV module, the following measurements are important to be conducted: •

The angle of incidence (AOI): It is the angle of the sun and the solar module at a certain time. And as the Sun is not a point source radiating waves at every angle, at a certain time, multiple waves would reach on the panel from multiple points of the Sun at different angles. The generalized equation to measure the angle of incidence can be expressed as below: G = I sin (θ + as) Here,

G = the direct irradiance on the module I = direct normal irradiance as = Angular elevation from the surface θ = Tilt angle •

Shading: Shading is the phenomenon when a solar module does not get the electromagnetic waves it was supposed to have due to any type of object disrupting the waves. Shading can disrupt the complete production process by creating fluctuation in the voltage and current. If the length of the object creating the shading is l, then the length of the shadow will be as follows: d = l (cos θM + sin θM cot as + cos (Am − As)) θM = angle of tilt

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AM = angle of azimuth of the PV module as = altitude of the Sun As = azimuth of the Sun •

Direct and diffuse irradiance: Sunlight gets scattered due to various reasons. The scattered rays of the sun reach the surface of the earth as defused light. On the other hand, the light rays that did not get scattered reach the surface as direct irradiance. Direct irradiance can be calculated using the equation stated below: GMdir = IedircosZ

The modules will be affected by two types of diffused irradiance: diffused from the sky and diffused from the ground. The sky view factor will have to be considered to compute the irradiance diffused from the sky. Sky view factor (SVF) = (1 + cos θM)/2

While the amount of radiation defused from the ground can be calculated using the equation below GMground = GHI × α × cos (As) × (1 − SVF)

GHI is used to express horizontal irradiance, and it can be calculated as stated below: GHI = DNI × cos (as) × DHI

Here, α = albedo of the ground. So the total irradiance on a PV module can be stated with the equation below: GM = GMdir + GMdif + GMground Components of PV systems

Apart from the PV module, there are several other components which are important for the system. These elements are as follows: • • • • •

Maximum power point tracking Treatment of PV converters Batteries Charge controllers Cables

Maximum Power Point Tracking This component is actually not an independent element. Rather it is generally

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supplied as a part of the DC-DC converter of a charge controller or a PV inverter. MPPT is uniquely utilized in the field of PV electronics. The behavior of a solar cell at an illuminated state can be measured using an I–V curve. If several cells or modules are interconnected, they do not change the pattern of the curve though the overall voltage is changed. This curve is also independent of the temperature. The operating point is a specific voltage and current in which the PV module operates during the whole operating period. When the temperature and the irradiance are comparatively constant, the value of the voltage and the current is unique and the value can be found from the I–V curve. At this operating point, the output can be derived as: P = I × V In order to generate the maximum power attainable, the V should be of the highest point of the P–V curve, and this highest point is known as the maximum power point. If the characteristics of I–V and P–V curves change, the maximum power point also changes. And determining the maximum power point is known as the maximum power point tracking or MPPT. MPPT can be of two types as mentioned below: •

Indirect MPPT: In this technique, the maximum power point is determined by using a coded algorithm. • Direct MPPT: In this technique, the direct date derived from I–V curve is used. Indirect MPPT can be conducted by following two methods: •

Fixed voltage method: The operating voltage is set and adjusted after a specific time period, and this technique is conducted by assuming that regardless the season of the year, irradiance would be the same. This assumption makes this method less efficient in most of the cases. This method works only at the places where the temperature difference between different seasons is minimum. • Fractional open circuit voltage method: This technique is the most frequently used indirect MPPT method. This method considers the irradiance to be variable, and so the approximated value of V in maximum power point value is not constant. It can be calculated using the equation below: VMPP = k + VOC Here, k is a constant depending on the material of the surface. For crystalline

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silicon, the value ranges from 7 to 8. VOC is the open circuit voltage that can be easily measured and sued to determine the voltage at maximum value point. Direct MPPT is the technique where the actual current voltage and power present in the system are measured to calculate the optimum values for maximum power point. This system is actually much faster than the indirect method. There are several algorithms for calculating maximum power point using direct MPPT. They are as follows: •



Perturb and observe algorithm: This algorithm is also renowned as the hill climbing algorithm. In this algorithm, the voltage is provided with the current perturbation of the system. This fluctuation causes the power output to change. Now, if increasing the voltage causes the power to increase, it can be stated that the operating point is still lower than the maximum power point. But if the increase in voltage causes power output to decrease, then it can be stated that the operating point is higher than the voltage of MPP. Same decision can be made if decreasing voltage causes the output to increase. The observations and the results indicated by them can be shown as below:

Table 4.2: Perturbation of the voltage of a PV system to attain the MPP using P & O algorithm Fluctuation of the voltage Positive Positive Negative Negative

Change in power Positive Negative Positive Negative

Next fluctuation find MPP Positive Negative Negative Positive

to

The biggest problem with this technique is that the achieved operating point is almost never the exact MPP rather a value really closes to it. Also the rapidly changing illumination causes this algorithm to suffer. •

G = I/V

Incremental conductance method: In this technique, the conductance is used to determine the maximum power point. The conductance of an electrical component is expressed with the letter G and can be calculated using the equation stated below:

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Here, I is the current and V is the voltage of the system. As the slope of the V–P curve at MPP is 0, it can be stated that, dP/dV = 0 This equation can be further modified as stated below: dP/dV = d(IV)/dV = 1 + (dI/dV) By accepting really small sampling steps, it can be stated that dI/dV = ΔI/ΔV ΔI/ΔV is known as the incremental conductance, and I/V is considered as the instantaneous conductance. Now the relation between V and VMPP can be described as below: V = VMPP when ΔI/ΔV = −(I/V)

Again, V > VMPP when ΔI/ΔV < −(I/V); And, V < VMPP when ΔI/ΔV > −(I/V)

Power electronics A PV system must be designed in a way that it achieves the capability to achieve the maximum power possible from the system at every given moment. An ideal converter attached to a PV system would be able to ensure that. The term inverter refers to two different components. While one type of inverter is the device used to convert the DC current into AC current, the other term is to describe the amount of unit energy produced. It can either contain an MPP tracker, a DC–AC converter, or a DC–DC converter. In a grid system, an inverter is directly connected to the PV array which converts the produced DC current into AC current. Along with that, it also contains an MPPT system. On the other hand, when the inverter is used in a standalone system, it is connected to the batteries. In this case, the inverter does not need to contain any converter or MPPT system. In the standalone systems, these inverters can also be used in charging the batteries as well as in preventing overcharging. It can also prevent the batteries getting discharged; by doing so, it helps to extend the lifetime of the battery. The inverters should be designed to be able to fulfill the following requirements properly •

The efficiency level of the inverter needs to be really high so that

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the system achieves the ability to deliver the highest possible output constantly. • To handle the potential within the generator and the earth, the system should have special facilities included. • Safety features to prevent system failure are a must for the component. • Electromagnetic interference controlling mechanisms is a really important component that should be included with the inverter. • The effect of the electromagnetic field on living entities will also have to be considered and so an electromagnetic field restricting option is a must-have component for the inverter. • An inverter should be designed to be able to operate at high temperatures. • The inverter should be capable of operating for a long period of time regardless the condition of the environment. Most acceptable operating period ranges from 10 to 25 years depending on the harshness of the environment. • The component should have proper mechanisms to minimize the noise. • It is extremely useful for the users of the system if the component is equipped with a monitoring system for the complete PV system. The most frequently used inverters can be of four types: •





Central inverter: This is the simplest form of inverter setup. In this system, the PV modules are connected in a series and several strings generate a PV array. The array is directly connected to an inverter that ensures highest power output. A standard central inverter is shown in Figure 4.14. Microinverter: Microinverter contains a completely different structure. In this system, the modules do not form an array, rather they are connected to the inverters individually or a few modules are connected to an inverter in a series connection. These inverters can work under several hundreds of watts. Generally, a two-staged conversion process takes place, initially boosting the voltage of the DC current and later transforming into AC current. String inverter: This type of inverter is a combination of several different types of inverters. In this type of setup, several PV modules connected in series connection are used to create a PV

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string and a three-staged conversion process is adapted to change the type of the current. Central inverter with optimizers: This type of inverter is a combination of the central and the microinverter. Every single module is connected to separate and own optimizer boxes where PMM is tracked and DC-DC voltage conversion is conducted. As every single module runs at their own maximum power point which varies due to various types of external influences, the whole system is much efficient and a higher amount of power can be achieved.

Figure 4.14: Different forms of system architectures used in different PV systems

Batteries Batteries are one really important element of the complete system. It transforms the electricity into chemical energy and stores it only to be retransferred into electricity when it is required. As electricity cannot be achieved during nighttimes using PV systems, it is essential to have sufficient energy stored during the daytimes to be able to keep the electricity supply functional. There are different types of batteries available for storing energy. Among them, the following are the most frequently used. • • •

Lead acid batteries Nickel-metal hydride batteries Nickel–cadmium batteries

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The structure and energy storing and delivering process of different types of batteries will be discussed in detail in the Energy Storage chapter of this book.

Charge controllers Charge controllers are used for controlling the currents flowing inward and outward the batteries from the PV array and the grid or the instruments. Its main work is to ensure the voltage and current of the battery to be at a controlled and specific range to prevent overcharging or discharging.

Cables Technically it is the quality and the condition of the cables that finally determine the overall performance of the PV system. They also help to separate and identify the flow of DC and AC current as well as prevent misconnection within these two types of current. In order to make the wiring less dangerous, much less confusing and extremely convenient, color conventions have been introduced. It establishes a specific color code for the specific type of electric current. The color specified for the specific type of electric flow varies depending on regional borders where there are specifically set rules defining every single types of wirings. PV systems contain parts having both AC and DC currents. A standard color convention for DC cables for a PV system can be listed as mentioned below: •

Red-colored wires are specified to be used to connect the positive (+) contacts of different systems within themselves. • Black-colored wires are specified to be used to connect the negative (-) sides of different components among each other. • To connect several modules in an array, the most commonly used cable is the black-colored cables as the colorful cables lack stability against UV radiation. In order to indicate the polarity, dedicated and marked connectors are frequently being used. These connectors can be delivered along with the flying cables as the same unit. The color variation used in determining AC current is more frequent than it is in the determining process of DC current.

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Differently colored cables as indicators used around the globe are described in short. •

In the countries who are the member of the European Union, blue-colored cables are used for neutral lines, green-yellow as the protective earth, and brown as the phase. • In the United States and Canada, silver-colored cables are used for neutral. In order to indicate the protective earth cables, greenyellow, green or colorless bare cables are used, and black-colored cables are used to identify the phase. • In the South Asian countries such as India and Pakistan, blackcolored cables are used for neutral, green-colored cables are used to indicate protective earth, and blue-, red-, or yellow-colored cables are used to identify the phase. Every single electric element contains resistance. This should be kept into consideration while using the cables, and the ones with minimum resistance should be used to minimize the resistive losses. If the resistance of the load of the system is RL and the resistance of the cable is Rcable, the power loss due to the resistance of the cables can be calculated using the equation stated below: Pcable = I × ΔVcable = I2Rcable

Here, ΔVcable is the change of voltage across the cable and can be calculated using the equation stated below: ΔVcable = V(Rcable/(RL + Rcable)

4.3.3 Basic stages of designing a Standalone System In order to set up a simple system, the following seven stages should be followed. • • • • • • •

Determine the total load current and operational time. Add system losses. Determine the solar irradiation in daily equivalent sun hours (ESH). Determine the total solar array current requirements. Determine the optimum module arrangement for the solar array. Determine the battery size for recommended reserve time. Choose a suitable charge controller.

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Load Profiles Loads can be of different types, and the system will have to be designed according to the required type of load and adapt to the most suitable load profile. Load profiles can be of four types: • •

• •

A simple load drawing a static and specific amount of power getting off the system throughout the whole operating time. A more complex profile where the current does not seem necessary to be constant, and their fluctuation shows a specific peak amount. Loads that can be switched on or off at the same time. Loads that can be switched on or off at different times.

Figure 4.15: Different types of load profile

Inverter efficiency while designing a grid system While designing a grid-connected PV system, it is extremely important to have the highest possible inverter efficiency. The most frequently used model for this is the Sandia National Laboratory model. According to this model, the relationship within PAC and PDC can be stated as below: PAC = ((PAC0/(A − B)) − C (A − B)) × (PDC − B) − (C (PDC − B) 2

Here, the coefficients of A, B, and C can be expressed as below: A = PDC0 (1 + C1 (VDC − PDC0)) B = Ps0 (1 + C2 (VDC − PDC0)) C = C0 (1 + C3 (VDC − PDC0)) Here,

PAC = AC power output from an inverter based on input power and

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voltage (W). PDC = DC power input to the inverter, typically assumed to be equal to the PV array maximum power (W). VAC = DC voltage input, typically assumed to be equal to the PV array maximum power voltage (V). PAC0 = Maximum AC power “rating” for the inverter at reference or nominal operating condition, assumed to be an upper limit value (W). PDC0 = DC power level at which the AC power rating is achieved at the reference operating condition (W). VDC0 = DC voltage level at which the AC power rating is achieved at the reference operating condition (V). PS0 = DC power required to start the inversion process, or selfconsumption by the inverter, strongly influences inverter efficiency at low power levels (W). C0 = Parameter defining the curvature (parabolic) of the relationship between AC power and DC power at the reference operating condition; the default value of zero gives a linear relationship (1/W). Ci = Empirical coefficient allowing PDC0 to vary linearly with DCvoltage input, default value is zero (i = 1, 2, 3, 1/V). This system counts the following losses into consideration: •

• •

Consumption of energy by the inverter itself. A certain amount of DC power is required in order to initiate the process and it is considered as the consumption of energy by the inverter. The decrease in power due to the drop of the fixed voltages and the semiconductors. Ohmic losses.

4.4 ALTERNATIVE TECHNOLOGIES OF THE CONVERSION OF SOLAR ENERGY Though PV technology is the most efficient system for converting the solar energy into usable electricity, there are several other technologies serving the same purpose. The major difference is that these technologies convert the solar radiation into a different form of energy while PV systems convert the solar radiation into electricity. The most frequently used alternative techniques are as stated below:

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• •

Solar thermal energy: In this process, the thermal energy of the solar radiation is absorbed using the laws of thermodynamics. Solar fuels: In this technique, the solar energy is stored in the form of fuel for future uses.

Solar Thermal Energy Solar thermal energy is the technique of using the thermal energy of the sunlight using the laws of thermodynamics. Heat is the type of energy that is being transferred. Every single molecule of all the objects over the temperature of 0 K displays movement or shaking. Because of this movement, a special type of kinetic energy is created within the molecules and atoms of the element. This kinetic energy is defined as heat. Heat is identified by the symbol Q and as it is one form of energy, the measuring unit of heat is Joule. If two different materials contain a difference in heat and those elements are kept in touch with each other, heat will be transferred from the warmer body to the cooler body. The transfer of heat will keep continuing till the temperature of the two bodies become equal. This heat can transform from the warmer to the cooler element using two forms: sensible heat and latent heat. And the active form of heat transfer is decided by the physical characteristics of the elements. Sensible heat is the form of heat that is caused by the fluctuation in the temperature of an object. It can be calculated using the following equation: Q = mCp (T2 − T1). Here,

Q = the amount of heat absorbed by the body of the component m = mass of the element in consideration Cp = the capacity of the element to store heat into its unit mass (T2 − T1) = the difference in the temperature levels.

Latent heat is the form of heat which does not change the temperature of the element when it is absorbed or released by the subject material. Rather, the physical form of the element gets changed as the result of the change of the heat. For example, water at 373 K temperature absorbs latent heat and turns into vapor, and water at 273 K temperature releases latent heat to become ice. The amount of latent heat absorbed or released can be expressed using the equation stated below:

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Q = mL Here, L is the specific latent heat for the specific material. The heat transfer can be conducted using three techniques: conduction, convection, and radiation. Several mechanisms can be designed using the properties of heat transfer to absorb the heat of the solar radiation and convert it to other forms for use. A prime example of this technique is a solar water heater. This setup is a combination of a solar collector system, a system for transferring the energy and a storage tank for the water. The collector system which is technically a solar array is the major part of the whole system. This array absorbs the solar radiation and then converts it into heat. Later on, the heat is driven into a transfer fluid known as the heat transfer fluid. The fluid collects the heat and then transports the heat to the heat collector. The heat collector then absorbs the heat and stores it for future use. But the heat is generally directly used and is hardly kept stored for a long period of time. The amount of heat created by the heater depends on the size, capacity, and characteristics of the array, the capacity of the collector, the capacity of the water storage, the amount of sunshine available on the array, and the demand of the hot water.

Figure 4.16: A solar water heating system https://energy.gov/sites/prod/files/styles/borealis_default_hero_respondxl/public/solar_water_heater_illustration.jpg? itok=MC2eWYQU

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A solar water heater can be of different types depending on the structure of the setup. Depending on the characteristics of the heating fluid, it can be divided into two types. They are shown in the diagram below:

Figure 4.17: Classification of solar water heating system depending on the character of the transfer fluid

A closed-loop system is the one where the liquid that is used to transfer the heat and the liquid that is heated are different liquids. In this case, the fluid collecting the heat from the collector only transports the heat to the exchanger and keeps circulating. On the other hand, in an open loop or direct system, the liquid transporting the heat and the one getting heated are the same. In this case, the liquid does not need to go through a heat exchanger; rather it goes straight to the output system. Another classification can be conducted depending on the transportation process of this heat transfer technique. The systems can be divided into the following two types • Passive induction and • Forced induction In the passive induction process, no motor is used to help the fluid to transport through the system. Rather, this type of system depends on the natural convection of the fluids to transfer the heat. On the contrary, a forced induction system contains motors that help the fluid transportation through the heating system.

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Concentrated Solar Power Concentrated solar power (CSP) is a system where water is vaporized using the heat generated from the solar radiation. Then this water vapor is used to run steam turbines which generate electricity. Though the initial CSP systems were built with the purpose to run small electric machines, largescaled power stations generating up to 80 megawatts of power have been established recently. The most suitable place for this type of setup is the desert regions of the planet where most of the solar energy reaches the surface in the form of direct radiation. The most important part of the system is a solar collector which collects the radiation and transfers the energy into heat. A storage system stores the water which is used to run the turbine. The collected heat is directly transferred to a boiler which vaporizes the water and generates steam. The steam is then transferred to a heat engine which is generally a steam turbine. The turbine transforms the heat into mechanical energy. This process of generating mechanical energy is known as the Rankine cycle; the naming was conducted after the inventor of the system, William John Macquorn Rankine. The diagram below shows a standardized CSP system.

Figure 4.18: A concentrated solar power system. https://www.engineering.com/Portals/0/BlogFiles/tlombardo/CSPTrough. JPG

CHAPTER 5

WIND ENERGY

CONTENTS 5.1 The Source of the Energy....................................................................................... 106

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(Wind or airflow is one of the most common phenomena on Earth. Airflow contains kinetic energy which can be harnessed and used. In this chapter, the characteristics of wind flow, potential achievable energy from wind, and the technologies developed to utilize this source of energy will be discussed) Wind energy is the process of harnessing the power of airflow. The energy is harnessed using wind turbines to turn the mechanical and kinetic energy of airflow into electricity. Wind energy is one of the renewable energy sources. Wind energy is becoming more and popular due to the environmentfriendly, renewable, and cost-efficient characteristics. Though the initial setup process is costly, it does not require any type of additional facilities or raw material cost after the setup is conducted. And so, in the long run, this source of energy is efficient. As airflow is the only source of energy in this system and sufficient airflow cannot be found everywhere, it is not possible to install this system at any place. Huge open places with very little or no vegetation or the coastal areas and islands are the most appropriate places for installing this type of energy sustaining system. Due to characteristics of airflow, wind power from a single turbine is not stable. The power out varies depending on the airflow present at the place. In order to achieve a static and specific amount of power, several turbines are set up and connected together.

5.1 THE SOURCE OF THE ENERGY Unlike other types of energy discussed in this book so far, this system does not use any type of stored potential energy to provide the sustained energy. The source of the power is the kinetic energy achieved by air when it generates motion. Technically, solar energy can be considered as the main source of this type of energy. Solar radiation causes the temperature of the air to increase. As air contains a very low capability of absorbing heat, on the upper portion of the atmosphere, the temperature difference due to solar radiation is very little. But the surface of the earth has a much higher capability of consuming solar radiation and containing heat. The surface of the Earth absorbs a certain portion of the solar energy and heats up, the layer of air adjacent to the soil absorbs the heat radiated from the surface, and the temperature of the layer of air adjacent to the surface rises up. But the temperature gradually reduces with increasing elevation.

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As the density reduces with increasing temperature, the place where the Sun’s solar energy reaches straight without any interruption makes the adjacent air warmer. The air loses density and so the layer of air above is suddenly much thicker than the warmer layer of air. Following the law of convection, warmer and less dense air travels upward really fast, leaving a vacuum at its previous place. In order to fulfill the vacuum and adjust the fluctuation of pressure, heavier and cooler air from nearby places start traveling to the vacuum and this is how airflow is created.

5.1.1 History of the Use of Wind Energy Using the power of airflow is one of the most ancient sources of energy. Humans started using the power of wind by developing sails for their boats. Moreover, the use of wind power to grind grains and pump water is a technology that has been being used for more than two thousand years. This technology is known as the windmill.

Figure 5.1: Windmill http://www.travelling-australia.info/MainGraphics2005/P056240195Bz-750. jpg

The most renowned examples of the use of windmills are the Dutch windmills and the farm windmills used in the United States. At the primary stages, these windmills used to have multiple rotors. Building materials used to be wood or metal. Generally, these windmills were built as water pumps. Even after the invention electricity and generators, these windmills were used to generate electricity too. The first windmill designed and used to generate electricity was introduced in 1887. The wind generator was

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situated in Scotland and it was designed by Prof James Blyth. The turbine had cloth made sails and it was only 10 meters high. The power generated by the generator was powerful enough to provide enough electricity to run the farmhouse in which it was built as well as the required electricity to run the scientific research. Thus, the holiday cottage of Prof James Blyth can be described as the first house to have electric supply generated by wind power. Even after the use of electricity became a common and affordable option, the usefulness of electric generator powered by windmills did not diminish. In the primary development stage of electricity, it was extremely hard and costly to establish power plants or even establish transmission lines. At the same time, the whole world was shifting to electric machinery. At that stage, electricity generator powered by windmills became extremely handy. The designs of these windmills powering standalone electricity generator were altered and upgraded and were vastly different. The changes were conducted to achieve higher efficiency. These new design contained propeller-like two or three rotors. Multiple rotors were less efficient and were not quite capable of generating enough electricity.

Figure 5.2: Modern wind turbine http://www.isustainableearth.com/wp-content/uploads/2013/08/wind-energyengineer-jobs.jpg

But, electric connections became available to even the most rural areas during the early stages of the 20th century. During that time period, windpowered electric generators became obsolete. But the recent environmental concerns, as well as the rapidly diminishing storage of fossil fuels have brought the air-powered electric generator back into the account.

Wind Farm The concept of the wind farm is comparatively new but really significant in the development path of wind power sustaining technologies. A wind farm

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is a place where several wind turbines are installed to generate electricity. The first wind farm was established in the United States during 1982. After that, many European countries adopted the idea and established their own wind farms. The biggest wind farm is presently situated in China and the combined production of electricity from those farms is more than 282 GW. The amount does not account for the electricity production of small individual wind turbines. The chart below shows the gradually increasing slope of the wind capacity of the wind power generators.

Figure 5.3: Global production of energy using wind power. http://www.gwec.net/wp-content/uploads/2012/06/Global-Cumulative-Installed-Wind-Capacity-2001-2016.jpg

One of the biggest advantages of a wind farm is that the land between the turbines can be used for other purposes, such as agriculture. The ground space can also be utilized to set up solar panels in order to achieve the solar energy along with wind energy. The following chart shows the biggest wind farms and their respective capacity: Table 5.1: The largest wind farms in the world Name of the farm

Country

Capacity (MW)

Gansu wind farm

China

6000

Alta wind energy center

The United States

1550

Muppandal wind farm

India

1500

Jaisalmer wind park

India

1064

Shepherd’s Flat wind farm

The United States

845

Roscoe wind farm

The United States

782

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Horse hollow wind energy The United States center Capricorn Ridge wind farm The United States

736

Fantanele cogealac wind Romania farm Fowler wind farm The United States

600

Whitelee wind farm

539

The United Kingdom

662

600

Along with vast open place, these wind firms require minimum wind speed of 4.5 ms−1. The most suitable places are selected depending on the wind atlas to achieve the highest output possible. The turbines more or less contain the same structural design. A horizontal axis turbine with three rotors with a long base is the most standardized design.

Figure 5.4: Gansu wind farm, China http://www.circleofblue.org/wp-content/uploads/2011/02/TS-Gansu305_1000x559.jpg

Though these wind farms require an extremely high amount of space, the turbines and the complete setup do not occupy a lot of ground space. The necessary space is mainly required to have proper clearance for the rotors to be able to rotate without any kind of obstacle to prevent a collision. As a result, the ground space can actually be used for other purposes. For example, the Gansu wind farm, containing more than a thousand turbines, can be considered. The ground space available is used for agricultural purpose.

Offshore Wind Farm Offshore wind firm is a specific type of wind farm. In order to generate

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electricity, this type of farm is constructed over the surface of the water rather than the land. Due to the presence of higher wind flow over the water bodies, these farms are capable of generating higher output. And as the surface of water landscape is completely flat, there is nearly zero disruption in the airflow. Waters covering more than 75% of the Earth’s surface make this type of farms more convenient. The only drawback is the higher construction cost.

Figure 5.5: An offshore wind farm http://assets.inhabitat.com/wp-content/blogs.dir/1/files/2012/11/Siemens6MW-Wind-Turbine-537x402.jpg

In spite of the higher setup cost, offshore wind farms are becoming more popular and more countries are being interested in setting up this type of power plant. This type of farm has enabled the comparatively smaller countries that do not have sufficient flat plane to establish wind farm but do have sea or big rivers within its geographical area to have wind farms. Even the countries with hilly terrains can now set up wind farms using offshore wind turbine technology. By evaluating the approaches of setting up offshore wind farms worldwide, it has been assumed that by the year of 2020 global energy production through offshore wind farm will exceed 75 GW.

5.1.2 Calculation of the Power of Wind The energy of wind is a form of kinetic energy as it is generated because of motion. If the mass of the air is considered to be m and the velocity v, then the kinetic energy generated by the air mass will be,

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Ek = (½) mv2.

And we know, mass m = Av t ρ Here, A is the area covered by the air v = velocity of the air t = amount of time passed ρ = density of the air By using this equation, it can be stated that, Ek = (½) A ρ t v3

And the power of wind can be calculated using the following equation. P = E/t = (½) A ρ m v3 The amount of specific power available at the site would be = (½) ρ v3

5.1.3 Power Extracted from the Wind It is not possible to extract all the power available to be extracted. The actual amount of power extracted by a wind-powered turbine is the difference between the power of the upstream and that of the downstream winds. The difference can be calculated using the equation stated below: P0 = (1/2) (flow of mass per second) (v2 − v02) Here,

P0 = mechanical power extracted by the rotor, i.e., the turbine power output, v = upstream wind velocity at the entrance of the rotor blades, and v0 = downstream wind velocity at the exit of the rotor blades. Mass flow rate of the air would be as follows:

Mass flow rate or the flow of mass per second = ρ A (v + v0)/2

And so, mechanical power extracted by the rotor of a turbine would be: P0 = (1/2) (ρ A (v + v0)/2) (v2 − v02)

5.1.4 Air Density The amount of power generated from the wind is largely depended on air density. And as air density is not static all the time, it requires necessary adjustments. Air density can be calculated with the help of the following equation: ρ = P/RT

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Here, P = air pressure R = gas constant T = temperature of the air in Kelvin scale Using the standard air pressure at sea level at SATP (1 atm and 25°C temperature), air pressure at varying heights can be calculated using the equation stated below ρ = ρ0 − (1.194 × 10−4 Hm)

here, Hm is the elevation of the selected site.

5.1.5 Wind Characteristics Wind is the flow of a specific gas at a large scale. In the case of the planet earth, the term wind indicates the flow of air. Wind is created by the fluctuation of pressure in the environment. As the source of energy generated from this source is solely depended on the airflow, it is extremely important to understand the wind characteristics. One of the most important concerns is the global circulation of wind. Wind follows a specific and well-defined pattern of flow. There are three cells in each hemisphere in which air circulation is conducted throughout the entire atmosphere of a certain specific area. These three cells are known as Hadley cell, Ferrel cell, and polar cell. The global pattern of wind is shown in the diagram below:

Figure 5.6: Global wind flow pattern

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https://laulima.hawaii.edu/access/content/group/2c084cc1-8f08-442b-80e8ed89faa22c33/book/chapter_4/global_winds2.gif

Types of Wind Turbines Wind turbines are generally of two types. This classification is conducted depending on the way the blades and the shafts are set up. • •

Horizontal axis Vertical axis

Figure 5.7: classification of wind turbines

Horizontal axis turbine This type of turbines is the most frequently used type of all the types available. The generator, along with the rotors and the alternator, is set up on a tall tower and the setup is done in a way that all the major components are parallel to the ground.

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Figure 5.8: Horizontal and vertical axis wind turbine http://www.cntimar.com/photo/nd3566905-the_contrast_of_horizontal_axis_ wind_turbine_and_vertical_axis_wind_turbine_eml.jpg

Vertical Axis Turbine In this type of turbine, the shaft and the blades are connected to the generator vertically to the ground. All the major mechanisms are situated at the surface and the rotors cover the whole length of the complete system, being able to utilize ground hogging airflows. Vertical turbines can be divided into further two types—drag-based turbines and lift-based turbines. The lift-based vertical turbine is the efficient option between these two options.

5.1.6 Wind Power Harnessing System (Wind Turbine) The wind turbine is the complete mechanism of harnessing energy from wind and transforming it into electricity. Though there are two different types of wind turbines with completely different structural designs, the components of the systems are exactly the same. And so, the most commonly used option, a horizontal axis wind turbine will be considered while discussing the complete setup of this system.

System Components Every single wind turbine contains several basic components. Those components are mentioned below.

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Tower structure A rotor with two or three blades attached to the hub of the system. Three rotors are the most frequently used option. A shaft with mechanical gears. Electricity generator Yaw mechanism Sensor and controlling system

Figure 5.9: Basic structural diagram of a wind turbine http://energyinformative.org/wp-content/uploads/2013/10/wind_energy_figure.png

Figure 5.10: Detailed structure and mechanisms of a wind turbine http://windeis.anl.gov/guide/basics/images/largeturbine.gif

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There are two types of brakes included into the system. One is known as the starting, which controls the speed of the turbine to maintain a static flow of energy. The second type of brake is known as the eddy current which is utilized to shut down the system completely and to keep the rotors static. This brake is generally used while servicing or during emergency situations to avoid a hazard. There are several additional types of equipment required in the modern wind turbines. They are as follows: Sensors: The controllers are required to have complete knowledge about the situation of the operating system at every moment. These sensors continuously provide detailed information about all the mechanical and electrical parameters of the system. Generally, there are several hundred sensors in a single turbine. And so, the number of sensors installed to monitor the complete system properly is extremely high. • Anemometer: This component measures the wind speed continuously and feeds the controller with the data. • Stall controller: This system is installed to prevent the turbine from breaking down. It receives the data provided by the anemometer and releases the brakes when the air velocity exceeds 8 miles per hour. It shuts down the turbine and the rotor if the wind speed exceeds a certain limit to prevent the rotors from overstressing as well as the generator from overheating. • Control electronics: It is generally a computer. Receiving, processing, and providing the operators with all the necessary information every moment. • Power electronics: These components are in the system to ensure that the delivered power is within the required parameters. • Battery: It is used to store the extra energy produced and utilize it when energy generation falls. This mechanism prevents energy wastage and increases efficiency. • Transmission link: Technically it is the setup connecting the turbine to the grid. There are several small yet extremely important components which are installed on the tower within the turbine and the rotors which are extremely important for the whole operation. Those components are as follows: •



Nacelle: This is an empty shell sitting behind the rotors. They are

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connected to the hub of the rotors and the shell is constructed on the tower. This shell connects the rotors with the tower and provides support. The outer body of the shell works as a removable cover for the components situated inside the shell. It contains a lowspeed and a high-speed shaft, a gearbox, a generator, a controller, and a brake. They are designed in such way that working on the components inside the shell is extremely easy. Low-speed or slow-rotating shaft: This is a long shaft that is installed right behind the rotor and directly connected to it. The rotation of the rotor blades turns this shaft. The rotation of the shaft stays within 30 to 60 revs per minute. Brake: It is generally a disk brake. It is connected to the rotor via the low-speed shaft and is capable of bringing the rotors to a complete standstill if necessary. The brakes can be connected to a hydraulic, mechanical, or electrical controlling system. Gearbox: Gearbox connects the low-speed shaft with the highspeed shaft. It contains step-up gears which enhance the 30–60 rpm of the low-speed shaft and rotates the high-speed shaft at a much higher rpm. High-speed shaft: It is a shaft with a really short length that connects the generator to the gearbox. This shaft achieves its rotating velocity from the slow-rotating shaft and rotates at 1200 to 1800 rpm. The gears of the gearbox help this shaft to have the higher rev per minute. Controller: This component has got a microchip installed with all the necessary commands for all possible situations. It observes the performance of the generator every second and adjusts the whole setup according to the achieved data. Vane: Vane or wind vane is a small device connected to the nacelle at the opposite end of the rotors. It measures the wind direction and sends the information to the Yaw drive. Yaw drive: Yaw drive is a big gear situated on the tower and connecting the nacelle with the tower. There is a motor connected to the drive named Yaw motor. Yaw drive receives the data fed by the vane and changes the direction of the whole nacelle along with the rotors to keep the direction of the setup and the wind direction on a straight line. Downstream wind turbines do not

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require this component as the direction change of the rotors is conducted by the airflow.

Tower The tower is the base structure of the complete turbine system. It is a tall generally circular-shaped structure which works as the support for the rotors and the nacelle. There is a Yaw circle at the top of the tower. The nacelle sits over the yaw circle. In the primary development period, the tower used to be from 20 to 50 meter long. In the modern turbines, the height of the tower is generally the same of the diameter of the rotors. But in the midsized and smaller turbines, the length and rotor diameter proportion changes. Generally, the length of the tower plays an important role in determining the power output the turbine. The graph below shows the relation between the height of a tower and its output.

Figure 5.11: Relation within the height of a tower and the output of the tower

Different types of materials are used to build the towers, but steel and concrete are the most preferred ones. Both tubular and lattice shapes exist. Generally, the shape and material of a tower are depended on the geographic nature of the venue. The designs are specially tweaked to reduce the wind resistance and ensure the fluent flow of wind as much as possible. Though there is no specific maximum height, the mandatory minimum height for the towers to be able to generate enough electricity to make the setup profitable is 25 meters. If the tower length is less than this limit, the rotors will be subjected to turbulent air only and energy generation will be extremely poor. Another important concern to be considered while designing is to reduce the vibration. The tower should be able to absorb the vibration created by the rotors as well as the vibration generated from the ground. The THM or top

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head mass is another important concern. The collective weight of the rotors and all the mechanisms that are to be set on the tower head will have to be considered while designing the tower. The tower will have to be capable enough to carry the weight without any problem. A proper wiring system as well as a transportation system to reach the top of the tower for maintenance purposes will also have to be included.

Blades or Rotors Blades are one of the most important components of a wind turbine. In the primary stages, wind turbines used to have multiple blades. But modern turbine designs have ditched the multiple blade concepts for higher efficiency. There are two types of turbines if the number of blades is considered such as turbines with three blades and turbines with two blades.

Figure 5.12: A standard wind turbine blade https://www.siemens.com/global/en/home/markets/wind/turbines-and-services/technology/blades/_jcr_content/chapter-parsys/content/parsys/mediatext_454060616/image.adapt.458.high.jpg/se-01153930.jpg

Modern blades or rotors are designed to work as airfoils to utilize the aerodynamic principles of air and attain as much energy as possible. A tinfoil structure requires the upper side of the surface to be longer while the dimensions of the lower side stay static. This shape lets the blade take advantage of the Bernoulli principle. A lift is generated on the surface of the airfoil by the air due to the difference of air pressure created in the wind flowing over the top and the bottom surface of the blade which is the result of the unique shape of the airfoil. This lift makes the rotors to move and as they are connected to the hub, the rotors achieve a circular motion. Along

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with the lift, this shape generates a drag on the surface of the blade and as it works in the perpendicular direction, it actually slows the blade down. The design is modified depending on the geographic and air behavior of the venue so that the highest lift to drag ratio is achieved.

Figure 5.13: Diagram showing the aerodynamic effects on an airfoil-shaped blade http://www.alternative-energy-tutorials.com/images/stories/wind/alt110.gif

Due to the constantly rotating nature of the rotors and the vibration created by the rotation as well as the friction of the air, these rotors are the most fragile and vulnerable part of the whole system. In order to ensure the continuous optimum performance along with high durability, the building component is extremely important. In the primary stage, the blades used to be built out of metal, but also steels; in addition, it has the tendency of catching rust. Aluminum was chosen to be the perfect material while building the blades. Due to the high durability with extreme strength, they reduce the risk of the turbine system breaking down. Along with that, aluminum being really lightweight makes the rotation much more efficient and increases power output. Recently though, fiberglass has also been used along with aluminum as the building material of the blades. Rotors made out of fiberglass are much stronger while being more than three times lighter than aluminum blades. As a result, using fiberglass has proved to be even more economical and efficient than aluminum blades. In order to achieve exact data about the output of the system, rotor slips and their effect requires measurement. Rotor slip is the situation when the movement of the rotors gets slipped and does not add to the energy input. This occurrence is the result of any type of malfunction in the gearbox as

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well as in any of the shafts. Slip of the rotor is identified with the letter s and can be calculated using the equation below: S = (Ns − Nr)/Ns Here,

Ns = synchronous speed Nr = speed of the rotor

5.1.7 Generator The mechanical power provided by the rotation of the rotors is needed to be converted into electricity in order to turn the harnessed energy into sustained and usable form. This transformation of the form of power is conducted using a DC or an AC generator. These generators can be either induction machine or synchronous machine. But the induction machine is the most widely used type.

Figure 5.14: Basic structure of a rotating or synchronous generator

A magnetic field is generated in both types of generators to create electricity. The angular speed of the rotating magnetic field is called the synchronous speed and is denoted with the letter Ns. and it can be calculated using the following equation: Ns = 60 (f/P) Here,

f = frequency of the stator excitation

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p = number of magnetic pole pairs The amount of voltage induced can be calculated using Faraday’s law of electromagnetic induction. The law states that “The induced electromotive force in any closed circuit is equal to the negative of the time rate of change of the magnetic flux enclosed by the circuit” (Michael Faraday, 1831). From the statement stated above, we can state that, e = −(dφ/dt) Here, e = induced voltage φ = the magnetic flux Circulating current is initiated in the rotor because of this voltage. The measurement of this torque can be conducted using the equation stated below: T =k φ I2 cos φ2 Here,

k = constant of proportionality. φ = magnitude of the solar flux wave I2 = magnitude of induced current in the rotor loops

φ2 = phase angle by which the rotor current lags the rotor voltage.

Speed control As the airflow is not static anywhere at any time, the large modern turbines are facing an extreme variation in the air velocity. Considering the extremely high velocity of air they can face, speed control systems have become really important in the modern systems. These control systems allow the turbines to withstand harsh weathers and help them maintain a constant serve of energy. There is a range of speed control systems in practice. They are mentioned below. •

Yaw and tilt control: As mentioned earlier, yaw control continuously adjusts the rotors direction and keeps it in a straight line to the direction of the airflow. But as the weight of the complete system is really high and the loads create a large amount of inertia, the torque generated from yaw system is really high. This torque creates loud noises and in order to reduce the noises, controlled yaw is the better option. Controlled Yaw restricts and

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controls the amount of yaw to have optimum amount of yaw along with much less noise Pitch control: Pitch control regulates the pitch of the system to keep the power generation constant if the airflow rate changes. Stall control: This controlling process is mainly used to reduce the output from a turbine when the velocity of the wind becomes extremely high. This system uses yaw and tilt control and pitch control collectively. The complete setup is set using these adjustment techniques. The setup is done in a way that the lift reduces while drag increases. The ratio falls down which slows the rotors down. The rotors are kept under the rotation limit by using this technique even if the airflow is extremely high. This technique prevents overstressing of the rotors and so prevents the generator from overheating too. No Control: There are a few systems which contain no control system at all. In this case, the complete system is designed especially so that they can withstand all types of potentially hazardous situation.

Importance of speed control The rotor speed requires being controlled due to three major reasons. They are as follows: • •

To capture optimum energy, To preserve the rotors, the generator, and other electronic equipment facing overloading, and • The control over the rotation of rotors can destroy the complete system by overcharging them if the generator is disconnected from the system. Controlling is a must to prevent this. Speed controls are required for the occurrence of following five situations: •



If the airflow speed is really slow that it cannot turn the turbines fast enough to generate electricity, the rotors are required to shut down completely. This minimum required speed is known as the cut in speed. It is not economically profitable to keep running the rotors under the cut in speed. The constant speed region Cp is another region where speed

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control is required. The control is needed to keep the speed of the rotation of the rotors constant.

Figure 5.15: Different regions requiring speed controls







During the period where wind velocity is really high, the rotor speed is increased up to a certain point. This highest speed is known as the highest constant limit. This limit is calculated depending on the design limit of the rotor blades as well as the complete system. If the wind speed is extremely high and frequently fluctuating, it is necessary to control the speed of the rotor. This type of situation occurs during a gust. The rotor speed is lowered using the brake. The brake is used rather than an electrical control system as decreasing the speed by electrically changing the capacity of the generator would overheat the complete system and burn it. Cutout speed is the highest speed at which the rotors can operate. Above that speed limit, the rotors can get damaged; even the rotor can come off the hub and cause additional damages along with destroying the complete system. If the airspeed reaches the cutout level, the system is shut down and the rotors are brought to a complete halt.

Rate Control The speed of the rotors cannot be increased or reduced at any time without any type of calculation. Rather the rate of acceleration and deceleration requires a lot of matters and concerns to be kept in context and as a result, extensive calculations are required to find the optimum rate of acceleration

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and deceleration at any given time. A sudden change in the rotation can overstress the rotors and the hub, as well as overheating the electrical mechanisms and the gears. The instantaneous difference between the mechanical power produced by the blades and the electric power delivered by the generator will change the rotor speed following the equation stated below: J (dω/dt) = (Pm − Pe)/ω Here,

J = polar moment of inertia of the motor ω = angular motion of the rotor Pm = mechanical power produced by the rotors Pe = electric power delivered by the generator

By integrating the equation above, the equation stated below can be achieved (1/2) J (ω22 − ω12) = (Pm − Pe) (t2 − t1)

5.1.8 Power Transportation to Shore in Offshore Farms The power generated in the offshore farms requires a sophisticated system to transport it to the shore. In general wind farms, the power generated by the sources can be directly sent to the grid. But as offshore firms are constructed over water and water is an excellent conductor and so a potential medium for electrical hazard, special approaches are required to be taken. Generally, offshore farms are equipped with power cables running under water. Most of the turbines of the offshore generators generate 690 V AC current. As it is not possible to set up any substation close to the turbines to establish transformers to step the voltage up, the voltage of the generator and the voltage of the cables will have to be exactly the same all the time. But the offshore firm as a whole operates at a distribution substation voltage level. The substation is situated at the land as close as possible from the turbines. In order to ensure the static voltage, individual transformers are placed under every single tower to step the voltage of the generator up to the voltage level of the substation. In order to achieve minimum power loss, the voltage requirement of the substation is set at a comparatively high voltage. Normally, the required voltage of the substation is around 35 kV. But the requirement of the voltage at the substation level rises with the capacity of the firm. For example, if the capacity of an offshore farm exceeds 350 MW, the transmission voltage will be required to reach over 150 kV; the

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required voltage rises up to 350 kV depending on the system. Generally, the turbines of an offshore farm are connected to each other in a radial configuration. This type of configuration increases efficiency by ensuring the highest amount of air supply available to every single turbine. In this type of configuration, several turbines are connected to a radial arm in a series connection. This type of setup has a big drawback; if one turbine breaks down, the output from all other turbines connected by the same cable will be shut off. This problem can be bypassed using ring formation.

Figure 5.16: Radial layout of wind farm turbines

The cables are not left to float neither they are set to pass through the water. The cables are buried under multiple meters of the surface of the ground under the water in order to prevent damage to the cables caused by sea current and ships and their anchors. But in the areas used by the big ships as traveling routes, the cables are laid in a way that they are at a safe distance from the shipping route. This is done as the anchors of the big ships often reach more than 12 meters into the ground under the water. And as finding multiple safe routes for multiple cables and setting up a single cable through each route is not economically profitable, only one cable is used in most of the offshore farms. Recently, a new technique has been developed in order to substitute the cables. In this technique, power is transferred into hydrogen and transferred to onshore using pipelines. The hydrogen will later be transferred back into electricity. But initial calculations indicate that this technique would turn out to be much costlier than the conventional technique using cables. All the offshore turbine farms have AC cable-based power transmitting system. Though this system has several advantages, they do have a few drawbacks. These drawbacks are stated below:

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The amount of power loss is higher and the rate of loss increases over time. • VAR compensation is required at both ends of the cable, whether by using synchronous machines or static power electronic compensators. • AC current limits the capacity of the cables. For example, the capacity of a polyethylene-insulated XLPE cable is limited to 200 MW with one 150-kV three-phase cable. A wind farm with the production capacity of 1000-MW would require five such cables in parallel, with possibly one more for reliability. In order to overcome these drawbacks, special types of DC cables known as high-voltage DC cables can be used. High-voltage DC cables transfer electricity at an extremely high voltage reducing the disadvantages stated above. Moreover, this type of cables is also useful to the onshore network due to their capability of reducing fault current contribution. The first time HVDC cables were installed as the submarine cable was back in 1954. The cable was 100 km long and connected Swedish island of Gotland with the mainland. The power essentials of the system were 20 MW 100 kV. More developed cables with a power rating of 6300 MW and the highest voltage of 600 kV have been used in modern systems. The utilization of this type of cables requires additional establishments. The most important are the converters. Converters are required to set on both ends of the transmitting system as the current generated by the turbines and the grid current are both AC currents while the HVDC cables transform electricity as DC current. As a result, an AC–DC converter is required at the turbines while on the onshore reception mechanism, a DC–AC converter is required. Due to the extra costs associated with the installation and maintenance of this type of cables, systems generate power under a certain level and the distance of the offshore plant being less than 50 km from the shores will not be economically profitable. But, recently several electronic device developers are offering new types of voltage service converter (VSC). The most notable of them are ABB and Siemens. Utilization of these devices can make using HVDC cables economical.

CHAPTER 6

HYDROPOWER

CONTENTS 6.1 Water Cycle........................................................................................................... 130 6.2 History of The Use of Hydropower........................................................................ 131 6.3 Hydropower Potential............................................................................................ 134

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(Hydropower is the most frequently used renewable source of energy. In this chapter the basic concepts related to hydropower and the techniques available that allow the utilization of hydropower will be discussed.) Hydropower is the power that is created from the energy of flowing water. The energy of running water can be harnessed using different ways and can be utilized for different purposes. The use of hydropower is a pretty old concept and has been used for centuries by different civilizations around the globe. With the development of modern technology, it has become possible to harness the power and turn the kinetic energy of the water into electricity or mechanical power. Hydropower is generated mostly due to the Sun’s solar energy and occasionally the gravitational force of the Earth. And so, the concepts of the evaporation of water due to the Sun’s heat, water cycle, and the gravitational force working on falling water are important to understand while studying hydropower.

6.1 WATER CYCLE The water cycle also known as the hydrologic cycle is a “circular” process by which water keeps transferring through the ecosystem of the planet. This cycle describes and explains the movement of water on the surface, below the surface as well as through the atmosphere. As the total mass of water in the Earth is constant and water is required for every single living being to survive, the water cycle plays an extremely important role in preserving life on the planet. In fact, it is one of the three most important cycles of the complete ecosystem of earth. Due to the solar radiation, water from the sources above the surface vaporizes. Generally, it is the seas that play as the biggest source of water vapor. As nearly 75% of the world’s surface is covered by water and a major portion of it are the seas and oceans, a huge amount of water gets exposed to the Sun’s heat and vaporizes continuously. This vaporized water travels upward and reaches a height where the temperature is relatively low. At that height, the temperature of water vapor falls down under the boiling point and extremely small drops of condensed water generate. These tiny water drops create the clouds. When the combined weight of the clouds becomes heavier than the weight of water, the water drops back on the surface. A considerable amount of water is absorbed by the land surface and keeps the

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underwater sources of water functional. Some important concepts associated with water cycle are mentioned below: •







Precipitation: This is the phenomenon of condensed water vapor being affected by gravity and reaching the surface. Most frequently occurring examples of precipitation are rain, snow, hail, fog, and sleet. Canopy interception: This term is used to indicate the precipitation getting interrupted by the existence of canopy and trees over the ground surface. The interrupted condensed water eventually evaporates again and reaches back to the atmosphere. Snowmelt: The water created by melted snow. Most of the biggest rivers of the world use the product of snowmelt as a major source of water. Runoff: This term indicates the different ways of water flow over the land.

Figure 6.1: The water cycle https://earthobservatory.nasa.gov/Features/Water/images/water_cycle.jpg

6.2 HISTORY OF THE USE OF HYDROPOWER Hydropower has been used for more than a couple of centuries. The primary use of hydropower was using the current of the rivers for transportation. This type of utilization is still used by vehicles using water as their medium

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of movement. But there have been several other ways in which hydropower was used. The use of hydropower began during the Han dynasty. They developed a new type of pot wheel pumps which were hydraulically operated and was ideal for watering the agricultural lands in the hilly areas. During the fourth-century BC, hydropower was used in the Indian subcontinent with the help of water wheels and watermills. During the reign of Romans, they used water-powered mills to produce flour from grain. They also used those mills in order to saw timbers and stones. During the time period of 50 to 100 AD, the use of hydropower in the mines to extract minerals began. In those mines, the wave and the kinetic energy of falling water were used to extract minerals and metal ores from the mining sites. This technique is known as hushing. This technique became quite famous and widely accepted in the mines all around Europe. During the “California Gold Rush,” this technique was improved was evolved into a technique known as the hydraulic mining. During the middle ages, Muslim scholar Al-Jazari developed more than 50 new types of machinery and almost all of them were water powered. Hydropower became the main source of energy during the initial stages of the industrial revolution in Britain. One of the most significant technologies was a water frame developed by Richard Arkwright. During the industrial revolution, steam-powered engines replaced the water-powered mechanisms in most of the big and midsized production plants and factories. But several small production plants kept using hydro-powered mechanisms. Technological advances made several upgrades to the hydro-powered systems. Up until the mid-19th century, most of the devices using hydropower were open water wheel system. But several attempts during the mid-19th century evolved these systems into closed water turbine or water motors. In 1948, James B. Francis developed a new design of turbine with 90% efficiency while he was working as the head engineer of Lowell’s Locks and Canals Company. His mathematically calculated and specifically designed plans enabled the company to build high-efficiency turbines with the ability to make turbines specifically for a production plant-specific water flow quantity. Even after more than 150 years of development, the primary design of the Francis reactions turbines is still being used. The first hydroelectric power scheme was developed in 1878 by William Armstrong. It was a small system, capable of generating enough power to

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light up a single arc lamp. First electric power plant to use hydropower in generating electricity was developed in 1881. It was known as the “Schoelkopf Power Station No. 1,” situated near Niagara Falls. Several new hydro-powered power stations were established within ten years of time and during 1889, there were more than 200 functional hydroelectric power stations in the United States alone. Hydroelectric power plants gained huge popularity and were vastly used by mid- and small-sized production plants for necessary power during the beginning period of the 20th century. By 1920, 40% of the power production in the United States was from hydroelectric sources. With the development and improvement of the hydroelectric power station designs, their dams were developed to serve multiple purposes. In the United States, federal supports were available in developing high-output hydroelectric plants with enormous dams. One of the biggest examples of the upside of the support is the Hoover Dam. When it established in 1928, the electricity output was 1345 MW. The most powerful hydroelectric power station at present is the Three Gorges Dam with the power output capacity of 22500 MW. The United States uses hydroelectricity more than any other country in the world and more than 49% of its renewable energy production is generated from more than 2000 hydroelectric power plants it currently has.

Figure 6.2: The Hoover Dam http://www.history.com/s3static/video-thumbnails/AETN-History_ VMS/21/154/History_Kaiser_Builds_Hoover_Dam_and_Warships_45407_ SF_HD_1104x622-16x9.jpg

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6.3 HYDROPOWER POTENTIAL The basic working outline of hydroelectric power plants is pretty simple. These plants require a continuous inflow of water; the kinetic energy of the water flow is harnessed and transformed into electricity. A height difference between the upstream intake of the power plant and the downstream outlet is a must to keep the flow continuous. In order to calculate the power of flowing water, a uniform water flow is considered within two cross sections of the selected water source. The power of the water can be expressed using the equation stated below: P = γ Q (H + (v12 − v22)/2g Here,

H = Difference in the elevation of water surface within two selected points Q = Amount of water flow within two sections v1 = Average velocity of the first section

v2 = Average velocity of the second section γ is a constant.

In order to calculate the power available from the water flow correctly, the hydrology of the site will have to be considered. Hydrology is the term to indicate the measurement of streamflow of a certain place. The amount of water and the velocity of the stream are not static. It continuously varies on every single day. Averaging the monthly discharges will not be able to provide proper calculation as the value is variable too. And so, a yearly average discharge can be considered but even that value is not constant at all. And so, to calculate the hydropower potential correctly, the criteria mentioned below will have to be considered. •

• • •

Minimum potential power is based on the smallest runoff available in the stream at all times, days, months, and years having a duration of 100 percent. This value is usually of small interest. Small potential power is calculated from the 95 percent duration discharge. Medium or average potential power is gained from the 50 percent duration discharge. Mean potential power results by evaluating the annual mean runoff.

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6.3.1 Hydroelectricity Generation Methods Though the main aim of all types of hydroelectric power plants is exactly the same, it can be achieved following a range of different approaches. The different available methods for generating electricity from hydropower currently in use are mentioned below: • • • •

Run-off river method, Storage schemes, also known as conventional hydroelectric power method, Pumped storage schemes, and Tidal power development method.

Run-off river method This type of hydroelectric power plant uses the instant flow of the water available at a certain moment rather than storing the water flow and having a constant flow. Establishing power plants of this type is economically possible at the tropical regions only where water do not freeze or dry up and there is a certain minimum amount of water flow available all the time of the year. The minimum amount of water supply throughout the whole year would allow the system to be operational all the time and generate a certain amount of minimum electricity throughout the whole year.

Figure 6.3: A run-off river power plant; Chief Joseph Dam, USA https://en.wikipedia.org/wiki/List_of_run-of-the-river_hydroelectric_power_ stations#/media/File: Chief_Joseph_Dam.jpg

As there is no storage facility in this type of hydroelectric power plants, it is not economically profitable to run them every day. They generate a huge amount of energy during the monsoon flows while the power generation falls

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down drastically during sprinkles. This fluctuation in the overall production will have to be accounted for during the planning phase. Moreover, during monsoon periods, the tail water of the rivers can rise over the operating capacity of the turbines as well as the generators of the system and cause the whole system to crash. Precautionary steps are required to avoid these drawbacks. Small reservoirs can be established to hold water for a short period of time. Those reservoirs can hold the water when the water flow exceeds the capacity as well as during the off-peak hours and can be used to generate enough electricity when water flow amount falls down as well as during the peak hours.

Figure 6.4: A simplified diagram of a run-off river hydroelectric power station http://www.eurelectric.org/images/water/figure02_big.jpg

One of the biggest problems with this type of power plants is that finding a suitable place for this type of setup is extremely hard. Another drawback is the environmental impact of this type of setups. Though there is extremely low environmental impact created by the small size setups, the impact is heavy enough to generate concern in the power plant designed to generate a considerable amount of power.

Storage Schemes Most significant characteristic of this type of power plants is the existence of reservoirs. These reservoirs are constructed by building dams across the source river or rivers. These reservoirs are generally really large in size and capable of storing a considerably high amount of water. As the turbines and the generators of these reservoirs have a fixed capacity of generating

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electricity and if the water supply is higher than the amount required to produce that fixed maximum amount of electricity, the mechanical components of the turbines can get overstressed while the generator can overheat. These phenomena can cause a complete system failure and damage the components. In order to prevent all these risks and regulate the power output to a stable amount, these reservoirs preserve the extra water during the monsoon periods and let them into the production system during the periods when the water flow reduces and there is an absence of enough water supply to maintain the predetermined energy output level. This type of system contains an overflow dam system to prevent the reservoirs from overflowing and flooding the surrounding area. These dams also prevent higher pressure being forced on the dams.

Figure 6.5: A hydroelectric power station with storage reservoir; Água Vermelha Dam of Brazil. http://jornal4cantos.com.br/wp-content/uploads/2016/01/Agua-Verm0801-1.jpg

Figure 6.6: A simplified diagram of a hydroelectric power station with storage reservoir

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http://152.87.4.98/power/images/hydro.png

Pumped up storage schemes In this type of power stations, there are two reservoirs built at different elevation levels. One reservoir is built at a higher elevation while the other one is set at a much lower elevation. Both these reservoirs can be developed by building a dam and creating a difference of elevation of the river on its both sides and using the natural area of the river as the reservoirs. But most of the times, the upper reservoir requires proper establishment or flooding can occur. During peak hours of the production process, the water from the reservoir at higher elevation flows through a turbine to the reservoir. The turbine is connected to a generator which turns the mechanical energy achieved by the turbine into electricity. During off-peak hours, the extra electricity generated is transferred to a water pump that pumps water from the reservoir at the lower elevation to the reservoir with the higher elevation. By doing these, the energy wastage is minimized.

Figure 6.7: A diagram of pumped-up storage hydroelectric power plant https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity#/media/File: Pumpstor_racoon_mtn.jpg

When water is transferred to the upper reservoir, the mechanical energy achieved by the rotation of the turbine is transferred to the water in the form of gravitational potential energy. During peak hours, the water runs through the turbine again and the energy is transformed into electricity this time. This technique makes this process highly efficient with higher outputs. Generally, the power saving process is conducted during the night when the demand

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for electricity in the grid is much less. Among these four techniques, this is the most preferred system. Power output from pumped storage hydroelectric power plants established worldwide delivers close to half of the total power delivered by all the hydroelectric power plants. China generates the highest amount of power using this type of power plants and the amount of power generated is 32 GW per year as of 2017.

Figure 6.8: A pumped-up storage hydroelectric power plant; Bath County Pumped Storage Station, USA. https://s3.amazonaws.com/ese-prod/uploads/project/image_1/218/consumersenergy-pumped-storage-facility-located-in-ludington-michigan.jpg

Tidal Power Development Method This type of hydroelectric power plant is completely different from the above three. While all three of the above systems utilize the kinetic power of water flow, this system utilizes the rise of water level of the seas. This system is generally installed at a bay. A dam is built on the connecting point of the bay and the sea. During the high tide, the water level rises, and the water level outside the bay starts increasing. Water passes through the turbines installed in the dams and enters the bay. When low tide occurs, water level falls down and the extra water from the bay flows back to the sea. This water flow can be used too. If more turbines are installed facing the opposite direction or the turbines include generators that can generate electricity by rotating in both directions, electricity can be generated using both water flows.

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Figure 6.9: A simplified diagram of a tidal power hydroelectric power plant.

One of the biggest disadvantages of this type of setups is finding the most suitable location. Finding bays big enough to contain enough water to make the system capable of generating enough electricity but not too big is extremely hard. And for these reasons, there are only a few places around the whole world that are suitable enough to generate enough electricity.

Figure 6.10: A tidal power hydroelectric power plant; Rance tidal power station, France. http://www.power-technology.com/wp-content/uploads/sites/7/2017/09/2-image-Rance.jpg

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Tidal hydroelectric power plants have a huge disadvantage that makes the use of this type of power plants much less efficient. Due to the rotation of earth and moon, the position of moon changes on a regular basis. As a result, the output from tidal power-driven power plants varies on a regular basis. And as tides have a 12.5 hours cycle, it is extremely hard to keep the balance of the power output with the peak and off-peak demand cycle.

6.3.2 Classification of Hydroelectric Power plants Depending on Size Though there is no specifically determined size of the plants to classify them in different sizes, there has been a classification depending on the powergenerating capacity. The standards are set by, Mosonyi (1991).

Figure 6.11: Classification of hydroelectric power generator depending on production capacity



Large facilities: This type of facilities is technically some of the largest power plants in the world while considering all different types of sources. Several hydroelectric power plants have more than two times the capacity of the largest nuclear-powered power plant in the world. Generally, power plants over several hundred megawatts capacities are considered as the large facilities. There are four operating hydroelectric power stations in the world with the production capacity of more than 10,000 MW or 10 GW. These plants are as follows:

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Table 6.1: The largest hydroelectric power plants of the world Rank

Station name

Country

1 2

Three Gorges Dam Itaipu Dam

3 4

Xiluodu Dam Guri Dam

China Brazil and Paraguay China Venezuela

Capacity (in MW) 22,500 14,000 13,860 10,200

Medium facilities: These facilities are considerably smaller than the big facilities. But still, they are capable of providing a hefty amount of energy in the form of electricity. These facilities are most suitable when the grid is designed for an individual city rather than multiple regions. • Small facilities: This type of production plant is most suitable for a small community or individual production plant. Most of the countries and authorities accept the maximum power output of 10 MW to indicate a power station to be identified as a small facility. But in some countries, such as Canada and the United States, hydroelectric power plants with 25 MW and 30 MW production capacity, respectively, are considered as small facilities. The compact design and comparatively higher yield as well as higher availability of suitable sites have made this type of facilities highly utilized one. As per 2008, the production of electricity worldwide using small hydroelectric facilities is at 85 GW; more than70% of that production is conducted by China. The biggest advantage of this type of facility is the usability of the system for different purposes. This facility can be developed as an additional source of power to the main grid. Again, this type of facility can be established as the main source of electricity of a grid situated in isolated areas where providing electricity from the main grid is hard and uneconomical. In short, this type of facility can be used as a standalone source for a small isolated community. Also, this type of system can be used in production facilities as the source of energy. These projects have minimum construction work and small reservoirs and so they have less impact on nature compared to the bigger options. •



Micro facilities: A microhydroelectric power plant contains generation capacity of from 10 KW to 100 KW. These systems

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can be designed to generate electricity for a single installation or a several small installations or buildings as they are extremely compact. They are one of the most preferred ways of producing electricity in the rural areas of the underdeveloped countries. Pico facilities: This type of hydroelectric power plant has a production capacity of less than 5 KW. Generally, this type of systems are run off river type and are most suitable for serving electricity where the requirement of power is really low.

6.3.3 Classification Depending on the Head of Water The term head of water is used to indicate the depth of water. The measurement of the upper surface of the water from the ground surface or the turbine is known as the head of water. Depending on the head of water or the depth of water, hydroelectric power plants can be of three major types: • • •

Low head power plant Medium head power plant High head power plant

Low Head Power plant In this type of power plant, the height of the water storage or the head of water is less than 30 meters.

Figure 6.12: Diagram of a low head hydroelectric power station

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Medium Head Power plant In this type of power plants, the head of all the operating levels of water is above 30 meters. The maximum limit of the head of water can be up to 300 meters.

Figure 6.13: A diagram of a medium head power unit

High head power unit The head or the height of water level is above 300 meters in these power plants. Generally, only the tidal power plants are of this type.

6.3.4 Calculating Power Generation A simplified equation to calculate the approximate amount of power generated at a hydroelectric plant is as mentioned below: P = ρhrgk Here, P = power generated in Watt unit ρ = the density of water h = height of elevation r = flow rate of water in cubic meters per second unit g = gravitational acceleration = 9.8 ms−2 k = coefficient of efficiency.

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6.3.5 Components of a Hydroelectric Power Plant A hydroelectric power plant requires a range of components for its operation to be conducted properly. But there are six components that are considered as a must. These components are mentioned below: • •

A dam Water reservoirs (one or multiple depending on the type of the power plant) • Intake or control gates • The penstock • Water turbines • Generators There are several other types of equipment that are considered really important for the system such as trash rack, forebay, surge tank, spillway, powerhouse, and draft tube.

Figure 6.14: Mandatory components of a hydroelectric power station

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Dam Dam is the most important element of a hydroelectric power plant. It is a barrier built with concrete which helps to achieve the difference in the elevation of the water level. It is the biggest establishment among all the elements of a hydroelectric power plant. A dam ensures continuous water supply to the turbines as well as helps the reservoirs to have sufficient amount of water. It works as the controlling mechanism of the water flow.

Water reservoir Water reservoirs are basically the storage facility of a power plant. In most of the plants, reservoirs are built at the higher elevation point to control the water flow. Every single power plant has a maximum output capacity. If the amount of available water exceeds the amount required to produce that specified amount of electricity, energy gets wasted. In order to reduce the energy wastage, these reservoirs save the extra water and release them when the water head falls down. These dams are also used to store water during off-peak hours when the demand for energy is less and makes them available for use during the peak hours. By helping the water head to increase, dams actually help increase the amount of potential energy of the water and increases output. There are reservoirs on both sides of the dam in a pumped up storage-type hydroelectric power plant. In this type of power plant, the reservoir at the higher altitude and the reservoir at the lower altitude are connected to each other through a pipe and a pump. The upper reservoir is used to conduct the same operation it does in other types of power plants. The reservoir, at the lower altitude on the other hand, conducts a unique feature. It keeps a certain amount of water stored during the off-peak hours. During the peak hours, it lets the water flow out to keep the production at its optimum. But during the off-peak hours, a creation amount of water is stored by controlling the outlet gates of this reservoir. This stored water limits the water passing through the turbines and brings the production down to provide the mechanical and electrical components an easier and lesser workload. When the pump connecting this reservoir with the one at higher altitude is turned on, using the extra power generated by the turbine, water from the lower reservoir moves to the upper one. In this way, energy wastage is minimized.

Intake or control gates These are gates controlling the inflow and outflow of water within the power

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plant. These gates hold the water in the reservoirs. When necessary, these gates are opened to have a higher water supply from the reservoirs. These gates are known as inlet gates as they let the water into the power generation unit.

The Penstock The penstock is the long shaft or pipeline that carries the water from the reservoir to the power generation unit. When the inlet gates open, the water stored in the reservoirs leaves the reservoirs and enters the penstock. They flow at an extremely high speed through the penstock, transforming the potential energy into kinetic energy. This energy rotates the rotors of the turbine and provides enough mechanical energy for the generator connected to the turbine to generate electricity. The total amount of energy generated by a hydroelectric power plant depends on the height of water, the amount of water passing through the penstock, as well as the velocity of water while passing through the penstock and reaching the turbine.

Water turbines A water turbine is situated in the power generation unit. Water reaches the turbine by falling through the penstock. These turbines have multiple blades on which the waterfalls. Water rotates these blades. Actually, the kinetic and potential energy of the water makes the blades and the rotors rotate. So, the kinetic and potential energy transforms into rotational kinetic energy which generates mechanical energy for the generator to produce electricity.

Figure 6.15: A diagram of a hydroelectric turbine

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https://water.usgs.gov/edu/graphics/hydroturbine.jpg

There are different types of hydroelectric turbines. This differentiation is conducted depending on the types of blades used in the turbine. Most frequently used ones are Francis turbine, Turgo turbine, Pelton turbine, and fixed pitch propeller turbine. The differences in the blades that are used in these different types of turbines are shown below:

Figure 6.16: Different types of blades used in hydroelectric turbines http://www.xindaenergy.com/pic/other/2012-09-11-14-41-268.jpg

Figure 6.17: Classification of hydroelectric turbines

Generally, the classification of turbines is conducted depending on the head of the water, depth of the turbine, efficiency, and cost of the blades. The

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available hydroelectric turbines can be classified into two major types. They are as follows: • •

Impulse turbine and Reaction turbine

Impulse Turbine An impulse turbine does not have any suction mechanism. This type of turbine generally uses the velocity of the water to move the blades and the whole work is conducted at atmospheric pressure. After hitting the blades, the water flows out of the system through the outflow pipe. This type of turbine is most suitable for a low-flow–high-velocity water supply. •



Pelton turbines: These turbines contain the Pelton wheels. A Pelton wheel has one or multiple jets releasing the water and turning the blades. There is no requirement of draft tubes as the blade needs to be above the surface of the tailwater level to be able to rotate. A turgo wheel is a variation of pelton wheel. It is a cast wheel resembling fan blades. The shapes of the blades are the only difference between these two types of turbine. After water stream falls over the blade at one side, it flows through the empty space within the blades and exits the system on the other side. Cross-flow: A cross-flow turbine is a drum-shaped turbine with numerous blades connected at a 90° angle from the base of the turbine. There is a rectangular-shaped nozzle over the wheel with a squirrel cage blower. The cross-flow turbines’ shape allows the system to use the water supply twice as the water flow through the blades twice while passing through the blades. During the first time, water flows from the outside to inner part of the blades. When the blades are at the downward facing position during their rotation period, the water sticking between two blades flows outward and leaves the turbine. This type of turbine was initially developed to achieve higher utilization of water and more efficiency from a lower head height.

Reaction Turbine The turbines falling under this category do not depend on the energy of moving water solely. The pressure of the moving water is increased to have higher output from the system. The blades are placed directly under the water

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stream so that all the blades are affected by the water stream continuously rather than single blades being affected by the water stream. The pressure of water is needed to be kept in complete control; otherwise, the blades will lose balance and mechanical overstress will cause the blades to break down. It can even cause the generator to fail. The water passes through the blades and leaves the system through an outlet pipe situated at the lowest point of the turbine casing. These turbines are the most suitable for water flow with lower head and higher velocity. There are different types of reaction turbines. •





Propeller turbine: A propeller turbine is built with twisted blades. There are three to six blades while other types of turbines contain a much larger number of blades. These blades are arranged in a way that waterfalls on the blades constantly. The pitch of the blades is adjustable so that they can be adjusted depending on water pressure available for optimum output. There are different types of propeller turbines, such as: – Bulb turbine: The turbine and the generator are sealed and placed directly under the water stream – Straflo: In this type of propeller turbines, the generator is attached to the perimeter of the turbine. – Tube turbine: In this type of turbine, the penstock is bent in such way that generator and the penstock are in a straight line. – Kaplan: The blades of these turbines are adjustable, making them adaptable to the fluctuation of water flow. Francis: This type of propeller contains specially designed blades with fixed vanes or buckets. There are usually nine of these buckets and water primarily falls on these buckets rather than falling on the blades directly. These buckets spread the water flow and ensure a constant flow of water in every direction. The movement of the water makes the bucket to spin which spins the blades even before the water reaches the blades. So, the turbine is affected twice by the water before it leaves the system through the outlet pipe. Kinetic energy turbines: This type of system uses the natural flow of water to turn the turbines. Generally, kinetic turbines are used in the tidal hydroelectric generators. This system does not require

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a lot of infrastructures and so the initial structural cost is really low.

Generators Generators are the electromagnetic mechanism that turns the mechanical energy achieved by the turbine into electricity. The rotation of the blades makes the shaft connecting the turbine to the generator to rotate. The shaft is connected to a magnet within the generator. The rotation of the magnet initiates electromagnetic field effect generating alternate current in the coils of the generator.

Figure 6.18: A cutout of a generator used in a hydroelectric power plant http://www.see.murdoch.edu.au/resources/info/Tech/hydro/image003.jpg

Other important elements of a hydroelectric power plant are as follows: •

Trash rack: Trash rack is technically one type of purifier. A trash rack is installed at the entry point of the water intake at the higher altitude side. The main objective of the trash rack is to prevent any kind of debris from entering the power generation system. Trash rack also prevents large elements from entering the system and choking up or damaging the turbine. During winter seasons, trash rack is heated to prevent ice piling up on the rack. It also prevents the ice to enter the system and damage the turbine.

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Figure 6.19: A diagram of a standard hydroelectric power station showing most important components of the system. http://img.bhs4.com/FA/8/FA89BF0370B42A4719540EFC583EFDDD331BFD22_lis.jpg





Forebay: Forebay is a temporary reservoir which starts storing water when the amount of water available is reducing. The water saved in the forebay acts like a jump starter when the water flow starts increasing again. In most of the power plants, the source canal is big enough to act as a forebay itself. And so, apart from some really small power plants, the source itself works as the forebay. The forebay is equipped with an outlet system to supply water directly to the penstock. Surge tank: Surge tanks are extremely important in maintaining the structure properly and preventing the damage to the infrastructure from the hammering of water. A fluctuation of the pressure in the penstock and the reservoir is created when the demand for electricity from the grid suddenly falls. With the suddenly reduced demand, the generator slows down rapidly. This deceleration causes the turbine to decelerate. As a result, the water demand falls down suddenly. This creates a chain effect which increases the pressure of water in the penstock to increase rapidly. This sudden surge of pressure creates hammering effect by the water in the penstock and it can cause the penstock to bend, leak, or even burst. To prevent this type of phenomenon from occurring, a surge tank is installed within the dam and the powerhouse and to connect the penstock with the surge tank, a water tube is installed. When the water pressure in the penstock rises, extra water enters into the surge tank from penstock till the

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increased pressure is neutralized. The motion of water inside the surge tank balances out the increased pressure. Again, when the generator starts rotating faster due to higher demand, water exits the surge tank and enters the penstock fulfilling the initial higher requirement of water. Spillway: Spillways are constructed to save the dams. During a flood or heavy rain, the water level rises incredibly high at an extremely fast rate. This huge amount of water creates higher pressure on the dam. The dam can suffer serious damage as well as leakage if the pressure rises above the maximum tolerance level of the dam. To protect the dams, spillways are installed in the dams at a certain height. By opening the gates of the spillways, extra water can be released, and the dam can be saved. Powerhouse: Powerhouse is the structure that contains all the controlling components. There are two parts in a powerhouse. First part is a substructure that contains all the support equipment for the hydraulic, mechanical, and electrical elements. The second part is a superstructure, built to protect and contain the main control equipment. The vertically rotating turbines are installed in the basement of the superstructure while the horizontally rotating turbines are installed on the ground floor along with the generators. The generators are installed on the ground floor of the superstructure in all types of designs. Draft tube: Draft tubes are generally installed in the systems containing reaction turbines. This type of tube is installed under the blades of the turbine with the necessary equipment to harness the leftover kinetic energy of the water passing through the blades.

6.3.6 Advantage and Disadvantages of hydroelectric power Using hydropower in generating electricity is one of the most preferred ways of energy generation. Due to the diminishing conventional nonrenewable fuels as well as the rising environmental concerns, clean and environmentfriendly sources are achieving more acceptability. And along with solar and wind energy, hydropower has become one of the major candidates to be the main power source of the future. The biggest advantage of using hydropower is that there is no requirement for fuel. As there is no fuel cost, the only costs associated with hydroelectric power plants are the maintenance and operation costs which

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are extremely low. Hydroelectric power plants cost less than half compared to the conventional power plants using fossil fuels. Another big advantage of this technique is that the operating and electricity generation process has no carbon footprint at all. Moreover, dams can be used in controlling flood. In most of the cases, the hydroelectric power plants are installed over existing water dams, further cutting the installation cost. This technique has got several drawbacks too. Often the dams cause a huge amount of surrounding area at the higher altitude side to be flooded, causing geographic and ecological change as well as requiring rehabilitation for the affected population. Moreover, the disrupted natural flow of the river can cause ecological and economic damage down the river stream.

CHAPTER 7

BIOMASS

CONTENTS 7.1 Source of The Energy of Biomass........................................................................... 156 7.2 Slagging and Fouling............................................................................................. 190

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(Biomass energy is a unique source of energy. In this chapter, the sources of the raw materials of biomass energy, techniques of harnessing fuel from the waste biomass compounds, and the utilization techniques of the energy harnessed from biomass will be discussed) Biomass consists in organic matters that can be used as a source of energy. It is an industrial term used for woods, crops, seaweeds, and animal wastes that can be used as an energy source. Biomass is listed as a renewable source of energy by the legal frameworks of United Nations and the European Union. The biomass energy generation process is completely different from every other source of renewable energy and contains more resemblance to the nonrenewable sources of energy, especially fossil fuels. But yet they are considered as renewable source of energy depending on the fact that trees, woods, animal waste are renewable and the stock of these sources can be replaced by replanting trees. Biomass is actually the oldest source of energy. When the ancient cavemen invented fire, they used natural elements such as leaves, branches of trees as the fuel. And these elements are considered as biomass. It has been the only source of energy for an extremely long time. Until humans invented the techniques of generating oil from animal fats and other sources, wood was the only way of generating fire. With the development of modern civilization, the use of biomass did not diminish. Rather humans developed newer ways to utilize the energy generated from biomass more efficiently. Biomass energy sources have significant similarity with fossil fuels in the case of being utilized. They share the same energy transformation potential along with the same type of reactions. Similar to fossil fuels, these biofuels use the oxygen present in the surrounding atmosphere to burn the carbon, change the chemical bonds to release the chemical energy in the form of heat. The heat or thermal energy is directly used in most of the cases. In several times, though, the heat can be transferred into electricity that can contribute to the grid.

7.1 SOURCE OF THE ENERGY OF BIOMASS By burning woods, plant body parts, and human waste, heat is generated. Technically it is combustion process. And in a combustion reaction, the chemical energy stored within the bonds of the atoms is released. So, the energy stored in the biomass materials is chemical energy. The concern is the primary source of this chemical energy.

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Solar energy can be considered as the primary source of the energy stored in biomass materials. It has already been discussed in the fossil fuel chapter that plants achieve energy from solar radiation and store this solar energy in the form of chemical energy. Animals achieve the necessary energy required for maintaining all the necessary body functions to stay alive. By burning the organic matters known as biomass, this stored chemical energy is released in the form of heat. The whole process is similar to the technique of fossil fuels; the only difference is that while the energy stayed stored for thousands of years in the case of fossil fuels, in biomass the stored energy is exploited within a much lesser time period.

7.1.1 Sources of Biomass Energy In the present situation of modern civilization, biomass is one of the most important sources of energy. Though it was tree body parts that were used as the source of energy, with the development of men’s knowledge, a range of new elements are now being used as biomass energy sources. The following figure shows the sources of biomass energy and their use in percentage.

Figure 7.1: Different sources of biomass energy https://www.researchgate.net/profile/M_Ahiduzzaman/publication/258570569/ figure/fig2/AS:297676131323911@1447982928600/FIGURE-2-Share-of-biomass-sources-in-primary-bioenergy-mix-48.png

In a broader sense, biomass sources can be classified into two major types: • Woody • Non-woody. Depending on sources, biomass materials can be divided into three major classifications. They are as mentioned below:

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Forests, Agriculture, and Wastes.

Figure 7.2: Sources and types of biomass materials for conversion into bioenergy http://www.wgbn.wisc.edu/key-concepts/grassland-biomass-sources/sourcesbiomass

Following are the most frequently used sources of bioenergy • • •

Wood Solid waste Landfill gas and biogas

Wood Wood accounts for nearly 70% of the total biomass energy generated. Wood and wood materials are frequently used as the source of heat in domestic use. This tendency is much frequent in the underdeveloped and many developing countries. Though electricity and fossil fuels are widely available in the developing countries, in the rural areas, wood and wood wastes are frequently used as the source of heat for daily necessities. It is not only the domestic use that makes woods the most used source bioenergy. Woods are widely used as the source of energy in various production plants. Generally, the paper mills and sawmills are the biggest users. They use the wooden waste materials as energy sources to generate electricity.

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The biggest source of energy derived from wood is known as the pulp liquor or the black liquor. It is basically a black waste material generated from wood and paperboard industries while making the pulp for papers.

Solid waste Solid waste is the organic waste materials produced by the living entities of the planet. Burning these trash and waste generates a huge amount of energy. In fact, the amount of energy that can be achieved by burning 1000 kg of waste materials is the same that can be achieved by burning 230 kg of coal. But, all the garbage generated is not biomass. Nearly half of the waste material created worldwide is plastic, which is basically polymerized form of petroleum and natural gas. Many countries run power plants using waste materials. These power plants are known as waste to energy plants. These power plants generate electricity from waste material following the same principles followed in the plants using fossil fuels. The only difference in these plants is the material that is used in the boilers to generate heat. Though energy generation by burning waste materials costs much more compared to the conventional sources of energy such as petroleum, natural gas, or coal, there is a huge upside of burning water materials for energy. Burning the waste materials can reduce the amount of garbage dumped by 90%, which is economically helpful.

Landfill gas and biogas Organic waste materials are used as a source of nutrition by bacteria and fungi. They break the cellulose of the wooden and non-wooden organic materials and turn them into sugar for their own consumption. This process causes the organic materials to rot and decay. During this process, a hydrocarbon with a single carbon named methane is generated. Though methane gas is color and odorless, it is highly flammable. And so, it is really dangerous keeping the waste material untreated and letting it decay. On the other hand, this methane gas can be collected, refined, and used as a source of energy due to its highly flammable characteristics. As methane is more effective than carbon dioxide in accelerating greenhouse effect, it is essential to burn methane and turn it into carbon dioxide rather than letting the gas roam free into the atmosphere. And it is even better to collect the gas and use it as a source of energy.

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7.1.2 Fuels of Biomass Energy From the primary stages of human civilization and up until the medium stages of the 20th century, biomass materials were used directly as a source of energy. But recent studies have developed several ways of developing fuels from these biomass materials so that the source can be used much efficiently. A sustainable biomass system creates a closed carbon cycle and having refined fuel from biomass increases the efficiency as well as economic and ecological acceptance of the cycle. And as a huge amount of carbon gets trapped into a closed cycle, fuel developed from biomass waste is really important from the environmental point of view. Generally, three major types of fuels can be developed using biomass fuels. They are mentioned below. • • •

Liquid fuel, Solid fuel, and Gas fuel.

Figure 7.3: Biomass waste-derived fuels

Biomass Engineering Biomass engineering indicates the specific techniques and processes developed to synthesize fuels from biomass materials and generate biofuels with higher efficiency from both economic and ecological perspectives.

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Different generation techniques are used for developing different types of energy from biomass materials.

Biomass Liquid Fuels Ethanol Ethanol is chemically known as ethyl alcohol and commonly is known by the term “alcohol.” Ethanol is a colorless transparent liquid with a sweet smell and burning taste. The molecular formula of ethanol is C2H5OH with a molecular weight of 46.07. It is extremely intoxicating and can be used as very effective sterilizing and disinfecting agent. Ethanol is highly combustible and volatile. It vaporizes really fast if kept in direct contact with air. Ethanol is easily soluble in water as well as in several other organic solvents. It also easily dissolves almost all the organic chemical compounds. Due to this characteristic, ethanol is frequently used in foods and drinks, medicines, cosmetics, perfumes, and many chemical industries. Moreover, due to its high flammability and ability to get the component carbons completely burnt has made it an affordable and cleaner substitute for conventional liquid fuels. The figure below shows a comparison of the conventional gasoline and the ethanol–gasoline mixture as fuel.

Figure 7.4: Properties of gasoline, methanol separately and as mixed compound

Source: Technology Survey Index No. 15, “Resource-economical back-

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ground of ethanol and its applicability to internal combustion engines” (Japan Automobile Research Institute, Inc., 1977).

Figure 7.5: Flowchart of ethanol production process

From the table above, it can be found that gasoline has a heating value of 44.37 MJ per kilogram which is 26.79 MJ per kilogram in the case of ethanol. This difference of heating value indicates that if a certain amount of gasoline generates a certain amount of heat, the same amount of heat can be created using 40% less ethanol. From the chemical formula of ethanol, it can be found that ethanol contains 35% oxygen which accelerates the combustion, uses less oxygen from the environment, and ensures higher efficiency. Moreover, the oxygen atom of ethanol reduces combustion temperature effectively, which makes the reaction to be free from soot and much less nitrogen-bound oxides. Another huge strength of ethanol is that it has higher octane value compared to gasoline.

Raw materials for Ethanol Production Ethanol is generated by the fermentation of conventional agricultural products containing starch and saccharine. Main raw synthetic material for ethanol is ethylene. SWL is another raw material that can be fermented and ethanol can be generated. SWL is one of the most recently developed organic matters used as the source of ethanol.

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One of the major sources of the raw materials of ethanol is sugarcane. The juice of sugarcane contains 11 to 17% sugar. Sugar consists of sucrose, glucose, and fructose. By properly processing and crystallizing sugarcane juice, sucrose can be obtained. Sucrose can also be found from sugarcane by directly fermenting it. Brazil is the world’s largest sugarcane producer with yearly production of more than 260 metric tons. About 60% of this production is used to produce ethanol while the rest 40% is left as sucrose and consumed as sugar. Along with sugarcane, sugar beet molasses is also used as a source of sucrose. Molasses is the residue of sugarcane or sugar beet juice after separation of sucrose. Some other organic materials used as raw materials are milk whey and the juice of the peel of orange. These are not used globally, rather contain regional signification. Mile whey is frequently used in New Zealand while orange peel juice is used as a source of sucrose in Japan. Another important raw material is the starchy materials. Starch is actually a polymer of glucose. And so, it is easier to produce starch using organic materials containing starch. Most frequently used starchy materials in the fermentation are rice, cereals, sweet potatoes, potatoes, and grapes. Apart from all these materials, in the tropical areas, cassava is used as a source of ethanol. Another important raw material for the production of ethanol is called SWL. SWL is a waste liquid material for the pulp industry. It contains about 4% sugar which can be used in ethanol production. It is, in fact, being used in North American and Scandinavian countries already. One of the few nonorganic raw materials of ethanol is ethylene. It can be achieved during the processing stage of crude oils or natural gas.

Principles of Ethanol Fermentation One of the most important stages of ethanol production is the fermentation of the saccharine. The sugar elements of saccharine get metabolized by Saccharomyces cerevisiae bacteria (also known as yeast) and ethanol is found as the result of this chemical reaction. The chemical reaction that breaks glucose and other saccharine and produces ethanol is as mentioned below: C6H12O6 = 2C2H5OH + 2CO2

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Here, a single molecule of glucose produces two molecules of ethanol and two molecules of carbon dioxide. The gram weight ratio of all the elements of this chemical reaction is 181: 92.1: 88. So, if 100 g glucose is fermented, around 51.5 g ethanol can be generated. While fermenting sucrose, a pre-fermentation reaction will have to be conducted, breaking the sucrose into glucose and fructose using an enzyme known as sucrase. The biggest drawback of using sugarcane juice is that sugarcane is seasonal vegetation. Due to its tendency of fast fermentation and heavier weight, extensive transportation of sugarcane is not possible. Assuming the sugar content, the fermentation ratio, and the distillation recovery of sugar cane to be 12%, 85%, and 99%, respectively, to produce 1 kL of 95 vol.% of ethanol, the required amount of sugarcane will be around 14.6 t. When the molasses of sugarcane or sugar beet is used, the concentration of sugar can be diluted down at 20%. In the case of molasses, assuming the sugar content, the fermentation ratio (for total sugar), and the distillation recovery to be 55%, 82%, and 99%, respectively, around 3.3 t of molasses will be required for producing 1 kL of 95 vol.% of ethanol. While using starchy organic materials as the raw material for the production of ethanol, the raw materials are required to be processed before they can undergo fermentation. Standard practice is to wash the starchy materials to get rid of all sorts of unwanted materials that can reduce the efficiency of the reaction, crushing them into small pieces and finally boiling them at 90 to 100°C temperature for half an hour. The mash found after boiling contains 15% sugar concentration. The temperature of the mashed material is reduced down to 55°C. To liquefy and saccharize the raw compound, alfa-amylase and glucoamylase are added to the mashed raw material and the mixture is kept for two hours. After the temperature of the mixture comes down at 34°C, yeast is added to the mixture and fermentation for four days generates 8% ethanol. The fermentation can be conducted following several approaches. They are as listed below: •

Batch-wise fermentation: Among all the techniques of fermentation, this is the simplest and easiest. The mash prepared for fermentation is mixed with yeast and then is left into a fermentation tank and a static temperature inside the tank is maintained. The fermentation process operates until the sugar

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available gets completely consumed by the yeast. Being extremely simple and having no necessity of separating the yeast from the ethanol produced, this technique is extremely popular and is used in a range of other different types of industries. Fed-batch fermentation: In the batch-wise fermentation process, the frequent occurrence of incomplete fermentation caused by the inhibited growth of yeast and unusually thick concentration of the raw material can be observed. This drawback can be eradicated by adapting to fed-batch fermentation technique. In this process, the density of the substance is kept at a lower position at the beginning of the process. More substance is gradually added after the previous raw substance gets completely consumed by the yeast. Unfinished fermentation can be avoided by using this process and ethanol with comparatively higher density can be produced. Melle-Boinot semi-continuous technique: This technique was invented in 1933 by a French company known as the Melle Co. This technique enables the reusing of used yeast. After the fermentation is complete, the fermented material is passed through a centrifuge. At that time, the yeast cell paste is separated from the fermented material before it enters the centrifuging mechanism. The yeast is then processed with diluted sulfuric acid which kills all the contaminating bacteria as well as unwanted residue, making the yeast capable of functioning again. Continuous fermentation process: This technique uses a constant amount of yeast and ethanol in the system. To maintain this type of condition, the amount of mash taken off the system equals the number of raw materials added to the fermentation system. As the input and output balance is maintained continuously, this technique requires a much smaller setup. But a big drawback of this system is that the concentration of ethanol achieved from the system is much poorer than it is in batch techniques. This lower concentration also causes the wastage of raw material. As the yeast is operating for a much longer time in the system, the risk of contamination is much higher. To minimize the contamination, extraction of the used yeast from the system and refining them before they are sent back into the system can be helpful. The continuous fermentation process can be divided into two major types. They are as follows:

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1. Multi-vessel continuous fermentation process 2. Biostil process In the multi-vessel continuous fermentation technique, multiple fermentation vessels are operational at the same time. Generally, from 4 to 7 vessels with interconnectivity mechanism are installed in a series connection. Used up yeast is collected from the end of the vessels using centrifugation and are recycled and decontaminated for reuse. This technique is one of the most common approaches due to the extremely high efficiency. In the biostil process, a conventional continuous fermentation setup is combined with a distillation tower. The centrifugation of the used yeast is conducted inside the vessel while the mash of the process is collected in the form of vapor. The vapor is collected by the distillation tower and is cooled down to liquefy.

Ethanol Distillation Technology Distillation is the process of separating certain liquid element from a mixture of multiple liquid elements using the difference in the boiling points of different elements. In this technique, the complete liquid mixture is heated to the boiling point of the specific liquid that is required to be extracted. The vaporized material is then collected and separated. When the temperature of the vapor comes down, the vapor condensates and returns to its previous liquid form. In the vessels, ethanol gets mixed with water and other liquid materials. But as ethanol has a lower boiling point than all other components resent in the vessel, it can be easily extracted from the vessel in the form of vapor. Later the vaporized ethanol is cooled down and the vaporized ethanol comes back to the liquid form. Distillation can be conducted using two separate approaches. They are as mentioned below: • Continuous distillation approach and • Pot still Complex continuous distillation approach requires a big and complex setup with multiple distillation columns, heaters, and condensers. This technique is most suitable for producing pure ethanol with higher concentration. This system consists of a mash column, a concentration column, an extraction column, a refining column, and an impurity column. This type of system is most effective in separating ethanol from densefermented mash especially where the concentration of ethanol is relatively

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high. This technique ensures purity of the extracted ethanol through several continuous condensations.

Figure 7.6: A continuous distillation system http://dacworldwide.com/assets/images/products/lg/w606ss12.jpg

On the other hand, the pot still technique is far simpler compared to the continuous distillation system. This technique is generally used in liquor industry to produce different types of drinks consisting different percentage of alcohol such as whiskey, brandy, vodka, and other spirits. Role and function of the different columns installed in a continuous distillation system: •





Mash column: Mash column extracts the ethanol portion of the mashed component from distillation waste liquid. But this conventional technique has recently been replaced by multieffect evaporator which is capable of extracting the ethanol at two different concentrations. Extraction column: Extraction column is installed in a condensation system to extract the aldehydes from ethanol. A limited amount of other hydrocarbons generate during the fermentation process and coexist with the ethanol in the mash. Methanol and ethanol stay at the bottom of the extraction column while other existing hydrocarbons vaporize and are separated through an extraction valve at the top of the extraction column. Refining column: Methanol is extracted from the high ethanol concentration in this column.

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Dehydration column: This column extracts the unwanted hydrocarbons which consist of the water–ethanol solution as a dissolved element. Vacuum column: After dehydration column, several alcohols with large chains with the similar boiling point of ethanol stay within the solution. To extract the large chained alcohols from the ethanol–water solution, the solution is taken in a vacuum column. The vacuum causes the boiling point difference within these alcohols to rise and enables the distillation of ethanol from other remaining alcohols.

The Production Process of Synthetic Ethanol Synthetic ethanol is the ethanol generated from petroleum and natural gas raw materials. The most common raw material for synthetic ethanol is ethylene which can be achieved from naphtha. Naphtha is primarily extracted from petroleum and petroleum is the only known source of naphtha so far. There are two established methods of producing synthetic ethanol from ethylene. They are as mentioned below: • •

Direct hydration method and Sulfate method

Figure 7.7: Classification of synthetic ethanol production methods

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Direct Hydration Method Direct hydration method can be divided into two types. • Shell method • VEBA method Shell method was developed in 1947 by Shell Chemical CO. of the United States while VEBA method was developed by a German fuel company known as Hibernia Chemie CO. which was later taken over by the Hills Company. There are several other techniques used by different production plants but all of them are more or less same as the shell method. Shell method involves a reaction of ethylene and pure water in the presence of a plasma catalyst in a solid container. The optimum temperature and pressure for the reaction are 240–260°C and 6.86 MPa, respectively. The reaction that occurs can be described in the mentioned format C2H4 + H2O = C2H5OH

Ethylene + water = ethanol (in the presence of H3PO4)

This is an exothermic expression of the reaction. In the complete reaction, diethyl is generated as a byproduct. Along with diethyl, aldehydes, hydrocarbons, higher alcohols, and ketones are also produced at an extremely little amount.

Sulfate Method This method was invented in 1930 and requires the presence of sulfuric acid to produce ethanol from ethylene. Compared to the shell method, the economic efficiency of this method is less and the components develop the tendency to decay due to the presence of sulfuric acid. Due to the constraints, hardly any company uses this technology. Ethanol production process is divided into two stages in this technique. During the first step, concentrated sulfuric acid absorbs ethylene and develops ethyl hydrogen sulfate. This step occurs at 55 to 85°C temperature and 1.63–3.43 MPa pressure. During the next and the final step, diethyl sulfate is hydrolyzed to ethanol. The required temperature and pressure stays the same of the first stage of the reaction. This technique requires lower temperature and pressure compared to direct hydration method. The formulas of the chemical reactions are mentioned below. First step: C2H4 + H2SO4 = C2H5HSO4 C2H4 + C2H5HSO4 = (C2H5)2SO4

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The second reaction can be explained as below: 2C2H5HSO4 = (C2H5)2SO4 + H2SO4 Second step:

C2H5HSO4 + H2O = C2H5OH + H2SO4

(C2H5)2SO4 + H2O = C2H5OH + C2H5HSO4

Figure 7.8: Production process of synthetic ethanol following direct hydration method

CIGR Handbook of Agricultural Engineering (Volume V) Energy and Biomass Engineering

7.1.3 Methanol General properties of methanol Methanol is an alcohol with only a single carbon atom. It is the smallest and simplest of the monovalent alcohols. In primary stage of the invention of methanol, it was produced using dry distilled wood. This technique was the only feasible way till 1923. Recent developments of the concept of hydrocarbon and organic chemistry have made it possible to attain methanol from many other sources such as natural gas, petroleum gas, naphtha. The chemical formula of methanol is CH3OH and the molecular weight of

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methanol is 32.04. With the melting point of −96°C and the boiling point of 64.6°C, methanol is generally found at a liquid state at atmospheric temperature. Similar to ethanol, methanol can be used in a varied way, such as in production and agriculture facilities, as solvent, detergent, and perfume. Methanol is not used for food or drinks preparation due to its toxic nature. The source of the toxicity is the single carbon atom that creates carbon monoxide when consumed and damages internal organs. Recently, the most frequent uses of methanol are as MTBE (which is an additive to increase the octane number of fuel), as an independent automotive fuel as well as a basic feedstock or raw material for a variety of production plants. The production process of MTBE is as below:

Figure 7.9: Chemical reaction of the production process of MTBE

As a fuel, methanol can be used in two ways; as a standalone substitute fuel of gasoline or as MTBE to increase the octane number of the conventional fuel.

The Production Process of Methanol Methanol can be produced following three stages. They are mentioned below: • Production of feedstock gas • Synthetic process • Distillation process Production of feedback gas: In the production process of methanol gas, hydrogen and carbon monoxide are used as the feedstock gas or raw materials. There are two techniques for achieving these feedstock gasses. They are known as the catalytic steam reforming method and partial oxidation method. In the catalytic stream reforming method, carbon monoxide and hydrogen gas are achieved by generating a reaction between CH4 and water or carbon dioxide. On the other hand, in partial oxidation method, the carbon molecule is entered into an oxidation reaction with the insufficient amount of oxygen.

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Among the mentioned techniques, catalytic stream reforming method is more accepted and frequently used method. The reactions occurring in this method are mentioned below: CH4 + H2O = CO + 3H2.

CH4 + 2H2O = CO2 + 4H2. CH4 + CO2 = 2CO + 2H2

Synthetic process: Using the carbon monoxide and hydrogen gas achieved at the previous stage, methanol synthesis is generated at an extremely high temperature of 250 to 400°C and high pressure of 5.07 to 30 MPa. During this reaction, Cu–Zn or Zn–Cr–Cu group is used as catalysts. The reaction taking place at this stage is shown below. CO + 2H2 = CH3OH.

Distillation process: Newly produced methanol requires purification to get rid of the unused ingredients of the reaction. At the pre-purifying chamber, ingredients and unwanted productions with low boiling points are separated. The menthol–water solution is treated in the rectifying column after that. During this step, ingredients and unwanted productions with a higher boiling point are extracted. Biodiesel (Vegetable oils and their waste) Conventionally vegetable oils are mostly used for cooking. But the recent increased use of biofuels has initiated the use of these vegetable oils as industrial raw materials as well as fuels for engines and generators serving a wide range of purposes. There are more than 4000 plant species from which oil extraction is possible. Vegetable oils are generally formed by fatty acids (FAA’s), monoglycerides, diglycerides and triglycerides, phosphatides, lipoproteins, and glycolipids, waxes, terpenes, gums, and other less important compounds.

Figure 7.10: Chemical structure of fatty acid (propanoic acid)

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Figure 7.11: Chemical structure of glycerol

The fatty acid is a long-chained hydrocarbon with a carboxyl group. The hydrogen atoms present are connected to the carbon atoms with single bonds. On the other hand, glycerol is a trihydric alcohol. It is mildly viscous, contains a sweet smell, fully soluble in water and other alcohols while being fully insoluble in hydrocarbons. 95% pure glycerol is known as glycerin as is used as a moisturizing element.

Energy applications Vegetable oils can be used in different applications, but they can be classified into two major types of utilities. •



Large networks: In this type of systems, vegetable oils are produced in a really large quantity and esters are produced from them. These esters can be used as the substitute or simply as a performance enhancer of conventional diesel oil. Generally, the production facilities are less interested in producing the esters themselves; rather they prefer buying this type of fuel from the facilities solely developed for generating fuel from vegetable oils. Onsite or local applications: This type of production technique refers to on farm, small-sized production and use of vegetable oil. The quantity of production is relatively low and so the whole process is pretty simple. This system requires less complicated and compact machinery and is suitable for generating energy for small-sized community or individual production plant.

Raw oil production from seeds The production process of raw oil from vegetable and grains seeds can be conducted following two methods. They are mentioned below:

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• Mechanical extraction and • Chemical extraction. The most suitable extraction process depends on the potential production amount of oil from the seeds. If the potential production amount is relatively low, only chemical extraction process is used. On the other hand, mechanical extraction is used when the potential output is calculated to be extremely high, but in this case, chemical extraction should also exist and is suitable to be conducted after completion of mechanical extraction. The complete oil extraction consists of following stages: •









Cleaning of the seeds: Cleaning the seeds is one of the most important steps to ensure the purity of the extracted oil. Cleaning process starts right after harvesting. First, oversized trash and unwanted matters need to be scalped out; after scalping, the seeds will have to be aspirated and screened to get rid of organic materials. Aspiration should be repeated after screening. Finally, the seeds will have to be destined and thus clean seeds free from all sorts of unwanted materials can be achieved. Drying the seeds: Seeds of different plant species have different moisture levels for storage (13% for soybeans, 10% for cottonseed, 8.5% for sunflower, and 7%for rapeseed). But the necessary moisture level for oil extraction from the seeds is static and the probability of that level varying from the existing moisture level is extremely high. And so, the seeds need to be dried before the extraction process begins. Generally, the most preferred technique for drying the seeds is the use of gravity flow dryers. Cracking: The seeds need to be reduced in size. To do that, they are passed within two rollerblades rotating in exactly opposite directions. These two roller blades crack the bigger pieces of the seeds and reduce them in dimensions. Hulling: This operation aims to remove the hull or pericarps of the seeds as this part of the seeds is completely oil free. Hulling makes the process much more efficient by reducing the useless pieces, reducing the requirement of press energy and minimizing the quantity of solvent needed. Conditioning: The temperature and the moisture level of the seeds are readjusted to accelerate the oil extraction process. During this stage, seed surface is treated with a thin layer of water, making

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the extraction of oil easier and faster. Adding water makes the oil to come out faster as oil is lighter than water and floats on water if mixed. Conditioning is generally conducted in the presence of a steam-heated rotary dryer. • Flaking: This stage is used to break down the fatty oily matters within the cells of the seeds. In this stage, the seeds are treated with cast-iron roller with smooth surface rotating in opposite directions at an extremely high velocity. The dimensions of the small pieces or flakes are brought down within the range of.25 to.4 mm. • Pressing: A screw press is used during this stage of the operation cycle. Generally, the press contains single screw but tow screws can be installed if higher pressure is needed. When the seeds are pressed within two surfaces of the press, oil is released from the small pieces of seeds and then the oil is collected in a transparent tank. The large solid participles that flowed into the tank with flowing oil settle at the bottom of the tank. The oil is transferred to a different tank while the foot (large particles settled at the bottom of the tank) is returned to the press. The transferred oil is stored as unfiltered oil; it is filtered and stored in another tank as filtered oil. The filter and the unfiltered tank are cleaned after a fixed period of time and the residues stored are transferred back to the press. Pressing can be conducted in two ways: full pressing and pre-pressing. Seeds with high oil content are treated with full pressing. Seeds containing fatty contents at a higher percentage than 20% are treated with full pressing. Full pressing can be conducted following one-stage or two-stage pressing. On the other hand, if the seeds have lower oil content, pre-pressing is conducted. After extraction of oil, the leftover termed as the cake is milled, dried, and processed to prepare it for chemical extraction. • Solvent extraction: The leftover after pressing is known as the cake. The cake is collected, dried, milled, and then transferred to the solvent extractor. The most frequently used extraction mechanism is the countercurrent percolation extractor. The complete duration of the process is the determining factor of the amount of oil extracted.

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Oil purification and refining A range of impurities can be present in the collected oil. Most common impurities are proteins, gums, phosphatides, ketones, and aldehydes. Moreover, all types of unrefined oils contain FFA, which can generate naturally or with the help of lipolytic enzymes. These impurities reduce the efficiency of the fuel drastically and it is a must to eradicate these unwanted substances.

Industrial processing There are two existing techniques of processing oil. • Conventional refining and • Physical refining. In conventional refining, FAA gets individual treatment known as the alkaline treatment; on the other hand, in physical refining process FAA is eliminated during deodorization stage. A comparative layout of two different refining techniques is shown in the diagram below.

Figure7.12: Refining process of raw oil

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Conventional refining Filtration: During filtration, the unrefined oil is passed through a filter that retains all the unwanted substances present in the oil in suspension. • Alkali refining: During and even before the oil extraction, FFAs are produced from the active lipase of the seeds. This process eliminates those FFAs. This stage is a must before the esterification is conducted. The amount of caustic elements is known as the treat. The amount of treat generated can be calculated using the equation below: Treat D [(0:142FFA) + excess] = (%NaOH = 100); •

Here, 0.142 is the ratio of molecular weight between sodium hydroxide and oleic acid. FFA is the percentage of free fatty acids Excess refers to the excess of caustic and % NaOH is the percentage of the strength of caustic With the help of the sodium balance method or by calculating the difference between oil input and output, refining loss can be calculated. The equation of the calculation is as stated below: Loss = [treat (Nar − Nas) − 100 Nao) = (Nas − Nao); Here,

Loss = the refining loss Treat = amount of caustic applied in percentage Nar = percentage of sodium present in the caustic Nas = percentage of sodium present in soap stock Na0 = percentage of sodium present in refined oil

To measure the instantaneous and batch losses, there are metering systems available. • Bleaching: This stage is used to eliminate coloring pigments such as carotenoids and chlorophyll present in the oil. This process uses the mixture of small amount of activated earth and active coal at the temperature range of 60 to 100°C temperature for maximum 30 minutes to soak up the pigments from the oil. The earth and coal are filtered, and as the pieces are big and easily separable, they can be eliminated fast.

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Deodorization: During this stage, the compounds that generate odor are filtered and eliminated. These compounds are FFA’s, volatile compounds (aldehydes and ketones derived from oxidation processes of unsaturated fatty acids), residual carotene, and natural toxic principles. Exposing the oil with superheated steam in a vacuum tank vaporizes these elements and separates them from the oil. Wintering: This stage eliminates the compounds present that have a higher melting point.

Physical refining Physical refining is a much shorter approach compared to conventional refining technique. The stages of physical refining are discussed below. The first stage of this approach is alkali refining. Different types of alkali that can exist in raw oil are listed below: •

All the hydratable phosphatides and most of the non-hydratable phosphatides; • chlorophyll • gossypol (by 1 = 2); • waxes (with low-temperature treatment only); • metal salts (by 1 = 3); • peroxides, aldehydes, and ketones (by 1 = 2); • FFA’s (to 0.05%); • Tocopherols and sterols (by 10%); • Soaps (to 50 ppm). After alkali refining, physical refining takes place that eliminates all the phosphatides, chlorophyll and gossypol, metal salts, peroxides, aldehydes, and ketones. After this stage, bleaching and deodorization take place.

Degumming As degumming is really important and holds special significance in the refining process, elaborate discussion of this process is required. Degumming can be done either at the extraction point of the impure and unrefined oil or at the refinery. Frequently used techniques of degumming are discussed below: •

Acid conditioning: This technique is also known as dry

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degumming. This technique is suitable if the raw oil contains a low concentration of gum contents. A citric or phosphoric acid is added at an extremely low percentage (.05–.2%) while the temperature is controlled from 60 to 70°C range. The time required depends on the existence of stirring. If the mixture is kept static or is slowly stirred, the process can take up to 20 minutes to remove all the gum while continuous stirring can bring the time under one minute. To neutralize the acid added to the oil, a treatment of alkali is a must. • Water degumming: This system is only suitable for chemical refining. If there is the presence of lecithin in the oil, this type of degumming is required. • Acid degumming: This stage is conducted before water degumming. Before water degumming is initiated, acid is added to the oil to soak up the easily extractable gumming materials. The temperature is required to be controlled and brought down to less than 25°C at this stage. There are several other degumming techniques available which are exclusively designed for commercial use. They are as follows: • • • • •

Super degumming Uni-degumming Special-degumming Total degumming process Alcon process

7.1.4 Biomass Gas fuels Methane Methane is one of the least useful forms of biofuels and is completely out of use. But still, the understanding and processing of the methane existing in the environment are important due to the contribution of this gas to the greenhouse effect.

Methane Fermentation Technology The idea and techniques of methane fermentation were developed in Southeast Asia and Indian subcontinent to have practical use of that gas. But after the oil crisis of 1973, a lot of farmers of different countries started

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establishing methane fermentation plants as a backup source of energy. As the fermentation is completely depended on bacteria and fungi absorbing nutrition from breaking animal and plant wastage, the output of methane production plant is not constant and falls drastically during the winter season.

Figure 7.13: A basic and simplified diagram of methane production plant

Figure 7.14: Principles of methane fermentation

Principles of Methane Fermentation The necessity of microbes The organic matters, such as bodies of animals and plants, livestock and human feces, food industry wastes, and garbage waste, are used as the raw

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material for methane production. These raw materials degrade from complex organic compounds to simple compounds by facultative anaerobes. This process consists of two separate stages: • Hydrolysis process or phase IA and • Acidic fermentation process or phase IB. So, microbes breaking the complex organic compounds are a mandatory element of the methane fermentation. In conventional fermentation, symbiotic fomenters living in the raw materials take part in the fermentation. If the sufficient growth of the anaerobes is hampered or any type of washout causes these microbes to extinct, the fermentation process would come to a complete halt. Even if the fermentation does not stop completely, the continuity of the process will be damaged greatly and the whole production process will become unstable. And so, it is extremely important to maintain the optimum environment for the fomenters to grow properly and preserve the pace of fermentation.

Required optimum conditions for methane fermentation In both conventional and two-phase processes, the optimum load of organic matter is static and it is not at all equal in these two different techniques. For a conventional system, the optimum loading of organic matter required in the conventional method is 3 kg/m3 per day and the required pH range is 6.5–7. In the conventional technique, the HRT is ranged from 20 to 30 days. On the contrary, the two-phase system can generate up to 30% more methane gas at same conditions compared to conventional method. The optimum load of organic matter is double than it is in the conventional technique. The range of optimum temperature for the methane fermentation technique is divided into two parts: mesophilic fermentation and thermophilic fermentation. While the optimum temperature for the first stage is from 35 to 37°C, the range rises from 54 to 56°C for the second stage.

Kinetic analysis of Methane fermentation The basic equation based on the mass balance of the cell of the methanogens can be stated as mentioned below: V (dX/dt) = F0X0 + F1X1 − (F0 + F1) X2 + (dX/dt) G − KDXV;

Here,

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V = the working volume of the reactor X = the density of the methanogen cell t = time in days F = the blow rate KD = the coefficient of decay.

By dividing the equation with F and further modifying the equation by using the value F1 = X0 = X1, we can achieve V (dX/dt) = −F0X2 + V (dX/dt)G − KDXV; Mass balance equation can be stated as: V (dS/dt) = F0S0 − F0S2 − V (−dS/dt)C;

7.1.5 Solid Fuels Solid fuels hold special significance in the field of biofuel since it was the solid fuel sources that were the only source of biofuel for centuries. Moreover, it contains special significance within all types of fuels as solid fuels were the first element used by humans as fuel. The use of solid fuels began from the time of the cavemen, and because of the availability, it is still one of the major fuels used worldwide. In the underdeveloped countries and rural areas of many developed countries, wood and other solid fuels are still the major sources of energy. Even in some extremely rural areas, they are the only source of energy. There are three major classifications of solid fuels. They are mentioned below: • • •

Fuelwood and charcoal Organic residues Energy crops

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Figure 7.15: Classification of Solid Fuels

Fuelwood and Charcoal Fuelwood was the first fuel ever used by humans. The surprising fact is, even after thousands of years, it still is one of the major sources of energy. Along with cooking, fuelwoods are used in brick making, textile manufacturing, baking and brewing and many other different types of small- and mediumscale industries. As these sources of fuel are easily available and extremely cheap, fuelwood and charcoal are still being used at a considerably high amount. Charcoal is the result of the partial burning of plant and animal bodies. Due to being partially burnt and the compounds creating the smoke being eliminated, charcoal is smokeless, and this characteristic specialty made it one of the preferable forms of solid biofuels. Moreover, charcoals are easier to burn, more efficient than woods, and much economical and easier to transport. Because of these advantages, numerous production techniques to produce charcoal have been developed at almost every part of the whole world. The basic principle of charcoal production, though, stayed the same, which is to initiate and achieve incomplete combustion of wood till the

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point where all the liquid residue and short-chained carbons are burnt and vaporized. Incomplete combustion can be achieved by limiting the amount of oxygen available for combustion. The basic chemical structure is quite similar in charcoal and woods. The carbons contain less unwanted materials which cause the carbon molecules of charcoals to be purer compared to wood. From 50% to 95% of charcoal is carbon. Depending on the processing procedure and amount of oxygen, amount of water and tar ranges within 5% to 40%. There are several different types of charcoals available depending on the percentage of carbon and source material. These different types of charcoals are mentioned below. •









Common charcoal: This type of charcoal is generated from peat, coal, wood, coconut shell or even petroleum by incomplete combustion process and is the most available type of charcoal. Sugar charcoal: This type of charcoal is produced by partial combustion or carbonization of sugar. The percentage of carbon is extremely high in this type of charcoal and it is the purest type of charcoal. To achieve maximum purity, these charcoals are boiled with acids to remove all types of mineral matters. To get rid of the hydrogen, these boiled charcoals are burnt in a flow of chlorine gas. Chlorine gas reacts with the existing hydrogen and generates hydrochloric acid vapor. Sugar charcoal was first developed by Henri Moissan as an attempt to produce synthetic diamonds. Activated charcoal: Activated charcoal contains several similarities with common charcoals. Their production process is completely identical. But activated charcoals are solely developed to be used for medical purposes. To produce activated charcoal, common charcoal is burnt to achieve a higher concentration of carbon. As impurities vaporize along with a certain amount of carbon, numerous small pores develop which provide activated charcoals the capability of sucking in and trapping chemicals. Lump charcoal: This type of charcoal is produced from hardwood. This type of charcoal is renowned for generating much less amount of ash. Japanese charcoal: This special type of charcoal gets the

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pyroligneous acid removed during the production process. As a result, Japanese charcoal can make almost no smell and gas while burning. There are two types of Japanese charcoals: white charcoal and black charcoal. Pillow shaped briquettes: A special type of charcoal produced in specialized production plants. It is produced by compressing conventional charcoal. A big difference from conventional charcoals is the use of a binder which is usually starch. It also contains brown coal and mineral carbon as sources of heat and several other flammable minerals as the ignition aids. Sawdust briquette charcoal: This type of charcoal is produced using sawdust excluding the use of binders and additives. Generally, this type charcoal has a round hole through the center and the intersection is hexagonal. Due to being odor and smokeless while delivering a higher amount of heat, this type of charcoal is most preferred for barbecue. Moreover, this type of charcoal produces comparatively less ash and has a really long burning period. Extruded charcoal: This type of charcoal is produced using raw ground wood or carbonized wood without the help of a binder. The extruding process creates heat and pressure which keeps the charcoal from separating into small pieces.

Use of charcoal The major use of charcoal almost everywhere around the world is as a fuel to prepare food. And as the lumps are easier to ignite, they are the most preferred type of charcoal used. In recent years with the quantity of stored fossil fuel reducing fast, several production plants are using charcoals as the substitute for coals. In industrial fields, charcoal has the edge over the conventional fossil fuel sources due to the following characteristics. • • • • •

Lower amount of sulfur and sulfur compounds, reducing the possibility of the existence of the oxides of sulfur, Much higher amount of carbon which implies to a higher amount of heat. Much less production of ash Much less uncreative impurities compared to conventional fuels Higher surface area allowing more evenly distributed heat

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The ability to generate much less smoke.

7.1.6 Organic Residues Organic residues are parts of plant body which contain extremely low or negative value. A negative value indicates that the subject element has no selling value; rather, it contains a certain amount of disposal cost. This lowcost characteristic makes these residues a cost efficient source of energy. These residues have another big advantage; there is hardly any production or processing cost related. But as these materials tend to contain a high concentration of moisture and the supply of these elements is not static, it is really hard to use these elements if the energy demanded is higher or continuous supply of a static amount of energy is required. In high-scale energy generation plants, these elements can be used in serving the following needs. •

During the development phase of newer and more advanced energy generation technologies, these elements can serve as a low-cost intermediate source of fuel. • While using agricultural or plantations as the main source of energy, these elements can be helped as a temporary source of energy while the plantation and crops reach a stage mature enough for energy extraction. The following compounds can be considered as organic residues. • • • • • •

Forestry crop and processing residues Agricultural crop residues Animal manures Municipal solid waste and sewage sludge Urban wood waste Landfills

Forestry crop residues Forestry crop residues are low-value tree body parts generated as the result of harvesting, thinning, and other operations during replanting vegetations. Forestry crop residues include tops, limbs, stems, roots as well as undersized crop plants. Collecting or processing these residues is not economically feasible and so they are often left untreated. Forestry processing residues are the byproducts and waste materials of the production processes using wood

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and wooden materials as raw materials. These residues can be classified into two major types depending on the operation level they are generated. Primary-level residues are generated from primary-level manufacturing operations such as pulp, paper, or lumber production plants. On the other hand, secondary operation residues are the byproduct or residues of secondary-level operations of manufacturing plants; they include furniture, paper-made products, and composite board production plants. Residues generated from these sources can be wood powder, sawdust, shavings, pole and post peelings, rejected chips, end cuts, lumbers with flawed dimensions, lower concentration pulps, etc. Primary forestry crop residues can contain moisture from 5% to 60% depending on the original source plant and the production process from which the residue generated. These residues contain a certain amount of bark which generates a huge amount of ash. The residue can contain impurities which get mixed during collecting and transportation process which make the ash content much higher. Secondary residues, on the other hand, are relatively drier as they are processed and dried before being used in the production process. As a result, these residues contain a much lower moisture level. As the raw materials are extensively purified, secondary operation residues are generally bark and earth free and so produce much less ash compared to primary residues. But these residues can contain glue, sander dust, paint or plastic coating as well as various other non-wood materials which can fluctuate the linearity of emissions as well as causing damage to the residue processing and conversion units. These residues can be of different sizes and shapes, starting from powder to large blocks. Due to the wide range of sources and characters of the residue elements, the moisture, density, size and other physical contents of the residues vary within a really wide range.

Agricultural crop residues Agricultural crop residues are the leftover portions of a crop vegetation body after the main concerned portion of the vegetation is extracted. Generally crops are grown for the specific body part or parts of the plant body rather than the whole plant body. For example, in the cultivation of rice and heat, it is the seeds that are the only concern. After the crops are grown, these desired portions are extracted while the remaining body parts of the plants are left. These leftovers can be collected after harvesting as well as after processing

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is conducted and the crop material is extracted. These residues are a huge concern due to the amount of them. The annual crop residue production worldwide exceeds 3 billion metric tons. These residues hardly have any economic value. But removing them from the crop fields or processing plants and treating them will generate cost. Along with the negative value, if they are dumped and left to rot, methane gas generates and causes damage to the environment. As a result, using them as fuel reduces the processing, transportation, and dumping cost along with fuel cost as they are far cheaper compared to conventional fuels. The table below shows several crops that generate the highest amount of residues. Name of the product (crop)

Main

Byproduct (residue) Ratio of main product and byproduct

Wheat

Grain

Straw

1:1.3

Barley

Grain

Straw

1:1.2

Maize

Grain

Straw

1:1

Oats

Grain

Straw

1:1.3

Rye

Grain

Straw

1:1.6

Rice

Grain

Straw

1:1.4

Millet

Grain

Straw

1:1.4

Pea

Grain

Straw

1:1.5

Bean

Grain

Straw

1:2.1

Soya

Grain

Straw

1:2.1

Biomass Potato

Tuber

Stalk

Cocoa

Nut

Shell and outer fiber 1:0.2

Sugarcane

Sugar

Bagasse (complete body part after the juice is extracted)

189

1:0.4

1:1.16

Source: Biomass Regenerable Energy, edited by D. O. Hall and R. P. Overend.

Another source of solid biofuels can be achieved from the crops after they are processed. After the desired portion of the plant body is extracted, they are processed to make that part consumable. During this processing period, a considerable amount of elements are left as residues. These residues include sugarcane bagasse, rice husks, cotton gin trash, grain dust and chaff, corn cobs, weed seeds, hulls from nuts (e.g., peanuts, almonds, and walnuts), nut shells (e.g., pecans and almonds), fruit pits and stones (e.g., olives, cherries, peaches, plums, and apricots), fruit pomace (e.g., apple, citrus, and grape), and other materials. As these materials are separated in the extraction and processing period, they are already in collected form and require no extra efforts in collecting.

Straw Rice and wheat straws along with the straws of several other crops are the biggest sources of crop residue. The table stated above shows that straws of a wide range of crops are left as residue and that can be used as energy sources. As rice and wheat are two major crops cultivated around the globe, the amount of straw generated from their cultivation is extremely high. In many third-world and developing countries that produce these crops at an appropriate level, uses these straws as a major source of energy. But a big drawback of the straw is they generate a lot of smoke as they contain a higher moisture level.

Sugarcane Sugarcane leaves and tops are really good fuel due to their high flammability. In the previous portion where liquid fuel generation from biomass has discussed, it included the use of sugarcane juice as a source of glucose. After extracting the juice, the complete body part becomes a considerably good

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source of energy. As most of the water is removed with the juice, the leftover body part can contain a really low moisture level after they are dried. The quality of the sugarcane bagasse depends on the species and the age of the sugarcane.

Rice Husks Rice husks are one of the major types of solid biofuels used around the globe. They are widely available as from each ton of rice, at least 200 kg of rice husks can be obtained and the worldwide production of rice during the 2017–2018 time period will be 481.04 metric tons as per the estimation of the United States Department of Agriculture (USDA). Other major sources of agricultural crop residues are cotton tin gash, grain cleanings, etc.

7.2 SLAGGING AND FOULING One of the major concerns of using agricultural crop residues is the amount of ash generated. As an extremely high amount of ash is produced if this type of energy source is used, this ash can create chemical deposits on the combustion chamber walls. This storage of ash generated on the chamber walls is known as slag. And if the ash gets stored on the heat transfer surface, it is known as foul. Slagging and fouling reduce the capacity of fuel usage as well as reduce the energy transferring potential of the production plants causing the wastage of a huge amount of fuel and energy. Potential slagging can be calculated using the equation stated below: kg alkali/GJ = 1 × 106/HHV kJ/kg (dry) × % ash × % alkali in ash:

7.2.1 Animal Manures Animal manures or animal fesses in simpler words are another available source of energy. This source of energy is used in rural areas of less developed countries due to their literally no production cost and higher capability of generating heat. As these elements contain a huge amount of nutrients, they can also be used as fertilizers in the agricultural fields.

Municipal solid waste and sewage sludge Municipal solid waste (MSW) is the raw untreated waste stream generated in the large municipal areas. MSW can be treated and converted into liquid

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fuel along with directly being used as fuel in electricity generation power plants. Sewage sludge is the solid residue left after MSW is treated and liquid fuel is extracted. These solid residues of the waste residue can be used as fuel in production facilities.

Urban wood waste Urban wood waste is the wastage of wood caused by landfill waste stream. Wood and wooden elements are used at an extremely high amount in the urban areas for different purposes. Some mentionable examples include wooden pallets, packaging materials, furniture, and toys; land-clearing, construction, and demolition debris; and dimension lumber, tree trimmings, forestry processing wastes, utility poles, and other wooden materials.

Energy Crops Energy crop is a recently developed idea of energy source compared to all other types of energy sources. During the time period of last 30 years, extensive cultivation of several crops has been undertaken solely for the purpose of energy generation. With the help of genetic engineering and extensive crossbreeding, the biomass productivity of these crops has been enhanced. With the help of genetic engineering, these crops are provided with a higher tolerance of flooding, drought, and other extreme natural conditions to ensure regulated supply of the crops. As a result, this source is one of the most regulated and available types of biofuels. Generally, these energy crops can be cultivated multiple times within a year, which distinguish them from other crops. Most common types of energy crops are SRWC, short rotation wood crops, and HSC, herbaceous energy crops. Though these energy crops can be transferred into any type of fuels, they are generally used in the solid and liquid forms. A wide variety of species have been considered for SRWC and success has been achieved in the cases of willows, eucalyptus, hybrid poplar, black locust, sycamore, sweet gum, silver maple, and few other species. SRWC plants are much faster in growth compared to the conventional woody plants of primary source species. While the natural plants require a time period of 20 to 30 years for development, these species can grow a lot faster and reach maturity within 3 years. Another advantage of these plants is that they can re-grow from the stem and so while extracting, the plants are chopped from the stamp rather than totally uprooting them. This technique

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allows them to regenerate faster and further reducing the required time for growth. Herbaceous energy crops, also known as HEC, are nonwoody plants providing energy. A wide variety of nonwoody plants have been genetically altered to be used a preferable source of energy. These nonwoody plants can be classified into two types: • •

Thin-stemmed grass and Thick-stemmed grass.

CHAPTER 8

GEOTHERMAL ENERGY

CONTENTS 8.1 The Concept of Geothermal Energy....................................................................... 195 8.2 Resources.............................................................................................................. 196 8.3 Use of Geothermal Energy..................................................................................... 198 8.4 Power Plant Components....................................................................................... 203

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(The energy radiated from the surface of the Earth is known as geothermal energy. In this chapter, the techniques to harness energy from this source will be discussed) Geothermal energy is the potential energy that can be achieved by utilizing the heat energy stored under the surface of the Earth. As discussed in the first chapter, thermal energy is the difference in temperature that causes heat transfer. Geothermal energy utilizes the heat stored under the Earth’s surface by exploiting heat transfer techniques. Geothermal energy is a source of clean energy with no carbon emission. Since the temperature of the Earth’s core is really high and being refilled due to solar radiation reaching the surface of Earth, geothermal energy is considered as one of the renewable sources of energy. The concept of using geothermal energy is an ancient one. It was during the Paleolithic period when the hot springs were used as a source of energy. More than 1000 years ago, American Paleo-Americans used the water of hot springs for cooking, cleaning, and bathing. During Qin dynasty in the thirdcentury BC, Chinese people used natural stone pools with hot springs. In the first-century AD, Romans used the hot springs under their control to supply warm water in public bath systems and under-floor heating system. First industrial use of geothermal energy began at the beginning of the 19th century. In 1827, the geyser system was developed in Italy which used the geyser steam to extract boric acid from volcanic mud. In 1892, world’s first geothermal power plant was established in the United States. During the 20th century, electricity became an available form of energy and the demand for electricity started rising fast. In order to cope up with the rising demand, geothermal energy came into consideration as the source of energy to generate electricity. The first geothermal generator was developed by PieroGinori Conti on July 4, 1904. By using the theory developed by him, the first geothermal power plant for commercial production of electricity was established in 1911. After that, there was a long gap of nearly fifty years until the Wairakei power plant of New Zealand was established in 1958. After that, a constant development encouraged the establishment of new power plants using geothermal energy and at present, it is one of the most renowned renewable sources of energy.

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8.1 THE CONCEPT OF GEOTHERMAL ENERGY At the initial stage of the formation of the earth which had occurred about 4.5672 ± 0.0006 billion years ago (BYL), it was an extremely hot cloud of gas. After formation, the cloud of gas started radiating energy. At about 4000 to 2500 million years ago, the upper surface of the then liquid earth became cool enough to solidify and created the earth’s crust. But even after 4 billion years of the generation of the earth’s crust, the inner layers of the planet are still extremely hot. For instance, the temperature at the center of Earth is actually close to the temperature of the center of the Sun, at about 5500°C. The amount of heat that is flowing outward from the core of the Earth is estimated to be 42 million megawatts. The diagram inserted below shows the temperature at different layers of earth.

Figure 8.1: Temperature at different layers of Earth http://www.spring8.or.jp/en/news_publications/research_highlights/no57_img/ fig1.png

The geothermal gradient, which indicated the difference of temperature between the core and the crust of the Earth, causes a continuous conduction of heat or thermal energy from the inner core toward the surface. Geothermal energy utilization aims to sustain the energy and use it as a replacement of the conventional sources of energy. The basic concept of the energy utilization process is pretty simple. Water can be heated and vaporized by digging a well deep enough to achieve higher temperature than waters’ boiling point. The water vapor is transported deep under the crust of earth toward the core and when it reaches the point where the temperature is higher than water’s boiling point, it vaporizes. Water vapor is lighter in density compared to liquid water, and so it travels toward the surface of the earth at a really high velocity. Using the pressure

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and the velocity of the water vapor or steam, a turbine is operated which generates electricity with the help of a generator.

8.2 RESOURCES The only resource of the energy used in the geothermal system is the high temperature of Earth’s core. The heat content of earth can be expressed as 1031 Joules, and the heat flows to the surface due to the temperature differences between the surface and the core of the planet. The heat transfer rate by conduction is 44.2 terawatts. Though the amount of power served is more than twice the current usage of the whole planet, most of the heat is extremely diffused and cannot be sustained. Moreover, a huge amount of heat fails to reach the upper surface of the earth due to the insulating characteristics of the crust of the Earth which keeps the energy stored under the topmost layer. The geothermal gradient of the crust of the earth is 25–30°C. The depths of the layers of Earth are shown in Figure 8.2. The figure shows that the crust of Earth is 30 to 40 km thick and since the lower geothermal gradient at the crust, the amount of energy that can be sustained using a geothermal pump can be enough for individual homebound use only. In order to avail sustainable amount of energy, higher temperature is needed, and it can only be achieved by reaching deeper portion of the crust of the Earth. In order to attain enough energy for industrial production of electricity from the geothermal sources, deep wells and other installations allowing the systems to reach the stored heat at a much deeper depth of earth need to be used. Though almost in every system available till now the hot springs and hydrothermal circulation methods are being used, the magma erupted through volcanic eruption, oil well and several other approaches can be used. Depending on the potential investment, electricity output from geothermal systems can vary from 35 GW to 2000 GW. A report published by MIT, the Massachusetts Institute of Technology, discussing the potential outcome from geothermal energy estimated that investing 1 billion dollars over a time period of 15 years can result in an electricity-generating capacity of 100 GW only in North America by 2050. It also predicted that with proportional investment and concerning technological advancement, it is possible to generate more than 2000 Zetta joules of electricity collectively, enough for the whole planet for several hundred years The only drawback in sustaining the huge amount of potential energy is reaching deep enough

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under the surface of earth. While the studies estimate the average depth of the extracting plants to be around 10 km, the deepest well serving geothermal energy is a little over 3 km. Resources of geothermal energy can be divided into three major types depending on the temperature of the source. They are as mentioned below. • • •

High-temperature source, Intermediate temperature source, and Low-temperature source.

Figure 8.2: Layers of Earth http://hyperphysics.phy-astr.gsu.edu/hbase/Geophys/imggeo/Earthsect2.gif

High-temperature source: The temperature of these sources rises over 180°C. The mentioned temperature is the lower temperature limit of these sources. Generally, these sources are created due to recent volcanic eruptions and are generally used in the direct use of the heat supplied by the source. There are a few non-volcanic areas on the surface of the earth that are able to deliver temperature of this range, these sites are being researched to be used in energy generation with the help of EGS. Intermediate temperature source: This type of source is frequently available on the surface of Earth. The temperatures of these sources are ranged within 100°C to 180°C limit. Generally, these sites are the deep sedimentary basins on the surface, and the areas are indirectly connected to volcanism and tectonic plates. These sites can be used for generating electricity.

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Low-temperature sources: These sources deliver a much less temperature. Generally, the temperature is lower than the boiling point of water and these sites are generally available in the form of natural hot springs.

8.3 USE OF GEOTHERMAL ENERGY Geothermal energy can be used in two major ways. • Heat supply for electricity generation, and • Direct heat delivery without any conversation. The first type of use requires the heat achieved from geothermal source to be really high; high enough to generate enough thermal energy and mechanical energy to generate electricity at an economically profitable amount. On the other hand, while heat achieved from geothermal sources is directly used, a much lower temperature can fulfill the need compared to the temperature required in electricity generation.

Enhanced Geothermal System (EGS) An enhanced geothermal system generates electricity without the help of any heat transfer through natural heat convection of the geothermal resources. In conventional geothermal systems, extracting geothermal energy has only become possible at places where the geothermal heat is available naturally. In these sources, heat reaches the surface with the help of the movement of magma and water. EGS technologies are developed to avail the heat without the help of the natural carriers. This system uses permeability of the rocks to achieve the temperature. Two long tunnels with thick walled high-pressureresistant pipes are planted through the earth till it reaches the depth of over a kilometer. Cold water or vapor is transferred downward through one pipe. The water or the vapor receives the heat and comes upward to the surface using the second pipeline at high pressure. The high-pressured gas is then used to rotate a generator and produce electricity.

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Figure 8.3: Diagram of EGS technique https://upload.wikimedia.org/wikipedia/commons/c/c6/EGS_diagram.svg

Geothermal Power Plants To generate electricity from geothermal sources, specially designed power plants are required. There are three basic types of geothermal power plants. They are as mentioned below: • • •

Dry stream plants, Flash stream plants, and Binary cycle power plants.

Dry stream plants This type of power plants uses hydrothermal fluids. Generally, geothermal steam is used as the hydrothermal fluid. The first power plant using this technique was established at Tuscany, Italy, in 1904. In this technique, the steam is directed to a turbine at high pressure. The kinetic and potential energy of the turbine rotates a turbine. The turbine is connected to a generator, and the rotation of the turbine provides enough mechanical energy for the generator to produce electricity. The temperature of the steam rotating the turbine is generally over 150 °C. The steam can contain water and vaporized hydrocarbon.

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Figure 8.4: Diagram of a dry stream power plant https://energy.gov/sites/prod/files/drysteam.gif

Figure 8.5: A dry stream power plant situated in California, USA https://energy.gov/sites/prod/files/dry_steam_geysers.jpg

Flash stream plants Flash stream power plants are the most common type of geothermal power generation plant. In this system, fluids are used at an extremely high temperature, higher than 182°C is used. Cold water is sent deep underground through pipelines. Water get extremely hot and come back on the surface due to its increased pressure. Water stays in liquid form because of the high pressure. When the water travels upward to the surface, pressure reduces, and a considerable amount of water vaporizes as the temperature is far

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201

above the boiling point of water at atmospheric pressure. The water stays liquid this long solely because of the increased pressure increasing the value of the boiling point. The steam is separated from the water and transferred to a sealed chamber over a turbine. The pressure of the vapor makes the turbine rotate, and the generator connected to the turbine generates electricity. The steam is referred as flash, hence the naming. The vapor is stored in a tank and these used vapors, as well as the leftover water, are injected back into the well. As the water circulates within the system continuously and it does not require a continuous supply of water or any external influence, this system can be considered as a potentially sustainable resource.

Figure 8.6: Diagram of a flash stream power plant https://energy.gov/sites/prod/files/flashplant.gif

Here, the injection well is used to send water and cold vapor under the surface, and the production well is used to have the geo-thermally heated gas back on the surface.

Binary cycle power plant This type of geothermal power plant enables the production of electricity using sources that can deliver much less heat. This system can operate at much less temperature than the minimum temperature required in the dry stream and flash stream plants. In binary cycle power plant, there are pumps installed that pump hot water from the geothermal well. This hot water is transported through a heat exchanger and then the cooled down water is again transferred back to the underground reservoir. Another fluid with much less boiling point (generally

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Physics of Energy Sources

hydrocarbon) is flown at high pressure through the other surface of the heat exchanger. This secondary fluid accepts the heat and vaporizes. The vapor is then directed through a turbine. The vaporized gas at high pressure rotates the turbine, and the connected generator transfers the rotating kinetic energy into electricity.

Figure 8.7: Diagram of a binary cycle power plant https://teeic.indianaffairs.gov/images/photos/Geotherm_Schematic3.jpg

The gas is condensed back to liquid form with the help of the cold water flowing downward and again cycled back through the heat exchanger and the turbine. Binary cycle power plants are completely closed systems, and the only component that emits from this type of power plant is water vapor. As a result, this type of power plant is considered to be environment-friendly green power plant. As this system can work at a much lower temperature compared to other types of geothermal plants, this system is more frequently usable. The optimum secondary fluid requires several characteristics. They are mentioned below: • • • • • •

The critical temperature and maximum pressure value are required to be relatively high. The triple point temperature of an optimum fluid should be low. Condenser pressure requires to be mid-ranged. A high enthalpy of vaporization. Thermal conductivity is required to be high. Nontoxicity and inertness are also required.

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203

The fluid should be affordable and easily available.

8.4 POWER PLANT COMPONENTS Different types of geothermal power plants require different types of infrastructures for the optimum performance. Yet there are many standard types of equipment that are compulsory for most of the systems. These components are as mentioned below: • Powerhouse equipment • Automatic control and communication system • Cooling system • Particulate and droplet erosion • Heat exchangers • Gas evacuation system • Re-injection system • Chemical injection system The powerhouse system is developed with several important components. They are as follows: • • •

Turbine Generator Condenser

CHAPTER 9

NUCLEAR POWER

CONTENTS 9.1 History of Nuclear Power...................................................................................... 207 9.2 Atomic Structure.................................................................................................... 211 9.3 Radioactivity......................................................................................................... 212

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(Nuclear power is the biggest source of global energy after fossil fuels and hydropower. This source of energy contains completely different characteristics. Nuclear power plants are extremely efficient as immense amount of energy in the form of heat can be generated from a little amount of raw material. In this technique, the energy stored in the subatomic level is harnessed. In this chapter, the basic concepts about nuclear reactions and nuclear power will be discussed along with the detailed discussion of the operating process of nuclear power plants.) Nuclear power is one of the major sources of energy in several countries of the world. Due to various reasons, the use of nuclear energy is limited to only a handful of countries. Though only 31 countries use nuclear energy, it still is responsible for 10.4% of global electricity production, which is much more than the contribution of oil and all other renewable sources combined. Moreover, if overall energy consumption is considered, nuclear power generates 5% of energy consumed globally. It is 2% more than the combined production of all renewable sources of energy except from hydroelectricity. And so, nuclear power can be considered as one of the most significant sources of energy.

Figure 9.1: Global primary energy consumption by source https://blogs-images.forbes.com/rrapier/files/2017/06/Primary.jpg? width=960

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Figure 9.2: Global electricity production of 2014 from all energy sources https://wattsupwiththat.files.wordpress.com/2017/04/world-electricity-gen-bysource.png

Nuclear power is the technique of generating energy by the use of nuclear reactions. An atom contains three smaller subatomic particles known as electron, proton, and neutron. These subatomic particles determine all the characteristics of an atom of every single material that exists. Changing the number of subatomic particles in an atom would literally change a material to a different one. In short, these subatomic particles are the determining characteristics of an atom of every single material in existence. These subatomic particles contain an extremely strong bond. If this bond is broken and a single subatomic particle is released from an atom, a huge amount of energy is released. This type of phenomenon is identified as nuclear reaction. In nuclear power plants, this character of a nuclear reaction is exploited, and the energy generated by altering the subatomic structure of an atom is used. In the nuclear reactions of these power plants, radioactive materials are used as raw materials. Radioactive materials have the tendency to release subatomic particles and become atoms of the lighter molecule. By systematically controlling these breaking down, energy is generated and harnessed.

9.1 HISTORY OF NUCLEAR POWER The phenomenon of energy generation due to a change in the subatomic structure of an atom was first observed by Ernest Rutherford in 1932. He observed that massive amount of energy was released if the protons of a lithium atom were split using a proton accelerator. He also observed that the energy generated follows the mass-energy equivalence discovered by

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Albert Einstein. But Rutherford along with other physicists such as Niels Bohr and Albert Einstein believed that attaining the capability of harnessing this immense amount of energy would be something achieved in far future. The same year, another subatomic substance neutron was discovered by Rutherford’s student James Chadwick. After extensive researches, Frédéric and Irène Joliot-Curie were able to discover radioactivity in 1934. In 1938, German chemists Otto Hahnand and Fritz Strassmann, along with Austrian physicist Lise Meitnerand Meitner’s nephew, Otto Robert Frisch, conducted experiments with uranium. They discovered that unlike all other types of nuclear decay where the decaying of only a partial mass of an atom takes place, the reaction they observed caused a complete change in the structure of the nucleus. The first time when electricity was successfully generated from a nuclear reaction was on the December 20, 1951, at the EBR–I research facility near Idaho. On June 27, 1954, world’s first nuclear power plant was established. It was the Obninsk nuclear power plant developed by USSR. After this, the use of nuclear power rose really fast. The energy production by nuclear power plants was less than 1 GW till the year of 1960. During the late 1970s, the production output rose to 100 GW. The output tripled within next 10 years and it was over 300 GW before the 1990s. After 1980s, the growth of nuclear power plants reduced drastically. The Second World War oil crisis of 1973 played an important role in the rapid growth of nuclear power plants but the accidents that occurred at Three Mile Island and Chernobyl power plants were the reasons that halted the construction of new plants, and eventually reduced the growth rate of power generation using nuclear reactions. The accident at Three Mile Island Dauphin County, Pennsylvania, USA occurred on March 28, 1979. Multiple mechanical failure and human errors are considered to be the reasons of the accident. The whole reactor was polluted with radiation and cleaning up all the radiation took 14 years and 4 months. The accident of Chernobyl power plant was much more devastating. The accident took place on April 26, 1986, in the No.4 light water graphite moderated reactor at the Chernobyl Nuclear Power Plant near Pripyat, which was a part of USSR. Now though, it falls in Ukraine. A late night safety test simulating a complete power failure and stationwide blackout with safety systems turned off was the initiating factor of the accident. Several design flaws in the system caused an uncontrolled reaction to generate. A failure in the water system generated a huge steam explosion

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resulting in an open-air graphite fire. Before the Fukushima nuclear disaster that occurred in Japan in 2011, it was the only nuclear disaster classified as a level 7 nuclear disaster. Level 7 is the highest level on the International Nuclear Event Scale. The whole power plant area, including the vast area adjacent to the power plant, is still extremely radioactive and completely inhabitable. Though a new approach of reinvesting in nuclear power plants was undertaken, the second level 7 occurrence of the Fukushima nuclear power plant in 2011 put a halt to it. At present, there are 449 nuclear power plants in operation in 31 countries. Most of these countries are gradually downsizing the nuclear power plant usage.

9.1.1 Atoms Since nuclear power plants use the effect of the changes in subatomic particles of an atom, it is extremely important to have a considerable idea of atoms. Atom is the smallest quantity of a matter which contains the properties and characteristics of that specific matter. In short, it is the unit defining particle of a matter. If atoms are further divided, the properties of the specific matter the atom belonged to will not exist anymore. The idea of atom was first provided by John Dalton in 1803 through his atomic theory. His theory consisted of four statements. They are mentioned below: 1) All matter is made of atoms. Atoms are indivisible and indestructible. 2) All atoms of a given element are identical in mass and properties. 3) Compounds are formed by a combination of two or more different kinds of atoms. 4) A chemical reaction is a rearrangement of atoms. Though the first statement was proven to be wrong afterward, his theory is still considered valid. Proving Dalton’s statement stating atom is indivisible, several research attempts during the mid-19th century proved that atom is actually divisible and it is made out of three subatomic particles. These particles are named electron, proton, and neutron.

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9.1.2 Electron During the late 1980s, extensive researches were conducted to understand radiation. A common equipment used in these experiments was a cathode ray tube.

Figure 9.3: A cathode ray tube http://cf.ydcdn.net/1.0.1.82/images/main/A5cathoderay.jpg

During the experiments, a ray emitting from the cathode to the anode was experienced and was named as cathode ray. Cathode ray appeared to be more fundamental than an atom and its existence in every matter as a static appearance was also discovered. J.J. Thomson proposed that the cathode ray is actually a stream of particles containing negative charge. This particle was later named as electron. He also measured the charge to mass of an electron to be 1.76 × 108 C/g. During the early 20th century, R.A. Millikan calculated the charge of a single electron to be −1.6022 × 10−19 C. Using the achieved data, he also measured the weight of a single electron. He used the following calculation. Mass of an electron = charge/(charge/mass) = (−1.6022 × 10−19 C)/ (−1.76 × 108 C/g) = 9.10 × 10−28 g

9.1.3 Proton It was established in the early 20th century that atoms are electrically neutral while electrons contain negative charge. As a result, it occurred to the researchers that an atom must have another particle with a positive charge

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of the same amount to provide the atom with the neutral condition. And this is when the concept of proton came into being. After extensive research, the existence of proton was proved. Proton is an electropositive subatomic particle whose electric charge is 1.6022 × 10−19 C, exactly the same of an electron. The mass of a proton is measured to be 1.672621898 × 10−27 kg.

9.1.3 Neutron Neutron is the third and the last subatomic particle present in an atom. It does not have any electric charge. So it is neutral like an atom. The mass of a neutron is identical to the mass of a proton 1.674927471(21) × 10−27 kg.

9.2 ATOMIC STRUCTURE Atomic structure implies the particular way proton electron and neutron are arranged in an atom. An atom can be divided into two major parts: the nucleus and the electron. Nucleus is a small amount of space in the center of the atom, where almost 99.9% of the weight of an atom is situated. Nucleolus engages less than 1% of the area of the whole atom. Inside a nucleon, the proton and the neutron are arranged in a three-dimensional circular form. Around the nucleus, the electrons are continuously circulating on a specific and exactly circular path. The difference in the characteristics of the charge of the electron and nucleus keeps the structure stable.

Figure 9.4: Model of an atom showing the structure of the nucleus and the circular pathway of the electrons

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https://byjus.com/chemistry/wp-content/uploads/2015/12/atom.png

The most important characteristics of the subatomic particles are listed below Table: 9.1: Properties of the subatomic particles Particle

Charge

Relative Charge

Proton Electron Neutron

1.6022 × 10−19 C 1 −1.6022 × 10−19 C −1 0 0

Mass in gram

Relative mass (amu)

1.6727 × 10−24 g 9.110 × 10−28 g 1.6750 × 10−24 g

1.007316 .000549 1.008701

9.3 RADIOACTIVITY Radioactivity or radioactive decay is the result of the lack of stability of an atomic nucleus. When the nucleus does not contain enough binding energy to hold the nucleus in its shape, radioactive decay occurs. The reason behind this lack of binding energy is the presence of excess amount of proton or neutron in the atom. Radioactive decay is frequent in the elements with higher atomic numbers as a higher atomic number indicates the presence of higher number of protons and neutrons in the nucleus. And while the nucleus holds an extremely small amount of area, it is extremely hard to keep too many protons and neutrons in a stable condition.

Figure 9.5: position of the radioactive elements in the periodic table

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https://www.sigmaaldrich.com/content/dam/sigma-aldrich/articles/biology/ marketing-assets/periodic-table-elements.png

Radioactivity causes different particles to blast out off the nucleus generating rays with high penetrative power. There are three types of radioactive decay. They are as follows: • • •

Alpha decay, Beta decay, and Gamma decay.

9.3.1 Alpha Decay An alpha particle is basically like a helium nucleus. So, an alpha particle contains two protons and two neutrons. These four subatomic particles stay connected with each other. During the beginning of the decay when the subatomic particles leave the atom, they primarily leave in the form of their parent atom following quantum mechanical prices. Later the protons repel from the nucleus due to the positive electromagnetic energy of the protons. Even the repelled protons repel each other because of this positive charge. This repelling reduces the number of protons in the nucleus, and a reduction in the number of nuclei transforms the original atom into a different atom of a much stable element. Generally, the mass number is reduced by four and the atomic number reduces by two at a single step. And so, if a uranium-238 suffers from alpha decay, it will become thorium-234. This radiated particle with two protons is known as the alpha particles.

Figure 9.6: Example of an alpha decay

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https://d2gne97vdumgn3.cloudfront.net/api/file/hCmldLDET1GEtR3oWut7

The characteristics of alpha particles are stated below. • • • • •

Energetic nucleus of helium which is relatively heavy. The amount of kinetic energy possessed by alpha particle is 5 MeV. It is really rare to have alpha decay only. Generally, this type of decay takes part along with gamma decay. Alpha particles ionize matters. They separate the matter’s positive ions from the electrons containing negative ions. They conduct the ionization frequently and lose their kinetic energy extremely fast. As a result, alpha radiation has a really short range.

9.3.2 Beta Decay Beta decay can be of two types: positive or negative. Each type of beta decay is expressed with symbols for easier identification. The symbols for these two different types of beta decay are β+ and β−. β−or negative beta radiation occurs due to the transformation of a neutron into a proton. Transformation continues, and an electron and an antineutrino are also created from a neutron. This type of reaction occurs when the atom contains extra neutrons. β+decay occurs from a similar type of reaction. But instead of a neutron being transformed, proton transforms and creates neutron, positron, and electron neutrino. Characteristics of beta decay are stated below: • • •

• •

These particles are energetic electrons. They are lighter and contain a single negative charge. The mass of this type of particle is identical to the mass of a single electron. These particles follow a zigzag path while running through any metal which is highly absorbing. This zigzag pathway makes the ultimately covered distance higher than the potential coverable distance if travelled straight. Having really low mass, they reach the relativistic engine. While traveling faster than the speed of light, these particles

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generate a shock wave of electromagnetic radiation. This radiation is known as the Cherenkov radiation. Beta decay shows continuous spectrum.

9.3.3 Gamma Decay After the occurrence of alpha or beta radiation, the nucleus is generally left with excess energy which pulls it into an excited state. In order to travel to a lower energy state, the electron emits a photon within the ultraviolet and infrared range. A nucleus cannot release a photon. The only way it can release its extra energy is by emitting gamma radiation. The characteristics of gamma radiation are as stated below: •

• • •

• • • •

Gamma rays are technically high-energy photons. The energy contained by gamma ray is 10000 times more than the visible photons. As photons do not have any mass and electrical charge, they cannot ionize any matters directly. They use indirect ionization process to ionize matters. Three major types of interactions a gamma radiation shows while reaching the surface of any metal are photoelectric effect, Compton scattering, and pair production. Gamma ray is able to travel at the speed of light. They have high penetration capability, and so they are able to travel a lot further compared to other types of radiations. Gamma ray can be prevented by using led or uranium shielding. Gamma rays frequently generate with alpha or beta radiations.

Nuclear Reactions Nuclear reactions are the basic working method of the nuclear power plant. Nuclear reaction is the process by which two nuclear particles interact and generate two or more nuclear particles along with gamma ray. Thus, a nuclear reaction changes at least one material into another. In this type of reaction, an element turns into another different and more stable element. Unlike chemical reactions, where the reaction takes place at an atomic level, the reaction in atomic one takes place in the subatomic level. The biggest characteristic of these reactions is that these reactions absorb or release energy at an immensely higher amount compared to chemical

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reactions. Pressure, temperature, catalysts, and other affecters of molecular level cannot affect these reactions.

Basic Classification of nuclear reactions Two major classifications of nuclear reaction are the direct reactions and the compound nucleus reactions. •

Direct reactions: In this type of reaction, a single interaction occurs within the projectiles taking part in the reaction. As there is only a single interaction, this type of reactions is active for an extremely short period of time. • Compound nucleus reactions: This type of reaction includes several interactions within the nucleuses taking part in the reaction. As a result, these reactions take much longer time period. Nuclear reactions can be generally classified into the following types: • Elastic scattering • Inelastic scattering • Capture reactions • Transfer reactions • Fission reactions • Fusion reactions • Spallation reactions • Nuclear decay. Among these reactions, nuclear fission, nuclear fusion, and nuclear decay are the most frequently occurring types of reactions. As nuclear decay has already been discussed in the radioactivity part of this chapter and nuclear fusion does not take place in the nuclear power plants, only nuclear fission reaction will be discussed.

Nuclear Binding Energy Nuclear binding energy is the amount of energy required to break a nucleus down and disassemble the nucleus of an atom into its components. The energy is needed to pull the subatomic particles away overcoming the strong nuclear force active within the subatomic particles present in the subject atom. The mass of the intact nucleus is always less than the mass of the separated particles. The binding energy present within the particles can be measured with the help of the difference of the mass. If the binding energy

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is expressed with Eb according to Einstein’s law of relativity, it can be stated that Eb = mc2. And as the value of c is constant, it can also be stated that the nuclear binding energy is depended on the rest mass of the particles.

Nuclear Fission In simple terms, nuclear fission is the nuclear reaction by which a heavy nucleus with a mass number over 200 breaks down and becomes a smaller nucleus of a lighter element. The heavier nucleus stays at an unstable form and so while it releases extra nucleus, it releases a huge amount of energy with it. The first nuclear reaction studied was the fission of uranium-235 isotope. More than 30 steps took place and finally strontium and xenon were found as the last result of the reaction.

Figure 9.7: A standard nuclear fission reaction layout http://www.atomicarchive.com/Fission/Images/fission.jpg

In nuclear physics, nuclear fission is considered as either a nuclear reaction or a radioactive decay. This reaction emits gamma radiation. The occurrence of decay during fission is extremely rare and is identified as spontaneous fission. Generally, neutron induced fission reactions are conducted in power plants. In this process, a heavy nucleus of an atom of an instable element is treated with a neutron which forms a more compound nucleus and brings it into an exciting form in such way that the changed energy level can be stated as, Excision > Ecritical. The excited compound nucleus reacts and breaks down into two fragments. During this breakdown, radiation is generated by the nucleus to get out of the excited form and a huge amount of heat is released with the radiation. While the big and heavy nucleus breaks down, it creates

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two smaller and lighter nucleuses; along with this, several neutrons break free of the nucleus and roam around as free neutrons. These neutrons repeat this process with other heavy nucleuses and initiate a chain reaction.

Chain Reaction The nuclear fission occurring in a nuclear reactor is a controlled chain reaction. A nuclear chain reaction is the most effective and efficient way of keeping nuclear fission operative repetitively. In this process, a single neutron reacts with a nucleus of Uranium or with any other heavy element. The nucleus breaks down following the fission process and turns into the nucleus of a smaller element and released a huge amount of heat and several free neutrons. These free neutrons react with other heavy nucleus available and repeat the precious reaction. The amount of free neutron keeps increasing and this reaction keeping occurring, at the multiplied proportion depending on the amount of neutrons being free at every stage. But if this process of chain reaction keeps continuing without any control, extreme amount of heat would be created, causing devastating effect on the surroundings— literally destroying everything that is close enough.

Figure 9.8: A chain fission reaction http://www.nuclear-power.net/wp-content/uploads/2014/10/chain-reaction. jpg? d484e7

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In order to control the heat production for safety as well as to cope up with the demand of energy, control rods are used. These rods attract and eliminate extra neutrons from the system, hence establishing control over the complete process.

Raw Materials for Nuclear Reaction In the nuclear power plants, specific heavy materials are used. Due to the higher atomic number, these elements stay in unstable condition and as a result are easier to break into a smaller nucleus. As primary fuel, uranium and plutonium are used. Generally, uranium is used as enriched oxide of uranium. But in several reactors, natural uranium is also used. Plutonium is used in a handful or reactors as a support source with uranium. Along with the fuel, water, heavy water, or graphite is added as moderator to control the reaction level. In order to keep the temperature of the process controlled, water or carbon dioxide is added as coolant.

Nuclear Power Plant Components In a nuclear power plant, the special form of potential energy known as the nuclear binding energy is used at the main source of energy. Using nuclear fission reaction, the heavier nucleus of the radioactive element is broken and nucleuses of two lighter and more stable elements are formed. In order to attain stability, the nucleus releases a huge amount of energy in the form of heat while breaking down. This energy is harnessed and used to run a turbine. The rotation of the turbine generates electricity. In order to complete the production process successfully, the power plant requires several specific mandatory components. These components are listed below. • • • • • • • • •

Nuclear reactor Steam generators Pressurizer Sub-cooling margin Reactor coolant pumps or cooling system Safety systems Steam turbine Generator Condenser

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Condensate-feedwater system

Nuclear Reactor Nuclear reactor is the most important component of a nuclear power plant, nuclear research facility or a nuclear-powered vessel. The operation of the reactor is to initiate and control the chain nuclear fission reaction. Along with nuclear power plants, nuclear reactors can also be used in nuclear research facilities as the source of neutron and as the source of fuel in nuclear propelled vessels.

Figure 9.9: A nuclear reactor https://media.licdn.com/mpr/mpr/shrinknp_400_400/AAEAAQAAAAAAAAhzAAAAJGRhZmZlYmUyLTE4NTEtNDg4Mi1iMTYwLWM2MzNjM2NiZTY3NA.jpg

Nuclear reactors can be classified into a range of different ways. This variation is caused due to the presence of a lot of factors that are important enough to be the determining factor of measurement. Considering the type of nuclear reaction occurring in the reactor, nuclear reactors can be classified into two major types. • •

Nuclear fission reactor and Nuclear fusion reactor

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Figure 9.10: Classification of nuclear reactors depending on the type of reaction

Nuclear fission reactor: In this type of reactor, fission reaction takes place. Generally, uranium and sometimes plutonium is used as the fuel of this type of reactor. A reaction is also possible using thorium fuel. Fission reactors can be further classified into two major types. They are discussed below in brief. •



Thermal reactors: Thermal reactors are the most frequently used type of reactors. This type of reactor uses slowed or thermal neutron to keep the fission operational. Almost all the nuclear plants operational at present use this type of reactor. A neutron moderator is used in this type of reactors. Moderators absorb extra neutrons as well as slow them down until the temperature of the neutrons is thermalized. The neutrons become thermalized when the kinetic energy of the neutrons equalize with the kinetic energy of the surrounding particles. Sometimes the moderator used in the reactor multitasks as the coolant also. Generally, water is used as the coolant. In order to increase the boiling point of the water so that the water can absorb a higher amount of heat, the war is supplied at an incredibly high pressure. The fuel, moderator, and the coolant are kept in a vessel known as the reactor vessel. There is a control unit to keep the temperature and reaction under control. To prevent radiation, the vessel is separated from the external environment with a radiation shield. The whole system is installed inside a containment building. Fast neutron reactors: These rectors use the opposite type of neutrons used in the reactors of the previous type. Since the fast neutrons are used and there is no requirement of slowing the process

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down, these reactors do not require any moderator. Moreover, less coolant is added to the fuel in this type of system. In this process, the fuel requires to be much more pure to successfully continue the chain reaction. As almost all the actinides come into the reach of the fast-moving neutrons, fission occurs to almost all of them and less transuranic waste is generated in this type of reactors. But still, this type of reactor is hardly used due to its much higher installation and operating cost. Nuclear fusion reactors: In fusion reaction, several smaller nucleuses along with one or multiple neutrons join and generate new nucleus with a higher number of neutrons. This type of reaction generally absorbs energy and so they are hardly used in any power plants. Farnsworth–Hirsch reactor is one of the few reactors that use nuclear fusion process. This reactor is used to generate neutron radiation. Depending on the type of moderator used, reactors can be classified into several major types. • Graphite-moderated reactors. • Water-moderated reactors. • Light element-moderated reactors. • Organically moderated reactors. Graphite-moderated reactors: This type of reactor uses graphite coolant. Though graphite coolant is a common moderator, in recent times, the use of this moderator has reduced. Water-moderated reactors: This type of reactor uses water as the moderator. There are two types of water-moderated reactors: •



Heavy water-moderated reactors: Heavy water is deuterium oxide. The reactors using un-enriched uranium generally use this type of moderator. The advantage of using heavy water as the moderator is that it slows down the neutrons which make it possible to induce nuclear reaction using un-enriched heavy elements. Water works as an excellent moderator due to the presence of hydrogen atoms whose mass is relatively similar to an independent neutron. Light water-moderated reactors: This type of reactors uses ordinary water as moderator. Light water is the most common type of moderator used. If the temperature of the water rises during the reaction, the density of water reduces and it creates less resistance

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223

to the neutrons and so reaction chain accelerates. As other types of moderators require more elaborate thermalization, heavy water and graphite moderators can make use of natural uranium possible. Generally, when light water is used as moderator, it also performs as the coolant for the radiator. There are three types of light water reactors available. They are as mentioned below: Pressurized water reactor (PWR), Boiling water reactor (BWR), and Supercritical water reactor (SWR).

Figure 9.11: A standard light water reactor https://en.wikipedia.org/wiki/File: Pumpless_light_water_reactor.jpg





Light element-moderated reactor: There are two different forms of light element-moderated reactors available. Molten salt reactors: This type of reactors uses the salt of light elements such as lithium and beryllium. They work as the constituents of the coolant and matrix salts, LiF and BeF2. Liquid metal cooled reactors: This type of reactors use a mix of lead and bismuth. Organically moderated reactors: This type of reactors uses organic materials as moderator. In the case of these reactors, moderator and coolant are always different due to the lower

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boiling point of the organic materials. If the development time and the time period of being used are considered, reactors can be divided into four types of reactors. They are mentioned below. •

Generation I reactors: These are the primary-level reactors. Mainly the prototype reactors, reactors designed for research and development, and reactors built for non-commercial use fall into this category. • Generation II reactors: These are the oldest design for the commercial power plants. Generally, the reactors established during the time period 1965–1996 are considered as the generation II reactors. • Generation III reactors: Those reactors that received alteration or modification after 1996 are considered as generation III reactors. • Generation IV reactors: The technological advancement required to establish this type of reactors is yet to achieve. New technologies are currently under development in order to provide more efficiency along with much more safety. When these technologies will be usable and will be installed in new reactors, those reactors will be marked as generation IV reactors. Though the reactors are in operation for more than twenty years, the naming and generation division was conducted within the time period of 2000 to 2003 AD. Depending on the physical state of the fuel when they are used in the reactor, reactors can be classified in three major ways. • Solid fueled, • Liquid fueled, and • Gas fueled. Depending on the utilization and the purpose of the energy generated from the nuclear reactions occurring in the reactors, the classification is as follows: • •

Reactors for electricity: These reactors are installed in nuclear power plants. Reactors for propulsion: These reactors are installed in different types of vessels. There are several different types of transportation mediums that present use and contain potential usability of

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reactors as the primary source of fuel. Already existing vessels are mostly non-civilian armored vehicles designed for water. Depending on the type of coolant used, the most significant and important classification of the nuclear reactors is conducted. Classification of nuclear reactors using coolants as the determining factor is as mentioned below: • • • •

Water-cooled reactor (generally light water is used) Liquid metal-cooled reactor Gas-cooled reactors Molten salt reactors

Water-cooled Reactors This type of reactors is the most common type of reactors that are in use at the present time. For example, out of 104 reactors currently operational in the United States, all of them use water-cooled reactors. Generally, water-cooled reactors use normal light water. These reactors can be further classified into three major types: • • •

Pressurized water reactors (PWR), Boiling water reactors (BWR), and Supercritical water reactors (SWR).

Pressurized water reactor The reactor vessel of this type of reactors is technically a pressure vessel. This vessel controls the pressure of the fuel, coolant, moderator, and control rods. In this type of system, the reactor and the reaction are cooled and moderated with high-pressured liquid water. Generally, the pressure provided to the liquid water is around 16 kPA. The reason found behind pressurizing the water is to increase the boiling point of water. Normally, during atmospheric pressure the boiling point of water sits at 100°C, but at 16 MPa, the boiling point rises dramatically at approximately 350°C. The water temperature while entering the vessel is exactly 290°C. In the reactor, the water flows through the core, receiving temperature from the moderators, fuel, and controller rods and while the water leaves the system, the temperature is approximately 325°C. Due to the higher pressure, water stays liquid during the entire process and eliminates the potential hazard that can be caused by unwanted steam in the reactor vessel.

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Figure 9.12: A reactor with pressurized water cooling system http://www.nuclear-power.net/wp-content/uploads/2014/10/WWER_nuclear_ reactor.jpg? d484e7

The heat achieved through this stage is transferred directly to a heat transfer process which brings the temperature of the coolant water down at 290°C. The released temperature is absorbed by a secondary flow of water. The water used in this flow is at a much less pressure compared to the first stream of water and so the water vaporizes easily using the temperature released by the coolant water. This vapor is then run through a steam turbine. The rotation of the turbine provides the necessary energy required by the connected generator to generate electricity. Though the pressure of the second stream is much less compared to the first stream containing high-pressure coolant water, yet 6 to 7 MPa is considerably high compared to atmospheric pressure. Due to this pressure, the boiling point of the water of the second stream is approximately 260°C.

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Figure 9.13: The pressure vessel of PWR reactor https://en.wikipedia.org/wiki/Pressurized_water_reactor#/media/File: Reactorvessel.gif

The extremely high pressure in the primary water circuit is maintained at the static point with the help of a pressurizer. Pressurizer is another circuit or stream of water that is continuously heated up to the desired boiling point of the coolant water in order to provide the coolant water with the desired pressure.

Figure 9.14: A diagram showing complete layout of pressurized water reactor https://upload.wikimedia.org/wikipedia/commons/a/a0/PressurizedWaterReactor.gif

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In order to conduct the transferring process of coolant and secondary water streams, pumps are installed in the system. The control system of this type of reactor uses the inlet valves of the turbines to control the reaction. When the inlets are closed, water flow in the primary stream or circuit reduces. As a result, heat transfer is disrupted and the temperature of the core rises. Higher temperature reduces the density of the water and as a result, moderating capability of the water reduces. Less moderation in the reactor reduces fission, thus ultimately slowing the energy production down. On the other hand, opening more valves would cause an opposite effect on the system. The temperature in the core would reduce, increasing the density hence moderating capability of water, thus ending up increasing fission and energy production. The biggest advantage of PWR is the higher stability and the character of reducing production with increased temperature. Moreover, the steam running the turbine never gets exposed to the radiation. And the water exposed to radiation stays in a sealed stream circuit. As a result, the potential damage of radiative contamination is much lower. Another advantage is the position of the control rods—the rods are electromagnetically hung from the roof of the core. As a result, a power failure or any type of serious system failure would drop the control rods completely into the core, shutting the reaction down. This safety measure is known as the full insertion safety. Due to the higher efficiency level as well as increased safety measures of PWR, it is the most commonly used layout of nuclear reactors. Along with the power plants, the naval vessels using nuclear power also use this type of reactor due to its compact size.

Boiling water reactor A boiling water reactor (BWR) is the second most common type of reactor. It works in a similar way of a PWR, but the pressure of the coolant water is far lower. Generally, in this system, the coolant water is exposed to a pressure of 7.6 MPA. Due to this difference in pressure, the water in BWR boils, hence the name. But boiling in the coolant water does not occur in pressurized water reactor. There are several other differences in a BWR. There is no steam generator in this system. Moreover, the coolant water is the only stream present in the system. The coolant water receives the water from the reactor vessel. Due to the lower pressure, the water boils and turns into steam. This steam is then run through the turbine to generate electricity. After the steam passes the

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turbine, the steam is sent to a condenser where it releases heat and turns back to the liquid form. This liquefied water is again used for cooling the system.

Figure 9.15: A diagram of a boiling water reactor https://en.wikipedia.org/wiki/File: Boiling_water_reactor_no_text.svg

The diagram above shows a standard boiling water reactor. The marked portions of the diagram indicate following components: 1. Reactor pressure vessel 2. Nuclear fuel element 3. Control rods 4. Recirculation pumps 5. Control rod drives 6. Steam 7. Feed-water 8. High-pressure turbine 9. Low-pressure turbine 10. Generator 11. Exciter 12. Condenser 13. Coolant 14. Pre-heater 15. Feedwater pump 16. Cold water pump

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17. Concrete enclosure 18. Connection to electricity grid The control system of this type of reactor is extremely important. Due to the use of only one stream of water, there is a higher probability of radiation spilling out of the protective layer and polluting the environment. And because of this reason, the control system holds significant importance. The controlling process has two different approaches. • Inserting or withdrawing control blades and • Controlling the coolant water flow through the core of the reactor. Using the control rods to control the whole reaction process is a common approach. The amount of control rods is inversely proportional to the amount of nucleus going through nuclear fission. This relationship is the result of the main work potential of the control rods. Control rods are installed in the system for only one single reason and it is to absorb the neutrons. Control rods absorb a specific amount of neutrons and keep the nuclear fission under control. If a control rod is withdrawn, the absorption of neutrons will be reduced. The reactor will have a higher amount of neutrons which will accelerate the reaction and heat generation will also increase. While the rods are installed from above in a PWR, it is installed from below in BWR to have more equivalent distribution of water. The second approach requires the supply of coolant to be controlled. This approach provides better control with the capability to control the efficiency of the plant within 30% to 100% power generation capacity of the reactor. If the amount of coolant supply is increased, steam bubbles will leave the system faster. This allows the core to have a higher amount of water. The higher amount of water slows the neutrons down by multitasking as a moderator. Slower neutrons react at an increased number, and so the energy output increases. On the other hand, if the water supply in the core is reduced, the reactor will have a higher amount of steam and less water. As a result, moderation of neutron decreases. Lack of moderation provides the reactor with fewer neutrons and as a result, the rate of fission decreases. The main feedwater system of the reactor controls the amount of water flow in the circuit. Recently, a more efficient and upgraded design of boiling water reactor has been developed. This design is known as the advanced boiling water reactor or ABWR. This system was first designed during the 1980s and 1990s and further upgrades to the design have been conducted which is

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still operational. This design includes more sophisticated and advanced technologies such as complete computer control, automation of the plant, improved safety system, advanced automated control rod removal and installation system, and an upgraded pumping system. These upgrades increase the output of a single reactor up to 1350 MW. The biggest advantage of ABWR is that the system is compatible with installing multiple reactors in a series. This type of reactor has several advantages. The whole system working at a lower pressure reduces the cost as well as potential risk of hazard. A pressure vessel is treated with less stress, enhancing the life cycle of the vessel. Lower operating temperature further reduces both the cost and risk. Moreover, this system requires fewer components compared to the PWR, as unlike that system, this type of reactor has only one stream flow. Even the recirculation loop is ditched in the newer modified designs which further simplify the process. Because of the emergency core cooling system of this type of reactors, it is assessed that BWR would be able to sustain higher scaled internal and external disasters compared to SWR. Moreover, this system does not require an external force and this further cuts the cost. And so, the pumps can be completely eliminated from the system. Not requiring boric acid eliminates the probability of corrosion.

Supercritical Water Reactor This type of reactor is a Generation IV reactor. This reactor exists in theory only. Necessary technological advancement is yet to be achieved. The design of this reactor shows the use of light water; in fact the design is based on basic light water reactor. The only difference is that the design is upgraded so that the operating condition includes supercritical pressure. Here, the term critical indicates the critical point of water, not the reactor. Though this system was under experiment during the 1950s and 1960s; it was the time period of 2010 to 2013 when detailed plans regarding these reactors were developed.

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Figure 9.16: Supercritical water reactor scheme https://upload.wikimedia.org/wikipedia/commons/thumb/5/59/SupercriticalWater-Cooled_Reactor.svg/482px-Supercritical-Water-Cooled_Reactor.svg. png

The supercritical water reactor or SCWR is designed to use supercritical water as a coolant. The neutron moderator is still light water like other conventional systems. The advantage of operating at a supercritical point is that above this point, the density of steam and water would be the same. Thus, the requirement of pressurizers, steam generators, recirculation pumps, steam separators, and driers is understood. The supercritical point also eliminates the necessity of boiling. The much simpler structure with much less amount of equipment reduces the establishment and construction cost by a huge margin. Moreover, this simpler system makes the whole process much safer and reliable.

Steam Generators Steam generators are heat exchangers. It is a compulsory element of the pressurized water reactors. It contains a heat transfer zone along with entry and exit ways for primary and secondary water streams. These streams enter and exit the system staying completely separated, without having any physical integration with each other. This separation is arranged to prevent radiative pollution.

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Pressurizer This element is also required for pressurized water reactor. This mechanism is a separate vessel with water steam at the desired temperature. The primary stream comes to thermal interaction, and the pressure of the primary stream is enhanced using this mechanism.

Steam Turbine The steam turbine is one of the major components of the power plant. It is the only mechanism that harnesses the heat generated from nuclear fission reaction and delivers it to the engine. The design of the steam turbine is more or less the same of the turbines used in wind energy, hydropower, and geothermal power plants. But, due to the sophisticated structure and work process of the whole system, specific types of blades and turbine setup can be used. For example, only two types of blades can be used in this system. The first one is the basic blades and the second one is the nozzles. As the energy output is really high compared to all other different types of power plants, the blades and other mechanisms of the power plant require being special purpose built depending on the data of planned output and every other related conditions. As the system works in extremely high temperature and pressure, multiple protective layers have been applied to reduce thermal and pressure damage. A special alloy of nickel—titanium and aluminum— has been developed for the blade-forming purpose only.

Generator Generators used in this system are a little bit different from the conventional types of generators used. As the energy output is much higher compared to other sources and the amount of mechanical energy delivered is extremely higher, the generator requires to be much more sustainable and capable of withstanding stress.

Main Condenser The main condenser is one of the most important elements of a nuclear power plant. The steam that runs the turbine requires cooling down and returning to liquid form to be usable again. Condenser carries out this responsibility. A condenser is a cross-flow pipe with continuous water flow submerging the cross-flow tube. The tube is built with materials that allow heat transfer. When the hot gas travels within the piper, the flowing water

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receives energy from the pipe, and the pipe receives temperature from the hot steam. Eventually, the steam cools down and turns into liquid form.

CHAPTER 10

ENERGY STORAGE

CONTENTS 10.1 Different Ways of Storing Energy......................................................................... 237 10.2 Classification Depending on Application............................................................. 251

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(With the continuous development of modern civilization, use of energy has diversified in an unthinkable way. Humans, as well as other living entities of the planet, require energy storage for surviving. Moreover, humans have developed wireless mobile devices which require off-grid source of energy. In order to fulfill these requirements, different types of energy storage technologies have been developed. In this chapter, different types of energy storage techniques will be discussed) Energy storage is the process of saving the produced energy so that it can be used later when it will be needed. There are different types of natural and artificial mechanisms of storing energy. The basic idea is to transform the more fluent form of energies, such as kinetic energy into more stable and storable forms of energy. Generally, energy is stored as different forms of potential energy. Mechanical and chemical energy are the preferable ways of storing energy. Storing energy is an ancient concept. Energy storing was considered important even in the times when humans used to live in caves. The moment humans started using clothes, they started storing energy. Cloths help reduce the amount of energy lost in the form of body heat. In the pre-agriculture stage of human civilization, humans used to store extra meat for future. This is another way of storing energy for later use. It is not only the living organisms that store energy. The sun is one of the biggest storages of energy where energy is stored in the form of chemical energy. With the gradual development of human civilization, humans started developing new mechanisms of storing energy. As they did not want to depend on nature for energy, they started to invent artificial ways of storing energy. During the entire 20th century and the first portion of the 21st century, human civilization has advanced rapidly. This rapid advancement requires a huge amount of energy to be supplied every single moment. To fulfill the requirement of the energy, grid-based energy delivery system has been delivered. But the main source of the conventional electricity supplied through the grid is fossil fuel. Fossil fuel is extremely harmful to the environment; also, the amount of stored fossil fuel under the surface of the earth is diminishing quickly. Several new environment-friendly and renewable sources are being developed such as solar energy, wind energy, wave energy, but these sources are still not developed enough to be able to continuously supply the necessary amount of energy. As a result, the

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importance of storing excess energy and using them when sufficient energy production is not achievable has been increasing rapidly. Off-grid use of energy was not a common phenomenon in the 20th century. But during the 21st century, the technological revolution has made portable devices and machines affordable and available, and many of those portable devices have become a part and parcel of the everyday life. As these devices cannot use electricity from the grid while being mobile, they require off-grid sources of electricity. As a result, developing highly efficient energy-storing technologies and mechanisms has become one of the most important concerns of modern science and technology.

10.1 DIFFERENT WAYS OF STORING ENERGY There is a variety of options available as energy storage. But all these storage systems can be classified into two major types. They are as mentioned below: • •

Natural storage of energy Artificial storage of energy

Figure 10.1: Two major classifications of energy storage

10.1.1 Natural Storage These are the storage and energy-storing mechanisms developed in natural ways. Most frequently used natural energy storages are mentioned below: • Fossil fuels • Biofuels • Glycogen, starch, and other nutrition Among these, fossil fuels have been discussed in the third chapter of this book and biofuel has been discussed in the eighth chapter of this book.

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So, here, only the nutrition materials or biological energy storage will be discussed.

Figure 10.2: Different types of natural storage of energy

Nutrition compounds or biological compounds are the different complex chain of compounds which contain a huge amount of energy stored in the form of chemical energy within their chemical bonds. These types of compounds are primarily created by the plants through photosynthesis process. Plants absorb the necessary energy from the Sun’s radiation, absorb carbon dioxide from the air through its leaves and other necessary elements through the roots in ionized form, and then reform the molecules to generate complex and stable compounds to store the energy. The reaction conducted in photosynthesis is as follows: H2O + CO2 = C6H12O6 + O2

In this equation, glucose works as the energy storage. The chemical bonds present in glucose are shown in the diagram below:

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Figure 10.3: chemical bonds in a glucose molecule http://www.chemicalformula.org/images/glucose.jpg

In the presence of oxygen, these bonds can be broken. When a human body requires energy, it burns the glucose molecules in presence of oxygen at the cellular level. These carbon bonds hold a huge amount of energy. Oxygen atoms free the carbons from weak H+ and OH− bonds and release the stored energy. This chemical energy has also been used in the creation of different types of energy storage too. Fossil fuels achieved their energy from these carbon bonds. The generation process of fossil fuels has been discussed in the third chapter of this book. When the living organisms were exposed to extreme temperature and pressure, these carbon bonds of different types of carbohydrates changed and turned into long chained hydrocarbons. So, it can be stated that the energy stored in nutrition compounds worked as the source of energy for fossil fuels.

10.1.2 Artificial Storage This type of storage does not contain naturally generated energy. These storages are developed with the help of advanced technologies by humans. The basic process of storing the energy is pretty much the same. Less stable forms of energy, in other words, different forms of kinetic energies are synthesized and stored as different forms of chemical energy. These artificial storages can be classified into several major types depending on the form of energy that energy gets stored into. They are as mentioned below: •

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Chemical energy Electrical and electromagnetic energy Mechanical energy Thermal energy

Figure 10.4: most frequent forms of energy used in energy storage

Among these, electrochemical energy storage is the most used type of storage. The most renowned electrochemical storage of energy is the rechargeable batteries. Most renowned storage having energy stored in electric form is the capacitor. Other storage techniques are superconducting magnetic, interseasonal thermal storage. Though mechanical and thermal storage is possible, they are not frequently used due to the economic disadvantages.

10.1.3 Battery The battery is the most frequently used technique for storing energy. Almost every single type of energy source use batteries to store energy. It is the most suitable and affordable energy storage technique among all the different techniques available. Due to the extremely high efficiency and other advantages, there has been a huge verity of batteries developed and used as

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energy storage. Batteries store energy in a unique electrochemical form and are designed to be usable at any time in any condition.

Classification of Battery There are two basic types of electrochemical batteries. They are as mentioned below: • •

Primary battery and Secondary battery.

Primary battery or non-rechargeable cells The primary battery converts the stored chemical energy into electrical energy. The chemical reaction occurring in the cell is irreversible. And so, primary batteries can be used only once. They cannot be recharged if the stored chemical energy is all used up. It is more suitable for the applications where high-density energy for a limited period of time is required.

Figure 10.5: Diagram of a standard primary battery http://images.tutorvista.com/cms/images/38/primary-battery. PNG

Primary batteries hold nearly 90% of the worldwide battery market. Though primary batteries provide a higher amount of energy, the lack of the opportunity of reusing the battery is a huge drawback. In every year, more than 15 million primary batteries are dumped after being used. A really limited amount of the dumped batteries are reused, leaving almost complete mass of the batteries exposed in the environment. And due to the presence of toxic heavy materials and the strong acids inside the shell of a battery, it is extremely dangerous and hazardous for the environment having that huge amount of batteries left untreated. Another drawback of primary nonrechargeable batteries is that a huge amount of energy is wasted during the

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production process of the batteries. In fact, the energy required to produce a battery is 50 times greater than the amount of energy it can deliver. Moreover, recycling the used up batteries require additional energy. Due to all these drawbacks, the use of primary battery is gradually reducing, making the secondary batteries a much preferable option. The overall reactions occurring in a standard cell is as below: Reaction in anode: Zn (s) = Zn2+ (aq) + 2e− Reaction in cathode: 2 e− + 2 NH4+ (aq) = 2 NH3 (g) + H2 (g)

2 NH3 (g) + Zn+2 (aq) = [Zn(NH3)2]2+ (aq)

H2 (g) + 2 MnO2 (s) = Mn2O3 (s) + H2O (l) Complete reaction:

Zn (s) + 2 NH4+ (aq) + 2 MnO2 (s) = [Zn(NH3)2]2+(aq) + Mn2O3(s) + H2O (l) The list below shows the most common primary or non-rechargeable cells.

Primary cells or Rechargeable Batteries Alkaline battery (zinc manganese oxide, carbon) Aluminum–air battery Atomic battery Betavoltaics Optoelectric nuclear battery Nuclear micro-battery Bunsen cell Chromic acid cell (Poggendorff cell) Clark cell Daniell cell Dry cell Earth battery Frog battery Galvanic cell Grove cell Leclanché cell Lemon/potato battery Lithium battery Pulvermacher’s chain

Silver-oxide battery Solid-state battery Voltaic pile Penny battery Trough battery Water-activated battery Weston cell Zinc–air battery Zinc–carbon battery Zinc chloride battery Lithium air battery Magnesium battery Mercury battery Molten salt battery Nickel oxyhydroxide battery Oxyride battery Organic radical battery Paper battery

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Secondary battery or rechargeable cells A secondary battery or secondary battery is a specific type of battery that can be reused over and over again. This type of batteries can be recharged if the energy stored in the barriers gets used up. When the stored energy finishes, the battery is called a load. A load can be recharged and reused. This type of battery is also known as accumulator. This reusable nature of the secondary batteries is the result of using reversible electrochemical reaction. These cells use specific chemical reactions which can be reversed while electricity is applied. Due to this reusable character, reusable batteries are replacing primary batteries fast. Secondary batteries can be of different shapes and sizes. Though the initial production cost of these batteries is much higher than primary cells, the ability to reuse for numerous times makes this type of battery far more economical compared to primary cells.

Charging When a secondary battery is charged, the positive material is activated and oxidized. The oxidized material produces electrons. The negative material consumes the electron and turns into a negative ion. This ionized dorm of the materials initiates electron flow through the circuit the battery is attached to. An electrolyte is placed on two sides of the battery as the buffer to prevent reaction of the elements inside the battery. In some batteries though, an active participant is placed. An electrical battery charger is used to recharge the loads. The chargers use AC current. The voltage of the source requires being slightly higher than the voltage of the battery so that the charges are forced to enter the battery. The charging time depends on the type of charger, adaptability of the charger, capacity of the source, etc. Charging can take from 15 minutes to more than 15 hours. The whole charging system is depended on the chemical components used in the cells.

Rate of discharge The rate by which a battery loses stored energy is expressed by the letter C. it is called C rate. C is the amount of charging or discharging occurring to a battery during the time span of one hour. A list of secondary batteries is included below.

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Secondary cells or Non-rechargeable Batteries:

Aluminum-ion battery Flow battery Vanadium redox battery Zinc–bromine battery Zinc–cerium battery Lead–acid battery Deep-cycle battery VRLA battery AGM battery Gel battery Glass battery Lithium air battery Lithium-ion battery Lithium ion lithium cobalt oxide battery (ICR) Lithium ion manganese oxide battery (IMR) Lithium ion polymer battery Lithium iron phosphate battery Lithium–sulfur battery Lithium–titanate battery Thin film lithium-ion battery Magnesium-ion battery Molten salt battery

Nickel–cadmium battery Nickel–cadmium battery vented cell type Nickel hydrogen battery Nickel–iron battery Nickel metal hydride battery Low self-discharge NiMH battery Nickel–zinc battery Organic radical battery Polymer-based battery Polysulfide bromide battery Potassium-ion battery Rechargeable alkaline battery Rechargeable fuel battery Silicon air battery Silver-zinc battery Silver calcium battery Sodium-ion battery Sodium–sulfur battery Sugar battery Super iron battery Ultra Battery Zinc ion battery

Types of Rechargeable Batteries There are six major types of rechargeable battery available. They are as follows: • Lead–acid (Pb acid) • Nickel–cadmium (Ni-Cd) • Nickel–metal hydrite (Ni-MH) • Lithium–ion (Li-ion) • Lithium–polymer (Li–poly) • Zinc–air Lead-acid (Pb-acid) This is the most common type of battery that is used in recent time. This type of battery received immense popularity because of its sustainability and high performance. Moreover, these cells are really cheap if performance– cost ratio is considered. Though these batteries contain the lowest efficiency

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if energy delivery is considered against weight and volume still they are highly preferred by the users. In lead acid batteries, generally sulfuric acid is used, and electricity is produced because of the reaction within lead and sulfuric acid. Lead sulfate and water are generated as the result of the chemical reaction. When the battery is being recharged, electron flow through water and lead sulfate reverses the reaction and generates lead and sulfuric acid. Lead and lead oxide is produced at the negative plate, while sulfuric acid is generated at the positive plate.

Figure 10.6: A Pb-acid cell http://www.electroschematics.com/wp-content/uploads/2010/01/LEAD-ACID-BATTERY.png

This battery can be found in various versions. In automobiles, shallow cycle version of this battery is most suitable as this form of the battery is capable of providing with the short but huge burst of energy required to initiate combustion in the engine. Another form of this battery is the deep-cycle version. This form of the Pb-acid battery is best for continuous full charge and discharge cycle.

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Figure 10.7: A diagram of a Pb–acid cell https://www.doitpoms.ac.uk/tlplib/batteries/figures/Lead_acid.png

Another form of the battery is the gel-cell battery. The electrolyte is turned into a gel to prevent spillage of electrodes. Because of the gel nature of the anode and cathode, this battery can be used upside down or sideways.

Nickel–Cadmium (NiCd) In this type of battery, the positive plate is built with cadmium and the negative plate is nickel hydroxide. Positive and negative electrodes are separated with the help of a nylon separator. The casing is built using stainless steel and the electrodes are placed within potassium hydroxide electrolyte. This type of batteries are light compared to conventional Pb-acid batteries and being sealed, they are free from the risk of spillage or creating a short circuit and so these batteries are used in the applications requiring frequent recharging. This type of batteries has a longer deep-cycle life and higher temperature tolerance compared to other types of cells. The biggest drawback of these batteries is the existence of memory effects. Memory effect is frequent in the batteries using nickel. If the batteries are frequently partially charged, they seem to “forget” their original capacity and start holding less charge than their original capacity. This effect can be repaired by charging each cell of the battery individually and taking them through a deep charge and discharge cycle.

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Figure 10.8: A cutout diagram of a standard NiCd cell http://www.upsbatterycenter.com/blog/wp-content/uploads/2014/05/c03_012. gif

Nickel-metal hydrite (NiMH) This battery is technically an improved version of the nickel–cadmium cell with higher energy output. Instead of cadmium, this battery uses metal hydride as the anode. This change eliminates the environmental concern along with providing better performance. Another advantage is that the memory effect is nearly inexistent in this type of battery. It has several drawbacks too. Generally, this battery has a faster discharge cycle, less capacity in providing high peak power. Moreover, damage by overheating occurs frequently if overcharged. Lithium–ion (Li-ion) This is one of the most recent developments in the field of energy storage. Compared to conventional lead acid cells, this type of battery provides with three times more output. This huge leap in the power was possible because of the use of lithium. Moreover, the cell voltage of this type of cell is 3.5 V. which is nearly double of the voltage of lead acid and three times more than the voltage of other cells. Higher voltage requires fewer cells to be present in a battery and so production cost is also much less.

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Figure 10.9: A standard Li-ion battery https://upload.wikimedia.org/wikipedia/commons/thumb/b/b2/Nokia_Battery. jpg/255px-Nokia_Battery.jpg

Similar to the types discussed earlier, this type of battery suffers from a few drawbacks. The biggest drawback is the tendency of reacting with any type of liquid electrolyte. Moreover, a layer of lithium is stripped away during the completion of every single charging cycle. As a result, a thick electrode is required to be installed in order to provide long enough life cycles. This enhances the production cost a lot and makes it more expensive compared to other conventional batteries.

Figure 10.10: Diagram of a Li-ion battery https://img.talkandroid.com/uploads/2016/12/diagram-of-a-lithium-ion-battery.jpg

This type of battery requires delicate usage with elaborate charging as overcharging can damage the battery. Preventive measures are required to stop the battery from overcharging.

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Lithium–polymer (Li-poly) This type of battery is technically a lithium battery that contains solid polymer instead of electrolytes. A film of metallic lithium is bonded with a layer of solid polymer and stored in a metal container in this type of battery. The polymer performs as the separator as well as the electrolyte of the battery.

Zinc–Air In this type of battery, oxidized zinc is used as an electrode, a potassium hydroxide as electrolyte, and a carbon-positive bar as the positive electrode. This type of battery absorbs oxygen from the environment and turns it into oxygen ion. While recharging, these oxygen atoms are released.

Figure 10.11: Cutout of a zinc air battery http://hear-better.com/blog/wp-content/uploads/2012/03/Inside-a-battery.jpg

Battery Design While designing a battery which is to be used in conducting specific applications, the following characteristics will have to be considered. • • • • • •

Voltage Current C/D period and duration Temperature while operating Lifetime in number of charged and discharged circles Cost, weight, and size constraints.

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Electrolysis and Electrolytic Cell Electrolysis is a process of transferring electric current through a liquid substance and causing a chemical change to the substance. Electrolysis is the basic principle of the working process of the renewable batteries. During this chemical change, the number of electron of the subject material changes. The system in which an electrolysis reaction takes part is known as the electrolytic cell.

Figure 10.12: An electrolytic cell http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch20/graphics/20_7. gif

Electrolysis is a special kind of redox reaction containing endothermic characteristics. Electrolysis is not a continuous reaction. External energy is supplied to the molecules taking part in the reaction, and those molecules achieve or lose electrons because of the external effect. Electrolysis reaction is generally conducted in an aqueous form. Electrolysis cell contains two electrodes. Electrodes are the long and thin plate of materials which achieve or release electron during electrolysis. Distinctive half cells exist, and each half cell contains their own polarity. Generally, the cathode is the positive (+) charge and an anode is the negative (-) charge. The charges occur this way because of the behavior of the battery connected to the cell.

Reactions at Anode Though oxidation occurs in anode, the polarity of anode is positive in electrolysis. External power source takes away certain amount of electron

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from the anode. Losing electron, atoms of anode become positive ions and experience free movement in aqueous.

Reactions at Cathode The external source of energy provides the cathode with extra electrons and so that the cathode achieves electronegative polarity. Due to its electronegative nature, positive ions of the liquid get attracted to the cathode. By receiving electrons, positive ions attain balanced form and become a part of the cathode. The longer this reaction continues, anode keeps decaying while cathode keeps increasing in volume.

10.2 CLASSIFICATION DEPENDING ON APPLICATION •





Automotive battery: This type of battery is built to supply necessary electricity to a motor vehicle. Generally lead-acid batteries are used as automotive batteries. But automotive batteries require several specific characteristics. An automotive battery requires to have the capability of providing a short-time energy blast in order to start the engine. It is also capable of quickly getting recharged using the electricity generated by alternator of the vehicle. Its additional duty is to supply additional required energy if the alternator cannot deliver the total required energy by itself. Backup battery: Backup batteries are designed to provide with emergency electric power when the primary source of electricity is not available. Backup batteries can be of different size and capacity. Starting from small single-cell batteries with the capacity to provide backup power for several minutes to large batteries in production plants to ensure continuous uninterrupted electricity supply. Some commons examples of backup batteries are aircraft emergency batteries, burger alarms, UPS for computers, etc. Battery (vacuum tube): During the early development stage of electric machineries, most of the electric devices contained vacuum tube. These tubes required batteries for power. Multiple batteries were required at each one of them had specific duty to fulfill. These batteries were A battery, B battery, and C battery. A battery was used to provide electricity to the filament of the vacuum tube. B battery was used to supply initiate voltage of

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a tube. And finally, C Battery was connected to have electricity supply to control grid. Battery pack: Battery pack is a combined set of several batteries or individual cells. They can have parallel, series, or a mixed connection within each other depending on the necessity of the consumer. One of the major uses of battery pack is electric vehicles. Battery room: Battery room is a bigger scaled battery pack. A considerable number of batteries are utilized in this type of system. Generally this type of facility is used to have uninterrupted electricity. Biobattery: This type of battery is not yet ready for commercial use. But the prototypes are showing a potential shakeup in the energy storage technology. This type of batteries uses the organic materials and compounds as their source of energy. Generally, the source of power for these batteries is glucose. The biggest potential advantage of this battery over other batteries is the capability of instant charging. Button cell: This type of battery is used in small electric machines such as wristwatch, calculators. This type of battery was named this way because of the button-like shape. CMOS battery: This is a coin-shaped battery designed for providing electrical support to the bios setup of a computer system. The expected lifetime of this battery is three years. Common battery: Common battery is a single-cell battery that is connected to two multiple circuits at the same time. Commodity cell: Commodity cells are the ones produced in bulk amount and are used in portable electronic devices. Electric vehicle battery: Technically this is one type of battery pack. In the full electric and plug in hybrid vehicles, large battery pack with high energy storage capacity is used to provide the vehicle with enough power so that it can be used in daily commute. Flow battery: This type of battery is also known as redox-flow battery. In this battery, chemical energy is provided by two different chemicals from separate containers being mixed with each other and releasing ion. Inverter battery: This type of battery works like an inverter.

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Lantern battery: Generally rectangular alkaline or zinc carbon primary battery is built to be used in flashlights and electric lanterns. These batteries contain multiple batteries in a single housing. • Nano-batteries: These batteries have been developed to provide power to the nano-scaled technology. These batteries are produced for nano-tech and so these batteries themselves are nano-scaled. Apart from these, several other lesser known types of batteries which are developed for being used in specific systems are as mentioned below. • • • • • • • • • •

Nano-wire battery: Local battery Polapulse battery Photoflash battery Reserve battery Smart battery system Watch battery Water-activated battery Wet cell Zamboni pile

Capacitor A capacitor is a two-terminal electrical component. It contains resistors and inductors in its physical structure. The capacitors are one of the fundamental passive components used. Almost every single circuit contains a capacitor or it. Capacitor is capable of storing electricity in an electrical field. Within two electrical conductors, the existence of capacitance can be observed. Capacitor enhances this capacitance. A capacitor holds the ability to store energy when there is no energy source connected to the circuit. And so, capacitors can be used as battery or any other electricity storage system. Compared to conventional batteries, the capability of capacitors is a little less. While conventional alkaline batteries can supply up to 590 J per kilogram, the amount is 360 Joules per kilogram in the case of capacitors. Super capacitors can hold a huge amount of electricity. It can absorb and supply electricity much faster. But the only drawback of the super capacitors is that they are nearly 10 times larger than the conventional batteries.

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Figure 10.13: classification and types of super-capacitors https://en.wikipedia.org/wiki/File: Supercaps-family.png

10.2.1 Hydroelectric Storage Hydroelectric storage is one of the most convenient ways of storing energy. Using this technique, extra energy is stored in the hydroelectric plants and used when they are required. In the hydroelectric power plants, the difference of elevation within the surface of the water and the turbine is used to transform the potential energy stored in water into electricity. During off-peak and monsoon periods, amount of water available exceeds the amount needed to fulfill the supply. In this situation, the extra water is stored in reservoirs built on the higher altitude source of water. These reservoirs keep the water stored and the potential energy of the water surface stays stored within. During peak hours or during the time period when the supply of water reduces due to various natural reasons, the extra water is released from the reservoir and the potential energy stored in the water can be utilized to harness necessary energy.

10.2.2 Thermal Storage In this type of energy storage, energy is stored in the form of heat. Hot water or any other liquid can be stored in special containers with insulated walls to prevent heat transfer that can hold the thermal energy for a certain period of time.

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10.2.3 Compressed Gas Energy can be stored in the form of compressed air or gas. Molecules of gas have the tendency of moving fast. So, when they are compressed, and the molecules cannot move the way they move in the environment, kinetic energy gets stored in the form of potential and heat energy. When the gas is allowed to leave the cylinders, they release the heat while expanding and, on that time, the heat can be utilized.

10.2.4 Biofuels Biofuels are one of the prime examples of energy storage. Biofuels are the organic materials that can be used to generate energy. Wood is one of the major sections of biofuel and also a really good storage of energy. Plants store the sustained energy within their cells and wood being a part of a plant body, the stored energy can be utilized when required. Human and animal wastes are another major part of biofuels. A lot of heat can be generated using these. The nerve of these biofuels can be stored for future use by processing those biomass materials and storing them in the form of conventional fuel such as charcoal, oil, and methane gas.

10.2.5 Gravitational Storage Another easy way of storing energy is to change the elevation of the certain object. The energy used to change the elevation and put it at a higher position than it previously was at gets stored inside the materials. The energy can be later released by letting the material fall freely.

REFERENCES

Websites 1. 2. 3. 4. 5.

https://www.wikipedia.org/ https://www.nasa.gov/ https://www.britannica.com/ http://www.bbc.co.uk/education/highlights https://www.thoughtco.com/

Links 6. 7.

https://en.wikipedia.org/wiki/Non-renewable_resource http://www.bbc.co.uk/schools/gcsebitesize/geography/energy_ resources/energy_rev2.shtml 8. http://nineplanets.org/sol.html 9. https://www.eia.gov/beta/international/data/browser/#/? 10. h t t p s : / / w w w . e n g i n e e r i n g . c o m / E l e c t r o n i c s D e s i g n / ElectronicsDesignArticles/ArticleID/9286/A-Review-of-

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Concentrated-Solar-Power-in-2014.aspx 11. https://cbc-wb01x.chemistry.ohio-state.edu/~woodward/ch121/ch2_ atoms.htm 12. https://www.britannica.com/science/electrolysis Reference Books 13. Chen, C. J. (2011). Physics of solar energy. New Jersey, United States: John Wiley & Sons. 14. CIGR—The International Commission of Agricultural Engineering. (1999). CIGR handbook of agricultural engineering: Energy and Biomass Engineering (Vol. 5). St Joseph, USA: The American Society of Agricultural Engineers. 15. Evans, R. D. (1955). The atomic nucleus. New York: McGraw Hill Book Company, Inc. 16. Heywoord, J. B. (1988). Internal combustion engine fundamentals. New York: McGraw-Hill Education. 17. Nelson, V. (2013). Wind energy: Renewable energy and the environment (2nd ed.). CRC Press. 18. Patel, M. R. (2005). Wind and solar power systems (2nd ed.). CRC Press. 19. Pfeiffer, D. A. (2006). Fossil, fuels oil, food and the coming crisis in agriculture. Gabriola, BC, Canada: New Society Publishers. 20. Schobert, H. H. (2013). Chemistry of fossil fuels and biofuels. Cambridge University Press. 21. Smets, A. H. M., Jäger, K., Isabella, O., van Swaaij, R. A. C. M. M., Zeman, M. (2016). Solar energy: The physics and engineering of photovoltaic conversion, technologies and systems. Cambridge: UIT Cambridge Ltd. Research Papers 22. Beckjord, E. S. (2003). The future of nuclear power: An interdisciplinary MIT study. Cambridge MA: Massachusetts Institute of Technology 23. Blodgett, L., & Slack, K. (2009). Geothermal 101: Basics of geothermal energy production and use. Washington DC: Geothermal Energy Association.

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24. Boundy, B., Diegel, S. W., Wright, L., & Davis, S. C. (2011 September). Biomass energy data book (4th ed.). Technical Report No. ORNL/TM2011/446. Oak Ridge, TN, USA: Oak Ridge National Laboratory. 25. Intensive programme “Renewable energy sources.” (2010 May). Železná Ruda-Špičák, Czech Republic: University of West Bohemia. 26. IPPC. (2011). IPPC special report renewable energy sources (SRREN) and climate change mitigation. Cambridge, UK and New York, NY, USA: Cambridge University Press. 27. Matis, H. (2003). Nuclear science—A guide to the nuclear science wall chart. Contemporary Physics Education Project (CPEP), Berkeley, California. 28. REN21. (2015). Renewables 2015 global status report. Paris: REN21 Secretariat. 29. World Energy Council. (2013). World energy resources: 2013 survey. London: World Energy Council.

INDEX

A Alarming information 27 Aromatic 41 Artificial approach 28 Artificial process 22 Artificial technique 17 Atmospheric pressure 225, 226 Atomic structure 211 Average temperature 66 B Biomass energy generation process 156 Biomass energy sources 157 Biomass engineering 160 Biomass material 255 Boiling water reactor (BWR) 228 Building materials 107

C Cadmium telluride 76 Carbon bond 239 Carbon dioxide 36, 44, 47, 66 Chemical energy 14, 16, 17, 34, 35, 53, 60, 61, 68, 75, 76, 95, 236, 238, 239, 241, 252 Chemical explanation 2 Chemical reaction 17 Chernobyl Nuclear Power Plant 208 Chromosphere 70, 73 Commercial sources 24, 25 Common phenomenon 237 Complete mechanism of harnessing energy 115 Complete turbine system 119 Complex mixture 42 Complex organic compound 181 Concentrated solar power (CSP)

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103 Conducting necessary processing 40 Consuming solar radiation 106 Controlling process 124 D Deep-cycle version 245 Density reduces 107 Development of human civilization 2 Direct current (DC) 83 Distribution substation voltage 126 Downstream wind 112 Drum-shaped turbine 149 E Earth orbiting satellites 77 Electrical component 92 Electrical control system 125 Electrical hazard 126 Electric connection 108 Electric energy 14, 18 Electricity 68, 74, 76, 78, 79, 82, 83, 84, 85, 86, 87, 95, 99, 103 Electricity production plant 24 Electricity storage system 253 Electrochemical energy storage 240 Electrolysis 250 Electromagnetic energy 213 Electromagnetic mechanism 151 Electromagnetic waves 79, 80, 89 Electron flow 243, 245 Energy crop 191 Energy production 72, 78 Energy sources 22, 23, 24, 25, 26, 27, 28, 29 Energy storage 236 Energy utilization process 195

Enhanced Geothermal System (EGS) 198 Etectricity generation plant 31 Ethanol 161, 162, 163, 166, 168 Ethanol production 162, 163, 168 Ethanol production process 169 Extra energy 254 F Financial currency transferring 25 Fossil fuel 34, 35, 36, 46, 47, 156, 157, 158, 159 Frequent process of energy 17 G Generating electricity 133, 135, 137, 153 Genetic engineering 191 Geothermal energy 194, 196, 197, 198 Geothermal gradient 195, 196 Geothermal power plant 194, 201 Geyser system 194 Global circulation 113 Global energy production 111 Global warming 27 Gradual development of human civilization 236 Gravitational energy 14, 15, 16 Gravitational potential energy 138 Grid-connected system 84 H Heat energy 255 Heat transfer 100, 101, 102, 226, 228, 232, 233 Human civilization 2, 4, 160 Human waste 156 Hybrid system 85

Index

Hydrocarbon 34, 35, 37, 40, 41, 42, 44, 45, 46, 47, 48, 60, 63 Hydroelectric power plant 133, 134, 135, 138, 139, 140, 141, 142, 143, 145, 146, 147, 151, 153, 154 Hydroelectric storage 254 Hydrologic cycle 130 Hydrology 134 Hydropower 129, 130, 131, 132 Hydrothermal fluid 199 I Internal combustion engine 61, 62 K Kinetic energy 12, 13, 106, 111, 130, 132, 134, 147, 153 Knowledge influenced modern physics 5 L Landfill waste stream 191 Liquid bitumen 43 Lithium battery 249 Lithium ion lithium cobalt oxide battery 244 M Maximum power point 87, 91, 92, 95 Mechanical energy 103, 138, 147, 151, 198, 199, 233 Mechanical power 112, 122, 126 Mechanism 233 Mentioned temperature 197 Methane fermentation 179, 180, 181

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Methane production 180, 181 Microscopic organism 36 Minimum potential power 134 Modern civilization 37, 47, 156, 157 Modern invention 77 Molecular transformation 44 Multiple fermentation vessel 166 Multiple liquid element 166 Municipal solid waste (MSW) 190 N Natural gas reservoir 47 Natural petroleum 45 Natural phenomena 22, 29 Natural philosophy 4 Natural reservoir 45 Nickel hydroxide 246 Non-living material 2 Nonrenewable energy sources 25, 26, 28, 29 Nonrenewable fuels 153 Nonrenewable source of energy 27 Nonrenewable sources 26, 27, 29 Nuclear energy 25, 27, 206 Nuclear fission reaction 216, 217, 219, 220, 233 Nuclear power 206, 207 Nuclear power plant 206, 207, 208, 209, 215, 216, 219, 220, 224, 233 Nuclear reaction 68 Nuclear reactor 218, 220 Nutrition compound 239 O Organic chemical compounds 34 Organic material 252, 255

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Organic matter 156, 157, 162, 180 Organic waste material 159 Oxidized zinc 249 P Perfect material 121 Petroleum industry 38 Photosynthesis 68, 75 Photovoltaic 77, 83 Photovoltaic effect 77 Physical system 7 Plutonium 219, 221 Potential energy 12, 14, 15, 16, 18, 194, 196, 199, 219 Produce electricity 198, 199 Production plant 132, 142 Propeller turbine 148, 150 Proximity analysis 52 Q Quantum physics 7 R Raw materials of ethanol 163 Renewable energy 25, 28, 29 Renewable sources 29, 30 Rotor diameter proportion 119 S Scientific knowledge 4 Single carbon atom 170, 171 Social build-up of human civilization 2 Solar energy 68, 69, 74, 75, 76, 77, 78, 82, 85, 99, 100, 103, 106, 107, 109 Solar system 69, 70, 75 Solar thermal energy 76, 100 Solar water heater 101, 102

Speed control system 123 Standalone electricity generator 108 Standalone system 93 Starchy organic material 164 Steam turbine 226, 233 Subatomic particle 207, 209, 212, 213, 216 Subatomic structure 207 Subatomic substance neutron 208 Suitable extraction process 174 Sulfuric acid 245 Supercritical water reactor 232 Surface layer 72 Surface mining 53, 54, 55 Sustained energy 106 Synchronous machine 122 Synthesizing natural gas 45 Synthetic ethanol 168 Systematized knowledge 2 T Temperature 68, 69, 70, 72, 73, 74, 91, 100 Temperature difference due 106 Thermal energy 240 Thermodynamic 7, 8, 10, 11 Thermodynamic system 8 Tinfoil structure 120 Total biomass energy 158 Transform electricity 128 Transportation system 120 Trash rack 145, 151 Turbine generates electricity 201, 219 Turbines include generators 139 U United States Department of Agri-

Index

culture (USDA) 190 V Ventilation system 57 Vertical turbines 115 Volatile matter value 52 Volcanic eruption 197 Voltage service converter (VSC) 128

W Waste material 158, 159, 186 Water turbine 132, 147 Water vapor falls 130 Whole production process 181 Worldwide battery market 241

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