Tidal Energy Systems: Design, Optimization and Control 0128148810, 9780128148815

Table of contents :
Front Matter
Copyright
About the Authors
Introduction to Energy Sources
Energy and Its Transformation
Types of Energy Sources
Primary and Secondary Energy
Commercial Energy and Noncommercial Energy
Nonrenewable Energy Resource
Categories of Nonrenewable Resources for Electricity Generation
Renewable Energy Sources for Electricity Generation
Mainstream Renewable Technologies
Solar Energy System
Wind Energy System
Horizontal and Vertical Axis Wind Turbine
Biomass Energy System
Biomass Conversion Process to Useful Electrical Energy
Thermal Conversion
Chemical Conversion
Geothermal Energy
Low Temperature Resources: Heating
High Temperature Resources: Electricity
Working of a Conventional Geothermal Power Plant
Wave Energy
Wave Energy Resources
Power Associated to a Sea Wave
Hydro Energy System
Hydro Power Basics: Head and Flow
Power and Energy
Worldwide Current Scenario of Renewable Energy System
Environmental Aspects of Renewable Energy Sources
Environmental Impacts of Different Technologies
Environmental Impacts of Wind Power
Environmental Impacts of Solar Power
Environmental Impacts of Geothermal Energy
Environmental Impacts of Biomass
Environmental Impacts of Hydroelectric Power
Exercise
Objective Type Question
Descriptive Type Question
Further Reading
Introduction of Tidal Energy
Historical and Parallel Scenario
Introduction
Global Scenario of Tidal Energy Systems
Indian Scenario of Tidal Energy System
Assessment of Tidal Energy System
Sihwa Lake Tidal Power Station, South Korea-254MW
La Rance Tidal Power Plant, France-240MW
Swansea Bay Tidal Lagoon, United Kingdom-240MW
MeyGen Tidal Energy Project, Scotland-86MW
Annapolis Royal Generating Station, Canada-20MW
Role of Tidal Energy in Nonconventional Energy Sources
Basic Principle of Tidal Power Plants
How the Tide Generates
Principles of Tidal Power Stations
Single-Basin System
Two-Way Tidal Barrage Generations
Two-Basin Tidal Energy Systems
Double-Basin System
Double-Basin With Linked Basin Operation
Double-Basin With Paired-Basin Operation
Available Technology and Concepts
Available Recent Technologies and Concepts
Advantages and Critical Points of Overtopping Converter
Basic OWC Components
Component of a Tidal Power Plant
Tidal System Component Classification Layer Description
Types of Turbines
Tidal Steam Generator
How Does It Work?
Advantages of Tidal Stream Generators
Disadvantages of Tidal Stream Generators
Tidal Lagoon
The Lagoon Wall
Estimation of Energy Calculation
Ocean With Single Basin Tidal Project
Tidal Dynamic and Structure of Tidal Currents
Tidal Current
Mathematical Function of Tidal Structure
Merits and Demerits of Tidal Energy Systems
List of Advantages of Tidal Energy
List of Disadvantages of Tidal Energy
Numerical
Exercise
Numerical
Objective-Type Question
References
Prefeasibility Assessment of a Tidal Energy System
Site Survey and Feasibility
Resource Assessment Models
One-Dimensional Resource Assessment
Two-Dimensional Resource Assessment
Three Dimensional Resource Assessments
Numerical Models for Resource Assessment
Theoretical Tidal Current Energy Resource
Technical Tidal Current Energy Resource
Practical Tidal Current Energy Resource Assessment
Accessible Tidal Current Energy Resource
Viable Tidal Current Energy Resource
Quantification of Tidal-Stream Resource
Resource Assessment by Regression Analysis
Software Used in Resource Assessment
Distances From the Load Center
Critical Path Method to Assess Duration to Generate Energy From a Tidal Power Plant
Advantages of CPM
Physical Boundaries of Assessment
Technical Boundaries
Geographical Boundaries
Surface Boundary Conditions
Momentum
Heat
Fresh Water
Lateral Boundary Condition
Bottom Boundary Conditions
Open Boundary Conditions
Boundary Condition for Time (Initial Condition)
Important Points Related to Physical Boundaries
Functional Physical Boundaries of Assessment
Static v/s Transect Field Survey
Quantitative Observations Through Static and Transect Survey
Qualitative Observations (Roving Surveys)
Data Analysis
The Challenge of Measuring Water Currents
Location Assessment by Farm Method
Tidal Optimal Unit Using Dynamic Programming Method
Resource Assessment by Flux Method
Maximum Steady-State Power Through Tidal Power Station
Transmission Line Analogy of a Tidal Power Plant
Primary Constant of a Transmission Line
Secondary Constant of a Transmission Line
Voltage Regulation of a Tidal Power Plant at a Suitable Site
Prefeasibility Assessment With Detailed Project Report Preparation and Appraisal
Simple Payback Period
Advantages
Limitations
Return on Investment (ROI)
Limitations
Net Present Value of a Tidal Power Plant
Internal Rate of Return of a Tidal Power Plant
Advantages
Exercise
Numerical
Objective-Type Questions
References
Further Reading
Optimum Sizing and Modeling of Tidal Energy Systems
Introduction
Modeling of Tidal Energy Conversion Systems
Modeling of a Tidal Energy System by HOMER Software
Modeling of Diesel Generator for Tidal Power Plant
Modeling of Battery Bank for Tidal Power Plant
Modeling of 9MW Tidal Power Plant Through MATLAB
Tidal Energy Device Variability
Characteristics of Towing Tanks
Limitations With Physical Model Effects for TECs
Water Tunnel
Characteristics of Enclosed Water Tunnels
TIDAL Basin
Tidal Energy Framework
Component Classification Layer Description
Hydrodynamic System
We have divided the working phenomena of the above components into seven segments:
Modeled Processes
Numerical Solution of Tidal Energy System
Swell Effect (Long-Length) Tidal
Energy Generation Through Tidal Power Plant
Basin Scale
Pressure Wave Velocity in Conduit
Head Loss Due to Friction
Tidal Current Modeling
Modeling of a Tidal Current Turbine
Turbine Power Output
The Power in the Tides
Forces on Blades and Torque of Tidal Turbine
Mathematical Modeling of Hydraulic Turbine
Tidal Energy Facility Size
Functional Requirements
Basic Requirements Imposed for Tidal Energy Generation by Grid Codes
Grid-Connected Marine Energy Infrastructures
Electrical Connection Functional Requirements
Electrical Configurations Schemes
AC Transmission-HVAC Transmission
Possible Configurations
DC Transmission
HVDC VSC
Possible Configurations
Elements of a Grid Connection Infrastructure
Cable Connectors
Offshore Substation
Subsea Cable
Technical Issues Related to AC transmission
Tidal Measurement Devices
Acoustic Doppler Profile
Radar Systems
Tide Gauge
Wave and Tide Sensor
Features
Software Used in Modeling of a Tidal Power Plant
Tidal Farmer
WaveDyn
Steps of a Tidal Turbine Power Plant
Inverter/UPS Rating
Required Number of Batteries
Backup Hours of Batteries
Battery Charging Time
Charging Current for Batteries
Charging Time Required for Battery
DC Load Is Connected As Well As Battery Charging
Rating of Charge Controller
Exercise
Exercise
References
Further Reading
Control System of Tidal Power Plant
Introduction
Automatic Control of a Tidal Power Plant
Need for automatic control of tidal power plant:
Control System for Unit Operation
Information and Control Signals
Local Manual (Mechanical or Push Button) Control
Local Control of Unit From UCB
Control of Unit of Central Control Room and Off Site Supervisory Control
Synchronizing of a Tidal Energy System
Manual Synchronizing
Automatic Synchronizing
Control Strategies of Tidal Energy Conversion Systems
Theory of Hydrokinetic Energy Conversion
Tidal Turbine Control
Angle of Attack
Power and Efficiency
Calculating the Tip Speed Ratio
The Power Curve
Control Strategies
Tidal-Dynamic Energy Assessment
Turbine Configuration and Control Objectives
Drivetrain Model
The Field Oriented Control Method
Electromagnetic Torque
Unity Power Factor Control
Generator-Side Converter Control
Reactive Power Control of Tidal Power Plant
Design of Passive Components
Power Factor Correction (Active and Reactive Power Control)
Reactive Power and Voltage Control
Voltage Control
Tidal Generator
Dynamic Control of Tidal Current Turbine
Load Frequency Control
Control Mechanism of Speed Governing System: Governor Servo System
Governor Drive and Speed Setting
Turbine Model
Generator-Load Model
Stability Analysis of a Tidal Power Plant
Definitions
Electrical Protection of a Tidal Generator
Possible Faults
Stator Faults
Rotor Faults
Loss of Excitation
Unbalanced Loading
Overvoltage
System Frequency Swing
Thermal Protection of Tidal Power Plant
Failure of Cooling
Backup Over Current Protection
Transformer Protection
Station Bus Zone Protection
Transmission Line Protection
Two Terminal Lines
Overcurrent Protection
Phase-to-Ground Faults
Distance Protection
Phase-to-Phase Faults
The Impedance Type
Exercise
Reference
Further Reading
Reliability Assessment Model
Introduction
Failure Distribution Model of a Tidal Energy System
Time-Dependent Failure Mode of a Tidal Energy System
Counting Process
Series System Failure Rate Equations
Parallel System Failure Rate Equations
Reliability Analysis of a Tidal Energy System
Constant Failure Rate Model
Model Uncertainties
Measurement Uncertainties
Constant Failure Modes of Tidal Energy Conversion Systems
Performance Assessment of Reliability Assessment
Reliability Analysis of Fault-Tree Analysis
Causes of Failure in a Tidal Renewable Energy System
Fault-Tree Construction and Analysis
Boolean Algebra and Reliability Calculation
Exercise
Further Reading
Tidal Energy Assessment and Economics
Introduction
Scenario of Tidal Energy System in India
Potential Location in India for Tidal Power Generation
India Lacks a Tidal Energy Policy
Grid Parity of Tidal Energy in India
Challenges With Tidal in Stream Technology
Government Support for Tidal Energy in India
List of Stakeholders Involved in the Development of Technology at the Central and State Levels
Harmonic Analysis of Tidal Power Plant
Assessment of Tidal Energy System by the Optimization Technique
Particle Swarm Optimization
Advantages and Disadvantages of PSO
Chaotic Particle Swarm Optimization (CPSO)
Big Bang Big Crunch
Teacher Learning-Based Optimization Technique
Teacher Phase
Learner Phase
Grasshopper Algorithm
Cuckoo Optimization Technique
Assessment of Tidal Energy System by Game Theory
Basic Concept of Game Theory
Game Theory in a Tidal Renewable Energy System
Mixed Strategy Nash Equilibrium
Role of Tidal Energy System in Clean Development Mechanism
The Role of the Kyoto Protocol and the CDM
Design of a Tidal Energy Project by Designated National Authorities (DNA)
Designated Operating Entities (DOE)
Private Gatherings
NGOs
CDM Project Completion Process
CDM and Forests
Present Status of CDM in India
CDM Potential From Gujarat
Present System for Public Sector CDM Projects in Gujarat
CDM and Waste Disposal
CDM's Role in Technology Transfer
CDM and Sustainable Development
CDM and Tidal Energy Promotion
Economic Analysis of a Tidal Power Plant
General Tariff Form
Investment Need, Appraisal, and Criteria
Criteria
Financial Analysis Techniques
Advantages
Limitations
Time Value of Money
Return on Investment (ROI)
Limitations
Internal Rate of Return
Advantages
Energy Performance Contracting and Role of ESCOS
Exercise
Objective-Type Questions
Reference
Further Reading
Index
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
Y
Z

Citation preview

TIDAL ENERGY SYSTEMS

TIDAL ENERGY SYSTEMS Design, Optimization and Control

VIKAS KHARE Associate Professor, Electrical School of Technology, Management and Engineering, NMIMS, Indore, India

CHESHTA KHARE Department of Electrical Engineering, SGSITS, Indore, India

SAVITA NEMA Department of Electrical Engineering, MANIT, Bhopal, India

PRASHANT BAREDAR Energy Centre, MANIT, Bhopal, India

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States © 2019 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/ permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-814881-5 For information on all Elsevier publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Katie Hammon Acquisition Editor: Raquel Zanol Editorial Project Manager: Karen R. Miller Production Project Manager: Bharatwaj Varatharajan Cover Designer: Mark Rogers Typeset by SPi Global, India

ABOUT THE AUTHORS Vikas Khare is an associate professor in School of Technology, Management, and Engineering, NMIMS, Indore M.P., India. He obtained his MTech (Honors) in energy management from DAVV Indore, India, and his PhD from National Institute of Technology in Bhopal, India. His main research interests are renewable energy systems, optimization techniques, and game theory. He is also a certified energy manager under the Bureau of Energy Efficiency in India. Dr. Khare has published various research papers in International repudiated journals and published books on the titles of “Renewable Energy” and the “Fundamentals of Electrical and Electronics Engineering”. Cheshta Khare obtained her ME(Honors) in power electronics at SGSITS, India, where she is also pursuing her PhD in power systems. Mrs. Khare is an assistant professor in the Department of Electrical Engineering at SGSITS in Indore, India. Savita Nema has over 20 years of experience in research in renewable energy and control systems, and holds both an ME in control systems and a PhD in solar photovoltaics. Dr. Nema has led several research projects and has published over 40 journal and conference papers. She is currently a professor and head at the Department of Electrical Engineering at MANIT in Bhopal, India. Prashant Baredar is an associate professor in the energy department at MANIT in India. He received his PhD in hybrid energy systems from Rajiv Gandhi Technological University in Bhopal. Dr. Baredar has 20 years of experience in mechanical engineering. He is on the editorial board of many international journals, including BLBIJEST and National Journal of Engineering Science, and is a reviewer for four international journals. He has successfully organized five national seminars and conferences on energy topics and has delivered 25 expert lectures and invited talks. He has guided 6 PhD theses and 42 MTech theses. He has published one patent on a reconfigurable mechanism for wind turbine blades. Dr. Baredar has published 102 research papers in national/international journals and at conferences, and has contributed to the books entitled Basic Mechanical Engineering, Practical Journal of Basic Mechanical Engineering, Renewable Energy Sources and Practical Journal of Basic Civil Engineering & Engineering Mechanics. He has served as a consultant on projects such as the investment grade energy audit of the Rajgarh Collectorate Building and finding a solution to reducing bearing temperature in hydro turbines in the Indira Sagar Hydro Power plant. A number of high level research projects funded by both state and central government are to his credit, and he is working on a project concerning the sensitivity analysis and optimization of a hybrid system combining solar, wind, and biomass power (Rs. 452,000), funded by Madhya Pradesh Council of Science & Technology in Bhopal.

vii

CHAPTER 1

Introduction to Energy Sources Contents 1.1 Energy and Its Transformation 1.2 Types of Energy Sources 1.2.1 Primary and Secondary Energy 1.2.2 Commercial Energy and Noncommercial Energy 1.3 Nonrenewable Energy Resource 1.3.1 Categories of Nonrenewable Resources for Electricity Generation 1.4 Renewable Energy Sources for Electricity Generation 1.4.1 Mainstream Renewable Technologies 1.5 Worldwide Current Scenario of Renewable Energy System 1.6 Environmental Aspects of Renewable Energy Sources 1.6.1 Environmental Impacts of Different Technologies Exercise Objective Type Question Descriptive Type Question Further Reading

1 3 4 4 5 7 8 9 25 31 34 37 37 37 38

1.1 ENERGY AND ITS TRANSFORMATION In physics and the field of engineering, energy is a versatile property of a generous system that cannot be directly pragmatic but can be evaluated from one circumstance to another with certain performance parameters. Energy plays an important role in any physical system and in different engineering applications, but it is difficult to give a definition of energy in a broad way because one form of energy converts into different forms of energy. However, the most frequent definition is that it is the capability of a system to perform desired work. A running person is said to be more energetic compared to a sleeping person. In physics, a moving particle is said to have more energy than an identical particle at rest. The characterization of work in engineering physics is the faction of a force throughout a distance and energy is deliberate in the identical units as work. If any human being pushes an entity n meters beside a conflicting force of f newton, fn joules(Newton-meters) of work has been done on the given entity; the personnel body has lost fn joules of energy and the entity has gained Fx joules of energy. In Fig. 1.1, a person emitted radiation energy from his or her own eyes, which shows how the power of the eye can be converted into radiation energy. The SI unit of energy is given by the joule (J) (the equivalent Tidal Energy Systems https://doi.org/10.1016/B978-0-12-814881-5.00001-6

© 2019 Elsevier Inc. All rights reserved.

1

2

Tidal Energy Systems

Fig. 1.1 Radiation energy from eyes.

to a newton-meter or a watt-second), the CGS unit is the erg, and the Imperial unit is the foot pound. Other energy units such as the electron volt,calorie,BTU, and kilowatt-hour (1 kWh ¼ 3600 kJ) are used in specific areas of science and commerce. Due to the conserved property, there is a major significance of energy in engineering because it depends on the law of conservation of energy, which states that energy can neither be created nor destroyed but can be changed into different forms. For example, in a mixer grinder, electrical energy converts into mechanical and sound energy. A hair dryer is one of the best examples that shows how one form of energy converts into a different form of energy. That’s because, in a hair dryer, electrical energy is converted into mechanical energy, thermal energy, and sound energy. Both examples show the phenomenon of energy transformation because energy transformation is the change of energy from one form to another. Energy transformation occurs everywhere every second of the day. Energy is converted from one form to another form; this conversion is also part of energy transformation, such as through fuel cell chemical energy conversion into useful electric energy. For electricity generation through hydro energy, first gravitational potential energy is converted into kinetic energy and then the kinetic energy is converted into useful electric energy through a DC or AC generator. Carnot’s theorem and the second law of thermodynamics presented some difficulties regarding when energy can be transformed into other forms of energy by work and heat. Energy is a scalar as well as vector quantity because the direction of conversion and transformation of energy is elaborated by entropy considerations. Most energy transformations are done on a small scale, but certain larger transformations, such as the transformation of electrical energy, are possible with the help of additional equipment. Fig. 1.2 shows energy transformation in which electrical energy, mechanical energy, thermal energy, sound energy, chemical energy, and light energy are converted from one form into another. Fig. 1.3 shows types of energy transformation in the form of renewable and nonrenewable energy sources. Transformation of energy into constructive work is an innermost and primary part of thermodynamics. At the primary level, the transformation of

Introduction to Energy Sources

Fig. 1.2 Two-way path of energy transformation.

Reversible transformation

Renewable energy source

Energy transformation Nonreversible transformation

Nonrenewable energy source

Fig. 1.3 Types of energy transformation.

energy is done in two ways: reversible thermodynamics and irreversible thermodynamics. In the mechanical-to-electrical analogy, thermodynamically reversible is related to renewable energy sources and thermodynamically irreversible is related to nonrenewable energy sources. A reversible process is one in which this kind of indulgence does not occur. In this case, the energy must partially continue as heat and cannot be entirely recovered as a useful form of energy.

1.2 TYPES OF ENERGY SOURCES Electricity through electrical energy is produced by the conversion and transformation of available energy, which is available in diverse forms such as several natural sources that include wind energy, kinetic energy of water, chemical energy of fuels, and nuclear energy of radioactive substances. Different natural energy sources are one of the major inputs for the monetary and financial growth of any nation. In different developing countries, conventional and nonconventional energy sectors are considered to be critically important for ever-increasing energy consumption, which required enormous investments to meet such demand. Besides nonconventional methods of electricity generation,

3

4

Tidal Energy Systems

conventional methods of power generation produce electrical energy through the use of prime movers such as diesel engines, petrol engines, and steam engines, which are also used for driving electrical machines for the conversion of electrical to mechanical and mechanical to electrical energy. The other methods of producing electrical energy without the use of prime movers are called nonconventional methods of electricity generation. Energy can be classified into several types based on the following criteria: • Primary and secondary energy. • Commercial and noncommercial energy. • Renewable and nonrenewable energy.

1.2.1 Primary and Secondary Energy Primary and secondary energy sources are the first stage of classification of different energy sources for electricity generation. Primary energy is the one that those sources that only engross insertion or exertion with or without partition from contiguous material, cleaning or grading, before the input energy personified in that source which can be converted or transformed into heat or mechanical work or thermal energy. Secondary energy is always the final and finishing touch of the primary energy source and also results from conversion and transformation of different types of primary energy sources. The best primary source is one that can be used directly as well as appear in the natural environment, such as coal, oil, natural gas, wood, nuclear fuels, the sun, the wind, tides, mountain lakes, the rivers, and the earth’s heat that supplies geothermal energy. There are several examples in which secondary energy sources derive from the transformation and conversion of primary energy sources such as petrol that is derived through the treatment of crude oil then electric energy obtained from the conversion of mechanical energy in hydroelectric plants and eolian plants. Fig. 1.4 shows the transformation of primary energy into secondary energy, in which waste, nonconventional, and conventional sources of energy are converted into electricity, bioproduct, and petroleum products.

1.2.2 Commercial Energy and Noncommercial Energy The energy sources that are used to generate electricity and that are available in the marketplace with a specific price are known as commercial energy sources. The most commercialized forms of commercial energy sources are electricity, coal, and advanced petroleum products. They are used for electricity generation on the basis of industrial, agricultural, transportation, and commercial development of the different countries of the modern world. In the well-stabilized industrialized countries, commercialized fuels are the major source not only for financial benefit, but also for the many domestic responsibilities of the general population.

Introduction to Energy Sources

Secondary energy

Primary energy

Waste

Biomass, wind, hydro, tide,sun

Petroleum product, solid fuels and gases Transformation

Crude oil, hard coal, natural gas, nuclear,etc.

Electricity & heat

Biofuels,etc.

Fig. 1.4 Transformation of primary energy into secondary energy.

On the other hand, the different energy sources that are not accessible in the profitable market with a price tag are classified as noncommercial energy sources. Noncommercial energy sources, which include fuels such as logs, cattle dung, and agricultural and urban waste, are conventionally gathered and not bought at a price used particularly in rural areas. These are also called traditional fuels and are often ignored in energy accounting. Fig. 1.5 shows types of commercial and noncommercial energy sources in which renewable and nonrenewable energy is related to the commercial energy sources.

1.3 Nonrenewable ENERGY RESOURCE An electricity-generated energy source that is not replaced or rarely replaced very slowly by natural processes is called a nonrenewable energy source. Fossil fuels, oil, natural gas, and coal are the prime examples of nonrenewable energy resources in which fossil fuels are frequently twisted by the decomposition of plant and animal waste; however, the rate of their production is extremely slow. A nonrenewable source is also known as a finite source and they do not renew themselves for sustainable financial extraction within significant human timeframes. For example, a nonrenewable energy source is created when original organic material, with the addition of heat and pressure, becomes a fuel such as oil or gas that is used for electricity generation. Metal ores are another example of nonrenewable resources in which the metals themselves are present in enormous amounts in the earth’s crust. They can never be fatigued, continually being intense and replenished over time scales of millions of years. In other words, metal ores are nonrenewable but generally

5

6

Tidal Energy Systems

Fig. 1.5 Types of commercial and noncommercial energy sources.

Energy sources

Renewable energy source Solar system Wind system

Nonrenewable energy source Traditional

Alternative

Gas

Thermal

Coal

Nuclear

Biomass system Geothermal Oil

Steam

Ocean system Hydro system

Fig. 1.6 Types of energy sources.

inexhaustible. In this respect, metal ores are considered to be in vastly greater supply to fossil fuels because metal ores are shaped by crustal scale processes that make up a much larger portion of the earth’s near-surface environment than those that form fossil fuels. This is also done without the need for specialized conditions where carbon-based life flourishes and fossil fuels can form. Fig. 1.6 shows types of energy sources in which solar, wind, etc., fall into the category of renewable energy sources and nonrenewable energy source are divided into two type’s, traditional and alternative. Traditional energy sources are used as an input in alternative energy sources for the generation of electricity. Table 1.1 presents types of energy sources, their conversion, and application.

Introduction to Energy Sources

Table 1.1 Types of energy sources and their application Energy sources Energy conversion and usage form

Hydro Energy System Biomass Energy system Geothermal Energy system Solar Energy system Direct solar Energy system Wind Energy system Wave Energy system Tidal Energy system

Power generation or electricity generation near to dam area Heat and power generation Urban heating, power generation, hydrothermal Solar home system, standalone or hybridized electricity generation Photovoltaic, thermal power generation as water heating system Power generation, wind generators, wind mills, water pumps Numerous designs of wave lagoon and wave dragon Barrages, single and double basin tidal stream

1.3.1 Categories of Nonrenewable Resources for Electricity Generation Nonrenewable resources can generally be separated into two main categories: fossil fuels and nuclear fuels. • Fossil fuels: Fossil fuels are the parts of organic matter, sometimes plants, that have decomposed and compressed over time. They have been compressed between different layers of the Earth’s sediments for billions of years. These deposits and the materials twisted from them tend to be highly explosive, making them an ideal nonrenewable energy source. They are difficult to obtain as they are naturally retrieved through drilling or mining, but fossil fuels are significant for the effort for the absolute amount of energy they produce. • Crude oil/petroleum: Crude oil is a nonrenewable or conventional energy resource that builds up in fluid form between the layers of the Earth’s crust. It is retrieved by drilling into the ground and by pumping the liquid out. The liquid product is then refined and used to generate many different electricity-generated products. Crude oil is a very resourceful fuel and is used to create plastics, artificial food flavorings, heating oil, petrol, diesel, jet fuel, and propane, among others. The worldwide top three oil-producing countries are Russia, Saudi Arabia, and the United States. • Natural gas: Natural gases congregate underneath the Earth’s crust and, like crude oil, they must be drilled and pumped out. Methane and ethane are the most frequent types of natural gases obtained through such processes, and these gases are most usually used in household heating as well as gas ovens and grills. Russia, Iran, and Qatar are the countries with the largest recorded natural gas reserves worldwide. • Coal: Coal, one of the major fossil fuels, is created by compacted organic matter similar to solid rock and it is obtained by mining. Out of all the developing countries, according to the Statistical Review of World Energy published in 2014 by BP, China produced an outstanding 48.3% (3240 million tons) of the world’s coal in 2014, followed by the United States,

7

8

Tidal Energy Systems

which produced a mere 14.8%. Coal is the most commercial and conventional energy source used typically in home heating and the running of power plants for electricity generation. • Nuclear fuels: The other form of nonrenewable resource used to produce energy, nuclear fuels, is primarily obtained through the mining and refining of uranium ore. Uranium is a naturally occurring element found within the Earth’s core. Most uranium deposits occur in small quantities, which miners gather together, refine, and purify. Once gathered, the uranium is brought together and compounded into rods. The rods are then submersed into tanks of water. When it reaches critical mass, uranium begins to break down and release energy that heats this water. This is known as “fission.” The heated water then creates pressure and it is this pressure that drives the turbines that generate the electricity we use every day. Nuclear fuels are key to maintaining the Earth’s environment because they are the cleanest of all nonrenewable resource.

1.4 RENEWABLE ENERGY SOURCES FOR ELECTRICITY GENERATION Renewable energy sources are also nonconventional energy sources that come from natural resources that are repeatedly replenished, such as sun rays, wind velocity, natural water resources, up and down tides, waves, and geothermal and thermal heat. In recent decades, about 16% of worldwide final energy consumption and electricity production was done by different renewable energy resources. About 10% of the electricity production comes from traditional biomass and 3.8% from hydroelectricity or by hydroelectric power plants. New renewable energy sources such as offshore wind energy systems and hydrogen energy accounted for another 3% and these techniques are growing very rapidly in different developing countries. Nowadays, the percentage of nonconventional resources in electricity production is around 20% with 15.8% of electricity coming from hydro power plants and 3% from other renewable energy sources. Renewable energy sources such as solar radiation, wind velocity, and the kinetic energy of water either directly or indirectly are likely to supply energy for almost another 1 billion years, at which point the predicted increase in heat from the sun is expected to make the surface of the Earth too hot for liquid water to exist. Renewable energy resources provide significant opportunities for energy conservation while improving energy efficiency and providing a pollution-free environment. This is part of sustainable development but, in contrast to other energy sources, it is concentrated in a limited number of countries. Rapid exploitation of renewable energy, energy efficiency, and scientific diversification of energy sources would lead to important energy security and financial benefits. Nowadays, renewable energy is replacing nonrenewable energy in four distinct areas: electricity generation, hot water/space heating, motor fuels, and rural (off-grid) energy services: • Power generation: Worldwide renewable energy sources provide 19% of electricity generation. Renewable power generators are increasing in many different countries and

Introduction to Energy Sources

unaccompanied wind energy systems are providing a major source of electricity in different countries, for example, 14% in one of the United States, 40% in the German state of Schleswig-Holstein, and 49% in Denmark. Some developed and developing countries get most of their electricity generation through renewable energy, such as Iceland (100%), Norway (98%), Brazil (86%), Austria (62%), New Zealand (65%), and Sweden (54%). • Heating: Solar heating systems are significantly involved in nonconventional heat in different countries, including China, which produced 70% of its heat generation through such types of heat-generating resources. Most of these heating systems are installed in multistory family unit apartment buildings, providing the hot water needs of an estimated 50–60 million households in China. Worldwide, the total installed solar water heating systems meet a portion of the water heating needs of more than 70 million households. The use of biomass for heating continues to grow as well and in Sweden, the national use of biomass energy has surpassed that of oil. • Transport fuels: Efficient renewable biofuels have contributed to a significant decline in oil consumption in the United States since 2006. The 93 billion liters of biofuel produced worldwide in 2009 displaced the equivalent of an estimated 68 billion liters of gasoline, equal to about 5% of world gasoline production. At the national level, at least 30 nations around the world already have renewable energy contributing more than 20% of energy supply. National renewable energy markets are projected to continue to grow strongly in the coming decade and beyond, and some 120 countries have various policy targets for longer-term shares of renewable energy, including a 20% target of all electricity generated for the European Union by 2020. Some countries have much higher long-term policy targets of up to 100% renewable energy. Outside Europe, a diverse group of 20 or more other countries target renewable energy shares in the 2020–2030 time frame that range from 10% to 50%. Fig. 1.7 shows different types of renewable energy sources that are used worldwide for electricity generation.

1.4.1 Mainstream Renewable Technologies Solar Energy System Solar energy or energy gathered through solar radiation is the most easily available and free source of electricity generation since primitive times. Energy from the sun comparable to more than 16,000 times the world’s annual commercial energy utilization reaches the ground every year. Solar energy can be used in two ways: solar electric energy and solar thermal energy. A solar thermal system produces hot water or air, cooks food, dries materials, etc., with the help of the sun’s heat. In a solar electric energy system, solar photovoltaic uses solar radiation to produce electricity for household appliances as well as commercial and industrial buildings. The solar electric energy system basically depends on the photovoltaic effect and where the photovoltaic effect is created by the beam and diffused solar radiation. When

9

10

Tidal Energy Systems

Renewable energy sources

Solar energy

Wind energy

Hydro energy

Bioenergy

Marine energy

Geothermal energy

Solar PV

Onshore

Run of the river

Bioenergy for electricity and heat

Waves

Convective system

Concentrating solar power

Offshore

Reservoir

Biofuel

Tidal range

Conductive system

Tidal current

Deep aquifer system

Solar heating

Pump storage

Ocean current

Ocean thermal

Salinity gradient

Fig. 1.7 Types of renewable energy sources.

the photovoltaic or solar cell absorb the global solar radiation which is the combination of photons then electrons are stimulated further electrons create moving very quickly and jump into the conduction band and they depart holes in the valence band. On the basis of the fundamental of p-n junction, some electrons are attracted toward the n-side to merge with holes on the nearby p-side. Similarly, holes on the near p-side are concerned to

Fig. 1.8 Typical solar system.

Introduction to Energy Sources

merge with the electrons on the nearby n-side.Fig. 1.8 presents a photovoltaic system consisting of different devices. A solar cell does not produce electricity regularly for 24 h, meaning that batteries are an essential part of a solar energy system as they store the energy generated by solar cells. Another group of batteries provides that energy in intervals to the demand side during cloudy days, nights, and days where the load demands are very high. The number of batteries is always considered with the concept of battery autonomy. The most ordinary type of batteries used in a solar energy system is the deep-cycle batteries, which are the combination of lead-acid and nickel-cadmium. They are more costly but they have a long life and can be discharged at a higher level. The charge controller is an important device from the battery point of view because it increases the life cycle of the battery. When the battery is fully charged, its life is reduced at a given time interval. Then, the charge controller doesn’t allow the electrical load to prolong the flow into the batteries, which increases the life cycle of the battery. In household, commercial, and industrial applications, the load may be alternating current (AC) or direct current (DC). If the output of the solar system is DC, then the inverter is connected with the whole system because it is a device that converts DC into AC. The usage of AC is essential because it has been mostly used for all kinds of domestic appliances as well as industrial sectors. An inverter is used where a source of incessant electric voltage is allocated and where an alternative electric voltage is used, as happens with installed solar cells on buildings. The efficiency of the inverter is quite high and varies between 94% and 96%. There are four major applications for PV power systems: Off-grid domestic photovoltaic systems: Off-grid systems are part of a standalone system, and such a system provides electrical energy at remote locations and villages that are not connected to the authorized electricity grid. A number of these systems have been installed worldwide and they are often the most appropriate method to meet the electricity demands of off-grid communities. Off-grid domestic systems are characteristically around 2–3 kW in size, and they offer a cost-saving alternative to extending the electricity distribution grid at distances of more than 2–3 km from existing distribution and transmission lines. Off-grid nondomestic photovoltaic systems: Such a system is designed for commercial and industrial buildings because these systems are the most appropriate arrangement, where a minute amount of electricity has a high value. This makes these systems commercially cost competitive with other small electricity-producing sources. Off-grid nondomestic solar systems provide power at a low operation and maintenance cost for a wide range of applications, such as communication, water pumping in agriculture sectors, vaccine refrigeration, and navigational aids.

11

12

Tidal Energy Systems

Grid-connected distributed photovoltaic systems: These solar energy systems provide energy to a commercial and industrial building or other load that is also associated with the authorized utility grid. These systems are usually incorporated into the built location and supply electrical energy to residential houses as well as commercial and industrial buildings. There is no need for battery storage units because such systems are connected directly to the authorized electricity grid. The overall costs of these systems are lower compared to an off-grid installation. Typical systems are between kW and MW in size and electricity is fed back into the authorized grid when the on-site generation exceeds the demand of the load. Grid-connected solar systems nicely match the residential load pattern during the summer season. Grid-connected centralized photovoltaic systems: These systems are installed for two main purposes: as an alternative to conventional centralized power generation or for strengthening the utility distribution system. Table 1.2 shows the summary of advantages and limitations of solar energy systems. Wind Energy System Wind is simply a form of moving air as well a part of the sun’s rays because, when the earth heats up from beam and diffuse radiation, it releases wind. This is a balanced reaction between sun rays and wind to cool the earth. The moving air inflates and easily reaches a maximum height then fresh and cool air falls down and moves as wind. Differential heating of the ground surface by the sun causes the movement of large air masses. Such a type of air or wind is used for electricity generation if the wind speed is between 5 and 25 m/s. Electricity generation through wind is done by wind energy conversion Table 1.2 Summary of benefits and challenges of solar energy Benefits Challenges

Solar energy is a clean and renewable energy source Solar energy causes no pollution

Once a solar panel is installed, solar energy can be produced free of charge Solar energy will last forever whereas it is estimated that the world’s oil reserves will last for 30–40 years Very little maintenance is needed to keep solar cell running

Electricity generation depends entirely on a country’s exposure to sunlight; this could be limited by climate A solar power station does not match the power output of similar-sized conventional power stations; they can also be very expensive to build

Introduction to Energy Sources

systems. Wind energy conversion systems convert the kinetic energy of the wind into electricity or other forms of energy. Wind power generation has had a marvelous expansion in the past decade, and has been recognized as an environmentally friendly and economically spirited means of electric energy production. Nowadays, wind power is a completely established and sustainable branch of electricity generation and it is worked accordingly. The energy generation is not the only basis to be considered when installing new wind turbines. The cost of system efficiency, the impact on the surroundings, and the impact on the authorized grid are some of the significant issues of interest when making decisions about new wind turbine installations. Electricity is traded like any other commodity on the market and therefore, there are standards that describe its quality. In the case of electric energy systems, they are commonly known as the power quality standards. Any piece of equipment connected to the electric grid must fulfill these standards. This is mainly an interesting and significant issue to be considered in the case of wind energy system installations because the stochastic nature of wind and the standardized parameters of electricity are joined together there. Fig. 1.9 shows the energy chain of electricity generation through a wind energy system, in which first wind energy is converted into mechanical energy and then further convert into usable electrical energy. A wind turbine is the main part of a wind energy system because a wind turbine detains the force of wind velocity with the help of rotor blades. Rotor blades are used to accelerate wind flow over one side of the blade, which leads to a low-pressure system at the given side. The rotor blades lift to the area of lower pressure just like an airplane wing, due to the difference in pressure between the two sides of the blade. When the rotor is connected to a shaft, due to the rotation of the shaft, a generator produces electrical energy. The electricity generated in the generator is transmitted and distributed through overhead lines from the wind turbine hub down the tower to an interconnection with the transmission system. There are two types of wind turbines used in wind energy conversion systems: a horizontal axis wind turbine and a vertical axis wind turbine. The power produced by a wind turbine depends on the average wind speed and wind speed Mechanical power

Rotor

Electrical power

Gear box

Generator

Power transmission

Power conversion

Wind power Power conversion & control

Fig. 1.9 Energy chains of wind energy.

Power converter

Power conversion & control

Supply chain

Power transmission

13

14

Tidal Energy Systems

distribution. The design of wind turbines and rotor blades is the important criterion of power generation because each wind turbine design is rated to generate electrical energy at a particular wind velocity. The wind velocity at which a wind turbine will start to generate power is referred to as the cut-in wind speed. Once wind reaches a turbine’s cut in speed, the wind turbine generate electrical energy, although very little at low wind speeds. As wind velocity increases, power generation increases until the wind reaches the speed of 25 m/s, which is called the rated wind speed. At the rated wind speed, the wind turbine generates the maximum amount of power for which it is rated. Wind turbines are also intended to shut down at very high wind velocity more than 25 m/s, referred to as cut-out wind speeds, for fear of potential damage to the system. The wind turbine is characterized by a nondimensional act as a function of tip speed ratio. The output of mechanical power captured from wind by a wind turbine can be formulated as: Kinetic energy ¼ half mass  velocity squared

(1.1)

Kinetic energy ¼ 0:5mV2

(1.2)

Power in the wind ¼ Kinetic energy in the wind per second P ¼ 0:5ρmνχv

(1.3)

Where ρ is the air density in kilograms per cubic meter (kg/m ), A is in square meters (m2) and V is in meters per second (m/s). The torque developed by the wind turbine can be expressed as 3

Tt ¼ P=ωm

(1.4)

where Pt is the output power, Tt the torque developed by wind turbine, CP the power coefficient, λ is the tip speed ratio, ρ is the air density in kg/m3, A is the frontal area of wind turbine, and V is the wind speed. λ ¼ ωR=V

(1.5)

where ω is the turbine rotor speed in rad/s, R is the radius of the turbine blade in m, and V is the wind speed in m/s. Horizontal and Vertical Axis Wind Turbine

Horizontal-axis wind turbines (HAWT) consists of a rotor shaft and an electrical generator at the apex of a tower and must be pointed into the wind. In HAWTs small turbines are connected by a simple wind vane and large turbines are generally connected with a wind sensor that is attached with an AC or DC servo motor. When a tower generates turbulence behind it, the turbine is usually located upwind of its supporting tower. Turbine blades are made rigid to put off the blades from being pressed into the tower by high winds. Additionally, the blades are located a substantial distance in front of the tower and are sometimes tilted forward into the wind a small amount.

Introduction to Energy Sources

Table 1.3 Comparison between horizontal and vertical axis wind turbines Performance Horizontal axis turbine

Vertical axis turbine

Generated power efficiency (%) Electromagnetic interference Mechanism of the wind steering Gear box mechanism Blade rotation space Wind confrontation capability Noise (Db) Cut in wind speed (m/s) Failure rate of system Operation and maintenance Revolving speed Cable position problem

70 No No No Quite small Strong 0–10 1.5–3 Low Convenient Low No

50–60 Yes Yes Yes Quite large Weak 5–60 2.5–5 High Complicated High Yes

Courtesy of Aeolos wind turbine http://www.windturbinestar.com/hawt-vs-vawt.html.

On the other hand, vertical-axis wind turbines (or VAWTs) have the main rotor shaft arranged vertically and the main advantages of this type of connection are that the turbine does not need to be pointed into the wind to be effective. This is a benefit of sites where the wind direction is highly uneven, for example when integrated into commercial and industrial buildings. The main limitations of this type of wind turbine include the low revolving speed with the significant higher torque and hence the larger cost of the drive train, the lower power coefficient, the 360-degree rotary motion of the aerofoil within the wind flow during each cycle and hence the highly dynamic loading on the blade, the vivacious torque generated by some rotor designs on the drive train, and the complexity of modeling the wind flow rate accurately and hence the confronts of analyzing and scheming the rotor prior to fabricating a prototype. Table 1.3 shows a comparative analysis between HAWTs and VAWTs under certain parameters. With a vertical axis, the electric generator and the mechanical gearbox can be located near the ground using a straight drive from the rotor congregation to the land-based gearbox. This improves accessibility for operation and maintenance. When a turbine is mounted on a rooftop, the building generally redirects wind over the roof and this can double the wind speed at the turbine. If the height of the rooftop-mounted turbine tower is approximately 50% of the building height, this is near the optimum for maximum wind energy and minimum wind turbulence. Fig. 1.10 shows different parts of the vertical and horizontal axis wind turbines. Table 1.4 shows advantages and limitations of wind energy systems. Biomass Energy System Electricity generation through a biomass system is a renewable and nonconventional energy source where biomass is a biological material that is derived from living or recently

15

16

Tidal Energy Systems

High speed shaft rotation

Low speed shaft rotation

Blade

Horizontal rotor

Vertical rotor

Tower

Fig. 1.10 Vertical and horizontal axis wind turbines.

Table 1.4 Summary of benefits and challenges of wind energy Benefits Challenges

The wind is free and with modern technology, it can be captured efficiency It is a pollution-free energy source

Remote areas that are not connected to the electricity power grid can use wind turbines to produce their own supply Many people find wind farms an interesting feature of the landscape Wind turbines are available in a range of sizes, which means a vast range of people and businesses can use them

The strength of the wind is not constant and it varies from zero to storm force A wind turbine can noisy. Each one can generate the same level of noise as a family car traveling at 70 mph When a wind turbine is manufactured, some pollution is produced

living organisms. A living organism refers to plants or plant-derived substances that are particularly called lingo cellulosic biomass. As a reversible or nonconventional energy source, biomass can either be used directly or indirectly after it is converted to different forms of biofuel. Conversion of biomass to biofuel can be done by three significant methods: thermal, chemical, and biochemical. Worldwide, biomass has always been an important energy source and offers different advantages, including that it is renewable or reversible, widely accessible, and carbon neutral. It can also offer momentous employment in the rural areas. Biomass is also competent at providing firm energy. Worldwide, about 32% of the total primary energy use is

Introduction to Energy Sources

Upgrading of biogas

Municipal organic waste

Gas used for transportation

Collecting Food industry waste

Large-scale anaerobic digestion

Heat and power production

Manure Harvest residue

Recovery

Ley crops

Cultivation harvesting

Farm scale anaerobic digestion

Spreading of digestate

Heat production

Fig. 1.11 Step-by-step process of electricity production through biomass.

still from biomass and more than 65% of the world’s population depends upon it for its energy needs. Biomass means all materials that come from living organisms such as the waste of plants and animals, wood, agricultural wastes, and dead parts of plants and animals. Because all living organisms hold carbon compounds, biomass has energy stored in the form of chemical compounds. The method of harnessing energy from each of them could be different. Direct burning of these materials generally causes pollution, but it is the most inexpensive form of energy. Using wood waste or dried cow dung as fuel generates a lot of pollution so that if cow dung is used in a biogas plant, clean fuel can be generated and it becomes a pollution-free energy generating source. Mostly in villages, all types of biomass are traditionally burned directly to produce heat. And if modern methods are used, they can be utilized properly. Fig. 1.11 shows the process of electricity generation through a biomass energy source. Biomass Conversion Process to Useful Electrical Energy Thermal Conversion

The thermal conversion processes use heat or thermal energy as the leading mechanism to convert biomass energy into another chemical energy. Energy created by burning biomass is predominantly suitable for developed countries where the fuel wood grows more quickly. There are a number of other less common, more investigational or proprietary thermal processes that may present settlement such as hydrothermal upgrading (HTU) and hydroprocessing. Some have been developed for use on high moisture content biomass, including aqueous slurries, that allows them to be converted into more convenient forms. Some of the functions of thermal conversion are the combination of heat, power, and cofiring. In a distinctive committed biomass energy generating plant, efficiencies range from 7% to 27%. Biomass cofiring with coal typically occurs at efficiencies near those of the coal combustor. This type of energy is technically called dendrothermal energy when it is used in energy-generating plants as a fuel for energy production.

17

18

Tidal Energy Systems

Chemical Conversion

A different variety of chemical processes may be used to convert biomass into other forms, such as to produce a fuel that is more conveniently used, transported, or stored or to exploit some property of the process itself. Many of these processes are based in large part on similar coal-based processes, such as Fischer-Tropsch synthesis, methanol production, olefins (ethylene and propylene), and similar chemical or fuel feedstocks. In most cases, the first step involves gasification, which generally is the most expensive and involves the greatest technical risk. Biomass is more difficult to feed into a pressure vessel than coal or any liquid. Therefore, biomass gasification is frequently done at atmospheric pressure and causes incomplete combustion of biomass to produce a combustible gas consisting of carbon monoxide, hydrogen, and traces of methane. This gas mixture, called a producer gas, can provide fuel for various vital processes such as internal combustion engines as well as substitute for furnace oil in direct heat applications. Because any biomass material can undergo gasification, this process is far more attractive than ethanol or biomass production where only particular biomass materials can be used to produce a fuel. In addition, biomass gasification is a desirable process due to the ease with which it can convert solid waste (such as wastes available on a farm) into producer gas, which is a very usable fuel. Table 1.5 shows the advantages and limitation of a biomass energy system. Geothermal Energy Geothermal energy is one of the renewable energy sources used by prehistoric people for heating and bathing purposes. Nowadays, geothermal energy is used for electricity generation. In the United States, 60 geothermal power plants generate electricity and many more are in development. Most of these geothermal energy plants are in California with the remainder in Nevada, Hawaii, Idaho, and Utah. The word geothermal is the combination of the two Greek words geo (Earth) and therme (heat). Geothermal energy is produced in the Earth’s core, which is almost 4000 miles underneath the Earth’s surface. The double-layered core is made up of very hot magma surrounding a solid iron center. Very Table 1.5 Summary of benefits and challenges of biomass energy Benefits Challenges

Biomass energy helps in cleanliness in villages and cities It provides manure for agriculture and gardens It’s generates comparatively less pollution It can be generated from everyday human and animal wastes, vegetables, and left-over agriculture Biomass energy is relatively cheap and reliable

A biogas plant requires space and produces a dirty smell Transportation of biogas through pipes over long distances is difficult It is difficult to store biogas in cylinders Crops used to produce biomass energy are seasonal and are not available over the whole year A continuous supply of biomass is required to generate biomass energy

Introduction to Energy Sources

high temperature levels are incessantly twisted inside the Earth by the deliberate decomposition of radioactive particles. Surrounding the external core is the mantle, which is 1800 miles thick and made of magma and rock. The farthest layer of the earth and the ground that forms the continents and ocean floors is called the crust. The crust is 3–6 miles thick under the sea and 15–35 miles thick on the continents. The crust is not a solid piece. It is like the shell of an egg, but it is broken down into pieces called plates. Magma comes close to the ground’s surface near the edges of these plates. The lava that erupts from volcanoes is partly magma. Deep underground, the rocks and water absorb the heat from this magma. We can dig wells and pump the heated underground water to the surface. Geothermal energy is called a renewable or reversible energy source because the water is replenished by precipitation and the heat is incessantly produced deep within the Earth. There is more than one type of geothermal energy, but only one kind is widely used to make electricity. It is called hydrothermal energy. Hydrothermal resources have two common ingredients: water (hydro) and heat (thermal). Depending on the temperature of the hydrothermal resource, the heat energy can either be used for making electricity or for heating. Low Temperature Resources: Heating

Hydrothermal resources at low temperatures (50–300 degrees Fahrenheit) are positioned in the United States some feet underground. This type of low-temperature geothermal energy is used for growing crops as well as drying lumber, fruits, and vegetables. In the United States, geothermal heat pumps are used to heat and cool homes and public apartments. Each year, about 60,000 geothermal exchange systems are established in the United States. High Temperature Resources: Electricity

Hydrothermal resources at high temperatures (300–700 degrees Fahrenheit) can be used to generate electrical energy. These high-temperature resources generate electricity from two types of wells: dry steam wells or hot water wells. Geothermal wells are 2–3 miles deep. In a dry steam power plant, the steam comes from the geothermal basin, which is piped directly from a well to a turbine generator and then the output is in the form of electrical energy. In a hot water plant, hot water is turned into steam, the steam is used to generate power, then a generator produces electricity. Working of a Conventional Geothermal Power Plant A geothermal system requires heat, permeability, and water for electricity generation. The heat from the Earth’s core incessantly flows outward and is used for electricity generation. Sometimes the heat is from magma and reaches the surface in the form of lava, but it usually remains underneath the Earth’s crust, heating nearby rocks and water. Fig. 1.12 shows types of geothermal power plants.

19

20

Tidal Energy Systems

Fig. 1.12 Types of geothermal power plants.

There are four commercial types of geothermal power plants: (a) flash power plants, (b) dry steam power plants, (c) binary power plants, and (d) flash/binary combined power plants. Flash power plant: In a flash power plant, geothermal-heated water under pressure is estranged in a surface vessel, which is called a steam separator. The steam is delivered to the turbine and then a generator is used to generate electricity. The liquid is injected back into the reservoir. Dry steam power plant: In a dry steam power plant, steam is generated directly from the geothermal reservoir to run the turbines and that power is used through the generator to generate electricity. In this type of power plant, no separation is necessary because wells only produce steam. Binary power plant: A binary power plant is a recent advancement in geothermal technology. It has made possible the financially viable production of electrical energy from geothermal resources lower than 150°C (302°F). Flash/binary combined cycle: This type of plant uses an integration of flash and binary technology and provides better advantages compared to the individual techniques. In such a plant, the geothermal water that flashes steam under condensed pressure is first transformed to electricity with the help of a backpressure steam turbine. Then, low-pressure steam exiting the backpressure turbine is condensed in a binary system. Table 1.6 shows the advantages and limitation of geothermal energy sources.

Introduction to Energy Sources

Table 1.6 Summary of benefits and challenges of geothermal energy Benefits Challenges

Geothermal power plant provides steady and predictable base load power Power plants are small, require no fuel purchase, and are compatible with agricultural uses Geothermal plants produce a small amount of pollutant emissions compared to traditional fossil fuel power plants

Although costs have decreased in recent years, exploration and drilling for power production remain expensive The productivity of geothermal wells may decline over time The success rate for discovering geothermal resources in new untapped areas is approximately 20% Using the best geothermal resources for electricity production may require an expansion or upgrade of the transmission system

Wave Energy Wave energy is another renewable or reversible energy system that is the part of energy transformation because it extracts energy directly from surface waves. Scientist believe that there is an adequate amount of energy in ocean waves to provide up to 3 terawatts of electricity. But one major limitation is wave energy cannot be harnessed everywhere and the western coasts of Scotland, Southern Canada, Southern Africa, and Australia as well as the northeastern and northwestern coasts of the United States are the rich areas for electricity generation through wave energy. The Pacific Northwest area alone is capable of producing 40–70 kilowatts (kW) per 3.3 ft (1 m). Wave Energy Resources

Wave energy can be measured as an intense form of solar and wind energy. Winds are produced by the differential heating of the earth and when air passes over open bodies of water, wind is converted into waves with the help of precise mechanisms. Such a mechanism is used to produce electrical energy with the help of wave energy. Three-step processes appear in which waves are generated. Initially, wind circulates over the sea surface and exerts a divergent stress on the water surface, with the resulting output in the form of waves. Table 1.7 shows the advantages and limitations of a wave energy system. In another process, disordered air flows close to the water surface, creating speedily unreliable shear stresses and pressure fluctuations. Where these fluctuations are in phase with accessible waves, further wave progress occurs. Finally, when certain waves have reached a definite size, the wind can in fact exert a stronger force on the upwind face of the wave. The process is maximized when the speeds of the wind and waves are equal. Wind energy converted into wave energy is the process of energy transformation. The amount of energy transferred and the size of the resulting waves depend on the wind

21

22

Tidal Energy Systems

Table 1.7 Summary of benefits and challenges of wave energy Benefits Challenges

Dependence on foreign companies for fossil fuels can be reduced if energy from wave power can be extracted up to its maximum The biggest advantages of wave power against most of the other alternative energy sources is that it is easily predictable and can be used to calculate the amount that it can produce Also unlike fossil fuels, creating power from waves creates no harmful byproducts such as gas, waste, or pollution The best thing about wave energy is that it will never run out. There will always be waves crashing upon the shores of nations near the populated coastal regions It is safe, clean, and one of the preferred methods to extract energy from the oceans

Depends on the waves—variable energy supply Needs a suitable site where waves are consistently strong

Must be able to withstand very rough weather

Wave power is in the very early stages of development, which makes speculating on costs harder Another downside is that it disturbs commercial and private vessels

velocity. At each step in the process, energy is concerted so that solar energy levels of typically about 110 W/m2 can be finally altered into waves with energy levels of over 1000 kW per meter of crest length. Power Associated to a Sea Wave Ocean waves convey mechanical energy. The power associated with a wave of wavelength λ, height h, and a front B is given by P ¼ 1=2ρgh2

(1.6)

where ρ is the specific weight of water and g is the gravity acceleration. The power PU across each meter of wave front associated with a uniform wave with height h (m) and wavelength λ (m) is then PU ¼ P=B ¼ 1=2ρgh2 λ

(1.7)

and is expressed in W/m. For irregular waves of height h (m) and period t (s), an equation for power per unit of wave front can be derived as Pi ¼ 0:42h2 T

(1.8)

and is expressed in kilowatts per meter (kW/m) of wave front. It is significant to note that wave power varies with the square of wave height. Then, when wave height is doubled, it generates four times as much power.

Introduction to Energy Sources

Hydro Energy System A hydro energy system is considered to be a renewable as well as a nonrenewable energy system. The characterization of a small hydro energy system changes but an electrical energy-producing capacity of up to 10 megawatts (MW) is generally established as the higher limit of what can be termed a small hydro energy power plant. This may be extended up to 30 MW in the United States and 50 MW in Canada. A hydro power plant can be further subdivided into a mini hydro, which is defined as 70% of the Earth have been acknowledged as a tremendous sustainable power source. It is a rising industry that can possibly fulfill the overall power interests. These days, there are a few strategies for extricating energy from the ocean, among which are tidal energy transformation methods. Tidal energy offers a gigantic and dependable wellspring of energy. The energy generation from the tides is around 3 TW, however just a little division of this potential would be saddled on the not so distant. This is because of the way that the energy is spread over a wide region. There is currently worry over worldwide environmental change as well as a developing mindfulness in the overall populace about the need for diminishing

51

52

Tidal Energy Systems

ozone-harming substance discharges. This has prompted an expansion in the control age for sustainable sources. Tidal energy can possibly assume a significant part in a reasonable energy future. Its primary preference over other sustainable sources is its consistency; tides can be anticipated for a long time. The energy extricated from the tides can originate from both the vertical developments of the water related with the ascent and fall, the potential energy, and from the motor energy, to be specific, tidal streams. A tidal flood saddles the potential energy while tidal stream turbines catch the energy from tidal ebbs and flows and countless deliver power by the customary energy framework and this framework causes abnormal amounts of environmental defilement. This issue is to a great extent overwhelmed by serious utilization of an option or a sustainable power source framework. For a long time, a few sustainable power sources, for example, sun-based energy, wind energy, geothermal energy, and wave energy have been connected for power age everywhere throughout the world. Wind energy and sun energy are universal, unreservedly accessible, and environmentally responsive, yet the breeze energy and sun-based energy framework may not be practical at all locales because wind speed and sun-powered radiation are arbitrary in nature. Tidal age has a huge preferred standpoint over numerous different types of inexhaustible age as it is splendidly anticipated over lengthy time span skylines. Along with, fusing tidal age into the framework ought to be less testing than different types of sustainable age which are profoundly eccentric. Tackling tidal energy from the ascent and fall of the tides has been used up to a business scale utilizing tidal blast frameworks. Then again, extraordinary endeavors to use the active energy from tidal streams have been coordinated. This innovation stays 15 years behind the breeze innovation industry. Still, the tidal current industry can profit by the advances in innovation and building that have come about because of the breeze business. The seas of the Earth speak to a huge wellspring of sustainable power sources. As a rule, sea energy can be partitioned into six sorts of various cause and qualities: sea waves, tidal range, tidal ebb and flow, sea ebb and flow, sea warm energy, and saltiness angles. Future energy security for the United Kingdom (UK) and concerns about environmental change from ozone-harming concerns have driven interest in sustainable, low-carbon energy innovation, with an objective of a 15% sustainable power source in the UK by 2020. Tidal-stream energy, the extraction of motor energy from tidal ebbs and flows to produce power, is turning into an inexorably supported type of sustainable power source because of various appealing highlights. For instance, the standard and unsurprising periodicity of the tide, and additionally the high energy thickness, make tidal-stream energy a more solid wellspring of low-carbon energy than other stochastic structures, for example, waves and seaward. Various examinations have been undertaken by the Carbon Trust, which have determined that 18 TWh every year is extractable inside 1450 km2 of UK waters by tidal-stream energy alone, which would meet 5% of the UK’s current power request. Still, the tidal-stream energy industry can be thought to be in its outset, with just a couple of UK extensions presently in the cutting edge phases of arranging. This includes the 400 MW MeyGen venture in

Introduction of Tidal Energy

the Pentland Firth inside a potential 1 GW of tidal stream limit that has been rented by the Crown Estate. Tidal power or tidal energy is a type of hydropower that changes the energy from tides into helpful types of energy, for the most part power. Despite the fact that it is not yet broadly utilized, tidal energy has potential for the future power age. Tides are more unsurprising than the breeze and the sun. Among wellsprings of sustainable power sources, tidal energy has customarily experienced a generally high cost and constrained accessibility of destinations with adequately high tidal ranges or stream speeds, in this way choking its aggregate accessibility. In any case, numerous innovative advancements and enhancements, both in plan and turbine innovation, show that the aggregate accessibility of tidal power might be substantially higher than previously expected, and that monetary and natural expenses might be brought down to focused levels. Tide factories have been utilized both in Europe and on the Atlantic shore of North America. The approaching water was contained in substantial capacity lakes, and as the tide went out, it turned waterwheels that utilized the mechanical power it created to process grain. The most recent events date from the middle Ages, or even from Roman circumstances. The way toward utilizing falling water and turning turbines to make power was presented in the United States and Europe in the 19th century. Individuals have dependably had an interest in tidal energy. In ancient periods, individuals depended vigorously upon the uses of a similar energy so as to contract the route crosswise overseas. Today, we have the unpretentious utilization of a similar energy–basically to produce control as power. • Tidal energy is perpetual in nature. • It occurs due to the interaction between the moon and the earth. • These interactions will never subside in the millions of years to come. • In other words, we can apply specially crafted water turbines in order to harness the tidal energy for consistent power. There are certain regions where tidal energy has high intensity in comparison with the rest of the geographic areas. Researchers are busy advocating companies to install various kinds of water turbines that can effectively help generate electrical power in a sustainable manner. One of the marked advantages of applying tidal energy is the fact that you can access it without causing any amount of pollution. There are various ways we can access tidal energies. In areas that experience lesser tides, we can collect the water in large water barrages, only to release it to rotate the turbines and thus produce energy.

2.3 BASIC PRINCIPLE OF TIDAL POWER PLANTS 2.3.1 How the Tide Generates Tidal power or tidal energy is a type of hydropower that changes the energy acquired from tides into valuable types of energy, principally power. In spite of the fact that it is not yet generally utilized, tidal energy has potential for the future power age. Tides

53

54

Tidal Energy Systems

are more unsurprising than the breeze and the sun. Tides or waves are the intermittent ascent and fall of the water level of the ocean. Tides happen because of the effects of the moon. At the point when the water is over the mean ocean level, it is called a surge tide. At the point when the water level is beneath the mean level, it is called an ebb tide. The sea tides rise and falls and water can be put away amid the ascent time frame and released amid fall. A dam is built, isolating the tidal bowl from the ocean, and a distinction in water level is reached between the bowl and ocean. At high tide, water streams from the ocean into the tidal bowl through the water turbine. The stature of the tide is over that of the tidal bowl. Subsequently, the turbine unit works and produces control, as it is specifically coupled to a generator. Tide changes proceed via the following stages: • Sea level rises over several hours, covering the intertidal zone; flood tide. • The water rises to its highest level, reaching high tide. • Sea level falls over several hours, revealing the intertidal zone; ebb tide. • The water stops falling, reaching low tide. Tidal Range: Tidal range is the difference in water levels between two consecutive high tides and low tides. The rise and fall of the water level in the sea during tides can be represented by a sine curve. One tidal day is of 24 h and 50 min and there are two tidal cycles in one tidal day. The normal tide is a semidiurnal tide with a period of 12 h and 25 min. Diurnal means daily, that is, activities of tide patterns during 24 h. Diurnal tides indicate two high and two low tides created by the moon during one rotation of the earth on its axis. The daily tidal cycle follows a sinusoidal pattern. Swaying ebbs and flows delivered by tides are known as tidal streams. The minute that the tidal flow stops is called slack water or slack tide. The tide at that point switches bearing and is said to turn. Slack water for the most part happens close to high water and low water. Still, there are areas where the snapshots of slack tide contrast fundamentally with those of high and low water. Tides are usually semidiurnal (two high waters and two low waters every day) or diurnal (one tidal cycle for each day). The two high waters on a given day are commonly not a similar height (the everyday disparity); these are the higher high water and the lower high water in tide tables. Essentially, the two low waters every day are the higher low water and the lower low water. The everyday imbalance is not predictable and is by and large small when the moon is over the equator. Fig. 2.10 shows a description of different types of tides. From the highest level to the lowest: Highest Astronomical Tide (HAT): The highest tide that can be predicted to occur. Note that meteorological conditions may add extra height to the HAT. Mean High Water Springs (MHWS): The average of the two high tides on the days of spring tides. Mean High Water Neaps (MHWN): The average of the two high tides on the days of neap tides.

Introduction of Tidal Energy

Fig. 2.10 Waveform of different types of tides.

55

56

Tidal Energy Systems

Low tide period

Tidal basin

Water flow

Sea

High tide period

Sea

Water flow

Tidal basin

Fig. 2.11 Schematic arrangement of low and high tide periods.

Mean Sea Level (MSL): This is the average sea level. The MSL is constant for any location over a long period. Mean Low Water Neaps (MLWN): The average of the two low tides on the days of neap tides. Mean Low Water Springs (MLWS): The average of the two low tides on the days of spring tides. Lowest Astronomical Tide (LAT) and Chart Datum (CD): The lowest tide that can be predicted to occur. Modern charts use this as the chart datum. Note that under certain meteorological conditions, the water may fall lower than this, meaning that there is less water than shown on charts. Fig. 2.11 shows the function of low level and high level tides.

2.3.2 Principles of Tidal Power Stations 1. Barrages make use of the potential energy from the difference in height (or head) between high and low tides. Barrages suffer from the problems of very high civil infrastructure costs, few viable sites globally, and environmental issues. 2. Tidal stream systems make use of the kinetic energy from the moving water currents to power turbines, in a similar way to wind mills using moving air. This method is gaining in popularity because of the lower cost and lower ecological impact. During the low tide period, water streams from the tidal bowl to the ocean, as the water level in the bowl is more than that of the tide in the ocean. Amid this period, the streaming water pivots the turbine and generator control. Tidal energy is created by the relative

Introduction of Tidal Energy

movement of the water, which cooperates through gravity. Intermittent changes of water levels and related tidal streams are because of the gravitational attraction by the sun and moon. The size of the tide at an area is the consequence of the changing places of the moon and sun in respect to the Earth, the impacts of Earth’s turn, and the neighborhood state of the ocean depths and coastlines. Because the Earth’s tides are caused by the tidal powers due to gravitational collaboration with the moon and sun, and the Earth’s pivot, tidal power is for all intents and purposes endless and delegated as a sustainable power source. The more grounded the tide, either in water level height or tidal flow speeds, the more prominent the potential for tidal power age. Tidal development causes a nonstop loss of mechanical energy in the Earth-moon framework because of pumping of water through the regular confinements around coastlines and because of thick scattering at the seabed and in turbulence. This loss of energy has made the turn of the Earth moderate in the 4.5 billion years since arrangement. Amid the last 620 million years, the pivot time has expanded from 21.9 h to the 24 h we see now; in this period the Earth has lost 17% of its rotational energy. While tidal power may take extra energy from the framework, expanding the rate of stoppage, the impact would not be perceptible for a huge number of years, hence rendering it unimportant. Progressively, the Earth and the moon are two masses that show diffusive powers on each other. To begin, we should consider a molecule of mass m that is situated on the world’s surface. Given Newton’s law of gravitational state, we present the condition: F ¼ G m1m2 R2

(2.1)

where F is the force created between mass1 and mass2, and G is the universal gravitational constant whose value depends only on the chosen units of mass, length, and force (typically 6.67  1011 N m2 kg2). If we then take the difference between the force toward the moon and the force necessary for Earth‘s rotation, we generate the tidalproducing force. The basic principle of the tidal power utilization is described broadly in two ways: 1. Altering the tidal energy by a barrage system into electricity. 2. Altering the kinetic energy of tides by the tidal current system into electricity. With a specific goal to make enough power to be monetarily practical, the size and design of the structure must be expanded enormously. Tidal energy is comprised of producing dynamic energy from potential energy. In the event that falling water is constrained through conduits with rotators connected to them, the rotors will turn, driving electric generators. Creating power from tides is fundamentally the same as the hydroelectric age, with the exception of the fact that the tides stream in two ways as opposed to one. For tidal power, the most widely recognized creating framework is the ebb-producing framework. In the plan, a dam or flood is built over an estuary. The tidal bowl is permitted to fill when the floodgate entryways are opened and high tide is in. The doors are then shut when the tide turns, catching the water behind the entryways. When low tide is

57

58

Tidal Energy Systems

Electric power from tidal flows Generator

Sea level G Turbine

Sea water

Concrete base

Fig. 2.12 Schematic diagram of a tidal energy system.

achieved, the doors are opened, and the water courses through the turbines situated underneath the water producing power. Fig. 2.12 shows the function of tidal power systems. Tides are the occasional ascent and fall of the ocean’s water level. Tides happen because of the fascination of ocean water by the moon. Tides contain an expansive measure of potential energy that is utilized for control age. At the point when the water is over the mean ocean level, it is called surge tide. At the point when the water level is beneath the mean level it is called ebb tide. The sea tides rise and fall and water can be put away amid the ascent time frame and it can be released amid fall. A dam is built isolating the tidal bowl from the ocean and a distinction in water level is gotten between the bowl and ocean. A tidal barrage is a sort of tidal power age conspire that includes the development of a genuinely low walled dam, known as a “tidal torrent” and consequently its name, crossing over the passageway of a tidal gulf, bowl or estuary making a solitary encased tidal repository, comparable in many regards to a hydroelectric impoundment supply. The base of this blast dam is situated on the ocean depths with the highest point of the tidal torrent being recently over the largest amount that the water can get too at the most elevated yearly tide. The blast has various submerged passages cut into its width, permitting the ocean water to move through them controllably by utilizing “conduit entryways” on their passageway and leave focuses. Settled inside these passages are colossal tidal turbine generators that turn as the ocean water surges past them, either to fill or exhaust the tidal store, accordingly creating power (Fig. 2.13). The sea water flows inside and outside of underwater tunnels, which are the collection of large amounts of kinetic energy. The job of the tidal barrage is to extract as much of this energy as possible, which it uses to produce electricity. Tidal barrage generation using the tides is very similar to hydroelectric generation, except the water flows in two directions rather than just one. On incoming high tides, the water flows in one direction

Introduction of Tidal Energy

Sluice gates

Head height

Barrage Tidal basin

Ocean

Turbine tunnel Ocean floor

Fig. 2.13 Schematic diagram of a tidal energy system with a tidal barrage.

and fills up the tidal reservoir with sea water. On outgoing ebb tides, the sea water flows in the opposite direction, emptying it. As a tide is the vertical movement of water, the tidal barrage generator exploits this natural rise and fall of tidal waters caused by the gravitational pull of the sun and moon. The gravitational effects of the sun or the moon on the world’s oceans causes huge amounts of sea water to be directed toward the nearest coastline. The result of this movement of water is a rise in the sea level. In the open ocean, this rise is very small as there is a large surface area with deeper depths for it to flow into. However, as the ocean water moves nearer the coastline, the sea level rises steeply, especially around inlets and estuaries because of the upward sloping gradient of the sea bed. The effect of this sloping gradient is to funnel the water into the estuaries, lagoons, river inlets, and other such tidal “bottlenecks” along the coastline. This increase in the sea level can create a tidal range of >10 m in height in some estuaries and locations that can be exploited to generate electricity. The tidal range is the vertical difference between the high tide sea level and the low tide sea level. The tidal energy extracted from these tides is potential energy as the tide moves in a vertical up-down direction between a low and high tide and back to a low, creating a height or head differential. A tidal barrage generation scheme exploits this head differential to generate electricity by creating a difference in the water levels on either side of a dam and then passing this water difference through the turbines.

2.3.3 Single-Basin System In a single-basin system, there is only one interface with the tidal energy generation process. There are two system seas and tidal basins separated by a dam and in this situation, water flows between through sluice valves so that only one basin is connected with the

59

60

Tidal Energy Systems

sea water. In this case, power can be generated at regular intervals of time at different tidal ranges and tidal currents. The power house, which consists of an electrical system, is installed inside the dam. The single-basin system also interacts with turbine and generator because the turbine converts kinetic energy into mechanical energy. Further, the generator converts mechanical energy into electrical energy. During high tide, when the water level increases, the tidal turbine valves are opened and the sea stream flows into the basin through the turbine, generating power. The necessary condition of generated power is the level of the sea water and the basin are equal. If water is pass into the basin, until the level reaches its maximum position and at this point find out the maximum power through tidal energy system. During low tide, the altitude of the basin is more than the altitude of sea water. Fig. 2.14 shows the operating cycle of single barrage tidal power plants. After attaining sufficient head, the turbine valves are opened and water flows from the basin to the sea through the turbine, generating power. Single-basin tidal power plants normally use reversible water turbines because, in this case power is generated in both directions. Figs. 2.15 and 2.16 show schematic diagrams of single-basin tidal energy systems. Fig. 2.17 shows types of single-basin tidal energy barrage schemes.

Standstill period

Standstill period Filling

Generation period w a t e r l e v e l

High amplitude tide

Single basin curve Tidal curve

Low amplitude tide

Half day Tidal frequency

Fig. 2.14 Operating cycle of a single-basin single effect plant.

High tide Dam Tidal basin Sea

Fig. 2.15 Schematic diagram of single-basin tidal energy system (high tide).

Introduction of Tidal Energy

Tidal generator Dam

Low tide

Tidal basin

Sea

Fig. 2.16 Schematic diagram of a single-basin tidal energy system (high tide).

Ebb generation Flood generation

Two way generation Single basin tidal energy barrage scheme

Fig. 2.17 Types of single-basin tidal energy barrage schemes.

(a) Single ebb cycle system: In a single ebb cycle system, water is stored during high tide in the basin and power is generated only during low tide. (b) Single tide cycle system: Power is generated only during high tide and it fills the basin. The water is drained out during low tide. (c) Double cycle system: Power is generated during both high tide and low tide as explained above. The basic principle of a single-basin tidal energy system depends on three main tidal energy barrage schemes that use this water differentially to their advantage: • Flood Generation: The tidal power is generated as the water enters the tidal reservoir on the incoming tide. • Ebb Generation: The tidal power is generated as the water leaves the tidal reservoir on the ebb tide. • Two-Way Generation: The tidal power is generated as the water flows in both directions during a flood and ebb tide. A Tidal Barrage Flood Generation (Fig. 2.18) utilizes the energy of an inward growing tide as it moves toward the sea surface. In this type of energy generation system, the tidal basin

61

62

Tidal Energy Systems

Sea level

Tidal stream

Concrete block Gravity Ocean floor Sunker pile

Fig. 2.18 Schematic diagram of tidal barrage flood generation scheme.

is emptied by sluice gates or lock gates that are located next to the section of the barrage and at the time of low tide, the basin is affectively empty. Further, the tide turns to 180 degrees and starts to return back, the sluice gates are fully closed, and the barrage holds back the increasing sea level, which creates a divergence in elevation between the levels of water on either side of the barrage dam. With respect to the sluice gates, these are worked in two forms. The first is when the sluice gates to the entrance to the dam’s tunnels can either be blocked as the sea water increases to allow for a sufficient head of water to develop between the sea level and the basin level before being opened, generating more kinetic energy as the water rushes through and turning the turbines as it passes. In the other way, the entrance may remain fully unlocked, which then fills up the basin more slowly and maintains the same water level inside the basin as out in the sea. The tidal reservoir is therefore filled through the turbine tunnels, which spin the turbines and generate tidal electricity on the flood tide and are then emptied through the opened sluice or lock gates on the ebb tide. Then a flood tidal barrage scheme is a one-way tidal generation scheme on the incoming tide with tidal generation restricted to about 6 h per tidal cycle as the basin fills up. The movement of the water through the tunnels as the tidal basin fills up can be a slow process, so low-speed turbines are used to generate the electrical power. This slow-filling cycle allows for fish or other sea life to enter the enclosed basin without danger from the otherwise fast-rotating turbine blades. Once the tidal basin is full of water at high tide, all the sluice gates are opened, allowing all the trapped water behind the dam to return back to the ocean or sea as it ebbs away. Flood generator tidal power generates electricity on an incoming or flood tide, but this form of tidal energy generation is generally much less efficient than generating electricity as the tidal basin empties, called “ebb

Introduction of Tidal Energy

Fig. 2.19 Schematic diagram of reservoir flooding and ebb generation scheme.

generation.” This is because the amount of kinetic energy contained in the lower half of the basin in which flood generation operates is much less than the kinetic energy present in the upper half of the basin in which ebb generation operates due to the effects of gravity and the secondary filling of the basin from inland rivers and streams connected to it via the land. A tidal barrage ebb generation (Fig. 2.19) uses the energy of an outgoing or falling tide, referred to as the “ebb tide,” as it returns to the sea, making it the opposite of the previous flood tidal barrage scheme. At low tide, all the sluice and lock gates along the barrage are fully opened, allowing the tidal basin to fill up slowly at a rate determined by the incoming flood tide. When the ocean or sea level feeding the basin reaches its highest point at high tide, all the sluices and lock gates are then closed, entrapping the water inside the tidal basin (reservoir). This reservoir of water may continue to fill up due to inland rivers and streams connected to it from the land. As the level of the ocean outside the reservoir drops on the outgoing tide toward its low tide mark, a difference between the higher level of the entrapped water inside the tidal reservoir and the actual sea level outside now exists. This difference in vertical height between the high level mark and the low mark is known as the “head height.” At some time after the beginning of the ebb tide, the difference in the head height across the tidal barrage between the water inside the tidal reservoir and the falling tide level outside becomes sufficiently large enough to start the electrical generation process and the sluice gates connected to the turbine tunnels are opened, allowing the water to flow. When the closed sluice gates are opened, the trapped potential energy of the water inside flows back out to the sea under the enormous force of both gravity and the weight of the water in the reservoir basin behind it. This rapid exit of the water through the tunnels on the outgoing tide causes the turbines to spin at a fast speed,

63

64

Tidal Energy Systems

generating electrical power. The turbines continue to generate this renewable tidal electricity until the head height between the external sea level and the internal basin is too low to drive the turbines, at which point the turbines are disconnected and the sluice gates closed again to prevent the tidal basin from overdraining and affecting local wildlife. At some point, the incoming flood tide level will again be at a sufficient level to open all the lock gates, filling the basin and repeating the whole generation cycle over again, as shown.

2.3.4 Two-Way Tidal Barrage Generations In the above article, it is already discussed that both the flood tidal barrage and the ebb tidal barrage installations are “single-way” tidal generation schemes that generate less power supplied to the load side. However, if we want to increase the electricity generation time and make the system more efficient, a generation system can use a special double-effect system that consists of turbines and generators that generate power in bilateral directions. A two-way tidal barrage scheme generates electricity for both the rising tide as well as the falling tide. In comparison to the single-way electricity generation system, two-way electrical generation requires a more precise control of the sluice gates. This includes keeping them blocked until the differential head height is adequate either way before being opened. When the tide ebbs and the water stream flows inside or outside the tidal reservoir through the same gate system, this flow of tidal water returns back and with the help of turbines and generators, generates electricity in both directions. Fig. 2.20 shows the operating cycle of a single-basin double-effect power plant. From the electricity generation point of view, two-way generation is in general less efficient than one-way flood or ebb generation if the required head height is much smaller, which reduces the amount of tidal current. Another limitation of two-way generation is bidirectional tidal generators are designed to operate in both directions and in this Barrage Sea Sluice Basin Reversible turbine

Single basin reversible turbine

W a t e r l e v e l

Electricity generation

Low amplitude tide

High amplitude tide

Electricity generation Time in hours

Single basin double effect tidal plant cycle

Fig. 2.20 Operating cycle of a single-basin double-effect power plant operating cycle.

Introduction of Tidal Energy

High tide Basin level Water level

Sluice gates closed

Head height sufficient

C B

Head Basin “empties”

Ebb tide

Sluice gates closed A

A Basin “fills-up”

Flood tide

Time Basin “fills-up”

D E

Head height too small Generation time

Low tide

Fig. 2.21 Operating cycle of a two-way barrage scheme.

case, it is generally more costly and less energy efficient than dedicated unidirectional tidal generators. One way of improving the operating time and efficiency of a two-way tidal barrage scheme is to use individual one-way unidirectional tidal turbines inverted along the barrage. Fig. 2.21 shows the operating cycle of a two-way barrage scheme that, by controlling the individual and group sluice gates, one set of mechanical equipment with just a tidal turbine can be made to work on the flood tide between points E-B while the other set works on the ebb tide concept between points C-D. While a two-way arrangement increases the total number of tidal turbines located along the tidal barrage, it has the beneficial effect that the electricity generation time is greatly extended. We have seen above that both Flood Tidal Barrage and Ebb Tidal Barrage installations are “one-way” tidal generation schemes, but in order to increase the power generation time and therefore improve efficiency, we can use special double-effect turbines that generate power in both directions. A two-way tidal barrage scheme uses the energy over parts of both the rising tide and the falling tide to generate electricity.

2.3.5 Two-Basin Tidal Energy Systems In a two-basin tidal energy system, the tidal turbine is located in two adjoining basins while the sluice gates are usually embodied in the dam across the month of two estuaries. At the beginning of the flood tide, the turbines are shut down. Basin A fills and B remains empty. As soon as the head difference of A and B is large enough, the water flows from A to B and the turbine starts.

65

66

Tidal Energy Systems

Double-Basin System Operation of a double-basin system (Fig. 2.22) is similar to ebb generation through a single-basin system. The only difference in these two types of systems is the electricity is used to pump water into the second basin, allowing a proper storage system for future use. All single-basin systems suffer from the disadvantage in which they work only for a single tidal cycle and that they only generate energy during one part of the tidal cycle and cannot rearrange their generating period to match the demand side requirement. Double-basin systems are advantageous because they provide a storage mechanism as well as a proper control system to find the desired electrical output. The two-basin system consists of the main basin and the auxiliary basin; the main basin operates just like an ebb generation single-basin system. A proportion of the power generated during the ebb phase would be used to pump water from the lower level to the higher level and the auxiliary basin to ensure that generation will continue for all types of tidal ranges. It is expected that multiple-basin systems are unlikely to become popular, as the efficiency of low-head turbines is likely to be too low to enable effective economic storage of energy. The overall efficiency of such low-head storage, in terms of energy out and energy in, is unlikely to exceed 30%. It is more likely that conventional pumped storage systems will be utilized. The overall efficiency of these systems can exceed 70%,a which is likely to prove more financially attractive. In a double-basin system as shown, the energy available in sea water is converted into electrical energy during both positive as well as negative cycles. In other terms, power is produced during flood tide (rising tide) when the basin is filled and also during the ebb tide (falling tide) when the basin is emptied, as shown in Fig. 2.23.

Basin 2

Basin 1

Power house Sluice

Fig. 2.22 Schematic diagram of two-basin tidal energy system.

Introduction of Tidal Energy

Barrage

Barrage

Basin

Sea

Basin Sea

Generator & turbine Rising tide

Generator & turbine Falling tide

Fig. 2.23 Schematic diagram of a tidal energy system with rising and falling tide.

A reversible water turbine is utilized on the grounds that the water stream through the turbine during rising and falling tides is inverse and goes about as a turbine for biheading of stream. In the two-basin power age framework, amid expanding tides, a vast amount of water streams into the basin through the tidal turbine by opening the conduit entryway. Filling of the basin proceeds with the age of electric power, until the point when the tide water levels of the ocean and the basin end up noticeably equivalent. At this position, the floodgate door is shut. Thus, amid falling tide water from the basin streams into the ocean through the turbine, electric power is produced. As the water level in the basin drops, a point is achieved when the distinction in water levels between the ocean and the basin turns out to be too little to produce a control mechanism.

2.3.6 Double-Basin With Linked Basin Operation A large basin is changed into two basins of appropriate measurements; the larger amount is called the high basin and the other the low basin. Fig. 2.24 shows a double basin with a

Sluice High basin Sea Sluice

Tidal plant

Low basin

Fig. 2.24 Double-basin with linked basin operation.

67

68

Tidal Energy Systems

Sea Sluice Barrage High basin Power plant

Sluice Power plant

Low basin

Sea

Fig. 2.25 Double basin with paired basin operation.

linked basin operation. The plan comprises three barrages, one isolating the high basin from the ocean and containing the filling doors, another isolating the low basin from the ocean and containing the discharging entryways while the third flood isolates the high basin from the low basin and contains the power house. The upper basin filling doors are opened just when the ocean level is higher than the upper basin. The exhausting entryways of the lower basin are opened just when the ocean level is lower than the lower basin.

2.3.7 Double-Basin With Paired-Basin Operation In a double basin with a paired basin operation (Fig. 2.25), two separate single-basin single-effect schemes are situated at a small distance from each other. Distances are selected such that there is a difference in the tidal phase between them, they never exchange water, and the systems are interconnected electrically. Both the basins operate in single-basin single-effect mode and during the operation, one basin produces electricity during the filling process while the other does so during the emptying process. Its operation leads to a continuous output but the power supply remains irregular. It is difficult to find two tidal sites close to each other that have the requisite difference in time of high water.

2.4 AVAILABLE TECHNOLOGY AND CONCEPTS Tidal current or tidal stream technologies have made enormous strides in development toward commercialization in the past 5–7 years. Almost 40 new devices are currently being developed anda few of them are being tested at full scale in UK waters. Tidal

Introduction of Tidal Energy

current or tidal stream technologies convert kinetic energy into useable energy. Technology developments are comparable to the development of wind turbines. Although most larger-scale demonstration projects use horizontal axis turbines, three main categories can be distinguished: Horizontal and vertical axis tidal turbines currently use blades that are positioned either in parallel (horizontal) or perpendicular (vertical) to the direction of the flow of water. The turbines are similar to designs used for wind turbines, but due to the higher density of water, the blades are smaller and turn more slowly than wind turbines. Furthermore, they have to withstand greater forces and movements than wind turbines. Most designs use blades that are connected to a central rotor shaft, which through a gearbox, is connected to a generator shaft. Open-center turbines have a different design in that the blades are mounted on an inner, open-centered shaft housed in a static tube. As the water flows through the shaft, it rotates and electricity is generated. The advantage of this design is that it eliminates the need for a gearbox. The blades of horizontal or vertical turbines can also be enclosed within a duct. Due to the enclosure, the ocean current is concentrated and streamlined so that the flow and power output from the turbines increase. Reciprocating devices have blades called hydrofoils shaped like airplane wings that move up and down as the tidal stream flows on either side of the blade. The up and down movement of the hydrofoils is subsequently converted into rotation to drive a rotating shaft, or connected to pistons to support a hydraulic system for power generation. The advantage of reciprocating devices is that the length of the blade is not constrained by water depth; however, it also requires complex control systems to pitch the blades correctly. Around 2% of all R&D investments in tidal current technologies went into reciprocating devices. There are a number of other designs that are in the research and development stage. This category includes rotating screw-like devices and tidal kites that carry turbines below their wings. Besides the conversion technology, there are a number of additional technological aspects that determine the performance and costs of tidal current technologies: (1) Support structures. (2) Array formation. (3) Electrical connections to shore. All tidal flow innovations need a help structure to keep the innovation set up and withstand the brutal conditions. The decision for the establishment depends–among other factors–on the position of the tidal ebb and flow innovation in the water, the profundity of the water, the structure of the ocean bed, and the accessibility of vessels and seawardboring gadgets to help the development. There are three classes of help structures (O’Rourke et al., 2010b). The principal classification comprises gravity structures frequently comprising an expansive mass of cement and steel interfacing with the advances to the seabed. The second classifications are heaped structures whereby at least one shaft is bored or stuck into the ocean bed. Establishments with one single bar are called

69

70

Tidal Energy Systems

monopoles. The third class is alleged gliding establishments that are associated with the ocean bed through either inflexible or adaptable wires or chains. In spite of the fact that there is, by all accounts, a union in tidal current advances toward even hub plans, there is still a significant assortment of mooring innovations being utilized. Of the diverse tidal flow ideas and activities, 56% utilize unbending association (generally seabed), 36% utilize mooring, and 4% utilize monopiles (Kempener, 2014). Another specialized viewpoint for tidal current advances is their arrangement as homesteads or exhibits. Single-generator units are constrained in limit, so multipush varieties of tidal turbines should be worked to catch the maximum capacity of tidal streams. Still, turbines affect the ebb and flow streams, so their design is a basic factor to decide their potential yield (SI Ocean, 2012). Also, network association for tidal current innovation organization requires thought. Turbines should be associated with each other through cluster links (ordinarily 33 kV (kV)). The cluster is then regularly associated with a seaward substation, which is associated through a fare link (ordinarily 150 kV) to a coastal substation and in the end to the lattice (the International Energy Agency actualizing understanding for Renewable Energy Technology Deployment). With the advancement of twist stops seaward, there is presently significant involvement in creating both seaward substituting flow (AC) and direct ebb and flow (DC) network foundations. However, lattice association remains one of the basic angles for tidal energy organization as deferrals and the expenses for framework association could put many ventures in danger. Tidal ebb and flow advances can likewise be utilized to create power from sea streams. Sea streams, albeit moderate, are a consistent stream driven by wind designs and thermohaline courses. Sea streams are a fascinating asset as they are extremely consistent yet with a moderate speed. Investigations of thoughts for coasting seaward stages are right now being embraced and so far, no not so distant future business applications have been accounted for. At present, the UK and United States are the most dynamic nations in creating tidal transformation innovations took after by Norway and Canada. Wave energy is as yet one of the slightest developed sustainable power source innovations; however, because the worldwide capability of wave energy is fundamentally higher than tidal energy, we expect huge advancement later on given satisfactory political help. Tidal energy consideration has been developing in current years. However, as of now a large portion of the tasks are still in the early stages. Inside tidal, current, and blast are two fundamental methodologies. Tidal flood is the best innovation so far in marine energy. It has been utilized in a large portion of the operational tasks far and wide. On the opposite side, tidal stream/current is by all accounts the most created innovation (in light of number of tasks and providers). With a push to build up a minimum cost alternative, tidal stream/ current innovation has achieved the early stages of development. Less establishment time allotment is one of the advantages being offered by tidal stream/current innovation. Some early research has likewise been directed in different procedures, including tidal

Introduction of Tidal Energy

ponds and tidal fences. Most of the new technologies in tidal and wave are still under testing or in the precommercial phase. However, a few of them have achieved commercial-scale production, the including axial flow turbine (tidal stream technology), the cross flow turbine (tidal stream technology), and the point absorber (wave energy technology). The readiness level for new technologies in tidal energy is summarized in Tables 2.4 and 2.5. Tidal energy conversion devices are still early stage technologies. Various prototypes have been rolled out to test improvements in turbines and technologies to harness energy from water movement. With tidal being the most predictable form of renewable energy, it has seen limited exploitation commercially. Within wave energy, the industry has yet to arrive on the consensus on technology/design, as the bulk of the wave projects are still in the testing or precommercial phase.

Table 2.4 Different type of technology used in tidal energy systems Technology type Readiness

Attenuator Axial flow turbine Closed cycle Cross flow turbine Hybrid Oscillating water column Oscillating wave surge converter OTEC closed cycle Overtopping device Point absorber Reciprocating device

Open water system testing and demonstration and operation Commercial-scale production/application System integration and technology laboratory demonstration System integration and technology laboratory demonstration Commercial-scale production/application Open water system testing and demonstration and operation Open water system testing and demonstration and operation System integration and technology laboratory demonstration Open water system testing and demonstration and operation Commercial-scale production/application System integration and technology laboratory demonstration

Table 2.5 Technology used in the largest power plants Details of operational tidal power plants name

Country

Technology

Capacity (MW)

Shiwa Lake tidal plant La Rance tidal power plant Annapolis Royal tidal plant The Jiangxia tidal power station The Kislaya Guba tidal facility

South Korea France Canada China Russia

Tidal barrage Tidal barrage Tidal barrage Tidal barrage Tidal Barrage

254 240 20 3.2 0.4

71

72

Tidal Energy Systems

2.4.1 Available Recent Technologies and Concepts (i) ATTENUATOR An attenuator (Fig. 2.26) is a floating device that operates parallel to the wave direction and effectively rides the waves. These devices capture energy from the relative motion of the two arms as the tide passes them. Attenuators are long, multisegment floating structures anchored so that they are aligned perpendicular to the direction of wave or tide travel. The segments flex at hinged joints as a wave passes along the device. The mechanical motion of the flexing is converted to electrical energy using hydraulic motors and generators. The electrical energy is fed down a single umbilical cable to a junction on the seabed. Several devices can be connected and linked to shore through a single underwater transmission cable. The energy-generating capacity of a single attenuator device can be up to 1 MW. Structural Elements: The structure is a steel structure that can be built locally using standard construction techniques available at most shipyards. The device structure has been designed using standard offshore construction principles, and a leading offshore technology consulting firm independently verified the design. Power Take Off: Each hinge of the device contains its own hydraulic power take off. Each power take off has a total of three hydraulic rams, which convert the motions into hydraulic pressure. Using accumulators and two 125 kW generator sets, the hydraulic power is generating electricity. The hinges and power conversion mechanism have undergone full-scale testing on a test rig and have been integrated into the full-scale

Fig. 2.26 Attenuator.

Introduction of Tidal Energy

device. The hydraulic systems use biodegradable hydraulic fluids, which complies with the German “Blue Angel” environmental standard. Mooring: The mooring consists of a three-point slack-mooring configuration. The mooring allows the device to turn into the wave direction within its mooring constraints. The mooring and survivability of the system have been simulated theoretically and tested in wave tanks. While the mooring is probably the least mature element in the overall system and will need to be looked at closely and adapted to the specific site requirements, it does not raise any concerns. The mooring and survivability have been independently analyzed and verified by one of the leading offshore technology consultancy firms, and is designed to withstand the 100-year storm wave. (ii) Point Absorber: The point absorber (Fig. 2.27) is an eccentric of waving energy twist that could potentially provide a large amount of power in a relatively small device, compared to other engineering science. Point absorbers are relatively small compared to wave length, and may be bottom mounted or a floating bodily structure. A point absorber is a floating structure that absorbs energy from all directions through its social movement at or near the water surface. It converts the motion of the buoyant tip relative to the base into electrical power. The power take-off organization may take a number of forms, depending on the configuration of the displacers/reactor. Moving ridge energy conversion has an essential difference from other renewable vim because the dependence between the devices design and the energy resource is stronger. Dimensioning is therefore considered a key stage when a design project of a wave energy converter (WEC) is undertaken. Location, WEC concept, power take off type, control scheme, and hydrodynamic resonance considerations are some of the critical aspects to take into account to achieve a good performance.

Float

Sea surface

Spar

Heave plate Below sea surface

Fig. 2.27 Point absorber.

Cables from other power buoys Under sea substation Cable to shore

73

74

Tidal Energy Systems

Outgoing wave direction

Shore

Paddle Cable

Hydraulic pump Motor

Generator

Fig. 2.28 Wave surge converter.

(iii) Oscillating Wave Surge Converter: Oscillating wave surge converters (Fig. 2.28) extract energy from wave surges and the movement of water particles within them. The arm oscillates as a pendulum mounted on a pivoted joint in response to the movement of water in the waves. The wave surge converter is a hydroelectric wave energy device that uses the motion of ocean waves to generate electricity. It is made up of a power connector frame (PCF), which is bolted to the seabed, and a power capture unit (PCU). The PCU is a hinged buoyant flap that moves back and forth with the movement of the waves. The movement of the flap drives two hydraulic pistons that feed high-pressured water to an onshore hydroelectric turbine, which drives a generator to make electricity. Oscillating wave surge converters harness the energy of near-shore ocean waves; they were designed to operate in water 10–12 m deep. The cscillating wave surge converter is made up of a PCF and a PCU. The 36-ton PCF is bolted to the seabed by 1-by-4 m concrete piles that are drilled 14 meters deep into the seabed. The PCF requires careful and accurate positioning and leveling to compensate for the uneven, rocky seabed. The PCU is a 200-ton, 18-by-12-by-4 m buoyant flap that is hinged to the PCF. In order to lower the PCU into the water to hinge it to the PCF, 120 tons of seawater must be pumped into ballast tanks within the PCU to provide sufficient negative buoyancy to aid its descent into the water. The PCU is almost entirely submerged underwater; only 2 m of the device poke above the water. The PCU sways back and forth with the movement of the waves, and this movement of the flap drives two hydraulic pistons that pump high-pressured water through three subsea pipelines to an onshore hydroelectric water turbine. The turbine then drives a 315 kW electrical generator, which converts the wave energy into electricity.

Introduction of Tidal Energy

There are several advantages to using a device such as the wave surge converter: • A wave surge converter has few moving parts that are worked inside water and the simplicity of these parts allows for survivability in extreme weather conditions. • Operation and maintenance of a wave surge converter is very simple because all the wave surge converter’s electrical components are located on land, and the hydroelectric generator is maintainable 24/7. • It uses nonconventional energy from ocean waves to generate pollution-free, zero-emission electricity. This energy system dominates the environmental risks involved compared to electricity that is produced from fossil fuels. There are also many disadvantages to using such a device: • The installation and production of a wave surge converter is difficult and expensive. • Its weighs >200 tons; it must be carried out to sea in a large flat-top barge and installed in several stages. • To deploy more wave surge converter units, new cables will be needed to install the devices into the national grid. • A wave surge converter’s offshore turbine and generator can produce noise pollution. However, most of this noise is expected to be masked by the surrounding noise generated by the wind and waves. • The installation and operation of the converter could interfere with marine life. • Deploying several surge converter units could result in loss of habitat for marine species. (i) Overtopping/Terminator device (Wave Dragon): Overtopping devices (Fig. 2.29) capture water as waves break into a storage reservoir. The water is then returned to the sea, passing through a conventional low-head turbine that generates power. An overtopping device may use collectors to concentrate the wave energy. Under the Danish Wave Energy Program, a number of WECs have been suggested and tested.

Fig. 2.29 Operation of overtopping terminator device.

75

76

Tidal Energy Systems

Anchor point

Wave reflector

Main plateform

Central buoy Main mooring line

Fig. 2.30 Schematic view of wave dragon.

Among these WECs are devices such as the Wave Dragon (Figs. 2.30 and 2.31), Wave Plane, Sucking Sea Shaft, Power Pyramida, and others. Furthermore, a number of devices have been proposed and some have been built internationally. All these devices have in common that they utilize wave energy by leading overtopping water to one or more reservoirs placed at a level higher than the mean water level (MWL). The potential energy obtained in the overtopping water is then converted to electrical energy by leading the water from the reservoir back to the sea via a low head turbine connected to a generator. The performance of these WEC technologies is not dependant on resonance

Fig. 2.31 Practical view of wave dragon.

Introduction of Tidal Energy

with the waves and can therefore be constructed very large. Central issues for floating overtopping WECs are to control and stabilize the floating structure to optimize power output. A linear systems approach may be used with overtopping devices. This considers the water oscillating up and down the ramp as the excited body, and the crest of the ramp as a highly nonlinear power take-off system. However due to the nonlinearity, it is too computationally demanding to model usefully. Therefore, a more physical approach is taken. The time series of the overtopping flow is modeled, thus relying heavily upon empirical data. Depending on the current wave state (Hs, Tp) and the crest freeboard Rc (height of the ramp crest above MWL) of the device, water will overtop into the reservoir (Qovertop). The power gathered by the reservoir is a product of this overtopping flow, the crest freeboard, and gravity. If the reservoir is overfilled when a large volume is deposited in the basin there will be loss from it (Qspill). To minimize this, the reservoir level h must be kept below its maximum level (hR). The useful hydraulic power converted by the turbines is the product of turbine flow (Qturbine), the head across them, water density, and gravity. Advantages and Critical Points of Overtopping Converter All in all, overtopping converters have points of interest that distinguish them from different gadgets. The variances of the energy delivered by these gadgets is, actually, generally small because the change happens in quiet conditions in the supply where the water is incidentally put away. The execution of these gadgets, at that point, is related with a higher financial attainability. For instance, it is conceivable to join them with different structures along the drift, for example, the regular sea walls for waterfront resistance. And that’s just the beginning, in light of the fact that on the back of the gadgets, there are set up quiet conditions. It is conceivable to utilize this zone to create recreational exercises, for example, aquaculture and fisheries. Also, after the generation of power, the water released through the turbine can be recalculated, keeping in mind the goal to enhance water quality, for instance, in a shut entryway. At last, the utilization of a slope that concentrates the passage of water into the bowl makes it conceivable to utilize the gadgets to flood, even in beachfront locales are not positive, described by a low thickness of wave energy. In light of the fact that these gadgets are normally introduced seaward, they require a proper securing framework. Indeed, high-control (80%–90% catch) and highproductivity gadgets require a tight mooring. Generally, the mooring costs (an enormous overwhelming stage or a tight seabed mooring) could cost effectively around 200%– 300% more than the essential gadget cost (barring the energy stockpiling implications) and requires great climate windows of chance to be worked or kept up. Bulge wave: Bulge wave technology consists of a rubber tube filled with water and moored to the seabed heading into the waves. The water enters through the stern

77

78

Tidal Energy Systems

Generator Air out

Turbine

Air in

Wave crest

Rising water column

Falling water column

Fig. 2.32 Oscillating water column.

and the passing wave causes pressure variations along the length of the tube, creating a bulge. As the bulge travels through the tube it grows, gathering energy that can be used to drive a standard low-head turbine located at the bow, where the water then returns to the sea. Rotating mass: Two forms of rotation are used to capture energy by the movement of the device heaving and swaying in the waves. This motion drives either an eccentric weight or a gyroscope causes precession. In both cases, the movement is attached to an electric generator inside the device. Oscillating Water Column: Oscillating Water Columns (OWCs) Fig. 2.32 are a type of wave energy converter (WEC) that harnesses energy from the oscillation of the seawater inside a chamber or hollow caused by the action of waves. OWCs have shown promise as a renewable energy source with a low environmental impact. Because of this, multiple companies have been working to design increasingly efficient OWC models. OWC are devices with a semisubmerged chamber or hollow open to the sea below, keeping a trapped air pocket above a water column. Waves force the column to act like a piston, moving up and down, forcing the air out of the chamber and back into it. This continuous movement forces a bidirectional stream of high-velocity air, which is channeled through a power take off (PTO). The PTO system converts the airflow into energy. In models that convert airflow to electricity, the PTO system consists of a bidirectional turbine. This means that the turbine always spins the same direction regardless of the direction of airflow, allowing for energy to be continuously generated. Both the collecting chamber and PTO systems will be explained further under “Basic OWC Components.”

Introduction of Tidal Energy

Basic OWC Components • Power Take Off The PTO system is the second main component of an OWC device because it transfers the pneumatic power into a desired energy source. The efficiency of a PTO system is very important because it increases the efficiency of the oscillating water column. It must be able to convert water velocity going both out of and into the collecting chamber to generate the energy. • Wells Turbine The Wells turbine, manufactured in the late 1970s by professor Alan Arthur Wells at Queen’s University Belfast, is a bilateral turbine that uses symmetrical airfoils. The airfoils will rotate the same direction in spite of the direction of water flow. The Wells turbine has both advantages and limitations. The advantages are that it has no moving parts other than the main water turbine rotor, making it easier to operate and maintain and more cost beneficial. But some limitation occurs such as some inefficiency at high airflow rates because the airfoil’s high angle of attack creates more drag. The angle of attack is the number of degrees the airfoil is from being parallel with the airflow. • Hanna Turbine In 2009, the Hanna turbine was invented by environmental activist John Clark Hanna. The Hanna turbine was a modified form of the pioneering Wells Turbine. Similar to the Wells, the Hanna device has no moving parts that come in indirect and direct contact with the ocean. The turbine has two rotating parts with back-to-back asymmetrical airfoils. The lift coefficients of airfoils are higher and have less drag force rather than the Wells Turbine. This makes the Hanna design less prone to stalling and offers more torque with a larger operating window. The Hanna design also drives two generators that operate outside the enclosed air duct in a relatively dry environment. This allows for easy maintenance of the generators.

2.5 COMPONENT OF A TIDAL POWER PLANT A new tidal energy design option is to construct (Fig. 2.33) circular retaining walls embedded with turbines that can capture the potential energy of tides. The created reservoirs are similar to those of tidal barrages, except that the location is artificial and does not contain a preexisting ecosystem. The lagoons can also be in double (or triple) format without pumping or with pumping that will flatten out the power output. The pumping power could be provided by excess to grid demand renewable energy from, for example, wind turbines or solar photovoltaic arrays. Rather than being curtailed, excess renewable energy could be used and stored for a later period of time. Geographically dispersed tidal lagoons with a time delay between peak productions would also flatten out peak production, providing near base load production at a higher cost than some other alternatives

79

80

Tidal Energy Systems

Generator Hydrodynamic system

Bearing

Transmission system Control system

Power conversion

Foundation

Fig. 2.33 Component of a tidal energy power plant.

such as district heating renewable energy storage. The proposed Tidal Lagoon Swansea Bay in Wales would be the first tidal power station of this type. The hydrodynamic subsystem is the region of the device where energy from the marine environment is converted into a more useful form of motion prior to any energy extraction taking place. For a tidal energy device, this is most likely to be some form of lift-force rotor but could also employ simple drag force paddles for example. Wave energy devices are far more varied. A common form for the hydrodynamic subsystem is to use a submerged or neutrally buoyant volume to move with the wave motion. Some devices use a hollow volume such that the wave motion moves air from which energy can be extracted. The power take-off subsystem is where the mechanical motion is converted to a more useful form of energy. In the majority of devices, this is electrical energy but a small number of concepts feature compressed fluid conveyed to shore or other forms of energy conversion. Generators for the conversion of mechanical to electrical energy may be driven by rotating or reciprocating inputs (shaft) and there may be some form of speed increase such as a gearbox. Ancillary systems such as cooling, reactive power, hydraulic compressors, etc., are also included within the power take-off subsystem. Immediately before the exit point of the device, there may be some form of power conversion, usually an electrical transformer to increase the transmission voltage from the device to the shoreline. Power conditioning may also be included to ensure the electrical output from the device is of a suitable quality to be fed into the main electrical grid system. The control subsystem encapsulates components used to control the device in terms of station keeping, power capture from the marine environment, and safety systems. For a tidal energy device, this will include means to control rotor speeds and their alignment to the tidal flow. Control for a tidal device may include strategies to optimize power capture from different sea states. The reaction subsystem is composed of the device support structure and foundations. These aspects of the device ensure that it maintains its spatial

Introduction of Tidal Energy

position within the marine environment. There are several methods of anchoring or fixing the device to the seabed or shoreline, including tubular piles, anchor chains, and gravity foundations. The support structure may take almost any form dependent upon the device and the nature of its components. Tidal System Component Classification Layer Description Layer 1 addresses the general form of the device. For both wave and tidal devices, this is regarded as the characterization/specification of the hydrodynamic subsystem. This system converts the wave/tidal motion into a more useful mechanical form suitable for power extraction. The form and motion paths of this subsystem provide the most meaningful method of classifying the type of device. Layer 2 addresses the power take off subsystem. Here, the converted mechanical motion from the hydrodynamic subsystem is converted into electrical power. There are a variety of different methods to generate electricity in terms of principle motion and operational speed. Often there is a gearbox or some means to increase the speed of motion between the hydrodynamic subsystem and the generator. Layer 2 also quantifies the “edge of device” electrical power output allowing estimates of efficiency to be made by the user. Layer 3 addresses the reaction and control subsystem, principally the method of keeping the device “at station” in the water and characterizing how the hydrodynamic subsystem is aligned to the waves/tidal current. Due to the large differences between wave and tidal energy devices (principally for the hydrodynamic and power take-off subsystems), each has been addressed with a separate classification template.

2.5.1 Types of Turbines The turbine choice will determine the operation conditions and the environmental impact. Fsor these reasons, several aspects such as head variability, flow rate, requirements for pumping or continuous operation, requirements for two-way generation operation, start-stop frequency, etc., have to be considered. It is worth mentioning that due to the development in turbine design, routine repair is carried out with greater ease, thus, maintenance is no longer consider a development issue. Nowadays, there are several types of turbines available; the most commonly used are bulb, rim, and tubular turbines. (i) Bulb turbines Bulb turbines (Fig. 2.34) are a type of hydro turbine. In present scenario a tidal energy system whose name comes from the framework of the high flow watertight outer configuration, which is the arrangement where the DC or AC generator positioned in the horizontal axis and is mount within the water tube as an essential unit with the turbine. This set up can offer a noteworthy reduction in dimensions, price, and construction as there is a low need for excavation and the draft tube improves the hydraulic behavior of

81

82

Tidal Energy Systems

Fig. 2.34 Working of a bulb turbine.

the bulb unit. During its working, water floods around the turbine so that its maintenance is very difficult, as water has to be barred from flowing through the turbine. So that when maintenance and preservation of the turbine or generator are needed, it has to be lifted out of the water. As a result, the turbine stops producing power for the extent of the process. A bulb turbine is considered the most competent solution for low heads up to 30 m. For this reason, they are the most popular turbines among barrage designers. Moreover, the turbine and generator are reversible, namely, they can generate power on the flood tide or act as a motor to pump seawater into the basin. Bulb turbines have proved to be very reliable and have been operated nearly constantly without major problems for >30 years at the La Rance tidal barrage. (ii) Rim turbine A rim turbine’s generator (Fig. 2.35) is separate from the turbine itself. It is mounted on the torrent and is associated through a pole that moves with the turbine; thus, just the turbine is in the water stream. Additionally, the rotor is shielded from the entrance of ocean water by particularly planned water seals. Concerning support, it is important to expel them when turbine upkeep is required, despite the fact that the generator can be reached when the water delta entryway is shut and the water depletion is off. Therefore, the generator support issue in knob turbines is unraveled. Early outlines were more reasonable for stream applications because of water seals spilling under weight; however, later enhancements have made them more dependable. There is a 20 MW Straflo turbine, 8.2 m distance across, that has been introduced in the Annapolis River Tidal Barrage in Canada. This sort of turbine is favored for its more noteworthy hypothetical proficiency and more noteworthy latency (to fulfill security criteria). In any case, it can just work on the ebb tide and can’t be utilized to direct capacity to the bowl because of their progressively fragile nature.

Introduction of Tidal Energy

Drive shaft transmission rods attached to rotor

Concrete barrage stator

Rotor

Rotor attached to turbine shaft

Fig. 2.35 Working of a rim turbine.

Bulb hanger Turbine blade Water flow

Generator

Bulb casing

Steady plinth

Fig. 2.36 Working of a tubular turbine.

(iii) Tubular turbines In tubular turbines, the generator (Fig. 2.36) is mounted on the highest point of the flood at a 45 degree edge with the turbine, and the cutting edges are associated with a long shaft. The genuine favorable position that they show is that the cutting edges can be balanced. This implies they can be changed to take care of power demand; smaller edges will produce less power while bigger edges will create more power. This enables the turbine to run all the more effectively, producing just the measure of energy required. Besides, this plan gives some space to a gearbox, which permits more effective operation of generators. Moreover, support can occur in areas where the water supply has been separated. Still, it displays some vibration issues of the long shaft and it can’t be turned around to work on a

83

84

Tidal Energy Systems

surge tide or used for pump stockpiling. Tubular turbines have been utilized as a part of some hydro plants in the United States; they are also proposed for the Severn tidal venture in the United Kingdom. (iv) Horizontal axis tidal current turbines: The turbine’s sharp edges turn about a flat hub that is parallel to the heading of the water stream. They are displayed submerged in lines, like some breeze ranches. The ideal working purpose of the turbines is for waterfront stream speeds in the vicinity of 4 and 5.5 mph. In those streams, a 15 m distance across the tidal turbine can create as much energy as a 60 m breadth wind turbine. The perfect areas for tidal turbine ranches are near the shore in water profundities of around 20–30 m. Level turbines have somewhat higher proficiency than vertical turbines. Still, as they rely upon the present heading, a system to influence the cutting edges to turn is required but, for the most part, they are exceptionally mindboggling. (v) Sea flow turbine A sea flow turbine (Fig. 2.37) has an 11 m diameter rotor with full traverse pitch control. It is mounted on a steel tubular heap, 2.1 m in breadth, set into the seabed and sufficiently tall to dependably extend over the surface of the ocean. It is introduced in a mean profundity of 25 m, 1.1 km off the closest landfall in North Devon, UK. Under great conditions, it has surpassed its 300 KW evaluated control with a 15 rpm rotor. It is not framework associated and dumps its energy into protection radiators. This gadget was created by Marine Current Turbines (MCT). It was produced by Hammerfest Strom. This turbine can be introduced on the seabed seaward or the close shore, contingent upon the tidal ebb and flow quality. The edges of 1516 m can pivot without anyone else tomahawks, enabling the turbine to be

Fig. 2.37 Sea flow turbine.

Introduction of Tidal Energy

enhanced to momentum conditions and furthermore work in the two headings of the tide. A 300 KW framework was tried, but a bigger outline is being created that will give 750–1000 KW of energy. (vi) Vertical axis tidal current turbines: Vertical hub turbines are cross-stream turbines, with the hub situated opposite to the heading of the water stream. Cross-stream turbines permit the utilization of a vertically arranged rotor that can transmit the torque specifically to the water surface without the need of complex transmission frameworks or a submerged nacelle. The vertical pivot configuration allows the saddling of the tidal spill out of any heading, encouraging the extraction of energy not just in two ways with the approaching and active tides, but by utilizing a full tidal oval of the stream. In addition, the cutting edges are effectively fabricated and their traverse can be effortlessly expanded. In any case, these kinds of turbines have a considerable measure of vibrations, as the powers applied on the bladders are altogether different. Subsequently, it is hard to achieve soundness. In vertical pivot turbines, as in level hub ones, the turn speed is low, around 15 rpm.

2.5.2 Tidal Steam Generator A tidal stream generator, regularly alluded to as a tidal energy converter (TEC), is a machine that concentrates energy from moving masses of water, specifically tides. This is in spite of the fact that the term is frequently utilized as a part of a reference to machines intended to separate energy from a continuously running waterway or tidal estuarine destinations. Certain sorts of these machines work particularly like submerged breeze turbines, and are subsequently frequently alluded to as tidal turbines. Tidal stream generators utilize the motor energy of moving water to turn a turbine as the way a breeze turbine utilizes twist to make power. In any case, the power accessible for tidal power in a given zone can be more prominent than a breeze turbine because of the higher thickness of water. These sorts of tidal generators have a tendency to be the least expensive (however, still very costly) and most naturally inviting of a tidal powerage. There are a few distinctive particular sorts of tidal stream generators that will be talked about beneath. These sorts of generators have a low visual effect and are, for the most part, submerged. Besides, they are less meddlesome to marine life because they deliver less commotion contamination. The thickness of water is likewise considerably higher than air, which implies that tidal turbines can be substantially smaller than twist turbines of a similar yield. This is additionally improved by the utilization of the Venturi impact, which is a method for motivating water to move quicker through these turbines. Likewise, with a wide range of tidal power innovation, the underlying venture costs are to a great degree high and it takes a long time to make back that investment. Lamentably, ocean water is very destructive, which prompts high upkeep costs.

85

86

Tidal Energy Systems

How Does It Work? Tidal stream generators look and work like underwater wind turbines. As opposed to using the rising and falling movement of the tides, tidal stream generators take advantage of the fast moving sea currents (tidal streams), which flow when tides are moving in and out. These tidal streams cause the turbines to rotate, turning the generators to generate electricity. Tidal stream generators have the advantage of being much cheaper to build, and do not have as much of an environmental impact as a tidal barrage. The turbines turn relatively slowly, hence do not affect sea life. This is different to tidal barrages, which can disrupt fish migrating up rivers from the sea. Advantages of Tidal Stream Generators

The operation and execution of tidal power plant is more difficult. This reasonable execution happens partially in light of the fact that every turbine remains alone without the requirement for a monstrous dam as in the tidal torrent framework. Such measured quality likewise takes into consideration smaller applications to be developed once the monetary practicality is settled in a little test venture and once natural effects are better caught on. One of the key preferences of tidal stream generators is the capacity to consolidate them into existing structures such as scaffolds and docks. This further lessens the cost as well as decreases the natural effect. At last, the acoustic properties of the sharp edges in water appear to keep untamed life from straying into the way. This is altogether different from how sharp edges work ashore where flying creatures, bats, and owls are frequently slaughtered. It appears that the effect of submerged turbines might be significantly less than that of surface turbines. Disadvantages of Tidal Stream Generators

Tidal stream generators generally cannot produce as much power as barrage systems. They are, like barrage systems, prone to corrosion from saltwater. Materials science has advanced enough, however, to make corrosion only a minor problem. Tests on the full impact of tidal stream generators on the environment are currently being tested at the Northwest National Marine Renewable Energy Center in the United States. Most predictions are that tidal stream generators will become an important, though small, part of the power supply in coastal nations.

2.5.3 Tidal Lagoon A tidal pond is a power station that creates power from the regular ascent and fall of the tides. Tidal ponds work correspondingly to tidal blasts by catching a vast volume of water behind a man-made structure, which is then discharged to drive turbines and produce

Introduction of Tidal Energy

power. Not at all like a torrent, where the structure traverses a whole stream estuary in a straight line, a tidal pond encases a zone of coastline with a high tidal range behind a jetty, with an impression deliberately intended for the nearby condition. As the tide comes in (surges), the water is kept down by the turbine wicket doors, which are utilized to control the course through the turbine and can be totally shut to stop water entering the tidal pond. This makes a distinction in water level stature (head) between the tidal pond and the ocean. Once the distinction between water levels is enhanced, the wicket doors are opened and water hurries into the tidal pond through the globule turbines mounted inside solid turbine lodgings in a segment of the sea wall divider. As the water turns the turbines, power is created. The water in the tidal pond at that point comes back to intently coordinate an indistinguishable level from the ocean outside. This procedure likewise occurs backward as the tide streams out (ebbs) in light of the fact that the turbines are bidirectional; thus, power can be created from the approaching and active tides. We can hold the tide inside the tidal pond for around 2.5 h as the ocean outside ebbs and the head fabricates. As the tides rise and fall normally, with no prerequisite for fuel, tidal power is really inexhaustible and, unlike other sustainable power sources, is totally unsurprising. As there are constantly two high and two low tides each day, tidal ponds will create power for more than four periods per day, each day of the year. As we hold the tides for 2.5 h four times each day, we can create control for up to 14 at regular intervals. The height and time of the tides can be anticipated a very long time ahead to a high level of exactness, permitting the exact operation of the tidal pond on each tidal cycle to be enhanced well ahead of time. Figs. 2.38–2.40 show tidal lagoons.

2.5.4 The Lagoon Wall The primary purpose of the lagoon wall is to dam up the ebb and of flood tide. To achieve this, the wall is required to have a very low permeability (leakage rate) to prevent the tide Sea Basin

Turbine house

Fig. 2.38 Generating on the flood tide (tidal lagoon).

87

88

Tidal Energy Systems

Basin

Turbine house

Sea

Fig. 2.39 Holding period at high or low water (tidal lagoon).

Basin Turbine house

Sea

Fig. 2.40 Generating on the ebb tide (tidal lagoon).

from escaping through the wall rather than flowing through the turbines. By constructing the central portion of the wall from a dense sand or gravel, and protecting it against the incoming waves and weather degradation with large armor rock, the wall will function as intended. This type of wall is commonly known as a rubble mound breakwater with a sand core and is similar to many seen in coastal defense schemes and harbor breakwaters throughout the world. The wall will be constructed using proven, well-established, marine construction methods. By partnering with leading global engineering consultancies as well as consultation with specialist marine construction companies, we have ensured a robust, constructible, and expert approach to our lagoon wall design. The concrete structures housing the turbines and sluice gates are built so that the turbines are permanently submerged. The size and shape of the lagoon depends on a lot of factors. As well as the tidal range, the water depth, sea conditions, environmental impacts, and navigation all have a big influence on which locations are suitable to build a lagoon. Swansea Bay Tidal Lagoon will have a breakwater of around 9.5km, enclosing an area of 11.5 km2 and including 16 turbines. Our future fleet of lagoons will have longer walls, larger enclosed areas, and potentially multiple turbine houses, allowing us to generate even more renewable energy.

Introduction of Tidal Energy

2.6 ESTIMATION OF ENERGY CALCULATION A tidal power station feeds different types of needs such as consumer, domestic, commercial, industrial, agricultural, etc. The present tidal power station invariably feeds a grid that delivers power to the load centers. Each device at the consumer terminals has its rated capacity. The connected load of a consumer means the sum of the continuous rating of all the devices and outlets installed on his distribution circuit. The maximum demand of a consumer means the maximum power that his circuit is likely to draw any time. Maximum Demand (Peak Load): It is characterized as the most extreme power enlivened by the request side amid a particular timeframe. It is likewise equivalent to the most extreme real power produced by the plant when the transmission misfortunes are disregarded. The greatest request of every purchaser is, hence, not as much as his associated stack. The most extreme request and the associated stack are connected by: Maximum demand (2.2) Connected load Average Load: It is the average power consumed by the load during a specific period of time and it is equal to the average power generated by the plant during the same period of time when neglecting transmission line losses. Demand factor ¼

Average Load ¼

Area under the load curve ðkWhÞ No: of hours ðhÞ

(2.3)

Load factor: It is the proportion of the normal load to the most extreme load for a specific timeframe. The load factor is called the day-by-day load factor if the timeframe is a day, and if the timeframe is a month, the heap factor is called the month-to-month stack factor, and correspondingly for the year stack factor. Average Load (2.4) Maximum Load Installed capacity (plant capacity, nameplate capacity): It speaks to the most extreme conceivable power that could be created (produced) from the power plant. The estimation of the introduced limit relies upon the plant outline. Installed capacity: It represents the maximum possible power that could be produced (generated) from the power plant. The value of the installed capacity depends on the plant design. Load Factor ¼

Installed capacity ¼ Nominal power value of the plant

(2.5)

Reserve capacity ¼ Installed capacity  Maximum demand

(2.6)

Plant capacity factor: The capacity factor of a power plant is the proportion of its normal yield control over some stretch of time to its greatest conceivable power that could be created. The net limit factor is the unitless proportion of a genuine electrical energy yield over a given timeframe to the most extreme conceivable electrical energy yield

89

90

Tidal Energy Systems

over a similar measure of time. The limit factor is characterized for any powerdelivering establishment, that is, a fuel-devouring force plant or one utilizing a sustainable power source, for example, wind or sun. The normal limit factor can likewise be characterized for any class of such establishments, and can be utilized to analyze diverse sorts of power generation. The maximum possible energy output of a given installation assumes its continuous operation at full nameplate capacity over the relevant period of time. The actual energy output over the same period of time and with it the capacity factor varies greatly depending on a range of factors. The capacity factor can never exceed the availability factor or the fraction of downtime during the period. Downtime can be due to, for example, reliability issues and maintenance, both scheduled and unscheduled. It can be determined as below: Plant capacity factor ¼ Plant use factor ¼

Average demand ðkWÞ Installed capacity ðkWÞ

Actual energy produced Installed capacity ðkWÞ  No: of operating hours

(2.7) (2.8)

In electrical engineering, utilization factor is the ratio of the maximum load that could be drawn to the rated capacity of the system. This is closely related to the concept of load factor. The load factor is the ratio of the load that a piece of equipment actually draws (time averaged) when it is in operation to the load it could draw (which we call full load). For example, an oversized motor—15 kW—drives a constant 12 kW load whenever it is on. The motor load factor is then 12/15 ¼ 80%. The motor above may only be used for eight hours a day, 50 weeks a year. The hours of operation would then be 2800 h, and the motor use factor for a base of 8760 h per year would be 2800/8760 ¼ 31.96%. With a base of 2800 h per year, the motor use factor would be 100%. Utilization factor ¼

Maximum demand ðkWÞ Installed capacity ðkWÞ

(2.9)

Diversity factor is the ratio of the sum of the individual maximum demands of the various subdivisions of a system (or part of a system) to the maximum demand of the whole system (or part of the system) under consideration. Diversity is usually more than one. Diversity factor ¼

Sum of individual maximum demandðkWÞ Maximum demand on power plant ðkWÞ

(2.10)

The technology required to convert tidal range into electricity is very similar to conventional hydroelectric power plants, but in this case, the current flows in both directions. This means that tidal barrages are unable to produce electricity at a constant rate, as they

Introduction of Tidal Energy

have to wait for sufficient hydrostatic head between both sides of the dam. However, electricity production from tidal barrages is totally predictable, allowing for ease of electricity supplies. Tidal barrages use the potential energy of the tides to generate electricity. Given a basin, the theoretical potential energy can be calculated as: E ¼ gρA zdz ¼ 0:5gρAH 2

(2.11)

where E is energy (Joule), g is acceleration of gravity (9.8 m/s ), ρ is seawater density (approximately 1022 kg/m3), A is sea area (m2), z is vertical coordinate of the ocean surface (m), and H is tide amplitude (m). For seawater: (gρ) ¼ 10.0156 kNm3. Tidal current innovation separates the motor energy comparable to gathering twist energy from air. In any case, there are a few contrasts in the working conditions. Working under comparable conditions, water is 832 times denser than air, and the water stream speed for the most part is considerably smaller. Because of the distinction in thickness between the two liquids, the power force in water ebbs and flows is essentially higher than air streams. Thus, a water flow turbine can be constructed significantly smaller than a comparable controlled turbine. Rather than environmental wind currents, the accessibility of tidal streams can be anticipated precisely. Another particular preferred standpoint of tidal current gadgets is the constrained natural effect as their establishment requires the least land utilized, and completely submerged gadgets will not optically or acoustically influence their environment. At long last, submerged marine current converters are considered to work in safe conditions. Unsettling influences caused by extraordinary climate conditions are altogether constricted to the profundities of 20–30 m, where the gadgets will be put, for the most part. In any case, because tidal ebb and flow turbines work in water, they encounter more prominent powers and minutes than wind turbines. Likewise, tidal current turbines must have the capacity to create amid both ebb and surge streams, and have the capacity to withstand the auxiliary burdens when not producing power. Consider a basin of surface area m2 at the maximum basin level. Let H be the range of the tide and V the volume of water stored from the low level to high tide level. The volume of water contained in an elemental strip of thickness dz; at surface area of AZ, at a depth z above the low tide in the basin, dV ¼ AZdz. 2

Ocean With Single Basin Tidal Project Assume that the basin is empty with its water level, z ¼ 0 and the ocean is at high tide level, z ¼ R. By instantaneously filling the basin, the energy potential available is Ef (Fig. 2.41) ð Z¼H ð Z¼H H2 Ef ¼ ρg Z:AZ dz ¼ AZ :ρ:g Zdz ¼ Aρg (2.12) 2 Z¼0 Z¼0

91

92

Tidal Energy Systems

Barrage

AZ

dz

R

Z

Datum

Ocean

Basin Turbine & generator

Fig. 2.41 Energy assessment through single basin system.

where ρ ¼ seawater density ¼ 1025 kg/m3, g ¼ gravity ¼ 9.81 m/m2. The above equation provides energy conversion from a single basin type with single effect, that is, either filling the basin or emptying the basin. The duration of time for the single effect is 6 h and 12.5 min, which is equal to 22,350 s. Ef H2 1 (2.13) ¼ Aρg  ¼ 0:225ARH 2 W time 2 time where, A ¼ area of the basin in m2, R ¼ range of the tide in m. The average power is calculated based on average operating head of H/2 for a limited period in a single-basin emptying operation. There are friction losses and conversion efficiencies of turbine and generator that reduce the power output. Hence, the optimal annual energy production is only 30% of the average theoretical power calculated above. Thus, the energy available from a tidal plant can be calculated in a similar way as for a hydroelectric plant. Assuming the following: H ¼ tidal range, that is, the difference between the maximum and minimum water levels in the basin, in m. A ¼ mean base area of the basin, in m. V ¼ volume of water that can be contained in the basin, in m ¼ AH. The average quantity of water Q in cubic meters per second that flows in or out from the basin. Therefore, Q ¼ AH/t where t is the total time in seconds required for filling or emptying the basin. Theoretical work done by Q quantity of water falling through H m is given by W ¼ ρQH kg m. Power measurement: ρQH Power generated at any point of time,P ¼ η hp (2.14) 75 P¼

where ρ ¼ 1025 kg/m3 for sea water; 1 hp ¼ 75 kg-m/s, η ¼ system η.

Introduction of Tidal Energy

ρQH η  736 W since 1 hp ¼ 736 W 75 ðt ρQH η  736dt Total energy per tidal cycle ¼ 75

Hence P ¼

0

There are on average 705 tidal cycles in a year. Yearly power generation from a tidal project ðt ðt ρQH 6 Pyear ¼ η  736  705dt ¼ 7:0914  10 η QHdtW o 75 0

(2.15)

2.7 TIDAL DYNAMIC AND STRUCTURE OF TIDAL CURRENTS Tides are defined as periodic, short-term changes in the height of the ocean surface caused by the moon and sun’s gravitational forces and the rotation of the earth. The dynamic theory of tides takes into account the effect of continents, shallow water, and partially enclosed ocean basins on tide formation. In the equilibrium theory of tides, we assumed that the shape of the sea surface was always in equilibrium with the forcing, even though the forcing moves relative to the Earth as the Earth rotates underneath it. From this Earth-centric reference frame, in order for the sea surface to “keep up” with the forcing, the sea level bulges need to move laterally through the ocean. The signal propagates as a surface gravity wave (influenced by rotation) and the speed of that propagation is limited by the shallow water wave speed, C ¼ gH, which at the equator is only about half the speed at which the forcing moves. In other words, if the system was in equilibrium at a time t ¼ 0, then by the time the Earth had rotated through an angle ø, the bulge would lag the equilibrium position by an angle/2. Laplace first rearranged the rotating shallow water equations into the system that underlies the tides, now known as the Laplace tidal equations. The horizontal forces are: Acceleration + Coriolis force ¼ Pressure Gradient force + Tractive Force Therefore, the relevant force, the tractive force, is the projection of the tide producing force onto the local horizontal direction. The equations are the same as those that govern rotating surface gravity waves and Kelvin waves. The tide is forced by the sum of the pressure gradient force and the tractive force, and propagates like a Kelvin wave. Tides can be predicted using a numerical ocean tidal model that incorporates these equations. Observational data in the form of sea level at the coast and altimeter data in the open ocean are often assimilated into the numerical model. The model results, such as the one at Oregon State University that you will look at in your problem set, are presented in the form of maps of phase and amplitude for each tidal component. Tidal components are added together to form the total tidal sea level variation.

93

94

Tidal Energy Systems

For each tidal constituent (or component), several quantities are defined: Corange lines link places having the same tidal range (amplitude). Cotidal lines link all points having the same phase. Numbers are hours of lag of high tide after the moon’s transit over the Greenwich meridian (0 degrees) or phase of the tide relative to Greenwich (e.g., a phase of 0 degrees has high tide at the same time as the moon is passing over Greenwich, 180 degrees has low tide at this time). Amphidromic points are points where the tidal range is zero. Wave crests move around the amphidrome once per tidal cycle. Near the coast, progression around amphidromes tends to be cyclonic (i.e., in the sense of a Kelvin wave), keeping the coast on the right (N Hem). Wide bays: Tides will propagate around the boundaries of a wide bay. How wide does the bay need to be to have tidal propagation around it? Kelvin waves have an offshore scale given by the barotropic Rossby radius: pffiffiffiffiffi . LR ¼ gH (2.16) f

The bay must be wide enough (L > 2 LR), relative to its depth H, so that the incoming and outgoing waves do not significantly overlap and interfere. Narrow bays: If the bay is narrow, the wave entering from the open ocean will be reflected to set up a standing wave. At this extreme, when the width of the bay is small with respect to the Rossby radius of deformation, rotation is unimportant to the dynamics. As the tide passes the opening of the inlet, it uniformly raises and lowers sea level there (because the length scale of the open ocean tide is much greater than the width of the opening). As the wave propagates into the inlet, it encounters reflections off the landward end from previous wave cycles, and interference occurs, leading to the possibility of standing waves. Narrow inlets (or fjords) and narrow channels allow the possibility of standing waves. Each fjord or harbor has a set of natural frequencies.

2.7.1 Tidal Current Horizontal movement of water is called current. It may be “tidal” or “nontidal.” Tidal current is the periodic horizontal flow of water accompanying the rise and fall of the tide. Nontidal current includes all current that is not due to the tidal movement. Nontidal current include the permanent current in the general circulatory system of the ocean as well as temporary current arising from meteorological conditions. The current experienced at any time is usually a combination of tidal and nontidal current. Tidal currents occur in conjunction with the rise and fall of the tide. The vertical motion of the tides near the shore causes the water to move horizontally, creating currents. When a tidal current moves toward the land and away from the sea, it “floods.” When it moves toward the sea away from the land, it “ebbs.” These tidal currents that ebb and

Introduction of Tidal Energy

flood in opposite directions are called “rectilinear” or “reversing” currents. Rectilinear tidal currents, which typically are found in coastal rivers and estuaries, experience a “slack water” period of no velocity as they move from the ebbing to flooding stage, and vice versa. Mathematical Function of Tidal Structure Nowadays, coastal oceanographers have recommended using the “Strouhal” number or its inverse, the “Stokes” number, to explain the consequence of bottom boundary layer turbulence on the vertical structure of both electric field density and currents. These are defined as the ratios of the frictional depth (γ) to the water column depth (d) or vice versa. Although numerous specialists have specified that the impacts of the Earth’s turn ought to be imperative, they have had a tendency to overlook it. Turn may have a vital influence on tidal streams, as the frictional profundity from a completely cyclonic to a completely anticyclonic tidal circle can shift by up to a request of extent at mid scopes. The Stokes number may seem smaller for cyclonic current ovals (bigger for anticyclonic) than it is without revolution, bringing about frictional impacts that are overestimated. Here, an approach to ascertain a Stokes number is proposed in which the impact of the world’s turn is considered. The standard Stokes and the rotational Stokes numbers are utilized as indicators for the position of the tidal blending fronts in the Irish Sea. Results demonstrate that utilization of the rotational number enhances the expectations of fronts in shallow cyclonic zones of the eastern Irish Sea. This proposes the impact of turn on the water section structure will be more essential in shallow rack oceans and estuaries with solid rotational streams. Stokes (1851) studied the flows over an oscillating plate (analogous to oscillatory flow over the bottom) and defined the depth of frictional influences denoted by the parameter. The ratio of γ to the total water column depth (d) is known as the Stokes number: γ Stokes ¼ (2.17) d This is equivalent to the ratio of friction to local accelerations in the momentum balance. If we define the oscillatory boundary layer thickness following Lamb (1932), k 1 U∗ (2.18) f where ω is the oscillatory frequency, for example the M2 semidiurnal frequency, and U∗ is the frictional velocity (U∗ ¼ Cd1/2U), where U is the M2 velocity amplitude, Cd is the quadratic drag coefficient, and c1 is a proportionality constant. The Stokes number can be expressed as follows: k1 U∗ γ ¼ (2.19) Stokes ¼ fd d γ¼

95

96

Tidal Energy Systems

The Strouhal number was originally defined by Strouhal (1978) while experimenting with wires experiencing vortex shedding and singing in the wind. This number is now used mainly to explain vortex shedding. The Strouhal number is defined as follows: fL (2.20) U where ω is the frequency of the vortex shedding, L is a characteristic length, and U is the velocity of the flow. In recent years the Strouhal number has commonly been used to assess the effect of friction in oscillatory flows and has been defined as following: fd d 1 ¼ ¼ (2.21) Stroke ¼ k1 U∗ γ Stroke Strouhal ¼

for example, as in Prandle (1982). Although this analysis is dimensionally correct, the use of the Strouhal number is dynamically incorrect as it is the ratio of local to advective accelerations. The aim of this paper is three-fold: (1) to establish the use of the Stokes number as the correct number to be used when considering the effects of friction over inertia, (2) to highlight the effect of the Earth’s rotation on frictional tidal processes, and (3) to use the rotational Stokes number as a predictor of tidal mixing fronts as a test of the influence Earth’s rotation. fd (2.22) Strouhal ¼ U Use of the Stokes number to describe tidal dynamics in estuaries and shelf seas: Stokes (1851) explained this problem in what has become known as the Stokes “second problem” in fluid mechanics; it has been published in several textbooks and it is applicable to any oscillatory case (i.e., waves and tides). The original problem was the flow due to an oscillating plate, in which the governing equation is dv d2 V ¼ Nz 2 dt dz with boundary condition v(0, t) ¼ V cosωt, and had a solution as follows:  1=2 ! 1 ω f zð 2 Þ2 cos ft  z v ¼ Ve 2NZ

(2.23)

(2.24)

where Nz is the eddy viscosity, and U and ω are the amplitude and frequency of the oscillating motion. The height of frictional influence or Stokes depth is given by following equation:   2NZ 1=2 k1 U∗ γ  (2.25) f f in the case of oscillatory flow forced by a horizontal pressure gradient due to the surface slope, as in the case of waves and tides. The equations of motions are

Introduction of Tidal Energy

dv d2 V dγ ¼ NZ 2  g  (2.26) dt dz dx where η is the surface elevation and g is gravity. With the pressure gradient given by the following equation, dγ ¼ Acosð ft Þ (2.27) dx and boundary conditions v ¼ 0 at z ¼ 0, and ∂ v/∂ z ¼ 0 at z ¼ h, we have the following solution:    z A z γ sinft  e sin ft  (2.28) V¼ f γ g

We can assume that the velocity far away from the boundary in the free stream will be given by Vinfinity ¼

A sin ft f

(2.29)

If u is normalized by A/f and we substitute ζ ¼ z/h, the solution becomes as follows:   τ 2  V ¼ sinft  e Stk sin ft  (2.30) Stroke This is a similar result to Ianniello (1977) and demonstrates how the Stokes number determines the profiles and residual currents in well-mixed tidal flow in closed estuaries. As the Stokes number increases, the height of penetration increases, so at small Stoke numbers the bottom boundary layer (δ) is small, as would be the case for wind waves or tides in the deep ocean (Stk ¼ 0.01); as the Stoke number approaches unity, the boundary layer will cover the entire water column.

2.8 MERITS AND DEMERITS OF TIDAL ENERGY SYSTEMS Tidal energy pertains to a form of power that particularly transforms the efficiency of the tides to beneficial forms of dynamism. Though it is not widely used, it serves as a significant investment when it comes to electricity generation. Currently, tidal energy is still in the early development stages, not being able to compete with fossil fuels. However, the focus on renewable energy sources and the demand for clean energy are contributing to a rapid development of methodologies to harness this type of energy source. Tidal energy is already offering many advantages, but keep in mind that it is also linked to some disadvantages. In order to completely understand its significance and effects, it would help to gain a clearer understanding of these opposing aspects.

97

98

Tidal Energy Systems

List of Advantages of Tidal Energy 1. It is renewable: Tidal energy’s source is a result of the effects of the sun and moon’s gravitational fields, combined with our planet’s rotation around its axis, which results in low and high tides. With this in mind, the power source of tidal energy is potentially renewable, whether we are talking about tidal barrages, stream generators, or the more recent technology, dynamic tidal power (DTP). Compared to nuclear reserves and fossil fuels, the sun and moon’s gravitational fields as well as the Earth’s rotation around its axis will not cease to exist any time soon. 2. It is green: A side from being renewable, tidal energy is also an environmentally friendly energy source because it does not take up a lot of space and does not emit any greenhouse gases. However, there are already some examples of tidal power plants and their effects on the environment. Important studies and assessments are being conducted on these things. 3. It is predictable: Sea currents are highly predictable, developing with well-known cycles. This makes it easier to construct tidal energy systems with the correct dimensions because the kind of power the equipment will be exposed to is already known. This is why both the equipment’s installed capacity and physical size have entirely other limitations, though tidal turbines and stream generators that are being used are very similar to wind turbines. 4. It is effective at low speeds: Water is a thousand times more dense than air, which makes it possible to produce electricity at low speeds. Based on calculations, power can be generated even at 1 min per second, which is equivalent to a little over 3 ft per second. 5. It has a long lifespan: So far, there is no reason to believe that tidal energy plants are not long lived. This means an ultimate reduction of the money spent on selling the electricity, making this energy source a very cost-competitive one. As an example, the La Rance tidal barrage power plant was constructed in 1966 and is still generating large amounts of electricity up to this day. 6. It reduces foreign importation of fuel: By harnessing tidal energy on a large scale, we can help reduce foreign fuel importation and enhance energy security, as people would no longer have to rely much on foreign fuel imports to satisfy the growing energy demand. 7. It serves as coastal protection: Small dams and barrages, which are used to harness tidal energy, could protect ship ports and coastal areas from the dangerous tides during storms and bad weather conditions.

List of Disadvantages of Tidal Energy 1. It still has some environmental effects: As previously mentioned, tidal power plants are suspected to have some environmental effects, but these are yet to be determined. As we know it, these facilities generate electricity with the use of tidal barrages that rely

Introduction of Tidal Energy

2.

3.

4.

5.

6.

7.

8.

9.

on ocean level manipulation, thus potentially having the same environmental effects as hydroelectric dams. Also, the turbine frames may potentially disrupt the natural movement of marine animals, and the construction of the whole plant may also disturb fish migration. Nevertheless, technological solutions are now being developed to resolve these issues. It is an intermittent energy source: Tidal energy is considered as an intermittent source of energy, as it can only provide electricity when the tide surges, which happens about 10 h per day on average. This means that tidal energy can only be considered as reliable when accompanied with effective energy storage solutions. It should be close to land: Tidal energy facilities need to be constructed close to land, which is also the place where technological solutions that come with them are being worked on. It is hoped that in a few years we will be able to use weaker tidal currents at locations further out to sea. In addition to this disadvantage, the areas where this energy is produced are far away from the exact locations where it is consumed or needed. It is expensive: We should know that the method of generating tidal energy is relatively a new technology. It is projected that it will be commercially profitable by 2020 in larger scales with better technology. Also, the plants that harness this type of energy are linked to higher upfront costs required for construction. Thus, tidal energy displays a lack of cost effectiveness and efficiency in the world’s energy markets. It is not cost-effective: The tidal energy technology is not that cost-effective, as more technological advancements and innovations are still needed to make power commercially viable. It is still considered a new technology: Still a more theoretic source of power, tidal energy is limited in real life to just a few prototype projects because the technology has just begun to develop and needs plenty of research and huge funds before it reaches commercial status. It requires long gestation time: The time and cost overruns can be huge for tidal power plants, which led to some of them being canceled, such as the UK’s Severn Barrage. In fact, some tidal power stations, such as the one being planned in Russia, will never be realized because of a very long gestation time. Lack of standardized experts to provide full initial concept appraisal: The scientific community active on the subject is very narrowly populated and unconvincing (in the experience of some developers), particularly with regard to unconventional concepts and innovation. It would be best assessed by people with genuine relevant experience of real tidal device technology. By its nature, marine energy technology requires expertise in many disparate areas that are unlikely to be accessible to any single person or institution. Incomplete or partial system concept submissions: In the words of a developer: “Rigorous evaluation before moving through stages should be mandatory if any public money is involved.”

99

100

Tidal Energy Systems

10. Lack of a general tidal dataset for early concept appraisal: Various developers were critical of those who utilize the best possible tidal sites to make their devices look more attractive than is either realistic or honest. 11. A lack of standardized modeling know-how and published information: There is a perceived lack of published fundamental marine turbine research and few publicly available agreed upon definitions of fundamental properties. 12. Incomplete appraisal of nontechnical factors: Technologies are noted by developers as often not taking into account the physical, environmental, commercial, and regulatory realities in their assessment. 13. Lack of resources to complete a robust early concept appraisal: The aforementioned proposed measures should help to improve and bring forward serious well thought through technology innovations; however, costs will be incurred. Although it can be argued that the private sector should be entirely responsible, the best ideas will not necessarily reside with those who have early financial access. Therefore, to bring forward the greatest economical benefit to all concerned, it may be appropriate for some state aid to incentivize innovation and prevent unnecessary monetary wastage at a later stage.

Numerical Q.1 A tidal generation station of 1 MW supplied a region that has the following demands: From

To

Demand (kW)

Midnight 4 a.m. 5 p.m. 7 p.m. 10 p.m.

4 a.m. 5 p.m. 7 p.m. 10 p.m. Midnight

100 No Load 700 800 400

Find the load factor, reserve capacity, plant capacity factor, plant use factor, the hours that the plant has been off, and the utilization factor. Solution: From

To

Demand (kW)

Energy (kWh)

Midnight 4 a.m. 5 p.m. 7 p.m. 10 p.m. Total

4 a.m. 5 p.m. 7 p.m. 10 p.m. Midnight

100 No Load 700 800 400

400 0 1400 2400 800 5000 kWh

Introduction of Tidal Energy

When the transmission line losses are neglected and the demand ¼ load. Installed capacity ¼ 1 MW ¼ 1000 kW and max. Load ¼ max. Demand ¼ 900 kW Average load ¼

Area under the load curve ðkWhÞ No:of hours ðhÞ

Average load ¼

ð4  100Þ + ð13  0Þ + ð2  700Þ + ð3  800Þ + ð2  400Þ 24

Average load ¼

400 + 0 + 1400 + 2400 + 800 5000 kWh ¼ ¼ 208:34 kW 24 h 24 h Load factor ¼

Load factor ¼

Average load Maximum load

208:34 kW ¼ 0:231 ¼ 23:1% 900 kW

Reserve capacity ¼ Installed capacity  Maximum demand Reserve capacity ¼ 1000kW  900kW ¼ 100kW Plant capacity factor ¼ Plant capacity factor ¼ Plant use factor ¼

Average demand ðkWÞ Installed capacity ðkWÞ

208:34 ðkWÞ ¼ 0:208 ¼ 20:8% 1000 ðkWÞ

Actual energy produced Installed capacity ðkWÞ  No:of operating hours

Plant use factor ¼ Utilization factor ¼

5000 kWh ¼ 0:45 ¼ 45% 1000 ðkWÞ  11 h

Maximum demand ðkWÞ 900 kW ¼ ¼ 0:9 ¼ 90% Installed capacity ðkWÞ 100 kW

Q.2 A tidal generation station of 1 MW supplied a region that has the following demands: From

To

Demand (kW)

Midnight 4 a.m. 5 p.m. 7 p.m. 10 p.m.

4 a.m. 5 p.m. 7 p.m. 10 p.m. Midnight

200 No load 600 900 300

101

102

Tidal Energy Systems

Find the load factor, reserve capacity, plant capacity factor, plant use factor, the hours that the plant has been off, and utilization factor. Solution: From

To

Demand (kW)

Energy (kWh)

Midnight 4 a.m. 5 p.m. 7 p.m. 10 p.m. Total

4 a.m. 5 p.m. 7 p.m. 10 p.m. Midnight

200 No Load 600 900 300

800 0 1200 2700 600 5300 kWh

When the transmission line losses are neglected and the demand ¼ load Installed capacity ¼ 1 MW ¼ 1000 kW and max. Load ¼ max. Demand ¼ 900 kW Average load ¼

Area under the load curve ðkWhÞ No:of hours ðhÞ

ð4  200Þ + ð13  0Þ + ð2  600Þ + ð3  900Þ + ð2  300Þ 24 800 + 0 + 1200 + 2700 + 600 5300 kWh ¼ ¼ 220:83 kW Average load ¼ 24h 24 h Average load Load factor ¼ Maximum load 220:83 kW ¼ 0:245 ¼ 24:5% Load factor ¼ 900 kW Reserve capacity ¼ Installed capacity  Maximum demand

Average load ¼

Reserve capacity ¼ 1000kW  900 kW ¼ 100kW Plant capacity factor ¼ Plant capacity factor ¼ Plant use factor ¼

Average demand ðkWÞ Installed capacity ðkWÞ

220:83 ðkWÞ ¼ 0:220 ¼ 20:0% 1000 ðkWÞ

Actual energy produced Installed capacity ðkWÞ  No:of operating hours

Plant use factor ¼

5300 kWh ¼ 0:48 ¼ 48% 1000 ðkWÞ  11 h

Introduction of Tidal Energy

Utilization factor ¼

Maximum demand ðkWÞ 900 kW ¼ ¼ 0:9 ¼ 90% Installed capacity ðkWÞ 100 kW

Q.3 A tidal power plant operates under an effective tidal range of 7 m and a discharge of water at 400 m3/s. Determine the work done by quantity of water falling through the head. Solution: Discharge Q ¼ 400 m3/sec Tidal range H ¼ 7 m Density of water ρ ¼ 1000 kg/m3 Work done is given by W ¼ ρQH W ¼ 1000  400  7 ¼ 28;000kgm=s: Q.4 A tidal power plant operates under an effective tidal range of 9 m and a discharge of water at 500 m3/s. Determine the work done by quantity of water falling through the head. Solution: Discharge Q ¼ 500 m3/sec Tidal range H ¼ 9 m Density of water ρ ¼ 1000 kg/m3 Work done is given by W ¼ ρQH W ¼ 1000  500  9 ¼ 45;000kgm=s: Q.5 A tidal power plant operates under an effective tidal range of 6 m and a discharge of water at 300 m3/s. Determine the work done by quantity of water falling through the head. Solution: Discharge Q ¼ 300 m3/sec Tidal range H ¼ 6 m Density of water ρ ¼ 1000 kg/m3 Work done is given by W ¼ ρQH W ¼ 1000  300  6 ¼ 18;000kgm=s: Q.6 A tidal power station is supplied from a sea of a capacity 3  107 m3 at a tidal range of 9 m. Determine the total energy available in kWh, if the overall efficiency of the plant is 75%. Solution: Discharge Q ¼ 3  107 m3 Tidal range H ¼ 9 m Density of water ρ ¼ 1000 kg/m3

103

104

Tidal Energy Systems

Efficiency η ¼ 0.75 Electrical power available: ρQHη  9.81 W-sec ¼1000  3  107  9  0.75  9.81 ¼198.652  1010 watt-sec. or joules ¼198.652  1010/(3600  1000) kWh ¼551.811 kWh Q.7 A tidal power station is supplied from a sea of a capacity 1  107 m3 at a tidal range of 11 m. Determine the total energy available in kWh if the overall efficiency of the plant is 70%. Solution: Discharge Q ¼ 1  107 m3 Tidal range H ¼ 11 m Density of water ρ ¼ 1000 kg/m3 Efficiency η ¼ 0.70 Electrical power available: ρQHη  9.81 W-sec ¼1000  1  107  9  0.70  9.81 ¼6.86  1010 watt-sec. or joules ¼6.86  1010/ (3600  1000) kWh ¼19.075 kWh Q.8 A tidal power plant operates under an effective tidal range of 9 m and the surface of the tidal energy harnessing plant is 16 km2. Determine the daily average power generated through the tidal power plant, if power conversion efficiency is 40%. (Assume two high tides and two low tides every day) Solution: Let us assume that the tidal range of tide at a particular place is ¼ 9 m (approx) The surface of the tidal energy harnessing plant is 16 km2 (4 km  4 km) ¼ 4000 m  4000 m ¼ 16  106 m2 Specific density of sea water ¼ 1025.18 kg/m3 Mass of the water ¼ volume of water  specific gravity ¼(area  tidal range) of water  mass density ¼(16  106 m2  9 m)  1025.18 kg/m3 ¼147.626  109 kg (approx) Potential energy content of the water in the basin at high tide ¼ ½  area  density  gravitational acceleration  tidal range squared ¼½  16  106 m2  1025 kg/m3  9.81 m/s2  (9 m)2 ¼6.51  1012 J (approx) Now we have two high tides and two low tides every day. At low tide the potential energy is zero. Therefore the total energy potential per day ¼ Energy for a single high tide  2 ¼8.04  1012 J  2

Introduction of Tidal Energy

¼13.03  1012 J Therefore, the mean power generation potential ¼ Energy generation potential/ time in 1 day ¼13.03  1012 J/86400 s ¼150 MW Assuming the power conversion efficiency to be 40%: The daily average power generated ¼ 150 MW * 0.40 ¼60.33 MW (approx) Q.9 A tidal power plant operates under an effective tidal range of 11 m and the surface of the tidal energy harnessing plant is 4 km2. Determine the daily average power generated through the tidal power plant if power conversion efficiency is 35%. (Assume three high tides and three low tides every day) Solution: Let us assume that the tidal range of tide at a particular place is ¼ 11 m (approx) The surface of the tidal energy harnessing plant is 4 km2 (2 km  2 km) ¼ 2000 m  2000 m ¼ 4  106 m2 Specific density of sea water ¼ 1025.18 kg/m3 Mass of the water ¼ volume of water  specific gravity ¼(area  tidal range) of water  mass density ¼(4  106 m2  11 m)  1025.18 kg/m3 ¼45.107  109 kg (approx) Potential energy content of the water in the basin at high tide ¼ ½  area  density  gravitational acceleration  tidal range squared ¼½  4  106 m2  1025 kg/m3  9.81 m/s2  (11 m)2 ¼2.43  1012 J (approx) Now we have three high tides and three low tides every day. At low tide the potential energy is zero. Therefore the total energy potential per day ¼ Energy for a single high tide  3 ¼2.43  1012 J  3 ¼7.29  1012 J Therefore, the mean power generation potential ¼ Energy generation potential/ time in 1 day ¼7.29  1012 J/86400 s ¼84.37 MW Assuming the power conversion efficiency to be 35%: The daily average power generated ¼ 84.37 W * 0.35 ¼29.53 MW (approx) Q.10 A tidal power station is supplied from a sea surface area of 36 km2 and a tidal range of 8 m. If the overall efficiency of the plant is 60%, find the rate at which the water level will fall when the station is generating 40 MW.

105

106

Tidal Energy Systems

Solution: Sea surface area A ¼ 36 km2 Tidal range H ¼ 8 m Density of sea water ρ ¼ 1025 kg/m3 Average power generated P ¼ ρQH  9.81  103η kW Q ¼ P/ρH  9.81  103η 40,000/1025  8  9.81  103  0.60 ¼ 828 m3 Rate of fall of water level ¼ Q/A ¼ (828/36  106)  3600  1000 ¼ 82.8 mm/h Q.11 A tidal power station is supplied from a sea surface area of 20 km2 and a tidal range of 9 m. If the overall efficiency of the plant is 70%, find the rate at which the water level will fall when the station is generating 30 MW. Solution: Sea surface area A ¼ 20 km2 Tidal Range H ¼ 9 m Density of sea water ρ ¼ 1025 kg/m3 Average power generated P ¼ ρQH  9.81  103η kW Q ¼ P=ρH  9:81  103 η 30,000=1025  9  9:81  103  0:70 ¼ 473m3 Rate of fall of water level ¼ Q/A ¼ (473/20  106)  3600  1000 ¼ 85.24 mm/h. Q.12 The annual load duration curve of a small tidal power plant shows 500 MWh of energy during the year. It is a peak load with 15% annual load factor. Find station capacity, if plant capacity factor is 25%. Find reserve capacity of the tidal power plant. Solution: Energy generated during 1 year Max :load  8760 500; 000 0:15 ¼ Max:load  8760 Max:load ¼ 380 kW   Max:load Capacity factor ¼  Load factor Plant capacity   Max:load 0:25 ¼  Load factor Plant capacity   0:380 0:25 ¼  0:15 Plant capacity

Annual load factor ¼

Plant capacity : 0:228MW Reserve capacity ¼ 0:380  0:228 ¼ 0:152MW

Introduction of Tidal Energy

Q.13 A tidal power station is to supply four areas whose peak loads are 10,000 kW, 6000 kW, 8000 kW, and 7000 kW. The diversity factor of loads at the station is 2.5 and annual load factor is 65%. Find maximum demand and annual energy supplied. Suggest installed capacity, taking into account the increase in maximum demand by 50%. Solution: Sum of maximum demand ¼ 31000 kW ¼ 31 MW Maximum demand ¼

Sum of max:demand 31 ¼ ¼ 12:4 MW Diversity factor 2:5

Annul energy ¼ 12:4  8760  0:65 ¼ 70605MWh Increase in maximum demand ¼ 12:4  0:5 ¼ 6:2MW Installed capacity ¼ 12:4 + 6:2 ¼ 18:6MW Q.14 A tidal power station is to supply five areas whose peak loads are 10,000 kW, 6000 kW, 8000 kW, 7000 kW, and 2000 kW. The diversity factor of loads at the station is 1.5 and annual load factor is 75%. Find maximum demand and annual energy supplied. Suggest installed capacity, taking into account the increase in maximum demand by 65%. Solution: Sum of maximum demand ¼ 33000 kW ¼ 33 MW Maximum demand ¼

Sum of max :demand 33 ¼ ¼ 22 MW Diversity factor 1:5

Annul energy ¼ 22  8760  0:75 ¼ 144540MWh Increase in maximum demand ¼ 22  0:65 ¼ 14:3MW Installed capacity ¼ 22 + 14:3 ¼ 36:3MW

EXERCISE Explain the global scenario of the tidal energy system. Explain the Indian scenario of the tidal energy system. Write the name of the five largest tidal power plants. Write the significance of the tidal energy system in a renewable energy system. Explain the basic principle of the tidal power plant and explain the working of each component. Q.6 What is the meaning of flood tide and ebb tide? Q.7 Define the term tidal range. Q.8 What is the utilization of the tidal barrage in the tidal power plant? Q.1 Q.2 Q.3 Q.4 Q.5

107

108

Tidal Energy Systems

Q.9 Q.10 Q.11 Q.12 Q.13 Q.14 Q.15 Q.16 Q.17 Q.18 Q.19

Q.20

Q.21 Q.22 Q.23

Explain with a neat sketch the single-basin tidal energy system. Explain with a neat sketch the two-way tidal barrage systems. Explain the principle of tidal barrage flood generation. Explain the principle of tidal barrage ebb generation. Explain the basic principle of a double basin with linked basin operation. What is the utilization of the attenuator in a tidal power plant; write its advantages and disadvantages. What is the utilization of the oscillating wave surge converter in a tidal power plant; write its advantages and disadvantages. What is the utilization of the point absorber in a tidal power plant; write its advantages and disadvantages. What is the utilization of the wave dragon in a tidal power plant; write its advantages and disadvantages. What is the utilization of the oscillating water column in a tidal power plant; write its advantages and disadvantages. Write short note on the following: (i) Bulb turbine (ii) Rim turbine (iii) Tubular turbine Write a short note on the following: (i) Horizontal axis turbine (ii) Sea flow turbine What is the utilization of the tidal steam generator in a tidal power plant; write its advantages and disadvantages. Derive the equation for energy and power for the tidal power plant. Write short note on the following: (i) Tidal dynamics (ii) Structure of tidal current

NUMERICAL Q.1 A tidal power plant operates under an effective tidal range of 13 m and the discharge of water is 900 m3/s. Determine the work done by the quantity of water falling through the head. Q.2 A tidal power plant operates under an effective tidal range of 4 m and the discharge of water is 800 m3/s. Determine the work done by the quantity of water falling through the head.

Introduction of Tidal Energy

Q.3 A tidal power plant operates under an effective tidal range of 3 m and the discharge of water is 100 m3/s. Determine the work done by the quantity of water falling through the head. Q.4 A tidal power station is supplied from a sea of a capacity 2  107 m3 at a tidal range of 9 m. Determine the total energy available in kWh, if the overall efficiency of the plant is 65%. Q.5 A tidal power station is supplied from a sea of a capacity 5  107 m3 at a tidal range of 11 m. Determine the total energy available in kWh, if the overall efficiency of the plant is 77%. Q.6 A tidal power plant operates under an effective tidal range of 9 m and surface of the tidal energy harnessing plant is 49 km2. Determine the daily average power generated through the tidal power plant, if power conversion efficiency is 50%. (Assume two high tides and two low tides every day). Q.7 A tidal power plant operates under an effective tidal range of 10 m and surface of the tidal energy harnessing plant is 6 km2. Determine the daily average power generated through tidal power plant, if power conversion efficiency is 45%. (Assume three high tides and three low tides every day). Q.8 A tidal power station is supplied from a sea surface area of 16 km2 and a tidal range of 8 m. If the overall efficiency of the plant is 50%, find the rate at which the water level will fall when the station is generating 30 MW. Q.9 A tidal power station is supplied from a sea surface area of 20 km2 and a tidal range of 9 m. If the overall efficiency of the plant is 60%, find the rate at which the water level will fall when the station is generating 20 MW. Q.10 The annual load duration curve of a small tidal power plant shows 600 MWh of energy during the year. It is a peak load with 25% annual load factor. Find station capacity, if plant capacity factor is 5%. Find the reserve capacity of the tidal power plant. Q.11 A tidal power station is to supply four areas whose peak loads are 10,000 kW, 6000 kW, 7000 kW, and 9000 kW. The diversity factor of loads at the station is 2.2 and the annual load factor is 55%. Find maximum demand and annual energy supplied. Suggest installed capacity, taking into account the increase in maximum demand by 50%. Q.12 A tidal power station is to supply five areas whose peak loads are 10,000 kW, 6000 kW, 7000 kW, 6000 kW, and 2000 kW. The diversity factor of loads at the station is 1.5 and the annual load factor is 65%. Find the maximum demand and annual energy supplied. Suggest installed capacity, taking into account the increase in maximum demand by 55%.

109

110

Tidal Energy Systems

OBJECTIVE-TYPE QUESTION Q.1

Worldwide installation of tidal energy systems up to 2020 will be (a) 100 MW (b) 200 MW (c) 300 MW (d) 400 MW

Q.2

The installed capacity of the tidal power plant in La Rance, France, is (a) 100 MW (b) 200 MW (c) 240 MW (d) 300 MW

Q.3

The installed capacity of the tidal power plant in South Korea is (a) 90 MW (b) 140 MW (c) 180 MW (d) 60 MW

Q.4

The 20 MW capacity of the Annapolis Royal tidal generating station is situated in (a) Canada (b) India (c) Japan (d) South Korea

Q.5

The approximate tidal range of the Tamil-Nadu coast India is (a) 7 m (b) 6 m (c) 5 m (d) 1 m

Q.6

Which one is considered to be under under the category of a conventional energy system (a) Thermal energy system (b) Nuclear energy system (c) Tidal energy system (d) Both (i) and (ii)

Q.7

Which one is considered to be under the category of a nonconventional energy system (a) Thermal energy system (b) Nuclear energy system (c) Tidal energy system (d) Both (i) and (ii)

Q.8

A tidal power station is similar to (a) Solar power system (b) Hydro power system (c) Thermal power system (d) Wind power system

Introduction of Tidal Energy

Q.9

When the water is above the mean sea level is called (a) Flood tide (b) Ebb tide (c) Both (i) and (ii) (d) None of the above

Q.10

When the water is below the mean sea level is called (a) Flood tide (b) Ebb tide (c) Both (i) and (ii) (d) None of the above

Q.11

The difference between the water levels between two consecutive high tides and low tides: (a) Tidal barrage (b) Tidal range (c) Tidal current (d) None of the above

Q.12

The average of the two high tides on the day of neap tides (a) Mean high water neaps (b) Min. high water neaps (c) Max. high water neaps (d) High tides

Q.13

A system in which only one basin interacts with the sea (a) Two basin system (b) Single basin system (c) Both (i) and (ii) (d) None of the above

Q.14

A system in which water is stored during high tide in the basin and power is generated only during low tides (a) Single ebb cycle system (b) Single flood cycle system (c) Two ebb cycle system (d) Two flood cycle system A system in which the tidal power is generated as the water flows in both directions during a flood or ebb tide (a) Single ebb cycle system (b) Single flood cycle system (c) Two way generation (d) None of the above

Q.15

Q.16

The technology used in the Shiwa Lake tidal plant Sin outh Korea is (a) Tidal Barrage (b) Tidal Lagoon (c) Both (i) and (ii) (d) None of the above

111

112

Tidal Energy Systems

Q.17

A device that is a floating device and operates parallel to the wave direction (a) Point absorber (b) Attenuator (c) Tidal lagoon (d) Wave converter

Q.18

The energy generating capacity of a single attenuator device can be up to (a) 5 MW (b) 4 MW (c) 3 MW (d) 1 MW

Q.19

A device that provides a large amount of power by tidal energy (a) Point absorber (b) Attenuator (c) Tidal lagoon (d) Wave converter

Q.20

A _________ is a floating structure that absorbs energy from all directions near the water surface (a) Point absorber (b) Attenuator (c) Tidal lagoon (d) Wave converter

Q.21

A ________ is a hydroelectric wave energy device that uses the motion of ocean waves to generate electricity (a) Point absorber (b) Attenuator (c) Tidal lagoon (d) Wave converter

Q.22

A ___________ is a type of wave energy converter that harnesses energy from the oscillation of sea water (a) Point absorber (b) Oscillating water column (c) Tidal lagoon (d) Wave converter A _________ is a tidal energy converter that extracts energy from moving masses of water (a) Point absorber (b) Attenuator (c) Tidal lagoon (d) Tidal steam generator

Q.23

Q.24

A ________ is a power station that generates electricity from the natural rise and fall of the tides (a) Point absorber (b) Attenuator (c) Tidal lagoon (d) Tidal steam generator

Introduction of Tidal Energy

Q.25

The value of a load factor is always (a) 1 (b) 1 (d) 0

Q.26

The reserve capacity of a tidal power plant is given by (a) Installed capacity  Maximum Demand (b) Maximum demand  Installed capacity (c) Maximum demand  Installed capacity (d) Maximum demand/Installed capacity

Q.27

In the horizontal force, the following relations are correct: (a) Acceleration + Coriolis force ¼ Pressure gradient force + Tractive force (b) Acceleration  Coriolis force ¼ Pressure gradient force  Tractive force (c) Acceleration + Coriolis force ¼ Pressure gradient force  Tractive force (d) Acceleration  Coriolis force ¼ Pressure gradient force + Tractive force

Q.28

A point where the tidal range is zero (a) Tide ebb (b) Tide flood (c) Amphidromic (d) None of the above

Q.29

A ________ is the periodic horizontal flow of water accompanying the rise and fall of the tide (a) Tidal barrage (b) Tidal current (c) Tidal range (d) None of the above

Q.30

Which power station generates fewer greenhouse gas emissions? (a) Nuclear power (b) Thermal power (c) Tidal power (d) Both (i) and (ii)

REFERENCES Adcock, T.A., Draper, S., Houlsby, G.T., Borthwick, A.G., Serhadlioglu, S., 2013. The available power from tidal stream turbines in the Pentland. Proc. Math. Phys. Eng. Sci. 469 (2157), 20130072. Allan, G.J., Lecca, P., McGregor, P.G., Swales, J.K., 2014. The economic impacts of marine energy developments: a case study from Scotland. Mar. Policy 43, 122–131. Black and Veatch, 2004. Phase I. UK Tidal-Stream Energy Resource Assessment. The Carbon Trust, London. Black and Veatch, 2005. Phase II. UK Tidal-Stream Energy Resource Assessment. The Carbon Trust, London. Blunden, L.S., Bahaj, A.S., 2007. Tidal energy resource assessment for tidal-stream generators. J. Power Energy 221, 137–146.

113

114

Tidal Energy Systems

Carballo, R., Iglesias, G., Castro, A., 2009. Numerical model evaluation of tidal-stream energy resources in the Rı´a de Muros (NW Spain). Renew. Energy 34 (6), 1517e24. Clarke, J., Connor, G., Grant, A., Johnstone, C., 2006. Regulating the output characteristics of tidal current power stations to facilitate better base load matching cover the lunar cycle. Renew. Energy 31, 173–180. Ianniello, J.P., 1977. Nonlinearly Induced Residual Current in Tidally Dominated Estruaies. Doctoral Dissertation. AAI7731185. Iyer, A., Couch, S., Harrison, G., Wallace, A., 2013a. Variability and phasing of tidal current energy around the United Kingdom. Renew. Energy 51, 343–357. Iyer, A., Couch, S., Harrison, G., Wallace, A., 2013b. Variability and phasing of tidal current energy around the United Kingdom. Renew. Energy 51, 343–357. Kempener, R., 2014. Salinity gradient energy: technology brief. IRENA, Ocean Energy Conversion, pp. 1–28. Lamb, H., 1932. Hydrodynamic, sixth ed. Cambridge University Press, New York. Lewis, M., Neill, S., Elliott, A., 2015a. Inter-annual variability of two contrasting offshore sand banks in a region of extreme tidal range. J. Coast. Res. 31 (2), 265–275. Lewis, M., Neill, S., Hashemi, M.R., 2014. Realistic wave conditions and their influence on quantifying the tidal-stream energy resource. Appl. Energy 136, 495–508. Lewis, M.J., Neill, S.P., Robins, P.E., Hashemi, M.R., 2015b. Resource assessment for future generations of tidal-stream energy arrays. Energy 83, 403–415. Minchinton, W.E., 1979. Early tide mills: some problems. Technol. Cult. 20, 777–786. Neill, S.P., Hashemi, M.R., 2013. Wave power variability over the northwest European shelf seas. Appl. Energy 106, 31–46. Neill, S.P., Hashemi, M.R., Lewis, M.J., 2014a. The role of tidal asymmetry in characterizing the tidal energy resource of Orkney. Renew. Energy 68, 337–350. Neill, S.P., Hashemi, M.R., Lewis, M.J., 2014b. Optimal phasing of the European tidal stream resource using the greedy algorithm with penalty function. Energy 73, 997–1006. Neill, S.P., Hashemi, M.R., Lewis, M.J., 2014c. Optimal phasing of the European tidal stream resource using the greedy algorithm with penalty function. Energy 73, 997–1006. Neill, S.P., Jordan, J.R., Couch, S.J., 2012. Impact of tidal energy converter (TEC) arrays on the dynamics of headland sand banks. Renew. Energy 37 (1), 387–397. O’Rourke, F., Boyle, F., Reynolds, A., 2010b. Tidal energy update 2009. Appl. Energy 87, 398–409. O’Rourke, F., Boyle, F., Reynolds, A., 2010d. Marine current energy devices: current status and possible future applications in Ireland. Renew. Sust. Energ. Rev. 14, 1026–1036. Prandle, D., 1982. The vertical structure of tidal currents. Geophys. Astrophys. Fluid Dyn. 22, 29–49. SI Ocean, 2012. Strategic Initiative for Ocean Energy. Intelligent Energy Europe. Stokes, G., 1851. On the effect of the internal friction on the motion of pendulums. Trans. Cambridge Philos. Sco. 9, 8–106. Strouhal, V., 1978. On an unusual sort of sound excitation. Annalen der physic and chemie third series 5, 216–251. Vlachogiannis, J.G., 2014. Marine-current power generation model for smart grids, CJ. J. Power Sources 249, 172–174.

CHAPTER 3

Prefeasibility Assessment of a Tidal Energy System Contents 3.1 Site Survey and Feasibility 3.1.1 Resource Assessment Models 3.1.2 Numerical Models for Resource Assessment 3.1.3 Theoretical Tidal Current Energy Resource 3.1.4 Technical Tidal Current Energy Resource 3.1.5 Practical Tidal Current Energy Resource Assessment 3.1.6 Accessible Tidal Current Energy Resource 3.1.7 Viable Tidal Current Energy Resource 3.1.8 Quantification of Tidal-Stream Resource 3.1.9 Resource Assessment by Regression Analysis 3.1.10 Software Used in Resource Assessment 3.2 Distances From the Load Center 3.2.1 Critical Path Method to Assess Duration to Generate Energy From a Tidal Power Plant 3.3 Physical Boundaries of Assessment 3.3.1 Technical Boundaries 3.3.2 Geographical Boundaries 3.3.3 Surface Boundary Conditions 3.3.4 Functional Physical Boundaries of Assessment 3.4 Static v/s Transect Field Survey 3.4.1 Quantitative Observations Through Static and Transect Survey 3.4.2 The Challenge of Measuring Water Currents 3.5 Location Assessment by Farm Method 3.5.1 Tidal Optimal Unit Using Dynamic Programming Method 3.6 Resource Assessment by Flux Method 3.6.1 Maximum Steady-State Power Through Tidal Power Station 3.6.2 Transmission Line Analogy of a Tidal Power Plant 3.6.3 Voltage Regulation of a Tidal Power Plant at a Suitable Site 3.7 Prefeasibility Assessment With Detailed Project Report Preparation and Appraisal 3.7.1 Simple Payback Period 3.7.2 Return on Investment (ROI) 3.7.3 Net Present Value of a Tidal Power Plant 3.7.4 Internal Rate of Return of a Tidal Power Plant Exercise Numerical Objective-Type Questions References Further Reading Tidal Energy Systems https://doi.org/10.1016/B978-0-12-814881-5.00003-X

116 121 127 128 129 130 130 131 132 132 136 139 139 142 142 149 151 154 155 157 159 160 162 169 172 173 175 175 178 178 179 179 183 184 185 187 187

© 2019 Elsevier Inc. All rights reserved.

115

116

Tidal Energy Systems

3.1 SITE SURVEY AND FEASIBILITY A site survey and feasibility assessment come under the category of prefeasibility assessment of any system. A feasibility or prefeasibility study is an assessment of how effectively a project of tidal power plant can be completed or the calculation of factors such as location assessment, economic and technical feasibility, and legal and scheduling factors that are incorporated in the whole process of plant development. Economic analysis is the most important assessment of any process and for that, project managers or top management use feasibility assessment to determine probable optimistic and pessimistic outcomes of a project or plant before investing a significant amount of time and money. Fig. 3.1 shows types of prefeasibility assessments. As another renewable energy system, a tidal energy resource study also focuses on understanding general tidal resource patterns and developing future predictions, both of which are desirable to support reliable and adaptable power system operation. As tidal energy system technologies mature all over the world, more and increasingly potential of power generation and overcome the crisis of generation of electricity through conventional power plant. Financing such tidal technologies requires commitment that they will generate the energy predicted through performance models. Otherwise, to be unsuccessful to meet the lowest amount of energy performance requirements can result in large financial penalties and require expensive risk mitigation measures. Such a problem is compensated by a set of accurate tidal current data that is the foundation of a successful design model and is decisive in reducing the expenditure linked with mitigating such a performance risk. Under the category of

Economic assessment

Technological assessment

Feasibility assessment

Legal and scheduling assessment

Fig. 3.1 Types of prefeasibility assessment.

Location assessment

Prefeasibility Assessment of a Tidal Energy System

prefeasibility analysis, tidal resource assessment provides the means to perfectly resolve the availability of tide current resources for developing and deploying cost-effective tidal energy technologies according to the tidal energy goals. The nature of a tidal flow or tidal current is usually predictable with high accuracy over long periods. Tidal current data varies due to the annual solstice/equinox cycle because the significant tidal components are approximately periodic over a cycle of 18.6 years as a consequence of the precession of the moon’s orbit. The major perturbations to the astronomic tides are changes in water flow caused by synoptic weather patterns such as storms, hurricanes, or anticyclones. These effects are included in the storm surge in which, under the category of positive surge, low pressure causes a rising of the oceanic surface and in a negative surge, high atmospheric pressure causes a lowering of the pressure. These above conditions can be assessed by long-term observations, or by numerical modeling and analysis. An associated effect is the set-up caused by the mass transport of wave action in a particular direction, causing the water level to rise on a lee shore. This elevation then creates a balancing current with a vertical structure, and can also be assessed by numerical modeling. All over the world, the tidal energy industry is undergoing rapid changes and at present, tidal turbine manufacturers are testing MW scale devices in real sea conditions while new offshore and laboratory testing facilities are being developed. The process of adaptable site selection for electricity generation through a tidal power plant requires detailed consideration of many aspects of both the natural and built environment. The preliminary importance is the assessment of the physical tidal resource itself and the quantification of specifically (volumetric) flow, depth, and velocity. Range and duration have to be evaluated at the supply side and other measurements are also considered such as electrical grid access, environmental impact, commerce, and social considerations. These parameters contribute to the economic and financial justification of a tidal energy project over other renewable energy options. Therefore, the importance of tidal energy resource assessment is increasing the accuracy and reducing the uncertainty regarding knowledge; understanding the physical flow regime cannot be understated. The primary target of this investigation is to assess the tidal current potential as a wellspring of sustainable power at a reasonable site. The principle point of site review is to gauge and depict this asset, keeping in mind the goal to comprehend the potential for the power extraction of a variety of specialized energy change framework and to guarantee that the tidal asset accessible is not over separated. Asset appraisal of a tidal energy framework is finished in two distinctive courses, for example, territorial (regional) evaluation and site evaluation. Provincial evaluation is one of the types of site screening and and it provide lot of information related to channel estuary. Fig. 3.2 shows types of resource assessment. In territorial appraisal or site screening, the asset evaluation ought to be qualified as local if the zone of study is huge and consolidates numerous potential sites, entire nations, or a huge part thereof. A potential advancement territory has been distinguished in a provincial evaluation and the asset appraisal winds up noticeably centered around an individual zone in site evaluation.

117

118

Tidal Energy Systems

Regional assessment

Very large & many potential site

Site assessment

Specific area wise study

Resource assessment

Fig. 3.2 Types of resource assessment.

Due to the nature of tidal currents, worldwide tidal energy generation sites are generally located in coastal areas with complex shorelines. At the coastal areas, the use of tidal diamonds from admiralty charts gives a first judgment of the tidal energy resource at the given area. Furthermore, tidal gauges and satellite altimetry provide information of the sea elevation height. In addition, current velocity data in the water column are obtained with acoustic Doppler current profilers (ADCP) installed on the seabed. The use of ADCPs presents temporal and spatial limitations. The temporal limitation of ADCP data due to finite battery life can be overcome through the application of harmonic analysis. Fig. 3.3 shows worldwide potential locations for tidal current generation. The spatial

Fig. 3.3 Potential location for tidal current generation. (Accad, Y., Pekeris, C.L., Solution of the tidal equations for the M2 and S2 tides in the world oceans from a knowledge of the tidal potential alone. Phil. Trans. R. Soc. Lond. A 290 (1368) (1978) 235–266.)

Prefeasibility Assessment of a Tidal Energy System

limitation is only solved through the deployment of a sufficient number of ADCPs to cover the area of interest. If bathymetry data are available at the site, the use of models to undertake a resource assessment can overcome the practical limitations of the information captured by tidal gauges and ADCPs. Models are able to capture geographical and temporal variations while they also account for other parameters such as bathymetry, seabed roughness, and climate conditions (i.e., wind, wave, and atmospheric pressure). In addition, models can capture the effects that energy extraction will have over the tidal energy resource and the environment. Data from tidal gauges and ADCPs are still required to calibrate and validate the models. • Resource Characterization: Resource information is very important to operations after sites have been built and are producing adaptable amounts of power. Coastal site operators, utilities, and all the federal agencies need to know about temporary and seasonal variations in the tidal resource. Fig. 3.4 shows the steps of the prefeasibility assessment. Resource characterization is the parameter assessment of the site area and is normally carried out to set up suitable geographic locations for deployment of tidal energy systems. It is concerned with the following objectives:
To ascertain the credible resource for tidal energy production with a plainly stated degree of ambiguity.
To identify constraint parameters on resource harvesting of a tidal power plant. • Site Assessment: Site analysis is usually carried out aforementioned to consumption to set up the comprehensive corporeal surroundings for a particular tidal energy project, with the following objectives:
To assess the tidal energy production throughout the life of the project.
To describe low and high tide conditions.
To describe the bathymetry of the site area to an unequivocally particular and suitable bathymetry.

Study planning Data collection & analysis Tide model setup Model calibration/validation Analyze model output Results presentation

Fig. 3.4 Steps of prefeasibility assessment.

119

120

Tidal Energy Systems


To establish intense (survivability) conditions with a defined return period and find out the payback period.
To identify potential interference between multiple pieces of equipment at the site area or coastal area.
To ascertain the spatial and chronological dissimilarity of the reserve with an explicitly stated degree of vagueness. • Main Necessary Conditions for Efficient Power Extraction at a Feasible Location: 1. Middle tidal current speeds more prominent than 1.1 m/s are monetarily reasonable for energy extraction. Perfect speeds are those for areas with mean spring top tidal streams in the scope of 2–2.5 m/s, or 4–5 knots. 2. Profundities in the vicinity of 20 and 50 m for original tidal turbine innovation are sufficient. For this situation, the usable portion of the water section, z, remains between 0.25 z over the bay base and 3 m beneath the mean low water springs (MLWS) in harbor territories, or 7 m underneath MLWS in open seaside regions powerless against high breeze waves. Fig. 3.5 shows methods of tidal resource assessment. 3. Territories with a tidal current field that inverts along a characterized pivotal heading are more appropriate for turbine establishments than locales with streams without an ideal course. 4. Even though seabed composition directly affects foundation design, it is not taken into account in this chapter. In this study, a fixed bottom is assumed, which means that turbine arrays do not affect bathymetry contours. Seabed erosion is an issue to be considered in a subsequent study.

Seabed friction

1 Dimensional

Channel dimension Head difference

Tidal resource assessment

Bathymetry 2 Dimensional

Variable coastal geometries Asymmetrical tidal energy extraction Velocity profile of the water column

3 Dimensional Effect of flow diversion

Fig. 3.5 Methods of tidal resource assessment.

Prefeasibility Assessment of a Tidal Energy System

3.1.1 Resource Assessment Models Resource assessment of modeling of a tidal energy system is done in three terms. There are three types of replicas used to carry out a resource assessment. First, one-dimensional (1D) hypothetical representations are used to evaluate the energy extracted from different types of channels. These models necessitate only factors such as the seabed friction, different channel dimensions, and low and high head difference between the ends of the channel and peak volume flow. However, 1D model cannot account for a variable bathymetry, changes in the channel geometry, or asymmetrical energy extraction. Second, two-dimensional (2D) models can defeat the confinements of 1D models as they can represent changes in bathymetry, variable beachfront geometries, and deviated tidal vitality extraction. Bathymetry is the investigation of the submerged profundity of lake or sea depths. At the end of the day, bathymetry is the submerged identical to hypsometry or geography. Bathymetry is the establishment of the study of hydrographs, which measures the physical highlights of a water body. Fig. 3.6 shows types of resource assessment models. Hydrography incorporates bathymetry as well as the shape and highlights of the shoreline; the qualities of tides, streams, and waves; and the physical and substance properties of the water itself. In the site, bathymetric issues portrayed bathymetric attributes of the site. Utilizing the information at first accessible or the study that may have been done, a guide with the bathymetric shapes ought to be given and the regions considered reasonably homogeneous for TECS establishment ought to be distinguished. In bathymetry evaluation, a yearly plot of the tidal range at the site should be depicted. In a month-tomonth profile, a 30-day plot of the tidal height over a datum at the site should be given.

Resource assessment model

2Dimensional model 1Dimensional model

Fig. 3.6 Types of resource assessment models.

3Dimensional model

121

122

Tidal Energy Systems

The spring cycles should be recognized unmistakably alongside the days where the most extreme speeds are required. Rearranged 2D models utilizing profundity normal speeds decrease computational prerequisites however in the meantime there is a blunder prompted. This blunder is viewed as small contrasted with the vulnerability associated with the mean speed itself. The 2D models are connected in medium to extensive asset appraisal and to recognize far field impacts due to tidal vitality extraction. At last, threedimensional (3D) models increment the exactness of asset evaluations as they can figure the speed profile of the water segment and can incorporate the impacts of stream redirection because of the nearness of tidal turbines. Notwithstanding, this expansion in precision displays a vital cost in computational prerequisites, and in that capacity, 3D models are normally confined to small-scale applications. One-Dimensional Resource Assessment In 1D resource assessment, seabed friction is the primary constitute to find out the depth of penetration of the coastal area. The seabed friction force is the sum of a diffusion resistance force in the seabed’s normal direction and a friction force in the direction tangential to the seabed plane and toward the friction target position. It also depends on the boundary condition of coastal areas with respect to the electric and magnetic field intensity of the tidal current. If explicit integration is used in the dynamic analysis then, in addition, seabed-damping forces are applied in the normal and tangential directions. The penetration resistance force depends on the choice of seabed model that is used, either the elastic seabed model theory or the nonlinear soil model theory. Channel Dimension: In a bigger nautical setting, as a geological place name, the term channel is another word for strait, which is characterized as a generally limited waterway that interfaces two bigger waterways. In this nautical setting, the terms strait, channel, sound, and entry are synonymous and normally tradable. Channel start alludes to the site on an ocean region where water starts to stream between identifiable banks. This site is alluded to as the channel head and it denotes an essential limit between slope slant forms and fluvial procedures. The channel head is the most upslope part of a channel organization and is characterized by streaming water between characterized identifiable banks. A channel head frames as overland stream or potentially subsurface stream aggregate to a point where shear stress can beat disintegration protection of the ground surface. Channel heads are regularly connected with colluviums, hollows, and avalanches. It is the essential advance to discover asset evaluation as far as channel measurement for power age through a tidal energy framework. The water flow rate in a channel head is given by:
 1 2 Water flow rate ¼ π ðPipe diameterÞ :Velocity (3.1) 4

Prefeasibility Assessment of a Tidal Energy System

Two-Dimensional Resource Assessment A tidal stream area is plainly unpredictable and three-dimensional; still, a scientific display of such can be to some degree improved as a two-dimensional issue by utilizing shallow water or Saint-Venant conditions and vertically find the middle value of the amounts. Shallow water is characterized in the scientific sense as having a profundity that is at most one-tenth of the width of the space it possesses. At this small perspective proportion, scale ponders have demonstrated that vertical speeds are irrelevant contrasted with stream insightful and transverse speeds. Under the presumption of a hydrostatic weight dispersion, the Navier-Stokes conditions for an incompressible liquid can be shown to lessen to the Saint-Venant conditions through profundity joining, which can be utilized to depict the streams in such areas, particularly in precarious twodimensional streams. The Saint-Venant equations are as follows: dh dðhuÞ dðhvÞ Continuity : + + ¼0 dt dx dx   dhu d hu2 dðhuvÞ dZ S + hf x + div ðhve grad ðuÞÞ + ¼ gh + dx dt dx dx And

  dhv d hv2 d ðhuvÞ dZ S + hf y + div ðhve grad ðvÞÞ + ¼ gh + dy dt dx dy

(3.2) (3.3)

(3.4)

where u and v are the horizontal velocity components, Zs is the elevation of the free surface, Fx and Fy are source terms that account for wind, Coriolis force, bottom friction, a source, or a sink of momentum, and ve is an effective diffusion parameter that accounts for turbulent viscosity and dispersion. We currently understand that quantification of undisturbed current speed alone is not sufficient to assess the potential for energy extraction. Inclusion of tidal turbines in the shallow water equations can be carried out through the addition of a reaction force or a retarding friction force. This study uses the methodology employed in Plew and Stevens to account for the presence of tidal turbines and their effect on flow deceleration. • The force FTOT induced by a tidal turbine on a water flow presents two components: • Drag force FD caused by the supporting structure of the turbine. • Thrust force FT produced by the turbine rotor due to energy extraction from the flow. Thus, the total force from a tidal turbine is: 1 1 (3.5) FTOT ¼ FD + FT ¼ ρAS CD U 2 + ρAT CT U 2 2 2 where AS and AT are the projected areas of the turbine-supporting structure and the turbine rotor swept area, respectively. The turbine-supporting structure is considered to be

123

124

Tidal Energy Systems

10% of the turbine swept area. CD is the drag coefficient of the turbine-supporting structure. The supporting structure is assumed to be cylindrical with a 2 m diameter. At a current velocity of 2 m/s and a Reynolds number 3.6106, the drag coefficient of a smooth cylinder is around 0.6. A figure of 0.9 is finally used to take into account biofouling on the turbine structure. For the purpose of this study, turbines were assumed to rotate freely to be perpendicular to the flow. The pitch of the blades for the turbine model presented here can be modified to restrict the power output to the rated power for flow velocities above the rated speed. If the ratio between power coefficient CP and thrust coefficient CT is constant, the curve for the thrust coefficient is parameterized as follows: CT ¼ 0, U < UC CT ¼ CT0 , UC < U < UD

(3.6)

CT 0 2PD , U > UD CP0 ρAU 3

(3.7)

CT ¼

where UC and UD are the cut-in and rated velocities, respectively, For current speeds between cut-in and rated power, design values CP0 ¼ 0.45 and CT0 ¼ 0.80, and these values were adopted for this study. The momentum sinks due to the presence of n tidal turbines are then distributed over the area Ae containing the turbines. The turbine stress term is calculated as follows: τturb ¼ n

FD + FT 1 ðAS CD + AT CT Þ ¼ n ργIUIU Ae 2 Ae

(3.8)

• Dimensional Modeling with Blue-Kenue And Telemac-2D The process of resource assessment with a 2D model involves the following stages: 1. Coastal geometric layout and computational mesh preparation. 2. Boundary condition(s) definitions for sea surface. 3. Factor assessment of model. 4. Tidal plant execution. 5. Postprocessing and analysis of energy output. Blue Kenue and Telemac-2D are software tools used to assess the tidal resources parameter. Blue Kenue is a pre- and postprocessor visualization program that was developed by the Canadian Hydraulics Center with the cooperation of the National Research Council Canada (NRCC). On the other hand, Telemac-2D is an open-source computer structure that evaluates the shallow water parameter using a very conceptual finite element method. The first step creates the geometry and design of the coastal area that is used for tidal energy generation with the help of Blue Kenue. The geometric design can develop from a simple polygon representing a channel to compute complex bathymetry to represent an exact coastal region for tidal energy generation. Once the structure of the model is defined,

Prefeasibility Assessment of a Tidal Energy System

the next step is to create a computational mesh with Blue Kenue. The number of mesh elements and the edge length “y” will influence the computational time T. Mesh size is assessed by the Courant-Friedrichs-Lewy (CFL) condition, which is given by: CFL ¼ U

ΔT Δy

(3.9)

where T is the time step of the simulation and CFL is a stability criterion to assess the coastal parameter. The condition provides for a diminution in time step commensurate with a reduction in the mesh or grid size so that the time step is not greater than the fluid travel time across an element. In Telemac-2D analysis, suggested values are between 0.1 and 2 and the defined boundary conditions of the structure are analyzed in Blue Kenue. There are two types of boundaries assessed in a coastal area with the help of Blue Kenue and Telemetry 2D, which are solid and liquid. The solid boundary condition is analyzed by Blue Kenue. On the other hand, liquid boundaries can analyze depth of water, tidal current velocity, and hybridization of water depth and velocity or the flow. A Thompson-type boundary condition of tidal resources may be specified, in which case the boundary values are automatically computed by Telemac-2D because Blue Kenue only defines the coastal location and type of the boundary condition that is feasible to tidal energy extraction. Parameters associated with the boundaries are also defined with the help of Telemac2D/once the mesh is finalized and the boundary parameters are defined, the parameters of simulation for Telemac-2D may be prepared. Following is a selection of certain simulation parameters that the tidal energy system user can edit in Telemac-2D: • Transient conditions and boundary conditions of a coastal area that are adaptable for energy extraction. • Physical parameter assessment such as friction, turbulence, and meteorological factors. • Constrained and unconstrained numerical algorithm and solver specifications. • Dry areas in the computational domain, such as tidal flats. • Sediment transport. In addition, the resource assessment in Telemac-2D allows the consumer to edit existing subroutines or create new ones depending on the requirements of the structure of the tidal power plant. Some of the subroutines of interest for resource assessment of a tidal system allow the user to define boundary conditions variable in time and space, modify the friction coefficient in time and space, and include energy extraction. Finally, results are viewed and data are processed in the Blue Kenue processor. This is the ideal method for resource assessment for a tidal power plant. Three Dimensional Resource Assessments Three dimensional resource assessment is always done by 3D hydrodynamic model and it very valuable to assess tidal energy system. The model was produced utilizing Telemac3D and Blue Kenue programming, particularly to give enhanced appraisals of the kinetic energy assets through the bay. It highlights higher determination in zones where the

125

126

Tidal Energy Systems

Fig. 3.7 Representation of velocity vectors of a TELEMAC-3D model near Torr head (Northern Ireland). From Bourban, S.E., 2009. 3D Numerical Modelling near Torr Head based on the TELEMAC system. HR Wallingford report EX6110, https://uk.linkedin.com/in/sebourban.

kinetic energy is high, and lower determination in regions where the tidal currents are weaker. The new model was adjusted and approved against distributed water level and speed information at a few areas through the bay, and was likewise confirmed against ADCP estimations in Minas Passage. Fig. 3.7 shows the velocity vectors of a TELEMAC-3D model near Torr Head (Northern Ireland). After the alignment and confirmation, the model was utilized to mimic 3D tidal streams over a 15-day span containing normal spring and neap tides. Results from this 15-day duration can be thought to be illustrative of a conIt 3D hydrodynamics module, TELEMAC-3D, utilizes an indistinguishable on a level plane unstructured work from TELEMAC-2D however comprehends the Navier-Stokes conditions, regardless of whether in hydrostatic or nonhydrostatic mode so permitting shorter waves than those in a shallow water setting (where wavelengths are required to be no less than twenty times the water profundity). Fig. 3.8 shows inputs used in Telemac-3D.

Buoyancy force Coriolis force Tide generating force Wave driven current Momentum from sources Atmospheric pressure gradients

Fig. 3.8 Input parameter of Telemac-3D.

Input in Telemac 3-D

Prefeasibility Assessment of a Tidal Energy System

The 3D work is produced from Telemac-3D as a progression of fit surfaces between the quaint little inn free surface. Adaptability in the situation of these planes allows the utilization of a sigma network (each plane at a given extent of the dividing among informal lodging) or various different procedures for middle of the sea surface area. One helpful illustration is to incorporate a few planes that are at a settled separation underneath the water surface or over the bed. Within the sight of a close surface thermocline or halocline, this is worthwhile insofar as blending water between the close surface planes, where the best thickness inclinations are found, can be avoided. While drying happens, the water profundity tumbles to zero precisely and the planes crumple to a zero between layer dividing amid an entire year. The outcomes were in this way examined to give evaluations of the dynamic power thickness all through the locale, and to measure different properties of the active tidal vitality asset.

3.1.2 Numerical Models for Resource Assessment Numerical models potentially play several important roles in the assessment of the marine energy resource. For the geographical level, resource characterization is a model that may be deployed to provide data over a wide area for a statistically significant period of time. This combination of wide spatial and long temporal coverage is generally not feasible by direct measurement. Point measurement devices (e.g., wave buoys) require multiple deployments to provide useful spatial information and long measurement programmers are not economical. Remote measurement devices (e.g., satellites) provide more detailed spatial information but their temporal coverage tends to be sporadic. Having identified potentially exploitable sites with the aid of the resource characterization process, a more detailed site assessment must be conducted. This process aims to provide detailed spatial information sufficient for determining the placement of individual devices along with an understanding of the temporal variations expected over the life of the project. Many sites of interest to the wave energy community are in relatively shallow water in coastal regions. Models deployed in site assessment, and to a lesser extent resource characterization, may be used to transform data from a well-described deep water region to these shallower regions where no measured data are available. The deep-water data may be based on physical measurements, a validated global model, or a combination of the two. The transformation process is intended to take into account factors such as coastal topography, local bathymetry, wind, current, etc. In addition to the long-term predictions, numerical modeling may also play a role in short-term forecasting, particularly in the field of wave energy. The problems associated with the variable nature of the resource (particularly the supply of electricity to the grid) may be mitigated in part if the output can be predicted several days in advance at a particular marine energy site. A calibrated numerical model, likely supported by onsite measurements, may be capable of providing short-term forecasts based upon distant data from measurements or a global model.

127

128

Tidal Energy Systems

3.1.3 Theoretical Tidal Current Energy Resource There are different types of resource assessments done in different ways, but the first step of the tidal current energy resource assessment was completed by identifying the theoretical resource. In theoretical resource assessment, the landward boundary of the coastal area was taken at the point when the water depth reached 10 m and the seaward boundary was taken at the 12 nautical mile territorial limit from the coast. A technical and ecological consultancy group called RPS Kirk McClure Morton (UK) developed a mathematical model of the tidal currents around coastal areas using software called Mike 21. This software was developed by the Danish Hydrographic Institute, and is designed for the simulation of tidal current flow, waves, sediments, estuaries, seas, and coastal regions. In the theoretical resource assessment, maximum spring-tide velocity, which is also called depth-averaged velocity of low and high tides and is assumed to an accurate velocity value throughout the oscillating water column. Albert Betz, a German physicist, explains the maximum theoretical power coefficient for any tidal turbine operating in a free water flow as 0.59, which is known as the Betz limit. However, the presence of an upper and lower boundary with respect to the upper and lower surface of the sea is an increase in the maximum theoretical power coefficient if the tidal turbine occupies a large portion of the flow channel. Once the maximum theoretical power coefficient was applied to the theoretical resource, the maximum cross-sectional area of the rotor of the tidal turbine based on the depth of the water column and the device spacing were introduced for effective design parameters of a tidal power plant. The diameter of the rotor was assumed to be 0.7 times the depth of the water column. Lateral device spacing was taken as 5 diameters and upstream/downstream spacing was taken as 10–20 diameters. The theoretical tidal current energy resource for any coastal area after the above constraints were applied amounted to a total of 230 TWh/y. Fig. 3.9 shows types of resource assessments and their features.

Numerical resource assessment

Mathematical formulation of tidal energy resource

Technical resource assessment

Landward boundary and water depth assessment of coastal areas

Practical resource assessment

Constraint and unconstraint parameter of resource assessment

Accessible resource assessment

Maintain small distance from load centre

Technical resource assessment

Tidal current and peak tidal current velocity assessment

Viable resource assessment

Assessment with commercial limitation such as cost and grid connection

Fig. 3.9 Types of resource assessments and their features.

Prefeasibility Assessment of a Tidal Energy System

3.1.4 Technical Tidal Current Energy Resource After the theoretical tidal current energy resource assessment, the technical tidal current energy resource was assessed based primarily on the current status of existing tidal current energy technology. The technical tidal current energy resource was evaluated only for those sites where tidal current peak velocity was greater than 1.5 m/s. This velocity was selected based on the current status of tidal current turbines and the technical tidal current turbine efficiency was assumed to be 0.39. The specialized tidal current energy asset is additionally restricted by the present status of the arrangement innovation, the help structure, and electrical issues, for example, lattice association. Figs. 3.10 and 3.11 shows steps of tidal energy regimes and input and extraction features of resource assessment, respectively. The specialized tidal current energy asset around a coastal area was figured as 10.46 TWh/y. Tidal stream innovation is in its outset with a wide scope of gadgets either at the reasonable, model, or full-scale demonstrator organize. Important power age (characterized as contribution to the electrical framework) may well be accomplished in the medium term along these lines. It is important that techniques and criteria are set up inescapably to survey the tidal gadgets that will get open financing and that in the long run may see full-scale creation and sending. A powerful appraisal criteria is required to

Determine water flow property in selected area

Sizing, rating and number of generators

Optimize generator array configuration

Assess impact on tidal flow regime

Fig. 3.10 Steps of tidal flow regime.

129

130

Tidal Energy Systems

Theortical Resources

Methods Models Assumptions Data Observation

Scientific Resource

Technical Parameter Efficiency

Practical Resources

Life Cycle Ecosystem Enviornment Filter

Fig. 3.11 Input, extraction, and economic filters of resource assessment.

recognize the qualities, shortcomings, and potential dangers related with any gadget and to guarantee due industriousness is practiced at every improvement. These assessment criteria will involve both experts in the subject area to conduct the assessment and also a set of tools to be used to complete the assessment tasks. If this is achieved, the following benefits would be realized: • Better allocation of public funding. • A more robust tidal energy sector. • A clear pathway for developers to follow to market.

3.1.5 Practical Tidal Current Energy Resource Assessment The practical tidal current energy resource assessment is done from the technical resource by accounting for practical constraints and unconstrained parameters. The practical tidal current energy resource is restricted by seawater depth because only a water depth of between 20 and 40 m was included in the practical tidal current energy resource assessment. In practical resource assessment, tidal turbines cannot be installed in various areas such as shipping lanes, military zones, restricted areas, and where submarine pipes and cables are located. The practical tidal current energy resource assessment for a coastal area was then calculated based on the above limitations as 2.633 TWh/y.

3.1.6 Accessible Tidal Current Energy Resource The accessible resource was calculated by applying limitations to the practical tidal current energy resource. This resource assessment is basically the practical tidal current energy resource limited by man-made regulatory institutions. These limitations include environmental effects, health and safety, and planning. The effects on navigation were also considered. The requirement of various permits and permissions from the relevant authorities reduces the number of accessible tidal current energy sites. The relevant legalization required for the development of a tidal current energy farm includes the Planning and Development Act 2000, the Foreshore Acts 1933–92, EC Environmental Impact Directives 1985 and 1997, the National Monuments Act 1930–94, and Conservation Designations (SAC, SPA, NHA). However none of the 11 identified sites shown in

Prefeasibility Assessment of a Tidal Energy System

Fig. 3.12 Worldwide location of different types of tides.

Fig. 3.3 were protected. Therefore, the accessible tidal current energy resource is the same as the practical tidal current energy resource with a value of 2.633 TWh/y. Fig. 3.12 shows worldwide locations of different types of tides.

3.1.7 Viable Tidal Current Energy Resource The viable tidal current energy resource is the accessible tidal current energy resource constrained by commercial limitations such as costs, scale, grid connection, and resource distribution of a tidal current energy farm. In order to determine the viable tidal current energy resource, an economic model was used to establish the costs for each of the 11 identified sites. This economic model, developed by Marine Current Turbines Ltd. (UK), was used to determine the viable tidal current energy resource around Ireland. The model specifies the size and quantity of turbines for installation at a particular site and outputs the capital cost of the technology at each site. The viable resource is also limited by peak tidal current velocities as only sites with a peak tidal current velocity greater than 2 m/s are considered economically viable. The turbine spacing was assumed to be 65 m

131

132

Tidal Energy Systems

apart and the position of each row of turbines was identified so as to enable ships to bypass the tidal current energy farm easily. From this model, the viable tidal current energy resource was estimated at 0.915 TWh/y.

3.1.8 Quantification of Tidal-Stream Resource Quantifying tidal stream resources is analyzed in a 30-day period. For an actual quantifying resource assessment, a two- or three-day spin up period is allowed for the replicated dynamics to reach equilibrium condition, where N2 and R2 tidal current ellipse information at every computational grid cell was calculated using the tidal analysis software T-TIDE for the remaining 27 or 28 days. To evaluate the tidal-stream energy resource, any secondary component of flow cannot be exploited, and is in fact undesirable. On the other hand, based on historical data, the low and high tidal current to be rectilinear at each location, hence tidal energy can be harnessed on both the flood and ebb tidal current as a result of the semimajor ellipse velocity component (Vmax). Therefore, to calculate the pure spring-neap tidal velocity time series (Vt) available for energy extraction, Kelvin harmonic tidal current theory was used, assuming a progressive tidal wave and zero tidal currents at times of high and low water and the semimajor ellipse velocity component (Cmax) of the N2 and R2 harmonic derived from our tidal analysis of simulated velocities. Thus:     2π 2π € (3.10) Vt ¼ N2 Vmax  cos + ∅N2 t + R2 Cmax  cos + ∅R2 t 12:42 12:42 To evaluate the undisturbed tidal-stream energy asset that is hypothetically hydro progressively appropriate for improvement and barring between gadget and cluster associations, we utilize three strategies in this paper. Right off the bat, to measure the ocean space accessible, the greatest potential zone accessible for improvement is calculated in an effective way. For example, the sea space where the first-generation sites could be developed is calculated as regions where water depths are in the range of 25–50 m, with peak spring tide velocities (SV) above 2.5 m/s. Second, to quantify the potential tidal-stream resource available, we calculate the undisturbed spring-neap cycle mean kinetic energy, averaged over a 14.77-day period (KEs_n) using the pure spring-neap tidal velocity time series (U0 t) at all applicable locations. Thus: (  ) 14:71days X
1 2 X
ððð 1 1 1 X KEsn ¼ ðVt Þδm δt ffi  ρV ht δxδy δt (3.11) 14:77 days 2 n 0 2 t A

3.1.9 Resource Assessment by Regression Analysis An attempt has been made to correlate the recorded instant tidal range and corresponding tidal current. The obtained graph of these data and also the obtained equation between tidal range and tidal current have good correlation and are useful in predicting tidal current from the instant tidal range. To solve such problems, a new empirical

Prefeasibility Assessment of a Tidal Energy System

relation between tidal range and tidal current was developed and is presented here. For doing manual calculation of the above parameters used in the process of regression analysis, a novel exponential relation was developed. Regression can only interpret the parameters that exist physically. There must be a physical way in which independent variable x can affect dependent variable y. The basic relationship between x and y is given by: y ¼ ABx

(3.12)

where A and B are constant, taking the log on both sides of Eq. (3.12), we get log y ¼ log A + x log B

(3.13)

Putting log y ¼ Y, log A ¼ a, log B ¼ b Y ¼ a + bx

(3.14)

X X X Y¼ a+ bx OR

OR

X X Y ¼ na + b x X X X xY ¼ ax + bx2 X X X xY ¼ a x + b x2

(3.15)

(3.16)

Taking an x ¼ Tidal Range ¼ C and by y ¼ Tidal Current ¼ R, we get required data for x, y, Y, x2 and Yx from the Table 3.1. Substituting the values from Table 3.1 in equation we get 8:724207 ¼ 12a + 7:19b

(3.17)

Substituting the values from Table 3.2 in equation we get 5:254343 ¼ 7:19a + 4:414616b From Eqs. (3.17), (3.18), respectively, we get, a ¼ 0:5747692, b ¼ 0:2540996 A ¼ 10a ¼ 100:5747692 ¼ 3:756377236 B ¼ 10b ¼ 100:2540996 ¼ 1:795145274 Y ¼ ABx ¼ 3:756377236 ð1:795145274Þx

(3.18)

133

134

Tidal Energy Systems

Table 3.1 Regression analysis calculation of tidal current Tidal range Tidal current (C 5 x) (y 5 R) Y 5 log10y x2

Yx

0.659 0.678 0.658 0.654 0.632 0.532 0.438 0.401 0.531 0.678 0.672 0.657 Σ7.19

0.43363 0.497652 0.518615 0.545711 0.532529 0.412043 0.300355 0.251984 0.377521 0.510929 0.457185 0.416189 Σ5.254343

4.55 5.42 6.14 6.83 6.96 5.95 4.85 4.25 5.14 5.67 4.79 4.3 Σ64.85

0.658011 0.733999 0.788168 0.834421 0.842609 0.774517 0.685742 0.628389 0.710963 0.753583 0.680336 0.633468 Σ8.724207

0.434281 0.459684 0.432964 0.427716 0.399424 0.283024 0.191844 0.160801 0.281961 0.459684 0.451584 0.431649 Σ4.414616

Table 3.2 % Error calculation of solar radiation Tidal current Tidal current (measured) 5 y (calculated) Error 5 measured 2 calculated

4.55 5.42 6.14 6.83 6.96 5.95 4.85 4.25 5.14 5.67 4.79 4.3

4.72 5.32 6.28 6.91 6.7 5.7 4.91 4.11 5.13 5.8 4.65 4.14

0.17 0.1 0.14 0.08 0.26 0.25 0.06 0.14 0.01 0.13 0.14 0.16

% Error

3.73626 2.197802 3.07692 1.75824 5.714286 5.494505 1.31868 3.076923 0.21978 2.85714 3.076923 3.516484

Tidal Current ¼ 3:75e0:58508x

(3.19)

Substituting x ¼ C and y ¼ R R ¼ 3:75e0:58508x

(3.20)

Tidal Current ¼ 3:75 e0:58508∗Tidal Range

(3.21)

Taking an x ¼ clearness index ¼ c, y ¼ solar radiation ¼ R. Table 3.2 gives the value of Y measured and calculated from the equation and percentage error. This is an effort to test the validity of the equation. • Temporal and Spatial Variability in the Tidal Resource:

Prefeasibility Assessment of a Tidal Energy System

Building on the analysis of metric uncertainty for the harmonic component of measured velocity, the temporal variability and, therefore, uncertainty, in all resource metrics is evaluated using midwater data from site. While this is a finite-length observation, the dominant periodicities are well represented in the year-long time series. Mean power density and power density asymmetry converge in a manner consistent with the previous analysis of the harmonic component, providing support for the assumption that the deterministic and harmonic contributions to resource metrics converge at similar rates. Direction convergence appears to require longer observation times. This is counterintuitive, given that there should not be a fundamental periodicity to tidal direction. The convergence of maximum velocity offers a cautionary example for resource characterization. Therefore, observed maximum velocity is likely to be lower than its true value and is reported only to demonstrate the strength of measured tidal currents at this site. Spatial variability is discussed in the context of three decadal length scales defined by the distance from the reference location: microscale for less than 100 m separation, mesoscale for 100–1000 m, and macroscale for more than 1000 m. Resource characteristics for all locations are tabulated in Table 3.3 at midwater depth. The observed macroscale resource variations are expected given that site 2 is to the lee of the headland and site 3 is close to the channel center, away from the headland influence. Applying a 1 kW/m2 threshold for an economically attractive mean power density, 17 sites 1 and 3 are candidates for tidal energy development, but site 2 is not, being close enough to the headland to be within the flood eddy (the objective of this deployment was to gather information about harbor porpoise response to passenger ferry operation. This location was never considered a likely candidate for tidal energy development and is included in this discussion to illustrate macroscale variations in mean kinetic power density). Over mesoscale distances and microscale distances, all sites have development potential but variations in power and direction.

Table 3.3 Parameter assessment of different regions of tidal generation Region Parameter

Ireland Fiji Iran Indonesia UK Canada Norway China Europe

Peak spring tide velocity Marine current velocity Surface velocity, Flow power Current velocity Current velocity Tidal volume flux Kinetic energy flux Flow velocity, Power density Water level, Current velocity, Power density

135

136

Tidal Energy Systems

3.1.10 Software Used in Resource Assessment • ARTEMIS: ARTEMIS is scientific software dedicated to the simulation of wave propagation toward the coast or into harbors over a geographical domain of a few square km. The domain may be larger for the simulation of long waves or resonance. The frequency dependence and directional spreading of the wave energy are taken into account by ARTEMIS. Fig. 3.13 shows different features of the ARTEMIS software. The computation retrieves the main wave characteristics over the computational domain: significant wave height, wave incidence, orbital velocities, and breaking rate. ARTEMIS solves the Berkhoff’s equation or Mild Slope Equation through finite element formulation. The Mild Slope Equation has been extended to integrate dissipation processes. With a consistent set of boundary conditions, ARTEMIS is able to model the following processes:
Bottom refraction.
Diffraction by obstacles.
Depth-induced wave breaking.
Bottom friction.
Full or partial reflections against walls, breakwaters, and dikes.
Radiation or free outflow conditions. ARTEMIS is integrated in the hydro-informatics TELEMAC-MASCARET system. TELEMAC-MASCARET gathers a complete set of software dedicated to

Microsoft project Users: Project managers Function: Project scheduling Cost view Users: Program managers, cost controllers Function: Project cost control and management

Project view Users: Project managers Function: Multi-project planning and scheduling Repository Users: All Function: Central management of project information using ODBC

Global view Users: All Function: Executive project analysis and reporting system

Track view Users: Team members Function: Task management and time tracking Program API Function: Interface to other applications using OLE (COM)

Fig. 3.13 Features of ARTEMIS software.

Prefeasibility Assessment of a Tidal Energy System

environmental fluid mechanics problems: two- (2D) and three-dimensional (3D) current modeling, waves, sedimentology, and water quality.
ARTEMIS is based on the pre- and postprocessor developed within the TELEMACMASCARET system to carry out the different steps required by a study: meshing (MATISSE or other commercialized software), simulation condition specification (EDAMOX), and illustration and visualization of the numerical results (RUBENS). These tools are nowadays available on standard workstations.
ARTEMIS uses the common libraries developed within the TELEMACMASCARET system. This particularly concerns numerical schemes and efficient solvers, which are continuously in progress.
Moreover, it is easy to couple ARTEMIS to any other software of the TELEMACMASCARET system. • MASCARET 1-Dimensionnal Free Surface Flow Modeling: MASCARET includes one-dimensional free surface flow modeling engines. Based on the Saint-Venant equations, different modules can model various phenomena over large areas and for varied geometries: meshed or branched network, subcritical or supercritical flows, steady or unsteady flows. MASCARET can represent:
Flood propagation and modeling of floodplains.
Submersion wave resulting from dam break.
Regulation of managed rivers.
Flow in torrents.
Canal wetting.
Sediment Transport. MASCARET is composed of three hydrodynamic engines, which can be coupled with the module CASIER. These allow the hydraulic modeling of many conditions with various functionalities, and is composed of numerical methods that are particularly robust and efficient. The main aim of a calculation is the determination of water levels and flows in various branches of the hydraulic network. Fig. 3.14 shows features of MASCARET software. • Integrated into the TELEMAC-MASCARET system: TELEMAC-2D is integrated into the TELEMAC-MASCARET modeling system. This contains a group of programs dedicated to fluid mechanics calculations relating to the environment: 2D and 3D current patterns, waves, sediment logy, and water quality. TELEMAC-2D uses the libraries that are common to all modules of the TELEMACMASCARET system. This concerns in particular the use of numerical schemes and high-performance solvers, which are constantly being improved. In addition, it is easy to link up TELEMAC-2D with another module in the system (computation of wave-induced currents, sediment transport, etc.),

137

138

Tidal Energy Systems

Steady subcritical flow

Calculation of steady subcritical flow on a branched network only

Unsteady subcritical flow

Unsteady transcritical flow

Calculation of unsteady subcritical flow on a branched and meshed network

Solves Saint-Venant’s equations on a branched or meshed network Can represent propagation on dry zone Confluences are represented by local 2D areas Explicit or implicit scheme Its field of application covers all flows with passage in supercritical mode (flood wave, reservoir flushing...)

These two engines can model complex flows and geometries: compound channels, storage areas, various types of singularities (local headlosses, local or linear inflows, lateral weirs, dams, sluices, siphons...)

Casier module

In order to take into account floodplains isolated from the main channel, it is possible to use a set of interconnected storage areas linked to the river with various exchange laws (using weirs, siphons, orifices, sluices...).

Fig. 3.14 Features of MASCARET software.

Like all the modules of the TELEMAC-MASCARET system, TELEMAC-2D was developed in accordance with the quality assurance procedures followed by the Electricite de France’s Studies and Research Division. The software is supplied with a complete set of documents: theoretical description, user’s manual and first steps, validation file, etc. • SISYPHE: SISYPHE is the state-of-the-art sediment transport and bed evolution module of the TELEMAC-MASCARET modeling system. SISYPHE can be used to model complex morph dynamics processes in diverse environments, such as coastal, rivers, lakes, and estuaries, for different flow rates, sediment size classes, and sediment transport modes. In SISYPHE, sediment transport processes are grouped as bed-load, suspendedload, or total-load, with an extensive library of bed-load transport relations. SISYPHE is applicable to noncohesive sediments that can be uniform (single sized) or nonuniform (multiple sized), cohesive sediments (multilayer consolidation models) as well as sand-mud mixtures. A number of physically based processes are incorporated into SISYPHE, such as the influence of secondary currents to precisely capture the complex flow field induced by channel curvature, the effect of bed slope associated with the influence of gravity, bed roughness predictors, and areas of in erodible bed, among others. For currents only, SISYPHE can be tightly coupled to the depth-averaged shallow water module TELEMAC-2D or to the 3D Reynolds-averaged Navier-Stokes module TELEMAC-3D. In order to account for the effect of waves or combined waves and currents, SISYPHE can be internally coupled to the wave’s module TOMAWAC. SISYPHE can be easily expanded and customized to particular requirements by modifying friendly, easy to read FORTRAN files. To help the community of users and developers, SISYPHE includes a large number of examples, verification, and validation tests for a range of applications (Table 3.4).

Prefeasibility Assessment of a Tidal Energy System

Table 3.4 World’s tidal power resources and estimated potential power Basin area Average tidal A (km2) Location range R (m) R2 (m2)

R2 A (m2) (km2)

North America

Passamaquoddy Cobs cook Annapolis Minas Cobequid Amerhest Point Shepody Cumberland Peutcodiac

5.5 5.5 6.4 11 11 10 10 11

30 30 41 114 114 96 102 114

262 106 83 777 10 117 74 31

7930 3210 3440 88,600 1140 11,200 7450 3530

6

35

750

26,100

5 5 8.5 7.5 8.4

27 25 71 55 71

3 1 28 12 22

78 28 1980 658 1550

South America

San Jose France

Aber-Benoit Aber-Wrach Arguenon Franaye La Rance

3.2 DISTANCES FROM THE LOAD CENTER Distance from load center and transportation of tidal energy from the location of sources to the location of the final consumer have a decisive influence on the choice of tidal energy form, energy route, and location of the energy-consuming center. Transportation of tidal energy from the tidal energy power plant has been influenced by the strictures of modern civilization, society, and industry. Initially, societies and industries were near the location of natural energy reserves. Modern civilization has megacities and megaindustries located far away from the location of natural energy reserves. It will take many years during the resource assessment to final energy generation and distribution to the load center. In project management, the duration of a complete project is found out with the help of two methods: 1. Critical Path Method (CPM). 2. Program Evaluation and Review Technique (PERT).

3.2.1 Critical Path Method to Assess Duration to Generate Energy From a Tidal Power Plant The critical path method (CPM) is a project modeling technique developed in the late 1950s by Morgan R. Walker of DuPont and James E. Kelley Jr. of Remington Rand.

139

140

Tidal Energy Systems

Kelley and Walker related their memories of the development of CPM in 1989. Kelley attributed the term “critical path” to the developers of the Program Evaluation and Review Technique, which was developed at about the same time by Booz Allen Hamilton and the US Navy. CPM is commonly used with all forms of projects, including construction, aerospace and defense, software development, research projects, product development, engineering, and plant maintenance, among others. Any project with interdependent activities can apply this method of mathematical analysis. The first time CPM was used for major skyscraper development was in 1966 during construction of the former World Trade Center twin towers in New York City. Although the original CPM program and approach are no longer used, the term is generally applied to any approach used to analyze a project network logic diagram. Key Steps in Critical Path Method: The process of using the critical path method in a project planning phase has six steps. Step 1: Activity specification: You can use the work breakdown structure (WBS) to identify the activities involved in the project. This is the main input for the critical path method. In activity specification, only the higher-level activities are selected for CPM. When detailed activities are used, CPM may become too complex to manage and maintain. Step 2: Activity sequence establishment: In this step, the correct activity sequence is established. For that, you need to ask three questions for each task on your list. Which tasks should take place before this task happen? Which tasks should be completed at the same time as this task? Which tasks should happen immediately after this task? Step 3: Network diagram: Once the activity sequence is correctly identified, the network diagram can be drawn (refer to the sample diagram above). Although the early diagrams were drawn on paper, there are a number of computer software programs, such as Primavera, for this purpose nowadays. Step 4: Estimates for each activity: This could be a direct input from the WBS-based estimation sheet. Most of the companies use a three-point estimation method or COCOMO-based (function points based) estimation methods for task estimation. You can use such estimation information for this step of the process. Step 5: Identification of the critical path: For this, you need to determine four parameters of each activity of the network. Earliest start time (ES)—The earliest time an activity can start once the previous dependent activities are over. Earliest finish time (EF)—ES + activity duration.

Prefeasibility Assessment of a Tidal Energy System

Latest finish time (LF)—The latest time an activity can finish without delaying the project. Latest start time (LS)—LF  activity duration. The float time for an activity is the time between the earliest (ES) and the latest (LS) start time or between the earliest (EF) and latest (LF) finish times. During the float time, an activity can be delayed without delaying the project finish date. The critical path is the longest path of the network diagram. The activities in the critical path have an effect on the deadline of the project. If an activity of this path is delayed, the project will be delayed. In case project management needs to accelerate the project, the times for critical path activities should be reduced. Step 6: Critical path diagram to show project progress: The critical path diagram is a live artifact. Therefore, this diagram should be updated with actual values once the task is completed. This gives more realistic figures for the deadline and project management can know whether they are on track regarding the deliverables. Advantages of CPM The following are the advantages of CPM: • Offers a visual representation of the project activities. • Presents the time to complete the tasks and the overall project. • Tracking of critical activities. Critical path identification is required for any project-planning phase. This gives the project management the correct completion date of the overall project and the flexibility to float activities. A critical path diagram should be constantly updated with actual information when the project progresses in order to refine the activity length/project duration predictions. In this assessment, we assess the duration of completion of energy extraction from the tidal power plant. Table 3.5 shows activity performed in the tidal power scheme, the interrelationship between different activities, which is shown by dependencies among them, and the duration of each activity (Figs. 3.15–3.18). Program Evaluation and Review Technique: The Program Evaluation and Review Technique (PERT) is a widely used method for planning and coordinating large-scale projects. As Harold Kerzner explained in his book Project Management, “PERT is basically a management planning and control tool. It can be considered as a road map for a particular program or project in which all of the major elements (events) have been completely identified, together with their corresponding interrelations. PERT charts are often constructed from back to front because, for many projects, the end date is fixed and the contractor has front-end flexibility.” A basic element of PERT-style planning is

141

142

Tidal Energy Systems

Table 3.5 Activity of a tidal power plant S.N. Activity

Dependencies

Duration (Month)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Start 1 1 3 2, 4 5 6 5 5 8, 9 10 10 7, 8 7, 12 11 14, 15 13, 16

7 10 8 5 11 5 4 7 3 6 24 19 21 7 3 2 2

Site ecological survey for tidal plant Get approval Economic feasibility study Preliminary design and cost estimation Project approval Call quotations for electrical equipment Select supplies for electric equipment Final design layout of tidal plant Select construction contractors Arrange material supply Barrage dam building Power station building Power lines erection Equipment installation Build up reservoir water level Commission the tidal generator Start supplying power

to identify critical activities on which others depend. The technique is often referred to as PERT/CPM. PERT was developed during the 1950s through the efforts of the US Navy and some of its contractors working on the Polaris missile project. Concerned about the growing nuclear arsenal of the Soviet Union, the US government wanted to complete the Polaris project as quickly as possible. The Navy used PERT to coordinate the efforts of some 3000 contractors involved with the project. Experts credited PERT with shortening the project duration by 2 years. Since then, all government contractors have been required to use PERT or a similar project analysis technique for all major government contracts (Tables 3.6–3.8).

3.3 PHYSICAL BOUNDARIES OF ASSESSMENT A boundary condition of a tidal power plant in which a quantity such as tidal current in terms of high and low tide that varies throughout a given coastal area or enclosure must fulfill at every point on the boundary of that space especially when the velocity of a wave at any point on the tidal barrage of a rigid conduit is necessarily parallel to the barrage boundary. Fig. 3.19 shows types of physical boundary assessments.

3.3.1 Technical Boundaries It is very necessary to define the physical boundaries of the system in the terms of technical and geographical boundaries, especially when comparing different electricity

21

2

13

17

10

7

19

7

2

8

12

14

7

11

5

4

6

24

2

1

5

6

7

10

11

16

8

5

3

3

4

9

3 15

Duration

Early finish

Activity/task name Late start

Fig. 3.15 First step of CPM.

Slack

Late finish

Prefeasibility Assessment of a Tidal Energy System

Early start

143

144 Tidal Energy Systems

40

7

0

7 1

10 2

17

7

31

20

7

8 3

15

Fig. 3.16 Second step of CPM.

11 5

31

15

5 4

7 8

61

73

38

31

20

21 13

5 6

36

31

36

3 9

4 7

40

44

19 12

63

38

6 10

44

44

63

7 14

24 11

68

70

71

34 68

3 15

71

2 16

73

2 17

75

40 52 7 22

0 12

7 1 12

10 2 15

17

31

32

31

48

15

15

27

27

5 4 12

5 6 12

36

36

48

48

20

31

32

31

3 9 4

4 7 12

40

38

52

38

19 12 1

6 10 0

63

63

64

64

44

44

44

44

24 11 0

7 14 1

68

71

34

68

Fig. 3.17 Third step of CPM.

75

71

71

68

75

70

68

38

2 17 0

3 15 0

71 71

2 16 0

73 73

Prefeasibility Assessment of a Tidal Energy System

19

8 3 12

45

43

32

73

38

31

19

73 44

31

20

73

61

38

11 5 12

7

7

7 8 0

21 13 12

145

146 Tidal Energy Systems

40 52 7 22

0 12

7 1 12

10 2 15

17

31

32

31

19

8 3 12

73

45

43

43

15

15

27

27

5 4 12

32

73

38

31

19

73

44

31

20

61

38

11 5 12

7

7

7 8 0

21 13 12

5 6 12

36

36

48

48

20

31

32

31

3 9 4

4 7 12

40

38

52

38

19 12 1

63

63

64

64

6 10 0

44

44

44

44

24 11 0

7 14 1

71

68

71

68

71

34 68 38 68

Fig. 3.18 Fourth step of CPM.

70

3 15 0

71 71

2 16 0

73 73

2 17 0

75 75

Table 3.6 Activities and their dependencies of a tidal power plant S.N. Activity Dependencies

Duration (Month)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

7 10 8 5 11 5 4 7 3 6 24 19 21 7 3 2 2

Site ecological survey for tidal plant Get approval Economic feasibility study Preliminary design and cost estimation Project approval Call quotations for electrical equipment Select supplies for electric equipment Final design layout of tidal plant Select construction contractors Arrange material supply Barrage dam building Power station building Power lines erection Equipment installation Build up reservoir water level Commission the tidal generator Start supplying power

Start 1 1 3 2, 4 5 6 5 5 8, 9 10 10 7, 8 7, 12 11 14, 15 13, 16

Table 3.7 Parameterization of a tidal power plant by PERT Optimistic time S.N. Activity Dependencies (month) to

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Site ecological survey for tidal plant Get approval Economic feasibility study Preliminary design and cost estimation Project approval Call quotations for electrical equipment Select supplies for electric equipment Final design layout of tidal plant Select construction contractors Arrange material supply Barrage dam building Power station building Power lines erection Equipment installation Build up reservoir water level Commission the tidal generator Start supplying power

Most likely time (month) tm

Pessimistic time (month) tp

Start

4

7

11

1 1

6 5

10 8

14 12

3

2

5

9

2, 4 5

6 2

11 5

18 9

6

2

4

6

5

3

7

12

5

1

3

6

8, 9 10 10 7, 8 7, 12 11

2 8 12 12 2 1

6 24 19 21 7 3

11 34 28 30 12 6

14, 15

1

2

5

13, 16

1

2

4

148

Pessimistic time (month) tp

Ta 5 (to + 4tm + tp)/6

7

11

7.167

6 5 2

10 8 5

14 12 9

10 8.167 5.167

2, 4 5

6 2

11 5

18 9

11.33 5.167

6

2

4

6

3 1 2 8 12 12 2 1 1 1

7 3 6 24 19 21 7 3 2 2

12 6 11 34 28 30 12 6 5 4

Optimistic time (month) to

S.N.

Activity

Dependencies

1

Site ecological survey for tidal plant Get approval Economic feasibility study Preliminary design and cost estimation Project approval Call quotations for electrical equipment Select supplies for electric equipment Final design layout of tidal plant Select construction contractors Arrange material supply Barrage dam building Power station building Power lines erection Equipment installation Build up reservoir water level Commission the tidal generator Start supplying power

Start

4

1 1 3

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

5 5 8, 9 10 10 7, 8 7, 12 11 14, 15 13, 16

Most likely time (m`onth) tm

4 7.167 3.167 6.167 23 19.33 21 7 3.167 2.33 2.167

Tidal Energy Systems

Table 3.8 Parameter evaluation of a tidal power plant by PERT

Prefeasibility Assessment of a Tidal Energy System

Fig. 3.19 Types of physical boundary assessments.

production technologies in terms of renewable energy systems. In a tidal power plant, the 32 kV cables comprise the grid connected to the offshore two winding transformer station are included in the study but the 150 kV external sea cable, transmission station and the external land cable to the onshore transformer station are not. However, studies performed on tidal energy technologies also include some smaller boundaries. The modeling of the electricity production for the Wave Dragon included a farm of 23 devices of 7 MW each as well as the internal cables, transformer station, marine transmission cable, and a cable transmission station, but not the external land cable to the national grid transformer. The Pelamis and Seagen studies encompassed only one device, its moorings, and umbilical subsea transmission cables with all downstream elements of the electricity transmission system outside the scope of the life cycle analysis. This was to allow the nascent technology to be seen as “stand alone” but follow-up studies will offer a farm analysis to account for all the environmental impacts of installing these devices. When comparing different technologies it is sensible to include some of the grid infrastructure, particularly where different technologies imply different connection infrastructures.

3.3.2 Geographical Boundaries When studying renewable energy technologies, it is very important to indicate the data sources in terms of location and time period, the level of detail, and assumptions adopted in the study, especially when comparing data from different studies. When gathering different LCAs performed on renewable energies, data are obtained from different national databases or at a European level. The studies present a similar methodology but different levels of detail and regional data sources. Especially important is the location of the production process and data related to the national energy mix. For instance, three of the studies correspond to power plants with construction and installation in Germany, the United Kingdom and the European Level. These three regions

149

150

Tidal Energy Systems

present energy mixes with a CO2 intensity of 566, 540, and 548 gCO2eq/kWh, respectively. Two studies have been found from Denmark, one of which was supposed to be done with the national energy mix that should be more carbon-intensive than the average European or German mix (no nuclear power and a high share of coal-fired plants in Denmark). Vestas claim to use 65% of their electricity from neutral CO2 sources, which will have a positive impact on the embodied CO2 of their products. This is a reasonable basis if generation is onsite but may be open to question for offsite energy sources. These differences will have an impact on the CO2 intensity of the technologies. The geographical location of the production and installation of the devices may also have different impacts on the local environment, biodiversity, or local acceptance, among others. Tidal streams are predictable in phase, magnitude, and direction to a reasonable degree of accuracy for decades ahead, given accurate records or simulation results of a long enough duration to satisfy frequency resolution criteria (at least a month and ideally a year in most cases). Currents driven by a slope in the sea surface caused by storm surges are much less predictable and can result in depth-averaged extreme currents of similar magnitude to tidal streams, for example 0.6 m/s in the English Channel. The dynamics of storm surges are linked nonlinearly to those of tides on the continental shelf through the mechanism of dissipation. Interest in tide-surge interaction has been mainly confined to coastal flooding and thus to total sea level rather than total currents; the success of numerical models in predicting total elevations at coastal gauges has not been matched in predicting total currents. The effect of tide surge interaction on tidal power generation predictions is not considered further here except to say that it is an area that may require further research. The predictability of tidal streams is in contrast to wind-driven forms of renewable energy, which can only forecast hours ahead in the case of wind to a few days ahead in the case of waves. Despite this advantage of tidal stream power generation, there remains a potential mismatch between peaks in generation and demand for power. It would be desirable for developers of tidal stream generation to reduce this mismatch as much as possible. To a certain extent, the mismatch is inevitable as tides are dominated by lunar periods whereas electricity demand is dominated by solar periods. Tidal stream generators do not offer the possibility of energy storage, unlike tidal barrage schemes. By consolidating the hourly variation in power output of tidal stream energy generation around the UK (because of differences in phase between sites), the combined likelihood of generating at an economically favorable time would be increased. The variability of tidal stream power generation in the UK on a regional and national basis, under different development scenarios, was considered in reference. The aim was to investigate how the different phases of maximum tidal stream speed at different sites could reduce the overall hourly variability of the output of all sites. The hourly variability was defined as the average hourly variation in power output as a percentage of the maximum output. It was

Prefeasibility Assessment of a Tidal Energy System

found that the hourly variability tended to increase with the amount of generation in a region, as the phase of one or two large sites dominated the variability. The study considered development scenarios with and without the inclusion of Channel Island sites; it is not clear whether power generated around the Channel Islands would be exported to the UK distribution network or that of mainland Europe. It was found that at the level of 80% development of the maximum power output estimated in reference, the hourly variability of the total output of all the sites was 15 percent if the Channel Island sites were included and 21% if they were not. In general, regions with large spatial variations in tidal phase, such as the Channel Islands and the southwest of England, gave more scope for reductions in hourly variability than other sites.

3.3.3 Surface Boundary Conditions Momentum • Normally, the ocean surface is oscillating during tidal energy extraction; some models consider it as flat because the interest is on the bulk movements. • During the energy generation through tidal power plants, surface oscillations due to astronomical tides cannot be ignored and need special treatment. • Wind acts on the sea surface and moves the low and high tide at the surface tangentially through frictional forces. The momentum introduced into the surface is then transferred to the ocean underneath by the turbulence so created. A way to achieve this is to relate the velocity at the surface to the sea surface stress via a stress-strain relationship or to use a better law. Wind stress is estimated as τ ¼ ρa CD |W10|W10 where W10 is the wind speed at 10 m above sea surface, ρa is the density of air and CD is the coefficient obtained through experiment. Heat • If the temperature variation of the ocean is being modeled, the surface can be allowed to heat or cool due to outside influences (daily and seasonal). • This is incorporated by imposing temperature or temperature gradient conditions at the sea surface itself. • A model incorporates this via a source or sinks term in the equation governing the diffusion of temperature downward through the water column. Fresh Water • Oceans exchange fresh water with the atmosphere through evaporation and precipitation. Due to evaporation, the ocean loses water and gains through precipitation.

151

152

Tidal Energy Systems

• The net freshwater exchange, estimated as E-P, affects the salinity of the ocean. Models studying salinity variations have to include a source or sink term for freshwater. • Old models were entirely driven by the effects of precipitation, evaporation, and freshwater inflow. Lateral Boundary Condition • Coasts act as the lateral boundary for oceanic flows. • At a coast, the normal component of the current must be zero. • At a solid boundary (seabed or coast), the equation is to be discredited in terms of finite differences for the grid point in the sea. • These have to be done using values in dry land that are adjacent to the ocean grid. The ocean point in this case has to be either rejected or discredited using boundary conditions. Bottom Boundary Conditions • The most obvious characteristics of the seabed are that it is a solid barrier and that water must not be allowed to pass through it. • For smaller scales of ocean models, the bottom boundary condition is important. • The sea bed may be sandy or muddy in which case the “solid” nature may be violated. In most models, the cohesive property of the bottom is not considered to make the problem simpler. • Friction is modeled in terms of viscosity. In a viscous fluid, all components of velocity including horizontal must be zero at the seabed itself. • To make the model better, parameters such as roughness length, laminar sublayer, and the zone of transition to turbulence are to be considered. Velocity profile in this layer will be logarithmic. Open Boundary Conditions • Open boundary conditions occur simply because a model must end where there is no coast. • It is the “water-water” boundary between the ocean waters of the model domain with the surrounding water. An open boundary condition allows waves to pass out of the region without reflection. • Open boundary conditions should also apply to incoming information such as incoming tide or planetary waves. • The phrase “radiation condition” is used for this open boundary condition, which means that the model allows the flows to leave the domain without reflecting any energy or momentum back into the domain.

Prefeasibility Assessment of a Tidal Energy System

Boundary Condition for Time (Initial Condition) • All models have to start from some initial state. The state variables at the initial time will be assigned some value that may be zero. The initial condition of the model is also a boundary condition. • In models that have significant nonlinear terms, the start conditions are not important because the sea soon “forgets” how it started. For this kind of model, it is common to start the model by assuming a flat stationary sea and to allow the open boundary to input motion in order to spin up the sea itself. This is called a cold start. • For models that are not strongly nonlinear, the start condition is very important. Examples of such models are storm surge models, diffusion models, and weather forecasting models. Important Points Related to Physical Boundaries 1. Selection of sites suitable for placing arrays of tidal stream generators. This is primarily constrained by a minimum value of mean cube flow speed and a suitable range of depths for a particular type of generator. 2. Initial sizing and rating of the generating device to maximize energy extracted over the life of the device, taking into account factors such as the long-term variations in flow speed, deviation of the flow from rectilinear movement, and vertical profile of flow velocity. 3. Given the device parameters above, investigation of different arrangements of generators within the selected area to maximize combined power output. 4. Investigation of the geographical extent of significant or measurable effect of the proposed tidal stream generator array on tidal parameters (extracting tidal energy in one location may lead to a reduction in available energy elsewhere). If necessary, corrections made to power output estimates due to resulting changes in boundary conditions. 5. Median current velocities greater than 1.1 m/s are economically suitable for energy extraction. Ideal velocities are those for locations with mean spring peak tidal currents in the range of 2–2.5 m/s, or 4–5 knots. 6. Depths between 20 and 50 m for first-generation tidal turbine technology are adequate. In this case, consider that the usable segment of the water column, z, stays between 0.25z above the bay bottom and 3 m below the MLWS, mean low water springs, in harbor areas, or 7 m below MLWS in open coastal areas vulnerable to high-wind waves. 7. Areas with a tidal current field that reverses along a defined axial direction are more suitable for turbine installations than regions with currents without preferable direction. 8. Even though seabed composition directly affects foundation design, it is not taken into account in this paper. In this study, a fixed bottom is assumed, which means that turbine arrays do not affect bathymetry contours. Seabed erosion is an issue to be

153

154

Tidal Energy Systems

considered in a subsequent study. In a future investigation, environmental, useconflict, and commercial feasibility constraints should be considered to identify appropriate zones and quantify power yield amounts where TEC could be installed. A number of interesting points were made with respect to the level of detail, accuracy, and limitations of the power capture, take off, and conversion parameters evaluated: • Conservative design assumptions should be used to avoid overly optimistic technology evaluations. • Sensitivities in flow velocity make for large differences in performance evaluations. • Effects of surface waves and turbulence are noted as being difficult to quantify both in real terms and in terms of power output. • Complexities in scaling accurately (subsequently noted with scaled models). • The entire system should be optimized as a whole to determine all primary design sensitivities. • To aid accurate evaluation and costing even at the earliest stages, advice and data from expert equipment manufacturers should be used where possible.

3.3.4 Functional Physical Boundaries of Assessment The configuration of the tidal energy electrical connection is selected to fulfill the following objectives: • Connect the offshore marine energy generators to the onshore electrical grid for transmission of the generated electrical power into the general grid system (export power). This may include the interconnection of an array of physically spaced generators, as in an offshore wind farm. • Where required, connect the offshore marine energy device to the onshore electrical grid for the supply of the marine energy device auxiliary electrical loads (import power). • Where required, connect the offshore marine energy device to the onshore electrical grid for the supply of electrical power to energies and start up of the marine energy device (peak import power). • Ensure that all equipment is being operated within its voltage and current limits throughout the power range of the marine energy farm and over the range of operation of the grid. • Ensure that all equipment operates stably and predictably during individual generator start up and during minor grid disturbances. • Ensure that the protection systems operate correctly and safely isolate faulty equipment. • Ensure that any adverse effects of the marine energy generators on the electrical grid are remedied according to the local grid connection requirements. • Ensure that grid support is provided as defined by the local utility in its grid connection requirements.

Prefeasibility Assessment of a Tidal Energy System

• Minimize energy losses in transmission of electrical energy back to shore. • Minimize the capital cost of the overall (onshore and offshore) connection to the grid. • Facilitate economic operation and maintenance of the marine energy farm in terms of isolation and access for maintenance and connection/disconnection of devices. • Maximize reliability of the grid connection. • Minimize down time of generators during routine operational procedures (e.g., device maintenance) and following failures of the electrical connection (e.g., due to grid disturbances).

3.4 STATIC V/S TRANSECT FIELD SURVEY Prefeasibility assessment and physical boundary assessment are done in different ways. It is the primary step of resource assessment but it is also classified into two broad categories: static survey and transect field survey. Fig. 3.20 shows types of field surveys. A transect field survey shows a broad analysis of resource assessment based on geographical data. It is a path along which one counts and records occurrences of the tidal current or low and high tides at particular time intervals. It requires an observer to move along a fixed path of coastal area and to count occurrences along that path and, at the same time, obtain the distance of the tidal energy generating station from that coastal area. A transect field survey also is a part of the probability assessment of resource parameter calculation and quantifying results in an estimate of the coastal area covered. It is also an estimate of the way in which detection ability increases from probability 0 to 1, where 0 shows a particular coastal area is not suitable to tidal energy generation and 1 means a coastal area is suitable to tidal electricity generation. Using the raw count measurement and this probability function, one can arrive at an estimate of the actual tidal current density of a coastal area. In the field of tidal energy systems, the aim of a transect survey is to provide an overview of the spatial variation in the velocity distribution over the site. This also allows validation of the spatial variation of the peak velocity estimated by the model used at this stage. Furthermore, the transect survey can help to evaluate the turbulence

Field survey

Static field survey

Fig. 3.20 Types of field surveys.

Transect field survey

155

156

Tidal Energy Systems

and flow reversal issues that can be associated with the site. On the other hand, a static field study is alleged in light of the fact that it comprises the sending of an estimation gadget at a site, either coasting or moored on the seabed. In the event that a static field study has been completed, and if the transects secured the static area, an examination of the outcomes ought to be utilized to check that the picked static area is illustrative of the general site under scrutiny and to confirm the nature of the two studies. To develop a concept for a commercial-scale tidal power plant, software runs were made for individual transect or cross-sections of the study area: X1 dP i ¼ (3.22) ρvz3 f 2 z where dPi ¼ density of tidal current power for each grid element (kW/m2), ρ is the sea water density (1022–1025 kg/m3), vz is velocity at a different frequency, and f is frequency distribution at a velocity. Transect measurements can be made manually or by geographical information system (GIS). The advantage of digitizing transect surveys of a tidal resource assessment in GIS is that it allows for the systematic measurement of spatial and temporal coastal channel changes without introducing the bias that typically occurs from manually measuring specific features, such as coastal channel bends. Step 1: Scan and register coastal tidal current sensing data (aerial photographs, maps) into GIS and rectify the data according to the requirement. Step 2: Identify locations of the active channel transect and floodplain transects of the coastal area that is used for tidal energy generation and these two transects are used in conjunction. The active channel transect is the entirety of the widths of the currently streaming channels in addition to the unvegetated bars. The floodplain transect is characterized as the Holocene valley base, which can be recognized utilizing geography maps and DEMs or LiDAR (Holocene is characterized as the day and age incorporating the most recent 8000 years to the present). Floodplain transects and dynamic channel transects stay stationary for each arrangement of information when following rates and headings of channel movement after some time. The transects ought to describe the applicable highlights, for example, horizontal relocation focuses, statement (bars), and side stations for all years. Step 3: Digitized floodplain transects perpendicular to the centerline of the coastal area of particular area. These transects are used to measure and delineate broadscale attributes, such as channel sinuosity, valley width, active channel width(s), location of the primary active channel, locations of historical channels, and secondary channels Step 4: Digitize active channel transects perpendicular to the centerline of the primary low-flow channel at discrete increments scaled to the size of the channel.

Prefeasibility Assessment of a Tidal Energy System

Active channel transects are utilized to measure the rate and bearing of channel development and to figure disintegration, statement, and separation over the period being referenced. Estimations are taken starting with one informational collection then on to the next figure rates and bearings of channel development through the span of the course of events being considered. Step 5: Overlay the centerline of the active channel transects with the centerline of the floodplain transects. For each transect, measure: • Width and area of the primary low-flow channel and the width, area, and number of other connecting channels, such as side channels. • Width and area of unvegetated gravel bars (e.g., filled-in side channels or sloughs), width and area of vegetated patches on gravel bars (vegetation that cannot resist flooding), width and area of permanently vegetated islands, and width and area of the floodplain with high flow and relic channels. Width and area of isolated (from the main channel) or partly isolated water bodies (e.g., oxbow lakes). Isolated or partly isolated water bodies are defined by their connectivity to the primary lowflow channel. Isolated water bodies are disconnected at both ends whereas partly isolated water bodies are only disconnected at one end. Width and area of LWD debris where visible. • Time Series: This kind of information is accumulated and introduced in a “time arrangement.” Tidal stream information is generally gathered at various statures circulated routinely through the water segment, contingent upon the estimation sensor. The normal estimation sensor for this application is the acoustic profiler (see underneath). The information might be displayed as size and course matches, or as orthogonal stream parts. Orthogonal streams thus might be displayed as (east, north) values, or in shaft bearings in respect to the instrument introduction. The Doppler tests spot stream rates, and a progression of these ought to be arrived at the midpoint of a reasonable time scale for important outcomes. For beginning efforts, an averaging administration of hourly esteems might be reasonable. However, for definite data, a normal example of 10 min ought to be utilized. Consideration ought to be paid to the possible exactness of the estimations with respect to the quantity of pings found in the middle value. Points of interest ought to be affirmed in the sensor’s specialized reference.

3.4.1 Quantitative Observations Through Static and Transect Survey • Set up a string transect line stretching out from the mean high water level down to the water’s edge at low tide. In the event that your transect line is not sufficiently long to achieve the water’s edge, you should move it down the shore, monitoring the flat separation from the mean high water level. The transect line should be secured at each end. • If the transect does not include any tide pools, several pools should be located and examined at another location.

157

158

Tidal Energy Systems

• Use a plastic quadrats sampler to delineate study quadrats at 1 m intervals along your transect. The quadrats sampler should be placed on one side or the other of the transect line at the meter marks—place the sampler on the same side of the line each time. • Within each study quadrat, estimate the percent of surface area covered by attached organisms, that is, encrusting coralline algae, algal mats, foliose algae, and invertebrates. For free-living invertebrates such as snails, crabs, etc., count the total number within the quadrat. Qualitative Observations (Roving Surveys) • Examine the distribution of algae and invertebrates as a function of height (relative to mean high water level) on the large rock outcrops at the study site. • Examine some large tide pools in the vicinity and make general observations about the diversity and abundance of flora and fauna. If tide pools were examined along your transect, compare the various pools with respect to size, position on the shore, and diversity and abundance of organisms. Data Analysis 1. Depict any watched contrasts in the wealth (e.g., numbers per unit region) and assorted variety of living beings as an element of flat and vertical position on the shore. 2. Describe the species composition of your tide pools, and relate this to the physical characteristics of the pools (location, area, depth, time of exposure). Be sure to distinguish between organisms that are true intertidal residents and subtidal residents that seek refuge in tide pools during low tide. 3. Your analysis should consider the importance of physical–chemical factors (e.g., wave action, duration of exposure to air, temperature, salinity, etc.) and biological factors (e.g., competition, predation, etc.) in determining the abundance, diversity, and distribution of organisms on rocky intertidal shores. 4. Compare your findings to observations you make on intertidal zones elsewhere on San Salvador. What conclusions can you draw about the biogeography and ecology of intertidal organisms found on San Salvador? 5. Compare your findings to those in published studies of rocky shores in other areas of the greater Caribbean. What conclusions can you draw about the biogeography and ecology of intertidal organisms found on San Salvador? The primary objective of the study was to collect tidal data as profiles of current velocity and direction along selected transects in a study area. Tidal current data collection consisted of two techniques: (1) Spatial surveys (a series of parallel transect lines). (2) Occupation of fixed stations at entrance channels of about 30–45 min each. Measurements were taken during the ebb and flood phases of the tide. The observations were presented as vector maps for the spatial surveys showing vertically averaged

Prefeasibility Assessment of a Tidal Energy System

tidal current arrows representing speed and direction, or as time series graphs for fixed-station observations separated into near-bottom and near-surface flow.

3.4.2 The Challenge of Measuring Water Currents The primary essential condition is that ebb and flow estimations are a test to get is the way that to convey and keep up a momentum meter is somewhere in the range of four to ten times as costly to do as comparable exercises to quantify water levels. This has critical ramifications for the quality and expansiveness of current perceptions and tidal current forecasts accessible today to the nation’s sailors. This expanded cost can be promptly valued by taking note of a couple of sharp complexities between the conduct of water levels and streams. Water level is moderately the same over a wide region; in this manner, water level estimations can be produced using the relative comfort of dry land along an adjacent shoreline. The variation in tidal current speed and change in tidal altitude can be exceptionally restricted, shifting incredibly finished short separations as base shapes and shoreline design adjust both the present’s speed and bearing of stream and also turning off whirlpools. Given these conditions, in the event that you wish to know the current at a specific area in the strait or channel, you should leave the solace of the shore and acknowledge the cost and bear the push to put your instrument precisely “there” or play out a parallel estimation to assess being precisely “there.” Getting “there” lights up additionally challenges. One can stack the workings of a water level station (tide house, water level sensor, hardware, etc., all esteemed at about $15,000) into a vast truck and drive to your favored shoreline area for a couple of hundred dollars each day. Establishment is done for the most part from the well-being and working comfort of dry land. By differentiating, the hardware and organization of current measuring gadgets is more costly and included. In the first place, the hardware to gauge streams (current sensor, gadgets and different base stays, links and buoys, and so on) is esteemed at about $40,000. Next, your truck will just get you to the ship’s dock. You and your equipment should be out on and in the water and the vessel to do that will ordinarily cost a few thousand dollars for every day. Staying “there” sufficiently long to get an important perception uncovers extra difficulties. The majority of the segments of a water level measuring framework are on dry land and consequently subject to moderate consumption and weathering. Routine upkeep on such an establishment commonly happens once every year. The majority of the ebb and flow measuring framework is regularly in salt water and therefore subject to both quick erosion and fouling by marine development. Such an establishment should routinely be cleaned and examined no less than four times each year. Furthermore, recollect that each visit requires a vessel and jumpers to perform even the least difficult review.

159

160

Tidal Energy Systems

A portion of the swearing off clarifies why the ebb and flow perceptions we do have are of shorter length, at fewer areas, and less breakthrough than we have for water levels. Indeed, persistent current perceptions just started a couple of years prior. Already, current perceptions were ordinarily made for just a couple of days, at most a month, at any area. Persistent water level perception at numerous areas backpedals to the mid-1800s. Also, the greater part of the present perceptions were made such a long time ago that the innovation for estimation, however modern at the time, is very primitive by the present guidelines. Also, as expressed above, streams are firmly impacted by neighborhood conditions and can change in sensational and obscure ways when those nearby conditions change. Actually, such changes happen constantly. For instance, shipping channels are dug further and more extensively, or regular procedures move sand bars or reshape the base. These progressions will modify the present quality and course in obscure ways and tidal current expectations and conjectures in view of more established perceptions are in any event faulty and may never again be substantial. The best way to know without a doubt is to reoccupy the site and mention new current objective facts.

3.5 LOCATION ASSESSMENT BY FARM METHOD The first method, called the farm method, should be used to calculate the energy generated by an array by simply multiplying the electrical energy output for each TECS by the number of TECS that could be installed, or by calculating the electrical energy output of each TECS and summing the results. The farm method for estimating energy extraction using a tidal stream farm is based on the concept of an array of tidal stream devices, each of which extracts an amount of energy related to the incoming energy. The resulting extracted energy is therefore purely dependent on the size and number of the devices, the conversion efficiency, and the packing density within the site area. The total resource estimated by the farm method shall be calculated simply by adding the Pmean divided by ηPT of each device that can be installed in the area. In the following equation, n is an index that represents a tidal energy conversion system. Pfarm ¼

Nr X n¼1

Pmean ðnÞ

. ηPT

ðnÞkW

(3.23)

To estimate the resource at a site with the farm method, one should first determine the size of the farm that could potentially be installed in the selected area in order to estimate the number of turbines that can be installed and the farm output power. To compute economic load division between tidal plant units, it is necessary to express the operating costs in terms of output. For the tidal turbine or tidal generator, the input is expressed in kJ per hour and the output or load in MW. In a tidal power plant, input will be in terms of m3/s of water flow and output in MW.

Prefeasibility Assessment of a Tidal Energy System

Efficiency measurement through this method is given by Output in MW  1000  100 Input in kJ per second

(3.24)

Output in MW  1000  3600  100 Input in kJ per hour

(3.25)

Efficiency ¼ Efficiency ¼

Input in kilojoules perkWh: Heat rate is defined as the ratio of the input to the output: Output In the input-output characteristics, if input is expressed in kJ/h and output in MW, the slope of the curve gives the incremental fuel rate in kJ/MWh and if the input is expressed in Rs per hour, the slope of curve gives the incremental fuel cost in Rs./MWh. Some basic points to be considered in resource assessment by the farm method: Maximum rotor diameter: A reasonable diameter is to be considered, dependent on the state of the technology. The diameter is believed to be currently limited to c. 20–25 m for a standard horizontal axis turbine. Top clearance: A top clearance (for the capture area of the rotor or equivalent) should be considered—whether or not the location considered is deemed suitable for surface breaking TECS. A minimum 5 m top clearance is normally recommended to allow for recreational activities (small boats, swimmers, etc.), and to minimize turbulence and wave-loading effects on the TECS as well as damage from floating materials. This is based on the assumption that an exclusion area could be created that (among other restrictions) restricts vessels that have a draught greater than 2 m. If this is not possible, then the top clearance should be based on known vessel movements in the area. Bottom clearance: It is recommended that a bottom clearance of 25% of the water depth or 5 m, whichever is greater, should be considered as a minimum to allow for potentially TECS-damaging materials that are moved along the seabed by the currents, and to minimize turbulence and shear loading from the bottom boundary layer. Three hydrodynamic mechanisms that result in tidal current conditions necessary for large-scale tidal current arrays are considered. These are: • Tidal streaming: Tidal streaming is the physical response of the tidal system to maintenance of the continuity equation; when a current is forced through a constriction, the flow must accelerate. • Hydraulic current: If two adjoining bodies of water are out of phase, or have different tidal ranges, a hydraulic current is set up in response to the pressure gradient created by the difference in water level between the two bodies. • Resonant system: Resonant systems occur as a consequence of a standing wave being established. A standing wave arises when the incoming tidal wave and a reflected tidal wave constructively interfere.

161

162

Tidal Energy Systems

3.5.1 Tidal Optimal Unit Using Dynamic Programming Method In normal practice, the number of tidal power unit installations at a particular site is analyzed for a complete demand cycle. Further, it is assumed that the load on each unit or combination of unit charges in a suitable but uniform step of size ΔPTLMW Let a cost function of tidal power plant Tn(y) be defined below: TN(y) ¼ the minimum cost in Rs/h of generating y MW by N units TN(z) ¼ Cost of generating z MW by the Nth unit TN-1(y  z) ¼ the minimum cost of generating (y  z) MW by the remaining (N 1) units The application of dynamic programming results in the following recursive relation: TN ðyÞ ! ftN ðzÞ + tN 1 ðy  zÞg Here the value of z is varied from minimum load level to the maximum load level in the discrete steps of ΔPTL providing a set of values of the expression {tN(z) + tN-1(y  z)}. The minimum of these values is the optimum value of tN(y). Q.1 The input-output curve of a 20 MW tidal power generating station is given by the following equation: I ¼ (7.5 + 0.125P + 0.16 L2)  106 where I is in kcal/h and P is in MW. Find the average heat rate of a tidal power station for a day when it was operating at a load of 20 MW for 16 h and was kept hot at zero for the remaining 8 h. Find the saving in the heat rate if the same energy is produced from the tidal power plant for the whole day at 100% load factor. Solution: from given data I ¼ (7.5 + 0.125P + 0.16L2)  106 Heat input per hour for full load of 20 MW,   I1 ¼ 7:5 + 0:125  20 + 0:16  202  106 ¼ 74  106 kcals Heat input per hour for zero load,   I0 ¼ 7:5 + 0:125  0 + 0:16  02  106 ¼ 7:5  106 kcals Total input per day ¼ I1  16 + I0  8 ¼ 74  106  16 + 7:5  106  8 ¼ 1:244  106 kcals Total units generated per day ¼ 20  16 + 0  8 ¼ 320 MWh Average heat rate ¼

Total input 1:244  106 ¼ 3887:5 kcals=kWh ¼ Total output 320  103

Prefeasibility Assessment of a Tidal Energy System

In the case when the same energy is produced at 100% load factor in 24 h Total units generated per day 320 ¼ ¼ 13:33 MW 24 24 Heat input per hour for 13.33 MW load   I ¼ 7:5 + 0:125  13:33 + 0:16  13:332  106 Average Load ¼

37:6  106  24 ¼ 2820 kcals=kWh 13:33  103  24 Now saving in heat rate ¼ 3887:5  2820 ¼ 1067:5 kcal=kWh Now heat rate ¼

Q.2 An input output curve of a 10 MW tidal power plant is given by an equation I ¼ (18 + 12P + 0.5P2)  106kcal/h where I is in kcal per hour and P is load on the power plant in MW, find (i) The load at which the efficiency of the plant will be maximum and (ii) The increase in input required to increase the tidal station output from 5 MW to 7 MW by using the input-output equation and by the incremental rate curve. Solution: (i) Let the maximum efficiency be at a load of y MW. So Output ¼ y  1000  3600 ¼ 3:6  106 y kJ=h   Input ¼ 18 + 12y + 0:5x2  106  4:18 kJ=h Efficiency η ¼

Output 3:6  106 y ¼ Input ð18 + 12y + 0:5y2 Þ  106  4:18 0:86y ¼ 18 + 12y + 0:5y2

Differentiate both sides of the above equation w.r.t.y, we have dη ð18 + 12y + 0:5y2 Þ  0:86  0:86yð12 + yÞ ¼ dy ð18 + 12y + 0:5y2 Þ2 ¼

0:86ð18  0:5y2 Þ ð18 + 12y + 0:5y2 Þ2

2 Efficiency will be maximum when dη dy ¼ 0 or 18  0.5y ¼ 0 or y ¼ 6 MW (ii) Input required for a load of 7 MW   ¼ 18 + 12  7 + 0:5  72  106 ¼ 126:5  106 kcal=h

Input required for a load of 5 MW   ¼ 18 + 12  5 + 0:5  52  106 ¼ 90:5  106 kcal=h

163

164

Tidal Energy Systems

So the required increase in input ¼ 126:5  106  90:5  106 ¼ 36  106 kcal=h Incremental rate of the plant is given by IR ¼

 dI d  ¼ 18 + 12P + 0:5P 2  106 dP dP ¼ ð12 + P Þ  106 kcal=MWh

Load in MW

Incremental rate in kcal/MWh

2 4 6 8 10

(12 + 2)  106 ¼ 14  106 (12 + 4)  106 ¼ 16  106 (12 + 6)  106 ¼ 18  106 (12 + 8)  106 ¼ 20  106 (12 + 10)  106 ¼ 22  106

Average incremental rate ¼ 18  106 kcal=MWh So the required increase in input for an output from 5 MW to 7 MW 18  106  ð7  5Þ ¼ 36  106 kcal=h Q.3 The input-output curve of a 20 MW tidal power generating station is given by the following equation: I ¼ (7.5 + 0.125P + 0.16P2)  106 where I is in kcal/h and P is in MW. Find the average heat rate of a tidal power station for a day when it was operating at a load of 20 MW for 16 h and was kept hot at zero for the remaining 8 h. Find the saving in the heat rate if the same energy is produced from a tidal power plant for the whole day at 100% load factor. Solution: from given data I ¼ (7.5 + 0.125P + 0.16L2)  106 Heat input per hour for full load of 20 MW,   I1 ¼ 7:5 + 0:125  20 + 0:16  202  106 ¼ 74  106 kcals Heat input per hour for zero load,   I0 ¼ 7:5 + 0:125  0 + 0:16  02  106 ¼ 7:5  106 kcals Total input per day ¼ I1  16 + I0  8 ¼ 74  106  16 + 7:5  106  8 ¼ 1:244  106 kcals

Prefeasibility Assessment of a Tidal Energy System

Total units generated per day ¼ 20  16 + 0  8 ¼ 320 MWh Average heat rate ¼

Total input 1:244  106 ¼ 3887:5 kcals=kWh ¼ Total output 320  103

In the case when the same energy is produced at 100% load factor in 24 h Total units generated per day 320 ¼ ¼ 13:33 MW 24 24 Heat input per hour for 13.33 MW load   I ¼ 7:5 + 0:125  13:33 + 0:16  13:332  106 Average Load ¼

37:6  106  24 ¼ 2820 kcals=kWh 13:33  103  24 Now saving in heat rate ¼ 3887:5  2820 ¼ 1067:5 kcal=kW Now heat rate ¼

Q.4 The input-output curve of a 10 MW tidal power generating station is given by the following equation: I ¼ (7.5 + 0.125P + 0.16P2)  106 where I is in kcal/h and P is in MW. Find the average heat rate of the tidal power station for a day when it was operating at a load of 10 MW for 16 h and was kept hot at zero for the remaining eight hours. Find the saving in the heat rate if the same energy is produced from the tidal power plant for the whole day at 100% load factor. Solution: from given data I ¼ (7.5 + 0.125P + 0.16P2)  106 Heat input per hour for full load of 20 MW,   I1 ¼ 7:5 + 0:125  10 + 0:16  102  106 ¼ 24:75  106 kcals Heat input per hour for zero load,   I0 ¼ 7:5 + 0:125  0 + 0:16  02  106 ¼ 7:5  106 kcals Total input per day ¼ I1  16 + I0  8 ¼ 24:75  106  16 + 7:5  106  8 ¼ 0:456  106 kcals Total units generated per day ¼ 10  16 + 0  8 ¼ 160MWh Average heat rate ¼

Total input 456  106 ¼ 1425 kcals=kWh ¼ Total output 320  103

In the case when the same energy is produced at 100% load factor in 24 h Average Load ¼

Total units generated per day 160 ¼ ¼ 6:67 MW 24 24

165

166

Tidal Energy Systems

Heat input per hour for 6.67 MW load   I ¼ 7:5 + 0:125  6:67 + 0:16  6:672  106 Now heat rate ¼

15:45  106  24 ¼ 2316 kcals=kWh 6:67  103  24

Now saving in heat rate ¼ 2316  1425 ¼ 891 kcal=kWh Q.5 The input-output curve of a 20 MW tidal power generating station is given by the following equation: I ¼ (5 + 0.125P + 0.25L2)  106 where I is in kcal/h and P is in MW. Find the average heat rate of the tidal power station for a day when it was operating at a load of 20 MW for 16 h and was kept hot at zero for the remaining 8 h. Find the saving in the heat rate if the same energy is produced from the tidal power plant for the whole day at 100% load factor. Solution: from given data I ¼ (5 + 0.125P + 0.25L2)  106 Heat input per hour for full load of 20 MW,   I1 ¼ 5 + 0:125  20 + 0:25  202  106 ¼ 100  106 kcals Heat input per hour for zero load,   I0 ¼ 5 + 0:125  0 + 0:25  02  106 ¼ 5  106 kcals Total input per day ¼ I1  16 + I0  8 ¼ 100  106  16 + 5  106  8 ¼ 1:640  106 kcals Total units generated per day ¼ 20  16 + 0  8 ¼ 320 MWh Average heat rate ¼

Total input 1:640  106 ¼ 3125 kcals=kWh ¼ Total output 320  103

In the case when same energy is produced at 100% load factor in 24 h Total units generated per day 320 ¼ ¼ 13:33 MW 24 24 Heat input per hour for 13.33 MW load   I ¼ 5 + 0:125  13:33 + 0:25  13:332  106 Average Load ¼

51:08  106  24 ¼ 3832 kcals=kWh 13:33  103  24 Now saving in heat rate ¼ 3831  3125 ¼ 706 kcal=kWh Now heat rate ¼

Q.6 The input-output curve of a 20 MW tidal power generating station is given by the following equation: I ¼ (7.5 + 0.125P + 0.16L2)  106 where I is in kcal/h and P is

Prefeasibility Assessment of a Tidal Energy System

in MW. Find the average heat rate of the tidal power station for a day when it was operating at a load of 20 MW for 14 h and was kept hot at zero for the remaining 10 h. Find the saving in the heat rate if the same energy is produced from the tidal power plant for the whole day at 100% load factor. Solution: from given data I ¼ (7.5 + 0.125P + 0.16L2)  106 Heat input per hour for full load of 20 MW,   I1 ¼ 7:5 + 0:125  20 + 0:16  202  106 ¼ 74  106 kcals Heat input per hour for zero load,   I0 ¼ 7:5 + 0:125  0 + 0:16  02  106 ¼ 7:5  106 kcals Total input per day ¼ I1  14 + I0  10 ¼ 74  106  14 + 7:5  106  10 ¼ 1:111  106 kcals Total units generated per day ¼ 20  14 + 0  10 ¼ 280 MWh Average heat rate ¼

Total input 1:111  106 ¼ 3967 kcals=kWh ¼ Total output 280  103

In the case when same energy is produced at 100% load factor in 24 h Average Load ¼

Total units generated per day 280 ¼ ¼ 11:67 MW 24 24

Heat input per hour for 11.67 MW load   I ¼ 7:5 + 0:125  11:67 + 0:16  11:672  106 Now heat rate ¼

30:74  106  24 ¼ 2634 kcals=kWh 11:67  103  24

Now saving in heat rate ¼ 3967  2634 ¼ 1333 kcal=kWh Q.7 An input-output curve of a 15 MW tidal power plant is given by an equation I ¼ (18 + 12P + 0.5P2)  106 kcal/h where I is in kcal per hour and P is load on the power plant in MW, find (i) The load at which the efficiency of the plant will be maximum and (ii) The increase in input required to increase the tidal station output from 7 MW to 10 MW by using the input output equation and by the incremental rate curve. Solution: (i) Let the maximum efficiency be at a load of y MW. So Output ¼ y  1000  3600 ¼ 3:6  106 y kJ=h

167

168

Tidal Energy Systems

  Input ¼ 18 + 12y + 0:5x2  106  4:18 kJ=h Efficiency η ¼

Output 3:6  106 y ¼ Input ð18 + 12y + 0:5y2 Þ  106  4:18 0:86y ¼ 18 + 12y + 0:5y2

Differentiate both sides of the above equation w.r.t.y, we have dη ð18 + 12y + 0:5y2 Þ  0:86  0:86yð12 + yÞ ¼ dy ð18 + 12y + 0:5y2 Þ2 ¼

0:86ð18  0:5y2 Þ ð18 + 12y + 0:5y2 Þ2

2 Efficiency will be maximum when dη dy ¼ 0 or 18  0.5y ¼ 0 or y ¼ 6 MW (ii) Input required for a load of 10 MW   ¼ 18 + 12  10 + 0:5  102  106 ¼ 188  106 kcal=h

Input required for a load of 7 MW   ¼ 18 + 12  7 + 0:5  72  106 ¼ 126:5  106 kcal=h So required increase in input ¼ 188  106  126:5  106 ¼ 61:5  106 kcal=h Incremental rate of the plant is given by IR ¼

 dI d  ¼ 18 + 12P + 0:5P 2  106 dP dP 106 kcal ¼ ð12 + P Þ  MWh

Load in MW

Incremental rate in kcal/MWh

2 4 6 8 10

(12 + 2)  106 ¼ 14  106 (12 + 4)  106 ¼ 16  106 (12 + 6)  106 ¼ 18  106 (12 + 8)  106 ¼ 20  106 (12 + 10)  106 ¼ 22  106

Average incremental rate ¼18  106 kcal/MWh So required increase in input for an output from 7 MW to 10 MW 18  106  ð10  7Þ ¼ 54  106 kcal=h

Prefeasibility Assessment of a Tidal Energy System

3.6 RESOURCE ASSESSMENT BY FLUX METHOD Pflux ¼ APD:Achannel ðkWÞ   APD ¼ Avg:power density kW=m2   AChannel ¼ Cross sectional area of channel m2

(3.26)

Depending on the stage of assessment, the Pflux shall be calculated across the crosssectional area as accurately as possible. If a different velocity distribution is available in several grid cells for the cross-sectional area considered, then the annual average kinetic power flux should be calculated for each cell, where APD is then calculated with the velocity distribution averaged over the cross-sectional area of the cell as below: Pfuelcell ¼ APDdcell :wcell

(3.27)

dcell ¼ Depth of the cell ðmÞ;wcell ¼ Width of the cell ðmÞ The total power flux through the site (Pflux) is then obtained by summing the power flux calculated for each cell across the site along a line perpendicular to the main flow direction. The annual average power is then the product of the power flux passing through the site and the significant impact factor. Pavailable ¼ Pflux :SIF ðkWÞ

(3.28)

The SIF represents the percentage of the total resource at a site that can be extracted without significant economic or environmental effects. There is clearly only a percentage of the total energy in a site that can be extracted without significant alteration to flow speed. Alteration to flow speed has an important effect on the economics of energy generation in addition to possible environmental impacts. In channels where the flow is governed by a head difference at either end of the channel, and the flow cannot affect the tidal elevation in the bodies of water at either end, significant effects on the flow can be noted when this percentage is around 10%. Other modeling by RGU has suggested that in areas where the flow has more freedom within its elevation boundary conditions, up to 50% extraction could be possible without significant effects. It is important to note that these percentages are based on theoretical modeling results, which have yet to be validated by physical experiment. Given the presently limited understanding of the SIF, and the current research on this critical issue, this document cannot give a methodology to calculate the SIF for a site. As a minimum, the power available calculated with the flux method can be compared with the power extractable obtained with the farm method, to verify that the power extractable is not more than 50% of the power available. An alternative part of the flux method is one in in which the output energy of the tidal power plant is represented by the potential energy during one tide

169

170

Tidal Energy Systems

cycle. Therefore, the flow and heads usually used by a hydraulic power plant can not be adopted as an index for a tidal power plant, but the tidal basin area and tidal range. This method assumed no gradient of water surface for the basin side during flood or ebb, namely the entire basin surface rises and falls concurrently, and instantly fills and drains the basin. For the regular semidiurnal tide, the energy during one tidal cycle is proportional to the square of average tidal range and basin area. Its averaged generation capacity and annual power theory can be calculated by the following equation: N ¼ 225A2 F E ¼ 1:97  106 A2 F N is mean power, A means tidal range, F is basin area km2, and E is annual electricity. Obviously, the power and annual electricity for the diurnal tide will decrease to half of the semidiurnal tide because of one time cycle of flood-ebb fluctuation, of which the equation can be described in the following equation:   15  2γ 2 N ¼ 0:5  225H F (3.29) 7   15  2γ 6 2 E ¼ 1:97  0:5  10 H F (3.30) 7 where γ is the tidal farm ratio. Vertical normal modes: In an ocean of finite depth, the internal tide generation problem can be tackled by projecting the vertical structure of the physical variable onto vertical modes depending only on the vertical profile of the buoyancy frequency N(z). The boundary condition imposed at the sea surface (z ¼ 0) and the sea floor (z ¼ –H) d 2 an + Cn2 N 2 an ¼ 0,an ð0Þ ¼ an ðH Þ ¼ 0 (3.31) dz2 where index n denotes the node number, C2 n is the eigen value, and an is the eigen function. Physically speaking, Cn is the eigen speed of the mode n internal wave. Furthermore the orthogonally relation for a set of an terms is given by ð0 an ðzÞam ðzÞN 2 ðZ Þdz ¼ IfICn δmn H

where f is the Coriolis parameter and δmn is the kronecker matrix. We define the horizontal wave number associated with the mode n as follows: pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ω2  f 2 Kn ¼ (3.32) Cn

Prefeasibility Assessment of a Tidal Energy System

where ω is the frequency of the barotropic tidal constituents, finally a dimensionless Cn a0n ðH Þ quantity Sn is defined as Sn ¼ where a0n ðzÞ ¼ dan dz f For the case of uniform stratification (N ¼ Const.), an can be readily evaluated analytically. In this case Kn and Sn are given by pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi nπ 2 N , (3.33) Kn ¼ ω2  f 2 NH nπ f Horizontal wave number Kn and nondimensional constant S2n are used in the calculation of energy conservation rate for the mode n denoted by Cn. The consensus has been basically reached on the calculation formula of the flux conservation of tide energy theory that is the average power of the tidal current energy passing some cross-section of the water channel. The specific calculation formula is: ð ð ð ρ t+T L 0 P¼ V 3 dzdxdt (3.34) 2T t 0 H where P is the theoretical potential of tidal current energy, t is the initial moment, T is the assessment period (1 year), L is the width of the water channel, H is the depth of water, and ρ is sea water density (1025 kg/m3). One of our objectives is to assess the time variability associated with observed depth and the integrated energy dissipation from the microstructure measurement. Hence the temporal behavior Of the vertical energy flux at the bottom needs to be calculated. The time-dependent vertical energy flux is defined as C  PW, where P and w are the bottom pressure perturbation and vertical velocity resulting from the interaction of the barotropic tidal current with bottom topography, respectively. A time-independent expression of the vertical energy flux is also used based on Nycander (2005). The calculation is based on linear wave theory, which is valid for subcritical slopes ffi. pffiffiffiffiffiffiffiffiffi 2 2 rh  ω f pffiffiffiffiffiffiffiffiffiffiffi , where ω is the tidal frequency, N the buoyancy frequency, 2 2 N ω

and f the Coriolis parameter. Horizontal averaging of the energy flux was performed using a Gaussian filter with an e-folding scale of αγM2/2, applied to all the model grid points located within a radius αγM2 around each observation point. Here, α is a dimensional coefficient and γ M2 is the cutoff length of the M2 tidal constituents as defined by Nycander. ð0 1:455 γM2 ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi N ðzÞdz (3.35) π ω2M2  f 2 H

171

172

Tidal Energy Systems

where H is the total ocean depth, γM2 is proportional to the horizontal wavelength of the first internal wave mode and is typically a few tens of km or less. The vertical energy flux time series were also averaged in time such that ð 1 t0 bs Cdt (3.36) CΔt ¼ Δt t0 bs Δt where t0bs are the time of observation and Δt the time averaging interval. The dissipation rate measurement was integrated vertically at each station: ð H + ΔH ρEdz (3.37) DΔH ¼ H + ΔH0

where ΔH0 was set to a constant so as to make the different stations more comparable to one another.

3.6.1 Maximum Steady-State Power Through Tidal Power Station If we consider the receiving end voltage UR ∠0 and sending end voltage US ∠δ where δ is the phase angle between sending and receiving end voltage, let the generalized line constant be given by


 A B UR US ¼ (3.38) C D IR IS A ¼ A∠α; B ¼ B ∠β; D ¼ D∠Δ The input voltage per phase and the input current of a transmission line can be expressed as US ¼ AUR + BIR IS ¼ CUR + DIR The complex power at the receiving end is given by the expression SR ¼ PR + JQR ¼ UR IRC

(3.39)

where IRC is the conjugate of the receiving end current IR Complex power at the receiving end is given by US UR A ∠β  δ  UR2 ∠β  α B B Separating real and reactive power components, we have Receiving end power, SR ¼ PR + jQR ¼

PR ¼

US UR A cos ∠β  δ  UR2 cos ∠β  α B B

(3.40)

(3.41)

Prefeasibility Assessment of a Tidal Energy System

US UR A (3.42) sin∠β  δ  UR2 sin∠β  α B B For fixed values of US and UR, the power received will be maximum when cos(β  δ) ¼ 1 or when β ¼ δ QR ¼

US UR A 2  UR cos ∠β  α B B Sending end power of the tidal power plant is given by PRmax ¼

D 2 US UR ∠β + δ U ∠β  Δ  B B S Separating real and reactive components, we have sending end true power SS ¼ PS + jQS ¼

D 2 US UR cos ∠β + δ US cos ∠β  Δ  B B And sending end reactive power D US UR QS ¼ US2 sin∠β  Δ  sin ∠β + δ B B For fixed values of US and UR, the power sent out will be PS ¼

(3.43)

(3.44)

(3.45)

(3.46)

D 2 US UR (3.47) US cos∠β  Δ + B B These above equations show power measurement of the tidal power plant at the sending side and the receiving side. PSmax ¼

3.6.2 Transmission Line Analogy of a Tidal Power Plant A transmission line of a tidal power plant consists of two or more parallel conductors, so energy can be transmitted either by the radiation of free electromagnetic waves or it can be constrained to move or carried in various conductor arrangements known as transmission line. Primary Constant of a Transmission Line The four line parameters R, L, C, and G are said to be the primary constants of transmission line. (i) Resistance (R) is the loop resistance per unit length of line; unit is ohms per km or ohms per meter. (ii) Inductance (L) is the loop inductance per unit length of line; unit is Henry per km or ohms per meter. (iii) Capacitance (C) is the shunt capacitance between the two wires per unit line length; unit is Farad per km or Farad per meter.

173

174

Tidal Energy Systems

(iv) Capacitance (C) is the shunt capacitance between the two wires per unit line length; unit is mhos per km or mhos per meter. Secondary Constant of a Transmission Line There are two secondary constants of transmission line of a tidal power plant, PT and ZT, where PT is called the propagation constant of high and low tide while ZT is called the characteristics impedance of high and low tide. sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi rffiffiffiffi R + jωL Z ZT ¼ ¼ G + jωC Y PT ¼

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi pffiffiffiffiffiffiffi ðR + jωL ÞðG + jωC Þ ¼ ZY Z ¼ R + jωL;Y ¼ G + jωC

where Z is the series impedance and Y is the shunt admittance. There are two special cases of a transmission line that is connected through a tidal power plant: (i) Lossless line: For lossless line R ¼ 0, G ¼ 0. So that secondary constant ZT and PT will be sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi rffiffiffiffi R + jωL L ¼ ZT ¼ G + jωC C P ¼ α + jβ ¼

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi pffiffiffiffiffiffiffi ðR + jωL ÞðG + jωC Þ ¼ jω LC

By comparing real and imaginary parts, we get pffiffiffiffiffiffiffi α ¼ 0;β ¼ ω LC Phase value of tidal current vtc ¼

ω ω 1 ¼ pffiffiffiffiffiffiffi ¼ pffiffiffiffiffiffiffi β ω LC LC

(ii) Distortionless line: Condition for distortionless R G ¼ L C sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi   pffiffiffiffiffiffiffi RC P ¼ α + jβ ¼ ðR + jωL Þ + jωC ¼ jω LC L rffiffiffiffi C P ¼ α + jβ ¼ ðR + jωL Þ L

Prefeasibility Assessment of a Tidal Energy System

Comparing real and imaginary parts we get, rffiffiffiffi pffiffiffiffiffiffiffi C α¼R β ¼ ω LC L sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi rffiffiffiffi rffiffiffiffi R + jωL R L ZT ¼ ¼ ¼ G + jωC G C Phase value of tidal current vtc ¼

ω ω 1 ¼ pffiffiffiffiffiffiffi ¼ pffiffiffiffiffiffiffi β ω LC LC

3.6.3 Voltage Regulation of a Tidal Power Plant at a Suitable Site By voltage regulation, we mean the voltage drop between the sending end to the receiving end due to resistance, reactance, skin effect, etc. Voltage Regulation ¼

Sending End Voltage through tidal power plant  Receiving End Volatage Sending end voltage through Tidal Power Plant

The voltage drop in 33 kV and 11 kV feeders should not exceed 5% at the farthest end under peak load condition and a normal system operation regime. However system voltage variation at various voltage levels with on load tap changing at power transformer if necessary should be maintained within the following limits: Above 33 kV 12.5% to +10% Up to 9% to +6% Low voltage 6% to +6%

3.7 PREFEASIBILITY ASSESSMENT WITH DETAILED PROJECT REPORT PREPARATION AND APPRAISAL In the current scenario, the distribution operators are expected to carry out their responsibilities at the least cost and optimum efficiency. The quality of supply and service depends on both the tidal energy generating station and the distribution operators because the tidal energy generation plant plays a key role in active voltage management. There is now a major shift from maintaining and expanding the network based on consumer demand to the concept of detailed project reports (DPRs) that are bankable. Fig. 3.21 shows physical and demographic features of a tidal power plant in DPRs. Fig. 3.22 shows project management of a tidal power plant. Some factors should be kept in mind while preparing DPRs of a tidal power plant: • Planning studies may cover a geographical condition of the study area. • Planning and design of the distribution system should meet load enhancement and ensure voltage conditions to be within permissible limits, optimum energy losses, and the least overall costly system.

175

176

Tidal Energy Systems

Name of tidal power plant Name of distribution circle District/town/village covered Location: latitude and longitude Coastal area and barrage area Population Boundary condition of tidal power plant Climatic condition of study area Status of development Access to electricity Economic structure-socio economic features Predomminantly urban/rural

Fig. 3.21 Physical and demographic features of tidal power plant in DPRs.

Specifying the technical requirements of selected tidal schemes

Analyzing merits of selected tidal scheme

Developing cost estimates of tidal power plant

Assessing benefits of tidal power plant

Estimating payback period and return on investment

Elaborating the impletation plan of tidal power plant

Fig. 3.22 Project management of a tidal power plant.

Prefeasibility Assessment of a Tidal Energy System

• Improvements in reliability, security, and quality of power supply through the tidal power plant. • Ensure safety of operation, evolving a scientific automation, and load management system. • Primary energy audit and energy accounting. • Estimation of transmission and distribution losses, technical power loss reduction, commercial power loss reduction, and improvement of voltage profile. • Mapping of the tidal energy system, data collection, and validation of tidal data. • Tidal technology options including integration of system modernization such as recent advancements of tidal generator technology. • Evaluation of various alternatives for least cost optimal system. Interest during construction (IDC): This is major cost head, second only to basic equipment costs. This was so far not very prominent in power project cost estimates at utilities as the finances were provided by the government. Fig. 3.23 shows a representation of IDC calculations for a tidal power plant.

Total project capital structure Year-1 Debt/equity/ grants Total equity/grant and so on IDC

Phasing≤ grant/equity

Grant/equity /loan IDC = Loan × 50% × Interest in that year Next year

To project cost

From similar cycle as shown above but for current year

Grant/equity /loan

IDC for next year

Fig. 3.23 Representation of IDC calculations for tidal power plant.

177

178

Tidal Energy Systems

With debt financing in the electricity sector a reality and financial institutions becoming major financers, this element will now become a prominent contributor to the project cost. The figure is repeated until the last time period of the construction schedule. Then the entire interest accrued in previous years is summed up as total IDC and added to the project cost like any other component costs.

3.7.1 Simple Payback Period Simple payback period (SPP) represents, as a first approximation; the time (number of years) required recovering the initial investment (first cost), considering only the net annual savings. The simple payback period is usually calculated as follows: Payback Period ¼

First Cost of Tidal Power Plant Yearly Benefits  Yearly Costs

Advantages A widely used investment criterion, the payback period seems to offer the following advantages: • It is simple, both in concept and application. Obviously, a shorter payback period generally indicates a more attractive investment. It does not use tedious calculations. • It favors projects that generate substantial cash inflows in earlier years, and discriminates against projects that bring substantial cash inflows in later years but not in earlier years. Limitations • It fails to consider the time value of money. Cash inflows in the payback calculation are simply added without suitable discounting. This violates the most basic principle of financial analysis, which stipulates that cash flows occurring at different points of time can be added or subtracted only after suitable compounding/discounting. • It ignores cash flows beyond the payback period. This leads to discrimination against projects that generate substantial cash inflows in later years.

3.7.2 Return on Investment (ROI) ROI expresses the “annual return” from the tidal power plant project as a percentage of the plant’s capital cost. The annual return takes into account the cash flows over the project’s life and the discount rate by converting the total present value of ongoing cash flows to an equivalent annual amount over the life of the project, which can then be compared to the capital cost. ROI does not require similar project life or capital cost for comparison. This is a broad indicator of the annual return expected from initial capital investment, expressed as a percentage:

Prefeasibility Assessment of a Tidal Energy System

ROI ¼

Annual Net Cash Flow of Tidal Power Plant  100 Capital Cost of Tidal Power Plant

ROI must always be higher than cost of money (interest rate); the greater the return on investment, the better the investment. Limitations • It does not take into account the time value of money. • It does not account for the variable nature of annual net cash inflows.

3.7.3 Net Present Value of a Tidal Power Plant The net present value (NPV) of a tidal project is equal to the sum of the present values of all the cash flows associated with it. Symbolically: n X CF 0 CF 0 CF n CF t NPV ¼ n¼ t 0 + 0 ……… ð 1 + K Þ ð1 + K Þ ð1 + K Þ t¼0 ð1 + K Þ

where NPV ¼ net present value; CFt ¼ cash flow occurring at the end of year “t” (t ¼ 0,1,2..n). The net present value represents the net benefit over and above the compensation for time and risk. Hence the decision rule associated with the net present value criterion is: “Accept the project if the net present value is positive and reject the project if the net present value is negative.” Advantages: The net present value criterion has considerable merits. • It takes into account the time value of money. • It considers the cash flow stream in its project life.

3.7.4 Internal Rate of Return of a Tidal Power Plant This method calculates the rate of return that in investment is expected to yield. The internal rate of return (IRR) method expresses each investment alternative in terms of a rate of return (a compound interest rate). The expected rate of return is the interest rate for which total discounted benefits become just equal to total discounted costs (i.e., net present benefits or net annual benefits are equal to zero, or for which the benefit/cost ratio equals one). The criterion for selection among alternatives is to choose the investment with the highest rate of return. The rate of return is usually calculated by a process of trial and error, whereby the net cash flow is computed for various discount rates until its value is reduced to zero.

179

180

Tidal Energy Systems

The internal rate of return (IRR) of a project is the discount rate: 0¼

n X CF 0 CF 0 CF n CF t + ……… ¼ n t 0 0 ð1 + K Þ ð1 + K Þ ð1 + K Þ t¼0 ð1 + K Þ

where CFt ¼ cash flow at the end of year “t”; κ ¼ discount rate; n ¼ life of the project. Advantages A popular discounted cash flow method, the internal rate of return criterion has several advantages: • It takes into account the time value of money. • It considers the cash flow stream in its entirety. • It makes sense to businessmen who prefer to think in terms of rate of return and find an absolute quantity, such as net present value, somewhat difficult to work with. Q.8 Calculate the simple payback period for a tidal power plant, that costs $10 million to purchase and install, $0.2 million per year on average to operate and maintain, and is expected to save $3 million by reducing transmission and distribution loss of tidal power plants. Payback Period ¼

First Cost of Tidal Power Plant Yearly Benefits  Yearly Costs

10 ¼ 3 year and 6 month 3  0:2 Q.9 Calculate the simple payback period for a tidal power plant that costs $20 million to purchase and install, $0.4 million per year on average to operate and maintain, and is expected to save $6 million by reducing transmission and distribution loss of tidal power plants. Payback Period ¼

Payback Period ¼

First Cost of Tidal Power Plant Yearly Benefits  Yearly Costs

20 ¼ 3 year and 6 month 6  0:4 Q.10 Calculate the simple payback period for a tidal power plant that costs $25 million to purchase and install, $0.5 million per year on average to operate and maintain, and is expected to save $8 million by reducing transmission and distribution loss of tidal power plants. Payback Period ¼

Payback Period ¼

First Cost of Tidal Power Plant Yearly Benefits  Yearly Costs

Prefeasibility Assessment of a Tidal Energy System

25 ¼ 3 year and 4 month 8  0:5 Q.11 Consider a tidal energy project that has the following cash flow stream: Payback Period ¼

Investment Saving in year

$1,000,000 Cash flow

1 2 3 4 5

200,000 200,000 300,000 300,000 300,000

If the discount rate is 10%, find the net present value at the end of 5 years. Solution: n X CF 0 CF 1 CF n CF t NPV ¼  + ……… ¼ n t 0 1 ð1 + K Þ ð1 + K Þ ð1 + K Þ t¼0 ð1 + K Þ 1000, 000 200;000 200; 000 300; 000 300;000 300; 000 NPV ¼  + + + + ð1:10Þ0 ð1:10Þ1 ð1:10Þ2 ð1:10Þ3 ð1:10Þ4 ð1:10Þ5 NPV ¼ 5273 Q.12 Calculate the simple payback period for a tidal power plant that costs $25 million to purchase and install, $0.5 million per year on average to operate and maintain, and is expected to save $8 million by reducing transmission and distribution loss of tidal power plants. Payback Period ¼

First Cost of Tidal Power Plant Yearly Benefits  Yearly Costs

25 ¼ 3 year and 4 month 8  0:5 Q.13 Consider a tidal energy project that has the following cash flow stream: Payback Period ¼

Investment Saving in year

$2,000,000 Cash flow

1 2 3 4 5

400,000 400,000 600,000 600,000 600,000

181

182

Tidal Energy Systems

If the discount rate is 10%, find the net present value at the end of 5 years. Solution: NPV ¼ 

n X CF 0 CF 1 CF n CF t + ……… ¼ n t 0 1 ð1 + K Þ ð1 + K Þ ð1 + K Þ t¼0 ð1 + K Þ

NPV ¼ 

2000, 000 400; 000 400; 000 600; 000 600; 000 600; 000 + + + + ð1:10Þ0 ð1:10Þ1 ð1:10Þ2 ð1:10Þ3 ð1:10Þ4 ð1:10Þ5

NPV ¼ 73,197 Q.14 Calculate the simple payback period for a tidal power plant that costs $25 million to purchase and install, $0.5 million per year on average to operate and maintain, and is expected to save $8 million by reducing transmission and distribution loss of tidal power plants. Payback Period ¼

First Cost of Tidal Power Plant Yearly Benefits  Yearly Costs

Payback Period ¼

25 ¼ 3 year and 4 month 8  0:5

Investment Saving in year

$1,000,000 Cash flow

1 2 3 4 5

200,000 200,000 300,000 300,000 300,000

Q.15 Consider a tidal energy project that has the following cash flow stream: If the discount rate is 25%, find the net present value at the end of 5 years. Solution: NPV ¼ 

n X CF 0 CF 1 CF n CF t + ……… ¼ n t 0 1 ð1 + K Þ ð1 + K Þ ð1 + K Þ t¼0 ð1 + K Þ

NPV ¼ 

1000, 000 200; 000 200; 000 300; 000 300; 000 300; 000 + + + + ð1:25Þ0 ð1:25Þ1 ð1:25Þ2 ð1:25Þ3 ð1:25Þ4 ð1:25Þ5

NPV ¼ 337,216

Prefeasibility Assessment of a Tidal Energy System

EXERCISE 1. 2. 3. 4. 5. 6.

7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

23. 24. 25. 26. 27. 28. 29. 30. 31. 32.

What is the meaning of prefeasibility and resource assessment? Write the types of resource assessments. What is the meaning of regional and site resource assessment? What is the meaning of resource characterization? Write different objectives related to site consideration. Write short notes on the following: (i) Dimensional Resource Assessment (ii) Dimensional Resource Assessment (iii) Dimensional Resource Assessment What is the significance of one-dimensional resource assessment? What is the significance of one-dimensional resource assessment? What is the significance of one-dimensional resource assessment? What is the significance of the Saint-Venant equation related to the resource assessment? Explain the resource assessment with Blue-Kenue and Telemac-2D. Write certain simulation parameters related to Telemac-2D. Explain theoretical resource assessment. Explain numerical resource assessment. Explain practical resource assessment. Explain accessible resource assessment. Explain technical resource assessment. Explain viable resource assessment. Write the significance of temporal and spatial variability in the tidal resources. Explain different types of software used in tidal resource assessment. What is the use of project management in a tidal power plant? Write short notes on the following: (i) Critical Path Method (ii) Program Evaluation and Review Technique What is the meaning of physical resource assessment? Write short notes on the technical and geographical resource assessments. Explain different surface boundary conditions. Explain different points related to physical boundary assessment. Explain objectives of functional physical boundaries of assessment. Explain static and transect surveys of resource assessment. Write the quantitative observation that comes through static and transect surveys. What are the challenges of measuring water current? Explain location assessment by the flux method. Explain location assessment by the farm method.

183

184

Tidal Energy Systems

33. Derive the equation for maximum steady-state power through a tidal power plant. 34. Derive the equation for the transmission line analogy of a tidal power plant.

Numerical Q.1 The input-output curve of a 20 MW tidal power generating station is given by the following equation: I ¼ (7.5 + 0.125P + 0.16P2)  106 where I is in kcal/h and P is in MW. Find the average heat rate of the tidal power station for a day when it was operating at a load of 20 MW for 16 h and was kept hot at zero for the remaining 8 h. Find the saving in the heat rate if the same energy is produced from the tidal power plant for the whole day at 100% load factor. Q.2 The input-output curve of a 20 MW tidal power generating station is given by the following equation: I ¼ (7.5 + 0.125P + 0.16P2)  106 where I is in kcal/h and P is in MW. Find the average heat rate of the tidal power station for a day when it was operating at a load of 20 MW for 16 h and was kept hot at zero for the remaining 8 h. Find the saving in the heat rate if the same energy is produced from the tidal power plant for the whole day at 100% load factor. Q.3 An input output curve of a 30 MW tidal power plant is given by an equation I ¼ (18 + 12P + 0.5P2)  106 kcal/h where I is in kcal per hour and P is load on the power plant in MW, find (i) The load at which the efficiency of the plant will be maximum and (ii) The increase in input required to increase the tidal station output from 15 MW to 25 MW by using the input-output equation and by the incremental rate curve. Q.4 The input-output curve of a 50 MW tidal power generating station is given by the following equation: I ¼ (5.5 + 0.125P + 0.16P2)  106 where I is in kcal/h and P is in MW. Find the average heat rate of the tidal power station for a day when it was operating at a load of 20 MW for 16 h and was kept hot at zero for the remaining 8 h. Find the saving in the heat rate if the same energy is produced from the tidal power plant for the whole day at 100% load factor. Q.5 An input output curve of a 10 MW tidal power plant is given by an equation I ¼ (18 + 12P + 0.5P2)  106 kcal/h where I is in kcal per hour and P is load on the power plant in MW, find (i) The load at which the efficiency of the plant will be maximum and (ii) The increase in input required to increase the tidal station output from 5 MW to 7 MW by using the input output equation and by incremental rate curve. Q.6 The input-output curve of A 20 MW tidal power generating station is given by the following equation: I ¼ (7.5 + 0.125P + 0.16P2)  106 where I is in kcal/h and P is in MW. Find the average heat rate of the tidal power station for a day when it was operating at a load of 20 MW for 16 h and was kept hot at zero for the remaining

Prefeasibility Assessment of a Tidal Energy System

Q.7

Q.8

Q.9

Q.10

8 h. Find the saving in the heat rate if the same energy is produced from the tidal power plant for the whole day at 100% load factor. An input output curve of a 10 MW tidal power plant is given by an equation I ¼ (18 + 12P + 0.5P2)  106kcal/h where I is in kcal per hour and P is load on the power plant in MW, find (i) The load at which the efficiency of the plant will be maximum and (ii) The increase in input required to increase the tidal station output from 5 MW to 7 MW by using the input-output equation and by incremental rate curve. The input-output curve of a 20 MW tidal power generating station is given by the following equation: I ¼ (7.5 + 0.125P + 0.16P2)  106 where I is in kcal/h and P is in MW. Find the average heat rate of the tidal power station for a day when it was operating at a load of 20 MW for 16 h and was kept hot at zero for the remaining 8 h. Find the saving in the heat rate if the same energy is produced from the tidal power plant for the whole day at 100% load factor. An input output curve of a 10 MW tidal power plant is given by an equation I ¼ (18 + 12P + 0.5P2)  106kcal/h where I is in kcal per hour and P is load on the power plant in MW, find (i) The load at which the efficiency of the plant will be maximum and (ii) The increase in input required to increase the tidal station output from 5 MW to 7 MW by using the input output equation and by incremental rate curve. An input output curve of a 10 MW tidal power plant is given by an equation I ¼ (18 + 12P + 0.5P2)  106 kcal/h where I is in kcal per hour and P is load on the power plant in MW, find (i) The load at which the efficiency of the plant will be maximum and (ii) The increase in input required to increase the tidal station output from 5 MW to 7 MW by using the input-output equation and by incremental rate curve.

Objective-Type Questions Q.1

A feasibility assessment of a tidal energy system is done by (a) (b) (c) (d)

Q.2

Location Assessment Economic Assessment Technological Assessment All of the above

The phenomenon_________ is the combination of positive and negative surge in a tidal power plant. (a) Surge Impedance (b) Storm Surge (c) Tidal current (d) None of the above

185

186

Tidal Energy Systems

Q.3

A phenomenon in which low pressure causes a raising of the oceanic surface (a) Positive surge (b) Negative surge (c) Both (a) and (b) (d) None of the above

Q.4

A phenomenon in which high pressure causes a lowering of the oceanic surface (a) Positive surge (b) Negative surge (c) Both (a) and (b) (d) None of the above

Q.5

Regional assessment of a tidal power plant consists of (a) Technical assessment (b) Very large and many potential sites assessment (c) Economical assessment (d) None of the above

Q.6

Current velocity data in the water column is measured by (a) Ammeter (b) Voltmeter (c) Acoustic Doppler Current profiles (d) Cathode ray oscilloscope Median current velocity greater than_______ m/s is economically suitable for energy extraction. (a) 3.3 (b) 2.2 (c) 1.1 (d) 0

Q.7

Q.8

Ideal velocities are those for locations with mean spring peak tidal current in the range of (a) 2 to 2.5 m/s (b) 4 to 5.5 m/s (c) 6 to 7.5 m/s (d) 0 to 2.5 m/s

Q.9

Velocity profile of the water column is analyzed by (a) One-dimensional method (b) Two-dimensional method (c) Three-dimensional method (d) All of the above

Q.10

Water flow rate is given by (a) 0.25π(Pipe Diameter)2  Velocity (b) 0.5π(Pipe Diameter)2  Velocity (c) π(Pipe Diameter)2  Velocity (d) 0.25π(Pipe Diameter)2  Velocity2

Prefeasibility Assessment of a Tidal Energy System

Q.11

The physical boundary assessment of a tidal energy system consists of (a) Technical Assessment (b) Graphical Assessment (c) Both (a) and (b) (d) None of the above

Q.12

A _______ is a path along which are counts and records of the tidal current at particular time intervals. (a) Static (b) Transect (c) Both (a) and (b) (d) None of the above

REFERENCES Nycander, J., 2005. Generation of internal waves in deep ocean by tides. J. Geophys. Res. 110, 1–9.

FURTHER READING Aly, H.H.H., El-Hawary, M.E., 2011. State of the art for tidal currents electric energy resources. In: 24th Canadian Conference on Electrical and Computer Engineering (CCECE), p. 1119e1124. https://doi. org/10.1109/CCECE.2011.6030636. American Public Power Association, 2018. Fact Sheet 2007 Clean Renewable Energy Bonds (CREBs). www.APPAnet.org. Bahaj, A.S., Myers, L., 2004. Analytical estimates of the energy yield potential from the Alderney Race (Channel Islands) using marine current energy converters. Renew. Energy 29 (12), 1931–1945. https://doi.org/10.1016/j.renene.2004.02.013. Ben, S.E., Elghali, M.E.H., Benbouzid, J.F., 2007. Charpentier, Marine tidal current electric power generation technology: state of the art and current status. In: Electric Machines & Drives Conference, 2007. IEMDC’07. IEEE International, IEEE, p. 1407e1412. https://doi.org/10.1109/IEMDC.2007. 383635. Boyle, G. (Ed.), 2004. Renewable Energy Power for a Sustainable Future, second ed. Oxford University Press, Oxford. California Energy Commission, 2005. Comparative Costs of Electricity Generation by Resource Type. http://www.energy.ca.gov/electricity/comparative_costsv1.html. Harris, C., 2006. Electricity Markets Pricing, Structures and Economics. John Wiley & Sons Ltd, Chichester. http://delftsoftware.wldelft.nl/index.php?option¼com_content&task¼view&id¼18&Itemid¼34. http://www.bolding-burchard.com/html/GETM/features.htm. http://www.ccalmr.ogi.edu/CORIE/modeling/elcirc/. http://www.cwr.uwa.edu.au/services/models/elcom/documentation/elcom_science_2_2_0/ELCOM_ Science.pdf. http://www.erm-smg.com/gemss.html. http://www.ifremer.fr/delec/modeles/autre_modele/autres_modeles.htm. http://www.prism.ie/NR/rdonlyres/9D1A7E8E-EBCC-441A-AEE5-09439DABA1DC/0/A7.pdf. IAEA International Atomic Energy Agency, 1984. Expansion Planning for Electrical Generating. A Guidebook. IAEA, Vienna.

187

188

Tidal Energy Systems

Khan, M.J., Bhuyan, G., Iqbal, M.T., Quaicoe, J.E., 2009. Hydrokinetic energy conversion systems and assessment of horizontal and vertical axis turbines for river and tidal applications: a technology status review. Appl Energy 86 (10), 1823–1835. https://doi.org/10.1016/j.apenergy.2009.02.017. Kirschen, D., Strbac, G., 2004. Fundamentals of Power System Economics. John Wiley & Sons Ltd, Chichester. Kolekar, N., Banerjee, A., 2015. Performance characterization and placement of a marine hydrokinetic turbine in a tidal channel under boundary proximity and blockage effects. Appl. Energy 148, 121–133. https://doi.org/10.1016/j.apenergy.2015.03.052. Li, Y., Colby, J.A., Kelley, N., Thresher, R., Jonkman, B., Hughes, S., 2010. Inflow measurement in a tidal strait for deploying tidal current turbines: lessons, opportunities and challenges. In: ASME 2010 29th International Conference on Ocean, Offshore and Arctic Engineering, American Society of Mechanical Engineers, p. 569e576. https://doi.org/10.1115/OMAE2010-20911. MacLeod, A.J., Barnes, S., Rados, K.G., Bryden, I.G., 2002. Wake effects in tidal current turbine farms. In: Proceedings of the MAREC Conference, Newcastle, September 2002, pp. 49–53. Maganga, F., Germain, G., King, J., Pinon, G., Rivoalen, E., 2010. Experimental characterization of flow effects on marine current turbine behaviour and on its wake properties. IET Renew. Power Gener. 4 (6), 498e509. https://doi.org/10.1049/iet-rpg.2009.0205. Milne, I.A., Sharma, R.N., Flay, R.G.J., Bickerton, S., 2013. Characteristics of the turbulence in the flow at a tidal stream power site. Philos. Trans. R. Soc. A Math. Phys. Eng. Sci. 371. https://doi.org/10.1098/ rsta.2012.0196. Mycek, P., Gaurier, B., Germain, G., Pinon, G., Rivoalen, E., 2014. Experimental study of the turbulence intensity effects on marine current turbines behaviour. Part I: one single turbine. Renew. Energy 66, 729–746. https://doi.org/10.1016/j.renene.2013.12.036. Mycek, P., Gaurier, B., Germain, G., Pinon, G., Rivoalen, E., 2014. Experimental study of the turbulence intensity effects on marine current turbines behaviour. Part II: two interacting turbines. Renew. Energy 68, 876–892. https://doi.org/10.1016/j.renene.2013.12.048. Myers, L.E., 2005. Operational Parameter of Horizontal Axis Marine Current Turbines, PhD Thesis. University of Southampton. Myers, L.E., Bahaj, A.S., 2005. Simulated electrical power potential harnessed by marine current turbine arrays in Alderney race. Renew. Energy 30, 1713–1731. https://doi.org/10.1016/j.renene.2005.02.008. Rourke, F.O., Boyle, F., Reynolds, A., 2010. Tidal energy update 2009. Appl. Energy 87 (2), 398–409. https://doi.org/10.1016/j.apenergy.2009.08.014. Thomson, J., Polagye, B., Durgesh, V., Richmond, M.C., 2012. Measurements of turbulence at two tidal energy sites in puget sound, WA. IEEE J. Ocean. Eng. 37 (3), 363e374. https://doi.org/10.1109/JOE. 2012.2191656. Vennell, R., Funke, S.W., Draper, S., Stevens, C., Divett, T., 2015. Designing large arrays of tidal turbines: a synthesis and review. Renew. Sustain. Energy Rev. 41, 454–472. https://doi.org/10.1016/j.rser.2014. 08.022.

CHAPTER 4

Optimum Sizing and Modeling of Tidal Energy Systems Contents 4.1 Introduction 4.2 Modeling of Tidal Energy Conversion Systems 4.2.1 Modeling of a Tidal Energy System by HOMER Software 4.2.2 Modeling of 9 MW Tidal Power Plant Through MATLAB 4.2.3 Tidal Energy Device Variability 4.2.4 Characteristics of Towing Tanks 4.2.5 Limitations With Physical Model Effects for TECs 4.2.6 Water Tunnel 4.2.7 TIDAL Basin 4.2.8 Tidal Energy Framework 4.2.9 Modeled Processes 4.3 Numerical Solution of Tidal Energy System 4.3.1 Swell Effect (Long-Length) Tidal 4.3.2 Energy Generation Through Tidal Power Plant 4.3.3 Pressure Wave Velocity in Conduit 4.3.4 Head Loss Due to Friction 4.3.5 Tidal Current Modeling 4.4 Modeling of a Tidal Current Turbine 4.4.1 Turbine Power Output 4.4.2 The Power in the Tides 4.4.3 Forces on Blades and Torque of Tidal Turbine 4.4.4 Mathematical Modeling of Hydraulic Turbine 4.5 Tidal Energy Facility Size 4.5.1 Functional Requirements 4.5.2 Basic Requirements Imposed for Tidal Energy Generation by Grid Codes 4.5.3 Grid-Connected Marine Energy Infrastructures 4.5.4 Electrical Configurations Schemes 4.5.5 Elements of a Grid Connection Infrastructure 4.5.6 Offshore Substation 4.5.7 Technical Issues Related to AC Transmission 4.5.8 Tidal Measurement Devices 4.5.9 Software Used in Modeling of a Tidal Power Plant Exercise Exercise References Further Reading Tidal Energy Systems https://doi.org/10.1016/B978-0-12-814881-5.00004-1

190 190 190 195 196 197 198 198 199 199 204 208 208 208 210 210 211 212 212 213 215 216 218 218 219 219 221 226 228 230 231 234 238 240 240 240 © 2019 Elsevier Inc. All rights reserved.

189

190

Tidal Energy Systems

4.1 INTRODUCTION Sustainable power sources that are normally renewed are those created from regular assets, for example, wind, sunlight, tidal, hydro, biomass, geothermal, and sea sources. Hydro and tidal energy system frameworks have disadvantages that include discontinuous wellsprings of energy, high starting costs, restricted areas and the awful impact on marine lives tidal momentum turbines can produce control of free streaming water with very nearly zero natural impacts. The energy is put away in seas in a few structures as concoctions and organic items, warm energy, and motor energy (waves and streams). The primary favorable position of tidal energy over other sustainable power source innovations is its consistency far from impacts because of evolving in climate designs. Tidal streams are the streams of water as a tide ebbs and surges. Despite the actuality that sea streams move gradually with respect to normal breeze speeds, water is 800 times denser than air. Along these lines, for a similar surface region, water moving 12 hitches applies a similar measure of drive as a steady 110 bunches wind. As a result of this physical property, tidal streams contain a huge measure of energy that can be caught and transformed into a usable form.

4.2 MODELING OF TIDAL ENERGY CONVERSION SYSTEMS 4.2.1 Modeling of a Tidal Energy System by HOMER Software HOMER programming means Hybrid Optimization Model for Multiple Energy Resources, and its reenactment is completed with and without grid association. HOMER software presents the analysis of hybrid renewable energy systems in the form of sensitivity analysis, optimization, and simulation (Fig. 4.1). HOMER nests three powerful tools in one software product so that engineering and economics can be done side by side. HOMER simulates the operation of a tidal power plant for an entire year, with time steps from 1 min to 1 h. Energy consumption data for an accurate study area are required for planning the optimal production capacity of a tidal

HOMER Sensitivity analysis Optimization Simulation

Fig. 4.1 Steps of HOMER software.

Optimum Sizing and Modeling of Tidal Energy Systems

renewable power system. The data of electricity consumption are usually the sum of energy of numerous devices without detailed information about the events on each individual. An ideal case is the one with a known consumption pattern and with details of various appliances. Yet another way is to consider statistical averages and sample data. Analyzing energy consumption data, we could identify the basic characteristics of load curves of devices that change on a periodical basis. In this modeling of a tidal energy system, we consider a peak load of 11 KW at a particular site in India (Fig. 4.2). This data were sampled every hour for 365 days. In a typical day, energy consumption is higher in the morning from 6 a.m. to 10 a.m. and in the evening from 6 p.m. to 11 p.m. Mathematical modeling is the first step in the design of any tidal renewable energy system; it gives an exact view of any renewable energy system (Table 4.1). Fig. 4.3 represents a block diagram of a conventional tidal-generator renewable energy system. The mathematical modeling and framework of the tidal energy conversion system includes tidal turbine dynamics and tidal generator modeling. Nondimensional performance as a function of the tip speed ratio is a basic characteristic of a tidal turbine (Table 4.2). Basically generated power largely depends on the cube of the tidal velocity. The output of mechanical power captured from the low and high tides by a tidal turbine can be formulated as
 Cp λρAVT3 PT ¼  2 And torque developed by a tidal turbine can be expressed as:  TT ¼ PT ωm where PT is the output power, TT the torque developed by the tidal turbine, Cp the power coefficient, λ the tip speed ratio, ρ the air density in kg/m3, A the frontal area of the tidal turbine, and VT the tidal velocity (Table 4.3 and Figs. 4.4 and 4.5). Modeling of Diesel Generator for Tidal Power Plant The determination of a diesel generator relies upon the classification and nature of the load. To decide the evaluated capacity of the motor generator to be introduced, the following two cases ought to be considered: 1. The rated capacity of the generator must be at least equal to the maximum load, and then it is possible for the diesel generator to directly connect to a load. 2. If the diesel generator works as a battery charger, then the current produced by the generator should not be greater than CAh/5 A, where CAh is the ampere hour capacity of the battery.

191

192 Tidal Energy Systems

Fig. 4.2 Month-wise load calculation of study area.

Optimum Sizing and Modeling of Tidal Energy Systems

Table 4.1 Load assessment

AC primary load Excess electricity Unmet load Capacity shortage Renewable fraction

41,975 kWh/year 26,746 kWh/year 0.0000173 kWh/year 0.00 kWh/year 87%

Batteries

DC load

Charge reg.

Tidal turbine

Rectifier

DC AC

AC

DC Inverter

Diesel/gasoline gen. AC load

Fig. 4.3 Modeling of tidal power plant.

Table 4.2 System architecture

Tidal turbine Generator Battery Inverter Rectifier

20 kW 10 kW 24 Battery 10 kW 10 kW

Table 4.3 Specification of tidal turbine

Mean output Production Maximum output Tidal penetration Hours of operation

7.6 kW 66,612 kWh/year 20 Kw 159% 7891 h/year

The overall η of the diesel generator is given by ηoverall ¼ ηbreakthermal  ηgenerator Here ηbreak thermal is the brake thermal efficiency of the diesel engine. Normally, diesel generators are modeled in the control of the hybrid power system in order to achieve required autonomy (Table 4.4).

193

Tidal Energy Systems

Power curve

Power (kW)

20 15 10 5 0 0

6

12

18

24

Tidal velocity (m/s)

Fig. 4.4 24 h tidal velocity of study area. Tidal resoureces 16 Tidal range (m/s)

194

12 8 4 0 Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Fig. 4.5 Month-wise tidal range of study area. Table 4.4 Generator specification Quantity

Value

Hours of operation Number of starts Operational life Capacity factor Electricity production Mean electrical output Minimum electrical output Maximum electrical output Fuel consumption Specific fuel consumption Fuel energy input Mean electrical efficiency

1222 h/year 89 Starts/year 12.3 years 11.4% 10,007 kWh/year 8.19 kW 3 kW 10 kW 3419 L/year 0.348 L/kWh 34, 237 kWh/year 29.2%

Modeling of Battery Bank for Tidal Power Plant The battery state of charge (SOC) is the cumulative sum of the daily charge/discharge condition of the battery. When the battery becomes fully charged, it contains the total amount of energy, which is known as the maximum battery capacity. At any hour, the

Optimum Sizing and Modeling of Tidal Energy Systems

state of the battery is related to the previous state of charge and to the energy production and consumption situation of the system during the time from t  1 to t. During the charging process, when the total output of all generators exceeds the load demand, the available battery bank capacity at hour t can be described by, BBAT ðtÞ ¼ BBAT ðt  1Þ  Bout ðtÞ  ηcharging

(4.1)

Where BBAT(t) is energy stored in the battery at hour t kWh, BBAT(t  1) is energy stored in the battery at hour t  1 kWh, Bout(t) is energized out of battery in time t, and ηcharging is battery charging efficiency (Tables 4.5 and 4.6).

4.2.2 Modeling of 9 MW Tidal Power Plant Through MATLAB A tidal power plant consisting of six 1.5 MW tidal turbines, which are used to convert the kinetic energy of tides into mechanical energy, is connected to a 25 kV distribution system that exports energy to a 120 kV grid through a 25 km 25 kV feeder. A similar simulation of a wind farm in MATLAB also simulated a tidal farm, with the wind velocity replaced by tidal range or tidal current. The 9 MW tidal farm is simulated by three pairs of 1.5 MW tidal turbines. Tidal turbines use squirrel-cage induction generators Table 4.5 Battery specification Quantity

Value

String size String in Parallel Bus voltage Nominal capacity Usable nominal capacity Autonomy Lifetime throughput Energy in Energy out Storage depletion Losses Annual throughput Expected life

1 24 4V 182 kWh 109 kWh 22.8 h 253,646 kWh 17,309 kWh/year 13,852 kWh/year 4.7 kWh/year 3453 kWh/year 15,487 kWh/year 12 Years

Table 4.6 Electricity production Component Production (kWh/year)

Fraction (%)

Tidal turbine Generator Total

87 13 100

66,612 10,007 76,619

195

196

Tidal Energy Systems

P Q

9 MW tidal farm A

N

A

A

a

A

a

A

B

B

b

B

b

B

C

C

c

C Yg D1c

C

120 kV

2500 MVA X0/X1 = 3

a

π

b

25 km line

120 kV/25 kV 47 MVA

B

m

m

c B25 (25 kV)

C

a

A B C d1 Yn N

b

Grounding Transformer X0 = 4.7 Ohms

0 No trip 3.3ohms

1 Trip

Trip A B

STATCOM m

mstatcom

C STATCOM (phasor type)

Fig. 4.6 MATLAB simulation of a tidal power plant.

(IG), which are used as the tidal generator. The stator winding of a tidal generator is connected directly to the 50 Hz grid and the rotor is driven by a variable-pitch tidal turbine (Fig. 4.6). The pitch angle of a tidal turbine is controlled in order to limit the tidal generator output power at its nominal value for tides exceeding the nominal value at the rated value of tidal current. In order to generate power from a tidal power plant, the tidal generator speed must be slightly above the synchronous speed. Speed varies approximately between 1 pu at no load and 1.005 pu at full load. Each tidal turbine has a protection system monitoring voltage, current, and machine speed. Reactive power absorbed by the tidal generator is partly compensated by capacitor banks connected at each tidal turbine low voltage bus. The rest of the reactive power required to maintain the 25 kV voltage at bus B25 close to 1 pu is provided by a 3 Mvar STATCOM with a 3% droop setting. The tidal turbine mechanical power as a function of tidal turbine speed is displayed for tidal velocity ranging from a low to a high value of the tidal range. The tidal turbine model and the statcom model are phasor models that allow transient stability-type studies with long simulation times.

4.2.3 Tidal Energy Device Variability The issue of component fluctuation inside a tidal energy system exhibit could be material because of the anticipated idea of the asset as far as tidal speed and bearing. A decreased asset in the focal point of a second era multipush cluster will remain constant for marine current components presented to the substituting bearing of the stream. It is fitting to outline components with various power take off frameworks or to simply diminish the evaluated control yield of components with a decreased inflow asset will no uncertainty administered by the cost/advantage investigation performed by designers. Changes in bathymetry and water profundity may likewise require distinctive physical sizes of

Optimum Sizing and Modeling of Tidal Energy Systems

components inside a cluster. Indeed, a decision can be made to successfully have two exhibits in closeness and total power yield or to regard them as a solitary substance. It might likewise happen that destinations with extremely uneven bed conditions won’t be reasonable for exhibit establishment because of the component inconstancy required. As the innovation develops to achieve second-era clusters, engineers will have various tidal energy component variations that will encourage the issues tendered above. As of now, more top-to-bottom talk of component inconstancy is not regarded as beneficial to the point when the business is more educated about tidal components working in fewer (first-era) clusters. Towing tanks are offices planned initially for maritime design work. A body demonstrated for a ship would be suspended in the tank and towed along behind or under a dolly or carriage, with estimations taken of drag, lightness, sideways push, and so forth. Lately, numerous tow tanks have been furnished with TIDAL creators, downstream vitality-retaining shorelines, and sensor hardware, then utilized for sea-keeping tests on vessel models. These capacities, alongside the huge size of a few offices and current control abilities on the tow carriages, make this an alluring suggestion when testing both tidal and TIDAL gadgets. The utilization of tow tanks for tidal gadget testing is natural, and towing tanks furnished with TIDAL age frameworks that have been able to create for some time peaked monochromatic and panchromatic tides have three applications for tidal vitality trials.

4.2.4 Characteristics of Towing Tanks The tank is equipped with a carriage for testing up to 15 m/s for traditional calm water tests. It is also used for sea-keeping tests and other tests performed with free-running models. It includes resistance, propulsion, seakeeping in head and following seas, and directional stability tests with free running models. The essential condition for a tow tank is a substantial length to expansiveness proportion, a trademark that makes the arrangement of 2D tides very tricky. Besides, a few offices might be very shallow in respect to width, constraining the idea of components that might be tried. All tanks have a carriage mounted on rails on either side of the tank along the fundamental pivot. This carriage conveys the test piece(s) and any extra actuators and control and checking frameworks. Gadgets might be inflexibly mounted to a hard point on the carriage, truly towed behind on an adaptable line, or mounted to extra actuator(s) to give different wanted movements. In a self-impelled vessel, the carriage will take after the vessel along the tank. Towing tanks can be utilized to test gadgets without towing them, either by connecting the gadget to the tank itself, as with mooring frameworks or TIDAL gadget tests, or suspending them from the carriage or other reasonable mounting. In these cases, tow tanks with TIDAL influencing offices can test mooring procedure survivability and so on just if the width permits the stay impression. TIDAL making and towing can be joined to show controlled TIDAL/current communications, conditions that are hard to accomplish in outside test offices, with critical

197

198

Tidal Energy Systems

repeatable control over the information conditions. The hydrodynamic qualities are to some degree not the same as those experienced in, say, a cavitation passage or flume. As the liquid is notionally very still, turbulence forces naturally diminish after each test, at last implying that low turbulence levels can be gotten if one is set up to hold up an adequate era between races to enable the tank to settle and wakes to disseminate. A result of this is if the liquid is to be seeded for flow representation purposes, or if molecule-based speed estimations are required, then some tumult or reseeding will be required to accomplish an altogether blended molecule dissemination if particles have been permitted to settle out between runs or overnight. Because of the occasionally extensive size of towing tanks, it is regularly tricky to raise or lower the liquid level.

4.2.5 Limitations With Physical Model Effects for TECs Blockage ratio: As the channel breadth and depth are relatively short compared with the length, it is possible that a scale device will occupy a significant portion of the channel cross-sectional area. In this situation, the proximity of the channel sides and bottom will alter the flow field in the vicinity of the device as compared with a device in isolation. For example, fluid that would normally flow around the device may be forced through the device instead, potentially altering the power characteristics. Vertical expansion of the wake will be inhibited by proximity to the bed/water surface. This will affect rotor characteristics, giving performance characteristics that cannot be attained in open sea conditions. Limitations with particle settlement: Particle-based flow measurement methods are affected by the settlement of particles seeded in the water during periods of settlement. Limitations associated with ambient turbulence levels being very low: This may alter device performance through lack of energy at the top end of the energy cascade as wakes may not dissipate as quickly as in more developed turbulence. Turnaround between runs may be significant if time is allowed for the tank to become quiescent if consistently low turbulence states are required. Limitations associated with carriages being self-propelled: This necessitates various highpower electronics systems to be mounted on the carriage, and also large lengths of cabling being used. EMC and interference from these on measurement systems can be an issue. Carriage power: Smaller tanks with overhead towing might not have sufficient power to tow a model tidal device at the desired towing velocities in order to overcome resistance in, for example, drag created by the test model and the drivetrain.

4.2.6 Water Tunnel Circulating water tunnels are a hydrodynamic extension of the wind tunnel concept: essentially, water is pumped though a working section where the test piece is mounted and the water is recirculated once it reaches the end of the working section. There are

Optimum Sizing and Modeling of Tidal Energy Systems

two main types: open flumes and closed tunnel, with the difference being that flumes possess a free surface while closed tunnels can be run at nonatmospheric pressures to reduce or increase the incidence of cavitation. As with wind tunnels, the fluid is pumped through a series of baffles and guide vanes and possibly a settling chamber before reentering the working section in order to control turbulence to some extent. Traditionally, cavitation tunnels have been used for propeller testing, making them typically well established for testing the turbo machinery types associated with tidal turbines. The flumes are traditionally used in civil engineering and naval architecture, and as such may be fairly shallow. Flumes may be gravity fed or an open tunnel. Characteristics of Enclosed Water Tunnels Enclosed water tunnels have similar characteristics to the open surface tunnels described above. With airtight seals, pressure in closed tunnels can be increased or decreased relative to atmospheric pressure. Historically, this has been used in the maritime industry to simulate marine propeller operation at varying depths in order to study cavitations. They are perhaps less useful for tidal energy testing unless pressure-specific issues are of interest. Access to the working section is often restricted by heavily sealed panels and thus access and installation issues may be significant.

4.2.7 TIDAL Basin TIDAL basins are water tanks that are relatively wide compared to their length; indeed they can often be over square in certain establishments, perhaps when floor space is limited. TIDAL generation systems are installed along one, or sometimes two, adjacent walls. Like towing tanks and TIDAL flumes, TIDAL basins are available in a variety of sizes that can accommodate both Stage 1 (circa λ ¼ 1:50) and Stage 2 (circa λ ¼ 1:10) WEC-scaled device test programmers. A physical size limitation factor is often the power required to generate the TIDAL at a facility, but modern and more efficient TIDAL producing systems are alleviating this constraint. TIDAL basins have several different origins, but these are mainly sea keeping and maneuvering tanks for the shipbuilding industry, deep basins for offshore engineering for the oil and gas industry, and shallower facilities for coastal protection work. The depth of the basin is usually linked to the initial purpose of construction, but often, advanced facilities have either movable floors or deep pools built in.

4.2.8 Tidal Energy Framework The classification characterizes the device in a progressive and compartmented manner in order to provide a complete and logically flowing description. The whole device has

199

200

Tidal Energy Systems

Cooling Reactive power Generator Hydrofoils

Brake

Seals

Control subsystem Bearing

Hydro foil pitch Yaw

Power conversion

Flow augmenter Reaction subsystem Support structure Tidal dynamic system Foundation

Fig. 4.7 Framework of a tidal power plant.

been divided into four discrete subsystems, as in Fig. 4.7. (The components shown within each subsystem are examples and not indicative of any particular device.) The above diagram has shown the complete structure of a tidal energy system in three layers. Component Classification Layer Description Layer 1 addresses the general form of the device. For both wave and tidal devices, this is regarded as the characterization/specification of the hydrodynamic subsystem. This system converts the wave/tidal motion in a more useful mechanical form suitable for the extraction of power. The form and motion paths of this subsystem provide the most meaningful method of classifying the type of device. Layer 2 addresses the power take-off subsystem. Here, the converted mechanical motion from the hydrodynamic subsystem is converted into electrical power. There are a variety of different methods to generate electricity in terms of principle motion and operational speed. Often, there has been a gearbox or some means to increase the speed of motion between the hydrodynamic subsystem and the generator. Layer 2 also quantifies the “edge of device” electrical power output, allowing estimates of efficiency to be made by the user.

Optimum Sizing and Modeling of Tidal Energy Systems

Layer 3 addresses the reaction and control subsystem, principally the method of keeping the device “at station” in the water and characterizing how the hydrodynamic subsystem is aligned to the waves/tidal current. Due to the large differences between wave and tidal energy devices (principally for the hydrodynamic and power take-off subsystems), each has been addressed with a separate classification template. To date, tidal energy devices appear to be relatively stabilized in terms of the methods employed to harness energy from tidal streams. To this end, Layer 1 of the tidal device classification can be kept quite simple and at present incorporates all known tidal energy devices. Tidal energy is present as a free stream kinetic energy flux in much the same manner as the wind energy resource. The principal differences are, of course, the velocity of the fluid and the density, but this has not prevented the majority of early tidal energy concepts from having remarkable similarities to early wind turbine design. A more simple classification might automatically designate “horizontal axis” and “vertical axis” devices as distinct device concepts. However, due to the constrained vertical height of the tidal resource and the often bidirectional nature, the rotational axes of device hydrodynamic subsystems (in this case a rotor) may occur in three distinct directions. The third of these is a horizontal axis aligned perpendicular to the principal flow direction. Hydrodynamic System

The hydrodynamic subsystem is the region of the device where energy from the marine environment is converted into a more useful form of motion prior to any energy extraction taking place. For a tidal energy device, this is most likely to be some form of lift-force rotor, but could also employ simple drag force paddles, for example. A common form for the hydrodynamic subsystem is to use a submerged or neutrally buoyant volume to move with the wave motion. Some devices use a hollow volume such that the wave motion moves air from which energy can be extracted. In a hydrodynamic system of tidal power plant inertia function is given by Reynold’s number. The equation is given by:
 Re ¼ Inertial=viscous ¼ ρu2 =ðuμ=L Þ ¼ ρuL=μ ¼ uL=v Where ρ ¼ Density of water u ¼ Velocity of sea water μ ¼ Dynamic viscosity L ¼ Characteristics length v ¼ μ/ρ Lift force rotor (LIFT) works in much the same way as that of a wind turbine or aircraft wing. The blade shape causes a pressure difference across its surface as fluid flows over it. By creating high- and low-pressure regions, the blade or lifting structure moves toward the low pressure region. Drag force (DRAG) structures rely on the force of the moving fluid to push on the element, forcing it in a certain direction.

201

202

Tidal Energy Systems

Venturi (VENTURI) devices use a tapered tube-like structure to accelerate the fluid flow. This faster-moving flow is used to move air above the water surface and energy is extracted from this as opposed to the water. Thus, the energy from the tidal stream is extracted indirectly. Vortex shedding (VORTEX) relies upon the unsteady effect of vortices shed from a body. If these are sequential in nature, a degree of oscillation or movement can be induced (Fig. 4.8). A linear oscillating (LIN-OSC) system encompasses a component that moves back and forth in the water, sweeping a rectangular area and extracting energy from the flow. The most common form is a hydrofoil blade working on the LIFT phenomenon detailed in the previous level. A rotational (ROT) system encompasses a hydrodynamic subsystem that rotates about a fixed axis. A linear (LIN) system moves in one direction. In the case of tidal energy systems, this has been defined as moving in a linear direction for each tidal cycle direction. In most cases during a tidal cycle (lasting approximately 12 h), the flow changes direction once flowing “in” and “out” of a site (Fig. 4.9). The power take-off (PTO) of a tidal or coastal energy converter is characterized as the apparatus with which the retained energy by the essential converter is changed into useable types of electrical energy. The essential converter can, for instance, be an enclosed chamber for a swaying water section or a point safeguard float. The PTO framework is of awesome significance as it influences not just specifically how productively the consumed tidal power is changed over into power, yet in addition adds to the mass, size, and basic flow of water in the tidal energy converter. Rather than the wind energy segment, there is no industry standard component for tidal energy change and this decent variety is LIFT

DRAG

VENTURI

VORTEX

Fig. 4.8 Principal motion of a hydrodynamic subsystem. Linear oscillating

Fig. 4.9 Way of turbine oscillation.

Rotation

Linear

Optimum Sizing and Modeling of Tidal Energy Systems

exchanged to the PTO framework. A wide range of PTO frameworks has been explored, and the kind of PTO framework utilized as a part of a tidal vitality converter frequently associates with its write. For instance, a wavering water segment kind of component used in an air turbine coupled to the electrical generator, while point safeguard sort of converter can utilize diverse PTO frameworks relying upon their setup and may require fell change components. This assortment implies that PTO frameworks are still at the advancement organize with little experience picked up for substantial scale components. To add to the troubles, PTO frameworks are hard to test at small scale as grinding turns into an issue. They would first be able to be tried on a bigger scale where costs are essentially expanded. The PTO framework is a vital part of a tidal energy converter. As already specified, it is likewise hard to plan because of the changeability of the energy source, the nature in which it is set, and scaling issues. The control subsystem embodies segments used to control the tidal component as far as station keeping, control catch from the marine condition, and security frameworks. For a tidal energy component this will incorporate intent to control rotor speeds and their arrangement to the tidal stream. A control for a tidal component may incorporate techniques to upgrade the control catch from various ocean states. The reaction subsystem is composed of the device support structure and foundations. These aspects of the device ensure that it maintains its spatial position within the marine environment. There are several methods of anchoring or fixing the device to the seabed or shoreline, including tubular piles, anchor chains, and gravity foundations. The support structure may take almost any form, depending upon the device and the nature of its components. The electrical power change in this sort of type is fundamentally the same as the creating arrangement of the wind control system. It is comprised of significant segments: a rectifier (variable AC-to-DC converter) and an inverter (DC-to-AC 60-Hz converter). We accept that the framework depicted in the given diagram depends on a detached rectifier; consequently, a DC-DC converter is utilized to coordinate and keep the DC transport voltage consistent. Note that this DC-DC converter will have the capacity to make up for the voltage drop (and diminish the copper misfortune along the feeder line) from the seaward generator to the substation coastal. With a dynamic rectifier, it is conceivable to control the DC transport voltage by using the dynamic rectifier alone. We have divided the working phenomena of the above components into seven segments: 1. Tidal motion As said above, water level increases and decreases during the high and low tide of the sea, and this is most important in this power generation system because it all depends upon the increasing and decreasing level of water.

203

204

Tidal Energy Systems

2. Barrage Barrage is the wall structure just like the dam structure. Its function is to stop the water on one side during high tide, release it when it reaches its maximum value, store it on the other side, and release it during low tide. 3. Potential energy A tidal barrage power generation system’s main source of energy is the potential energy of water stored at some high level due to the barrage. This energy will be converted to kinetic and then to electrical energy. 4. Opening of barrage doors Barrages store water during high tide, and when it reaches its maximum value, the barrage doors are opened to let the water flow to the other side. 5. Kinetic energy As water stored at some height has some potential energy and when doors are of water start to flow to the other side and potential energy is converted in to kinetic energy which will be used to produce the electrical energy. 6. Using turbines Up to now the potential energy of water is converted into kinetic energy and now this kinetic energy will be converted into the rotational energy of turbine blades when they strike them. Blades are attached to a shaft and the shaft is attached to the generator. 7. Electrical energy Water rotates blades, which rotate the shaft, and the shaft rotates the generator, which will produce electrical energy, meaning that one cycle is completed. This process will be continuous until there is a difference in the water level.

4.2.9 Modeled Processes In general spectral models, create a framework for the following processes: (a) Tide generation by wind (b) Nonlinear interaction (c) Whitecapping (breaking in deep water) (d) Bottom friction (e) Shallow-water breaking (depth induced) (f ) Advection (g) Refraction shoaling While nonlinear interaction is theoretically well defined, all the other listed processes are critically dependent on the input information to the model. This is because electricity generation of the tidal power plant significantly depends on the value of the tidal current and mathematically, the tidal current shows a nonlinear relationship with generated electrical energy. Nonlinear wave-wave interactions are accounted for via quadruplet

Optimum Sizing and Modeling of Tidal Energy Systems

(four-wave) and triad (three-wave) interactions. Quadruplet interactions occur irrespective of water depth, but should be deactivated in the model when no forcing wind is present. Triad interactions only occur in intermediate or shallow water regions. Nearshore spectral wave models account for tidal energy dissipation through the processes of whitecapping, bottom friction, and wave-induced breaking. Energy loss through whitecapping is primarily controlled by tidal steepness. However, it involves a number of highly nonlinear processes and has not yet been fully theoretically defined. Structures can be represented as an obstacle within the model through which a proportion of tidal energy can be transmitted or against which tides can be reflected. The obstacle is defined as a subgrid line that is narrow compared to the grid mesh resolution, and the width of the obstacle should be at least the size of one grid cell. The proportion of tidal energy transmitted through the obstacle is set by a user-defined transmission coefficient, which applies a constant energy reduction across the whole spectrum, leaving the spectral shape in the lee of the obstacle unchanged. It is also possible to set a transmission coefficient dependent on the height of the obstacle in addition to the incident tidal conditions, which can also apply to submerged obstacles. Reflection is implemented by a coefficient determining the proportion of energy reflected. It can be either specular (angle of reflection equals the angle of incidence), or diffuse, that is, the incident waves are scattered after reflection. Any such obstacle will also cause diffraction of waves around its ends. Tidal generation also depends on the wind speed, fetch, and duration of constant wind speed. Energy from wind is transferred to the tides. The greater the wind speed, the higher the tidal current and the larger the wind duration, the higher the tidal current. Also, the greater the distance over which the wind blows, the higher the tides. Whitecapping depends on the input wave spectrum. The tidal energy dissipation at each frequency is to be done due to whitecapping only. It should be a function of the excess of the spectral density above a dimensionless threshold spectral level, below which no breaking occurs at this frequency. Dissipation at a particular frequency above the peak demonstrates a cumulative effect, depending on the rates of spectral dissipation at lower frequencies. Level processes depend on the bathmetry and on the quality of the bottom characteristics and composition (mainly its material and grain size). For resource assessment purposes, local tidal modeling will be applied to characterize a particular site. The actual domain of the model will, however, extend beyond the boundary of the site to a point where suitable input information is available. This input information may take the form of a wave buoy but is more likely obtained from a global wave model. In the following sections, we discuss how the accuracy of the results depends on this input information and on modeling of the various processes (Tables 4.7 and 4.8). The relative importance of these factors is summarized in Table 4.7.

205

206

Tidal Energy Systems

Table 4.7 Physical process of a tidal power plant Physical process Deep oceans

Shelf seas

Shoaling zone

Harbors

Diffraction Depth refraction/shaling Current refraction Quad interactions Triad interactions Atmospheric input Whitecapping Depth breaking Bottom friction

1 3 2 4 2 4 4 2 4

2 4 3 2 3 2 2 4 2

4 3 1 1 2 1 1 1 1

1 1 1 4 1 4 4 1 1

Table 4.8 Different models of tidal power plant Models

Equations

Qualities

Drawback

Operational forecasting

MARS 2D MARS 3D

Saint Venant (Primitive equations)

Nested models

Yes

TELEMAC2D TELEMAC3D

Saint Venant + Boussinesq Navier Stockes equations

Input and output files format

No

ROMS

Primitive equations

No atmospheric pressure forcing

Yes

HYCOM

Primitive equations

Computation time Drying cells Meteorological forcing Bathymetry mesh creation Finite elements Drying cells Meteorological forcing Wave-induced currents Hydrostaticity or not Integrated in a complete water modeling system Pre- and postprocessing tools Netcdf input and output files AGRIF nested models Meteorological forcing Existing global model that can provide boundary conditions Hybrid vertical coordinates Meteorological forcing

Yes

Optimum Sizing and Modeling of Tidal Energy Systems

Table 4.8 Different models of tidal power plant—cont’d Models

Equations

Qualities

NCOM 3D

Primitive equations

Existing global model that can provide boundary conditions Meteorological forcing Existing global model that can provide boundary conditions Pre and postprocessing tools AGRIF nested models Meteorological forcing Meteorological forcing Wave-induced currents Unstructured mesh technique Finite volume method Wet-dry capability Integrated in a complete water modeling system Drying cells Meteorological forcing Finite volume method Meteorological forcing Integrated in a complete water modeling system Meteorological forcing Hydrostaticity or not

OPA-NEMO

MIKE 21 MIKE3

Saint Venant + Boussinesq Primitive equations

POM

Primitive equations

MOHID

Primitive equations

SYMPHONIE

Navier Stokes equations

Drawback

Operational forecasting

Yes

Main applications are not coastal

Yes

No information about nesting procedure commercial application

Yes

Yes

Yes

Yes

207

208

Tidal Energy Systems

4.3 NUMERICAL SOLUTION OF TIDAL ENERGY SYSTEM 4.3.1 Swell Effect (Long-Length) Tidal Swell alludes to the long-length tidals that are frequently in excess of 150 m and are produced from inaccessible tempests. Long separation scattering makes the swell range smaller and the energy more amassed than nearby wind-created tidals. The attributes empower swells to spread far beneath the ocean surface and in this way have a noninsignificant impact on the tidal flow turbine framework. Another important parameter is the swell period TSWELL, which can be calculated from the sea tidal dispersion relation.
 L ¼ gT 2SWELL =2π tanh ð2πd=L Þ The swell impact on the marine current speed can be assessed by feeds show. Feeds models figure the swell initiated current speed segment is considered and it can be ascertained by the following condition: TSWELL is abbreviated as T in the equation Vx ðtÞ ¼ πH=T cosh ð2π ðz + d Þ=L Þ= sinh ð2πd=L Þ cos 2π ðt=T  x=L Þ Vx ðt Þ ¼ πH=T cosh ð2π ðz + dÞ=L Þ= sinh ð2πd=L Þ cos2π ðt=T  x=L Þ

  3½πH 2 =4TL ð cosh ð4π ðz + dÞ=L ÞÞ= sinh 4 ð2πd=L Þ cos ðt=T  x=L Þ When we consider that the typical sea depth for tidal current turbine installation is about 30–50 m and that the typical swell length is about 150–250 m, then the smallest d/L is 0.12, which corresponds to a ratio of about 0.05 between the magnitude of the second term. More than one frequency component should be considered to model a realistic swell effect. Therefore, the total tidal current speed can be calculated by: X V ðtÞ ¼ Vtide + ½2πai =Ti cosh ð2π ðz + dÞ=Li Þ= sinh ð2πd=Li Þ cos 2π ðt=Ti  x=Li + φi Þ i

4.3.2 Energy Generation Through Tidal Power Plant Energy yield is the integral of electrical power output P over a time duration T, summed over all Ni turbines in a tidal farm: ðT X Ni Pi ðtÞdt Y¼ 0 i¼1

Where the subscript i refers to the ith turbine in the farm. The power of each tidal turbine is, in general terms, a nonlinear function of the rotor local inflow velocity (Ui), the turbulence intensity (Ii), and the turbulence length scale (Li) Pi ¼ pi ðUi ÞðIi ÞðLi Þ

Optimum Sizing and Modeling of Tidal Energy Systems

Each turbine exerts a thrust force opposing the water velocity, which can be defined by a similar functional form as the power Ti ¼ Ti ½ðUi ÞðIi ÞðLi Þ Finally, the rotor local velocity, turbulence intensity, and turbulence length scale are also nonlinear functions of time, position, and applied thrust of all turbines in the form: Ui ¼ Ui ½t, x, T ð1 : N Þ Ii ¼ Ii ½t, x, T ð1 : N Þ Li ¼ Li ½t, x, T ð1 : N Þ Traditionally, turbine performance has been characterized as a function of inflow conditions for upstream of the turbine, known as the free stream condition (U0, I0, L0). Often, the dependence on turbulent condition has been neglected, so in the context of the free stream, the traditional performance coefficients are:

 CT ðU0 Þ ¼ ðTU 0 Þ= 1=2 ρU02 A , CP ðU0 Þ ¼ ðPU 0 Þ= 1=2ρU03 A Where T is the thrust force that the turbine applies resisting the flow, P is the shaft power of the turbine, ρ is the water density, and A is the rotor cross-sectional area. The turbine performance parameters are defined by:

 CT∗ ¼ ðTU 0 Þ= 1=2ρU02 Af , CP∗ ¼ ðPU 0 Þ= 1=2ρU03 Af Where Af is the frontal area of the turbine rotor. Basin Scale The horizontal grid resolution of the basin scale simulation is larger than a turbine diameter and therefore the forces of the turbine are distributed over a horizontal region in space that is larger than the actual turbine. For any grid cell in the basin scale model, the turbine force per unit volume is given by
 fbasin ¼ 1=2Af =V ρCT∗ |□ ! ┬U |U Where Af is the portion of the turbine frontal area contained within the grid cell and V is the cell volume. The basin scale simulation calculates the power output using: Pbasin ¼ 1=2ρU 3 CP∗ Af The porous disk method specifies the drag per unit volume using: fðd, cfdÞ ¼ 1=ð2td Þ ρk|Ux |U

209

210

Tidal Energy Systems

Where k is a nondimensional resistance parameter and td is the pore’s disk thickness in the CFD mesh. The turbine thrust force T was found by numerically integrating fd over the porous disk volume region. ð T ¼ fd dv v

Similarly, the power was found by numerical integration of the product of the local forcing term and local axial velocity. ð P ¼ fðd, cfdÞ Ux dv v

This formulation gives an idealized power output that assumes that all the applied force contributes directly to power production.

4.3.3 Pressure Wave Velocity in Conduit The pressure wave velocity “a” depends upon the characteristics of the liquid such as the bulk modules and density; the characteristics of the pipe material, including the conduit size wall thickness and wall material; the external constraints, including the type of supports; and the freedom of conduit movement in the longitudinal direction. The wave velocity in a thin-walled elastic conduit with multiple joints is given by the classical Korteweg’s equation, which is given by: a ¼ √ ðK=ðρð1 + DK=eE ÞÞÞ The wave velocity for a perfectly rigid pipe where E is infinite, simplifies to a ¼ √ ðK=ρÞ The time taken for the pressure wave to travel the length of the penstock to the open surface is given by Te ¼ L/a. The theoretical period Tth for a conduit having constant diameter and constant wall thickness is given by Tth ¼ 4L=a

4.3.4 Head Loss Due to Friction The head loss is a measure of the reduction in the total head of the fluid as it moves through a pipeline. Head loss along the pipe wall is called friction loss or head loss due to the friction. The head loss due to the friction Hf in a given conduit for a given discharge is usually determined by the Darcy-Weisbach equation: Hf ¼

f ðLV 2 Þ D2g

Optimum Sizing and Modeling of Tidal Energy Systems

The dimensionless friction factor f is a function of velocity, roughness, viscosity of the fluid, and conduit diameter. The friction factor f in a laminar regime is independent of the wall roughness and inversely proportional to the Reynolds’s number. The friction factor for a laminar flow is calculated from the Hagen-Paiseuille equation as: f ¼ 64=Re Relative roughness 1/(√ f ) ¼  2 log 10(ε/3.7D + 2.51/(Re √ f )) The global structure of a tidal energy conversion system generally depends on the tidal generator, the component of power electronics, and the given load condition.

4.3.5 Tidal Current Modeling There are three important values of tidal current velocity: the cut in tidal speed, the nominal tidal speed or rated tidal speed, and the cut out tidal speed. These speeds define the tidal turbine operation, which is commonly measured with an instrument or by weather station in m/s. The usual models are: Weibull Distribution: This is the general model that describes the tidal current variations. This model optimizes the turbine design to minimize the electricity production cost. The Weibull coefficient reflects the distribution of tidal current speed and is determined by the Weibull distribution curve. The function of probability density Weibull is given as: f ðuÞ ¼ k  c ðkÞ  uðk1Þ eððu=cÞkÞ Where the probability density f(u) is the frequency distribution of the measured velocities, and k and c are the Weibull parameters, where the parameter k (distribution shape factor) characterizes the shape of the frequency distribution. The two parameter k and c are used for the calculation of mean tidal current speed. We use the following expression to obtain the scale factor for the tidal energy system. C ¼ Umean =ðγ  ð1 + 1=kÞÞ Where γ is the gamma function, the area under the curve is defined by f ðuÞ ¼ 1  eððu=cÞkÞ Rayleigh Distribution: It is a special case of the Weibull distribution when the shape factor k is equal to 2, and its probability density function is given by f ðuÞ ¼ 2u=c 2  eððu=cÞ2Þ Shaft Model: Two Mass Models: The two mass models are very much used in scientific research which are driving by the hydrodynamic toque TTa the rotor of the tidal turbine

211

212

Tidal Energy Systems

runs at speed ωTr. The low speed shaft torque TT1S acts as a braking torque on the rotor. The dynamics of the rotor are characterized by the first-order differential equation: JTr ωTt ¼ TTa  TT 1S  KTr ωTt The low speed shaft result TT1S is from the torsion and friction effects due to the difference between ωTt and low shaft speed ωT1S. The torque acts as a braking torque on the rotor. TT 1S ¼ BT1S ðθTt  θT 1S Þ + KT 1S ðωTt  ωT 1S Þ Using the gearbox G, the torque and speed of the low shaft are provided to generate a torque on the high shaft. TThs ¼ TT1S =GT θTg ¼ GT  θT 1S ωg ¼ GT  ωT 1S Through the gearbox, the low shaft speed ωT1S is increased by the gearbox ratio to obtain the generator speed ωTg while the low speed shaft torque TT1S is increased. If we assume an ideal gearbox with a ratio G, we can assume the following: GT ¼ TT 1S =TThS ¼ ωTg =ωT1S ¼ θTg =θT 1S The generator is driven by the high-speed shaft torque TThS and broken by the generator electromagnetic torque TTem. Its dynamic is given as: JTg ωTg ¼ TThS  KTg ωTg  TTem

4.4 MODELING OF A TIDAL CURRENT TURBINE 4.4.1 Turbine Power Output In general, the turbine converts the kinetic energy of the working fluid, in this case water, into the rotational motion of the turbine shaft. Swiss mathematician Leonhard Euler showed in 1754 that the torque on the shaft is equal to the change in angular momentum of the water flow as it is deflected by the turbine blades and the power generated is equal to the torque on the shaft multiplied by the rotational speed of the shaft (Fig. 4.10). Torque ¼ T ¼ ρQ ðrin vin  rout vout Þ Power ¼ P ¼ ωT ¼ ωρQðrin vin cos βin  rout vout cos βout Þ Q ¼ Water flow rate ρ ¼ Fluid density β ¼ Incident angle v ¼ Tangential fluid velocity r ¼ Turbine radius

Optimum Sizing and Modeling of Tidal Energy Systems

qin bin Vin

rin

rout

bout Vout

qout Turbine

Fig. 4.10 Euler’s turbine equation.

ω ¼ Turbine rotational speed T ¼ Torque P ¼ Power output This result does not depend on the turbine configuration or what happens inside the turbine. All that matters is the change in angular momentum of the fluid between the turbine’s input and output.

4.4.2 The Power in the Tides A tidal turbine converts the kinetic energy of tides into mechanical energy. The total power of the tides is just equal to the time rate of kinetic energy. 1 Kinetic energy ¼ mVT2 2 The amount of water passing in unit time through an area A with velocity VT ¼ AVT Mass m ¼ ρAV T Where ρ is the density of water 1 Kinetic energy per unit volume ¼ ρAVT3 Watts 2 1 Total power ðPtotal Þ ¼ ρAVT3 Watts 2 All this power cannot be extracted because the tide velocity would have been reduced to zero, which means that the tidal turbine would accumulate static water around it that

213

214

Tidal Energy Systems

would prevent its operation. From the equation, tidal power is proportional to the intercept area. Thus a tidal mill with a large swept area has a higher power. Normally, area is circular with diameter D, thus πD2 4 1 3 πD2 1 ¼ ρπD2 VT3 Watts Total power ¼ ρVT 4 2 8 A¼

Most commonly used tidal turbine is propeller type. Consider this tidal turbine Let a ¼ Inlet plane b ¼ Exit plane Pi ¼ Incoming water pressure Vi ¼ Incoming tidal velocity Pe ¼ Water pressure at exit from blade Ve ¼ Water velocity at exit from blade V ¼ Specific volume ¼ 1/ρ Applying the total energy equation Vi2 V2 ¼ P a VT + a 2 2

Pi VT + Pi +

Vi2 V2 ¼ Pa + a 2VT 2VT

(Or) Pi + ρ

Vi2 V2 ¼ Pa + ρ a 2 2

Similarly for exit area Vi2 V2 ¼ Pb + ρ a 2 2 The tidal velocity decreases from a to b because kinetic energy is converted to mechanical work. Therefore Vi > Va Pe + ρ

Vb > Ve Pa > Pi Pb < Pe Pa  Pb ¼ Pi + ρ

Vi2  Va2 V 2  Vb2  Pe + ρ a 2 2

Optimum Sizing and Modeling of Tidal Energy Systems

Assume that at the exit end away from the turbine at e, Pe ¼ Pi Vt ¼ Va ¼ Vb  2  Vi  Ve2 Pa  Pb ¼ ρ 2 If A is the projected area of the tidal mill perpendicular to the tidal stream, the axial force F is given by  2  Vi  Ve2 F ¼ ðPa  Pb ÞA ¼ ρA 2 Axial force is also equal to the change of momentum F ¼ 4mV m ¼ ρAV Tt F ¼ ρAV Tt ðVi  Ve Þ  2  Vi  Ve2 ¼ ρAVTt ðVi  Ve Þ ρA 2 VTt ¼

Vi + Ve 2

4.4.3 Forces on Blades and Torque of Tidal Turbine The torque causing the rotation of the tidal turbine shafts depends on the turbine rated power output and the rotor angular velocity. Thus Tt ¼

PT πdn

Where, T ¼ Torque on the tidal turbine ω ¼ Angular velocity of the tidal turbine wheel (m/s) n ¼ Speed of the tidal turbine wheel d ¼ Diameter of the tidal turbine wheel (m) rffiffiffiffiffiffi 4A d¼ π Tidal turbine power is given by 1 PT ¼ η ρπd 2 Vi3 8

215

216

Tidal Energy Systems

And torque on the tidal turbine is given by 1 ρπd 2 Vi3 1 ρdVi3 ¼η 8 πdn 8 n 3 3 1 ρdVi 2 ρdVi The maximum torque across the tidal turbine is TTmax ¼ 16 27 8
n ¼ 27 n The axial force on the tidal turbine is given by F ¼ π8 ρd 2 Vi2  Ve2 π F ¼ ρd 2 Vi2 9 TT ¼ η

4.4.4 Mathematical Modeling of Hydraulic Turbine The hydraulic turbine can be considered as an element without memory because the time constants of the turbine are smaller than the time constants of the reservoir, penstock, and surge chamber, if exists, which are series connected elements in the system. For parameters describing the mass transfer and energy transfer in the turbine, we will consider the water flow through the turbine Q and the moment M generated by the turbine, and that is transmitted to the electrical generator. These variables can be expressed as nonlinear functions of the turbine rotational speed N, the turbine gate position Z, and the net head H of the hydro system q ¼ qðh, n, GÞ m ¼ mðh, n, GÞ Through linearization of above two equation around the steady-state values, we obtain: dq dq dq 4h+ 4n+ 4G dh dn dG Q ¼ a11 H + a12 N + a13 g

4q ¼

4m ¼

dm dm dm 4h+ 4n+ 4G dh dn dG

M ¼ a21 H + a22 N + a23 g Where the following notations were used: Q¼

4q 4n 4m 4h 4G , N¼ , M¼ , H¼ , g¼ q0 n0 m0 h0 G0

Which represent the nonlinear variations of the parameters around the steady-state values. The hydraulic feed system has a complex geometrical configuration consisting of pipes or canals with different shapes and cross-sections. Therefore, the feed system will

Optimum Sizing and Modeling of Tidal Energy Systems

be considered as a pipe with a constant cross-section and a length equal to the real length of the studied system. In order to consider this, it is necessary that the real system and the equivalent system contain the same water mass. Let us consider M1, M2, …, MN as the water masses in the pipe zones having the lengths L1, L2, …, LN and the cross-sections a1, a2, …, aN of the real feed system. The equivalent system will have the length l ¼ L1 + L2 + ⋯ +LN and the cross-section A, conveniently chosen. In this case, the mass conservation law in both systems will lead to the equation: a

N X i¼1

Li ¼

N X

Li ai

i¼1

Because the water can be considered incompressible, the flow qi through each pipe segment with cross-section Ai is identical and equal with the flow q through the equivalent pipe q ¼ v  a ¼ qi ¼ vi ai for i ¼ 1,2,…:,n Where v is the water speed in the equivalent pipe and vi is the speed in each segment of the real pipe. From the mass conservation law: q qi ΣLi q v¼ ¼ a ΣLi qi The dynamic pressure loss can be computed considering the inertia force of the water exerted on the cross-section of the pipe: Fi ¼ MA ¼ l  a  ρ  a Where L is the length of the penstock or the feed canal, A is the cross-section of the penstock, γ is the specific gravity of water (1000 Kgf/m3), a is the water acceleration in the equivalent pipe, and g ¼ 9.81 m/s2 is the gravitational acceleration. The dynamic pressure loss can be expressed as: hd ¼

Fi γl dv γl Σli dQ ¼ ¼ a g dt g ΣLi ai dt

Using nondimensional variations, from Nakamura et al. (2002) it results:  4q d = q 4hd q0 ρlΣLi 0 ¼   hd0 hd0 ΣLi ai dt Or in nondimensional form: Hd ¼ TW

dQ dt

217

218

Tidal Energy Systems

Where TW is the integration constant of the tidal power system and the variables have the following meaning: Hd ¼

4hd 4q q0 ρlΣLi , Q¼ , TW ¼  hd0 hd0 ΣLi ai q0

It must be noted that this is a simplified method to compute the hydraulic pressure loss, which can be used for run-of-the river hydropower plants with a small water head. Hd ðsÞ ¼ sTW  QðSÞ and QðSÞ ¼  QðSÞ ¼

1 Hd ð S Þ STW

A12 A13 N ðSÞ + gðSÞ 1 + A11 TW S 1 + A11 TW S

Hd ð S Þ ¼

A12 TWS A13 TWS N ðS Þ  gðSÞ 1 + A11 TW S 1 + A11 TW S

The mechanical power generated by the turbine can be calculated with the relation P ¼ . η.Q.H, which can be used to obtain the linearized relations for variations of these values around the steady-state values: P ¼ ηgQ0 H + ηgh0 Q

4.5 TIDAL ENERGY FACILITY SIZE 4.5.1 Functional Requirements The configuration of the tidal energetic electrical connection is selected to fulfill the following objectives: 1. Tie the offshore tidal energy generators to the onshore electrical grid for transmission of the generated electrical energy into the general grid system. This may include the interconnection of a collection of physically spaced generators, as in an offshore tidal farm. 2. If it is required, connect the offshore tidal energy device to the onshore electrical grid for the supply of the tidal energy device auxiliary electrical loads for import power. 3. If it is also required, connect the offshore tidal energy device to the onshore electrical grid for the supply of electrical power to energies and start up the tidal energy device for import peak power. 4. Ensure that all the components are being operated within their rated voltage and rated current limits throughout the power range of the tidal energy farm and over the range of operation of the grid. 5. Ensure that all the components operate stably without fluctuation and predictably during individual tidal generator start up and during minor grid disturbances.

Optimum Sizing and Modeling of Tidal Energy Systems

6. Ensure that the overall protection systems operate correctly, and the circuit breaker safely isolates faulty equipment from an unfit circuit. 7. Ensure that any adverse effects of the tidal energy generators on the electrical grid are remedied according to the local grid connection requirements. 8. Ensure that grid hold is provided as defined by the confined utility in their grid connection requirements. 9. Minimize power losses in the transmission of electrical power back to shore. 10. Minimize the capital cost of the overall (onshore and offshore) connection to the grid. 11. Facilitate economic operation and maintenance of the tidal energy farm in terms of isolation and access for maintenance and connection/disconnection of the components. 12. Maximize reliability of the grid connection and reduce fault condition. 13. Minimize the downtime of generators during routine operational procedures and following failures of the electrical connection, for example due to grid disturbances.

4.5.2 Basic Requirements Imposed for Tidal Energy Generation by Grid Codes Active power and frequency control: Several grid codes (GCs) require active tidal farm power control to secure frequency stability, avoid network overloading, etc. The required extent of modulation of the power might change between the different GCs. Frequency control must be within acceptable limits to secure supply, avoid overloading, and comply with quality power standards. Frequency range and voltage range: This is the requirement to be able to continue to operate even when the system is in difficulty, that is, when voltage or frequencies are far from the nominal values. Tap changing transformers: Some GCs require that tidal farms are equipped with a tap-changing grid transformer in order to be able to vary the voltage ratio between the tidal farm and the grid in case requirements fall under this category. Tidal farm modeling and verification: Some codes require tidal farm owners/developers to provide models and system data to enable the operator to investigate by simulation the interaction between the tidal farm and the power system. They also require installation of monitoring equipment to verify the actual behavior of the farm during faults, and to check the model.

4.5.3 Grid-Connected Marine Energy Infrastructures The current advancement of tidal energy innovations has underlined the requirement for broad, vast ocean-testing activity to evaluate the proficiency and gainfulness of the planned advances and to distinguish conceivable elements for streamlining and change.

219

220

Tidal Energy Systems

Because the essential extent of a large portion of the tidal energy converters is the creation of electrical energy to be conveyed to the lattice, a considerable number of testing offices officially manufactured or to be worked on later incorporate the likelihood given to the engineers to interface their component to the network while giving them an arrangement of structures and gear particularly intended for this task. In spite of the fact that it is far-fetched that the layouts characterized for these undertakings are material to substantial scale establishments, the beginning period of tidal energy arrangement in different regions will likely need to confront comparative difficulties. Electrical Connection Functional Requirements Tidal energy components right now make utilization of an extensive variety of innovations for essential energy transformation, yet the majority of the ideas for creating power must incorporate an electrical generator in the plan. This is, for the most part, determined by a moderate mover yet at times it is specifically determined by the movement of the component itself. The significance of tidal energy converters at a propelled arrangement have been thinking about water-powered frameworks for energy transformation. The movement of the component is for this situation exchanged to a pressure-driven engine, which runs an ordinary revolving generator. The Pelamis, for instance, runs a pressure-driven engine combined with an offbeat generator running at 1500 rounds per minute. Different advances, basically hurling point safeguards, change over the power through specifically determined straight generators, deciphering at a variable speed and producing a consequent yield at variable voltage and recurrence. Tidal power plant components, particularly flat pivot turbines, give more likenesses wind turbine change system, with a gearbox interfacing between the pole and the rotor of an electrical generator. Utility power grids are 3-phase AC. Therefore, almost all generators used in power plants are 3-phase AC. Large power plants (hundreds of MWs) invariably use fixed-speed synchronous generators. In a distributed power generation, a power plant usually consists of a limited number of small units (up to a few MW) that may have induction generators. Efficient exploitation of renewable energy sources, such as marine renewable, demands variable-speed electric generators. Because voltage frequency is not constant in these machines, a power electronics AC/DC-DC/AC converter is required. The frequency on the grid side can be kept constant while it can be varied on the generator side according to the needs of system dynamics. The machine-converter system is usually referred to as the electric drive. Besides the device concept, some parameters to be taken into account are: – Cost and efficiency – Weight and volume – Maintenance requirements – Reliability

Optimum Sizing and Modeling of Tidal Energy Systems

The decision of what sort of generator would impact the level of energy hardware required and also the kind of grid association interface and control. A short synopsis of the current advancements connected to marine vitality gadgets is given below: • Synchronous machine: The field source is provided by DC electromagnets, usually located on the rotor. The current in field coils can be adjusted to load, so that the power factor can be kept low or within prescribed values. An external electric power source is needed to feed rotating DC coils. • Permanent magnet synchronous machine: Instead of electromagnets, rare-earth (usually NdFeB) permanent magnets are implemented. In machines rated up to a few MWs, PMs allow for remarkable improvements in terms of power density and design/manufacturing simplicity (no DC power source required). • Variable reluctance synchronous machines: Magnets are replaced by toothed iron in the rotor, magnetized by the armature windings field. This is a cheap, simple design with remarkably low power density. Variable-speed synchronous machines do require full-rated (MVA) power converters. • Induction generators: There is no autonomous field source. Rotor circuits hold lowfrequency AC currents induced by the armature field in the stator. No-load voltage is therefore zero and the power factor is always lower than unity. The air-gap length is determinant for performance (the smaller the better). Squirrel-cage machines have solid bars of conducting material while rotor-wound have wires. • Doubly fed induction generators: The frequency of the rotor currents is controlled by a power converter. Because the converter is rated at only a fraction of maximum machine power capability, it represents a very convenient solution for application where the speed is varied within limits (say, 30%) of the rated value. Induction machines are cheap and reliable, but encumbrance and inefficiency may make them unfit for certain applications. Low-speed, direct-drive energy conversion, for example, requires generators with torque/force density as high as possible. This is the case of linear generators for tidal power, where the speed rarely exceeds 1–2 m/s.

4.5.4 Electrical Configurations Schemes Tidal energy components have been working while associated with the framework and dependably temporarily and at a little scale, the issue of appropriately planned electrical design, gear, and foundation has not yet drawn much consideration among the tidal energy group of analysts and engineers. Continuous tasks generally concern single sea converters to be sent at short separation from shore and are primarily for showing innovation instead of expanding power transmission. Arrangement destinations have been regularly picked for handy and conservative reasons, contingent upon the area of appropriate grid association focuses at the coastline and the necessity for the extra electrical framework was insignificant to evade extra expenses. The constrained

221

222

Tidal Energy Systems

separation to shore permits a sensibly productive power transmission at low or medium voltage. Hence, a few components have been really working without conveying any sort of energy converter. As the sizes of offshore farms increase, so does the need for higher voltage transmission. Presently, tidal prototypes are connecting at 11 kV and in most cases less than 6.6 kV because lower voltage levels greatly reduce the issues of insulation and subsea connection. Transmission of offshore power could be achieved using high voltage direct current (HVDC), but this is only economic for very large-scale farms transmitting over long distances. However, this could become more viable in the future when new silicon devices become more readily available. An expansion in interconnections may relieve the discontinuous impacts of wind and tidal systems by empowering bigger power streams between nations. HVDC could likewise be utilized to gather the energy from bigger homesteads, which are foreseen to be found exceptionally far seaward. To guarantee a more successful connection between seaward inexhaustible and the framework organize, it is likely that subsea or seaward substations will be required for the bigger homesteads to marshal and gather the generator’s energy before transmission to the shore and the more extensive electrical system. On account of numerous synchronous generators, these substations would gather the AC control at different frequencies, change it to a typical lattice recurrence, raise the voltage, and transmit it to the shore. Electrical cable connection is a key issue, particularly for TIDAL devices where the power take off is subject to tidal lift and fall or where the device needs to reorient itself to capture the tidal flow or the TIDALs’ energy. In these cases, flexible cables are required. These issues have, to some degree, been solved for oil and gas applications, but their applicability to TIDAL energy is limited by the higher power and voltage ranges required there. Besides, ensuring cable reliability remains an area of concern. It is not yet clear if generic or standardized electrical connection techniques can be developed for all marine renewable technologies, but future economies of scale can be expected to reduce the impact of these components of the global cost of the installation. From a theoretical point of view, any marine energy device might be directly connected to the grid without any additional element, assuming that a proper power converter is installed onboard. However, for efficient and economical reasons, it is likely that power produced by arrays of converters will be collected and transformed before being transmitting across the sea. This can be achieved in several ways and through several possible configurations that will be introduced below. A first distinction should be made based on the type of power transmission between offshore and onshore locations. Electrical energy can be transported by alternating current (AC) or direct current (DC): for offshore plants the choice of whether to use a DC or AC transmission line is mainly determined by the distance to shore and the installed capacity. For projects located far from the grid connection point, or with several hundred MWs of capacity, AC transmission becomes costly or impossible due

Optimum Sizing and Modeling of Tidal Energy Systems

to cable-generated reactive power using up much of the transmission capacity. In such cases, HVDC transmission is becoming an option. Such a system requires an AC/DC converter station both offshore and onshore; both stations are large installations whose building and operation might impose a number of engineering and economical challenges (Fig. 4.11). AC Transmission-HVAC Transmission Most of the existing tidal energy transmission systems use high voltage alternating current (HVAC) for the transport of electrical power between the mainland and stations located on (or under) the sea. It is a very well-established technology and an HVAC system generally contains the following main components: • AC collecting system on the platform. • Offshore transforming substation with transformers and reactive power compensation. • Three-phase submarine cable. • Onshore transforming substation with transformers and reactive power compensation. At the point when the voltage of the transmission line and the framework voltage are equivalent, the transformer isn’t necessary because of their development, circulated capacitance in submarine links is significantly higher than capacitance in overhead lines.

1. Farm 2. Device 3. Converter 4. Bus 5. Hub 6. Subsea cable 7. Onshore station 8. Transmission 9. Connection 10. Grid

Fig. 4.11 Facility condition of a tidal power plant.

223

224

Tidal Energy Systems

In this manner, the transmission length is diminished for tidal applications. Responsive power increments with voltage and length of the link and long-transmission separations require huge, receptive pay gear at the two closures of the line. Possible Configurations

A first essential idea of electrical transmission may consider a different association between each tidal energy component and the inland substation. For this situation, the establishment of a seaward substation would be maintained at a strategic distance from the demand site. This kind of arrangement is probably material for the beginning period of tidal homesteads or a single component, particularly if it puts it at a restricted separation from the coastline. In Fig. 4.12, it can be seen that each converter was accepted to convey a converter and a transformer. Because the transformer ought to be introduced onboard, it is likely that main constrained voltages are reachable (11–33 kV). This arrangement has the preferred standpoint of keeping away from the workings of a substation, yet the requirement for a few links and the low voltage transmission make it reasonable just for a few components and a short separation to shore. Also, middle-of-the-road connectors among umbilical and transmission links would be required. The main preferred standpoint emerging contrasted with a setup with an interconnection of the components and a special link would be because of a higher accessibility (Figs. 4.13 and 4.14). DC Transmission An HVDC LCC or established HVDC framework depends on line commutated converters utilizing thyristors as the exchanging component. The root of the converter’s name is the need for a current AC arrangement, keeping in mind the end goal to accomplish appropriate substitution. This sort of transmission framework can just exchange control between (at least two) dynamic networks and an assistant start-up framework

Electric grid

Onshore substation

Hub

Fig. 4.12 First possible configuration of system.

Protection

Transmission cable

Tidal system

Optimum Sizing and Modeling of Tidal Energy Systems

Electric grid

Onshore substation

Hub

Protection

Transmission cable

Tidal system

Protection

Transmission cable

Tidal system

Fig. 4.13 Second possible configuration of system.

Electric grid

Onshore substation

Hub

Fig. 4.14 Third possible configuration of system.

would be important in the seaward marine homestead. Use of an HVDC LCC submarine transmission has just been utilized for the association of high-voltage lattices; there is no single converter station situated in the ocean. HVDC LCC systems have the following main components at each end of the transmission line: • Transformers • LCC power converter based on thyristors • AC and DC filters • DC current filtering reactance • Capacitors or STATCOM for reactive power compensation • DC cable Substations at the two ends require transformers so as to raise the voltage to the essential level for the transmission line. Separation and insurance of DC stations are especially testing and require costly arrangements.

225

226

Tidal Energy Systems

HVDC VSC

With the discovery of the insulated-gate bipolar transistor (IGBT), a new world of opportunities opened for HVDC transmission. HVDC VSC is a recent technology where thyristors are substituted for by IGBTs, which was only made available for use in commercial applications a few years ago. Because of its complexity, only two companies manufacture it, ABB with the HVDC light and Siemens with the HVDC plus. HVDC VSC systems allow independent and total control of active and reactive power at each end of the line and power transmission can be controlled with high flexibility. At the offshore station, reactive power can be supplied for the marine generators and at the onshore substation, reactive power can be used to regulate voltage at the grid connection point. HVDC VSC converter stations are more compact than HVDC LCC, so the offshore platform size can be smaller and less expensive. VSC converters can even provide black start capability, thus no additional startup mechanism is necessary offshore. An HVDC VSC system has the following main components: • Transformers • HVDC VSC converter substations (offshore and onshore, possibly hosting the transformer as well) • AC and DC filters • DC current filtering reactance • DC cable All filters and reactances in an HVDC VSC are smaller than the equivalent HVDC LCC components because of the higher switching frequency of the converter. There is no need for reactive power compensation because the converter is able to control reactive power. An HVDC VSC can also increase the flexibility of the generating technologies and the cost of power converters if very high voltage. Possible Configurations

Fig. 4.14 demonstrates a conceivable alternative for an HVDC transmission setup. Here again it has been expected that all components are furnished with a converter and a transformer. Power could be produced and transmitted to a seaward substation at 11 kV where a substantial transformer would lift the voltage to 132 kV or more. An LCC converter (or a VSC converter) would then amend the current to transmit the vitality along the link. The coastal station ought to incorporate another converter and potentially a transformer to bring down the voltage, relying upon the network voltage at the association point.

4.5.5 Elements of a Grid Connection Infrastructure The definition of the rated power of the farm and the distance to shore is the first step to determine a suitable configuration for the electrical connection. The assessment of different options could be based on a preliminary level on the evaluation of their efficiency

Optimum Sizing and Modeling of Tidal Energy Systems

and accordance to the grid requirements. However, electrical connection infrastructures in offshore locations often represent real challenges for offshore and civil engineers and usually require huge investments to assure reliable structures. It is therefore clear that the design of the grid connection of a marine energy farm must take into account several aspects related to the actual feasibility of the proposed solution. The decision of the proper scheme should be based on a detailed estimation of the economic impact of the required investments. Generally, the grid connection of a medium- to large-scale marine energy farm would require the following physical elements: • Device cabling and conversion equipment (power converter, transformer, and umbilical cable) • Cable connectors • Offshore substation • Subsea transmission cables • Onshore substation Hardware and umbilical links for gadget interconnection are at present gadget particular and reliant on the generator write considered. It is normal that later on, a large portion of the marine vitality advances will be furnished with the locally available converter and transformer while the plan of the umbilical link will most likely be managed by the sending site. Umbilical links for control transmission have been utilized as a part of the seaward business for a considerable length of time. However, their application to marine vitality innovations may require intentionally planned arrangements as unique loads because the movement of the gadgets (especially wave vitality skimming advancements) is altogether different from the ones ordinarily experienced in seaward stages gave a few outcomes in light of dynamic investigation that affirm the requirement for exceptional items). In view of this, the past experience of the seaward breeze industry is exceptionally valuable to comprehend the specialized issues identified with the outline of these components.

Cable Connectors Connection of tidal energy devices to the offshore substation should be performed through connecting elements capable of transmitting efficiently the electrical power while allowing quick and easy connection and disconnection. Commercial off-the-shelf muteable power umbilical terminations, also known as umbilical termination assembly (UTAs), are widely available for ROV (remotely operated vehicle) applications. Those connection systems are expensive, high-performance devices that should be adapted from oil-related industries. They consist basically of free-flooding structures to which the cable armor is fixed. One of the main limitations of their application to the offshore tidal

227

228

Tidal Energy Systems

renewable industry is the relatively low power (up to about 100 kW) and voltage transmission capability (generally up to 1 kV). Connected devices are usually in two categories: • Dry mate: Topside mating and subsea deployment. • Wet mate: Either topside or subsea mating.

4.5.6 Offshore Substation Seaward substations are utilized to diminish electrical misfortunes by expanding the voltage and, after that, trading the ability to shore. By and large, a substation should not be introduced if: The project is small (100 MW or less). • It is close to shore (15 km or less). • The connection to the grid is at collection voltage (e.g., 33 KV). At the beginning, tidal energy ventures are probably going to fulfill these prerequisites, hence the working of an appropriately planned seaward substation isn’t yet an essential requirement for a tidal energy system. In any case, most future ranches will be substantial as well as situated a long way from shore, and they will require at least one seaward substation. Various seaward substations have been introduced and worked for seaward tidal energy cultivation; their vast size legitimized the high cost connected with their development. Normally, tidal substations are settled stages in light of solid establishments, and would most likely not be appropriate for profound water organizations with the end goal that is conceivably required for tidal energy components. In future high cost of tidal energy arrangements would likely need to rethink the plan of intentionally manufactured substation because settled structures with heaped establishments, as presented, would be excessively costly for profound tidal establishments. In such cases, there would be essentially two options: Floating substations: This option would allow the adoption of standard electrical equipment onboard, provided that watertight integrity is maintained. This would also be relatively easy to maintain and operate. The design of these structures would be, however, rather challenging because they should be capable of withstanding possibly very large tidal loads and, at the same time, guaranteeing a very limited footprint. Otherwise, umbilical connections from devices might suffer severe damage. Some solutions of this kind have been proposed, but they are still at an early development stage and no concept has actually proven to be feasible. Experience from the oil and gas industry is the key in many proposed designs, such as moored semisubmersible platforms or tension-leg platforms. Subsea-substations: Subsea installations would guarantee more safety in terms of load resistance and positioning, but would require very expensive protection equipment for the electrical devices. Most likely, the switchgear should include sealed compartments full of pressurized oil. Moreover, maintenance would be very difficult or almost

Optimum Sizing and Modeling of Tidal Energy Systems

impossible in some cases, as installations placed on the seabed would be operated only by remotely operated vehicles unless the water depth is low enough to allow divers. Disconnection of the cables would be extremely difficult and mostly require the adoption of wet-mate connectors, which are more expensive than the dry-mate ones. Subsea substations would probably be permanent structures and therefore would require very high reliability and redundancy to assure tidal farm availability. Subsea Cable Electric energy created by tidal energy systems requires at least one submarine link to transmit the power produced by the inland utility network that serves the end clients of this sustainable power source. A cross-area plan of regular submarine links for AC control transmission Subsea links is by and large created by a few components: Conductors: The copper conduit has medium and high voltage. Aluminum can also be used, although it has a lower current conveying limit and requires more noteworthy distances. Limit increments relatively with the cross-sectional zone, which can go up to around 2000 mm2 before the link ends up clumsy and the twisting span is excessively extraordinary. Expansive links may have a twisting range of 6 m. The amperage is the capacity of voltage, length, protection write, laying arrangement and internment profundity. • Number of conductors: If possible, in AC cables the three phases are bundled in order to reduce cable and laying costs. It also produces weak electromagnetic fields outside the cable and has lower induced current losses than three single-core cables laid separately. • Screening: A semiconductive screening layer of paper or extruded polymer is placed around the conductor to smooth the electric field, to avoid concentrations of electrical stress, and to assure a complete bond of the insulation to the conductor. • Insulation: Diverse sorts of cable protection are utilized for tidal energy transmission for long separations. Low-pressure oil-filled (LPOF) or fluid-filled (LPFF) links protected with liquid-impregnated paper have generally been the most common links for submarine AC transmission. The protection is impregnated with manufactured oil whose weight is normally kept up by drawing stations on either end. The pressurized liquid keeps voids from forming in the protection when the conductor grows and contracts as the heap changes. The helper pressurizing hardware speaks to a noteworthy segment of the framework cost. LPFF links risk liquid spillage, which is a natural hazard. Similar in construction are the solid, mass-impregnated paper-insulated cables, which are traditionally used for HVDC transmission. The lapped paper insulation is impregnated with a high-viscosity fluid; these cables do not have the LPOF cable’s risk of leakage. Cross-linked polyethylene (XLPE, also called PEX) has a lower cost than LPOF of a similar rating and has lower capacitance, leading to lower losses for AC applications. XLPE can be manufactured in longer lengths than LPFF. Another extruded insulation used in submarine cables is ethylene propylene rubber (EPR), which has similar properties to XLPE at lower voltages, but at 69 kV and above, has a higher capacitance.

229

230

Tidal Energy Systems

Sheath: An internal sheath is utilized to earth the cable in general and to convey blame current if the cable is harmed. It additionally makes a dampness obstruction further in AC links, current will be initiated in this sheath, prompting circling sheath misfortunes; different sheath-establishing plans have been produced to lessen coursing streams that emerge in the sheath.

4.5.7 Technical Issues Related to AC transmission The most cost effective AC technology for this type of interconnection is solid dielectric, also called extruded dielectric or polymeric insulated cable, usually with cross-linked polyethylene (XLPE) insulation. This is the cable system technology used for all offshore wind farms constructed to date (all of which are located in Europe) primarily as a result of: • Interconnection • Installation • Maintenance • Operational reliability • Cost effectiveness The main difference between XLPE cables and the old oil-impregnated paper (OIP) cables is the insulation. The XLPE insulation can support higher temperatures, 90°C in the conductor in a steady state and 250°C in a 3 s short circuit. Also, the losses of XLPE are significantly lower than the OIP ones, and because it does not use oil, it is environmental friendly, easy to install, and requires less maintenance. From its components, it is important to note two things: • The optic fiber, which is used to communicate between the farm and the management center on the shore. • The sea shielding and the polypropylene thread, which have two objectives: to provide both electric isolation and mechanical protection to the cable. The greatest electrical contrast among cable and overhead lines is the expansive capacitance of the initial ones. This condition builds the reactive power produced by the links, diminishing its ability to transmit dynamic power, particularly finished long separations. Along these lines, it is important to give reactive compensation at the cable’s furthest points. The capacitance of the HVAC-protected link assumes a noteworthy part in restricting the financially possible length of the HVAC cable. Capacitance causes charging current to stream along the length of the cable. The cable must convey this present and additionally the helpful load current, this physical restriction diminishes the heap conveying ability of the cable. Because capacitance is circulated along the whole length of the cable, the greater the link, the higher the capacitance and the resultant charging current. As the cable framework plan voltage is expanded to limit line misfortunes and voltage drop, the charging streams additionally increment, exacerbating the circumstance.

Optimum Sizing and Modeling of Tidal Energy Systems

4.5.8 Tidal Measurement Devices Acoustic Doppler Profile The central rule of activity of the acoustic Doppler profile (ADP) depends on the dispersion of acoustic energy from inside the water section. The energy is transmitted into the water from transmitter/finder heads (normally piezo-electric materials). The recurrence of the first flag will be moved by the neighborhood speed of little particles suspended in the stream (the Doppler effect). The recurrence moved (scattered) sound is then identified by a similar instrument. The situation of the flag in the water is dictated by the phase/ time of flight instruments and is typically found in the middle value of a small volume to give a neighborhood estimation along the pillars. These cells or bins can be chosen by the user, but are typically of the order of 0.5–1 m. The volume of the cell will depend on the degree to which the beam diverges as it propagates through the water. This is determined by the transmitter head design and bean angles are typically of the order of 4 degrees. One may wish to limit the bin size to match the cells with the needs of the measurement or to satisfy the need for a good signal-tonoise ratio (a larger volume will typically provide more “signal” at the cost of lower spatial resolution). ADPs are often deployed on the seabed, but can be placed in midwater using subsurface buoys. This allows the use of higher-frequency instruments, but care has to be taken to ensure that wave-induced motions do not affect the measurements. Measurements can be made at repetition rates up to several per second. The range of the beam is dependent on the properties of the water through which it is moving and the properties of the instrument. Scatter can be heavily affected by suspended sediment that reduces power (range) rapidly. This is dependent on beam frequency with a higher-frequency beam energy being attenuated faster than low frequency. This means, for example, that in shallow water, frequencies above 1 MHz can be used. The higher-frequency beams can be made to diverge less and give better measurement resolution. In deeper water, it is not possible to deploy instruments with enough battery power to support higher-frequency beams and one would typically use ADP units with a frequency on the order of 600 MHz. These beams can penetrate further through the water column but will have lower resolution/ accuracy. Radar Systems The radar system is a shore-based remote sensing system using the over-the-horizon radar technology to monitor ocean surface currents, waves, and wind direction (Gurgel, 1999). This long-range, high-resolution monitoring system operates with radio frequencies between 5 and 50 MHz. A vertical polarized electromagnetic wave is coupled to the conductive ocean surface and follows the curvature of the earth. The rough ocean surface interacts with the radio wave and due to the Bragg effect, backscattered signals can be

231

232

Tidal Energy Systems

detected from ranges of more than 200 km. This effect was first described in 1955 by Crombie and the first radar system using that effect was developed by Barrick et al. at NOAA in 1977. The Bragg effect describes the coupling of the electromagnetic wave with the ocean wave field. To fulfill the Bragg conditions, the electromagnetic wavelength needs to have twice the wavelength as the ocean wave, for example, for a 30 MHz radar signal with Lambda 10 m, the corresponding ocean wave is 5 m. Reflections from waves that fulfill this condition will generate a dominant signature in the received signal spectrum due to in-phase summation of amplitudes. The accuracy and reliability of ocean current maps has been controlled from an extreme dynamic ocean area off the French coast near Brest. A WERA deployment on the Brittany coast of France, owned by SHOM (Oceanographical and Hydrographical Service of the French Navy) and operated by Actimar, has provided data for a few years. The radar operates at a center frequency of 12.38 MHz with a bandwidth of 100 kHz (range cell size of 1.5 km) at 30 W rf-power. Over a period of more than 12 months, a study was carried out to validate the quality of the provided data by means of a comparison with buoy data. Furthermore, the reliability was qualified by comparing the user’s demands for data availability with the resulting data. The accuracy and reliability was studied by SHOM using an ADP and a Wave Rider buoy for ground truthing. Tide Gauge A tide gauge (also known as a mareograph or a marigraph as well as a sea-level recorder) is a device for measuring the change in sea level relative to a vertical detum. Sensors continuously record the height of the water level with respect to a height reference surface close to the geoid. Water enters the device by the bottom pipe (far end of the tube, see picture), and electronic sensors measure its height and send the data to a tiny computer. Historical data are available for about 1450 stations worldwide, of which about 950 provided updates to the global data center since January 2010. At some places, records cover centuries, for example in Amsterdam, where data dating back to 1700 is available. When it comes to estimating the greater ocean picture, new modern tide gauges can often be improved upon by using satellite data. Tide gauges are used to measure tides and quantify the size of tsunamis. The measurements make it possible to derive the mean sea level. Using this method, sea level slopes up to several 0.1 m/1000 km and more have been detected. A tsunami can be detected when the sea level begins to rise, although warnings from seismic activity can be more useful (Fig. 4.15). Wave and Tide Sensor Wave and Tide Sensors 5218/5218R are compact, fully integrated sensors for measuring the wave and/or tide conditions. The sensor is designed to be mounted on the Aanderaa SEAGUARD platform or via cable connected to a SmartGuard Datalogger. The sensor may also be used as a standalone with the RS-232 output. The 5218R sensor is designed

Optimum Sizing and Modeling of Tidal Energy Systems

Fig. 4.15 Tidal gauge.

for use with long cables by means of an RS-422 full duplex interface. The R-version cannot be used in SeaGuard applications. The sensor is also available in a vented version. This means that the sensor is automatically compensated for air pressure. This is done by use of a compensating unit placed in air and an air pipe in the cable between the sensor and the compensating unit. The sensor application areas are in fixed installations, either deployed in a seabed installation in shallow waters or mounted onto a fixed structure in the upper water column. Typical applications for the sensor are measurements of tides and waves in ports and harbors, marine operations, weather forecasts, and climate studies. Features

• • • • • • • •

Smart sensor technology plug and play Sensor calibration coefficients are stored in the sensor Minimal and simple maintenance needs Low current drain Power: 5–14 VDC, 50 mA max Output formats: AiCaP CANbus, RS-232/RS-422 Short update interval: 1 s to 255 min 2 and 4 Hz sampling frequency

233

234

Tidal Energy Systems

• New updated wave parameters every 1 s • 256, 512, 1024, and 2048 samples • Outputs: pressure, temperature, tide pressure, tide level, significant wave height, maximum wave height, mean periode, mean zerocrossing periode, energy periode, steepness, irregularity of sea state, cut-off frequency, pressure time series, last pressure sample index, and wave spectrum

4.5.9 Software Used in Modeling of a Tidal Power Plant Tidal Farmer TidalFarmer is the first commercially available three-dimensional array modeling tool for the tidal industry. It has the ability to test array formations virtually. Important design decisions can be tested beforehand, including technology choice, device location, and yawing strategy. This lets you maximize energy yields before construction has even begun to minimize project risk and costs. TidalFarmer is built on validated wake models that capture wake mixing processes downstream of tidal power devices. It combines these models with survey measurements, site-specific constraints, descriptions of the tidal device, and local bathymetry. Based on this bespoke input, it enables you to generate: • Resource assessments • Accurate energy yields • Array-generated wake maps The software also includes advanced validation features to ensure accuracy. A tide data analysis module is available as an optional module. WaveDyn WaveDyn is the first fully coupled simulation tool designed for wave energy. It allows you to simulate the performance and loading on a wave energy device. It enables you to model hydrodynamics calculations and control and power take-off systems. Our WaveDyn numerical modeling tool also offers greater analysis of the structural design and a more detailed design of each component in the structure. There is a diverse range of devices in wave energy. So WaveDyn, a multibody software tool, lets you build a model of your machine using a collection of different components covering a wide range of devices. WaveDyn’s calculation modules include: Hydrodynamics • Inclusion of first-order hydrodynamic loads • Diffraction, radiation, and nonlinear hydrostatics • Processing of flow solver data output • Dedicated plug-ins to couple with commercial flow solvers

Optimum Sizing and Modeling of Tidal Energy Systems

Power take-off (PTO) and control • Explicit models and real system templates • Linear and nonlinear formulations • Motion, force, and moment constraints • Incorporation of internal PTO dynamic states • Built-in actuation, rectification, and smoothing system models • Control logic, controller demands, transducer signals • Independent discrete time controller DLL interface • Direct drive template Moorings • Catenary systems and tension legs • Quasistatic formulation based on nonlinear force-displacement look-up tables • Mooring line damping forces • Verified against fully dynamic models and validated with experimental data Steps of a Tidal Turbine Power Plant Suppose we are going to install a tidal power system for a total load of 800 W where the required backup time of the battery is 3 h (you may use your own as this is just for a sample calculation). So that in this case load ¼ 800 W. We consider required backup time for batteries ¼ 3 h. What do we need to know? Inverter/UPS Rating

If we connect the DC generator as a tidal generator so it is necessary to convert the DC supply into the AC supply so that we used inverter. The inverter/UPS rating should be >25% of the total load (for the future load as well as taking losses into consideration). 800  ð25=100Þ ¼ 200W Our load + 25%extra power ¼ 800 + 200 ¼ 1000W This is the rating of the UPS (inverter), that is, we need a 1000 W UPS/inverter for tidal power plant installation, according to our needs (based on calculations). Required Number of Batteries

We already know that the battery is used for storage purposes. In this analysis, we consider the required backup time of batteries in hours ¼ 3 h. Suppose we are going to install 100 Ah, 12 V batteries,

235

236

Tidal Energy Systems

12V  100Ah ¼ 1200Wh Now for one battery (i.e. the backup time of one battery) 1200Wh=800W ¼ 1:5h But our required backup time is 3 h. Therefore, 3/1.5 ¼ 2 ! that is, we will have to connect two batteries each of 100 Ah, 12 V. Backup Hours of Batteries

If the number of batteries is given, and you want to know the backup time for these given batteries, then use this formula to calculate the backup hours of batteries. 1200Wh  2 Batteries ¼ 2400Wh 2400Wh=800W ¼ 3h In the first scenario, we will use a 12 V inverter system. Therefore, we will have to connect two batteries (each of 12 V, 100 Ah) in parallel. But a question is raised below: Battery Charging Time

Series or parallel connection for batteries Why batteries in parallel, not in series? Because this is a 12 V inverter system, so if we connect these batteries in series instead of parallel, then the rating of the batteries becomes V1 + V2 ¼ 12 V + 12 V ¼ 24 V while the current rating would be the same, that is, 100 Ah. In series circuits, the current is same in each wire or section while the voltage is different, that is, voltage is additive, meaning V1 + V2 + V3 … Vn. That’s why we connect the batteries in parallel because the voltage of batteries (12 V) remains the same while its Ah rating will be increased. That is, the system would become ¼ 12 V and 100 Ah + 100 Ah ¼ 200 Ah. In a parallel connection, the voltage will be the same in each wire or section while the current will be different, that is, the current is additive, for example, I1 + I2 + I3 … + In. We will now connect two batteries in parallel (each of 100 Ah, 12 V), that is, 2, 12 V, 100 Ah batteries will be connected in parallel ¼ 12 V, 100 Ah + 100 Ah ¼ 12 V, 200 Ah (parallel). Charging Current for Batteries

Now the required charging current for these two batteries. (Charging current should be 1/10 of batteries Ah)

Optimum Sizing and Modeling of Tidal Energy Systems

200Ah  ð1=10Þ ¼ 20A Charging Time Required for Battery

Here is the formula for charging time of a lead-acid battery. Charging time of battery ¼ Battery Ah=charging current T ¼ Ah=A For example, for a single 12 V, 100 Ah battery, the charging time would be: T ¼ Ah=A ¼ 100Ah=10A ¼ 10h ðIdeal caseÞ due to some losses (it has been noted that 40% of losses occurred during battery charging). This way, we take 10–12 A charging current instead of 10 A. Therefore, the charging time required for a 12 V, 100 Ah battery would be: 100Ah  ð40=100Þ ¼ 40 ð100Ah  40%of lossesÞ The battery rating would be 100 Ah + 40 Ah ¼ 140 Ah (100 Ah + losses). Now the required charging current for the battery would be: 140Ah=12A ¼ 11:6h If DC load is not connected ¼ only battery charging We know the famous power formula (DC) P ¼ VI ðpower ¼ voltage  currentÞ Putting the values of batteries and charging current. P ¼ 12V  20A P ¼ 240W This is the required wattage of a tidal plant (only for battery charging, and then the battery will supply power to the load. That is, the direct load is not connected to the plant).

DC Load Is Connected As Well As Battery Charging

Now suppose there is a 10 A directly connected load to the panels through an inverter (or maybe a DC load via a charge controller). During the sunshine, the solar panel provides 10 A to the directly connected load +20 A to the battery charging, that is, solar panels charge the battery as well as provide 10 A to the load. In this case, the total required current is 20 A for battery charging and 10 A for a directly connected load. In this case above, the total required current in amperes,

237

238

Tidal Energy Systems

20A + 10A ¼ 30A Now, I ¼ 30 A, then required power P ¼ V  I ¼ 12V  30A ¼ 360W Rating of Charge Controller

As we have calculated above that the charging current for a 200 Ah battery is 20–22 A (22 A for battery charging + 10 A for direct DC load), therefore we can use a charge controller about 30–32 A.

EXERCISE Q.1

HOMER software is used in a tidal power plant for (i) Sensitivity analysis (ii) Cost optimization (iii) Simulation (iv) All of the above

Q.2

The (i) (ii) (iii) (iv) The (i) (ii) (iii) (iv)

rectifier is used in a tidal power plant for AC to DC conversion DC to AC conversion Both None of the above inverter is used in a tidal power plant for AC to DC conversion DC to AC conversion Both None of the above

Q.4

The (i) (ii) (iii) (iv)

battery is used in a tidal power plant for AC to DC conversion DC to AC conversion Storage purposes None of the above

Q.5

The (i) (ii) (iii) (iv)

generator is used in a tidal power plant for Electrical to mechanical conversion Mechanical to electrical conversion Both None of the above

Q.6

The (i) (ii) (iii) (iv)

transformer is used in a tidal power plant for To transform electrical energy from one to another circuit Electrical to mechanical conversion Mechanical to electrical conversion None of the above

Q.3

Optimum Sizing and Modeling of Tidal Energy Systems

Q.7

The (i) (ii) (iii) (iv)

induction generator gives output in terms of DC AC Both None of the above

Q.8

The (i) (ii) (iii) (iv)

pitch angle of a tidal turbine is controlled in order to limit the Turbine output Tidal generator output Battery Inverter

Q.9

Water tunnels are based on the principle of (i) Hydrokinetic (ii) Hydrodynamic (iii) Both (iv) None of the above

Q.10

Cooling in the transformer is used in the form of: (i) Natural cooling (ii) Forced cooling (iii) Oil cooling (iv) All of the above

Q.11

The unit of electrical energy generated by a tidal power plant is: (i) KW (ii) KVA (iii) KWh (iv) None of the above the capacity of a battery is measured in the form (i) Ah (ii) KWh (iii) KW (iv) None of the above

Q.12

Q.13

Which type of generator is used frequently in tidal power plants? (i) Induction generator (ii) Synchronous generator (iii) DC generator (iv) None of the above

Q.14

An nduction generator is also known as a (i) Doubly excited machine (ii) Singly excited machine (iii) Both of the above (iv) None of the above

239

240

Tidal Energy Systems

Q.15

The (i) (ii) (iii) (iv)

approximate efficiency on f induction tidal generator is in the range of: 80%–85% 85%–90% 90%–95% 95%–100%

EXERCISE 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

Explain the different functions of HOMER software. What is the importance of HOMER in the modeling of a tidal energy system? What is the importance of the battery of a tidal power plant? What is the importance of the tidal generator in a tidal power plant? What is the importance of the inverter in a tidal power plant? What is the importance of a rectifier of a tidal power plant? Explain the modeling of a tidal power plant by MATLAB. Explain different characteristics of the towing tank. Write different limitations of the aphysical model for tidal energy conversion system. Explain the working of the water tunnel. Explain the component classification of a tidal energy device by three-layer descriptions. Derive the equation for the hydrodynamic principle of a tidal energy system. Explain the power take-off concept of the tidal energy converter. Explain the swells effect of a long-length tidal current. Derive the equation for turbine power output.

REFERENCES Gurgel, K.W., 1999. Wellen Radar: a new ground wave HF radar for ocean remote sensing. Coastal Eng. 37, 219–234. Nakamura, T., Morimoto, S., Sanada, M., Takeda, Y., 2002. Optimum control of IPMSG for wind generation system.PPC-Osaka Conf IEEE3, pp. 1435–1440.

FURTHER READING Abdullah, M.A., Yatim, A.H.M., Tan, C.W., Saidur, R., 2012. A review of maximum power point tracking algorithms for wind energy systems. Renew. Sust. Energ. Rev. 16, 3220–3227. Chiniforoosh, S., Jatskevich, J., Yazdani, A., Sood, V., Dinavahi, V., Martinez, J.A., Ramirez, A., 2010. Definitions and applications of dynamic average models for analysis of power systems. IEEE Trans. Power Delivery 25 (4), 2655–2669. Datta, R., Ranganathan, V.T., 2003. A method of tracking the peak power points for a variable speed wind energy conversion system. IEEE Trans. Energy Convers. 18 (1), 163–168. E.ON Netz GmbH, 2006. Grid code for high and extra high voltage. Technical report, E.ON Netz GmbH, Bayreuth, Germany. EEA, 2010. Tracking progress towards Kyoto and 2020 targets in Europe. Technical Report 7/2010, European Environment Agency, Copenhagen. Grant Gross, M., 1987. Oceanography, A View of the Earth. Prentice-Hall, Englewood Cliffs, New Jersey. Hardisty, J., 2009. The Analysis of Tidal Stream Power. John Wiley & Sons, Chichester, West Sussex.

Optimum Sizing and Modeling of Tidal Energy Systems

Hong, Y.Y., Lu, S., Chiou, C.S., 2009. MPPT for PM wind generator using gradient approximation. Energy Convers. Manag. 50, 82–89. Idjdarene, K., 2010. Contribution à l’etude et la commande de generatrices asynchrones à cage dediees à des centrales electriques eoliennes autonomes. PHD, University of Bejaia-USTL de Lille, Bejaia. Kesraoui, M., Korichi, N., Belkadi, A., 2011. Maximum power point tracker of wind energy conversion system. Renew. Energy 36, 2655–2662. Mahdi, A.J., Tang, W.H., Jiang, L., Wu, Q.H., 2010. A comparative study on variable-speed operations of a wind generation system using vector control. In: ICREPQ’10: International Conference on Renewable Energies and Power Quality.pp. 1–6. Meharrar, A., Tioursi, M., Hatti, M., Boudghe`ne Stambouli, A., 2011. Expert Syst. Appl. 38, 7659–7664. Munteanu, I., Bratu, A.I., Cutululis, N.A., Ceanga, E., 2008. Optimal Control of Wind Energy Systems. Springer-Verlag, London. Thongam, J.S., Ouhrouche, M., 2011. Fundamental and Advanced Topics in Wind Power. InTech. book Chap. 15.

241

CHAPTER 5

Control System of Tidal Power Plant Contents 5.1 Introduction 5.2 Automatic Control of a Tidal Power Plant 5.2.1 Control System for Unit Operation 5.2.2 Information and Control Signals 5.2.3 Local Manual (Mechanical or Push Button) Control 5.2.4 Local Control of Unit From UCB 5.2.5 Control of Unit of Central Control Room and Off Site Supervisory Control 5.2.6 Synchronizing of a Tidal Energy System 5.3 Control Strategies of Tidal Energy Conversion Systems 5.3.1 Theory of Hydrokinetic Energy Conversion 5.3.2 Tidal Turbine Control 5.3.3 Tidal-Dynamic Energy Assessment 5.3.4 Turbine Configuration and Control Objectives 5.4 Reactive Power Control of Tidal Power Plant 5.4.1 Design of Passive Components 5.4.2 Power Factor Correction (Active and Reactive Power Control) 5.4.3 Reactive Power and Voltage Control 5.5 Dynamic Control of Tidal Current Turbine 5.5.1 Load Frequency Control 5.5.2 Control Mechanism of Speed Governing System: Governor Servo System 5.6 Stability Analysis of a Tidal Power Plant 5.6.1 Definitions 5.6.2 Electrical Protection of a Tidal Generator Exercise Reference Further Reading

243 246 247 248 249 250 250 251 252 254 255 263 266 272 273 274 274 276 276 278 282 282 283 291 293 293

5.1 INTRODUCTION A control system is a system that provides the desired response by controlling the output. Also, the control system of a tidal energy system is a combination of different elements that work together to reach the desired output. In the case of a tidal energy system, the desired output is to fulfill the electricity demand of the consumers. For such a requirement, it is necessary to develop a type of system that generates the required amount of electricity. Fig. 5.1 shows the simple block diagram of a control system. Here, a single block represents the control system. Because the output is controlled by the varying input parameters, it is also necessary to output according to the requirement Tidal Energy Systems https://doi.org/10.1016/B978-0-12-814881-5.00005-3

© 2019 Elsevier Inc. All rights reserved.

243

244

Tidal Energy Systems

Input

Control system

Output

Fig. 5.1 General block diagram of a control system.

because, according to the output, the control system is classified into two categories: an open-loop system and a closed-loop system. Based on the concept of a tidal power plant, if the generation of electricity is according to the requirements, then the system is controlled by the open-loop system. But if the generated electricity doesn’t fulfill the consumer’s requirements, then it is necessary to change some input parameters. In this case, the path is provided from output to input and such a type of control system is called a closed-loop system. The traffic light control system comes under the category of an open-loop system as well as a closed-loop control system. Here, a sequence of input signals is applied to this control system and the output is one of the three lights that will be on for some duration of time. During this time, the other two lights will be off. Based on the traffic study at a particular junction, the on and off times of the lights can be determined. Accordingly, the input signal controls the output. So, the traffic light control system operates on a time basis, but the timing of the red and green lights does not depend on the density of the vehicle. As this is part of an open-loop system, we can’t change output according to the input. On the other hand, it is possible to develop a sensor that changes the time duration of the red and green lights according to the density of the vehicle. Then, the traffic control system becomes a closed-loop control system. Rather than open-loop and closed-loop control systems, the control systems are also classified into the following categories: 1. Continuous-time control system 2. Discrete-time control system 3. Single-input and single-output control system 4. Multiinput input and multioutput control system 5. Multiinput and single-output system Continuous control is a system in which the variables and parameters are continuous and analog. Discrete control is a system in which the variables and parameters are discrete, mostly binary discrete. In a single-input single-output system, only one output parameter is found out with the help of a single input, but in the multiinput multioutput system, n numbers of input and output parameters are used to control the overall system. Industrial control systems used in the process industries have tended to emphasize the control of continuous variables and parameters. By contrast, the manufacturing industries produce

Control System of Tidal Power Plant

Actuating signal

Input

Output

Controller

Plant

Fig. 5.2 Control system for a plant.

discrete parts and products, and the controllers used here have tended to emphasize discrete variables and parameters (Fig. 5.2). Here, an input is applied to a controller and it produces an actuating signal or controlling signal. This signal is given as an input to a plant or process that is to be controlled. So, the plant produces an output, which is controlled. The traffic light control system, which we discussed earlier, is an example of an open-loop control system. In closed-loop control systems, output is fed back into the input. So, the control action is dependent on the desired output (Table 5.1). Fig. 5.3 shows the block diagram of a negative feedback closed-loop control system. Table 5.1 Comparison between continuous and discrete control systems of a tidal power plant Continuous control in a tidal Discrete control in a tidal Comparison power plant power plant

Typical measurement of product output Typical quality measure Typical variables and parameter Typical equipment Typical process time constant

Site assessment, depth of water Consistency, absence of gust Tidal current, tidal range, voltage, current Tidal turbine, generator, motor RPM, kWh

Error detector

–

Switches, wires Less than a second

Actuating signal

Tidal current input

+

Wind velocity, number of components Dimensions, absence of defects Limit switches, kWh

Tidal power plant

Controller Error signal Feedback Feedback signal

Fig. 5.3 Block diagram of a closed-loop control system.

Parameter

Electricity output

245

246

Tidal Energy Systems

Controller

Process

Comparison

Measurement

Output

Fig. 5.4 Cyclic process of a control system.

The error detector produces an error signal, which is the difference between the input and the feedback signal. This feedback signal is obtained from the block (feedback elements) by considering the output of the overall system as an input to this block. Instead of the direct input, the error signal is applied as an input to a controller. So, the controller produces an actuating signal that controls the plant. In this combination, the output of the control system is adjusted automatically until we get the desired response. Hence, the closed-loop control systems are also called automatic control systems (Fig. 5.4).

5.2 AUTOMATIC CONTROL OF A TIDAL POWER PLANT Based on the foregoing analysis, the control of the tidal power generation system may be organized in a cascaded manner because, in a tidal power plant, the output of the tidal turbine is worked as the input of the generator. The tidal power plant consists of two control loops. The inner loop controls the field excitation current of the tidal generator and the outer power control loop regulates the generator’s input power against varying operating conditions, which depends on the value of the tidal current, the tidal range, and wind velocity. Further varying or fluctuating conditions are controlled by using different types of relays, switches, contractors, analog and digital timers, isolators such as a single break isolator, a double break isolator, a bus isolator, a line isolator, and different logic components.

Control System of Tidal Power Plant

Manual control: Whereby each component of tidal power plant in the string of the pre starting checks of the component, synchronization between tidal turbine and tidal generator, loading and stopping sequence of tidal plant is selected and performed in turn by hand whether mechanically or by the push buttons of each component. Semiautomatic control: A solitary manual beginning drive a unit might be conveyed to the prepared to synchronize condition by the programmed choice, execution, and giving of an arrangement of tidal component controls. Synchronizing and stacking and running control stay manual capacities from the nearby and remote control, focuses. Fully automatic control: Fully automatic control system are provided for running up, automatically synchronizing, and loading up to a predetermined quantity on receipt of a single starting impulse. Subsequent manual variations of loading and excitation may be provided as a remote control function. The corresponding stopping impulse will cause the load to be reduced, the unit to be disconnected from the bus bars, and the turbine to be shut down completely. Offsite supervisory control: Starting, stopping, switch closing or opening, and other functions are initiated from a remote point, together with indications of successful operations of voltage and load control and of the repetition of alarm conditions at the remote control point. The equipment is ancillary to either a semiautomatic or a fully automatic unit control. Need for automatic control of tidal power plant: 1. Installation cost and control with protection equipment is very costly in a tidal plant. Automatic control will provide all time protection to a relatively cheaper cost. 2. Tidal plants can start and stop more frequently compared to other power plants. 3. Tidal plants provide more effective and very smooth operation. 4. Generally, tidal plants are situated in a remote area so manual control is very difficult; in this situation, automation is a very good option. 5. The operating costs will decrease significantly.

5.2.1 Control System for Unit Operation The control system of the unit activity of a tidal power plant is for the most part as takes after and this kind of unit is begun from the single unit control board (UCB) situated close to the tidal unit or senator board, however synchronization and the stacking of the general creation of tidal power plant are performed from the focal control room which is close to the age framework. Generally, a tidal unit might be begun, blended, and stacked from the focal control room in the incorporated control framework. The two sorts of controls have their own focal points and disservices. In view of control unit activity and the kind of control plans of pre-begin checks beginning, synchronizing, stacking

247

248

Tidal Energy Systems

and preventing from a focal control room is made. Beginning of the unit might be performed by methods for a succession main controller switch introduced on the control board of every unit. The main controller switch in the initial step of its arrangement for the most part opens the principle channel valve and begins unit helpers. In the next step, the turbine is begun and raised to speed no heap and field breaker is shut. In the third step, the paralleling of the unit is done and the unit is synchronized with the generator transport by an end generator breaker. In the last advance, the stacking of the unit to a preset esteem is completed. The master controller switch comparably is utilized for controlling activity close down. Beginning, synchronizing, and stacking naturally on receipt of a single beginning motivation is given at programmed tidal stations. A control conspiracy for the programmed quickened beginning of the preselected unit on the framework recurrence drop is here and there given in the recurrence controlling station as in La-Rance tidal control plant. The control framework gets input signals from fundamental hardware, for example, the turbine or the generator, and from different embellishment gear, for example, the senator, exciter, and programmed synchronizer. Status inputs come from control switches and level and capacity switches characteristic of weight, position, and so on all through the plant. The best possible mix of these contributions to the control framework rationale will give yields to the representative, the exciter, and the other gear to begin or shut down the unit. Any variations from the norm in the sources of info must keep the unit’s startup or if its online, give an alert or start its shutdown. For different unit destinations, every unit might be outfitted with a unit control found physically near the individual units and an incorporated control board situated in the control room. For a plant with just a single unit, the unit control switchboard might be situated in the control room. The UCB is designed to perform the following functions of a tidal power plant: 1. Information receipt and monitoring of tidal current and tidal range. 2. Start/stop control sequencing of a tidal turbine and tidal generator. 3. Annunciation of alarm conditions during the lower value of tidal current. 4. Temperature information monitoring of the coastal area. 5. Metering and instrumentation signals display of electricity generation through the tidal power plant. 6. Event recording when required. 7. Synchronizing and connecting the tidal turbine to the system. 8. Control of real/reactive power of the tidal energy system.

5.2.2 Information and Control Signals Basically, there are four types of signals that may be provided between the control board and any particular component of a tidal power plant. 1. Analog inputs to transmit variable signals from the instrument transformer such as current and potential transformer, resistance temperature detectors (RTDs),

Control System of Tidal Power Plant

thermocouples for temperature measurement of sea water, pressure of wind velocity, flow of tidal current, level of water, vibration of tidal range, or other transducers. 2. Digital inputs (typically contact closures) to provide status, or digitized values of variable quantities from the equipment. 3. Digital outputs to send command signals (ON and OFF) from the control board to the tidal component. 4. Analog outputs to transmit variable signals from the control board to equipment such as the governor, voltage regulator, etc. The correspondence connections between the control board and the hardware ought to be sufficient to transmit data and control signals. Data signals are the signs sent to the control board. Control signals are the yields, leaving the control load up to a different gear. Information signals to the control board come from the following: 1. Generator neutral and terminal component. 2. Head water and tail-water level component. 3. Tidal turbine. Information and control signals are needed between the control board and each of the following: 1. Step up transformer. 2. SF6 and other circuit breakers and operating switches. 3. Tidal generator. 4. Intake gate (and/or inlet valve) and draft tube gate. 5. Tidal turbine speed controller. 6. Tidal generator excitation system. 7. Auxiliary component of the tidal plant. Depending upon the method of control and the location of control points, the control of unit operation may be discussed under the following main headings in the existing power station.

5.2.3 Local Manual (Mechanical or Push Button) Control In this sort of control, unit helpers are begun physically or by electrical push catches mounted locally. The effective task of assistants is demonstrated by lights mounted at the hardware or confirmed by visual examination. Any unusual activity of these assistants amid running is given by a caution fitted locally. Fundamental electrical interlocks in the beginning circuit of the turbine might be incorporated. The tidal turbine is begun from the representative board. An administrator at the board changes the speed of the turbine and the excitation to convey the unit to prepare to synchronize condition. At that point, he exchanges the unit to control space for synchronizing and stacking. Once the unit is synchronized, the modifications of load and excitation are done by the control room administrator. At the point when a unit is removed from benefit, the control room administrator initially empties the unit and after that, excursions the principle electrical

249

250

Tidal Energy Systems

switch. The halting of the unit and its assistants is performed by the administrators at the machine level. This kind of control is straightforward; however, it requires an expansive number of working staff at different floors of the powerhouse. Smaller lengths of control links and a smaller number of control transfers are required. Such plans are hard to adjust for changing over the controls to remote/programmed control write. These are not utilized for extensive power stations.

5.2.4 Local Control of Unit From UCB For the most part, the controls of assistants and the unit are conveyed to a midway control board close to the generator at the machine floor level. This board is called the unit control board (UCB). In such a kind of station, valves in cooling water, weight oil, and air supply circuits are engine-worked. Links are kept running from different engine starters to the UCB for start/stop activities. An administrator at the UCB begins the unit assistants. Their fruitful activity is demonstrated on the UCB. The vital interlocks are incorporated into the turbine’s beginning circuit. The administrator at that point begins the turbine and conveys it to speed no heap position by changing the speed and excitation. At that point the exchanges, the unit to the focal control space for synchronizing and stacking. This sort of control includes a link association among the UCB and different helpers. The plan empowers the single administrator to oversee the unit and its assistants from the UCB. In any case, isolated administrators are required at the control room. This plan is supported particularly for control stations having an extensive number of units on the grounds such that the cost of the links for taking all controls in the focal control room would be high. Generators, transformers, and busduct defensive hand-off boards might be mounted close to the UCB while caution signs might be taken to the focal control room. Line and busbar defensive hand-off boards might be mounted behind the control boards in the control room if the link lengths required between the switchyard hardware and the control rooms are smaller. On the off chance that the separation is more prominent, these boards are mounted in a different switch room at the switch yard and just fundamental controls and signs are conveyed to the focal control room. This kind of unit control still requires coappointment of administrators at two levels, one at the UCB and the other at the control room.

5.2.5 Control of Unit of Central Control Room and Off Site Supervisory Control In this kind of control, the controls of the helpers and the unit are conveyed to a work area/board in the control room. This includes taking all links from the unit and its assistants in the focal control room. Henceforth, this plan is regularly suggested for stations having fewer units. The plan empowers administrators at the focal control work area to

Control System of Tidal Power Plant

oversee and control the unit from a solitary controlling point. There is no issue of coordination among the administrators as the duty of beginning helpers, turbines, and their control of a solitary administrator in the control room. All alerts and signs convey to a typical annunciator board in the control room. The defensive transfer boards of the generator, transformer, and transport channels might be situated close to the unit in the machine corridor and just signs might be conveyed to the regular annunciator board. Busbar and line defensive hand-off board areas rely on the separation between the switchyard and the control room and the plan might be as clarified previously. The unit control from the focal control room might be by the grouping controller switch as in the Bhakra Left Dehar Plant or it might be completely programmed as in the La-Rance tidal power plant. In the previous, the control switch puts the unit in task by playing out the four grouping stages, that is, opening the channel valve and beginning unit assistants, opening turbine entryways, parallel and stacking. The grouping control switch in the turnaround stops the turbine. In the last, a solitary beginning drive invigorates an ace begin hand-off, which begins unit assistants, opens turbine doors parallel, and loads the unit to a foreordained esteem.

5.2.6 Synchronizing of a Tidal Energy System Before connecting a tidal generator in parallel with the other machines, it is necessary to prove that the incoming machine and the running system have the same frequencies and voltages and are in phase; this type of system is called synchronization. The methods employed in tidal power stations are described below. Manual Synchronizing In this method, incandescent lamps are connected across the respective phases of the incoming and running voltage buses. The voltage of the incoming machine is matched with the system voltage by manually adjusting the excitation of the machine. Lamps indicate the frequency and phase angle difference. Lamps will flicker with a frequency equal to the difference between the frequencies of the incoming machine and the running system. When the phase and frequencies are matched, the lamps will extinguish. This is the indication of the synchronism of the machine with the system. The breaker is then closed manually. Manually synchronization is simple and cheap. This requires personal supervision and judgment of the operator. This type of synchronizing is not suited for automatic or remote control of the unit. However, this has normally been provided as a standby in power stations for use in case of the failure of automatic/ synchronizing equipment. Automatic Synchronizing Synchronizing equipment in tidal power plants performs the following functions automatically.

251

252

Tidal Energy Systems

(i) It continuously controls the terminal voltage of the incoming machine until it is almost equal to the voltage of the system to which it is to be connected. (ii) It controls the speed of the prime mover so that the frequency difference is within the predetermined value. (iii) It energizes the closing coil of the circuit breaker associated with the incoming machine at an instant when the phase difference between the two sources is sufficiently small and only when conditions (i) and (ii) have been simultaneously satisfied. The autosynchronizing equipment performs the above functions through the speed, voltage, and phase matching relays. It energizes a breaker closing coil at an exact time in advance of synchronism so that the time consumed by the breaker in closing is just equal to the time consumed by the generator in arriving at the exact synchronism. The time for advance action of closing is adjustable in autosynchronizing equipment. The main disadvantage of the automatic synchronizer is that if the system is disturbed, the frequency of the system is failing due to the tripping of certain generators or due to the sudden addition of large loads. It may then take a very long time to synchronize the unit with the system. Sometimes it may not be even possible to synchronize the machine. Under such conditions, the manual synchronization method could be used.

5.3 CONTROL STRATEGIES OF TIDAL ENERGY CONVERSION SYSTEMS The primary control and automation systems at a tidal power plant are coupled with start and stop mechanisms of the single and multiunit and optimum running control of active, reactive, and real power, maximum voltage and fundamental frequency which is also composed number of harmonics. Supervisory control and data acquisition and retrieval are used to cover the some deficiency related to instantaneous system efficiency, monthly plant factor, and demand factor. It also sends the essential technical information to the operators and managers. The type and amount of control equipment and different paths of control to be applied to a tidal power plant are affected by such factors as number, rating, and type of tidal turbine and tidal generators. The robust control system for a tidal power plant includes essential control circuit/ logic, a number of control devices, indicating and recording instruments, proper protection and annunciation on the main circuit board and on the single UCB for tidal electricity generation, conversion, and transmission operation, including the grid interconnected operation of tidal stations. These special features are necessary to provide operators with the facilities required for the organization and management of the tidal station’s major and auxiliary equipment. In the design of these features, considerations must be given to the size and importance of the tidal station with respect to other stations in the conventional and nonconventional power system, the distance between the main control room with respect to the equipment to be controlled, and all other station features that influence the control system.

Control System of Tidal Power Plant

Application of protective relay technology in a tidal power plant: Protective relay innovation has changed essentially in recent years. Acceptance plate transfers for every individual protecting capacity were regularly utilized. Strong state static transfers for protecting capacity were presented in the 1980s and ARE 3231–1965 was in a like manner reconsidered in 1987. Chip-based multiwork transfers are presently being presented. The advantages claimed for these relays are: (i) Assessment of the operating status of the tidal power plant on a long-term basis and to alarm when to function. (ii) Multiple protective functions in one relay reduce the panel space and wiring end. (iii) Self-calibration by software programming. (iv) Programmable set points by software programming. In a tidal power plant, a microprocessor-based relay has increased boundless acknowledgment between the two utilities and requests for side administration. The transfer capacities are the same as those in electromechanical and strong-state electronic hand off. However, microprocessor-based relays have highlights that give included advantages. Microprocessor-based relays may have a few weaknesses, so that there may be extra considerations when these are connected to the utility-purchaser interconnection. The advantages of microprocessors is that they incorporate the capacity to consolidate hand-off capacities into a spearing unit. Where an electromechanical overcurrent hand off might just be a solitary stage gadget, a chip transfer will regularly incorporate three stages and a nonpartisan. It could likewise incorporate unwinding, directional components, over/under voltage, and over/under recurrence. A transmission line transfer could consolidate different zone stages and ground remove components, over current blame locators, pilot plot rationale, and reclosing. An electromechanical plan will typically comprise of individual transfers for each zone on stage and ground insurance, isolate blame finders, and extra transferring for pilot conspire rationale. Correspondingly, a chip transformer transfer may join differential and overcurrent security and a generator hand off could incorporate differential, overcurrent, negative, grouping, recurrence, voltage, stator ground, and other defensive capacities. These same gadgets can incorporate nonrelaying capacities, for example, metering, occasion recording, and oscillography. These capacities are contained in a fenced area that requires less space than the blend of transfers and different gadgets they copy. Microprocessor relays have potentially reduced maintenance costs when compared to individual relays. Although there are fewer disadvantages than advantages. The operating energy for most electromechanical relays is obtained from the measured currents and/or voltages, but most microprocessor relays require a source of control power. Another disadvantage is that the multifunction feature can result in a loss of redundancy. For instance, the failure of a single phase or overcurrent relay is backed up by the remaining phases and neutral relays. In a microprocessor scheme, the phase and neutral elements are frequently combined in one package and a single failure can disable the protection. Similarly, a microprocessor/transformer

253

254

Tidal Energy Systems

package that has both differential and overcurrent relaying provides less redundancy than a scheme comprising separate relays. The self-diagnostic ability of the microprocessor relay and its ability to communicate failure alarms mitigate some of the loss of redundancy. It may also be economical to use multiple microprocessor relays. Microprocessor relays require more engineering in the application and setting of the relay, though less work in the tidal turbine design and wiring. The increased relay setting flexibility is accompanied by an increase in setting complexity that requires diligence to avoid setting errors. Also, some relays have experienced numerous software upgrades in a short period of time. Microprocessor relays have relatively shorter product life cycles because of the rapid advances in technology. As a result, a specific microprocessor relay model may only be available for a relatively short period of time. As a failure may require replacement rather than repair, it may not be possible to use an exact replacement, which may require more engineering and installation work. Although less frequent testing may be required, when it is, it requires a higher level of training for the technician and more test equipment than is normally used with electromechanical relays in order to obtain the full benefit of all the features of the microprocessor relay. The self-monitoring capability of these relays is only effective if the alarm output can be communicated to a manned location such as a control center. Also, the remote communication ability assumes there is a communication channel available to the relay.

5.3.1 Theory of Hydrokinetic Energy Conversion The concept of hydrokinetic energy is a part of the control strategy of a tidal power plant and is a fundamental principle of tidal turbines. The basic ideology applied to the pulling of hydrokinetic energy from the rated value of tidal currents at different tidal ranges is the same as those for wind and hydro energy systems. The power delivered in a moving fluid is a function of the mass flow rate, which is a measure of the mass of fluid passing a point in the system per unit time; it is working as the active element of the system. It is defined as follows: dm (5.1) ¼ ρAVtidal dt where m is the mass of the fluid, ρ is the density of water, Vtidal is the velocity of the flow, and A is the swept area of the tidal turbine rotor. Considering the kinetic energy per unit time, or power, of a fluid passing through the swept area of a turbine rotor, we obtain the following formula: 1 dm 2 1 3 (5.2) Vtidal ¼ ρAVtidal 2 dt 2 This formula provides a computation of the amount of active power that could be extracted per unit area from a hydrokinetic resource if the given power from the tidal PT ¼

Control System of Tidal Power Plant

power plant could be extracted at 100% efficiency. It is a functional measure for determining the ability of the tidal resource. However, in practice a tidal turbine will only be able to extract a fraction of this available power. The above equation is modified to give the actual power that a tidal turbine is able to extract. This is given by the following equation 1 3 (5.3) PT ¼ ρCp ðλ, βÞAVtidal 2 Cp is a dimensionless term that describes the hydrodynamic efficiency of a turbine. The Cp value is a ratio between the actual power extracted by the rotor to the total kinetic energy incident over the cross-sectional area of the rotor: PT (5.4) 1 3 ρAVtidal 2 Due to the Betz limit, it is only possible to extract a total of 59.3% of the total kinetic energy available in the flow of tidal current. In addition, the conversion efficiency of hydrodynamic, mechanical, and electrical processes reduces the overall output further. So in practice, most real turbines have efficiencies that are lower than the Betz limit, with values in the range 0.4–0.5 for modern axial flow turbines. The tip speed ratio (TSR) is the ratio between the rotational velocity at the tip of the rotor blade and the flow speed, and is given by Cp ¼

λ¼

ΩR Vtidal

(5.5)

where Ω is the rotational velocity of the rotor of the tidal turbine and R is the radius of the rotor of the tidal turbine. In the same way that active and reactive power is expressed by a nondimensional power coefficient, the thrust CT on the turbine rotor can be expressed in a similar way as: CT ¼

T 1 2 ρAVtidal 2

(5.6)

5.3.2 Tidal Turbine Control Control of the operation of the tidal turbine is a most essential task of the tidal power plant because the speed and load control of the tidal turbine and the tidal governor are the main controller performances in which the governor regulates the flow of seawater through the tidal turbine to balance the input power of the tidal power plant with the load. In the case of a small tidal power plant, the load control is also used where the excess load

255

256

Tidal Energy Systems

is sidetracked to the model load to maintain a constant speed of the tidal turbine. With an isolated tidal energy system, the governor controls the frequency of the overall plant and in an interconnected system, the governor may be used to regulate the unit load as well as contribute to the system frequency control. A tidal turbine is a revolving machine that converts the kinetic energy of the water into mechanical energy. This mechanical energy is then converted into electricity by the tidal generator that is sent to a power grid. The tidal turbine components responsible for these energy conversions are the rotor and the generator. The rotor is the area of the tidal turbine that consists of both the turbine hub and blades. As tidal current strikes the turbine blades, the hub rotates due to aerodynamic forces. This rotation is then sent through the transmission system to decrease the revolutions per minute. The transmission system consists of the main bearing, the high-speed shaft, the gearbox, and the low-speed shaft. The ratio of the gearbox determines the rotation division and the rotation speed that the generator sees. For example, if the ratio of the gearbox is N to 1, then the generator sees the rotor speed divided by N. This rotation is finally sent to the generator for mechanical-to-electrical conversion. Fig. 5.5 shows the major components of a tidal turbine: gearbox, generator, hub, rotor, low-speed shaft, high-speed shaft, and the main bearing. The purpose of the hub is to connect the blades’ servos that adjust the blade direction to the low-speed shaft. The rotor is the area of the turbine that consists of both the hub and blades. The components are all housed together in a structure called the nacelle. Angle of Attack The amount of area available for the incoming tidal current is key to increasing aerodynamic forces on the rotor blades. The angle at which the blade is adjusted is referred to as the angle of attack, α. This is necessary to control the fluctuation of power to control the angle of attack. This angle is measured with respect to the incoming tide direction and the chord line of the

Fig. 5.5 The major components of a tidal turbine.

Control System of Tidal Power Plant

Fig. 5.6 The critical angle of attack (αcritical) with respect to the blade.

blade. There is also a critical angle of attack, αcritical, where air no longer streams smoothly over the blade’s upper surface. Fig. 5.6 shows the critical angle of attack with respect to the blade and the applied control mechanism w.r.t. the angle of attack. Power and Efficiency This section explains what affects the power extracted from the tide and the efficiency of this process. Consider Fig. 5.7 as a model of the turbine’s interaction with the tide. This diagram indicates that the tide exists on either side of the turbine, and the proper balance between rotational speed and the velocity of tide are critical to regulate performance. The balance between rotational speed and water velocity, referred to as the tip speed ratio, is calculated using Eq. (5.7): EQ 1 : λ ¼ Where f is the blade’s frequency of rotation (Hz). r is the length of a blade (m).

Fig. 5.7 Direction of wind.

2πfr v1

(5.7)

257

258

Tidal Energy Systems

Calculating the Tip Speed Ratio

The efficiency of a tidal turbine is called the power coefficient, or Cp. Theoretically, the power coefficient is calculated as the ratio of actual to ideal extracted power. You can find this calculation in the equation. Also, you can adjust Cp by controlling the angle of attack, α, and the tip speed ratio, λ. The calculation for this case is shown in the equation. In the equation, c1–c6 and x are coefficients that wind turbine manufacturers should provide. Note that the maximum power coefficient that you can achieve with any turbine is 0.59, or the Betz limit.
 Pactual 0:25ρA v12  v22 ðv1 + v2 Þ EQ 2 : Cp ¼ ¼ (5.8) Pideal 0:5ρAv31 The power coefficient is calculated as the ratio of actual to ideal extracted power.   1 1 x EQ 3 : Cp ðλ, αÞ ¼ c1 c2  c3 α  c4 α  c5 ec6 Λ Λ

(5.9) 1 1 0:035 ¼  Λ λ + 0:08α 1 + α3 can adjust the by controlling the angle of attack, α, and the tip speed ratio. Finally, you can calculate the usable power from the tides using the equation. From this equation, you can see that the main drivers for usable power are the blade length and tidal speed. EQ5 : P ¼

Cp ðλ, αÞρπr 2 v13 2

(5.10)

Where ρ ¼ density of air (1.2929 kg/m3). The Power Curve It is important to understand the relationship between power and water speed to determine the required control type, optimization, or limitation. The power curve, a plot you can use for this purpose, specifies how much power you can extract from the incoming tide. Fig. 5.8 contains an ideal tidal turbine power curve. The cut-in and cut-out speeds are the operating limits of the turbine. By staying in this range, you ensure that the available energy is above the minimum threshold and the structural health is maintained. The rated power, a point provided by the manufacturer, takes both energy and cost into consideration. Also, the rated tidal speed is chosen because speeds above this point are rare. Typically, you can assume that a turbine design that extracts the bulk of energy above the rated tidal speed is not cost-effective. From Fig. 5.8, we can see that the power curve is split into three distinct regions. Because Region I consists of low tidal speeds and is below the rated turbine power, the turbine is run at the maximum efficiency to extract all power. In other words, the

Control System of Tidal Power Plant

Rated speed

Cut-in

Cut-out Rated current

Power (kW) I

II

III

Tidal current

Fig. 5.8 Ideal tidal turbine power curve.

Fig. 5.9 Pitch adjustment and yaw adjustment.

turbine controls with optimization in mind. On the other hand, Region III consists of high tidal speeds and is at the rated turbine power. The turbine then controls with limitation of the generated power in mind when operating in this region. Finally, Region II is a transition region mainly concerned with keeping rotor torque and noise low. In a tidal power plant, we use different control methods to either optimize or limit the power output of the tidal power plant. Control a tidal turbine by controlling the tidal generator speed, the blade angle adjustment, and the rotation of the entire tidal turbine. Blade angle adjustment and tidal turbine rotation are also known as pitch and yaw control, respectively. A visual representation of pitch and yaw adjustment is shown in Fig. 5.9. The function of pitch control is to preserve the optimal blade angle to achieve certain rotor speeds or tidal power output. By stalling a tidal turbine, you increase the angle of attack, which causes the flat side of the blade to face further into the water in terms of tidal current. Furling decreases the angle of attack, causing the edge of the blade to face the

259

260

Tidal Energy Systems

incoming tides. Pitch angle alteration is the most efficient way to limit tidal output power by varying the aerodynamic force on the blade at high wind speeds. Yaw refers to the rotation of the entire tidal turbine in the horizontal axis. Yaw control ensures that the tidal turbine is constantly facing into the tides to maximize the effective rotor area and, as a result of the required amount of tidal power, fulfills the requirements of the consumer. Tide direction can vary quickly; the turbine may misalign with the oncoming tides and cause power output losses. We can approximate these losses with the following equation: EQ 6 : 4P ¼ α cos ðεÞ Where 4 P is the lost power and ε is the yaw error angle. The final type of control deals with the electrical subsystem. A tidal power plant can achieve this dynamic control with power electronics, or, more specifically, electronic converters that are coupled to the tidal generator. The two types of tidal generator control are done by controlling the performance of the stator and rotor. The stator and rotor are the stationary and nonstationary parts of a tidal generator, respectively. In each case, you disconnect the stator or rotor from the grid to change the synchronous speed of the generator independent of the voltage or frequency of the grid. Controlling the synchronous generator speed is the most effective way to optimize the maximum power output at low tidal speeds. Fig. 5.10 shows a system-level layout of a tidal energy conversion system as well as the signals used. Notice that control is most effective by adjusting pitch angle and controlling the synchronous speed of the generator. Control Strategies Recall that controlling the pitch of the blade and the speed of the tidal generator are the most effective methods to adjust output power. The following control strategies use pitch and generator speed control to manage turbine functionality throughout the power

Fig. 5.10 System-level layout of a tidal energy system.

Control System of Tidal Power Plant

Cut-in

Rated speed

Cut out

Power

Rated power

Tidal speed

Fig. 5.11 Power curves for different control strategies.

curve: fixed-speed fixed-pitch, fixed-speed variable-pitch, variable-speed fixed-pitch, and variable-speed variable-pitch. Fig. 5.11 shows the power curves for different control strategies explained below, with variable-speed variable-pitch, VS-VP, being the ideal curve. Fixed-speed fixed-pitch (FS-FP) is the one mechanism where it is impossible to grade the performance of a tidal power plant with an active control method. With this type of arrangement, the tidal turbine and tidal generator are directly united to the power grid, causing the tidal generator speed to padlock to the power line frequency with a reduction of harmonic frequency and fixing the rotational speed in RPM. These tidal turbines are regulated using passive stall methods at higher values of tidal currents. The gearbox ratio selection becomes important for this passive control because it ensures that the rated power is not exceeded. Fig. 5.11 shows the power curve for FS-FP operation. It is apparent that the actual power does not match the ideal power, implying that there is a lower energy capture. It implies that the tidal turbine operates at maximum efficiency only at a limited value of the tidal current in the low-speed region. This implies poor power regulation as a result of constrained operations. Fixed-speed variable-pitch (FS-VP) configuration operates at a fixed pitch angle below the rated value of the tidal current and continuously adjusts the angle above the rated value of the tidal current. To clarify, fixed-speed operation of a tidal turbine implies a maximum output power at a limited value of tidal current. We can use both feather and stall pitch control methods in this configuration to limit the power of the tidal power plant. Keep in mind that feathering takes a significant amount of control design and stalling increases unwanted thrust force as stall increases. Fig. 5.11 shows that the power curve for FS-VP uses either feather or stall control. Below the rated value of the tidal current, the FS-VP turbine has a near optimum efficiency around Region II. Exceeding the rated tidal speed, the pitch angles are continuously changing, providing little to no loss in power.

261

262

Tidal Energy Systems

A variable-speed fixed-pitch (VS-FP) configuration continuously adjusts the rotor speed relative to the tidal current through power electronics controlling the synchronous speed of the tidal generator. This type of control, which is based on automatic, manual, or microprocessor, assumes that the tidal generator is from the grid so that the tidal generator’s rotor and drivetrain are free to rotate independently of grid frequency. Fixed-pitch relies heavily on the blade design to limit the power through passive stalling. Variable-speed variable-pitch (VS-VP) configuration is a derivation of VS-FP and FS-VP. Operating below the rated tidal current, variable speed and fixed pitch are used to maximize energy capture and increase power quality. Operating above the rated tidal current, fixed speed and variable pitch permit efficient power regulation at the rated power of the tidal power plant. Our tidal turbine controls and systems provide higher availability, reliability, and optimized energy output of our tidal turbine, wherever your operations, whatever the conditions. Electrical pitch systems for optimum performance: Located in the rotating hub, the pitch control system of the tidal power plant enables operators to gain optimal power from tides at below rated tidal current by adjusting the blade angle; to control the speed of the tidal current by holding a constant level at a rated tidal range; and to minimize mechanical loads due to variable speed operations of the tidal turbine in the tidal power plant. Nacelle cabinets for tidal power distribution and tidal turbine control: The nacelle cabinet is split in the power cabinet and the control cabinet. The nacelle cabinet collects all signals and controls all devices in the hub and nacelle, including that of the water- and oilcooling system, heating system, brakes and fans, yaw system, pressures and temperatures, wind speeds, tidal current, and oil and monitoring signals. Yaw controls for maximum power output of a tidal power plant: Yaw controls ensure that the tidal turbine is constantly facing into the incoming tides to maximize the effective rotor area or swept area and, as a result, optimum power comes from a tidal power plant. All aspects of effective control systems mean we can optimize the performance of the yaw controls so they are fully integrated into the turbine’s entire control scheme. Converter systems for optimized connection to any grid frequency: The converter system of an effective control system of a tidal power plant, utilizing a power module power converter, coordinates uneven speeds of the tidal turbine with the fixed frequency of a grid, fulfilling worldwide grid codes and maintaining the capability for both low voltage ridethrough and reactive power management. Tower base cabinet for full control: The tower base cabinet allows full control and operation of the tidal turbine and provides information on all operated and measured signals that are used to test the performance of the tidal power plant. Pitch control system design: Pitch control means that the blades can pivot on their own longitudinal axis. The pitch control is used for speed control, optimization of power production, and to start and stop the turbine. The control system structure used to generate the pitch angle reference is given in Fig. 5.11. The pitch controller

Control System of Tidal Power Plant

consists of two paths: a nonlinear feed forward path that generates β0 and a linear feedback path that generates 4β. The feed forward path uses the information about the desired power output, wind velocity, and turbine speed to determine the pitch angle required. The equation gives the pitch angle as a function of the measured variables. sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi  ffi 2Pref e0:17γ 1 (5.11) β0 ¼ γ  5:6  Pw 0:022 However, the feed forward term assumes that all the components are ideal and does not account for the losses in the system. The feedback path compensates for the losses by decreasing the pitch angle if the output power is less than the desired power, to increase the power captured. The P-I controller (proportional integration) for the system is designed using the Zeigler-Nicholas rules for tuning PID (proportional integration and differentiation) controllers.

5.3.3 Tidal-Dynamic Energy Assessment Separating the energy accessible in a streaming fluid should be possible in various ways. Utilizing a turbine to change over the hydrokinetic power into mechanical power is the most widely recognized choice. Various distinctive sorts of turbines or rotors might be utilized to accomplish this: drag or lift style forces, pivotal or vertical hub turbines, crossbreed turbines consolidating parts of a few variations, turbines with variable or settled pitch edges, ducted turbines, and so forth. Other, more novel ways to deal with control take off incorporate the utilization of swaying hydrofoils and variable geometry sails. Nonetheless, this proposition will center around the more regular turbine-based ideas, of which there are three: Axial turbines: These are turbines in which the rotational pivot of the rotor is parallel to the approaching stream. Turbines of this composition will more often than not utilize lift write sharp edges that are formed as airfoils and turn with respect to the stream. The movement of the liquid around the airfoil creates the lift drive at a point in respect to the edge harmony, known as the approach, causing a weight contrast on one side of the cutting edge when contrasted with the other. The lift power will dependably be opposite to the point of relative liquid speed. A drag constrain is likewise created as the liquid streams around the airfoil. The drag compel acts parallel to the relative liquid speed and obstructs revolution, yet for lift gadgets the normal digressive power created by the lift beats the impeding drag constrain, and the net distracting power acting at a range on the turbine cutting edge produces positive torque and power. Hub stream turbines are a typical decision among engineers of tidal vitality converters and are comparative in idea and configuration to cutting edge wind turbines. The outline of hub stream turbines will fluctuate with designers utilizing diverse edge numbers and even channels to streamline

263

264

Tidal Energy Systems

and focus the stream toward the rotor. Engineers have additionally thought of various outlines to defeat the issue of producing power amid both the surge and ebb phases of the tidal cycle, when the liquid will stream in various ways. Yaw instruments have been proposed as well as pitch actuators equipped for pitching the cutting edges through 180 degrees to permit a bidirectional task of the turbine. The utilization of two restricting rotors has additionally been proposed. Vertical axis turbines: These are turbines where the rotational hub of the rotor is vertical to the water surface and opposite to the approaching stream. Turbines of this composition utilize either lift or drag write sharp edges, with a few outlines utilizing a mix of both. Savonius rotors are drag constructed and depend on being pushed by the stream, for the most part at a speed slower than the free stream speed of the stream. The rotor produces high torque at low speeds, making it attractive for applications such as water pumping. The architecture of the traditional Savonius rotor is straightforward and shoddy to manufacture—two half barrels are set with their sunken sides confronting each other and, after that, balanced with a little cover. The drawback of Savonius rotors is their low effectiveness contrasted and lift based gadgets; thus, numerous have rejected their utilization referring to the way that they are excessively wasteful, making it impossible to rival different outlines. Darrieus turbines are a typical kind of vertical hub outline. They are described by airfoil-formed sharp edges and depend on producing lift to influence them to pivot around a focal hub. The fundamental hindrance of Darrieus rotors is that they are not self-starting and have low beginning torque. Hence, they are regularly utilized as part of a conjunction with Savonius rotors, which can give substantial torque at low speeds. Another issue with the Darrieus turbine is torque wavering. Regardless of these issues, Darrieus turbines are usually utilized as a part of wind and marine vitality applications. A depiction of a Darrieus turbine being utilized to change over hydrokinetic vitality into power in the Sudan is given by Fraenkel (2007). The Gorlov helical turbine is another individual from the vertical hub family and, like the Darrieus turbine, it utilizes airfoil-molded sharp edges and is lift-based. As discussed by Hardisty, the turbine has various alluring qualities. It is self-starting and, as with all vertical pivot turbines, because of its hub symmetry it will turn a similar way, paying little heed to whether the tidal current is in surge or ebb. TST engineer GHK Technology is known to utilize a Gorlov helical turbine plan. There is no all-inclusive concurrence on the frame that tidal stream turbines should take and what rotor composition is ideal. This is clear from the wide number of plans being proposed by designers. Initially, unmistakably drag-based gadgets such as the Savonius rotor will be less productive than lift-based gadgets; moreover, drag-based gadgets will typically pivot slower than the free stream speed. It is feasible for Savonius rotors to have TSRs more prominent than 1.0; however, typically they will turn altogether slower than lift-based gadgets. The moderate rotational speed of drag gadgets makes them harder to incorporate with a generator without a high proportion gearbox

Control System of Tidal Power Plant

to venture up the rotational speed. In light of these components, it is impossible that dragbased turbine outlines will be aggressive with lift-based plans. With the prohibition of the Savonius rotor, the other lift-based vertical pivot and cross-stream rotors could make sensible plan alternatives. The Darrieus is especially able to accomplish generally great efficiencies of 30%–35%. Also, for the most part, it is simpler to work vertical hub and cross-stream outlines in bidirectional streams than it is for hub turbines, which will require a yaw instrument or some other strategy to empower a bidirectional task. Another regularly referenced favorable position of vertical pivot plans is the way that the pole is opposite to the stream, which means the generator can be put over the water surface, making access less demanding. Cross-stream turbines don’t have this favorable position and access to the drive-prepare will be dangerous. In spite of these focal points, vertical hub or cross-stream plans similar to the Darrieus and Helical Gorlov rotor are still prone to be less effective than an all-around outlined hub stream turbine rotor. These incorporate an expanded affectability to cavitation, contrasted with hub stream rotors, and a quick corruption of execution caused by fouling and surface unpleasantness on the rotor. Besides, the Darrieus and Helical Gorlov rotors are not effortlessly controllable in high stream speeds. The yield control can’t be controlled without much of a stretch and the best way to stop the rotors is by utilizing a brake or spoilers. Interestingly, there are various compelling direction techniques (slow down or pitch) that have been created over numerous years in the breeze business that can be connected to pivotal stream rotors. The wide knowledge base that as of now exists on framework outline and execution of hub stream rotors, predominantly because of advances that have been made in the breeze business, is maybe the primary motivation behind why numerous tidal engineers are utilizing this sort of rotor. This is proven by the way that more than 50% of gadgets depend on base-mounted, low robustness, even hub stream rotors. So despite the fact that there is as yet countless planning distinctive sorts of gadget a specific measure of meeting has occurred. The work in this proposal expects the utilization of a pivotal stream rotor plan, and addresses the ramifications of controlling. It is clear that the TST will rotate at roughly a third the speed of the wind turbine. The fact that TST blades are short and rotate relatively slowly means that the centrifugal forces, which balance the bending forces on large wind turbines, are small. This means they do little to restrict the large bending forces acting on the blades of a TST. The slower rotational speed of the TST also has implications on torque developed by the rotor. By the relationship between angular velocity and torque given it is clear that if the tidal stream turbine rotates slower than the wind turbine, then to generate the same amount of power it will have to impose more torque. This is the difference between wind turbines and tidal stream turbines and one that needs to be taken into consideration when designing drivetrains. Gearbox failures are one of the main causes of downtime in the wind industry. If TSTs are developing high torques, then it is logical to assume that there will be added stress on the gearbox and

265

266

Tidal Energy Systems

drive shaft, which may cause unwanted failures. High operational torques coupled with the fact that TST rotors are smaller and therefore likely to have lower inertia than an equivalent wind turbine means that they will accelerate faster as the flow changes. Therefore, regulating rotor speed will be more difficult on a TST, particularly in locations where rapid variations in flow speed occur.

5.3.4 Turbine Configuration and Control Objectives There are numerous conceivable TST designs. The originator can pick between an immediate (direct drive) drive framework or an adapted (geared) framework, the generator can be synchronous or offbeat, and association with the lattice can be through a full-control converter, an in part appraised converter, or straightforwardly associated. The utilization of a PMSG in an immediate drive arrangement is an alluring arrangement. At the point when it is utilized in conjunction with a full-control converter, the generator is decoupled from the network and full factor speed activity can be accomplished. Variable speed activity builds the vitality yield of the turbine by enabling it to work at its greatest power coefficient over an extensive variety of stream speeds (Fig. 5.12). The framework comprises a PMSG and a full-control converter comprised of consecutive voltage source converters. Utilization of two six-switch converters associated with a consecutive setup with a middle-of-the-road DC connected to a capacitor has the benefit of taking into account vector control on both the generator and lattice side converters. This topology permits a bidirectional current stream and one has full control over the generator control factor and torque. An option is to utilize a diode rectifier on the generator side, which improves the control and decreases the cost. The detriments of utilizing a diode rectifier are for the most part identified with proficiency. The diode rectifier has been accounted for as presenting large amounts of symphonious mutilation

Transformer

Tidal turbine

Generator

Grid

RL filter

AC/DC converter Rotor side control

Fig. 5.12 Rotor and generator side control.

DC/AC converter Grid side control

Control System of Tidal Power Plant

in the generator, which influences productivity and can present throbbing torques. Hence the full-control converter with dynamic rectifier is utilized as a part of this work. 3 1 ρAVflow CP ðβ, λÞ τT ¼ : τr 2

(5.12)

The block diagram of the hydrodynamic system is shown in Fig. 5.13. For modeling purposes, this is a mapping function that is expressed through a lookup table. This model simply converts the flow incident on the turbine rotor into hydrodynamic torque and does not include any structural dynamics or any dynamic inflow effects, such as shear or tower shadowing. The tip speed ratio (TSR) is calculated based on the flow speed and the rotor speed. An initial condition is set such that the rotor speed is nonzero at the start of the simulation. The calculated TSR and the blade pitch angle are then mapped to the appropriate value using the lookup table. Drivetrain Model The hydrodynamic torque generated by the rotation of the rotor is transferred to the generator via the drivetrain. In this case, a direct-drive system is used, meaning the rotor is connected directly to the generator via a single shaft. To model the TST drivetrain, a two-mass model is used whereby the rotor and hub are considered to be one lumped mass and the generator is considered to be another lumped mass. The two masses are connected together via a flexible shaft that has a stiffness and damping. The model is shown in Fig. 5.13 where one end of the shaft is driven by the turbine rotor, generating a torque. The other end of the shaft is loaded by the generator, which generates a torque.  
 d 2 θr dθr dθg τhy ¼ Jr 2 + Kdt θr  θg + Ddt  (5.13) dt dt dt  
 d 2 θg dθr dθg  (5.14) τhy ¼ Jg 2 + Kdt θr  θg + Ddt dt dt dt dθg dθr ¼ Ωr , ¼ Ωg (5.15) dt dt where θr and θg are the angular positions of the rotor shaft and the generator shaft, and Jr and Jg are moments of inertia for the rotor and generator, respectively. The electrical equations used to model the PMSG are represented in the rotating reference frame, in which the -axis is oriented along the rotor flux vector position and the -axis leads the -axis by 90 degrees. Expressing the electrical equations in this way allows the torque producing and magnetizing flux components of the machine to be separated. Therefore, this allows for the development of a control strategy that provides independent control of the torque. In this model, the three phase quantities of the machine

267

268

Tidal Energy Systems

Jr

Ddt Jg Wg & qg

Wr & qr

thy

tem

Kdt

Generator

Shaft

Rotor

Fig. 5.13 Drive train model of rotor and generator.

(voltages, currents, and magnetic flux) can be described using just two complex vectors. This means that a three-phase machine can be modeled as a two-phase machine. disd (5.16) Lsd  Ωe Lsq isq dt

disq Lsq  Ωe Lsd isd + ψ pm (5.17) Vsq ¼ isq Rs + dt where isd and isq are the stator currents, Rs is the stator resistance, Ωe is the electrical PMSG rotor speed, Lsd and Lsq are the equivalent self-inductances of the stator, and ψ pm is the flux produced by the permanent magnets. It is assumed that the PMSG used in this work is of the surface-mounted type and exhibits no saliency. The voltage source converters and DC link capacitor are modeled using blocks from the SimPowerSystems library within Simulink. The grid is modeled using an AC voltage source from the SimPowerSystems library in series with an impedance. The operation of the axial flow variable speed TSTs for optimal power extraction is illustrated in Fig. 5.14, which shows the ideal power curve for a typical turbine. The turbine operates between the cut-in flow speed and the cut-out flow speed. Below the cut in, the available energy in the flow is so low that the losses and operating costs make it uneconomic to operate the turbine. Above the cut-in speed, although there is a lot of energy available, these flow speeds occur so infrequently that their contribution to the annual energy yield is minimal. Between these two limits, three operating modes are possible. In region 1 (between and), the objective is to extract as much energy from the flow as possible by running the turbine at its optimum hydrodynamic efficiency. Region 2 (between and) is a transition area between the optimum power curve and the constant power region. Here, the speed of the turbine is limited to avoid Vsd ¼ isd Rs +

Control System of Tidal Power Plant

C

D

B Power (kW) 1

2

3

A Vmin

Vn Tidal current (m/s)

Vmax

Fig. 5.14 Power curve of tidal current.

overspeeding the generator, and as a consequence, cavitation. In region 3 (between and) the objective is to limit power to avoid overloading. An open-loop control is used whereby the generator torque demand is continuously set proportional to the square of the rotor speed: ΩρR5 CP :Ωr 2 (5.18) 2λN 3 Where R is the rotor radius, ρ is the fluid density, Ω is the TSR, and N is the gearbox ratio. For practical reasons, a rotor speed measurement is usually not available, so the control of the equation is achieved using the generator speed measurement, which is the rotor speed scaled up by the gearbox ratio. τd ¼

The Field Oriented Control Method The field-oriented control method allows for separate closed-loop control of both the flux and torque, hence, achieving a similar control structure to that of a separately excited DC machine. By separating the stator current into a magnetic flux-producing part and a torque-producing part, independent control of each is achieved. Using a two-phase machine model reduces the number of equations and makes control design simpler. By deriving an equation for the electromagnetic torque, it can be shown that the torque, and therefore the speed of the PMSG, can be controlled using just the -axis stator current. Electromagnetic Torque

Assuming a balanced system, the equations of active and reactive power in the reference frame can be expressed in terms of the voltages and currents. When going from a three-phase to a two-phase system, the input power must remain invariant.

269

270

Tidal Energy Systems

Hence, a scaling factor is used when expressing the power input to the machine in the two-phase reference frame.  3
(5.19) Vsd isd + Vsq isq 2  3
(5.20) Qdq ¼ Vsq isd + Vsd isq 2 By substituting for and in Eq. (5.19) from Eqs. (5.20) and (5.21), the input power in the reference frame can be expressed in terms of armature resistive losses, rate of change of armature magnetic energy, and air-gap power.   

di

  3 disd sq 2 2 Pdq ¼ RS isd + isq + Lsq isq + Lsd isd + Ωe Ψpm + Lsd  Lsq isd isq (5.21) dt dt 2 Pdq ¼

The term associated with the air-gap power on the right side of Eq. (5.21) can be extracted to give Eq. (5.22).
  3 
(5.22) Pair gap ¼ Ωe Ψpm + Lsd  Lsq isd isq 2 The electromagnetic torque is obtained by dividing the air-gap power by the mechanical rotor speed, giving Eq. (5.22) where the number of machine pole pairs
  3 
(5.23) τem ¼ npp Ψpm isq + Lsd  Lsq isd isq 2 The term on the left of Eq. (5.23) is referred to as the permanent magnet torque and is dependent on the rotor flux Ψpm and the axis current isdand isq. The term on the right is the reluctance torque and it is dependent on the q-axis and d-axis currents and on the difference between the stator self-inductances. For a nonsalient PMSG, the reluctance term disappears because and are assumed equal, and Eq. (5.23) reduces to:  3 
(5.24) τem ¼ npp Ψpm isq 2 From Eq. (5.24), it is clear that the electromagnetic torque is directly proportional to the axis stator current.

Unity Power Factor Control The aim of this control strategy is to utilize the full volt ampere (VA) rating of the converter for active power transfer. The -axis current is used to control the electromagnetic torque while the -axis compensates the reactive power demand of the generator. Maintaining the unity power factor reduces the amount of current in the stator windings,

Control System of Tidal Power Plant

as they only have to carry the active power obtained in the conversion. This reduces resistive losses in the stator winding and improves efficiency. For a given power output, the VA rating of the converter is also minimized. The disadvantage of this control strategy is that it does not use all the stator current to generate torque. Thus, for the same generator torque, its efficiency is lower than that achieved by the maximum torque per ampere control strategy. Generator-Side Converter Control In this work, the maximum torque per ampere control strategy was used to control the speed of the PMSG. The measured parameter are isa, isb, isc, rotor electrical position θe, and the rotor speed Ωg. It is assumed that the rotor position is measured using an encoder mounted on the rotor. The controller consists of an inner current loop and an outer torque loop. The torque-producing current reference isq∗ is obtained by dividing the torque reference by the generator torque constant Kt. The inner current loop insures that the q-axis component of the measured current isq reaches the q-axis current references isq∗, the d-axis component of the measured current isd, and the d-axis current reference isd∗.    3 2 2π 2π 2 3 sin θe + 6 sin ðθe Þ sin θe  3 7 isa   3 7 26 Isd 7 4 isb 5 ¼ 6 6 7     Isq 34 2π 2π 5 isc cos ðθe Þ cos θe  cos θe + 3 3 The d-axis and q-axis voltage references Vsq∗ and Vsd∗ are generated as below: ð ∗ Vsd ¼ KPi esd + KIi esd dt + Πe Lsq isq (5.25) ð

Vsq∗

¼ KPi esq + KIi esq dt + Πe Lsd isd + ψ pm

(5.26)

Where KPi and KIi are the proportional and integral gains of the respective PI controller, and esd and esq are d- and q-axis current errors. 2 3 cos ðθe Þ 1 sin ðθe Þ 6 7    72 3 6  2 3 6 7 Vsd 2π 2π Vsa∗ 6 cos θe  17 4 Vsb∗ 5 ¼ 2 6 sin θe  3 7 4 Vsq 5 3 6 7 3 6 7 ∗ Vsc 6     7 0 4 5 2π 2π sin θe + cos θe + 1 3 3

271

272

Tidal Energy Systems

5.4 REACTIVE POWER CONTROL OF TIDAL POWER PLANT Reactive control by complementing the primary technologies in tidal turbines can help significantly in attaining or perhaps even improving the industry’s objectives of safe and cost-efficient energy production through tidal power plants. It is necessary to understand and improve the material properties that are used in the manufacturing of tidal power plant. Active control can alleviate the requirements on materials at any stage of the technological development in tidal technology. The effective control requirements for tidal turbines, together with the control means and sensors typically employed in modern tidal turbines, will provide background and serve as a focal point for subsequent discussion of the applicability of modern control theory to tidal turbines. The tidal turbine control problem has at least three important requirements: 1. Setting upper bounds on and limiting the torque and power experienced by the drivetrain, principally the low-speed shaft. 2. Minimizing the fatigue life extraction from the rotor drivetrain and other structural components due to changes in tidal direction, speed, and turbulence as well as startstop cycles of the tidal turbine. 3. Maximizing energy production through the tidal generator. The control problem is the judicious balancing of these requirements. The control theory discussion here will be cast in terms of a pitch-controlled, variable-speed wind turbine. The discussion is general in the sense that the combination of sensors and control means is thought to span the space of current practical control techniques. We recognize that stall-controlled and other tidal turbines may not require all the sensors and control means discussed. To the extent that this is true, these architectures represent simpler cases. However, for all tidal turbine architectures, research may reveal other analogous techniques for control that are functionally equivalent to the particular techniques. In any case, there will remain the general requirements for control of the torque and power in the drivetrain, the minimization of fatigue life extraction, and the maximization of energy production. The control effectors and commands, together with the sensors and quantities they measure for a pitch-controlled, variable-speed tidal turbine. By controlling effectors, we mean the physical devices that implement angular or linear motion of a tidal turbine control surface or component, examples of which are electric motors and hydraulic pistons. The control actuators execute motion in response to commands from the control computer. The control computer executes the algorithms derived from the application of control theory. The algorithms, in turn, utilize information from the tidal turbine sensors to generate the commands and assess their effects. For a constant-speed tidal turbine without power electronics, the generator load is the utility grid. The nacelle yaw drive may be an electric or hydraulic motor acting through gearing to rotate the nacelle and rotor. The function of the yaw drive is to orient the tidal turbine relative to the prevailing direction of tidal currents.

Control System of Tidal Power Plant

The blade pitch actuator affects the rotation of the rotor blades about their pitch axis. With the blade pitch angle set at the full-power angle, maximum power is extracted from the incident wind flow field. As the blade pitch angle is rotated toward the full feather position, the blades become less efficient at converting the power in the wind flow field to shaft power. The tidal generator torque may be controlled by the power electronics, acting on the electrical characteristics of the tidal generator. The power electronics, acting as the load for the tidal generator can electronically vary the load and thus the drivetrain torque. The reactive power delivered to or received from the utility grid may also be controlled by the power electronics. The values of the tidal current and the torque in the low-speed shaft are important to control and may be estimated from the sensor measurements.

5.4.1 Design of Passive Components The GSC needs passive components on both the DC and AC sides to perform storage and filtering functions. A capacitor is used as its DC passive component, and its value is decided according to the following expression: Cdc ¼

Tr ΔPdc 2Vdc ΔVdc

(5.27)

Where Cdc is the capacitance of the DC-link capacitor, Tr is the control delay introduced because of the filtering of the DC-bus voltage and AC current control, ΔPdc is the maximum allowable DC power variation, Vdc is the nominal DC-bus voltage, and ΔVdc is the allowable DC-bus voltage ripple. Variables Tr, ΔPdc, Vdc, and ΔVdc, along with the dynamic response, size, and cost, are used as a trade-off to design the DC-link capacitor value. For high-power applications, the DC-link capacitor value can be simply set to 4.0 pu to obtain a fair trade-off between different design factors. The pitch control system is one of the most widely used control techniques to regulate the output power of a tidal turbine generator. The method relies on the variation in the power captured by the turbine as the pitch angle of the blades is changed. Hydraulic actuators are used to vary the pitch angle. The tidal turbine generator describes the design of the pitch controller and discusses the performance of the system in the presence of disturbances. The control system consists of two controllers are inverter controller that keeps the load voltage constant and the pitch controller acting on the blade angle by using simulation. The variable speed induction generator using the Volts/Hz control enables efficient tidal energy capture. The output of the generator-side converter can be varied to control the speed of the induction generator. The grid-side converter can be controlled to inject the desired power and reactive power into the grid. Thus, the tidal system is capable of providing reactive power support, if required. The disadvantage of this configuration is the large cost associated with the power converter because the converter has to be rated for the maximum power output of the generator. For fixed-speed turbines,

273

274

Tidal Energy Systems

the active stall can be used to limit the power, not by reducing the pitch angle as in pitch controlled, but by increasing the pitch angle to a point where the blade stalls and in that way reduces the force on the turbine. By regulating the angle to be on the limit of stalling, fast torque changes from the tides will be neutralized.

5.4.2 Power Factor Correction (Active and Reactive Power Control) An asynchronous generator contains no permanent magnet and is not separately excited. That means that an asynchronous generator has to get exciting current from the grid and the magnetic field is only established when the generator is connected to the grid. When the generator excites current from the grid, the generator consumes reactive power from the grid. The current in the cable to the generator will consist of two parts: 1. Active current corresponding to the active power production (KW). 2. Reactive current corresponding to the reactive power consumption (KVAr). Because of the excitation current, there is a phase shift between the current and the voltage. The current is delayed compared to the voltage by an angle (θ). A term of the phase shift is the power factor (cos θ). A part of the generator’s exciting current/reactive power is delivered from the capacitors, which is called power factor correction. The capacitors are connected to the grid a little later than the generators are disconnected, before the generator is disconnected from the grid. The advantage of the power factor correction is that the loss in the grid decreases because the grid current decreases. At no load, the grid current is about zero Amp because the generator’s no-load current (only reactive current) is delivered from the capacitors.

5.4.3 Reactive Power and Voltage Control When the unit is serving an isolated load, its terminal voltage is held to a schedule value by means of a continuously acting automatic voltage regulator. The reactive power requirements of the load connected to it are adjusted by excitation control called power factor control. When the unit is connected to a large power system, that is, to an infinite bus, the voltage, the frequency of the bus, and hence of the generator terminal are held under control and the bus voltage is not affected by changes in the excitation of the generator. Once the generator is paralleled with the system, it assumes the system voltage and any change in its excitation results only in changing its kilovar loading and its power factor. Generally, the unit is operated at a rated kilovar load. The maximum and minimum excitation applied to the generator are dependent on the reactive power capability of the unit. On the high side, the limitation is field and armature overheating, and on the low side the limitation is stability and loading power factors. Associated with each hydroelectric station will be a number of hydraulic items to be brought to the power station control room. These items may be selected from the following.

Control System of Tidal Power Plant

(i) (ii) (iii) (iv) (v) (vi) (vii) (viii)

Headrace storage, level indication, and gate control. Tailrace level indication. Secondary storage level indication and gate control. Flood control, including special gate operation, position indication, discharge, and alarm. Intake gate control and indication. Irrigation water release and discharge indication. Surge tank water level indication. River control and discharge indication for statutory obligations to other users such as fishery authorities, chemical works, and water supply authorities. Any spillway gates may be operated locally by hand or motor control, remotely by supervisory or direct control of motor winches, or automatically. When automatic operation occurs, it is desirable to give an alarm at the attended point, and preferably to record the duration of the flood discharge. Many dams and intake works have sufficient indication and control facilities to warrant supervisory control equipment. The necessary pilot cables must be taken from a route not affected by floods at any time.

Voltage Control A tidal energy system is said to be well premeditated if it gives a good quality of reliable supply that is without fluctuation. Good quality means the voltage regulation and voltage level are within the reasonable limits. Generally, all the components on the conventional and nonconventional power systems are designed to operate satisfactorily, meaning only when the voltage levels on the system correspond to their rated voltages or at the most, the variations are within 5%. If the voltage variation is more than a prespecified value or 5%, the performance of the equipment suffers and the life of most of the equipment is also sacrificed. The picture on a television set starts rolling if the voltage is below a certain level and the fluorescent tube refuses to glow if the voltage is below a certain level. The torque of an induction motor varies as the square of the terminal voltage and so on. Thus the necessity of controlling the voltage on the system is very strong. At the point when control is provided to a heap through a transmission line, keeping the sending end voltage steady, the less than desirable end or load voltage experiences variances relying on the size of the heap and the power factor of the heap. The higher the heap with a smaller power factor, the more prominent the voltage variety. The voltage variety at a hub means that the unbalance between the responsive power produced and devoured by that hub. On the off chance that the receptive power produced is more prominent than that expended, the voltage goes up and vice versa. At whatever point the voltage level of a specific transport experiences variety, this is because of the unbalance between the two vars at that transport.

275

276

Tidal Energy Systems

Node 1 is a tidal generator node to voltage VT1 and load node with voltage VT2. Assuming the interconnector to be lossless (R ¼ 0) VL2 ¼ VT 1  IZ

(5.28)

VT∗ 1 I ¼ PT  jQT

(5.29)

I¼

P  jQ VT∗ 1

PT  jQT X VT1   QT PT j VL2 ¼ VT 1  VT 1 VT 1

(5.30)

VL2 ¼ VT 1  j

(5.31)

In a tidal power plant, the reactive power absorbed by the transmission line will be ¼ I2TωL. Due to the shunt capacitance of the line, the reactive vars supplied by the line are: ¼ V2TωC IT2 ωL ¼ VT2 ωC rffiffiffiffiffi VT L ¼ ¼ ZT IT C Tidal Generator It is known that the power transmitted from a tidal generator bus to an infinite bus bar is given by: ET V T sin δ (5.32) X Where ET is tidal generator voltage, VT is infinite bus bar voltage, X is the reactance of the unit, and δ is the angle between ET and VT. A similar relation for the reactive power for a round rotor machine is given by PT ¼

QT ¼

VT ET V2 cos δ  T X X

(5.33)

5.5 DYNAMIC CONTROL OF TIDAL CURRENT TURBINE 5.5.1 Load Frequency Control In an isolated system consisting of a generator and a load, the varying demand of the load can be satisfied entirely by the governor action. The governor of the unit is set to maintain the frequency at 50 Hz by setting the speed droop indicator to zero.

Control System of Tidal Power Plant

The machine speed will be maintained exactly at 50 Hz with varying load demands, provided that the amount of load is not greater than the unit’s ability to carry it. When a unit is operating in a large interconnected system, it is not—and is indeed virtually—impossible to set all governors to respond isochronously to maintain constant frequency. In such cases unit, speed droop is set at 3%–5%, depending on the system’s load sharing requirement. A governor set on 5% speed droop will cause its generator to accept 100% of its capacity when there is a frequency droop of 5%. Depending on its regulating ability, the unit can be adjusted to help maintain system frequency, which is the exact indication of the balance between supply and demand. The operator in the control room, on receipt of orders from the central load dispatch office, adjusts the speed level of the unit to assist the system to maintain frequency at 50 Hz. In the case of units fitted with automatic load-frequency control devices, the speed level is adjusted by load frequency control equipment and even by the load dispatch office itself. In a large tidal energy system, optimized and ideal manual regulation is not feasible and, therefore, the load frequency component is installed with each tidal generator. Similarly for voltage control purposes, the voltage regulation component is installed with each tidal generator. Fig. 5.15 gives the schematic diagram of load frequency and excitation voltage regulators of a turbo generator. The tidal controllers are set for a meticulous operating condition and they take care of small variations in load demand without the voltage and frequency exceeding the predetermined rated value. If the existing operating conditions change materially, the tidal controllers must be reset, either manually or automatically. It is known that small variations in the demand side of the load depend upon the change in tidal generator rotor angle and are independent of the bus voltage. However, the bus voltage is dependent on tidal generator excitation and on the reactive generation

Load frequency controller

Tidal current

Control mechanism

Frequency sensor

Turbine

Voltage sensor

Generator Controller excitation

Fig. 5.15 Load frequency control of a tidal power plant.

Voltage controller

277

278

Tidal Energy Systems

Q, but is independent of tidal generator rotor angle. Therefore, the two closed-loop controls, load frequency, and excitation voltage controls are noninteractive for sudden variations and can be modeled and assessed independently. The load frequency controller is moderate acting as a result of the extensive time consistent contributed by the turbine and the generator snapshot of inactivity, and excitation voltage control is quick going about as the time steady of the field winding is generally littler, subsequently the drifters in excitation voltage control vanish considerably quicker and don’t influence the flow of load recurrence control. We will consider here just the heap recurrence control part of direction. It is to be noted here that the controller intended for control ought not be heartless to quick, irregular changes, generally the framework will be inclined to chasing, bringing about over the top wear and tear of control types of gear and the turning machines. The main objective of the load frequency controller is to exert control of frequency and, at the same time, of real power exchange via the outgoing lines. The change in frequency and the tie-line real power is sensed, which is a measure of the change in rotor angle δ, that is, the error Δδi to be corrected. The error signals Δfi and ΔPtie are amplified, mixed, and transformed into a real power command signal ΔPci, which is sent to the prime mover to call for an increment in the torque. The prime mover, therefore, brings change in the generated output by an amount ΔPGi that will change the values of Δfi and ΔPtie. The process continues until the deviation Δfi and ΔPtie are well below the specified tolerances.

5.5.2 Control Mechanism of Speed Governing System: Governor Servo System To meet the intermittent oil demands of the servo motors, each turbine has its own oil/ air reservoir fed by oil pumps with an automatic unloading valve. The initial air charge may be provided by a separate compressor, but the subsequent air leakage must be compensated for by an automatic air compressor controlled by the sump level. The oil pressure receiver that is partially filled contains enough energy stored in the pressure oil so as to ensure full closure of the nozzles or guide vanes in an emergency. The servomotor oil admission is controlled by the governor. The main servomotor operates through direct mechanical linkage the deflector plates, the nozzle of the impulse turbines, or the guide vanes of reaction turbines. Frequent load fluctuations entail continuous pumping, which may overheat the oil, and governor instability sometimes results. Water cooling is therefore sometimes provided in the oil sump. Governor Drive and Speed Setting The permanent magnet generator (PMG) attached to the generator shaft supplies the electric power to drive a synchronous motor that drives the rotating portion of the

Control System of Tidal Power Plant

speed-sensitive device of the mechanical hydraulic governor. Mechanical governors are not used now. Electromechanical PID governors with speed and power control sections and mechanical hydraulic actuator sections are now generally employed. Speed/ power control sections and hydraulic actuator sections may be installed in separate locations. In case of small tidal currents, sensing may be done by taking frequency signals from PTs. Governors are designed to regulate the speed and thereby the loading at the unit within a desired range by increasing or decreasing the amount of water supplied to the turbine runner. Turbines are fitted with gate limiters that can be remotely controlled. The gate limiter is used for speed no load setting; desired control setting and overload of generators. The gate limiter adjustment usually extends down to zero and thus affords a means for remote stopping and starting at a safe and controlled rate. In a tidal power plant, we consider the saturated condition in which the main valve of the water supply is closed, the water valve is opened by a definite magnitude, the tidal turbine output balances the tidal generator output, and the tidal generator and tidal turbine are running at a particular speed when the frequency of the system is fs, the tidal generator output PGTO, and the steam valve setting corresponding to these conditions is X0E. Let the point A of the speed changer lower down by an amount ΔXA. As a result, the commanded increase in power is ΔPc then ΔXA ¼ K1ΔPc. The movement of linkage point A causes small position changes ΔXc and ΔXD of the linkage points C and D. With the movement of D upward by ΔXD, high-pressure oil flows into the hydraulic amplifier from the top of the main piston. Therefore, the steam valve will move downward a small distance ΔXE, which results in increased turbine torque and hence power increase ΔPG. This further results in an increase in speed and hence the frequency of generation. The increase in frequency Δf causes the link point B to move downward a small distance ΔXB proportional to Δf. We assume that the movements are positive if the points move downward. Because all the movements are small, we have the linear relationship. Two factors contribute to the movement of C: (i) Increase in frequency causes B to move by ΔXB when the frequency changes by Δf as then the fly ball moves outward and B is lowered by ΔXB. Therefore, this contribution is positive and is given by K1Δf. (ii) The lowering of the speed changer by an amount ΔXA lifts the point C upward by an amount proportional to ΔXA, that is, let this be K20 ΔXA or K2ΔPc. ∴ΔXC ¼ K1Δf – K2ΔPc (20.1) The positive constants K1 and K2 depend upon the length of the linkage arms AB and BC and upon the proportional constants of the speed changer and the speed governor. The movement of D is contributed by the movement of C and E. Because C and E move downward when D moves upward, therefore, ΔXD ¼ K3ΔXC + K4ΔXE.

279

280

Tidal Energy Systems

The positive constants K3 and K4 depend upon the length of the linkage CD and DE. Assuming that the oil flow into the hydraulic cylinder is proportional to position ΔXD of the pilot valve, the value of ΔXE is given by ðt ΔXE ¼ K5 ðΔXD Þdt 0

The constant K5 depends upon the fluid pressure and the geometries of the orifice and the cylinder. Taking the Laplace transform of equations, we obtain ΔXC ðsÞ ¼ K1ΔF ðsÞ  K2ΔPc ðsÞ ΔXDðsÞ ¼ K3ΔXC ðsÞ + K4ΔXEðsÞ ΔXE ðSÞ ¼  KS5 ΔXD ðSÞ, we obtain K2 K3 ΔPC ðsÞ  K1 K3 ΔF ðsÞ s K4 + K5   KG 1 ¼ ΔPC ðsÞ  ΔF ðsÞ 1 + sT G R

ΔXE ðSÞ ¼

(5.34)

Where ¼ KK21 , speed regulation of the generator KG ¼ KK2 K4 3 ¼ gain of speed governor TG ¼ K41K5 ¼ time constant of speed governor Turbine Model The model requires a relation between changes in power output of the steam turbine to changes in its steam valve opening 4 XE. We consider here a nonreheat turbine with a single gain factor KT and a single time constant TT. Thus, in the crudest model representation of the turbine, the transfer function is given as GT ðsÞ ¼

ΔPT ðsÞ KT ¼ ΔXE ðsÞ 1 + sT T

Typically the time constant TT lies in the range 0.2–2.0 s. Fig. 5.15 shows the linearized model of a nonreheat turbine controller, including the speed governor mechanism. Generator-Load Model The model gives a relation between the change in frequency as a result of the change in generation when the load changes by a small amount. Let 4PD be the change in load;

Control System of Tidal Power Plant

as a result the generation also swings by an amount 4PG. The net power surplus at the bus bar is 4PG  4PD and this power will be absorbed by the system in two ways: (i) By increasing the kinetic energy of the generator rotor at a rate dW/dt, where W is the new value of kinetic energy. Let W0 be the K.E. Before the change in load occurs when the frequency is f 0, let W be the K.E. when the frequency is f 0 + 4f. Because the K.E. is proportional to the square of the speed of the generator, therefore, the two kinetic energies can be correlated as  0 2 0 f + Δf W ¼W f0   2Δf 0 W ¼W 1+ 0 f Neglecting the higher terms as 4 f/f 0 is small dW 2W 0 d ¼ 0 : ðΔf Þ f dt dt (ii) The load on the motors increases with an increase in speed. The load on the system being mostly the motor load, the rate of change of load with respect to frequency can be regarded as nearly constant for small changes in frequency, D ¼ dPdfD , where D can be obtained empirically. If the net power surplus W at the bus bar, H is the inertia constant of the generator in MW sec/MVA and P is the rating in MVA, then W 0 ¼ HP. Rewriting the above balance equation ΔPG  ΔPD ¼

2W 0 d ðΔf Þ + DΔf f 0 dt

ΔPG  ΔPD ¼

2HP d ðΔf Þ + DΔf f 0 dt

Dividing throughout by P we get, 2H sΔF ðsÞ + DðsÞΔF ðsÞ f0   2H ¼ ΔF ðsÞ 0 s + DðsÞ f

ΔPG ðp:u:Þ  ΔPD ðp:u:Þ ¼

281

282

Tidal Energy Systems

ΔFs ¼

ΔPG ðsÞ  ΔPD ðsÞ 2H s + DðsÞ f0

ΔF ðsÞ ¼

½ΔPG ðsÞ  ΔPD ðsÞ 2H s + DðsÞ f0

ΔF ðsÞ ¼ ½ΔPG ðsÞ  ΔPD ðsÞ TP ¼

KP 1 + sTP

2H and KP ¼ 1=D Df 0

5.6 STABILITY ANALYSIS OF A TIDAL POWER PLANT Voltage stability or voltage collapse has been seen as a steady-state problem involving static power flow studies for analysis. The ability to transfer reactive power from sources to sinks during steady operating conditions is a major aspect of voltage stability. It is to be noted that the network maximum power transfer limit is not necessarily the voltage stability limit. Voltage instability or collapse is a dynamic process. The word stability itself implies a dynamic system and the power system is a dynamic system. In a large, complex power system, the voltages of various buses, the flow of active and reactive power, etc., keep on changing with time. It is to be noted that, in contrast to rotor angle stability, the dynamics mainly involve the loads and the means for voltage control. Voltage stability, hence, has been called load stability. Voltage stability is a very important aspect of overall power system stability. The voltage stability is analogous to the stability of any other physical system. Some of the definitions of power system voltage stability are given here.

5.6.1 Definitions 1. A power system at a given operating state is small disturbance voltage stable if, following any small disturbance, voltages near loads are identical or close to the predisturbance values. 2. A power system at a given operating state and subject to a given disturbance is voltage stable if voltages near loads approach postdisturbance equilibrium values. The disturbed state is within the region of attraction of the stable postdisturbance equilibrium. 3. A power system at a given operating state and subject to a given disturbance undergoes voltage collapse if postdisturbance equilibrium voltages are below acceptable limits. Voltage collapse may be total (blackout) or partial.

Control System of Tidal Power Plant

Voltage stability results in a progressive voltage decrease or increase. However, destabilizing controls reaching limits or other control actions, for example load disconnection, may establish global stability. A voltage stability study normally requires a sudden increase in load or transfer of power and is almost always a periodic decrease in voltage. Oscillatory voltage instability may be possible but control instabilities, which may be due to too high a gain on a static var. compensator or too small a dead band in a voltage relay controlling a shunt capacitor bank, are excluded. Overvoltage phenomena and instability such as the self-excitation of rotating machines are outside the scope of definitions. Overvoltages are normally more of an equipment problem than a power system stability problem. Sometimes the term “voltage security” is used, which means the ability of a system not only to operate stably but also to remain stable following large contingencies or load increases. This, in fact, requires the presence of a large margin between the operating point and the voltage instability point or to the maximum power transfer point following large contingencies. Even though voltage stability requires analysis of the power system under dynamic conditions, static power flow methods are often useful for fast but approximate analysis. The phrases “equilibrium points” and “region of attractions” used in the definition are further explained in the succeeding section.

5.6.2 Electrical Protection of a Tidal Generator Possible Faults All faults associated with the unit may be classified as either insulation failure or abnormal running conditions. An insulation failure will result in either an interturn fault, a phaseto-phase fault, or an earth fault, but more commonly the last one because most insulation failures eventually bring the winding into direct contact with the core. The abnormal running conditions to be protected against comprise are: (a) Overloading (b) Loss of excitation (c) Unbalanced load (d) Lubrication oil failure (e) Failure of prime mover (f ) Overspeeding (g) Rotor displacement (h) Excessive vibration Stator Faults Break down of winding insulation may result in any of the following types of faults: (a) earth faults, (b) phase faults, or (c) interturn faults.

283

284

Tidal Energy Systems

Other faults originating from defective joints or inadequate or defective end turns or terminals will, if undetected, reach a stage where there is a breakdown of insulation. An earth fault is liable to be caused by arcing to the core and may not only damage the conductor, but also cause burning and welding of the laminations. To limit this damage, it is almost universal practice to connect impedance or an earthing resistance between the generator winding neutral and the earth. Practice varies with the method adopted for earthing and the impedance used. Phase to phase or a three-phase short circuit is not limited by the earthing impedance. Rotor Faults The field system is not normally connected to earth, so an earth fault does not give rise to any fault current and is thus not in itself a danger. If a second earth fault develops, however, a portion of the field winding may be short circuited, resulting in an unbalanced magnetic pull on the bearing. This can cause rotor vibration and consequent failure of the bearing surface or even displacement of the rotor sufficient to bend the shaft in addition to this mechanical trouble. Loss of Excitation Failure of DC excitation causes the machine to run as an induction generator, with the stator drawing magnetizing currents from the AC system. Due to saliency, normal hydrogenerators may carry 20%–25% of normal load without field and not lose synchronism. Loss of field when a hydrogenerator is carrying a full load may cause overloading of the stator by operating at a low power factor, and of overheating the rotor owing to induced currents in the rotor body and damper windings. The unit will impose VAR drain on the system. Unbalanced Loading An unbalanced load can be resolved into positive, negative, and zero sequence components. The positive sequence component is similar to the normal balanced load while the negative sequence component is also similar, except that the resultant reaction field rotates counter to the DC field system and produces a flux that cuts the rotor at twice the rotational velocity. The double frequency eddy currents thus induced in the rotor are liable to cause heating of the rotor. Water wheel generators have a low rotational velocity and thus the heating in the rotor caused by small eddy currents is generally of less practical significance. It is only provided as backup. Overvoltage Water wheel generators have a high overspeed factor and the provision of overvoltage protection is more desirable so that the insulation is not damaged. This protection also serves to avoid damage if the voltage regulator system fails to operate correctly.

Control System of Tidal Power Plant

The potential danger of such a failure cannot be ignored with the high speed and high range of modern regulators, designed to meet long-distance transmission stability requirements. System Frequency Swing Large hydrogenerators connected to an EHV power system sometimes lead to severe system frequency swings because of the complexity of the modern EHV power system. This may cause the generator to go out of step. Thermal Protection of Tidal Power Plant Overheating of the tidal generator stationary winding and core due to overloading due to the large electricity demand, failure of tidal generator cooling system and heat loss due to eddy and hysteresis loss detected by temperature sensors entrenched at various points in the stator winding. Temperature sensors are sometimes thermocoupled for protection of the tidal generator stator winding incessantly monitor temperature of the stator winding and the heat sensors are normally connected to a supervisory control and data acquisition system for scanning, recording and alarm and tripping for an abnormal temperature rise. Failure of Cooling Large tidal generators provide a closed-loop system-based air-cooling system connection with an air/water cooler on the stator frame. Distortion of the cooling system can result in gradual deterioration of the stator core insulation and/or the stator winding conductor and insulation. The cooling air temperature, the cooling water supply pressure, and the temperature for each cooler are monitored for alarms and tripping of the machine for abnormal conditions. Backup Over Current Protection Backup over current protection finished current insurance might be given to tidal generator it is possible that as standby security against flaws in the system or as a defend against disappointment of the tidal generator unit assurance. The topic of setting must be deliberately viewed as and the quick decrement of blame current nourished by the tidal generator must be considered. It is vital that the tidal generator isn’t stumbled because of framework blames even through the tidal generator is working under its most extreme excitation condition and the transfer setting must be segregated with the active circuit assurance. The principle point is to give a move down insurance and the over current transfers are set, less with the intension of stumbling under through shortcomings but instead to make preparations for blame streams encouraged again from the framework upon the event of an in zone blame. So it is most for the most part gave a voltage protection and reverse time postpone includes with the goal that stumbling happens just in the event that there is a fall in the generator. In the second utilize, the over current hand-

285

286

Tidal Energy Systems

off fills in as an exceptionally valuable standby arrangement of insurance for such periods as, when the differential security is being tried at which time the overcurrent settings can be shifted at watchfulness to suit the transitory condition. With the appearance of present day static fast reaction, write programmed voltage controllers controlling substantial stores of excitation control, the generator circuit decrement in blame condition is postponed thus that over-current/times settings can be picked as to surrender back cover against through blame conditions too. In such cases, be that as it may, conceivable controller is out of circuit for support. Transformer Protection Faults in the winding conventionally start as failures turn to turn, but may occur from winding to ground. Turn-to-turn faults cause very high local heating and customarily some arc under but very little current in the external circuit. Such a fault has to involve more of the winding until adequate current appears in the external circuit to operate the differential relay. In order to rehabilitate a transformer it is compulsory to disassemble and restack the core in whole or in part. This is the more sumptuous part of the rehabilitation, so that as far as the windings are concerned, there is no head for prodigiously high speeds in clearing a transformer winding fault. However, undue delay is undesirable for the following reasons: (i) The arc may damage the major insulation and the second winding, or excess current may damage heating parts or winding, which could otherwise be used again. (ii) Prolonged arcing under oil may disintegrate it into gases, which may form an explosive mixture at the top of the transformer. This may be ignited by a tiny spark and cause a severe explosion. The speed of clearance should be sufficiently fast so that the time of any internal fault causing a serious disturbance will not conflict with the timing on any line or backup protection. The speed of clearance should be sufficiently fast that the time of any internal fault causing a serious disturbance will not conflict with the timing on any line or backup protection. The current transformers on the various sides of the transformer zone should be such a ratio that, for a healthy zone, the sum of the incoming and outgoing is zero. This requires that the current transformer ratio for each voltage rating of the transformer bank should be inversely proportional to the voltage. Where available current transformers do not satisfy these requirements, autotransformers in the secondary circuit can be used to obtain a proper balance. For a star-delta transformer bank, the current transformers on the star side must be connected in delta and those on the delta side in star because on the star side, the current transformers are in the “leg” and on the delta side, they are in “line.” The protection scheme recommended by the Central Board of Irrigation and Power (CBIP manual on transformers, 1987) for transformers, interlinking transformers, etc., is as follows:

Control System of Tidal Power Plant

Station Bus Zone Protection The bus differential is the easiest of the zone differentials because it includes the assurance of the transport wiring. In any case, because numerous arrangements of current transformers might be associated in parallel, extraordinary care must be utilized as a part of planning this insurance with the goal that the coveted affectability and steadiness are acquired. The every single current transformer are correct copies and weights have been diminished to a base, contrasts in current transformer execution may at present be experienced to begin with, because of D.C. immersion at high estimations of present, second, because of the condition where all short out current may stream out to an outside blame through one arrangement of current transformers yet may stream into zone through various arrangements of current transformers. Clearly, the present transformers conveying the aggregate blame current will work on an alternate segment of the immersion bend than those on the different approaching leads. In this way, uncommon class C.T.S. are utilized. Transmission Line Protection In any power framework, most deficiencies happen on overhead transmission lines, with these being the most uncovered components of the framework. Defensive transferring for transmission lines is, consequently, generally critical. The greater part of flaws on high voltage lines start with the flashover of the protection at a certain point; that is, an L-G blame because of lightning or superfluous questions on lines, for example, trees, kites and so on. Nonetheless, L-L-G deficiencies are very normal because of lightning, and every so often, a synchronous L-L-L-G blame because of lightning will happen. The L-G and L-L-G shortcomings will create a remaining current on a grounded nonpartisan framework, yet the L.L.L.G blame does not for the most part do as such. Deficiencies of the L.L and L.L-L write will happen in wind or slush storms because of conductors swinging together. These deficiencies don’t create leftover streams. Line assurance must, accordingly, cover stage-to-stage shortcomings that are free of the ground and, in addition, stage-to-ground issues. An investigations are required to be conveyed before advancing the assurance for the transmission lines. Lines may be divided into the following three classes: (a) Two terminal lines (b) Parallel lines (c) Radial lines Two Terminal Lines

Transmission lines, unlike apparatus or buses, have their terminals some distance apart. For this reason the zone differential that has been found to be the ideal protection for station zones cannot be used in its usual form on lines.

287

288

Tidal Energy Systems

The general requirements for ideal line protection are as follows: (a) The relays must operate instantaneously for the transmission system of a tidal power plant. (b) The relay scheme must be inherently selective according to the km range of the transmission line of the tidal power plant. (c) The relays at both ends of the line must operate simultaneously for all line faults during the operation of the tidal energy system. (d) The relays must not respond to surging between generating sources as long as the generators do not fall out of step, in which case the relays should operate. (e) The protection must cover all phases and ground faults of the tidal power plant. The protective schemes in general used for phase and ground protection of two terminal lines are as follows: (a) Overcurrent—with or without direction (b) Distance protection—usually with direction (c) Pilot wire for short lines (d) Carrier current for long lines Overcurrent Protection The overcurrent relay plot in either the rapid or planned enlistment write isn’t generally attractive for transmission lines due fundamentally to varieties in the extent of the overcurrent under different framework working conditions and to the relative estimation of the base overcurrent and the full load current of the line. A rapid overcurrent transfers must be set securely over the most extreme through shortout of the line area, their zone of safe particular task is normally constrained to just a little segment of the line. The coordinated acceptance overcurrent hand-off used to cover the rest of the line must be set securely over the most extreme load current with adequate planning to particular or outside flaws. Directional transfers of either the watt meter composition or the fast sort are utilized with the overcurrent transfers where heading is required. Where least estimations of blame current are close to the full heap of the line, overcurrent transfers are not relevant. In any case, where they can be utilized, they have the upside of straightforwardness. Phase-to-Ground Faults On a framework with grounded neutrals, any present that leaves a line conductor and comes back to the neutrals by means of the ground, as in a blame to ground, is a leftover current and can be estimated in the impartial (normal) heap of the star-associated secondaries of an arrangement of current transformers in the three periods of that line. This current skewering by and large speaks to a blame current that is very autonomous of load. It can, in this way, be utilized as a part of a present transfer of a delicate setting.

Control System of Tidal Power Plant

Where fast ground security is required, the directional hand-off can be achieved in a rapid sort for either present or voltage polarization. The above kind of ground security is of use on a framework that is grounded through a high protection or reactance. For this situation, the estimation of the nonpartisan current is controlled by the impartial condition and the area of the blame has little effect on the estimation of the unbiased current. On such a framework, some kind of separation hand-off would need to be utilized and directioned by the above sort of directional hand-off. Distance Protection The distance relay of the impedance and reactance and more types is used. Phase-to-Phase Faults The Impedance Type

In this type, phase-to-phase voltage is mechanically balanced in the relay against the current of the proper phase, with the current acting to close the contacts. For a ratio E/I greater than a certain value, which is adjustable and is the distance setting of the relay, the contacts will be kept open, whereas for lower values the contacts will be closed. This ratio represents an impedance that, neglecting the resistance of a fault itself, is a constant for any given length of line, that is, an impedance relay can be set to cover any desirable length of line. For all types of faults involving more than one phase wire of a line, the impedance relay has the following desirable features: (a) It gives accurate and dependable high-speed protection for these faults over approximately 80% of the line. It gives timed protection over the whole line with a back-up effect for terminal H.V. buses. Terminal station zones and tandem line sections must clear sufficiently fast to be selective with this timing. (b) It is to a very large extent independent of connected generating capacity and the configuration of the system, both for its accuracy and speed, and will even operate on fault currents below full load. It will operate accurately on any current that will give a 5% drop over the section protection. It can be designed to operate in 1/60 s or less for all faults except those close to the boundary conditions of the fault current or distance. (c) It can be used on any line sufficiently long that the fault impedance (arc resistance) does not add a sufficient amount to the line impedance to prevent operation. The arc resistance is proportional roughly to the length and usually about 300–500 V per foot. A high-speed relay will cause tripping before an arc starts to expand. (d) The impedance relay is relatively simple in construction. Q.1 Two tidal energy generating stations T1 and T2 have the full load capacity of 100 and 55 MW, respectively. The interconnector connecting the two stations has an induction motor/synchronous generator (plant T3) of full load capacity 15 MW.

289

290

Tidal Energy Systems

Percentage changes of speeds of T1, T2, and T3 are 5, 4, and 3, respectively. The loads on bus bars T1 and T2 are 35 and 15 MW, respectively. Determine the load taken by the set T3 and indicate the direction in which the energy is flowing. Solution: Assume x MW flows from T1 to T2 Load on station T1 ¼ (35 + x) 5 % drop in speed T1 ¼ 100 ð35 + xÞ and Load on station T2 ¼ (15  x) 4 ð35 + xÞ % drop in speed T2 ¼ 55 5 3 4 100 ð35 + xÞ + 15 x ¼ 55 ð35 + xÞ 0:05x + 0:2x + 0:073x ¼ 1:095  1:75 x ¼ 2.027 MW Which means that the power of magnitude 2027 MW will be T2 to T1. Q.2 Two tidal generators rated for 50 and 100 MW have governor drop characteristics of 3% from no load to full load. They are connected in parallel to share a load of 125 MW. Determine the load shared by each machine, assuming free governor action. Solution: Because the two machines are working in parallel, the percent drop in frequency from both the machines due to different loadings must be the same. Let x be the power supplied by the 50 MW unit. The % drop in speed ¼ 3x 50 3 Similarly % drop in speed of 100 MW until will be 100 ð125  xÞ 3x 3 ¼ ð125  xÞ 50 100 x ¼ 41.67 MW Power shared by 100 MW unit will be 125 MW—41.67 ¼ 83.33 MW Power supplied by 50 MW unit ¼ 41.67 MW Power supplied by 100 MW unit ¼ 83.33 MW Q.3 A 200 MVA 50 Hz tidal generator operates at no load at 4000 r.p.m. A load of 55 MW is suddenly applied to the machine and the steam valves to the turbine commence to open after 0.6 s due to the time lag in the governor system. Assuming inertia constant H of 5.5 KW/s per kVA of generator capacity, calculate the frequency to which the generated voltage drops before the steam flow commences to increase to meet the new load. Solution: By definition H ¼ Stored energy/capacity of machine The energy stored at no load ¼ 5.5  200 ¼ 1100 MJ Before the steam valves open the energy lost by the rotor ¼ 55  0.6 ¼ 33 MJ As a result of this there is a reduction in speed of the rotor and, therefore a reduction in frequency. qffiffiffiffiffiffiffiffiffiffiffiffiffi The new frequency will be: fnew ¼ 110033 1100  50 ¼ 49:18 Hz

Control System of Tidal Power Plant

EXERCISE What is a control system? Write and explain different types of control systems. What is a manual control system? What is an automatic control system? What is the requirement of an automatic control system in a tidal power plant? Explain the load frequency control of a tidal power plant. What is the meaning of synchronization of a tidal power plant? Explain the unit control system of a tidal power plant. Derive the equation for the theory of hydrokinetic energy conversion of a tidal power plant. 10. Explain tidal dynamic energy assessment. 11. Explain the phenomenon of dynamic control of a tidal current turbine. 12. Explain the phenomenon of reactive power control of a tidal power plant. 1. 2. 3. 4. 5. 6. 7. 8. 9.

Q.1 Two tidal energy generating stations T1 and T2 have the full load capacity of 300 and 165 MW, respectively. The interconnector connecting the two stations has an induction motor/synchronous generator (plant T3) of full load capacity 45 MW. Percentage changes of speeds of T1, T2, and T3 are 5, 4, and 3 respectively. The loads on bus bars T1 and T2 are 95 and 45 MW, respectively. Determine the load taken by the set T3 and indicate the direction in which the energy is flowing. Q.2 Two tidal generators rated for 150 and 300 MW have governor drop characteristics of 3% from no load to full load. They are connected in parallel to share a load of 325 MW. Determine the load shared by each machine, assuming free governor action. Q.3 A 600 MVA 50 Hz tidal generator operates at no load at 3000 r.p.m. A load of 155 MW is suddenly applied to the machine and the steam valves to the turbine commence to open after 0.4 s due to the time lag in the governor system. Assuming inertia constant H of 3.5 KW/s per kVA of generator capacity, calculate the frequency to which the generated voltage drops before the steam flow commences to increase to meet the new load. Q.1

The (i) (ii) (iii) (iv)

forward path of the control system is the path that follows: Input to output Output to input Both (i) and (ii) None of the above

Q.2

The (i) (ii) (iii) (iv)

feedback path of the control system is the path that follows: Input to output Output to input Both (i) and (ii) None of the above

291

292

Tidal Energy Systems

Q.3

A traffic control system is one example of (i) Open-loop (ii) Closed-loop (iii) Both (i) and (ii) (iv) None of the above

Q.4

A washing machine is one example of (i) Open-loop (ii) Closed-loop (iii) Both (i) and (ii) (iv) None of the above

Q.5

Field (i) (ii) (iii) (iv)

Q.6

The (i) (ii) (iii) (iv)

control system of the tidal energy system follows the Series manner Parallel manner Cascaded manner None of the above

Q.7

The (i) (ii) (iii) (iv)

advantages of microprocessor-based multifunction relays are Self-monitoring Multiple protective function Self-calibration All of the above

Q.8

The (i) (ii) (iii) (iv)

unit control board is designed to perform Start/stop control Annunciation of alarm Control of real/reactive power All of the above

Q.9

The (i) (ii) (iii) (iv)

automatic control operating cost of an overall system Increases Constant Decreases Independent from cost

Q.10

The (i) (ii) (iii) (iv)

unit control board is designed to perform Information receipt Start/stop control Temperature information of the coastal area All the above

excitation current is the path of Inner loop control Outer loop control Both (i) and (ii) None of the above

Control System of Tidal Power Plant

Q.11

An automatic control system gathers the information in terms of (i) Analog signal (ii) Digital signal (iii) Both (i) and (ii) (iv) None of the above

Q.12

A manual control system is not used in (i) Small tidal power system (ii) Large tidal power system (iii) Medium size tidal power system (iv) All of the above

Q.13

Two tidal generators connected in parallel at the same frequency and at the same voltage level are called (i) Synchronization (ii) Cascaded (iii) Hybrid (iv) None of the above

Q.14

A tidal turbine is a revolving machine that converts the kinetic energy of tides into (i) Electrical energy (ii) Mechanical energy (iii) Chemical energy (iv) Fuel energy

REFERENCE Fraenkel, P., 2007. Marine current turbine: pioneering the development of marine kinetic energy converter. Proc. Inst. Mech. Eng. A: J. Power Energy 221 (2), 159–169.

FURTHER READING Bosche, J., 2003. Analyse et commande par placement de poles en DU-stabilite robuste. Ph.D. Thesis. Universite de Poitiers. Chilali, M., Gahinet, P., 1996. H∞ design with pole placement constraints: an LMI approach. IEEE Trans. Autom. Control 41 (3), 358–367. Choi, J.S., Jeong, R.G., Shin, J.H., Kim, C.K., Kim, Y.S., 2007. New control method of maximum power point tracking for tidal energy generation system. In: Proc. International Conference on Electrical Machines and Systems, Seoul, Korea, Oct. 8–11. Dahmane, M., Bosche, J., El Hajjaji, A., 2013a. Renewable energy management algorithm for stand-alone system. In: International Conference on Renewable Energy Research and Applications (ICRERA), Madrid. Dahmane, M., Bosche, J., El Hajjaji, A., Pierre, X., 2013b. MPPT for photovoltaic conversion systems using genetic algorithm and robust control. American Control Conference (ACC), pp. 6595–6600. Dali, M., Belhadj, J., Roboam, X., 2010. A hybrid solare–wind system with battery storage operating in gridconnected and standalone mode: control and energy management—experimental investigation. Energy 35, 2587–2595.

293

294

Tidal Energy Systems

Haque, M.E., Negnevitsky, M., Muttaqi, K.M., 2010. A novel control strategy for a variable speed wind turbine with a permanent magnet synchronous generator. IEEE Trans. Ind. Appl. 46 (1), 331–339. Hong, S.-K., Langari, R., 2000. An LMI-based H∞ fuzzy control system design with TS framework. Inform. Sci. 123, 163–179. Jiang, Y., Rong, M.F., Hua, L.Y., 2009. Variable speed constant frequency tidal current energy generation and control strategy for maximum power point tracking and grid connection. In: International Conference on Sustainable Power Generation and Supply (SUPERGEN), Nanjing, China, April 6–7. Knight, A.M., Peters, G.E., 2005. Simple wind energy controller for an expanded operating range. IEEE Trans. Energy Convers. 20 (2), 459–466. Li, D., Yao, Y., Chen, Q., Ye, Z., 2005. Numerical simulation of tidal current energy in Yangtze EstuaryHangzhou Bay, China. In: OCEANS, Genoa, Italy, May 18–21. Liu, M., Li, W., Billinton, R., Wang, C., Yu, J., 2015. Probabilistic modeling of tidal power generation. In: Proc. 2015 IEEE Power & Energy Society (PES) General Meeting, Denver, CO, July 26–30. Lopez, M., 2008. Contribution a l’Optimisation d’un Systeme de Conversion Eolien pour une Unite de Production Isolee. PhD Thesis. UniversiteParis Sud. Muljadi, E., Yu, Y., 2015. Review of marine hydrokinetic power generation and power plant. Electr. Power Compon. Syst.. 43 (12). (Special Issue: Renewable Energy Devices and Systems—State-of-the-Art and Future Trends, Taylor & Francis Publications.). Okorie, P.O., Owen, A., 2008. Turbulence: characteristics and its implications in tidal current energy device testing. In: OCEANS, Quebec City, Canada, Sept. 15–18. Orlando, N.A., Liserre, M., Monopoli, V.G., Mastromauro, R.A., Dell’Aquila, A., 2008. Comparison of power converter topologies for permanent magnet small wind turbine system. In: IEEE International Symposium on Industrial Electronics (ISIE), pp. 2359–2364. Qi, W., Liu, J., Chen, X., Christofides, P.D., 2011. Supervisory predictive control of standalone wind/solar energy generation systems. IEEE Trans. Control Syst. Technol. 19 (1). Uddin, M.N., Chy, M.M.I., 2010. A novel fuzzy-logic-controller-based torque and flux controls of IPM synchronous motor. IEEE Trans. Control Syst. Technol. 46 (3). Urtasun, A., Sanchis, P., San Martı´n, I., Lo´pez, J., Marroyo, L., 2013. Modeling of small wind turbines based on PMSG with diode bridge for sensorless maximum power tracking. Renew. Energy 55, 138–149.

CHAPTER 6

Reliability Assessment Model Chapter Outline 6.1 Introduction 6.2 Failure Distribution Model of a Tidal Energy System 6.3 Time-Dependent Failure Mode of a Tidal Energy System 6.3.1 Counting Process 6.3.2 Series System Failure Rate Equations 6.3.3 Reliability Analysis of a Tidal Energy System 6.4 Constant Failure Rate Model 6.4.1 Model Uncertainties 6.4.2 Measurement Uncertainties 6.4.3 Constant Failure Modes of Tidal Energy Conversion Systems 6.4.4 Performance Assessment of Reliability Assessment 6.4.5 Reliability Analysis of Fault-Tree Analysis 6.4.6 Causes of Failure in a Tidal Renewable Energy System 6.4.7 Fault-Tree Construction and Analysis 6.4.8 Boolean Algebra and Reliability Calculation Exercise Further Reading

295 297 302 305 310 313 313 316 316 316 317 320 323 327 327 329 330

6.1 INTRODUCTION Reliability is defined as the probability of a device or system performing its purpose adequately for the intended operating period of time. Power system reliability is defined as the ability of an electrical power system to supply the system load with reasonable continuity and quality of supply. Major subdivisions of power system reliability are “system adequacy” and “system security.” The term adequacy is related to the existence of sufficient facilities within the system to satisfy the consumer load demand and system operational constraints. Figs. 6.1 and 6.2 explore the step and process of reliability analysis, respectively. Fig. 6.1 shows that, in reliability analysis, direct and indirect information are first collected to further system security and system adequacy is determined through direct and indirect acquisition, respectively. Fig. 6.2 shows that the success and failure rate are determined through the reliability analysis. The total success of any system always depends on the minimum and maximum anticipated success of different components of a given system. The definition brings into focus four important factors: • The reliability of a device is expressed as a probability. • The device is required to give adequate performance. Tidal Energy Systems https://doi.org/10.1016/B978-0-12-814881-5.00006-5

© 2019 Elsevier Inc. All rights reserved.

295

296

Tidal Energy Systems

System reliability

Direct information acquisition

Indirect information acquisition

System security

System adequacy

Fig. 6.1 Steps of reliability analysis.

Complete failure

Minimum acceptable success

Minimum anticipated success

Maximum anticipated success

Maximum tolerable failure

Maximum anticipated failure

Minimum anticipated failure

Total success

Fig. 6.2 Process of reliability analysis.

• The duration of adequate performance is specified. • The environment or operating conditions are prescribed. Reliability is defined as the ability of an item to perform a required function under stated conditions for a certain period of time, which is often measured by probability of survival and failure rate. The reliability of RES depends on the system architecture, lower level components, assemblies, environmental and operational stresses, and human factors. Field experiences reveal that the power electronic converter is usually one of the most critical assemblies in terms of failure rate, lifetime, and operations and maintenance costs in renewable energy. Reliability is a measure of the continuous delivery of correctional service. The objectives of reliability engineering on the order of priority are: 1. To apply engineering knowledge and specialist techniques to prevent or to reduce the likelihood or frequency of failure. 2. To identify and correct the causes of failure that do occur, despite the effort to prevent them.

Reliability Assessment Model

3. To determine ways of coping with failure that does occur if their cases have not been corrected. 4. To apply methods for estimating the likely reliability of new designs and for analyzing reliability data. To get the real profit of renewable system as well as confidence by the continual working of the hybrid system to supply the load, we require calculating the system reliability. Several reliability indices have been used. 1. Loss of load expected (LOLE). 2. Loss of energy expected (LOEE). 3. Loss of power supply probability (LPSP) 4. Equivalent loss factor (ELF) LPSP is defined as the probability that an insufficient power supply results when the hybrid system is unable to satisfy the load demand. It is a feasible measure of the system performance for an assumed or known load distribution.

6.2 FAILURE DISTRIBUTION MODEL OF A TIDAL ENERGY SYSTEM The failure rate is the frequency with which an engineered system or component fails, expressed in failures per unit of time. It is often denoted by the Greek letter λ (lambda) and is highly used in reliability engineering. The failure rate of a system usually depends on time, with the rate varying over the life cycle of the system. For example, an automobile’s failure rate in its fifth year of service may be many times greater than its failure rate during its first year of service. One does not expect to replace an exhaust pipe, overhaul the brakes, or have major transmission problems in a new vehicle. A mistake that is often made when calculating reliability metrics is trying to use the failure rate function instead of the probability of failure function. These two functions, along with the probability density function (pdf ) and the reliability function, make up the four functions that are commonly used to describe reliability data. In this article we will provide a brief overview of each of these four functions, followed by a discussion of how to obtain the pdf and reliability functions from the failure rate function. The failure rate is the frequency with which an engineered system or component fails, expressed, for example, in failures per hour. In practice, the closely related mean time between failures (MTBF) is more commonly expressed and used for high quality components or systems. The failure rate is usually time-dependent, and an intuitive corollary is that the rate changes over time versus the expected life cycle of a system. For example, as an automobile grows older, the failure rate in its fifth year of service may be many times greater than its failure rate during its first year of service (Fig. 6.3).

297

298

Tidal Energy Systems

Failure model

Times between failures

Number of failures

Fig. 6.3 Types of failure model.

The Jelinski-Moranda model: The Jelinski-Moranda model is a time between failure model. This model makes the following assumptions about the fault detection and correction process: • The rate of fault detection is proportional to the current fault content of the program. • All failures are equally likely to occur and are independent of each other. • Each failure is of the same order of severity as any other failure. • The failure rate remains constant over the interval between failure occurrences. • During the test, the software is operated in a similar manner as the expected operational usage. • The faults are corrected instantaneously without introduction of new faults into the program. Failure density: This is the ratio of the number of failures during the operation of a tidal energy system at a given unit interval of time to the total number of components at the commissioning of the tidal energy system or the total number of components at the very beginning of the test. For the example being considered, the total number of components at the beginning of the tidal energy project was 500. This is also known as the total initial population of the tidal energy system. During the first unit interval of the tidal energy system, the number of components that fail is 70. Then, at that time the failure density of the tidal energy system is given by 70 ¼ 0:140 500 During the second interval of operation of the tidal energy system, 50 more components fail. Thus the value of failure density during the second interval of operation 50/500 ¼ 0.1. Similarly, during the 10th unit interval, the failure density has a value 16/500 ¼ 0.032. Sometimes the failure density is also called the ratio part failure rate. Let n1 be the number of tidal components that fail during the first unit interval, and let n2 be the number that fail during the second unit interval and so on. Let N be the total population. Then, The failure density during the first unit interval ¼ fd1 ¼ n1 =N The failure density during the first unit interval ¼ fd1 ¼ n1 =N The failure density during the ith unit interval ¼ fd1 ¼ ni =N

Reliability Assessment Model

Table 6.1 Parameter of reliability Time No. of Cumulative t failure f failure F

A B C D E F G H I J K L M N O P Q R S T

130 83 75 68 62 56 51 46 41 37 34 31 28 64 76 62 40 12 4

0 130 213 288 356 418 474 525 571 612 649 683 714 742 806 882 944 984 996 1000

No. of survivors S

Failure density fd

Failure rate Z

Reliability R

1000 870 787 712 644 582 526 475 429 388 351 317 286 258 194 118 56 16 4 0

0.130 0.083 0.075 0.068 0.062 0.056 0.051 0.046 0.041 0.037 0.034 0.031 0.028 0.064 0.076 0.062 0.040 0.012 0.004

0.139 0.101 0.100 0.101 0.101 0.101 0.101 0.100 0.100 0.101 0.103 0.103 0.283 0.486 0.714 1.110 1.200 2.000

1 0.869 0.788 0.713 0.645 0.581 0.525 0.474 0.429 0.387 0.350 0.316 0.287 0.257 0.193 0.119 0.056 0.016 0.004 0

Failure rate ZT: This is the ratio of the number of failures during a particular time interval to the average population during that interval of the tidal energy system. The failure rate of the tidal energy system during the first time interval is given by 65 65 Z ð1Þ ¼ ð500 + 435Þ ¼ ¼ 0:139 =2 467:5 The failure rate is also known as the hazard rate, sometimes called the instantaneous failure rate. This is the ratio of the survivors at any given time to the total initial population. The reliability at the end of the first hour will be R(1) ¼ 435/500 ¼ 0.87. As the test proceeds, more components fail, with the result that the reliability factor decreases progressively. Mean failure rate: The data in Table 6.1 show that the failure rate ZT varies with time. If Z1 is the failure rate for the first hour, Z2 is the failure rate for the second hour, and ZN the failure rate for the Nth hour, the mean failure rate for N hours will be h ¼ ðZ1 + Z2 + ⋯ZN Þ=N If the interval is made much smaller than 1 h, we get a more accurate value of the mean failure rate.

299

300

Tidal Energy Systems

Table 6.2 Failure hours v/s specimen numbers Specimen number

Time to failure hours

Specimen number

Time to failure hours

1 2 3 4 5

405 410 415 420 430

6 7 8 9 10

450 460 480 490 500

Mean time to failure (MTTF) of tidal energy system: In the life testing of 10 specimens of a tidal turbine, the time to failure for each specimen is recorded as given in Table 6.2. Calculate the mean failure rate h for N ¼ 450 h and the mean time to failure for all 10 specimens. ðT Þ The mean failure rate is obtained from the formula hðT Þ ¼ T1 N ð0NÞN : ð0Þ Where h(T) is the mean failure rate for T hours, N(0) is the total population at T ¼ 0, and N(T) is the population remaining at time T. In other words, N(0)  N(T) is the number of specimens failed in T hours. In the present case, we have 1 10  0 ¼ 1=500 500 10 As indicated by the data, all 10 specimens of the tidal turbine do not fail at the same time. They have different times of failure. Hence we can calculate the mean time to failure for all 10 specimens as: hð500Þ ¼

MTTF ¼ 1=10ð405 + 410 + 415 + ⋯ + 500Þ ¼ 4460=10 ¼ 446 h In general, if t1 is the time to failure of the first specimen, t2 is the time to failure for the second specimen, and tN the time to failure of the Nth specimen, the mean time to failure for N specimens will be MTTF ¼ ðt1 + t2 + ⋯ + tN Þ=N In the life testing of 50 specimens of a tidal turbine, the number of failures during each time interval of 20 h is shown in Table 6.3. Estimate the MTTF for these specimens. Table 6.3 Number of failure during the interval Time interval hours Number of failures during the interval

T  500 500 < T  510 510 < T  520 520 < T  530 530 < T  540 540 < T  550

0 12 20 10 5 3

Reliability Assessment Model

Therefore the mean time to failure is 1 ½12ð510Þ + 20ð520Þ + 10ð530Þ + 5ð540Þ + 3ð550Þ 50 MTTF ¼ 523h MTTF ¼

Mean time between failures: In many times, a tidal energy system unit can be repaired immediately after the breakdown. In such cases the mean time between failures refers to the average time of breakdown until the tidal turbine is beyond repair. Example: Table 6.4 gives the values of average wind velocity at a given sea location of the Kerala state for the tidal energy system installation. The average wind velocity data recorded correspond to 1980–2017. The wind velocity is measured in m/s. Let us first rearrange the data in Table 6.4 as an ordered sample in an increasing order. Table 6.5 shows the result. A tidal turbine has a constant failure rate λ ¼ 5.28  104/h. The probability that the turbine survivors 1 month (t ¼ 730 h) in continuous operation is Rðt Þ ¼ eλt ¼ e0:000528:730 ¼ 0:680 The mean to failure is MTTF ¼ 1=λ ¼ 1=5:28  104 h ¼ 1894h ¼ 79 days

Table 6.4 Yearwise wind velocity in m/s Year Wind velocity Year

Wind velocity

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998

15 9 10 11 13 7 6 5 10 11.5 12.5 7.5 10.5 14 13 12 15 16 10

14 13 10 9 15 16 12 8 9 7 6 5 11 17 9 18 16 14 13

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017

301

302

Tidal Energy Systems

Table 6.5 Sampling of wind velocity data Order V Order

V

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

11.5 12 12 12.5 13 13 13 13 14 14 14 15 15 15 16 16 16 17 18

5 5 6 6 7 7 7.5 8 9 9 9 9 10 10 10 10 10.5 11 11

20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

Q.1. It is observed that the failure pattern of a tidal turbine follows an exponential distribution with mean time to failure of 500 h. What is the probability that the system failure occurs within 375 h? Because MTTF is 500 h, 1/λ ¼ 500. From the probability of failure within 375 h is F ð500Þ ¼ 1  e375=500 ¼ 1  e0:75 ¼ 0:528

6.3 TIME-DEPENDENT FAILURE MODE OF A TIDAL ENERGY SYSTEM K out of n tidal turbine: A tidal energy system that is functioning if and only if at least K out of the n tidal turbines are functioning is called a K out of n structure (Koon). In series, the tidal energy structure is therefore an n out of n (noon) structure and a parallel structure is a 1 out of n (100n) structure. 8 n X > > 1 if xi  K > < i¼1 ∅ðxÞ ¼ n X > > > 0 if xi < K : i¼1

A three tidal turbine-based tidal energy system that provides a sufficient amount of electricity to the load if at least two of its three turbines are functioning is an example of a 2 out of 3 (2oo3) structure (Fig. 6.4).

Reliability Assessment Model

TT1

TT2

TT1

TT3

TT2

TT2

TT3

TT3

TT1

Fig. 6.4 Parallel connection of turbine.

Structure function of the 2 out of 3 structure may also be written łðxÞ ¼ x1 x2 [ x1 x3 [ x2 x3 ¼ 1  ð1  x1 x2 Þð1  x1 x3 Þð1  x2 x3 Þ ¼ x1 x2 + x1 x3 + x2 x3  x21 x2 x3  x1 x22 x3  x1 x2 x23 + x21 x22 x23 ¼ x1 x2 + x1 x3 + x2 x3  2x1 x2 x3 • Cut set, minimal cut sets: A cut set K is a set of tidal turbines in C that, by failing, causes the system to fail. A cut set is said to be minimal if it cannot be reduced without losing its status as a cut set. Consider the reliability diagram (Fig. 6.5) and the tidal turbine set C ¼ {1, 2, 3} Path sets Cut sets f1, 2g∗ f1g∗ f1, 3g∗ f2, 3g∗ f1, 2, 3g f1, 2g f1, 3g f1, 2, 3g The minimal path sets and cut sets are marked with an * In this case the minimal path sets are:P1 ¼ f1, 2g P2 ¼ f1, 3g

TT1

TT2

TT3

TT4

TT1

TT1

TT2

TT2

TT3

TT3

TT5

Fig. 6.5 Series connection of turbine.

303

304

Tidal Energy Systems

Table 6.6 Constant failure rate. K/n 1 2

1 2 3 4 5

1/λ

3/2λ 1/2λ

3

4

5

11/6λ 5/6λ 1/3λ

25/12λ 13/12λ 7/12λ 1/4λ

137/60λ 77/60λ 47/60λ 9/20λ 1/5λ

Minimum time to failure (MTTF) of some K out of n system of identical and independent components with constant failure rate λ (Table 6.6). The 2 out of 3 structures: Consider the 2 out of 3 structure of 3 tidal turbine components P1 ¼ 0:98, P2 ¼ 0:96, P3 ¼ 0:94 The tidal system reliability is hðP Þ ¼ P1 P2 + P1 P3 + P2 P3  2 P1 P2 P3 ¼ 0:9957 Birnbaum’s measure: It measures for components 1, 2, and 3, respectively, is I B ð1Þ ¼

dhðP Þ ¼ P2 + P3  2P2 P3 ¼ 0:0952 dP1

I B ð2Þ ¼

dhðP Þ ¼ P1 + P3  2P1 P3 ¼ 0:0776 dP2

I B ð3Þ ¼

dhðP Þ ¼ P1 + P2  2P1 P2 ¼ 0:0584 dP3

Hence, in this particular case: IB(1) > IB(2) > IB(3) Risk achievement worth: The Raw of components 1, 2, and 3, respectively, is I RAW ð1Þ ¼

1  hðo1 , P Þ 1  P2 P3 ¼ ¼ 22:7 1  ðP1 P2 + P1 P3 + P2 P3  2P1 P2 P3 Þ 1  hðP Þ

I RAW ð2Þ ¼

1  hðo2 , P Þ 1  P1 P3 ¼ ¼ 18:3 1  hðP Þ 1  ðP1 P2 + P1 P3 + P2 P3  2P1 P2 P3 Þ

I RAW ð3Þ ¼

1  hðo3 , P Þ 1  P1 P2 ¼ ¼ 13:8 1  hðP Þ 1  ðP1 P2 + P1 P3 + P2 P3  2P1 P2 P3 Þ I RAW ð1Þ > I RAW ð2Þ > I RAW ð3Þ

• Cause and effect model of a tidal energy system: The cause and effect diagram of a tidal energy system is used to identify all the potential causes that may result in a specified event. A cause and effect diagram has some similarities with a fault tree, but is less structured and does not have the same binary restriction as a fault tree. Cause and effect diagrams consider the following five categories are frequently used: Manpower, methods, material, machinery, and milieu (environment).

Reliability Assessment Model

1 2

C

n

Fig. 6.6 Parallel structure of n turbine.

The square root method for dependent failure: Let Ti represent the situation where the tidal turbine i is in a failed state at time t and let qi ¼ Pr(Ti) denote the unavailability of component i for i ¼ 1, 2. The unavailability of the system is then Q0 ¼ Pr (T1 \ T2) because (T1 \ T2)  Ti Pr ðT1 \ T2 Þ  Pr ðTi Þ for i ¼ 1,2 The β factor model: It was introduced by Fleming (1974) and is today the most commonly used model for common cause failure. Let a tidal energy system be composed of n tidal turbines, each with constant failure rate λ. The situation is furthermore assumed to be such that the failure of a component may be due to one of two possible causes: 1. Circumstances that concern only the tidal turbine. 2. Occurrence of external events and due to the external faults. Let λi denote the failure rate due to failure causes of type 1 and let λc denote the failure rate due to failure causes of type 2. λ ¼ λi + λc Now introduce β as the “common cause factor” β¼

λc λc ¼ λi + λc λ

λc ¼ βλ λi ¼ ð1  βÞλ Parallel structure with common cause “tidal turbine” C (Fig. 6.6).

6.3.1 Counting Process Four types of counting processes (Table 6.7): Homogeneous Poisson processes. Renewal processes. Imperfect repair. Nonhomogeneous Poisson processes. Possible state of a system of two components (Table 6.8) Downtime and downtime distributions: The downtime of a tidal turbine or a tidal energy system is the time in a specified time period where the tidal generator or tidal turbine is not able to generate electrical or mechanical energy, respectively. The unplanned

1. 2. 3. 4.

305

306

Tidal Energy Systems

Table 6.7 Number of failure v/s interoccurence time Number of failures N(t)

Calendar time Sj

Interoccurrence time Tj

0 1 2 3 4 5 6 7

0 177 242 293 336 368 395 410

0 177 65 51 43 32 27 15

Table 6.8 State of two component State

Tidal generator 1

Tidal generator 2

3 2 1 0

Functioning Functioning Failed Failed

Functioning Failed Functioning Failed

downtime of tidal energy system or tidal turbine failure are occur due to the internal or external parameter such as gross error, environment impacts, labor strikes and sabotage etc. The planned caused by planned preventive maintenance, operation, new installation and holiday etc. Assume that we have identified N independent causes of unplanned downtime and let di be the random downtime associated to cause i for i ¼ 1, 2, …, N. Let Fdi(D) denote the distribution function of di and let pi be the probability PN that a specific downtime has cause i. The distribution of the downtime d is then i¼1 Pi Fdi ðDÞ and the mean downtime is P MDT ¼ N P MDT i ¼ 1, 2,…,N i i¼1 i Mean system downtime: Consider a series structure of N independent components. Component i has a constant failure rate λi. When component i fails, the system will have a downtime MDTi for i ¼ 1, 2, …, N.  The probability that the system failure is caused by component i is λi PN λ and the j¼1 j PN λ MDTi i¼1 i mean system downtime for an unspecified failure is MDT ¼ P N λ j¼1 j

Availability: Consider a repairable tidal component that is put into operation at time t ¼ 0. When the tidal component fails, a repair action is initiated to restore the function of the tidal component. The state of the tidal component at time “t” is given by the state variable  1 if the component is functioning at time“ t ” X ðt Þ ¼ 0 otherwise

Reliability Assessment Model

The availability A(t) at time “t” of a repairable tidal component is the probability that the tidal component is functioning at time “t” AðtÞ ¼ Pr ðX ðt Þ ¼ 1Þ A(t) is sometimes referred to as the point availability. The unavailability A0 (t) at time “t” of a repairable tidal component is the probability that the component is not in a functioning state at time “t” A0 ðtÞ ¼ 1  AðtÞ ¼ Pr X ðtÞ ¼ 0 The average interval or mission availability Aav(t1, t2) in the time interval (t1, t2) is ð t2 1 Aðt Þdt Aav ðt1 , t2 Þ ¼ t2  t1 t1 Bayes’ theorem: It is a formula that describes how to update the probabilities of hypotheses when given evidence. It follows simply from the axioms of conditional probability, but can be used to powerfully reason about a wide range of problems involving belief updates. Given a hypothesis H and evidence E, Bayes’ theorem states that the relationship between the probability of the hypothesis before getting the evidence P(H) and the probability of the hypothesis after getting the evidence P(HjE) is P ðH " EÞ ¼

P ðE " H Þ P ðH Þ P ðE Þ

Many modern machine-learning techniques rely on Bayes’ theorem. For instance, spam filters use Bayesian updating to determine whether an email is real or spam, given the words in the email. Additionally, many specific techniques in statistics, such as calculating p-values or interpreting medical results, are best described in terms of how they contribute to updating hypotheses using Bayes’ theorem. Q.2. A tidal turbine with MTTF ¼ 1000 h. and MDT ¼ 5 h has average availability Aav ¼

MTTF 1000 ¼ ¼ 0:995 MTTF + MDT 1000 + 5

On the average, the machine will perform its function 99.5% of the time. The average unavailability is 0.5%, which has 44 h of downtime per year when the machine is supported and run continuously. Q.3. Consider a tidal energy system with two tidal turbines 1 and 2. Each turbine can have two states: a functioning state (1) and a failed state (0). A turbine is considered to be in the failed state (0) also during repair. Turbine 1 is supplying 100 MW when it is functioning and 0 MW when it is not functioning. Generator 1 is supplying 50 MW when it is functioning and 0 MW when it is not functioning. Generator 2 is supplying 50 MW when it is functioning and 0 MW when it is not functioning (Table 6.9).

307

308

Tidal Energy Systems

Table 6.9 State of two tidal generator System state State of G1 State of G2

System output

3 2 1 0

150 MW 100 MW 50 MW 0 MW

1 1 0 0

1 0 1 0

Solution: λ1 and λ2 are the failure rate of Generator 1 and 2. μ1 and μ2 are the repair rate of Generator 1 and 2. 0 μ2 μ1 0 ðμ1 + μ2 Þ B λ2 ðλ2 + μ1 Þ 0 μ1 B A ¼B @ λ1 0 ðλ1 + μ2 Þ μ2 0

λ1

λ2

1 C C C A

ðλ1 + λ2 Þ

 ðμ1 + μ2 ÞP0 + λ2 P1 + λ1 P2 ¼ 0 Q.4. A vital unit of a tidal energy system consists of three subunits, A, B, and C. For the successful operation of the unit, all three units of tidal energy system A, B, and C have to work satisfactorily. The probability that tidal subunit A does not meet the specification is 0.079, the probability that tidal subunit B does not meet the requirement is 0.049, and the probability that tidal subunit C does not meet the specifications is 0.06.What is the probability that the unit comprising the three tidal subunits does not work satisfactorily? Solution: For the failure of the system, it is necessary that at least one of the subunits fails. The probability that at least one tidal subunit fails is: 1  ð1  0:079Þð1  0:049Þð1  0:06Þ 1  ð0:921Þð0:951Þð0:94Þ ¼ 1  0:8233 ¼ 0:177 This means that, on average, 17 or 18 out of 100 units are rejected as being defective. Q.5. A vital unit of a tidal energy system consists of three subunits, A, B, and C. For the successful operation of the unit, all three units of tidal energy system A, B, and C have to work satisfactorily. The probability that tidal subunit A does not meet the specification is 0.069, the probability that tidal subunit B does not meet the requirement is 0.059, and the probability that tidal subunit C does not meet the specification is 0.07.What is the probability that the unit comprising the three tidal subunits does not work satisfactorily? Solution: For the failure of the system, it is necessary that at least one of the subunits fails. The probability that at least one tidal subunit fails is: 1  ð1  0:069Þð1  0:059Þð1  0:07Þ 1  ð0:931Þð0:941Þð0:93Þ ¼ 1  0:8147 ¼ 0:1853

Reliability Assessment Model

This means that, on average, 18 or 19 out of 100 units are rejected as being defective. Q.6 The probability of tidal generator A to fulfill the electricity demand is 0.8 and that of another tidal generator B to fulfill the electricity demand is 0.7. If both tidal generators A and B aim to fulfill the electricity demand simultaneously, what is the probability that the electricity demand will be fulfilled by either tidal generator A and B? Solution: Here, P(A and B) is equal to P(A)  P(B) because the two events are independent. Hence P ðAandBÞ ¼ 0:8  0:7 ¼ 0:56 P ðAorBÞ ¼ P ðAÞ + P ðBÞ  P ðAandBÞ ¼ 0:8 + 0:7  0:56 ¼ 0:94 Q.7 A manufacturer of a tidal generator buys his requirements for a generator from four different suppliers. On average, firm A1 supplies 30% of his requirements, firm E2 supplies 25%, firm A3 supplies 22%, and firm A4 supplies 23%. A quality test carried out on the tidal generator supplied by each firm reveals that 6% of the supplies from A1 are below standard 8% of the supplies from A2 are below standard 10% of the supplies from A3 are below standard 12% of the supplies from A4 are below standard Whenever a substandard sensor is used, the actuator is found to give unsatisfactory performance. Solution: According to Baye’s theorem: From the data given P ðA1Þ P ðEjA1Þ ¼ ð0:3Þ ð0:06Þ ¼ 0:018 P ðA2Þ P ðEjA2Þ ¼ ð0:25Þ ð0:08Þ ¼ 0:020 P ðA3Þ P ðEjA3Þ ¼ ð0:22Þ ð0:10Þ ¼ 0:022 P ðA4Þ P ðEjA4Þ ¼ ð0:23Þ ð0:12Þ ¼ 0:0276 Q.8 A tidal energy system is composed of four tidal units connected in series. The failure rates for these units are λ1 ¼ 0.002, λ2 ¼ 0.003, λ3 ¼ 0.004, and λ4 ¼ 0.007. It is desired that the maximum failure rate for the system be λ5 ∗ ¼ 0:01. Allocate this among the four units. Solution: The sum of the unit failure rates is λs ¼ λ1 + λ2 + λ3 + λ4 ¼ 0:002 + 0:003 + 0:004 + 0:007 ¼ 0:016

309

310

Tidal Energy Systems

Hence the allocated unit failure rates are

λ1 ∗ ¼ ð0:01=0:016Þ  0:002 ¼ 0:0013 λ2 ∗ ¼ ð0:01=0:016Þ  0:003 ¼ 0:0019 λ3 ∗ ¼ ð0:01=0:016Þ  0:004 ¼ 0:0025 λ4 ∗ ¼ ð0:01=0:016Þ  0:007 ¼ 0:0044

6.3.2 Series System Failure Rate Equations Consider a system consisting of n components in series. For this configuration, the system reliability, Rs, is given by: Rs ¼ R1  R2 ⋯Rn where R1, R2, …, Rn are the values of reliability for the n components. If the failure rates of the components are λ1, λ2, …, λn, then the system reliability is: Rs ¼ eλ1 t  eλ2 t ⋯eλn t ¼ eðλ1 + λ2 + ⋯ + λn Þt Therefore, the system reliability can be expressed in terms of the system failure rate, λS, as: Pn

Rs ¼ eλs t

where λS ¼ i¼1λi and λS is constant. Note that because the component failure rates are constant, the system failure rate is constant as well. In other words, the system failure rate at any mission time is equal to the steady-state failure rate when constant failure rate components are arranged in a series configuration. If the components have identical failure rates, λC, then: λS ¼ nλC It should be pointed out that if n blocks with nonconstant (i.e., time-dependent) failure rates are arranged in a series configuration, then the system failure rate has a similar equation to the one for constant failure rate blocks arranged in series and is given by: n X λS ðtÞ ¼ λi ðtÞ i¼1

where λS(t) and λi(t) are functions of time. Please see the Hot-Wire article “Failure Rate of a Series System Using Weibull++” for more details about this equation.

Reliability Assessment Model

Parallel System Failure Rate Equations Consider a system with n identical constant failure rate components arranged in a simple parallel configuration. For this case, the system reliability equation is given by: RS ¼ 1  ð1  RC Þn where RC is the reliability of each component. Substituting the expression for component reliability in terms of the constant component failure rate, λC, yields:  n RS ¼ 1  1  eλct Notice that this equation does not reduce to the form of a simple exponential distribution like for the case of a system of components arranged in series. In other words, the reliability of a system of constant failure rate components arranged in parallel cannot be modeled using a constant system failure rate model. To find the failure rate of a system of n components in parallel, the relationship between the reliability function, the probability density function, and the failure rate is employed. The failure rate is defined as the ratio between the probability density and reliability functions, or: λS ¼

fS RS

Because the probability density function can be written in terms of the time derivative of the reliability function, the previous equation becomes: dRS λS ¼ dt RS 

The reliability of a system of n components in parallel is: RS ¼ 1  ð1  RC Þn and its time derivative is: dRS dRC ¼ nð1  RC Þn1 dt dt Substituting into the expression for the system failure rate yields: λS ¼

dRC dt 1  ð1  RC Þn

nð1  Rc Þn1

For constant failure rate components, the system failure rate becomes:  n1 nλC eλC t 1  eλC t λS ¼ 1  ð1  eλC t Þn

311

312

Tidal Energy Systems

Table 6.10 Tidal Turbine failure rate Day Failures

Failure rate

1 2 3 4 5 6 7 8 9 10

0.018 0.012 0.010 0.007 0.006 0.005 0.004 0.003 0 0.001

18 12 10 7 6 5 4 3 0 1

Thus, the failure rate for identical constant failure rate components arranged in parallel is time-dependent. Taking the limit of the system failure rate as t approaches infinity leads to the following expression for the steady-state system failure rate: λS , Steady State ¼ lim λS t!∞

nλC e  λC tð1  e  λC t Þn1 t!∞ 1  ð1  eλC t Þn  n1 eλC t 1  eλC t ¼ nλC lim n t!∞ 1  ð1  eλC t Þ ¼ lim

Applying L’Hopital’s rule one obtains: λS ,Steady State ¼ λC So the steady-state failure rate for a system of constant failure rate components in a simple parallel arrangement is the failure rate of a single component. It can be shown that for a kout-of-n parallel configuration with identical components: λS ,Steady State ¼ nλC Example (tidal turbine failure rate) (Table 6.10) Q. Consider a system with the reliability function of the tidal current given by Rðt Þ ¼

1 for t > 0 where t in months ð0:2t + 1Þ2

d 0:4 Probablity density function f ðtÞ ¼  RðtÞ ¼ dt ð0:2t + 1Þ3

Reliability Assessment Model

f ðtÞ 0:4 ¼ RðtÞ 0:2t + 1 ð∞ Mean time to failure ðMTTFÞ MTTF ¼ RðtÞdt ¼ 5 months failure rate λðtÞ ¼

0

6.3.3 Reliability Analysis of a Tidal Energy System Designing a tidal turbine to achieve satisfactory levels of performance and durability starts with knowledge of the aerodynamic forces acting at the critical interface between the tidal parameter and the machine. This efficiency of the tidal turbine is usually characterized by its power coefficient as given below, and the maximum value of Cp can be 0.5926 according to Betz criteria Cp ¼

I:V : cos∅ ηmechanical ηalternator 0:5ρπR2 V 3

Where Cp is the power performance of the tidal turbine. The power coefficient is given by in the equation. In this study, electrical and mechanical equipment losses were assumed to be ηalternator ¼ 0.98 and ηmechanical ¼ 0.97 . The power performance of a tidal turbine can be expressed from fixed angular speed. This parameter is defined by CM ¼ CP/λ. The tidal turbine indicates various CP values depending on tidal currents. The tip speed ratio is given by λ ¼ ωR/Vr where λ is a tip speed ratio, R is maximum rotor radius, ω is rotor speed, and Vr is tidal velocity. Energy of kinetic energy ¼ Availability ¼ Vr 2 =2 Mean time between failures ¼ 1=λ

6.4 CONSTANT FAILURE RATE MODEL The subassemblies and therefore the turbine are repairable and the power law process is commonly used in the reliability analysis of complex repairable equipment; it comes under the category of constant failure rate model (Figs. 6.7–6.9; Tables 6.11 and 6.12). Its intensity function λ(t) describes the failure rate of a piece of machinery such as a tidal turbine and has the form: β  t β1 λðtÞ ¼ θ θ β is a parameter that describes the shape of the intensity function, θ is the scale parameter and has dimensions of time θ > 0 Early failures β < 1 Constant failures β ¼ 1 Deterioration β > 1

313

314

Tidal Energy Systems

Rotor Pitch control

Electrical system

Hydraulics Reliability assessment

Main shaft bearing

Gear box

Electrical controls

Generator

Mechanical brake

Fig. 6.7 Reliability assessment of a tidal energy system.

Selection of a tidal turbine system or component

Rotor blade, bearing, gearbox, tower foundation, offshore, support structure

Formulation of limit state function

Failure modes, fatigue, micropitting

Uncertainty quantification

Physical uncertainties, material properties and external loads, measurement uncertainity, statistical uncertainty, and model uncertainty

Evaluation of reliability failure probablity

Reliability analysis method, performance function evaluation

Fig. 6.8 Reliability assessment of tidal system.

Reliability Assessment Model

Design principles

Deterministic approach

Probabilistic approach

Partial safety factor extreme environment conditions with return period of 1 year/50 years/100 years

Uncertainties related to the considered parameter (stochastic variable)

Design based on fufillment of the limit state equation including partial safety factors

Specification of the probability of failure of a designed object, economical optimization based on cost consideration, and the resulting reliability of the device

Fig. 6.9 Probabilistic reliability assessment.

Table 6.11 Worldwide annual failure rates for tidal turbine subsystems Subsystem 2016 2017

Rotor Pitch control Main shaft bearing Gearbox Generator Mechanical brake Electrical controls Hydraulics Electrical system

0.223 0.097 0.024 0.101 0.120 0.039 0.224 0.110 0.341

0.230 0.095 0.050 0.120 0.050 0.100 0.260 0.210 0.490

Table 6.12 Failure and load cases Case

Description

Normal operation Total loss of electricity Failure of floater lifting system Wrong tide state measurement Failure control system

Floater out of water during storm Electricity connection broken and onboard DG fails Failure of auxiliary pump or its valve and failure of motor or pump Failure of bearing pressure sensor and ultrasonic sensor broken Software failure of control system

315

316

Tidal Energy Systems

6.4.1 Model Uncertainties Model uncertainties consider uncertainties related to physical models in order to estimate, for example, environmental conditions, loads, or stresses. In the following, examples where modeling uncertainties should be considered for tidal energy conversion system applications are given: • Wave conditions modeled with the wave models. • Load calculation models. • Stress estimations based on loads onto the structure (structural analysis). • Models to assess damage/fatigue. Model uncertainties are often applying specific and tidal energy conversion system model type specifically due to the fact that the same resistance and load models are not always considered or the environmental conditions are different. In order to determine modeling uncertainties, validation of the model is necessary. Validations assess the accuracy of the model.

6.4.2 Measurement Uncertainties For wave energy converters, measurement uncertainties related to wave/wind/current characteristics are of importance. Furthermore, measurement uncertainties are present when measuring loads at a prototype or a lab-scaled device during tank tests or when performing material tests in order to detect the characteristics of the considered material. Load and material characteristics measurement uncertainties might be provided by the manufacturer of the devices used to measure. The measurement uncertainty can be reduced by calibration and quantified by validation.

6.4.3 Constant Failure Modes of Tidal Energy Conversion Systems Structural failure, which means complete or partial loss of load-carrying capacity, of components or structural systems may occur due to different failure modes. Failure modes are used to describe a certain type of structural failure and are also considered as limit state conditions when designing structural parts. Commonly, failure modes are divided into the following categories: Ultimate Limit States (ULS), which contain structural failures due to excess of maximum load carrying load capacity. • Loss of structural resistance (excessive yielding and buckling). • Failure of components due to brittle fracture. • Loss of static equilibrium of the structure, or of a part of the structure, considered as a rigid body, such as overturning or capsizing. • Failure of critical components of the structure caused by exceeding the ultimate resistance (in some cases reduced by repeated loads) or the ultimate deformation of the components.

Reliability Assessment Model

• Transformation of the structure into a mechanism (collapse or excessive deformation). Fatigue Limit States (FLS) focus on failure modes due to cyclic loading and structural damage accumulation. • Cumulative damage due to repeated loads. Accidental Limit States (ALS) are failure modes resulting from accidental loads caused by, for example, collisions, floods, explosions, or fire. • Ultimate resistance of damaged structures. • Maintain structural integrity after local damage or flooding. • Loss of station keeping (free drifting). Serviceability Limit States (SLS) occur when excessive vibrations, leakages, deflections or drainage disable the function for which the structural part was built. • Deflections that may alter the effect of acting forces. • Deformations that may change the distribution of loads between supported rigid objects and the supporting structure. • Excessive vibrations producing discomfort or affecting nonstructural components. • Motion that exceeds equipment limitations.

6.4.4 Performance Assessment of Reliability Assessment Reliability assessment methods appeared many decades ago. In the 1970s, the first comprehensive mathematical models were introduced, first for generation reliability and then for transmission reliability. Generation reliability analysis models are well developed. However, transmission system reliability methods are not as well developed due to the difficulties arising from the huge computational problem associated with the transmission reliability analysis. Contingency selection and ranking: The impact of outage states on the system reliability is taken into consideration in the contingency selection and ranking method. Reduction of the state space is based on the elimination of the states whose impact on the system is small, and the consideration of only those outages that affect system reliability. We refer to these methods as contingency selection and ranking methods. Component and event model: The system states (contingencies) and electric load states are generated from a Markov model of system components and electric load levels. Specifically, each component (circuit or unit) is modeled with a two-state Markov model, that is, the component is either working (up) or failed. Based on the two-state Markov model of each component, a Markov state of a power system is defined by a particular condition where every component is in a given operating state of its own. All the possible states of a system make up the state space. The electric load is modeled as a nonconforming load model. This model relates the bus loads to a small set of independent random variables. Discretization of the independent random variables provides discrete load states that are described by an equivalent

317

318

Tidal Energy Systems

Markov model where each load level is characterized with a probability and transition rates to any other load levels. In addition, each bus load is separated into interruptible, firm, and critical components and associated with a voltage dependency assumed as follows: for the normal range of the bus voltage, the load is constant; for values below the normal voltage range, the load is dependent upon the voltage with a linear relationship. State enumeration: The state enumeration involves (1) enumeration of contingencies, including both circuit and unit outages, and (2) enumeration of electric load levels according to a specified electric load model. Contingency enumeration: The objective of contingency enumeration is to identify the contingencies that may lead to unreliability. The enumeration of contingencies is based on the use of multiple contingency ranking schemes. Additional truncation of contingencies is obtained by truncating the depth level of contingencies and by neglecting contingencies with very small probabilities. The depth level is defined with three parameters: (a) maximum allowable number of simultaneous outages (units or circuits), (b) maximum allowable number of simultaneous circuit outages, and (c) maximum allowable number of simultaneous circuit outages. The reasons for the use of multiple contingency ranking schemes are: First, complete and thorough evaluation of all contingencies is impractical. Thus, it is necessary to avoid the evaluation of contingencies that are not likely to affect system reliability. This task is achieved with contingency-ranking methods. Second, the present state-of-the-art contingency-ranking methods do not possess the desired speed and accuracy for reliability analysis. Generally, contingency-ranking methods may be classified into two categories: (a) Performance index (PI) methods, and (b) screening methods. PI methods use the derivative of a performance index (or first-order approximation) with respect to an outage to determine the severity of a contingency. In this work the single-phase quadratized power flow (SFQPF) model has been applied toward the development of a contingency selection method using several metrics as performance indices. It is well known that performance index approaches lead to misrankings because of the nonlinearities of the model involved. The quadratized power flow model has milder nonlinearities (by construction) and therefore performs better. The quadratized power flow model will be described later. Screening methods use approximate network solutions to identify cases causing limit violations. In this approach, contingencies are first analyzed with an approximate model. If the approximate model indicates that the contingency may have severe effects on the system, then the contingency is analyzed to determine its effects on the system. The disadvantage of these methods is the fact that the approximate analysis has to be performed on each contingency. Because of the large number of contingencies, the method is inefficient. PI methods are typically much faster than screening methods. To take advantage of the best properties of the two approaches, the critical contingencies are selected with a

Reliability Assessment Model

hybrid scheme that separates contingencies into two groups: (a) contingencies with mild nonlinearities and (b) contingencies with potential nonlinearities. The separation is performed with a very simple rule. The first set of contingencies represents the majority and is ranked with PI-based methods with multiple PIs. The second set of contingencies is ranked with screening methods. Computational savings are achieved by applying the screening methods only to a small set of contingencies. The Wind-Chime enumeration scheme, as shown in Fig. 3.3, illustrates the contingency enumeration procedure using the ranking order obtained by the hybrid ranking method. The procedure starts with the base case. All the first-level contingencies are enumerated and ranked in decreasing severity order. The second outage level contingencies are obtained from each contingency in the first outage level by having one more component on outage and ranked in the same way. The new outage component should be selected according to certain rules to make sure the obtained contingencies are distinct. This procedure continues until it reaches the predefined depth level or probability criteria of contingencies. In each outage level, contingencies are evaluated in decreasing severity ranking order. The most severe contingencies are evaluated first. If there are several successive contingencies that are evaluated but have zero contribution to system unreliability, then it is reasonable that the remaining contingencies that have lower severity indices need not be investigated. There are three types of contingencies: (1) contingencies that are evaluated and have a nonzero contribution to unreliability, (2) contingencies that are evaluated but have a zero contribution to unreliability, and (3) contingencies that Contingency ranking/selection: Contingency analysis is necessary to determine the level of security and/or reliability of a given system following a disturbance (contingency). Because of the large number of possible contingencies, this analysis can be extremely costly from the computational point of view. Fortunately for practical power systems, only a small number of contingencies are potentially critical to system security and/or reliability. If these contingencies can be identified, then only these contingencies should be analyzed to determine their effect. The problem of identifying the critical contingencies is known as contingency ranking. That is, contingencies are ranked in terms of their severity. Contingency ranking methods can be divided into two categories: PI methods and screening methods based on approximate power flow solutions. In the first case, the contingency ranking is facilitated by the use of performance indices that provide a measure of system “normality.” These methods are computationally simple and efficient; however, they are prone to misranking. On the other hand, the methods based on approximate power flow solutions are generally less efficient and require more computation; their accuracy depends on the level of approximation used. In this study, we are interested only in PI methods and we use them to evaluate the system state after certain disturbances, therefore to estimate the severity of each disturbance. The more severe disturbances are to be further analyzed using reliability analysis methods. Several different performance indices can be defined and used, depending on the network quantities that

319

320

Tidal Energy Systems

Mean time to recover Mean delay time logistics Availability of component

Production

Transportation

Onshore Offshore

* Production time * raw material availability * Different subcomponent * Capacity of production site * Transportation availability * distance onshore * Boat and crew availability * distance offshore * Weather condition

Mean time to repair

Installation

* Experience specialists * Accessibility of component at tidal energy device * Time for testing after installation

Fig. 6.10 Mean Delay time logistics.

are considered more important for the specific study. The security indices provide a quantitative way to access the security of the system. Contingencies that may impact system security can be recognized by the change of the performance indices. Thus, in order to rank contingencies on the basis of their impact on security, we can use the changes in the performance indices due to the contingency. In general, the exact change of the performance indices or due to a contingency can be computed by first obtaining the system post contingency solution (power flow solution) and then computing the performance index by direct substitution. This procedure is computationally demanding and negates the objectives of a contingencyranking algorithm. Specifically, the objective of contingency ranking is to compute the approximate change of the security indices due to a set of postulated contingencies with a highly efficient computational method. Such methods were introduced in the late 1970s. In this work, the quadratized power flow (QPF) model has been applied toward the development of a contingency selection method using metric performance indices. It is well known that performance index approaches lead to misrankings because of the nonlinearities of the model involved. The idea here is to use the quadratized power flow model that is expected to have milder nonlinearities and therefore should perform better. This is indeed the case. In addition, the quadratized power flow model is better suited to use current-based ratings of circuits as opposed to powerbased ratings of circuits. It is pointed out that most capacity limitations of circuits are thermal limitations, that is, electric current limitations. Thus, using current limits results in a more realistic approach (Fig. 6.10).

6.4.5 Reliability Analysis of Fault-Tree Analysis Reliability is defined as the probability of a device or system performing its purpose adequately for the intended operating period of time. It is also defined as the ability of an

Reliability Assessment Model

electrical power system to supply the system load with reasonable continuity and quality of supply. There are different reliability prediction analyses used in a study, such as a reliability block diagram, fault-tree analysis, and Markov analysis. Fault-tree analysis is a systematic and stylized process in which an undesired event is defined. In this analysis, an event is resolved into its immediate causes and the resolution of events continues until the basic causes are identified. Fault trees and reliability block diagrams are both symbolic analytical logic techniques that can be applied to analyze system reliability and related characteristics. The fault tree of the hybrid renewable energy system is established according to the past performance data. The faults are summarized on the basis of the working process of the hybrid renewable energy system. Fig. 6.11 shows a flow diagram of fault-tree analysis. All the events are connected by the logical symbols, AND gate and OR gate. In FTA analysis, Boolean algebra is commonly used to simplify the formula, getting the expression of the top event. So if the fault probability of each unit is acquired, the fault probability of the whole system can be instantly obtained. The fault tree explicitly shows all the different relationships that are necessary to result in the top event. It is also a tangible record of the systematic analysis of the logic and basic causes leading to the top event. The fault tree provides a framework for thorough qualitative and quantitative evaluation of the top event. Fig. 6.12 shows the events of a fault tree in which the top event is distributed in two intermediate events. The top event are connected with the AND gate function further intermediate event take basic event with the connectivity of OR gate function. Table 6.13 presents the fault conditions and failure rates of hybrid renewable energy systems. In this table, the alphabetical symbol represents condition of fault and the event or failure rate is converted into the top event, intermediate event, and basic event. In this fault-tree analysis, a hybrid FTA objective

FTA top event

FTA scope

FTA resolution

FTA design

FTA evaluation

Interpret/evaluate result

Fig. 6.11 Flow diagram of fault-tree analysis.

FTA ground rules

321

322

Tidal Energy Systems

Top undesired event

Intermediate event

Intermediate event

Basic event

Fig. 6.12 Fault-tree event. Table 6.13 Fault condition and failure rate of a tidal energy system Symbol

Condition of fault

Events/failure rate

a b

Tidal energy does not develop sufficient amount of energy The generator does not work properly

c

The tidal energy system primary fails

d

The battery does not work properly

e f g h i j k l m n o p q r s t u v

Bad environment condition Component fault in tidal energy system Unimproved power quality Effect of tidal current Effect of temperature Tower shadow effect Wind turbulence Switching of tidal mills Tidal turbine blade Due to synchronism of tidal mill Variation due to surface of coastal area Variation with height Tidal turbine performance Controller in tidal system Deteriorate the performance of tidal turbine Uncontrolled operation of controller Improper arrangement of converter with tidal energy system Improper switching regulator with tidal energy system

Top event Intermediate event Intermediate event Intermediate event Basic events Basic event Basic event 0.0408 0.025 0.022 0.022 0.025 0.019 0.022 0.0011 0.03 Basic event Basic event 0.001 0.001 0.035 0.022

Reliability Assessment Model

Table 6.13 Fault condition and failure rate of a tidal energy system—cont’d Symbol

Condition of fault

Events/failure rate

w x y z aa bb cc dd ee ff gg hh

Bad environment condition Component fault Unimproved power quality Effect of variation of insolation Effect of variation of temperature Voltage fluctuation Current fluctuation Fault in tidal system arrangement Controller in overall system Improper arrangement of converter with tidal energy system Improper switching regulator with tidal energy system On the basis of thickness of active material of tidal turbine system On the basis of junction structure of tidal system On the basis of type of active material of tidal system Unbalance of system component Improper distribution panel of overall tidal energy systems Improper wiring and connector of overall tidal energy systems Improper arrangement of junction box of overall tidal energy systems

Basic event 0.045 Basic event 0.0015 0.00155 0.025 0.025 0.055 Basic event 0.045 0.045 0.0018

ii jj kk ll mm nn

0.0018 0.0018 Basic event 0.055 0.055 0.055

renewable energy system does not develop a sufficient amount of energy to work as a top event. The working conditions of solar and wind energy systems is considered as an intermediate event. Based on Table 6.13, develop a fault-tree diagram (Fig. 6.13) of a renewable energy system that is connected with the AND and OR gate function. In this figure, fault B, C, and D are connected with top event A by the OR gate function, then the equation is developed A ¼ B + C + D and a similar procedure is followed for all the fault conditions. The four necessary steps to begin a fault tree are: 1. Define the undesired event to be analyzed. 2. Define the boundary of the system. 3. Define the basic causal events to be considered. 4. Define the initial state of the system.

6.4.6 Causes of Failure in a Tidal Renewable Energy System Reliability analysis is a well-developed statistical tool for predicting the system performance in many industries. There are several tools used for reliability prediction, but fault-tree analysis provides a diagrammatic representation of a system’s reliability. The objective is to estimate the probability of a critical fault occurring because fault-tree analysis provides a static picture of the combinations of failures and events

323

324

Tidal Energy Systems

A

= OR GATE

A=B+C+D

= AND GATE

B = E + F + G; C = KK; D = W + X + Y E = H*I; H = O*P

C

B

D

E = O*P*I F = Q + R; Q = S + T; R = U * V

E

G

F

W

F = S + T + U*V

Y

X

G = J + K + L; J = M*N H

I

Z J

O

K

L

N

B = (O*P*I) + (S + T + U*V) + M*N + K + L

W = Z*AA

EE

X = DD*EE LL

MM

NN FF

R

GG

DD = HH*II*JJ EE = FF + GG

HH U

CC

C = KK = LL*MM*NN DD

Q

T

BB

KK

P M

S

G = M*N + K + L

AA

II

JJ

V

Y = BB*CC D = (Z*AA) + (HH*II*JJ) + (FF + GG) + (BB*CC)

Fig. 6.13 Fault-tree analysis of a tidal energy system.

that can cause the specified critical fault to occur. Fault tree basically divides into three types: (i) Top undesired event. (ii) Intermediate event. (iii) Basic event. In this analysis, the top undesired event is that a hybrid renewable energy system does not develop a sufficient amount of energy. In another way, a solar-wind renewable energy system does not fulfill the load demand. In this paper, we develop fault analysis in two ways, the first is related to wind energy and the second is a solar energy system. Tidal energy system: Reliability and performance of tidal energy systems are mainly affected by bad environmental conditions and unimproved power quality. Effect of tidal current and the effect of temperature are the parts of the bad environmental condition that mainly affects the production of electricity from the tidal energy system. A tidal current fluctuates with time and for electric power generation, the minimum average tidal current speed required is 2 m/s. A site is not considered favorable for tidal power generation if the tidal current velocity is 5 m/s. Reliability of the system is also affected by the distribution of tidal energy on the surface of the coastal area and some failures also occur in a system with a variation of tidal range. Failure of a tidal energy system is also affected due to unimproved power quality. Unimproved power qualities extensively affect the reliability of the whole tidal renewable energy system. A disturbance in power quality occurs due to the tower shadow effect, wind turbulence, and switching of tidal mills. A tower shadow effect due to be aggravated in tidal power farms consisting of several

Reliability Assessment Model

tidal mills due to a tendency of the tidal mills due to a tendency of the tidalmill to operate in synchronism with each other, particularly in cases where the fault level of the system is weak. Q.1 All over the world, 200 identical units are reliability tested for 50 h. One unit fails just before completing 12 h of operation, and two units fail just before completing 50 h of operation. 1. What is the reliability estimate of these units for a mission of 50 h? 2. What is the reliability estimate for the end of each failure period, including previous failures, when the failed units are replaced with good ones? 3. What is the reliability estimate for the each failure period if the failed units are not replaced? Solution: NF ðt Þ 2+2 1. R ðt ¼ 50 hÞ ¼ 1  N ¼ 1  1 +50 T ðt Þ R ¼1

5 ¼ 1  0:025 ¼ 0:975 ¼ 97:5% 200

2. R1 ðfor 0  12 hÞ ¼ R ðt ¼ 12 hÞ R1 ¼ 1  R2 ¼ 1  R3 ¼ 1 

NF ð t Þ 1 ¼ 1  0:005 ¼ 0:995 ¼ 99:5% ¼1 NT ðtÞ 200

NF ðtÞ 1+2 ¼ 1  0:015 ¼ 0:985 ¼ 98:5% ¼1 NT ð t Þ 200

NF ðt Þ 1+2+2 ¼1 ¼ 1  0:025 ¼ 0:975 ¼ 97:5% NT ð t Þ 200

1 ¼ 1  0:005 ¼ 0:995 ¼ 99:5% 3. R1 ð0  12 hÞ ¼ 1  200 2 R2 ð12  20 hÞ ¼ 1  ¼ 1  0:01005 ¼ 98:995% 200  1 2 ¼ 1  0:01015 ¼ 98:985% R3 ð20  50 hÞ ¼ 1  200  1  2 Q. A tidal energy system’s operational readiness is 90%, mission reliability is 95%, and design adequacy is 98%. 1. What is system effectiveness? 2. If there were NT ¼ 200 such systems in various states of existence, how many will be available to start their mission successfully? 3. How many such systems will complete their mission successfully? 4. How many system’s worth of mission objectives would be achieved?

325

326

Tidal Energy Systems

Solution: 1. System effectiveness: (SE) ¼ OR  RM  DA ¼ 0.9  0.95  0.98 ¼ 0.838 ¼ 83.8% 2. Number of system NAV that will start a mission is obtained from NAV ¼ NT  OR ¼ 200  0:90 ¼ 180 systems NCM CM 3. Number of system RM ¼ N NAV ¼ NT OR

NCM ¼ NT  OR  RM ¼ 200  0:9  0:95 ¼ 171 systems 4. NAC ¼ NT  OR  RM  DA ¼ NT  SE NAC ¼ 200  0:838 ¼ 168 systems Example: A tidal power plant has two tidal generators, TG1 and TG2, one located at the stern and another at the bow. Each tidal generator is connected to its respective main switchboard, SW1 and SW2. The distributive switchboard DSB receives the supply from the main switchboard through cables C1 and C2 and respective junction boxes J1 and J2. The two main switchboards are interconnected through a long cable C3 and the junction box A and B. Let us assume that the basic components subjected to failure are Tidal generators TG1 and TG2 (y1 and y2) Main switchboards SW1 and SW2 (y3 and y4) Interconnected cable C3 and junction box A and B, all treated as one unit (y5) Junction box J1 and J2 (y6, y7) Distributive switch board DSB (y8) From the logic diagram, the successful paths are identified as y1 y3 y6 y8 y1 y3 y5 y4 y7 y8 y2 y4 y7 y8 y2 y4 y5 y3 y6 y8 The tidal energy system as a whole is working in two states: a functioning state and a failed state. These two states depend on the states of the elements of the system. If the functioning state is represented by 1 and the failed state by 0, then element yk can be equal to either 1 and 0. The state of the system is represented by x and is a function of all the elements. X can also either be a 1 or a 0. Thus X ¼ xðy1 , y2 , y3 …y8 Þ ¼ 1 or 0 Now, consider one of the successful paths y1y3y6y8. This tells us that if elements y1 and y3 and y6 and y8 are functioning, then the system also functions. This group is a conjunction of four elements, none of which can fail if the system is to function. Similarly, y1y3y5y4y7y8 is a conjunction of elements, none of which can fail without affecting the system. If the successful paths are represented by P1, P2, … then we can represent the functioning of the system in a matrix form as y1 y3 y6 y8 P1 x ðx1 , x2 , …x8 Þ ¼ y1 y3 y5 y4 y7 y8 P2 y2 y4 y7 y8 P3 For the successful functioning of the system, at least one of the paths P1 or P2 or P3 or P4 should function.

Reliability Assessment Model

6.4.7 Fault-Tree Construction and Analysis The system fails when there is no power supply from the distributive switch board (DSB). There can be two reasons for this, namely (a) The DSB is burnt. (b) There is no supply of power to the DSB through cables C1 and C2. Assuming cables C1 and C2 are not damaged, the causes are (i) No power from the junction box J1. (ii) No power from the junction box J2. Let us first consider the junction box J1. For no power from the junction box J1, the causes can be (a) The junction box J1 is burnt. (b) There is no supply to the junction box J1. The reason for no power supply to the junction box J1 can be (a) The main switchboard (SW-1) is burnt. (b) There is no power supply to SW-1. For no power supply to SW-1, the reasons are (a) Tidal generator TG1 is not working. And (b) There is no power supply through the interconnecting junction box A and B. The reasons for no supply through A and B can be (a) The tidal generator TG2 is not working. Or (b) The junction boxes A and B are burnt. Or (c) The main switchboard SW-2 is defective.

6.4.8 Boolean Algebra and Reliability Calculation The list is as follows: Failure of tidal generator TG1 ¼ A1 Failure of tidal generator TG2 ¼ A2 Failure of switchboard 1 ¼ A3 Failure on switchboard 2 ¼ A4 Failure of the junction boxes A and B ¼ A5 Failure of the junction box J1 ¼ A6 Failure of the junction box J2 ¼ A7 Failure of the distributive switchboard ¼ A8 We have used the (+) sign to indicate the OR operation and the dot () to denote the AND operation. For no power coming through A and B F1 ¼ A2 + A5 + A4;

327

328

Tidal Energy Systems

For no power coming to SW-1, F2 ¼ A1  F1 ¼ A1  ð A2 + A5 + A4Þ For no power to junction box J1 F3 ¼ A3 + F2 ¼ A3 + ½A1  ð A2 + A5 + A4Þ For no power from junction box J1 F4 ¼ A6 + F3 ¼ A6 + A3 + ½A1  ð A2 + A5 + A4Þ Similarly from the right half of the fault-tree diagram, we have For no power from junction box J2 F8 ¼ A7 + A4 + ½A2  ðA1 + A5 + A3Þ; For no power coming to DSB, F9 ¼ F4 and F8 F9 ¼ fA6 + A3 + ½A1  ðA2 + A5 + A4Þg  fA7 + A4 + ½A2  ðA1 + A5 + A3Þg For the total failure (Figs. 6.14 and 6.15)

X1

X2

X3

X6

X5

X8

X4

X7

X1

X3

X6

X8

X1

X3

X5

X4

X2

X4

X7

X8

X2

X4

X5

X3

Fig. 6.14 Series and parallel connection of component.

X7

X8

X6

X8

Reliability Assessment Model

Total failure of system

OR DSB IS BURNT

No power coming to DSB

AND No power from J1

No power from J2

OR No power to J1

J1 IS BURNT

OR MSB-1 IS BURNT

No power to MSB-1

AND TG1 IS BURNT

No supply through A & B

OR TG2 IS BURNT

MSB-2 IS BURNT

Fig. 6.15 Fault tree diagram of component.

Exercise 1. What is the reliability and what is the importance of reliability in a tidal energy system? 2. How is reliability related to the failure rate in a tidal energy system? 3. Explain different types of reliability assessment. 4. Explain four important factors of reliability that are used in the tidal energy conversion system. 5. Explain the process of reliability from complete failure to total success rate w.r.t. the tidal energy system. 6. What is the different objective of reliability engineering in the field of power systems? 7. Write and explain the names of reliability indices. 8. What is the meaning of the failure distribution mode of a tidal energy system? 9. Write the significance of the Jelinski-Moranda Model. 10. Write short notes on the following: (a) Failure density (b) Failure rate (c) Mean failure rate

329

330

Tidal Energy Systems

11. What is the significance of mean time to failure in tidal energy system? 12. Derive the operational model for K out of the n tidal energy system. 13. Explain the significance of the square root method of dependent failure in the field of tidal energy systems. 14. What is the counting process in tidal energy systems and write types of counting processes. 15. Derive the equation for series system failure rate. 16. Explain the application of fault-tree analysis in the tidal energy system. 17. Write short notes on the following: (a) Mean time between failure (b) Downtime and downtime distribution (c) Mean system downtime (d) Bayes’ theorem (e) Model uncertainties (f ) Measurement uncertainties (g) Constant failure modes

FURTHER READING Billinton, B., Allan, R.N., 1988. Reliability Assessment of Large Electric Power Systems. Kluwer Academic Publishers. Billinton, R., Allan, R., 1996. Reliability Evaluation of Power Systems, second ed. Plenum Press, New York. Borges, C.L.T., Falca˜o, D.M., 2006. Optimal distributed generation allocation for reliability, losses, and voltage improvement. Int. J. Electrical Power Energy Sys. 28 (6), 413–420. Borges, C.L.T., Pinto, R.J., 2008. Small hydro power plants energy availability modeling for generation reliability evaluation. IEEE Trans. Power Sys. 23 (3), 1125–1135. Menniti, D., Burgio, A., Pinnarelli, A., Sorrentino, N., 2007. The reliability evaluation of a power system in presence of photovoltaic and wind power generation plants and UPS.Proceedings of EPQU 2007, October 9–11, Barcelona. NASA, 2002. Fault Tree Handbook with Aerospace Applications, Version 1.1. NASA Publication. Park, J., Liang, W., Choi, J., El-Keib, A.A., Shahidehpour, M., Billinton, R., 2009. A probabilistic reliability evaluation of a power system including solar/photovoltaic cell generator. IEEE Trans. Power Sys. 24 (2). Srinath, L.S., 1991. Reliability Engineering, third ed. East-West Press Pvt. Ltd.

CHAPTER 7

Tidal Energy Assessment and Economics Contents 7.1 Introduction 7.2 Scenario of Tidal Energy System in India 7.2.1 Potential Location in India for Tidal Power Generation 7.2.2 India Lacks a Tidal Energy Policy 7.2.3 Grid Parity of Tidal Energy in India 7.2.4 Challenges With Tidal in Stream Technology 7.2.5 Government Support for Tidal Energy in India 7.2.6 List of Stakeholders Involved in the Development of Technology at the Central and State Levels 7.3 Harmonic Analysis of Tidal Power Plant 7.4 Assessment of Tidal Energy System by the Optimization Technique 7.4.1 Particle Swarm Optimization 7.4.2 Chaotic Particle Swarm Optimization (CPSO) 7.4.3 Big Bang Big Crunch 7.4.4 Teacher Learning-Based Optimization Technique 7.4.5 Grasshopper Algorithm 7.4.6 Cuckoo Optimization Technique 7.5 Assessment of Tidal Energy System by Game Theory 7.5.1 Basic Concept of Game Theory 7.5.2 Game Theory in a Tidal Renewable Energy System 7.5.3 Mixed Strategy Nash Equilibrium 7.6 Role of Tidal Energy System in Clean Development Mechanism 7.6.1 The Role of the Kyoto Protocol and the CDM 7.6.2 Present Status of CDM in India 7.6.3 CDM and Waste Disposal 7.6.4 CDM’s Role in Technology Transfer 7.6.5 CDM and Sustainable Development 7.6.6 CDM and Tidal Energy Promotion 7.7 Economic Analysis of a Tidal Power Plant 7.7.1 General Tariff Form 7.7.2 Investment Need, Appraisal, and Criteria 7.7.3 Criteria 7.7.4 Financial Analysis Techniques 7.7.5 Time Value of Money 7.7.6 Return on Investment (ROI)

Tidal Energy Systems https://doi.org/10.1016/B978-0-12-814881-5.00007-7

332 333 334 337 340 340 341 343 343 346 350 355 357 360 361 362 364 364 367 368 369 371 377 378 379 380 381 382 384 385 385 387 388 388

© 2019 Elsevier Inc. All rights reserved.

331

332

Tidal Energy Systems

7.7.7 Internal Rate of Return 7.7.8 Energy Performance Contracting and Role of ESCOS Exercise Objective-Type Questions References Further Reading

388 389 389 390 393 393

7.1 INTRODUCTION Nowadays, TIDAL power systems are playing a vital role in the field of electricity generation in the form of nonconventional or renewable energy systems. India is a good place for generating electricity by the TIDAL energy system because India is densely populated and has a high TIDAL range. India’s theoretical TIDAL power reception on just its land area is about 5000 (PWh/year). The daily average TIDAL range incidents over India varies from 4 to 7 kWh/m2 with about 1500–2000 sunshine hours per year. The amount of TIDAL energy produced in India in 2007 was 250 MW in the Gulf of Kutch or Khambhat. India’s initial endeavor to outfit tidal power for producing power would be as a 3 MW plant proposed at the Durgaduani brook in the Sundarbans delta of West Bengal. The Gulf of Kutch, the Gulf of Cambay in Gujarat, and the Ganga delta in the Sunderbans, the world’s biggest mangrove forest, are the three locales recognized as potential territories for tidal power. The recognized capability of tidal energy is around 9000 MW in West Coast Gulf of Cambay (7000 MW), Gulf of Kutch (1200 MW) and in East Coast the Ganges delta in the Sunderbans in West Bengal for little scale tidal power improvement evaluates the potential in this locale to be around 100 MW. Fig. 7.1 shows, location-wise, the tidal energy installed capacity in India. The aggregate accessible capability of wave energy in India along the 6000 km of India’s drift is assessed to be around 40,000 MW, although these are preparatory appraisals. This energy is, however, less escalated than what is accessible in the more northern and southern scopes. In 2000, NIOT Goa propelled a program on innovations for creating superb clean drinking water and energy from the sea. The goal was to create 2–3 lakh liters of freshwater for each day by utilizing the low temperature thermal desalination

333

334

Tidal Energy Systems

Fig. 7.1 Location-wise tidal energy installed capacity in India.

innovation by the 1 MW OTEC power plant. Be that as it may, it was dropped because of challenges in establishments. In 2010, the Kalpasar Tidal Power Project at the Gulf of Khambhat was distinguished as a promising site for the tidal power era by a United Nations Development Programme (UNDP) expert. In January 2011, the territory of Gujarat declared plans to introduce Asia’s first business-scale tidal current power plant; the state government endorsed the development of a 50 MW venture in the Gulf of Kutch. Table 7.1 shows the geographical condition for the tidal power station. However, India’s Ministry of New and Renewable Energy said in February 2011 that it might give monetary motivators to as much as 50% of the cost for ventures looking to exhibit tidal power. In 2014, Atlantis Energy proposed to introduce and create a 50–200 MW tidal stream-based power plant at the Gulf of Chambey.

7.2.1 Potential Location in India for Tidal Power Generation Gulf of Khambhat: The Gulf of Khambhat, also known as the Gulf of Cambay, is a bay on the Arabian Sea coast of India, bordering the state of Gujarat. The Gulf of Khambhat is about 200 km long, about 20 km wide in the north, and up to 70 km wide in the south.

Tidal Energy Assessment and Economics

Table 7.1 Geographical condition for a tidal power station State

Location

Latitude

Longitude

Neap tidal range

Spring tidal range

West Bengal

Sagar Island Malta River Diamond Harbor Calcutta Garden Short Island Chandbali Gopalpur Vizag Cocanda Sacramento Shoal Cuddalore Negapattam Pambam Channel Tuticorin Quilon Cochin Beypore Calicut Manglore Malpe Bhatkal Karwar Bay Gulf of Cambay Alber Victor Nava Bander Porbander GoK, Okha Point GoK, Navinar Point GoK,Khori Creek GoK, Harshtal Point GoK, Navlakhi GoK, Naviwat Kori, Creek

21.4 20.5 22.11

88.03 88.3 88.11

1 0.9 1.7

4.6 2.9 5.3

22.33 20.47 20.4 19.16 17.41 16.56 16.36

88.18 87.04 86.44 84.55 83.17 82.15 82.19

1.2 0.9 0.6 0.3 0.5 0.5 0.4

4.9 3 2.5 1.7 1.4 1.4 1.4

11.43 10.45 9.16

79.47 79.47 79.12

0.2 0.3 0.1

1 0.6 0.8

8.48 8.53 9.58 11.1 11.15 12.51 13.2 13.58 14.48 21.45 20.57 20.45 21.38 22.28

78.1 76.34 76.15 75.48 75.46 74.5 74.41 74.32 74.06 72.14 71.32 71.05 69.37 69.05

0.1 0.2 0.1 0.3 0.2 0.3 0.6 0.2 0.4 3 0.8 0.3 0.4 1

0.8 0.9 0.8 0.9 1.2 1.5 1.7 1.4 2.1 10.9 3.2 2 2.4 3.9

22.45

69.43

2.2

5.8

22.58

70.14

3

6.7

22.56

70.21

2.6

6.3

22.58 23.05 23.31

70.27 70.20 68.21

3.5 3 0.6

7.2 6.7 3.2

Orissa

Andhra Pradesh

Tamil Nadu

Kerala

Karnataka

Gujarat

335

336

Tidal Energy Systems

The Gulf of Khambhat was shaped by a noteworthy fracture that brought about a downsliding of the Khambhat locale. The region is structurally dynamic today, and a few deficiencies can be found in the inlet. Marine prehistoric studies in the Gulf of Khambhat focused on discoveries made in December 2000 by the National Institute of Ocean Technology (NIOT). Fig. 7.2 shows the installed capacity and technology of the tidal energy system in a given location. According to the researcher, such highlights are probably not going to be because of regular marine geographical procedures. This influenced the researchers to presume that human workmanship more likely than not been included here. The overviews were followed up in the next years and two palaeo channels of old streams were found amidst the Khambhat range under 20–40 m water profundities at a separation of around 20 km from the present day drift. One of the main controversies surrounding the Gulf of Khambhat is the dated piece of wood. Another controversial issue is the artifacts retrieved from the site during the various excavations. It is disputed that many of the items that have been identified as artifacts by the NIOT investigators are actually man-made. Instead, their artificial nature is contested and they are argued to be stones of natural origin. Gulf of Kutch: The Gulf of Kutch is an inlet of the Arabian Sea along the west coast of India in the state of Gujarat, which is renowned for extreme daily tides. The maximum depth of the Gulf of Kutch is 402 ft (123 m). It is a region with the highest potential of tidal energy generation. It is about 99 miles in length, and divides Kutch and the Kathiawar

Gulf of Khamnhat (700 MW with tidal barrage technology & 1425 MW with tidal stream technology)

Gulf of Kutch (2000 MW with tidal stream technology)

Palk Bay-Manner Channel (230 MW with tidal barrage technology)

Hoogly River, South of Haldia, Sunderbans (900 MW with tidal barrage technology)

South Gujarat/North Maharashtra/Orissa (900 MW tidal range and stream)

Fig. 7.2 Installed capacity of tidal energy system in a given location.

Tidal Energy Assessment and Economics

peninsula regions of Gujarat. The Rukmavati River empties into the Arabian Sea nearby. The Gulf of Khambhat lies south and the Great Rann of Kutch is located north of the gulf. Marine National Park in the Gulf of Kutch is situated on the southern shore of the Gulf of Kachchh in the Devbhumi Dwarka District of Gujarat state, India. In 1980, an area of 270 km2 from Okha to Jodiya was declared a marine sanctuary. Later, in 1982, a core area of 110 km2 was declared a Marine National Park under the provisions of the Wildlife (Protection) Act, 1972, of India. There are 42 islands on the Jamnagar coast in the Marine National Park, most of them surrounded by reefs. The best-known island is Pirotan. Palk Bay Mannar Channel: The Gulf of Mannar is a large shallow bay forming part of the Laccadive Sea in the Indian Ocean. It lies between the southeastern tip of India and the west coast of Sri Lanka, in the Coromandel Coast region. The Gulf of Mannar is a shallow bay, part of the Laccadive Sea in the Indian Ocean. A chain of low islands and reefs known as Adam’s Bridge, also called Ramseth, which includes Mannar Island, separates the Gulf of Mannar from Palk Strait, which lies to the north between India and Sri Lanka. Table 7.2 shows naturally occurring currents along the Indian coastline. Figs. 7.3 and 7.4 show tidal current variations over approximately 2000 days in the Gulf of Khambhat, the Gulf of Kutch, the Gujarat, and the Sunderbans.

7.2.2 India Lacks a Tidal Energy Policy It is astounding that a nation so plentifully supplied with the capability of tidal energy does not have a tidal energy arrangement set up. A solid approach set up to have lucidity on the business advancement and in addition the levy of the power produced through a specific sort of energy source. A solid approach would be the initial move toward creating enthusiasm among designers and getting the correct concentration toward improvement of tidal energy as a power source. In spite of the fact that India can possibly grow >8000 MW of power through tidal power, take note that the activities arranged before were eliminated because of high capital expenses. Before taking a gander at this inexhaustible wellspring of energy, India needs to consider factors such as the natural effect of these activities on the Table 7.2 Naturally occurring currents along the Indian coastline Tidal Potential Coastal region Tidal range (m) current (m/s) energy/m2 (MW)

Kinetic energy/m2 (W)

Khambhat Kutch South Gujarat Karnataka Tamil Nadu coast Andhra coast Orissa coast Sunderbans

2604.3 4500.2 1333.4 562.5 85.3 166.7 562.5 2604.3

5–11 4–9 2–4 1–1.5 1 1–2 2–4 4–7

2.5 3 1.5–2.5 1.5–2 0.8 1 1.5 2–3

10.9 7.2 1.5 0.2 0.1 0.2 1.5 7.2

337

338 Tidal Energy Systems

2076.000

No.of days 1.000

Kutch

Khambhat

No.of days 1.000 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0

250

500

750 1000 1250 1500 1750 2000 No.of days

Fig. 7.3 Tidal current range of Khambhat and Kutch.

2076.000

8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0

250

500

750

1000 1250 1500 No.of days

1750

2000

No.of days 1.000

2076.000

6.0

12

5.5

11

5.0

10

4.5

9

4.0

8

Sunderbans

Gujarat

No.of days 1.000

3.5 3.0 2.5

7 6 5 4

1.5

3

1.0

2

0.5

1 0 0

250

500

750 1000 1250 1500 1750 2000 No.of days

Fig. 7.4 Tidal current range of Gujarat and Sunderbans.

0

250

500

750

1000 1250 1500 1750 No.of days

2000

Tidal Energy Assessment and Economics

2.0

0.0

2076.000

339

340

Tidal Energy Systems

biological community and the transmission necessities of the power from beachfront locales to the populated focal piece of the nation. In addition, India must set up a solid tidal energy arrangement to draw in speculators.

7.2.3 Grid Parity of Tidal Energy in India Grid parity is the tip at which the revenue of generating electricity from tidal energy produces power at a cost that is equal to or less than the price of the purchasing power from the grid. As a result of the condition, the exact position of “grid pricing” varies not only from location to location but also customer to customer and even hour to hour. Grid parity is very imperative terminology in the tidal energy system and preferably a tidal energy component because the capital cost of the tidal component is extremely high in the current scenario. Within grid parity, tidal energy is compared with natural gas because it is most expensive forms of power and tidal energy considered as peaking power plant. India’s tidal power costs could plummet by >40% by 2030, allowing the industry to compete against domestic oil and gas firms without the help of state subsidies. That would enable tidal power to become a more viable option to coal, which costs around 2 rupees a unit, in fueling Asia’s third-largest economy and the world’s third-largest carbon polluter. Under the National Tidal Mission Plan, issued in 2017, India is to produce 0.3 GW of power by 2023 and 0.8 GW by 2027 at an overall investment of about $70 billion. India will reach grid parity in the tidal energy system in 2035.

7.2.4 Challenges With Tidal in Stream Technology There are several issues confronting the development of tidal current devices. Overall, survivability and reliability are the most significant technical challenges due to the costs related to their failures. Other challenges include • Intermittent supply—Cost and environmental problems, particularly barrage systems, are less attractive than some other forms of renewable energy. Global estimates put the price of generation at 13–15 cents/kWh (no Indian estimates available). • Cost—The disadvantages of using tidal and wave energy must be considered before jumping to the conclusion that this renewable clean resource is the answer to all our problems. The main detriment is the cost of these plants. • The altering of the ecosystem in the bay—Damages such as reduced flushing, winter icing, and erosion can change the vegetation of the area and disrupt the balance. Similar to other ocean energies, tidal energy has several prerequisites that make it only available in a small number of regions. For a tidal power plant to produce electricity effectively (at about 85% efficiency), it requires a basin or a gulf that has a mean tidal amplitude (the differences between spring and neap tide) of 7 m or above. It is also

Tidal Energy Assessment and Economics

• •

• • • • • • • • • •

desirable to have semidiurnal tides where there are two high and two low tides every day. A barrage across an estuary is very expensive to build and affects a very wide area, changing the environment for many miles upstream and downstream. Many birds rely on the tide uncovering the mud flats so that they can feed. There are few suitable sites for tidal barrages. Only provides power for around 10 h each day when the tide is actually moving in or out. Present designs do not produce a lot of electricity, and barrages across river estuaries can change the flow of water and, consequently, the habitat for birds and other wildlife. Expensive to construct. Power is often generated when there is little demand for electricity. Limited construction locations. Barrages may block outlets to open water. Although locks can be installed, this is often a slow and expensive process. Barrages affect fish migration and other wildlife. Many fish such as salmon swim up to the barrages and are killed by the spinning turbines. Fish ladders may be used to allow passage for the fish, but these are never 100% effective. Barrages may also destroy the habitat of the wildlife living near them. Barrages may affect the tidal level—the change in tidal level may affect navigation and recreation while causing flooding of the shoreline and affecting local marine life. Tidal plants are expensive to build. They can only be built on ocean coastlines, which means that, for communities far away from the sea, they are useless.

7.2.5 Government Support for Tidal Energy in India The Indian government has as of late declared that it will soon offer tidal energy incentives. Nonetheless, this option introduces a few drawbacks that should be tended to first. Tidal energy is something a few nations are investigating. Still, the new wellspring of energy can cost anywhere between Rs. 17–36 for each unit (Indian rupees). Fig. 7.5 shows government incentives for tidal energy in India. It is surprising that India, a nation with such capability for tidal energy, still does not have a tidal energy strategy. As advancements happen, it is basic to set solid approaches for the greatest clearness. The administration should duty the power created through this specific sort of energy source. On the off chance that the Indian specialists need to produce enthusiasm among designers, the initial step is setting up a solid approach. India’s aggregate potential concerning tidal power is immense; it could deliver >8000 MW of power. An imperative notation is that the past activities were closed down because of

341

342

Tidal Energy Systems

Renewable energy certificates Duties and tax exemptions

Tidal energy purchase obligation

Common incentives for tidal energy sector

Incentives offered in India in Tidal energy system

Grants/S ubsidies Feed in tariffs

Fig. 7.5 Incentives offered in India in tidal energy systems.

their high capital expenses. What’s more, there are as yet a few impediments in the method for creating tidal energy frameworks. India needs to address factors such as the natural effect. In the interim, there’s the transmission of the power from beachfront areas (where it is produced) to the populated parts of the nation (where it is required). The Gujarat government is all set to develop India’s first tidal energy plant. The state government has approved Rs. 25 crore for setting up the 50 MW plant at the Gulf of Kutch. It will produce energy from the ocean tides. The state government signed an MoU with Atlantis Resource last year to develop the plant. “The proposal was approved in this year’s budget session,” says Rajkumar Raisinghani, senior executive with Gujarat Power Corporation Limited (GPCL). Atlantis Resource is a UK-based developer of tidal current turbines. “The equipment has been imported and work will start anytime soon. We are awaiting Coastal Regulation Zone clearance from (the) Ministry of Environment and Forests, which is expected soon,” adds Raisinghani. According to the GPCL officials, if this 50 MW plant is successfully commissioned, its capacity will be increased to 200 MW. As per a study conducted by Atlantis Resource and the state government two years ago, the Gulf of Kutch has a total potential of 300 MW. The biggest operating tidal station in the world, La Rance in France, generates 240 MW. According to the estimates of the Indian government, the country has a potential of 8000 MW of tidal energy. This includes about 7000 MW in the Gulf of Cambay in Gujarat, 1200 MW in the Gulf of Kutch, and 100 MW in the Gangetic delta in the Sunderbans region of West Bengal. But despite the huge potential, India has no policy on tidal energy. The government must also provide subsidies to reduce the cost of importing wave technology so that consumers can get the cheapest rate on per unit consumption, Raisinghani adds. The Gujarat government last year approved a 10 MW tidal energy plant proposed by Urja Global Limited in

Tidal Energy Assessment and Economics

association with the United States company Ocean Energy Industries. But no date has been given for starting the project. “The Ministry of New and Renewable Energy should prepare a proper policy on tidal energy (because) the development of this sector is primarily their responsibility,” says an official of the GPCL, wishing anonymity. No developer will come forward unless the policy shows assured benefits, he adds. The uplifting news today is that the legislature is interested in profit from tidal energy. As indicated by the Power Minister, tidal frameworks require a 5-m base tidal development. This implies that Maharashtra and Gujarat are the main locales where control plants could conceivably be set up. The Minister has additionally talked about the capability of rooftop sun-based energy. In an offer to advance it, the administration promised up to 30% sponsorship to offset the high beginning expense.

7.2.6 List of Stakeholders Involved in the Development of Technology at the Central and State Levels Various stakeholders are involved in the development of the marine technology at the central and state levels. The exhaustive list is mentioned below: • Research and Information Institutes such as the Indian Institute of TechnologyMadras, the National Institute of Ocean Technology, the National Institute of Oceanography, the Indian National Center for Ocean Information Services, the Indian Ocean Global Ocean Observing System, the Susi Global Research Center, the Naval Physical and Oceanographic Laboratory, and the National Center for Earth Science Studies. • Educational institutes and universities such as IIT-Madras, the Kunjali Marakkar School of Marine Engineering, the Cochin University of Science and Technology, the Department of Meteorology and Oceanography, Andhra University, the Department of Ocean Engineering and Naval Architecture, and IIT Kharagpur. • Private-sector developers involved in the development of ocean energy such as DCNS energy, Alstom India, EDF France, and Atlantis UK. • Others government, public, and private agencies involved include the Ministry of New and Renewable Energy, the Ministry of Earth Sciences, the Indian Renewable Energy Development Agency Limited, AFD-France, and CRISIL.

7.3 HARMONIC ANALYSIS OF TIDAL POWER PLANT Tidal power generation has been growing at a very fast pace for the past decade, and its influence and impact on the electric power grid is significant. As in a conventional power plant, a tidal power plant (TPP) must ensure that the quality of power being delivered to the grid is excellent. At the same time, the tidal turbine should be immune to small disturbances coming from the grid. Harmonics are one of the more common power quality issues presented by large TPPs because of the high switching frequency of the power

343

344

Tidal Energy Systems

converters and the possible nonlinear behavior from electric machines (generator, transformer, reactors) within a power plant. This continual growth has led to the development of new standards and grid codes aimed at establishing guidelines for the successful integration of TPPs into the grid. One of several technical aspects of TPP integration is the importance of maintaining the quality of the power generated by the tidal turbines. Like conventional plants, TPPs are required to provide energy to the electric system with good power quality (i.e., constant voltage and frequency, minimum disturbances, low harmonics emission) to ensure reliability and stability and satisfy customers connected to the power system network. As TPPs have been integrated into the main grid, harmonic distortion has been one of the issues related to power quality. Tidal turbine generators (TTGs) are classified into four basic types, known as Type 1 through Type 4. Type 1 and Type 2 TTGs use soft starters to reduce in-rush currents and voltage dropouts, which can produce harmonic currents that are low in magnitude and short in duration. On the other hand, Type 3 (doubly fed induction generator) and Type 4 TTGs are equipped with controlled back-to-back power electronic converters, and they may produce harmonics to the grid. Harmonic distortion from TPPs could interact with preexisting harmonic network distortion and cause several issues if some of the harmonic frequencies involved excite a resonant point. Harmonic resonance is caused by the interaction of inductive and capacitive elements. Inside a TPP, several elements can resonate with each other (transformers, power cables, capacitor banks, etc.). When a frequency (voltage or current) experiences an inductive element reactance equal to a capacitive element reactance, a resonance occurs. Harmonic overvoltage or harmonic overcurrents can appear in a power system because of parallel or series-resonant conditions, respectively. Tidal turbine harmonic emissions are different from the emissions found in typical harmonic sources, such as industrial facilities or residential areas, and important efforts have been made to analyze them. The waveforms in alternating current electrical systems are ideally pure sinusoidal and have a constant magnitude and frequency to meet the expectations of the customers connected to the grid. A periodical deviation from this ideal condition, with a period of one cycle of the grid frequency, can be classified as a harmonic distortion. Harmonics in power systems can cause several issues. The unwanted harmonic currents in Type 1 and Type 3 TTGs can cause unnecessary extra losses in the copper windings and torque pulsations, and they may even excite mechanical modes of the turbine components. When problems related to resonance are addressed, two basic aspects should be considered: the harmonic circuit and the harmonic source. Every harmonic current frequency injected into the electrical system experiences different impedances; hence, each harmonic current takes a different path into the system. Harmonic circuit: Many elements exist inside a TPP. The collector system consists of miles of underground cables, and every TTG has its own pad-mounted transformer, capacitor compensations (Type 1 and Type 2), and LC filters (Type 3 and Type 4); thus,

Tidal Energy Assessment and Economics

resonance caused by harmonics can appear as an element of a TPP. Modeling the harmonic circuit in a TPP is not a trivial issue. Transformers, power cables, generators, capacitors, and power factor correction devices such as static VAR compensators must be included in an analysis of harmonics to represent an actual system condition. The network impedance determines resonance, and different configurations inside a WPP may lead to different resonant points. Therefore, it is important to analyze different operative cases in a single WPP harmonic analysis to account for every possible situation. Harmonic source: Knowing harmonic content at the point of common coupling of the TPP is important to ensure acceptable harmonic voltages at this point and also to assess possible resonance conditions and possible solutions aimed toward solving these issues. In Type 1 TTGs, harmonic current generation primarily comes from the soft starter installed in the turbine to reduce the in-rush current during start-up; however, this harmonic current is low in magnitude and short in duration. Harmonic currents could also appear in TPPs that have Type 1 and Type 2 TTGs—for example, as caused by the transformer during energization. A transformer’s energization can cause a considerable amount of low-order harmonics, and the DC component can be part of the harmonic content. Another source of harmonics in a power transformer is magnetic saturation, which is an undesired operating condition. Transformers are usually designed to operate very close to the saturation point. This condition can generate harmonics because of the nonlinear relation between voltage and current, especially when the transformer is operated in an overvoltage condition. Odd harmonics are associated with overexcited transformers; if it is assumed that triplen harmonics are blocked by the delta windings, then the harmonics being generated are of the orders 5th, 7th, 11th, 13th, 17th, 19th, and so on—that is, those of orders 6 k
1 where k is an integer. In most TPPs, however, triplen harmonics can be neglected, but these harmonic orders could appear as a result of an asymmetry on a grid’s voltage. In Type 3 TTGs, power converters can generate harmonics. Converters are based on power electronics, which normally use nonlinear devices to control the real and reactive power of the TTGs, but they could produce nonsinusoidal voltages and currents. In the study presented in, relatively high harmonic levels are shown for Type 3 WTGs. Predominantly low-order harmonics are present (5th, 7th, 11th, and 13th). According to, these low-order harmonics are introduced because of the interaction of a WPP with the source power system. Harmonics injected by Type 3 TTGs at higher orders are associated with pulse width modulation (PWM) switching. The system was modeled as follows: (1) Infinite bus and line feeder—An infinite bus and line feeder were represented by a Thevenin equivalent, and a simple R-L line model was used to model the line feeder. (2) Transformer—A three-phase transformer with a 6% impedance was considered. Because the magnetizing inductance of a transformer is usually much larger than the leakage inductance, only leakage inductance was taken into account. For a large transformer ideally designed for maximum efficiency, an efficiency of 98% at full load

345

346

Tidal Energy Systems

and considering the copper loss equal to the core loss is a normal assumption; thus, we can approximate the winding resistance, normally very small for efficient transformers. (3) Capacitors—The compensating capacitor is represented by the capacitance C in series with its parasitic resistance RC to represent the losses in the capacitor. An additional 1.5 MVAR to the original 400-kVAR manufacturer reactive compensation was considered. Harmonic frequency range: In most guidelines and standards, the requirements for the individual and total harmonic distortion are up to the 50th order. This is generally valid for line- or load-commutated current source converters where the higher order harmonics generally have negligible magnitude with respect to the low-order harmonics. As discussed earlier with voltage source converters, high-order harmonics in excess of 10 kHz can be generated. At such high frequencies, current distortion generally does not penetrate far into the system but the possibility of exciting a system resonance at the switching frequency and multiples thereof can exist. In an attempt to address these harmonics, the IEC standard 61400-21 requires that harmonics should be stated individually up to the 50th harmonic and then grouped in spans of 200 Hz from 2 to 9 kHz. Fast control action of the turbine converter can give rise to very low-order harmonics, both below and above the fundamental frequency. Although low in terms of the emission levels, these harmonics have the potential to destabilize the system operation when coinciding with a system resonance frequency. The instability phenomena originated from the supersynchronous components is generally referred to as control stability. Instability caused by subsynchronous components generally lies in the category of subsynchronous interaction, which includes instabilities caused by the interharmonics. Harmonics related to the saturation characteristics of the transformer generally contain frequency components up to 1 kHz. This will be discussed in more details in the next subsection.

7.4 ASSESSMENT OF TIDAL ENERGY SYSTEM BY THE OPTIMIZATION TECHNIQUE Each issue from financial to logical and designing fields is at last gone up against with a typical errand, viz., enhancement. A streamlining issue can be characterized by indicating the arrangement of every achievable hopeful and a measure for assessing their value. The objective is to locate the best solution(s). In the plan of airfoils, for example, the parameters that characterize the geometry of the airfoil are advanced to accomplish the coveted surface weight conveyance. In the plan of a satellite receiving wire, the radio wire design is enhanced to boost the fundamental shaft pick up while limiting the side projection pick up. In robot direction arranging, the position, introduction, speed, and quickening that indicates robot direction are enhanced for possible hindrance-free movement. The base of optimization method can be taken from 300 BCE, when Euclid perceived the immaterial partition between two concentrations to be a length of a straight line

Tidal Energy Assessment and Economics

joining the two. Moreover, he exhibited with the assistance of an enhancement strategy that a square has the best district among the rectangles with a given total length of the edges. The improvement of examination of varieties, the streamlining issues like, choosing perfect estimations of wine barrel in 1615 by J. Kepler, a proof that light goes between two concentrations in irrelevant time in 1657 by P. De Fermat was clarified. I. Newton (1660s) and G.W. Von Leibniz (1670s) made logical examinations that structures the commence of investigation of varieties in light of advancement method and L. Euler’s creation in 1740 began the examination on the general speculation of math of assortments as streamlining strategy. The word ideal is Latin, and means “a definitive perfect.” In other words, ideal means “the best.” In this way, to upgrade means to bring whatever improvement we are managing toward its definitive state. A chance to investigate what that implies as far for instance, and in the meantime brings the meaning of the term streamlining forward, as the logical field comprehends and utilizes it. Enhancement is the exhibition of achieving the best outcome under given conditions. The goal of each such decision is either to limit effort or to increase advantage. The effort or the preferred standpoint can be, for the most part, conveyed as a component of certain blueprint factors. From this time forward, enhancement is the method of finding the conditions that give the best or the base estimation of a limit. The traditional enhancement methods are valuable in finding the ideal arrangement or unconstrained maxima or minima of persistent and differentiable capacities. These are expository techniques and make utilization of differential analytics in finding the ideal arrangement. The traditional strategies have constrained extension in common-sense applications, as some of them include target capacities that are not ceaseless and additionally differentiable. However, the investigation of these traditional methods of streamlining shapes a reason for growing the vast majority of the numerical systems that have developed into cutting edge strategies more appropriate to the present viable issues. Three main types of problems can be handled by the classical optimization techniques: • Single variable functions. • Multivariable functions with no constraints. • Multivariable capacities with both equity and imbalance limitations. In issues with equity requirements, the Lagrange multiplier strategy can be utilized. In the event that the issue has disparity imperatives, the Kuhn-Tucker conditions can be utilized to recognize the ideal arrangement. Optimization technique programming is subdivided into the following categories: • Linear programming: Studies the case in which the objective function f is linear and the set A is specified using only linear equalities and inequalities (A is the design variable space). • Integer programming: Studies linear programs in which some or all variables are constrained to take on integer values.

347

348

Tidal Energy Systems

• Quadratic programming: Allows the objective function to have quadratic terms while the set A must be specified with linear equalities and inequalities. • Nonlinear programming: Studies the general case in which the objective function or the constraints or both contain nonlinear parts. • Stochastic programming: Studies the case in which some of the constraints depend on random variables. • Dynamic programming: Studies the case in which the optimal strategy is based on splitting the problem into smaller subproblems. • Combinatorial optimization: Concerned with problems where the set of feasible solutions is discrete or can be reduced to a discrete one. • Infinite-dimensional optimization: Studies the case when the set of feasible solutions is a subset of an infinite-dimensional space, such as a space of functions. • Constraint satisfaction: Studies the case in which the objective function f is constant (this is used in artificial intelligence, particularly in automated reasoning) (Fig. 7.6). The objective function of a tidal power plant is the cost minimization function, which is optimized with different optimization techniques. Fig. 7.7 shows the block diagram

Start Generate initial population

Evaluate fitness function

Find optimization criteria

Selection process

Re-generation process

Fig. 7.6 Flow chart of optimization technique.

Tidal Energy Assessment and Economics

Tidal turbine A C

Generator

B u s

Load

Converter

D C B u s

Battery

Fig. 7.7 Block diagram of a tidal power plant.

of a tidal power plant. At present, a large number of countries produce electricity by conventional or nonrenewable energy systems. These systems produce large amounts of atmospheric pollution. This problem is largely overcome by intensive use of alternative or renewable energy systems. The work reported in the chapter is an in-depth study of performance prediction and investigation of tidal renewable energy systems using different optimization techniques. The work on a macro level includes a proposed novel tidal system in the coastal area of Cochin, India, and modeling of a tidal solar energy system by HOMER software. Optimization of the HOMER software cost assessment result for the study area using teaching, learning based optimization, cuckoo optimization and through the grasshopper optimization technique further Reliability and Life cycle analysis of the proposed system and result are validated by regression analysis. The cost minimization function of a tidal power plant is given by following equation: NPV X

  i i i i NTidal  C + C + C Turbine capital, Tidal Turbine OandM , Tidal Turbine Replacement, Tidal Turbine

i¼1

++

N WT X

  j j i i NBattery  Ccapital, Battery + COandM + C , WT Replacement, Battery + Ccapital cost_Generator

j¼1

+ COandM cost_Generator + Cfuel cost_Generator  Csalvage value where, NTT, NBattery are the number of tidal turbine and the number of batteries, respectively. For the example, cost is varied from minimum to maximum value and optimized by different optimization techniques.

349

350

Tidal Energy Systems

Component

Cost (Rs.)

Cost range

Tidal system

Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost

14,000–11,000 5500–3500 3500–1500 2400–1900 300–100 1100–900 5200–3200 5945–3900 392–92

Generator

Battery

7.4.1 Particle Swarm Optimization Particle Swarm Optimization (PSO) is a developmental calculation streamlining procedure (a hunt strategy in view of a characteristic framework) created by Kennedy and Eberhart. The framework at first has a populace of arbitrary specific arrangements. A PSO strategy can produce amazing arrangements inside a shorter figuring time and have steadier merging qualities than other stochastic strategies. PSO is a met heuristic, as it makes few or no suspicions about the issue being streamlined and can look at extensive spaces of applicant arrangement. The decision of the PSO parameter can largely affect streamlining execution. In connection to PSO, the word “unions” normally means one of two things, despite the fact that it is regularly not cleared up which definition is implied and now and then they are erroneously thought to be indistinguishable. The initial step is to locate a potential arrangement. Every potential arrangement is known as a molecule. Every molecule is given an arbitrary speed and is flown through the issue space. The particles have memory and every molecule monitors its past best position (called Pbest) and its relating wellness. There exist various Pbests for the separate particles in the swarm and the molecule with the most prominent wellness is known as the worldwide best (gbest) of the swarm. (I) Swarm Intelligence Principle: Swarm intelligence can be described by considering five fundamental principles: (i) Proximate Principle: The population should be able to carry out simple space and time computation. (ii) Quality Principle: The population should be able to respond to the quality factor in the environment. (iii) Diverse Response Principle: The population should not commit its activity along excessively narrow channels. (iv) Stability Principle: The population should not change its mode of behavior every time with the environment change. (v) Adaptability Change: The population should be able to change its behavior when it is worth the computational price.

Tidal Energy Assessment and Economics

Start Set up parameters Generate initial velocity and position randomly for each particle Calculate fitness value for each particle Update the local best(Pbest) and Global best for each particle Satisfy the specified number of generations

Yes

No End

Fig. 7.8 Flow chart of particle swarm optimization.

The basic concept of the PSO technique lies in accelerating each particle toward its Pbest and gbest locations, with a random weighted acceleration at each time step. Fig. 7.8 presents a flow chart of the PSO technique. The following step describes how the PSO algorithm and selection process are used for analysis. • Initialize a population of particles with random positions and velocities in d dimensions of the problem space and fly them. • Evaluate the fitness of each particle in the swarm. For every iteration, compare each particle’s fitness with its previous best fitness (Pbest) obtained. If the current value is better than Pbest, then set Pbest equal to the current value and the Pbest location equal to the current location in the d dimensional space. In this analysis, find out the best minimum cost of the hybrid system component for the different cost variable. • For every iteration, compare each particle’s fitness with its previous best fitness (Pbest) obtained. If the current value is better than Pbest, then set Pbest equal to the current value and the Pbest location equal to the current location in the dimensional space. In this analysis, 1000 iterations are. Compare each minimum cost of different variables according to its previous best minimum cost value. • Compare the Pbest of particles with each other and update the swarm global best location with the greatest fitness (Gbest). Velocity updating is represented by the following equation:

351

352

Tidal Energy Systems

vi ðj + 1Þ ¼ w vi ð jÞ + c1 :r1 ðPbest ð jÞ  xð jÞÞ + c2: r2 :ðgbest  xð jÞÞ xi ðj + 1Þ ¼ xi ð jÞ + vi ðj + 1Þ where w is the weighted function, c1 and c2 are two positive numbers referred to as the cognitive and social acceleration constant that pulls it toward the global best position, and r1 and r2 are two random numbers with uniform distribution in the interval [0, 1]. The w is given by. wmax  wmin w ¼ wmax   Iter Iter max where wmax is the final weight and wmin is the initial weight selected in 0.9 and 0.4, respectively. A larger inertia weight helps in a good global search while a smaller value facilitates local exploration. In this study, Itermax and Iter are the maximum and the current iteration number, respectively. • PSO Algorithm Parameters: There are a few parameters in PSO calculation that may influence its execution. For any given streamlining issue, some of these parameters esteems and decisions largely affect the proficiency of the PSO strategy, and different parameters have little or no impact. The fundamental PSO parameters are the swarm size or the number of particles, the quantity of cycles, speed segments, and increasing speed coefficients. Furthermore, the PSO is likewise impacted by latency weight, speed clasping, and speed narrowing.  Swarm size: Swarm size or population size is the number of particles n in the swarm. A big swarm generates larger parts of the search space to be covered per iteration. A large number of particles may reduce the number of iterations needed to obtain a good optimal result. In contrast, huge amounts of particles increase the computational complexity per iteration, and make it more time consuming. From a number of empirical studies, it has been shown that most of the PSO implementations use an interval for the swarm size.  Iteration numbers: The number of iterations to obtain a good result is also problem-dependent. A low number of iterations may stop the search process prematurely while too large iterations add unnecessary computational complexity and require more time.  Selection of pbest and gbest: When moving, particles keep a record of their personal best position (pbest) and the global best position (gbest). If a particle’s fitness value in the current iteration is better than the fitness value of the pbest form the previous iteration, then the position and fitness value of pbest are updated with the current position and fitness value. If the fitness value of pbest is better than gbest in the previous iteration and is the best value in the current iteration, gbest is updated by pbest.

Tidal Energy Assessment and Economics

Each particle then adjusts its direction based on pbest and gbest in the following iteration.  Velocity components: (i) The term vi(j + 1) is called the inertia component that provides a memory of the previous flight direction that means movement in the immediate past. This component represents a momentum that prevents drastically changing the direction of the particles and to bias toward the current direction. (ii) The term c1.r1(Pbest( j)  x( j)) is called the cognitive component, which measures the performance of the particles relative to past performances. This component looks like an individual memory of the position that was the best for the particle. The effect of the cognitive component represents the tendency of individuals to return to past positions that satisfied them the most. The cognitive component is referred to as the wistfulness of the particle. The term c2.r2.(gbest  x( j)) for gbest PSO or for lbest PSO is called the social component, which measures the performance of the particles relative to a group of particles or neighbors. The social component’s effect is that each particle flies toward the best position found by the particle’s neighborhood.  Acceleration coefficients: The acceleration coefficients C1 and C2, together with the random values r1 and r2, maintain the stochastic influence of the cognitive and social components of the particle’s velocity, respectively. The constant expresses how much confidence a particle has in itself while expresses how much confidence a particle has in its neighbors.  Velocity clamping: The velocity-clamping impact was acquainted with maintaining a strategic distance from the marvel of the “swarm blast.” With no limitation on the most extreme speed of the particles, a straightforward one-dimensional examination of the swarm dynamic infers that the molecule speed can become unbounded while the molecule sways around streamlined, expanding its separation to the ideal on every emphasis (Table 7.3). • Application of PSO in tidal energy systems: The first practical application of PSO was in the field of neural network training and was reported together with the algorithm itself. Many more areas of application have been explored ever since, including telecommunications, control, data mining, design, combinatorial optimization, power systems, signal processing, and many others. To date, there are hundreds of publications reporting applications of PSO algorithms. Although PSO has been used mainly to solve unconstrained, single-objective optimization problems, PSO algorithms have been developed to solve constrained problems, multiobjective optimization problems, problems with dynamically changing landscapes, and to find multiple solutions (Table 7.4).

353

354

Tidal Energy Systems

Table 7.3 The basic variant of PSO Basic variant Function

Advantages

Disadvantages

If all velocity becomes equal to Vmax, the particle will continue to conduct searches within a hypercube and will probably remain in the optima but will not converge in the local area Achieve optimality convergence strongly influenced by the inertia weight

Velocity clamping

Controls the global exploration of the particle Reduces the size of the step velocity so that the particles remain in the search area, but it cannot change the search direction of the particle

VC reduces the size of the step velocity so it will control the movement of the particle

Inertia weight

Controls the momentum of the particle by weighing the contribution of the previous velocity To ensure the stable convergence of the PSO algorithm.

A larger inertia weight at the end of the search will foster the convergence ability. Similar to inertia weight

Optimization in parallel processing

Improved convergence rate

Constriction coefficient

Synchronous and asynchronous coefficient

A • • • • • •

When the algorithm converges, the fixed values of the parameters might cause the unnecessary fluctuation of particles Higher throughput: More sophisticated finite element formulations Higher accuracy (mesh densities)

number of research directions are currently being pursued, including: Theoretical aspects. Matching algorithms to problems. Application to more and/or different classes of problems. Parameter selection. Comparisons between PSO variants and other algorithms. New variants.

Tidal Energy Assessment and Economics

Table 7.4 At a glance comparison between PSO and tidal power plant Component Cost (Rs.) PSO

Tidal system

Generator

Battery

Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost

12,600 4400 2470 2040 190 901 4176 4880 183

Advantages and Disadvantages of PSO • Advantages:  PSO is based on intelligence.  It can be applied to both scientific research and engineering. PSO has no overlapping and mutation calculation.  The search can be carried out by the speed of the particle. During the development of several generations, only the most optimistic particle can transmit information onto the other particles, and the speed of the research is very fast.  The calculation in PSO is very simple. Compared with the other developing calculations, it occupies the bigger optimization ability and can be completed easily.  The PSO adopts the real number code, and it is decided directly by the solution. The number of the dimension is equal to the constant of the solution. • Disadvantages:  This method easily suffers from partial optimism, which causes it to be less exact at the regulation of its speed and direction.  This method cannot work out the problems of scattering and optimization.  This method cannot work out the problems of noncoordinate systems, such as the solution to the energy field and the moving rules of the particles in the energy field.

7.4.2 Chaotic Particle Swarm Optimization (CPSO) PSO is a productive, straightforward, and ripe optimization algorithm. In any case, it experiences untimely meeting; in addition, the execution of PSO depends fundamentally on its parameter settings. To upgrade the execution of PSO, this is a transformative calculated strategy through individual change in addition to populace participation and rivalry. A half-breed PSO calculation is proposed by consolidating confusion. Disordered molecule swarm advancement is another system that utilizes confused specialists to seek promising territories that are investigated by PSO. Furthermore, PSO

355

356

Tidal Energy Systems

with AIWF and disorder are hybridized to shape a disorganized PSO, which sensibly joins the populace based developer looking capacity of PSO and turbulent seeking conduct. Tumult is a sort of attribute of a nonstraight framework, which is limited, precarious dynamic conduct that displays delicate reliance on starting conditions and incorporates unbounded shaky intermittent movements. Because of the simple usage and uncommon capacity to abstain from being caught in nearby optima, mayhem has been a novel improvement system and disarray-based looking calculations have stimulated serious intrigue. In PSO, the proper control of global exploration and local exploitation is crucial in finding the optimum solution efficiently. The performance of PSO greatly depends on its parameters. The inertia weight w is the modulus that controls the impact of previous velocity on the current one. So the balance between exploration and exploitation in PSO is dictated by the value of w. Thus, proper control of the inertia weight is very important to find the optimum solution accurately and efficiently. The adaptive inertia weight factor is determined as follows:

w¼

8 < :

wmin +

ðwmax  wmin Þðf  fmin Þ f  favg favg  fmin wmax f > favg

where wmax and wmin denote the maximum and minimum of w, respectively, f is the current objective value of the particle, and favg and fmin are the average and minimum objective values of all particles, respectively. In the above equation adaptive inertia weight factor shows w is varied depending on the objective value over average value will be disrupted. A good particle tends to perform exploitation to refine results by local search while bad particle tends to perform large modifications to explore space with large steps. AIWF provides a good way to maintain population diversity and sustain good convergence capacity. Based on the proposed PSO with AIWF and the chaotic local search, a two-phased iterative strategy called chaotic PSO is proposed, in which AIWF is applied to perform global exploration and a chaotic local search is employed to perform a locally oriented search for the solution resulting from PSO. The results proved that this method enhances the search efficiency significantly and improves the search quality. CPSO can be divided into two types: • In the first type, chaos is embedded into the velocity updating equation of PSO. c1 and c2 are generated from the iteration of a chaotic map instead of using the rand function. • In the second type, chaotic search is fused with the procedure of PSO. This type is a kind of multiphase optimization technique in that chaotic optimization and PSO can switch to each other, according to certain conditions. The parameters r1 and r2 are important control parameters. The use of a chaotic sequence in the PSO can be useful to escape local minima than the general PSO method.

Tidal Energy Assessment and Economics

Table 7.5 Cost analysis by CPSO Component Cost (Rs.)

Tidal system

Generator

Battery

Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost

CPSO

12,600 4400 2470 2040 190 901 4176 4880 183

A chaotic sequence based on a logistic map is used as:   z1k + 1 ¼ a∗z1k ∗ 1  z1k where a is the value for which the logistic map is attracted. Another logistic map uses the same equation to generate the variable z2k in the range [0, 1]. Other parameters remain the same. Hence, the velocity of particles is updated as:     vik + 1 ¼ wvik + c1 z1k pbestki  xki + c2 z2k gbest ki  xki The position of the particles is modified the same as in the equation (Table 7.5).

7.4.3 Big Bang Big Crunch Arbitrariness can be viewed as proportionate to the vitality scattering in nature while meeting a nearby or worldwide ideal point can be seen as a gravitational fascination. Vitality dissemination makes the issue from requested particles, we will utilize haphazardness as a change from a focalized arrangement (arrange) to the introduction of absolutely new arrangement applicants (issue or disarray). The proposed technique is like the GA in regard to making an underlying populace haphazardly. The making of the underlying populace arbitrarily is known as the Big Bang stage. In this stage, the hopeful arrangements are spread everywhere throughout the pursuit space in a uniform way. The Big Bang is typically thought to be a hypothesis of the introduction of the universe, albeit in fact, it does not precisely portray the root of the universe but instead endeavors to clarify how the universe created from an exceptionally small, thick state into what it is today. It is only a model to pass on what happened and not a portrayal of a real blast, and the Big Bang was neither Big (in the first place the universe was smaller than the span of a solitary proton), nor a Bang (it was more a snap or a sudden swelling). The enormous detonation and huge crunch streamlining calculation is another improvement technique that depends on the huge explosion and huge crunch

357

358

Tidal Energy Systems

hypothesis, one of the speculations of the advancement of the universe. The BB-BC hypothesis, presented by Erol and Eksin, has a low computational time and a high joining speed. As per the BB-BC, the enormous detonation stage vitality scattering produces issue and irregularity is the primary highlights of this stage where in huge crunch stage arbitrarily conveyed particles are drawn into a request. The modified BB-BC produces arbitrary focuses in the enormous detonation stage and psychologists these focuses to a solitary delegate point through a focal point of mass in the huge crunch stage. The BB-BC strategy has been appeared to outflank the improved established GA for some benchmark test capacities. The BB-BC algorithm by two phase’s performances in the search space allowed navigates solution vector for minimizing the objective function. A global search is done in the first phase by this algorithm to find the region where the optimum solution exists, and then the second phase is begun around the best answer obtained from the first phase (Tables 7.6 and 7.7). The Big Bang-Big Crunch approach takes the following steps: 1. Determine the center of mass that has the global best fitness using the equation. The candidates are arranged in the ascending order of their fitness (fitness) and the first candidate will be the candidate with the best fitness (minimum loss). 2. Generate new candidates around the center of mass by adding/subtracting a normal random number. 3. Calculate the fitness function values of all the candidate solutions. Table 7.6 At a glance comparison between BB-BC and game theory BB-BC Tidal energy system

Center of mass Population size in Big Bang phase Fitness function Best value

Tidal current and tidal range Coastal area Efficiency and cost function Optimum value of electricity

Table 7.7 Cost assessment by BB-BC Component Cost (Rs.)

Wind system

Generator

Battery

Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost

BB-BC

12,600 4400 2470 2040 190 901 4176 4880 183

Tidal Energy Assessment and Economics

Find the center of mass according to the following equation N X 1

x!i i f x!c ¼ i¼1 N X1 i¼1

fi

where xc ¼ center of mass, xi ¼ is a point within an n-dimensional search space generated, fi ¼ is a fitness function value, and N ¼ population size in the Big Bang phase. xnew ¼ xc + l:r=k where l ¼ upper limit of the parameter, r ¼ normal random number, and k ¼ iteration step (Fig. 7.9).

Fig. 7.9 Flow chart of big bang big crunch optimization technique.

359

360

Tidal Energy Systems

7.4.4 Teacher Learning-Based Optimization Technique Teacher Phase In this phase, the teacher tries to improve the mean result of all students. Suppose there is “d” number of subjects (i.e., variables to be optimized), “n” is the number of students (i.e., population size j ¼ 1,2, …. n), and μ, k is the main result of a student at kth iteration; the teacher will try to move this mean toward the best value (Xkbest). The difference between the existing mean and the desired mean is given by: Diff_meank ¼ rand (Xbestk  Tfμk) (Hesse, 1971) Where Tf learning factors can be either 1 or 2 as: Tf ¼ round (1 + rand (2–1)). Based on this difference, the parameter values are updated as: k k X_teacher k i ¼ Xold , i + Diff _mean Þ

Now, calculate the fitness function value corresponding to X_teacher I k and this fitness function value is compared to the fitness function value of Xkold, i (i.e, the previous value of the particles) to generate a new population for the next phase as:  9 8   < X_teacher k i if f X_teacher k i  f xkold, i = xknew, i ¼     : ; xkold, i if f xkold, i < f X_teacher k i This xknew,i value plays the role of input for the learner phase of ith particle (student). Learner Phase In this phase, the ith student increases his/her knowledge by interacting randomly with jth students such that: xknew,i 6¼ xknew,j. Now, if the fitness function value corresponds to the newk, i (i.e., fitness function value of ith student, (f(xknew,i) is less than the fitness function value of jth student, f(xknew,j) then the particle values are updated as:   X_learner k i ¼ xknew, i + rand xknew, i  xknew, j Otherwise, X_learner

k

k i ¼ xnew , i

 + rand

xknew, j  xknew, i



The parameter values for the next iteration are obtained using following equation:  9 8   < X_learner k i if f X_learner k i  f xknew, i = xki + 1 ¼     ; : xknew, i if f xknew, i < f X_learner k i where f indicates the intensity of attraction and l is the attraction length scale. The G component is calculated as follows: Gi ¼  geg.

Tidal Energy Assessment and Economics

Table 7.8 At a glance comparison between BB-BC and game theory TLBO Tidal energy system

Teacher and learner Research space Fitness function Best value

Tidal current and tidal range Coastal area Efficiency and cost function Optimum value of electricity

Table 7.9 Cost assessment by TLBO Component

Tidal system

Generator

Battery

Cost (Rs.)

TLBO

Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost

12,600 4400 2470 2040 190 901 4176 4880 183

Where g is the gravitational constant and eg shows a unit vector toward the center of earth (Tables 7.8 and 7.9).

7.4.5 Grasshopper Algorithm The GOA algorithm proposed mathematical models and mimics the behavior of grasshopper swarms in nature for solving optimization problems. Grasshoppers are insects that are considered pests due to their damage to crop production and agriculture. Although grasshoppers are usually seen as individualistic in nature, they join in one of the largest swarms of all creatures. The mathematical model employed to simulate the swarming behavior of grasshoppers is presented as follows: X i ¼ S i + Gi + A i where Xi defines the position of the ith grasshopper, Si is the social interaction, Gi is the gravity force on the ith grasshopper, and Ai shows the wind advection. In random behavior, the equation can be written as: Xi ¼ r1 Si + r2 Gi + r3 Ai where r1, r2 and r3 are random numbers in [0, 1].

361

362

Tidal Energy Systems N X  ! Si ¼ S dij dij j¼1

where dij is the distance between the ith and jth grasshopper calculated as dij ¼ j Xj  Xi j, S is a function to define the strength of social forces and X X ! ¼ jdij i is a unit vector from the ith to jth grasshopper. The S function, which dij defines the social forces, is calculated as follows: r

Sðr Þ ¼ fe l  er where f indicates the intensity of attraction and l is the attraction length scale. The G component is calculated as follows: Gi ¼ geg where g is the gravitational constant and eg shows a unit vector toward the center of earth. The A component is calculated as follows: Ai ¼ uew Where u is a constant drift and e_w is a unit vector in the direction of tides. A nymph grasshopper has no wings, so their movements are highly correlated with wind direction. Substitute S, G, and A in the equation and it can be expanded as follows: X ^ X_i ¼ _ðj ¼ 1ÞN▒〖S ðj X_j  X_i j Þ〗 ðX_j  X_iÞ=d_ij  ge_g + ue_w where S(r) ¼ fe ^( r/l)  e ^(r) and N is the number of grasshopper. The mathematical model cannot be used directly to solve optimization problems, mainly because the grasshoppers quickly reach the comfort zone and the swarm does not converge to a specified point. X_id^ ¼ c

X    _ðj ¼ 1ÞN^ ▒〖c ð〖Ub〗_d  〖lb〗_dÞ=2 S j X_jd^  X_id^ 〗 ðX_j  X_iÞ=d_ij

 ge_g + T_d

where 〖Ub〗_dthe upper bound is in the Dth dimension, 〖lb〗_d is the lower bound in the Dth dimension. T_d is the value of the Dth dimension in the target, and c is the decreasing coefficient (Tables 7.10 and 7.11).

7.4.6 Cuckoo Optimization Technique Cuckoos search for the most suitable area to lay eggs in order to maximize their egg survival rate. After the remaining eggs grow into a mature cuckoo, they form some societies. In order to solve the optimization problem, it is necessary that the value of the problem variable be formed as an array. In genetic algorithm and PSO technologies, this array is called “chromosome” and “particle position.” But in cuckoo optimization, it is called the

Tidal Energy Assessment and Economics

Table 7.10 At a glance comparison between BB-BC and game theory Grasshopper Tidal energy system

Grasshoppers swarms Research space Fitness function Grasshopper interaction

Tidal current and tidal range Coastal area Efficiency and cost function Optimum value of electricity

Table 7.11 Cost analysis by grasshopper Component Cost (Rs.)

Tidal system

Grasshopper

Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost

Generator

Battery

12,600 4400 2470 2040 190 901 4176 4880 183

“habitat” and in an Nvar dimensional optimization problem, a habitat is an array of 1  Nvar representing the current living position of the cuckoo. The array is defined as follows: Habitat ¼ ½x1 , x2 ……………::xNvar  Each of the variable values (x1, x2…xNvar) is a floating point number. The profit of a habitat is obtained by the evaluation of the profit function fp at a habitat of (x1, x2…xNvar). So Profit ¼ fp ðhabitatÞ ¼ fp ðx1 , x2 …xNvar Þ Profit ¼ costðhabitatÞ ¼ fc ðx1 , x2 …xNvar Þ To start the optimization algorithm, a candidate habitat matrix of size NPOP  Nvar is generated (Tables 7.12 and 7.13). Table 7.12 At a glance comparison between BB-BC and game theory Cuckoo Tidal energy system

Egg survival rate Habitat Fitness function Cuckoo interaction

Tidal current and tidal range Coastal area Efficiency and cost function Optimum value of electricity

363

364

Tidal Energy Systems

Table 7.13 Cost assessment by cuckoo optimization Component Cost (Rs.)

Tidal system

Generator

Battery

Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost Capital cost Replacement cost O and M cost

Cuckoo

12,600 4400 2470 2040 190 901 4176 4880 183

7.5 ASSESSMENT OF TIDAL ENERGY SYSTEM BY GAME THEORY The well-defined method for a formal diversion theoretic investigation is the investigation of a duopoly of Antoine Cournot’s in 1838. The mathematician Emile Borel recommended a formal hypothesis of diversions in 1921, which was advanced by the mathematician John Von Neumann in 1928 out of a hypothesis of parlor recreations. Diversion hypothesis was set up as a field directly after the 1944 distribution of the amazing volume, “Hypothesis of Amusements and Financial Conduct” by Von Neumann and the business analyst Oskar Morgenstern. In 1950, John Nash showed that limited amusements have dependably had a balance point at which all players pick activities that are best for them given their rival’s decisions. In the 1960s, the amusement hypothesis was widened to the hypothetical and connected to issues of war and governmental issues. Since the 1970s, it has driven an unrest in financial hypothesis. It has discovered applications in humanism and brain science and set up joins with development and science. Amusement hypothesis got exceptional consideration in 1944 with the granting of the Nobel Prize to Nash, John Harsanyi, and Reinhard Selten. Toward the end of the 1990s, a prominent use of diversion hypothesis was planned for closeouts. Fig. 5.1 demonstrates the order of the amusement hypothesis idea (Fig. 7.10). The quality of game theory is the approach, it accommodates organizing and breaking down issues of key decisions. The procedure of formally displaying a circumstance as an amusement requires the leader to count unequivocally the players and their methodology alternatives and to think about their inclinations and responses. Game theory, hypothesis are acquainted with this part with display the arranging of cost investigation of the tidal sustainable power source framework.

7.5.1 Basic Concept of Game Theory Game theory is the branch of science worried about the examination of methodologies for managing focused circumstances where the result of a member’s decision depend

Tidal Energy Assessment and Economics

Study of Duopoly [1838]

Formal Theory of games: Emile Borel [1921]

Theory of Games : John Neumann [1928]

Economic Behavior : John Neumann [1944]

Finite games of equilibrium : Nash [1950]

Fig. 7.10 Chronology of game theory.

basically on the activities of other members. Game theory is an investigation of key basic leadership. In particular, it is the investigation of numerical models of contention and participation between insightful reasonable leaders. Game theory is the way to demonstrate vital cooperation between at least two players in a circumstance containing set guidelines and results. Theory based on decision-making is the formal investigation of basic leadership where a few players must settle on decisions that conceivably influence the premiums of alternate players. Let’s start out by defining a few terms commonly used in the study of game theory: (i) GAME: Any arrangement of conditions that has an outcome subject to the activities of at least two chiefs. (ii) Players: A key leader inside the setting of the amusement. (iii) Strategy: A total arrangement of moves a player will make given the arrangement of conditions that may emerge inside the diversion. (iv) Payoff: The result a player gets from landing at a specific result. The result can be in any quantifiable item from dollars to Rs. in utility. (v) Information set: The data accessible at a given point in the diversion. The term dataset is most normally connected when the diversion has a consecutive part. (vi) Equilibrium: The point in a division where the two players have settled on their choice and a result is reached. (vii) Nash Equilibrium: It is additionally called key harmony, and is a rundown of procedures for every player that has the property that no player can singularly change his technique and show signs of improved results. Game theory has a wide range of applications in the field of economics, but in the field of computer science, especially in the optimization algorithm, it is seldom used (Table 7.14). • Solution Concepts: A game is only a model of collaboration. It does not determine how to play, what moves the players should make, or the specific end goal to accomplish their targets (boosting results for our situation). The focal inquiry that game theory is endeavoring to answer is the manner by which players pick their techniques of play.

365

366

Tidal Energy Systems

Table 7.14 At a glance comparison between tidal and game theory Tidal energy system Game theory

Component Study area Prefeasibility Cost minimization function

Player Research space Strategies Payoff function

There are two main points of view:  Prescriptive—Analyze and specify how players should play (recommendation).  Descriptive—Analyze and predict how players will play (explanations, prediction). These two methodologies are connected; we need to configure amusements utilizing the prescriptive approach and break them down utilizing the portrayed approach. At last, we need a clear investigation to foresee that players would play in the way we proposed when we outlined the diversion. We center around the prescriptive approach. This is on the grounds that our fundamental objective is to configure recreations that have a decent equilibrium(s) and a great result for all players. An idea offers proposals on what moves to make. Assumptions: 1. The amusement is given infrequently and it is composed by us. Everyone knows the tenets (every accessible activity). It is very much characterized and players cannot transform it. 2. Awareness: All utilities of the greater part of the players are known, and a player knows all activities accessible to him. 3. Perfect Information: A player knows all the actions of other players. For strategic form games this is the same as Assumption 2. For extensive form games, this is not necessary. 4. No computational restrictions (here cryptography will come into play). Is finding a strategy feasible? Is playing a strategy feasible? 5. Players are rational: they try to maximize the payoff. 6. All actions of all players are taken simultaneously. Game theory is invigorating because, regardless of the way that the measures are fundamental, the applications are clearing. Related decisions are everywhere, potentially consolidating any endeavor in which self-captivated pros take an interest and furthermore battle. Apparently, the most entrancing beguilements incorporate correspondence because such immense quantities of layers of frameworks are possible. • Nash Equilibrium: In game theory, the Nash balance is an answer idea of an agreeable diversion including at least two players in which every player knows the balance procedures of alternate players, and no player has anything to pick up by changing just their

Tidal Energy Assessment and Economics

own technique. Let (s, f ) be a game with N players where Sk is the strategy set for player k, S ¼ S1  S2  …. .  SN is the set of strategy profiles, and f(x) ¼ (f1(x), …… fN(x)) is its payoff function evaluated at x 2 S. Let xk be a strategy profile of player k and x k be a strategy profile of all players except for player k. when each player k 2 (1…. N) chooses strategy xk resulting in strategy profile x ¼ {x1………xN} then player k obtains payoff fk(x).

7.5.2 Game Theory in a Tidal Renewable Energy System Game theory is the branch of decision theory concerned with independent decision. A game is given by G ¼ (N, S, U) in which the set of players is N, the set of strategies is S, and the set of the payoff function (utility function) is U. A payoff is a number, also called a utility, that reflects the desirability of an outcome for a player for whatever reason. When the outcome is random, the payoffs are usually weighted by their probabilities. If the set of player N is equal to 3 ¼ (tidal energy, diesel generator, and battery are the set of players), then the tidal system, battery, and generator worked as player 1, player 2, and player 3, respectively (Fig. 7.11). A. Set the strategies: S • When the tidal system is sufficient to fulfill the entire requirement and the battery bank is in recharge mode. • The tidal system is providing a sufficient amount of energy and the battery is set to supply power to the load. If the power demand is higher than the power available from tidal energy sources and the battery current is higher than the maximum discharging current, the hybrid controller automatically turns on the diesel generator to provide the extra current. Start Renewable energy

Tidal energy

Capital cost

Replacement cost

O & M cost

Design game theory based HRES Strategic decision making Pavoff matrix

Fig. 7.11 Key step of game theory in hybrid renewable energy system.

367

368

Tidal Energy Systems

According to game theory, the concept of fairness is applicable in a tidal system in the following ways. • Parity: Equal treatment of equals. That means an equal contribution from the tidal and grid energy systems in the generation of electricity. • Proportionality: There are several proportionality conditions applied in atidal energy system, such as: 1. The tidal system output is directly proportional to the amount of tidal currents. 2. Tidal power is directly proportional to the cube of the tidal currents. • Normal form: The strategic and normal form of the game are generally displayed by a lattice that demonstrates the players, techniques, and settlements. All the more by and large, it can be spoken to by any capacity that partners a result for every player with each conceivable blend of activities. In going with the mixture framework, there are two individual frameworks: one picks the line and the other picks the section. At the point when a diversion is displayed in an ordinary shape, it is assumed in this technique that the measure of the tidal and diesel generators is being ascertained in the most troublesome month. By and large, the month that is most ideal in the tidal speed is additionally positive for tidal current. So, we are obliged to measure the framework in the two most horrible months (ominous tidal current month and ideal tidal month). At the point when the framework works in this month, it consequently works in the other month.

7.5.3 Mixed Strategy Nash Equilibrium A mixed strategy is one in which a player plays his accessible unadulterated methodologies with specific probabilities. Blended systems are best comprehended with regards to rehashed recreations, where every player’s point is to keep alternate player(s) speculating. In the event that every player in an n-player diversion has a limited number of unadulterated techniques, at that point there exists no less than one balance in blended systems. In the event that there is no unadulterated procedure balance, there must be a special blended system balance. Table 7.15 presents the blended technique of a tidal sustainable power source framework. Let P be the probability of a sufficient amount of solar radiation that gives solar system worked properly. So that 1  P is the probability when the amount of solar radiation is less and the condition of tidal velocity is better. • Let Q be the probability that the condition of tidal velocity is better and the tidal energy system worked properly so that 1  Q is the probability when the tidal velocity is not perfect and the condition of solar radiation is better. • To find mixed strategies, we add the P-mix and Q-mix strategies to the payoff matrix.

Tidal Energy Assessment and Economics

Table 7.15 Mixed strategy of a tidal renewable energy system Tidal current Tidal velocity

Tidal current

Tidal velocity

Q-mix

Tidal current

50, 50

80, 20

Tidal velocity

90, 10

20, 80

P-mix

50P + 90(1  P) 50P + 10(1  P)

80P + 20(1  P) 20P + 80(1  P)

50Q + 80 (1  Q) 50Q + 20 (1  Q) 90Q + 20 (1  Q) 10Q + 80 (1  Q)

• Algebraically: 50P + 10ð1  P Þ ¼ 20P + 80ð1  P Þ 50P + 10  10P ¼ 20P + 80  80P 40P + 10 ¼ 80  60P 100P ¼ 70,SO P ¼ 70=100 ¼ 0:7 If tidal velocity is perfect, then the probability of success of the tidal energy system is 70% and the success rate of the generator is 30%. 50Q + 80ð1  QÞ ¼ 90Q + 20ð1  QÞ 50Q + 80  80Q ¼ 90Q + 20  20Q 80  30Q ¼ 70Q + 20 60 ¼ 100Q,SO Q ¼ 60=100 ¼ :60 If tidal velocity is perfect, then the probability of success of the tidal energy system is 60% and the success rate of the generator is 40%.

7.6 ROLE OF TIDAL ENERGY SYSTEM IN CLEAN DEVELOPMENT MECHANISM The clean development mechanism (CDM) is one of the adaptability components characterized in the Kyoto Protocol (IPCC, 2007). It accommodates emanations decrease

369

370

Tidal Energy Systems

ventures which create Certified Emission Reduction units which might be exchanged outflows exchanging plans. The CDM is viewed as a standout among the most essential globally executed, market-based systems to lessen carbon outflows. The tidal energy framework is one of the strategies from the sustainable power source framework that decreases greenhouse gases amid the age of power then again made under the Kyoto Protocol, the CDM was intended to enable created countries to meet household ozone depleting substance (GHG) diminishment duties by putting resources into ease outflow lessening ventures in creating nations. The CDM has rapidly developed to finance a large number of tasks worldwide and achieve a few billion-euro advertises esteem. The CDM is defined in Article 12 of the protocol, and is intended to meet two objectives: (1) To help parties excluded in Annex I in accomplishing maintainable improvement and to add to a definitive target of the United Nations Framework Convention on Climate Change (UNFCCC), which is to avert hazardous environmental change. (2) To help parties incorporated into Annex I in accomplishing consistence with their evaluated outflow constraint and lessening responsibilities (ozone depleting substance (GHG) discharge tops). “Add I” parties are those nations that are recorded in Annex I of the bargain, and are the industrialized nations. Non-Annex I parties are creating nations. The CDM tends to the second goal by permitting the Annex I nations to meet part of their emanation-decreasing duties under the Kyoto Protocol by purchasing certified emission reduction units from CDM outflow lessening ventures in creating nations. The activities and the issue of CERs are liable to guarantee that these outflow decreases are genuine and “extra.” The CDM is regulated by the CDM executive board (CDM EB) and is under the direction of the Conference of the Parties (COP/MOP) of the United Nations Framework Convention on Climate Change (UNFCCC). The flexible mechanisms consist of: • CDMs, a project-based mechanism for international trading with greenhouse gases (Article 12). • Joint Implementation (JI), a project-based mechanism described in Article 6 of the protocol, which applies only to Annex B countries. • Emission Trading (ET), a way to trade emission rights without being tied to a project. The CDM is a piece of the Kyoto convention’s natural understanding and the CDM ventures are intended to fortify economical improvement through focused, participatory, and formative action to lessen greenhouse gas (GHG) outflows. The historical backdrop of CDM starts from the mid-1990s with the expanding acknowledgment and activities by the researchers and others because of increment in GHG outflows from the human exercises like substantial businesses and enormous horticulture hones with higher thought processes of benefits and aimless creations, which have included the climatic change

Tidal Energy Assessment and Economics

Clean development mechanism

Joint implementation

Tidal energy system

Emission trading

Fig. 7.12 Clean environment toward a tidal energy system.

and ascend in temperature not in the Indian circumstance, but rather likewise at worldwide level (Fig. 7.12). Much of the world has concurred that GHG emanation needs to be decreased. This was showed in the Kyoto Protocol in 1997, which was embraced at the third Conference of Parties (COP). The COP is held by the UNFCC as an approach to gather the nations of the world and examine environmental change and measures. The Kyoto Protocol was that the Annex I countries should bring down their outflow on a normal of 5.2% from 1990 years level, the decrease ought to be accomplished by 2008–12 (the primary responsibility time frame). The non-Annex I nations were not given any headings other than to gauge the discharge and to report the outcome (IPCC 2003-04-04).

7.6.1 The Role of the Kyoto Protocol and the CDM The Kyoto Protocol is a worldwide treaty endorsed by >190 nations to lessen the discharge of ozone-harming substances that could cause worldwide atmospheric impacts. Arrangements to figure a universal settlement on worldwide atmosphere security started in 1991 and brought about the inception of the UNFCCC in May 1992. The UNFCCC was opened for signature amid the Earth Summit in Rio de Janeiro, Brazil, in June 1992, and went into operation in March 1994. The goal of the convention is to balance out climatic centralizations of ozone-depleting substances at safe levels. To accomplish this goal, all parties have resolved to address environmental change, adjust to its belongings, and report their activities to actualize the convention. The convention separates nations into two gatherings: Annex I parties, which contain developed nations and economies on the move, and non-Annex I parties, which incorporate fundamentally developing nations. The convention built up the COP as its representative body with the obligation to propel execution and regulate advance toward the convention’s objectives. Amid the COP-3 meeting held in Kyoto, Japan in 1998, the parties consented to a legitimately

371

372

Tidal Energy Systems

restricting arrangement of commitments that required Annex I nations to bring down their GHG emanations to around 5.2% beneath their 1990 levels. The discharge decrease objective should be proficient over the dedication time of 2008–12. The non-Annex I nations likewise consented to emanation decrease goals under the guideline of “normal yet separated duties,” but did not attempt to restrict commitments to accomplish outflow diminishment targets. This assention is known as the Kyoto Protocol. So as to give parties a level of adaptability in meeting their emanation decreases, the protocol created three incentive systems, known as the Clean Development Mechanism, Joint Implementation, and International Emissions Trading. 1. The CDM was set up under Article 12 of the Kyoto Protocol. The CDM empowers Annex I parties to execute ventures that diminish GHG emanations in non-Annex I parties as a byproduct of guaranteed emanation diminishments (CERs). CDM ventures exercise and is characterized as a unit extends likewise help have Gatherings in accomplishing maintainable advancement and in adding to a definitive target of the Convention. The CDM executive board (EB) regulates the CDM. 2. The fundamental standards of the Joint Implementation (JI) system are characterized in Article 6 of the Kyoto Protocol. Under JI, an Annex I party with an outflow lessening and restriction responsibility under the protocol may execute a discharge diminishment or emanation evacuation venture in the region of another Annex I party with an emanation decrease and confinement duty under the protocol. The party executing the undertaking may check the subsequent outflow decrease units (ERUs) toward meeting its own particular Kyoto target. Most JI ventures are actualized in EIT nations. 3. Global Emissions Trading (IET), as set out in Article 17, accommodates Annex I parties to secure emanation units from other Annex I parties and utilize those units toward meeting part of their objectives. These units might be the underlying allotment, or assigned amount units (AAUs), removal units (RMUs), a unit issued for the sum created from residential sink exercises, CERs under the CDM, or ERUs produced through JI. AAUs and RMUs are issued in developed countries. The CDM’s EB was built up by the Marrakesh Accords amid the Seventh Conference of the Parties. It includes 10 board individuals with 10 interchanges from industrialized nations with emanation-diminishing responsibilities (Annex B) and in addition nonAnnex B nations. Individuals serve on the board for a term of 2 years (most extreme of two back-to-back terms), with the seat and bad habit seat chose by the Executive Board, with one being a part of an Annex B Party and one being a part of a non-Annex B Party. The seat and bad habit seat interchange every year between individuals from Annex B and non-Annex B Parties. To help with completing its duties, the EB may build up boards or working gatherings. There are currently five panels/groups: • CDM registration and issuance team: Responsible for assessing requests for registration for tidal energy projects.

Tidal Energy Assessment and Economics

• Main panel: Responsible for developing guidelines and recommendations on methodologies based on submitted proposals of tidal energy systems. • Forestation and reforestation working group: Responsible for developing recommendations on affo/refo methodologies in collaboration with the Main Panel of the tidal energy system framework. • Small scale working group: Responsible for developing recommendations on small scale step-by-step methods for developing tidal energy projecst. • Accreditation Panel: Responsible for preparing material related to accrediting operational entities of tidal power plants. The long haul eventual fate of the CDM is guided by the procedures of the COP, held yearly since 1995 and containing delegates from all nations that are parties to the UNFCCC. Since the passage of the Kyoto Protocol in February 2005, another yearly occasion, joined with the COP, is the Meeting of the Parties to the Kyoto Protocol. The principal COP/MOP was held in Montreal in December 2005, and the second COP/MOP2 was held in Nairobi, Kenya, in November 2006. Design of a Tidal Energy Project by Designated National Authorities (DNA) At a national level, every nation engaged with the CDM has a Designated National Authority (DNA) in charge of conceding endorsement to neighborhood tidal vitality ventures that have satisfied national criteria for practical improvement and with a decent shot of prevailing at possible enrollment, and in addition going about as a point of convergence for CDM exercises. The UNFCCC keeps a rundown of DNAs and contact people, and most DNAs will have devoted sites and online assets. It is a necessity for parties who have endorsed the Kyoto Protocol to indicate that DNA buyers will require endorsement from the DNA of the industrialized nation where they have business activities while sellers will require endorsement from have nation DNAs. In the event that you have a particular enthusiasm for a specific nation, please get in touch with us for more data on endorsement forms, refreshed DNA contacts, or general inquiries. Designated Operating Entities (DOE) These are outsider autonomous gatherings that go about as “evaluators” for the tidal vitality framework CDM venture. These organizations must be confirmed by the CDM EB as Designated Operating Entities (DOE) before they can give this support of task proprietors. DOEs are in charge of checking and approving the tidal vitality framework configuration report (PDD); this is a specialized record that completely portrays the CDM venture. Private Gatherings

On the other side, these incorporate venture proprietors situated in have nations—these are ordinarily elements that possess the benefits that might be created into CDM

373

374

Tidal Energy Systems

ventures, for example, ranches, synthetic industrial facilities, steel plants, bond plants, or state-claimed vitality organizations looking to create elective power age sources as far as a tidal vitality source. Venture proprietors may likewise be the undertaking engineers if the CDM movement is identified with their center enterprises notwithstanding, there is a developing business sector here for natural/specialized experts who prompt on execution, order the required task documentation and which deal with the greater part of the CDM procedure. DNAs will ordinarily have a rundown of prescribed specialists that attempt this work locally. On the request side, there is a wide range of clients extending from open and private utilities, oil organizations, venture banks, government software engineers, and institutional and private speculative stock investments. While a few buyers approach sellers straightforwardly, others like to work through specialists. Dealers are additionally liable to have the capacity to get to a significantly more extensive market of intrigue purchasers through utilizing a CER merchant. NGOs Nonadministrative associations, for example, the WWF, CDM Watch, and numerous neighborhood nonbenefit associations, assume a critical part in advancing and bringing issues to light regarding the manageability of the tidal vitality framework-related CDM ventures. This might be through checking recorded CDM ventures, taking part in nearby and global partner meetings, or playing a dynamic part in venture advancement. Key issues featured by these associations incorporate the potential effects of palm oil biomass extension on deforestation, huge hydropower on town uprooting, and lowquality undertaking reports that do not address enough neighborhood concerns and perspectives. CDM Project Completion Process

The process for a CDM project takes too much time as it involves various steps as mentioned below (Fig. 7.13). 1. Project Identification: This involves the examination of emissions reduction resulting from the tidal energy project and to ascertain if it contributes to the development priorities of the nation. 2. Government Endorsement: In this step, a tidal energy project idea note is prepared and submitted for endorsement to the nodal agency of the country. 3. Project Development: To establish the “additionality” of a project, it is necessary to first define a baseline against which tidal energy project emissions can be measured, and estimate the quantum of GHG reductions in terms of tons of carbon dioxide equivalents. 4. Validation: The project idea note, the baseline study, and other relevant details are submitted for validation by an independent agency identified by the CDM EB as a

Tidal Energy Assessment and Economics

Project design of tidal energy project

National approval of tidal energy project

Validation of tidal energy project

Registration of tidal energy project

Monitoring of tidal energy project

Verification certification

Issuance of certified emission reduction through tidal energy system

Fig. 7.13 Steps of a tidal power plant in CDM.

DOE (designated operational entity). Validation is the independent evaluation of a project against the requirements of the CDM. 5. Registration: Registration is the formal acceptance by the EB of a validated project as a CDM project activity.

CDM and Forests

Forests play a critical role in the global carbon cycle, accounting for 20% of the global CO2 emissions at 1.6
0.8 Gt C annually (during the 1990s) (Ravindranath and Sathaye, 2002). The forest sector also provides mitigation opportunities to offset 10%–20% of global CO2 emissions during the coming decades (Renewindia.org, 2003-04-10). Mitigation through the forest sector has been a controversial issue during the COP meetings and for the purpose of negotiations, forestry activities are included under the category of land use. Land Use Change and Forestry (LULUCF) was debated during several COP meetings and many of the developing countries as well as some Annex-1 countries opposed the inclusion of LULUCF activities under CDM due to several reasons: • “Low hanging fruit.” This means that the developing countries are worried that the CDM would give away the low-cost options in emission limitation. This would leave only expensive options for GHG limitation for the developing countries to manage in the future.

375

376

Tidal Energy Systems

• There is a high uncertainty when it comes to measuring, monitoring, and verifying carbon stock changes. • The “loophole” issue, as feared by developing countries that carbon credits from LULUCF activities would encourage Annex 1 countries to continue to emit CO2 from fossil fuel. These are three key issues that have to be addressed for a satisfactory accounting of carbon credits from LULUCF projects, baseline, leakage, and permanence (Ravindranath and Sathaye, 2002). To establish a baseline, a scenario where no project under CDM has taken place, must be evaluated. This is a hard task because all eventual future scenarios must be evaluated. This requires historical knowledge of the specific area as well as the local socioeconomic situation and wider economic trends, which may affect the conventional output of a project. The Indian government has also proposed the creation of an International Methodology Development Fund, which will scrap charges for first-time project developers to keep foreign investment flows liquid. The Indian delegation says that removing the burden of cost will allow the Indian CDM to pass Phase III (201220). India and the largest CDM project developer, China, have come under heavy criticism for failing to sign up for a legal binding agreement to reduce emissions. It is mandatory that any government or institution that wants to design and implement a CDM project must follow the norms that are universal in nature. The following aspects should be considered while designing CDM project activities: • Social well-being: The CDM project should lead to poverty alleviation by generating additional employment, removing social disparities, and contributing to the provision of basic amenities for people that leads to improvement in their quality of life. • Economic well-being: The CDM project activity should bring in additional investment consistent with the needs of the people. • Environmental well-being: This should include a discussion of the impact of the project activity on resource sustainability and resource degradation, if any, due to the proposed activity as well as biodiversity friendliness, the impact on human health, and reduction of levels of pollution in general. • Technological well-being: The CDM project activity should lead to the transfer of environmentally safe and sound technologies with a priority to the renewable sector or energy-efficient projects that are comparable to best practices in order to assist in upgradation of the technological base.

Tidal Energy Assessment and Economics

7.6.2 Present Status of CDM in India Among the main nations on the planet, India ranks second in CERs after China. China represents >55% of aggregate CERs issued under the UNFCCC while 15% of the aggregate CERs are issued India. Gujarat is the number one state in the nation and records 42% of the aggregate CERs created from India. There is as yet colossal potential in formative undertakings of the state in investigating CDM conceivable outcomes through further arranging and documentation. Since the interesting moderation methodology of carbon exchange was conceptualized in the Kyoto Protocol, India appears to have been one of the busiest nations to test the idea vigorously. Before the end of June 2011, India had 645 CDM ventures listed with the UNFCCC, 261 of which had just been issued 93,834 kCERs. By then, India represented 1603 CDM ventures (it went up to 1914 as of November 8, 2011), including the listed and CER-issued ones, with 922 at approval and another 36 at different phases of enrollment. Taken together, the undertakings claim to decrease a whopping 444,293 million tons of CO2 by 2012 (meaning that a similar measure of tradable CERs will be credited to the ventures if UNFCCC registers them all). The related figures for 2020 are 1,516,432 kt CO2, implying that, taken together, the ventures will lessen around 1520 million tons of GHGs. With such expressive figures on the board, one gets a kick out of the chance to know a little about the truth of this outflow diminishment. Indeed, even the most quick gander at the Indian CDM situation sees very little other than great and strong corporate profiteering. The monetary retreat and the resultant break in the carbon showcase worldwide couldn’t reduce the Indian market’s ease back to-take-off yet unbridled eagerness for carbon credits. Taking a gander at India’s CDM situation as far as corporate cooperation, we find that the vitality productivity division, including HFC, is creating the greatest CERs. Enormous organizations, for example, Tata, ITC, Reliance, Ambuja, Birla, Bajaj, GFL, HFL, NFIL, and numerous others that customarily discharge huge amounts of carbon dioxide into the biosphere, gain nice-looking returns for the sake of a “clean advancement system.” The present market cost of a huge amount of CO2 lessened and sold in these types of CERs in the worldwide market is in the vicinity of 6–10 Euros, even in this “bearish” circumstance, though the most hopeful people of carbon advisors would not have given in excess of 5 dollars in 2005! Benefits in terms of sustainable development not just from extensive businesses facilitating vitality proficiency ventures, yet additionally moderately serene and “maintainable” sustainable power source extends in the biomass and wind areas went to the corporate segment up to May 16, 2011, companies apprehended around 90% of the nation aggregate of 8108 kCERs issued to biomass activities, and they likewise claim the majority of the CDM twist extends in India.

377

378

Tidal Energy Systems

CDM Potential From Gujarat Gujarat is currently leading the nation in terms of the volume of total CER generated as well as the annual potential of CER generation, even though the state has a fewer number of projects. It means Gujarat has more large-scale projects than small-scale projects. The major credit earning projects in Gujarat are from HFC and CFC reduction. For further development of CDM projects, the state has good potential in the public sector and small-scale projects. Present System for Public Sector CDM Projects in Gujarat Endeavors are produced using diverse offices to get ventures through the CDM. For tasks related to the Urban Development Department, GUDC is taking care of CDM exercises, and comparably different divisions such as industries, power, and renewable energy are striving for their CDM ventures. In such endeavors, a powerful outcome is hard to accomplish and is extremely intense for effective consummation of a CDM venture. In this procedure, there are a couple of pivotal issues to be cleared such as strategy connected, also endorsement, convenient enlistment of task, estimation and check of discharge lessening and so forth. Thus, it is not feasible for a task executing office or smaller association (such as a small ULB of Urban Department) to effortlessly profit from the advantage. For building up a more engaged and result-oriented cell, it is necessary to have a solitary cell at the state level for a wide range of CDM ventures. The cell should be outfitted with CDM specialists and venture facilitators for centered CDM modalities. With Gujarat being the main state in the nation that has a separate Department of Climate Change, a fulltime CDM cell can be set up.

7.6.3 CDM and Waste Disposal The CDM is supposed to stimulate sustainable development and emission reductions by facilitating the development of clean technologies to replace the dirty ones that have caused the climate crisis. In practice, however, the CDM often invests in dirty, discredited, and unsustainable technologies, some of which increase rather than decrease GHG emissions. For example, as of May 2008, out of 90 projects funded by the CDM to improve municipal waste management, 83 were landfills with gas recovery and another five included incinerators—the two worst waste management technologies. Only three projects included composting. Incinerators emit huge amounts of carbon dioxide (CO2) and landfills are a major source of methane, an even more potent GHG. But they cause far greater emissions by destroying usable materials (paper, metals, plastic, etc.) that instead should be recycled and reused. When industry is deprived of recycled materials, it increases the demand for virgin materials, which are far more energy intensive and polluting to produce.

Tidal Energy Assessment and Economics

The waste disposal industry attempts to “neutralize” its GHG emissions by generating energy from waste through incineration and landfill gas capture. However, landfill gas systems may capture as little as 20% of a landfill’s total emissions. Similarly, when all factors are considered, incinerators emit significantly more greenhouse gases than coalpowered plants for every kilowatt of electricity generated. Waste disposal systems are one example of CDM-funded back-end strategies that do not address the root causes of the problem and therefore do not offer real solutions. If the CDM is to fulfill its mandate, it must cease wasting money on such projects and turn toward genuine solutions in all sectors.

7.6.4 CDM’s Role in Technology Transfer While historically developed countries have been the main contributors of GHG emissions, more recently emissions from developing countries, primarily the large emerging economies, have been on the rise. An International Energy Agency study concluded that 56% of the growth in emissions between now and 2030 will be from China and India. By incentivizing the private sector to seek out low-cost emission reduction opportunities in developing countries, international offset programs bring human resources, information, and capital to these countries while also transferring mitigation technologies. The UNFCCC and the Kyoto Protocol both require participating countries to promote and cooperate in the development, application, and diffusion (transfer) of technologies. Although the CDM does not have an explicit technology transfer mandate, it does appear to contribute to the transfer of technology to developing countries. In each CDM PDD, project developers include a description of whether the technologies proposed are environmentally safe and if there will be a transfer in technological “know-how” to the developing country. It may be inferred from the information in PDDs that project developers almost universally interpret technology transfer to mean the acquisition of equipment and/or knowledge not previously available in the host country. Seres and Haites (2008) analyzed the claims made in 3296 PDDs and found that technology transfer was involved in 36% of the reviewed projects accounting for 59% of the annual emission reductions. They also concluded that technology transfer varied widely across project types, but occurred more often in larger projects. It was also more common for projects that have foreign participants, possibly because those projects tend to be larger. Five countries were the sources of >70% of the transfer of equipment or knowledge under the CDM: Japan, Germany, the United States, France, and Great Britain (16% of the high-tech equipment and 11% of the hired expertise used in CDM projects came from the United States). Greater participation by the United States in the CDM would likely increase the technology transfer of US technologies to developing countries, thereby leading to greater exports and business opportunities for US businesses.

379

380

Tidal Energy Systems

7.6.5 CDM and Sustainable Development The notion of sustainable development within the CDM can also be seen from different perspectives and the indicators will necessarily have to relate to the perspective taken. The following are some possible perspectives that can be taken for regarding sustainable development in the CDM: • From the global investment perspective This would include the perspective from both the UNFCCC as well as global investment funders. Their objective would be to maximize both the climate change reduction potential and the sustainable development of a portfolio of CDM investments across the globe. It would therefore encompass elements that enable some geographic distribution across the developing countries (to ensure some level of equitable distribution of projects) as well as across technologies and sectors. Experience so far has shown that it is likely that a small number of developing countries (e.g. China, India, South Africa, Brazil, and a few Latin American countries) could effectively account for almost all CDM projects if there is no concerted effort to enable other (smaller and poorer) developing countries to access the CDM market. This is explicitly recognized in the UNFCCC negotiating text for the Kyoto Protocol, where it recommends an equitable geographical distribution of CDM projects. • From the individual project’s perspective Each potential CDM project needs to be assessed on its own merits with respect to sustainable development indicators that will need to be applied in a very specific and local context. This includes carrying out appropriate Environmental Impact Assessments (EIAs) and Social Impacts Assessments (SIAs), as required by the national laws of each host country (or by the international funding agencies). One important consideration is the need for transparency and openness in making decisions, including the involvement of stakeholders and communities in decision-making. For specific CDM projects, countries (and project developers) have approached the issue of defining sustainable development criteria in different ways. In a number of cases, attempts have also been made to develop specific sustainability criteria and indicators for CDM projects by different groups (see Annex 1 for an example). Examples of assessing sustainable development benefits of potential CDM projects have been made for India, China, Zimbabwe Columbia, Kenya, Nepal, Sri Lanka, Bangladesh, and Indonesia. These studies have shown that CDM projects indeed can have substantial potential for enhancing sustainable development locally as well as nationally if they are designed with the sustainable development goals as part of their criteria. • From a development agency’s perspective One of the criteria agreed regarding the CDM is that it should be for projects that represent additional resources to those provided by OECD countries under their

Tidal Energy Assessment and Economics

Official Development Assistance (ODA). The question has therefore been raised as to whether development aid should be used to finance CDM projects (Kete et al., 2001). This is a difficult question to answer definitively. However, as one of the objectives of the CDM is to promote sustainable development in developing countries, it may be possible for development agencies to fund certain activities related to CDM (Sugiyama and Michaelova, 2001). These could include capacity building, especially for the LDCs who may not be able to attract projects from the private sector on their own and also for identifying potential CDM projects in the LDCs (DFID, 2000). The World Bank’s “CDM Assist” project in Africa is a good example of such development support (CDM Assist, 2000). In addition, it is possible that a part of the CDM market (albeit only a niche) may put a higher value on the sustainable development elements of certain projects than only on their CERs and price of CERs. Thus it is conceivable that in some cases, the sustainable development goals of projects may be the primary goal for the investor and the CERs the secondary goal. There is evidence already from the experience of the World Bank’s Prototype Carbon Fund that investors value projects with clear sustainable development benefits higher than others (PCF, 2001).

7.6.6 CDM and Tidal Energy Promotion The CDM increases the revenues for tidal energy generation. Most of the tidal energy projects in the CDM pipeline involve electricity-generating technologies. The basic economic barrier is the relatively higher electricity generation costs for RET, although the scale of the difference varies from technology to technology and from country to country. For example, in Thailand costs for electricity from biomass are almost competitive with the average electricity tariff while wind electricity is about double the average price. The revenues attained from selling CERs from a CDM project can help compensate for this price difference, to an extent. Nevertheless, tidal energy projects do not get as much out of the CDM as other project types. Among the 1700 projects currently at an advanced stage of the CDM project cycle, biomass projects make up the largest share, accounting for 21%, followed by hydropower projects (including large hydro) at 19% and wind energy at 12%. In total, renewable energy projects constitute 59% of the project portfolio. In terms of CERs, the market is dominated by projects to reduce hydrofluorocarbons (HFCs), nitrous oxide (N2O), and methane (CH4), which in total account for about two-thirds of all expected CERs. This is due to the high global warming potential of these gases, which in the case of HFC-23 is 11,700 times that of CO2. In fact, a mere 41 HFC, PFC, and N2O reduction projects account for 40% of all expected CERs from the >1700 projects in the project cycle.

381

382

Tidal Energy Systems

Tidal energy projects thus receive a disproportionately small financial benefit from the CDM. At current CER prices, the increase in the internal rate of return from the sale of CERs from a CO2-based renewable energy project is estimated at about 2%. This additional CER revenue can be enough to lift projects across the threshold of being economically viable. However, in some countries, energy subsidies tilt the energy market against RET such that CER revenues are not enough for a single one of the RETs. CDM projects are currently in the pipeline to become profitable. Instead, these projects must rely on further support from official development assistance. The carbon intensity of a country’s electricity mix is also an important factor. For example, countries such as Thailand or Egypt have an average electricity carbon intensity of approximately 500 kg CO2/MWh. This is much lower than the likes of China (916 kg CO2/MWh) and India (896 kg CO2/MWh). The economic outcome under the logic of the CDM is that high carbon intensity countries benefit almost double from CERs for each conventional kWh substituted by renewable energy. By contrast, the CDM strongly promotes renewable energy projects (biogas for example) that avoid methane emissions. Methane has 21 times the global warming impact of CO2. Projects thus yield high volumes of CERs and this has a very strong impact on profitability. The other key financial barrier is the high specific upfront costs of RET. The CDM could alleviate this problem if buyers were willing to front-load their payments. RET project developers would then receive the CER revenues when they most need them. However, while there are some purchasing programmers where this is possible, buyers have mostly limited their role to purchasing CERs for payment on delivery. As a result, project developers have been forced to finance their projects from other sources.

7.7 ECONOMIC ANALYSIS OF A TIDAL POWER PLANT In the economic analysis of a tidal power plant, the depletion premium is the amount equivalent to the opportunity cost of extracting the resource at some time in the future, above its economic price today, and should be added to the economic cost of production today. It is defined as follows: 〖DP〗_t ¼ ðð〖PS〗_T  〖CS〗_t Þ 〖ð1 + r Þ〗^tÞ=〖ð1 + r Þ〗T^ where t ¼ year, T ¼ year to complete exhaustion, 〖PS〗_T ¼ price of the substitude at the time of complete exhaustion, 〖CS〗_t ¼ price of domestic resources in year “t”, and R ¼ discount Rate. Import parity price ¼ Price of imported coal + freight from port to domestic consumer ¼ price of domestic coal (at import parity) + freight from mine to domestic consumer + incremental quality adjustment

Tidal Energy Assessment and Economics

IP ¼ P  E  ðG_2=G_1 Þ + SCF ½ðG_2=G_1 Þ   ðF_1  F_2 Þ  SCF  A IP ¼ Import parity price of coal at mine gate in local currency/ton, E ¼ Exchange rate, F1 ¼ Freight/Ton (financial prices) from port to consumer (market) in local currency, F2 ¼ Freight/Ton (financial prices) from mine to consumer in local currency, SCF ¼ Standard correction factor (which adjusts for the tax component of domestic costs), P ¼ Cif import price, in $US, A ¼ Coal quality penalty, G1 ¼ Gross calorific value of imported coal (kcal/kg), and G2 ¼ Gross calorific value of domestic coal (kcal/kg). The annual real interest rate is related to the nominal interest rate by the equation given below.   i ¼ i^0  f =ð1 + f Þ where: i ¼ real interest rate i0 ¼ nominal interest rate (the rate at which you could get a loan) f ¼ annual inflation rate For example, if the nominal interest rate is 8% and the inflation rate is 3.5%, the annual real interest rate is 4.35%. By defining the interest rate in this way, inflation is factored out of the economic analysis. All costs, therefore become real costs, meaning that they are defined in terms of constant dollars. The assumption is that the rate of inflation is the same for all costs. Project lifetime: The project lifetime is the length of time over which the costs of the system occur. The project lifetime to calculate the annualized replacement cost and analyze the capital cost of each component, as well as the total net present cost of the system. System fixed capital cost: The system fixed capital cost is the capital cost that occurs at the start of the project, regardless of the size or architecture of the power system. It is used to calculate the other analyzed capital costs, so it affects the total net present cost of each system but it affects them all by the same amount. It therefore has no effect on the rankings system. Capacity shortage penalty: The capacity shortage penalty is a cost penalty that HOMER applies to the system for any capacity shortage that occurs during the year. HOMER uses this value to calculate the other O and M cost. Total net present cost: The total net present cost of a system is the present value of all the costs that it incurs over its lifetime, minus the present value of all the revenue that it earns over its lifetime. Costs include capital costs, replacement costs, O and M costs, fuel costs, emissions penalties, and the costs of buying power from the grid. Revenues include salvage value and grid sales revenue.

383

384

Tidal Energy Systems

HOMER calculates the total net present cost using the following equation: C_NPC ¼ C_ðann, tot Þ=ðCRF ði, R_projÞÞ where: Cann,tot ¼ total annualized cost ($/yr) CRF() ¼ capital recovery factor i ¼ interest rate (%) Rproj ¼ project lifetime (yr)

7.7.1 General Tariff Form Quite a large number of tariffs have been proposed from time to time and are in use. They are all derived from the following equation: A ¼ cx + dy + f where A ¼ Total amount of bill for a certain period x ¼ Maximum demand during the period (kW or kVA) y ¼ Total energy consumed during the period (kWh) c ¼ Unit charge for maximum demand d ¼ Unit cost of energy, Rs. per kWh f ¼ Constant charge, Rs. Flat demand rate: The demand rate can be expressed in the form, A ¼ cx. The bill depends only on the maximum demand, irrespective of the amount of energy consumed. Straight meter rate: This can be represented by the Eq. A ¼ Dy. Block meter rate: To remove the inconsistency of the straight meter rate, the block meter rate charges the customers on a sliding scale. A certain unit rate is for a certain block of energy and for each succeeding block of energy, the corresponding unit charges decrease. Hopkinson demand rate: This tariff, also known as a two0part tariff, can be expressed in the form A ¼ cx + dy Simple Tariff: Cost=kWh ¼ ðAnnual fixed cost + Annual Operating CostÞ=ðTotalnumber ofunitssuppliedtotheconsumers per annum Þ Three-part tariff or Doherty tariff: In this tariff, the total charge is split into three elements: fixed charge, semifixed charge, and variable charge. So the general expression for the recovery of the cost split into the three sections mentioned above can be written as: Total Charge : Rs:a + bkW + c kWh where a is a constant charge made each billing period, b ¼ unit charge in Rs/Kw, and C ¼ unit charge of energy in Rs. per kWh of energy consumed.

Tidal Energy Assessment and Economics

Basic equipment cost: Basic equipment cost is the purchase cost of hardware based on data either on a previously executed project cost or a fresh budgetary quotation with necessary adjustment in order to retain the estimate on realistic footings. Excise duty: This is statuary on all indigenous procurement and is normally included by the supplier while giving the budgetary quotation. Customs duty: This is statutory and applicable in the case of imported procurements. The rates for a particular item are available in the customer manual. In the process of energy management, at some stage, investment would be required for reducing the energy consumption of a process or utility, modifications/retrofitting, and incorporating new technology. It would be prudent to adopt a systematic approach for a merit rating of the different investment options vis-à-vis the anticipated savings. It is essential to identify the benefits of the proposed measure with reference not only to energy savings but also to other associated benefits such as increased productivity, improved product quality, etc. The cost involved in the proposed measure should be captured in totality, namely: • Direct project cost of tidal power plant. • Additional operations and maintenance cost of tidal power plant. • Training of personnel on new technology etc.

7.7.2 Investment Need, Appraisal, and Criteria To persuade your organization to commit itself to a program of investment in energy efficiency, you need to demonstrate: • The size of the energy problem it currently faces. • The technical and good housekeeping measure available to reduce waste. • The predicted return on any investment. • The real returns achieved on particular measures over time. The need for investments in energy conservation can arise under the following circumstances: • For new equipment, process improvements etc. • To provide staff training. • To implement or upgrade the energy information system.

7.7.3 Criteria Any investment has to be seen as an addition to and not as a substitute for having effective management practices for controlling energy consumption throughout your organization. Spending money on technical improvements for energy management cannot compensate for inadequate attention to gaining control over energy consumption. Therefore, before you make any investments, it is important to ensure that: • You are getting the best performance from the existing plant and equipment. • Your energy charges are set at the lowest possible tariffs.

385

386

Tidal Energy Systems

• You are consuming the best energy forms—fuels or electricity—as efficiently as possible. • Good housekeeping practices are being regularly employed, at least by key personnel. When listing investment opportunities, the following criteria need to be considered: • The energy consumption per unit of production of a plant or process. • The current state of repair and energy efficiency of the building fabric, plant, and services, including controls. • The quality of the indoor environment—not just room temperatures but indoor air quality and air change rates, drafts, under- and overheating, including glare, etc. • The effect of any proposed measure on staff attitudes and behavior. In most respects, investment in energy efficiency is no different from any other area of financial management. So when your organization first decides to invest in increasing its energy efficiency, it should apply exactly the same criteria to reducing its energy consumption as it applies to all its other investments. It should not require a faster or slower rate of return on investment in energy efficiency than it demands elsewhere. The basic criteria for financial investment appraisal include: • Simple payback: A measure of how long it will be before the investment makes money, and how long the financing term needs to be. • Return on investment (ROI) and internal rate of return (IRR): A measure that allows comparison with other investment options. • Net present value (NPV) and cash flow: Measures that allow financial planning of the project and provide the company with all the information needed to incorporate energyefficient projects into the corporate financial system. Initially, when you can identify no or low-cost investment opportunities, this principle should not be difficult to maintain. However, if your organization decides to fund a rolling program of such investments, then over time it will become increasingly difficult for you to identify opportunities that conform to the principle. Before you reach this position, you need to renegotiate the basis on which investment decisions are made. It may require particular thoroughness to ensure that all the costs and benefits that arise are taken into account. As an approximate appraisal, simple payback (the total cost of the measure divided by the annual savings arising from it expressed as years required for the original investment to be returned) is a useful tool. It is essential to keep a careful watch on your organization’s maintenance policy and practices in order to protect any investment already made in reducing your organization’s energy consumption. There is a clear dependence relationship between energy efficiency and maintenance. This operates at two levels: • Initially, improving energy efficiency is most cost effectively done at existing facilities through normal maintenance procedures.

Tidal Energy Assessment and Economics

• Subsequently, unless maintenance is regularly undertaken, savings from iinstalling technical measures, whether in new build or existing facilities, may not be realized. As the process becomes more sophisticated, financial criteria such as discounted cash flow, internal rate of return, and net present value may be used. If you do not possess sufficient financial expertise to calculate these yourself, you will need to ensure that you have access, either within your own staff or elsewhere within the organization, to people who can employ them on your behalf. There are two quite separate grounds for arguing that, at least toward the later part of your energy management program, your organization could begin to apply a slower rate of return to its investments in energy efficiency than it applies elsewhere. The benefits arising from some energy saving measures may continue long after their payback periods. Such a measure does not need to be written off using fast discounting rates, but can be regarded as adding to the long-term value of the assets. For this reason, short-term payback can be an inadequate yardstick for assessing longer-term benefits. To assess the real gains from investing in saving energy, you should use investment appraisal techniques:

7.7.4 Financial Analysis Techniques Simple payback period (SPP) represents, as a first approximation, the time (number of years) required to recover the initial investment (first cost), considering only the net annual saving: The simple payback period is usually calculated as follows: First Cost Simple Pay Back Period ¼ ðFirst CostÞ=ðYearly Benefits  Yearly CostsÞ Advantages A widely used investment criterion, the payback period seems to offer the following advantages: • It is simple, both in concept and application. Obviously a shorter payback generally indicates a more attractive investment. It does not use tedious calculations. • It favors projects that generate substantial cash inflows in earlier years and discriminates against projects that bring substantial cash inflows in later years but not in earlier years. Limitations • It fails to consider the time value of money. Cash inflows in the payback calculation are simply added without suitable discounting. This violates the most basic principle of financial analysis, which stipulates that cash flows occurring at different points of time can be added or subtracted only after suitable compounding/discounting.

387

388

Tidal Energy Systems

7.7.5 Time Value of Money A project usually entails an investment for the initial cost of installation, called the capital cost, and a series of annual costs and/or cost savings (i.e., operating, energy, maintenance, etc.) throughout the life of the project. To assess project feasibility, all these present and future cash flows must be equated to a common basis. The problem with equating cash flows that occur at different times is that the value of money changes with time. The method by which these various cash flows are related is called discounting, or the present value concept.

7.7.6 Return on Investment (ROI) ROI expresses the “annual return” from the project as a percentage of capital cost. The annual return takes into account the cash flows over the project life and the discount rate by converting the total present value of ongoing cash flows to an equivalent annual amount over the life of the project, which can then be compared to the capital cost. ROI does not require similar project life or capital cost for comparison. This is a broad indicator of the annual return expected from initial capital investment, expressed as a percentage: ROI ¼ ðAnnual Net Cash FlowÞ=ðCapital CostÞ ROI must always be higher than cost of money (interest rate); the greater the return on investment, the better the investment. Limitations • It does not take into account the time value of money. • It does not account for the variable nature of annual net cash inflows.

7.7.7 Internal Rate of Return This method calculates the rate of return that in investment is expected to yield. The internal rate of return (IRR) method expresses each investment alternative in terms of a rate of return (a compound interest rate). The expected rate of return is the interest rate for which total discounted benefits become just equal to total discounted costs (i.e., net present benefits or net annual benefits are equal to zero, or for which the benefit/cost ratio equals one). The criterion for selection among alternatives is to choose the investment with the highest rate of return. The rate of return is usually calculated by a process of trial and error whereby the net cash flow is computed for various discount rates until its value is reduced to zero. The internal rate of return (IRR) of a project is the discount rate, which makes its net present value (NPV) equal to zero. It is the discount rate in the equation:

Tidal Energy Assessment and Economics

IRR ¼ 0 ¼X ðCF_0Þ=〖ð1 + K Þ〗^0 + ðCF_1Þ=〖ð1 + K Þ〗^1 + ……: + ðCF_nÞ=〖ð1 + K Þ〗^ n ^ ¼ _ðt ¼ 0Þ^n▒ðCF_t Þ=〖ð1 + K Þ〗t

Advantages A popular discounted cash flow method, the internal rate of return criterion has several advantages: • It takes into account the time value of money. • It considers the cash flow stream in its entirety. • It makes sense to businessmen who prefer to think in terms of rate of return and find an absolute quantity, such as net present value, somewhat difficult to work with.

7.7.8 Energy Performance Contracting and Role of ESCOS If the project is to be financed externally, one of the attractive options for many organizations is the use of energy performance contracts delivered by energy service companies, or ESCOs. ESCOs are usually companies that provide a complete energy project service from assessment to design to construction or installation, along with engineering and project management services and land financing. In one way or another, the contract involves the capitalization of all the services and goods purchased as well as land repayment out of the energy savings that result from the project. In performance contracting, an end user (such as an industry, institution, or utility) seeking to improve its energy efficiency contracts with ESCO for energy efficiency services and financing. In some contracts, the ESCOs provide a guarantee for the savings that will be realized and absorb the cost if real savings fall short of this level. Typically, there will be a risk management cost involved in the contract in these situations. Insurance is sometimes attached, at a cost, to protect the ESCO in the event of a savings shortfall. Energy efficiency projects generate incremental cost savings as opposed to incremental revenues from the sale of outputs. The energy cost savings can be turned into incremental cash flows to the lender or ESCO, based on the commitment of the energy user (and in some cases, a utility) to pay for the savings.

EXERCISE 1. What is the recent scenario of a tidal energy system in India? 2. What is the use of an optimization technique in the cost assessment of a tidal power plant? 3. What is the use of the particle swarm optimization technique in the cost assessment of a tidal power plant? 4. What is the use of the chaotic particle swarm optimization technique in the cost assessment of a tidal power plant? 5. What is the use of BB-BC in the cost assessment of a tidal power plant?

389

390

Tidal Energy Systems

6. 7. 8. 9. 10.

What is the use of TLBO in the cost assessment of a tidal power plant? What is the use of CUCKOO in the cost assessment of a tidal power plant? What is the use of GRASSHOPPER in the cost assessment of a tidal power plant? What is the requirement of game theory in a tidal power plant? Explain the concept of a clean development mechanism and write its importance in a tidal power plant.

Objective-Type Questions Q.1

Q.2

Q.3

Q.4

Q.5

Q.6

Q.7

Tidal energy system is one of the part of (a) Nonrenewable energy (b) Renewable energy (c) Both (d) None of these The installed capacity of a tidal energy system in the Gulf of Kutch is (a) 1000 MW (b) 2000 MW (c) 9000 MW (d) 300 MW The installed capacity of the tidal power plant in the Gulf of Cambay is (a) 9000 MW (b) 7000 MW (c) 1800 MW (d) 6000 MW The spring tidal range of Sagar Island is (a) 5 m (b) 4.6 m (c) 5.6 m (d) 3 m The approximate tidal range of Calicut Kerala is (a) 7 m (b) 6.3 m (c) 5 m (d) 1.2 m The maximum depth of the Gulf of Kutch is (a) 110 m (b) 123 m (c) 115 m (d) 100 m The tidal range of Khambhat is (a) 2–3 m (b) 5–11 m (c) 10–15 m (d) 0–6 m

Tidal Energy Assessment and Economics

Q.8

Q.9

The tidal range of the Andhra Coast is (a) 3–5 m (b) 6–7 m (c) 1–2 m (d) 10–12 m The approximate tidal energy production in India in 2023 will be (a) 1 GW (b) 0.8 GW (c) 0.3 GW (d) 2 GW

Q.10

The approximate tidal energy production in India in 2027 will be (a) 1 GW (b) 0.8 GW (c) 0.3 GW (d) 2 GW

Q.11

The biggest operating tidal station is the world is (a) La Rance in France (b) Gulf of Kutch in India (c) Sagar Island (d) None of the above

Q.12

The duopoly concept of game theory is given by (a) Antonie Cournot (b) Blackberg (c) Thomson (d) None of the above

Q.13

A strategic decision-maker within the context of the game is called (a) Payoff (b) Duopoly (c) Player (d) Decision-maker

Q.14

What a player receives from arriving at a particular outcome is called (a) Payoff (b) Duopoly (c) Player (d) Decision-maker

Q.15

Tidal power is directly proportional to the (a) Tidal current (b) Square of the tidal current (c) Cube of the tidal current (d) None of the above

Q.16

An optimization technique is used to assess (a) Maximization function (b) Minimization function (c) Both (i) and (ii) (d) None of the above

391

392

Tidal Energy Systems

Q.17

The approximate value of the final weight in PSO is (a) 1.2 (b) 0.9 (c) 0.4 (d) 0.7

Q.18

The approximate value of the initial weight in PSO is (a) 1.2 (b) 0.9 (c) 0.4 (d) 0.7

Q.19

A device that provides a large amount of power by tidal energy is a (a) Point absorber (b) Attenuator (c) Tidal lagoon (d) Wave converter

Q.20

A _________ is a floating structure that absorbs energy from all directions near the water surface (a) Point absorber (b) Attenuator (c) Tidal lagoon (d) Wave converter

Q.21

A ________ is a hydroelectric wave energy device that uses the motion of ocean waves to generate electricity (a) Point absorber (b) Attenuator (c) Tidal lagoon (d) Wave converter

Q.22

A ___________ is a type of wave energy converter that harnesses energy from the oscillation of sea water (a) Point absorber (b) Oscillating water column (c) Tidal lagoon (d) Wave converter

Q.23

A _________ is a tidal energy converter that extracts energy from moving masses of water (a) Point absorber (b) Attenuator (c) Tidal lagoon (d) Tidal steam generator

Q.24

A ________ is a power station that generates electricity from the natural rise and fall of the tides (a) Point absorber (b) Attenuator (c) Tidal lagoon (d) Tidal steam generator

Tidal Energy Assessment and Economics

Q.25

The value of a load factor is always (a) 1 (b) 1 (d) 0

Q.26

The reserve capacity of a tidal power plant is given by (a) Installed capacity  Maximum Demand (b) Maximum demand  Installed capacity (c) Maximum demand  Installed capacity (d) Maximum demand/Installed capacity

Q.27

In the horizontal force, the following relations are correct: (a) Acceleration + Coriolis force ¼ Pressure gradient force + Tractive force (b) Acceleration  Coriolis force ¼ Pressure gradient force  Tractive force (c) Acceleration + Coriolis force ¼ Pressure gradient force  Tractive force (d) Acceleration  Coriolis force ¼ Pressure gradient force + Tractive force

Q.28

A point where the tidal range is zero (a) Tide ebb (b) Tide flood (c) Amphidromic (d) None of the above

Q.29

A ________ is the periodic horizontal flow of water accompanying the rise and fall of the tide (a) Tidal barrage (b) Tidal current (c) Tidal range (d) None of the above

Q.30

Which power station generates fewer greenhouse gas emissions? (a) Nuclear power (b) Thermal power (c) Tidal power (d) Both (i) and (ii)

REFERENCE Hesse, P.R., 1971. A Textbook of Soil Chemical Analysis. William Clowes and Sons Limited, London.

FURTHER READING Census of India, 1981. District Census Handbook. Uttar Kannada District, B.K. DAS of the Indian Administrative Service, Director of Census Operations, Karnataka. Chaffey, D., Aziz, A., Djurfeldt, G., Haldin, G., Paranjape, J., Suder, S., Svanqvist, N., Tejwani, K.G., 1992. An Evalution of the SIDA Supported Social Forestry Projects in Tamil Nadu and Orissa, India. . FAO, 2001. Global forest resources assessment 2000. Main report. FAO Forestry Paper 140Food and Agriculture Organization of the United Nations, Rome. Haripriya, G., 2001. Managing forest in India to mitigate carbon. J. Environ. Plan. Manag. 44, 701–720.

393

394

Tidal Energy Systems

Haripriya, G., 2003. Carbon budget of Indian forest. Clim. Chang. 56 (3), 291–319. Harvey, D., 2000. Climate and Global Environmental Change. Pearson Education Ldt, Harlow, Essex, United Kingdom. IPCC Special Report, 2000. Watson, R.T., Ravindranath, N.H., Noble, I.R., Verardo, D.J., Bolin, B., Dokken, D.J. (Eds.), Land Use, Land Use Change and Forestry.. Kadekodi, G.K., Ravindranath, N.H., 1997. Macro-economic analyses of forestry options on carbon sequestration in India. Ecol. Econ. 23, 201–223. Lohmann, L., 2006. Carbon Trading. A Critical Conversation on Climate Change, Privatisation and Power. Dag Hammarskj€ old Foundation, Uppsala. Marland, G., Schlamadinger, B., 1997. Forests for carbon sequestration or fossil fuel substitution? A sensitivity analysis. Biomass Bioenergy 13, 389–397. Michaelowa, A., 2005. CDM: Current Status and Possibilities for Reform. Hamburg Institute of International Economics Paper No. 3. Michaelowa, A., 2006. Climate policy after 2012—cutting the Gordian Knot. Intereconomics 41 (2), 60–77. Olsen, K.H., 2007. The clean development mechanism’s contribution to sustainable development: a review of the literature. Clim. Chang. 84 (1), 59–73. Pew Center on Global Climate Change, 2007. Climate change mitigation measures in the People’s Republic of China. In: International Brief 1. Pew Center on Global Climate Change, Washington, DC. Roberts, J.T., Parks, B.C., 2007. A Climate of Injustice Global Inequity, North-South Politics, and Climate Policy. MIT Press, Cambridge, MA. Schneider, S., Grashof, G., 2007. Capacity Development for the Clean Development Mechanism—Lessons € Learned in Ghana, India, Indonesia, South Africa and Tunisia Lambert (Oko-Institut e.V.). GTZ, Eschborn 41 pp. Sirohi, S., 2007. CDM: is it a ‘win–win’ strategy for rural poverty alleviation in India? Clim. Chang. 84, 94–110.

INDEX Note: Page numbers followed by f indicate figures, and t indicate tables.

A Accidental limit states (ALS), 317 Accreditation Panel, 373 Acoustic Doppler current profilers/acoustic Doppler profile (ADCP), 118–121, 231 Adam’s Bridge, 337 Adaptive inertia weight factor (AIWF), 355–356 Alternating current (AC) transmission, 222–223 HVAC transmission, 223–224 technical issues, 230 AND gate function, 321–323 Annapolis Royal power plant, 42–43, 43t, 45f, 50–51 ARTEMIS software, 136, 138f Assigned amount units (AAUs), 372 Atlantis Resources, 333, 342–343 Attenuators, 72 mooring, 73 power take off, 72–73 structural elements, 72 Automatic control, tidal power plants automatic synchronization, 251–252 central control room, unit control, 250–251 fully automatic control, 247 information and control signals, 248–249 inner loop, 246–247 local control of unit, UCB, 250 local manual (mechanical/push button) control, 249–250 manual control, 247 manual synchronization, 251 need for, 247 offsite supervisory control, 247, 250–251 outer power control loop, 246–247 semiautomatic control, 247 unit operation, 247–248 Axial turbines, 263–264

B Barrages, 56, 340–341 Basin scale model, 209–210 Battery bank, 194–195, 195t Bayes’ theorem, 307, 309

Berkhoff’s equation, 136 β factor model, 305 Betz limit, 128, 255, 258 Bhakra Left Dehar Plant, 251 Binary power plant, 20 Biomass conversion process, electrical energy chemical conversion, 18 thermal conversion, 17 Biomass energy electricity generation, 15–17 environmental impact of, 36 Birnbaum’s measure, 304 Blue Kenue, 124–125 Boolean algebra, 321, 327–328 Bragg effect, 231–232 Bulb turbines, 81, 83f Bulge wave technology, 77–78

C Carnot’s theorem, 2 Cavitation tunnels, 199 Central Board of Irrigation and Power (CBIP), 286 Certified Emission Reduction units, 369–370 Chaotic particle swarm optimization (CPSO), 355–357 Chart Datum (CD), 56 Clean development mechanism (CDM) COP, 371 DNA, tidal energy project design, 373 DOE, 373–374 emission trading, 370 flexible mechanisms, 370 GHG outflows, 370–371 Kyoto Protocol, 369–376 NGOs CDM project completion process, 374–375 and forests, 375–376 objectives, 370 outflow lessening ventures, 370 present status, in India, 377–378 and sustainable development development agency’s perspective, 380 global investment perspective, 380

395

396

Index

Clean development mechanism (CDM) (Continued) individual project’s perspective, 380 technology transfer, 379 and tidal energy promotion, 381–382 UNFCC, 371 and waste disposal, 378–379 Coal, 7, 31–33 COCOMO-based estimation method, 140 Combinatorial optimization, 348 Commercial energy sources, 4–5 Conductors, 229–230 Conference of Parties (COP), 371 Constant failure rate model, reliability assessment ALS, 317 Boolean algebra and reliability calculation, 327–328 causes, tidal renewable energy system, 323–326 failure and load cases, 322–323t fault-tree construction and analysis, 320–323, 327 FLS, 317 intensity function, 313 measurement uncertainties, 316 model uncertainties, 316 performance assessment of component and event model, 317 contingency enumeration, 318 contingency selection and ranking, 317, 319–320 PI methods, 318–319 screening methods, 318–319 state enumeration, 318 probabilistic reliability assessment, 322f SLS, 317 ULS, 316–317 Constraint satisfaction, 348 Control system, tidal power plants automatic control automatic synchronization, 251–252 fully automatic control, 247 information and control signals, 248–249 inner loop, 246–247 local control of unit, UCB, 250 local manual (mechanical/push button) control, 249–250 manual control, 247 manual synchronization, 251 need for, 247 offsite supervisory control, 247 outer power control loop, 246–247 semiautomatic control, 247

unit of central control room and off site supervisory control, 250–251 unit operation, 247–248 block diagram of, 243, 244f closed-loop system, 243–245, 245f continuous-time control system, 244–245, 245t cyclic process of, 246, 246f discrete-time control system, 244–245, 245t multiinput and single-output system, 244–245 multiinput input and multioutput control system, 244–245 open-loop system, 243–244 reactive power control blade pitch actuator, 273 control actuators, 272 nacelle yaw drive, 272 passive components, design of, 273–274 power electronics, 273 power factor correction, active and reactive current, 274 tidal generator, 276 tidal turbine control requirements, 272 and voltage control, 274–276 single-input and single-output control system, 244–245 stability analysis of definition, 282–283 tidal generator, electrical protection of, 283–290 TEC systems chip-based multiwork transfers, 253 electromechanical relays, 253–254 hydrokinetic energy conversion theory, 254–255 microprocessor-based relay, 253–254 protective relay technology, application of, 253 remote communication ability, 254 self-monitoring capability, 254 tidal-dynamic energy assessment, 263–266 tidal turbine control (see Tidal turbine) turbine configuration and control objectives, 266–271 tidal current turbine, dynamic control of (see Tidal current turbine) traffic light control system, 244 Converter systems, TPP, 262 Cost minimization function, 348–350 Critical path method (CPM), 139–140 advantages of, 141–142 steps in, 140–141, 144–146f, 149f

Index

tidal power plant, activity of, 141, 142t Cross-linked polyethylene (XLPE), 229–230 Crude oil/petroleum, 7 Cuckoo optimization technique, 362–363

D Darcy-Weisbach equation, 210 Darrieus turbines, 264 Data signals, 249 DC-DC converter, 203 Deep-cycle batteries, 11 Dendrothermal energy, 17 Designated National Authority (DNA), 373 Designated Operating Entities (DOE), 373–374 Detailed project reports (DPRs), tidal power plant factors, 175–177 IDC calculations, 177, 177f internal rate of return, 179–182 net present value, 179 physical and demographic features, 175, 176f project management of, 175, 177f ROI, 178–179 simple payback period, 178 Diesel generator, 191–193, 194t Direct current (DC) transmission, 224–226 Distributive switch board (DSB), 327 Diverse response principle, 350 Doubly fed induction generators, 221 Downtime distributions, 305–306 Drag coefficient, 123–124 Drag force, 123 Drivetrain model, 267–269 Dry steam power plants, 20 Durgaduani brook, 333 Dynamic programming, 348

E Earth faults, 283–284 Earth-moon framework, 41–42, 56–57 Earth-sun framework, 41–42 Ebb generation, 61–63, 65f Ebb tide, 53–54, 58, 63–64 Economic analysis, TPP capacity shortage penalty, 383 criteria, 385–387 energy performance contracting and ESCOs, 389 financial analysis techniques, 387 general tariff form basic equipment cost, 385 block meter rate, 384

customs duty, 385 excise duty, 385 flat demand rate, 384 Hopkinson demand rate, 384 simple tariff, 384 straight meter rate, 384 three-part tariff/Doherty tariff, 384 inflation, 383–384 investment need, appraisal and criteria, 385 IRR method, 388–389 project lifetime, 383 real costs, 383–384 ROI, 388 system fixed capital cost, 383 time value of money, 388 total net present cost, 383 Electrical pitch systems, 262 Electricity generation, nonconventional energy sources, 8 power generation, 8 solar water heating systems, 9 technologies biomass energy system, 15–17 PV power systems, 11–12 solar energy system, 9–12 wind energy system, 12–15 transport fuels, 9 Electromagnetic torque, 269–270 Emission trading (ET), 370 Enclosed water tunnels, 199 Energy sources, 41–42 commercial and noncommercial energy, 4–5 conventional energy source, 3–4 nonconventional energy sources, 3–4, 51–53 nonrenewable energy resource, 5–8 primary and secondary energy, 4 prime movers, 3–4 renewable energy sources electricity generation, 8–24 environmental aspects of, 31–36 transformation, 1–3 worldwide renewable energy scenarios biomass plants, 32t countries in, 25–26, 26–27t, 31 customary biomass, 25–26 electrical energy development, 25–26 essential energy, 27–28 free market activity, 27–28 geothermal plants, 32t hard rock, 26–27

397

398

Index

Energy sources (Continued) inexhaustible sources, 25–26 IRENA, 28–29 modern jazz, 26–27 nonconventional energy source investment, 30–31 noncustomary energy sources and powers, 28 nonregular energy speculation, patterns in, 28 solar farms, 32f sustainable power sources, 25 unfinished symphony, 26–27 utility-scale ventures, 28 wind farms, 32t Environmental impact assessments (EIAs), 380 Eolian plants, 4 Equivalent loss factor (ELF), 297 Ethylene propylene rubber (EPR), 229 Euler’s turbine equation, 212–213, 213f

F Failure distribution model density, 298 function, probability of, 297 Jelinski-Moranda model, 298 mean failure rate, 299 mean time between failures, 301 MTTF, 300 probability density function, 297 rate of, 299 reliability engineering, 297 Farm method, location assessment bottom clearance, 161 efficiency measurement, 161 heat rate, 161 hydraulic current, 161 input-output characteristics, 161 maximum rotor diameter, 161 resonant system, 161 TECS, 160 tidal optimal unit, dynamic programming method, 162–168 tidal streaming, 161 top clearance, 161 Fatigue limit states (FLS), 317 Feed forward, 263 Feeds models, 208 Field-oriented control method, 269–270 Fischer-Tropsch synthesis, 18 Fish ladders, 341

“Fission,”, 8 Fixed-speed fixed-pitch (FS-FP), 261 Fixed-speed variable-pitch (FS-VP), 261 Flash/binary combined cycle, 20 Flash power plants, 20 Floating substations, 228 Flood tide, 54 Fossil fuels, 7 Friction loss, 210–211

G Game theory, tidal energy system amusement hypothesis, 364 basic concept of, 364–367 chronology of, 364, 371f diversion hypothesis, 364 mixed strategy Nash equilibrium, 368–369 parlor recreations, 364 tidal renewable energy system, 367–368 Ganga delta, 333 General tariff form, TPP economic analysis basic equipment cost, 385 block meter rate, 384 customs duty, 385 excise duty, 385 flat demand rate, 384 Hopkinson demand rate, 384 simple tariff, 384 straight meter rate, 384 three-part tariff/Doherty tariff, 384 Generator-side converter control, 271 Geographical information system (GIS), 156–157 Geothermal energy crust, 19 earth’s core, 18–19 electricity generation, 18–19 high temperature resources, electricity, 19 hydrothermal resources, 19 low temperature resources, heating, 19 magma, 19 plates, 19 renewable/reversible energy source, 19 Geothermal power plants benefits and challenges of, 20, 21t binary power plant, 20 dry steam power plants, 20 earth’s core, 19 flash/binary combined cycle, 20 flash power plants, 20

Index

GHG. See Greenhouse gas (GHG) Global emissions trading, 372 Gorlov helical turbine, 264 Grasshopper algorithm, 361–362 Greenhouse gas (GHG), 34–36, 370–371 Grid codes (GCs), 219 Grid pricing, 340 Gujarat, India CDM potential from, 378 public sector CDM projects, present system for, 378 Gujarat Power Corporation Limited (GPCL), 342–343 Gulf of Cambay, 333 Gulf of Khambhat, 333–336 Gulf of Kutch, 333–334 Gulf of Mannar, 334–336, 339f

H Hagen-Paiseuille equation, 211 Hanna turbine, 79 Harmonic analysis, TPP circuit, 344–345 conventional power plant, 343–344 distortion, 344 frequency range, 346 overvoltage/harmonic overcurrents, 344 power quality, 343–344 power systems, 344 resonance, 344 source, 345 TTGs, 344–345 Head and flow, hydro power basics, 23–24 Helical Gorlov rotors, 265 Highest astronomical tide (HAT), 54 High level tide, 56, 59f High tide, 54 High voltage alternating current (HVAC), 223–224 High voltage direct current (HVDC), 222 HVDC LCC systems, 224–226 HVDC VSC system, 226 HOMER software, 348–350, 383–384 battery bank, modeling of, 194–195, 195t diesel generator, 191–193, 194t load assessment, 191, 193t mathematical modeling, 191, 193f month-wise load calculation of study area, 190–191, 192f

simulation, 190–191 steps of, 190, 190f system architecture, 191, 193t Homogeneous Poisson process, 305 Horizontal axis tidal current turbines, 68–69, 84, 88f Horizontal-axis wind turbines (HAWT), 14–15 Hub stream turbines, 263–264 HVDC. See High voltage direct current (HVDC) Hybrid Optimization Model for Multiple Energy Resources. See HOMER software Hydraulic turbine, 216–218 Hydrodynamic subsystem, 200–204 Hydroelectric plants, 4 Hydroelectric power energy, impact of, 36 Hydro energy system, 23 Hydro power basics, 23–24, 25t Hydroprocessing, 17 Hydrothermal upgrading (HTU), 17 Hydro torrent frameworks, 190

I Impedance relay, 289–290 Imperfect repair process, 305 India, tidal energy system, 44–47 business-scale tidal current power plant, 333–334 government support, 341–343 grid parity, 340 low temperature thermal desalination innovation, 333–334 naturally occurring currents along coastal region, 44–46, 47t stakeholders, marine technology development, 343 state-wise tidal energy potential, 44–46, 49f state-wise tidal range in, 44–46, 47t stream technology, challenges in, 340–341 tidal energy policy, 337–340 tidal power generation Gulf of Khambhat, 334–336, 338f Gulf of Kutch, 336–337, 338f Palk Bay Mannar Channel, 337 wave energy, 333 Induction generators, 221 Infinite-dimensional optimization, 348 Insulation failure/abnormal running conditions, 283 Integer programming, 347 Interest during construction (IDC), 177, 177f

399

400

Index

Internal rate of return (IRR) method, 179–182, 388–389 International Atomic Energy Agency (IAEA), 35–36 International Methodology Development Fund, 376 International Renewable Energy Agency (IRENA), 28–29 Interturn faults, 283–284 Irreversible thermodynamics, 2–3 IRR method. See Internal rate of return (IRR) method

J Jawaharlal Nehru National TIDAL Mission, 332–333 Jelinski-Moranda model, 298 Jiangxia tidal power plant, 42–43, 43t, 45f Joint implementation (JI) system, 372

K Kalpasar Tidal Power Project, 44–46, 333–334 Kelvin harmonic tidal current theory, 132 Kelvin waves, 93 Kislaya Guba tidal power plant, 42–43, 43t, 45f Korteweg’s equation, 210 Kuhn-Tucker conditions, 347 Kyoto Protocol, 369–376

L Laccadive Sea, 337 Lagrange multiplier strategy, 347 Land use change and forestry (LUCF), 375–376 Laplace tidal equations, 93 Laplace transform of equations, 280 Law of conservation of energy, 1–2 L’Hopital’s rule, 312 Lift force rotor (LIFT), 201 Linear oscillating (LIN-OSC) system, 202, 202f Linear programming, 347 Linear (LIN) system, 202, 202f Load stability. See Voltage stability Loss of energy expected (LOEE), 297 Loss of load expected (LOLE), 297 Loss of power supply probability (LPSP), 297 Lowest astronomical tide (LAT), 56 Low level tide, 56, 59f Low-pressure fluid-filled (LPFF), 229

Low-pressure oil-filled (LPOF), 229 Low tide, 54 LPSP. See Loss of power supply probability (LPSP)

M Machine-converter system, 220 Mannar Island, 337 Mareograph. See Tide gauge Marine National Park, 336–337 Markov model, 317–318 Marrakesh Accords, 372–373 MASCARET software, 137, 143f MATLAB, 195–196 Mean high water neaps (MHWN), 54 Mean high water springs (MHWS), 54 Mean low water neaps (MLWN), 56 Mean low water springs (MLWS), 56, 120 Mean sea level (MSL), 56 Mean system downtime, 306 Mean time between failures (MTBF), 297 Mean time to failure (MTTF), 300, 304, 312–313 Metal ores, 5–6 MeyGen tidal energy project, Scotland, 50, 56f Mike 21 software, 128 Mild Slope Equation, 136 MTTF. See Mean time to failure (MTTF)

N Nacelle cabinets, 262 Nacelle cabinets, tidal power distribution, 262 Nash equilibrium, 366 National Institute of Ocean Technology (NIOT), 334–336 National Tidal Mission Plan, 340 Natural gas, 7 Navier-Stokes conditions, 123 Nearshore spectral wave models, 204–205 Net present value (NPV), 179, 386 Noncommercial energy sources, 4–5 Non-governmental organizations (NGOs) CDM project completion process, 374–375 and forests, 375–376 Nonhomogeneous Poisson process, 305 Nonlinear programming, 348 Nonrenewable energy resource electricity generation coal, 7 crude oil/petroleum, 7

Index

fossil fuels, 7 natural gas, 7 nuclear fuels, 8 Nontidal current, 94–95 NPV. See Net present value (NPV) Nuclear fuels, 8 Numerical models, resource assessment, 127

O Offshore substation, 228–230 Oil-impregnated paper (OIP) cables, 230 One-dimensional (1D) resource assessment model, 121–122, 121f Open-center turbines, 69 Optimization technique airfoils, 346 base of, 346–347 big bang big crunch, 357–359 CPSO, 355–357 cuckoo optimization technique, 362–363 enhancement methods, 347 flow chart of, 348, 351f Grasshopper algorithm, 361–362 multivariable capacities, 347 multivariable functions, 347 programming, 347–348 PSO, 350–355, 365f satellite receiving wire, 346 single variable functions, 347 streamlining issues, 346–347 teacher learning-based optimization technique learner phase, 360–361 teacher phase, 360 OR gate function, 321–323 Oscillating water columns (OWCs), 78–79, 82f Oscillating wave surge converters, 74, 76f Overcurrent protection, 288 Overtopping devices, 75, 76f Overvoltage, 283–285 OWCs. See Oscillating water columns (OWCs)

P Parallel system failure rate equations, 311–313 Particle swarm optimization (PSO) advantages, 355 algorithm parameters acceleration coefficients, 353 application, tidal energy systems, 353 iteration numbers, 352

pbest and gbest, selection of, 352 swarm size, 352 velocity-clamping, 353 velocity components, 353 basic variant of, 353, 354t best position, 350–351 disadvantages, 355 flow chart of, 351–354, 365f potential arrangement, 350–351 swarm intelligence principle, 350 velocity updation, 351 weighted function, 351 Performance assessment, constant failure rate model component and event model, 317 contingency enumeration, 318 contingency ranking/selection, 319–320 contingency selection and ranking, 317 PI methods, 318–319 screening methods, 318–319 state enumeration, 318 Permanent magnet generator (PMG), 278–279 Permanent magnet synchronous generator (PMSG), 266–269, 271 Permanent magnet synchronous machine, 221 PERT. See Program evaluation and review technique (PERT) PEX. See Cross-linked polyethylene (XLPE) Phase faults, 283–284 Phase-to-phase faults, 283, 289–290 Photovoltaic (PV) power systems, 11–12 grid-connected centralized photovoltaic systems, 12 grid-connected distributed photovoltaic systems, 12 off-grid domestic photovoltaic systems, 11 off-grid nondomestic photovoltaic systems, 11 Pirotan island, 336–337 Pitch control system, 262–263, 273–274 PMSG. See Permanent magnet synchronous generator (PMSG) Point absorber, 73, 75f Porous disk method, 209 Power capture unit (PCU), 74 Power connector frame (PCF), 74 Power take-off (PTO), 78–79, 202–203, 235 Prefeasibility assessment detailed project report preparation and appraisal factors, 175–177 IDC calculations, 177, 177f

401

402

Index

Prefeasibility assessment (Continued) internal rate of return, 179–182 net present value, 179 physical and demographic features, 175, 176f project management, 175, 177f ROI, 178–179 simple payback period, 178 load center and transportation, distance from, 139 critical path method (see Critical path method (CPM)) PERT, 141–142, 147–148t location assessment, farm method bottom clearance, 161 efficiency measurement, 161 heat rate, 161 hydraulic current, 161 input-output characteristics, 161 maximum rotor diameter, 161 resonant system, 161 TECS, 160 tidal optimal unit, dynamic programming method, 162–168 tidal streaming, 161 top clearance, 161 physical boundary assessments, 153–154 functional physical boundaries, 154–155 geographical boundaries, 149–151 surface boundary conditions, 151–154 technical boundaries, 142–149 types of, 142, 155f resource assessment (see Resource assessment) site assessment, 116–117 asset appraisal, 117 efficient power extraction, conditions for, 120 objectives, 119 provincial evaluation, 117 resource characterization, 119 tidal current generation, potential locations for, 118–121, 118f steps of, 119, 119f types of, 116–117, 116f Pressure wave velocity, 210 Private gatherings, 373–374 Program evaluation and review technique (PERT), 141–142, 147–148t Proportional integration and differentiation (PID) controllers, 263 Proportional integration (P-I) controller, 263 Proximate principle, 350

PSO. See Particle swarm optimization (PSO) PTO. See Power take-off (PTO) Pulse width modulation (PWM) switching, 345

Q Quadratic programming, 348 Quadratized power flow (QPF) model, 319–320 Quality principle, 350

R Radar system, 231–232 Radiation energy, 1–2, 2f Rance tidal power plant, 42–43, 43t, 45f, 49, 55f, 247–248, 251 Rayleigh distribution, 211 Rectilinear tidal currents, 94–95 Regression analysis, 132–135 Reliability assessment model, tidal energy system adequacy, 295 constant failure rate model ALS, 317 boolean algebra and reliability calculation, 327–328 causes, tidal renewable energy system, 323–326 failure and load cases, 322–323t fault-tree analysis, reliability analysis of, 320–323 fault-tree construction and analysis, 327 FLS, 317 intensity function, 313 measurement uncertainties, 316 model uncertainties, 316 performance assessment of, 317–320 probabilistic reliability assessment, 322f SLS, 317 ULS, 316–317 definition, 295–296 direct and indirect acquisition, 295 factors, 295–296 failure distribution model failure density, 298 failure function, probability of, 297 failure rate, 299 Jelinski-Moranda model, 298 mean failure rate, 299 mean time between failures, 301 MTTF, 300 probability density function, 297 reliability engineering, 297

Index

power system reliability, 295 process of, 295, 296f steps of, 295, 296f system adequacy, 295 system security, 295 time-dependent failure mode cause and effect model, 304 counting process, 305–310 cut set, minimal cut sets, 303 K out of n (Koon) tidal turbine, 302 reliability analysis, 313 series system failure rate equations, 310–313 Remotely operated vehicle (ROV), 227–228 Removal units (RMUs), 372 Renewable energy sources electricity generation nonconventional energy sources, 8 power generation, 8 solar water heating systems, 9 technologies, 9–24 transport fuels, 9 environmental aspects of benefits, 33f biomass energy, impact of, 36 electricity supply, 33 environmental pollution, 33–34 geothermal energy, impact of, 35–36 hydroelectric power energy, impact of, 36 life cycle emissions, 33t solar power, impact of, 35 water pollution, 33–34 wind power, impact of, 34–35 Renewal process, 305 Resistance temperature detectors (RTDs), 248 Resource assessment accessible tidal current energy resource, 130–131 bathymetry, 121–122 farm method (see Farm method, location assessment) flux method, tidal power plant annual power theory, 169–170 averaged generation capacity, 169–170 cross-sectional area, 169 maximum steady-state power, 172–173 significant impact factor, 169–170 transmission line, 173–175 vertical energy flux, 171–172 vertical normal modes, 170–171 voltage regulation, 175

methods of, 120, 120f numerical models, 127 one-dimensional models, 121–122, 121f practical tidal current energy resource, 130 regression analysis solar radiation, error calculation of, 133–136, 134t temporal and spatial variability, 134 tidal range and current, 132–133, 134t software ARTEMIS, 136 MASCARET 1-dimensionnal free surface flow modeling, 137, 143f SISYPHE, 137, 139t TELEMAC-2D, 137 static vs. transect field survey, 155–156, 176f floodplain and dynamic channel transects, 156–157 quantitative observations, 157–159 time series, 157 water currents, challenge of, 159–160 technical tidal current energy resource, 129–130 theoretical tidal current energy resource, 128 three-dimensional models, 121–122, 125–127 tidal flow/current, 116–117 tidal-stream resource, quantification of, 132 two-dimensional models, 121–125, 121f types of, 117, 118f, 128, 129f viable tidal current energy resource, 131–132 worldwide high potential areas, 121–122, 126f Return on investment (ROI), 178–179, 386, 388 Reversible thermodynamics, 2–3 Reversing tidal currents, 94–95 Reynold’s number, 201 Rim turbine, 82, 84f ROI. See Return on investment (ROI) Rotational (ROT) system, 202, 202f Rukmavati River, 336–337

S Saint-Venant equations, 123 Savonius rotors, 264–265 Sea flow turbine, 84, 88f Sea streams, 70–71 Sea wave, power associated to, 22 Semidiurnal tidal amplitude, 42–43, 44f Serviceability limit states (SLS), 317 Shaft model, 211–212 Significant impact factor (SIF), 169–170

403

404

Index

Sihwa lake tidal power station, South Korea, 42–43, 43t, 48, 50f Simple payback period (SPP), 178, 386–387 SimPowerSystems library, 267–268 Single-basin double-effect power plant, 64, 66f Single-basin tidal energy system double cycle system, 61 schematic diagrams of, 59–61, 61–62f single-basin single effect plant, operating cycle of, 59–61, 61f single-basin tidal energy barrage schemes, types of, 59–61, 63f single ebb cycle system, 61 single tide cycle system, 61 tidal barrage ebb generation, 61–64, 65f tidal barrage flood generation scheme, 61–63, 64f Single-phase quadratized power flow (SFQPF) model, 318 SISYPHE software, 137, 139t Slack water, 54 Social impacts assessments (SIAs), 380 Solar energy system, 9–12 Solar power, impact of, 35 Solar radiation, 133–136, 134t Solar water heating systems, 9 SPP. See Simple payback period (SPP) Square root method, dependent failure, 305 Stability principle, 350 State of charge (SOC), 194–195 Stochastic programming, 348 Stokes number, 95–97 Strangford Lough seagen, 42–43, 43t, 45f Strouhal number, 96 Subsea cable, 229–230 Subsea-substations, 228–229 Surface boundary conditions bottom boundary conditions, 152 fresh water, 151–152 heat, 151 lateral boundary condition, 152 momentum, 151 open boundary conditions, 152 time, 153 Surge tide, 53–54, 58 Swansea bay tidal lagoon, United Kingdom, 49 Swarm intelligence principle, 350 Swell effect (long-length) tidal, 208 Synchronous machine, 221

T Teacher learning-based optimization technique learner phase, 360–361 teacher phase, 360 TECS. See Tidal energy conversion system (TECS) Telemac-2D analysis, 124–125, 137 TELEMAC-3D model input parameter of, 126, 128f velocity vectors of, 125–126, 126f TELEMAC-MASCARET system, 136–137 Thevenin equivalent, 345 Three-dimensional (3D) resource assessment model, 121–122, 125–127 Three-point estimation method, 140 Thrust force, 123 Tidal barrage ebb generation, 61–64, 65f Tidal barrage flood generation scheme, 61–63, 64f TIDAL basins, 199 Tidal current organization projections for, 41–42 Rayleigh distribution, 211 rectilinear/reversing currents, 94–95 shaft model, 211–212 tidal structure, mathematical function of, 95–97 Weibull distribution, 211 Tidal current turbine angular velocity, 215 hydraulic turbine, mathematical modeling of, 216–218 load frequency control, 276–278 power in tides, 213–215 power output, 212–213 speed governing system, control mechanism of generator-load model, 280–282 governor drive and speed setting, 278–280 turbine model, 280 torque, 215–216 Tidal energy conversion system (TECS) component variations, 196–197 constant failure rate model, reliability assessment chip-based multiwork transfers, 253 electromechanical relays, 253–254 hydrokinetic energy conversion theory, 254–255 microprocessor-based relay, 253–254 protective relay technology, application of, 253 remote communication ability, 254 self-monitoring capability, 254 tidal-dynamic energy assessment, 263–266

Index

tidal turbine control (see Tidal turbine) turbine configuration and control objectives, 266–271 farm method, 160 HOMER software battery bank, modeling of, 194–195, 195t diesel generator, 191–193, 194t load assessment, 191, 193t mathematical modeling, 191, 193f month-wise load calculation of study area, 190–191, 192f simulation, 190–191 steps of, 190, 190f system architecture, 191, 193t modeled processes, 204–207 9MW tidal farm, MATLAB simulation of, 195–196 physical model effects, limitations, 198 TIDAL basins, 199 towing tanks, 197–198 water tunnels, 198–199 Tidal energy system advantages of, 98 CDM (see Clean development mechanism (CDM)) disadvantages of, 98–100 double-basin system, 65–67, 67–68f earth-centric reference frame, 93 earth-moon framework, 41–42 earth-sun framework, 41–42 electrical configurations schemes, 221–226 energy sources (see Energy sources) equilibrium theory of tides, 93 friction loss/head loss due to friction, 210–211 functional requirements, 218–219 Game theory (see Game theory, tidal energy system) global semidiurnal tidal amplitude, 42–43, 44f grid codes, 219 grid-connected marine energy infrastructures, 219–221 grid connection infrastructures cable connectors, 227–228 in offshore locations, 226–227 offshore substation, 228–230 subsea cable, 229–230 in India (see India, tidal energy system) Laplace tidal equations, 93 narrow bays, 94

new technologies, readiness level for, 70–71, 71t nontidal current, 94–95 numerical ocean tidal model, 93 optimization (see Optimization technique) prefeasibility assessment (see Prefeasibility assessment) pressure wave velocity in conduit, 210 single-basin system (see Single-basin tidal energy system) swell effect (long-length) tidal, 208 with tidal barrage, 58, 60f tidal current modeling Rayleigh distribution, 211 shaft model, 211–212 Weibull distribution, 211 tidal current turbine angular velocity, 215 hydraulic turbine, mathematical modeling of, 216–218 power in tides, 213–215 power output, 212–213 torque, 215–216 tidal ebb and flow innovation, 69–70 tidal measurement devices acoustic Doppler profile, 231 radar system, 231–232 tide gauge, 232 wave and tide sensors, 232–234 tidal power plants (see Tidal power plant (TPP)) tidal stream/current innovation, 70–71 tides, types of, 53–56 wide bays, 94 worldwide tidal energy resources, 42–43, 48f TidalFarmer, 234 Tidal generator, electrical protection of backup over current protection, 285–286 distance protection, 289 failure of cooling, 285 loss of excitation, 284 overvoltage, 284–285 phase-to-ground faults, 288–289 phase-to-phase faults, 289–290 possible faults, 283 rotor faults, 284 station bus zone protection, 287 stator faults, 283–284 system frequency swings, 285 thermal protection, tidal power plant, 285 transformer protection, 286

405

406

Index

Tidal generator, electrical protection of (Continued) transmission line protection L-L-G deficiencies, 287 overcurrent protection, 288 phase-to-ground faults, 288–289 two terminal lines, 287–288 unbalanced loading, 284 Tidal lagoon, 86–87 Tidal power generation Gulf of Khambhat, 334–336, 338f Gulf of Kutch, 336–337, 338f Palk Bay Mannar Channel, 337 Tidal power plant (TPP), 100–107 Annapolis tidal power generating station, 42–43, 43t, 45f, 50–51 attenuators, 72 basin scale simulation, 209–210 block diagram of, 348–350, 359f bulge wave technology, 77–78 component of, 83f hydrodynamic subsystem, 80–81 lagoon wall, 87–88 power take-off subsystem, 80–81 reaction and control subsystem, 80–81 tidal lagoon, 86–87 tidal stream generators, 85–86 turbines (see Turbines) country-wise installed capacity of, 42–43, 45–46f CPM (see Critical path method (CPM)) double basin with a paired basin operation, 68, 73f double-basin with linked basin operation, 67–68, 72f DPRs (see Detailed project reports (DPRs), tidal power plant) economic analysis of (see Economic analysis, TPP) energy calculation, estimation of average load, 89 diversity factor, 90 installed capacity, 89 load factor, 89 maximum demand, 89 plant capacity factor, 89–90 single basin tidal project, 91–93 tidal barrages, 90–91 tidal current innovation, 91 utilization factor, 90 energy generation, 208–210 framework of, 199–204, 200f harmonic analysis (see Harmonic analysis, TPP)

help structures, classification of, 69–70 HOMER software battery bank, modeling of, 194–195, 195t diesel generator, 191–193, 194t load assessment, 191, 193t mathematical modeling, 191, 193f month-wise load calculation of study area, 190–191, 192f simulation, 190–191 system architecture, 191, 193t horizontal and vertical axis tidal turbines, 68–69 Jiangxia tidal power plant, 42–43, 43t, 45f Kislaya Guba tidal power plant, 42–43, 43t, 45f La Rance tidal power plant, France, 42–43, 43t, 45f, 49, 55f low and high tide periods, 56–57, 59f MeyGen tidal energy project, Scotland, 50, 56f models of, 206–207t 9MW tidal farm, MATLAB simulation of, 195–196 open-center turbines, 69 oscillating water column, 78–79, 82f oscillating wave surge converters, 74, 76f overtopping/terminator device, 75, 76f PERT, 141–142, 147–148t physical process of, 205, 206t point absorber, 73, 75f principles of, 56–59 reciprocating devices, 69 resource assessment (see Resource assessment) Sihwa lake tidal power station, South Korea, 42–43, 43t, 48, 50f single-basin system (see Single-basin tidal energy system) Strangford Lough seagen, 42–43, 43t, 45f Swansea bay tidal lagoon, United Kingdom, 49 technology used in, 70–71, 71t tidal barrage generation, 58–59 tidal ebb and flow innovation, 69–70 TidalFarmer, 234 tidal flow innovations, 69–70 tidal turbine power plant, 235–238 tides, types of, 53–56 two-basin tidal energy system, 65–67, 67–68f two-way tidal barrage generations limitation, 64–65 single-basin double-effect power plant operating cycle, 64, 66f single basin with reversible turbine, 64, 66f

Index

two-way barrage scheme, operating cycle of, 64–65, 67f Uldolmok tidal power plant, 42–43, 43t, 45f WaveDyn, 234–235 worldwide potential of, 44–46, 48f Tidal range, 41–42, 54 Tidal streams, 52–54, 56, 150–151, 190 Tidal streams generators advantages of, 86 disadvantages of, 86 turbines, types of, 85 Tidal torrent, 58, 190 Tidal turbine control of angle of attack, 256–257 control strategies, 260–263 Nacelle cabinets, 262 power and efficiency, 257–258 power curve, 258–260 transmission system, 255–256 month-wise tidal range of study area, 191, 194f specification of, 191, 193t tidal velocity, 191, 194f Tidal turbine generators (TTGs), 344–345 Tidal velocity, 191, 194f Tide gauge, 232 Time-dependent failure mode cause and effect model, 304 counting process, 305–310 cut set, minimal cut sets, 303 K out of n (Koon) tidal turbine, 302 reliability analysis, 313 series system failure rate equations, 310–313 Tip speed ratio (TSR), 255, 258, 267 Tower base cabinet, 262 Towing tanks, 197–198 TPP. See Tidal power plant (TPP) Transmission coefficient, 204–205 Transmission line, tidal power plant, 173–175 Transport fuels, 9 TSR. See Tip speed ratio (TSR) TTGs. See Tidal turbine generators (TTGs) T-TIDE software, 132 Tubular turbines, 83, 87f Turbines axial turbines, 263–264 bulb turbine, 81, 83f Horizontal axis tidal current turbines, 84, 88f rim turbine, 82, 84f

sea flow turbine, 84, 88f tidal stream generators, 85 tubular turbines, 83, 87f vertical axis tidal current turbines, 85, 92f Two-basin tidal energy system, 65–67, 67–68f Two-dimensional (2D) resource assessment model, 121–125, 121f Two mass models, 211–212 Two-way tidal barrage generations limitation, 64–65 single-basin double-effect power plant operating cycle, 64, 66f single basin with reversible turbine, 64, 66f two-way barrage scheme, operating cycle of, 64–65, 67f

U UCB. See Unit control board (UCB) Uldolmok tidal power plant, 42–43, 43t, 45f Ultimate Limit States (ULS), 316–317 Umbilical termination assembly (UTAs), 227–228 Unit control board (UCB), 247–248, 250 United Nations Framework Convention on Climate Change (UNFCCC), 370 Unity power factor control, 270–271 Urja Global Limited, 342–343 Utility-scale solar system, 35

V Variable-speed fixed-pitch (VS-FP), 262 Variable-speed synchronous machines, 221 Variable-speed variable-pitch (VS-VP) configuration, 262 VAWTs. See Vertical-axis wind turbines (VAWTs) Velocity components cognitive component, 353 inertia component, 353 social component, 353 VENTURI, 202, 202f Vertical axis tidal current turbines, 68–69, 85, 92f, 264 Vertical-axis wind turbines (VAWTs), 15 Voltage stability analysis definition, 282–283 tidal generator, electrical protection of, 283–290 Volt ampere (VA) rating, 270–271 VORTEX, 202

407

408

Index

W Water tunnels, 198–199 Water wheel generators, 284–285 Wave and tide sensor, 232–234 Wave dragon, 75, 76f, 78f, 80f, 142–149 WaveDyn, 234–235 Wave energy, 21–22 Wave energy converter (WEC), 73–77 WBS. See Work breakdown structure (WBS) Weibull distribution, 211 Wells turbine, 79 Whitecapping, 204–205

Wind-Chime enumeration scheme, 319 Wind energy system, 12–15 Wind power, impact of, 34–35 Wind stress, 151 Wind tunnels, 199 Work breakdown structure (WBS), 140

Y Yaw controls, 262

Z Zeigler-Nicholas rules, 263