Renewable Energy, Second Edition A First Course
Robert Ehrlich Harold A. Geller
CRC Press
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Library of Congress Cataloging-in-Publication Data
Names: Ehrlich, Robert, 1938- author. | Geller, Harold, 1954- author.
Title: Renewable energy : a first course / Robert Ehrlich, Harold A. Geller.
Description: Second edition. | Boca Raton : Taylor & Francis, CRC Press, 2017. | Includes bibliographical references and index.
Identifiers: LCCN 2017018670| ISBN 9781498736954 (pbk. : alk. paper) | ISBN 9781138297388 (hardback : alk. paper)
Subjects: LCSH: Renewable energy sources.
Classification: LCC TJ808 .E34 2017 | DDC 333.79/4--dc23
LC record available at https://lccn.loc.gov/2017018670
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2.2.8.5 Impacts on the Land 45
2.2.9 Carbon Sequestration and “Clean” Coal 46
2.3 Petroleum and Natural Gas 48
2.3.1 History of Petroleum Use 48
2.3.2 Resource Base of Oil and Gas 49
2.3.3 Formation and Location of Oil and Gas 50
2.3.4 Are Coal, Oil, and Gas Really Fossil Fuels? 51
2.3.5 Peak Oil 53
2.3.5.1 Example 4: How Many Years Are Left? 55
2.3.6 Petroleum and Natural Gas
2.3.6.1 Extraction of Oil and Gas
2.3.6.2 Refining of Gas and Oil 56
2.3.7 Gas and Oil Power Plants 57
2.3.7.1 Example 5: A Binary Cycle Plant 58
2.3.8 Environmental Impacts of Oil and Gas 59 2.4
3.1
3.3 Discovery of the Atomic Nucleus
3.4 Mathematical Details of the Rutherford Scattering Experiment
3.4.1 Example 1: Setting an Upper Limit to the Nuclear
3.5 Composition and Structure of the Atom and Its Nucleus
4.8 Reactor Accidents 111
4.8.1 Fukushima 111
4.8.2 Chernobyl 112
4.8.2.1 Causes of Chernobyl 113
4.8.3 Reactor Accidents: Three Mile Island 115
4.9 Front End of the Fuel Cycle: Obtaining the Raw Material 116
4.10 Back End of the Fuel Cycle: Nuclear Waste 117
4.10.1 Shipping Nuclear Waste 119
4.11 Economics of Large-Scale Nuclear Power 120
4.12 Small Modular Reactors 123
4.13 Nuclear Fusion Reactors 126
4.14 Summary 128 Problems 128 References 131
5 Biofuels 133
5.1 Introduction 133
5.2 Photosynthesis 135
5.2.1 Example 1: Efficiency of Photosynthesis 137
5.2.2 Example 2: Best Wavelengths of Light for Photosynthesis 138
5.3 Biofuel Classifications 139
5.3.1 Choice of Feedstock for Biofuels 139
5.3.2 Biofuel Production Processes 143
5.3.3 Example 3: Loss of Energy When Combustible Material Is Moist 145
5.3.4 Generation of Biofuels 146
5.4 Other Uses of Biofuels and Social–Environmental Impacts 147
5.4.1 Biofuels from Wastes and Residues 147
5.4.2 Agricultural Wastes 148
5.4.3 Central Role of Agriculture in a Sustainable Future 149
5.4.4 Vertical Farming 150
5.5 Artificial Photosynthesis 151
5.6 Summary 151 Problems 152 References 154
6.1 Introduction 157 6.1.1 History and Growth of Usage 157
6.1.2 Geographic Distribution 157
6.1.3 Sources of the Earth’s Thermal Energy 158
6.1.4 Comparison with Other Energy Sources 159
6.2 Geophysics of the Earth’s Interior 160
6.3 Thermal Gradient 160
6.4 Characterization and Relative Abundance of the Resource 163
6.4.1 Impact of the Thermal Gradient 163
6.4.2 Example 1: Relative Energy Content for Two Gradients 164
6.4.3 Questioning Our Assumptions 164
6.4.4 Other Geologic Factors Affecting the Amount of the Resource 166
6.4.5 Hot Dry Rock Formations 166 6.5 Geothermal Electricity Power Plants 168
6.5.1 Example 2: Efficiency of a Geothermal Power Plant 169
6.6 Residential and Commercial Geothermal Heating 169
6.6.1 Economics of Residential Geothermal Power 171
6.7 Sustainability of Geothermal Power 172
6.7.1 Depletion of a Geothermal Field 172
6.7.2 Example 3: Lengthening the Lifetime 173
6.7.3 Example 4: A 100 MW Power Plant 174
6.8 Environmental Impacts 174
6.8.1 Released Gases 174
6.8.2 Impact on Land and Freshwater 175
6.8.3 Do Heat Pumps Cut Down on CO2 Emissions? 176
6.9 Economics of Geothermal Electricity 176
6.9.1 Drilling Costs 176
6.9.2 Beating the Exponential? 177
6.9.3 Why the Exponential Dependence of Cost on Well Depth? 178
6.9.4 Is Spallation Drilling the Answer? 178
6.9.5 Why Spallation Drilling Cost Might Be a Linear Function of Depth 179
6.10 Summary 180 Problems 181 References 183
7 Wind Power 185
7.1 Introduction and Historical Uses 185
7.2 Wind Characteristics and Resources 187
7.2.1 v-Cubed Dependence of Power on Wind Speed 189
7.2.2 Wind Speed Distributions 190
7.2.3 Wind Speed as a Function of Height 193
7.2.4 Example 1: Turbine Power versus Height 194
7.3 Power Transfer to a Turbine 195
7.4 Turbine Types and Terms 197
7.4.1 Lift and Drag Forces and the Tip–Speed Ratio 197
7.4.2 Example 2: The Cup Anemometer 199
7.4.3 Horizontal versus Vertical Axis Turbines 199
7.4.4 Number of Turbine Blades, and Solidity 201
7.4.5 Variable and Fixed Rotation Rate Turbines 203
7.5 Controlling and Optimizing Wind Turbine Performance 204
7.5.1 Example 3: Turbine Power and Typical Blade Diameter 205
7.5.2 Maximizing Power below the Rated Wind Speed 206
7.5.3 Limiting Power above the Rated Wind Speed 207
7.6 Electrical Aspects and Grid Integration 208
7.6.1 Asynchronous Generator 209
7.7 Small Wind 212
7.7.1 Example 4: Comparing Two Turbines 213
7.8 Offshore Wind 213
7.9 Environmental Impacts 214
7.10 Unusual Designs and Applications
7.10.1 Airborne Turbines
8.1 Introduction to Hydropower
8.1.1 Advantages of Hydropower
8.1.4 Design Criteria for Optimum Performance
8.1.5 Example 1: Designing a Pelton Turbine 227 8.1.6 Reaction Turbines
Turbine Speed and Turbine Selection
8.2 Wave, Tidal, and Ocean Thermal Power Resources
8.2.1 Wave Motion and Wave Energy and Power
2: Power of a Wave
8.2.3 Devices for Capturing Wave Power
8.3 Introduction to Tidal Power and the Cause of Tides 239 8.3.1 Tidal Current Power
8.3.2 Impoundment (Barrage) Tidal Power
8.3.3 Dynamic Tidal Power
8.4 Ocean Thermal Energy Conversion
8.5 Social and Environmental Impacts of Hydropower
9
Solar Radiation and Earth’s Climate 249
9.1 Introduction 249
9.2 Electromagnetic Radiation 250
9.3 Types of Spectra 251
9.3.1 Blackbody Spectrum 251
9.4 Apparent Motion of the Sun in the Sky 254
9.4.1 Example 1: Finding the Solar Declination 257
9.5 Availability of Solar Radiation on Earth 258
9.5.1 Example 2: Finding the Number of Daylight Hours 258
9.6 Optimum Collector Orientation and Tilt 260
9.7 Greenhouse Effect 261
9.7.1 Expected Average Surface Temperature of the Planet 261
9.7.2 Natural Greenhouse Effect 262
9.7.3 Climate Change Feedbacks 264
9.7.3.1 Positive Feedbacks 265
9.7.3.2 Negative Feedbacks 266
9.7.4 Four Greenhouse Gases 266
9.7.5 Global Temperature Variation and Its Causes 268
9.7.6 Climate Projections for the Coming Century 269
9.7.7 Tipping Points in the Climate System 271
9.7.8 Categories of Positions in the Global Warming Debate 272
9.7.9 Arguments of Global Warming Skeptics and Deniers 273
9.8 Summary
10.2 Solar Water-Heating Systems 282
10.3 Flat-Plate Collectors
A
10.6 Thermal Losses in Pipes
10.6.1 Example 2: Thermal Loss in a Pipe
Water Tanks and Thermal Capacitance
10.7.1 Example 3: Insulating a Hot Water Tank to Reduce Thermal Losses
Passive Solar Hot Water System
10.8.1 Example 4: Finding the Fluid Flow Rate in a Thermosiphon Hot
Increasing the Conductivity of Semiconductors through Doping
Example 2: Effect of Doping on Conductivity
11.4 pn Junction 323
11.5 Generic Photovoltaic Cell 325
11.6 Electrical Properties of a Solar Cell 326
11.7 Efficiency of Solar Cells and Solar Systems 327
11.7.1 Fill Factor 327
11.7.2 Temperature Dependence of Efficiency 328
11.7.2.1 Example 3: Impact of Temperature on Efficiency and Power Output 328
11.7.3 Spectral Efficiency and Choice of Materials 328
11.7.4 Efficiency of Multijunction Cells 330
11.8 Efficiency of Solar Systems 331
11.9 Grid Connection and Inverters 331
11.10 Other Types of Solar Cells 332
11.10.1 Thin Films 332
11.10.2 Dye-Sensitized Cells 333
11.11 Environmental Issues 334
11.12 Summary 334 Appendix: Basic Quantum Mechanics and the Formation of Energy Bands 334
11.A.1 Finding Energy Levels and Wave Functions 335
11.A.2 Coupled Systems and Formation of Energy Bands 337 Problems 339 References 340
Energy Conservation and Efficiency 341
12.1 Introduction 341
12.1.1 Example 1: What Went Wrong? 344
12.2 Factors Besides Efficiency Influencing Energy-Related Choices 345
12.2.1 Biking to Work 345
12.2.2 More Efficient Solar Collectors 346
12.3 Lowest of the Low-Hanging Fruit 347
12.3.1 Residential Sector 347
12.3.2
12.3.3 Example 2: Lighting Cost
Thermoelectric Effect: Another Way to Use Cogeneration
Conservation and Efficiency in Transportation
Thermoelectric
12.3.7.2 Example 3: What Efficiency of a Thermoelectric Generator Is Needed?
12.3.7.3 Regenerative Brakes and Shock Absorbers
12.3.7.5 Lighter and Smaller Vehicles
12.3.7.6 Alternate Fuels
12.3.7.7 Alternatives to the Internal Combustion Engine
12.3.7.8 Using Automobiles and Trucks Less or Using Them More Efficiently
Is Energy Efficiency and Conservation Ultimately Futile?
13 Energy Storage and Transmission 369
13.1 Energy Storage 369
13.1.1 Introduction 369
13.1.2 Mechanical and Thermal Energy Storage 371
13.1.2.1 Pumped Hydro 372
13.1.2.2 Thermal Storage 373
13.1.2.3 Compressed Air Energy Storage 373
13.1.2.4 Flywheel Energy Storage 376
13.1.3 Electric and Magnetic Energy Storage 381
13.1.3.1 Batteries 381
13.1.3.2 Ultracapacitors 386
13.1.3.3 Fuel Cells 389
13.1.4 Hydrogen Storage and Cars Powered by It 390
13.1.5 Battery-Powered Electric Cars 393
13.1.6 Magnetic Storage 394
13.1.7 Nuclear Batteries 395
13.1.8 Antimatter 396
13.1.9 Summary 396
13.2 Energy Transmission 397
13.2.1 Introduction 397
13.2.1.1 Electricity Transmission 397
13.2.1.2 Alternating Current Transmission and Distribution 398
13.2.1.3 Alternating vs. Direct Current 399
13.2.1.4 High-Voltage Transmission Lines 401
13.2.1.5 Skin Effect 402
13.2.1.6 Direct Current Power Transmission 403
13.2.1.7 Example 6: Power Losses with HighVoltage AC and HVDC
15
How Important Are International Agreements?
What Are the Top Three GHG Emitters Doing?
14.2.3 United States
14.3 How Much Time Does the World Have to Move Away from Fossil Fuels?
Introduction
1.1 WHY ANOTHER BOOK ON ENERGY?
The idea for this book arose as a result of one of the author’s first time teaching a course on renewable energy. The course was not Energy 101, but it was intended for students who had completed an introductory physics sequence and taken a few courses in calculus. Most available books were either too elementary or too advanced, and the handful of books at the right level seemed too focused on technicalities that obscured the basic ideas. In addition, many of those texts lacked the desired informal writing style, with even some occasional touches of humor that can enhance readability. Moreover, any course focused on renewable energy must also cover nonrenewable energy (fossil fuels and nuclear, specifically), because only then could useful contrasts be drawn. Renewable energy is a multidisciplinary subject that goes well beyond physics, although it is fair to say that this book has a physics orientation. Physicists do have a certain way of looking at the world that is different from other scientists and from engineers. They want to understand how things work and strip things down to their fundamentals. It is no accident that many new technologies, from the laser, to the computed tomography scanner, to the atomic bomb, were invented and developed by physicists, while their refinement is often done by engineers.
1.2 WHY IS ENERGY SO IMPORTANT TO SOCIETY?
Those of us who are fortunate to live in the developed world often take for granted the availability of abundant sources of energy, and we do not fully appreciate the difficult life faced by half of the population of the world, who substitute their own labor or that of domestic animals for the machines and devices that are so common in the developed world. A brief taste of what life is like without access to abundant energy sources is provided at those times when the power goes out. But while survival during such brief interludes may not be in question (except in special circumstances), try to imagine what life would be like if the power were to go out for a period of, say, 6 months. Not having cell phones, television, Internet, or radio might be the least of your problems, especially if the extended power failure occurred during a cold winter when food was not available, and your “taking up farming” was a complete joke, even if you had the knowledge, tools, and land to do so. As much as some of us might imagine the pleasures of a simple preindustrial lifestyle without all the trappings of our high-technology society, the reality would likely be quite different if we were suddenly plunged into a world without electricity. It is likely that a large fraction of the population would not survive 6 months. The idea of a prolonged failure of the power grid in many nations simultaneously is not just some outlandish science
prospect and could occur as a result of a large solar flare directed at the planet. The last one that was large enough to pose a threat of catastrophic damage was apparently the Carrington event, which occurred in 1859 before our electrified civilization existed, but it did cause telegraph systems all over North America and Europe to fail.
1.3 EXACTLY WHAT IS ENERGY?
In elementary school, many of us learned that “energy is the ability to do work” and that “it cannot be created or destroyed” (conservation of energy). But these memorized and parroted phrases are not always easy to apply to real situations. For example, suppose you had a hand-cranked or pedal-driven electric generator that was connected to a light bulb. Do you think it would be just as hard to turn the generator if the light bulb were unscrewed from its socket or replaced by one of lower wattage? Most people (even some engineering students) who were asked this question answer yes and are often surprised to find on doing the experiment that the answer is no—the generator is easier to turn with the bulb removed or replaced by one of lower wattage. This of course must be the case by conservation of energy, since it is the mechanical energy of your turning the crank that is being converted into electrical energy, which is absent when the light bulb is unscrewed. Were the handle on the generator just as easy to turn regardless of whether a bulb is being lit or how brightly it glows, then it would be just as easy for a generator to supply electric power to a city of a million people as one having only a thousand! Incidentally, you can probably forget about supplying all your own power by using a pedal-powered generator, since even an avid cyclist would be able to supply at most only a few percent of what the average American consumes.
Aside from misunderstanding what the law of energy conservation implies about specific situations, there are also some interesting and subtle complexities to the law itself. Richard Feynman was one of the great physicists of the twentieth century who made many important discoveries, including the field of quantum electrodynamics, which he coinvented with Julian Schwinger. Feynman was both a very colorful person and a gifted teacher, who came up with novel ways to look at the world. He understood that the concept of energy and its conservation was more complex and abstract than many other physical quantities such as electric charge where the conservation law involves a single number—the net amount of charge. With energy, however, we have the problem that it comes in a wide variety of forms, including kinetic, potential, heat, light, electrical, magnetic, and nuclear, which can be converted into one another. To keep track of the net amount of energy and to recognize that it is conserved involve some more complicated “bookkeeping,” for example, knowing how many units of heat energy (calories) are equivalent to how many units of mechanical energy (joules).
HOW MANY JOULES IS EQUAL TO 1 CALORIE?
The calorie is the amount of heat needed to raise 1 g of water by 1°C. But since this amount slightly depends on temperature, one sometimes sees slightly different values quoted for the conversion factor commonly taken to be 4.1868 J/cal.
In presenting the concept of energy and the law of its conservation, Feynman made up a story of a little boy playing with 28 indestructible blocks (Feynman, 1985). Each day, the boy’s mother returns home and sees that there are in fact 28 blocks, until one day, she notices that only 27 are present. The observant mother notices one block lying in the backyard and realizes that her son must have thrown it out the window. Clearly, the number of blocks (like energy) is “conserved” only in a closed system, in which no blocks or energy enters or leaves. In the future, she is more careful not to leave the window open. Another day when the mother returns, she finds that only 25 blocks are present, and she concludes that the missing three blocks must be hidden somewhere—but where?
The boy seeking to make his mother’s task harder does not allow her to open a box in which blocks might be hidden. However, the clever mother finds that when she weighs the box, it is heavier than it was when empty by exactly three times the weight of one block, and she draws the obvious conclusion. The game between the mother and the child continues day after day, with the child finding more ingenious places to hide the blocks. One day, for example, he hides several under the dirty water in the sink, but the mother notices that the level of the water has risen by an amount equivalent to the volume of two blocks. Notice that the mother never sees any hidden blocks, but can infer how many are hidden in different places by making careful observations, and now that the windows are closed, she always finds the total number to be conserved. If the mother is so inclined, she might write her finding in terms of the equation for the “conservation of blocks”:
Number of visible blocks number hidden in box n + + u umber hidden in sink 28, +… =
where each of the numbers of hidden blocks had to be inferred from careful measurements, and the three dots suggest any number of other possible hiding places.
Energy conservation is similar to the story with the blocks in that when you take into account all the forms of energy (all the block hiding places), the total amount works out to be a constant. But remember that in order to conclude that the number of blocks was conserved, the mother needed to know exactly how much excess weight in the box, how much rise in dishwater level, etc., corresponded to one block. Exactly the same applies 1.3 Exactly What Is Energy? 3
Chapter 1 – Introduction
to energy conservation. If we want to see if energy is conserved in some process involving motion and heat, we need to know exactly how many units of heat (calories) are equivalent to each unit of mechanical energy (joules). In fact, this was how the self-taught physicist James Prescott Joule proved that heat was a form of energy. Should we ever find a physical situation in which energy appears not to be conserved, there are only four possible conclusions. See if you can figure out what they are before reading any further.
1.4 MIGHT THERE BE SOME NEW FORMS OF ENERGY NOT YET KNOWN?
Feynman’s story of the boy and his blocks is an appropriate analogy to humanity’s discovery of new forms of energy that are often well hidden and found only when energy conservation seems to be violated. A century ago, for example, who would have dreamed that vast stores of energy exist inside the nucleus of all atoms and might actually be released? Even after the discovery of the atomic nucleus, three decades elapsed before scientists realized that the vast energy the nucleus contained might be harnessed. Finding a new form of energy is of course an exceptionally rare event, and the last time it occurred was in fact with nuclear energy.
It remains conceivable that there exists some as-yet undiscovered forms of energy, but all existing claims for it are unconvincing. The likelihood is that in any situation where energy seems not to be conserved, either the system is not closed or else we simply have not accounted for all the known forms of energy properly. Likewise, those who believe in energy fields surrounding the human body that are not detectable by instruments, but which can be manipulated by skilled hand-waving “therapeutic touch” practitioners, are deluding themselves. The idea that living organisms operate based on special energy fields different from the normal electromagnetic fields measureable by instruments is essentially the discredited nineteenth-century belief known as “vitalism.” This theory holds that there exists some type of energy innate in living structures or a vital force peculiar to life itself.
FOUR POSSIBLE CONCLUSIONS IF ENERGY APPEARS NOT TO BE CONSERVED
• We are not dealing with a closed system—energy in one form or another is entering or leaving the system.
• Energy stays within the system but is in some form we neglected to consider (possibly because we did not know that it existed).
• We have made an error in our measurements.
• We have discovered an example of the violation of the law of conservation of energy.
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