wind and solar power systems

wind and solar power systems

(Parte 1 de 5)

Mukund R. Patel, Ph.D., P.E.

U.S. Merchant Marine Academy Kings Point, New York


Principal Engineer, General Electric Company Fellow Engineer, Westinghouse Reasearch Center

Wind and Solar Power Systems

Boca Raton London New York Washington, D.C. CRC Press

Library of Congress Cataloging-in-Publication Data

Patel, Mukind R., 1942.


Wind and solar power systems/ Mukund R. Patel.

Includes bibliographical references and index. ISBN 0-8493-1605-7 (alk. paper) 1. Wind power plants.2. Solar power plants.3. Photovoltaic power systems.I. Title. TK1541.P38 1999

This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use.

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© 1999 by CRC Press LLC

…dedicated to my mother, Shakariba, who practiced ingenuity, and to my children, Ketan, Bina, and Vijal, who flattered me by being engineers.

(Cover photo: Baix Ebre wind farm in Catalonia. With permission from Institut Catalia d’Energia, Spain.)

© 1999 by CRC Press LLC


The total electricity demand in 1997 in the United States of America was three trillion kWh, with the market value of $210 billion. The worldwide demand was 12 trillion kWh in 1997, and is projected to reach 19 trillion kWh in 2015. This constitutes the worldwide average annual growth of 2.6 percent. The growth rate in the developing countries is projected to be approximately 5 percent, almost twice the world average.

Most of the present demand in the world is met by fossil and nuclear power plants. A small part is met by renewable energy technologies, such as the wind, solar, biomass, geothermal and the ocean. Among the renewable power sources, wind and solar have experienced a remarkably rapid growth in the past 10 years. Both are pollution free sources of abundant power. Additionally, they generate power near the load centers, hence eliminate the need of running high voltage transmission lines through rural and urban landscapes.

Since the early 1980s, the wind technology capital costs have declined by 80 percent, operation and maintenance costs have dropped by 80 percent and availability factors of grid-connected plants have risen to 95 percent. These factors have jointly contributed to the decline of the wind electricity cost by 70 percent to 5 to 7 cents per kWh. The grid-connected wind plant can generate electricity at cost under 5 cents per kWh. The goal of ongoing research programs funded by the U.S. Department of Energy and the National Renewable Energy Laboratory is to bring the wind power cost below 4 cents per kWh by the year 2000. This cost is highly competitive with the energy cost of the conventional power technologies. For these reasons, wind power plants are now supplying economical clean power in many parts of the world.

In the U.S.A., several research partners of the NREL are negotiating with

U.S. electrical utilities to install additional 4,200 MW of wind capacity with capital investment of about $2 billion during the next several years. This amounts to the capital cost of $476 per kW, which is comparable with the conventional power plant costs. A recent study by the Electric Power Research Institute projected that by the year 2005, wind will produce the cheapest electricity available from any source. The EPRI estimates that the wind energy can grow from less than 1 percent in 1997 to as much as 10 percent of this country’s electrical energy demand by 2020.

On the other hand, the cost of solar photovoltaic electricity is still high in the neighborhood of 15 to 25 cents per kWh. With the consumer cost of electrical utility power ranging from 10 to 15 cents per kWh nationwide, photovoltaics cannot economically compete directly with the utility power as yet, except in remote markets where the utility power is not available and

© 1999 by CRC Press LLC the transmission line costs would be prohibitive. Many developing countries have large areas falling in this category. With ongoing research in the photovoltaic (pv) technologies around the world, the pv energy cost is expected to fall to 12 to 15 cents per kWh or less in the next several years as the learning curves and the economy of scale come into play. The research programs funded by DOE/NREL have the goal of bringing down the pv energy cost below 12 cents per kWh by 2000.

After the restructuring of the U.S. electrical utilities, as mandated by the

Energy Policy Act (EPAct) of 1992, the industry leaders expect the power generation business, both conventional and renewable, to become more profitable in the long run. The reasoning is that the generation business will be stripped of regulated price and opened to competition among electricity producers and resellers. The transmission and distribution business, on the other hand, would still be regulated. The American experience indicates that the free business generates more profits than the regulated business. Such is the experience in the U.K. and Chile, where the electrical power industry had been structured similar to the EPAct of 1992 in the U.S.A.

As for the wind and pv electricity producers, they can now sell power freely to the end users through truly open access to the transmission lines. For this reason, they are likely to benefit as much as other producers of electricity. Another benefit in their favor is that the cost of the renewable energy would be falling as the technology advances, whereas the cost of the electricity from the conventional power plants would rise with inflation. The difference in their trends would make the wind and pv power even more advantageous in the future.

© 1999 by CRC Press LLC

About the Author

Mukund R. Patel, Ph.D, P.E. , is an experienced research engineer with

35 years of hands-on involvement in designing and developing state-of-theart electrical power equipment and systems. He has served as principal power system engineer at the General Electric Company in Valley Forge, fellow engineer at the Westinghouse Research & Development Center in Pittsburgh, senior staff engineer at Lockheed Martin Corporation in Princeton, development manager at Bharat Bijlee Limited, Bombay, and 3M distinguished visiting professor of electrical power technologies at the University of Minnesota, Duluth. Presently he is a professor at the U.S. Merchant Marine Academy in Kings Point, New York.

Dr. Patel obtained his Ph.D. degree in electric power engineering from the

Rensselaer Polytechnic Institute, Troy, New York; M.S. in engineering management from the University of Pittsburgh; M.E. in electrical machine design from Gujarat University and B.E.E. from Sardar University, India. He is a fellow of the Institution of Mechanical Engineers (U.K.), senior member of the IEEE, registered professional engineer in Pennsylvania, and a member of Eta Kappa Nu, Tau Beta Pi, Sigma Xi and Omega Rho.

Dr. Patel has presented and published over 30 papers at national and international conferences, holds several patents, and has earned NASA recognition for exceptional contribution to the photovoltaic power system design for UARS. He is active in consulting and teaching short courses to professional engineers in the electrical power industry.

© 1999 by CRC Press LLC

About the Book

The book was conceived when I was invited to teach a course in the emerging electrical power technologies at the University of Minnesota in Duluth. The lecture notes and presentation charts I prepared for the course formed the first draft of the book. The subsequent teaching of a couple of short courses to professional engineers advanced the draft closer to the finished book. The book is designed and tested to serve as textbook for a semester course for university seniors in electrical and mechanical engineering fields. The practicing engineers will get detailed treatment of this rapidly growing segment of the power industry. The government policy makers would benefit by overview of the material covered in the book.

Chapters 1 through 3 cover the present status and the ongoing research programs in the renewable power around the world and in the U.S.A. Chapter 4 is a detailed coverage on the wind power fundamentals and the probability distributions of the wind speed and the annual energy potential of a site. It includes the wind speed and energy maps of several countries. Chapter 5 covers the wind power system operation and the control requirements. Since most wind plants use induction generators for converting the turbine power into electrical power, the theory of the induction machine performance and operation is reviewed in Chapter 6 without going into details. The details are left for the classical books on the subject. The electrical generator speed control for capturing the maximum energy under wind fluctuations over the year is presented in Chapter 7.

The power-generating characteristics of the photovoltaic cell, the array design, and the sun-tracking methods for the maximum power generation are discussed in Chapter 8. The basic features of the utility-scale solar thermal power plant using concentrating heliostats and molten salt steam turbine are presented in Chapter 9.

The stand-alone renewable power plant invariably needs energy storage for high load availability. Chapter 10 covers characteristics of various batteries, their design methods using the energy balance analysis, factors influencing their operation, and the battery management methods. The energy density and the life and operating cost per kWh delivered are presented for various batteries, such as lead-acid, nickel-cadmium, nickel-metal-hydride and lithium-ion. The energy storage by the flywheel, compressed air and the superconducting coil, and their advantages over the batteries are reviewed. The basic theory and operation of the power electronic converters and inverters used in the wind and solar power systems are presented in Chapter 1, leaving details for excellent books available on the subject.

© 1999 by CRC Press LLC

The more than two billion people in the world not yet connected to the utility grid are the largest potential market of stand-alone power systems. Chapter 12 presents the design and operating methods of such power systems using wind and photovoltaic systems in hybrid with diesel generators. The newly developed fuel cell with potential of replacing diesel engine in urban areas is discussed. The grid-connected renewable power systems are covered in Chapter 13, with voltage and frequency control methods needed for synchronizing the generator with the grid. The theory and the operating characteristics of the interconnecting transmission line, the voltage regulation, the maximum power transfer capability, and the static and dynamic stability are covered.

Chapter 14 is about the overall electrical system design. The method of designing the system components to operate at their maximum possible efficiency is developed. The static and dynamic bus performance, the harmonics, and the increasingly important quality of power issues applicable to the renewable power systems are presented.

Chapter 15 discusses the total plant economy and the costing of energy delivered to the paying customers. It also shows the importance of a sensitivity analysis to raise confidence level of the investors. The profitability charts are presented for preliminary screening of potential sites. Finally, Chapter 16 discusses the past and present trends and the future of the green power. It presents the declining price model based on the learning curve, and the Fisher-Pry substitution model for predicting the market growth of the wind and pv power based on historical data on similar technologies. The effect of the utility restructuring, mandated by the EPAct of 1992, and its expected benefits on the renewable power producers are discussed.

At the end, the book gives numerous references for further reading, and name and addresses of government agencies, universities, and manufacturers active in the renewable power around the world.

© 1999 by CRC Press LLC


The book of this nature on emerging technologies, such as the wind and photovoltaic power systems, cannot possibly be written without the help from many sources. I have been extremely fortunate to receive full support from many organizations and individuals in the field. They not only encouraged me to write the book on this timely subject, but also provided valuable suggestions and comments during the development of the book.

Dr. Nazmi Shehadeh , head of the Electrical and Computer Engineering

Department at the University of Minnesota, Duluth, gave me the opportunity to develop and teach this subject to his students who were enthusiastic about learning new technologies. Dr. Elliott Bayly , president of the World Power

Technologies in Duluth, shared with me and my students his long experience in the field. He helped me develop the course outline, which later became the book outline. Dr. Jean Posbic of Solarex Corporation in Frederick, Mary- land and Mr. Carl-Erik Olsen of Nordtank Energy Group/NEG Micon,

Denmark, kindly reviewed the draft and provided valuable suggestions for improvement. Mr. Bernard Chabot of ADEME, Valbonne, France, provided the profitability charts for screening the wind and photovoltaic power sites.

Mr. Ian Baring-Gould of the National Renewable Energy Laboratory,

Golden, Colorado, has been a source of useful information and the hybrid power plant simulation model.

Several institutions worldwide provided current data and reports on these rather rapidly developing technologies. They are the American Wind Energy

Association , the American Solar Energy Society , the European Wind

Energy Association , the Risø National Laboratory , Denmark, the Tata

Energy Research Institute , India, and many corporations engaged in the wind and solar power technologies. Many individuals at these organizations gladly provided help I requested. I gratefully acknowledge the generous support from all of you.

(Parte 1 de 5)