Integration of Renewable Sources of Energy

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3 Integration of Renewable Sources of Energy

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5 Integration of Renewable Sources of Energy Felix A. Farret M. Godoy Simões Second Edition

6 This edition first published John Wiley & Sons, Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at The right of Felix A. Farret and M. Godoy Simões to be identified as the author(s) of this work has been asserted in accordance with law. Registered Office John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA Editorial Office 111 River Street, Hoboken, NJ 07030, USA For details of our global editorial offices, customer services, and more information about Wiley products visit us at Wiley also publishes its books in a variety of electronic formats and by print on demand. Some content that appears in standard print versions of this book may not be available in other formats. Limit of Liability/Disclaimer of Warranty The publisher and the authors make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties; including without limitation any implied warranties of fitness for a particular purpose. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for every situation. In view of on going research, equipment modifications, changes in governmental regulations, and the constant flow of information relating to the use of experimental reagents, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert or instructions for each chemical, piece of equipment, reagent, or device for, among other things, any changes in the instructions or indication of usage and for added warnings and precautions. The fact that an organization or website is referred to in this work as a citation and/or potential source of further information does not mean that the author or the publisher endorses the information the organization or website may provide or recommendations it may make. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this works was written and when it is read. No warranty may be created or extended by any promotional statements for this work. Neither the publisher nor the author shall be liable for any damages arising here from. Library of Congress Cataloguing in Publication Data Names: Farret, Felix A., author. Simões, M. Godoy, author. Title: Integration of renewable sources of energy / Felix A Farret, M. Godoy Simões. Other titles: Integration of alternative sources of energy Description: 2nd edition. Hoboken, NJ : John Wiley & Sons, Inc., Revised edition of: Integration of alternative sources of energy / Felix A. Farret, M. Godoy Simões. Includes bibliographical references and index. Identifiers: LCCN (print) LCCN (ebook) ISBN (cloth) ISBN (pdf) ISBN (epub) Subjects: LCSH: Power resources. Renewable energy sources. Classification: LCC TJ163.2.F (print) LCC TJ163.2 (ebook) DDC dc23 LC record available at Cover image: Floriana/Gettyimages Cover design by Wiley Set in 10/12pt Warnock by SPi Global, Pondicherry, India Printed in the United States of America

7 To my children Matheus,Angelica, Patrick, and Samara, parts of my life and my knowledge - FAF To Ahriel, Lira, Rafael, Luiz, and Deborah, all with love and deep happiness to be my family. - MGS

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9 vii Contents Foreword for the First Edition xix Foreword for the Second Edition xxi Preface for the First Edition xxiii Preface for the Second Edition xxvii Acknowledgements xxxi 1 Alternative Sources of Energy Introduction Renewable Sources of Energy Renewable Energy versus Alternative Energy Planning and Development of Integrated Energy Grid Supplied Electricity Load Distributed Generation Renewable Energy Economics Calculation of Electricity Generation Costs Existing Plants New Plants Investment Costs Capital Recovery Factor European Targets for Renewable Powers Demand Side Management Options Supply Side Management Options Integrating Renewable Energy Sources Integration of Renewable Energy in the United States Energy Recovery Time Sustainability Modern Electronic Controls for Power Systems Issues Related to Alternative Sources of Energy 31 References 35

10 viii Contents 2 Principles of Thermodynamics Introduction State of a Thermodynamic System Heating Value First and Second Laws of Thermodynamics and Thermal Efficiency Fundamental Laws and Principles Example of Efficiency in a Power Plant Practical Problems Associated with Carnot Cycle Plant Rankine Cycle for Power Plants Brayton Cycle for Power Plants Geothermal Energy Kalina Cycle Energy, Power, and System Balance Examples of Energy Balance Simple Residential Energy Balance Refrigerator Energy Balance Energy Balance for a Water Heater Rock Bed Energy Balance Array of Solar Collectors Heat Pump Heat Transfer Analysis Simple Steam Power Turbine Analysis Planet Earth: A Closed But Not Isolated System 77 References 79 3 Hydroelectric Power Plants Introduction Determination of the Available Power Expedient Topographical and Hydrological Measurements Simple Measurement of Elevation Global Positioning Systems for Elevation Measurement Pipe Losses Expedient Measurements of Stream Water Flow Measurement Using a Float Measurement Using a Rectangular Spillway Measurement Using a Triangular Spillway Measurement Based on the Dilution of Salt in the Water Civil Works Hydropower Generator Set Regulation Systems Butterfly Valves Waterwheels 93

11 Contents ix 3.6 Turbines Pelton Turbine Francis Turbine Michell Banki Turbine Kaplan or Hydraulic Propeller Turbine Deriaz Turbines Water Pumps Working as Turbines Specification of Hydro Turbines 107 References Wind Power Plants Introduction Appropriate Location Evaluation of Wind Intensity Meteorological Mapping Weibull Probability Distribution Analysis of Wind Speed by Visualization Technique of the Balloon Topography Purpose of the Energy Generated Accessibility Wind Power Wind Power Corrections Wind Distribution General Classification of Wind Turbines Rotor Turbines Multiple Blade Turbines Drag Turbines (Savonius) Lifting Turbines Starting System Rotor Lifting Speed Multipliers Braking System Generation System Horizontal and Vertical Axis Turbines Magnus Turbines System TARP WARP Accessories Generators and Speed Control Used in Wind Power Energy Analysis of Small Generating Systems Maximization of C p 145 References 148

12 x Contents 5 Thermosolar Power Plants Introduction Water Heating by Solar Energy Heat Transfer Calculation of Thermally Isolated Reservoirs Steady State Thermal Calculations Transient State Thermal Calculations Practical Approximate Measurements of the Thermal Constants R and C in Water Reservoirs Heating Domestic Water Thermosolar Energy Parabolic Trough Parabolic Dish Solar Power Tower Production of Hydrogen Economics Analysis of Thermosolar Energy 168 References Photovoltaic Power Plants Introduction Solar Energy Conversion of Electricity by Photovoltaic Effect Photovoltaic Cells Equivalent Models for Photovoltaic Panels Dark Current Electric Parameters of a Photovoltaic Panel Measurement of I λ Measurement of R p Measurement of I d Measurement of η Measurement of I s Measurement of R s Power, Utilization, and Efficiency of a PV Cell Solar Cell Output Characteristics Dependence of a PV Cell Characteristic on Temperature and PV Cells Model of a PV Panel Consisting of n Cells in Series Model of a PV Panel Consisting of n Cells in Parallel Photovoltaic Systems Irradiance Area Solar Modules and Panels Aluminum Structures Load Controller Battery Bank Array Orientation 200

13 Contents xi 6.7 Applications of Photovoltaic Solar Energy Residential and Public Illumination Stroboscopic Signaling Electric Fence Telecommunications Water Supply and Micro irrigation Systems Control of Plagues and Conservation of Food and Medicine Hydrogen and Oxygen Generation by Electrolysis Electric Power Supply Security Video Cameras and Alarm Systems Economics and Analysis of Solar Energy 209 References Power Plants with Fuel Cells Introduction The Fuel Cell Commercial Technologies for the Generation of Electricity Practical Issues Related to Fuel Cell Stacking Low and High Temperature Fuel Cells Commercial and Manufacturing Issues Constructional Features of Proton Exchange Membrane Fuel Cells Constructional Features of Solid Oxide Fuel Cells Reformers, Electrolyzer Systems, and Related Precautions Advantages and Disadvantages of Fuel Cells Fuel Cell Equivalent Circuit Water, Air, and Heat Management Fuel Cells and Their Thermal Energy Evaluation Experimental Evaluation of the Fuel Cell Equivalent Model Parameters Determination of FC Parameters Aspects of Hydrogen as Fuel Load Curve Peak Shaving with Fuel Cells Maximal Load Curve Flatness at Constant Output Power Future Trends 260 References Biomass Powered Microplants Introduction Fuel from Biomass Biogas Biomass for Biogas Biological Formation of Biogas Factors Affecting Biodigestion 277

14 xii Contents 8.7 Characteristics of Biodigesters Construction of a Biodigester Typical Size for a Biodigester Generation of Electricity Using Biogas 282 References Microturbines Introduction Principles of Operation Microturbine Fuel Control of Microturbine Mechanical Side Structure Electrical Side Structure Control Side Structure Efficiency and Power of Microturbines Site Assessment for Installation of Microturbines 305 References Earth Core and Solar Heated Geothermal Energy Plants Introduction Earth Core Geothermal as a Source of Energy Earth Core Geothermal Economics Examples of Earth Core Geothermal Electricity Solar Heat Stored Underground as a Source of Energy Heat Exchange with Nature Heat Exchange with Surface Water Heat Exchange with Circulating Fluid Solar Geothermal Heat Exchangers Horizontal Serpentines Vertical Serpentines Mixed Serpentines Pressurized Serpentines Heat Pump Heat Exchange with a Room 328 References Thermocouple, Sea Waves, Tide, MHD, and Piezoelectric Power Plants Introduction Thermocouple Electric Power Generation Thermocouples Power Conversion Using Thermocouples Principle of Semiconductor Thermocouples A Stack of Semiconductor Thermocouples 338

15 Contents xiii A Plate of Semiconductor Thermocouples Advantages and Disadvantages of the Semiconductor Thermocouples Power Plants with Ocean Waves Sea Wave Energy Extraction Technology Energy Content in Sea Waves Tide Based Small Power Plants Small Central Magnetohydrodynamic Small Piezoelectric Power Plant Piezoelectric Energy Conversion Piezoelectric Based Energy Applications 352 References Induction Generators Introduction Principles of Operation Representation of Steady State Operation Power and Losses Generated Self Excited Induction Generator Magnetizing Curves and Self Excitation Mathematical Description of the Self Excitation Process Grid Connected and Stand Alone Operations Speed and Voltage Control Frequency, Speed, and Voltage Controls The Danish Concept: Two Generators on the Same Shaft Variable Speed Grid Connection Control by the Load versus Control by the Source Economics Considerations 387 References Permanent Magnet Generators Introduction PMSG Radial Flux Machines Axial Flux Machines Operating Principle of the PMSG Permanent Magnets Used for PMSGs Modeling a Permanent Magnet Synchronous Machine Simplified Model of a PMSG Core Types of a PMSG PSIM Simulation of the PMSG Advantages and Disadvantages of the PMSG 408 References 411

16 xiv Contents 14 Storage Systems Introduction Energy Storage Parameters Lead Acid Batteries Constructional Features Battery Charge Discharge Cycles Operating Limits and Parameters Maintenance of Lead Acid Batteries Sizing Lead Acid Batteries for DG Applications Ultracapacitors (Supercapacitors) Double Layer Effect High Energy Ultracapacitors Applications of Ultracapacitors Flywheels Advanced Performance of Flywheels Applications of Flywheels Design Strategies Superconducting Magnetic Storage System SMES System Capabilities Developments in SMES Systems Pumped Hydroelectric Storage Storage Capabilities of Pumped Systems Compressed Air Energy Storage Heat Storage Hydrogen Storage Energy Storage as an Economic Resource 453 References Integration of Alternative Sources of Energy Introduction Principles of Power Interconnection Converting Technologies Power Converters for Power Injection into the Grid Power Flow Instantaneous Active and Reactive Power Control Approach Integration of Multiple Renewable Energy Sources DC Link Integration AC Link Integration HFAC Link Integration Islanding and Interconnection Control DG PLL with Clarke and Park Transformations Clarke Transformation for AC Link Integration Blondel or Park Transformation for AC Link Integration 492

17 Contents xv 15.7 DG Control and Power Injection 494 References Distributed Generation Introduction The Purpose of Distributed Generation Modularity Efficiency Low or No Emissions Security Load Management Sizing and Siting of Distributed Generation Demand Side Management Optimal Location of Distributed Energy Sources DG Influence on Power and Energy Losses Estimation of DG Influence on Power Losses of Sub transmission Systems Equivalent of Sub transmission Systems Using Experimental Design Algorithm of Multicriterial Analysis Voltage Quality in DG Systems 525 References Interconnection of Alternative Energy Sources with the Grid 533 Benjamin Kroposki, Thomas Basso, Richard Deblasio, and N. Richard Friedman 17.1 Introduction Interconnection Technologies Synchronous Interconnection Induction Interconnection Inverter Interconnection Standards and Codes for Interconnection IEEE National Electrical Code NFPA 70: National Electrical Code NFPA 853: Standard for the Installation of Stationary Fuel Cell Power Plants UL Standards UL 1741: Inverters, Converters, and Controllers for Use in Independent Power Systems UL 1008: Transfer Switch Equipment UL 2200: Standard for Safety for Stationary Engine Generator Assemblies 543

18 xvi Contents 17.4 Interconnection Considerations Voltage Regulation Integration with Area EPS Grounding Synchronization Isolation Response to Voltage Disturbance Response to Frequency Disturbance Disconnection for Faults Loss of Synchronism Feeder Reclosing Coordination Dc Injection Voltage Flicker Harmonics Unintentional Islanding Protection Interconnection Examples for Alternative Energy Sources Synchronous Generator for Peak Demand Reduction Small Grid Connected PV System 555 References Micropower System Modeling with HOMER 559 Tom Lambert, Paul Gilman, and Peter Lilienthal 18.1 Introduction Simulation Optimization Sensitivity Analysis Dealing with Uncertainty Sensitivity Analyses on Hourly Data Sets Physical Modeling Loads Primary Load Deferrable Load Thermal Load Resources Solar Resource Wind Resource Hydro Resource Biomass Resource Components PV Array Wind Turbine Hydro Turbine Generators Battery Bank 585

19 Contents xvii Grid Boiler Converter Electrolyzer Hydrogen Tank System Dispatch Operating Reserve Control of Dispatchable System Components Dispatch Strategy Load Priority Economic Modeling 598 References 601 Appendix A Diesel Power Plants 603 A.1 Introduction 603 A.2 The Diesel Engine 604 A.3 Main Components of a Diesel Engine 604 A.3.1 Fixed Parts 605 A.3.2 Moving Parts 605 A.3.3 Auxiliary Systems 605 A.4 Terminology of Diesel Engines 606 A.4.1 The Diesel Cycle 606 A.4.2 Combustion Process 608 A Four Stroke Diesel Engine 609 A.5 Cycle of the Diesel Engine 609 A.5.1 Relative Diesel Engine Cycle Losses 610 A.5.2 Classification of the Diesel Engine 610 A.6 Types of Fuel Injection Pumps 611 A.7 Electrical Conditions of Generators Driven by Diesel Engines 612 References 614 Appendix B The Stirling Engine 615 B.1 Introduction 615 B.2 The Stirling Cycle 616 B.3 Displacer Type Stirling Engine 619 B.4 Two Piston Stirling Engine 621 References 623 Index 625

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21 xix Foreword for the First Edition Integration of Renewable Sources of Energy is an important work about technology that has the potential to advance environmental goals and eventually support a sustainable future for society. Several countries such as Denmark, Australia, Spain, Germany, the United Kingdom, and others have begun the transition away from fossil fuels and nuclear energy as a response to increasing concerns about fuel supplies, global security, and climate change. Renewable energy includes all sources and technologies that minimize environmental impacts relative to conventional hydrocarbon resources and economical issues related to fossil fuel resources. Therefore, fuel cells, natural gas, and diesel might be alternatives in respect to coal or nuclear power. Renewable energy sources are those that are derived from the sun or other natural and replenishing processes including solar (light and heat), wind, hydro (fall and flow), sustainable biomass, wave, tides, and geothermal energy. Throughout this book, the fundamentals of the technologies related to the integration of such alternative and renewable energy sources are reviewed and described with authority and skill and from the critical engineering point of view for the end user of energy. In Chapters 1 15, the authors cover the principles of hydroelectric, wind, solar, thermal, and photovoltaic power plants. Induction generators important electric machines for wind and hydropower generation are described in detail. The chapters on fuel cells and biomass are of paramount importance in the current age of the hydrogen economy. Literature on microturbines is scarce; therefore, the authors make important contributions to the technical description of such important devices that have contributed, in the last few years, toward shifting traditional generation to distributed generation. A comprehensive evaluation of storage technology is complemented by the description of integrating control and association of sources into microgrids. There are two chapters authored by outside contributors that describe the standards and interconnection issues of alternative energy sources to the grid and principles of economic optimization. The book is complemented by three appendices covering some important sources of power and heat directly related to the rational use of energy, namely, diesel, geothermal, and Stirling engines.

22 xx Foreword for the First Edition I applaud the initiative taken by the authors to more closely cover, in this timely book, the electrical rather than the mechanical aspects of energy sources. I am sure this work will contribute in understanding how to integrate renewable energy sources for home, commercial, rural, and industrial applications. I strongly recommend this textbook to a wide audience, including engineering educators and students of electrical and mechanical engineering. Marian P. Kazmierkowski Professor in Power Electronics Warsaw University of Technology, Warsaw, Poland

23 xxi Foreword for the Second Edition The world is undergoing a dramatic evolution in its energy system structure as more and more power is now coming from renewable and sustainable energy sources, and this development is expected to be even more progressive in the next decades it is driven by a goal of not only reducing carbon emission but also obtaining more security of supply for every nation and continent. Despite the fluctuating prices for carbon based energy although currently the prices are rather low a lot of national programs are implemented in order to use more renewables. Furthermore, final energy prices for some of the renewables are more competitive than those of conventional fueled systems and such technologies will accelerate the implementation even more. Especially energy cost of the wind power technology and photovoltaics is very low, and it is a matter of scale to push that further down. In 2016 it was expected that more than 100 GW installation would be done for these technologies and that was more than half of the total installed new electrical power capacity generation for this year. Most of the renewable energy sources need power to operate properly, and we have also seen continuous improvement in this technology, which has become smaller, cheaper, more efficient, more reliable, and smarter, so energy sources facilitate a smooth and intelligent connection to the electrical grid. The second edition of this book is very timely and covers many important aspects of integrating renewable energy sources. It starts with an overview of all renewable sources that exist today, and then the basics about thermodynamics are covered to get a full understanding of energy. A wide range of different relevant technologies are covered, including hydropower, solar power, wind power, fuel cell based power, photovoltaics, geothermal power, microturbines, and ocean power systems as well as biomass based systems. Different energy storage systems are also covered, as well as conventional power generators like induction and synchronous generators (also with permanent magnets) in some of the presented systems, energy sources that have to be integrated, and methods of proper interconnection of the electrical power based generator systems. The book ends with examples of a micro power system.

24 xxii Foreword for the Seond Edition The book gives a solid introduction to the many aspects of present and future energy technology for the society and an inspiration for future research. It also demonstrates that the energy system requires not a single solution but a number of them with different energy carriers in order for the society to fully rely on renewable energy sources. Enjoy reading! Frede Blaabjerg Professor Aalborg University, Denmark

25 xxiii Preface for the First Edition Our goal in writing this book is to discuss the electrical side of renewable energy sources. From the beginning, we felt that the approach would be a challenge that is very difficult to fulfill. Most of the current technical works explore just one or two types of alternative energy sources, but the integration of sources is our main objective. We also noticed that most of the works on this subject were exclusively concerned about those parts of the primary energy directly related to extraction and conversion of power and not really about processing energy and giving the user a final product. This product energy should be ready to feed a new reality and the dreams powered by renewable or alternative sources of energy. Those sources of energy have a lot in common. However, when discussing hydropower, wind, solar, and other sources of energy, the complexity of their aspects is soon realized. Not long ago, huge power generation plants dominated the whole field of energy production. It seemed there was no way to develop and deploy small and disperse alternatives. For several decades, small plants nearly vanished. This was a worldwide trend because of the argument that electrical efficiency and concentrated sites would be incontestably the best economical and rational factors to generate electricity. Throughout those decades, small rural communities and remote areas were simply outside the scope of the centralized model. Population growth and the development of nations soon made our society realize that more and more energy production would be necessary for continuous industrial growth. On the other hand, the availability of energy would not be enough or would be so distant from the perspective of consumption that central power plants would have devastating effects on ecology, scenery, and quality of life. For a future with sustainable energy, massive fossil fuel powered plants are not economical; most of them waste more than 50% of the primary energy due to irrecoverable thermal losses. In addition, they demand the use of massive coolers and heat sinkers to guarantee operational conditions, quality, and stability of the final product. The energy must be transported throughout long and congested transmission lines: waste that is no longer reasonable.

26 xxiv Preface for the First Edition Small, dispersed generating units do have the possibility of adding representative amounts of energy to the network without a noticeable long term impact on the environment and economic investments. Current computer and power electronics technology supports the integration and distributed generation of energy to sites that have been so far neglected. The Earth has sunlit deserts, windy remote locations, offshore sea sites, glaciers, and streams, with each environment contributing to the world energy frame. They are not wastelands anymore. Who can guarantee for how long we will have plentiful and available petroleum, at the right quantity corresponding to demand, for the years to come? How can mankind believe in a sustainable future if the only admissible alternative is nuclear energy? How can we quantify only economic benefits to mankind from fossil fuel and nuclear power and neglect other important issues such as avoided healthcare costs, air quality, space, sea and river poisoning, sound and visual pollution, or an unpredictably safe future? Nobody wants to go to war to sustain our future. In this book, we review and organize all pertinent subjects in an orderly way. After a general introduction on the subject in Chapter 1, we review some general principles of thermodynamics in Chapter 2. Initially, we choose to explore the most common alternative energy sources such as hydro, wind, solar, fossil fuel, solar thermal, and fuel cell power plants (fuel cell plants are expected to soon become widespread). After we cover the basis of the primary sources, our approach is to show how to integrate them for electrical power production and integration into the main grid; these subjects are covered in Chapters 3 8. The means of interfacing the primary energy through microturbines, induction generators, and power electronics for electrical power are dealt with in Chapters 9 and 10. Chapter 11 is a special chapter on energy storage systems. Our main concern is the means of integrating, transforming, and conditioning the energy sources into more useful electrical applications, rather than coping with the distribution of sources throughout the electrical network. Power transmission is left for the reader to study in other related books. Problems related to system operation, maintenance, and management are briefly tackled in Chapters 13 and 14. These chapters also refer the reader to other more specialized texts and literature on the subject. Chapter 14 discusses the standards for interconnection. Finally, the last chapter gives the reader the opportunity to learn more about the HOMER Micropower Optimization Model, which is a computer model developed by the US National Renewable Energy Laboratory (NREL) to assist in the design of micropower systems and to facilitate the comparison of power generation technologies across a wide range of applications. HOMER software can be downloaded from the NREL website. This book is especially dedicated to those people who believe that there is a way to work for a clean, long lasting, and beautiful world and to those students, engineers, and professionals who believe that engineering is decisive in its

27 Preface for the First Edition xxv contribution to this journey and who dedicate their professional lives to this mission. Many of these readers will be found in senior years of study or first graduate level programs in advanced courses on energy, electrical, environmental, civil, chemical, and mechanical engineering and agronomic sciences. Felix A. Farret, Santa Maria, Rio Grande do Sul, Brazil M. Godoy Simões, Golden, CO, USA Spring 2005

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29 xxvii Preface for the Second Edition It has been 10 years since we released the first edition of our book Integration of Alternative Sources of Energy. The friendship, partnership, and academic interaction of the authors remain solid when in 2002 we decided to make renewable and alternative sources of electrical power an easy and understandable subject for our students both at Colorado School of Mines, USA, and at the Federal University of Santa Maria, Brazil. For the past 15 years or so, Drs. Farret and Simões have been working in several joint books and papers, sharing research and educational materials, exchanging ideas, and cooperating with students; the very book that you now hold in your hands is our joint piece of art that we developed along these years. We are really happy that we can share with you what we learned and what we made available in this textbook, because the future that we believe has to be a sustainable one. The second edition is our masterwork. We hope that students and engineers all over the world can appreciate and get in a deeper learning on this area of renewable and alternative energy systems. In the second edition, we polished our knowledge about alternative sources of energy with many comments received from our readers. We included new applications and a discussion of new sources, and we expanded details that were not so obvious in the first edition but made us to get a better comprehension for this book. There were many suggestions of so many topics and ideas to explore in this second edition that we could keep working on. But we think that this version has a good coverage and stature to be useful in teaching senior undergraduate and first year graduate courses. We corrected, enriched, enlarged, and detailed many topics that at the beginning were difficult to understand, since this area is very multidisciplinary, and anyone to master these topics must have a very curious mind. Our work is such as the one performed by a curator, since curare from Latin means to take care, that is, a curator interprets a heritage material for a certain art collection. As in a traditional curator s concern, we decided that in this book we would make available the cultural heritage necessary to educate students in all aspects of renewable and alternative energy systems. Several topics

30 xxviii Preface for the econd Edition are fruits of research conducted in our academic career, while others were curated in order to make such an educational bridge that can be useful for the current generation of students and young engineers. In the second edition, we added three new chapters about renewable sources of energy to be better explored in the next few years. One is geothermal energy, particularly the available thermal heat in shallow underground, which is not yet recognized and not fully explored but has a potential paradigm transformation, since it is available all over the world. The other one is electrical generators that involve permanent magnet synchronous machines, particularly with designs aiming to convert energy directly without inefficient gearboxes and operating at very low speed, compatible with the sources of nature, such as wind, water streams, ocean and sea water, or fluids in the industrial, commercial, and residential settlings. In addition, we included a chapter about the other promising types of electrical power generation such as semiconductor thermocouples, sea wave energy conversion systems, tidal power, gas microturbines, and piezo electric harvesting and magneto hydrodynamic energy systems. These possibilities are fascinating, and we expect that people all over the world will become excited to contribute with these energy sources and place everything at their right place and that we will live in a sustainable society, free of fossil fuel. We envision that sources of energy should be classified into three main categories: those coming from the sun, those coming from the Earth, and those considered ambiguous (see our Table 1.5 on Chapter 1). Those coming from the sun, like hydro, wind, photovoltaic, and solar thermal power and photosynthesis, can be welcomed since they are clean for our planet, whereas those coming from the earth like coal, uranium, big plantations, and petroleum are not welcome, since they can contribute to pollution. In some ambiguous ones, like geothermal, fuel cell, and biomass, the surface geothermal can be very welcome to mankind because the sun has evenly warmed up the Earth s surface since billions of years ago, which will continue for more billions of years further. On the other hand, deep geothermal is not really a good source since obtaining boiling water from the earth core to feed steam turbines and exchange it with cold water to fill back the source where the steam was originally trapped may not be sustainable and not even possible for a continuous and worldwide use. Fuel cells fed by hydrogen from petrol hydrocarbons are obviously not welcome but still are marketed by giant multinational companies. Fuel cells are good solutions when the hydrogen is acquired by splitting water molecules through heat from sun irradiation concentrated by mirrors, but some economics studies are further needed to decide the direct use of irradiation heat for hydrogen and other applications. Biomass used in bio digesters and fed from rubbish in order to produce electrical power is welcome. However, using biomass from wood burning is not. Wood is such an important gift of our nature, and human beings must use them with care and respect. It would be better to