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Wind Energy and Wind Turbines 1996
WIND ENERGY AND WIND TURBINES VAUGHN NELSON Alternative Energy Institute WIND ENERGY AND WIND TURBINES Published by Alternative Energy Institute West Texas A&M University Box 248,Canyon,TX 79016 USA 806 656 2295 Fax 806 656 2733 email aei@wtamu.edu Copyright ©1996 by Alternative Energy Institute,draft copy 1994. Chapters on Instrumentation and Measurement and Siting were added in June 1995. Revised March 1996.All rights reserved.This includes the right to reproduce any portion of the book by any method,electronic or mechanical,including photocopying,recording, or any other information storage retrieval system without the explicit written permission of the Director,Alternative Energy Institute. PREFACE This book is from the lecture notes of an course that the author has presented at West Texas A&M University.It is an elementary course for students and the lay public interested in wind technology.The course includes numerous slides and field trips to the Wind Test Center of the Alternative Energy Institute and the Wind Test Site at the Conservation and Production Laboratory,Agricultural Research Service,United States Department of Agriculture (USDA),Bushland,Texas.Quite a bit of the material has been used in seminars in the United States and overseas. About the Author Vaughn Nelson is Professor of Physics and Dean of the Graduate School, Research,and Information Technology,West Texas A&M University.He has served as director of the Alternative Energy Institute (AEl)since its inception in 1977.The Alternative Energy Institute's programs and projects are primarily in the area of wind energy,from education and information dissemination to applied research and development.AEI and USDA have installed and operated over 30 wind turbines, primarily prototypes and first production models at the AEI Wind Test Center,USDA,and other locations.Besides publishing over 50 papers and reports on wind energy,Dr. Nelson has presented workshops and seminars on wind energy and wind turbines and consulted for industry and government from the local to international level.Dr.Rohatgi and Dr.Nelson published a book in 1994 on Wind Characteristics,An Analysis for the Generation of Wind Power. ACKNOWLEDGMENT Many students have provided invaluable information and positive contributions to the course.Students,both undergraduate and graduate,who have worked at the Alternative Energy Institute (AEl)have also influenced the course.|am deeply indebted to my colleagues,present and past,interns and visiting researchers from overseas,and personnel from the wind group at the U.S.Department of Agriculture.Specifically Kenneth Starcher has been indispensable at AEI since he started working as an undergraduate in 1977.Dr.Nolan Clark,Dr.Forrest Stoddard,Joe McCarty,and Jun Weihavealsohadasignificantimpactontheprogram.Special thanks are due to the Ling Shitao,who sat through the course and made it possible to finally finish this project The faculty of the Department of Mathematics,Physical Sciences and Engineering Technology have accepted with equanimity that much of my time has been devoted to wind energy.In the department,David Patterson,Gene Carlisle and Betty Jackson have taken quite a bit of the load.Dennis Camp is always available for those sticky problems with computers.The secretaries,present and past of AEI,are an integral part of this effort; Becky Millen,Carolyn Talley,Patricia Dixon,and numerous students.Dr.Earl Gilmore and Dr.Robert Barieau were instrumental in the initial phases of AE].Meg Lowrey and Pam Mayes,two friends from the early days at AEI,made life brighter. Horace Bailey,Dean,College of Agriculture,Nursing and Natural Sciences has been a staunch supporter of AE!.Financial support for AEl has been provided by the State of Texas through line item funding and grants from state agencies;from the early days of TENRAC to the State Energy Conservation Office today.Local support has been provided by WTAMU and by the Killgore Research Center.USDA has also provided support as AEI and USDA have had a cooperative agreement since 1976.AEI has a cooperative agreement with the Natural Energy Institute,Inner Mongolia Engineering University.AEI personnel have given seminars in Inner Mongolia and there has been an interchange of personnel for training. Special thanks are due to my wife Beth for her forbearance that we had to inspectandtakephotosofallthewindturbinesonthosetripstoconferencesintheUnitedStatesandabroad.The personnel of the American Wind Energy Association have always been helpful.Again,the interaction of others has enriched my life from the nascent industry ofthe70's,through adolescence and the acceptance by Wall Street today.These have been very interesting times. TABLE OF CONTENTS 1 INTRODUCTION...0..ecsscssssssssesessesssecesencsesesansnssssacesessusesesseeceueususuacaneneseasares 1 1.1 DUTCH WINDMILL...ccceccssensesssssssssssssscsnsnsesssssssssensnsssssseeesees 1 1.2 FARM WINDMILL...sscecssssesseesssssssssssansesesesssesesesssseseesesesseseeceees 3 1.3 WIND CHARGERS........ccssssssscssssssssssessssssssssescssssssarscsessssssssssesseesenenenes 4 1.4 GENERATION OF ELECTRICITY FOR UTILITIES .........scsseeeseeeeees 4 REFERENCES .....csssssssccsssersessssscesescssssssecsesescessseccscacaesesesssesusecacasssessnencasanes 12 2 ENERGY.........cccccssessscseseescecsssscssserscsessesesessrsseeccssseaseracsssecsessensaeseeacsesesaearersesaesess 14 2.1 PHILOSOPHY...cecsssscssscssssssssssssssceescscscssesesssseressessesersssasseacscsceneessvass 14 2.2 DEFINITION OF ENERGY AND POWER..........cccssssscscscsssssesscesssesesersees 14 2.3 FUNDAMENTALS CONCERNING ENERGYV...........cccccssscssssssresseesessees 15 2.4 EXPONENTIAL GROWTH ........ccccsssscsssssssscsssssssscsssesesscsesssssassesssssaeacsessees 16 2.5 USE OF FOSSIL FUELS...essssssssssescsescesseseecsssssesssesssnseseeeseeseees 18 2.6 MATHEMATICS OF EXPONENTIAL GROWTH.............csessccseseeseseeeeee 22 2.7 LIFETIME OF A FINITE RESOURCE ..........csssssssssscsscscersscssessecssesesesases 23 2.8 USE OF ENERGY......cs ecccsssssreescsesessssssesecceseseseesecsseasessesesesseessaseesonseoes 24 2.9 SUMMARY .........cccscssscsscssssscsssssssserscecsessssssassssacesscessanscessaesceesacceasscescatscees 25 REFERENCES ........cssssssssecssssescscscessscsesescsceccsssesseaesesessnsseessaseracseseeseeereeanss 26 PROBLEMS.......ce ccssssesesssscsesesssssecssessssssessecscessacsceseseaseacarsceesacasensarsceneacseeessenses 27 3 WIND CHARACTERISTICS...ccscsssscscsssscessecessenesseessenseseesesassseneesesseasenses 28 3.1 GLOBAL CIRCULATION ..........esssssssesesesscsssssscssseesessceesesssessaseseseoeseees 28 3.2 EXTRACTABLE LIMITS OF WIND POWER.............ccssssssssssssctseseeeseees 28 3.3 POWER IN THE WIND...scssesessssesesscscssesessseessesesesesecsesssesesseeesenene 30 3.4 CHANGE IN WINDSPEED WITH HEIGHT...eetssseseesteeeeseeeseneee 32 3.5 WIND DIRECTION...sescscscscsesesccsssessrsssessceescsscssersseeserssssssessesssssacesens 34 3.6 WIND POWER POTENTIAL..........cccssscsssssesssessesssorssssessersseeneseseseseseeeeaes 35 3.7 WIND MAPG........ccscssscsssssccesesscsesersceesscesesseseseesenarsesscsasacsecaseessesesaseesansoss 38 3.8 WINDSPEED MEASUREMENT .............ecsssssssssscesscsscsarsccerssesenessenssense 42 3.9 VARIATIONS IN POWER ..........cssccsssssssscssssssessscesseseseecsscseaseneesseeesensenenes 43 3.10 WINDSPEED HISTOGRAMG.........cccsssssssesssssessesssessssescsseesseseseeseeaes 46 3.11 DURATION CURVE .........cccssssssssssessssessssesssesersesseseetsesseseaseseeeeeetenseeseas 48 3.12 WINDSPEED DISTRIBUTIONS...cee eccesseeeseceessseesseesesesseeseeseseses 49 3.13 GENERAL COMMENTS wu...eeceessceesseseseesseesenseseneesesesscsseeseseeeseensens 51 REFERENCES ........ccscsssccscssscssrssscceresscsssossssesscsssesassesesecsesenaseenesessesssansenseeesesess 51 PROBLEMSG .........ccesssesseccesssseseeesessesessesssasesescesecsesasasesseosecenesessueesecessecseseeneeeoees 52 4 INSTRUMENTATION AND MEASUREMENT............::cssssscsssesessecceseesenerenees 53 4.1 INSTRUMENTATION..........ccccsssscscsssseccsessesssscsesessccssseseeseeseseesensesesseseeees 54 4.1.1 CUp ANQMOMETEL.........ce eseseeseessescensecesenscsesecseseserstsevesssesesssanassseess 54 4.1.2 Propeller ANEMOMETETS.......ccsscssssssssesssssnecsssesenssessesssseeesereenesens 55 4.1.3 WiNd Direction ..........cc cescsccsssssscersescssssscsessesesesesseceessecersesseseeerens 55 4.1.4 RECOIESS.......cs cecssesscesssssesessssessseseessrsesseesesassesessenscenssasanceesaserensons 56 4.2 CHARACTERISTICS OF INSTRUMENTS ...........cscssssssssesssesnsesesesecenes 56 4.3 MEASUREMENTG.............cccccsccssscesssesssseccesesessecesesesseseceesssssesesesssesevansenees 57 4.4 VEGETATION INDICATORS ..........cssesscsesssseressesesersssesssusessccensceesserasensens 57 REFERENCES ........cccccsssssccsssseccscsscscscesesesceseeesessesessssenssesseeusesssenseeesesassecesansenans 59 PROBLEMS .........ccccssssssssssssssssesssesccsesesscseecseseceesecseseoessessseessassnsessesssesasssaeeesenaes 59 5.1 DRAG DEVICE..u..escecsssssscesscscsssssssscssscsesscacssserseseesseceenencaesessnsaeseesens 59 5.2 LIFT DEVICE...cseccscssssssssssesssscscssscssscssscssscsssetsrssssssscessenseceeseacerarseacoes 60 5.3 ORIENTATION OF ROTOR AXIS.........cccccsssssssssesessssssescssecsssseseesstesansesenes 60 5.4 DESCRIPTION OF SYSTEM ..........cscsscssssrssssssssssssssscensacecsacsssesecenesesesees 62 5.5 AERODYNAMICS ........ccsssssscessssesscsscsrscssesscsssccsssssssceseeseneneseseseseacaeesseass 62 5.6 CONTROL ........sssssssssssssssssssssssesessssscsssesessecessecorsrsesesrssestacacacscsessesacarseseers 64 5.6.1 Normal Operation uu...ssssssssssssssessssessscssessssscesscscesnsescscaseres 65 5.6.2 Faults....csssscsscsssessssesssscsssscsssssscssssesesssesessseesssessssseesaseerssessseees 67 5.7 ENERGY PRODUCTION..........cc csssssssssssessssssssscsssssssecensseesssetessersnsatsearers 67 5.7.1 Generator SiZ@.....eessessssscssssssencsescscscsseseesetseasaressesssssesssasseaees 67 5.7.2 Rotor Area and Wind Map..............csssssscessesescesseeesesessesseeerseens 67 5.7.3 Manufacturer's Curve.........ccccsssscsscssscssscssessersssescnseessssseesacess 68 5.8 CALCULATED ANNUAL ENERGV............ccscssssssscsssessecesssssesssseceseseee 69 5.9 INNOVATIVE WIND SYSTEMS.......ce sssesessscssssesssssensecessecersrsrsceseneees 70 5.10 APPLICATIONS .......escsessssssesscsssssscesssssssssscsesscsssessessassceeseroressarersecsssenes 73 5.10.1 Electrical Energy...esssssssssesssssscssessesesseserssseseressssessenes 73 5.10.2 Mechanical Energy .........ccsscssssssscssssssssessesesserescenseescessesenes 74 5.10.3 Thermal Energy uu...csesssesesessccssesssessessesseesseenecesesesssssensesnaes 74 5.10.4 Hybrid SyStems.........csseeetsessseseesececsesescessssesesesenscesesseeveves 74 5.10.5 SuUMMary......eeccessccesssesesscsseesecsseesessseeseesseessenesesessssenesseeesenees 74 5.11 STORAGEuu...eececssssesssseesesessesssescseasesssseeeesseseerseaesessessssseseesesessceasenseors 74 REFERENCES.0...cccsssscssscsssesscssssescsereesesecarsesssaesesesassesasoessaceenaeoseeaseeeseaassens 75 PROBLEMS .......ccssssscssscscssssscsetscserssseserarsesetaescseseracsesoeaeseseesesseensecesensseasensesons 76 6 DESIGN OF WIND TURBINES........ce eesssececeesesseseeseseceenesassensseseseseeesenseees 78 6.1 INTRODUCTION.........ce ccssscsscsecssesssssseseessesssenseoesseseorssessenessseeseseeeenseses 78 6.2 AERODYNAMICS...essssscsssseseosesssesseseneensssseenssssessessssensnsssenscsasseses 78 6.3 MATHEMATICAL TERMG.........cccssssscessessssssesesesessesscenseseseesesesessecenevess 78 6.4 ANALYSIS OF EXTRACTABLE POWER...........sssssssessssssensscersesesenesens 79 6.5 DRAG DEVICE.........cccscssscsssssscsssssscsssssssensssesonseeseeesesseneseusceeseusesesenasseserens 80 6.6 LIFT DEVICE...........cccssssssnsscssessssssesserssessesssesessssssseeseensesseesesseeensnsseenseneees 81 6.6.1 Maximum Theoretical POW?.........:ssssssesessesssssesscsesssssesesesenenes 83 6.6.2 Rotation...ccccsscsccecsccereseesccsssssssessesessseteaseesssssssssvesstsssesesseeseners 83 6.7 AERODYNAMIC PERFORMANCE PREDICTION ...........cssssssesssessreees 84 6.8 MEASURED POWER AND POWER COEFFICIENT..........ssssssssesessees 85 REFERENCES ........csscssscsssscesssescssesssscsessceseesaseccssssesssssscsusescssesenseesseonssusesesevess 89 PROBLEMS ........cccccssssesesescssscesssssecesencacscscacscecnesenecaeaeseseseneecananasassesseeseseeseseouos 90 7 ELECTRICAL ASPECTS.........sssssssssssssssssecssecessssescecsssanenessscsssssevesasseseeseenees 92 7.1 FUNDAMENTALG..........:cccsscssssssescsesessesesssssssssssessssensssssssssessssesenscsenereres 92 7.1.1 Faraday's Law of Electromagnetic Induction..........cccesssseees 94 7.1.2 Phase Angle and Power Factot........cssssssserssssseseneseeresenenesneees 94 7.2 GENERATORS ........ccscccsccssscsssccsessssesesseeesessscssesesessesssscersscessceanecsseeseensaeses 98 7.3 INDUCTION GENERATORG.........cccscsessssesessecesssssssnscssnevssssnessesensreescesees 100 7.4 OTHER GENERATORG.........ccscsecesessesecesnesessessssessssessesesaseetssssteeeesseseees 102 REFERENCES .u.....ccsscssssssessscssececscssnseccesseoesesescssesesesvesssaesssessnsnensssuceasataseareneees 104 PROBLEMS ......ccecsscsssssssssssescsssrsssesscessecesseseceecssssersesscessscessesssessesesesenaeetserans 104 8 SYSTEM PERFORMANCE ............cscssssssssssesssssssssessscsessssesssesersssscenserssssesseseees 105 8.1 PERFORMANCE uc ccsscsssscssccsscssssscscssssccsssscerssseceasssssscecssesessssccersrase 105 8.2 OTHER MEASURES OF PERFORMANCE ..........e:ecccccssscssesssesssseseeceees 106 8.3 PERFORMANCE REPORTS .......c.cccsccscceccescsccecssccscsesesscsesescsscssceceersars 108 8.3.1 California oo...cccscssssscssccsccsscsssscscceccscesssersssssceosssessscscessrscarsecsreses 108 B.3.2 WINDSTATS uu...ccssscsccssssvescssescsesssscsessesssssssscsesasacesceseecsesscseceees 1098.4 PERFORMANCE OF ENERTECH 44 u0......ccccssesssccsccccescscsssscsrseceeesreers 110 8.5 PERFORMANCE OF BERGEY EXCEL .u0.......sesescsscsscssssscssscscsesenseresees 113 8.6 WATER PUMPING uu...csccsscsscssssscesscssssscscsessessssecessssccersescsesesensasensenesess 114 8.6.1 Farm Windmill...ce cssssscsscsscsscssssscsessssesssscscsesssscsscessessessesssseenses 114 8.6.2 Electric to Electric SYSteM ..........cesesesseeseesssessssssssessseeseseseessseceees 1158.7 COMMENTS2...ccscscsssscssssscsscscessscscscsecssseccscssesecsssessesssesessssesevesesaseaseness 115 REFERENCES .........ccssscsscsssssossssesecsssessscessssscesssassavessesessesesenssceesseseusassaceesarenees 117 PROBLEMS ........cccccssssssscssssvscsessecsesassecesssesessessseesesecsassscasscssesecsncenseserseesasasonsas 118 oS)NC re 119 9.1 INTRODUCTION...ccc sccscsscscssccsssserscssscsscsccessssessssssensssessssssesesssssseserens 119 9.2 LONG TERM REFERENCE STATIONS w..00.....cccscsssssscsesssssessessseseesereee 119 9.3 SITE EVALUATION FOR WIND PLANTS uuu...eeesceccceccesssersscssssesesesees 1209.4 WAKE AND ARRAY LOSSESuu...cccsescsscsssssscssssesssscssessesssesserenass 121 9.5 DIGITAL MAPS .........ccccccsscsessssssssssssscssssssccsessecssssesssseserssessesssessetscesssessnens 121 9.6 GEOGRAPHIC INFORMATION SYSTEMS u.........ccccscsessccccsssesssessescesees 121 9.7 WIND RESOURCE SCREENING...ecsccsccesscsesccsssccessecceessesesscessees 122 9.7 WIND POWER PRODUCTION uuu...seesecsccscscescscsessecesevsccssessessesesssenes 125 9.7.1 Wind Power for Texas Panhandlle ..........cccccsccccsssccsessccssesesseses 126 9.7.2 Wind Power for TeXaS .........ccsccsscsssscsssscesssesseccesssscessssesesesseeee 126 9.8 SUMMARY uu...sccssscsscscsssstsssscssssssssssssessessssssssseeserssessseeseesseaseaseeesenes 127 REFERENCES uu...cssccsscssscscsscsssssesscssssscsssssssssssssesseessescecsessecseassessonsseesees 127 GEOGRAPHIC INFORMATION SYSTEMS...ccscccceccscssessessssstessessses 128 PROBLEMS .......ccccccsssssssssscssssssecssssssscssscsecesseneseessesserscensessseseassoescsteneeesssenseees 128 10 WIND INDUSTRY...ccccssccsssseccssssssssssssssecsscssessesssssssssessecsscssacesevsesoees 129 10.1 INTRODUCTIONuuu cc ccsccevssssevsscssersesesensessecssrsesessrssesssessereses 12910.2 NEW WIND INDUSTRYuuu.ec escccccssecssrsscessssecssesssesseesecseeseressesene 132 10.2.1 Wind Industry 1970-1980...esesseessseseeetetseseseseeesesesenees 132 10.2.2 Wind Industry 1980-1990...eessssecsesstsesenetetesssesseseseeees 134 10.2.2 Wind Industry 1990-2000...sessssssseessesscesssenessseessessees 13410.4 LARGE WIND TURBINESuu...ccc eccsccsectsscsnsssscsnsesesensssscevsessaneansnes 135 REFERENCES .......ccccccccsesscscssstcccccssscsscvsssssssecsesssssossssesssessecssesssessarsossescenseases 138 11 INSTITUTIONAL ISSUESwo ecccssscccstesssessssvecscsssssesscsssesssesseessascossees 140 114.1 INTRODUCTION uuu ccc ecsccsescscssesssesssssessesesssssenseessceseseansrssseenees 140 11.2 AVOIDED COSTS wu ccccccscssscssssesscssssesstssscseseressersersessesseessseesseneess 140 11.3 UTILITY CONCERNS...ccc seccccssevscscssecssercsesssscsssessessssesssesssenseansees 141 11.4 SAFETY ueccccccccccsccsscssccscscsssssssssssssssssssssssscssesesessessssesssssesssessesseeesteseseses 141 11.5 QUALITY OF POWERuu...ce cccscscccssesssssccsssssssssesstessesecesessersserarsecesteene 141 11.6 CONNECTION TO THE UTILITY...ccscctesscersccssrersessssesnreees 141 11.7 REGULATIONS ON INSTALLATION AND OPERATION............006 142 11.8 ENVIRONMENTALuuu...cccscsssccssscsscsscsssesresssessessesstessssseeeseeseesseseneees 142 11.9 POLITICS woe eeccssscsccrsssccsscssssvesersstssssssscssscssssesesessseerseerearecseesserens 143 11.9.1 Federal Support...ccsesssssssesesessesssssesssesesssssssssssceeserssees 143 11.9.2 Division of the Spoils...........csssesessesescscessseseeseesesssreseatseatsees 144 11.9.3 INCENTIVES 00...sesssesecsesesesessesecesscesesncessesscasecscssecesasessssossseseseses 145 11.10 OTHER...eee essssesssssssessscsssssssssssscscssssessssssssanssasscesessecsesessnseesessoecaees 145 REFERENCES...essscscssscssscssssssessesescscscscscsesssssesssssssessrscsssescaescaescacacacacecessecs 145 QUESTIONS...eesssscsssscssssssasssscesssessscocscsesesceseseesecoesesesrsesnenensacscaraseneeesears 146 12 ECONOMICS 2.0.ceesscssssssecscessssssssesescssscsessssessssesesssssssecsceesesesearscsencasacaracsess 14712.1 INTRODUCTION 0...essssscssscsssssssssssssscsesesssserssessseararsesesrensseasanscscnsees 147 12.2 FACTORS AFFECTING ECONOMICS.0...ccssssesesetsssssescerssenseeees 14712.3 GENERAL COMMENT G.........cssssssssssscsssessssessccssssscsesessessseseasensccress 148 12.4 ECONOMIC ANALYSIS0.0...eecessetcssecssssacscssscsssesssessstenssesenseeseses 14912.4.1 Simple Payback............csssessscssecsscssessesssecssesesesnessecsseseseraseseetas 149 12.4.2 Cost Of Energy......csessecscsssescssssssssssesessssesersevssscsesesceseseseoesees 150 12.4.3 Value Of EMergy uu...sesssssssssesscessesssesscsssesscsssessesssscneseserssetes 15112.5 LIFE CYCLE COSTS2.0.ccssssssssssscsessssscessseseesesesseacsesscsesnenesseasesees 15312.6 COST TRENDS...ee esssecssssssesessessssesseaescesscesesessseaeseseseoessnseeneresecneses 154 12.7 PRESENT WORTH AND LEVELIZED COSTS ......cessesssssesererereeseees 154 12.8 EXTERNALITIES...eseccssscssesscecessssssscssecsesesssessseasesaesenseeeseonersx 155 12.9 VALUE OF WIND ENERGY FROM WIND PLANTS.........cece 156 12.10 SUMMARY........cc escssssssescssssssnsnssssssssseasscscsssseceesecssaeseaceesenseesenesecseees 157REFERENCESuu...essscsecscccecsescscssnssscssacseseneosssenssesescseaseeeseecssasacssecscnonesenss 157 PROBLEMS .........ecscsssessssscsseceecsesessecessssacecseseseneessssesesessasascesseesenssessessascnonenenes 158 vi 1 INTRODUCTION Industrialized societies run on energy.Economists look at monetary values (dollars)to explain the manufacture and exchange of goods and services.However,in the final analysis,the physical commodity is the transfer of energy units.While industrialized nations comprise only one-fourth of the population of the world,they use four-fifths of the world's energy.Most of these forms of energy are solar energy,which are subdivided into the two classifications. Stored Solar Energy:Fossil fuels;coal,oil and natural gas which are finite and therefore are depletable. Renewable Energy:Radiation,wind,biomass,hydro and ocean thermal.Many people discount renewable solar energy,some even calling it an exotic source of energy.But presently it is the source of all food,most fiber and in many parts of the world the source for heating and cooking [1].Other formsof energy are tides (due to gravitation),geothermal (heat from the earth)andnuclear(fission and fusion). The:main source of energy in industrialized nations is fossil fuels and when that factor is combined with the increasing demand and increasing population of the world,a switch to other energy sources is imminent.Whether this will be rational or catastrophic depends on the enlightenment of the public and their leaders.The use of wind as an energy source begins in antiquity.At one time wind was a major source of energy for transportation (sailing),for grinding grain and for pumping water.Except for pleasure sailing,the main long term use of wind has been for pumping water., 1.1.DUTCH WINDMILL The Dutch windmills for pumping large volumes of water from a low head are a famous attraction (Fig.1.1).Windmills of the same type were also used for grinding grain (Fig.1.2)and even for sawing wood.These large machines were as large as 25 m indiameterandwerealmostallofwood.They were quite sophisticated in termsof theaerodynamicsofthetherotorandblades.Another famous example is the sailwing turbines for pumping water for irrigation on the island of Crete. Figure 1.1 Dutch windmills for pumping water. angie of shufiers ConwoliedbyrodsandbellcranksConnectedtocross-shapedsoxderonrodpasengHoughCenteofwindshaft stock H ilLt} y) vantotemcapolma wheelandcabiefor¢eS angie Of snuners Brough wedaneh cnain wheel torturningcapbyhand $8Ck Norst (Orrven of man snafy ganon Figure 1.2 Diagram of Dutch windmill for grinding grain. 1.2 FARM WINDMILL Farm windmills were one of the primary factors in the settlement of the great plainsoftheUnitedStates[2].Beginning in the mid 19th century,water pumping windmills weremanufacturedinthetensofthousands.These early factory built machines of wood (Figs.1.3)have largely disappeared from the landscape,except for an isolated farm house or in museums. By 1900,almost all windmills were made of metal,still with multiblade vanes,and the fan or blades were 12-16 ft in diameter (Fig.1.4).Although the peak use of farmwindmillswasinthe30's and 40's when over 6 million were in operation,these windmills are,stil being manufactured and are being used to pump water for livestock andresidences. By3.Old WwFigure1 The farm windmill proves that wind power is a valuable commodity.For example, there are an estimated 30,000 operating farm windmills in the Southern High Plains of the United States.Even though the power output is low,0.2 to 0.5 kilowatt (kW),they collectively provide an output of 5 million watts or 5 megawatts (MW).If these windmills for pumping water were converted to electricity from the grid,it would require 15 megawatts of thermal power at the generating station and over one billion dollars (1990 dollars)for the transmission lines,electric pumps,etc.This does not count the dollars saved by not using fossil fuel to produce 130 million kilowatt hours (kWh)per year (equivalent to 80,000 barrels of oil per year).However,because many of these windmills are 30 years or older and maintenance costs are $200 to $300 per year,farmers and ranchers are looking at alternatives such as solar water pumping rather than purchasing new farm windmills. Figure 1.4 Farm windmill for pumping water for livestock and residences. 1.3.WIND CHARGERS As electricity became practical,isolated locations were too far from generating plants and transmission lines were too costly.Therefore,a number of manufacturers built stand alone wind systems for generating electricity (Figs.1.5,1.6).Most of these systemshadadirectcurrentgenerator,6 to 32 volts,and stored the electricity in batteries.Someofthelatermodelswere110volts. These systems are quite different from the farm windmill in that two or three propeller blades are used.The farm windmill is too inefficient for generating electricity, although it is well engineered for pumping low volumes of water. The wind chargers became obsolete when inexpensive electricity (subsidized) became available from rural electric cooperatives in the 40's and 50's.After the energy crisis of 1973,a number of these units were repaired for personal use or to sell.Small .companies also imported wind machines from Australia and Europe to sell in the United States during the 70's. 1.4 GENERATION OF ELECTRICITY FOR UTILITIES There were a number of attempts to design and construct large wind turbines for utility use [3-8].These designs centered on four different concepts for capturing wind energy (Fig.1.7):Magnus Effect,Savonius,and airfoil shaped blades with the axis of the rotor being horizontal or vertical. Figure 1.5 Wincharger,'small DC system (100 W)with air brakes. VERTICAL AXIS WIND TURBINE D SAVONIUS GIROMILL DARRIEUS HORIZONTAL AXIS WIND TURBINE ST RR mics EFFECTWIND .z -__ Aeea-_-ee san,eee ,aia NSS ,-, , Figure 1.7 Examples of rotors for wind turbines. A rotating cylinder in an airstream will experience a force or thrust perpendicular to the wind,the Magnus Effect.In 1926 Flettner built a horizontal axis wind turbine with four blades where each blade was a tapered cylinder driven by an electric motor.Thecylinders(blades)were 5 m long and 0.8 m in diameter at the midpoint.The rotor was 20mindiameterona33mtower.Rated power was 30 kW at a windspeed of 10meters/second (m/s). Madaras proposed mounting rotating cylinders (vertical)on railroad cars whichwouldgoaroundacirculartrackpropelledbytheMagnusEffect.The generators wouldbeconnectedtotheaxlesoftherailroadcars.In 1933,a prototype installation,which consisted of a cylinder 29 m tall and 8.5 m in diameter mounted on a concrete base,was spun when the wind was blowing to measure the force.Results were inconclusive and the prospect was abandoned. The Magnus Effect has been used for ships,called Flettner rotors,[9,10]and one ship operated using rotors for fuel saving from 1926 to 1933.In 1984 the Costeau Society had a sailing ship,Alcyone,built which used two fixed cylinders with an aspirated, turbosail [11]. 'In Finland,Savonius built 'S'shaped rotors which were similar to two halves of a cylinder separated by a distance smaller than the diameter.With a vertical axis there are no orientation problems due to different wind directions. In 1927,Darrieus invented a wind machine where the shape of the blade was similar to a jumping rope.His patent also covered straight vertical blades,a giromill. Later the Darrieus design was invented again by researchers in Canada. In 1931 the Russians built a 100 kW wind turbine (Fig.1.8)near Yalta on the Black Sea.The rotor was 30 m in diameter on a 30 m rotating tower.The rotor was kept facing into the wind by moving the inclined supporting strut which was on a carriage on a circular track.The blade covering was galvanized steel and the gears were of wood.Rotational speed and power were controlled by the adjustable pitch of the blades. had 4 Smith Putnam,1,250 kW©ont§aemM.nkPte,Figure 1.8 Russian wind turbine,100 kW.Figure 1. The Smith-Putnam wind turbine (Fig.1.9)was developed,fabricated and erected in two years,1939-1941 [3].The turbine,which was located on Grampa's Knob,Vermont,was connected to the grid of Central Vermont Public Service.The rotor was 53 m in diameter on a 38 m tower.Blades were stainless steel with a 3.4 m chord and each weighed 8,700 kg.The generator was synchronized with the line frequency by adjusting the pitch of the blades. At windspeeds above 35 m/s the blades were changed to the feathered position to shut the unit down.Rated power output was 1,250 kW at 14 m/s.The rotor was on the downwind side of the tower and the blades were free to move independently (teeter;perpendicular to the wind)due to wind loading. Testing continued from October,1942 until February,1943 when a main bearing failed.In May,1942,after 360 hours of operation,cracks were discovered in the blades near the root.The root sections were strengthened and further cracks were repaired by arc welding.The bearing was not replaced until March,1945 because of a shortage of materials due to the war.After the bearing was replaced,the unit was operated as a generating stationforthreeweekswhenabladefailedduetostressattheroot.Total running time was around1,100 hours.Even though the project was considered successful,it was not further pursued because of economics. -Percy Thomas,an engineer with.the Federal Power Commission,pursued .the feasibility of wind machines.He compiled the first map (Fig.1.10)for wind power in the United States and published reports on design and feasibility of wind turbines [4]. LINES OF EOuaL wine veLocries & an RELECTED WEATHER GUREAU STATION VALUES PARREEE ECAR WELTY 1 THE EE,GARRET ORL,SOW 668 Oc7te PNeOeNE I RIOTS Fe REEDERAN ME EO F009. After World War Il research and development efforts on wind turbines were centered inEurope.E.W.Golding summarized the efforts in Great Britain [5]and further efforts arereportedintheconferenceproceedingsoftheUnitedNations[6]. The British built two large wind turbines.One was built by Enfield,based on a designbytheFrenchman,Andreau,and was erected at St.Albans in 1952.The other was built by John Brown on Costa Hill,Orkney in 1955.The John Brown unit (Fig.1.11)was rated at 100kWat16m/s.Rotor diameter was 15 m on a 24 m tower.The unit only ran intermittently in 1955. Figure 1.11 John Brown wind turbine,100 kW,on Island of Orkney. The Enfield-Andreau wind turbine rotor was 24 m in diameter on a 30 m tower (Fig. 1.12),with a rated power of 100 kW at 13 m/s.This unit was quite different in that the blades were hollow and when they rotated the air flowed through the generator at ground level and out of the tip of the blades.This unit was moved to Grand Vent,Algeria,for further testing in 1957.Frictional losses were too large for this unit to be successful. The French also built several prototype wind turbines from 1958 to 1966.These included the 130 kW Neyrpic machine (Fig.1.13),which had a rotor diameter of 21 mon a 17mtower;a 800 kW wind turbine (Fig.1.14)located at Nogent Le Roi,which had a rotordiameterof31mona32mtower;and another unit located at St.Remy-Des-Landes with a rated power of 1000 kW at 17 m/s. Dr.Hutter of Germany designed wind turbines with lightweight fiberglass blades (Fig.1.15).The larger unit had a rotor 35 m in diameter and produced 100 kW at 8 m/s [12].This machine ran for one year 1957-1958. Figure 1 13 Neyrpic wind turbine,120 kW. 10 tN inFigure1.14 Nogent Le Roi wind turbine,Figure 1.15 German wind turbines: 800 kW.left 100 kW,right 10 kW. .Sng Since the Danes did not have any fossil fuel resources,they looked at connecting wind turbines into their national grid.The Danes had the only successful program.It began in 1947 with a series of investigations on the feasibility of using wind power and continued until 1968 [6,pp.229-240].A prototype wind turbine of 7.5 m diameter was built and remained in operation until 1960,when it was dismantled.A wind turbine at Bogo (Fig.1.16), originally constructed for direct current (DC)power in 1942 was reconstructed for alternating current (AC)in 1952.Rotor diameter was 13.5 m with a 45 kW generator.The results of the two experimental wind turbines were encouraging and culminated in the 200 kW Gedser wind turbine (Fig.1.16).This unit was erected in 1957 and was on line until 1968 when maintenance costs became too high.The rotor was 35 m in diameter on a prestressed concrete tower 26 m high.Blades were fixed pitch with tip brakes for overspeed control.In 1976 the ERDA (US)and DEFU (Denmark)furnished money to place the Gedser wind turbine in operation for a short time period. The successful program of the Danes was overshadowed by the failure of other large machines.The machines failed due to technical problems,mainly stresses due to vibration and control at high windspeeds.Others were economic failures.Everyone agreed there were no scientific barriers to the use of wind turbines tied to the utility grid. In the 60's development of wind machines was abandoned since petroleum was easily available and inexpensive. 11 h wind turbines:left,45 kW at Bogo;right,200 kW Gedser. Badin Figure 141 6 Danis 12 REFERENCES 1. 2. 3. Vaclav Smil and William E.Knowland,Energy in the Developing World,Biomass Energies,Plenum,1983. T.Lindsay Baker,A Field Guide to American Windmills,University of Oklahoma Press, 1984. Palmer Cosslett Putnam,Power from the Wind,D.Van Nostrand,1948. Percy H.Thomas,Electric Power from the Wind,March 1945;The Wind Power _Aerogenerator,March 1946;The Aerodynamics of the Wind Turbine,1949;and Fitting Wind Power to the Utility Network,1954,Federal Power Commission Reports. E.W.Golding,The Generation of Electricity by Wind Power,Halsted Press,John Wiley, 1955. New Sources of Energy,Proceedings of the Conference,Vol.7,United Nations,August1961.Wind Energy Developments iin the 20th Century,NASA Lewis Research Center,1979. Frank R.Eldridge,Wind Machines,2nd Ed.,Van Nostrand Reinhold,1980. Stephen D.Orsini,"Rotorships:Sailwing Ships Without Sails,"Oceans,16:16-29,Jan/Feb,1983. C.P.Gilmore,"Spin Sail,"Popular Science,224:70-73,Jan 1984. .JA.Constants,et al.,Alcyone,Daughter of the Wind,The Ship of the Future,Regional Conference on Sail-Motor Propulsion,Asian Development Bank,1985. .U.Hitter,"Operating Experience Obtained with a 100-kW Wind Power Plant,”Kanner Associates,N73-29008/2,NTIS,1964. 13 2 ENERGY 2.1 PHILOSOPHY Scientists have been very successful in understanding and finding unifying principles.Many people take the resulting technology for granted and do not understandthelimitationsofhumansasbeingpartofthephysicalworld.There are moral laws (or principles),civil laws and physical laws.Moral laws have been broken such as,murderandadultery;civil laws have been broken,as most everybody has driven over the speed limit,BUT NOBODY BREAKS A PHYSICAL LAW. Therefore,we can only work with nature and we can not do anything which violates the physical world.A major unifying concept is energy and how energy is transferred. The area which deals with heat,a form of energy,is called thermodynamics. 2.2 DEFINITION OF ENERGY AND POWER To understand wind turbines,the definitions of energy and power are needed. Work is the force on an object moved through some distance. Work =ForceX Distance W =FD,Joule (J)=Newton (N)meter (m)2.1 A number of symbols will be used and with the easy availability of personal computers and calculators,sample calculations will be used for illustration and understanding. Many people have a mental block as soon as they see mathematical symbols,but everybody uses symbols.Ask most any person what piano means and they understand the symbol,but to a South Seas Islander,a piano is "A big black box,you hit him in teeth and he cries.".By the same token,equation 2.1 can be understood as a short hand notation for the words and concepts written above. Moving objects,doing work,and changing position requires energy,so energy and work are measured by the same units. Joule,calorie,BTU,kilowatt hour (kWh) calorie =amount of energy required to raise 1 gm of water 1 degree centigrade British Thermal Unit (BTU)=amount of energy required to raise 1 lb of water 1 degree Fahrenheit. Some conversion factors: ical =4.12 J kilocalorie (1 Cal),the unit used in nutrition =1000 calories1BTU=1055J1barrelofoil(42 gal)=6.12 X109J =1.7X 103 kWh1tonofcoal=2.5X107BTU =2.2X 1019 J 1 quad =1015 BTU 1kWh =3.6X 106 J 14 Objects in motion can do work,therefore they possess energy,kinetic energy (KE): KE =0.5mv2 | 2.2 where m is the mass of the object and v is its speed. Example:A car with a mass of 1000 kilograms (kg)moving at 10 m/s has a kinetic energyof KE =(1/2)(1000)(10)2J =50,000U =5X 104J Because objects interact,for example by gravity,then due to their relative position they can do work or have energy,potential energy (PE).To raise a 1 kg mass 1 meter requires 10 J of energy.At that upper level,that object has 10 J of potential energy.. Power is the rate of energy use or production. Power =Energy/Time P =EA,Watt 2.3 If it takes one second to raise that 1 kg mass,because the energy used is 10 Joules,then the power is 10 watts.If either power or energy is known then the other can be calculated for any time period. E=Pt:2.4 Example:A 10 kilowatt electric motor which runs for one hour consumes 10 kWh of energy.A kilowatt (kW)is a measure of power and a kilowatt hour (kWh)is a measure of energy. Example:Ten,100 Watt,light bulbs which are left on all day will consume 24 kWh of energy. 2.3 FUNDAMENTALS CONCERNING ENERGY Today's understanding of energy can be embodied in the following laws or principles:) 1.Energy is conserved.Energy is not created or destroyed,only transformed fromoneformtoanother.In layman's terms,this means that all you can do is break even.A number of patents have been issued for perpetual motion machines [1],a device which produces more energy than the energy needed to run the machine. A number of people have invested money in such machines,but needless to say,the money was lost since the devices contradict the first law of thermodynamics. 2.Thermal energy,heat,cannot be transformed totally into work.In layman's terms,you cannot even break even.Another way of looking at it is that systems tendtowarddisorderandintransformationsofenergy,disorder increases.In succinct terms,entropy is increasing. This means that some forms of energy are more useful than other forms.For example,the energy in a gallon of gasoline is not lost but only transformed into heat by a 15 car.However,after the transformation,that energy is dispersed into a low grade form (more entropy)and cannot be used to do more work. 2.4 EXPONENTIAL GROWTH Our energy dilemma can be analyzed in terms of the fundamental principles.A corollary of the first law;it is a physical impossibility to have exponential growth of anyproductorexponentialconsumptionofanyresourceinafinitesystem. The present rate of consumption and the size of the system give a tendency for people to perceive the resource as either infinite or finite.The total energy output of the sun and the amount of mass in the solar system appear to be an infinite source at the present rates of use,even though the solar system is finite.The energy dilemma is defined within the context of the system and our present energy dilemma is due to the finite amount of fossil fuels on the earth. The easy way to understand exponential growth (Fig.2.1)is to use the example of money.Suppose Sheri receives a beginning salary of $1/year with the stipulation that the salary is doubled every year,a 100%growth rate.It is easy to calculate the salary by year (Table 2.1).After 30 years,her salary is one billion dollars per year. 250 200 150 100 50 0 0 1 2 3 4 5 6 7 8 Figure 2.1 Exponential growth curve - Notice that for any year,the amount needed for the next period is equal to the total sum for all the previous periods plus one. Suppose a small growth is used,the doubling time (T2)can be calculated by, Ta =69/R --where R is the %growth per unit time.2.5 16 Table 2.1.Salary by year with a growth rate of 100%,doubling time of one year. year salary amount =2t cumulative 0 $1 20 $1 1 2 21 3 2 4 22 7 3 8 23 15 4 16 24 31 5 32 25 63 t at at+1-4 30 1 X 109 231-4 There are numerous historical examples of growth;population,2-3%/yr;gasoline consumption,3%/yr;world production of oil,5-7%/yr;electrical consumption,7%/yr. Notice that if we plotted the value per year for smaller rates of growth (Fig.2.2),the curve would be the same as Figure 1,only the time scale along the bottom would be different. THE FINAL RESULT IS STILL THE SAME.WHEN CONSUMPTION GROWS EXPONENTIALLY,ENORMOUS RESOURCES DO NOT LAST VERY LONG. 0 q T T 1000 1400 1800 2200 Figure 2.2 Growth of human population since the year 1000 A.D. 17 Doubling times for some different yearly rates are given in Table 2.2. Table 2.2.Doubling times for different rates of growth. Growth Doubling Time %/year years 1 69 2 35 3 23 4 18 5 14 6 12 7 10 8 9 9 8 10 7 15 5 2.5 USE OF FOSSIL FUELS The night sky of the Earth taken by satellite (Fig.2.3)illustrates the tremendous amount of energy radiating into space.In the United States,6%of the world's populationconsumes30%of the world's energy resources and 50%of the mineral resources.The United States uses twice as much energy as the following countries combined:Canada, Mexico,Central America,South America,Africa and all of Asia except for Japan.Asia contains the two most populous countries in the world,China and India.It is physically impossible to continue to consume fossil fuels exponentially.The magnitude of the problem can be seen by the cost for oil imports in the US.When consumption was 16millionbarrelsofoilperdayandapproximately40%was imported,the cost was $500 million per day or around $100 billion per year for oil at $40/bbl.Even though consumption of imported oil was reduced in the 80's,the cost for imported energy was still quite expensive.In the 90's oil consumption and imports in the US increased again toward the previous levels where one half is imported.An order of magnitude calculation makes the analysis quite clear. M.King Hubbert,a world authority on estimating energy resources,began his analysis in the early 50's when he was with Shell Research.Much of the data and graphs on our energy dilemma come from his publications [2]. The important concept is that crude estimates of resources give fairly good answers as to when the resource will be consumed under exponential growth.Also,predictions onthefutureuseoftheresourcecanbemadefrompastproductionasafiniteresourcewillprobablybesimilartothebellcurve(Fig.2.4).In 1956,he predicted that United States oil production would peak around 1970,which it did.Notice in Figure 2.5 that even if a larger resource base is assumed,with exponential growth,the larger resource is used up at about the same time.Also,as the resource is used,it becomes more difficult to obtain the resource (Fig.2.6),i.e.it takes more energy to obtain the resource.The predictions can also be made for natural gas (Fig.2.7)and coal. 18 ae s .*gt «3ewefo0¢.S 6 ..eae.. *cr rs ."3 Ppa el .yx?..8 8M Peete.a anosrdSaraar :.r)te °oss *. si:ens al «a ry e . .-a ae aM . :eset hr ee 's a-_Rage pes on 8 eM REIN ase , *aOR cee . +,"nyt *ae . .F oa te :2 are Teas al .a 4 "¢a »?”.ow bd *.7 ete ..es «agetwy.wyte-."qe .°y3*f..SS.”y .So ey aa oe a ...Je hia ss eo?i)cd ''a .".: "e ce} --%..2 a igen: ry . *') ue '.e.6 . . o Figure 2.3 Radiation from lights and fires.Left,North and South America.Right,Europe, Africa,Middle East,India,and former Soviet Union.From The Earth at Night,mosiac of 40 satellite images,W.T.Sullivan. The bell curve will not be exact as advanced technology will allow us to recover more of the fossil fuels and extend the time the resource is available.However the end result is still the same.The actual production for oi!and gas in Texas (Figs.2.8,2.9) corroborates the above analysis [6].Texas is a major producer in the United States for oil and gas,however in the years 1994-95 Texas became an net importer of energy.: In long terms,the use of fossil fuels could be called the fickle finger of fate (Fig. 2.10).Possible futures are conservation (saving of energy,more efficient use of energy), steady state with no growth,catastrophe and/or catastrophe with some revival (Fig.2.11). K RN NX Figure 2.4 The bell curveUf”19 0 \ iW Vs _-P| .1850 1900 1950 2000 2050 Figure 2.5 Prediction in 1955 of the peak in the rate of US crude oil production. 300 NoOOoofExploratoryHolesooOBarrelsofCrudeOilperFoot1 2 3 4 5- Cumulative Total Footage of Exploratory Drilling in Billions of Feet Figure 2.6 Estimation of crude oil production per foot of exploratory drilling in the US. 24 20 16 12 0 1875 \\ \'Lr---XXXXRGREGG=WN 1925 1975 YEAR 2025 2075 Figure 2.7 Estimate in 1955 of natural gas to be produced in United States. 2 Oo 1200 7 Cumulative (54 Bbbl) 1000 8 1991 =644 MMbbi =800 +Advanced technology =4 ($20 -25/bbI,1990$) 2 600 + =] 8. =400 -Texas Comptroller[e)4 ($20 -25/obl,1991$) 200 -Existing technology 24($20 -25/bb!,1990S)Qateg 0 Tc oT LI U qt 1 J q T q TT Lu q UJ qv Li qT t >q q q 1940 1960 1980 2000 2020 2040 Year Figure 2.8 Texas crude oil production and prediction for the future (W.L.Fisher,1992). 10 7 /Cumulative (273 Tcf) 8 ow 3Sco 1991 =5.5 Tet Advanced Ss 50 technology 3 ($3/Mef,1990$) 8a4 3.6 7)2 So 4 Texas Comptroller ($20 -25/bbI 24 oil price,1991$)by,1Existingtechnology2.0 <6 5 ($3/Mct,19908)ha,o ated 0 ee Se ee es eee Oe ee Se ee eee ee eee ee ee ee eee ee ee ee ee ee 1940 1960 1980 2000 2020 2040 Year Figure 2.9 Texas natural gas production and prediction for the future (W.L.Fisher,1992). 21 -5 -4 -3.-2 -1 0 +1 +2 #+3 +4 +5 Figure 2.10 Fossil fuel exploration in human history. 10- 84 6 = 1990 5 billion 4- 2m 0 ¥T T 1000 1400 1800 2200 2400 Figure 2.11 Possible future paths for the population of earth. 2.6 MATHEMATICS OF EXPONENTIAL GROWTH Values of future consumption,r,can be calculated from the present rate,ro,and the fractional growth per year,k. "1 =Ioekt 2.6 where e is the base of the natural log and t is the time. ' Example:Present consumption is 100 units/year and growth rate is 7%. fo =100 units/year k =0.07 suppose t =100 years. 22 r =100 60.07°100 =10067 =100x 1097 =1x 10°. The consumption per year after 100 years is a 1000 times larger than the present rate of consumption. DOUBLING TIME . Doubling time,Ta in years,for any growth rate can be calculated from Eq.2.6. TeK KTr=21y=18 2,or 2=e ".Take the In of both sides of the equation. In2 =kTo,which is 0.69/k =To or . T2 =69/R which is Eq.2.5,where R is the percentage growth rate per year. The total sum of the resource used from any initial time to any final time,T,can be estimated by summing up the consumption per year.This can be done by using a spread sheet on personal computers.If r is known as a function of time then the total consumption can be found by integration.For exponential growth,the total consumption is given by Tc={rdt=|roe dt0 -.C =e (e--1).2.7 2.7 LIFETIME OF A FINITE RESOURCE lf the magnitude of the resource is known,or can be estimated,then the time,Te, when that resource is used up,can be calculated for different growth rates.Size ofresource,S =C is put in Eq.2.7,and the resulting equation is solved for Te In {ke +1}2.8 If the demand is small enough or is reduced exponentially,a resource can essentially lastforever.However,with increased growth,Te can be calculated for different resources, and the time before the resource is used up is generally short (Table 2.3). 23 Table 2.3:Time when domestic oil will be used up for US.In 1970,fo =3.3 x 109 bbl/yr. Resource base R1 is for the contiguous US,94 x 109 bbl R2 includes Alaska,104 x 109 bbl R3 includes oil shale,209 x 109 bbl Demand Growth Rate . Years %/Y ear Ri R2 R3 0 29 32 =63 5 18 19 29 10 14 14 20 Similar calculations can be made for world oil reserves (Table 2.4).Historically world oil production has been increasing at 7%/yr,which says,if it continues at that rate,the supply will only last 30 to 50 years.Physically,wworld oil production cannot increaseexponentially.. Table 2.4:Time for use of world oil resources. fo =1.7 x 1019 bbl,as of 1973 R1 =1.7x 1012 bbl R2 =2.45 x 1012 bbl,includes oil shale %/Year 'Years: R1 R2 0 100 144 1 69 89 3 46 56 5 36 42 7 30 34 According to the energy companies,the continued growth in energy use in theUnitedStatesistobefueledbyourlargestfossilfuelresource,coal,and nuclear.How long can coal last if we continue to increase production to offset decline in production ofoilandtoreducetheneedforimportationofoil?The preceding analysis will allow you tomakeorderofmagnitudeestimates. 2.8 USE OF ENERGY Energy can be used to do work (mechanical energy),to heat an object or space(thermal energy)and be transformed to electrical energy or stored as potential orchemicalenergy.In each transformation,an upper limit on efficiency can be determinedbythesecondlawofthermodynamics.: 24 In thermal processes,this efficiency is determined by the temperatures of the hot and cold reservoirs. _TH-Te,eft =HE 2.9 In an electrical generating plant which uses steam at 700 deg C (973 deg K)and on the down side is cooled by water to 300 deg C (573 deg K),the maximum efficiency possibleisaround0.41 or 41%.Modern power plants have efficiencies of around 40%.In other words,60%of the stored chemical (or nuclear)energy is rejected and 40%is converted into electricity. Temperature is a measure of potential for heat transfer and is not a measure of energy. Tdeg K =Tdeg C +273 Since efficiency is always less than 1,for a system or device to continue to operate, energy must be obtained from outside the system.For every energy transformation there is an efficiency,and the total efficiency is the product of the individual efficiencies (multiply). Example:Lights in your home. Transformation Efficiency,% Production of coal 96 Transportation 97 Generation of electricity 38 Transmission of electricity 93 Incandescent bulb 5 Overall Efficiency 1.6% You can see why fluorescence lights for commercial buildings and compact fluorescence lights for your home are so important. As a corollary to the second law efficiency,a system for producing energy must beanetenergygainer.In the physical world,subsidies or economics ($)do not change theoutcome.For example,at some point in the future it will take more energy to drill for oil than the amount of energy in the oil produced.At that point,it is foolish to subsidize thedrillingforoilasanenergysource.It might be that the productis so useful as a liquid fuelorasasourceforotherproducts,that it could be subsidized by other energy sources. 2.9 SUMMARY Continued exponential growth is a physical impossibility in a finite (closed)system.Previous calculations made about the future are just estimations and possible solutions to our energy dilemma are: 25 1.Conservation and more efficient use of energy.Since the first energy crisis,this has been the most cost effective mode of operation.It is much cheaper to save a barrel of oil than to discover new oil. Reduce demand to zero growth rate and begin a steady state society. 3.Redefine the size of the system:colonize the planets and space.From our present viewpoint,the resources of the solar system are infinite and our galaxy containsover100billionstars.Because the earth is finite for population and its use of the earth,a change to asustainablesocietywhichdependsprimarilyonrenewableenergybecomesimperativeonalongtimescale.hoREFERENCES GENERAL Lester R.Brown,et.al.,State of the World,1986,W.R.Norton,1986. Wilson Clark,Energy for Survival:The Alternative to Extinction,Anchor Press, 1974.K.Eric Drexler,Engines of Creation,Anchor Press/Doubleday,1986.Thomas H.Lee,Ben C.Ball,and Richard D.Tabors,Energy Aftermath,HarvardBusinessSchoolPress,1990.Amory Lovins,Soft Energy Paths,Toward a Durable Peace,Ballinger,1977. John Naisbitt,Megatrends,Warner Books,1982. Norris W.Firebaugh and Lon C.Ruedisili,Editors,Perspectives on Energy,Oxford University Press,1978. Timothy J.Healy,Energy,Electric Power and Man,Boyd &Fraser,1974. Nicholas Lenssen,"Providing Energy in Developing Countries,"State of the World 1993,W.W.Norton,1993,p.101. Howard T.Odum,Environment,Power and Society,Wiley-Interscience,1975. Robert H.Romer,Energy,An Introduction to Physics,W.H.Freeman,1976. Managing Planet Earth,Special Issue,Scientific American,Sep 1989. Energy for Planet Earth,Special Issue,Scientific American,Sep 1990. SPECIFIC '1.Ken Adler,"The Perpetual Search for Perpetual Motion",American Heritage ofInventionandTechnology,Summer 1986,p 58. 2.M.King Hubert,"Energy Resources",Resources and Man:National Academy ofSciences,W.H.Freeman,1969,pp 157-242,also in Perspectives on Energy,p 109,and "Energy Resources of the Earth",Sci.Am.,1971,p 60. 3.R.C.Lindholm,"The Oil Shortage -A Story Geologists Should Tell",Journal of Geological Education,V.28,1980,p 36. 4.Albert A.Bartlett,"Forgotten Fundamentals of the Energy Crisis",Amer.J.Phys.,46(9),Sept 1987,p 876. G.Pazik,"Our Petroleum Predicament",Fishing Facts,Nov 1976,p 1. 6.State of Texas Energy Policy Partnership,STEPP,Volume One,Printed by TheRailroadComission,Austin,Texas,March 1993.nn26 PROBLEMS 1. 2. A snowball,mass =0.5 kg,is thrown at 10 m/s.How much kinetic energy does it possess?What happens to that energy after you are hit with that snowball? The Chamber of Commerce and the Board of Development are always promoting their city as the place for new industry.If a city has a population of 100,000 and a growth rate of 10%/year,what is the population after 5 doubling times?How many years is that? The world population in 1985 was around 4.5 billion.How many people will there be on the earth by the year 2050?Assume present rate of growth of population.How does today's population,compare with your prediction for this year? If the growth rate of population could be reduced to 0.5%/year,how much longer would it take to reach the same population as in problem 3? The most economical size of nuclear power plants is around 1000 megawatts.How many nuclear power plants would have to be built in Texas over the next 50 years to meet the long term historical growth of 7%/year in demand for electricity?In 1993 the generating capacity for the State was around 50,000 megawatts. From problem 5,what is the total cost if the installed cost of a nuclear plant is around $1800/kW?Suppose coal plants were installed at $1200/kW,what is the cost. If the plants in problem 5 were fueled by coal,how many tons of coal would be needed for the year 2050?Use the following conditions;plants were operated at 95%capacity and the efficiency of conversion is 35%. What is the efficiency at a nuclear power plant if the incoming steam is at 700 degrees C and the outgoing steam is at 310 degrees C. The Hawaii Natural Energy Institute tested a 100 kW OTEC system (ocean thermal energy conversion).The surface temperature is 30 degrees C and at a depth of 1 kmthetemperatureis10degreesC.Calculate the maximum theoretical efficiency of an OTEC engine.. Assume the coal reserves of the United States are 1.5 x1012 metric tons.At today's rate of consumption,how long would that last? .For problem 10,assume a growth rate of coal consumption of 10%per year.How long will the coal last? For your home,estimate the power installed for lighting.Then estimate the energy used for lighting for one year. From problem 12,estimate the energy saved if you converted your lighting fromincandescenttocompactfluorescence.Fluorescence lights are more efficient,more light per watt. What is the maximum power (electrical)used by your residence (all you appliances, lights,etc.are on at the same time)? 27 3 WIND CHARACTERISTICS 3.1 GLOBAL CIRCULATION The motion of the atmosphere can vary in distance and time from the very small to the very large (Table 3.1).There is an interaction between each of these scales and the flow of air is complex;global circulation which encloses eddies which enclose smaller eddies until finally the microscale is reached. Table 3.1.Time and Space Scale for Atmospheric Motion. Name Time Length Example general circulation Weeks to years .1000 to 40,000 km tradewinds jet stream synoptic scale _.days to weeks 100 to 5000 km cyclones .anti-cyclones hurricanes mesoscale minutes to days 1 to 100 km tornadoes thunderstorms land-sea breeze microscale seconds to minutes <1km turbulence The two main factors in global circulation are the solar radiation and the rotation of the atmosphere and the earth.The seasonal variation is due to the tilt of the earth's axis to the plane of the earth's movement around the sun.Since the solar radiation is larger per area when the sun is directly overhead,there is a transport of heat from the regions near the equator toward the poles (Fig.3.1).Because the earth is rotating on its axis and there is conservation of angular momentum,the wind will be shifted in the northern hemisphere as it moves along a longitudinal direction.The three cell model explains the predominate surface winds (Fig.3.1).Those regions in the Northeast Tradewinds are generally good locations for the utilization of wind power.However,there are exceptions, as Jamaica is not nearly as windy as Hawaii. Superimposed on this circulation is the migration of cyclones and anti-cyclones across the mid-latitudes which disrupt the general flow.Also the jet streams,the fast core of the general westerlies at upper levels,influence the surface winds. Local winds are due to local pressure differences and are influenced by thetopography;friction of the surface due to mountains,valleys,etc.The diurnal (24 hr)variation is due to temperature differences between day and night.The temperature differences between the land and sea also cause breezes,however,they do notpenetrateveryfarinland(Fig.3.2). 3.2 EXTRACTABLE LIMITS OF WIND POWER Solar energy drives the wind which is then dissipated due to turbulence and friction at the earth's surface.The earth's atmosphere can be considered as a giant duct,and ifenergyistakenoutatonelocation,it is not available elsewhere.Therefore,it is importanttodistinguishbetweenthekineticenergyinthewindandtherateandlimitsofthe extraction of that energy;the power in the wind and the maximum power extractable [1]. 28 Q. A NORTH POLE WARM AIR EQUATOR POLAR EASTERLIES KS DOLDRUMS EQUATOR Figure 3.1 General atmospheric circulation. WARM AIR SEA BREEZE COOL AIRLAND BREEZE LAND LAND . SEA SEA Figure 3.2 Sea breezes,day,and land breezes,night. A comparison can be made on the basis of the kinetic energy of the winds per unitareaoftheearth's surface.Of the solar input only 2%is converted into wind power,and 35%of that is dissipated within one kilometer of the earth's surface.This is the wind power available for conversion to other forms of power or energy. The amount extracted would be limited by the criteria of not changing the climate. The uncertainties are very large in determining such criterion.Man would be substitutingwindturbinesfornaturallyoccurringfrictionalfeaturessuchastrees,mountains,etc. 29 Gustavson assumed the extractable limit as 10%of the available wind power within 1 km of the surface.When these values are applied to the contiguous 48 states,the limit would be 2 x 1012 watts (2 million MW),or 62 quads/year.Through 1980-1993,the United States used around 80 quads/year,so wind energy represents a very large energy source. On a global scale,wind can be compared to other renewable sources (Table 3.2). In locations with high windspeeds,wind power is comparable to or better than the amount of solar power.The wind energy available represents approximately twenty times the rate of global consumption. Table 3.2.Summary of Global Values for Renewable Sources. Extractable Power Power Energy Watts Watts quads/yr solar 1.8 x 1017 wind .3.6 x 1015 1.3 x 1014 3900 hydro 9x 1012 2.9 x 1012 86 geothermal 2.7 x 1018 1.3 x 1011 4 tides 3 x 1012 6 x 1011 1.9 3.3 POWER IN THE WIND The moving molecules of air have kinetic energy,so locally the amount of molecules moving across some area during some time period determines the power (Fig. 3.4).This area is not the surface area of the earth,which was referred to in the estimation of extractable power and energy,but the area perpendicular to the wind flow. P =KEt =0.5mv2/t 3.1 The mass,m,in the volume of the cylinder which will pass across the area,A,in time,t, can be determined from the density of the air,p,and the volume of the cylinder,V. p=mV .V =areaXlength =AL m=pV=pAL Substitute this value of mass into Eq.3.1. P =05pALv2/t Only those molecules with a velocity,v =L/t,will cross the area in time,t,and those further to the left will not.The power across that area is P=O05pv3A. or P/A =0.5pv3,Watts/m2 3.2 30 The wind power per unit area perpendicular to the flow of the wind is proportional to thevelocitycubed.Therefore,windspeed is the most important factor in determining wind power and wind energy. Figure 3.4 Flow of wind through a cylinder of area A. As a first estimate,the average density of air is assumed to be 1 kg/m3 and thepower/area is P/A =0.5 v3 .3.3 From Eq.3.3 the power/area in the wind can be calculated for different windspeeds (Table 3.3). Table 3.3.Estimated Wind Power per Area (Perpendicular to the Wind). Windspeed Power m/s kW/m2 0 0 5 0.06 10 0.50 15 1.68 20 4.00 25 7.81 30 13.50 Note that if the windspeed is doubled,the power is increased eight times,and the power at 25 m/s is 125 times the power at 5 m/s.Because there is so much power and energy in the wind at high windspeeds,there is usually some damage during severe storms.This isalsothereasonwindturbinesdonotextractalltheavailableenergyathighwindspeeds. All wind turbines have some means of control,or they would be destroyed in high winds. Example:A wind turbine with a radius of 2 m,area =12.6 m2,would have approximately100kWofwindpoweracrossthatareaduetoa25m/s windspeed. A first estimation of wind power potential (power/area)can be calculated using the annual mean windspeed,which can be estimated from the mean hourly speeds or othermeasurementsofwindspeed.However,use of average or mean windspeeds willunderestimatethewindpowerbecauseofthecubicrelationship.For example,Culebra, 31 Puerto Rico,Tiana Beach,NY,and San Gorgonio,CA have an annual average windspeed of 6.3 m/s,but their annual average power potential is 220,285,and 365 W/m2,respectively [2].For a better estimate of the wind power potential for any extended time period,you would need to know the frequency distribution of the windspeeds;length of time for each windspeed value or the number of observations within each windspeed range. Example:Suppose the wind blows at 5 m/s for one hour and 15 m/s for another hour. During the two hour period,the average windspeed is (5 +15)/2 =10 ms. Power/area calculated from the average windspeed is 500 watts/m2.However, the power/area for the first hour is 62.5 and for the second hour is 1687.5,and the average for the two hours is 875 W/m2,which is 375 W/m2 larger than the value calculated by using the average windspeed.. Wind power also depends on the air density. Pr-VP 273p=1.2029-Se,kg/m3 3.4 where Pr =atmospheric pressure,mm of Hg VP =vapor pressure,mm of Hg T =temperature,degrees Kelvin. The vapor pressure term is a small correction,around 1%,and can be neglected.High temperatures and low pressures reduce the density of air,which will reduce the power per area.A major factor for change in density is the change in pressure with elevation.A 1000 m (3,280 ft)increase in elevation will reduce the pressure by 10%and thus reduce the power by 10%.If only elevation is known,air density can be estimated by p =1.226 -(1.194x10"}z where z is the elevation in meters. The standard density for comparing output of wind turbines is 1.226 kg/m?,which corresponds to a temperature of 15 degrees C.For example,the average density for Amarillo,Texas is around 1 kg/m'.When compared to sea level at 0 deg C (273 deg K), there would be 23%less power at Amarillo for the same windspeeds.With the measurement of windspeed,pressure,and temperature,wind power can be calculated from Eq.3.2. The energy per area for a time period of the same windspeed is E/A =(P/A)t,kWh/m2 3.5 3.4 CHANGE IN WINDSPEED WITH HEIGHT Friction reduces the windspeed near the surface.The change in windspeed withheight,wind shear,has been measured for different atmospheric conditions [3,Ch.4].The windspeed at some other height can be approximated by a power law. 32 av=Voli].3.6 where Vo =measured windspeed Ho =height of known windspeed vo H =height The exponent a is around 1/7 for a stable atmosphere (decrease in temperature with height),however «will vary,depending on terrain and atmospheric conditions.From Eq. 3.6 the wind shear,change in windspeed with height,can be estimated (Fig.3.5). HEIGHT WINDSPEED m/s m 12.6 50 a 12.240 a 11.7 30 > 14 20 a 10 10 38 a 5 -a "SURFACE ---- Figure 3.5 Change in windspeed with height,wind shear.Calculations are for known windspeed of 10 m/s at 10 m,a =1/7. Other formulas for estimating windspeed with height are __In(H/Zo)V=Vo inl Jt.)3.7 In(1 +H/Zp)3.8 where Zo is the roughness parameter.Equation 3.8 allows a zero windspeed at thesurface.The roughness parameter ranges from 0.02 m for flat open terrain with shortgrasstolargerthan1mforroughterrain(Table 3.4). 33 Table 3.4.Typical Values of the Roughness Parameter,Zo. Surface Zo (cm)References Smooth Mud Flats 0.001 Sellers (1965) Desert 0.03 Sellers (1965) Snow 0.10 Priestly (1959) Grass (5-6 cm)0.75 Sellers (1965) (4 cm)0.14 Sellers (1965) (2-3 cm);0.32 Sellers (1965) Short Grass (1.5 cm)0.20 Priestly (1959) (3.0 cm)0.70 Priestly (1959) (4.5 cm)1.7-2.4 Priestly (1959) Thick Grass (10cm)2.3 Sutton (1953) Thin Grass (10cm)0.7 Sutton (1953) Long Grass (60-70 cm)3.7-9.0 Priestly (1959) Thick Grass (50cm)9.0 Sutton (1953) Thin Grass (50 cm)5.0 Sutton (1953) Wheat 22.0-23.3 Sellers (1965) Corn 71.5-127 Sellers (1965) Large City 165 Sellers (1965) Citrus Orchard 198 Sellers (1965) Fir Forest 283 Sellers (1965) Forest (17 m)500-850 Munn (1966) Trees,Fields,Buildings,40-260 Slade (1969) Irregular Topography Water 0.164 Keyser and Anthes (1977) Cropland 20 Keyser and Anthes (1977). Swamp 25 Keyser and Anthes (1977) Cropland with Pastures 35 Keyser and Anthes (1977) and Forest Forest with some 50 Keyser and Anthes (1977) Cropland and Pasture Forest and Woodland 75-100 Keyser and Anthes (1977) Urban 100 Keyser and Anthes (1977) 3.5 WIND DIRECTION Changes in wind direction are due to the general circulation of atmosphere,again on an annual basis (seasonal)to the mesoscale (4-5 days).The seasonal changes of prevailing wind direction could be as little as 30 degrees in trade-wind regions to as high as 180 degrees in temperate regions.In the plains of the US,the predominate direction of the winds are from the south to southwest in the spring and summer and from the north in the winter.Traditionally,wind direction changes are illustrated by a graph indicating % of winds from that direction or a rose diagram (Fig.3.5). 34 --FREQUENCY DIRECTION , eme=WINDSPEED Tr7,r ref 32 "7,32 we --12 Cd >20 eo : c=we eww e QO la}ZX 99 Re =-beu Z 20 wiWP-f ---+8 1o L QZzFB0OS0=N NE E SE S SW W NW N NE E SE S SW W NW Amarillo,TX Kahua Ranch,Ht N Figure 3.5 Wind direction for a continental location (Amarillo,TX)and trade wind location (Kahua Ranch,Hl). 3.6 WIND POWER POTENTIAL The most comprehensive,long term source of information on windspeeds, pressure,and temperature is data collected at the National Weather Service Stations (NWS).Other sources on record at the National Climatic Center,Asheville,NC,are from FAA stations,US air bases,Coast Guard,etc.In the early 60's anemometers were changed from their previous locations (20 to 30 m heights)on airport control towers, hangers,etc.,to towers (around 6 m height)close to the runways and at least 1 km from buildings. The best source of long term data is the NWS data collected after 1970.Windspeed data are recorded on a strip chart and the observer estimates a windspeedover1to2minuteseachhour.Windspeed data along with pressure,temperature,and other climatological data are put on magnetic tape for every hour.Data are available on tapes and CD-ROMs,data can be down loaded to your computer through internet,anddatasheetsofmonthlysummaries(Table 3.5)can be purchased.The National Weather Service _is converting to automated surface observation systems as of 1993-94. Windspeed and direction are sampled at 1 Hz,averaged over 5 seconds and rounded. Then a 2 minute running average is calculated from 24,5 second samples. 35 Table 3.5 Excerpt from monthly summary for NWS,Amarillo,TX,March 1984.For the days shown,average daily pressures (in of Mercury)are:1,26.23;2,26.30;4,26.28;5, 26.40;7,26.35;8,26.53. OBSERVATIONS AT 3 HR INTERVALS 7 eeeroyVIST= =|lenin emperature}|wind |_|[wiST TEMPERATURE ||KIND lE Jes}S foment}fe [FE]ETE E}so |iweammer]fs fe [El 2"VE [eg]=|=-/212 [E/E]=Else]=[F s/EIB E/ETE NAR 1st NAR 2nd 7 03)of UNL!-20 31/26 416 [54/23 |8]8)200)20 38 133]25 |60/09 |506|ol unt}30 32126 [16 152)30 |10]oj unt]20 34130 (24 /o7/01 |803}O/UNL]30 38|30 416 |41/32 [12]of UNL}15 41136 |28 |60/34]912)of uNt|30 53.141 124132)36 |8]o|uN]20 57143 |26 |30/05 |715)8]UNL]30 65 145.121 119/01 |4]t}unt]30 62.145 [23 (22/17 }1118}10]UNL]20 63}4420}19]02 |4]9]unt}30 60 |44 |23 |24)16 11219]unt]30 46137124 42}11 |9]a}uNtt 30 65136 |24 144145 |1024lrol200]30 42135124 149115 |91 alum}30 41135 |25 tealta [10NAR4thHARSth 03|4{unt)30 36 [32 [27]70/36 1141 10)60)30 33.427 [14 146)00 [13Db|9|too}30 33130126 |76101 [45 |tol 55]30 3025 {14 [51]02 |1503110)2501 30 35.131 126 |70/02 18 |to]55)30 28 |24/16 [64/01 |15121a)|30 41 134124 151]05 |17 |10]100}30 35 |28 115 |44lo2 |t615110150]30 40 133 121 |47]36 |20 |10)200 30 39.129)6 |281 36 |1118)5)UAL)20 39.132 ]}19 |45/02 |201 a)um!20 39/29]7 |26/02 11121110]70)20 35129117 |48/02 |18}ol unt]30 30/23 |6 |36}00 |024,BLUME)20;1 133 }27 117 }s2lo2 1151 2}unt,30 20 lie]6 [sai 21 |6NAR7thNAR8th 03)of UNL]30 23/18]7 (50/24 |6]ojuNL!20 33.]27 [15 |48]03 [140b)Ol UNL]30 22/18}7/52/30 |4]thon!29 25 120 |7 |46)02 |1003]o|NL]30 37129413 |37}26 1 |unt]20 27.}22|9/47/07 |812)o}ut]30 62.137 }12 |20/32 [121 a}unt}20 33128 |6 {25/16 |615]|UNL!30 0141]8/13/28]5]9]unt)20 48135 |12 |23122 |418)0}uNt|20 58/40 110 (15,00 |o}81250]20 45133 143 [27/97 [13Bi}of unt!20 a4 }3r]7 faa}3}ojuni|20 35 127 412 |39]15 |12paloluwtl20139130112L33to6L15|of unt 20 24123]10 b4asi1e 1131 If the windspeeds are known,then the average wind power or average windenergyperunitareacanbeestimatedforanyconvenienttimeperiod,usually months,seasons,or year.The wind power per area is sometimes referred to as the wind powerpotentialorwindpowerdensity. P; ) A 0.5 Pj ve 3.9 where is N is the number of observations. Average values of temperature and pressure can be used to calculate an averagedensityandthentheaveragepower/area can be calculated form Eq.3.10.The result willbefairlyclosesincethepressureandtemperaturewillnotvaryasmuchasthewindspeed. 36 3Vio Watts/m2 3.10 Example:Calculate the average wind power for Amarillo for March 1,1984.Use the average pressure and temperature and the N =8 observation of windspeeds from Table 3.5.1 knot =0.514 m/s (knot is a nautical mile/hr),1 m/s =2.24 mph Tayg =45degF =7degC =280degK Pravg =26.38 inHg =26.38 x 25.4 =670 mmHg From Eq.3.4 the average density for the day is670273 ===3p=1.2029 San =1.11 kg/m The power for each 3 hr period can be calculated from Eq.3.10; (P/A)j =(0.5)(1.11)vj3.The process is shown in the following table. The total (P/A)is 398 W/mé2 and (P/A)avg for the day is 401/8 =50 W/m2. Of course the windspeed was not constant for each 3 hour period,but if enough data points are known,a good approximation of the average wind power potential can be obtained. Hr v(knots)v(m/s)v3(m/s)3__P/A(watts/m2) 00 8 4.1 69 03 10 5.1 133 74 06 12 6.2 238 132 09 8 4.1 69 38 12 4 2.0 8 4 15 4 2.0 8 4 18 9 4.6 99 55 21 9 4.6 99 55 Total 401 If the observations of windspeeds are compiled into a histogram,then the number of observations,nj,in each windspeed histogram could be changed to a frequency or probability by dividing the number of observations in a bin by the total number of observations. Pm7 :.N i=i=,i¢=number of bins or classes If the windspeed units are changed or if the windspeed is changed due to height,then theresultinghistogramorfrequencydistributionshouldbenormalizedtocontainthesame number of observations. 37 The average power/area can be calculated from a windspeed histogram or windspeed frequency distribution by PA =os Pavg x nj ve =0.5 Pavg x fi ve 3.11 Of course,if a large number of observations are available,a simple computer program would alleviate a lot of drudgery.The use of spread sheets (Table 3.6)is also a simple way to calculate wind power using Eq.3.11.Notice that the average windspeed is just the summation of the probability times the windspeed for each class. Vava =>ty,avg 4d Table 3.6 Average Annual Number of Observations (NWS data,data point at 3 hours,1 m/s bin width)for Corpus Christi,Texas,1959-1972 [5].Frequency =number/2920. Values at 0.5 and 1.5 m/s have been adjusted for instrumentation limitation.Windspeeds adjusted to 10 m height by power law with a =1/7. Windspeed #Freq Freq Duration fj Vj f viem/s 3 hr obs %Cum 0.5 21 0.7 0.7 100.0 0.00 0 1.5 52 1.8 2.5 99.3 0.03 0 2.5 254 8.7 11.2 97.5 0.22 1 3.5 425 14.6 25.7 88.8 0.51 6 4.5 432 14.8 40.5 74.2 0.67 13 5.5 382 13.1 53.6 59.5 0.72 22 6.5 354 12.1 65.7 46.4 0.79 33 7.5 343 11.8 77.5 34.2 0.88 50 8.5 284 9.9 87.4 22.5 0.84 61 9.5 197 6.7 94.1 12.6 0.64 57 10.5 92 .3.2 97.3 5.9 0.33 37 11.5 43 1.5 98.7 2.7 0.17 23 12.5 21 0.7 99.5 1.2 0.09 14 13.5 11 0.4 99.9 0.5 0.05 10 14.5 3 0.1 100.0 0.1 0.01 3 15.5 1 0 100.0 0.01 2920 100 5.95 335 Average windspeed is 5.95 m/s and average power/area is (0.5 pavg 335)W/m2. 3.7 WIND MAPS A number of wind power or wind energy maps have been prepared for the UnitedStates[10-12].Earlier maps did not take into account the height differences of theanemometers.As part of the overall evaluation of wind energy,two major contracts wereawardedtoGeneralElectricandLockheedin1975.They also estimated the wind energypotential.The estimates for a height of 50 m indicate that most of the United States has a fairly large wind power potential.The problem is that these values are estimated from 38 data taken at a height of 6 m.Elliott made a synthesis of the national assessments (Fig. 3.6)in 1977 [4]. Figure 3.6 Wind potential for United States.Values are estimated for 50 m height. The most comprehensive assessment of the wind energy potential was overseen by Battelle,Pacific Northwest Laboratory.The 12 volume,Wind Energy Resource Atlas, covers the United States and the territories [6].Wind power by year and season,are estimated for the United States,and each state (Fig.3.7)and region.The information for each state is more detailed as wind power classes (Table 3.7)are estimated for a grid of 20 minutes longitude by 15 minutes latitude (16 by 15 miles).This Atlas and the wind maps (Fig.3.8)were updated in 1985 [2].The different wind power maps are similar in the gross features.Regions of better wind power are in the Great Plains,along the coasts, Hawaii,and selected sites such as mountain passes. Wind power maps and isovent maps (contour lines of windspeed)are available for a number of countries [7]and regions around the world [3,Ch.5],as wind energy has become part of many national energy policies.More detailed assessments are available from measurements taken to promote and/or delineate locations for wind farms.Even micrositing for wind turbines within wind farms is important. 39 Table 3.7 Classes of Wind Power Potential at 10 and 50 m Levels.Values at 50 m arebasedon1/7 power law from data at 10 m. 10m 50 m Class Power Speed Power SpeedW/m?m/s Wim2 m/s 1 0 0 0 0 5 100 4.4 200 85.6 3 -150 5.1 300 6.4 4 _200 5.6 400 7.0 5 250 386.0 5007.5 6 -_-300 6.4 600 8.0 7 -_-400 7.0 -800 8.8 -1000 9.4 2000 11.9 104 102 100 98 Y turtles ma |"8 urtle|M Mtns A Pembina 1 4j i 4!I 1 ;H I Minot Devils,3 5 Se |Lake ag Grand':.WD 44Forks 48 |5 'a owe UxjoPo!4 Hy I t i oi Tv?9 ®]FinleyH|!1 |Eat }:i 3 2 3 H t :3 ' i 1 ot !i lj $Sf - o:_1 'eo giDickenson[Bismark "T- %47 ;!1]j m i ®i Fargoif1ia2;---Jamestown -+-1-4!;:0 10 ; ='1 MILESMissouritj50f10yPigteauf;i 17 --som ereseeeeeeaojittif 46 hit it i tot !vo: Figure 3.7 Annual wind power map for North Dakota from Wind Atlas. 40° Figure 3.8 Annual average wind power for the United States. SIMNSU |eVOWEY ByaNEg Aq A6s0uU3 JO JUaWedaQ °S'N aU)40) pojesEdO A10,810QE7 JSOMYVON 2))198d (130001 =431784 IVIOT S31VWI1S3 183489 39014€we) g992-6 11 0002 Ll2Z- v6 o001i -- - --- L 461-88 oos -2£SL-O02 00b a 9 64t-o08009----EvlL- v9 ooc S$ 991- 9 4---- 00S ---- »£1 - 09 ----- 052 Tore] p 2sot-o2 oop $z7i-9gs - 002 £ Evi-evg9 ooe ---Sstt-Uts ost z GzL_-g9'sS 002 86 -?bb ooL \ o-oO i) o-oO 0 ydw Syuw rervy yaw Syw cM/AA ssv15 Q33dS ¥3MOd ONIM Q33dS Y3MOd ONIM yaMOd Qsp9b) WOS Q)€€) wor GONIM ALISN3G 8Y3MOd GNIM 30 S3SSV19 41 3.8 VARIATIONS IN POWER Since the motion of the atmosphere varies on a scale from seconds to years,then wind power and wind energy will also vary on the same time scale.The annual average wind power for Amarillo,TX was 220 watts/m2 for the period 1962-1977,however the variation from one year to the next can be quite large (Fig.3.9).Notice the large change in wind power when the anemometer height at Lubbock,TX was changed from 20 m to 6 m between 1965 and 1966.This is expected as windspeed varies with height.A minimum of two years of data are needed to obtain an estimate for the annual wind power potential and five years are needed to obtain a mean value within 6%of the long term mean and ten years gives a value within 3%.Most people assume that if you have 10 years of data,then that suffices for a long term mean. The following are 10 year means for Amarillo,TX: 63-72 14.1 mph 6.6m/s 73-82 13.8 mph 62m/s 83-92 12.9mph 5.7 m/s Is this a long term trend,or it this due to other factors? The seasonal variation for most of the United States is high windspeeds in the spring with low windspeeds in the summer (Fig.3.10).The most notable exceptions are the mountain passes in California where the windy season corresponds to heating of the deserts in the summer.At the present time the largest concentrations of wind turbines in the world are located in these passes. 250 - 125 POWER/AREAWatts/m2Amarillo,TX 0 Wichita Falls,TX o Oklahoma City,OK A U |Lj T T LU if Ly T LU T |T rd 60 62 64 66 68 70 72 YEAR Figure 3.9a Power per unit area by year for different locations. 42 250K Lubbock,TX 9 SE Midland,TX a 2 Tucumcari,NM O = < Ww <©125; =Oo oo YEAR Figure 3.96 Power per unit area by year for different locations. 300 Fr POWER/AREAW/m2onfo)T||,1 {san 1 i 5 i t t El Paso,TX qv LJ v LU LI u LJ Ly Li ' J FM AMJ JA SON OD Figure 3.10 Average power/area by month for 17 years of data.Error bars are one standard deviation. There are also variations with the movement of synoptic weather patterns,which is represented by a 4 to 5 day variation.The diurnal (daily)variation is due to heatingduringtheday.These frequency representations (Fig.3.11)are common to manylocations.The peak at 0.01 cycles/hr corresponds to a period of 100 hrs which is the 4 to5dayvariationandthepeaknear0.1 cycle/hr corresponds to the diurnal variation. 43 otspectral gap POWERSPECTRALDENSITY(m/s)?0 |1 n l |i 0.001 0.01 0.1 1 10 100 1000 ._FREQUENCY cycles/hr Figure 3.11 Example of power spectrum for windspeed. In those areas which have seasonal thunderstorms,during that season the peak windspeeds are shifted toward late afternoon and evening.The diurnal variation is muchsmallerornonexistentat50morhigher.Many meteorologists attribute this to a low leveljet.Measurements taken at heights of 10,20,and 50 m for the Northwest Texas Region[8]confirm this lack of diurnal variation at 50 m and above.The implications are that largewindturbineswillactuallyinterceptmoreenergythanthatpredictedfrommeasurements taken at 10 m. 3.9 WINDSPEED HISTOGRAMS Since the power is mainly dependent on the windspeed,average values can be used for the pressure and temperature and the power/area can be calculated from a windspeed histogram (Figs.3.12)or frequency distribution (Fig.3.13).A windspeed histogram shows the number of hours (or whatever time period is used)the wind blew at each windspeed class (Tables 3.6,3.8). If an average air density is known,then an energy histogram curve can be calculated from the windspeed cubed times the number of hours (Fig.3.14).Notice that there is little energy in low windspeeds because of low windspeed and little energy athighwindspeedsbecauseofthesmallamountoftimeofhighwindspeeds. The data in Table 3.8 were collected at a sample rate of 1 Hz,a stark contrast to the previous data which were a 2 minute sight average of an analog trace,once every threehours.The annual windspeed frequency histogram in Figure 3.14 has a different shapethantheoneinFig.3.12,which could be due to location,sample rate and instrumentation. 3.10 DURATION CURVE. ;Wind data can also be represented by a speed-duration curve (Fig.3.15)which is a plot of cumulative frequency starting at the largest windspeed (subtract 100 from percent frequencies of cumulative frequencies if starting at the lowest windspeed).The percent duration is usually converted (multiplying by 8760)to number of hours in a year.From windspeed duration curves,estimates of the time the windspeed is above a given value 44 can be obtained.The data in Table 3.8 and the curve show,for example,that a wind of 2.5 m/s or feyoa)NUMBEROFOBSERVATIONS(onceper3hr)Figure Ing behavior o However, 300 greater blows 87%of the time or 7600 hours in a year. Amarillo oO Del Rio a WINDSPEED,m/s Figure 3.12 Windspeed histograms for Amarillo and Del Rio,TX. 14 i = 12 --25 L>10 aWw| >8 | S Lo cCéetas a ae Pyes4=n||teTTT"a0aas -n 0 5 10 15 20 25 30 WINDSPEED m/s 3.13 Windspeed frequency histogram,1 m/s bin width,for Perryton,Texas. (Data in Table 3.8). eneral,whatever the windspeed is at any point in time,over the next hour the ught to be similar.This is called persistence;v(t +to)=v(to),where t is variable. a histogram does not give a time sequence of data nor does a windspeeddurationcurvetellthelengthofcalmperiods.As more wind turbines are installed,utilities 45 will be interested in predicting windspeeds,average variation by season and time of day,duration of low windspeeds,and values for the next 1 to 36 hours. 45 35 i o a 40 F o ++4 30 .35 -Og T .+425 < 30 oO = c i 20=25 Oo +mi x=r +o20.+Oo 415 > i 415+ L +a 10 210-+o ; r +=5050O4 .Oo | 0 haere a {A I Pi I Fi l :|Onl 0 0 2 4 6 8 10 12 14 16 WINDSPEED m/s Figure 3.14 Average annual windspeed histogram ()and energy/area (+)for each windspeed bin for Corpus Christi,Texas (1959-1972).Data in Table 3.6. 3.11 WINDSPEED DISTRIBUTIONS If data are not available,then the windspeeds can be predicted from one or two parameters.A number of different distributions have been tried,but only two are in general use;Weibull and Rayleigh distributions.These distributions give poor estimates of power for low mean windspeed situations.At higher windspeeds,both give adequate estimates for many locations,however for those regions with steady winds,such as the trade winds,the Weibull distribution is better.The Rayleigh distribution is simpler because it depends only on the mean windspeed. The Rayleigh distribution is n{(v\ --{-]|:3.11#fa(i)| where F(v)=frequency of occurrence associated with each incremental windspeed of Av centered at v. Av =width of class or bin Va =mean windspeed _F(v)=Av=aadQ°2Va 46 Example:The Rayleigh distribution is calculated for two values,v =3 m/s,v =9 m/s. Vq =8 ms,Av =2 m/s >F(3)=2 3 exp|-2(3 =0.147¢0-11 =0.147x 0.895 =0.1322PLals)| x9 w {9 2]F(9)=2 exp (3)=0.442 e994 =0,442x0.37 =0.16484 The values for all the windspeeds are calculated and then you have a frequency distribution (Fig.3.17)and can calculate a windspeed histogram (Figs.3.18). The windspeed histogram for one year can be calculated from 8760 F(v). Table 3.8 Windspeed Frequency and Duration Data for Perryton,Texas at 20 m Level. (1982-86)[8].Data sampled at 1 Hz and stored in 1 m/s bins. Windspeed,m/s_Frequency,%Duration,% 0.5 3.81 96.19 1.5 2.88 93.31 2.5 6.10 87.21 3.5 9.44 77.77 4.5 12.14 65.63 5.5 13.32 52.31 6.5 12.28 40.03 7.5 10.45 29.58 8.5 8.60 20.98 9.5 6.70 14.28 10.5 4.98 9.30 11.5 3.39 5.91 12.5 2.16 3.75 13.5 1.50 2.25 14.5 0.84 1.41 15.5 0.53 0.88 16.5 0.34 0.54 17.5 0.21 0.33 18.5 0.13 0.20 19.5 0.08 0.12 20.5 0.05 0.07 21.5 0.03 0.04 22.5 0.02 0.02 23.0.01 0.01 24.5 0.01 0 25.5 0 0 47 WINDSPEEDm/sanPURprreryprefe)STEN ONT PTT TET OTS PT OP PPTL.-1 0 10 20 30 40 50 60 70 80 90 100 FREQUENCY Figure 3.16 Speed duration curve for Perryton,TX. -The Weibull distribution is characterized by two parameters:The shape parameter,k (dimensionless)and the scale parameter,c (m/s).The Rayleigh distribution is a specialcaseoftheWeibulldistributionwherek=2.For regions of the trade winds where the winds are fairly steady,the shape factor may be as high as 4 to 5.For most sites in Europe and the United States,k varies between 1.8 to 2.4. "exp ;(x),3.12 In many parts of the world the windspeed data are sparse.If only the average windspeed by day or month are known,then the average values and deviation of theaveragevaluesareusedtoestimatethetwoparameters.Rohatgi and Nelson [3,Ch.9]give details on estimating the Weibull parameters by three methods:a plot of c and k fromlog-log paper,analysis of standard deviations and analysis of the energy pattern factor. k-1F(v)=Av «(2 3.12 GENERAL COMMENTS Previous studies of the behavior of the wind were done by meteorologists who were mainly interested in turbulence and momentum transfer.Since 1975,numerous studies have been funded on wind characteristics as it pertains to wind energy potential and the effects on wind turbines,primarily through Battelle Pacific Northwest Laboratories(PNL).A list of publications is available from the National Renewable Energy Laboratory(NREL)as the PNL group in wind has been transferred to NREL.States and universities have also funded projects for estimating wind energy potential.After using the National Atlas,contact your State Energy Office or the American Wind Energy Association for other sources of information on wind energy. 48 0.2 ---PROBABILITY°l°o 0 a a Oe =et_I 0 10 20 30 WINDSPEED,m/s Figure 3.17 Rayleigh distribution for an average windspeed of 8 m/s 1500 F 1000 NUMBEROFHOURS500 -- 0 th tt He ;J 20010 30 WINDSPEED,m/s Figure 3.18 Windspeed histogram from Rayleigh distribution (Fig.3.17) REFERENCES GENERAL Horace Robert Byers,General Meteorology,McGraw Hill,1974,Technical,Chs.7-9. Franklin Cole,Introduction to Meteorology,John Wiley,1975,Ch.10. Frederick Lutgens and Edward Tarbuck,The Atmosphere,an Introduction toMeteorology,Prentice Hall,1979,Ch.7. 49 E.N.Lorenz,"The Nature and Theory of the General Circulation of the Atmosphere," World Meteorological Organization,1967. Janardan Rohatgi and Vaughn Nelson,Wind Characteristics,An Analysis for the Generation of Wind Power,Alternative Energy Institute,1994.Resource book. SPECIFIC 1.M.R.Gustavson,"Wind Power Extraction Limits,"Vaughn Nelson,Ed.,Proceedings National Conference,Fall 78,American Wind Energy Association,1978,p 101. 2.D.L.Elliott,et.al,Wind Energy Resource Atlas of the United States,DOE/CH 10093-4,October 1986,Available from NTIS. 3 Janardan Rohatgi and Vaughn Nelson,Wind Characteristics,An AnalysisfortheGenerationofWindPower,Alternative Energy Institute,West Texas A&M University,1994. 4.Vaughn Nelson and Earl Gilmore,"Potential for Wind Generated Power in Texas", Report NT/8,Governor's Energy Advisory Council of Texas,October,1974. 5. D.L.Elliot and W.R.Barchet,Synthesis of National Wind Energy Assessments, BNWL-2220 WIND-5/UC-60,Battelle Pacific Northwest Laboratories,July,1977. Available from NTIS. 6.Wind Energy Resource Atlas,Vol.1-12,PNL-3195 WERA-1/UC-60,Battelle Pacific Northwest Laboratories,April,1980.Available from NTIS. 7.1.Troen and E.L.Petersen,European Wind Atlas,Riso National Laboratory, Roskilde,Denmark,1989. 8.Earl Gilmore,Wind Characteristics Northwest Texas Region,May 1978-December 1985,Alternative Energy Institute,Report 87-1,January 1987. PROBLEMS 1.Calculate the power,in kW,across the following areas for windspeeds of 5 to 40 m/s by 5 m/s increments.Use radius of 5,10 and 50 meters for the area.Air density =1.0 kg/m3. 2.Calculate the factor for the increase in windspeed if the original windspeed was taken at a height of 10 m.New heights are at 30 m and 100 m.Use the power law with an exponent a =1/7. 3.Do problem 2 with an exponent of 0.30. 4.Houston Intercontinental Airport is surrounded by trees (20 m tall).Calculate thefactorforincreaseinwindspeedfrom10to100m.Use the In relationship and an estimated Zo from Table 3.4. 5.From Table 3.5,calculate the average power/area in the wind for two days. Windspeeds are in knots.1 knot =0.514 m/s. 6.From Figure 3.9,calculate average power/area from 1 to 5 hours.Assume a density of 1 kg/m'.Use estimated values of windspeed at 15 minute intervals. 7.What is the air density difference between sea level and a height of 3000 m? 8.In the Great Plains there is a wide temperature difference between summer (100 deg F)and winter (-20 deg F).What is the difference in air density?Assume you are at the same elevation;average pressure is the same. 50 Calculate the windspeed distribution using the Rayleigh distribution for an average windspeed of 7 m/s.Use 2 m/s bin widths. Graph the windspeed histogram (#hours versus windspeed)for one year using the Rayleigh distribution in problem 8. Calculate the windspeed distribution for a Weibull distribution for c =6 m/s and k =1.7. Calculate the windspeed distribution for a Weibull distribution for c =6 m/s and k = 3. From Figure 3.13,for Amarillo,TX calculate the average windspeed and then estimate the power from the average windspeed.Density =1.1 kg/m3. What is the average power/area per year for Lubbock before and after the anemometer height was changed?(see Fig.3.10) From the wind map for the United States,what is the annual average power/area for Albuquerque,NM? From the wind map for the United States,what is the wind class for the area closest to your home?What is the estimated power at 50 m? For the wind map for the United States,what is the annual average power/area for Corpus Christi,TX? From Table 3.8 calculate the mean windspeed.From the mean windspeed, calculate power/area.Hint,use Rayleigh distribution. From Table 3.8 calculate the annual power/area.Density =1.1 kg/m3.If you did problem 18 compare the two answers. Class Windspeed #Obs i m/s 1 1 20 2 3 30 3 5 50 4 7 100 5 9 180 6 11 150 7 13 120 8 15 80 9 17 40 10 19 10 The following problems refer to the above table. 20. 21. 22. 23. 24. Calculate the power/area for i =5 bin;for the i=10 bin.Density =1.1 kg/m3. Calculate the frequency distribution. Calculate the average (mean)windspeed. Calculate the wind power potential (power/area).Density =1 kg/m3. From the answer to problem 22,use the mean windspeed and calculate a Rayleigh distribution for the same wind classes.Remember Av =2 m/s. 51 4 INSTRUMENTATION AND MEASUREMENT An anemometer is a device for measuring air flow.There are a number of measuring devices:pitot tube,cup anemometer,vane anemometer,propeller anemometer,hot wire anemometer,hot film anemometer,sonic,and laser doppler.The common devices are the cup and propeller anemometers,since they are cheaper. However their response time to changes in windspeed are slower.Wind turbines also have a response time to changes in windspeed,so cup anemometers are adequate for determining the wind energy potential. An anemometer can be obtained to measure the amount of wind that has passed,a wind run.From the wind run,the average windspeed can be calculated for the time period.An anemometer can also be obtained to measure the fastest mile,the maximum windspeed. Meters and strip charts (Fig.4.1),which give analog outputs,are still used. However analyzing strip chart data becomes quite tedious and the time resolution is fairly coarse unless the paper feed rate is large.Today the major difference is the availability of microprocessors for sampling,storing,and even analyzing data in real time.Also, computers alleviate most of the problems in analyzing large amounts of data. Digital instruments or analog inputs which are digitized typically have sample rates of 0.1 to 1 Hz (Hertz =#/second).Values can be stored in a histogram of windspeeds or windspeed and other selected variables can be stored for selected time periods.Events such as maximums and time of occurrence can also be recorded and stored.Micro dataloggers were designed specifically for wind potential measurements and record time sequence data (averaging time is selectable)on chips.The chips can store data from a number of channels and the instruments can even be queried by telephone or radio link; data transmitted directly to your base computer.Psy°o|WINDSPEEDmphTIME hr Figure 4.1 Strip chart recording of windspeed.Sample rate =0.5 Hz. More detailed information on instrumentation and measurement can be found in Rohatgi and Nelson [1],as much of this chapter was taken from that book.Also see the U*WRAP manual [2]on wind measurements and quality assurance. 52 4.1 INSTRUMENTATION There are three general types of instrumentation for wind measurements:<1)» instruments used by national meteorological services,2).instruments designed specifically for determining the wind resource,and 3)instruments for high sampling rates in determining gusts,turbulence,and inflow winds for measuring power curves,stress, fatigue,etc.for wind turbines.The data collection by meteorological services is the most comprehensive and long term,however,in many cases the data is almost worthless for determining wind power potential.The reasons are the following:few stations,most locations are in cities and airports which are generally less windy areas,sensors are mounted on buildings and control towers,the quantity of data actually recorded is small (one data point per day or sometimes monthly averages),and lack of calibration after installation.As an example of the problem of using meteorological data,the annual mean windspeed for Brownsville,Texas is 5.4 m/s compared to 2.8 m/s for Matamoros,Mexico which is just across the Rio Grande river. There are several types of instruments for measuring windspeed,from hand held anemometers,$400,to fully automatic micro dataloggers,$3,000.Companies sell instruments that sample at rates of 0.1 to 1 Hz and with the output displayed on analog devices (meters and recorders)or digital devices (stored on tape or chips).Instruments will record and analyze time sequence data as not only windspeeds and direction can be stored for selected time intervals,the power can be calculated and selected events such as maximums,gusts,and time of occurrence are also available.Companies which sell instrumentation specifically for wind measurements,also sell digital readers and provide software for analyzing the data.Towers are available specifically for wind measurements from 10 m,$500,to 50 m (with gin pole),$5,000. 4.1.1 Cup Anemometer A widely used anemometer for wind resource measurements has a circular magnet(4 pole)in the cup housing and then one or two coils for pickup of the signal!(Fig.4.2).The transducer counts zero crossings (sampling time is generally 1 second).The counts are related to the windspeed.The advantage is that signals can be transmitted 150 m without loss of accuracy (none of the problems of attenuation and amplification neededwithanalogsignals).An estimate of the accuracy of cup anemometers in wind tunnels is reported to be +2%[3]. Figure 4.2 Photo of a Maximum cup anemometer and wind vane.Anemometer is about15cmacross. 53 Another type of cup anemometer has a disc containing up to 120 slots and a photocell.The periodic passage of slots produce pulses in the each revolution of the cup. This gives a better resolution,so the sampling rate can be increased to 5 Hz. 4.1.2 Propeller Anemometers -The propeller anemometers (Fig.4.3)has faster response and behaves linearly in changing windspeeds.The windspeed is measured by measuring the voltage output of aDCgenerator.The propeller is kept facing the wind by a tail-vane,which also works as adirectionindicator.The accuracy normally is about 2%for windspeed and direction.The propeller is usually made of polystyrene foam or polypropylene.However for turbulent winds,the values may be misleading in determining power curves for wind turbines. Figure 4.3 Photo of a propeller type anemometer showing U-V-W set up. A propeller anemometer is better suited to measure the three components of windvelocity,because it responds primarily to wind parallel to its axis.An array of three unitsinmutuallyperpendiculardirectionsmeasuresthethreecomponentsofwind. 4.1.3 Wind Direction ___The wind direction is measured by a wind vane which is counterbalanced by aweightfixedontheotherendofarod.However,in the case of propeller anemometers,the vane is a part of the propeller's axis.The vane requires a minimum force to initiate 54 movement.The threshold windspeed for this force,usually,is of the order of 1 mvs. Normally the motion of the vane is damped to prevent rapid changes of directions. Wind vanes generally produce signals either by contact closures or by potentiometers.The accuracy obtained from potentiometers is higher than that obtained from contact closures,but the latter are less expensive. 4.1.4 Recorders Whether a commercial or PC based system is employed,for time sequence data the amount of data is large.For example,suppose you want to measure windspeeds, wind direction,pressure and temperature (1 Hz sampling rate),average values and statistics stored every ten minutes.That would be around 130 kB of data per month.A 60 minute magnetic tape will store 180 kB or data chips will store 128 or 256 kB.You would need to retrieve the data at least once per month. The logistic problems have to be taken care of to insure high data recovery and to insure the quality of the data analyzed.Calibration and replacement of sensors must be part of a routine maintenance program.For example anemometers bearings should be replaced once per six months to two years,depending on the number of revolutions and the environment.Some of the mechanical anemometers have an automatic oiling device for the bearings. 4.2 CHARACTERISTICS OF INSTRUMENTS Sensors,transducers and signal conditioners measure and transform signals for recording.Resolution is the smallest unit of a variable that is detectable by a sensor. Recorders may limit the resolution.Reliability is a measure of an instruments ability to produce useful data over a period of time.The best indicator of reliability is the past performance of similar instruments Accuracy and precision are two separate measures of system performance that are often treated ambiguously.Accuracy refers to the mean difference between the output of a sensor and the true value of the measured variable.Precision refers to the dispersion about the mean.For example,an instrument may produce the same measured valueeverytimebutproduceavaluethatis50%off.That system has a high precision but low accuracy. The accuracy,however,may be a function of time,or dependent on maintenance.Anemometers are generally calibrated in wind tunnels,where the airflow is steady.Undertheseconditions,they may produce a signal that is accurate to within 1 to 2%of the truewindspeed.Under normal use in the atmosphere,good anemometers should be accurate within 4 to 5 %. The distance constant is the length of fluid flow past a sensor required to cause it to respond to 63.2%(I-1/e)of a step change in speed The larger and heavier cupanemometersusuallyhavedistanceconstantsof3to5m.For light weight and smallercupanemometers,such as those used for turbulence,the distance constant is typicallyabout1m.The time constant is the period that is required for the sensor to respond 63.2%of a step change in input signal. The damping ratio is a constant which describes the performance of a wind vane inresponsetoastepchangeinwinddirection.It is calculated from the relative amount ofovershootontwosuccessiveswings(half cycle)of a decaying oscillation.The damping ratio is dimensionless and is generally between 0.3 and 0.7. 55 Sampling rate is the frequency (Hz)at which the signal is sampled.This may include the time for recording the data.For example a compilator which measures and stores a windspeed histogram has a sampling rate of 1 Hz,measurement for 850 ms and recording takes 150 ms. 4.3 MEASUREMENTS Anemometers mounted on towers should be mounted away from a lattice tower adistanceof2to3towerdiameterstoreducetheeffectofthetowerontheairflow.For solid towers,they should be mounted 6 tower diameters away.Anemometers have to be located away from the influence of obstacles;trees,buildings,etc..A standard [4]for the collection of atmospheric data is published by the American Wind Energy Association (AWEA). The time and money spent for measuring the wind resource depends on whether it is for a small wind turbine or for a wind plant.Individuals tend to over estimate the wind resource before their turbine is installed and then bemoan the lack of wind afterwards. The difference between finding a class 4 and a class 5 wind site will easily determine the economic viability for a wind plant. Instrumentation for measuring turbulence and the wind inflow for wind turbine response uses multiple anemometers and a higher sampling rate.A system for characterizing turbulence [5]developed and tested by Pacific Northwest Laboratory consists of two towers and 9 anemometers (Fig.4.3),data sampled at 5 Hz .The propeller-vane anemometer for horizontal measurements were replaced by cup anemometers due to problems of maintenance and errors in measurement of windspeed. 4.4 VEGETATION INDICATORS Vegetation can indicate regions of high windspeed where there are no measurements available.Deformation or flagging of trees is the most common indicator (Fig.4.5).In some cases the flagging of trees is a more reliable indicator of the wind resource than the data available.For example,the Arenal Region of Costa Rica has highwinds,which have now been measured (average for 12 stations)at 11 m/s [6].There is a meteorological station in the region,however the purpose is for collecting data forhydrology.The anemometer height is less than two meters as they were interested in determining evaporation and furthermore the station was located close to trees. Therefore the windspeed data indicated no wind power potential. 56 Temperature Probe DirectionVane\CUP\paampritCablesnm:mF Guy q Cable ! Propellerft"Anemometer Sensor jf}: Ca bles i 4 40 m Tower }30 m Tower Data Acquisition --19m -- Figure 4.5 Examples of flagging of trees:left photo,tree on plains,Canyon,Texas (6 m/saveragewindspeed);right photo,tree at South Point,Hawaii (10 m/s average windspeed). 57 REFERENCES 1 Janardan Rohatgi and Vaughn Nelson,Wind Characteristics,An Analysis for the Generation of Wind Power,Alternative Energy Institute,West Texas A&M University,1994. 2.U*WRAP Manual 3.V.Ramsdell and J.S.Wetzl,Wind Measurement Systems and Wind Tunnel Evaluations of Selected Instruments,Pacific Northwest Laboratory,PNL-3435,1981. 4.Standard Procedures for Meteorological Measurements at a Potential Wind Turbine Site,AWEA Standard 8.1-1986,American Wind Energy Association. 5.LL.Wendell,V.R.Morris,S.D.Tomich,G.L.Gower,"Turbulence Characterization for Wind Energy Development,"Proceedings Windpower '91,American Wind Energy Association,1991,pp.254-265. 6.T.dela Torre,"International Developments:New Wind Power Projects,Wind Electric Power Development in Costa Rica,"Windpower '93,American Wind Energy Assn., 1993,pp.429-435. PROBLEMS 1.You have a tall tower from NRG,5 inches in diameter.How far should the anemometer be placed away from the tower? 2.You are installing anemometers are an existing guyed lattice tower for radio communication.The tower is 1.5 mon a side.How far should the anemometer beplacedawayfromthetower? 3.You are installing anemometers are a stand alone,lattice tower for radio communication.The tower is 4 mona side at 10 m.Compare the recommended length of the boom with a practical length. 4.Why were the propeller anemometers for horizontal wind measurements on the turbulent characterization tower (Fig.4.4)replaced with cup anemometers? 5.Are there any examples of vegetation indicators of wind in your region?What windspeed do they indicate? 6.With a laser system for measuring windspeed,you do not need a tower.What is the reason for not employing laser sensors? 7.You want to measure the windspeeds and direction at 3 levels (10,25,and 40 m)at6sitesfortwoyears.Estimate the cost for equipment and time (installation,datacollection,and data analysis).You may choose any type of system you want. 58 5S WIND TURBINES Wind turbines are classified according to the interaction of the blades with the wind,orientation of the rotor axis with respect to the ground,and innovative or unusual types ofmachines.The interaction of the blades with the wind is by drag or lift or a combination ofthetwo. 5.1 DRAG DEVICE In a drag device (Fig.5.1),the wind pushes against the blades forcing the rotor toturnonitsaxis.Drag devices are inherently limited in efficiency since the speed of thebladecannotbegreaterthanthewindspeed.An example is when a sailboat is travelingdownwind. FLAP PLATE CUP PANEMONE TURBINE onshield WXE rotation y,WIND Figure 5.1 Examples of drag devices. The most common drag device is the farm windmill,which is well designed to pump small volumes of water at low windspeeds.Since the farm windmill has a large number of blades,it will start under a load;it has a large torque.However,the large number of blades means it takes a lot of material and the unit is inefficient at high windspeeds. Power ratings are around 0.5 kW for a 5 m diameter rotor.Other examples of drag devices are cup anemometers,vanes,and paddles which are shielded from the wind on half the rotor. A Savonius rotor is not strictly a drag device,but it has the same characteristic of large blade area to intercept area.This means more material and problems with the force of the wind at high windspeeds,even if the rotor is not turning.An advantage of the Savonius wind turbine is the ease of construction. 59 5.2 LIFT DEVICE Lift devices use airfoils (Fig.5.2)for blades,similar to propellers or airplane wings. Using lift,the blades can move faster than the wind and are more efficient in terms of use of material (Fig.5.3)and aerodynamics.The tip speed ratio is the speed of the tip of the blade divided by the windspeed.One blade rotating very fast can extract as much energy from the wind as many blades rotating slowly.This saves on material,however,most modern wind turbines have two or three blades.The MBB Monopteros and the FLAIR design were single bladed wind turbines built in Germany,while a one bladed (5 kW)unit was built by Riva Calzoni in Italy.MBB and Riva Calzoni are collaborating on a 20 kW one bladed unit.In Italy a large one bladed unit is being constructed.A rotor with a large number of blades based on the design of a bicycle wheel was invented by Thomas Chalk. BLADE PATH ae Figure 5.2 Cross section of airfoil showing lift and drag forces due to relative wind. <4 ATTACK ANGLE => WIND 5.3 ORIENTATION OF ROTOR AXIS Wind turbines are further divided by orientation of the axis of the rotor with respect to the ground;horizontal axis wind turbine (HAWT)and vertical axis wind turbine (VAWT)(see Fig.1.7).The rotors on HAWTs need to be kept perpendicular to the flow of the wind to capture the maximum energy.This rotation of the unit about the tower axis,yaw,isaccomplishedbyatailonupwindmachines,by coning on downwind units (Fig.5.4)or byamotor(wind or electric)to drive the unit around the yaw axis. VAWTs have the advantage of accepting the wind from any direction.However,theDarrieusisnotreliablyself-starting as the blades have to be moving faster than the wind to generate power while the giromill has articulated blades which change angle so it canbeself-starting.Another advantage of VAWTs is the speed increaser and generator canbeatgroundlevel. 60 16 14+ 12+POWER0 |j ]j j it j j ! 0 1 2 3 4 5 6 7 8 9 10 SPEED RATIO Figure 5.3 Power for amount of material in blades for drag and lift devices [1]. 61 DOWNWIND UPWIND WIND CONING ANGLE Figure 5.4 Downwind unit with passive control for yaw and upwind unit. 5.4 DESCRIPTION OF SYSTEM The total system consists of the wind turbine and the load.A typical wind turbineconsistsoftherotor(blades and hub),speed increaser (gear box),conversion system,controls and the tower (Fig.5.5).The nacelle is the covering or enclosure of the speedincreaserandgenerator.The output of the wind turbine,rotational kinetic energy,can beconvertedtomechanical,electrical or thermal energy.Generally it is electrical energy. Blade configuration may include a non-uniform planform,twist along the blade,andvariable(blades can be rotated)or fixed pitch.The pitch angle is the angle of the chord at the tip of the blade to the plane of rotation.For units connected to the utility grid,50 or 60 Hz,the generators can be synchronous or induction connected directly to the grid,or a variable frequency alternator or direct current generator connected indirectly to the grid through an inverter.Some DC systems and permanent magnet alternators do not need a speed increaser.Some HAWTs use slip rings to transfer power and control signals.A total system is called a wind energy conversion system (WECS). 5.5 AERODYNAMICS The blades of the wind turbine convert part of the power in the wind to rotational power. 5.1 P=To where T is the torque (N m)and @ (rad/s)is the angular velocity.The same power can be transferred with a large T and small o or a small T and a large w.The torque-o characteristics of the rotor should be matched to the torque-w characteristics of the load. From conservation of energy and momentum,the maximum theoretical efficiency for the capture of wind energy is 59%.Highest experimental efficiencies for wind turbines are around 50%with average annual efficiencies around 20%to 25%. 62 HIGH SPEED SHAFT GENERATORGEARBOX ere | LOW SPEED SHAFT NACELLE ]YAW CONTROLLER BLADE PITCH ACTUATOR TARY Figure 5.5 Schematic diagram of wind turbine or WECS. Lift and drag forces are measured experimentally for different airfoils as a functionoftheattackangle;the angle of the relative wind to the chord of the airfoil (Fig.5.2).Acomponentoftheliftontheblades,which depends on the angle of attack,makes the rotor turn about the axis.The relative wind as seen by the blade is composed of two parts;the motion of the blade and the motion of the wind far away from the unit (Fig.5.6).Maximum power output for any windspeed can be obtained by increasing the rpm of the rotor as the windspeed increases or by variable pitch of the blades to obtain the correct attack angleforconstantrpmoperation.A fixed pitch blade,constant rpm rotor only reaches maximumpowercoefficientatasinglewindspeed.Power coefficient is the power output divided by the power input (power in wind across the rotor area).Even though efficiency decreases above maximum power coefficient,power output of the wind turbine can remain high since power available is increasing as the cube of the windspeed. Computer programs are available for estimating the aerodynamic performance of wind turbines,both HAWT and VAWT.Inputs include airfoil lift and drag versus attack angle;radius,twist and pitch of the blade;and solidity.Solidity is the ratio of blade area to intercept area.Windspeeds or tip speed/windspeed (also called the tip speed ratio)can be varied to obtain power,forces,moments,etc. Figure 5.7 shows the theoretical calculation fora VAWT.Each point on the curve is an operating point (power)and the rated windspeed is at 10 m/s.Wind turbines can be operated at constant tip speed/windspeed (line of maximum power coefficient),constant rpm (line A)or a constant torque (line C).The rpm is variable along line B,the operation of maximum power coefficient.Notice that the constant torque operation soon reaches very high values of rpm.It is very difficult to connect a constant torque load to a wind turbine and obtain much efficiency. 63 DRAG LIFT DRAG LIFT WINDSPEED DUE TO MOTION ';OF BLADE .;RELATIVE :;WIND 'poees ere F ,GROUND .v WIND NACELLE Figure 5.6 Wind produces forces on the blade.Relative wind (wind the blade sees)is the vector sum of the blade speed plus the ground wind.Rotor perpendicular to ground wind. 5.6 CONTROL Because the power in the wind increases so rapidly,all wind turbines must have a way to dump power (not capture power)at high windspeeds.The methods of control are: 1.Change aerodynamic efficiency a.variable pitch,feather or stall b.operate at constant rpm c.spoilers 2.Change intercept area a.yaw rotor out of wind b.change rotor geometry 64 3.Brake a.mechanical,hydraulic b.air brake c.electrical (resistance,magnetic) All of these methods are used alone or in combination for control in high windspeeds and for loss of load control. 20,000 F CONSTANT WINDSPEED 15,000 E Zz LW 2 &10,000e 5,000 25 mis Cc 0 0 100 200 300 400 500 ROTOR SPEED rpm Figure 5.7 Theoretical curves of torque versus rpm for different windspeeds. A pitch control system (Fig.5.8)is one method to control rpm,start up (high torque), and overspeed.Blades are changed to the feather position (chord parallel to the wind)for starting torque and then changed to the run position.The alternator could be variable frequency and in the run position the tip speed ratio is constant.The unit operates at maximum power coefficient.The pitch can be changed to maintain a constant rpm for synchronous generators.For high windspeeds and overspeed control,the blades are moved to the feather or stall position to shut the unit down. Part of the control system can be electronic,generally a microprocessor or microcomputer (Fig.5.8).In constant rpm operation,such as an induction generator,the unit is connected to the utility line after the rpm is above the synchronous rpm of the generator.In reality an induction generator is not strictly constant rpm as there is a small change in rpm (slip)with power output. 5.6.1.Normal Operation :A power curve,power versus windspeed,describes the normal operation of a wind turbine (Fig.5.9).At the cut-in windspeed the unit starts to rotate or produce power,then reaches rated power (size of generator)at the rated windspeed and shuts down at the cut- out windspeed.Some units continue to operate at any windspeed. 65 anemometerAPitchControl B Positionsensor B C Latch ATC | D Pitch meter |_[D E F main shaft|[ees +Ny,a ROTOR rpm sensor orsliprings E remote power tower logic,GenerFjcomputer,and \Y power ae utility 4 a ground logic,lines =<<computer and power power supply contactor Figure 5.8 Block diagram for system with pitch control. f oa a men 20 ? =/i ac nm iJf 0 10-f T CUT-IN ig RATED CUT-OUT ;ia tr 0 5 10 15 20 Figure 5.9 Power curves for a rotor with two different generators sizes. _The most important parameter in determining energy production is the rotor area.Energy will increase as the square of the radius.A larger generator does not necessarily mean more energy production because the efficiency at low windspeeds will change with generator size.Although a larger generator is probably desirable in the best wind 66 regimes,the optimum size for a given rotor radius for a given wind regime is stillundetermined. 5.6.2 Faults Wind turbines are shut down for faults such as loss of load,vibration,loss of phase, current or voltage anomalies,etc.Each of these safety features could save the unit,but _the most important feature is a method of controlling the rotor when there is a loss of load during high winds (overspeed control).If the unit is not shut down within a few seconds,it will reach such high power levels it cannot be shut down and will self-destruct. 5.7 ENERGY PRODUCTION Annual energy production is the most important factor.Approximate annual energy can be estimated by the following methods: 1.Generator size 2.Rotor area and wind map 3.Manufacturer's curve of energy versus annual windspeed 5.7.1.Generator Size This method gives a very rough approximation because wind turbines with the same size rotors can have vastly different size generators.The effect of the wind regime and the rated power can be estimated by changing the efficiency factor. AKWH =CF GS 8760 5.2 where AKWH =annual energy production,kWh/yrCF=capacity factor or efficiency factor GS =generator size (rated power),kW 8760 =number of hours in a year. A capacity factor of 0.25 would suffice for a generator rated at a windspeed of 10 m/s and a wind turbine in a good wind regime.Use lower values for the efficiency factor if the unit is over rated and/or for a lower wind regime.The capacity factor,for whatever time period, is the average power (energy production/time)divided by the rated power. Example:Wind turbine has the following specifications: Rated power =25 kW at 10 m/s Rotor diameter =10 m,CF =0.2 AKWH =(0.2)(25 kW)8760 hr/yr =43,800 kWh/yr For a poor wind regime AKWH would be closer to 30,000 kWh. 5.7.2 Rotor Area and Wind Map The cross sectional area or intercept area of different types of wind turbines can be calculated from the dimensions of the rotor (Fig.1.7). HAWT area =1 12 VAWT Giromill area =HD Savonius area =HD Darrieus area =0.65HD The annual average power/area can be obtained from a wind map and then the wind energy through the rotor can be calculated from Eq.5.3. WE =A,;P/A 8760, watt-hr/yr 5.3 where P/A =power/area in watts/m2 and A;is the area of the rotor.The annual energy production then depends on the efficiency of the wind system. AKWH =EFF WE 5.4 The efficiency factor should reflect the annual average efficiency of a wind turbine,around 0.20 to 0.25 and remember to convert Watts to kW. Example:Use the same wind turbine as in the previous example. area =mr2 =(3.14)25 =78.5 m2 Suppose P/A =180 watts/m?from the wind map,then WE =(78.5)(180)8760 =124,000,000 watt-hours/yr WE =124,000 kWh/yr That is the amount of energy which passes through the intercept area of the rotor in one year and the annual energy production is AKWH =0.2 WE =24,800 kWh/yr. 5.7.3.Manufacturer's Curve Some manufacturers assume a Rayleigh distribution for the windspeeds.From the windspeed distribution and the power curve for their wind turbine,an estimate is made of the annual energy production (Fig.5.10).This curve was taken from the brochure of the Windworker 10,which is 10 m diameter,rated power of 9 kW at 8 m/s.From Figure 5.10, the annual energy production should be 48,000 kWh in a wind regime with an average windspeed of 7 m/s. 60,000F So Pe=40,000F ' >'O 'oc a 'uJ ' <' 20,000 F '10 ms 0 ly 1 I '|i 7 t i]1.j 5 10 15 20 mph WINDSPEED Figure 5.10.Estimated annual energy production based on mean yearly windspeed. 68 5.8 CALCULATED ANNUAL ENERGY If the windspeed histogram or windspeed distribution is known from experimental data,then a good estimation can be calculated from the histogram or distribution and the power curve for the wind turbine.For each interval (a bin width of 1 m/s is adequate),the number of hours at that windspeed is multiplied by the corresponding power to find the energy.These values are added together to find the energy production for those total number of hours. Values from the power curve for the Carter 25 were multiplied by the number of hours at that windspeed from the annual windspeed histogram (14 years of data)for Amarillo,TX.The summation was around 55,000 kWh.Figure 5.11 graphically shows the process.However,a wind turbine will be down for maintenance and operation and an availability factor of 0.9 reduces the value to 50,000 kWh/yr.HOURSPOWERkW/ENERGYk¥théFigure 5.11.Left curve,windspeed histogram.Center curve,power curve for Carter 25.Right curve,energy in wind and hatched part is the energy captured by the wind turbine. Availability is the time that the wind turbine is operational and does not depend onwhetherthewindisblowing.Experimental values of availability of wind turbines in the field were poor for first production models,however,availabilities of 95%and above are 69 reported for those units which have a good program of ongoing maintenance. Remember a wind turbine does not have problems when the wind is not blowing. Therefore preventive maintenance is a must to keep the units producing energy. A note of caution;histograms and power curves have to be corrected for height and density.So when the density correction is made from 1.2 to 1.0,kg/m?for the area ofAmarillo,TX,that reduces the 50,000 kWh/yr to 42,800 kWh/yr.Experimental values are around 40,000 kWh/yr.If the unit had an availability above 95%and was kept operating during windy periods,this unit should produce 45,000 kWh/yr. Calculation of estimated production is simpler using spread sheet programs or by writing a program to do the calculation from a histogram and a power curve.The datawouldbeintabularformandcanbegraphedusingspreadsheetsorgenericplot programs.A spread sheet program for calculating annual energy production written in Quattro Pro is in the Appendix. 5.9 INNOVATIVE WIND SYSTEMS Innovative or unusual wind systems (Figs.5.12-13)have to be evaluated the same as other wind turbines.The important categories are system performance,structural requirements and quantity and characteristics of materials.Innovative ideas include thetornadotype,tethered units to reach higher winds,tall tower to use rising air,torsion- flutter,electrofluid,diffuser-augmented and the Magnus Effect.Many of these have been reported in Popular Science [1-3].Most innovative concepts remain at the feasibility or lab experiment stage.Not all innovative systems are recent inventions,for example,sail wings,wings on railroad cars and the Magnus Effect (Madaras concept was rotating cylinders on railroad cars). The West German government funded the construction of a 200 m tall tower inSpain[4].A 240 m diameter greenhouse at the bottom provided the hot air to drive the wind turbine,rated at 75 kW,in the tower.A private entrepreneur in California has constructed a Magnus type wind turbine,17 m in diameter,rated capacity of 110 kW.The unit was later moved to the wind test site of Southern California Edison,which is located in San Gorgonio Pass. The most different concept is the electrofluid unit which has no moving mechanical parts.A somewhat similar device consists of a balloon covered with a thin conductive layer.Static electricity generated by wind friction would be conducted through a cable to the surface [5].Oscillations of piezoelectric polymers driven by the wind would also make a unique type of wind turbine. The Solar Energy Research Institute (SERI)was the lead agency in innovative concepts (Table 5.1)and reports on the projects funded by SERI are available in conference proceedings [6-8].Funding for this program was discontinued by the Department of Energy. Winglets or tips [9]on the ends of the blades (dynamic inducer)to reduce the drag due to the tip vortex were tested by Aerovironment and the University of Delth,The Netherlands.The results were inconclusive due to the variability of the windspeeds.In some cases energy production could be improved but the cost of the winglets could be offset by increasing the radius of the blades.Where the windspeed variability is not afactor,winglets can reduce drag and increase lift as on the Boeing 747,jumbo jet. 70 -- ee = TC?HIND STRE Ars AUJUSTAREE - VERTICOL |VANES LOSESVAYESCAa FSYSlaNcuoren Hh ["GRO-_STATIONARY°°S"AUCTUREc--_” TURS'NE FXHAUSI _*_”eg:e--BEARING E30"PUVWHECLS t CONFINED VORTEX a :*i |'y e } '} Vopsertiatyr FRONT VIEW a Boe.OPTIONAL io-7 SHROUD --=.SHELLS fo .™OPTIONAL ASSHROUDVede SHELLS TOP VIEW TOROIDAL ACCELERATOR ROTOR PLATFORM DIFFUSER AND AUGUMENTOR [i--- =_) TETHERED GENERATOR DELTA WIND VORTEX GENERATOR Figure 5.12 Diagrams of innovative wind turbines. 71 a @ an |'tious -sant?tyne |Slama sce Awl Cy Oy 7s cestneren rrccrsceeao.-@ MyH YOLAC!feu UY C;i>%MiClaan upg,SVd1e e t }.}[Spas'|Pa Low-7 t 7 ¥v veya sy T v v rr UF PA ra ELECTRO FLUID DYNAMIC GENERATOR POWER TOWER "le?a ' t ' ( ' i] ' 4 ' TENSION FIELD OSCILLATING VANE Oo Figure 5.13 Diagrams of innovative wind turbines. Table 5.1 Solar Energy Research Institute,Innovative Wind Program. Innovative Wind Turbines (VAWT)West Virginia University Tornado Type Wind Energy System Grumman Aerospace Diffuser Augmented Wind Turbines Grumman Aerospace Wind/Electric Power Charged Aerosol Generator Marks Polarized Electrofluid Dynamic Wind Generator University of Dayton Energy from Humid Air South Dakota School,M&T Madras Rotor Power Plant Phase |University of Dayton Vortex Augmentors Polytechnic Inst,New York Yawing Wind Turbine,Blade Cyclic Pitch Washington University,St.LouisOscillatingVaneUnitedTechnologies Dynamic Inducer Aeroviroment A simple sail wing consisting of a pipe spar and a trailing cable was designed andbuiltbyThomasSweeney[10].The advantages are light weight and ease of repair.The 72 patent rights were purchased by Grumman who built a couple of prototypes but never puttheunitintoproduction.WECS Tech built a number of sail wing units,most of which were failures,on a wind farm in Texas and others for wind farms in California.The operating history was fairly poor.The same design was used on a prototype project bytheInstitutodeInvestigacionElectricasinMexico. The idea of a confined vortex,a tornado,was invented by T.J.Yen.DOE funded theoretical and model studies of this concept.Another concept was to use unconfined vortices produced along the edges of a delta wing and then place two rotors at those locations.Again DOE funded model studies.Existing structures could be modified or new buildings would incorporate features to increase the windspeed which then would be captured by a WECS.Since windspeed increases with height,if rotors could be placed inlowaltitudejetsbyuseoftetheredballoonsorairfoils,a large amount of energy could be obtained from small size rotors. Other ideas are lift translators with horizontal or vertical axis,which is similar to the railroad car with wings,except cables hold the sails or airfoils.Both concepts need wind from a predominate direction as large units cannot be oriented.An idea for reducing weight is to use cables for tension,as proven in suspension bridges.An oscillating vane or airfoil could extract energy from the wind,but the intercept area is fairly small for the amount of material. 5.10 APPLICATIONS The kinetic energy of the wind can be transformed into mechanical,electrical,and thermal energy.Historically the transformation has been mechanical where the end use was grinding grain,powering ships,and pumping water. The applications can be divided into wind assist and stand alone systems.The wind assist system is where the wind turbine works in parallel with another source of energy to provide power.The advantages of such a system are:power is available on demand,generally there is no storage,and there is better matching between load and power sources.Stand alone systems will only provide power when the wind is blowing and the power output is variable,unless a storage system is connected to the wind turbine.A third application which is now emerging are hybrid systems for villages and for telecommunications. 5.10.1 Electrical Energy Most wind turbines are designed to provide electrical energy.In a wind assist system,wind turbines are connected to the utility line either directly through induction generators and synchronous generators or indirectly where variable frequency alternators and DC generators are connected through inverters.The utility line and generating capacity of the power station act as the storage system.For a stand alone system,battery storage would double the cost of the system. The U.S.Department of Agriculture (USDA),Bushland,TX and the Alternative Energy Institute (AEI),West Texas A&M University are evaluating stand alone,electric toelectricsystemsforpumpingwater[11].The wind turbine generator is connected directlytoaninductionmotororasubmersiblepumpwhichisrunatvariablemm.The advantages of such a system are higher efficiency and higher volumes of water,enoughforvillagewatersupplyandlowvolumeirrigation.Such systems are now commercially available. 73 5.10.2 Mechanical Energy A wind turbine can be connected mechanically to another power source,again a wind assist system.The other power source could be an electrical motor or an internal combustion engine.Both systems have been tested. The major use for windmills has been the pumping of water.The farm windmill is suited to pumping small volumes of water but is too inefficient to pump large volumes of water. The Brace Research Institute combined a modern 3 bladed wind turbine,a transmission from an Austin truck and a conventional centrifugal pump on a prototype project to pump irrigation water on the Island of Barbados [12].The rotor was not self starting and the blades of fiberglass were expensive.A person had to manually shift the transmission to match the load of the pump to the output of the wind turbine at different windspeeds.'In 1976,the Alternative Energy Institute studied the feasibility of using wind power for pumping irrigation water with positive displacement pumps and air lift pumps. There are problems in matching the power output of the wind turbine with the power needed by the irrigation pump.Calculated maximum efficiencies were very low,of the order of 10%,for both types of pumps. The airlift pump has the advantages of no moving parts in the well.Airlift pumps were in use at the turn of the century for pumping water from mines,but were replaced by other types.Bowjon manufactured a wind powered airlift pump to compete with the farm windmill.For maximum efficiency the submergence,depth of pump below the water level, should be equal to the lift.For wells with little water at large depths,this presents a problem for airlift pumps. 5.10.3 Thermal Energy Thermal energy can be obtained directly by churning water or some fluid with viscosity.The load matching between the wind turbine and the churn is very good.A prototype system for providing heat to a dairy was tested by a research group at Cornell University [13,14]. Conversion of electrical energy to thermal energy by resistance heating has been tested a few times [15].At one time,a company marketed such a wind system. 5.10.4 Hybrid Systems A large market exists for wind assist to diesel generated electricity for isolated communities,farms,and ranches [16].This has now been expanded to include other sources of energy and hybrid systems for community electricity and for remote telecommunications have been installed.The hybrid systems consist of wind, photovoltaic,diesel,battery storage and an inverter to provide alternating currentelectricityforvillageswithanenergyuseof20to200kWh/day [17]. 5.10.5 Summary Applications will be considered in more detail after more is learned about designandconstructionofwindturbines.Wind power for generating electricity is the most usedapplication.The problems of load matching in pumping water for irrigation has to be partofthedesignconsiderations. 5.11 STORAGE Of course if a way could be found to cheaply store energy,then the economics ofstandalonewindsystemswouldimproveandwindplantscouldprovidefirmpower. 74 Batteries are used with stand alone systems,hybrid systems,and even for lead levelingforshorttermfluctations.Ideas have been to change the energy to chemical energy suchastheproductionoffertilizerorhydrogen.Another idea would be to store the energy inflywheels,which would be a good load match between the wind turbine and the load. Compressed air,pumped water storage and superconducting magnets have all been considered and some prototype systems with wind turbine input have even been constructed. REFERENCES 1.Ben Kocivar,"Tornado Turbine,"Popular Science,Jan 1977,p 78 2.Victor Chase,"13 Wind Machines,"Popular Science,Sep,1978,p 70 3.Jim Schefter,"5 Wild Windmills,"Popular Science,Jul 1983,p 68 4.Blain Juchau,"650 -Foot Power Tower,"Popular Science,Jul 1983,p 68. 5.Gabriel Lorente,"Nuevo Concepto de Generador Elctro-Eolico,"Metalurgia yElctricidad,Numero 532,Marzo 1982,p 51. 6.SER!Second Wind Energy Innovative Systems Conference,SERI/CP -635-938; Vol.|and Il,SERI/CP -635-1051,Dec 3-5,1980. 7.Proceedings -Fifth Biennial Wind Energy Conference &Workshop (WWYV),Vol.|,SERI/CP -635 -1340,Oct 5-7,1981,p 415-523. _8.Proceedings -Sixth Biennial Wind Energy Conference and Workshop,AmericanSolarEnergySociety,Jun 1-3,1983. 9.David Scott,"Tip-Vane Windmill Doubles Output Efficiency,"Popular Science,Sep 1983,p 78. 10.Stephen Kidd and Doug Garr,"Electric Power from Windmills?"Popular Science, Nov 1972,p 70 and E.F.Lindsey,"Windpower,"Popular Science,Jul 74,p55. 11.Alternative Energy Institute and US Department of Agriculture have numerous publications on wind power for water pumping;mechanical,wind assist (both electrical and mechanical),and wind-electric autonomous systems. 12.RE.Chilcott and E.B.Lake,"Proposal for the Establishment of a 10hp Windmill Water Pumping Pilot Piant in Nevis,West Indies,"Brace Research Institute pub.no. 1.45,Apr,1966. T.A.Lawand,"Proposal No.ll:The Evaluation of a Windmill Water Pumping Irrigation System,"Brace Research Institute pub.no.1.58,Jun,1968. 13.W.W.Gunkel,et al.,Wind Energy for Direct Water Heating,Report No.DOE/SEA- 3408-20691/81/2,May 1981.Available from NTIS. 14.M.Rolland and D.Cromack,"Wind Driven Fluid Devices for Water Heating,"V. Nelson,Ed.,Proceedings,National Conference,Summer 1980,Am Wind Energy Assn,Jun 1980,p 93. 15.Michael Edds,"UMASS Wind Furnace Performance and Analysis,"V.Nelson,Ed., Proceedings,National Conference,Fall 78,Am Wind Energy Assn,Sep 1978,p 142. 16 Ray Hunter and George Elliot,Eds.,Wind Diesel Systems,A Guide to the Technology and Its Implementation,Cambridge University Press,1994. 17.|Lawrence Flowers,et al.,"Decentralized Wind Electric Applications for DevelopingCountries,Proceedings,Windpower '93,Am Wind Energy Assn,1993,p 421. 75 PROBLEMS 1. 2. 3. 4. 5. Estimate the difference in the amount of material in the rotor for a giromill and a Savonius rotor with H =10 m,D =10 m. For a conventional HAWT,radius of 5 m,estimate annual energy output for two different regions from U.S.Wind Power Map. For a Darrieus unit,24 m X 16 m,estimate annual energy output for two different regions from U.S.Wind Power Map. For a Giromill,H =10 m,D =12 m,estimate annual energy output for two different regions from U.S.Wind Power Map. A Carter 25 is rated at 25 kW.Estimate annual energy output using equation 4.2. From Figure 4.10,estimate the annual energy production for a region where the average windspeed is 10 m/s. Calculate the power from Figure 4.7 at 20 m/s for the VAWT for the following conditions.Remember rpm has to be converted to radians/second. a.Wind turbine is operating at 100 rpm. b.Wind turbine is operating at maximum power coefficient. c.Wind turbine is operating at constant torque of 2000 N-m. Given the following power curve for a wind turbine.Calculate the annual energy production for a mean windspeed of 5 m/s,average density =1.1 kg/m'.Use the Rayleigh distribution to obtain a windspeed histogram. Windspeed,m/s Power,kW 3 0 5 40 7 100 9 200 11 250 13-21 300 23 0 76 6 DESIGN OF WIND TURBINES 6.1 INTRODUCTION The design of wind turbines has developed from a background of work on propellers,airplanes and helicopters.Computer codes developed for analyzing aerodynamics and vibration have been modified for wind turbines.Theory and experimental procedures are well developed and no scientific breakthroughs are needed for wind turbines.However,there are problems of predicting loads from unsteady aerodynamics that remain to be solved.These loads lead to fatigue and less life then predicted by the design codes. Someone made the comment that you could use brooms for blades and the rotor would turn.Of course,the efficiency would be low,control would be a problem,and the strength would not be adequate. 6.2 AERODYNAMICS The analysis of aerodynamic performance begins with a disk or area in a stream flow of air.The fundamentals of conservation of energy and momentum are used to determine the limit on the amount of extractable energy. Forces of lift and drag on airfoils are measured experimentally in wind tunnels.As previous measurements were for use with airplanes,NACA has published a lot of data.Airfoils were developed for sail planes which had a large ratio of lift to drag.Which airfoilsareusedforwindturbinesdependsonanumberoffactors,not just the ratio of lift to drag. Starting in the late 80's airfoils designed specifically for wind turbines were developed as the requirements are different.A major change was to design airfoils less sensitive to surface roughness. Different theories (strip theory,circulation,vortex shedding)and experimental data on airfoils are used to predict the performance of wind turbines.This theoretical performance can be checked against the measured output of models in wind tunnels,truck or railroad car testing for small diameter units,or field testing (atmospheric)of wind . turbines.Overall efficiencies include the efficiencies of the rotor,drive train and energy converter (generator,etc.). The complete analysis on design of wind turbines,primarily rotors and structures, can be found in more advanced texts [1-6],however beginning physics can be used for a qualitative understanding of rotor performance. 6.3 MATHEMATICAL TERMS Momentum of a particle is the mass times the velocity.Boldface indicates that it is avector,which has both magnitude and direction.In two dimensions,it takes two components to define a vector and in three dimension,three components.In ananalyticalrepresentationthevectorcanberepresentedbyitscomponentsalongtwoaxes(perpendicular or orthogonal axes for this presentation). p=mv .6.1 Any particle can be treated as a single particle with the mass,M,concentrated at a point(center of mass,R).Position vector is indicated by r. 77 MR =m1ry +Mofo +...+MF; Forces on particles make them accelerate.The dynamics or motion is described by Newton's second law, F =Ap/At,Newton (N)6.2 Expressed in words the force is the change in momentum over the change in time.Inotherwords,to change the momentum of a particle requires a force.Torque makes a particle turn around some point,which can be thought of as theleverarmtimestheforce.A large torque can be obtained by increasing the length of the lever arm or by increasing the force. T=rXF,Nm 6.3 If a particle is attached to a stick which is free to rotate about the end (Fig.6.1),andaforceisapplied,the torque will make the particle rotate,and there will be power available. P=Ta,Watts 6.4 The amount of power is the product of the torque and angular velocity («, radians/second).That power is available at the shaft.Notice that the power can be transmitted by large m and small T or small @ and large T.Most operations of transferring shaft power try to have a large w because of structural considerations.Finally the rotating particle will have rotational kinetic energy. KErt =0.5mv2 =0.5mr2o2,Joules 6.5 where the speed of the rotating particle depends on the radius,v =@ r. @ Figure 6.1 Mass rotating about a point. 6.4 ANALYSIS OF EXTRACTABLE POWER __The power coefficient is the power delivered by the device divided by the poweravailableinthewind.Since the area cancels out,the power coefficient is Cp =Power Out/(0.5 p v3)6.6 78 6.5 DRAG DEVICE The work or energy to move an object is the force times the distance through which it moves. Work (energy)=F-Ar.The dot between the vectors means only the parallel component of the F is used (W =Fos 6 Ar). Divide both sides by time .=F-.ar and thus the power is P=F-y 6.7 The power from a drag device (Fig.6.2)can be calculated from the force on the device and the speed of the device,u.From Eq.6.7 the P =Fu. ae, a a v u Oo a ee eee eel + Figure 6.2 A drag device in the wind. The force/area of the air on a stationary object in a windspeed,v,is FIA =0.5pv2Cp,Ni/m2 6.8 The force/area is also the pressure,so the wind blowing against an object creates a pressure.If the winds are high enough as in hurricanes,the pressure can destroy buildings. From Eq.6.8,the power loss due to drag of struts can be calculated.Dragcoefficients,Cp,are given in Mark's Handbook [7],but the simplest procedure is to use Cp =1 for round pipe and wires. The relative velocity of the wind for a person on the drag device is Vr =Vo-U then the power per unit area is P Fu 2 2A=A =SPM UCD =0.5 p (Vo -u)uCp . 69 Notice that at u =0 and at u =Vo,the power is zero.A drag device cannot move faster than the wind.From Eqs.6.6 and 6.9,the maximum power coefficient for a drag device 79 can be calculated.The maximum power coefficient,Cp(max)=4/27,occurs when the dragdeviceismovingatu=1/3 the windspeed.Cpimax)can be calculated exactly or can be estimated from a graph of P/A versus windspeed (Eq.6.9). 6.6 LIFT DEVICE A lift device can produce on the order of 100 times the power per unit surface areaofbladeversusadragdevice(see Fig.4.3).See Rohatgi and Nelson [8,Ch.6]for more details. Example:Suppose we have a blade,5 m long,0.1 m wide.As a drag device its capturecrosssectionareais0.5 m2.As a lift device in a HAWT,its capture cross sectional area is 78.5 m2.If the differences in efficiencies are included the ratio of the power out per blade area for a lift device over a drag device is over 600. An example of a lift device is a sailboat,a lift translator (Fig.6.3),where the sails form an airfoil. S '| Figure 6.3 Lift translator,direction of motion is perpendicular to Vo,S is cross sectional area of the blade or sail. Besides sailing ships,there have been proposals to use lift translators for generating power (see 4.9).The problems are the large speeds of the devices as lift devices can move faster than the wind,the proximity to the ground and the necessity for having a predominate wind direction. The simple analysis for a lift device assumes streamline flow (irrotational, incompressible)and conservation of energy and momentum.The windspeed interacts with the disk (propeller,rotor,screw,or whatever)and there is a pressure drop across thedisk(Fig.6.4).The thrust (force)loading,T,is uniform across the disk.Also there is no friction or drag force.At large distances behind the disk,then the windspeed andpressurewillhavethesamevaluesasatalongdistanceinfrontofthedisk.As stated earlier,the pressure,p,is the force/area. 80 _vo,U,Ya,Vo Po pt Po Figure 6.4 Windspeeds and pressures at infinity,at the disk,and behind the disk. From conservation of momentum,momentum in equals momentum out.The mass flow, Am/At,across any area is constant.Across the area of the disk,the mass flow is the product of density,(p),area (A),and windspeed,so Am/At =pA1Vo =pAU =pAovo. Am AmUseEq.6.2.F=T="Ar Ye -Ar 2PALSNarate: T==(Vo -vp)=PAU(Vo Vo)6.10 The thrust loading on the disk due to the pressure drops across the disk is T =A (pt -p')6.11 Bernoulli's theorem relates the velocity and pressures in streamline flow (kinetic energy and pressure is a constant for horizontal flow).If the velocity increases,then the pressure _ decreases;the two are related through conservation of energy and momentum.The windspeed and pressure upstream and downstream of the disk are related by. upstream disk downstream O.5pve +po =0.5pU2 +pt 0.5p U2 +p'=O.5pvs +Po PY =Osa 4%-45eU*P72 05 aVe +P.-0.52" From the two equations,substitute the pressure difference (p+-p*)into 6.11 T =0.5pA(ve -v5)6.12 The thrusts are equal so set Eq.6.12 equal to Eq.6.10. PAU (Vo -V2)=O.5PAVS -V2)=25 0ACYNS)U,-Vu)18 81 From Eq.6.13 the windspeed at the disk is the average of the windspeeds before and after the disk (wake). U =0.5 (Vo +Vo)6.14 The axial interference factor is defined by what ratio the windspeed is reduced by the disk. (Vo -U)U ar =1 _-_ Vo Vo U =vo(1 -a)Vp [tee )=0.5(Voe 2) Substitute into Eq.6.14 and the wake windspeed is AV,Ct)2 Vy *Vy AVMs -Dw7 Vy WA, Vo -V.+V2 =Vo(i-20)or a=Woe 2 Va =2p.=VaVoVyxVe(1 20) If the disk or rotor absorbs all the energy,v2 =0 and a =0.5.That is physical nonsense as all the mass would pile up at the rotor. As in Eq.3.1,P =AKE/t or AKE _(KE)us -(KE)us _mP=,=0.5 vg -0.5 v3 =0.5 p AU (v5 -vB) P =0.5pAve4a(1 -a)?6.15 6.6.1.Maximum Theoretical Power The maximum power can be found by plotting the curve (Eq.6.15)versus a or by using © calculus.The answer is «=1/3 or 1.Of course,«=1 means that there is no reduction of windspeed and the disk does not take out any power.For a =1/3,the maximum power is 6.16 Then the maximum power coefficient,from Eq.6.6 is Cp =16/27 =0.59.Real rotors will have smailer power coefficients due to drag,frictional losses and losses due to rotation of the wake,however measured values can reach 50%. 6.6.2 Rotation From conservation of angular momentum,there will be a rotation of the wake in the opposite direction of the disk,since the disk is rotating (Fig.6.5). 82 Region 1 .>an Region 2'(wake) ;f a"a Wwvo,-)C -Flow Roe, Figure 6.5 The rotor imparts a rotation to the wake. From conservation of energy KE;=Energy Extracted (by rotor)+KEo +KE (rotation of wake) The torque acting on the rotor makes it rotate and power can be extracted.In order to obtain maximum power,then a high angular velocity,Q,and a low torque,T,are desirable because a large torque will result in a large wake rotational energy (angular velocity of the wake =@). Power (rotor)=TQ A similar analysis,as previously described,is used to obtain the power extracted where conservation of angular momentum is included.An angular induction factor,a',is used. The main difference is that the rotor velocity is a function of the radius,so the values have to be calculated for different radii (strips)along the blade. 6.7 AERODYNAMIC PERFORMANCE PREDICTION Performance predictions of power,torque,force and power coefficient can be obtained for a blade (rotor)using a numerical technique.Values are calculated for sections of the blade (strip theory)and then summed to obtain the total performance.Tip losses and hub losses can be included along with wind shear and yaw (off axis components)...The main limitations with the programs are the treatment of unsteady aerodynamics in the region of dynamic stall and the use of 2-D data for lift and drag.- Aerodynamic performance prediction programs are now available for personal computers with menu driven interactive editing and graphical display to facilitate its use as a design tool;PROP93 [9].The inputs to the program include the blade characteristics, lift and drag coefficients for different angles of attack for the airfoil and operating characteristics such as tip speed ratios,rpm,or windspeed.Graphs of the planform (Fig. 6.6),lift,and drag data can be produced.The tabular output (Table 6.1)of PROP93 canbedirectedtothescreen,printer,or to a data file.Graphs (Figs.6.7-9)of the standard output parameters can be displayed as functions of blade station,pitch,windspeed or tipspeedratio.Calculated values can then be compared with experimental values.Theseprograms,which are steady state,do not predict the high loads seen in the field due to gusts (dynamic stall). 83 0 1 2 3 4 ba)6 7 8 9 10 fr a eePm ae ee ee Figure 6.6 Planform and twist for Carter 25 wind turbine.Blade divided into ten sections for analysis.Station is at the midpoint of the section. 6.8 MEASURED POWER AND POWER COEFFICIENT A common specification is the power output of the wind turbine versus windspeed, a power curve.The power curve generally includes all efficiencies from wind to electrical output,not just the rotor efficiency.Since all wind turbines must control power output at high windspeeds;at some point efficiency is lower.Control can be by changing blade pitch or by operating fixed pitch blades at constant angular speed. The experimental power and power coefficient curves (Fig.6.10)are for a wind turbine which has an induction generator,operation at constant angular speed.Therefore it reaches maximum power coefficient at only one point and the decreased aerodynamic efficiency at windspeeds above this point make the power coefficient also decrease.The increased power in the wind and the decreased aerodynamic efficiency combine to give a constant power output above 12 m/s. Besides the tip and hub losses of the blades on the rotor,there will be a further reduction of the power coefficient due to the inefficiencies of the mechanical system (drive train,coupling)and the generator.Under the optimum design conditions,the modern two or three bladed rotors at tip-speed ratios in the range of approximately 4-10 will have power coefficients of about 0.4 to 0.5 (Fig.6.11). 84 Table 6.1.Sample output from PROP93.Output parameters for ten stations and then thetotalissummarizedatthebottom. Propprint3BLADEELEMENT DATA FOR DELTA BETA=0.00 X=45.52 YAW=0.00 ELEMENT 1 2 3 4 5 6 7 8 THETA 180.000 180.000 180.000 180.000 180.000 180.000 180.000 180.000 VEL 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 A 72.049 =-1.114 -0.720 =-0.119 0.543 1.115 1.209 1.271 AP -0.021 -0.006 -0.003 -0.001 -0.001 0.010 0.001 0.001 CL 0.347 -0.453 -0.199 -0.020 0.040 0.085 .0.094 0.089 cD 0.009 -0.019 0.008 0.008 0.007 0.007 0.008 0.008 PHI 37.147°17.246 .8.590 4.008 1.274 -0.258 -0.403 -0.453 ANG 4.853 -6.054 -3.210 -1.292 -0.826 -0.358 -0.403 -0.453 TC -5.872 -8.950 -4.957 -0.537 1.107 2.344 2.625 2.837 oc -0.424 -0.356 -0.241 -0.088 <-0.081 <-0.118 -0.154 -0.204 Pc -19.292 -16.203 -10.966 -4.002 =-3.679 <-5.369 -7.025 -9.265 TD.1lbs/ft -0.728 -1.849 -1.707 -0.259 0.686 .1.775 2.350 2.930OD.ft-ibs/ft -0.840 -1.176 -1.327 -0.678 -0.801 1.429 -2.210 -3.363 PD.kw -0.005 -0.032 -0.036 -0.018 -0.022 -0.039 -0.060 -0.092 Propprint3 BLADE ELEMENT DATA FOR DELTA BETA=9.00 X=45.52 VAW=0.00ELEMENTaa THETA 180.000 180,000 VEL 1.660 1.000 A 1.337 1.405 AP 0.001 0.005 cL 0.085 0.082 cD 0.008 0.008 PHI 0.496 -0.532 ANG -0.496 -0.532 TC 3.076 3.333 oc -0.263 -0.332 PC "11.966 -15.119 TD.Lbs/ft 3.600 4.360 OD.ft-ibs/tt -4.922 -6.952 PD.kw -0.134 -0.190 PITCH xX Tc ;oc PC ETA vo TD MD OD PD .ib ft-lbs ft-lbs kw 0.0 45.5 1.705 0.209 -9.515 0.179 1.3 37.6 291.9 73.7 -1.256 85 CARTER.AEI by Windspeed mph 6 rene eee -- 1 Blade Station Figure 6.7 PROP93:Prediction of power output by blade station for four windspeeds, Carter 25 wind turbine. CARTER.AElforEntireRotor 29 porn 28 PowerkWLdNOwien5s 3 +t t+3 § -4 2 0 2 4 Pitch Angle -dagrees Figure 6.8 PROP93:Prediction of power output for different pitch angles.The Carter 25 wind turbine is a fixed pitch,constant rpm machine . CARTER.AEIforEntireRotor 10 :20 :30 15 25 35 Wind Speed mph Figure 6.9 PROP93:Predicted power curve for Carter 25 wind turbine. 86 30f 20-oy POWERkWss10r- 2 4 6 8 10 12 14 16 18 20 POWERCOEFFICIENTi]i |l |l |{|J 2 #4 6 8 10 12 14 16 #18 «20 WINDSPEED m/s Figure 6.10 Experimentally measured power curve and power coefficient curve foraCarter25;rated 25 kW,10 m diameter. 87 06C THEORETICAL TWO BLADE,HAWTFARMWINDMILL SAVONIUS 2rsPOWERCOEFFICIENT°ipDARRIEUS 500 kWDARRIEUS 100 kw 0 2 4 6 8 10 12 14 TIP SPEED RATIO Figure 6.11 Power coefficients for different rotors compared to the theoretical value.Experimental data for type of rotor:farm windmill [10],Savonius [11],100 kW Darrieus[12],500 kW Darrieus [13],horizontal axis wind turbine,HAWT (Carter 25 data,Fig.6.10). REFERENCES 1.Robert E.Wilson,Peter B.S.Lissman,and Stel N.Walker,Aerodynamic Performance of Wind Turbines,ERDA/NSF/04014-76-1,UC-60,June 1976. Available from NTIS. 2.David M.Eggleston,and Forrest S.Stoddard,Wind Turbine Engineering Design,Van Nostrand Reinhold,1987. 3.D.Le Gouriérés,Wind Power Plants,Theory and Design,Pergamon Press, Oxford,1982. L.L.Freris.Ed.,Wind Energy Conversion Systems,Prentice Hall,1990. 5.Wind Energy Conversion,C00-4131-Ti.Available from NTIS. Methods for Design Analysis of Horizontal Axis Wind Turbines_Aerodynamics of Horizontal Axis Wind TurbinesDynamicsofHorizontalAxisWindTurbines Drive System Dynamics Experimental Investigation of a Horizontal Axis Wind Turbine Nonlinear Response of Wind Turbine Rotor Effects of Tower Motion of the Dynamic Response of Windmill Rotor Free Wake Analysis of Wind Turbine Aerodynamics .Aerodynamics of Wind Turbine with Tower Disturbances6.E.H.Lysen,Introduction to Wind Energy,Consultancy Services Wind Energy Developing Countries,Netherlands,May 1983. 7.Mark's Standard Handbook for Mechanical Engineers. 8.Jaqnardan S.Rohatgi and Vaughn Nelson,Wind Characteristics,An Analysis for the Generation of Wind Power,Alternative Energy Institute, WTAMU,June 1994.>OONOARON>88 Joe McCarty,"PROP93:Interactive Editor and Graphical Display,"ProceedingsWindpower'93,Am.Wind Energy Assn.,Jul 1993,p.495. J.van Meel and P.Smulders,Wind Pumping,A Handbook,World BankTechnicalPaperNo.101.1989,p.30. M.H.Khan,"Model and Prototype Performance Characteristics of a Savonius Rotor Windmill,”Wind Engineering,Vol.2,1978,p.75. R.E.Akins,D.E.Berg,W.T.Cyrus,Measurement and Calculations of Aerodynamic Torques for a Vertical-Axis Wind Turbine,SAND86-2146,UC-60,Oct 1987. T.D.Ashwill,"Measured Data for the Sandia 34-Meter Vertical Axis Wind Turbine, SAND91-2228,Jul 1992. PROBLEMS 1. 10. Find the power loss for three struts on a HAWT.Struts are 4 m long,2.5 cm in diameter.Rotor speed is 180 revolutions per minute.Use approximation by dividing up into 1 m sections and calculate at midpoint of section.Cp =1. Calculate the power loss for the struts on a VAWT.Struts are at the top and bottom, 2 m long from torque tube to blades,diameter =5 cm,rotor speed is 80 rpm.Cp =1. For those that know calculus,find the value of u (speed of drag device)which produces the maximum Cp for a drag device.Use Eq.5.9,where Vo is the windspeed at infinity. For those that do not know calculus,find the value of u which produces the maximum Cp for a drag device by plotting the curve (Eq.5.9)for different values of u. If the solidity of the rotor increases,what happens to the aerodynamic efficiency as a function of tip speed ratio? Explain the difference in performance of a wind turbine if it a.operates at a constant tip-speed ratio b.operates at constant rpm. What is the maximum theoretical efficiency for a wind turbine?What general - principals were used to calculate this number? If the solidity of the rotor is very small,for example a one bladed rotor,what is the value of the rpm for maximum Cp compared to same size rotor with higher solidity? For those that know calculus,calculate the value of axial interference factor for which Cp is a maximum for a lift device.Then show that this gives Cp =59%. For those that do not know calculus,find the value of a which produces the maximum Cp by plotting the curve (Eq.5.)for different values of a. A rotor reaches maximum Cp at a tip-speed ratio of 7.Calculate rotor rpm for three different wind turbines (radius of 5,10,50 m)at windspeeds of 10,20 and 30 m/s. For a wind turbine which operates at constant rpm,it will reach maximum efficiency at only one windspeed.What windspeed should be chosen? 89 Specifications for a Wind Turbine,induction generator (constant rpm =60),fixed pitch rated power =250 kW,hub height =50 m rotor hub radius 1.5m 2 blades,radius to tip of blade =12m,mass of one blade =2750 kg 11.How fast is the tip of the blade moving?. 12.How fast is the inner part (where attached to hub)of the blade moving? 13.Put the mass at the midpoint and calculate the kinetic energy for one blade.Assume the mass of the blade is distributed evenly over ten sections.Now what is the kinetic energy for one blade? 14.At rated windspeed,calculate the torque since you know power and rpm. 15.At10m/s,what is the thrust force on the rotor trying to tip the unit over?Calculate for that windspeed over whole swept area. 16.If the unit produced 800,000 kWh/yr,calculate output per rotor swept area. 90 7?ELECTRICAL ASPECTS 7.1 FUNDAMENTALS Electricity and magnetism are concerned with charges and the movement ofcharges.Charges which can easily move are electrons and the fundamental ideas of moving electrons from the atomic to the macroscopic level are discussed in introductoryphysicstexts.The following terms are discussed only superficially to give a backgroundforoperationofcontrolsandgenerators. Current:Current is a flow of charge (electrons in most cases)past some point.Directcurrent(DC)is when the flow is in one direction and alternating current (AC)is whentheflowchangesdirection.Electric utilities in the U.S.have a standard AC which changes 60 times per second,60 Hertz (Hz).Overseas utilities also use 50 Hz alternating current.If the utility AC is plotted versus time,it looks a sine curve (Fig.7.1). |=Aq/At,Amperes 7.1 Voltage:It takes energy to move charges around and the potential energy to movechargedividedbythechargeiscalledthepotentialdifferenceandismeasuredin volts.For AC,the voltage also changes with time,just like the current. V =PE/q,Volts 7.2 Resistance:There is a resistance to the flow of charge across different elements in a circuit.A circuit consists of a source (voltage),current through the wires,and a load or resistance. R=V/A,Ohms 7.3 In metals the amount of current is linearly proportional to the voltage,a relationship - known as Ohms Law. V =IR :7.4 Also,in metals the resistance increases with temperature which means more energy is lost as the temperature is increased,i.e.because of the current.. Power:The power in a circuit is the voltage times the current. P =Vi 7.5 For AC circuits the instantaneous power will vary with time because the voltage and current vary with time.The power lost due to heating of the conductor (metals) depends on the square of the current. P =Vi =(e2&R 7.6 91 The implications are that electricity power needs to be transmitted at higher voltages. For wind generators,in general at 240 or 480 V,this means they need to be fairly close to the load or the utility line.With higher voltages,smaller diameter wire can be used. Capacitance:Capacitors are devices for storing charge.An example of a capacitor is two metal plates separated by a small distance. Inductance:Inductors are devices for storing magnetic fields.A example of an inductor is a coil of wire. Electric Field:Electric fields,E,originate or terminate on charged particles.If a charged particle feels a force,it is in an electric field.E =F/q Magnetic Field:Magnetic fields,B,are due to moving charges or to intrinsic spin (apropertyofparticlesjustlikechargeisapropertyofparticles).If a moving charge feels a force at right angles to its motion,it is in a magnetic field.AMPLITUDE°: 1 KF Md ue Si tf °TIME ' Figure 7.1 Illustration of sine waves with different frequencies. Also,changing magnetic fields can be created by changing electric fields.Maxwell formulated the theory of electromagnetism in all of its elegance of four equations,called Maxwell's equations.This is the theoretical basis for all of the electric power industry and communication by electromagnetic waves which we accept as commonplace today. If charged particles are placed in external electric fields and if moving charged particles are placed in external magnetic fields,there is a force on the charged particles. The amount of force depends on the strength of the electric and magnetic fields,the amount of charge,and the velocity of the charge. F =qE +q(vXB)7.7 This equation is then the basis for understanding the conversion of electric energy tomechanicalenergy,a motor,and the conversion of mechanical energy to electric energy, a generator. 92 A loop of wire has moving charges (current)in it.The loop is in an external magnetic field (Fig.7.2),therefore,there is a force on the charges and a torque on the wire,a motor (Fig.7.3).The torque on the loop is given by the current in the wire,|,the area of the loop,A,and the strength of the magnetic field,B. T =1(AXB) Figure 7.4 shows a loop of wire which is moved by an external force.The shaft power,P =To,in our case comes from the rotor,either directly or through a gearbox.The moving charges are in an external magnetic field,and there is a force on the charges,a generator (Fig.7.5). 7.1.1.Faraday's Law of Electromagnetic Induction Another way of looking at electromotive forces is by Faraday's Law of Electromagnetic Induction.The amount of magnetic flux is equal to the strength of the magnetic field times the area. Oy =BeA 7.8 The electromotive force is then equal to the change in magnetic flux with time. E =-AD/At 7.9 In generators and motors,the magnetic field and area can be kept constant and the angle between the two changed.This gives an alternating current which varies like a sine wave.If the load is purely resistive,then the voltage is in phase with the current.For a capacitor the voltage lags the current by 90 degrees and for an inductor the voltage leads the current by 90 degrees (Fig.7.6).In all real circuits there is some self inductance, capacitance and resistance so the current and voltage will not be completely in phase (Fig.7.7). 7.1.2 Phase Angle and Power Factor For a resistor the voltage and current are in phase and the average power is 1/2 Vplp.For capacitors and inductors,the voltage and current are 90 degrees out of phase and the average power is zero.The phase is the difference in the angle from zero (selected arbitrarily).In the figure,all the voltages have a phase angle of zero and the current is out of phase with the voltage. The instantaneous power to an arbitrary AC circuit (Fig.7.7)is given by Eq.7.5. That means the power oscillates because both voltage and current oscillate. p =vi =Vp sin(at)|,sin(ot+>) The average power is (by integrating over one cycle) _Vplp Cos avg -P) 93 Figure 7.2 Forces on the sides of a current-carrying loop in a magnetic field.The resultant of the set of forces gives a torque T which makes the loop rotate. Figure 7.3 Schematic diagram of a DC motor.Magnetic field from field coils,F. 94 Figure 7.4 Rectangular loop rotated by outside force with constant angular velocity,@,in a uniform magnetic field. (b) Figure 7.5 Diagram of AC generator and DC generator with split commutator. 95 i,v f,ot |WiaRb (a)(b)(c) ) i,v a-------4i Thi v Cc Qt V p----, wt a b (a)(o)«) fANe), 2 LO (a)ee (b) (c) Figure 7.6 Relationship of current and voltage across a resistor,capacitor,and inductor,showing phase relationship between the two. 96 However,what is measured for AC circuits are the average values of current and voltagegivenbytherootmeansquareofthepeakvalues. Vp l=]Ip/2 ms > Then the real power generated or consumed is given by V=Vims = Payg =VI coso 7.10 Where @ is the angle between the instantaneous voltage and current,and cos@ is the power factor.Adding a number of induction generators to the line could change the power factor and reduce the actual power delivered,a concern of the utility company.The utility grid supplies the reactive power for the induction generator.Therefore some wind turbines and wind plants have capacitors added to the system.© Figure 7.7 Instantaneous power input to an arbitrary AC circuit. 7.2 GENERATORS The main classifications of generators are direct current,synchronous,induction generators and permanent magnetic alternators.The direct current generator and alternating current alternators can operate at any rpm while the AC synchronous generator needs to be regulated to the correct rpm and synchronized with the grid.Outputcanbeasinglephaseorthreephase(Fig.7.8). .Induction generators are used for wind turbines because induction motors are mass produced;inexpensive,reduced operation and maintenance costs,simplicity ofcontrol.The generator is brought past synchronous speed and is then connected to the line.All the features of synchronous generators for control of speed,excitation,and synchronizing are eliminated as the utility line provides this aspect. A generator is composed of the armature and the field.Power is taken from the armature,and the field which controls the power can be permanent magnets or an energized coil of wire (Fig.7.9).In the latter case,there are two coils of wire with onebeingstationary(stator)and the other rotating (rotor).In a DC generator,the armaturerotatesandpoweristakenoffacommutatorbybrushes.Brushes need maintenance, 97 therefore alternators are used.In an alternator,the field rotates and the AC is converted to DC by a rectifier circuit. oO Figure 7.8 Schematic drawing of a three-phase AC generator.Rotating magnetic fieldproducesACvoltagesacrosseachpairofterminals;phase separation of 120 degrees. oO Field ShuntCoilArmatureBietaCoil Field Coilre)° (a)fb} Figure 7.9 Two types of field-coil excitation circuits for DC generators.(a)shunt excitation; (b)compound excitation. The advantages of the DC or permanent magnetic alternator is the constant Cp operation,which is aerodynamically more efficient and the elimination of a speedincreaserforsmallwindturbines(Watts to 10 kW).Jacobs used a direct drive,self excitedgeneratorwheretheresidualmagnetizationgivestheinitialvoltageoutput(Fig.7.10). Feedback from this is used to increase the field and give more power output. For HAWTS,then the power is transferred to ground level through slip rings (Fig. 7.11)or the power cord has enough slack to twist during yaw revolution.The second method has the desirable feature of eliminating the slip rings,always a potential problem for control signals and even for power transfer.However,strict observation schedules onlengthofthepowerdropcordoratriprelayforyawhavetobemaintained. A number of wind turbines also use direct drive but with a permanent magnet alternator (Fig.7.12).Output is rectified to DC and then converted to AC,60 Hz by an inverter.Output is 120 or 240 volts AC,single or three phase.However,they are now producing larger wind turbines which do not have a gear box.This means low rpm generators with a large number of poles. 98 Upper Negative Brush Hole in End-Bell Field Post on Brush Holder Board Figure 7.10 Schematic of Jacobs DC generator Synchronous generators and self-commutated inverters require a means of disconnect for safety during faults on the utility line because they are power sources.For small wind turbines,synchronous generators will probably not be acceptable for interface - with the grid,primarily due to complications of the control of the rotor rpm. 7.3.INDUCTION GENERATORS A rotating magnetic field induces currents in a set of copper loops in the rotor (Fig. 7.13).Magnetic forces on these current loops exert a torque on the rotor and cause it torotate(a motor).When it is forced to rotate past the synchronous speed (1200 or 1800 rpm)it becomes a generator.The rotating field is provided by the utility grid.The relationship of power,torque,efficiency and rpm is given in Figure 7.14. The switching mechanisms must not allow the generator to operate below synchronous speed or you would have a gigantic fan.The control mechanism needs to measure rpm,with some lee way for windspeeds at the cut-in value,to turn the generator on and off. 99 ¥CULEEEEELG@--Power Wires Generator Saddle Chain Passac :q----_TurntableTowerCap.ST BearingCastingL-|---|--4 @-_§Saddle Tube Drip Ring «-Silicon Rubber 4---Felt Washer Lower Casting ----_»>5 5OFCollectorS- Brushes Q Or @ Height m Adjust aed j«<-Control ChainScrew|a =Collector OO Housing Figure 7.11 Power connection diagram for Jacobs Wind Turbine. Wind From This Direction Hydraulic Governor het AJternator Blade Attaches Here --» Hydraulic Cylinder Overspeed and Vibration Shutdown ."SyPitchControlShaft High Wind Shutdown Pilot Tube Blade Hinge Figure 7.12 Schematic of Windworker;10 m diameter,10 kW. 100 IA STATOR ROTOR Figure 7.13 Schematic of induction generator with squirrel cage rotor. Induction generators are the most common generators for wind turbines from 5 to hundreds of kilowatts because the controls for synchronization to the line are simple and they are mass produced.When there is a failure on the utility grid,they automatically disconnect and do not present a safety problem.The induction generators decrease the power factor and correcting capacitors are installed on individual wind turbines or at the wind farm.It is possible to have a resonance condition with inductance and capacitance, however the variability of the wind insures that the generator output decreases rapidly when there is a fault on the line.. Remember the induction generator is essentially constant rpm operation for the rotor,which is fixed by the frequency of the utility grid.The rotor only reaches a peak efficiency at one windspeed. 7.4 OTHER GENERATORS The generator for the MOD-5B is rated at 3.2 MW,and is a variable-speed (1330- 1780)wound-rotor induction generator.A cycloconverter system maintains a constant frequency output. The Westinghouse,600 kW,wind turbine has a synchronous generator andfrequencyiscontrolledbythevariablepitchoftheblades.A power control algorithmlimitshighinstantaneouspoweroutput(spikes caused by wind gusts)by derating maximum power by 10%when a power spike exceeds 800 kW. Project EOLE located at Cap Chat,Canada,is the largest VAWT in the world at thistime;rated at 4 MW.Since this is a direct drive system,the generator is quite large,12 m 101 U.S.ELECTRICAL MOTORS 1800 44,35 1680 +421-30 1]RPM [™.J a 1700 +404-25 |100 -NS fNA 1720 78+20 had Ia ra ae Zé po)N, "a \.1740+-6+44+60 PFA Rwy aialALanes176074-40-40)ppWAA a 1780 +2+4+-5720 4 | * 1660 +o "10 HP,OPEN FRAME HORIZONTAL,480V,60HZ ==uO 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16,00a¥=ut HORSEPOWERoc[omta TI ii yrt Hl tH 7reGenerator|r+-Motor}yl Ht t7i]t n @Hta pAHtc _|NN lo it Efficiency Lf Sy A Seget ha 8fea Z'®o fo |oy 5 -tr Mechanical=cy Slip Horsepower 14 ,12 .10 .08 .06 .04 002 O .02 .04 06 .08 10 112 .14 Figure 7.14 Operating characteristics of induction machine as a motor/generator. 102 in diameter with 196 poles.The output is rectified to DC and then inverted back to 60 Hz AC.Therefore the wind turbine can be operated at different rpm. The Sandia VAWT test bed (34 m diameter,rated at 500 kW),located at USDA, Bushland,TX,is designed as a variable speed,constant frequency system.The system isaloadcommutatedinverter,AC adjustable speed drive,with a synchronousmotor/generator rated at 625 kW.Such systems are currently operated in industrial applications.Power electronics and inverters allow wind turbines to operate at either constant rpm or variable rpm. REFERENCES GENERAL,PHYSICS Sears,Zemansky and Young,University Physics,5th ed.,Addison Wesley,1975. Resnick and Halliday,Physics,Wiley. Arthur Kip,Fundamentals of Electricity and Magnetism,2nd ed.,McGraw Hill, 1969. GENERAL,GENERATORS T.S.Jayadev,Induction Generators for Wind Energy Conversion Systems,AER-75- 00653,February 1976,Available from NTIS $5.25. A.F.Veneruso,Induction Generators for Windpower Conversion,Presented at Electrical Engineering Aspects of Wind Energy Systems,October 26,1976.Advanced Energy Projects,Division 5715,Sandia Laboratories,Albuquerque,NM 87115. G.L.Johnson and H.S.Walker,"Three-Phase Induction Motor Loads on a Variable Frequency Wind Electric Generator",Wind Engineering,Vol.I,no.4,1977,p 268. David Curtice Jim Patton,Jeff Bohn,Neil Sechan,Study of Dispersed Small WindSystemsInterconnectedwithaUtilityDistributionSystem,RFP-3093/94445/3533/80/7,March 1980.Available from NTIS,$6.50. Michael Hackleman,The Homebuilt Wind-Generated Electricity Handbook, Earthmind,Saugus,CA 91350. J.E.Barble and R.W.Ferguson,"Induction Generator Theory and Application, AIEE,"February 1954,p 12. L.L.Freris,Wind Energy Conversion Systems,Prentice Hall,1990,(Ch.9). David Eggleston and Forrest Stoddard,Wind Turbine Engineering Design,Van Nostrand Reinhold,1987,(Ch.14). Gary Johnson,Wind Energy Systems,Prentice Hall,1985,(Chs.5-7). PROBLEMS 1.What is the voltage drop across a 100 ohm resistance if the current is 20 amps? 2.How much power is lost as heat through that resistance? 3.If the maximum power rating of the Carter 25 is 30 kW and it has a 240 volt generator,what is the maximum amps produced?What minimum size wire will be needed to connect it to the utility line? 4.What is the peak voltage for 110 VAC,240 VAC,480 VAC? 103 5.If the phase angle in a 240 VAC,20 amp circuit is 20 degrees,how much is the power reduced from maximum power? What does a 3 phase generator mean? 7.The synchronous point on an induction generator is 1800 rpm.If the generator is rated at 300 kW,what is the shaft torque into that generator? 8.Look at Figure 6.14,at what slip is the efficiency a maximum? 9.ifthe Carter 25 has a 480 volt generator,what minimum size wire will be needed to connect the wind turbine to the load which is 50 m away?Remember you need to count the length of wire down the tower. 10.A100 kW,480 volt generator,3 phase is connected to a transformer 40 m from the base.Tower is 50 m high.What minimum size wire is needed? For problems 9-10 use the following table.Other tables on conductors are in Handbooks.>Copper,480 Volts,3 phase,2%voltage drop.From Agriculture Wiring Handbook OverheadinCable,Conduit,Earth in Air®LengthofRuninFeet Load Gare'oe nt ;ie Types Types RH,Covered Compare size shown below with size shown to left of double ine.Use the larger size. Ampa =A,T,TW RHW,THW Conductors 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 900 1000 1200 1400 5 12 12 10 12 42 12 «12 «22 =«12 «32 «12 «12 «12:«12 «sss 10-10 10 8 8 7?12 12 10 12012 «1202«212 =«2:222 2 10 «10 «10:«10:10 10-8 8 8 8 6 10 v2 12 10 12°12 #12 12 «12 «10 10 10 10 8 6 8 6 6s 8 6 6 6 4 15 12 12 10 12,12 #12 #10 10 10 8 8 8 @ 6 6 6 6 6 6 4 4 4 20 12 12 10 12 12 10 10 6 8 8 6 6 6 6 6 4 4 4 4 4 3 2 e 25 10 10 10 12,10 10 8 8 6 6 6 6 4 4 4 4 4 4 3 3 2 1 30 10 10 10 12,10 8 8 6 6 6 6 4 4 4 4 4 3 3 2 2 1 1 35 8 8 10 10 10 8®6 6 6 4 4 4 4 4 3 3 3 2 2 1 1 t+) 40 8 8 10 10 8 8 6 6 4 4 4 #4 3 3 3 2 2 2 1 1 o 00 45 6 8 10 io 8 6 6 6 4 4 4 3 3 2 2 2 2 1 1 9 o =8600 50 6 6 10 10 8 6 6 #4 4 #€3 3 2 2 2 &£FF 8 4 0 0O 000 60 a 6 8 8 6 6 4 4 4 3 2 2 2 1 1 1 o 0 0 OO 000 000 70 4 4 8 8 6 4 4 4 3 2 2 1 i 1 o 0 0 00 00 900 000 4/0 80 2 4 6 8 6 4 4 3 2 2 1 #1 +40 0 O 00 06 00 000 000 4/0 250 90 2 3 6 6 6 4 3.02 2 1 i 0 0 0 906 00 00 000 000 4/0 250 250 100 1 3 6 6 4 4 3 2 1 1 0 9 00 00 00 000 000 000 4/0 4/0 250 300 15 te]2 4 6 4 3 2 1 1 0 ©00 00 000 000 000 4/0 4/0 4/0 250 300 350 130 00 i a 6 4 3 2 1 9 0 060 00 000 000 000 4/0 4/0 4/0 250 300 350 400 150 000 (*)2 4 3 2 1 0 0 00 00 000 000 4/0 4/0 4/0 250 250 300 300 400 500 175 4/0 00 2 4 3 1 0 ©00 000 000 4/0 4/0 4/0 250 250 300 300 350 350 500 500 200 250 000 |4 2 i Q@ 00 000 000 4/0 4/0 250 250 300 300 300 350 400 400 $00 600 104 SYSTEM PERFORMANCE 8.1 PERFORMANCE Itis important to remember that it is a system (Fig.8.1)and the load is part of that system.The most common application is the generation of electricity which is a good match between the characteristics of the rotor and the load.The other major application for wind power is pumping water,which a poor load match when the rotor is connected to a positive displacement pump (constant torque device).However the farm windmill is well designed to pump low volumes of water with a positive displacement pump,even though it is inefficient. WECS GENERATOR, TRANSDUCER PUMP,LOAD ?ROTORFigure 8.1 Block diagram of a wind energy conversion system. Overall performance of a system is measured by annual energy production and/or annual average power for that wind regime.Compromises on efficiencies for each component of the system should be combined to maximize annual energy production within the initial costs and the life cycle costs.The last two factors may be opposed as reducing the initial costs could increase life cycle costs.An electrical system will be used as the first example. Component Efficiency rotor 0.40 -0.50 drive train 0.95 generator 0.50 -0.95 overall efficiency 0.19 -0.45 For constant rpm operation,such as an induction generator,the rotor will operate at peak efficiency at only one windspeed (see Fig.6.10 ).Also the rotor efficiency will decreaseaboveratedwindspeedaspoweroutputismaintainedattheratedvalue.To increase generator efficiency,some units have two generators with one operating at lowwindspeedsandtwooperatingathighwindspeeds.The Vestas V27 has a 50/225 kWasychronousgeneratorwithsynchronousspeedsof750/1000 rpm.Another possibility toincreasegeneratorefficiencyistochangethenumberofpolesofthegeneratorbetween low and high windspeeds. Power curves and power coefficients have been measured experimentally andpeakvaluesarearound0.40 for vertical axis wind turbines to 0.50 for horizontal axis wind 105 turbines (see Fig.6.11).Annual average efficiencies in the range of 0.20 to 0.25 are expected. 8.2 OTHER MEASURES OF PERFORMANCE Capacity Factor:Capacity factor is the average power,which is equivalent to an average efficiency factor. CF =average power/rated power 8.1 The time periods vary,however the most representative time period would be one year. During periods of high winds,the capacity factor will be larger.Carter Wind Systems hasreportedacapacityfactor0.38 for a period of six months.Capacity factors of 0.3 would be good,while'those of 0.10 would be too low.Capacity factors are somewhat arbitrarybecauseofthedifferentsizegeneratorsforthesamerotordiameter.In general,capacity factors are calculated from the kWh produced during a time period. Availability:The availability is the percentage of time the unit is available to operate and is a measure of reliability.For prototypes and early production models,the availabilities were low,0.50 or even lower.Third generation models have availabilities of 0.95-0.98. Manufacturers define availability differently,so be careful in comparing availability of different wind turbines.Reliability and maintenance and operation affect the system performance. Connect time:The connect time,or energized hours,is the amount of time or percent of time the unit was actually generating power.In the Texas Panhandle,a typical unit should be generating power around 60%of the time.This is a large number and can be put into perspective by comparing wind turbines to automobiles (a mature industry). Suppose your car went 100,000 miles with no maintenance.At an average speed of 33 mph,that is only 3000 hours of operation,which is equivalent to half a year operation for a wind turbine. Lifetime:Wind turbines are designed for lifetimes of 25 years.This can be done within the statistical lifetime for the components [1]and with preventive maintenance.Some components such as bearings in gearboxes will have to be replaced within that time period.As noted above,25 years of operation for a wind turbine would be equivalent to 5,000,000 miles for a car. Jamie Chapman,who was with U.S.Windpower at the time,made the following statement,"Estimated minimum standards for non-routine maintenance are 1 down tower per 5 years and 1 up tower per year."Down tower means that the nacelle or rotor had to be removed,a major problem.Some first generation wind turbines had quite a few problems and those units were replaced within five years or dismantled.Others have had major retrofits. Designs of generators and gear trains are well known.Loads produced by the rotor are the major unknown factor,especially loads due to the turbulent character of the wind,stochastic loads.As the industry matures,engineers are now designing rotors (blades),gear boxes and generators specifically for this wind turbines.The National Renewable Energy Laboratory (US)has designed airfoils for horizontal axis wind turbines with characteristics to improve overall performance of increased energy production. Reliability:Most of the first generation wind turbines [2]suffered from a lack of reliability and quality control.Prototypes generally have failures within the first few months.Lack of 106 reliability means larger maintenance and operation costs.Manufacturers and dealers were caught in a bind,as retrofit programs in the field cost a lot of money. If a dealer has to service a small WECS over one time during the first year ofwarranty,he has probably lost money.Typical service charges are $50/hour and a largeserviceareameansthedealerisspendingmostofhistimeontheroad.The mostsuccessfulwindplantsarethosethathavereliablewindturbinesandthathaveagood operation and maintenance program. Specific Output:The most important factors for determining the annual energy production are the wind regime and the rotor swept area.One way to compare wind turbines is by the annual kWh/m2.Stoddard [3]tabulated some data for wind turbines in California (Table 8.1)where the best values are 1,000 kWh/m2.This still does not take out the factor of the wind regime,however if the average of a large number of units are compared for similar locations it will give a good estimate of performance.The annual kWh/(weight of rotor or weight on top of the tower)gives an idea of the goal for cost comparisons,as a mature industry costs would be based primarily on $/(weight of material).Another specific output is the KWh/kW. The wind turbines manufactured in Denmark were more massive and captured over 50%of the California wind farm market.This was due to their more rugged construction and they were perceived as more reliable.However,after five years,a major problem developed with blade deterioration from fatigue.The repair and replacement market for blades was estimated at 80 million dollars. Table 8.1 Specific output and income by manufacturer in California for second quarter 1988 and for 1989.Values are averages per turbine. Turbine Dia Rated #of Units Apr-Jun 1989 1989 1989 m kW 1988 |Income kWh/m2 kWh kWh/m2 $ Bonus 65 15 65 644 400 113,000 630 8,475 Vestas 15 15 65 1330 290 53,000 290 3,975 Micon 60 16 60 531 335 95,000 480 7,125 Nordtank 60 16 60 152 330 170,000 850 12,750 Micon 65 16 65 126 360 184,000 920 13,800 Nordtank 65 16 65 375 310 100,000 500 7,500 US Windpower 17 100 3286 390 173,000 750 12,975 Vestas 17 17 100 1071 310 145,000 640 10,875 Micon 108 20 108 967 300 230,000 790 17,250 Bonus 120 20 120 316 300 276,000 930 20,700 Carter 250 21 250 24 #300 250,000 750 18,750 Nordtank 150 21 150 164 270 240,000 730 18,000 Flowind 19 21 250 200 215 103,000 300 7,725 Danwin 23 23 160 151 300 390,000 920 29,250 Vestas 23 25 200 20 340 434,000 900 32,550 WEG MS2 25 250 20 410 560,000 1100 42,000 Mitsubishi 25 250 360 343 486,000 990 36450 WEG MS3 33 500 1 1,100,000 *1290 *82,500 DWT 400 35 400 35 *1,000,000 "1040 *75,000 Villas Floda 36 500 3 300 890,000 875 66,750 "*Estimated 107 8.3 PERFORMANCE REPORTS 8.3.1.California The California Energy Commission (CEC)instituted a program in 1984 for Wind Performance Reporting System regulations [4].All California wind projects greater than 100 kW that sell electricity to a power purchaser have to report quarterly performance. The quarterly reports contain the following information:turbine manufacturers,model numbers,rotor diameters and kW ratings;number of cumulative and new turbines installed;the projected output per turbine;the output for each turbine model;and the output for the entire project.The annual report is a compilation of data from the four quarters and contains summary tables reflecting resource areas The reports do notprovideinformationoneverywindenergyprojectinCaliforniaasnon-operating windprojectsandthoseturbineswhichdonotproduceelectricityforsale,such as those installed by utilities,government organizations and research facilities,do not file reports. For 1985,wind farms produced 671 million kWh,which was only 45%of that predicted by the plant operators.Average capacity factor was 13%,which is much lower than the 20 to 30%reported in technical reports.Foreign wind turbines,which were the newer wind turbines,had a capacity factor of 17%.The ten largest manufacturers had 80%of the installed capacity and four of those had 53%of the installed capacity.Theaveragecostofthe10,900 wind turbines was $2,000/kW,with a range of $700 to $2,300. In 1987,wind farms in California produced 1.7 billion kWh of electricity and by 1990 there were 1,500 megawatts installed and they produced 2.4 billion kWh,enough to power the residential needs of San Francisco [4]. In 1991 there were 1,679 megawatts installed (16,000 wind turbines)which produced 2.7 billion kWh (Fig.8.1).The annual capacity factor is an average from operational wind turbines and was 0.20 for both 1990 and 1991.For projects with new turbines,only one-half of new capacity is included in the capacity factor calculation during the quarter of installation.When only wind turbines installed since 1985 are selected,the capacity factor was 0.25.Some projects exceed 0.30 capacity factor and one project had a value of 0.34,San Gorgonia Farms.Of the ten largest manufacturers,U.S.Windpower had the largest installed capacity (Fig.8.2).An example of the problem with capacity factor is demonstrated by Fayette which had the fourth largest capacity,however the capacity factor for Fayette is very low as these turbines were over rated (90 kW,10 m diameter).The vertical axis wind turbines (Flowind)also had a low capacity factor,the same as HMZ. Another factor was noted for 1991,new installed capacity was primarily with wind turbines above 200 kW.The older wind turbines were primarily in the range of 51-100 kW (55%of the capacity installed).Horizontal axis wind turbines predominate with 94%of the capacity and 100%of the new wind turbines installed.The following trends continued into 1994,larger size wind turbines (200 to 500 kW),better capacity factors,and increased reliability for the third generation wind turbines. The annual specific output for the ten largest manufacturers varied from 566 to 867 kWh/m?(Fig.8.3).Again Fayette shows the problem of a too large generator as inefficiency leads to lower specific output.The largest value was 1,195 kWh/m2 for San Gorgonio Farms,which shows the type of performance that can be expected with goodwindturbinesinanexcellentwindregime. 108 feeeereen!SESSESESESSSeas!ENERGYmillionKWh°S1 TP ey tLe aa 1985 1986 1987 1988 1989 1990 1991 1992(>)|Figure 8.1 Energy production by year for California wind plants. 450 30 400 +h 1 25 350 4 20300 250 200 4 CAPACITYMW150 10a CAPACITYFACTOR%100 USWVestasEFMitsubishiFayetteMiconBonusFlowindNordtank|HMZ|Danwin[Figure 8.2 Ten largest manufacturers of wind turbines for California wind plants,cumulative capacity and capacity factor,1991. 8.3.2 WINDSTATS WINDSTATS Newsletter [5]contains reports and wind energy production tables on wind turbines:ID,manufacturer,kW rating,swept area,tower height,estimated annual energy production,monthly and quarterly energy production,quarterly capacity factor, specific output (kWh/m2 and kWh/kW),annual production for the previous one or twoyears,and date installed.Countries covered are Belgium Sweden,The Netherlands,Germany and Denmark,plus data from California.In addition for Denmark,there is 109 information on reliability.The information for over 2,300 wind turbines is available on computer disk for Danish statistics.The quarterly reports of the CEC and the monthlyvaluesintheWINDSTATSprovidebetterinformationonloadmatchingtoutilities. 900 800 +-| 1 - 4 3 =600 an ae _-a24-.500 +an Lt}EE UL Lt} =)4Q.75400+4 =o Kt}bY LU Lt}LY 5.42300 H Hy HY OHH Hb feOo 200 +Ht Ht OH tt "”= 100 44 td bY ty tL th o-=”=®c ”x N c6£&%§8 2 €&2 3>o =s =@g z 3 G>2 uu iL o a s za Figure 8.3 Annual average,specific output for the ten largest manufacturers,California wind plants,1991 8.4 PERFORMANCE OF ENERTECH 44 A long term performance test of an Enertech 44 [6]provides monthly values of kWh, connect time,availability and windspeed (Table 8.2).The prototype wind turbine was installed at the USDA Conservation and Production Laboratory,Bushland,TX in May 1982.All three models had the same size rotor,13.4 m diameter.The original turbine was a 240 V,single phase induction generator,rated capacity 25 kW.The gearbox and generator were changed to a three-phase,480 V,40 kW induction generator (Table 8.3a)in 1984 and later that year,a three-phase,480 V,60 kW induction generator (Table 8.3b)was installed (both were early production units).In July 1988 a different gear box wasinstalledtoreducethepeakpowerto50kW.During the eleven years of operation theunitwasconnectedfor55,700 hours and produced 840,000 kWh.The wind turbine operated for 61.6%of the hours and had an average capacity factor of 23%.The windturbinehadanavailabilityof97%,even though it was a prototype unit and there wereseveralcomponentfailures.The 3%down time was estimated at 1%for routine maintenance and service,1%for repair of component failures and 1%for weather related events,mainly icing. 110 The average power output varied by season and by year (Fig.8.4).The four monthdowntimeforreplacementofthegeneratorisevidentinNov86-Feb 87.Also notice that1992wasalowyearforwindpower. Table 8.2 Summary of performance of Enertech 44.Averages for the time period. YEAR DAYS CONNECT ENERGY POWER AVAIL SPEED COMMENT HOURS %kWh kW %nvs 83 365 5471 62.0 57,143 10.6 95.7 6.0 44/25 84 =213 3218 63.0 49,476 15.4 99.9 5.7 44/40 85 365 4905 56.0 91,732 18.7 94.9 5.7 44/60 86 300 4121 57.2 77,522 18.8 100 5.8 87 §=6303 3849 52.9 65,638 17.1 99.6 5.5 88 288 3928 56.8 71,643 18.2 95.2 5.6 gearch 50 89 367 5907 67.1 83,452 14.1.99.2 5.5 90 366 5819 66.3 86,592 14.9 98.0 5.8 91 365 5705 65.1 82,390 14.4 96.6 5.9 92 364 5599 64.1 72,662 13.0 98.0 5.4 93 364 5754 -65.9 88,363 15.4 96.4 5.7 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC isgat peat 'Pe EON : 1985 1986 1987 1988 1989 1990 1991 1992 1993 Figure 8.4 Average power (kW,legend on right)by Month for Enertech 44.|_|TSAeeegt,fF!PYWhen the energy produced for equivalent time periods by the three generators is compared,the 40 and 60 kW generators clearly out produce the 25 kW generator.However the energy differences between the 40,50 and 60 kW generators were not 111 significant.This is an effect of the power curves (Fig.8.5),which include generatorefficienciesandthewindregime.The same information is presented by the powercoefficientcurves(Fig.8.6).In other words,there are not enough winds above 12 nvs forthelargergeneratorstooffsetthedifferencesingeneratorefficiencyatlowerwindspeeds. Table 8.3a.Performance,Enertech 44/40,Bushland,TX.(1984)Anemometer at 10 m ht. Time No.of |Operating Connect NetEnergy Availability WindspeedPeriodDays_Time (hrs)(%)Produced (kWh)(%)(m/s) 3/20-4/01 12 70.7 ---1,384 shakedown --- 4/02-4/30 29 570.5 82 11,148 100 7.4 5/01-5/31 31 567.5 76 9,087 99.7 6.4 6/01-6/30 -30 511.3 71 8,281 100 6.3 7/01-7/31 31 430.0 58 5,017 100 5.0 8/01-8/31 31 301.8 41 2,443 99.7 4.1 9/01-9/30 30 460.6 64 7,240 100 5.8 10/1-10/31 31 412.3 55 6,260 100 5.3 5.7Summary2133,218 63 49,476 99.9 Table 8.3b.Performance,Enertech 44/60,Bushland,TX,12/1/84-9/30/86. Time No.of |Operating Connect Energy Availability Windspeed Period Days Time (hrs)(%)|Produced (kWh)(%)(m/s) 11/17-30 17 50.3 ---1194 shakedown --- 12/1-12/31/84 31 366.2 49 7877 87.3 5.6 1985 365 4896.5 56 91732 94.9 5.7 1/1-31/86 31 450.8 61 9790 100.0 5.7 2/1-28 28 342.0 51 7578 100.0 5.5 3/1-31 31 441.7 59 8803 99.9 5.9 4/1-30 30 466.0 65 8635 99.8 6.5 5/1-31 31 430.0 58 9103 100.0 6.2 6/1-30 30 360.9 50 5638 100.0 5.1 7/1-31 31 518.1 70 9839 100.0 6.4 8/1-31 31 369.5 50 5293 100.0 5.3 9/1-30 30 445.0 62 8226 100.0 6.0 Summary 669 9087 57 171,614 96.6 5.8 112 cbeewiveaQ i 0 2 4 6 8 10 12 14 16 18 20 Wind Speed -m/s Figure 8.5 Power curves for Enertech 44. 0.5 *Cp 25 0.4|*Cp 40 PowerCoefficient0 2 6 8 10 12 14 16 18 20 Wind Speed -m/s Figure 8.6 Power coefficients for Enertech 44. 8.5 PERFORMANCE OF BERGEY EXCEL ;A Bergey wind turbine was installed at the AEI Wind Test Center in August 1991. The specifications are:three-phase,240 V,permanent magnet alternator,rated at 10 kW. The variable voltage,variable frequency is converted to DC,which is then inverted to 60 Hz for connection to the utility line.Power and windspeed are sampled at 1 Hz and then averaged over 15 minutes.This time sequence data is then averaged over one month for each 15 minute period to give an average day for the month.The power will vary quite a bit because of the cubic relationship to windspeed (Fig.8.7).From this data it is also noted that spring 92 was a below average wind period.Also at the height of the wind turbine,25 m,the diurnal variation is very noticeable,low winds at night.This type of performance data is also useful for utility companies as it will heltp to determine load matching from wind turbines. 113 geesB®rege pea'?3 S Figure 8.7 Power by time of day (15 min average for month)for Bergey Excell,10 KW. 8.6 WATER PUMPING Performance for water pumping is given by a water flow curve and the amount of water pumped by month or year.In general for the farm windmill,tables are used to estimate performance for different wind regimes. 8.6.1 Farm Windmill The farm windmill is an old technology,with no design changes since the 30's.It is well designed for the purpose;to pump small volumes of water for livestock and residences.It is primarily a drag device which operates at peak efficiency of 15 to 18 %at a tip speed ratio around 1.The rotor efficiency is much higher (see Fig.6.11)and it is the pump efficiency which limits the system performance.Since it is connected to a positivedisplacementpump,the rotor needs a lot of blades to obtain a high starting torque.Forthemechanicalfarmwindmillwithapositivedisplacementpump,the water flow rate (Fig.8.8)is directly related to the number of strokes per minute Overall efficiency or averageannualefficiency(wind to water pumped)is around 5 to 6%[7].The flow rate is similar to the efficiency curve 114 II 1t--J1!t -t--4||jtI>1!It-I|1FLOWRATEliter/minrevyprrrprrryprrryprrryrywana ban4--bd -+--+--4 ! l 4 { 6 68 10 12 14 16 18 ©20 WINDSPEED m/s Figure 8.8 Water flow rates for mechanical,multibladed windmill (Aermotor)with a pistonpump(5 cm diameter),21 m lift [8]. Since 1980,various methods have been tried to improve the performance of the farm windmill.These include a higher speed rotor (less solidity,tip speed ratio of 2), counter balance,and various mechanisms such as variable stoke and spring resonance to improve the efficiency.The higher speed rotor means less starting torque and a leak hole in the pump was provided.The variable stroke mechanism will pump more water as there is a better match between the rotor and the load.However the problem is the rotor and gear mechanism would have to be redesigned to handle the larger stresses and loads. 8.6.2 Electric to Electric System A very promising development is wind electric to electric,water pumping system [9]. The wind turbine generator is connected directly to a motor and centrifugal or turbine pump,which is a better match between the characteristics of the rotor and the load.The overall efficiency is 12 to 15%,which is double the performance of the farm windmill.The water flow is higher at the higher windspeeds for the wind-electric system (Fig.8.9),as this is the region where the farm windmill is furled.The costs of a farm windmill and a 1.5 kW wind-electric system using a submersible pump are almost the same.The wind electric system pumps over twice the amount of water from the same depth (Fig.8.10). The other aspect is that larger systems can pump enough water for villages [10]or for low volume irrigation.A Rayleigh distribution for different average windspeeds and experimental data of water flow rates from a submersible pump were used to estimate the annual water pumped (Fig.8.11).Wind electric systems could even be used for dual purposes,generation of electricity and for pumping water. 8.7 COMMENTS System performance,annual,monthly or by period of peak demand,will determine economic viability and will help in comparisons of wind turbines.However you need to remember that inefficient systems are used and will be used for some of the following reasons;initial costs are lower,local materials and low technology,easier to maintain and operate,lack of knowledge,and lack of infrastructure for more advanced or efficient systems. 115 Flow Rate -L/min Wind Speed -m/s Figure 8.9.Rate of water pumped by a wind-electric system (Bergey 1.5 kW)using a submersible pump.LITERS/DAY(Thousands)Jan Feb Fy "-3 ee 7 4 . 3 5 om :ri Mar Apr May Jun wut Aug Sep Oct Navi tne. Figure 8.10 Estimated average daily water pumped for a mechanical windmill (left)and awind-electric water pumping system (right)for Panhandle of Texas wind regime,20 m lift. 100 Os 3 60 w =sE 40 DE3 20Qo 0 AVERAGE WINDSPEED m/s Figure 8.11 Predicted annual water pumped by 10 kW wind-electric water pumpingsystem.Annual average windspeed is 6 m/s.Lift of 20 m. 116 REFERENCES 1. 2. 3. 10. R.N.Clark,"Reliabilty of Wind Electric Generation",ASAE Paper No.83-3505,St. Joseph,MI 49085. William Pinkerton,"Long Term Test:Carter 25",V.Nelson,Ed.,Proceedings,Wind Energy Expo '83 and National Conference,Am Wind Energy Assn,p 307. F.S.Stoddard,Wind Turbine Blade Technology:A Decade of Lessons Learned, 1980-1990,California Windfarms,Alternative Energy Institute,WTAMU,1990. Results from the Wind Project Performance Reporting System,Publications Unit, California Energy Commission,MS 13,1516 Ninth St.,Sacramento,CA 95814. Specify year. WindStats Newsletter,Box 496007,Ste 217,Redding,CA 96049-6007 or Vrinners Hoved,DK-8402 Knebel,Denmark. R.N.Clark and R.G.Davis,"Performance of an Enertech 44 During 11 Years of Operation,"Proceedings Windpower '93,Am Wind Energy Assn,1993,p 204. R.N.Clark,"Performance Comparisons of Two Multibladed Windmills,"Eleventh ASME Wind Energy Symposium,SED-Vol.12,1992,p 147. R.N.Clark,and K.E.Mulh,"Water Pumping for Livestock,"Proceedings Windpower '92,Am Wind Energy Assn,1992,,p 284. J.W.McCarty and R.N.Clark,"Utility Independent Wind Electric Water Pumping Systems,"Proceedings Solar '90,Am Solar Energy Soc,1990,p 573. M.L.S.Bergey,"Sustainable Community Water Supply:A Case Study from Morocco,"Proceedings Windpower '90,Am Wind Energy Assn,1990,p 194. 117 PROBLEMS 1.From Table 8.1 calculate (annual kWh/kW)for five different wind turbines. 2.From Table 8.3a calculate for summary values (a)KWh/m2 (b)kWh/kW_(c)capacity factor 3.From Table 8.3b calculate for summary values (a)kWh/m2 (b)KWh/kW_(c)capacity factor 4,From Table 8.3b calculate the monthly values.Does specific output depend on the wind? 5.From Table 8.2 calculate kWh/m?for the year 1990. Specification for two commercial wind turbines Carter 300 Vestas V27 diameter,m 24 a7 rated power,kW 300 225 tower height,m 50 31.5 installed cost for Panhandle $180,000 $225,000 estimated annual energy production,kWh 600,000 500,000 weight specification,kg (1 kg =2.2 Ibs) rotor (blades and hub)1,340 2,900 tower head (nacelle)3,091 7,900 tower (includes gin pole)8,023 12,000 guy cables,winch 1,336 control box and panel 155 TOTAL 14,250 22,800 6.For the Carter 300,calculate (a)kwh/m2(b)KWh/kKWs(c)KWh/kg_ss (d)KWh/S$IC 7.For the Vestas V27,calculate (a)kwh/m2 (b)KWh/kKW_s(c)kWh/kg_ss (d)KWh/$IC 8.Estimate the annual capacity factor for the Carter 300 and Vestas V27. 9.For the farm windmill (use Fig.8.8),estimate water pumped for one month that has an average windspeed of 4 m/s.Use Rayleigh distribution (2 m/s bin widths). 10.For the wind-electric system (use Fig.8.9),estimate water pumped for one month that has an average windspeed of 4 m/s.Use Rayleigh distribution (2 m/s bin widths). 11.Foran annual average windspeed of 4.5 m/s,compare the predicted annual energy production for the Enertech 44 for the 25 kW and 60 kW wind generator.Use Fig.8.5 for power curves and use Rayleigh distribution (2 m/s bin widths). 118 9 SITING There are quite different criteria for siting small wind turbines as compared to a wind plant.Much of the material in this chapter is based on the material in Rohatgi and Nelson [1]and in an Alternative Energy Institute report on wind resource screening [2]for the Panhandle of Texas.Also refer to Reference 1 for information on numerical models for predicting winds. 9.1.INTRODUCTION The crucial factor is the annual energy production from the wind turbine or wind plant and how does the value of that energy compare to other sources of energy.Fora small wind turbine,a measuring program may cost more than the wind turbine.Much of the data from meteorological stations in the world is of little use in predicting wind power potential.Therefore for small wind turbines,other types of information are needed.Also reference stations located in better sites,not the major sites,for a region would be useful. For wind plants,long term data is a necessity and a minimum of two years is recommended.Then the questions are,what is the long term interannual variability and how well can you predict the energy production for a wind plant (also called wind park or wind farm).The siting of turbines over an area the size of a wind plant,about 5-15 km2, has been termed micrositing.Thus,the wind turbines should be located within the wind plant to maximized annual energy production or the largest financial return. It is obvious that a small wind turbine should be located above (10 m if possible) obstructions and away from buildings and trees.Towers for small wind turbines should be a minimum of 20 m and as higher towers generally capture more energy,even towers of 35 m are sometimes used.As a general rule of thumb for avoiding most of the adverse effects of building wake for siting a wind turbine,the turbine should be located:(1)upwind a distance of more than two times the height of the building;(2)downwind a minimum distance of ten times the building height;or (3)at least twice the building height above ground if the turbine is immediately downwind of the building.The above rule of thumb is not foolproof because the size of the wake also depends upon the building's shape and - orientation to the wind (Fig.9.1).Downwind from the building,power losses become small at a distance equal to 15 times building height.However a small wind turbine cannotbelocatedtoofarawayfromtheloadasthecostofwiringwillbecomeprohibitive. 9.2 LONG TERM REFERENCE STATIONS To determine if data from a historical site is adequate to describe the long-term wind resource at another site,then the analysis should be done rigorously.Simon and Gates [3]recommend that the annual hourly linear correlation coefficient be at least 0.90betweenthesiteandoff-site data.If the two sites are not similar in windspeed and direction trends and do not have similar topographic exposure,then they will probably not have that correlation value.Long-term reference stations should be installed in all locations in the world where there is wind power potential.These stations should continue to collect data even after a wind plant has been installed.Not only will this improve siting of wind plants,they will serve as reference sites for delineating the windresourceforsinglewindturbinesinthatregion. 119 aenehcA cE HIGH 15"ep pece ING AEM?TURBULENCE pee eN-aDooStaBUYWEseem3UROgbWinoP9% Figure 9.1 Estimate of speed and power decrease and turbulence increase for flow over a building [4].Estimates shown are for height of the building. 9.3 SITE EVALUATION FOR WIND PLANTS The number of anemometers stations and the time period for data collection to predict the energy production for a wind plant varies depending on the terrain.In general, numerical models of wind flow will predict windspeeds to within 5%for relatively flat terrain and 10 to 15%for complex terrain,which means an error in energy of 15 to 45%. Therefore a wind measurement program is imperative for wind plants.For complex terrain,you may need one anemometer per 3 to 5 wind turbines.For wind turbines of 500 kW,you may need an anemometer per 1 to 2 wind turbines.With more homogeneous terrain as in the plains,an anemometer per 8 to 12 wind turbines may suffice. The key factors for array siting for the Zond wind plants [5]in Tehachapi Pass were an extensive anemometer data network,the addition of new anemometers during the planning period,a time frame of one year to refine the array plans,a project team approach to evaluate the merits of different siting strategies,and the use of initial operating results to refine the rest of the array.The large number of anemometers was needed because the spatial variation of the wind resource over short distances in complex terrain is greater than expected.The energy output from two projects,98 wind turbines and 342 wind turbines,was within 3%of the predicted value.This experience shows it is possible to forecast long term production from a wind plant with acceptable accuracy for the financial community.One of the key factors is an extensive network of anemometers. In some older wind plants,the lowest producing wind turbines have been relocated.The money spent on micrositing is a small fraction of the project cost,but the value of the information gained is critical to accurately estimate the energy production. There are fewer problems with low energy production because of poor siting. 120 9.4 WAKE AND ARRAY LOSSES The wakes from wind turbines create turbulence and along with the windspeeddeficit,result in array losses which is reflected in reduced annual energy production.Thetradeoffbetweenlandareaandturbinespacingisstillunclearforwindplants.The threeprimarymethodsofwakeandarraylossresearchhavebeennumericalmodeling,windtunnelsimulations,and field measurement.Cleijne [6]published a data base of literatureonwindturbinewakesandwakeeffects. Field measurements of wake effects inside of wind plants have generally be limitedto2to4rowsofwindturbines.Energy deficit of 10 to 15%in row 2 and 30 to 40%in row 3 have been reported.Measurements of wake deficits downwind of large arrays indicate that the losses may be larger and extend farther downwind than expected.Energy deficits of 15%were estimated at 5 km downwind from a 50 MW array [7]. Energy production of a single turbine can be easily calculated using spread sheets. However,in a wind plant,turbines are located at different elevations and terrain with different roughness factors.In complex terrain the wind distributions depend on the direction of the wind.Finally the turbine wakes will increase the turbulence and decrease the windspeed for the turbines downwind.Therefore it is more difficult to predict output without an extensive wind measurement program. 9.5 DIGITAL MAPS The Pacific Northwest Laboratory (PNL)has created various digital wind maps andrelateddatasetsfortheUnitedStates.They used a pixel or grid cell size of 1/4 degreelatitudeby1/3 degree longitude (around 25 by 27 km).Digital maps are useful as they give a general overview of the wind resource,confidence of the data,and its relation to other land uses. 9.6 GEOGRAPHIC INFORMATION SYSTEMS A geographic information system (GIS)is a computer system capable of holding and using data which is spatial oriented.A GIS typically links different data sets or a base set is displayed and overlays of other data sets are placed on the base set.Information is linked as it relates to the same geographical area.A GIS is an analysis tool,not simply a computer system for making maps. There are two general methods of representing the data,raster and vector.Raster based means every pixel has a value and vector means that the data is represented mathematically;end points for lines and lines for polygons.Each pixel can represent an attribute and that the number of attributes depends on the number of bits;16 to 256 colors or shades of gray.Therefore pixels or vectors can have different attributes and are linked to a database,which can be queried.A GIS gives you the ability to associate information with a feature on a map and to create relationships that can determine the feasibility of various locations,for example a hierarchical system for locating anemometer stations for wind prospecting. An overlay is a new map with specific features which is overlaid on the base map.Overlays are one form of database query functions.The overlay can be a raster or vectorimagewiththebasemapbeingarasterorvectorimage.The number of overlays isgenerallyonlylimitedbytheamountofinformationthatcanbepresentedwithclarity. 121 The main types of terrain data are the Digital Elevation Model (DEM)data and the Digital Line Graph (DLG)data.These are available at different scales,for example the DLG at 1:2,000,000,1:100,000,1:24,000.Depending on the scale,the DLG contain highways,roads (even down to trails),lakes and streams,transmission lines (utility and gas),etc.The problem is that the data may be taken from fairly old maps and therefore itisincomplete.The DEM data give the terrain height to 1 m on a latitude-longitude gridwitharesolutionof3arcseconds(pixel around 90 m by 90[cos latitude]m). The Pacific Northwest Laboratory coupled the DEM database with software to produce shaded relief maps of 1 degree by 1 degree.A technique of terrain enhancement [8]was used to identify windy areas in the Midwest.In the flat or rolling terrain found in most of the Midwest,the two most important factors influencing windspeed are terrain elevation and surface roughness.The wind map (normalized wind map from PNL digital map)was adjusted to an average elevation and average surface roughness in a 12 kilometer circle around that point.The USGS Terrain Elevation Data was the base map,which consisted of average elevations in one km square grid cells rounded to the nearest 6 m.Terrain exposure was determined by subtracting actual elevation from the average (12 km radius)elevation for each 1 km x 1 km grid cell.Then a power correction factor was calculated by Pavg Ha}(9.1)In Zz(2) where P =corrected power/area Pavg =power/area from normalized wind map Hh =hub height,50 m E =exposure in meters Zo =roughness length 0.03m_cropland 0.1 to 0.3 m cropland/mixed woodland/ 0.8to 1.0 m_forest Care must be taken on use of Payg.Do you use the bottom or the middle of the wind class?Do you limit the number of wind class changes to one,especially for mountainous terrain? 9.7 WIND RESOURCE SCREENING The Alternative Energy Institute acquired the DEM data (3 arc resolution)for use in wind resource screening along with DLG data.Data for utility transmission lines (69 kW and higher)were input by hand.Two GIS systems,IDRIS!and PC ARC INFO,for personal computers were used.IDRIS!has built in functions that enhance its use for wind resource screening:slope,hill shading,aspect,and orthographic projection.A data sheet accompanies these which shows bin size,max,min,etc.The limitations on resolution are the pixel size of the original data. The original DEM data were in blocks of 1 degree by 1 degree.The Panhandle of Texas has rolling hills in the East to the high plains above the Caprock and the elevation 122 rises from 450 m in the Southeast to 1460 m in the Northwest.The Canadian River goesfromwesttoeastintheNorthCentralRegion.The other notable feature is Palo DuroCanyon.All of the figures displayed can be viewed in color or gray scale,numberselectableupto256.At 256 colors,a DEM map for all of the Texas Panhandle would display contours 4m apart.The base map (Fig.9.2)is the DEM data for the Panhandle. Most of the images were created using 16 shades of gray because the print command for images is limited to that number.The elevation data of the base map can be analyzed by the different commands in IDRISI.Instead of the whole area,subsets of the data can be analyzed in the same manner. Figure 9.2 Digital elevation map of the Panhandle with county boundaries and majorhighways.Contour lines are 62 m apart. 123 The Panhandle has a large wind energy potential since it has class 3 and 4 windsoverthewholearea.On the flat open plains,which describes much of the Panhandle, close to 100%of the area will be in the same wind power class.In general windspeed increases with height,therefore modest relief may increase the wind power dramatically. Terrain exposure selects those areas which are above and below the average.We used a 15 km radius to determine an average elevation,then the maximum change from this average is 190 m.An orthographic projection with the overlay of terrain elevation shows more clearly the areas of higher elevation.On this basis of terrain exposure,a revised wind map [2]can be drawn (Fig.9.3)which uses Equation 9.1 to modify the PNL wind classes.Some of the regions with positive exposure have been changed to a higher wind class by this process and low areas have been changed to a lower wind class. CLASS 3 CLASS 4 crass 5 Figure 9.3 Revised wind power map for the Panhandle.Overlays are county boundaries(white lines)and electric transmission lines (black lines). GIS was used to screen the wind resource in terms of the following criteria;windpowerclass,terrain type,vicinity of transmission line,slope,and aspect.Within eachcriteria,classes or levels can be selected to exclude or limit the area for wind plants.Thisestimatewasbasedonthefollowingvalues: 1.Wind class 3 and above. 2.Slope of 0 to 3 degrees. 3.Aspect from 155 to 245 degrees for area where slope is greater than 1 degree.4.Within 5 miles of transmission line (69 kV and above). 124 The total area (Fig.9.4)which meets all these above criteria in the Panhandle is 28,600 km2,around 37 percent of the land. CLASS 3 CLASS 4 CLASS 5 |*-ae AR Sos eg Figure 9.4 Wind map of Panhandle showing area which satisfy screening parameters. 9.7 WIND POWER PRODUCTION PNL estimated the capturable wind power for Texas at 50 m height as 134,000 MW from class 3 and above winds and 28,000 MW for class 4 winds.Class 4 winds are located primarily in the Panhandle.The PNL estimate was made in the following manner. The total power intercepted over a given land area is a function of the number of wind turbines,the rotor swept area,and the available power in the wind.Environmental sensitive land,urban areas,and terrain that is in valleys and canyons were excluded. The following formula is used to calculate the power captured by the wind turbines. P;=PaArN (9.2) where Pa,=average wind power potential,W/m2 A,=rotor area,m1 D2/4,m2 N =number of wind turbines. 125 The number of turbines that can be placed on the land area is N =A/y(Sr Sc)(9.3) where A;=land area,m2 S;=spacing between turbine rows,D Sc =spacing within turbine rows,D D =turbine rotor diameter,m. Note (S;S¢)is the land area devoted to one turbine.If the cost of land is high,then this number is smaller,however the output from the wind plant will be reduced due to array effects.In California,some wind plants have turbine spacing of 2D within the rows and 7D to the next row.In general,wind plants remove 5 to 10%of the land from other uses. The average intercepted power can be calculated from Equation 9.2 or the intercepted power per unit land area can be calculated from Pi n Pa Al 488,04) 9.7.1 Wind Power for Texas Panhandle The average power capturable for the Panhandle was calculated for the following conditions:50 m hub height because a revised wind map based on terrain enhancement was used,10D by 10D spacing,25%efficiency,and essentially no array losses since the spacing is large. The amount of land which satisfies the screening parameters of Section 9.6 is 28,600 km2,which is around 37%of the area in the Panhandle.Using the techniques described above,the capturable wind power is estimated at 23,500 MW.This corresponds to a annual energy production of 205 billion kWh.For class 5 areas which meet the above criteria,the capturable wind power is estimated at 825 MW.The problem was there was not any excluded land for environmental,urban,and other none usable areas. 9.7.2 Wind Power for Texas The same procedures of terrain enhancement and GIS were used to estimate the capturable wind power for Texas [9].The selection criteria are: 1.Wind class 3 or higher from revised wind map using terrain exposure. 2.Slope of 0 to 3 degrees 3.Excluded lands:urban,federal and state parks,lakes,wildlife refuges,and federalwetlands. 4.Within 16 km (10 miles)of transmission lines (115 kV)and above. The capturable annual power for Texas (Table 9.1)was calculated for the followingconditions:50 m hub height,10D by 10D spacing,25%efficiency and no array losses(reasonable since the spacing is large).With these assumptions the annual capturablewindpoweris131,200 MW (525,000 MW of wind turbines at 25%efficiency)with anannualenergyproductionof4,143 billion kWh.These results agree closely with theestimatesdeterminedbyPNL. 126 Table 9.1 Estimated annual wind power and energy production for Texas. Wind Power Area %of State Potential Annual Class sq km Land Capacity Production MW Billion kWh 3 143,400 21.13 396,000 860 4 29,700 4.38 101,600 231 5 5,000 0.74 48 6 300 0.04 1,600 4 Total 178,400 26.29 524,800 1,143 9.8 SUMMARY IDRIS!provides a very flexible and powerful tool for terrain analysis relevant to wind energy prospecting.It can be used to reclassify the existing wind maps and to identify areas for meteorological measurements for possible wind plant sites.In addition, it can be used to quantify the wind power potential and,in conjunction with numerical models,to quantify the annual energy production. Once an location is selected,then GIS can be used in micrositing.The wind turbines should be located within the wind plant to maximize annual energy production. However the 90 m resolution may not be detailed enough for micrositing in complex terrain.PNL used a technique of spline interpolation to fill in a finer grid from the 90 m data.Of course if the DEM data at 10 m resolution are available,then the interpolation technique is not needed. REFERENCES 1.Janardan Rohatgi and Vaughn Nelson,Wind Characteristics,An Analysis for the Generation of Wind Power,Alternative Energy Institute,West Texas A&M University,1994.. 2.Ling Shitao,Joe McCarty and Vaughn Nelson,Wind Resource Screening in the Texas Panhandle,Alternative Energy Institute,Report 94-2,August 1994. 3.RL.Simon and R.H.Gates,"Long-Term Interannual Wind Resource Variations in California,"Proceedings,Windpower '91,American Wind Energy Assn.,September 1991,pp.236-243. 4.H.L.Wegley,J.J.Ramsdell,M.M.Orgill and R.L.Drake,A Siting Handbook for SmallWindEnergyConversionSystems,U.S.Department of Energy,Report PNL-2521, 1980. 5.RL.Simon and RH.Gates,"Two Examples of Successful Wind Energy Resource Assessment,"Proceedings,Windpower '92,American Wind Energy Assn.,October 1992,pp.75-83. 6.W.Cleijne,Literature Data Base on Wind Turbine Wakes and Wake Effects,NT-TNOReport90-130,TNO,Apeldoorn,The Netherlands. 7.D.L.Elliott,"Status of Wake and Array Loss Research,"Proceedings,Windpower '91, American Wind Energy Assn.,September 1991,pp.244-253. 127 8.M.C.Brower,M.W.Tennis,E.W.Denzler and M.M.Kaplan,Powering the Midwest, Renewable Electricity for the Economy and the Environment,Report,Union of Concerned Scientists,1993. GEOGRAPHIC INFORMATION SYSTEMS Information is provided for PC versions of GIS;IDRIS!and PC ARC/INFO.Mention of IDRISI and PC ARC/INFO does not imply any endorsement for use by the Alternative Energy Institute. IDRISI ARC/INFO Clark Labs for Cartographic Environment Systems Research In Clark University 950 Main St.380 New York St Worchester,MA 01610-1477 Redlands,CA 92373-9870 Tel:508 793 7526,Fax:8842 714 793 2853,Fax:5953 Internet:idrisi@vax.clarku.edu Cost 1996 $DOS Windows Acad/non-profit/govt DOS $360 500 $1,700 Com/private $720 990 $6,000 PROBLEMS 1. 2. A building is 20 by 15 m and 15 m tall.You want to install a 10 kW wind turbine.How tall of a tower and how far away from the building would you place it. There are a number of trees (20 to 30 m in height)close to you house.You want to install a 10 KW wind turbine.What is the minimum height of the tower?What is the approximate cost of that tower? Refer to Fig.9.1.The building is 15 m tall.What is the power reduction at 15 m height at a distance of 60 m downwind?at 150 m downwind?Would it be cheaper to use a taller tower or to move the location further away from the building?Show all cost estimates. Use Eq.9.1.Calculate the corrected power for a class 3 wind area if the terrain exposure was 80 m and area was grass land.Use the bottom and middle value for the wind power class. Estimate the annual energy production for a 50 MW wind plant where the average wind power potential is 300 W/m'.You select the size of turbine from commercial turbines available today.Land is high price,so select a close spacing and estimate array losses. Do problem 5,however now the land is cheap,so select a large spacing between the wind turbines. Estimate the annual energy production for a 50 MW wind plant where the averagewindpowerpotentialis500W/m".How big of land area do you need to lease? Remember if your spacing between turbines is too close you will have array losses. In your opinion,what are some advantages and disadvantages of using vector or raster base GISs in determining wind energy potential? 128 10 WIND INDUSTRY 10.1 INTRODUCTION World energy production in 1995 from wind turbines connected to the grid is estimated at 5 billion kWh from over 22,000 wind turbines with an installed capacity of around 4,000 megawatts (Table 10.1).That is enough electricity each year for 700,000 residences (3 million people)which use 7,000 kWh per year.The largest concentration of wind turbines are in the passes in California,with a significant portion of those imported from Europe and Japan.In 1992 in Denmark,450 MW of wind turbines produced 900 GWh,3%of the total electric consumption in the country. Table 10.1 Wind industry overview. Grid Connected Number 22,000 Installed Capacity,megawatts 4000 Production,kWh/yr 5,000,000,000 Isolated Systems 100-200 W,number in China 80,000 Farm windmill Number 150,000 Production,number/yr 2000 Hybrid Systems Number Telecommunication 20-50 Village 10-30 The installed price of wind turbines is less than $1000/kW,operation and maintenance costs are around $0.01/kWh,and availability is 98%at well maintained wind plants.Wind plants in excellent wind regimes produce electricity for $0.06 to 0.08/kWh. New wind plants are competitive with other energy sources for the generation of electricity,less than the cost for new coal and nuclear power plants.The goal of the US Department of Energy,advanced wind turbine program is to develop wind turbines forclass3windregimes(5 to 5.5 m/s average)which would produce electricity at $0.04/kWh and have operation and maintenance costs of $0.005/kWh.This is very realistic as contracts were signed for $0.04/kWh in 1995 (included tax credit). The Europeans are now installing a number of units and the projection is 4,000 MW by the year 2000 (Table 10.2)and their goal is 25,000 MW by the year 2010.ThetrendintheUnitedStatesistoward3,500 MW by the year 2000.Of course predictions are always risky and the predicted megawatts change as projects and programs are implemented and also canceled. 129 Table 10.2 Installed capacity and projected capacity,megawatts. YEAR 1995 YEAR 2000 United States 1740 3700 Europe 1870 4000 India 200 2000 China 50 1000 Rest of world 75 1000 The rotor diameter of commercial wind turbines (Fig.10.1)varies from 1 to 40 m and in contrast to photovoltaic systems,there are economics of scale.Of course energy production depends on the wind regime,however it is the rotor area (Fig.10.2),not the generator size which determines annual energy production for that wind regime. METERS |70 -=60 =<>50 -40 |307a Tt"+10 Dia 2.7 7 10 23 40m Power 1 10 25 300 500 kW Cost $3,000 20,000 35,000 220,000 500,000 COE .20-.30 .15-.20 12-.15 .05-.08 .04-.08 $/kWh Figure 10.1 Relative diameter and hub height of wind turbines,drawn to scale. 130 500 kW 1257 m? 300 kW 415 m2 SEE 4 1 kW 6 m? Figure 10.2 Relative area of wind turbines of Figure 10.1 drawn to scale. Comments The most economical size of wind turbines has not been determined.The megawatt size units,100 m in diameter,are still at the prototype stage.Developers of wind power plants are now purchasing units in the 200 to 700 kW range,20 to 40 meters in diameter.Commercial units in this size range can be purchased today,primarily European.European governments are also funding prototypes in the megawatt range, because they have less land available. Three driving forces for installation of wind plants are economic costs,the Rio Treaty and the negative public perception of nuclear power,as some countries have even voted to shut down their nuclear power plants.The US will spend $430 million within two 131 years to reduce emission of carbon dioxide.Much of that will be for wind turbines,since they are commercially available and will produce electricity at a competitive price today. Another market that is just beginning is for village electrification in developing countries.It is cheaper to have distributed electricity than to extend transmission lines. The primary source of energy will be renewable energy,solar and wind.Large lending institutions,such as the World Bank,now realize there is alternative to large scale projects for producing power. Wind turbines for farmers,ranchers,and agribusinesses will be similar to the farm implement business.Wind turbines in the range of 10 to 50 kW will be purchased and serviced just as another piece of machinery.The farmer will expect a payback of around 5 years and service life of 15 to 20 years with O&M costs of less than $0.01/kWh. In time,some land owners will harvest the wind much as they now harvest the sun. Since financing for large wind power plants requires millions of dollars,the land owner will probably lease the land and receive a royalty from the energy produced by the wind turbines,similar to the oil and gas industry.The difference is that the wind resource can be fully determined before large amounts of money are invested. 10.2 NEW WIND INDUSTRY 10.2.1 1970-1980 The first step was the development of small wind turbines (at that point in time defined as <100 kW).Most wind turbine companies began by importing wind turbines; finding abandoned units to refurbish for personal use or to sell;and then by designing and building similar systems to the wind chargers of the 30s and 40s (direct current,0.1 - 4 kW,up to 5 m diameter).A number of home builders turned to the Savonius type because of its simplicity and ease of construction.Electricity consumption had also increased over the small demand of the 1930s.There was a need for larger wind turbines,as 5 m (16 ft)diameter rotors could not meet the demands of farmers and ranchers.In addition there were other applications for electricity which required larger units. Since the electric distribution system was almost everywhere,there was a market for wind turbines which were fully compatible with the utility system:120,240,or 480 volts,alternating current (AC).Inverters with solid state electronics were now available to connect direct current (DC)units and alternators to the utility line.Enertech and Carter were early proponents of induction generators which could be connected directly to theutilitygrid.' The second step was the influx of federal funding for research through the EnergyResearchandDevelopmentAgencyandlatertheDepartmentofEnergy(DOE).Federalsupportforwindenergybeganwith$300,000 in 1973 and by 1980 had increased to $67 million.The federal program for development of wind turbines was geared to large unitstoconnecttotheutilitygrid.However,a group of wind enthusiasts convinced the federal officials to support a program for small wind turbines (<100 kW).The SWECS prototypeprogramawardedcontractsin1978and1979(Table 10.3) The third step was the passage of the National Energy Act of 1978.The section entitled Public Utility Regulatory Policy Act (PURPA)provided for connection of renewable power sources to the electric grid without penalty and for payment to the producer forelectricitysoldtotheutilitycompany.The value of that electricity was determined by theavoidedcost,which was implemented by the states. 132 Table 10.3.Small Wind Energy Conversion Systems,Prototype Development ProgramFundedbyDOE. Contractor Type Size,ft 1 kW at 20 mph:High reliability,Remote:$1.9 Aerospace/Pinson Giromill 15x 18 Enertech HAWT 16 North Wind Power HAWT 16 4 kW at 16 mph:$1,425,000 North Wind Power HAWT 30 Structural Composites dropped out at design stage _ TUMAC Darrieus 30 x 38 8 kW at 20 mph:$2,260,000 Alcoa dropped out at design stage Grumman HAWT 33 United Technologies HAWT 32 Windworks HAWT 33 15 kW at 20 mph:$3,230.00 Enertech HAWT 44 United Technologies HAWT 46 40 kW at 20 mph:$4,450,000 Kaman HAWT 64 McDonnell-Douglas giromill 59 x 42 By 1980 there were over 50 companies producing wind energy conversion systems (WECS)in the United States.However the installed capacity of small WECS was only around 3 megawatts from 1700 units [1].A few large wind turbines were also developed and installed in the United States (Table 10.4),most with government funding [2].The Hamillton Standard WTS-4,four Wind Turbine Generators,Bendix-Schackle,and the Alcoa units were developed primarily through private funds. Table 10.4 Large Wind Turbines Developed in United States and Canada,1975-1980. #Dia Rated Tower Manufacturer built m kw ms m DOE MOD-0 1 38 100 8 30 Westinghouse DOE MOD-0A 4 38 200 11 30 DOE MOD-1 1 61 2000 11 41 General Electric DOE MOD-2 5 91 2500 8 61 Boeing WTG 4 24 200 13.24 Wind Turbine Generator Mehrkam 1 49 2000 14 137 #Metals Engineering WTS-4 2 78 4000 17 +80 Hamilton Standard Schackle 25 3000 28 £37 Bendix DAF 55X25 200 11 Dominium Alum Fab ALCOA (18328229)56X25 500 16 Alcoa 133 10.2.2 Wind Industry 1980-1990 From 1980 to 1990,four features characterize the wind industry,which is synonymous with the wind farms in California.The decade can be characterized by: 1)Rapid state of growth.2)Development of intermediate size wind turbines (100 to 600 kW)without government funding.3)The aerospace companies in the United States dropped out,even those who received government funding for design and development. 4)Strong foreign competition,primarily from Europe,in the wind farm market. The five years from 1980-1985 were the nascent stage of wind industry.Theexponentialgrowthofthewindindustryfrom3to900MWwasdrivenbytheboomofwindplantsinCalifornia.The California wind market was due to tax shelters (solar andinvestmenttaxcredits)and due to the avoided costs and standard contracts set by theCaliforniaEnergyCommission.As with any new industry there were a lot of manufacturers,as many as 60 in the United States.Only small wind turbines (<100 kW)were available commercially and there were many problems with reliability.In the United States,the aerospace companies dropped out of the industry,even those who received government funding for design and development.Foreign manufacturers,with Denmark leading the way,became an important factor. The next five years,1986-1990 were primarily consolidation and shakeout within the industry.The tax credits ended in 1985,however contracts from previous years meantwindturbineswerestillbeinginstalledinCalifornia,but not at the increased pace of the previous 5 years.There were less than 10 US manufacturers in 1990,and only one major manufacturer,US Windpower.Federal support for wind energy fell to a low of 8 million dollars in 1988 (see Ch.11).However the Europeans increased their support for wind energy during this period.Japan,especially Mitsubishi,entered the world market and was determined to be a major manufacturer. 10.2.3 Wind Industry 1990-2000 World energy production in 1995 was estimated at 5 billion kWh/year from over 22,000 wind turbines with an installed capacity of around 4,000 megawatts.The American Wind Energy Association has set a very optimistic goal for the US of 10,000 MW by the year 2000.This will be difficult to achieve,although there is a lot of activity in other states outside of California.Presently there are planned projects for over 1,000 MW of wind power.Government regulations and incentives in Europe will result in the installation of wind turbines (4000 MW by year 2000 and 11,500 MW by 2005),which will surpass that of the United States. This period is and will be characterized by: 1)Commercial wind turbines in the range of 200 to 700 kW (20 to 40 m diameter)are being built,again primarily European. 2)Federal funding in the United States has been provided to develop advanced wind turbines to compete with foreign manufacturers.The DOE is sponsoring a range of programs aimed at assisting the wind industry with system design,development, and testing [3].The goals are units which will produce electricity for $0.05/kWh byyear1995and$0.04/kWh by year 2000 in a mean wind of 13 mph.Two of the recipients of the first round of funding,R.Lynette and Associates and Northern Power Systems are building prototypes;the WC 86 (26 m diameter,275 kW)and the NW 250 [4,5]. 134 3)Megawatt size units are still at the prototype stage;funded by European governments since they have less available land. 4)Hybrid systems will be developed for village electrification market in the third world. 5)Use of renewable energy systems to meet the Rio Treaty for reduction of carbon dioxide emissions.Wind energy is the most cost effective renewable energy at the present time (1994-98). 5)Development of infrastructure for distributed wind turbines.Wind turbines for farmers,ranchers,and agribusinesses will be similar to the farm implement business. The Utility Wind Interest Group has published a number of brochures (see references)onallaspectsofthewindindustry.This information is primarily for planners in utilities andpolicymakersiinstategovernments. 10.4 LARGE WIND TURBINES The main goal of the ERDA,now DOE,program was the development of largewindturbinesfortheutilitymarket[2].These units were to produce power in the range of $0.02 to 0.04/kWh.The program was managed by NASA-Lewis starting with the MOD-0O (100 kW,38 m diameter)and progressing to megawatt size (Fig 10.3).The MOD-5A wasnotbuiltandonlytheMOD-5Bis still operating as all the others have been taken downduetofailuresorO&M was too high.The MOD-5B was built at 3,200 MW,rather than the original plans for 7,200 MW.Over half of the federal funding,$350 million,from 1973 to 1990 was spent on the development of large wind turbines.This program was largely a failure because they proceeded to the next stage without fully developing the wind turbines at the previous stage.Design of wind turbines was much more difficult than the engineers in the aerospace companies had anticipated. The market is now dominated by groups which started from the other end,50 to 100 kW.DOE is assisting the US industry to meet the foreign competition through the advanced wind turbine program [3].The market will be driven toward more light weight, flexible designs.There will probably be a convergence between the two generic designs;3 bladed,rigid rotor,heavy and 2 bladed,teeter rotor,light.Fixed and variable pitch will both be used.Table 10.5 shows the different large units and their date of first installation. The megawatt units are prototypes developed with government funding. 135 500 --- WIND ->-- 400 ;- 300 }- (E>250 200 ;- | -L. 100 +- P : ol.tt i MOD-0A MOD-1 MOD-2 WTS-4 MOD-5A MOD-5B 200 kW 2000 kw 2500 kw 4000 kw 6200 kw 7200 kw Figure 10.3 DOE large wind machine program.Size in feet. Table 10.5.Large wind turbines. Name Country Diameter,m Rated Power,kW Year Monopteros 50 Germany 28 650 89 Monopteros 400 Germany 48 400 82 WKA 60 Germany 60 1200 89 WEC HSW Germany 25 250 88 Growian Germany 100 3000 82 Enercon Germany 33 330 92 Enercon Germany 36 400 92 Enercon Germany 36 500 Tacke Germany 33 300 95 Tacke Germany 36 600 92 Tacke Germany 33 300 95 Ventis Energietechnik Germany 500 95 Hausumer Schiffswerft Germany 1000 95 Seewind Energ Germany 750 95 VAWT UK 18x25 130 86 WEG MS-1 UK 20 250 83 WEG LS-1 UK 60 3000 88 WEG MS-2 UK 25 250 87 WEG MS-3 UK 33 300 88 Howden UK 22 300 83 Howden UK 45 750 88 Howden UK 55 1000 89 Table 10.5.Large Wind Turbines.Continued. Name -Country ._---Diameter,m Rated Power,kW Year Tvind Denmark 54 2000 78 Nibe A Denmark 40 630 79 Nibe B Denmark 40 -630 80 Tjareborg Denmark 60 2000 88 WINDANE Denmark 40 750 87 ELSAM Denmark 60 2000 88 AWP Denmark 200 BONUS Denmark 23 150 88 BONUS Denmark 450 V25 Denmark 25 200 87 V23 Denmark 23 200 87 V39 Denmark 39 500 92 V39 Denmark 39-44 600 95 WINDANE Denmark 34 400 87 DANWIN24 Denmark 24 200 88 Micon Denmark 24 250°88 Micon Denmark i 600 NedWlind Denmark 41 500 Nordtank Denmark 500 94 Wind World Denmark 500 NORDEX Denmark 26 225 88 NEWECS-45 Netherlands 45 1000 85 HAT Netherlands 25 81 6LW 'Netherlands.-6x15 -450 88 BOUMA Netherlands 21 200 84 BOUMA Netherlands 25 250 88 Nedwind Netherlands 25 250 ? Nedwind ,.Netherlands 40 500 93 HMZ :Belgium 23 250 88 HMZ Belguim 33 500 89 MEDIT Italy 32 225 86 M30 Italy 33 200 89 Made _Spain 330 Made Spain 500 95 Ecotecnia Spain |500 95 DAF-Indal Canada 24x37 230 75 DAF-Indal Canada 24x37 500 77 Eole Canada 64x94 4000 87 KEPCO Japan |33 300 84 Mitsubishi Japan 22 250 85 Mitsubishi Japan 450 95 Sumitomo Japan 20 200 WTS-3 Sweden 78 3000 Nasudden Sweden 75 2000 82 Nasudden Il Sweden ?3000 92 137 Table 10.5.Large Wind Turbines.Continued. Name -Country Diameter,m Rated Power,kW Year Zephyr Sweden 28 250 90 NWP Sweden 35 400 92 VAWTPOWER 185 USA 18 185 83 WWG-640 USA 640 88 Carter USA 20 300 FloWind F-19 USA 19 300 84 Wind Eagle USA 22 300 90 Cannon USA 26 250 92 Zond USA 40 500 94 AWT-26 USA 26 275 94 NW-250 USA 25 250 94 REFERENCES GENERAL Frank Eldridge,Wind Machines,Van Nostrand Reinhold,1980. Paul Gipe,Wind Power for Home and Business,Renewable Energy for the 1900's and Beyond,Chelsea Green,P.O.Box 130,Post Mills,VT 05058-0130,1993. Paul Gipe, E.W.Golding,The Generation of Electricity by Wind Power,E.&F.N.Spon, London,1955.Reprinted by Halsted Press,1976. Donald Marier,Wind Power for the Homeowner,Rodale Press,Emmaus,PA,1981. David A.Spera,ed.,Wind Turbine Technology,Fundamental Concepts of Wind Turbine Engineering,ASME Press,1994. Paul N.Vosburgh,Commercial Applications of Wind Power,Van Nostrand Reinhold,1983. Wind Energy Developments in the 20th Century,NASA Lewis Research Center,1981. Available from Superintendent of Documents,U.S.Government Printing Office, Washington,D.C.20402. Wind Energy in Europe,European Wind Energy Association,Oct 1991.Available from EWEA,Via Bormida 2,1-00198 Rome RM,Italy Wind Energy,Research and Technological Development,1990,In Denmark,Ministry of Energy,Danish Energy Agency Building Interest in Wind,EPRI Journal,Dec 1992,pp.4-15. Wind Power,Todays Energy Option,1989.Available from NTIS Utility Wind Interest Group Brochures An old idea takes new shape for electric utilities,Nov 1990. Economic lessons from a decade of experience,Aug 1991. American takes stock of a vast energy resource,Feb 1992. Integrating an ever-changing resource,Jul 1992 The evolving wind turbine,Mar 1993 Wind power and the environment,Aug 1993 138 SPECIFIC 1.Vaughn Nelson,SWECS Industry in the United States,Report 84-2,Alternative Energy Institute,WTSU,Jan 1984.Most of the text is in "A History of the SWECS Industry in the U.S.",Altemative Sources of Energy,Mar/Apr,1984,p 20. R.L.Thomas and D.H.Baldwin,"The NASA Lewis Large Wind Turbine Program," Proceedings,Fifth Biennial Wind energy Conference &Workshop,SERI/CP-635-1340, October,1981,p 39. A.S.Laxson,S.M.Hock,W.D.Musial and P.R.Goldman,"An Overview of DOE's Wind Turbine Development Program,"Proceedings,Windpower '92,Am Wind Energy Assn., Oct 1992,p 426. R.Lynette,"Development of the WC-86 Advanced Wind Turbine,"Proceedings, Windpower '92,American Wind Energy Assn,Sep 1992,p.450. C.Coleman,"Northern Power Systems Advanced Wind Turbine Development Program,"Proceedings,Windpower '93,Am Wind Energy Assn.,Jul 1993,p 152. 139 11 INSTITUTIONAL ISSUES 11.1 INTRODUCTION The interconnection of wind turbines to utility grids and regulations on installation and operation are the main institutional issues.The National Energy Act of 1978 was a response to the energy crisis.The main purpose was to encourage conservation ofenergyandtheefficientuseofenergyresources.The Public Utility Regulatory PoliciesAct(PURPA)covers small power producers,up to 80 megawatts [1,2].Sections 201 and210ofPURPAencouragestheuseofrenewableenergybymandatingthepurchaseof power from qualifying facilities and exempting such facilities from much of the federal andstateregulations.States had a large amount of flexibility in implementing PURPA.The main aspects of PURPA are: Utilities must offer to buy energy and capacity from small power producers at the marginal rate (avoided cost)the utility would pay to produce the same energy. Utilities must sell power to these facilities at non-discriminatory rates.Qualifying facilities are entitled to simultaneous purchase and sale.They have the right to sell all their energy to the utility and purchase all the energy needed. Qualifying facilities are exempt from most federal and state regulations that apply to utilities The implementation of PURPA was determined by public utility commissions, utilities,small power producers,and the courts.Determination of avoided costs and wheeling of power from the best wind sites to areas of high electrical rates was and will be the main points of contention between small power producers and utilities. The National Energy Strategy Bill of 1992 included the provision of wheeling power over utility transmission lines.The Federal Energy Regulatory Commission can order the owner of transmission lines to wheel power at costs determined by FERC.The utilities are allowed to recover all legitimate,verifiable economic costs incurred in connection with the transmission services and necessary associated services,including, but not limited to,an appropriate share,if any of the costs of any enlargement of transmission facilities.From the standpoint of wind power,this legislation is very important since the major source of wind energy is in the Great Plains which is far from the major load centers. Cavallo [3]argues that wind energy could become a high capacity system by wheeling power from the Great Plains to California or from the Texas Panhandle to Dallas-Fort Worth.He conducted a paper study of a 2 GW wind farm in Kansas which could have a capacity factor of 60%.The first large wind plant (initial 35 MW,expansion to 250 MW)in Texas will be in the Trans-Pecos Region and power will be wheeled to the Lower Colorado River Authority area. 11.2 AVOIDED COSTS The avoided costs are to be established by the public utility regulatory body in each state.The Federal Energy Regulatory Commission defines avoided cost as the incremental or marginal cost to an electric utility of energy and/or capacity,which the utilitywouldhavetogenerateorpurchasefromanothersourceifitdidnotbuypowerfromthe qualifying facility.The avoided cost includes not only present but also future costs. 140 Utilities can set a standard purchase rate for qualifying facilities under 100 kWcapacity.Contact your public regulatory body for more information on small powerproduction.The California Public Utilities Commission set the avoided costs and types of contracts for qualifying facilities [4].Standard Offer Number 4 set the avoided costs for aperio"of ten years,while Standard Offer Number 1 was variable depending on the costoffuel. Some utilities state that they have excess capacity and therefore the avoided costisequaltothevalueofthecostoffuelattheplant.The fuel adjustment cost for Southwestern Public Service in January 1994 was $0.02/kWh. 11.3.UTILITY CONCERNS For a few wind turbines on a large utility there would be no problems with theamountofpower.It would be considered as a negative load;a conservation device which is the same as turning off a load.For large penetration,20%and greater,otherfactorssuchasthevariabilityofthewindanddispatchingbecomeimportant.For all wind turbines the utilities are concerned with safety and power quality. 11.4 SAFETY Safety is a primary consideration.This includes energizing a dead utility line, grounding of equipment and lightning.This issue has been resolved as the large number of wind turbines have been connected safely to the utility line.Induction generators have to be energized by the utility line,so when there is a fault on the line they do not operate. Inverters have sensors for loss of load to disconnect them from the utility line. Of course safety in installation and operation is of concern as with any other industrial enterprise.High voltages,rotating blades and machinery,and large weights make for a hazardous work place.Safety is the first consideration for working around wind turbines.Never climb a tower if you are the only person at the site. 11.5 QUALITY OF POWER Quality of power refers to harmonics,power factor,voltage and frequency control. A number of wind turbines on the end of a feeder line could require extra equipment to maintain quality of power.Utility companies have to supply reactive power for induction generators and they may require capacitors on the wind turbine or at the wind plant to maintain the power factor. 11.6 CONNECTION TO THE UTILITY The utility should be informed at the earliest possible stage of the intention toconnectawindturbinetotheirsystem.Information for the utility should include: Specifications of the wind turbine Schematic (block diagram)of the electrical systemDescriptionofmachinecontrolswhenthereisloss of load (utility power).Liability for damage is another concem of utilities.The utilities would like to beinsuredagainstalldamageduetothewindturbineoperation.Of course,the small powerproducerwouldliketobeinsuredagainstdamagetothewindturbineasaresultofutilityoperation,however that is impossible to obtain.Insurance should be available as part ofyourhomeownerpolicyoraspartofyourbusinesspolicy.Some electric cooperatives 141 are requiring proof of a $500,000 liability policy for connection of a wind turbine to their system. 11.7 REGULATIONS ON INSTALLATION AND OPERATION Permits are required in residential areas for construction and even in rural areas in some states.The major zoning issues are tower height,setbacks,noise,aesthetics, environmental impact,and safety.The probability of failure such as a thrown blade is the most common objection.However,risks are accepted from other areas such as Cars, utility lines (electric and gas),etc.Signs,trees and even utility poles have failed in high winds or under conditions of icing. Tower access needs to be controlled as does access to the high voltage.One factor which can never be dismissed.Anything that interferes with TV will be unacceptable to the public. Most locations do not have specific zoning regulations for wind turbines.Be prepared to educate public boards and your neighbors [5-8]. 11.8 ENVIRONMENTAL The three main environmental issues are visual impact,noise,and birds.The visual impact can be detrimental,especially in those areas which are located close to scenic areas or parks.It is the same story,people are in favor of renewable energy,but not in my backyard.The turbines should be drab colors,not highly reflective,and the rotors should be rotating in the same direction. Noise measurements have shown in general that wind turbines are below the ambient noise,however the repetitive nose from the blades stands out and one would not want their residence in the middle of a wind plant.The whine from gearboxes on some units is also noticeable. Avian mortality has become an issue in Altamont Pass as wind turbines have killed some raptors.Transmission line poles had caps put on them to keep the birds from using them as a perch,thereby extending their wings between the lines and being electrocuted. There is a major study to find out the effect of rotating blades on raptors and if there are methods to make them stand out to birds;color,noise,etc.Another possibility is that the trust towers make natural perches,since there are no trees in the area.One wind planthasstipulatedtubulartowersasaprecaution. Another area that has experienced problems is in Southern Spain [9].Tarifa is a temporary roosting area for migratory birds to and from Africa.Biologist believe the problem of avian mortality at the site is partly due to aerodynamics as the soaring birdstraveltheaircurrentsthatpropelthemuptheridgeswherethewindturbinesarelocated. The large birds do not have the maneuverability of the smaller birds. From the example in Spain,it is obvious that some locations will be off limits to wind plants.For example a wind plant could not be located next to a wild life refugee foranendangeredspeciesofbird,such as the whooping crane.Even though thousands ofbirdsarekilledbycommunicationtowers,buildings,hunters and even cars,the Sierra Club and other environmental groups will become adversaries if the wind industry doesnotsolvetheproblem. There will be land areas which are excluded because of environmental considerations;national and state parks,wetlands,and some wild life refugees.Environmental impact statements will have to be done as the Environmental Protection 142 Agency has jurisdiction over many aspects.In addition some states and even counties have regulations concerning the environment which will have to be met before a wind turbine or a wind plant can be installed.First check with local officials before you install your wind turbine. Regulations,from federal to local,play a part in any project.Sometimes there seem to be competing regulations from different agencies and the number of agencies can be large.Industry maintains that regulations are now a major portion of their cost of doing business.In many cases,industry says they cannot meet proposed regulations because it is uneconomical. 11.9 POLITICS As with any endeavor,politics enters the situation.To make a change in behavior, especially when the competition is an entrenched industry,you need INCENTIVES, PENALTIES,AND EDUCATION.Someone estimated that the amount of each type of energy used is in direct proportion to the amount of subsidies for that type of energy. Subsidies are in the form of taxes,tax breaks,and regulations,all of which generally require legislation,POLITICS. Incentives are usually in the form of tax breaks,or incentives can be in terms of regulations.Public utility commissions are now demanding that utilities use integrated resource planning,which means they have to consider renewables and conservation in the planning process.Can utilities make money for kWh saved?Who is suppose to take the risk,the consumers or the shareholders?Three Mile Island and the nuclear utility industry are good examples of politics,from the local to national level.The Price Anderson Act,a federal law,limited the amount of liability from a nuclear accident. Without that legislation,the nuclear industry could not have sold plants to utilities. Penalties are generally in the form of taxes and regulations.Environmental groups have already indicated that utility planners will be held accountable for the risk of a carbon tax if they plan on new coal plants.In other words,their opinion is that the shareholders and not the consumers should take the risk. Education is public awareness of the possibilities,a realistic cost/benefit comparison over the lifetime of the energy systems.Remember you can not fool mothernatureandyouwillpayonewayoranother. 11.9.1.Federal Support The Federal government continues to support wind energy through the Department of Energy budget for renewables.As always,the budget for renewable energy is lessthanthebudgetfornuclearenergy.In 1973,the amount was $300,000 and thatincreasedsteadilyto$67 million in 1980.During Reagan's term,that was reduced everyyear,and in 1988 the amount budgeted was $8 million (Table 11.1).A major part of thefundinghasgonetowarddevelopmentoflargehorizontalaxiswindturbines. The tone or direction is set by the administration,which changes with the President.The early direction was R&D plus demonstration projects,which was suppose to lead tocommercialization.During the Reagan years,commercialization was a bad word andprivateindustrywassupposetocommercializewindturbines.Federal funding was forgenericR&D,such as aerodynamics,wind characteristics,etc.Funding increase slightlyduringtheBushyears,as the advanced technology program was initiated.This programistorecapturepartofthemarketacquiredbyforeignwindturbinesthroughdevelopment of advanced wind turbines. 143 Table 11.1.Federal Budget for Wind Energy. Fisical Year $Millions 73 0.3 80 67 89 8 90 9 91 11.2 92 21.4 93 24.0 94 30.5 Under Clinton there is renewed interest in renewable energy and the direction is now commercialization.The Climate Change Action Plan moves DOE from focusing primarily on technology development to playing an active role in renewable energycommercialization.This initiative is backed up with $72 million for FY 95 ($18 million forwind)and a total of $432 million through the year 2000.DOE is looking primarily to windfortheemissionsreductionsfromrenewables,since it is the most economical at this time. Again with the change in Congress,the Republicians are now calling for the elimiantion of DOE. 11.9.2 Division of the Spoils When there is money available,then every federal lab and university wants part of that money and there is a proliferation of new institutes and consulting groups.The wind money was divided in the following manner: Large HAWTs (>100 kW)NASA Lewis Small wind turbines (<100 kW)Rocky Flats,Rockwell International Vertical axis wind turbines Sandia Labs Wind Characteristics Battelle Pacific Northwest Laboratory Innovation wind turbines Solar Energy Research Institute Agricultural applications U.S.Department of Agriculture The innovative program and the agricultural program were terminated after a few years. The Wind Energy Research Center at Rocky Flats was in charge of the small wind systems program.The Rocky Flats location was chosen because of politics,too much publicity on environmental problems.[Early in the program they purchased units fortestingandthenstartedafieldevaluationprogram[10].The field evaluation program wastoinstalltwounitsineverystateandtheterritories,definitely a political plus.After 40 units were installed,this program was abandoned due to costs and the small wind industry was not ready. The small wind machine program was transferred to the Solar Energy Research Institute (SERI).In addition,NASA Lewis retired from the large HAWT program, transferring what was left to SERI.The President designated SERI as the National Renewable Energy Laboratory (NREL),on an equal footing with the other national labs, which had their beginnings from the development of nuclear weapons and/or high energy physics.The expected progression is that the NREL will absorb all the other programs associated with renewable energy,that is if the program receives continued funding. There is a bit of political infighting going on at the present time. 144 11.9.3 Incentives The major impetus to the wind industry was due to the Federal Tax Credits,the National Energy Act of 1978,and the avoided costs set by the California Public Utilities Commission.The Federal Tax Credits for wind turbines were terminated in 1985.For small systems for personal use,the tax credits were 40%of the cost up to a maximum of $4,000.For a business,the tax credits were 25%off the bottom line.During this period, tax shelters for California wind plants were the primary method of financing. A part of the National Energy Strategy Act of 1992 provides a $0.015/kWh incentive for production of electricity by wind energy.An investor can claim the tax credit under section 45 of the IRS code [11].The provisions are: The investor owns the wind facility which is placed in service during the period December 31,1993 to July 1,1999. The investor produces the electricity at the wind facility. The investor sells the electricity to an unrelated party. The credit applies to production through the first ten years of the facilities operation.The credit is intended to serve not only as a price incentive but also as a price support.The credit is phased out as the average national price exceed $0.08/kWh,based on the average price paid during the previous year for contracts entered into after 1989.Both values will be adjusted for inflation.The credit can be carried back for three years and carried forward for 15 years to offset taxes on income in the other years. Politics will continue to influence which and how much different energy sources are subsidized.Present ideas include a carbon tax and or a rebate or incentive for electrical energy produced from renewable energy.States are also competing for renewable energy as a way to offset importation and as a way to create jobs.Minnesota passed legislation requiring Northern States Power to acquired 425 MW of wind power by the year 2002 in exchange for permission from the state legislature to store waste from its Prairie Island Nuclear facility in dry casks outside the plant...Texas passed legislation that the Lower Colorado River Authority can acquired renewable energy from plants located on state lands outside of their service territory.This paved the way for a 35 MW wind plant in the Delaware Mountains in the Trans-Pecos region with an extension for another 200 MW. 11.10 OTHER REFERENCES 1.Donald Bain,"An Introduction to PURPA,Sections 201 and 210",V.Nelson,ed., Proceedings National Conference,Summer 1980,Am Wind Energy Assn,p 33. 2.United States of America,Federal Energy Regulatory Commission,Order No.69, Final Rule Regarding the Implementation of Section 210 of the Public Utility Regulatory Policies Act of 1978 (Docket No.RM79-55). 3.A.J.Cavallo,"High Capacity Factor Wind Turbine-Transmission Systems,"SED-Vol 15,Wind Energy -1994,ASME,p 87. 4.John E.Bryson,"New Directions for Utilities,"V.Nelson,ed.,Proceedings National Conference,Summer 1980,Am Wind Energy Assn,p 68. 5.D.M.Dodge and C.Lawless-Butterfield,Small Wind systems Zoning Issues andApproaches,RFP-3386,UC-60,Wind Energy Research Center,SERI. 145 6.Handbook on Wind Zoning for Municipal Officials,Executive Office of Energy Resources,Commonwealth of Massachusetts. 7.Zoning for Wind Machines,A Guide for Minnesota Communities,Energy Division, Minnesota Department of Energy and Economic Development,Aug 1983. 8.Margaret Moorehead,Reference Guide to Wind Energy Land Use,Issues and Actions,Oregon Department of Energy,Feb 1984. 9.A.Lue,A.W.Hosmer,and L.Harrison,"Bird Deaths Prompt Rethink on Wind Farming in Spain,"Windpower Monthly,Vol 10,No.2,Feb 1994,p 14. 10.Vaughn Nelson,SWECS Industry in the United States,Report 84-2,AlternativeEnergyInstitute,WTSU,Jan 1984.Most of the text is in "A History of the SWECS Industry in the U.S.",Alternative Sources of Energy,Mar/Apr,1984,p 20. 11.E.T.C.Ling,"Making Sense of the Federal Tax Code:Incentives for Windfarm Development,"Proceedings,Windpower '93,Am Wind Energy Assn,Jul 1993,p 40. QUESTIONS 1. 2. 3.>What type of incentives should there be for renewable energy,particularly wind energy?How much support should the federal government provide for wind energy?Why? What type of projects should the federal government support? Should state and local governments provide incentives for wind energy?If the answer is yes,list and explain why? What type of education would be most effective for promoting renewable energy?At what level and to whom? What are the major environmental concerns if a renewable energy system is planned for your area?At what level should the federal government fund R&D for renewable energy?wind energy?nuclear energy?Compare your numbers to federal budget for this fisical year. 146 12 ECONOMICS 12.1.INTRODUCTION The most critical factors in determining the value of energy generated by wind turbines are:1)initial cost of the installation and 2)the amount of energy produced annually.In determining economic feasibility,the unit worth of energy available from competing technologies and the price for which the electrical energy can be sold are also critical.For wind energy to have widespread use,the return from the energy generated must exceed all costs in a reasonable time. In general,installed costs for small WECS are around $2000 to $3000 per rated kilowatt,which translates to a value of electricity produced of around $0.15/kWh to$0.20/kWh.Costs for WECS in wind plants has fallen below $1,000/kW,which translates to a value of electricity produced of $0.06 to 0.08/kWh.Operation and maintenance costs for wind plants are $0.01 to 0.015/kWh.In mass production,installed costs should decrease to $500 to $750/kW which would reduce the value of electricity to around$0.035 to 0.05/kWh.The goal for O&M is $0.005/kWh.Contracts are being signed in1995for$0.04/kWh,which includes the kWh tax credit,so the real value is closer to $0.05/kWh. Systems of 1 kW are not cost effective when connected in parallel to the utility grid, even for single residences.For residences connected to the utility grid,units of 5 to 10 kW are needed.Farms,ranches and businesses need a minimum size WECS of around 15 to 25 kW (around 10 m diameter)or even as large as 50 kW.In Denmark,a cooperative of owners buy larger wind turbines.There are economies of scale and the size of units for agribusiness will probably increase to the 100 to 300 kW range.For wind plants,it now appears the most economical size of wind turbines is in the range of 300 to 750 kW. -A WECS or'a number of WECS should be selected that would produce between 50 and 100%of the annual energy consumed at the site.The kWh consumed can be obtained from the monthly electric bill or by calling the local utility to obtain the monthly use.To maximize the return on the WECS,most of the energy shouid be used on site, because that energy is worth the retail rate and energy sold to the utility is generally worth less. 12.2 FACTORS AFFECTING ECONOMICS The following list includes most of the factors that should be considered when purchasing a wind turbine. 1.Initial Installed Cost A.Purchasing Price B.Shipping CostsC.Installation Costs (foundation,utility intertie,labor,etc.) D.Cost of Land 2.Production of Electrical Energy A.Wind Turbine Availability _B.Type(s)and Size(s)of Wind Turbine(s)- Warranty Company (type,time,past history) C.Wind Regime Variations within a year 147 Variations from year to year3.Selling Price of Energy Produced and/or Unit Worth of Energy and Energy Cost Changes (Escalation)of Competing Sources 4.Operation and Maintenance Costs A.General Operation,Ease of Service B.Emergency Services and Repairs C.Insurance 5.Cost of Money (Interest Rate,fixed or variable) 6.Inflation 7.Legal Fees (Negotiation of Contracts,Titles,Easements,Permits) 8.Depreciation if Wind Turbine is Business Expense 3 GENERAL COMMENTS The general uncertainty regarding future energy costs,and to some extentavailability,have provided the driving force for development of renewable sources.Thepredictionofenergycostsescalationisahazardousendeavor,as the cost of energy isdrivenprimarilybythecostofoil.Predictions at the present time are for a gradualincreaseto$30/barrel by year 2020,compared to today's values of $15 to 20/barrel. Prices increases have not been and will not be uniform,either in terms of time or geography.At the point in time where demand exceeds production,there will be a sharp increase in the price of oil. Every effort should be made to benefit from all incentives,mainly federal and state tax credits.As an example,the tax credits for wind lasted from 1980-85.There was an income tax deduction of 40%of the first $10,000 for personal use or 25%(15%solar tax credit,10%investment tax credit)with no upper limit for business.State credits will vary. The cost of land is a real cost,even to those using their own land.This cost is often obscured because it occurs as unidentified lost income.Wind turbines occupy space and will reduce the amount of land available for farming or ranching.For wind plants,the amount of land taken out of production can run from 5 to 15%. Wind turbine availability is important in determining the quantity of energy produced.For optimum return,the machine must be kept in operation as much of the time as possible,consistent with safety considerations.Background information on machine performance,including failures,should be sought out and used to estimate the down time. Availability for earlier machines was low,however,recent figures are 95%.The wind regime at a site is the primary factor in determining the rate of production of electrical energy.The distribution of this energy throughout the year can affect the value of the energy.If most of the energy comes during a time of increased demand on the utility system,or during the time energy is needed on the site,then that energy is clearly of more value. 12 Wind turbines can produce electricity 1)for consumption on or near the site,2)to sell to a utility or 3)both.The higher the selling price the more economically feasible the project becomes.In general,where there is one or a few wind turbines,the owner will use part of the energy and sell the excess energy to the utility.The electricity used on site displaces electricity at the retail rate.For those states which have net energy billing,even the energy fed back to the utility is worth the retail rate.If more energy has been produced than was used during the billing period,then that energy is sold for avoided cost.For 148 locations where the retail rate is higher than the avoided cost paid for excess energy by the utility,economic feasibility improves with increasing on-site consumption (see example).The price paid by the utility is either negotiated with the utility,or it is decided by a public regulatory agency. Example:Wind turbine produces 2000 kWh in a month.There are two meters which measure from (8000 kWh)and to (1200 kWh)the grid.The load displaced by the wind turbine is 800 kWh (2000 -1200).Retail rate (from grid)is $0.08/kWh.Avoided cost (to grid)is $0.04/kWh. Bill if use two meters. Meter 1 3000 kWh =$0.08 $240 Meter 2 1200 kWh =$0.04 -48 (meter charge for 2nd meter)_15Total $207 Net Energy Billing One meter,runs forward and backward 1800 kWhMeter1800kWh=$0.08 $144 Clearly net energy billing is preferable,because all the energy produced by thewindturbineisworththeretailrate,up to the point where the meter reads no difference from the previous month. The costs of routine maintenance and operation for individuals represents the time and parts costs.Until machine reliability and durability are better known for long time periods,the costs of repairs will be difficult to estimate.It is important that the owner has a clear understanding of the manufacturer's warranty and that the manufacturer has a good reputation.Estimates should be made on costs of repairing the most probable failures. Insurance costs may be complicated by companies that are uncertain about the risks involved in a comparatively new technology.However,the risks are less than operating a Car. Inflation will have its principal impact on expenses incurred over the lifetime of the product.The costs of operation,maintenance and especially the unanticipated repairs fall into this category.On the other hand,cheaper dollars would be used to repay borrowed money (for fixed rate loans). 12.4 ECONOMIC ANALYSIS Economic analysis both simple and complicated provide guidelines.Simple calculations should be made first.Commonly calculated quantities are 1)simple payback 2)cost of energy (COE)and 3)cash flow. A wind turbine is economically feasible only if its overall earnings exceed its overall costs within a time period up to the lifetime of the system.The time at which earnings equals cost is called the payback time.The relatively large initial cost means that this period could be a number of years,and in some cases earnings would never exceed the costs.Of course,a short payback is preferred and a payback of 5 to 7 years is acceptable. Longer paybacks should be viewed with caution. 12.4.1.Simple Payback A simple payback calculation can provide a preliminary judgment of economic feasibility. SP =IC/(AKWH*$/KWH -IC*FCR -AOM)12.1 149 where SP =simple payback,years IC =initial cost of installation,$ AKWH =energy produced annually,kWh/year $/KWH =price obtained for energy generated FCR =fixedcharge rate AOM =annual operation and maintenance cost,$ The FCR could be the interest paid or the value of interest received if you displaced money from savings.An average value for a number of years (five)will have to be assumed for $/KWH. Example: IC =$40,000 FCR =0.10 =10% AOM =0.03x40,000 =$1200/yrAKWH =66,000 kWh/yr $/KWH_=10.5 cents/kWh =$0.105/kWh Amount earned per year =66000x0.105 =$6930Cost/yr =40000x0.10 +1200 =$5,200 SP =40000/(6930-5200)=40000/1730 =23.1 yr This equation involves several assumptions;same number of kWh are produced each year,the value of the electricity is constant,and no inflation.More sophisticated analysis would include details such as escalating fuel costs of conventional electricity and depreciation.These factors might reduce the payback to around 10 years. 12.4.2 Cost of Energy The cost of energy (COE,value of the energy produced by the wind turbine)gives a levelized value over the life of the system (assumed to be 20 years or greater). COE =(IC *FCR +AOM)/AKWH 12.2 The COE is not a measure of economic feasibility,but when compared to the price of electricity from other sources (primarily the utility company)and when compared with the price for which wind generated energy can be sold,it gives an indication of feasibility.If the COE is up to 30%above these prices,further analysis is justified. Example:-Enertech 44/25 in the Panhandle of Texas IC =$40,000 FCR =17.2%=0.172 AOM)=2%of IC =0.02 x 40,000 =$800/year AKWH =60,000 kWh/year COE =(40000 x 0.172 +800)/60000 =$0.128/kWh COE =12.8 cents/kWh The COE should be compared with an estimated average cost of electricity from the utilityoverthenext10years. 150 A sensitivity analysis (Fig.12.1)shows how the different factors in Eq.12.2 affect the cost of energy.The most important factor is the wind regime.A 10%increase in energy production would reduce the COE to 11 cents/kWh.Also notice that initial cost is the other major factor. AKWH =60,000 kwhyyear 20 f+IC=$40,000 FCR =17.2%/year Initial is t AOM=$800/year Cost -i6f Fixed =Charge=Rate-147 3 _ s Operation+ Al 12 Maintenance °o @ Oo 2 10 3 Energy Production 6 dn rT 1 1 1 1 4 4 2 ] -50 -30 -10 O +10 +30 +50 Change (%) Figure 12.1 Sensitivity curve for the cost of energy for an Enertech 44/25 in the Panhandle of Texas. The formula for cost of energy was and is used for estimating the value of energy from wind turbines.It is interesting to see how predictions (Fig.12.2)made in the past compare with the actual values today.Remember that these numbers are for $1978, before the boom in wind plants in Califomia [1]. 12.4.3 Value of Energy Another formula for estimating the value of energy from Efficient Use of Energy is fi (1+rt orl2 c 12.3(1 +a)t-1]q +rt.1] 151 where fo =value of the energy saved per year,$ Cc =initial installed cost,$ L =years to payback a =fuel inflation rate r =interest rate 60-7 mph 92"Hi PRE PROOUCTION3016(Vs) -ue"a 4 LIMITED PRODUCTION<<10,&Dp wl ee >= f 2 %28 co "i MATURE PRODUCTWegtvk(10's) eSue 7OL-r 6o=SPECIALIZED CASES Oo ”5 .& 2 433 USEFUL MARKEY AWIDESCALEUSE 2 wb 0 FIRST SECOND THIRD GENERATION GENERATION GENERATION{MOD-OA}(MOD-4)(MOD-X) 30 -¥men 1979 12"EH PRE PRODUCTIONzo*(Va) 12 Ws'4 warren PRoouction 10 1980 w@ (26'9) &'7 a 129>3 do 140 mature Proouct oo %1100's)ae)st 1% We 1963 gS 7 Sl etoeos-SPECIALIZED CASES N83 4 FUL MARKEYS3USEFUL % -WIDE SCALE USE x2 31 0 FIRST SECOND GENERATION GENERATION ADVANCED SYSTEMS (MOD-1){MOD-2)(MOD---5)(MOD-Q) Figure 12.2 Cost trends (1978)for intermediate (top)and large (bottom)wind turbines. 152 Because there is not a factor for operation and maintenance,the interest rate should be increased by 1 to 2%.Eq 12.3 can be solved by iteration by using different values of L tocalculatetherighthandsideandthencomparingthattotheleftsideoftheequation.Asinterestratesincrease,payback times increase;as fuel inflation factors increase and as cost of electricity increases,payback times decrease. CAUTION:A WECS may be overrated and the actual power output versus windspeed is lower than the manufacturer's curve,or the wind regime is not as good as expected.Alsooperationandmaintenancecostscouldincreaseaftertheinitialperiod. 12.5 LIFE CYCLE COSTS Life cycle costing is the best way of making purchasing decisions.On this basis,many wind turbines are economical.Computer programs for calculating life cycle costsforwindturbinesareavailablefromtheNationalRenewableEnergyLaboratory.The financial evaluation can be done on a yearly basis to obtain cash flow,break-even point,and payback time.A cash flow analysis will be different in each situation.Cash flow for a business will be different from a residential application because of depreciation and tax implications.The payback time is easily seen,If the data are graphed. Example:Residential application (done when there was a tax credit) installed cost =$20,000 down payment $6,600 loan 7 years at 19% maintenance 2.5%*IC =$500/yrenergyproduction=50,000 kWh/yr,75%consumed directly displacing 8 cents/kWhelectricityand25%sold to the utility at 4 cents/kWh with utility escalation at 5%/year Year 0-1 2 3 4 5 6 7 8 9 Down Payment 6600Principal1070 1273 1515 1803 2145 2553 3083 Interest 2546 2342 2100 1812 1470 1062 £577 Maintenance 500 500 500 500 500 500 500 500 500 Insurance 50 50 50 50 50 50 50 50 50 Property Tax 65 65 65 65 65 65 65 65 65 Costs 10831 4230 4230 4230 4230 4230 4230 615 615 Energy Used 3000 3150 3308 3473 3647 3829 4020 4421 4433 Energy Sold 500 525 551 579 608 638 670 704 739 Tax credit 4000 Income 7500 3675 3859 4052 4255 4467 4690 5125 5172 Cash Flow -8331 -555 -378 -178 25 237 460 4510 4557 Cumulative -3886 -4257 -4435 -4410 -4173 -3713 797 5354 153 In this analysis the breakeven point is at the end of year 5 and the payback time is in year 8.There are a number of assumptions about the future in such an analysis.A more detailed analysis would include inflation and increases on costs for operation and maintenance as the equipment becomes older. A cash flow analysis for a business with a $0.015/kWh tax credit on electric production and depreciation of the installed costs would give a different answer.Also all operating expenses are a business expense. Other examples of cash flow analysis for wind turbines can be found in thereferences.The economic utilization factor is calculated from the ratio of the costs of electricity used at the site and electricity sold to the utility. 12.6 COST TRENDS A number of estimates on future value of electricity from WECS for different wind regimes and different level of production of machines are given in Figures 12.3-12.5.The first three are DOE estimates using Eq.12.1.The next two are from Reference 3 using an annualized value of electricity calculated from life cycle costs. 12.7.PRESENT WORTH AND LEVELIZED COSTS Money increases or decreases with time depending on interest rates for borrowing or saving and inflation.Many people assume energy costs in the future will increase faster than inflation.The same mechanism of determining future value of a given amount of money can be used to move money backward in time.If each cost and benefit over the lifetime of the system were brought back to the present and then summed,the present worth can be determined. (costs total for year S)-(financial benefits totals for year S) (14d)PW =12.4 where the following are used for above and following equations: PW total present worth Costs Total total negative cash flow Financial Benefits Total total positive cash flow specific year in the WECS lifetime number of year in the lifetime of the alternative years from the present to year S discount ratea=zuMnThe discount rate determines how the money increases or decreases with time. Therefore the proper discount rate for any life cycle cost calculation must be chosen with care.Sometimes the cost of capital (interest paid to the bank,or alternately,lostopportunitycost)is appropriate.Possibly the rate of return on a given investmentperceivedasdesirablebyanindividualmaybeusedasthediscountrate.Adoption ofunrealisticallyhighdiscountratescanleadtounrealisticlifecyclecosts.The cost ofcapitalcanbecalculatedfrom (1 +loan interest rate)_CC =(1 +inflation rate) 154 If the total dollars are spread uniformly over the lifetime of the system,this operationiscalledlevelizing. PW d(14d)?12.5-(da+aP-4AnnualizedCost= One further step has been utilized in assessing WECS versus other sources of energy such as electricity.This is the calculation of the annualized cost of energy from each alternative.The annualized cost calculated from Eq 12.5 is divided by that alternative source. COE =annualized cost /AKWH It is important that annualized costs of energy calculated for WECS be compared to annualized costs of energy from the other sources.Direct comparison of annualized cost of energy to current cost of energy is not rational.Costs of energy calculated in the above manner provide a better basis for the selection of the sources of energy. Ken Karas compared the different methodologies for estimating costs or value of wind energy [2].General issues such as project ownership,cost of financing,and inflation;performance issues such as hub height and wind regime,and computational conventions such as levelization,base year,current year,nominal cost and real cost, must be clearly specified when presenting a cost of energy estimate.Published estimates range from $0.02 to 0.26/kWh and contracts are now (1994)being signed for wind plants as low as $0.042/kWh.The Electric Power Research Institute (EPRI TAG method)is similar to Eq.12.2 with the addition of a term for fuel costs for conventional power plants. 12.8 EXTERNALITIES Externalities are the cost/benefits for the environment,etc.These are now playing a role in integrated resource planning (IRP),as future costs for pollution,carbon dioxide, etc.are added to the life cycle costs.Values for externalities range from zero (past and present value assigned by many utilities)to as high as $0.08/kWh for steam plants fired with dirty coal.Again values are being assigned by legislation and regulation (public utility commissions). As always there is and will be litigation by both sides.The Lignite Energy Council has Petitioned the Minnesota Public Utilities Commission to reconsider its interim externality values.The council represents major producers of lignite,investor-owned utilities,rural electric cooperatives and others.They focused their protest on values assigned to COs emissions,as there is an acknowledged lack of reliable science that COz2 emissions are harmful to society. 12.9 VALUE OF WIND ENERGY FROM WIND PLANTS Integrated Resource Planning is nowa fact of life for utilities,since wind plants areinacompetitivesituationwithotherenergysources.In many states,renewable energy isnowmandatedforsomeportionofnewpowerplantsbythelegislatureorpublicutilitycommission.For example,the 1992 New York State Energy Plan Executive Summarystates,"New York should take action to accommodate the growth and expansion that will 155 be necessary for renewable resources to make a meaningful contribution to the State's energy future.State energy policy and regulatory decision-making should account fully for the environmental and national security benefits of renewable resources." Therefore utilities are issuing Request for Proposals for supply and demand-side management (DSM).In some cases there will be some fraction set aside for renewables. As an example,Niagara Mohawk issued a RFP for 350 MW of resources by October 1994 and they receive 108 bids consisting of 33 DSM projects representing 165 MW and 75 supply-side bids offering 7,115 MW of capacity [3].The final award group consisted of seven DSM bids offering 36 MW of savings and two supply projects representing 405 MW.Their analysis was based on the following factors,with the major factor being price (85%)and the next was environmental (22%).Points were assigned to each item. price avoided costs/payments economic risk breakeven score,front load security success technical/environmental feasibility site acquisition design &engineering permit &licensing facility availability project team experience additional contract deposit level of development construction/operation thermal energy financing economic development longevity fuel supply debt coverage ratios operation and maintenance optional operation security operational operations optimization unit commitment dispatch automatic gen control black start ability planning optimization location unit size fuel diversity fuel flexibility quick start ability environmental impact . air emissions water effects land effects benefit public access &recreation environmental concerns enhanced/mitigated On the above basis combined cycle gas turbines were the winners.Niagara Mohawkplannedfor6MWofwindbutthereareeffortstoexpandthatto30MW. 156 12.10 SUMMARY Either by mandate (legislation or regulation)or on a voluntary basis,there will bemoreuseofrenewableenergy.Pacific Gas &Electric estimates that up to 40%of theirpowercouldcomefromrenewables,without adding storage.New England ElectricSystemshasagreenRFPunderwhichtheutilityagreedtoacquire200millionkWh/yearfromrenewableresources.Green pricing is where the consumer is offered the option of agreeing to pay a surcharge for electricity generated by renewable sources.One other driving force for renewable energy is economics and jobs at the local or state level.That is because renewable energy is local,it does not have to be shipped from another state or country. The American Wind Energy Association has set a national target of 10,000 MW by the year 2000 for the United States.The European Community has a goal of 4,000 MW by the year.2000,which they will reach since the incentives are already in place.Ed DeMeo,Electric Power Research Institute,expects the cost of wind generated electricitytodeclineto$0.04/kWh in moderate winds within the next ten years. REFERENCES GENERAL H.C.Wolfe,Ed.,Efficient Use of Energy,AIP Conference Proceedings,No.25, American Institute of Physics,New York,1975. Paul Gipe,Wind Power for Home &Business,Renewable Energy for the 1990's and Beyond,1993,may be purchased from the American Wind Energy Association. Robert J.Brown and Rudolph R.Yanuck,Life Cycle Costing,A practical Guide for Energy Managers,Fairmont Press,Box 14277,Atlanta,Ga,30324,1980. W.R.Briggs,SWECS Cost of Energy Based on Life Cycle Costing,Technical Report RFP-33120/3533/80/13,UC-60,May 1980,Wind Energy Research Center,NREL, Golden,CO 80402-0464. J.M.Sherman,M.S.Gresham,and D.L.Fergason,Wind Systems Life Cycle Cost Analysis,RFP-3448,UC-60,July 1982,Wind Energy Research Center,NREL,Golden, CO 80402-0464. SPECIFIC . 1.G.P.Tennyson,"The Federal Wind Energy Program:An Overview,"Vaughn Nelson,ed.,Proceedings,National Conference,Spring 1979,Am Wind Energy Assn,Apr 1979,p 1.. 2.J.A.Glose and R.G.Putnam,"Wind Turbine Technology in a Competitive Bidding Situation,"Proceedings,Windpower '92,Am Wind Energy Assn,Oct 1992,p 135. 3.K.C.Karas,"Wind Energy:What Does It Really Cost,"Proceedings,Windpower '92, Am Wind Energy Assn,Oct 1992,p 157. 157 PROBLEMS 1.o15. 16. Calculate the cost of energy for an Enertech 44/60.Installed cost is $60,000 and itwillproducearound90,000 kwh/yr.Assume a fixed charge rate of 10%and M&O of$0.01/kwh. Calculate the cost of energy for an Enertech 44/60,same as problem 1.Now the installed cost is $80,000,fixed charge rate of 10%,and M&O is 2%of installed cost. What is the most important factor in the cost of energy formula? Use simple payback.A Carter 25 will produce 40,000 kwh/yr.Installed cost is $32,000.Do not use interest or O&M costs.If electricity is displaced at the retail rate, what is the time period to the breakeven point? Use simple payback for problem 4 (Eq 12.2).Assume 10%for FCR and 1%of IC for O&M. Estimate the years to payback using Eq.12.3 for problem 5.Assume a fuelescalationrateof7%.This problem has to be done numerically,assume an L, calculate and then modify L in terms of your answer and do calculation again. Explain life cycle costs for wind turbines.Make a comparison to nuclear power plants. Why were wind turbines installed primarily in California during 1981-1985?Discuss in terms of economics.Graph the costs and income in the table from example of life cycle costs (pg 152). What are the equivalent $1994 compared to $1978?How does that change the estimates in the Figure 12.2 for comparison to todays values for wind turbines,$0.06 to 0.08/kWh?To tomorrow's wind turbines,year 2000,$0.04 to 0.05/kWh? .What are today's values for fuel inflation,discount rate,interest rate?What is your estimate,average/yr between now and the year 2000? Karas is President of Zond,a major wind plant developer with 1000s of wind turbines.From his article,what are the limitations on COE and what are his recommendations? A 35 MW wind plant will be installed in the Delaware Mts,Culberson County,TX. Average windspeed is 9 m/s.The units are US Windpower,300 kW units,33 m diameter.At 5 cents/kWh for electricity,estimate the income from that plant. For problem 13,estimated production is 800 kWh/m2 per year.How much energy will the wind plant produce per year? For problem 13,assume that the installed costs are $800/kW.What is the COE? From Table 8.2,use the annual average energy values for the years 89-93.Calculate the COE if the installed costs are $1,000/kW. 158