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DevelopmentandEncouragementofrenewableenergytechnologies1.1ProjectBackgroundSinceitsinceptioninthe1970s,theU.S.DepartmentofEnergy(DOE)hasoperatedasubstantialprograminthedevelopmentandencouragementofrenewableenergytechnologies.Aspartofitsongoingefforttodocumentthestatusandpotentialofthesetechnologies,DOE,alongwithitsnationallaboratoriesandsupportorganizations,developedthefirstsetofRenewableEnergyTechnologyCharacterizations(TCs)in1989.TheTCsweredesignedtorespondtoDOE’sneedforasetofconsistentcostandperformancedatatosupportthedevelopmentofthebiennialNationalEnergyPolicyPlans.ThatfirstsetofTCswassubsequentlyusedtosupporttheanalysesthatwereperformedin1991byDOEfortheNationalEnergyStrategy.TheTCswereupdatedin1993,butuntilnowhadnotbeenformallypublishedandexistedonlyindraftform.TheElectricPowerResearchInstitute(EPRI),operatingonbehalfofitsmemberutilities,hasconductedaprogramintheassessment,evaluationandadvancementofrenewablepowertechnologiessincethemid-1970s.Inthatrole,EPRIhasbeencalleduponbyitsmembers,andoftenbytheenergycommunityingeneral,toprovideobjectiveinformationonthestatusandoutlookforrenewablesinprospectiveelectric-powerapplications.Towardthataim,EPRIhasjoinedwithDOEtoproducethissetofRenewableEnergyTechnologyCharacterizations.ThisjointprojectisoneofanumberofactivitiesthatDOEandEPRIareconductingunderthejointDOE-EPRISustainableElectricPartnershipenteredintoformallybybothorganizationsinOctober1994.ItbuildsuponanumberofactivitiesconductedjointlybyDOEandEPRIoverthepasttwodecades.1.2Objectives,ApproachandScopePurposeandAudience:Inresponsetogrowinginterestinrenewablepowertechnologiesandtheneedforconsistent,objectiveassessmentsoftechnologyperformanceandcosts,DOEandEPRIcollaboratedtopreparetheRenewableEnergyTechnologyCharacterizations(TCs)presentedinthisdocument.Together,throughthisdocument,DOEandEPRIaimtoprovidefortheenergycommunityandthegeneralpublicanobjectivepictureofthestatusandexpectationsfortherenewablepowertechnologiesinelectric-powerapplicationsintheUnitedStates.TheseTCsrepresentaconsensusbetweenDOEandEPRIonthecurrentstatusandprojecteddevelopmentpathoffiverenewableelectricitygeneratingtechnologies:biomass,geothermal,photovoltaics,solarthermalandwind.Inaddition,recognizingtherolethatstoragecanplayinenhancingthevalueofsomerenewablepowerplants,aTCforstoragetechnologies,withastrongemphasisonbatteries,isincludedinanappendix.TheTCscanservetwodistinctpurposes.First,theyaredesignedtobeareferencetoolforenergy-policyanalystsandpower-systemplannersseekingobjectivecostandperformancedata.Second,theextensivediscussionsoftheassumptionsthatunderliethedataprovidevaluableinsightsforR&DprogramplannersastheystrivetoprioritizefutureR&Defforts.Approach:Buildingonthebestavailableinformationandexperiencefrommanyyearsofdirectinvolvementinthedevelopmentandassessmentofrenewableenergytechnologies,expertsfromDOE,itsnationallaboratoriesandsupportorganizationspreparedcharacterizationsofthemajorrenewabletechnologies.Theseweresubjectedtoin-depthreviewbyEPRItechnicalstaffinrenewablesandselectedoutsidereviewers,andthendiscussedatlengthintwotechnicalworkshopsinvolvingthewritersandthereviewers.Thecharacterizationswerethenrevised,reflectingdiscussionsatandsubsequenttotheworkshops,resultinginthisconsensusdocument.Insomecases,EPRIstaffparticipatedinpreparationofoverviewsections.DocumentScope:TheTCsdonotdescribespecificproductsorhardwareconfigurations.Theydescribetypicalsystemconfigurationsatfiveyearincrementsthroughtheyear2030,basedonaprojectedevolutionofthetechnologiesduring1-2thattimeframe.Theyoftenportraychangesinexpectedtechnologyconfigurationovertime.Allowingachangingconfigurationensuresthat,ineachtimeframediscussed,theTCrepresentsthemostcost-effectiveconfigurationprojectedtobeavailableinthattimeframe.Forexample,thesolarthermalpowertowerevolvesfromahybridplantwithaconventionalreceivertoasolar-onlyplantwithanadvancedreceiver.TheTCsdonotattempttopickwinnersamongavarietyofchoices.Inthatspirit,thinfilmPVsystemsare,forexample,describedonlyinagenericway,notspecifyinganyparticularthinfilmtechnologyinanygiventimeframe.ThisviewofthetechnologyfuturemirrorstheR&DportfolioapproachthatDOEtakes,allowingthetechnologyitselfandthemarketplacetodeterminewinnersandlosers.EachTCshouldbethoughtofasadescriptionofthattechnologyinaparticularapplication,typicallyasagridconnectedsystemforbulkpowersupply.However,someTCsdobrieflydescribeotherapplicationsthatcouldusesubstantiallythesametechnologyconfiguration.TheseTCsdifferfromEPRI’sTechnicalAssessmentGuide(TAG™)inthattheyprovidemoreextensivediscussionsoftheexpectedtechnologyevolutionthrough2030.However,thecostandperformancedatapresentedherearebeingusedasabasisforTAG™revisionsthatarecurrentlyinprogress.SimilartotheTAG™,theseTCsdonotdescribearecommendedeconomicanalysismethodology,butinsteaddescribevariousapproachesthatcouldbetakentocalculatelevelizedcostofenergyorotherappropriatefinancialfiguresofmerit.Theseapproachesspanarangeofpossibleownershipscenariosinaderegulatedutilityenvironment.CautionaryNote:Thecostandperformanceinformationpresentedrepresentthebestjudgmentsoftheindividualsinvolvedinthepreparationandreviewofthisdocument.Asthesetechnologiesenterthecommercialmarketplace,normalcompetitiveforcesandcommercialexperiencemayhaveimpactsthataredifficulttopredictatthistime.Forexample,thereareindicationsthatpricesforsomeconventionalpower-plantcomponentsandassociatedengineeringservicesaredroppingascompetitioninpowergenerationbecomesmorewidespread.Basedonveryrecentcommercialexperience,thistrendisalreadyreflectedinthegeothermal-hydrothermalflash-steamplantcostspresentedinthisdocument.Similarcostimpactsmaybeobservedinotherrenewablepowerplantsemployingconventionalthermalgenerationcomponentsoncethetechnologiesbecomeestablishedsufficientlytoattractmultiplecommercialsuppliers.Readersareurgedtousecautioninapplyingnumericaldatafromthisdocumentincommercialsituationswithoutconsultingengineeringfirmsactivelyinvolvedinthecommercialmarketplace.RelationshiptoOngoingRenewablesProgramsatDOEandEPRIThetechnologiesdiscussedinthisdocumentareconsideredbytherenewablescommunity,andbythemanagementsoftheDOEandEPRIrenewablesprograms,tohavegoodpotentialforcontributingsignificantlytotheU.S.electricalenergysupply.Consequently,thesetechnologiescontinuetoreceivetechnicalandmarket-developmentsupportwithintheprogramsofDOEandEPRI.Ofcourse,thereisnoguaranteethatallofthesetechnologieswilldevelopandcontributeasprojectedinthisdocument.Rather,theirindividualprospectsandroleswilldependnotonlyonthedegreeofsupportreceived,butalsoonthepaceofprogressandonsocietalneedsandpriorities.Ultimately,themarketplace,reflectingbothcommercialandsocietalforces,willdecide.Development-SupportAssumptionTheprojectedprogressforthesetechnologiesisbasedontheassumptionthatrobustprogramscontinueinbothtechnologyandmarketdevelopment.Ingeneral,theseprogramsneedbothpublicandprivatesectorsupport,withthebalanceshiftingmoretowardthecommercialsectorastechnicalmaturityisapproached.Ifsupportforaparticulartechnologyiscurtailed,thentheprojectedprogressalmostcertainlywillnotoccur.1.3GenericBenefitsandIssuesThebenefitsofusingrenewableenergyresourcesaremany.Mostofthesebenefitsarisefromtheirvirtuallyinexhaustiblenature.Solarandwindresourcesarereplenishedonadailybasis.Biomasscanbegrownthroughmanagedagriculturalprogramstoprovidecontinuoussourcesoffuel.Geothermalpowerisextractedfromthevirtuallyunlimitedthermalenergyintheearth’scrust.RenewableenergyresourcesarebroadlyavailableacrosstheU.S.Certainregions,however,tendtohavemoreaccessibleresourceofonetypethananother.Figure1illustratesthisdiversity.Forexample,intheMidwest,biomassandwindresourcesareexcellent,asisthesolarradiationneededforflat-platephotovoltaics.IntheSouthwest,highlevelsofdirectnormalinsolationareideallysuitedtosolarthermalandsunlight-concentrationphotovoltaictechnologies.GeothermalresourcesareconcentratedinthewesternpartsoftheU.S.Theavailabilityofeachoftherenewableresourcesisexploredfurtherinthetechnologyoverviewsinthisdocument.Thebenefitsofrenewableenergyextendbeyondabundanceanddiversity.Asindigenousresources,theyfosterbothlocalcontrolandeconomicgrowth.Aninvestmentinrenewableenergycontributestolocaleconomicsecurity.Inaddition,theincorporationofrenewablesinagenerationportfoliomayreducetherisksassociatedwithfluctuatingfossil-fuelpricesandsupplies.Asrenewableenergytechnologiesbecomemorecost-competitive,theirtrueeconomicbenefitsarebeingrealized.Sincemanyrenewableenergyplantsdonotneedtobebuiltinlargescaletoachievethelowestpossibleplantcosts,theycanbebuiltinsizeincrementsproportionatetoloadgrowthpatternsandlocalneeds.Thisisoftenreferredtoastheirmodularity.Giventheirsmallersize,theycanalsobelocatedclosertothecustomerload,reducinginfrastructurecostsfortransmissionanddistribution,andhelpingtoguaranteelocalpowerreliabilityandquality.Such“distributed”applicationsappeartohaveapotentiallyhigheconomicvaluebeyondjustthevalueoftheelectricitygenerated.Severaloftherenewableenergytechnologies,namelyphotovoltaics,solar-thermalandwind,producenoemissionsduringpowergeneration.Biomassplants,withaproperlymanagedfuelcycleandmodernemissioncontrols,producezeronetcarbonemissionsandminimalamountsofotheratmosphericeffluents.Thesituationismuchthesameforgeothermalplants.Whenthesetechnologiesdisplacefossilfuels,theyavoidemissionsthatwouldotherwisebegenerated.Withthegrowingconcernaboutclimatechangeandcarbonemissions,renewableenergytechnologiescanbesignificantcontributorstoglobaleffortstoreducegreenhouse-gasemissions.Thevalueofrenewable-generatedelectricityisdeterminedinpartbythetimeofdayatwhichtheelectricityisdeliveredtothegridandalsobytheprobabilitythatitwillbeavailablewhenneeded.Forexample,solaroutputtendstofollowutilitysummer-peakloadsinmanylocations.Becausepowerdeliveredduringpeakperiodsismorevaluabletotheutilitysystem,renewableenergytechnologiescanprovidehighvalueelectricityandcanbesignificantcontributorstoareliablepowersupplysystematcriticaltimesinthoseregions.Biomass,geothermalandfossil-hybridrenewablesystemsarefullydispatchableandcompetemostcloselywithconventionalfuel-basedsystems.Insomecases,suchasthesolar-thermalpowertowerwithhotsaltstorage,energy-storagecapabilitymaybeincludedeconomically.Inthesecases,thedegreeofdispatchabilityachieveddependsontheamountofstorageincluded.Intermittentsystems,suchaswindandsolarwithoutstorage,willhavevalueasdeterminedprimarilybythetimeofdayandyearatwhichelectricityoutputisavailable.Furtherdiscussionsoftheissueofvaluearecontainedthroughoutthisdocument.Itisimportanttorealizethattheproperuseoffinancialmodelstodetermineprojectattractivenessrequiresaccurateprojectionsaboutthevaluetocustomersofthepowerfromthatsystem.Inmostcases,therelativemeritofaparticularrenewablepowertechnologyisnotdeterminedsolelybyalevelizedcostofenergy.OverallPerspectivesontheRenewableTechnologiesWhileeachofthecharacterizedrenewabletechnologiesisdiscussedindetailinthisdocument,thefollowingsummarypresentsanoverviewofcurrentstatusandapplicationsforeach.Biomass:Theuseofforestryandagriculturalresiduesandwastesindirect-combustionsystemsforcogenerationofelectricityandprocessheathasbeenawell-establishedpracticeintheforest-productsindustryformanyyears.Useofthesefeedstocksinutilityelectricpowerplantshasalsobeendemonstratedinseveralareasofthecountrywithaccesstoappropriatefuels,ingeneralwithacceptabletechnicalperformanceandmarginaleconomics.Themarginaleconomicsareduetothesmallsizeofmanyoftheexistingplantsandtheconsequenthighoperatingcostsandlowefficiencies.Also,fuelshortageshaveoftendrivenfuelpricesupandmadeoperationtooexpensive.Thelarger-sizedplants,inthe50MWrangeratherthanthe10-to-25MWsizerangeofmanyprojectsbuiltinthe1980s,haveeeeconomicsthatareacceptablewhenfuelcostsarecloseto$1/MMBtu,orwhensteamorheatfromthedirectcombustionbiomassboilerisalsoavaluedproduct.Inadditiontoactivitywithcurrenttechnology,developmentisproceedingonadvanceddirect-combustionsystems.Onetechnologycanusedirectcombustionofbiomassfuelstodaywithoutincurringthecapitalexpenseofanewboileroragasificationcombined-cyclesystem.Thistechnologyisbiomassco-firing,whereinbiomassisco-fired,orburnedtogether,withcoalinexistingpowerplants.Thoughitdoesnotincreasetotalpowergeneration,thismodeofoperationcanreducepower-plantemissionsandserveasaproductiveuseforawastestreamthatrequiresdisposalinsomeway.Co-firingcanbecarriedoutasaretrofit,oftenwithverylowincrementalcapitalandO&Mcosts.Biomassco-firinghasbeensuccessfullydemonstratedinanumberofutilitypowerplants,andisacommerciallyavailableoptioninlocationswhereappropriatefeedstocksareavailable.1-5Biomassgasificationandsubsequentelectricitygenerationincombustion-turbineorcombined-cycleplantsisalsobeingpursued.Thismodeofoperationcanbemoreattractivethandirectcombustionbecauseof(a)potentiallyhigherthermalefficiency,(b)theabilitytomaintainhighperformanceinsystemsoverawiderangeofsizesfromabout5MWtoabout100MW,and(c)increasedfuelflexibilitybecauseofopportunitiestoreduceunwantedcontaminantspriortothepowergenerationstage.Thesesystemsareinthedevelopmentanddemonstrationphase.Thekeyissuerequiringsuccessfulresolutionissufficientcleanupofthebiogassothatturbinedamageisavoided.Thegasmustbecleanedofalkalistogas-turbine-entrancestandards,andthiscleanupmusttakeplaceinanenvironmentthatispronetotarformation.Geothermal:Commercialelectricityfromgeothermalsteamreservoirshasbeenarealityforover30yearsinCaliforniaandItaly.However,steamreservoirsarerareandhavealreadybeenexploited,atleastinthedevelopedcountries.Ofgreaterpotentialinbothdevelopedanddevelopingcountriesaregeothermal-hot-water,orliquid-dominatedhydrothermal,resources.Anumberofhydrothermalplants,perhaps30to40,bothdevelopmentalandcommercial,havebeenbuiltandareinoperation.Someuseconventionalsteam-separationandsteam-cyclepower-plantequipment,whileothersemployabinarycyclethattakesadvantageofworkingfluidswithlowervaporizationtemperaturesthanwater.Commercialattractivenessdependslargelyonthequalityofthehydrothermalresource:temperatureofthehotwater,permeabilityoftherockformation,chemistryofthehotwater,andnecessarydrillingdepth.Toascertainthisquality,wellsneedtobedrilled.Sincetheoutcomeisnotassuredpriortodrilling,locatingsuitableresourcespresentsamajorcommercialrisk.Anothergeothermal-powerapproachisintheresearchstage.Thisinvolvesdrillingdeepholes(one-to-fivekilometers)toreachhotdryrockthatisclosetolocationswheremagmaorotherhotintrusionsfromthemoltenmantleoftheEarthcomeunusuallyclosetothesurface.Inthiscontext,“dry”rockimpliesthatnonaturalwatersourceisassociatedwiththehotrock,unlikethesituationinthehydrothermalcase.Waterfromasurfacesourcewouldbeinjected,heated,usedinasteam-orbinary-powercycle,andthenre-injectedforrecycling.Ifsuccessful,thisapproachcouldmakeavailableahugeresourcerelativetopresentgeothermalresources.However,technicaluncertaintiesandrisksareveryhigh,sothecommercialpotentialofthisapproachcannotbeestimatedaccuratelytoday.Photovoltaics:Photovoltaicpowersystemsconvertsunlightdirectlyintoelectricitythroughasolid-state-electronicprocessthatinvolvesnomovingparts,nofluids,nonoiseandnoemissionsofanykind.Thesefeaturesareattractivefromoperating,maintenanceandenvironmentalstandpoints,andhavepositionedphotovoltaicstobethepreferredpowertechnologyformanyremoteapplicationsbothinspaceandontheground.Relativetoconventionalgridpower,photovoltaicelectricityissomefive-to-ten-timesmoreexpensive.Hence,itiscurrentlyusedinlocationsorapplicationswhereutilitydistributionlinesarenotreadilyavailable.Newer,potentiallylower-costphotovoltaicntechnologyisemergingfromongoingindustry-governmentresearchanddevelopmentprograms,anditsuseincommercialanddemonstrationapplicationsisbeginning.Althoughincreasingusecouldoccurmorerapidlyinsomedevelopingcountries,grid-competitivephotovoltaicelectricityisprobablyten-to-twentyyearsoffinthedevelopedworld.However,interestisgrowinginanewmodeofphotovoltaicdeployment,calledbuilding-integrated,wherethephotovoltaiccellsormodulesbecomeintegraltostructural,protectiveorcosmeticelementsofabuildingsuchasroofsandfacades.Intheseapplications,thehighcostofthephotovoltaiccomponentsispartiallymaskedbythecostofthebuildingelements,andthedecisiontoemployphotovoltaicsismadeonthebasisofsuchfactorsasaestheticsandsocialconscienceratherthancostofelectricityalone.Manybelievethatthiscommercialentrystrategywillultimatelysucceedinreducingphotovoltaiccoststhroughproductionexperiencetothepointwheretheycanapproachcostsofgridpower.Severalgovernmentsandmanycommunitiesinthedevelopedworldareincentivizingtheseapplicationsbasedonthisbelief.Becauseofthegrowingprominenceofbuilding-integratedandotheron-siteapplicationsofphotovoltaics,asectiononresidentialrooftopphotovoltaicsystemsisincludedinthisdocument.Anotherapproachtopowerplantsemployingphotovoltaicsusesconcentratedsunlightinconjunctionwithunusuallyhigh-performancephotovoltaiccells.Whileattractivetechnicalperformancehasbeendemonstratedinsomeinstances,anearlymarketforthesesystemshasnotmaterialized.Unlikeflat-platephotovoltaicsystemsthathaveestablishedthemselvesinremotepowerapplications,thepotentiallyhigh-performanceconcentratorsystemshavenotyetestablishedatrackrecordinthefield.This,coupledwiththeneedtobuildrelativelylargesystems(atleastseveraltensofkW)torealizetheircostadvantageandtheaddedcomplexityassociatedwithrequiredsunlighttracking,hasseriouslyhamperedmarketentryuptonow.SolarThermal:Solarthermalpowersystemsuseconcentratedsunlighttoheataworkingfluidthatgenerateselectricityinathermodynamiccycle.Threegeneralapproacheshavereceiveddevelopmentattention.Thefirst,calledthecentralreceiverorpower-towerconfiguration,employsafieldofmirrorsthattrackthesunandreflectsunlighttoacentralreceiveratopatower.Theworkingfluidiscirculatedthroughandheatedinthereceiver,andisthenusedtodriveaconventionalturbine.Thefluidanditsthermalenergycanbestoredtodecouplethecollectionofthesolarenergyandthegenerationofelectricity,enablingthispowerplanttobedispatchedmuchlikeconventionalthermalpowerplants.Thisisanattractivefeaturetoelectricutilitiesandpowersystemmanagers.Severalexperimentalanddemonstrationpower-towersystemshavebeenbuilt;andone,employingthermalstorage,iscurrentlyundertestandevaluationinCalifornia.Asyet,thecommercialprospectsforthisapproachcannotbeaccuratelyprojected.Anotherapproachemploysparabolicdishes,eitherassingleunitsorinfields,thattrackthesun.Areceiverisplacedatthefocalpointofthedishtocollecttheconcentratedsolarenergyandheatthesystem’sworkingfluid.Thatfluidthendrivesanengineattachedtothereceiver.Dishsystemsalsohavepotentialforhybridization,althoughmoredevelopmentalworkisrequiredtorealizethispotential.Incontrasttotheothertwoapproaches,whicharetargetedatplantsinthe30MWandhigherrange,andwhichuseasingleturbine-generatorfedbyallofthesolarcollectors,eachdish-receiver-engineunitisaself-containedelectricity-generatingsystem.Typically,thesearesizedatabout10to30kW.Hence,alargerpowerplantisobtainedbyemployinganumberoftheseunitsinconcert.Withsomeinterruptionsduetochangingmarketconditions,dishsystemsusingStirlingengineshavebeendeployed,withbothpublicandprivatesupport,forexperimentalanddemonstrationpurposessincetheearly1980s.Currentdevelopmentanddemonstrationactivitiesareaimedatkeytechnicalandeconomicissuesthatneedtoberesolvedbeforecommercialprospectscanbeclarified.Stirling-enginedevelopmentforprospectivevehicularapplicationsisalsounderway.Ifsuccessful,transportationsectormarketpenetrationwouldsubstantiallyimprovethecommercialoutlookforsolardish-Stirlingsystems.Thethirdapproachemploysafieldofsunlight-trackingparabolictroughsthatfocussunlightontothelinearaxisofthetrough.Aglassormetallinearreceiverisplacedalongthisaxis,andaworkingfluidiscirculatedthroughandheatedinthisreceiver.Thefluidfromafieldoftroughspassesthroughacentrallocationwherethermalenergyisextractedviaaheatexchangerandthenusedtodriveaconventionalturbine.Thisconfigurationlendsitselfwelltohybridoperationwithfossilfuelcombustionasasupplementalsourceofthermalenergy.Intheearly1980s,federalandCalifornia-statefinancialincentiveswereestablishedtoencouragethecommercialdeploymentanduseofemergingrenewables.Twotechnologieswereinapositiontobenefitfromtheseincentives:solarthermaltroughsandwindturbines.Troughsystemsweredeployedonacommercialbasisinthe1980sandearly1990s,andcontinuetooperatetoday.Inadditiontothegovernment-tax-creditincentives,theseplantswerepartiallysupportedbyabove-marketenergypaymentsthatarenolongeravailable.Hencetroughsystemshavenotbeenofferedcommerciallysince1991.Shouldconventionalenergycostsrisetotheabove-marketsupportlevelsofthelate1980s(whensignificantincreasesinoilpriceswerebeingprojected),orshouldsignificantincentivesforrenewableenergyariseinthenearfuture,troughtechnologywouldbeavailabletoplayanimportantroleinareaswithgoodsunlight.Inaddition,effortsareunderwaytorevivethistechnologyforuseindevelopingcountriesthathaveurgentneedsfornewelectricpowersources,suchasIndiaandMexico.Althoughthesolar-thermaltrough(andwind)systemsfieldedintheearly1980sexperiencedconsiderabletechnicaldifficulties,theoverallresultofthedeploymentsofthe1980sandtheassociatedexperienceandtechnicaldevelopmentwasthatbothtroughsystemsandwindsystems(seewinddiscussionbelow)hadachievedtechnicalandcommercialcredibilitybytheearly1990s.Energycostsfromthesesystemswereapproachingthecompetitiverangeforgridpower.Trough-energycostsweresomewhathigherthanwind-energycosts;but,owingtohybridizationwithnaturalgas,thetroughplantsweredispatchable.Hencetheirenergyhadhighervalueinsomeinstances.Windenergy,incontrast,wasavailableonlywhenthewindblew.Wind:Asmentionedabove,windpowersystemsprogressedsubstantiallyasaresultofthe1980sgovernmentincentives,withasteadytrendofcostreductionsthroughoutthe1980s.Since1990,thecostofenergyfromthewindhascontinuedtodecline,duetocontinueddeploymentandtopublic-privatedevelopmentprogramsintheU.S.and,toanevengreaterextent,inEurope.Windpowerisnowonthevergeofbecomingacommerciallyestablishedandcompetitivegrid-powertechnology.AlthoughexpansionoftheU.S.windmarkethasbeenslowedsincetheonsetofelectric-sectorrestructuringin1995,thewindmarketsinEuropeandelsewhereintheworldhavecontinuedtogrow,ledbyfirmsinDenmarkandGermany.ThegrowthofwindinEuropehasbeenfueled,inpart,byaggressivegoalsforrenewablepowerdeploymentinresponsetostrongpublicandpoliticalsupportforcleanenergyandgrowingconcernoverglobalclimatechange.AndtherearesignsthatthepaceofwinddeploymentintheU.S.isagainontherise.WiththeexceptionoftheSoutheast,mostregionsoftheU.S.havecommerciallyattractivewinds.Inadditiontowindresourcequality,otherissuesthatneedtobeconsidered,aswithmostcommercialpowerplants,aretransmissionrequirementsandpotentialenvironmentalimpacts.MostU.S.windfacilitiesinstalledtodatearewindfarmswithmanyturbinesinterconnectedtotheutilitytransmissiongridthroughadedicatedsubstation.Thereisgrowinginterestindistributedwindfacilities,withasmallnumberofturbinesconnecteddirectlytotheutilitydistributionsystemwithoutasubstation.Suchinstallationsaccountformorethanhalfoftheover4,000MWofwindinEurope,buttheU.S.todatehaslittleexperiencewiththismode.Hencethisdocumentfocusesoncentral-stationwindapplications.Thegreatmajorityofwindpowerexperiencehasbeenobtainedwiththetraditionalwindturbineconfiguration,inwhichtherotorrevolvesaboutahorizontalaxis.Inaddition,severaldevelopmentprogramsoft