风能英文简介.doc

风能英文简介.doc

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Windpower

Windpoweristheconversionofwindenergyintoausefulformofenergy,suchasusingwindturbinestomakeelectricity,windmillsformechanicalpower,windpumpsforpumpingwaterordrainage,orsailstopropelships.

Attheendof2009,worldwidenameplatecapacityofwind-poweredgeneratorswas159.2gigawatts（GW）.（ByJune2010thecapacityhadrisento175 GW.）Energyproductionwas340TWh,whichisabout2%ofworldwideelectricityusage;andhasdoubledinthepastthreeyears.Severalcountrieshaveachievedrelativelyhighlevelsofwindpowerpenetration,suchas20%ofstationaryelectricityproductioninDenmark,14%inIrelandandPortugal,11%inSpain,and8%inGermanyin2009.AsofMay2009,80countriesaroundtheworldareusingwindpoweronacommercialbasis.

Windpower:

worldwideinstalledcapacity1996-2008

Large-scalewindfarmsareconnectedtotheelectricpowertransmissionnetwork;smallerfacilitiesareusedtoprovideelectricitytoisolatedlocations.Utilitycompaniesincreasinglybuybacksurpluselectricityproducedbysmalldomesticturbines.Windenergy,asanalternativetofossilfuels,isplentiful,renewable,widelydistributed,clean,andproducesnogreenhousegasemissionsduringoperation.However,theconstructionofwindfarmsisnotuniversallywelcomedbecauseoftheirvisualimpactbutanyeffectsontheenvironmentaregenerallyamongtheleastproblematicofanypowersource.

Theintermittencyofwindseldomcreatesproblemswhenusingwindpowertosupplyalowproportionoftotaldemand,butastheproportionrises,increasedcosts,aneedtoupgradethegrid,andaloweredabilitytosupplantconventionalproductionmayoccur.Powermanagementtechniquessuchasexportingandimportingpowertoneighboringareasorreducingdemandwhenwindproductionislow,canmitigatetheseproblems.

BurboBankOffshoreWindFarm,attheentrancetotheRiverMerseyinNorthWestEngland.

History

Humanshavebeenusingwindpowerforatleast5,500yearstopropelsailboatsandsailingships.Windmillshavebeenusedforirrigationpumpingandformillinggrainsincethe7thcenturyADinwhatisnowAfghanistan,India,IranandPakistan.

IntheUnitedStates,thedevelopmentofthe"water-pumpingwindmill"wasthemajorfactorinallowingthefarmingandranchingofvastareasotherwisedevoidofreadilyaccessiblewater.Windpumpscontributedtotheexpansionofrailtransportsystemsthroughouttheworld,bypumpingwaterfromwaterwellsforthesteamlocomotives.Themulti-bladedwindturbineatopalatticetowermadeofwoodorsteelwas,formanyyears,afixtureofthelandscapethroughoutruralAmerica.Whenfittedwithgeneratorsandbatterybanks,smallwindmachinesprovidedelectricitytoisolatedfarms.

Medievaldepictionofawindmill

InJuly1887,aScottishacademic,ProfessorJamesBlyth,undertookwindpowerexperimentsthatculminatedinaUKpatentin1891.IntheUnitedStates,CharlesF.Brushproducedelectricityusingawindpoweredmachine,startinginthewinterof1887-1888,whichpoweredhishomeandlaboratoryuntilabout1900.Inthe1890s,theDanishscientistandinventorPoullaCourconstructedwindturbinestogenerateelectricity,whichwasthenusedtoproducehydrogen.Thesewerethefirstofwhatwastobecomethemodernformofwindturbine.

Smallwindturbinesforlightingofisolatedruralbuildingswerewidespreadinthefirstpartofthe20thcentury.LargerunitsintendedforconnectiontoadistributionnetworkweretriedatseverallocationsincludingBalaklavaUSSRin1931andina1.25megawatt（MW）experimentalunitinVermontin1941.

Themodernwindpowerindustrybeganin1979withtheserialproductionofwindturbinesbyDanishmanufacturersKuriant,Vestas,Nordtank,andBonus.Theseearlyturbinesweresmallbytoday'sstandards,withcapacitiesof20–30 kWeach.Sincethen,theyhaveincreasedgreatlyinsize,withtheEnerconE-126capableofdeliveringupto7MW,whilewindturbineproductionhasexpandedtomanycountries.

Windmillsaretypicallyinstalledinfavourablewindylocations.Intheimage,windpowergeneratorsinSpainnearanOsbornebull

Windenergy

TheEarthisunevenlyheatedbythesun,suchthatthepolesreceivelessenergyfromthesunthantheequator;alongwiththis,drylandheatsup（andcoolsdown）morequicklythantheseasdo.ThedifferentialheatingdrivesaglobalatmosphericconvectionsystemreachingfromtheEarth'ssurfacetothestratospherewhichactsasavirtualceiling.Mostoftheenergystoredinthesewindmovementscanbefoundathighaltitudeswherecontinuouswindspeedsofover160 km/h（99 mph）occur.Eventually,thewindenergyisconvertedthroughfrictionintodiffuseheatthroughouttheEarth'ssurfaceandtheatmosphere.

Thetotalamountofeconomicallyextractablepoweravailablefromthewindisconsiderablymorethanpresenthumanpowerusefromallsources.Themostcomprehensivestudyasof2005foundthepotentialofwindpoweronlandandnear-shoretobe72 TW,equivalentto54,000MToE（milliontonsofoilequivalent）peryear,oroverfivetimestheworld'scurrentenergyuseinallforms.Thepotentialtakesintoaccountonlylocationswithmeanannualwindspeeds ≥6.9 m/sat80m.Thestudyassumessix1.5megawatt,77mdiameterturbinespersquarekilometeronroughly13%ofthetotalgloballandarea（thoughthatlandwouldalsobeavailableforothercompatibleusessuchasfarming）.Theauthorsacknowledgethatmanypracticalbarrierswouldneedtobeovercometoreachthistheoreticalcapacity.

MapofavailablewindpowerfortheUnitedStates.Colorcodesindicatewindpowerdensityclass

Thepracticallimittoexploitationofwindpowerwillbesetbyeconomicandenvironmentalfactors,sincetheresourceavailableisfarlargerthananypracticalmeanstodevelopit.

Distributionofwindspeed

Thestrengthofwindvaries,andanaveragevalueforagivenlocationdoesnotaloneindicatetheamountofenergyawindturbinecouldproducethere.Toassessthefrequencyofwindspeedsataparticularlocation,aprobabilitydistributionfunctionisoftenfittotheobserveddata.Differentlocationswillhavedifferentwindspeeddistributions.TheWeibullmodelcloselymirrorstheactualdistributionofhourlywindspeedsatmanylocations.TheWeibullfactorisoftencloseto2andthereforeaRayleighdistributioncanbeusedasalessaccurate,butsimplermodel.

Distributionofwindspeed（red）andenergy（blue）forallof2002attheLeeRanchfacilityinColorado.Thehistogramshowsmeasureddata,whilethecurveistheRayleighmodeldistributionforthesameaveragewindspeed

Becausesomuchpowerisgeneratedbyhigherwindspeed,muchoftheenergycomesinshortbursts.The2002LeeRanchsampleistelling;halfoftheenergyavailablearrivedinjust15%oftheoperatingtime.Theconsequenceisthatwindenergyfromaparticularturbineorwindfarmdoesnothaveasconsistentanoutputasfuel-firedpowerplants.

Electricitygeneration

Inawindfarm,individualturbinesareinterconnectedwithamediumvoltage（often34.5kV）,powercollectionsystemandcommunicationsnetwork.Atasubstation,thismedium-voltageelectriccurrentisincreasedinvoltagewithatransformerforconnectiontothehighvoltageelectricpowertransmissionsystem.

Typicalcomponentsofawindturbine（gearbox,rotorshaftandbrakeassembly）beingliftedintoposition

Thesurpluspowerproducedbydomesticmicrogeneratorscan,insomejurisdictions,befedintothenetworkandsoldtotheutilitycompany,producingaretailcreditforthemicrogenerators'ownerstooffsettheirenergycosts.

Gridmanagement

Inductiongenerators,oftenusedforwindpower,requirereactivepowerforexcitationsosubstationsusedinwind-powercollectionsystemsincludesubstantialcapacitorbanksforpowerfactorcorrection.Differenttypesofwindturbinegeneratorsbehavedifferentlyduringtransmissiongriddisturbances,soextensivemodellingofthedynamicelectromechanicalcharacteristicsofanewwindfarmisrequiredbytransmissionsystemoperatorstoensurepredictablestablebehaviourduringsystemfaults（see:

Lowvoltageridethrough）.Inparticular,inductiongeneratorscannotsupportthesystemvoltageduringfaults,unlikesteamorhydroturbine-drivensynchronousgenerators.Doubly-fedmachinesgenerallyhavemoredesirablepropertiesforgridinterconnection.Transmissionsystemsoperatorswillsupplyawindfarmdeveloperwithagridcodetospecifytherequirementsforinterconnectiontothetransmissiongrid.Thiswillincludepowerfactor,constancyoffrequencyanddynamicbehaviorofthewindfarmturbinesduringasystemfault.

Capacityfactor

Sincewindspeedisnotconstant,awindfarm'sannualenergyproductionisneverasmuchasthesumofthegeneratornameplateratingsmultipliedbythetotalhoursinayear.Theratioofactualproductivityinayeartothistheoreticalmaximumiscalledthecapacityfactor.Typicalcapacityfactorsare20–40%,withvaluesattheupperendoftherangeinparticularlyfavourablesites.Forexample,a1 MWturbinewithacapacityfactorof35%willnotproduce8,760 MW·hinayear（1×24×365）,butonly1×0.35×24×365 = 3,066 MW·h,averagingto0.35 MW.Onlinedataisavailableforsomelocationsandthecapacityfactorcanbecalculatedfromtheyearlyoutput.

Unlikefueledgeneratingplants,thecapacityfactorislimitedbytheinherentpropertiesofwind.Capacityfactorsofothertypesofpowerplantarebasedmostlyonfuelcost,withasmallamountofdowntimeformaintenance.Nuclearplantshavelowincrementalfuelcost,andsoarerunatfulloutputandachievea90%capacityfactor.Plantswithhigherfu