风能英文简介Word格式.doc
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风能英文简介Word格式.doc
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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×
365
=
3,066
h,averagingto0.35
MW.Onlinedataisavailableforsomelocationsandthecapacityfactorcanbecalculatedfromtheyearlyoutput.
Unlikefueledgeneratingplants,thecapacityfactorislimitedbytheinherentpropertiesofwind.Capacityfactorsofothertypesofpowerplantarebasedmostlyonfuelcost,withasmallamountofdowntimeformaintenance.Nuclearplantshavelowincrementalfuelcost,andsoarerunatfulloutputandachievea90%capacityfactor.Plantswithhigherfu
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