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1、WindEnergy-EnergyfromMovingAirWindissimpleairinmotion.Itiscausedbytheunevenheatingoftheearthsurfacebythesun.Sincetheearthsurfaceismadeofverydifferenttypesoflandandwater,itabsorbsthesunheatatdifferentrates.Duringtheday,theairabovethelandheatsupmorequicklythantheairoverwater.Thewarmairoverthelandexpan
2、dsandrises,andtheheavier,coolerairrushesintotakeitsplace,creatingwinds.Atnight,thewindsarereversedbecausetheaircoolsmorerapidlyoverlandthanoverwater.Inthesameway,thelargeatmosphericwindsthatcircletheeartharecreatedbecausethelandneartheearth,sequatorisheatedmorebythesunthanthelandneartheNorthandSouth
3、Poles.Today,windenergyismainlyusedtogenerateelectricity.Windiscalledarenewableenergysourcebecausethewindwillblowaslongasthesunshines.TheHistoryofWindSinceancienttimes,peoplehaveharnessedthewindsenergy.Over5,000yearsago,theancientEgyptiansusedwindtosailshipsontheNileRiver.Later,peoplebuiltwindmillsto
4、grindwheatandothergrains.TheearliestknownwindmillswereinPersia(Iran).Theseearlywindmillslookedlikelargepaddlewheels.Centurieslater,thepeopleofHollandimprovedthebasicdesignofthewindmill.Theygaveitpropeller-typeblades,stillmadewithsails.Hollandisfamousforitswindmills.Americancolonistsusedwindmillstogr
5、indwheatandcorn,topumpwater,andtocutwoodatsawmills.Aslateasthe1920s,Americansusedsmallwindmillstogenerateelectricityinruralareaswithoutelectricservice.Whenpowerlinesbegantotransportelectricitytoruralareasinthe1930s,localwindmillswereusedlessandless,thoughtheycanstillbeseenonsomeWesternranches.Theoil
6、shortagesofthe1970schangedtheenergypictureforthecountryandtheworld.Itcreatedaninterestinalternativeenergysources,pavingthewayforthere-entryofthewindmilltogenerateelectricity.Intheearly1980swindenergyreallytookoffinCalifornia,partlybecauseofstatepoliciesthatencouragedrenewableenergysources.Supportfor
7、winddevelopmenthassincespreadtootherstates,butCaliforniastillproducesmorethantwiceasmuchwindenergyasanyotherstate.ThefirstoffshorewindparkintheUnitedStatesisplannedforanareaoffthecoastofCapeCod,Massachusetts(readanarticleabouttheCapeCodWindProject).HowWindMachinesWorkLikeoldfashionedwindmills,todayw
8、indmachinesusebladestocollectthewindkineticenergy.Windmillsworkbecausetheyslowdownthespeedofthewind.Thewindflowsovertheairfoilshapedbladescausinglift,liketheeffectonairplanewings,causingthemtoturn.Thebladesareconnectedtoadriveshaftthatturnsanelectricgeneratortoproduceelectricity.Withthenewwindmachin
9、es,thereisstilltheproblemofwhattodowhenthewindisblowing.Atthosetimes,othertypesofpowerplantsmustbeusedtomakeelectricity.WindPowerPlanWindpowerplants,orwindfarmsastheyaresometimescalled,areclustersofwindmachinesusedtoproduceelectricity.Awindfarmusuallyhasdozensofwindmachinesscatteredoveralargearea.Th
10、eBigSpringWindPowerProjectinTexashas46windturbinesthatgenerateenoughelectricitytopower7,3homes.Unlikepowerplants,manywindplantsarenotownedbypublicutilitycompanies.Insteadtheyareownedandoperatedbybusinesspeoplewhoselltheelectricityproducedonthewindfarmtoelectricutilities.Theseprivatecompaniesareknown
11、asIndependentPowerProducers.Operatingawindpowerplantisnotassimpleasjustbuildingawindmillinawindyplace.Windplantownersmustcarefullyplanwheretolocatetheirmachines.Oneimportantthingtoconsiderishowfastandhowmuchthewindblows.Asarule,windspeedincreaseswithaltitudeandoveropenareaswithnowindbreaks.Goodsites
12、forwindplantsarethetopsofsmooth,roundedhills,openplainsorshorelines,andmountaingapsthatproducewindfunneling.Windspeedvariesthroughoutthecountry.Italsovariesfromseasontoseason.InTehachapi,California,thewindblowsmorefromAprilthroughOctoberthanitdoesinthewinter.ThisisbecauseoftheextremeheatingoftheMoja
13、veDesertduringthesummermonths.Thehotairoverthedesertrises,andthecooler,denserairabovethePacificOceanrushesthroughtheTehachapimountainpasstotakeitsplace.InastatelikeMontana,ontheotherhand,thewindblowsmoreduringthewinter.Fortunately,theseseasonalvariationsareagoodmatchfortheelectricitydemandsoftheregi
14、ons.InCalifornia,peopleusemoreelectricityduringthesummerforairconditioners.InMontana,peopleusemoreelectricityduringthewintermonthsforheating.WindProductionAlltogether,windmachinesintheUnitedStatesgenerate17billionkWhperyearofelectricity,enoughtoserve1.6millionhouseholds.Thisisenoughelectricitytopowe
15、racitythesizeofChicago,butitisonlyasmallfractionofthenation,stotalelectricityproduction,about0.4percent.Theamountofelectricitygeneratedfromwindhasbeengrowingfastinrecentyears,triplingsince1998.Newtechnologieshavedecreasedthecostofproducingelectricityfromwind,andgrowthinwindpowerhasbeenencouragedbyta
16、xbreaksforrenewableenergyandgreenpricingprograms.Manyutilitiesaroundthecountryoffergreenpricingoptionsthatallowcustomersthechoicetopaymoreforelectricitythatcomesfromrenewablesources.Windmachinesgenerateelectricityin30differentstates.ThestateswiththemostwindproductionareCalifornia,Texas,Minnesota,Iowa,andWyoming.TheUnitedStatesranksthirdintheworldinwindpowercapacity,behindGermanyandSpain.MostofthewindpowerplantsintheworldarelocatedinEuropeandintheUnit
