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1、GeothermalEnergy(TPO21-1)Earth’sinternalheat,fueledbyradioactivity,providestheenergyforplatetectonics,continentaldrift,mountainbuilding,andearthquakes.Itcanalsobeharnessedtodriveelectricgeneratorsandheathomes.Geothermalenergybecomesavailableinapracticaformwhenunde
2、rgroundheatistransferredbywaterthatisheatedasitpassesthroughasubsurfaceregionofhotrocks(aheatreservoir)thatmaybehundredsorthousandsoffeetdeep.█Thewaterisusuallynaturallyoccurringgroundwaterthatseepsdownalongfracturesintherock;lesstypically,thewaterisartificiallyin
3、troducedbybeingpumpeddownfromthesurface.█Thewaterisbroughttothesurface,asaliquidorsteam,throughholesdrilledforthepurpose.█Byfarthemostabundantformofgeothermalenergyoccursattherelativelylowtemperaturesof80℃to180℃centigrade.█Watercirculatedthroughheatreservoirsinthi
4、stemperaturerangeisabletoextractenoughheattowarmresidential,commercial,andindustrialspaces.Morethan20,000apartmentsinFrancearenowheatedbywarmundergroundwaterdrawnfromaheatreservoirinageologicstructurenearPariscalledtheParisBasin.Icelandsitsonavolcanicstructureknow
5、nastheMid-AtlanticRidge.Reykjavik,thecapitalofIceland,isentirelyheatedbygeothermalenergyderivedfromvolcanicheat.Geothermalreservoirswithtemperaturesabove180℃centigradeareusefulforgeneratingelectricity.Theyoccurprimarilyinregionsofrecentvolcanicactivityashot,dryroc
6、k;naturalhotwater;ornaturalsteam.Thelattertwosourcesarelimitedtothosefewareaswheresurfacewaterseepsdownthroughundergroundfaultsorfracturestoreachdeeprocksheatednéetherecentactivityofmoltenrockmaterial.Theworld’slargestsupplyofnaturalsteamoccursatTheGeysers,120kilo
7、metersnorthofSanFrancisco,California.Inthe1990senoughelectricitytomeetabouthalftheneedsofSanFranciscowasbeinggeneratedthere.Thisfacilitywastheninitsthirddecadeofproductionandwasbeginningtoshowsignsofdecline,perhapsbecauseofoverdevelopment.Bythelate1990ssome70geoth
8、ermalelectric-generatingplantswereinoperationinCalifornia,Utah,Nevada,andHawaii,generatingenoughpowertosupplyaboutamillionpeople.Eighteencountriesnowgen
