Thetidephenomenoniscausedbythechangeofthemoon'sgravity.Thetidecausesthesealeveltoriseandfallperiodically.Theenergyproducedbytheriseandfallofseawaterandtheflowoftidalwateriscalledtidalenergy.Thisenergyiseternal,pollution-freeenergy.Theenergyoftidalenergyisproportionaltothetidalvolumeandtidalrange,orinotherwords,proportionaltothesquareofthetidalrangeandtheareaofthereservoir.Comparedwithhydroelectricpowergeneration,theenergydensityoftidalenergyisverylow,whichisequivalenttothelevelofmicro-hydroelectricpower.
Application
Thereishugeenergyintheoceantides.Intheprocessofhightide,thesurgingseawaterhasgreatkineticenergy,andasthewaterlevelofthesearises,thegreatkineticenergyoftheseawaterisconvertedintopotentialenergy;duringtheebbtide,theseawaterrushesaway,andthewaterlevelgraduallydecreases.,Thepotentialenergyistransformedintokineticenergy.Thelargestvalueoftidalrangeintheworldisabout13-15m,butgenerallyspeaking,theaveragetidalrangeabove3mhaspracticalapplicationvalue.Tidalenergyvariesfromplacetoplace.Differentareasoftenhavedifferenttidalsystems.Theyallobtainenergyfromdeep-seatides,buttheyhavetheirownuniquecharacteristics.Althoughthetidesarecomplicated,thetidesinanyplacecanbeaccuratelyforecasted.Themainwaytousetidalenergyistogenerateelectricity.Tidalpowergenerationistheuseoffavorableterrainsuchasbaysandestuariestobuildwaterdikesandformreservoirstofacilitatetheaccumulationofalargeamountofseawater,andbuildhydropowerplantsinornearthedamtogenerateelectricitythroughhydroelectricgeneratorsets.Itisonlypossibletoextractenergyfromthetidewhenthereisalargetide,whentheenergyisconcentrated,andwherethegeographicalconditionsaresuitablefortheconstructionofatidalpowerstation.Althoughsuchplacesarenotavailableeverywhere,countriesaroundtheworldhaveselectedaconsiderablenumberofsitessuitableforthedevelopmentoftidalpowerstations.
Significance
ThedevelopmentofnewenergysourcesliketidalenergycanindirectlyslowdowntheincreaseinCO2contentintheatmosphere.Tidesareaworldwidephenomenonofperiodicchangesinsealevel.Duetotheactionofthetwosourcesofuniversalgravitation,themoonandthesun,thesealevelrisesandfallstwiceadayandnight.Asanaturalphenomenon,tidesprovideconvenienceforhumannavigation,fishingandsaltdrying.Whatismoreworthpointingoutisthatitcanalsobetransformedintoelectricity,bringinglightandpowertopeople.
Source
Tidalenergyistheenergyproducedbytidalphenomena.Itisrelatedtothegravitationofcelestialbodies.Theattractionandheatoftheearth-moon-sunsystemarethesourcesoftidalenergy.
Formationmethod
Tidalenergyiscausedbythetidalforceofthesunandthemoontocauseperiodicmovementsandchangesintheearth’slithosphere,hydrosphereandatmosphere,respectively.Collectively.Theelastic-plasticdeformationofthesolidearthcausedbythetidalforceofthesunandthemooniscalledsolidtidalenergy.
Asacompletetidalscience,theresearchobjectshouldbetheearthtide,oceantideandairtideasaunifiedwhole,butbecausetheoceantidephenomenonisveryobvious,anditisrelatedtopeople'slife,economicactivities,transportation,etc.Therefore,itiscustomarytonarrowlyunderstandthetermtidalenergyasoceantide.
Phenomenon
Thedifferencebetweenthereallunargravityandtheaveragegravityiscalledtheinterferenceforce.Thehorizontalcomponentoftheinterferenceforceforcestheseawatertomovetothelinebetweentheearthandthemoonandproducewaterpeaks.Thewaterpeakcorrespondingtotheclimaxoccurstwiceevery24hoursand50minutes(thatis,thetimeittakesfortheearthtofacethemoonforthefirsttimetothemoonforthesecondtimeatthesamelongitudeoftheearth),thatis,themoonevery12hoursand25minutes.Causestheseatoriseonce,andthiskindofriseiscalledahalf-daytide.
Thetidecausesthesealeveltoriseandfallperiodically.Everymonthwhenthefullmoonand
newmoon,thesun,theearthandthemoonarearrangedinastraightline.Atthistime,duetothecumulativegravitationalactionofthesunandthemoon,thegeneratedtideishigherthanusual.Thiskindoftideiscalledthespringtide.Whentheearth,themoon,theearth,andthesunareatrightangles,thegravitationalforcescanceleachotherout,andtheresultinglowtideisaneaptide.Theaveragetidaldistancevariesfromplacetoplace.Forexample,thecoastlineofsomeareaswillcauseresonancetoincreasethetidaldistance,whilethecoastlineofotherareaswillreducethetidaldistance.TheCoriolisforce,anotherfactoraffectingthetidaldistance,originatesfromtheconservationofangularmomentumoffluidflow.Iftheoceancurrentflowsnorthwardinthenorthernhemisphere,itmovesclosetotheaxisoftheearth,sotheangularvelocityincreases.Therefore,theoceancurrentwillbebiasedtowardstheeast,thatis,theseawaterontheeasterncoastishigher;similarly,iftheoceancurrentinthenorthernhemisphereflowstothesouth,theseawateronthewesterncoastishigher.
Principleofpowergeneration
Themainprincipleoftidalpowergenerationistousethekineticenergyofhorizontalflowofseawatercausedbythetidalforceofcelestialbodiestoproduceelectricity.
Formsofpowergeneration
Theflowoftidalwaterisdifferentfromtheflowofriverwater.Itchangesdirectioncontinuously.Therearethreeformsoftidalpowergeneration:
Thesinglereservoirone-waypowerstationusesonlyonereservoirandgenerateselectricityonlyduringhightide(orlowtide).TheShashantidalpowerstationinWenlingCity,ZhejiangProvince,mycountryisofthistype.
Singlereservoirtwo-waypowerstationusesonereservoir,butitcangenerateelectricityathightideandlowtide,butitcannotgenerateelectricityatlowtide.ZhenkouTidalPowerStationinDongguanCity,GuangdongProvinceandJiangxiaTidalPowerStationinWenlingCity,ZhejiangProvince,Isthistype.
Shuangkutwo-waypowerstationusestwoadjacentreservoirs,sothatonereservoirenterswaterathightide,andtheotherreservoirdischargeswateratlowtide,sothatthewaterleveloftheformerreservoirisalwayshigherthanthatofthelatterreservoir.Thewaterlevelishigh,sotheformeriscalledtheupperreservoirandthelatteriscalledthelowerreservoir.Thewaterturbinegeneratorsetisplacedinthedambetweenthetworeservoirs.Thetworeservoirsalwaysmaintainawaterleveldifference,soitcangenerateelectricityallday.
Conditionsavailable
Therearetwophysicalconditionsthatmustbemettousetidalpowertogenerateelectricity.
First,thetidemustbelarge,atleastafewmeters.
Second,thetopographyofthecoastmustbeabletostorealargeamountofseawaterandbeabletocarryoutcivilworks.
AdvantagesandDisadvantages
Themainmethodoftidalenergyutilizationispowergeneration.Theworkingprincipleoftidalpowergenerationissimilartothatofconventionalhydropowergeneration.Itusesthepotentialenergyofthewaterleveldifferenceproducedbytheriseandfallofthetidetogenerateelectricity.Thedifferenceisthatseawaterisdifferentfromriverwater.Theaccumulatedseawaterhasasmalldrop,buttheflowislargeandintermittent.Therefore,thestructureofthetidalpowerturbineshouldbesuitableforthecharacteristicsoflowheadandlargeflow.Specifically,itistobuilddams,gatesandpowerhousesinthebaysorestuarieswhereconditionspermit,toseparatethebay(orestuary)fromtheopenseatoformareservoir,andtoinstallhydro-turbinegeneratorsinthedamsorpowerhouses.Theperiodicriseandfalloftheoceantidelevelissimilartoasinewave.Acertainheightdifference(ie,workinghead),whichdrivesthehydro-generatorsettogenerateelectricity.Fromanenergypointofview,itistheprocessofconvertingthepotentialandkineticenergyofseawaterintoelectricalenergythroughahydroelectricgeneratorset.CharacteristicsofChina'stidalenergyresources
1)Thereservesareveryconsiderable.
2)ThegeographicaldistributionoftidalenergyresourcesinChinaisveryuneven.Inthecoastaltidalrange,theEastChinaSeaisthelargest,followedbytheYellowSea,andthesouthernBohaiSeaandtheSouthChinaSeaarethesmallest.TheestuarytidalenergyresourcesarethemostabundantintheQiantangRiverestuary,followedbytheYangtzeRiverestuary,followedbythePearlRiver,Jinjiang,MinjiangandOujiangestuary.Intermsofregions,itismainlyconcentratedonthecoastofEastChina,withFujian,Zhejiang,andShanghaiNorthBranchoftheYangtzeRiverbeingthemost,accountingfor88%ofthetidalenergythatcanbedevelopedinChina.
3)Intermsoftopographyandgeology,China’scoastsaremainlyofplaintypeandporttype.Straight,flatterrain,composedofsandorsilt,withsmalltidalrange,andlackofsuperiorharbordamsites;southofHangzhouBay,therearemanyharborcoasts,theterrainissteep,thecoastlineistortuous,theslopeissteep,andthewaterisdeep.Thegulfandcoasthavelargetidalrange,andtherearesuperiorpowergenerationdamsites.However,thecoastsofZhejiangandFujianprovincesaresiltyharbors.Althoughthereareabundanttidalenergyresources,therearegreatdifficultiesindevelopment.Itisnecessarytofocusonsolvingtheproblemofsedimentationinreservoirs.
DevelopmentandUtilization
Tidalenergyisaninexhaustiblerenewableenergythatdoesnotconsumefuel,hasnopollution,isnotaffectedbyfloodsordrywater.Amongthevariousmarineenergysources,thedevelopmentandutilizationoftidalenergyisthemostrealisticandsimplest.Chinabegantousetidalenergyasearlyasthe1950s,andinthisregard,itisanearlycountryintheworld.TheJunbianTidalTurbinePumpingStationinFujianProvince,builtin1956,usestidesasadrivingforcetoraisewaterandirrigatethefields.By1958,tidalpowerstationswerebloomingalloverthecountry.Accordingtostatisticsfromthe"FirstNationalConferenceonTidalPowerGeneration"heldinOctober1958,thereare41tidalpowerstationsthathavebeenbuiltand88areunderconstruction.Theinstalledcapacityrangesfrom144kilowattstoassmallas5kilowatts.Mainlyusedforlightinganddrivingsmallagriculturalfacilities.Forexample,theShashanTidalPowerStationinWenlingCounty,ZhejiangProvince,builtin1959,wasfurtherbuiltasapowerstationin1961withaninstalledcapacityofonly40kilowattsandanannualpowergenerationcapacityof100,000kilowatthours.Thetotalinvestmentintheoriginalconstructionandreconstructionwasonly40,000yuan(RMB,belowsame).Accordingtostatisticsin1986,itscumulativeincomefrompowergenerationhasexceeded10timesitsinvestment.Therearenearly10tidalpowerstationsinoperationinChina.Amongthem,theJiangxiatidalpowerstationinYueqingBay,Zhejiang,hasacostequivalenttoasmallhydropowerstationbelow600kilowatts.Thefirstunitstartedgeneratingelectricityin1980andwasfullycompletedattheendof1985.Theamountcanreach10.7millionkilowatt-hours,andtheelectricitypriceperkilowatt-hourisonly0.067yuan.Itseconomicbenefitseachyearinclude670,000yuaninpowergeneration,740,000yuaninaquacultureand1.9millionyuaninfarmincome,totalingupto3.3millionyuan.Thesocialbenefitcanbeupto50millionyuanbasedonthesocialoutputvalueof5yuanperkilowatt·hourofelectricity.ThisisthelargesttidalpowerstationinChinaandAsia,secondonlytotheLancetidalpowerstationinFranceandtheAnnapolistidalpowerstationinCanada,rankingthirdintheworld.
Tidalenergyisthepotentialenergyoftidalrange.Thebasicmethodofdevelopmentandutilizationissimilartothatofhydropowerstations:firstbuilddikesandsluicesatbaysorestuaries,opensluicestodivertwaterintothereservoirathightide,andreleasewatertodriveatlowtide.Hydro-turbinegeneratorsgenerateelectricity,whichistheso-called"single-storageone-waypowergeneration".Thistypeofpowerstationcanonlygenerateelectricityatlowtide,twiceaday,foramaximumof5hourseachtime.
Inordertoimprovetheutilizationrateoftidesandtrytobeabletogenerateelectricityatbothhightideandlowtide,peopleusecleverloopfacilitiesortwo-waywaterturbines,sothatbothhightideandlowtidecanbeusedtogenerateelectricity.Powergeneration,thisis"single-storagetwo-waypowergeneration",liketheJiangxiatidalpowerstationmentionedaboveisofthistype.
However,neitherofthesetwotypescangenerateelectricitywitharelativelystablevoltagewhenthewaterinthereservoirisdischargedwhenthetideisflat(nowaterleveldifference)orwhenthetideisstopped.Sopeoplecameupwiththeconfigurationoftwodifferenthighandlowreservoirsfortwo-waypowergeneration,whichis"double-storagetwo-waypowergeneration".Thismethodnotonlycancontinuouslygenerateelectricityduringthewholeprocessofrisingandfallingtides,butalsomakesthepoweroutputrelativelystable.Itisespeciallysuitableforthoseisolatedislands,sothattheislandscangetastablepowersupplywithoutinterruptionatanytime.TheHaishantidalpowerstationonMaoluIslandinYuhuanCounty,ZhejiangProvinceisofthistype.Ithastwoupperandlowertidalstoragereservoirs,andisequippedwithasmallpumpedstoragepowerstation.Inthisway,itcangenerateelectricityfor25daysamonthandproduce10,000kilowatt-hoursofelectricity.Inordertopumpwaterandstoreenergy,ithastouse5,000kWhofelectricityatthecostof3kWhfor1kWhpermonthtoobtainthecontinuityandbalanceofpowersupply,sothereisacertainamountofpowerloss.
Fromanoverallpointofview,thecurrenttechnicalproblemsinthedevelopmentandutilizationoftidalenergyhavebeenbasicallysolved.Therearemanysuccessfulexamplesathomeandabroad,andthetechnologyisupdatedveryquickly.
Asasymbolofforeigntechnologicalprogress,theFrenchLancetidalpowerstation,builtin1968,isequippedwith24lightbulbgeneratorsetscapableofforwardandreversepowergeneration,thediameteroftherunneris5.35meters,andtheunitcapacityis110,000kilowatts,withanannualpowergenerationcapacityof540millionkilowatt-hours.TheAnnapolisTidalPowerStationinCanada,builtin1984,isequippedwithaone-waywaterturbineunitwiththeworld’slargestcapacityof20,000kilowatts.Therunnerdiameteris7.6meters.Thegeneratorrotorislocatedontheouteredgeoftheturbineblade.Thesealingtechnologyhasfastcoolingandhighefficiency.
Thecostis15%lowerthanthatoftheFrenchbulb-typeunit,andthemaintenanceisalsoveryconvenient.AmongChina'sself-designedtidalpowerstations,JiangxiaPowerStationisrelativelyformalandhasrelativelymaturetechnology.Thepowerstationwasoriginallydesignedtoinstall6bulb-typeunitswithasingleunitcapacityof500kilowatts.Infact,only5unitswereinstalled,andthetotalcapacityreached3,200kilowatts.Thestand-alonecapacityhasthreespecificationsof500kilowatts,600kilowattsand700kilowatts,andthediameteroftherunneris2.5meters.Advancedmethodshavealsoachievedgoodresultsinanti-corrosionofoffshorebuildingsandunits,andpreventionofmarineorganismsfromattaching.Inparticular,thelasttwounitshavereachedtheadvancedforeigntechnologylevel.Theyhavemultiplefunctionsoftwo-waypowergeneration,waterdischargeandpumpingandstorage.Theyuseaplanetarygearspeed-increasingtransmissionmechanismwithhightechnicalcontent,sothatthereisnoneedtoincreasethesizeoftheunit.,Whichincreasesthepowergenerationandreducesthecostofconstruction.
Tidalpowergenerationusesthepotentialenergyoftidalrange.Thehighesttidalrangeintheworldisonlymorethan10meters.Thehydroelectricpowergenerationofmorethanameter,andthewaterturbinegeneratingunitfortidalpowergenerationmustadapttothecharacteristicsof"lowheadandlargeflow",andthewaterwheelismadelarger.However,ifthewaterwheelbecomeslarger,thecostofsupportingfacilitieswillincreaseaccordingly.Therefore,howtosolvethisproblemhasbecomeasignthatreflectsthelevelofitstechnology.GuangdongGanzhutanHongchaoPowerStation,whichwasputintooperationin1974,isasuccessfulrepresentative.Itischaracterizedbybothfloodandtidestorage,aslongasthereisadropof0.3metershigh,itcangenerateelectricity.ThetotalinstalledcapacityoftheGanzhutanPowerStationis5,000kilowatts,withanaverageannualpowergenerationof10.3millionkilowatt-hours.Itsrunnerdiameteris3meters,coupledwiththeuseofalargenumberofcementsubstitutecomponents,thecostislow,anditisofgreatreferenceforprivatesmall-scaletidalpowerstations.
Applicationstatus
Duetothecompetitionoflow-costelectricityfromconventionalpowerstations,fewcommercialtidalpowerstationshavebeenbuiltandputintooperation.However,duetothehugetidalenergyreservesandthemanyadvantagesoftidalpowergeneration,peoplestillattachgreatimportancetotheresearchandtestingoftidalpowergeneration.
Accordingtooceanographers’calculations,theworld’stidalenergyresourcesaremorethan1billionkilowatts,whichisalsoanastronomicalfigure.Thetidalenergycensuscalculationmethodistofirstselectthesitesuitablefortheconstructionoftidalpowerstations,andthencalculatethepowergenerationcapacitythatcanbedevelopedatthesesites,andadduptotheestimatedamountofresources.
Atthebeginningofthe20thcentury,somecountriesinEuropeandtheUnitedStatesbegantostudytidalpowergeneration.ThefirsttidalpowerstationwithcommercialutilityvaluewastheFrenchLancepowerstationbuiltin1967.ThepowerstationislocatedatthemouthoftheLanceRiverinSaint-MaloBay,France.ThelargesttidalrangeatthemouthoftheLangsRiveris13.4meters,andtheaveragetidalrangeis8meters.A750-meter-longdamstraddlestheRanceRiver.Abovethedamisahighwaybridgeforvehicles,andunderthedamisashiplock,asluicegateandageneratorroom.Thereare24two-wayturbinegeneratorsinstalledinthemachineroomofLanceTidalPowerStation,whichcangenerateelectricityatbothhightideandlowtide.Thetotalinstalledcapacityis240,000kilowatts,andtheannualpowergenerationismorethan500millionkWh,whichisinputintothenationalgrid.
In1968,theformerSovietUnionbuiltan800-kilowatttesttidalpowerstationinKislayaBaynearMurmanskinthenorth.In1980,Canadabuiltanintermediatetesttidalpowerstationwithacapacityof20,000GWintheBayofFundy.Thepilotpowerstationandthepilotpowerstationareusedfordemonstrationandpreparationfortheconstructionofalargerpracticalpowerstation.Morethan20placesintheworldsuitablefortheconstructionoftidalpowerstationsareallresearching,designingandconstructingtidalpowerstations.Theseinclude:CookBayinAlaska,UnitedStates,BayofFundyinCanada,SevernEstuaryintheUnitedKingdom,SanJoseBayinArgentina,DarwinVanDimenBayinAustralia,CambayEstuaryinIndia,OkhotskHaipinBayintheRussianFarEast,SouthKoreaIncheonBayandotherplaces.Withtechnologicalprogress,thecostoftidalpowergenerationcontinuestodecrease.Inthe21stcentury,large-scalemoderntidalpowerstationswillcontinuetobebuiltandused.
ThetheoreticalreservesoftidalenergyinChinahavereached110millionkilowatts.TherearemanyhighenergydensitiesalongthecoastofChina,especiallythesoutheastcoast,withanaveragetidalrangeof4-5mandamaximumtidalrangeof7-8m.Amongthem,ZhejiangandFujianhavethelargestreserves,accountingforabout80.9%ofthecountry'stotal.mycountry'sJiangxiaTidalExperimentalPowerStation,builtinJiangxiaPortonthenorthsideofYueqingBayinZhejiangProvince,withaninstalledcapacityof3,200kW,wasofficiallyputintooperationin1980.
China’shydropowerreservesamountto680millionkW,accountingforabout1/6oftheworld,rankingfirstintheworld.Aftercompletion,theThreeGorgesHydropowerStationontheYangtzeRiverwillbetheworld’slargesthydropowerstationwithinstalledcapacityThecapacityis18.2millionkW.
Thefirstgrid-connectedtidalenergyprojectintheUnitedStatesisputintooperation.TheprojectislocatedintheBayofFundybetweenMaineandCanada.Therearehundredsofbillionsoftonsofwaterflowingthroughiteveryday,formingabout15meters.Highwavescanbring5884kilowattsofelectricity.Theprojectwillbecompletedinseveralphasesandwilleventuallyreachapowergenerationcapacityof4megawatts,whichcanbeusedby1,000householdsandcommercialorganizations.
Thefirstphaseoftheprojectwasofficiallyconnectedtothegridlastweek.Thedailypowergenerationcapacityis180kilowatts,whichisenoughtomeettheneedsof25to30households.Butsofar,ithasnotreallycontributedonekilowatt-hourofelectricitytothegridbecauseofinsufficientgovernmentsupport.TheEuropeangovernment'sstablepolicypreferencesandsubsidieshavegiventheEuropeanoceanenergyindustryafirmfoothold.
ThistidalenergyprojectinMaineisnotthefirsttidalenergyprojectinNorthAmerica(thefirstwasthetidalenergypowerstationinNovaScotia,Canadain1984),butitwasItisthefirsttidalenergygeneratorsetwithoutadam,sothatitwillbasicallynotaffectthenormallifeofmarinelife.