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ThermalenergystorageWikipedia,thefreeencyclopedia
Thermalenergystorage
FromWikipedia,thefreeencyclopedia
Thermalenergystorage(TES)isachievedwithgreatly
differingtechnologiesthatcollectivelyaccommodateawide
rangeofneeds.Itallowsexcessthermalenergytobecollected
forlateruse,hours,daysormanymonthslater,atindividual
building,multiuserbuilding,district,townorevenregionalscale
dependingonthespecifictechnology.Asexamples:energy
demandcanbebalancedbetweendaytimeandnighttime
summerheatfromsolarcollectorscanbestoredinterseasonally
foruseinwinterandcoldobtainedfromwinteraircanbe
Districtheatingaccumulationtower
providedforsummerairconditioning.Storagemediumsinclude:
fromTheissnearKremsander
wateroriceslushtanksrangingfromsmalltomassive,masses
DonauinLowerAustriawitha
ofnativeearthorbedrockaccessedwithheatexchangersin
thermalcapacityof2GWh
clustersofsmalldiameterboreholes(sometimesquitedeep)
deepaquiferscontainedbetweenimpermeablestratashallow,
linedpitsfilledwithgravelandwaterandtopinsulatedandeutectic,phasechangematerials.
Othersourcesofthermalenergyforstorageincludeheatorcoldproducedwithheatpumpsfromoff
peak,lowercostelectricpower,apracticecalledpeakshavingheatfromcombinedheatandpower
(CHP)powerplantsheatproducedbyrenewableelectricalenergythatexceedsgriddemandandwaste
heatfromindustrialprocesses.Heatstorage,bothseasonalandshortterm,isconsideredanimportant
meansforcheaplybalancinghighsharesofvariablerenewableelectricityproductionandintegrationof
electricityandheatingsectorsinenergysystemsalmostorcompletelyfedbyrenewableenergy.[1][2][3]
Contents
1 Solarenergystorage
2 Economics
3 Heatstorageintanksorrockcaverns
4 Heatstorageinhotrocks,concrete,pebblesetc
5 Electricthermalstorageheaters
6 Icebasedtechnology
7 Cryogenicenergystorage
8 Moltensalttechnology
9 Pumpedheatelectricitystorage
9.1 Isentropic
10 ElectrolysisofWater
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10 ElectrolysisofWater
11 Othersystems
12 Research
13 Seealso
14 References
15 Externallinks
16 Furtherreading
Solarenergystorage
Mostpracticalactivesolarheatingsystemsprovidestoragefromafewhourstoaday'sworthofenergy
collected.However,thereareagrowingnumberoffacilitiesthatuseseasonalthermalenergystorage
(STES),enablingsolarenergytobestoredinsummerforspaceheatinguseduringwinter.[4][5][6]The
DrakeLandingSolarCommunityinAlberta,Canadahasnowachievedayearround97%solarheating
fraction,aworldrecordmadepossibleonlybyincorporatingSTES.[4][7]
Moltensaltisameansofstoringheatatahightemperature.Thisisacurrentcommercialtechnology
usedinconjunctionwithconcentratedsolarpowerforlateruseinelectricitygeneration,toallowsolar
powertoprovideelectricityonamorecontinuousbasis.Thesemoltensalts(Potassiumnitrate,Calcium
nitrate,Sodiumnitrate,Lithiumnitrate,etc.)havethepropertytoabsorbandstoretheheatenergythatis
releasedtothewater,totransferenergywhenneeded.Toimprovethesaltpropertiesitmustbemixedin
aeutecticmixture.
Theuseofbothlatentheatandsensibleheatarealsopossiblewithhightemperaturesolarthermalinput.
Variouseutecticmixturesofmetals,suchasAluminiumandSilicon(AlSi12)offerahighmeltingpoint
suitedtoefficientsteamgeneration,[8]whilehighaluminacementbasedmaterialsoffergoodthermal
storagecapabilities[9]
Economics
Highpeakloadsdrivethecapitalexpendituresoftheelectricitygenerationindustry.Theindustrymeets
thesepeakloadswithlowefficiencypeakingpowerplants,usuallygasturbines,whichhavelower
capitalcostsand,sincetherecentdropinnaturalgasprices,havelowfuelcostsaswell.Akilowatthour
ofelectricityconsumedatnightcanbeproducedatmuchlowermarginalcost.Utilitieshavebegunto
passtheselowercoststoconsumers,intheformofTimeofUse(TOU)rates,orRealTimePricing
(RTP)Rates.
Heatstorageintanksorrockcaverns
Asteamaccumulatorconsistsofaninsulatedsteelpressuretankcontaininghotwaterandsteamunder
pressure.Asaheatstoragedevice,itisusedtomediateheatproductionbyavariableorsteadysource
fromavariabledemandforheat.Steamaccumulatorsmaytakeonasignificanceforenergystoragein
solarthermalenergyprojects.
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LargestoresarewidelyusedinScandinaviatostoreheatforseveraldays,todecoupleheatandpower
productionandtohelpmeetpeakdemands.Interseasonalstorageincavernshasbeeninvestigatedand
appearstobeeconomical.[10]
Heatstorageinhotrocks,concrete,pebblesetc
WaterhasoneofthehighestthermalcapacitiesHeatcapacity4.2J/(cmK)whereasconcretehasabout
onethirdofthat.Ontheotherhand,concretecanbeheatedtomuchhighertemperatures1200Cby
e.g.electricalheatingandthereforehasamuchhigheroverallvolumetriccapacity.Thusintheexample
below,aninsulatedcubeofabout2.8mwouldappeartoprovidesufficientstorageforasinglehouseto
meet50%ofheatingdemand.Thiscould,inprinciple,beusedtostoresurpluswindorPVheatdueto
theabilityofelectricalheatingtoreachhightemperatures.Attheneighborhoodlevel,the
WiggenhausenSdsolardevelopmentatFriedrichshafenhasreceivedinternationalattention.This
featuresa12,000m(420,000cuft)reinforcedconcretethermalstorelinkedto4,300m(46,000sqft)of
solarcollectors,whichwillsupplythe570houseswitharound50%oftheirheatingandhotwater.[12]
Electricthermalstorageheaters
ThesearecommonplaceinEuropeanhomesandconsistofhighdensityceramicbricksorfeoliteblocks
heatedtoahightemperaturewithelectricity,andwellinsulatedtoreleaseheatoveranumberofhours.
Icebasedtechnology
Airconditioningcanbeprovidedmoreeconomicallybyusingcheaperelectricityatnighttofreezewater
intoice,thenusingthecooloftheiceintheafternoontoreducetheelectricityneededtohandleair
conditioningdemands.Thermalenergystorageusingicemakesuseofthelargeheatoffusionofwater.
Onemetrictonofwater,onecubicmeter,canstore334millionjoules(MJ)or317,000BTUs(93kWh
or26.4tonhours).Infact,icewasoriginallytransportedfrommountainstocitiesforuseasacoolant,
andtheoriginaldefinitionofa"ton"ofcoolingcapacity(heatflow)wastheheattomeltonetonofice
every24hours.Thisistheheatflowonewouldexpectina3,000squarefoot(280m2)houseinBoston
inthesummer.Thisdefinitionhassincebeenreplacedbylessarchaicunits:onetonHVACcapacity=
12,000BTU/hour(~3.5kW).Eitherway,anagreeablysmallstoragefacilitycanholdenoughicetocool
alargebuildingforadayoraweek,whetherthaticeisproducedbyanhydrousammoniachillersor
hauledinbyhorsedrawncarts.
Assuchtherearedevelopinganddevelopedapplicationswhereiceisproducedduringoffpeakperiods
andusedforcoolingatlatertime.
Inadditiontousingiceincoolingapplicationsitisalsobeingusedinheatpumpbasedheatingsystems.
Intheseapplicationsthephasechangeenergyprovidesaverysignificantlayerofthermalcapacitythatis
nearthebottomrangeoftemperaturethatwatersourceheatpumpscanoperatein.Thisallowsthe
systemtorideouttheheaviestheatingloadconditionsandextendsthetimeframebywhichthesource
energyelementscancontributeheatbackintothesystem.
Cryogenicenergystorage
Thisusesliquificationofairornitrogenasanenergystore.
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Apilotcryogenicenergysystemthatusesliquidairastheenergystore,andlowgradewasteheatto
drivethethermalreexpansionoftheair,hasbeenoperatingatapowerstationinSlough,UKsince
2010.[11]
Moltensalttechnology
Moltensaltcanbeemployedasathermalenergystoragemethodtoretainthermalenergycollectedbya
solartowerorsolartroughofaconcentratedsolarpowerplant,sothatitcanbeusedtogenerate
electricityinbadweatheroratnight.ItwasdemonstratedintheSolarTwoprojectfrom19951999.The
systemispredictedtohaveanannualefficiencyof99%,areferencetotheenergyretainedbystoring
heatbeforeturningitintoelectricity,versusconvertingheatdirectlyintoelectricity.[12][13][14]The
moltensaltmixturesvary.Themostextendedmixturecontainssodiumnitrate,potassiumnitrateand
calciumnitrate.Itisnonflammableandnontoxic,andhasalreadybeenusedinthechemicalandmetals
industriesasaheattransportfluid,soexperiencewithsuchsystemsexistsinnonsolarapplications.
Thesaltmeltsat131C(268F).Itiskeptliquidat288C(550F)inaninsulated"cold"storagetank.
Theliquidsaltispumpedthroughpanelsinasolarcollectorwherethefocusedsunheatsitto566C
(1,051F).Itisthensenttoahotstoragetank.Thisissowellinsulatedthatthethermalenergycanbe
usefullystoredforuptoaweek.[15]
Whenelectricityisneeded,thehotsaltispumpedtoaconventionalsteamgeneratortoproduce
superheatedsteamforaturbine/generatorasusedinanyconventionalcoal,oilornuclearpowerplant.A
100megawattturbinewouldneedatankofabout9.1metres(30ft)talland24metres(79ft)indiameter
todriveitforfourhoursbythisdesign.
SeveralparabolictroughpowerplantsinSpain[16]andsolarpowertowerdeveloperSolarReserveuse
thisthermalenergystorageconcept.TheSolanaGeneratingStationintheU.S.has6hoursofstorageby
moltensalt.
Pumpedheatelectricitystorage
Inpumpedheatelectricitystorage(PHES),areversibleheatpumpsystemisusedtostoreenergyasa
temperaturedifferencebetweentwoheatstores.[17][18][19]
Isentropic
OnesystemcurrentlybeingdevelopedbytheUKbasedcompanyIsentropicoperatesasfollows.[20]It
comprisestwoinsulatedcontainersahotvesselstoringthermalenergyathightemperatureandhigh
pressure,andacoldvesselstoringthermalenergyatlowtemperatureandlowpressure.Bothvesselsare
filledwithcrushedrockorgravelwhichactsastheheatstoragemedium.Thevesselsareconnectedat
topandbottombypipesandthewholesystemisfilledwiththeinertgasargon.
Duringthechargingcyclethesystemusessurpluselectricitytoworkasaheatpump.Argonatambient
temperatureandpressurefromthetopofthecoldstoreiscompressedadiabaticallytoapressureof12
bar,heatingittoaround500C(900F).Thecompressedgasistransferredtothetopofthehotvessel
whereitpercolatesdownthroughthegravel,transferringitsheattotherockandcoolingtoambient
temperature.Thecooled,butstillpressurized,gasemergingatthebottomofthevesselisthenexpanded
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(againadiabatically)backdownto1bar,whichlowersitstemperatureto150C.Thecoldgasisthen
passedupthroughthecoldvesselwhereitcoolstherockwhilebeingwarmedbacktoitsinitial
condition.
Theenergyisrecoveredaselectricitybyreversingthecycle.Thehotgasfromthehotvesselis
expandedtodriveageneratorandthensuppliedtothecoldstore.Thecooledgasretrievedfromthe
bottomofthecoldstoreiscompressedwhichheatsthegastoambienttemperature.Thegasisthen
transferredtothebottomofthehotvesseltobereheated.
Thecompressionandexpansionprocessesareprovidedbyaspeciallydesignedreciprocatingmachine
usingslidingvalves.Surplusheatgeneratedbyinefficienciesintheprocessisshedtotheenvironment
throughheatexchangersduringthedischargingcycle.[17][20]
Thedeveloperclaimsthataroundtripefficiencyof7280%isachievable.[17][20]Thiscomparesto>80%
achievablewithpumpedhydroenergystorage.[18]
ElectrolysisofWater
Ithasalsobeensuggestedthataninnovativemethodof'storing'solarenergyistouseelectricity
generatedbyPhotovoltaicpanelstoelectrolysewatertoproducehydrogenfuelthatcanbestoredand
usedtopowercarsandfuelcellsrenewablyandcleanly.[21]
Othersystems
Anotherproposedsystemusesturbomachineryandiscapableofoperatingatmuchhigherpower
levels.[19]
Research
Storingenergyinmolecularbondsisbeinginvestigated.Energydensitiesequivalenttolithiumion
batterieshavebeenachieved.[22]
Seealso
Districtheating
Eutecticsystem
Firelesslocomotive
Heatcapacity
Icestorageairconditioning
Liquidnitrogeneconomy
Listofenergystorageprojects
Phasechangematerial
Pumpableicetechnology
Steamaccumulator
Storageheater
USDOEInternationalEnergyStorageDatabase
References
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1. Jacobsonetal.,Lowcostsolutiontothegridreliabilityproblemwith100%penetrationofintermittentwind,
water,andsolarforallpurposes.In:ProceedingsoftheNationalAcademyofSciences112,No.49,(2015),
1506015065,doi:10.1073/pnas.1510028112(https://dx.doi.org/10.1073%2Fpnas.1510028112).
2. Mathiesenetal,SmartEnergySystemsforcoherent100%renewableenergyandtransportsolutions.In:
AppliedEnergy145,(2015),139154,doi:10.1016/j.apenergy.2015.01.075(https://dx.doi.org/10.1016%2Fj.a
penergy.2015.01.075)
3. Henning,Palzer,AcomprehensivemodelfortheGermanelectricityandheatsectorinafutureenergysystem
withadominantcontributionfromrenewableenergytechnologiesPartI:Methodology.In:Renewableand
SustainableEnergyReviews30,(2014),10031018,doi:10.1016/j.rser.2013.09.012(https://dx.doi.org/10.101
6%2Fj.rser.2013.09.012).
4. WongB.(2011).DrakeLandingSolarCommunity(http://www.districtenergy.org/assets/pdfs/2011Annual_C
onf/Proceedings/A24WONGv03.pdf).PresentationatIDEA/CDEADistrictEnergy/CHP2011Conference.
Toronto,June2629,2011.
5. SunStor4Project,Marstal,Denmark.Thesolardistrictheatingsystem(http://wk.bakuri.dk/filarkiv/solarmars
tal.bakuri.dk/file/del_af_annex_1(1).pdf),whichhasaninterseasonalpitstorage,isbeingexpanded.
6. "ThermalEnergyStorageinThermalBanks".ICAXLtd,London.Retrieved20111121.
7. NaturalResourcesCanada(2012).CanadianSolarCommunitySetsNewWorldRecordforEnergyEfficiency
andInnovation(http://www.nrcan.gc.ca/mediaroom/newsrelease/2012/6586).5Oct2012.
8. ^Khare,SDell'Amico,MKnight,CMcGarry,S."Selectionofmaterialsforhightemperaturelatentheat
energystorage".Solarenergymaterialsandsolarcells,2012.
9. ^Khare,SDell'Amico,MKnight,CMcGarry,S."Selectionofmaterialsforhightemperaturesensibleheat
energystorage".Solarenergymaterialsandsolarcells,2013.
10. ^Gebremedhin,AlemayehuHeimoZinko."SEASONALHEATSTORAGESINDISTRICTHEATING
SYSTEMS"(PDF).LinkpingUniversity,Linkping,Sweden.Archivedfromtheoriginalon20110713.
Retrieved20110713.
11. RogerHarrabin,BBCEnvironmentanalyst(2October2012)."Liquidair'offersenergystoragehope' ".BBC
News,ScienceandEnvironment.BBC.Retrieved20121002.
12. Mancini,Tom(10January2006)."AdvantagesofUsingMoltenSalt".SandiaNationalLaboratories.
Archivedfromtheoriginalon20110714.Retrieved20110714.
13. MoltensaltenergystoragesystemAfeasibilitystudy(http://adsabs.harvard.edu/abs/1977htec.proc...39J)
Jones,B.G.Roy,R.P.Bohl,R.W.(1977)Smithsonian/NASAADSPhysicsAbstractService.Abstract
accessedDecember2007
14. Biello,David."HowtoUseSolarEnergyatNight".ScientificAmerican.ScientificAmerican,aDivisionof
NatureAmerica,Inc.Retrieved19June2011.
15. Ehrlich,Robert,2013,RenewableEnergy:AFirstCourse,CRCPress,Chap.13.1.22Thermalstoragep.
375ISBN9781439861158
16. ParabolicTroughThermalEnergyStorageTechnology(http://www.nrel.gov/csp/troughnet/thermal_energy_st
orage.html)ParabolicTroughSolarPowerNetwork.April04,2007.AccessedDecember2007
17. Economist.com(20140312)."Electricitystorage:Pumpingheat".TheEconomist.Retrieved20140619.
18. "ENERGYSTORAGE:THEMISSINGLINKINTHEUK'SENERGYCOMMITMENTS".IMechE.p.27.
19. JacquesRueretal."PumpedHeatEnergyStorage"(PDF).Retrieved20140716.
20. "Isentropic'sPHESTechnology".Retrieved16July2014.
21. http://news.stanford.edu/news/2014/november/catalystenergystorage110514.html
22. Kolpak,AlexieM.(20June2011)."AzobenzeneFunctionalizedCarbonNanotubesAsHighEnergyDensity
SolarThermalFuels".NANOLetters.AmericanChemicalSociety.Retrieved14July2011.
Externallinks
ASHRAEwhitepaper(http://www.pwienergy.com/main/whitepapers/tsdereg.htm)onthe
economiesofloadshifting
MSNarticleonIceStorageAirConditioning(http://archive.is/20130119140153/http://msncnet.c
om.com/Icepowered+air+conditioner+could+cut+costs/21001008_36101045.html?part=msncn
et&subjns_36101045&tag=msn_home>1=8486)
ICETESThermalEnergyStorageIDETech(http://www.idethermalenergystorage.com/?page_i
d=12)
http://thermalbatterysystems.com/featuredsystems/laramiewyomingthermalbatterysystem
https://en.wikipedia.org/wiki/Thermal_energy_storage
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example/#.U8Whdo1dXx8
"PreparedfortheThermalEnergyStorageSystemsCollaborativeoftheCaliforniaEnergy
Commission"Reporttitled"SourceEnergyandEnvironmentalImpactsofThermalEnergy
Storage."TaborsCaramanis&Assocenergy.ca.gov(http://www.energy.ca.gov/reports/5009500
5_TESREPORT.PDF)
Furtherreading
Hyman,LucasB.SustainableThermalStorageSystems:Planning,Design,andOperations.New
York:McGrawHill,2011.Print.
HenrikLund,RenewableEnergySystems:ASmartEnergySystemsApproachtotheChoiceand
Modelingof100%RenewableSolutions,AcademicPress2014,ISBN9780124104235.
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