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Large-scale

electricitystorage

2 LARGESCALE ELECTRICITY STORAGE

Large-scale electricity storage

Issued: September 2023 DES8702

ISBN: 978-1-78252-666-7

The text of this work is licensed under the

terms of the Creative Commons Attribution

License which permits unrestricted use,

provided the original author and source are

credited.

The license is available at:

creativecommons.org/licenses/by/4.0

Images are not covered by this license.

This report can be viewed online at:

royalsociety.org/electricity-storage

Cover image: © iStock.com / Bjoern Wylezich.

LARGESCALE ELECTRICITY STORAGE 3

Contents

Executive summary 5

Major conclusions 5

Modelling the need for storage 6

Storage technologies 6

Average cost of electricity with all large-scale storage provided by hydrogen 7

Addition of other types of store 7

Market and governance issues 7

Caveats and avenues for further work 7

Chapter one: Introduction 9

1.1 Scope of this report 9

1.2 Supply and demand in a net zero context 9

1.3 Storage 11

1.4 Cost considerations 15

Chapter two: Electricity demand and supply inthe net zero era 16

2.1 Introduction 16

2.2 Future electricity demand in GreatBritain 17

2.3 Weather, wind and sun 17

2.4 Matching demand and direct wind and solar supply 19

2.5 Residual demand, energy and power 23

2.6 Generating costs 27

2.7 Demand management 28

Chapter three: Modelling the need for storage 29

3.1 Introduction 29

3.2 Modelling and costing with a single type of store 29

3.3 Modelling and costing with several types of store 32

Chapter four: Green hydrogen and ammonia asstorage media 34

4.1 Introduction 34

4.2 Hydrogen and ammonia production 34

4.3 Transport 38

4.4 Storage 38

4.5 Electricity generation 41

4.6 Safety 44

4.7 Climate impact 44

Chapter ﬁve: Non-chemical and thermalenergystorage 45

5.1 Advanced compressed air energy storage (ACAES) 45

5.2 Thermal and pumped thermal energy storage 48

5.3 Thermochemical heat storage 49

5.4 Liquid air energy storage (LAES) 50

5.5 Gravitational storage 50

5.6 Storage to provide heat 51

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Large-scaleelectricitystorageLarge-scaleelectricitystorageLARGE-SCALEELECTRICITYSTORAGEIssued:September2023DES8702ISBN:978-1-78252-666-7©TheRoyalSocietyThetextofthisworkislicensedunderthetermsoftheCreativeCommonsAttributionLicensewhichpermitsunrestricteduse,providedtheoriginalauthorandsourcearecredited.Thelicenseisavailableat:creativecommons.org/licenses/by/4.0Imagesarenotcoveredbythislicense.Thisreportcanbeviewedonlineat:royalsociety.org/electricity-storageCoverimage:©iStock.com/BjoernWylezich.2ContentsExecutivesummary5Majorconclusions5Modellingtheneedforstorage6Storagetechnologies6Averagecostofelectricitywithalllarge-scalestorageprovidedbyhydrogen7Additionofothertypesofstore7Marketandgovernanceissues7Caveatsandavenuesforfurtherwork7Chapterone:Introduction91.1Scopeofthisreport91.2Supplyanddemandinanetzerocontext91.3Storage111.4Costconsiderations15Chaptertwo:Electricitydemandandsupplyinthenetzeroera162.1Introduction162.2FutureelectricitydemandinGreatBritain172.3Weather,windandsun172.4Matchingdemandanddirectwindandsolarsupply192.5Residualdemand,energyandpower232.6Generatingcosts272.7Demandmanagement28Chapterthree:Modellingtheneedforstorage293.1Introduction293.2Modellingandcostingwithasingletypeofstore293.3Modellingandcostingwithseveraltypesofstore32Chapterfour:Greenhydrogenandammoniaasstoragemedia344.1Introduction344.2Hydrogenandammoniaproduction344.3Transport384.4Storage384.5Electricitygeneration414.6Safety444.7Climateimpact44Chapterfive:Non-chemicalandthermalenergystorage455.1Advancedcompressedairenergystorage(ACAES)455.2Thermalandpumpedthermalenergystorage485.3Thermochemicalheatstorage495.4Liquidairenergystorage(LAES)505.5Gravitationalstorage505.6Storagetoprovideheat51LARGE-SCALEELECTRICITYSTORAGE3Chaptersix:Syntheticfuelsforlong-termenergystorage526.1Electro-fuels526.2Liquidorganichydrogencarriers(LOHCs)52Chapterseven:Electrochemicalandnovelchemicalstorage547.1Electrochemicalstorage547.2Novelchemicalstorage59Chaptereight:PoweringGreatBritainwithwindplussolarenergyandstorage608.1Technologychoices608.2Additionalcosts608.3Provisionofallflexiblepowerbyasingletypeofstore638.4Multipletypesofstore678.5UseofnaturalgaswithCCS708.6Possibleusesandvalueofsurpluselectricity728.7Contingenciesagainstperiodsoflowsupply728.8Differentlevelsofdemand738.9OtherstudiesofthecostofstorageinGreatBritain74Chapternine:TheGrid,electricitymarketsandcoordination759.1Thegrid759.2Marketsissues759.3Possiblereforms76Chapterten:Conclusions,furtherstepsandopportunities7810.1Conclusions7810.2Furthersteps8110.3Demonstrators,deploymentandopportunities83AnnexesAnnexA:Glossaryandabbreviations84AnnexB:Contentsofsupplementaryinformation89Acknowledgements924LARGE-SCALEELECTRICITYSTORAGEExecutivesummaryExecutivesummaryTheUKGovernmenthasastatedambitiontoMajorconclusionsdecarbonisetheelectricitysystemby2035•In2050GreatBritain’sdemandforelectricityandiscommittedtoreachingnetzeroby2050.AsGreatBritain’selectricitysupplyiscouldbemetbywindandsolarenergydecarbonised,anincreasingfractionwillbesupportedbylarge-scalestorage.providedbywindandsolarenergybecausetheyarethecheapestformoflow-carbon•Thecostofcomplementingdirectwindgeneration.Windandsolarsupplyvaryonandsolarsupplywithstoragecomparestimescalesrangingfromsecondstodecades.veryfavourablywiththecostoflow-carbonHoweverhightheaveragelevelofsupplyalternatives.Further,storagehasthepotentialmightbe,therewillbetimeswhenwindandtoprovidegreaterenergysecurity.solargenerationisclosetozeroandperiodswhenthereisenoughtomeetpartofbut•Windsupplycanvaryovertimescalesofnotalldemand,aswellastimeswhenitdecadesandtensofTWhsofverylong-exceedsdemand.durationstoragewillbeneeded.Thescaleisover1000timesthatcurrentlyprovidedToensurethatdemandisalwaysmet,thebypumpedhydrointheUK,andfarmorevolatilewindandsolargeneratedelectricitythancouldconceivablybeprovidedbythatisfeddirectlyintothegridmustbeconventionalbatteries.complementedbyotherflexiblelow-carbonsources,and/orusingexcesswindandsolar•Meetingtheneedforlong-durationstorageenergythathasbeenstored.Theexcesscouldwillrequireverylowcostperunitenergybestoredinavarietyofways,forexamplestored.InGB,theleadingcandidateisstorageelectrochemicallyinbatteries,gravitationallyofhydrogeninsolution-minedsaltcaverns,bypumpingwaterintodams,mechanicallyforwhichGBhasamorethanadequatebycompressingair,chemicallybymakingpotential,albeitnotwidelydistributed.Thehydrogen,orasheat.fall-backoption,whichwouldbesignificantlymoreexpensive,isammonia.Thisreportconsiderstheuseoflarge-scaleelectricitystoragewhenpowerissupplied•ThedemandforelectricityinGBin2050ispredominantlybywindandsolar.Itdrawsonassumedtobe570TWh/yearinmostofthisstudiesfromaroundtheworldbutisfocussedreport.Inprincipleitcouldallbemetbywindontheneedforlarge-scaleelectricalenergyandsolarsupplysupportedbyhydrogen,andstorageinGreatBritaina(GB)andhow,andatsomesmall-scalestoragethatcanrespondwhatcost,storageneedsmightbestbemet.rapidly,whichisneededtoensurethestabilityofthetransmissiongrid.Withthereport’scentralassumptions,thiswouldrequireahydrogenstoragecapacityrangingfromaround60to100TWhb(dependingonthelevelofwindandsolarsupply).Theaveragecostofelectricitythatisavailabletomeetdemandvariesverylittleoverthisrangeastherisingcostofwindandsolarsupplyisoffsetbythedecreasingcostofthestoragethatisneeded.aNorthernIrelandisexcludedfromthestudyasitselectricitygridisintegratedwiththatoftheRepublicofIreland.bThisisthethermalenergycontentofthestoredenergyexpressedintermsoftheLowerHeatingValue–seetheGlossary.LARGE-SCALEELECTRICITYSTORAGE5Executivesummary•Althoughsomehydrogen(orammonia)Modellingtheneedforstoragestoragewillbeneeded,itisquitelikelythataToquantifytheneedforlarge-scaleenergyportfolioofdifferenttypesofstoragewouldstorage,anhour-by-hourmodelofwindandlowertheaveragecostofelectricity.solarsupplywascomparedwithanhour-by-hourmodeloffutureelectricitydemand.The•Includingsteadynuclear(‘baseload’)supplymodelswerebasedonrealweatherdatainthewouldincreasecosts,unlessthecostof37years1980to2016andanassumeddemandnuclearisnearorbelowthebottomoftheof570TWh/year.Thirty-sevenyearsisnotrangeofprojectionsmadebytheDepartmentenoughtoprovideafullsampleofrareweatherforBusiness,EnergyandIndustrialStrategyeventswhichcanseriouslyaffectthesupply(BEIS)and/orthecostsofstoragearenearofwind-generatedelectricity.Contingencyisthetopoftherangeofestimatesinthisaddedtoallowforthis,andforthepossiblereport.Theadditionofbioenergywithcarboneffectsofclimatechange.Studiesbasedoncaptureandstoragegeneration(BECCS)lessthanseveraldecadesofweatherdatawouldlowerthecostifitattractsacarbonareliabletoveryseriouslyunderestimatethecreditoforder£100/(tonneCO2saved)orneedforstorage,andoverestimatetheneedmore,butitcouldnotprovideGBwithmoreforothersourcesofflexiblesupply.Thesethan50TWh/yearwithoutimportsofbiomass.under/overestimatesareespeciallylargeinstudiesthatlookonlyatindividualyearsrather•Usingnaturalgasgenerationequippedwiththansequencesofyearsorexamineselectedcarboncaptureandstorage(CCS)toprovideperiodsofhighstress.flexibility,insteadofstorage,wouldleadtounacceptableemissionsofCO2andmethane,Storagetechnologiesandalsotohighercosts.Usedasbaseload,itThecontentsofstoreswithlargecapitalcostswouldonlylowercostsappreciablyifaddedperunitofenergystoredhavetobecycledinamountsthatwouldleadtounacceptablefrequentlyinordertorecovertheinvestment.emissions;thefuturepriceofnaturalgasThestoragetechnologiesconsideredinthisislowerthanexpected;andstoragecostsreportcanbegroupedintothreecategoriesarehigh.accordingtothetypicaltimeinwhichtheircontentsmustbecycled:•Usingacombinationofstorageandgas1.Minutestohours:conventionalplusCCStoprovidetheflexibilityrequiredtomatchwindandsolarsupplycouldlower(non‑flow)batteries;costssignificantly,withoutnecessarilyleadingtounacceptableemissions.Whetherit2.Daystoweeks:flowbatteries,advancedwouldlowercostsdependsonthecostsofcompressedairenergystorage,Carnotstorage,windandsolarpower,andgasplusbatteries,pumpedthermalstorage,pumpedCCS,thepriceofgasandthecarbonprice.hydro,liquidairenergystorage;orItwouldnotremovetheneedforlarge-scalelong-termstorage,althoughitwouldreduce3.Monthsoryears:syntheticfuels,therequiredscalesofstorageandwindammonia,hydrogen.plussolarsupply.Whileitwouldprovidediversity,itwouldexposeGB’selectricityStoresincategoryonearegenerallymorecoststofluctuationsinthepriceofgas,andefficientthanthoseintwo,whicharemoreincreasingrelianceonimportsasGB’sgasefficientthanthoseinthree.Higherefficiencyreservesdecline.cancompensateforhighercostsdependingonhowthestoresareused.6LARGE-SCALEELECTRICITYSTORAGEExecutivesummaryAveragecostofelectricitywithalllarge-scaleAddingothertypesofstoretohydrogenandstorageprovidedbyhydrogenACAEScouldlowerthecostfurther.Acaseinwhichalldemandismetbywindandsolarenergysupportedbyhydrogenstorage,Marketandgovernanceissuesplus15GWofbatteries(usedtostabilisetheThecostofelectricityprovidedbystoragegrid),wasanalysedandusedasabenchmarkwillbemanytimesthecostofwindandagainstwhichtheotheroptionswereassessed.solarsupplythatisfeddirectlyintothegrid.Theaveragecostofelectricityfedintothegrid,Buildingthestorageneededtoprovidethiswascalculatedwitharangeofassumptionsexpensivebutessentialelectricitywilltakeforthe2050costofstorageandofsolarandlargefinancialinvestmentsandtime.Whilewindgeneratedelectricity.In2021pricespricedifferentialsinwholesaleandbalancingitrangesfrom:marketsmayincentivisetheconstructionof•£52/MWh–withthelowassumptionsforthesignificantamountsofshort-termstorage,newmechanisms,includingformsofguarantees,costsofstorageandwindplussolarpowerwillbeneededtomakeinvestmentinlarge-(£30/MWh)anda5%discountrate;toscale,long-durationstorageattractive.Tocontainstoragecosts,generatorsandowners•£92/MWh–withthehighassumptionsfortheofstoragewillhavetocooperatetoancostsofstorageandwindplussolarpowerunprecedenteddegreeinschedulingcharging(£45/MWh)anda10%discountrate.anddispatchofenergyfromdifferenttypesofstore.EnsuringthiscooperationislikelytoTheoverallaveragecostisdominatedbytherequireradicalreforms.costofthewindandsolarsupply.Theaveragecostofelectricitywouldbeatleast£5/MWhCaveatsandavenuesforfurtherworkhigherifallstoragewereprovidedonlybyThisreportisfocussedonthelarge-scaleammonia.Itappearsveryunlikelythatanyotherstoragethatwillbeneededin2050inGB.formofstoragecouldmeetallneedsonitsown.WhilethepossiblerolesofnuclearandofgasplusCCSareconsidered,themodellingdoesForcomparison:in2010–2020,thewholesalenottakeaccountofcontinuingcontributionspriceofelectricityhoveredaround£46/MWh,fromburningwasteandbiomass,hydropowerbutitwasmorethan£200/MWhduringandinterconnectors,ortherelativelocationsmostof2022.ofsupply,storage,anddemand,andtheirimplicationsforthegrid.AdditionofothertypesofstoreAdvancedcompressedairenergystorageThedesignandimplementationofprocedures(ACAES)wasstudiedindetailasanexemplarofforschedulingtheuseofamixtureofdifferentstoresinthesecondcategoryidentifiedabove.typesofstoretogetherwithotherflexibleAcombinationofACAESwithhydrogenstoragesupplyneedtobestudiedfurther.Moreworkisprovidesthebenefitsofthegreaterefficiencyalsoneededonthelong-termvariabilityofwindoftheformerandthelowerstoragecostofandsolarsupplyandtheneedforcontingency.thelatter.ThecostsandefficienciesoflargeTheneedforhydrogenforlarge-scaleACAESsystemsarepoorlyknown.However,electricitystorageshouldbestudiedtogetherforawiderangeofassumptions,itwasfoundwithotherusesforgreenhydrogen.ThiswouldthatcombiningACAESwithhydrogenwouldalmostcertainlyrevealsystemsbenefitsthatbelikelytolowerthecostrelativetothatfoundwouldlowercosts.withhydrogenalone(byupto5%,orpossiblymore),althoughthisisnotassured.Whentheyareoptimallycombined,thecapacityofACAESismuchsmallerthanthatofthehydrogenstore,butACAESdeliversmoreenergybecauseitiscycledmorefrequently.LARGE-SCALEELECTRICITYSTORAGE7ExecutivesummaryTheunderlyingassumptionsonthecostofGBwillneedlarge-scaleenergystoragetostorageandofprovidingwindandsolarpowercomplementhighlevelsofwindandsolarshouldbeunderpinnedbydetailedengineeringpower.Nolow-carbonsourcescandosoatestimates.Meanwhile,itshouldbestressedthatacomparablecost.Constructionofthelarge-thecostestimatesinthereport,whichareinscalehydrogenstoragethatwillbeneeded2021prices,areobviouslysensitivetoincreasesshouldbeginnow.incommoditypricesandotherformsofinflation,anddependcriticallyonestimatesofthefutureMoredetailsandbackgroundcostofwindandsolarpower.informationareprovidedinsupplementaryinformationavailableatConstructingthelargenumberofhydrogenroyalsociety.org/electricity-storage.storagecavernsthatthisreportfindswillbeThisincludesadescriptionofunpublishedneededtocomplementhighlevelsofwindandworkconductedinsupportofthisreport.solarsupplyby2050willbechallengingbutForexample,informationrelevanttosectionappearspossible.3.2isreportedin,andreferencedasSI3.2.ThecontentsofthesupplementaryinformationcanbefoundinAnnexB.ExchangeratesCostestimatesinthereportarefirstquotedin$sor€swhenthatwasthecurrencyusedintheoriginalsource,andthenconvertedat£1.00=$1.35=€1.188LARGE-SCALEELECTRICITYSTORAGEChapteroneIntroduction1.1Scopeofthisreport1.2.2TheneedforflexiblesupplyThisreportdrawsonstudiesfromroundtheTheavailabilityofwindandsolarpowerworldbutisfocussedontheneedforlarge-variesontimescalesrangingfromsecondsscaleelectricalenergystorageinGreatBritaintodecades,dependingontheweather,(ietheUKexcludingNorthernIreland,whereseefigures1and2(andSI1.2).Demandisalsoelectricityprovisionispartofaseparatevariable,andmismatchesbetweensupplyandIrishmarket),andhow,andatwhatcost,itdemandoccurontimescalesrangingfrommightbestbemet.Theneedforstorageandmillisecondstoyears(seefigure1B)asaresulthowitcanbemetdependonlocalfactors,oflong-termvariationsinwindspeeds,causedincludingtheweatherandclimate,andbytheNorthAtlanticOscillation(NAO).potentialstoragesites.Themethodologyneededtostudystorage,andconclusionsAstherearetimeswhenthesunisnotshiningonstoragetechnologiesare,however,andthewindisnotblowing,windandsolargenerallyapplicable.supplycannotmeetdemanddirectlyontheirown,howevermuchgeneratingcapacity1.2Supplyanddemandinanetzerocontextisinstalled.Theythereforehavetobe1.2.1Netzeroemissions,electrification,andsupplementedby:windandsolarenergy•large-scaleflexiblelow-carbongeneration;Reducinggreenhousegasemissionstonetzeroby2050willrequiremajorchangesinand/orenergyproductionandconsumption.Fossilfuelswillhavetobereplacedinproviding•importingelectricitywhenneeded;and/orindustrialprocessheat,spaceheatingandtransport.Thiswillrequiregreaterelectrification,•generatingelectricityfromthesurpluswindandhencealargeincreaseinelectricitysupply.andsolarenergythathasbeenstored.Itisgenerallyexpectedthat,astheUKmovestowardsnetzero,anincreasingfractionwillbeprovidedbywindandsolargeneration,whicharethecheapestformsoflow-carbongeneration1.Thereispotentiallymuchmorethanenoughforthemtomeetthecountry’sfutureelectricityneeds2.LARGE-SCALEELECTRICITYSTORAGE9ChapteroneFIGURE1Modelledprofilesofwindandsolargenerationandelectricitydemand.Profilesofi)windandsolarelectricitygeneration,basedonactualweatherdatainatypicalyear(1992)scaledto570TWh/yearaveragedover37years(with,forreasonsexplainedinChapter2,80%fromwindand20%fromsolar)andii)amodel(describedinChapter2)ofpossibleGBdemandof570TWh/yearin2050.Flexiblesupplyfromothersourcesand/orimportsand/orstoredsurplusesarerequiredtofillthegapbetweendemandandwind+solarsupply.A)JanuaryKEY140Demand120WindSolar10031GW8060402000510152025B)July140120100GW80604020005101520253110LARGE-SCALEELECTRICITYSTORAGEChapteroneFIGURE2Modelledannualdifferencebetweenwindplussolarsupplyandelectricitydemand.Thedifferencebetweendemandandwindplussolarsupply,basedonactualhour-by-hourweatherdataintheyears1980–2016,scaledtoaverage570TWh/yearover37years(with80%windand20%solar),andthemodelofGBdemandof570TWh/yearusedinfigure1.YearsApriltoMarchareusedinordertoincludecontiguousquarters3and4andnotdilutetheeffectsofseverewinters.604020TWh0-20-40-6005101520253036Year1.3StorageThescaleoffutureenergystorageneeded1.3.1Energystoragetodayandthescaleinsystemswithhighlevelsofwindandsolaroffutureneedssupplycanbeinferredfromfigure2.ItshowsStorageisneededinallenergysystemsthat,withonlywindandsolargeneration,tobuffermismatchesbetweensupplyandbalancingsupplyanddemandover37yearsdemand.Theaverageamountofenergystored(with100%efficientstorage)wouldrequireintheUKin2019isshowninBox1(seeSI1.3).storingtensofTWhsforoverseveraldecadesByfarthelargestamountwasstoredinfossilinordertofillthedeficitsinyears29–31offuels,whicharebeingphasedout.theperiodstudied.Atthelevelsofadditionalsupplyneededtocompensateforstorageinefficiencies,itremainstruethatthereisaneedtostoretensofTWhsformanyyears(seefigure13andSI1.3).Thescaleoftheneedandthetimeoverwhichenergyhastobestoredinvolvesatrade-offbetweenthesizeofthestore,therateatwhichitisfilledandthelevelofwindandsolarsupply.LARGE-SCALEELECTRICITYSTORAGE11ChapteroneBOX11.3.2StoragetechnologiesGreatBritain’sexpectedneedofmanytensEnergyStoredintheUKin2019cofTWhofelectricitystoragecouldnotallbeprovidedbythestoresshowninBox1:thecostFossilfuelsonaveragestored:oftensofTWhofbatterieswouldbeprohibitive•35TWh–coal(falling)andthepotentialforpumpedhydroismuchtoosmall.•18TWh–gas(9averagedays’supply)Thereisatrade-offbetweenthecapitalcostof•160TWh–crudeoilandpetroleumenergystoragesystemsandtheirefficiencies.products(notusedtogenerateelectricity)Theybroadlyfallintothreeclassesthat:1.havehighcosts,andhavetobecycledSupportedby:•Pumpedhydro–30GWhcapacityeveryfewhourstorecovertheinvestment,buthavehighefficiency;•Hotwatertanks–40GWh2.havelowcostsandcanstorelarge•Gridconnectedbatteries–1.8GWhamountsofenergyforyears,buthavelowefficiencies;or•320KtbiomassatDraxpowerstation→560GWhelectricity3.haveintermediatecharacteristics.TomodelthisneeditisnecessarytocompareIncostingstorageinthisreport,specialmodelsofwindandsolarsupplywithmodelsattentionispaidtoonetechnologyineachofdemand,hour-by-hour,overaslongaperiodcategory:lithium-ionbatteries,whicharetheaspossible,andidentifythemismatchesinobviouschoiceinthefirst;hydrogenstorage,supplyanddemand.Thefuturelevelandhourlywhichemergesastheleadingcandidateinprofileofelectricitydemandareveryuncertain,thesecond;andadvancedcompressedairthebiggestuncertaintybeinginthedegreeenergystorage(ACAES),whichischosentowhichspaceheatingwillbeelectrified.Theasanexemplarofmanytechnologiesinthemainconclusionsofthisreportarebasedonlastclass.Thatfinalclassalsoincludesflowamodelof2050demandkindlyprovidedbybatteries,CarnotbatteriesandLiquidAirAFRYconsultingdandvariationsthereonwithEnergyStorage(LAES).higherandlowerlevelsofdemand,andtherenewables.ninjamodelofwindandsolarSomestorageisrequiredthatcanrespondsupplythatisbasedon37yearsofrealweatherveryrapidlyinordertoregulatethevoltagedata(1980to2016).andfrequencyandmaintainthestabilityofthegridwhentherearesuddenchangesinsupplyordemand.Providingthese‘rapidresponsegridservices’takesrelativelylittleenergy.Itthereforehasalmostnoimpactontheneedforlarge-scalestorage,andhowitisprovidedisoutsidethescopeofthisreport.Itcan,however,beexpensiveandanestimateofwhatitmightcostisincluded,assumingthatitisprovidedbylithium-ionbatteries.cEnergyStoredintheUKin2019;datafromDigestofUKEnergyStatistics(DUKES),EnergyTrends(UKgas)andtheRenewableEnergyPlanningDatabase(GBonlydata).dBasedonresultsofsimulationsusingtheBID3powermarketmodel.Seehttps://afry.com/en/service/bid3-power-market-modelling(accessed15May2023).12LARGE-SCALEELECTRICITYSTORAGEChapterone1.3.3Featuresofstorage•ThetotalamountofdemandthatastoreHydrogenstorage,whichthisreportfindswillmeetsdependsonhowoftenitisfilledandbeneededinGB,isusedheretoillustratethreeemptied.Forexample,inonecaseinwhichgeneralfeaturesofstorage(seefigure3):bothhydrogenstorageandACAESare•Theelectricityprovidedbystorageisdeployed,itisfoundthathydrogenstoresandACAESmustbecapableofdeliveringgenerallymuchlessthantheinputbecauseof37TWhe/cycleand2.4TWhe/cyclelosses.Withtheoverall(roundtrip)efficiencyrespectively.However,hydrogendeliversof41%assumedforhydrogen,thesurplus36TWhe/year,whilethemuchsmallerACAESwindandsolarenergythatisstoredmustbestoresdelivers55TWhe/year,becauseACAESatleastfactorof1/0.41=2.4largerthantheiscycledmuchmorefrequently.Thismightdeficitsthatthestoredhydrogenisrequiredsuggestthathydrogenstorageisnotneeded.tofill.WindandsolarsupplymustthereforeHowever,thisreportfindsthatbecauseofitsbegreaterthandemandifnoothersourcesofhighercostperunitofenergystored,andthesupplyareavailable:withthemodellingusedneed–implicitinfigure1B–tostoreenergyhere,ademandof570TWh/yearcanonlybeforlongperiods,usingACAESalonewouldbemetwithhydrogenstoragealoneifwindandmoreexpensivethanusinghydrogenstoragesolarsupplyisgreaterthan703.5TWh/year.alone.Acombinationofthetwo,whichwouldbenefitfromtheefficiencyoftheformerand•Theamountsofhydrogenaddedtoandthelowstoragecostofthelatter,wouldquitewithdrawnfromthestoremustbeequalwhenlikelybecheaperthaneitheralone.averagedoveralongperiod.However,agivenoutputcan,withinlimits,beprovidedbyarelativelysmallstoragecapacitychargedrapidlywithmanyelectrolysers,orbyalargestoragecapacitychargedslowlybyfewerelectrolysers.Thecostdependsontherelativecostsandsizesoftheelectrolyserandofthestore.Asystemwiththesmallestpossiblestore,whichwouldhavetobechargedbyelectrolyserswithenoughpowertostorethelargestdeficits,wouldgenerallynotbethecheapest.LARGE-SCALEELECTRICITYSTORAGE13ChapteroneFIGURE3Schematicoftheuseofhydrogentostoreelectricity.Thefuelcellsand/or4-strokeenginesthatconverthydrogentoelectricitymustbesizedtobeabletomeetalldemandwhenthewindisnotblowingandthesunnotshining.Withinlimits,demandcanbemetwitharelativelysmalltotalstoragecapacitychargedbyverypowerfulelectrolysers(whichconvertelectricitytohydrogen),oralargercapacitychargedbylesspowerfulelectrolysers.VolatilewindandsolarsupplyVaryingdemandElectricityElectrolysersHydrogenstoredinsaltcavernFuelcell/4-strokeengineCapacitydependsonsizeofcavernandhydrogenpressureLossesLossesRound-tripeciency(energyout/energyin)≈41%14LARGE-SCALEELECTRICITYSTORAGEChapterone1.4Costconsiderations1.4.2CostsandsizeInthisreport,theaveragecostoftheelectricityThecostsofstores,andofdevicesthatconvertthatwillhavetobeprovidedtothegridtomeetelectricalenergytotheforminwhichitis2050demandisstudiedbecausei)AFRY’sstoredandreconvertittoelectricity,dependmodelofdemandisforelectricityenteringthestronglyontheirsize.Forexample,thecostgrid,andii)itisrelativelyinsensitivetochangesperunitstoragecapacityofsolution-minedintransmissioncosts,whichonlyaffectthecostsaltcavernsthatareusedtostorehydrogenoftransmittingenergyfromwindandsolarfarmsvariesapproximately3as(thecapacity)-0.5,tostores.whilethecostsperkWofcompressorsandexpanders(whichareusedinACAES)varies1.4.1Averagecostofelectricityapproximately4as(thepowerrating)-0.4.ItisThemoreelectricitythatisprovideddirectlytothereforeimportanttospecifythesizeofthethegridbywindandsolar,thelesshastobesystemforwhichtheyareapplicablewhenprovidedbyothersources(includingstorage).makingorcomparingcostestimates.However,theseothersourcesmuststill(collectively)beabletomeetthefulldemand1.4.3OperationandmaintenanceforpowerwhenthewindisnotblowingandThecostofusingsystemsthatoperatewiththesunnotshining.Withhighlevelsofwindlowloadfactors(whichmakesvariablecostsandsolar,theflexiblesourcesthatcomplementrelativelyunimportant),suchaslong-termthem(includingstorage)willthereforespendstorage,isverysensitivetofixedoperationandalotoftimeidleoroperatingwellbelowfullmaintenance(O&M)costs.Forexample,ifthecapacity.Thepowertheydoprovidewillcapitalcostisdiscountedat5%over30years,thereforebeexpensive.Itis,however,theafixedannualO&Mcostof2%ofcapexwouldaveragecostofelectricitythatmatters,mostofcontribute24%ofthetotalannualisedcost;anwhichwillbeprovideddirectlybylow-costwindannualO&Mcostof4%wouldcontribute38%.andsolarwhosecontributionsdilutethehighEstimatesoffixedO&Mcostsaremadecase-costofelectricityprovidedbystorage.by-caseinthisreport,buttheyarenecessarilyimprecisewithoutlongoperationalexperience.LARGE-SCALEELECTRICITYSTORAGE15ChaptertwoElectricitydemandandsupplyinthenetzeroera2.1IntroductionCustomerdemand(asdefinedbytheNationalThefutureroleofenergystoragedependsonGrid)5excludesthedemandforelectrolyticthelevelandprofileofdemand,thevariabilityofproductionofhydrogen,bothforstoringwindandsolarsupply,potentialcomplementaryelectricity(whichisconsideredtobepartofsupplyandthescopeformanagingdemand,supply)andforotherpurposes.Co-productionwhichmustbeconsideredinthecontextoftheofhydrogenforotherpurposeswouldalmostwholeelectricitysystem(seefigure4).Thesecertainlyreducethecostofusinghydrogentofactorsareconsideredinturninthischapter.storeelectricity.Allusesshouldbemodelledtogether,butthisiscurrentlyimpossibleasThefirststepinmodellingsystemswithhighestimatesofthedemandforgreenhydrogenlevelsofvariablerenewablegenerationistovaryverywidely.understandhowmuchofthequantitylabelled‘Basicdemand’infigure4canbemetdirectlybywindandsolarsupply.Demand(basicorcustomer)thatcannotbemetdirectlyandmustbeprovidedbycomplementarysourcesand/orstorage,isknownasResidualDemand(seeBox2):itisfoundbycomparingwindandsolarsupplywith(basicorcustomer)demand.FIGURE4Elementsoftheelectricitysystem.Storageincludesalltypes(batteries,compressedair,liquidairetc)exceptoff-gridstorage.Off-gridgenerationisalsonotshown.InterconnectorsGBelectricityCurtailedsurplusesgenerationExportElectrolysishydrogenWindStorageTransmissionandandsolardistributionlossesBasicCustomerdemanddemandexcludesexcludeselectrolysiselectrolysisComplementarygeneration16LARGE-SCALEELECTRICITYSTORAGEChaptertwoBOX2Inmostofthemodellingofstorageinthisreport,basicGBdemandwillbeassumedtobeResidualdemandand570TWh/yearin2050,althoughsomeresultsresidualenergywillalsobereportedbasedonsimplemodelsofdemandsof440TWh/yearand700TWh/year.ResidualdemandisdefinedasDemand570TWh/yearisthelevelinAFRY’shour-by-–(Demandmetdirectlybywind+solar).Ithourprofilee(whichisbasedontheweatherinplaysakeyroleinstudyingsystemswith2018)thatwasshowninfigure1AforJanuaryhighlevelsofwindandsolargeneration.andJuly.Itcomprisesbasecontribution355TWh,heating96TWh,andEVchargingWhenwindandsolarsupplyexceed119TWh.Profilesofdemandintheperioddemand,thetermResidualEnergyor2012–2017areshowninSI2.2.ResidualPowerisused,whichisequaltoWind+SolarSupply-Demand2.3Weather,windandsun2.3.1Temporalandspatialvariation2.2FutureelectricitydemandinGreatBritainMeansolarandwindpoweracrossagridBasicelectricitydemandwas317TWhin2021.coveringthelandmassofGBisshowninItisexpectedtoincreaseinthefuture,byanfigure57(thedataarescaledtotheirmulti-yearamountthatwilldependon:theextenttowhichaverages,sothisplotprovidesnoinformationtheprovisionofheat,transport,andindustrialontherelativepotentialsofwindandsolarprocessingareelectrified;increasesintheusepower).Thedifferentprofilesofsolarandwindofairconditioning;improvementsinefficiency,powerarecomplementaryand,asshownlater,economicgrowth,changesinpopulationanappropriatemixturecanonaverageroughlyandchangesinbehaviour.Projectionsformatchtheseasonalprofileofdemand.The2050rangefrom518TWhinoneofthevariabilityofwind,whichdominatesthemixture,NationalGrid’snetzerocompliantFutureishigherthansolarvariationinallmonths,EnergyScenarios(FES)5to672TWhinBEIS’6andwilldominatethedesignofGB’senergyhighdemandmodel.Thehigherprojectionssupply.MoreinformationontheavailabilityandassumehighlevelsofelectrificationofspacebehaviourofwindisprovidedinSI2.3.heating.ThelowerFESprojectionsassumeverybigimprovementsinefficiency,and/orInfrequentbutextremeweathercanhaveachangesinbehaviour.majorimpactonsystemsthatrelyheavilyonwindandsolarpower.GB’selectricitysystemwillbeaffectedbythethreetypesofextremeweathereventsdescribedintable1whichwereidentifiedinastudybasedonhistoricaldataandmodelling8.Thisstudyfound“thatclimatechange,ratherthanclimatevariabilitywillhavethegreatestimpactontemperaturedrivendemandinthefuture…butclimatevariabilityisshowntohaveagreaterimpactonwindspeedandsolarirradiance”.eKindlyprovidedbyAFRYManagementConsulting,basedonresultsofsimulationsusingtheBID3powermarketmodelseehttps://afry.com/en/service/bid3-power-market-modelling(accessed15May2023).LARGE-SCALEELECTRICITYSTORAGE17ChaptertwoFIGURE5Distributionofmeanwindandsolargeneration1979to2013.Distributionofdaily-meanwindandsolargenerationineachmonthin1979to2013scaledtotheirall-yearaverages.Thelinesandshadingindicatethemedians,25thand75thpercentiles,and5thand95thpercentilesofthedailydata.KEY4WindSolarPVNormalisedpower3210JanFebMarAprMayJunJulAugSepOctNovDecSource:MetOffice.TABLE1Weatherstressevents.StresseventsDescriptionFrequencySummerwinddrought–frequentOneortwoperyearOnefulldayofverylowwindspeedSummerwinddrought–infrequentinsummerOnceevery10yearsWinterwinddroughtUptofourweeksofverylowwindEveryfewyearsspeedinsummerUptoaweekofverylowwindspeedinwinter18LARGE-SCALEELECTRICITYSTORAGEChaptertwoWinterwinddroughts,whichoccurwhenwindGreateruncertaintyiscausedbythefactspeedsovertheNorthSeaarelow,posethethatthe37-yearperiod(1980–2016)doesbiggestchallengetoveryhighrenewablenotprovideafullyrepresentativesampleofsystems9becausetheycoincidewithcoldweatherevents.AstudybytheMetOffice13airovermanypartsofCentralandNorthernfoundthatthereisapproximatelya10%chanceEurope,resultinginhighenergydemand.perdecadeofawintermonthwithwindspeedslowerthanintheperiodstudied.AsthedistancebetweenwindandsolarfarmsThisuncertaintyisaccommodatedbyaddingincreases,theiroutputsbecomelesscorrelatedcontingencytothesizeofthehydrogenstore:(seeSI2.3).Connectingfarmsindifferentotherpossiblemeasuresarediscussedinlocationsthereforereducestheshort-termsection8.7.Abetterunderstandingofthevariabilityofsupply.Atalargescale,strongerpersistenceandcharacteristicsofperiodsofelectricityinterconnectorsacrossEuropelowwindspeedsisrequired.Thiscouldbewouldsmoothweather-drivengenerationobtainedbystudyingtheperiod1960–1980,fluctuationsinhighwindpowerregionsinwhenanegativephaseoftheNAOledtolowerNorthernEuropeandhighsolarpowerregionswindspeedsthanin1980–2016,if/wheninSouthernEurope,andtransitoryhighandlowweatherdatafromthatperiodareconvertedwindpatternsinWesternandEasternEurope.intowindandsolaroutput.However,althoughtemporallyaveragedcorrelationsfallwithdistance,theweatherin2.4MatchingdemandanddirectwindanddifferentpartsofEuropeislinked.ImportstoGBsolarsupplyarevulnerabletopan-Europeanwinddroughts2.4.1Theoptimalwind/solarmixandcoldperiods,watershortages,andWindandsolarsupplyvaryindifferentways(potentially)politicalfactors.Itwouldthereforebetweenwinterandsummer,asshowninbewisetodesignaGBsystemthatwouldcopefigure5.Theycanthereforebemixedinawhenimportsarenotavailable.Contributionswaythatminimisesthesupplythathastobefrominterconnectorsarethereforenotincludedcurtailed,stored,orusedforotherpurposesinthemodellinginthisreport.whenitexceedsdemand.Withthe70/30offshore/onshoremixassumedfor2050in2.3.2Modellingwindandsolargenerationthisreport(seeSI2.4),andtotalwindplussolarRenewables.ninja10,11(RN)providesimulationssupplyfixed,thesolar/windmixturecanbeof(hypothetical)hourlypoweroutputfromwindchosentominimisetheamountthatcannotbeandsolarpowerplantslocatedanywhereintheusedtomeetdemanddirectlybycomparingworldbasedonhistoricalsatelliteweatherdata.37yearsofRNwindandsolardatawithAFRY’sInthisreport,theirsimulationsofUKsolarandhourlymodelof2050demandrepeated37onandoffshorewindgenerationareusedfortimes.Asshowninfigure6,theminimumisat1980–2016,whichwasthelargestandlongestaroundasolar/windmixof20/80.datasetavailablewhentheworkwasdone.Theyear-to-yearvariabilityofwind(andtoalesserextentsolar)powerisexpectedtocontinueattoday’slevelintothefuture,andtohaveabiggerimpactonelectricitysupplythanclimatechange12(someoftheeffectsofclimatechangearediscussedinSI2.3).Thescaleofprojectedchangesinwindspeedandsolarirradianceduetoclimatechangediffersbetweenmodelsandishighlyuncertain12.Thisuncertaintycancurrentlyonlybedealtwithbyincludingcontingencywhenusingmodelsoffuturewindandsolarsupply.LARGE-SCALEELECTRICITYSTORAGE19ChaptertwoFIGURE6Fractionofdemandnotmetdirectlybywindplussolar.Demandthatcannotbemetdirectlybywindplussolarsupplyasafunctionofthewind/solarmix,for570TWh/yeardemandanddifferentlevelsofwindplussolarsupply,withnobaseloadsupply.Unmetdemand/demand0.7KEY0.60.50.20.40.60.8Averagewindplus0.4solarsupply0.30.2800TWh/year0.1600TWh/year400TWh/year001FractionofsolarinwindplussolarsupplyTheadditionofconstantbaseloadsupplyComparisonof37yearsofRN’smodelofsupplyleadstoasomewhatbiggerwinter/summerwithAFRY’smodelof2050demandrepeateddifference:matchingitrequiresmore37timestakesaccountofcorrelationsbetweenwind/lesssolar.supplyanddemandtotheextentthatdemandislowerinthesummerthaninthewinterinThesolar/windmixthatmaximisesthedirecttheAFRYmodel,andloweratnightwhentheuseofrenewablesisnotnecessarilythatwhichsunisnotshining.However,itdoesnottakeminimisestheoverallcost,whichdependsaccountofcorrelationsthatoccurduringwinterontherelativecostofsolarandwindandtheanticycloneswhenitiscoldandwindspeedscostsandcharacteristicsofthecomplementaryarelow.Modelling(seeSI2.3andSI2Annex1)supply.However,thecostvariesverylittleforfindsthatitisprobablysafetoneglectthesesolarcontributionsintherangeof10%to30%correlationsforquantitiesthatdependonvery(seesection8.3).long-termbehaviour,suchasthechoiceofthewind/solarmixandtheneedforstorageonadecadaltimescale,althoughitwillleadtounderestimatesoftheneedforstorageonshortertimescales.Thesubstantialcontingencythatisincludedinthesizeofthelong-termhydrogenstore,providesprotectionagainstunderestimatesoftheneedforstoragesincehydrogenstoragewillbeavailableonallexceptveryshorttimescales.20LARGE-SCALEELECTRICITYSTORAGEChaptertwoFIGURE7Cumulativedifferencesbetweensupplyanddemand1980to2016.Cumulativedifferencesbetweensupplyanddemand,ineachquarterandover37years,withtheAFRYmodelofhour-by-hourdemandof570TWh/yearandwindplussolarsupply(mixed80/20)scaledtoaverage570TWh/year.Cumulativesurplus/deﬁcit(TWh)150130110198519901995200020052010201690Year70503010-10-30-501980KEYQuarterlycumulativetotalCumulativetotalLARGE-SCALEELECTRICITYSTORAGE21Chaptertwo2.4.2SurplusesanddeficitsThevariationand37-yearaveragesoftheFigure7showsthecumulativedifferencequarterlydeficitsandsurplusesseeninfigure7betweensupplyanddemand,ineachquarterareshowninfigure8.Thedifferencesbetweenandover37years,obtainedbycombiningthethemeanvaluesindifferentquartersaresmallAFRYandRNmodels,withrenewablesupplycomparedtothevariationsbetweenyears,scaledtobeequaltodemandoverthewholeandtotheaverageoftheabsolutevaluesperiod.Thelargevariationfromyeartoyear,ofannual/quarterlyresidualenergy,of123/whichisstrikinglymanifestedintheverylarge30.8TWh.Withawind-solarmixaround80/valuereachedbythecumulativetotalinthe20,residualenergy,andtheneedforstorage,middleoftheperiod,showsthatstudiesofaredominatedbyvolatilityonalltimescales,singleyearsorevendecadeswillgenerallynotbyseasonaldifferences.Thisremainsgivemisleadingresults.Ifdisplacedupwardsbyapproximatelytrueforsolarcontributions50TWh,thecumulativetotalwouldrepresentintherange10–30%,although(seeSI2.4)theamountofenergyinahypothetical100%with30%solarthereisanoticeable(althoughefficientstorethatinitiallycontained50TWh,smallcomparedtovolatility)surplusinthewhichcouldbeusedtoexactlybalancesupplysummer,whilewith10%solarthereisasmallanddemandover37years.Suchastorewouldsurplusinthewinter.havetobeabletoaccommodate192TWh(thedifferencebetweenthemaximumandminimumofthecumulativetotal)andbechargedbyasystemcapableofstoringallresidualpower,whichrangesupto123GWinthiscase.Intherealisticcaseofmuchlowerefficiencies,amuchhigherlevelofwindandsolarsupplywouldbeneededtomeetdemand(assumingtherearenoothersourcesofsupply).However,whilethevolumeofstorageandthepowerneededtofillthestorearestilldauntinglylargeattheminimum(‘threshold’)levelofwindandsolaratwhichdemandcanbemet,theydecreaseveryrapidlyasthelevelincreasesabovethethreshold,asdiscussedinthenextchapterandshowninfigure12.22LARGE-SCALEELECTRICITYSTORAGEChaptertwoFIGURE8Netquarterlysurplusesanddeficitsaveragedover37years.Xisthemean,thecentralverticallineshowsthemedian,thehorizontallineextentshowstherangeofthedata,andthecolouredboxesshowtheinterquartilerange(themiddle50%ofthedata).Quarter1Quarter2Quarter3Quarter4-50-40-30-20-100102030405060Netquarterlysurplusordeﬁcit(TWh)2.5Residualdemand,energyandpowerTheseplotsshowthatforrenewablesupply2.5.1Residualdemandandenergyupto50%ofdemand,almostalloftheThefractionofdemandthat(accordingtotherenewablesupplycouldinprinciplebeusedAFRY/RNmodel)canbeprovidedbywindinanaverageyear.Inpractice,however,andsolarenergydirectlyinanaverageyear,isthiscouldonlyhappenifallothersourcesofshowninfigure9aasafunctionoftheaveragesupplywereinstantlyturneddownwheneverlevelofwindandsolargenerationdividedbytheircontributionsplusthoseofrenewablesannualdemand(expressedinthisway,residualexceededdemand.Figure10showsthedemandvariesverylittleacrossawiderangesituationifsomeofthedemandismetbyofmodels–seeSI2.5).Thesurplus,whichinflexiblyoperated‘baseload’supply.isimplicitinfigure9a,isshownexplicitlyinfigure9b;itcanbestoredandusedtomeetallorpartofresidualdemand,curtailed,orusedforotherpurposes,asdiscussedinsection8.6.LARGE-SCALEELECTRICITYSTORAGE23ChaptertwoFIGURE9A)Fractionofdemandthatcanbemetdirectlybywindandsolarinanaverageyear.Demandmet/demand1KEY0.9RdieresicdtulyabldyewminadndancdansnoolatrbemetAverageyear0.8BestyearWorstyear0.70.60.50.40.3Ddieremcatlnydbmyewtindandsolar0.20.101.11.21.31.41.51.61.71.81.9200.10.20.30.40.50.60.70.80.91Averageannualrenewablegeneration/demandB)Percentageofwindandsolargenerationthatcannotbeusedtomeetdemanddirectly,andisthereforeavailabletobestoredorusedinotherways.Percentageofwindandsolargeneration7060504030201001.11.21.31.41.51.61.71.81.9200.10.20.30.40.50.60.70.80.91Averagewindplussolargeneration/demand24LARGE-SCALEELECTRICITYSTORAGEChaptertwoFIGURE10A)AsinFigure9inthecasethataconstantbaseloadsupplygenerates150TWh/year.1KEYDemandmetdirectly/demand0.9AverageyearBestyear0.8MetbybaseloadWorstyear0.70.60.50.40.30.20.101.11.21.31.41.51.61.71.81.9200.10.20.30.40.50.60.70.80.91Averagesolarpluswindgeneration/demandB)Thesurpluselectricityafterdemandismetbybaseloadgenerationandwindandsolar.Percentageofwindandsolargeneration70KEY60With150TWhbaseload50Nobaseload4030201001.11.21.31.41.51.61.71.81.9200.10.20.30.40.50.60.70.80.91Renewablegeneration/demandLARGE-SCALEELECTRICITYSTORAGE25ChaptertwoFIGURE11Spectrumofresidualdemandfor741TWh/yearaveragewindplussolargeneration.Spectrumofresidualdemandover37yearswithanaverageof741TWh/yearwindplussolarsupplyandtheAFRYmodelfor570TWh/yeardemandusedineveryyear.Theinclusionofdetailedcorrelationsbetweentheweatheranddemandwouldincreaseandbroadenthepeak.Residualdemand(GW)100908050k100k150k200k250k300k350k706050403020100-100Hoursin37years2.5.2ResidualpowerMaximumdemandis98.4GWintheAFRYFigures9and10showthatwithhighlevelsofmodel,whiletheminimuminsupplyis0.4windandsolar,residualdemandforenergyisGWinthe37yearsstudied(thespectrumofrelativelysmall.However,residualdemandfordemandandsupplyinthesemodelsisreportedpowercanreachveryhighlevels,asseenininSI2.5).Ithappensthatthesevaluesneverfigure11,whichalsoshowsthatwithsupply=coincide,andthemodelfindsamaximum1.3xdemand=741TWh/yearthereisasurplusresidualdemandforpowerof88.2GW.63%ofthetimeinanaverageyear.WhateverHowever,correlationsbetweentheweathermeetsthisdemand(storageorothersources)anddemand,whichwillincreaseresidualwillbeoperatingmostofthetimewellbelowdemand,andbroadenthepeakinfigure11,thepeakpowerthatitwasbuilttoprovide:thecannotbeignoredinthiscasebecausetheelectricityitprovideswillthereforeinevitably37yearsstudieddonotcoverallpossibilities.beexpensive.Itwouldthereforebeunwisetoassumethatsuchacoincidencecanneverhappen,andstoragepluscomplementarygenerationshouldbedesignedtomeetmaximumdemand.Thecostingofstorageinthisreportallows(prudently)formaximumresidualpowerof100GWwhenusingAFRY’smodelof570TWh/yeardemand.26LARGE-SCALEELECTRICITYSTORAGEChaptertwoTABLE2Attributesofcomplementarysourcesofelectricity.CostsfromBEIS(2020)areforplantscommissionedin2040,exceptfornuclearwhichisfromBEIS(2016)forreactorscommissionedin2030LowcarbonCostofpower–FlexibilityEnvironmentalCommentsoptions£/MWhcredentialsCostverysensitivetoNuclearExpensivetorunflexibly:bestasbaseload.discountrate.SmallModular66–99with90%Cost(63+17.5/LF)=£78/MWhifLF=90%Goodreactorscouldbecheaper.Gaswithloadfactor(LF)CarbonAvailabilityofbiomasslimitsCaptureand79–85with92%Expensivetorunflexibly:bestasbaseload.CompromisedbyGBpotentialtosome50StorageLFassuminggasCost(62+18.4/LF)if£82/MWhifLF=92%leakedmethaneTWhe/year(withoutimports).Bioenergycosts£21.8/MWhandfugitiveCO2withCCSBestrunasbaseloadasitis:emissionsPotentiallimitedinGB.182–211fori)expensive(ifnotsupportedbycarbonDelivered5.5TWhein2021Hydropowerpostcombustioncredits);andNegative(including1.8TWhefromcapturef,with90%ii)carbonnegativeemissionsifpumpedhydro).BiomassLFGoodbiomasscarefullysourced75forlarge-scalehydroGooddependingonsite90–105Characteristicsaredifferentforplantmassdedicated(whichcontributed27.1TWhin2021),biomassandbiodegradablewaste,landfillgas,anaerobicdigestionetc(whichtogethercontributed8.79TWh)2.6Generatingcosts•£35/MWh,justaboveBEIS’slowprojection1Thedesirablelevelofwindandsolarfor2040(of£34.9/MWh);andgeneration,andtheneedforstorage,willbedeterminedbytheircosts,andbythe•£45/MWh,justaboveBEIS’shighprojection1availability,characteristics(especiallycost(of£39.6/MWh)for2040.andflexibility),andenvironmentalcredentialsofgenerationbyotherlow-carbonsources.SI2.6includesadetailedanalysisoftheotherInestimatingtheaveragecostofelectricityformsoflow-carbonelectricitygeneration.in2050,threevalueswillbeusedfortheTable2summarisesthekeyfeaturesofweighted(80%wind–70/30offshore/themainlow-carbonoptionsforGB.Onlyonshore+20%solar)averagecostofwindplusnuclear,gaswithCCS,andBioenergy,withorsolarpower:withoutCCS(BECCS)arecapableofmeeting•£30.2/MWh,avaluederivedfromtheIEA’sasignificantfractionofdemand.Allareexpensiveorveryexpensiveifoperatedflexibly2020projection14ofcostsinEuropein2040tocomplementfluctuationsinsupplyandusingthecapacityfactorsassumedbyBEISvariationsindemand.fortheUKin2040;fAreportforBEISprojected£138/MWhwithchemicallooping,butBEIS‘hasgreatestconfidence’inpost-combustioncaptureLARGE-SCALEELECTRICITYSTORAGE27Chaptertwo2.7DemandmanagementProlongedperiodsoflowwind,whichcanThetermdemandmanagementisusedtooccasionallylastafewyears,riskemptyingdescribebothreducingdemandandshiftingenergystoresiftheyarenotprovidedwithitintime.ModelssuchasAFRY’sandtheenoughcontingency.IftheseperiodscouldbeNationalGrid’sscenariosbuildinassumptionsforecastinadvance,theriskcouldbereducedaboutoverallreductionsindemandandbytakingsomeofthemeasuresdescribedimprovementsinenergyefficiency,whichwillbytheIEA16,17inananalysisofresponsestonotbeconsideredhere.Inordertoevaluatetheprolongedshortfallsinelectricitysupplies,needforstorage,itisimportanttounderstandwhichhaveoccurredoccasionallyinmanythescopeforemergencytimeshiftingcountries.leadingtotemporaryreductions,whichcouldprovidesomecontingencyfordealingwithTheIEAfoundthatlargesavingscanberareweatherevents.made,especiallywhenproblemsareforeseenwellinadvance.Examplesincludea14%TheNationalGrid’sDemandFlexibilityServicereductionover9monthsinCaliforniain2002,providesincentivesthatencourageshiftingandsavingsof15%inJapaninthesummerdemandduringpeakwinterdays,whileitsfollowingtheFukushimadisaster(morenetzerocompatible2050scenarios5assumeexamplesaregiveninSI2.7).Successfuldemand-sideresponseflexibilityof24,34andstrategiesthathavedealtwithsuchshortfalls37GW.Thislooksachievable(seeSI2.7)andinclude:raisingprices;campaignstochangewouldhelpflattentheeveningpeakindemand,behaviour,whichurgedmeasuressuchanddealwithshorttermmismatchesbetweenadjustingschedulesfortheuseofelectricity-supplyanddemand.However,itcouldnotdealintensiveequipment;andrationing,whichcanwithlongerperiodsofscarcewindandsolarbesupplementedbytradingofentitlements.supply,whichcanlastuptotwoweeks.Norcoulditcopewiththefactthat,asshownbyastudyofwindandsolarsupplyinGermany15themaximumenergydeficitoccursoveramuchlongerperiodbecausemultiplescarceperiodscanfolloweachotherclosely(asdiscussedinSI2.7andseenonayearlyscaleinfigure2).28LARGE-SCALEELECTRICITYSTORAGEChapterthreeModellingtheneedforstorage3.1IntroductionTherearealsoveryshort-termfluctuationsinManyestimateshavebeenmadeoftheneedresidualdemandduetosuddenchangesinforstorage(seeSI3.1).Theyarenotalwayssupply(createdbysystemtripsforexample)easytocompareasdifferentassumptionswereanddemand(includingmakingtheproverbialmade,forexampleontheacceptablelevelofhalf-timecupofteaduringmajorfootballCO2emissionsandwhatsourcesofsupplyarematches).However,asdiscussedinsectionavailable,whiletheneedforstoragedepends1.3,thestoragethatisneededtodealwithontheclimateandweather.Further,whilethesefluctuationsissmall-scaleandisoutsidetheamountofenergythathastobesuppliedscopeofthisreportg.Apartfromthisneed,bystoragedependsonlyonthescaleandandtheneedforstoreswithlowcapitalcoststemporalprofilesofsupplyanddemand,thetoprovidelong-termstorage,itisnotpossiblestoragecapacityrequiredtoprovidethisenergytochoosestoragetechnologiesbymatchingdependsontheefficiencyofwhateverstoresthetimescalesneededtorecovercostswitharedeployedandtheratesatwhichtheycanthecharacteristictimesonwhichresidualbechargedanddischarged.demandfluctuates.3.1.1Timescales3.2ModellingandcostingwithasingletypeThecharacteristicperiodsonwhichresidualofstoredemandfluctuatesare:3.2.1Theinterplayofchargingrates,storage•Daily–drivenbyday/nightvariationsincapacitiesandthelevelofwindandsolarsupplydemandandsolarsupply.Atthethreshold,theminimumlevelatwhichwindandsolarsupplyandstoragecanmeet•Weekly–drivenbyweek/weekenddemand,allsurpluseshavetobestored.differencesindemand.Abovethreshold,itisnotnecessarytostoreallsurpluses,andthereisachoice(within•Fromdaystoweekstoafewmonths–drivenlimits)betweenarelativelysmallstoragebyrandomweathervariationsandfrontalcapacitychargedrapidlybyapowerfulcohortweathersystemsthataffectwindand(viaofelectrolysersandalargercapacitychargedcloudcover)solarsupply.moreslowlybyalesspowerfulcohort.Thealloweddomainisshowninfigure12inthe•Seasonally–drivenbydemand,windsupplycasethatallGB’slarge-scalestorageneedsbeinghigherinwinter,andsolarsupplyaremetbyhydrogen,andwindandsolararebeinghigherinsummer.Withthe20/80theonlysourcesofsupply.Iftheelectrolysers’solar/windmixusedinthisstudyofGB,thepowerwaslessthanthevalueatthebackedgelargeseasonalvariationsthatareseeninofthesurfaceinthefigure,theywouldnotbemostyearsaverageoutovermanyyears:abletoreplenishthestorefastenoughtokeeptheunderlyingproblemisvariabilitynotpacewithdepletion,anddemandcouldnotbeseasonality(asshowninfigure10).met;atthefrontedgeofthesurface,thereisenoughpowertostoreallsurplusesandthere•Multi-year–drivenbylong-termchangeswouldbenopointininstallingmore(seeSI3.2inwind,linkedtochangesintheforfurtherdiscussion).magnitudeandfrequencyoftheNAOinatmosphericpressure.gVeryshort-termneedscannotbeseenoranalysedusingthemodelsofdemandandtheweatherusedinthisreportwhichhaveatimeresolutionofonehour.LARGE-SCALEELECTRICITYSTORAGE29ChapterthreeFIGURE12Levelofwindandsolargenerationandhydrogenstorageparametersforwhichalldemandcanbemet.Hydrogenstoragecanmeetdemandprovidedthestoragecapacity(V)isabovethesurfaceshownhereasafunctionoftheelectrolyserpower(G)andthelevelofaveragewindandsolargeneration.ThesurfacewasconstructedusingtheAFRY/Renewables.ninjamodelsofdemand/windandsolarsupply,andassuminganefficiencyof74%forelectrolysersand55%forconvertinghydrogentopower.ThecoloursshowthevaluesofVminonthesurface,accordingtothescaleontheright.Thedashedredlineshowsthevaluesofelectrolyserpowerforwhich,forgivenwindplussolarsupplyandtheassumedratioofthecostsofelectrolysersandstorage,theaveragecostofelectricityisaminimumwith20%contingencyaddedtothevolume,V=1.2xVminMinimumstoragecapacity(VminTWh)Thresholdat703.5TWh/year220G=169GW,Vmin=236TWh20025050180100160200150140200120150Electrolyserpower(GW)1001008060504000700720740760780800820840880250Averagewindplussolarsupply(TWh/year)3.2.2CostsStep1Thewayinwhichtheelectrolyserpower,theForafixedaveragelevelofwindandsolarsizeofthestoreandthelevelofwindandsolargeneration,takenforpurposesofillustrationsupplyandthecorrespondingaveragecosttobe1.3xdemand=741TWh/year,calculateofelectricityarefoundwillbeillustratedusingthecostofelectricityasafunctionofthethe2050costestimatesintable5,usinga5%electrolyserpower(G)andstoragevolumediscountrate,assumingthatan80/20mixtureV=(1+0.2)xVmin,where0.2isthe20%ofwindandsolarpowerwillcost£35/MWhandcontingency(VminandGaredependentandthat20%contingencyshouldbeaddedtothemustlieonthesurfaceinfigure12).Withthecapacityofthehydrogenstore.TherearetwobasecostsforGandV,thevaluesthatminimisesteps(whichcanbecombined):thecostofelectricityareG=89.4GW,V=123.1TWh.Thevaryinglevelofhydrogeninthestoreobtainedwiththesevaluesisshowninfigure13overthe37yearsstudied.30LARGE-SCALEELECTRICITYSTORAGEChapterthreeFIGURE13Levelofstoredhydrogenina123TWhLHVhydrogenstorefilledby89GWofelectrolysers.Levelofstoredhydrogenassumingaverageofwindplussolargenerationof741TWh/year,electricitydemandof570TWh/yearandthatallelectricityisprovidedbywindandsolarsupportedbyhydrogenstorage,apartfromasmallamountneededtoregulatevoltageandfrequency.Itisnotpossibletoseehourlyincreasesanddecreaseswiththisresolution,whichleadstothefalseimpressionthatthestoreisfrequentlyfullforsustainedperiods.GWh140k120k100kStudyingthese23years80kwouldgiveverydierentconclusions60k40kContingency20k50k100k150k200k250k300k00Hoursin37yearsFigure13exhibitstwostrikingfeatures.First,aStep2studyofthe23years1984–2006wouldhaveFindthelevelofwindandsolarsupplythatfoundastoragevolumeverymuchsmallerthanminimisestheaveragecostofelectricitybyfoundbystudying1980–2016.Second,thereallowingittovary,asshowninfigure14.Attheisaverylargecallonstorageintheperiodthresholdlevel,theminimumstoragevolume2009–2011whichreflectspersistentlylowandtherequiredelectrolyserpowerarebothwindspeedsthatleadtothelargedeficitsseenverylarge,asseeninfigure12,buttheirsizesinfigure2(someoftheenergythatfillstheseandcostsfallrapidlyasthelevelincreases.deficitswouldhavebeeninthestoresinceMeanwhile,thecostofthewindandsolar1980).Thesefeaturesreinforcetheconclusionsupplyincreases,leadingtoaverybroadthatitwouldbeprudenttoaddcontingencyminimumintheaveragecostofelectricityatagainstprolongedperiodsofverylowsupplyaround8%abovethethreshold,wherewindandthepossiblegreaterclusteringof2009toandsolarsupply=1.33xdemand,whichis2011-likeyears.analysedfurtherinsection8.3.1.LARGE-SCALEELECTRICITYSTORAGE31ChapterthreeFIGURE14Averagecostofelectricityprovidedtothegrid.Windplussolar@£35/MWh.Discountrate5%.Averagecostofelectricityprovidedtothegridwithdifferentassumptionsaboutcosts.Herelow/base/highrefertotheassumedcostsofelectrolysers,storageandgeneratingpowerfromhydrogen.ThesignificanceofthedashedlineisexplainedinSection3.2.3.90KEYHighstorage80costsBasestorage70costs£/MWhBasestoragecosts–surplus60soldLowstorage50costsCostofwindplussolarsupply40700710720730740750760770780790800Averagewindplussolarsupply(TWh/year)3.2.3Residualsurpluses3.3ModellingandcostingwithseveraltypesExceptatthethresholdforstoragetoworkoverofstorethewhole37-yearperiod,aresidualsurplusGridoperatorswillhavetodecidehowtoofwindandsolarenergyinevitablyremainsassignsurplusestodifferenttypesofstore,aftertheassumeddemandhasbeenmet.Ifandwhichstorestodischargetofilldeficits.additionaldemands(beyondthoseassumedAnassumptionabouthowthiswillbedoneintheAFRYmodel)thatcouldmakeuseofhastobemadeinordertomodelstorageandtheresidualsurplusarefound,itcouldhaveaestimatetheaveragecostofelectricity.Givensignificanteffectoncosts.Iftheentiresurplusesthecostsofallitselements,asystemthatwouldwerevaluedatcost(£35/MWh),whichwouldhavedeliveredelectricityattheleastcostoverrepresentapresumablyunrealisticupperagivenhistoricalperiodcanbedesignedwithbound,itwouldreducetheaveragecostofhindsight.Suchhindcastingcanprovideusefulelectricitytothevaluesshownbythedashedinsights,butasystemthatworkedatthelowestlineinfigure14.Possibleusesofthesurpluscostinthepastwouldnotnecessarilydoso(orarediscussedinChapter8.Thealternativetoevenwork)inthefuturegiventhevagariesofusingthesurplusesistocurtailor‘spill’parttheweather.orallofthem.32LARGE-SCALEELECTRICITYSTORAGEChapterthreeToillustratetheschedulingprocedureusedinMoreworkisneededonproceduresforthisreport,whichdoesnotrequireforesight,schedulingstoringanddispatchingelectricity,considercombiningACAESwithhydrogenandoncombiningstoragewithothersourcesstorage.TheadditionofACAESdecreasestheofflexiblesupply.Itwouldbeinterestingtoneedforhydrogenstorage.AddingACAESwillstudyschedulingproceduresthatuseseasonal,onlybeworthwhileiftheconsequentreductionaswellasweather,forecasts.ItisgenerallyincostsisgreaterthanthecostoftheACAESnotpossibletopredictday-to-daychangessystem.ThisismostlikelytohappenifACAESintheweatherinmuchdetailbeyondaweekisnormallyhgivenpriorityinstoringsurpluses,ahead,butthereliabilityoflong-rangebroad-andindischargingelectricitytofilldeficits.Thisbrushforecastsisimproving18.KeyaspectsisbecausethemoreenergythatisstoredinofEuropeanandNorthAmericanwinteranddeliveredbyACAES,i)thesmallerthesizeclimatescanbepredictedmonthsaheadwithandcostofthehydrogensystem,whichmustreasonablereliability19.Thismakesitpossiblehandletheremainder,andii)thelowerthetomakeprobabilisticforecastsofnear-surfaceamountandcostofthewindandsolarenergywindspeedandairtemperatureandthereforethatisrequiredsinceACAESismoreefficient.predictenergysupplyanddemand20.Implementinganyschedulingproceduredesignedtoleadtolowcostswouldrequireclosecooperationbetweentheelectricitygeneratorsandtheoperatorsofstorage.Thisraiseschallengesforthegovernanceanddesignoftheelectricitymarket,whicharediscussedinChapter9.hIf,usingforecastsofsupplyanddemand,itisfoundthatalwaysgivingprioritytoACAESwouldresultinitbecomingmorethan~90%fullinthenext12hours,priorityinchargingisswitchedtohydrogen.Conversely,ifitwouldbecomelessthan~10%full,priorityindischargingisswitchedtohydrogen.(ThepreciselevelatwhichtheswitchismadedependsontheassumedefficiencyofACAES:fordetailsseeSI3.3).Theintroductionofthisrefinementchangesthedemandsoneachstoretoabsorbandprovidepowerandreducestheaveragecostofelectricityby~2%relativetothevaluethatisfoundifACAESisalwaysgivenpriority.LARGE-SCALEELECTRICITYSTORAGE33ChapterfourGreenhydrogenandammoniaasstoragemedia4.1Introduction4.2HydrogenandammoniaproductionHydrogenandammoniacanbeusedtostore4.2.1Hydrogenelectricalenergyinthesequence:Worldwide,dedicatedhydrogenproductioncurrentlyamountstosome69Mtp.a.mainlyelectricity→hydrogenorammonia→transport/bysteammethanereforming,withathermalstore→electricity.energycontentofapproximately2,300TWhLHV(equivalenttotheenergycontentofaroundHydrogenhasahighergravimetricenergy9%ofannualglobalelectricitysupply)21.Indensity(kWh/kg),butamuchlowervolumetricaddition,48Mtp.a.isproducedasaby‑productenergydensity(kWh/litre)thanammonia,fromthecatalyticreforminginoilrefineriesmethaneorpetroleum(seefigure15),unlessandtheproductionofchlorineandolefins.itiscompressedtoseveralhundredtimesAsmallamount(around2%)isproducedatmosphericpressure,liquifiedat-253°C,electrolyticallyasaby-productofchlorineandorstoredasacomponentofachemicalcaustic-sodaproduction.Dedicatedelectrolysiscompound(suchasmethanolCH3OH,orprovidedlessthan0.1%in2019,butsincethenammoniaNH3)fromwhichitcanbereadilyelectrolysercapacityhasgrown,from242MWbeseparated.Ammoniaismoreexpensiveto1398MWin2022,with5,517MWanticipatedtoproducethanhydrogen,butitbecomesin202321,22.liquidatjust-33°Catatmosphericpressure.ItisthereforecheapertotransportandtostoreTheproductionprocessofinterestinthisthanhydrogen.Foruseswhereeitherhydrogenreportiselectrolysisofwater,poweredbyorammoniawouldserve,theformerbeing‘green’carbon-freerenewableenergytomakecheaperwillusuallybepreferredifthepointlow-carbon‘green’hydrogen,whichcanbeofuseiscloseintimeandspacetothepointuseddirectlyasanenergystore,ortomakeofproductionandlarge-scalestorageand‘green’ammonia.transportarenotneeded.Inelectrolysis,adirectelectriccurrentisusedtosplitwaterintohydrogenandoxygen,onthecathodeandanodesidesofanelectrochemicalcell,whichareseparatedbyanion-conductingelectrolyte.Electrolysers,whichconsistofanumberofcellsbuiltintostacks,canrangefromdomesticappliancesizetoindustrialproductionfacilities.Theoutputscaleswiththesurfaceareaoftheiranodesandcathodes.34LARGE-SCALEELECTRICITYSTORAGEChapterfourFIGURE15Energydensitiesofenergycarriersi.PetroleumPetroleumMethaneMethaneAmmoniaLiquidammoniaLiquidhydrogenHydrogenHydrogen700barHydrogen350bar246810051015202530350Energydensity(KWh/litre)Massenergydensity(MWh/t)ThecharacteristicsofthreetypesofwaterInmodellingstorageinthisreport,theelectrolysersjaresummarisedintable3.following2050electrolyserparametersareTheprojectionsofcostsandperformanceassumed:cost(includingrectifier,balancespanwiderangesastheydependonthesizeofplant,installationandashareofsiteofthemoduleandthescaleofproduction,costs)$450+/-50%/kWe;efficiency74%asdiscussedinSI4.2.Forexample,although(theconclusionsarenotverysensitivetotheIRENA’ssummarytablequotesa2050efficiency);operatinglifetime30yearsk;annualcostof<$200/kWforalkalineandpolymerO&Mcostof1.5%ofthecapitalcost;outputelectrolytemembraneelectrolyserstheirtexthydrogenpressureof30bar(thehigherthegives$307/kWand$130/kWforcumulativepressure,thelesscompressionisneededpriorproductionof1TWand5TWrespectively.tostorage).iHereandthroughoutthisreporttheenergydensity/thermalenergycontent(or‘equivalentcalorificvalue’)ofhydrogenisquotedintermsofitslowerheatingvalue(LHV).Thehigherheatingvalue(HHV)isalsooftenused.Inthecaseofhydrogen,theHHVis18%largerthantheLHV(seeglossaryfordefinitions).jAnionExchangedMembraneElectrolysers,whicharediscussedinSI4.2,areconsideredtobeapromisingfourthoption,buttheyarelessmaturethantheotherthreeandlimitedinformationisavailableabouttheirlong-termoperation,reliabilityandrobustness.kWiththeloadfactorofaround30%foundinthehighhydrogenstoragescenariodiscussedinChapter3,alifetimeof30yearscorrespondstosome80,000operatinghours.Thedeteriorationofelectrolyserperformancewithuseisignoredincostingstorageinthisreportasitonlyhasasmalleffectontheirnetpresentvaluebecausethefaderateissmallandlateryears,whenfadeissignificant(perhaps30%attheendoflife),arediscounted.LARGE-SCALEELECTRICITYSTORAGE35ChapterfourTABLE3Propertiesofdifferenttypesofelectrolysers.AlkalinePolymerElectrolyteSolidOxideMembraneAvailabilityCommerciallyavailableNotyetdemonstratedformanyyearsCommerciallyavailablebutatscaleElectrolyte/potentialforimprovementmembraneSodium,orpotassiumOxygenionconductinghydroxideAqueouselectrolyteceramic,typicallyzirconiapolymericmembrane(ZrO2)basedLoadCanfollowCanfollowveryfastAbilitydependsonthefollowingIRENA23transients<1secdesign43–67%Efficiency>74%IEA21IRENA23IEA21IRENA23IEA21today500–100063–70%<20070–80%40–67%55–60%61–74%74–81%2050(IRENA)60500–1400/Future(IEA)200–700>74%67–74%>83%77–90%10060–90Costtoday<30700–14001100–1800>20002800–$/kW100–1505600>701–30<200200–900<3002050/Future50–8030–90<20500–1000–Lifetime10–30today1000operating100–120100–1508075–100hours<7030–80<1012050/Future>70–>20–Outputpressure(bar)today2050/FutureLHVofproducedhydrogen/electricalenergyinput–basedonACpowerinput.Fullsystemcosts.Rangesdependonscaleofmanufacturingandsizeofmodule–seetext.Intheirsimulations,IEAassumeafuturecostof$450/kWandanefficiencyof74%.36LARGE-SCALEELECTRICITYSTORAGEChapterfourTurningtothedifferenttypes,whichareTheoptimalwaytosourceelectrolyticdiscussedinmoredetailinSI4.2:hydrogenatscalemaybefromamixtureoffacilitiesthatusedifferenttechnologies,forAlkalineelectrolysersmaytakeupto30exampleusingalkalineelectrolyserswhenminutestostartfromcold,butcanbekeptsteadyorslowlychangingpowerisavailablewarmwhennotworking,andcanloadfollowandPEMelectrolysers(whichcurrentlyhavewhenworking,subjecttosomeconstraintshigherunitcapitalcosts)toprovideadditionalonrampingrates.Whenstoringvolatilewindflexibilityandfasterresponsetotransientsinandsolarpower,electrolysersarelikelytothepowersupply.beswitchedonandoffsome200times/year.ThiscouldpossiblyreducethelifetimeWiththeelectrolysercostandefficiencyusedofalkalineelectrolysers,althoughrecentinthisreport(summarisedabove),thecostofmeasurements24supporttheexpectation(seegreenhydrogen(withoutthecostoftheinputSI4.2)thatthiswillnotbeaseriousissue.powerwhichdominatesthetotalcost)wouldbe$(5.97/loadfactor)/MWhLHVwitha5%discountPolymerElectrolyteMembrane(PEM)rate,and$(8.40/loadfactor)/MWhLHVwith10%.electrolysersusebothplatinumandiridiumasThecost/tonneisgivenbymultiplyingby33.3.catalysts.Theavailabilityofplatinumisunlikelytolimitdeployment(asdiscussedbelowin4.2.2Ammoniarelationtofuelcells),buttheavailabilityofAmmoniaistodayproducedbytheHaber-Iridiumwillconstrainrapidlarge-scaleglobalBosch(HB)process,inwhichhydrogenandrolloutofPEMelectrolysers.Reduction/nitrogenarecombinedathightemperatureandeliminationofIridiumshouldbeahighprioritypressureinthepresenceofametalcatalyst.forfutureR&D.ItispossibletosynthesiseammoniaSolidOxide(SO)electrolysershavenotyetdirectlyfromairandwaterusingacatalyticbeendemonstratedatscale,sotheirfutureelectrochemicalprocess.Theratesobservedincostsareuncertain.Theyarefedbysteamthelaboratoryarecurrentlyverylow,andthere(whichcouldbeprovidedelectricallyorbyaremanychallengestobeovercomebeforewasteheat)whichleadstoasomewhathigherdirectsynthesiscouldbecommercialised.efficiencythanforlowtemperaturealkalineDirectsynthesisisthesubjectofR&Delectrolysersespeciallyifwasteheatisused.worldwide:successwouldbeagamechanger.Theyhavethemajoradvantagethattheycan,inprinciple,beoperatedreversibly–asTheHBprocesscurrentlyrequirescontinuouselectrolyserswhenthereissurpluswindandrunninginordertomaintainefficiencyandsolarpower,andasfuelcellswhenthereisaavoiddegradationofthecatalystortheprocessdeficit.Thiscouldprovideacostadvantageequipment.Wheninputenergyorhydrogenforstoragethatwouldprobablymorethansupplyisvariable,bufferingbyelectricity,andoffsetthefactthattheyproducehydrogenat/ormorelikelybyhydrogenandnitrogenambientpressure.storage,wouldberequiredtoensureconstantrunning.Thiswillincreasecostscomparedtousingaplantwithaconstantpowersupply.LARGE-SCALEELECTRICITYSTORAGE37ChapterfourNaturalgas-basedammoniaistodayalmost4.3TransportallmadeinintegratedplantsthatincludeaIncostingtheuseofstoredhydrogen,itismethanereformer(toproducehydrogen),anassumedinthisreportthatelectrolysers,storesair-blownsecondaryreformerwhichintroducesandwhateverisusedtogenerateelectricitynitrogen,andanHBsynthesislooptoproducefromhydrogen,areco-located.Ifnot,itwouldammonia.Forgreenammonia,thereformersbenecessarytotransporthydrogento/fromwouldnotbenecessary,butnitrogenwouldthestoresinpipelinesasusingtrainsortankershavetobesuppliedfromanairseparationunitwouldbemuchmoreexpensive(seeSI4.3for(ASU).Analysisofthecostsofexistingammoniaacomparisonoftheoptions).Thesizeandcostplants,andcostestimatesfoundintheliteratureofthepipesthatwouldberequireddependsandprovidedbyindustrysources,whichareonthemaximumflowrate,whichhastobedescribedinSI4.2,leadstotheconclusionthatcalculatedcase-by-case(forwhichpurposethefullcostofanASUandanHBisaroundtheunitcostsandflowratesusedbyIEAwere$900pertonneofammoniaperyearonaUSassumedinthisreport).IfGBwerepoweredGulfCoastbasis.Forcomparison,theIEAgivesentirelybywindandsolarenergysupportedacapitalcosttodayof$945pertonneammoniabyhydrogenstorage,andelectrolysersandperyear,andprojects$760pertonneammoniageneratorswere100milesfromthestore,peryearforthelong-termcost.Inrecognitiontransportinghydrogenwouldaddsomethatcostsmayevolveovertime(althoughthe£22/MWhetothecostofthe15%ofelectricitytechnologyismature),$760pertonneammoniathatisprovidedbyhydrogenstorage,andperyearisassumedhereforgreenammonia£3.3/MWhetotheaveragecostofelectricity,productionin2050,excludingthecostoftheunlessitwerepossibletouserefurbishedassociatedelectrolysers.naturalgaspipelines.Withthisassumption,theestimatedcostof4.4Storagehydrogenabove,annualO&Mof4%ofcapex,4.4.1Hydrogenafinancialprojectlifetimeof30years,thecostOntheTWhscale,thecostofstoringhydrogenofmakingammonia,excludingthecostofinputinsolution-minedsaltcavernslisanorderofpower,wouldbe:magnitudelessthanthecostofstorageinhigh•$(32.6forhydrogenproduction+79.8forpressuretanksorasaliquid25.GBcurrentlyhasanundergroundcavernstoragecapacityammoniasynthesis)/(loadfactor)pertonneforsome25GWhofhydrogenandover20ofammoniaperyear,witha5%discountrate;TWhofnaturalgas,which(if/whennaturalorgasisphasedout)couldhousesome7TWhofhydrogen(muchlessthanwillbeneeded).•$(49.4forhydrogenproduction+111.0forSaltcaverns,whicharewidelyusedtostoreammoniasynthesis)/(loadfactor)pertonnenaturalgas,are‘recognisedforbeingverygasofammoniaperyear,witha10%discountrate.tightandthereforewellsuitedforhydrogenstorage’26.ThreesaltcavernsareusedforThisassumesthathydrogenproductionandhydrogenstorageinTexas(theyhavevolumesammoniasynthesisareconcurrent(ifnot,of580,000m3,566,000m3and906,000hydrogenstoragewouldaddtothecost).m3,andhavebeeninoperationsince1983,2007and2017respectivelym).AclusterofTheoverallefficiency[MWhLHVammoniathree70,000m3caverns(whichhavebeenproduced)/(MWhinputenergy)]is:inoperationsince1972)areusedtostore((1.14/(electrolyserefficiency))+0.07)-1=62%hydrogenonTeesside.foranelectrolyserefficiencyof74%.lThereisapotentialforstoringhydrogeninunderseaaquifers,relativelyclosetoshore.On-goingresearchisexploringthispossibility.Lossesofhydrogencouldbeanissue.mThestoragecapacities,whichdependonthepressurerange,whichdependsonthedepth,are69,194and232GWhLHV.TheclusterofcavernsonTeessidecanaccommodate26GWhLHV.38LARGE-SCALEELECTRICITYSTORAGEChapterfourFIGURE16Basin-widestoragecapacities.Basin-wideenergystoragepotentialinthethreestudyregions,afterexcludingareasoccupiedbytowns,roads,railways,mineworkings,waterways,rivers,canals,protectedareas,geologicalfaults,formationboundariesandareasofwetrockhead.Foreachvalueonthehorizontalaxis,theheightofthebaristhetotalamountofenergystorageavailableinthebasinincavernsofthatcapacityorgreater.Totalbasinstoragecapacity(TWh)1600KEY14001200Cheshire1000WessexEastYorkshire800600400200040801201602002402803203604004404800Percavernstoragecapacity(GWh)ThisreportusestheH21NEconsortium’sThecostofstoringhydrogeninsolution-minedestimateofthecostofstoringhydrogeninsaltcaverns(describedinfigure17),dependsonclustersof10300,000m3solution-minedmanyfactorsincluding:cavernsinEastYorkshire26.Eachcavernwould•Thegeology,thedepthandthedistancefromhouse122GWhLHVofuseablehydrogen.TheBritishGeologicalSurveyhasestimatedthesiteswherebrinecanbedisposed.potentialstoragecapacityasafunctionofthecapacityinthreeregions27(seefigure16).•Thesizeandpressure.ForexampleastudyAltogethertherearemorethan3000potentialbytheArgonneNationalLaboratoryforcavernlocationsinEastYorkshirethatcouldtheUSDepartmentofEnergy3foundthateachstore122GWhintheconditionsassumedthecostofstoringbetween50and3000byH21NE26.Thedistributionwouldallowthemtonnesofuseablehydrogenat150barvariestobegroupedinclustersof10caverns,whichapproximatelyas(mass)-0.52.couldallbewithin15milesoftheseatherebylimitingthecostofbrinedisposaln.Thepotential•Theovergroundequipment,managementcapacityinEastYorkshirealoneisfarmorecostsandcontingencythatareincluded.thanrequiredtoprovidethe~100TWhLHVofhydrogenstoragethatwouldbeneededtosupportGB’selectricitysysteminthecaseofhydrogenstorageonly.nJWilliams,BritishGeologicalSurvey,privatecommunication.LARGE-SCALEELECTRICITYSTORAGE39ChapterfourFIGURE17H21NE26basedtheirestimatesofsubsurfacecostsonexperiencefromanoperationalgasSolution-miningasaltcavern.storageplantatAldbroughandusedquotationsfromsupplierstoestimatethecostofcriticalNotesplitverticalscale:thetopofthe300,000equipment(compressors,coolersetc).Them3cavernscostedbyH21NEareatadepthestimatesincludesitepreparationandservices,of1700m.Theyhaveaheightof100m,andanmanagementcosts,brinedisposal,andotheraverageradiusof31m.costs,suchasinsurance,aswellassomecontingency.TheirestimatesareconsistentBrinewiththosemadebytheArgonneNationalLaboratory,althoughlowerthansomeothersinWatertheliterature,asdiscussedindetailinSI4.4.NitrogenblanketArangeofonetotwotimestheH21NE26Blanketestimate,of£325Mforaclusterof10cavernswhichwouldtogetherhouse1.22TWhLHVofSumpuseablehydrogen,willbeassumedhere.oThemiddleofthisrangeistakenastheimage:©DEEP.KBBGmbH.basecase,reflectinguncertaintiesincostingundergroundworkandthelimitedexperienceofbuildingundergroundhydrogenstoragefacilities.Thecostcouldbelowerifconstructingcavernssubstantiallylargerthan300,000m3ispracticable,compressorcostsreduce,andelectrolyseroutputpressuresgoup.Itwould,however,berashtoassumethatthecostofstoringhydrogenin2050willbelowerthanthatestimatedbyH21NE26.TheH21NEstudyassumesO&Mcostsof4%/yearofcapex.Thisisforasystemthatiscycledregularly,whereasthemodellingofstoragedescribedinchapter3suggestsaverylowthroughput/volume,and1.5%oftotalstoragecapexisassumedhere.Afinanciallifetimeof30yearsisassumed.oThecompressorpowerintheH21NE26designissufficienttohandlehydrogenproducedatthelowerpressureandhighertemperatureassumedinthisreport,asitisprovidedatthelowerrateneededforhydrogenstorage.40LARGE-SCALEELECTRICITYSTORAGEChapterfourAclusteroftencavernsofthesizeconsidered4.5Electricitygenerationherecouldbebuiltinfiveyears,according4.5.1Hydrogentoawellinformedindustrysource,providedHydrogencanbeusedtogeneratepowerthecavernsaresolution-minedinparallel.usingfuelcells,internalcombustionengines,orIfsufficientfreshwaterisnotavailable,seaturbines.Althoughitisexpectedthathydrogenwatercouldbeused.Ifallthestorageneededburningturbineswillbeavailablebytheendtocomplementhighlevelsofwindandsolarofthisdecade,theywillnotbediscussedhereisprovidedbyhydrogen,some85clustersasitappears(seeSI4.5)thatusingfuelcellsorof10cavernseachwillberequired(without4-strokeengineswouldbecheaper.contingency,whichwouldbeaddedattheend).Buildingthismanyclustersby2050wouldSomesavingscouldpossiblybemadebybechallenging,butthetechnicalcapabilitiesconvertingpartoftheexistingfleetof~30neededtoexecutesuchprojectsalreadyexistGWofCombinedCycleGasTurbinestoburnintheUK.However,theUK’sonshorenaturalhydrogen.However,hydrogenfiringpresentsgasstoragecouldbeconvertedtoprovide7technicalissues,andretrofittingofGTstoburnTWhofhydrogenstorage,whilewhen–as100%hydrogenhasnotyetbeendemonstratedproposed28–theoffshoreRoughstorageatscale.Thecostoftransportinghydrogentofacilityisconverted,itwouldprovideanotherCCGTsthatarenotclosetowhereitisstored10TWh.Togethertheseexistingfacilitieswouldwouldreduceorremovepotentialsavings.providethesamecapacityas14oftheclustersconsideredhere.FuelcellsFuelcellscanbeusedtogenerateelectricity,4.4.2AmmoniaandalsotoprovideindustrialheatandAtalargescale,thecheapestwaytostorecombinedheatandpower.Theoptions,noneammoniaisasaliquid,at-33°Candambientofwhicharecurrentlydeployedforgridscalepressure.Theworld’slargesttankscanstorehydrogenpoweredelectricitygeneration,are:50,000tonnes.Littlepublicinformationisavailableaboutthecostofsuchtanks,butProtonElectrolyteMembrane(PEM)fuelcellsaccordingtoasourceintheindustry(privateThesehavehighefficiency(todaytypically55%communication),costsfora50,000-tonneforpowerapplication)andareincreasinglyusedtankandcompressorinEuropewouldstartattopowercars,buses,forklifts,etc,aswellastoaround€60M.Similarestimatescanbefoundprovidebackuppowerforthegridp,30,31.Manyintheacademicliterature29andacostof€60Mstudieshavebeenmadeofthecostoffuelcellswillbeusedinthisreport.Withtheexchangemanufacturedatlarge-scaleforuseinvehicles:rateusedinthisreport,thiscorrespondsareviewfortheUSDepartmentofEnergy32,to£197/MWhLHV,whichis74%ofH21NE’s26forexample,foundthatthecostof237kWestimateofthecostofahydrogenstoragestacks,producedatascaleof20GW/year,facility.Incostingammoniastorage,itwillbecouldfallto$86/kWe.assumedthatsuchtankshavealifetimeof30years,andthatannualO&Mwouldbe1.5%oftheircapitalvalue.pTheycontainacatalystconsistingofplatinumnanoparticles.Itisexpectedthatsupplyofplatinumwillbeabletomeetdemandforfuelcellsforpowergeneration,andforpoweringvehicles,whichisexpectedtobemuchlarger,although‘therecouldbesignificantsupplyrisksduetoresourcelocation’and‘reducingplatinumloading…,increasingrecyclingrates,andimprovingthereliabilityoftheplatinumsupplychainareappropriatemeasurestoaddresstherisks’(HaoHetal.2019SecuringPlatinum-GroupMetalsforTransportLow-CarbonTransition.OneEarth1,117–125.doi:10.1016/j.oneear.2019.08.012).LARGE-SCALEELECTRICITYSTORAGE41ChapterfourHydrogenpoweredcellsdesignedforuseinSolidoxidefuelcells(SOFCs)powergenerationwillbemoreexpensiveasThesearecurrentlybestsuitedforstationarytheywillnotbemanufacturedatsuchalargeapplications,andcanuseavarietyoffuelsscale,balanceofplantcostshavetobeadded,(methane,hydrogenandammonia33).SOFCsandtheywillhavetosatisfydifferentdemandspoweredbynaturalgasarearound60%(onoperatingpoint/powerrating,powerefficient,althoughthiscouldbeincreasedelectronics,andstackmaterialloading).to85%ormorebyusingwasteheat.LittleinformationisavailableonwhichtobaseOnthebasisofareviewofcostestimatescostprojections,butSOFCsthatoperateatintheliterature(seeSI4.5),abasevalueoforbelow700°Ccouldbecomecompetitive$425/kWeisassumedinthisreport(thisisthewith,orcheaperthan,PEMcellsinthecentralvaluefoundbyHunteretal,whogiveafutureasmanufacturingscalesupandtherangeof340to528/kWe111)forthefull/installedtechnologymatures.Asdiscussedabove,capitalcostofwhatevertechnologyisusedtoSOFCscanbereversedandoperatedasgenerateelectricityfromhydrogenin2050,electrolysers.PEMelectrolysersandfuelcellsassuminglargesystemsdeployedatscale.Acurrentlyusedifferentcatalystsandcannotbebottomofrangecostof$300/kWeisassumed,operatedreversibly.basedonthepossiblefuturecostofothertypesoffuelcells,themuchlowercostsfoundHightemperatureprotonconductingceramicforPEMcellsdesignedforuseinvehicles,andfuelcells34,35estimates(below)ofthepossiblecostofusingThese,likephosphoricacidfuelcells,4-strokeengines.Thetopoftherangeistakenusecatalystsbasedonmaterialsthataretobe$425/kWe+50%($638/kWe).widelyavailable,butareatanearlystageofdevelopment.Proponentsbelievethatby2050Afinanciallifetimeof30yearsisassumedtheycouldbecheaperandmoreefficientthan(typicalprojectionsintheliteraturearelowertemperaturePEMcells.ofoperatinglifetimesof80,000hours,correspondingtoamuchlongercalendarInternalcombustionengineslifetimegiventhattheloadfactoronpowerFour-strokeinternalcombustionenginesgenerationisonly10%intheall-hydrogenarewidelyusedasstandbygenerators,andstoragescenarioq),anefficiencyof55%.An–atlargerscales–arraysofenginesareoperationandmaintenancecostof1.5%/yearbecominglyincreasinglycompetitivewithgasofthecapitalcostisassumed,whichistheturbines.Forexample,WärtsilähavedeliveredvaluegivenbytheIEAforelectrolysers,whicha600MWpeakpowerprojectinJordanaresimilardevices(O&Mwouldbehigherforbasedon38multi-fuelengines36.Thenine-4-strokeengines).enginesinthe76MWgasburningplantinKansascostapproximately£30M($395/kWe)‘includingappurtenances’37.qThedeteriorationoffuelcellperformancewithuseisignoredincostingstorageinthisreport.Itonlyhasasmalleffectontheirnetpresentvaluebecausethefaderateissmall(verysmallwiththeloadfactorof10%foundintheall‑hydrogenstoragecase)andlateryearswhenfadecouldbecomesignificantarediscounted.42LARGE-SCALEELECTRICITYSTORAGEChapterfourPurehydrogenengines,whichwouldbespark-Fuelcellsignitionratherthancompressionignition(unlessAmmoniacanbeusedasafuelinsolidoxideapilotfuelwereincluded)38,arecomingintothefuelcells,buttheheatrequiredtocrackmarketplacetoday39andarealreadyavailableammoniawouldreducetheefficiencybyfromINNIO.Theyarebeingdevelopedbyatleast13%comparedtousinghydrogenJCB40,Mercedes41,Toyota42,Wärtsilä43anddirectly,andammoniaSOFCsarestillfarfromothercompanies.Muchofthedevelopmentdevelopedtoenablequickresponsetolargebeganbyconsideringmodificationsofpetrolpowerloads.ResearchisunderwayonPEMfuelengines,butsomemanufacturersarefocussingcellsthatuseammoniadirectly,buttheyarenotontheultra-leanburnconditionsthatarelikelytobecommercialisedwithinthisdecade.allowedbyhydrogen’sflammability,butareAlkalineFuelCells,whichunlikePEMsarenotnotaccessibleforpetrolordieselengines,poisonedbyammoniaarebeingdevelopedinwithlowtemperature(whichasaside-benefittheUK45.Onestudy46describedadevicethatmitigatesNOXformation).Itseemsthatlargeusesaceramicmembranetocrackammoniatoenginesdesignedtooperateinthisregimepurehydrogenat250°C,raisingthepossibilitycouldbe(atleast)asefficientasPEMcellsofconstructingacombinedcrackerandprotonandnotcostmuchmorethanpetrolandgasconductingceramicammoniafuelcell.engines.Althoughsuchenginesareonlyattheprototypestage,itseemspossiblethatlarge,Internalcombustionenginesmass-producedhydrogenburningmotor-Ammoniacombustionhasbeenactivelygeneratorsetscouldfallbelowthe$350/researchedsincethe1930s.MAN,Wärtsilä,andkWecostoftheenginesintheKansasplant.Ifothershipenginemanufacturershaveidentifiedso,4-strokehydrogen-burningenginescouldthepotentialofammoniaasazero-carbonbecostcompetitivewithfuelcellsnotonlyinfuelandareengagedintestingprogramsfortheshort,butinthelongterm.Agraphofthetheimplementationoftwoandfourstrokeefficiencyofelectricvehiclespublishedbyenginesinthemarinesector.MANexpecttoMcKinsey44contains‘illustrative’lineswhichbemarketingtwostrokeengineswith50%showhydrogenenginesbeingmoreefficientefficiencyin202447.thandieselenginesforalloutputandmoreefficientthatfuelcellsaboveabout60%ofAmmoniaisasuitablefuelforgasenginestothemaximumoutput.generatepowerinstationaryapplications,mostlikelyusingarraysof4-strokeenginesof20–4.5.2Ammonia30MWeach48.TheperformanceandreliabilityAmmoniacanbeconvertedbacktohydrogenofammoniagasturbineshavebeenassessedthroughacatalyticprocess,whichconsumesatnumerically,experimentally,andunderindustrialleast13%oftheenergycontentoftheproducedconditions49,50.TokyoGas,wholedaJapan-hydrogen.ThishydrogencouldbeusedinAustraliainnovationproject,havecreatedacombustionbutwouldneedpreconditioningroadmaptoproducethefirst100MWammoniaforuseinsometypesoffuelcells.Ammoniagasturbineby2030.canalsobeuseddirectlytogenerateelectricityusing:LARGE-SCALEELECTRICITYSTORAGE43ChapterfourIncostingtheuseofammoniainenergy4.7Climateimpactstorage,itwillbeassumed(possiblyHydrogenisagreenhousegas,thoughoptimistically)thatin2050itwillbepossibleammoniaisnot.Analysisbasedonrecentgenerateelectricityfromammoniaatthecost,estimatesofhydrogen’sglobalwarmingandwiththesameefficiency,assumedforpotential51andofhydrogenleakage52,findshydrogenabove.thatcontinueduseofhydrogenstorageatthemaximumlevelenvisagedherewouldlead4.6SafetytoatemperaturerisewhichwouldstabiliseHydrogenandammoniaareproducedinbelow0.00013°Cafter300years(or0.00047°Cmatureindustrialprocessesataverylargewithoutmeasurestolimitventinghydrogenscale,storedinavarietyofforms,andduringelectrolysis,which‘wouldberelativelytransportedoverlongdistances.Safetyissues,easytoincorporate52),with99%confidenceandpotentialhazardsandthemeasuresthatonleakageratesbutignoringuncertaintiesincanmitigatethem,arediscussedinSI4.6.ThetheglobalwarmingpotentialandtheclimateuseofhydrogenandammoniainGBissubjectscience(seeSI4.7).Theconclusionisthatthetostringentcontrols,andconcernsaboutuseoflarge-scalehydrogenstorageinGBwillsafetyarenotexpectedtopreventtheuseofnothaveasignificantclimateimpact,buttighthydrogenandammoniaforenergystorageoncontrolofleakagewillbeimportantifhydrogenthescaleenvisagedinthisreport.userisestolargelevelsglobally.44LARGE-SCALEELECTRICITYSTORAGEChapterfiveNon-chemicalandthermalenergystorageTherearemanywaystostoreenergyasheatIntheseplants,andintheoperatingplantsorasmechanicalpotential,whichcanbethatburngastoprovideheat,thepressureofusedaloneorincombinationwithchemicalthestoredairfallsasitisreleasedduringtheenergystorage.Storedheatcanbeusedtoexpansionphase.A10MWhdemonstratorofgenerateelectricityand/orheat.Althoughaninterestingandpotentiallymoreefficientthisreportisfocussedonelectricitystorage,alternative,inwhichhydrostaticcompensationbotharediscussedasthelatterispotentiallymaintainsthestoredairatconstantpressure,veryimportantandcouldreducetheneedcameintooperationin2019inOntario58,59.fortheformer.Such‘isobaricACAES’systemswillnotbeconsideredfurtherheresincetheyhavenot5.1Advancedcompressedairenergyyetbeendeployedatscaleandinstallingthemstorage(ACAES)incavernsatthedepthneededtoprovidea5.1.1Introductionlargestoragecapacity,whichhasnotbeenEnergycanbeusedtocompressair,whichdemonstrated,couldbechallenging.wouldbestoredinundergroundcavernsinlarge-scalesystems.Whenexpandedto5.1.2UndergroundACAESstoragecapacityatmosphericpressure,withheatprovidedtoinGreatBritainpreventfreezing,theaircandriveaturbineABritishGeologicalSurveyledstudy60foundandgenerateelectricity.Inanetzerosystem,that‘Solution-minedsaltcaverns(whichpermittheheatmustcomefromacarbon-freehighinjection/withdrawalratesrequiredforsource,orfromstoringandreusingtheheatrapidcyclestorage)arethelikelyfirstchoicegeneratedwhentheairiscompressedr.TheforCAESintheUK…atleastintheshortterm’.latterpossibility,knownasAdvancedCAESorThereareotheroptions,but‘seriousdoubtsACAES,isdiscussedhere(seefigure18).existoverthelikelydevelopmentofporousrockCAES,withnoplantshavingoperatedThreegrid-connectedACAESplantsarecommercially…AquiferstoragefortheUK…nowinoperationinChinas.Thefirstisawouldberemoteoffshore,therebyincreasing10MWe/100MWheplant,whichhasbeenincosts…Depleted[gas]fieldstoragesappearoperationsinceSeptember2021,withairevenmoreunlikelywithapotentialhazardstoredinasaltcavernandheatinsupercriticalposedbyresidualhydrocarbons…”(theoptionswater53.Thesecondisa50MWe/300MWhearediscussedfurtherinSI5.2).plant,whichhasbeeninoperationsinceMay2022,withairstorageinasaltcavern,andheatstoredinthermaloil54,55.Thethirdisa100MWe/400MWheplant,whichstartedoperationinSeptember2022,withairstorageinanartificialminedrockcavernandheatstoredinsupercriticalwater56,57.rTwolarge-scalecompressedairenergystorage(CAES)plantsarecurrentlyoperational(inHuntorf,GermanyandMacIntosh,USA)thatburngastoheattheaironexpansion.MoreinformationabouttheseplantsandplanstobuildmoreisobaricsystemsaregiveninSI5.2.sThissummaryincludesinformationkindlyprovidedbyChinesecolleaguesviaProfessorYulongDing(UniversityofBirmingham).LARGE-SCALEELECTRICITYSTORAGE45ChapterfiveFIGURE18Schematicofadvancedcompressedairenergystorage.ChargingHeattransferDischargingAirHeattransferHeatElectricitystoreGeneratorElectricityMotorMultistageMultistageexpanderAircompressorGeologicalcavityInmodellingandcostinglarge-scaleACAESitis5.1.3ACAESdesignassumedinthisreportthatthecompressedairThedesignandcostofACAESsystemswillbestoredinthe300,000m3solution-mineddependon:saltcavernsthatwerestudiedandcostedas1.ThesizeofthecavernanditsdepthwhichhydrogenstoresbytheH21NE26consortium(seeChapter4),andthatthecavernswillbedeterminethepossiblepressurerange.atadepthof1000to1700m,atwhichtheModellingof300,000m3cavernsinadepthallowedpressurerangeisbigenoughtorangeof1000–1700mfinds(seeSI5.2)enablelarge-scalestorage.Onthebasisofthattheycouldtypicallystore10GWhewiththemodellingbelow,andBGS’sestimatesofthesupportof7.5GWhofthermalstoragethepotentialnumberofsuchcavernsquoted(mostoftheenergyofcompressionisstoredinChapter4,upto20TWheACEASstorageasheat:thecompressedairmainlystorescapacitycouldinprinciplebeprovidedin‘exergy’–theabilitytodowork),anddeliverEastYorkshire,withperhapsasmuchagain6.8GWhofelectricity,correspondingtoainCheshireandWessex.Inpractice,20TWhe68%round-tripefficiency.Higherefficiencies(whichwouldrequiresome3000caverns)arepossibleinprinciplebutrequireshouldberegardedasastrongupperbounddemonstration.The10GWheneededtoontheonshorecapacity.Itisworthnotingthatcompresstheairgeneratessome9.7GWhinthemodellingusedinthisreport,thevolumeofthermalenergy,ofwhichonly7.5GWhrequiredtodeliveragivenamountofelectricityisneededtosupportelectricitystorage:issome20timeslargerforACAESthanforausingtheexcessforotherpurposes,suchhydrogenstore.asdistrictheating,wouldimproveutilisationoftheinputenergyandgeneraterevenuewhichcouldbeoffsetagainstthecostofusingACAEStostoreelectricity.46LARGE-SCALEELECTRICITYSTORAGEChapterfive2.Howtheheatisstored.Inthemodellingin2.Thermalstoragecostthisreport,itisassumedthatcompressionOnthebasisofthefullcostofanoperationaliscarriedoutinmany,typicallysix,stages.200,000m3water-pitstoreinDenmark61,Thisallowsdeliveryofthethermalenergyatandthecostsofotherprojects,fullcostsalowenoughtemperaturefortheheattobeareestimatedtobe€30/m3forvolumesstoredinwater,ratherthaninmoltensalts,>100,000m3.Withaclusterof10caverns,asassumedinmoststudies,whichwould10x140,000m3ofwaterwouldbeneededbemuchmoreexpensive.Withawateraccordingtothefiguresabove,whichoperatingtemperaturerangeof35°Ctowouldpresumablybeprovidedbyfewer90°C,117,000m3ofwaterwouldbeneededthan10pits,butmorethanonetoprovidetostore7.5GWhofheat.flexibility.Giventhatcostsfallwithsize,itwouldseemsafetoassumeatotalcostof5.1.4ReadinessandcostofACAES£50/m3includingashareofmanagementNoACAESsystemsoftheverylargescalecosts,siteservicesandpurchaseoftheenvisagedinthisreporthavebeenbuiltt,butsite.Witheachcavernstoring10GWhe,thereiswideexperienceofmakingsolution-thesumofthecavernandthermalstorageminedsaltcavernsandofthermalstorage.costscorrespondsto£2.6/(kWhstored).AircompressorsandexpandersarewidelyThisisverymuchlowerthanotherestimatesusedforavarietyofpurposes.ThecostisusedinotherstudiesofCAESbecausecomprisedof:oftheassumptionmadeherethatvery1.Caverncostlargesolution-minedcavernsandwaterpitthermalstoragewouldbeused.ThecostsusedherearebasedonH21NE’s26estimatesofthecostof3.Compressorsandexpandersconstructingclustersof10300,000m3ThemodellingdescribedinChapter8findscavernswhichsharefacilities.Removingtheaneedformulti-stagecompressorsandcostofthehydrogensurfacefacilities,afterexpanderswithapowerratingofaroundattributingmanagementandmiscellaneous70MWifthereisonecompressorandcostsproratatothemandtothecostofexpanderpercavern.Aratingof233MWthecavern,leavesacostof£125.4Mforwouldbeneededif,forexample,threewereconstructingaclusterof10caverns.Asinprovidedforeachclusterof10caverns.costinghydrogenstorage,a‘base’valueSuchcompressorsandexpandersaretodayof1.5x£125.4Mwillbeused,toreflectcustommade.uncertaintiesinundergroundcostingsandthelackofdataonactualcosts.tAlthoughSiemenshasproducedavideoandaflyer(https://www.siemens-energy.com/global/en/offerings/storage-solutions/thermo-mechanical-energy-storage/caes.html)thatshowa6GWhesysteminwhichcompressedairisstoredinasaltcavern.LARGE-SCALEELECTRICITYSTORAGE47ChapterfiveItisnotclearwhatcompressorsandexpanders5.2ThermalandpumpedthermalenergytailoredtotheneedsofACAESwillcostinthestoragefuturewhenmanufacturedatthescalethatwillThermalenergycanbestoredatlowcostv.beneededifACAESiswidelydeployed.ThereHighgradeheat(>100°C)canbestoredinareestimatesintheliterature,butitisoftennotmoltensalts,solids,thermaloils,liquidmetalsclearwhattheyinclude,orthepowerratingorassteam.Atlowertemperatures,waterorthatwasassumed,althoughthecostperkWotherliquidsorsolidscanbeused.Potentially(atleastoversomerangeforsimilardevices)importantsystemsinclude:variesas(powerrating)-0.6.Intheabsenceofmorepreciseinformation,arangeofcostswasWaterpitstoragestudiedofupto£500/kWforthefullinstalledWaterpitstorageisalreadydeployedtocost(includingsitepurchaseandpreparationprovidedistrictheatinginAustria,Denmarketc)ofcompressorsandofexpandersandandGermany.Withatemperaturerangeofassociatedheatexchangers.Information70°C,watercanstore82kWh/m3ofthermalobtainedfromtwoleadingmanufacturersenergy.Lossesarebelow0.1%/dayinlargesuggeststhatthecostcouldbewellbelowsystems,whichcanachieve(heatout)/(heatin)£500/kW,butthisisnotassuredu.efficienciesofover90%forheatstoredinlatesummeranddeliveredinwinter.AsdiscussedSubstantialsavingscouldinprinciplebemadeaboveinthecontextofACAES,wherecostsbyreplacingeachpairofcompressorsandarequoted,theworld’slargestsystemhasexpanderswithsinglereversiblecompressor/avolumeof200,000m3.expandersifhighefficienciescanbeobtainedinbothroles.MoltensaltsMoltensaltsstoreheatintherange300–580°C.IncostingelectricityprovidedbyACAES,aTheyareusedatconcentratedsolarpowerfinanciallifetimeof30yearswillbeassumed.plantsandcouldbeusedinconjunctionwithThecavernandwaterpitareexpectedtonuclearpowerplantstobuffertheoutputlastmuchlongerandwillneedverylittleandrendernuclearflexible.Plantsizesaremaintenance.Compressorsandexpanderstypically50MWeupwards(a1.2GWhestorewasarealsoexpectedtolastatleast30years,installedatthenowdefunctCrescentDunesassumingregularmaintenance.O&McostsofConcentratingSolarPowerplant),lossesare1%/yearand4%/yearoftheircapitalcosts<0.1%/day,costsareintherange£(24–59)/wereassumed.kWheandthedensityofstoredenergyis53.6kWhe/m3assumingatemperaturerangeof200°C.uArangeupto£500/kWiscompatiblewithestimatesintheACAESliterature,e.g.MITassume2050costsof$(344–452)/kWforcompressorsand$(469–627)/kWforexpanders,albeitforpowerratingsthatarenotstated(butarepresumablylessthanthosefoundfortheverylargesystemsconsideredhere).OtherestimatesarediscussedinSI5.2.vStorageaslatentheat–thethermalenergyrequiredtochangethephaseofamaterial(solid-liquid,solid-gas,liquid-gas)–isnotsuitedtoprovidinglarge-scaleelectricitystorage,butmayplayotherroles,e.g.inheatingandcoolingbuildings.48LARGE-SCALEELECTRICITYSTORAGEChapterfiveCarnotbatterieswithresistive5.3ThermochemicalheatstorageelectricalheatingThermochemicalheatstorageinvolvesaThesestoreheat(providedbyaresistivereversiblereaction,inwhich:heater)athightemperature,forlaterdeliveryaschemicalX+heat↔chemicalY+Z.electricalpowerprovidedbyaturbine.ArangeIfYandZarestoredseparately,longperiodsofdifferentconfigurations,storage,andchargeofenergystoragewithlowenergylossesare/dischargecyclesarebeingconsidered.possible(seeSI5.3).AnumberofreactionsEnergyNest62useconcretemoduleswithhavebeenconsidered67,68,including:embeddedstainlesssteelheattransferpipestoCaCO3↔CaO+CO2,Ca(OH)2↔CaO+H2O)provideascalableenergystoragesolutionupandMgSO47H2O↔MgSO4+7H2O.tomulti-GWhcapacity.ThematerialscostsareWhilethedensityoftheenergystored(1.8,1.4downto$25/kWhthdependingonsystemscaleand1.6MJrespectively)issmallcomparedto/locationandoperatingtemperatures.Siemenstheenergydensityofcoal(whichrangesfromGamesabuilta30MWhigh-temperature(>18MJ/kgforligniteto33MJ/kgforanthracite),600°C)thermalstorethatused1000tonnesofmultiplecharge/dischargecyclesarepossiblevolcanicrockstostore130MWh63,64,65thermalbecausethereactionsarereversible.energy,withclaimedelectrical–electricalround-tripefficiencyofupto45%,buttheyhaveThermochemicalstoragecouldbeusedatcurrentlyabandonedplanstofollowthisupwithsmallscale,forexampletoprovidespaceacommercialplant.heating69,oratlargescale,forexampleforstoringindustrialwasteheatorinconcentratingTwohundredsystemsthatcoulddeliveroversolarpowersystems.Itisatanearlystage5GWheand100MWwouldbeneededtoofdevelopment(TRL1–4),withtechnologiesstore1TWh,eachofwhichwouldhavetovalidatedinlabconditions,atsmallscalehaveavolumeofaround37m3assumingagenerallyforsmallnumbersofcycles.Furtherrockdensityof1t/m3(typicalofpumice).Itisresearchisrequiredtodevelopmaterials,thereforepossibletoimaginesuchCarnotreactorsandsystemsfordifferentapplications.batteriesprovidingover1TWhofstorageinGB.Nodetailedcostestimatesareavailable.Intermsofcostperunitofenergystored,theyareexpectedtobeoneofthecheapeststorageoptions,buttheywillbemoreexpensivethanhydrogenstoragewithoutbeingmuchmoreefficient(seeSI5.3).Pumpedthermalenergystorage(PTES)PTESsystemsareCarnotbatteriesthatuseheatpumpstotransferthermalenergybetweentwothermoclinegravelpackedbeds.Thestoredheatisusedlatertogenerateelectricityusingaturbine.PTESisatTechnologyReadinessLevel(TRL)4–6.Theroundtripefficiencyisexpectedtobeover50%.Onestudy66foundathermalenergydensityof70–430kWh/m3andacapitalcostof€50–180/kWh.Itwillnotbepossibletomakeaccurateestimatesuntilworkingsystemsareinoperation.LARGE-SCALEELECTRICITYSTORAGE49Chapterfive5.4Liquidairenergystorage(LAES)5.5GravitationalstorageLiquidairenergystorage(LAES)useselectricity5.5.1Pumpedhydroelectricstoragetocoolairuntilitliquefies.TheliquifiedairPumpedhydrostoreselectricalenergyasisstoredintanks.Energyisreleasedwhengravitationalenergybypumpingwaterfromtheliquidisbroughtbacktoagaseousstatealowertoahigherreservoir.Theenergyisandtheexpandinggasdrivesaturbine,convertedbacktoelectricitybyallowingthewhichinturngenerateselectricity70.Liquidairwatertoflowbackthroughawaterdrivencanbebroughtbacktoagaseousstatebyturbine.TheUK’shydropowergeneratingexposuretoambientair,orwithheatstoredcapacityiscurrently4.7GW,including2.8GWwhentheairisliquefiedorwasteheatfromofpumpedhydro72withastoragecapacityofanindustrialprocess.26.7GWh73.Primaryhydropowerdelivered5.9TWhin2019,whilepumpedhydrogeneratedLAESsystemsuseoff-the-shelfcomponents1.8TWh,downfromamaximumof4.1TWhwithlonglifetimes,resultinginlowin200874.technologyrisk.LAESisatTRL7–9.The15MWh,5MWHighviewPowerLAESplantistheTheexpansionoftheUK’spumpedstoragelargestoperationaldemonstrator.Highviewarecapacityisrestrictedtoareaswithsuitablebuildinga50MW/300MWhsystemwhichwillterrain,predominantlyinWales,Scotlandbecompletedinearly202571.andpartsofNorthernEngland.Plannedandproposedprojectsincludea1.5GW,30GWhLAESisnotsuitableforsmall-scaledistributedpumpedhydroelectricsystematCoireGlas75.applicationsbecausetheefficiencyislowatConnectionsbetweenallsuitablepairssmallscale.Theminimumsizeforcommercialofexistingreservoirswithin20kmwouldapplicationsislikelytobe10MW/40MWh.inprincipleprovideastoragecapacityofIfthereleased‘cold’fromthedischarge0.5TWh76,althoughnothingonthisscaleisprocesscanbeeffectivelyrecovered,theforeseen,letalonethetheoreticalpotentialofround-tripefficiencycouldbeupto55%(ifnot,5.3TWhthatwouldbeprovidedbybuildingitwouldbe35%orless).Thepowercostcouldnewreservoirswithin20kmofexistingones.beupto£2500/kW,fallingtoperhaps£850/kWasthetechnologymatures.EstimatedtotalWhileadditionalpumpedhydrostoragestoragecosts(liquidair,hotandcoldstores)arecapacitywillbehelpful,itisclearthatitwouldintherange£200–500/kWh.onlyhaveamarginalimpactonGB’sneedfortensofTWhoflarge-scalestoragetocomplementhighlevelsofwindandsolar.50LARGE-SCALEELECTRICITYSTORAGEChapterfive5.5.2Othergravitationalstorage5.6StoragetoprovideheatAnumberofcompaniesareconsideringstoringStoredheatcanreducedemandforelectricalenergybyliftingweightsandlater,releasingheatingandplayapotentiallyimportantrolethestoredenergybydroppingtheweightandinshiftingelectricitydemandawayfrompeakpoweringanelectricgenerator.Ideasinclude:hours.Itcanbedistributedthroughheatliftingweightsinundergroundshafts77;usingnetworks,whichcurrentlyprovideonly2%ofcranes78,haulingwagonsloadedwithballasttheUK’sheatw,althoughinsomeEuropeanupinclinedrailtracks79;andusinghydrauliccountries,suchasDenmark,localheatpressuretoliftlargerockpistonsindeepnetworksmeetover50%ofspaceandwatershafts80orundergroundcaverns81.Suchdevicesheatdemand.Large-scaleheatstores,chargedcouldreleaseenergyveryquickly(providingwithsolarenergyinsummerandprovidingheatgridservices),ormoreslowlyprovidingpeakthroughlocaldistrictheatnetworksinwinter,shaving.TheproponentsexpecthighroundarewidelydeployedinGermany,DenmarktripefficiencyandclaimthattheirschemeswillandAustria.Intheabsenceofaclearideaofbecheaperthanusinglithium-ionbatteries,whetherdistrictandlocalheatstoragearealthoughtheredonotappeartobeanydetailedlikelytoexpandtotheTWhscaleinGB,thiscostestimatesinthepublishedliterature.MostpossibilityisnotincludedinthemodellingwouldstoreMWhratherthanGWh(droppingandescribedinthisreport.However,giventheir11msidedcubeofgranitethrough100mwouldpotential,heatstorageandheatnetworksxrelease1MWh).Cycledfrequentlytheycoulddeservemuchmoreattention.deliversignificantamountsofenergyifbuiltinlargenumbers,butnotenoughtohavemoreAtalocallevel,the40GWhthatisstoredinthanamarginalimpactonGB’sneedfortensofhotwatertanksintheUKycouldbemanagedTWhoflarge-scalestoragetocomplementhightoavoidthembeingchargedduringpeaklevelsofwindandsolar.hours,whichwouldhaveasignificantimpactonpeakenergydemand.Anovelpossibility,whichisworthdeveloping,wouldbetostoreheatprovidedinsummerbyheatpumps,orintegratedsolarthermalsystems,thermochemicallyanduseittomeetorreducepeakwinterdemand.TheuseofheatfromnucleargenerationiscoveredinseparateworkfromtheRoyalSociety82.w6.5TWhissuppliedtothedomesticsectorand5.5TWhtonon-domesticloads.OftheUK’s17,000existingnetworks,11,500arecommunalnetworksthatsupplydifferentcustomersinasinglebuilding,whilethereare5,500districtnetworksthatsupplytwoormorebuildings(oftenonasinglesite,egaschool,hospitalorfactory)seehttps://www.theade.co.uk/resources/publications/market-report-heat-networks-in-the-uk(accessed15May2023).xArecentUKGovernmentConsultationrefersto‘asignificantpotentialforthenumberandscaleofheatnetworkstoincreasedramatically’andreportsan‘estimatethatupto£16billionofcapitalinvestmentcouldbeneededforheatnetworkstodelivertheir[undefined]fullcontributiontonet-zero’.See,https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/878072/heat-networks-building-market-framework-condoc.pdf.(accessed15May2023).TheDecember2020EnergyWhitePaperexpressesenthusiasmforheatnetworks,butonlyreportedacommitmentto“£122millionoffundingtowardsanewHeatNetworkTransformationProgramm”’.yUsingtechnologiessuchasthoseprovidedbyhttps://www.mixergy.co.uk/mixergy-tank(accessed15May2023).LARGE-SCALEELECTRICITYSTORAGE51ChaptersixSyntheticfuelsforlong-termenergystorageEnergycanbestoredincarbon-hydrogen6.2Liquidorganichydrogencarriersbondsinsyntheticallyproducedorganic(LOHCs)moleculesknownas‘electro-fuels’(e-fuels),Energycanbestoredbyattachinghydrogensuchase-methane,e-keroseneandchemicallytocertainorganicliquids,andlatere-methanol83,84,85,86,or‘liquidorganichydrogendetachingthehydrogen.Methylcyclohexanecarriers’(LOHCs)87,88,aswellasinfossilfuels.isanexamplethathasattractedcommercialE-fuelscanberegardedascarbon-containinginterest:itconsistsofthreehydrogenmoleculeshydrogenstores,justasammoniaisanitrogen-attachedtotoluene,whichcouldbere-cycledbasedhydrogenstore.Synthetichydrocarbonsfollowingdehydrogenation.LOHCshavetypicallyprovidetheeaseoftransportandparticularpromisewherecombinedheatandenergydensityoffossilhydrocarbons,andinpowerisrequired,especiallyatthebuildingorsomecasescanbeadrop-inreplacement,districtlevel.thusleveraginggenerationsofinnovationincombustion.SeeSI6foradetailed,analysisAcomparativeanalysisoftheround-tripofsyntheticfuelsandenergystorage.efficienciesandcostsofusingdifferentliquidstostoreelectricity,andotherfactorsthataffect6.1Electro-fuelsthechoiceofenergystoragevector,isprovidedE-fuelscanbemadebycombininggreeninSI6.Theconclusionsarethat:hydrogenwithcapturedcarbondioxide(as•Ifcavernstorageisnotavailableforhydrogen,showninfigure19),orwithcarbonmon-ordi-oxideproducedbygasificationofbiomassthenammoniaandLOHCsappeartobeorwaste.E-fuelsareexpectedtoplayarolelowercostsolutionsthangaseousorliquidintransport–seetheRoyalSocietyPolicyhydrogenstorage.Briefing,Sustainablesyntheticcarbon-basedfuelsfortransport89.Theycanbeusedto•Wheresaltcavernsareavailableforhydrogenstoreelectricity,butitisgenerallycheaperstorageinlocationswithaccesstomarketsatandmoreefficienttostorethehydrogenusedreasonabletransmissioncosts,thenaddingtomakethem.asynthesisplanttomakehydrocarbonsorammonia,orliquidorganichydrogencarriers,appearstoreduceefficiencyandincreasecostsoverall.•LOHCscouldplayaroleindistributedcombinedheatandpowersystems.GiventhatthepotentialhydrogenstoragecapacityinGBisverylarge,andthatitsfocusisonlarge-scaleelectricitystorage,e-fuelsandLOHCsarenotconsideredfurtherinthisreport.52LARGE-SCALEELECTRICITYSTORAGEChaptersixFIGURE19Productionofe-fuelsusingelectrolysis.SustainableCarbonelectricitydioxideSynthesisEfuelWaterElectrolysisHydrogenSource:Sustainablesyntheticcarbonbasedfuelsfortransportreport,theRoyalSociety.LARGE-SCALEELECTRICITYSTORAGE53ChaptersevenElectrochemicalandnovelchemicalstorage7.1ElectrochemicalstorageTherearevarioustypesoflithium-ion7.1.1Grid-connectedlithiumbatteriesbatteries95:NickelManganeseCobalt(NMC)Lithium-ionbatteriesaredrivingtheconsumerandNickelCobaltAluminium(NCA)batteries,electronicsrevolutionandthemarketforwhichareusedinvehiclesbecauseoftheirelectricvehicles(EVs).Increasingly,lithium-ionrelativelyhigh(forbatteries)energydensities,batteriesarebeingusedtosupporttheNationalcanalsobeusedinstoragethatsupportstheGridconfiguredintolarge-scalemodulestoelectricitygrid.NCAbatteriesareusedinTeslaprovidegridservices,suchasmaintaininggridcarsandinthegrid-connectedTeslabatteryinstabilityandpeakshifting.Off-gridbatteriesareSouthernAustralia.Lithium-ionphosphate(LFP)allowingenergyprovidedbysolarpanelsinthebatteriesalsouserelativelycheapmaterialsdaytobestoredandusedlater.buthavelowerenergydensitythanNMCchemistries.EnergydensityislesscriticalinGloballithiumresourcesshouldbeabletostationaryapplications,makingLFPapotentiallymeetexpecteddemandasthemarketexpands,significantstationarystoragetechnologyalthoughsupplychainsmaybecomestrained.by2030.Investmentinrecyclingandsecond-lifestrategiesisrequiredtosupportsustainableAmongtheemergingalternatives,sodium-iongrowth90.Theavailabilityofcobalt,acomponentbatteriesuseabundantmaterialsandcouldinofmostlithium-ionbatteries,couldbeamoreprinciplebecheaper,butinitiallyhighcostsatseriousconstraint:thereareconcernsaboutitslowlevelsofproductionmaybeabarriertosources,althoughcobaltcontenthasfallenandachievingmanufactureatscale.furtherreductionsareexpected,andlithium-ironphosphate(LFP)batteriesarecobalt-free.CostsThecoreelementsofagridconnectedbatteryLithium-ionbasedenergystoragefacilitiesarethebatteryitselfandtheinverter(whichhavesufferedcatastrophicfailuresresultingconvertsACto/fromDCanddeterminestheinfires91,92,93.Theproblemispotentiallypowerrating).Ameta-analysisofprojectionsofmostseriousforverylargesystems,butthefuturecosts(seefigure20),whichdependbothcomponentsofstationarybatteriesdonotneedonthecapacityandtheminimumdischargetobepackedcloselyanditshouldbepossibletimes(orequivalentlyenergycapacity/powertodesignsafesystems,whichincorporateflamerating),madebytheUSNationalRenewableretardantsandothersafetymeasures94.SomeEnergyLaboratory,showscostsfallingrapidly96.typesoflithium-ionbatteries(egLFP)aresaferHowever,thesecostestimatesarewithoutandmorethermallystablethanothers.markup.PricescurrentlyquotedbyTeslafor1000unitsof2and4hour3.9MWh‘megapack’batteriesarerespectively43%and31%higherthanNREL’smidprojectionfor2022.54LARGE-SCALEELECTRICITYSTORAGEChaptersevenFIGURE20Resultsofameta-analysisofprojectedcapitalcostsoffullyinstalled2-,4-and6-hourbatteries.Thecostisdefinedhereintermsoftheuseablecapacityperunitofdeliveredenergy,whichisequaltothenameplatecapacity[asnormallydefined]x(thedepthofdischarge)/(dischargeefficiency)anddoesnotincludemark-up.5002,500KEYBatterycapitalcost2020($/kWh)2-hrbatteriesBatterycapitalcost2020($/kWh)4002,0004-hrbatteries6-hrbatteries3001,50020010001005000203020402050020302040205020202020YearYearSource:USNationalRenewableEnergyLaboratory.LARGE-SCALEELECTRICITYSTORAGE55ChaptersevenTocalculatewhatitcoststostoreelectricityin3.Operationandmaintenance(O&M)costsbatteries,itisnecessarytoknownotonlytheItisgenerallyagreedthatvariableO&Mcapitalcost,butalso:willbenegligiblysmall.Estimatesoffixed1.Theround-tripefficiencyannualO&Mvary,ranginguptothe2.5%ofcapexadvocatedbyNREL103whoincludeTheliteraturecontainsarangeofestimatesprovisionsforperiodicinjectionsofcapitalofefficiencies97,98,99whichvaryoveraintendedto‘counteractdegradation’104.battery’slifetime,anddependonthedutyTeslaquoteslightlyover0.2%forannualcycle.Theestimatesofthecostofusingmaintenance,towhichoperationalcostsbatteriesinthisreportareratherinsensitiveshouldbeadded105.totheefficiency,forwhichaconstant(2050)ACtoACvalueof90%,nearthetopoftheCombiningthesefactorsleadstothecostsofrange,ispossiblyoptimisticallyassumed.deliveringelectricityfromabattery(withoutthecostoftheinputelectricity)showninfigure212.Lifetimeintheconditionsdescribedinthecaption.WithBatterychemistrychangeswithuseandtheNREL’shighandlow2050projectionsofcapex,capacity‘fades’asbatteriesarecycled100.thecostsinthisfigureshouldbemultipliedbyHigh-energydensitylithium-ionautomotivefactorsof1.66and0.58respectively.Thecostofbatteriesaretodaytypicallyexpectedtooperatingexpensiveorcheapbatterieswouldachievearound1000cyclesbefore20%notbeexpectedtobeverydifferent.Withhighofratedcapacityislost,whichisgenerallyvaluesofcapex,itwouldthereforebenaturaltousedasanend-of-lifecriteriafortheiruseinchoosearelativelylowvalueofFixedO&Masaelectricvehicles.However,recentresearchpercentageofcapex,andvice-versa.indicatesthata‘million-mile’battery,correspondingto4000–5000cycles,7.1.2Vehicletogridstoragecouldbepossible,althoughthisisnotyetaTherearecurrently33millioncarsintheUK.commercialreality101.Inlarge-scalestationaryIfallwereelectric,andhadfullycharged70storage,degradationwilloccurmoreslowlykWhbatteries,theywouldprovideacombinedastemperatureandchargeanddischargestoragecapacityofaround2TWh.If10%ofratescanbebettercontrolled,andthethosevehicleswereaccessibletotheoperatorfactthatdensityisnotamajorconstraintoftheelectricitygridatanytime,theycouldwillallowtheuseofLFPorLTO(Lithium-inprincipleprovidethegridwith200GWforTitanium-Oxide)batteries.Infigure21itisuptoanhour.TheNationalGridinitsFESassumedthatin2050batteriesusedfor20225,lessoptimisticallyproposesthreenetstationarystoragewillbeusedfor5,328zerocompatible2050scenarioswhichincludecycles102,afterwhichtheircapacitywillhavevehicletogrid(V2G)capacitiesof16,34anddroppedto70%ofthenameplatevalue(this39GW.Thiswouldstillbeaverysignificantisdoublethenumberofcyclesfoundintestscontribution.Itisworthnoting,asNationalGridofanNMCbattery:theperformanceofLFPdoes,that‘lesswillbeavailableduringwinterbatteriescouldbebetter),oruntil25yearspeak5–6pmduetovehicleusage’.Somehaveelapsed(whicheverhappenssooner).workhasbeendonetotesttheappetiteforLittleseemstobeknownaboutfadeasaallowingthegridoperatorstoaccessvehiclefunctionoftime,ratherthanthenumberofbatteries.Atrial106foundthatcustomerscycles:costswiththelifetimelimited4000offered30p/kWhtoprovidepowertothegridcyclesor15yearsarereportedinSI7.1.onaverageearned£360/year.Theuseofafleetofelectricbusestosupportforgridisbeingtrialled107.56LARGE-SCALEELECTRICITYSTORAGEChaptersevenFIGURE21Costofelectricitydeliveredbya4-hourbattery.Thecost,whichdoesnotincludethecostoftheinputelectricity,isshownasafunctionofthenumberofcycles/year[whichisequaltothe(annualamountdelivered)/(day1useablecapacityxdischargeefficiency)],assumingi)NREL’smidcapitalcostprojectionof$149/(useablekWh)in2050(withoutmark-up),ii)alifetimeofthesmallerof5,328cycles(duringwhichcapacityisassumedtofadeby30%x(numberofcycles)/5328)and25years,iii)variousvaluesofFixedOperatingCostsandiv)twovaluesofthediscountrate.$/MWh400KEY3503005%discountrate250200Fixedoperations150andmaintenance1002.5%ofcapex1.5%500.5%5010%discountrate1.5%100150200250300350400Cycles/yearEVbatteriesarelikelytostillhaveusefulstoragecapacitieswhenthevehiclesthemselveshavereachedtheendoftheirlives.Thereisthereforeacompellingcaseforconsideringusing‘secondlife’EVbatteriesforthelessdemandingprovisionofstationaryenergystorage.Agenerationofsecond-handbatteriesfrom30millioncarswouldprovidearound1.7TWh.EVbatteriesshouldbedesignedwithaneyetore-useand/orrecyclingthematerialstomakenewbatteries.LARGE-SCALEELECTRICITYSTORAGE57ChaptersevenFIGURE22Elementsofaflowbattery.–Electrode+ElectrolyteNon-selectivemembraneFLOWCELLElectrodeElectrolytetanktankPumpPumpPowersource/load7.1.3FlowbatteriesThecapacityofthebattery,whichisdeterminedRedoxflowbatteries(RFBs)arecandidatesforbythevolumeoftheelectrolytetank,ismedium-scalestationaryenergystorageandindependentofitspower,whichisdeterminedarecurrentlyataTRLof7–8.Singleunitscouldbytheactiveareaoftheelectrodes/cellandhavecapacitiesofmanyGWh.therateofreaction.Consequently,RFBsofferhighlyflexibleandscalablestorage.Arange‘Redox’isshorthandforoxidation-reductionofRFBchemistriesareindevelopment,ofreactionsinwhichelectronsaretransferredwhichtheall-vanadiumdesignisthemostbetweentwospecies.Chemicalenergyiscommerciallymature.providedbychemicalsindifferentstatesofionization,dissolvedinliquidsthatarepumpedthroughacellbetweenelectrodesonoppositesidesofamembrane,asdescribedinSI7.1andillustratedinfigure22.58LARGE-SCALEELECTRICITYSTORAGEChaptersevenThecapitalcostofRFBsislargelydictatedby7.2Novelchemicalstoragethecostofthemembraneandelectrolyte,asChemicalenergycanbestoredby‘reducing’wellasthebalanceofplantwhichmusthandleironoxidetoironandlateroxidisingitinhighlycorrosivereactants.Forlargerscalethereactions:energystorage,theelectrolytecostsbecomethemostimportantfactor,duetotheincreasingiron+water→iron-oxide+hydrogen,oramountsofelectrolyteneeded.Thisisreflectediron+air(oxygen)→ironoxide+heatinthecostbreakdownsfortheenergyandpowerratedcomponentsofflowbatteriesTheheatproducedcouldbeusedtodriveareportedinaPPNLreport97,whichprojectsturbine.Thissuggeststhata‘strategicreserve’costsof$573/kWhand$306/kWrespectivelyofironcouldplayaroleasanemergencyin2025(correspondingtoatotalcostofsourceofhydrogenorelectricity,tobeused$650/kWhand$2598/kWfora4-hourbattery).duringonce-in-a-decadewinddroughtsifThecostperkWhissignificantlyhigherthanhydrogenusedtostoreelectricitythatisthatfoundforlithium-ionbatteries.normallyproducedbyelectrolysisrunsout.However,thescaleofinvestmentintheThehighcostandpricevolatilityofvanadiuminfrastructureneededtooccasionallybuthasaffectedtheprospectsofverylargerapidlyconvertirontohydrogenrulesoutthis(TWh)scaleapplicationsofV-RFBsandhaspossibilityincurrentconditions(seeSI7.2).highlightedpotentialbenefitsofalternativeReduction/oxidisationofotherelementssuchlower-costredoxcouples.Forexample,theassiliconorboroncould,however,playaroleuseofamuchlowercost(andabundant)asportablelocalsourcesofhydrogen,formanganeseredoxcouplepairedwithaexampleinpoweringshipsorfuellingvehicles.hydrogenstoreisbeingpioneeredbyUKcompanyRFCPower108,whilebothRFCPowerandFormEnergyintheUSareseekingtodevelopverylow-costsystemsbasedaroundtheuseofsulphurspeciesinalkalineelectrolytesasaredoxcouple.ThedeploymentofRFBsystemstypicallyspanskWhtoMWhapplications,withdischargetimesof3–5hours(forexample10MW,40MWh).Historically,applicationstargeteduninterruptedpowersupplyandloadshifting,butthereisagrowingappetiteforlarge-scaleenergystoragewhichleveragestheinherentscalabilityofthetechnology,withsystemsapproaching1GWhindevelopment109.RFBscantypicallyrespondrapidly.Self-dischargeisminimalsolonger-termstorageisfeasible,withcapacityscalingwiththesizeoftheelectrolytereservoir.Ifflowbatteriesusingmaterialsthataresignificantlycheaperthanvanadiumbecomeavailable,theycouldplayanimportantroleingrid-scalestorage.LARGE-SCALEELECTRICITYSTORAGE59ChaptereightPoweringGreatBritainwithwindplussolarenergyandstorage8.1Technologychoices8.2AdditionalcostsSomekeyattributesofpotentiallylarge-scaleThecostofelectricityfedintothegridincludesstoragetechnologiesaresummarisedintablenotonlythecostsofwindandsolarenergyand4,wheretheyareseparatedintothethreelarge-scaleenergystorage,butalso:categoriesintroducedinsection1.3.2and•ThecostoftransmittingwindandsolardiscussedinSI1.3.generatedelectricitytothepointwhereInprovidingestimatesofthecostofpoweringitwillbestored.GBwithwindandsolargeneratedelectricityThisislikelytobecheaperthantransportingsupportedbystorage,Li-ionbatteriesarehydrogen,unlessitcouldbedonewithchosenasarepresentativeofthefirstoftherepurposedgaspipelines.Onthebasisofthreecategoriesoftechnologiesintable4.currenttransmissionchargesandlosses,thiswouldcost£2.1/MWhifwindplussolarIncategorytwo,ACAESischosenasanpowercosts£35/MWhor£2.2/MWhitcostsexemplarofmanyrelativelyhighefficiency£45/MWh.Thegovernment’sview110isthat,technologiesthataresuitableforstoringenergyastheelectricitysectorgrows,thecostofforweeksorpossiblymonths(butnotyears)transmissionperMWhwill‘staybroadlybecauseitcouldinprincipleprovideupto20thesameorevendecreasegivenwiderTWhofstorageinGBandithasrecentlybeenefficienciesandthegreatlyincreasedsupplydeployedonasignificantscaleinChina:itsofelectricity’.Inviewoftheuncertainties,likelycostishardtoestimate,butthisisalsoandthefactthatlossesintransmissionfromtrueofthealternatives.ThechoiceofACAESremotewindfarmswillbeaboveaverage,itshouldnotbetakenasimplyingabeliefthatitwillbeassumed–conservatively–thatitwillwillplayadominantrole–inpracticeavarietycost£3/MWhin2050.of‘large-scalemedium-term-turnover’storagetechnologiesmaywellbedeployed.•Thecostofprovidingrapidresponsegridservices.Forthethirdcategory,hydrogenstorageThisdoesnotrequirelargeamountsofischosenbecauseitischeaperthantheenergy.Itcanthereforebeignoredinalternatives.However,whilethepotentialmodellingotherstores,butitsimpactonthecapacityofsolution-minedsaltcavernsinGBaveragecostofelectricityshouldbeincluded.ismorethanadequate,theirpossiblelocationsItwillbeassumedthat15GWofpowerwillarelimited.Anestimatewasthereforealsobeneededin2050toprovidethesegridmadeofthecostofusingammonia,whichservices,andthatitwillbeprovidedby1-hourcouldbedeployedanywhereacrossGB,butLi-ionbatteriesthatarekeptonstand-by,fullyitwasfoundthatusingammoniaratherthancharged,forusewhencalleduponbythehydrogenwouldincreasetheaveragecostofoperator.UsingNREL’smedium2050capitalelectricitybyatleast£5/MWh(seeSI8.1).costprojection,thiswouldadd£0.64/MWhtotheaveragecostofelectricityassuminga5%discountrate,and£0.83/MWhwith10%.Toallowforthesetwocosts,atotalof£4/MWhisincludedinthefollowingestimatesoftheaveragecostofelectricity.60LARGE-SCALEELECTRICITYSTORAGEChaptereightTABLE4Large-scaleelectricitystoragetechnologies.TechnologyMaximumunitRound-tripcapacityefficiencyTechnologyreadinesslevelandcommentsStoragetime:minutestomonths–limitedbyneedtorecoverinvestmentNonflowLargestinstallation≲90%Lithium-ion–TRL9;otherchemistriesatlowerbatteriestoday3GWhTRLStoragetime:hourstoweeks,insomecasesmonthsFlowbatteriesLargesttodayis70–80%TRL7–8400MWh.ManyGWhpossible.ACAESSinglecavern≲10≲70%Compressors,Expanders,storagecavernsandGWhthermalstorageareatTRL9.Completesystemsarearound7–8.LargeCarnotGWh45%TRL7withresistiveheating.batteryPumpedThermal<GWh50%TRL4–6EnergyStorageLiquidairenergy<GWh≲55%Systemsinoperation–TRL9.storageLarger/moreadvancedsystems–TRL7.AbletoprovidemonthsoryearsofstorageSyntheticfuelsSinglelargetank~≲30%TRL6–7.Expectedtoplayaroleintransport,TWhbutoutclassedbyammoniaandhydrogenforelectricitystorage.AmmoniaSinglelargetank≲35%Productionandstorage–TRL9.~250GWhConversionofpureammoniatopower–TRL5.Moreexpensivethanhydrogen,butcouldbedeployedacrossGB.Mayplayaroleasanimportedfuel.HydrogenSinglelargecavern~40%Atgridscaleelectrolysers–TRL8.~200GWhStoragecaverns–TRL9.PEMcells–TRL7–8.Conversiontopowerby4-strokeenginesTRL6–7.PotentialstoragesiteslimitedtoEastYorkshire,CheshireandWessex.TRLsdefinedintheglossaryCapacityisdefinedhereastheelectricalenergydeliveredonfulldischargeLARGE-SCALEELECTRICITYSTORAGE61ChaptereightTABLE5Assumptionsusedinmodellingandcostinghydrogenstoragein2050.Thestoragecostsarefortheverylargesystemsassumedinthisreport.Assumptionsfor2050Input£/kWeStorage£/MWhe–deliveredOutput£/kWeCapex–low/base/high167/333/500485/727/970222/315/472Opexp.a.1.5%ofcapex1.5%ofcapex1.5%ofcapexFinancialLife30years30years30yearsEfficiency74%Round-trip40.7%55%CostofWindandSolarEnergybeforetransmissiontoconsumersortostore,foran80/20wind/solarmix:£30.2/MWh(IEA2040projectionadaptedforUKloadfactors),£35/MWh(BEISlow2040projection)or£45/MWh(BEIShigh2040projection)ModellingusestheAFRYmodelof570TWh2050electricitydemandandtheRenewables.ninjamodelof80%wind(30%/70%on/offshore)and20%solarsupplyFIGURE23Breakdownofaveragecostofelectricity.Breakdownoftheaveragecostofelectricityfordifferentlevelsofwindandsolarsupply,withthebasecostsforhydrogenstorageanda5%discountrate.Thecostofwindandsolarsupplydominatesthetotal(notethesuppressedzero).£/MWh65100GW100GWKEY95.6TWh76TWh6077.7GW58GWPowergeneration100GWStorage–with5520%contingency123.2TWhElectrolyserWindplussolar50supply89.4GW4540760TWh/year800TWh/year741TWh/yearWindplussolarsupply62LARGE-SCALEELECTRICITYSTORAGEChaptereightTABLE6Annualisedcostscorrespondingtothebasecostsintable4fora5%discountrate.Basecosts+5%discountrateElectrolysersStorageElectricityAnnualisedcost(capexandOM)£26.7M/GW£32.1M/TWLHVGeneration£25.2M/GW8.3ProvisionofallflexiblepowerFigure24showstheminimumcostforthethreebyasingletypeofstoredifferentassumptionsaboutthe2050costofTheuseofhydrogenaloneisconsideredan80/20mixofwindplussolargeneratedfirstbecauseinallcasessomelarge-scaleelectricityintable5(whichwerediscussedinhydrogenstoragewillbeneededtomeetlong-section2.5),assuming5%and10%discounttermneedsanditprovidesabenchmarkforrates,forthelow,baseandhighcostsofcomparisonwithothercases.storageintable5.8.3.1HydrogenwithoutbaseloadForcomparison:Theassumptionsthatwillbeusedincosting•thewholesalepriceofelectricity(whichishydrogenstoragearecollectedintable5.slightlylargerthantheamountpaidforpowerTheannualisedcoststhatcorrespondtothefedintothegridasitincludesa0–5%basecostsintable4areshownintable6foralocationdependentTransmissionAdjusted5%discountrate(seeSI8.3fortheresultswithLossFactor)hoveredaround£46/MWh(nota10%discountrate,andfordetailsofhowthecorrectedforinflation)in2010–20.InmostofcontributionsofACAESandLi-ionbatteriesare2022itwasover£200/MWh.calculated).Thecontributionthat,forexample,thecostofelectrolysersmakestotheaverage•Thestrikeprices(indexeduptoMarchcostofpoweristhengivenby:2023)forpowerbeinggeneratedfrombiomassatDraxandnuclearpowerthatwill£[26.7x(electrolyserpowerinGW)/570]/MWhbeprovidedbyHinkleyCare£142/MWhfordemandof570TWh/year.and£128/MWhrespectively.ThecorrespondingbreakdownoftheaverageTheaveragecostofelectricityisrelativelycostofelectricity,whichwasplottedinfigure14,insensitivetoestimatesofstoragecosts.Thisisshowninfigure24.Thisfigureshowsthewayisbecausestorageonlyprovidessome15%ofinwhichtheriseinthecostofprovidingwindtheelectricityfedintothegrid,whoseaverageandsolarpoweriscompensatedbythefallincostisdominatedbythecostofthewindthesizeandcostofprovidingstorage.andsolarsupply.LARGE-SCALEELECTRICITYSTORAGE63ChaptereightFIGURE24Estimatesofaveragecostofelectricityprovidedtothegrid,2050.Rangeofestimatesoftheaveragecostofelectricityprovidedtothegridin2050assumingthatlarge-scalestorageisprovidedbyhydrogen,andthatwindplussolargeneratedelectricityaretheonlysourcesofsupply,fordifferentcostsofwind+solarpower(mixed80%,20%)anddiscountrates.Thedotsindicatecostsobtainedwithlow,baseandhighestimatesofhydrogenstoragecosts(in2021prices).20%contingencyisincludedinthestoresize.£4/MWhisincludedfortheestimatedcosttransmittingpowerfromwindandsolarfarmstostoresandproviding15GWof1-hourbatteriestomaintaingridstability.100KEY5%discountrate9010%discountrate80£/MWh70605040IEABEIS:LowBEIS:Low£30.2/MWh£35/MWh£45/MWhAveragewindplussolarsupply(TWh/year)Costofwindplussolarpowerprojectionsfor204064LARGE-SCALEELECTRICITYSTORAGEChaptereightFIGURE25Averagecostofelectricityintogridwithandwithoutnuclear.Averagecostofelectricityfedintothegridwithoutnuclearandwith50and200TWh/yearofnuclearbaseloadcosting£78/MWh(withtheloadfactorassumedbyBEIS,ageneratingcapacityof25GWwouldbeneededtoprovide200TWh/year).Thecostofprovidinggridservicesandtransmittingpowerfromwindandsolarfarmstostorageisnotincludedinthisplot.80KEYDeliveredenergycost(£/MWh)75Nonuclear50TWh/year70nuclear65200TWh/yearnuclear605550450475500525550575600625650675700725750775800Averagewindplussolarsupply(TWh/year)Otherfactorstowhichtheaveragecostof3.Theassumptionthat100GWofgeneratingelectricityispotentiallysensitiveinclude:capacityisneeded.Thisisslightlymore1.Theassumedefficiencies.IfelectrolyserthantheAFRYmodel’smaximumdemandof98.3GW,butitcouldbearguedthatitefficiencywas10%lowerthantheassumedshouldbeincreasedtoallowforsurges.Invalueof74%,theaveragecostofelectricitythebasecase,100GWofgeneratingpowerwouldbejustunder1%higher.Thecostiscontributes£4.6MWhtotheaveragecostofmoresensitivetotheefficiencyofpowerelectricityfora5%discountrate(£6.7/MWhgenerationbecauseitaffectstherequiredfor10%)andallowingfor10or20%moreorstoresizeandelectrolyserpower:reducinglessgeneratingpowerwouldonlyhaveatheassumed55%by10%to49.5%,wouldmodestimpact.increasethecostbyjustunder3%.Reducingtheefficiencyofboththeelectrolysersand4.The80/20windsolarmix.Itturnsoutgenerationby10%wouldincreasethecost(seeSI8.3)thattheaveragecostofby5.3%(seeSI8.3).Thisisforthecentralelectricityisnotverysensitivetothecostassumptionsandwindplussolarcostingmix.Thisisreassuringasitwillbepartly£35/MWh.Ifitcosts£45/MWh,5.3%woulddeterminedbynon-technicalandfinancialincreaseto6.5%.factors,suchasplanningpermission,theavailabilityofonshoresitesforsolarand2.The20%contingencyincludedinthestorewind,andtheappetiteofinvestors.size,whichcontributes£0.92MWhfora5%discountrate(£1.4/MWhfor10%).LARGE-SCALEELECTRICITYSTORAGE65Chaptereight8.3.2Hydrogenstoragewith(nuclear)baseloadNuclear‘cogeneration’ofelectricityandgenerationhydrogenmightlowercosts.TheelectricityIfconstantbaseloadsupplyisadded,thewouldbeuseddirectlywhenneeded,andatdemandthathastobemetbywindplussolarothertimesbeusedtoproducehydrogen.Thesupply,supportedbystorage,isreducedheatfromnuclearcouldbeusedtoimprovebyaconstantamount.Thisallowsthesizetheefficiencyofelectrolysis,thoughthegainofthewind,solarandstoragesystemtobeismodestexceptathightemperaturereactorsreduced.However,thecostperMWhofthewhicharenotlikelytobewidelydeployedinelectricitythatwind,solarandstorageprovidestheforeseeablefuture.Modelling(seeSI8.3)willincreasebecauseremovingaconstantofaconstantnuclearsupplyof10GWfindsincreasesthevolatilityoftheremainingdemandthatwithaPWRcogenerationwouldonlythattheyhavetomeet.Itfollowsthatthecostreducetheaveragecostofpower(relativetoofelectricitywillbeincreasedbytheadditionthecasewithhydrogenstorageonly)ifnuclearofbaseloadunlessitscostislessthanthegeneratedelectricitycostslessthan£60/MWh.averagecostofelectricitywithoutbaseload.Cogenerationofelectricityandheat,tobeInthecaseofnuclearbaseload,thiswillonlyusedbyindustryortoprovidespaceheating,happenifthecostofnuclearistowardsthecouldbeattractiveifalarge-scaleflexibleneedbottomoftherangeshowninTable2and/orforheatprovidedbynuclearreactorscouldthecostwithoutnuclearistowardsthetopofbeidentified,and/orsuitabledistrictheattheprojectedrangeshowninfigure24.networkswereinplace82.Thisconclusionisillustratedinfigure25intheBaseloadcouldalsobeprovidedbycaseofBEIS’scentralprojectionof£78/MWh•naturalgasgenerationequippedwithCCSforthe2040costofnuclearpower,thecentralvaluesforthecostofhydrogenstorage,a5%whichisdiscussedinsection8.5;ordiscountrateandwindplussolarpowercosting£35/MWh.Withoutbaseload,theminimumin•BECCS.WithBEIS’scentral2040projectiontheaveragecostofelectricity,whichisreachedof£181/MWheforcost,addingBECCSwouldwithaveragewindplussolarsupplyofaroundincreasetheaveragecostofelectricity.760TWh/year,is£60.1/MWh(withoutthecostHowever,ifthecarbonitsavesattractedaofprovidinggridservicesortransmittingcarboncreditofmorethan£100/(tonneCO2powerfromwindandsolarfarmstostore).saved)itcouldreducethecost,dependingonWith50TWh/yearofnuclearbaseloadcostingthecostbeforeitwasaddedaa.£78/MWh)theminimumintheaveragecostofelectricity(whichisreachedataround700TWh/yearofwindplussolarsupply),increasesto£61.9/MWh.With200TWh/yearofnuclearat£78/MWh,theminimum(whichisreachedat500TWh/year)is£67.6/MWhz.zWith200TWh/year[50TWh/year]thecost/MWhofthewind,solarandstorageincreasesby2.8%[0.4%]relativetowhatitwouldbewithoutnuclear,andtheadditionofnuclearwouldonlylowertheaveragecostofelectricityifitcostslessthat£57.1/MWh[£59.7/MWh].aaAcreditofover£139/tonnewouldoffsetthegeneratingcost.IfBECCSwereentirelypaidforbycarboncredits,thenwith50TWh/yearofBECCS,theaveragecostofelectricitywouldbe£55/MWh,withwindplussolarcosting£35/MWh,storageprovidedbyhydrogen,withthebasecosts,and15GWofbatteries,anda5%discountrate.66LARGE-SCALEELECTRICITYSTORAGEChaptereightTABLE7Costsusedinmodellingtheimpactofadvancedcompressedairenergystorage(ACAES).Assumptionsfor2050Input£/kWeStorage£/MWhe–Output£/kWeCapexUpto£500/kWdeliveredUpto£500/kWOpexp.a.4%ofcapex39114%ofcapexFinancialLife30years2%ofcapex30yearsEfficiency√round-trip30years√roundtripRangeFullcostforpowersofaround80MW.Thecost/kWisthoughttovaryas(powerrating)-0.4Themodellingusedinthisreportfound68%:arangewasconsideredincostingACAES8.4Multipletypesofstore8.4.1ACAESandhydrogenTable7givesthecostsusedinmodellingtheimpactofACAES.ACAES,whichisusedheretorepresentaclassofstoragetechnologies,costsmorethanhydrogenperunitofenergystored,butitismoreefficient.Whileitcannotremovetheneedforhydrogenstorageab,itcanreducetheaveragecostofelectricitywhencombinedwithhydrogen,asshowninfigure26.With68%round-tripefficiency,thevaluefoundinChapter4fortheACAESsystemthatwasmodelled,addingACAEStoastoragesystemwouldleadtoacostreduction,providedcompressorsandexpanderseachcostlessthan£500/kW(seealsoSI8.5).TheanalysisinChapter5suggeststhatthe2050costoflargecompressorsandexpandersmanufacturedinsignificantnumbersmayverywellbeunder£450/kW,althoughthisisnotassured.abModellingwithbothACAESandhydrogenstorageneverfindscasesinwhichACAESaloneischeaperthanhydrogenalone,noracombinationofACAESandhydrogen.IftheconditionthatACAESprovidesallstorageisimposed,itisfoundthatthecostismuchhigherthanusinghydrogenalone,(egwithcompressorsandexpandersareassumedtocost£300/kWandaround-tripefficiencyof65%,thedifferenceintheaveragecostofelectricityprovidedtothegridwouldbe14%)andthatanACAEScapacityof20TWhewouldberequired,whichisapproachingthemaximumthatcouldtheoreticallybeprovidedonshoreinGB.Furthermore,theACAEScostsusedinthisreportignoreheatlossesfromthethermalstore–whicharenegligibleifACAESiscycledonatimescaleofweeksbutwouldbeimportantifACAESwereusedprovideallstorage,whichwouldrequirestoringsomeofthecontentformanyyears.LARGE-SCALEELECTRICITYSTORAGE67ChaptereightFIGURE26PercentagereductioninthecostofelectricitywithACAES+H2storagecomparedtoH2storageonly.ReductionintheaveragecostofelectricitywithhydrogenstorageandACAESrelativetothecostwithonlyhydrogenstoragefordifferentassumptionsaboutthecostsofcompressorsandexpanders(whichareassumedtocostthesame)andtheround-tripefficiency.12KEY10CostreductionsCostreduction(%)>10%Eciency(%)88–10%6–8%6814–6%42–4%2720–2%00%6080100631301602002402903404004805306005445Powercost(£/kW)68LARGE-SCALEELECTRICITYSTORAGEChaptereightTABLE8Exampleofstorageparametersforhydrogenstorage(basecosts)togetherwithACAES,withcompressorandexpandercostsof£340/kWand66%roundtripefficiencywithoutcontingency.TheadditionofACAESlowersthelevelofwindandsolarsupplythatisneededbecauseitismoreefficientthanhydrogen.Correspondingly,itincreasestheamountofenergythathastobeprovidedbystorage.CapacitytodeliverperHydrogenonlyHydrogen+ACAESACAEScycleTWhe56Hydrogen2.4[6.8GWhe/cavern]32.5Electrolyser/77compressorpower884029[82MWe/cavern]GWe856523[65MWe/cavern]Generation/expanderpowerGWe3652AnnualdeliveryTWheTheimpactofaddingACAESonthescaleof8.4.2Addingbatterieshydrogenstorage,andtheACAESparametersBatteriescanbeandarebeingusedtostorethatminimisethecost,areillustratedinenergyforshortperiodstoprovidepeakoneparticularcase(towhichnoparticularshaving,whichattractshighpaymentsandsignificanceshouldbeattached)intable8.generatesrevenuefromarbitrage,aswellasNotethatalthoughthecapacityofACAESisaprovidinggridservices.However,accordingfourteenththatofthehydrogenstore,itdeliverstothemodellingandcostingsusedinthismoreenergy/year,becauseitiscycledmuchreport,oncehydrogenstorageandACAESaremorefrequently.available,theywillbeabletomeettheseneedsatalowercostthanbatteries,unlessbatteryThenumberofclustersofcavernsthatcostsfallmuchfasterthananticipated.However,wouldbeneededturnsouttobe84(withoutneitherhydrogenstoragenorACAEScancontingency)withhydrogenonly,andalsoinprovidegridservices(frequencyregulationandthecasewithACAES,inwhich35cavernsarevoltagestability).neededforhydrogen(towhichcontingencyshouldbeadded)and49forACAES.LARGE-SCALEELECTRICITYSTORAGE69Chaptereight8.5UseofnaturalgaswithCCSUsinggas+CCStoprovidebaseloadpower8.5.1IntroductionAddingbaseloadtoa‘hydrogenstorageonly’ThecostofusingwindplussolarenergyandsystemwillonlylowertheaveragecostofstoragetoprovideGB’selectricitymightbeelectricityifthecostofthebaseloadislessloweredbyallowingsomeuseofgaswithCCS.thanthecostwithoutbaseload.WithBEIS’sThiswouldhavetobesubjecttoensuringthat:assumptions,the2040costofbaseload•FugitiveCO2emissionsarecostedataelectricityprovidedbygas+CCSwouldbe£82/MWh,whichistowardsthetopoftherangelevelthatwouldpayfortheirremoval(inwithoutbaseloadshowninfigure24.Ifgascompetitionwithremovingemissionsfromcosts95p/therm(asassumedina2021BEISmuchhardertoabatesectors).reportonthecostofbluehydrogen),thecostofgas+CCSwouldbewelloutsidetherange.If•Methaneemissions,whicharecurrentlyitcosts40p/therm,gas+CCSwouldcost£64/notpenalisedfinancially,arekepttoaveryMWh(or£72/MWhifthecarbonpricewerelowlevel.twicethatassumedbyBEIS),whichisinthemiddleoftherange.Addingenoughgasplus•RiskstoenergysecurityfromrisesintheCCStohaveasignificantimpactontheaveragepriceofgas,andincreasingdependenceoncostofelectricitywouldproducesubstantialimportedgas,areaccepted.greenhousegasemissions.Theadditionof150TWhe/year,forexample,wouldgenerate•Adequatestorageofnaturalgasisavailable.fugitiveCO2emissionsof5.7Mt/year,plusa‘CO2equivalent’of13.3Mt/yearfrommethaneForcomparison,55Mtofcarbondioxidewereleakage,assuming47%generationefficiency,emittedbypowergenerationintheUKin2021.that90%oftheCO2iscaptured,andmethaneTheclimateimpactfactorofmethaneistakenleakagecanbelimitedto0.5%.tobe128timesthatofcarbondioxide.ThisistherelativesizeofthetemperaturerisesUsinggas+CCStoprovidetheflexibilitycausedbysteadyemissionsofequalmassesofneededtocomplementwindandsolarcarbondioxideandmethane20yearsaftertheUsingforecastsofsupplyanddemand,itcouldemissionsstart(ratherthantheGlobalWarmingbepossibleforCCGTsequippedwithCCStoPotentialwhichdescribesrisescausedbyprovidemostoftheflexibilityneededtomatchemittingsinglepulsesofeach).variationsinwindandsolarsupplyanddemand.8.5.2UseofnaturalgaswithCCStogenerateUsingBEIS’sestimateofthecostofgaspluselectricityCCS,ifgasplusCCSwereusedtoprovideallThreeoptionswerestudiedusingBEIS’sflexibility,thenwithagaspriceof:2020estimatesofthe2040costofelectricity•65p/thermandwindplussolarcosting£35/generatedbygaswithpostcombustionCCS(fordetailsseeSI8.5).BEISpresentedresultsMWh(or£45/MWh),theaveragecostofforanassumedfuturegaspriceof65p/thermelectricitywouldbeabove(orcloseto)the[£22.4/MWhHHV],atwhichlevelitcontributestopoftherangeofcosts(seefigure24)found£47/MWhetothecostofelectricity,andacarbonifstorageprovidesallflexibility.priceof£220/tCO2,atwhichlevelitcontributes£8/MWhe.Forcomparison,thewholesale•40p/thermandwindplussolarat£35/MWhcostofgasfluctuatedaround40p/thermfrom(or£45/MWh),thecostwouldbeinthemiddleOctober2015toOctober2020,butwasover(oratthebottom)oftherangeinfigure24.100p/thermfromOctober2021toMarch2023.UsinggasplusCCStoprovideallflexibilitywouldthereforecostmorethanusingstorageunlessthefuturegaspricesarelowandstoragecostsarehigh.70LARGE-SCALEELECTRICITYSTORAGEChaptereightMoreseriously,itwouldleadtolarge8.5.3Useofbluehydrogengreenhousegasemissions.With,forexample,BluehydrogencanbemadebySteamgasat65p/thermandwindplussolarat£35/MethaneReforming(SMR)orAuto-ThermalMWh,theaveragecostofelectricitywouldbeReforming(ATR).ATRisconsideredhereminimisedwithwindplussolarsupplyofaboutbecause,accordingtoareportforBEIS,itis400TWh/year.84%efficient(HHV)and95%oftheCO2canbecaptured,whileforSMRthecorrespondingSome375TWh/yearofthiscouldbeusedtofiguresare74%and90%.IncontrasttoSMRs,meetdemanddirectly(theremaining25TWhthereissomescopeforrampingATRsupwouldbecurtailed),leaving195TWhe/yeartoanddown,althoughatafarslowerratethanbemetbygas+CCS,whichwouldgenerateelectrolysers,andtheycannotbereadilyturnedfugitiveCO2emissionsof7.4Mt/year,plusonandoff.BEISconcludesthat‘ATRactsverya‘CO2equivalent’of17.2Mt/yearfrommuchasabaseloadproducer’.Combiningmethaneleakage.baseloadpowergeneratedbybluehydrogenwithstorageofgreenhydrogenwouldputUsinggas+CCSflexiblyincombinationwithuptheoverallcost,unlessthefuturecostofhydrogenstoragegasislessthan47p/therm.Alternatively,blueCombininggasplusCCSwithstoragecouldhydrogencouldbefedintothehydrogenlowerthecostofelectricityasitwouldreducestore,whenitisnotfull.Simplemodellingthelevelofwindandsolarsupplythatis(seeSI8.5)findsthatthiswouldincreasetheneededandthesizeofthestoragesystem.averagecostofelectricityunlessthefutureTheadditionof20GWeofgasgeneratedcostofgas(whichdominatesthecostofbluepower,assumedtobeavailablewhenneeded,hydrogenproduction)islowerthanthe95p/wasmodelled(seeSI8.5).ThiswouldleadtothermassumedbyBEISinthiscase,andthefugitiveCO2emissionsof2.1Mt/year,assumingcostofstorageisintheupperpartoftherange90%capture,towhichmethaneleakagewouldfoundinthisreport.Withacontinuoussupplyadd4.8Mt/year‘CO2equivalent’.Itwouldlowerof20GWLHVofhydrogen,thecostwouldbetheaveragecostofelectricitysignificantlyminimisedwithabout600TWh/yearofwindifBEIS’scentralestimateofthecostofgasplussolar,a65TWhLHVstoreand30GWofplusCCSiscorrect,gascosts64p/therm,andelectrolysers.Withthe95%captureanticipatedhydrogenstoragecostsareintheupperhalfofinATR,asteadysupplyof20GWLHVofbluetherangeinfigure24.ThesizeofthereductionhydrogenwouldleadtoCO2emissionsofdependssensitivelyontheassumedcosts2.5Mt/yearand‘CO2equivalent’methaneandonhowgasgenerationisoperated,butisemissionsof7.7Mt/year.relativelyinsensitivetothecarbonprice.8.5.4ConclusionWith20GWeofgasgeneratedpoweravailableThereareplausiblecircumstancesinwhichondemand,thecostwouldbeminimisedforcombininghydrogen(togetherwithotheraveragesolarpluswindsupplyof620TWh/formsof)storagewithflexiblesupplyfromyear(comparedto760TWh/yearwithnogas),gasplusCCSwouldlowercosts,althoughwith50GWofelectrolysersanda57.7TWhfugitiveCO2emissionsandmethanehydrogenstore(comparedto76.9GWandleakagecouldnotbeavoided,andthereare80.2TWhwithoutgas,withnocontingencyinsome–morecircumscribed–conditionseithercase).Whileitwouldhaveamajorimpactinwhichtheotherusesofgas+CCSandonthelevelofwindandsolarsupplyandthebluehydrogenconsideredherecouldlowersizeofthestoragesystem,theadditionofcosts.ThecircumstancesdependonthegaswithCCSwouldnotremovetheneedforcostsofprovidingstorage,windandsolarthetensofTWhoflong-termstoragethatarepower,naturalgasandgasplusCCS,andtherequiredtocopewiththelong-termvariabilitycarbonprice.Thispossibilitywouldbeworthofwindpower.analysinginmoredetailasestimatesoffuturecostsbecomefirmer.LARGE-SCALEELECTRICITYSTORAGE71ChaptereightAddinggasplusCCSwouldprovidediversity,UsingresidualsurplusesmightnotbebutitwouldexposeGB’selectricitysupplytostraightforwardastheyvarybylargeamountsanylargeincreasesinthepriceofgas,andfromyeartoyear(seefigure9andSI3.2).increasingrelianceonimportsasGB’sgasHowever,meetingsomeofthepossibleusesreservesdecline.However,itwouldnotremovetowhichtheycouldcontribute,suchasco-theneedforlarge-scalelong-termstorage.productionofgreenhydrogenfordifferentpurposes,couldwarrantadditionalinvestment8.6Possibleusesandvalueofsurplusingeneratingcapacity.electricityTheaveragecostofelectricityissensitiveto8.7Contingenciesagainstperiodsoflowthevalue,ifany,oftheresidualsurplusesthatsupplyremainafterthedemandthatwasmodelledArangeofunknownshavebeenoutlinedinhasbeenmet(seefigure14).Possibleusestothisreport,notleastthevariabilityofthewindwhichtheycouldbeput(whichareconsideredandsunshine.Forthisreason,20%contingencyinmoredetailinSI8.6)include:wasaddedtothesizeofthehydrogenstore•Producinggreenhydrogenforpurposesinestimatingtheaveragecostofelectricity,whichcontributesabout£1/MWhtothecostotherthanstoringelectricity,forwhichofelectricity.TounderstandwhetherthistherecouldbeademandoftensofTWh5.contingencycouldbeprovidedinotherways,Co‑productionofgreenhydrogenfordifferentconsiderwhatwouldhavehappenedifthepurposeswouldbeexpectedtoleadtolowerneedforstoragehadbeenunderestimatedcosts.OneUSstudy111foundthatproducingandthestorehadbeenmade20%smallerthanhydrogenforothermarketscouldreduceneededtomeetdemandoverthe37yearsthecostofelectricitydeliveredbyhydrogenstudied(therebysaving~£1/MWh).Inthatcase,systemsbyupto39%.demandcouldhavebeenmetinallbut322hours,inaperiodof1,211hoursinMarch–May•Exportingelectricitythroughinterconnectors.2011(seefigure13),whenitwouldnothaveGBbecameanetexporterofelectricityduringbeenpossibletomeet11.5TWhofdemand.2022forthefirsttimeintwelveyears.InsomeofBEIS’sscenarios112GBwillbeanetimporterInthose322hours,theaverageunmetin2050,butitwillbeanetexporteraccordingdemand,showninfigure27,was35GW,toalltheFES113(of148TWh/yearinonecomparedtoanaveragedemandof65GW.scenario).ThevolumeofimportsandexportsItwouldbeprohibitivelyexpensivetokeepwilldependonrenewablecapacityinGBothersources,capableofprovidingtensofandtherestofEurope,andgenerationcostsGW,availableforuseinjust0.1%ofthetimewhentherearesurpluses(whichwilloftenin37years(seeSI8.7).Furthermore,itisoccuratthesametimeindifferentplaces).impossibletoimaginedemandmanagementSinceGBhasaverylargewindresource,itiscompensatingfortheseclustersoflargepossiblethatitcouldbeexportingona100amountsofunmetdemand.However,asTWhscalein2050,whilealsoimportingsolardiscussedinsection3.3,long-rangeforecastingenergyfromsouthernEurope.canbeusedtoanticipateprolongedperiodsoflowsupply,duringwhichmeasuressuchas•Heating,ortoppingupthermalstoresthosediscussedinsection2.7couldhavebeenconnectedtodistrictheatnetworks.usedtoreducedemandandpreventthestorebecomingempty.Thisdeservesmoreanalysis•Meetingnewneedsthatmayarisethatcan(seeSI8.7forapreliminaryinvestigation).makegooduseofspasmodicpower,suchasdryingbiomass.72LARGE-SCALEELECTRICITYSTORAGEChaptereightFIGURE27Unmetdemandwithanundersizedhydrogenstore.DemandthatcouldnothavebeenmetusinghydrogenstorageinMarch–May2011,withahydrogenstorethatis20%smallerthanneededtomeetalldemandintheperiod1980–2016.Gw80706010020030040050060070080090010001100120050Hours4030201000Withoutabetterunderstandingofthevagaries8.8Differentlevelsofdemandoftheweather,itisunclearhowmuchToprovideafeelingforwhatwouldhappenifcontingencyisneeded.Bythetimelargebasicdemandwerehigherorlowerthan570amountsofstoragehavebeenbuilt,however,TWh/year,modelswerestudied(seeSI8.8)improvedmodelling(andstudiesofearlierwithdemandsof440and700TWh/year,whichperiodsoflowwind)shouldmakeitpossibleareatthelowerandupperendsoftherangetounderstandbetterthescaleoftheneedforofcurrentprojectionsfor2050.Withhighercontingency,andthescopeforpre-emptivedemand,thelevelofwindsolarsupplyandthedemandmanagement.sizeofstoragesystemwouldhavetobemuchgreater.However,thecostofelectricitywasfoundtoincreasebyunder2%inmovingfrom440to700TWh,despitetheprofileofdemandbecomingmuchmoreskewedbetweenwinterandsummerasmoreheatingwasassumedtobeelectrifiedinthesecondcase.LARGE-SCALEELECTRICITYSTORAGE73Chaptereight8.9OtherstudiesofthecostofstorageinStudiesbyAFRYmanagementconsultancyGreatBritaincarriedoutforBEIS119theNationalGrid/ESO,AnumberofstudieshavebeenmadeofandtheClimateChangeCommittee,whichresidualdemandandtheneedforelectricityusedthemasinputtotheirreportDeliveringastorageinGB114,115,116,117,118,119,andofthecostofReliableDecarbonisedPowerSystem120,lookedprovidingit,includingbyBarrettetal(thefirstonlyatindividualyears,withoutallowingforanytostudymulti-decadalweathersequence,seeinter-annualstorage(thesereportsareanalysedSI2Annex2),andoneinthecontextofEuropeinSI3Annex2).Whilethisworkcastshelpfulasawhole,allowingforthepossiblyofgreaterlightontheneedforshort-termstorage,studiesinterconnection118.thatdonotconsiderlongsequencesofyearsunderestimatetheneedforlong-termstorage.Allbutoneofthesestudies,whoseStudiesofsingleyearscannotcastlightdirectlyassumptionsandapproachesaresummarisedontheneedforstoragelastingover12monthsandcomparedinSI8.9,werebasedonweatherandoverestimatetheneedforothersuppliesac.inconsecutiveyears,overperiodsrangingfrom9years114,115(whichtheauthorsnotedisDespiteusingdifferentmethodologies,andprobablynotenough),through21and27years,makingverydifferentassumptionsabouttothe37years117usedinthisreport.Thesestoragecosts,thestudiesthatusedmulti-yearstudiesreachedsimilarconclusionsontheweathersequencestocostsystemswithhighneedforstoragerelativetotheassumedscalelevelsofwindandsolarsupportedbylong-termofdemand.storagefoundaveragecostsofelectricitythatarenotdissimilar(seeSI8.9).Thisisbecausethecostofprovidingstorageonlycontributesasmallfractionoftheaveragecostofelectricity,whichisdominatedbythecostofwindandsolarpower.Thestudiesthatallowedforacontributionfromnuclearbaseload105,106foundthatitwillputuptheaveragecostofpowerunlessthecostofnuclearisnearorbelowthecurrentrangeofexpectations.acInordertobalancesupplyanddemand,amuchgreaterlevelofsupplyisrequiredfromothersources,and/orwindandsolar,thanwouldhavebeenrequiredifstoragehadbeenallowedtotransferenergybetweenyears(especiallyinlowwindyears,suchas2010,whichwasonethatAFRYstudied,whentheamountneededfromothersourceswouldhavebeenfarmorethaninmostotheryears,ascanbeseeninFigure2).ThiseffectisexacerbatedbyAFRY’sstudyofcalendaryearssinceperiodsofexceptionallylowwindandsolarsupplytypicallyrunfromDecembertoMarch(asseeninfiguresSI2.5AandB).74LARGE-SCALEELECTRICITYSTORAGEChapternineTheGrid,electricitymarketsandcoordinationTherewillbemajorchangesinthescaleandInconventionalpowerstations,theelectricitynatureofGB’selectricitysystemasheating,thatisfedintothegridisgeneratedbytransportandpartsofindustryareincreasinglysynchronisedrotatingmachinery,whoseelectrified,therolesofwindandsolarenergymechanicalinertiaprovidesstabilityandhelpsgrow,andstorageiswidelydeployed.Thesemaintainaconstantvoltageandfrequency.changeshaveimportantimplicationsfortheWindandsolarplantsusepowerelectronicstoelectricitygridandarelikelytorequiremajorprovideACpowertothegrid.Ifwindandsolarchangesinelectricitymarkets(seeSI9forasupplyiscombinedwithenergystoresthatcanmoredetailedanalysis).beaccessedquickly,problemsarisingfromtheabsenceofmechanicalinertiacanlargely9.1Thegridbeovercome.Thereis,however,anurgentThetransmissiongridwillhavetobeneedforengineeringresearchtoguidehowenlargedtoconnectnewsolarandwindtheincreasinglyubiquitouspowerelectronicfarmsatdispersedandoftenremotesites.convertersshouldbedesignedandused,Itwillalsohavetobestrengthenedtodealandmodellingisneededtounderstandtheirwithlargerfluctuations,dominatedbyimpact.Newsupporttoolsbasedonadvancedvariationsinsupply,andhigherpeakloads.stochasticmethodswillhavetobedevelopedThedistributionnetworkswillalsohavetothattakeaccountoftheuncertaintyinwindandbestrengthenedtohandleadditionalloadssolarsupplyanddifferentwaysofschedulingcreatedbychargingelectricvehiclesandtheuseofstorage.electrificationofheatingandaccommodateanincreasingnumberofrenewablesources9.2Marketsissuesconnectedtoitdirectly.DecisionsonthemajorinvestmentsthatwillbeneededduringtheenergytransitionmustEnsuringthatsupplyremainsreliableensureanappropriatebalancebetween(iedesignedandoperatedsothatitisgeneratingcapacity,differentstorageuninterrupted)andresilient(iecanbetechnologies,andtransmissionanddistribution,restoredquicklyifitfails)willbecomeandenableflexibledemand.Closecoordinationincreasinglyimportantastheroleofbetweengeneratorsandoperatorsofstorageelectricitygrows.Reliabilityandresiliencewillbeneededinordertoscheduletheusearecurrentlymainlyprovidedbydispatchableofstoragecost-effectivelyandensurethatunabatedgasgeneration.However,inanetdemandforelectricitycanbemetreliably.Itzerofuture,withsystemsinwhichhighlevelsisveryunlikelythatGB’scurrentwholesaleofrenewablesupplyaresupportedbystorage,marketarrangements,inwhichbothlong-termreliabilitywilldependcriticallyontheprovisioninvestmentdecisionsandshort-termdispatchofdispatchablestorage.arelargelygovernedbyasinglepricesignal(iethesystemmarginalcost),willbeabletomeettheseaimsevenwithaveryhighcarbonprice.LARGE-SCALEELECTRICITYSTORAGE75ChapternineInvestorsingenerationandstorageareTraditionalspotmarkets,whichweredependentonrevenuestreamsoverlongdevelopedtodealwithgasandcoalpowered(20+years)assetlives,duringwhichprices,generation,arenotautomaticallysuitableforregulationsandgovernmentpolicywillchangeoradaptabletotechnologieswhicharesubjectinunpredictableways.Inthecaseofstorage,tomorecomplex,intermittencyandoperatinginvestorswillhavetotakeaviewonthefutureconstraints,suchaswind,solar,andstorage.costofbuyingenergy,thesellingprice,theFindingalternativepricingarrangementsoptimumtimingofsales,andthebehaviourwillbecomeincreasinglyimportantasi)theofcompetitors.Theseinvestorswillrequirecomplexitiesofmanaginglowcarbonsystemssomeformoflong-termcontractualassurance.grow,andii)schedulinganddispatchdecisionsItcouldbeprovidedbyaregulatedassetincreasinglyrelatetocomplexoperatingbaseapproach,orgovernmentcommitments,regimes,suchasthoserequiredwithstorage,forexamplethroughContractforDifferenceratherthansimplemeritorderranking.(CfDs)orfeedintariffs121.However,incentivestoinvestinstoragebasedonoutputcouldleadto9.3Possiblereformsoperatorsreleasingenergywheneverpossible,Itiswidelyrecognisedthatreachingnetzeroleavingstoresinprofitbutemptyinacrisisemissionscost-effectivelywillrequireanwhentheyareneeded.unprecedentedlevelofcoordinationanda‘wholesystem’approachthatextendsacrossIfpaidonlyonthebasisofshort-runcosts,thetheenergysector.Itisdifficulttoimaginelarge-scalelong-termstoragethatthisreportexistingmarketsandregulationsdeliveringaargueswillbeneededcouldneverrecoverportfolioofgenerationandstoragethatwoulditscapitalcostssinceitwillbeidlemuchofleadcost-effectivelytoanetzeroelectricitythetime.Capacitymarketscanbedesignedsystemorensuringtheoperationalcoordinationtoaddressthisproblem(forstorage,capacitynecessarytocontrolcosts.Ifalternativesarenotcouldmeanstoragevolume,and/orinputoradoptedbeforelarge-scalestorageisneeded,outputcapacity).Anotherpossibleremedyisanotenoughwillbebuilt.‘capandfloor’mechanisminwhichinvestors’incomeispartlydeterminedbyenergymarketsbuttheirexposuretodownsiderisksandpotentialupsidegainsislimited.ThisapproachiscurrentlyusedforGB’sinterconnectorsandhasbeenproposedforstoragecapacity122.76LARGE-SCALEELECTRICITYSTORAGEChapterninePossiblealternatives,presentedpurelytoprovokediscussion,include:1.Centrallydrivencoordinationofinvestmentplans,whicharequitecommoninternationally(examplesincludeFrance’sEDFandGermany’sEnergiewende123).2.Closecooperationbetweenmembersofumbrellagroups(suchas‘powerpools’intheUS)whichimplicitlyassumeresponsibilityforreliability(whichcanraisecompetitionpolicyquestions)and/orreverseauctionsoftheobligationtoprovide‘firm’,dispatchable,power124(whichwouldrequirecooperationbetweengeneratorsandprovidersofstorage).3.Thecreationofa‘centralbuyer’,responsiblenotonlyforprocuringcapacity,butalsoforbuyingpowerfromgeneratorsandsellingittoretailsuppliersandlargeconsumers:whilenotinvolvingownershipofgeneration,storageortransmission,thismodelwouldbesimilartopublicownershipinmanyways,butwithoutremovingcompetitionandrequiringtaxpayerstobearallrisks.LARGE-SCALEELECTRICITYSTORAGE77ChaptertenConclusions,furtherstepsandopportunities10.1ConclusionsWhenseveraldifferenttypesofstoreareGreatBritain’sdemandforelectricitycoulddeployed,aprocedureforschedulingtheirusebemetlargely(orevenwholly)bywindisrequired.Operatingprotocolsdesignedtoandsolarenergysupportedbylarge-scaleminimisethecostwillrequireclosecooperationstorageatacostthatcomparesfavourablybetweengeneratorsandoperatorsofstorage.withthecostsoflow-carbonalternatives,whicharenotwellsuitedtocomplementing10.1.2Chapterfour:Greenhydrogenandintermittentwindandsolarenergyandvariableammoniaasstoragemedia.demand.Thefollowinglistofchapter-by-Hydrogenandammoniaaretechnicallyviablechapterheadlinessupplementsthenarrativeoptionsforstoringpower,althoughtheround-synthesisofconclusionsintheExecutivetripefficienciesarelow,andthecostsareSummary,whiletable4providesasummaryhigh.Hydrogenproductionisalreadyfullyofthecharacteristicsofstoragetechnologiescommercialisedforsomeelectrolysertypes.thatareconsideredinthisreport.WhilethisHydrogenend-usetechnologiesarestillreportfocussesonGB,themethodologyanddeveloping.Electrochemically-drivenammoniaconclusionsonstoragetechnologiesare,productionhasbeenpracticedextensivelyinhowever,generallyapplicable.Norway,butammoniaend-usetechnologieslagthoseusinghydrogen.10.1.1Chaptersone–three:Introduction;electricitydemandandsupplyinthenetzeroProvidedhydrogencanbestoredunderground,era;modellingtheneedforstorage.ammoniawillnotbeabletocompetehead-to-InordertoassesstheneedforstorageitisheadwithhydrogenforstoringpowerintheUKnecessarytoexamineaslongaperiodof(unlessoruntilmuchcheaperwaysofmakingweatherdataaspossible.Studiesofperiodofammoniaaredeveloped,byaprocessthatcanafewyears,orevenoneortwodecades,canloadfollow).Itmay,however,playaroleinareasseriouslyunderestimatetheneedforstorage.inwhichitisnotpossibletostorehydrogenundergroundandthecapacitytotransmitThelong-termvariabilityofwindcreatesaneedpowerfromotherregionsislimited.tostoretensofTWhsformanyyears.TheUKhasamorethanadequatepotentialTheneedtocurtailwindandsolarpowerinGBforundergroundhydrogenstorage,althoughisminimisedforawind/solarmixaround80itislimitedtoEastYorkshire,Cheshireand/20.Withthismix,residualdemand/energyWessex.Buildingthenumberofcavernsthataveragedissmallinallfourquartersoftheyearthisreportfindswillbeneededby2050willbewhenaveragedovermanyyears,butitvarieschallenging,butnotimpossible.enormouslyfromyeartoyear,ieitisvariabilityratherthanseasonalitywhichistheissue.Thesamestorageneedscanbemet(withinlimits)byarelativelysmallstoragecapacitychargedrapidlyoralargercapacitychargedrelativelyslowly.Thelowestcostconfigurationdependsontherelativecostsofconvertingelectricitytoastorableformandstoringit.78LARGE-SCALEELECTRICITYSTORAGEChapterten10.1.3Chapterfive:Non-chemicalandthermal10.1.5Chapterseven:Electrochemicalandenergystorage.novelchemicalstorage.ManydifferentformsofstorageweredescribedLithium-ionbatteriesarealreadydeployedinthisChapter:ACAES,thermalandpumpedinsupportoftheelectricitygridandhomethermalstorage,thermochemicalstorage,storageandareverylikelytoplayamajorroleliquidairenergystorage,gravitationalstorageinprovidingveryrapidresponsegrid-services.(includingpumpedhydro)andstoragedesignedAlthoughtheircostsarefalling,themodellingtodeliverheat.MostcouldpotentiallystoreinChapter8findsthatatgrid-scale,theyareTWhofenergy,usingmultipledistributedunitslikelytobeoutclassedbyhydrogen,ACAESwithstoragecapacitiesuptomultipleGWhorotherformsofstorageforprovidingpeakandoutputsfromafewkWtohundredsofMW.shavingandshort-termarbitrage,if/whentheyMostwouldbenefitfromfurtherresearchandaredeployed.Amongthealternatives,sodium-developmentandneedtobedemonstratedionbatteriescouldinprinciplebecheaper,butatscale,anditneedstobeshownthathighcostswhentheyareproducedinitiallyinactualefficienciescanapproachtheoreticalrelativelysmallnumbersmaybeabarriertoefficiencies.However,theyarepotentiallylowachievingmanufactureatscale.costcomparedtobatteries,havelowself-dischargerateswithpotentiallygoodroundIfasignificantfractionofGB’sfuturefleetoftripefficiencies,andcouldplayimportantroleselectricvehicleswerefromtimetotimeunderinshorttointermediate-termstorage.Onlythecontroloftheoperatoroftheelectricitythermochemicalstoragehasthepotentialtogrid,theflexiblepowerreservethattheywouldplayamajorroleinreallylong-termstorage,butprovidewouldmakeanextremelyvaluableitisataveryearlystageofdevelopment.contributiontomangingthesystem.10.1.4Chaptersix:Syntheticfuelsforlong-termFlowbatteries,whosecapacitiesandpowerenergystorage.ratingsareindependent,offerhighlyflexibleSyntheticFuelsareexpectedtoplayaroleandscalablestorage.Theall-vanadiumintransportbutareoutclassedbyammoniadesignisthemostcommerciallymaturebutandhydrogenforelectricitystorage.Liquidisexpensive.If/whenflowbatteriesthatorganichydrogencarrierscouldplayaroleinusesignificantlycheapermaterialsbecomedistributedcombinedheatandpowersystems.available,theycouldplayanimportantroleingrid-scalestorage.LARGE-SCALEELECTRICITYSTORAGE79Chapterten10.1.6Chaptereight:PoweringGreatBritainwith10.1.7Chapternine:TheGrid,electricitymarketswindandsolarenergyandstorage.andcoordinationWithwindandsolarsupplysupportedbyEnsuringthatelectricitysupplyisreliablewillhydrogenstorage(andsomebatteries),itwasbecomeincreasinglyimportantastherolefoundthat,withtherangeofinputassumptionsofelectricitygrowsintransport,heatingandmadeinthisreport,theaveragecostofindustry.Insystemsinwhichhighlevelsofelectricityfedintothegridin2050wouldberenewablesupplyaresupportedbystorage,between£52/MWhand£92/MWhin2021reliabilitywilldependcriticallyontheprovisionprices(seefigure23).Theadditionofinflexibleofenoughstorageincludingcontingency:if‘baseload’supply,forexamplefromnuclearstoredenergyrunsout,thelightsreallywillgoorgaswithCCS,wouldincreasetheaverageoutwhenthewindisnotblowingandthesuncostofelectricityunlessthecostperMWhofnotshining.thebaseloadislessthanthatoftheaveragewithoutbaseload.BECCSwouldsatisfythisGaspoweredelectricity,whichisgeneratedconditionifthegeneratingcostisoffsetbythebysynchronisedrotatingmachinerywhosecarboncreditsthatitshouldattractasacarbonmechanicalinertiaprovidesstability,isnegativesource.increasinglybeingreplacedbywindandsolargenerationthatusespowerelectronicstoCombiningACAES(orothertypesofstoresprovideACpowertothegrid.Ifthissupplyforwhichitservedasanexemplar)withiscombinedwithenergystoresthatcanbehydrogenstoragecouldlowertheaverageaccessedquickly,problemsarisingfromthecostofelectricitybyupto5%,orpossiblymore,absenceofmechanicalinertiacanlargelydependingonwhatisassumedaboutitscostbeovercome.Thereis,however,anurgentandefficiency.needforengineeringresearchtoguidehowtheincreasinglyubiquitouspowerelectronicUsingacombinationofstorageandgasplusconvertersshouldbedesignedandused.CCStoprovidetheflexibilityrequiredtomatchwindandsolarsupplycouldlowercostsInGB’scurrentwholesaleelectricitymarkets,significantly.Whetheritwouldlowercostsbothlong-terminvestmentdecisionsandshort-dependssensitivelyonthecostsofstorage,oftermdispatcharelargelygovernedbyasinglewindandsolarpower,andofgasplusCCS,andpricesignal(iethesystemmarginalcost).Thethepriceofgasandthecarbonprice.Itwouldlarge-scalelong-termstoragethatthisreportnotremovetheneedforlarge-scalelong-termfindswillbeessential,couldneverrecoveritsstorage,althoughitwouldreducetherequiredcapitalcostsinsuchasystemsinceitwillbescalesofstorageandwindplussolarsupply.idlemuchofthetime.Existingmarketsandregulationswillalsonotbeabletodelivertheoperationalcoordinationbetweenwindandsolargeneratorsandoperatorsofstoragethatwillbeneededtoscheduletheuseofdifferenttypesofstorecosteffectivelyandensurethattheydonotbecomeempty.Thereisanurgentneedtorecognisetheseproblemsandexplorepossiblesolutions.80LARGE-SCALEELECTRICITYSTORAGEChapterten10.2FurtherstepsTheunderlyingassumptionsonthecostofThisreportfocussesonthelarge-scalestoragestorageandofprovidingwindandsolarpowerthatGBwillneedin2050.ThisneedshouldshouldbeunderpinnedbydetailedengineeringbeincorporatedinmodelsofGB’selectricityestimates,whichshouldbeupdatedperiodicallysystemthattakeaccountoffactorswhatwereinthelightofexperiencegainedfrombuildingnotconsideredhere,includingcontributionsrealsystemsordemonstrators.fromburningwasteandbiomass,hydropowerandinterconnectors,andtherelativelocationsThecostofprovidinganelectricitysystemofofsupply,storage,anddemand,andtheirthekindenvisagedinthisreportshouldbeimplicationsforthegrid.analysedindetail.200GWofwindandsolarcapacityand100TWhofstoragecapacitywillThereisalsoaneedto:beneeded,assuming570TWh/yeardemand•Modeltheprovisionofgreenhydrogenfor(thesecapacitiesareapproximatelyproportionaltodemandbutwouldobviouslybereducedifstoringelectricityandmeetingotherneedssubstantialnuclearcapacityisavailable).Thetogether,basedonviewsofthescale,requiredinvestmentswouldbeoftheorder:flexibilityandtemporalprofileofotherneeds;•£210billionforwindandsolarcapacity(mixed•Takeaccountofthepossibleuseofaasassumedinthisreport),accordingtoBEIS’scombinationofstorageandgas+CCSto2020estimatesofthecostsandcapacityprovidetheflexibilityneededtocomplementfactors,assumingcommissioningin2040;windandsolarsupply;•£100billionforstorage;and•Studypossiblebarrierstotherapidconstructionofthelargenumbersof•£100billionbetweennowand2050tosaltcavernsthatwillbeneededforenlargeandstrengthenthetransmissiongrid,hydrogenstorage;accordingtoNationalGrid101.•Explore/developalternativeswaysofThesecostestimates,whicharesensitiveschedulingtheuseofstorage,whichcouldtocommodityprices,assumethatessentialtakeaccountoflong-(aswellasshort-)termmaterialswillbeavailable.TheIEAfinds125thatweatherforecasts;lackofcriticalmaterialswillnotpreventthetransitiontoalowcarboneconomy,although•Examinetheimpactofimprovedperformancetemporaryshortagesordisruptionscouldleadofwindturbinesatlowwindspeeds,andto‘amoreexpensive,delayedorlessefficientassesswheretheywouldbestbesitedtakingenergytransition’,anditcouldclosesomeaccountofthesystemvalueofminimisingavenues,includingthewidespreaddeploymentcorrelationsintheiroutputs;ofPEMelectrolysers,whichappearstobetheonlytechnologyconsideredinthisreportthatis•Developmodelsofelectricitydemandreallyseriouslythreatenedintheircurrentform.thattakeproperaccountofcorrelationswiththeweatherintheyearsstudiedandincludedemandmanagementmeasuresinthemodelling.LARGE-SCALEELECTRICITYSTORAGE81ChaptertenGiventheoutlinesofwhatitmightcomprise,Marketmechanismwillhavetobeinplacemodelsofpossiblepathwaystoanetzerothatmakeinvestmentinlarge-scalestorageelectricitysystempoweredlargelybywindandattractivebeforeitisactuallyneededandsolarcanbedeveloped.Inordertomovetoacanaccommodateamixtureofsupplyhighwindandsolarplusstoragesystem,theprovidedbywindandsolardirectly(atlownecessarywind,solarandstoragecapacitiescost)andviastorage(atlowmarginalbutwouldhavetobeinplacebeforecarbonhighabsolutecost).Iftherequiredreformsdioxideemittingsourcesareswitchedoff.Thearenotidentifiedandimplementedrelativelypossiblepathwayswilldependontherateatsoon,GBcouldbecomelockedintoasub-whichcapacitycanbeinstalled,whichneedsoptimalmixtureofinfrastructure.tobestudiedindetail.Inthecaseofwindandsolargenerationcapacity,thecurrentratewouldR&Disneeded.Althoughitisunlikelythathavetoincreaseinordertoreach200GWin‘newscience’willbeabletomakeamajor2050.TheNationalGrid’sscenariosadsuggestcontributionby2050,basicresearchisthatthiswouldbepossible,althoughitmightbeimportantforthelongterm–forexamplecheapeasierwithsomewhatlesssolarandmorewinddirectsynthesisofammoniafromairandwaterthanassumedhere(whichwouldhaveverylittlewouldbetransformative.Meanwhile,thereisimpactontheaveragecostofelectricity).hugescopeforimprovingexistingtechnologies,andcombiningtheminnewways,forexampleinwind-integrated-storage,andreversibleelectrolysers/fuelcellsandcompressors/expanders,andtherearespecificR&Dchallenges,suchasreducingoreliminatingiridiuminPEMelectrolysers.adWithBEIS’s2040projectionsofcapacityfactorsandthewind/solarmixespousedinChapter2,generating741TWh/yearwouldrequirecapacitiesof60GWonshorewind+70GWoffshorewind+150GWsolar.Incomparison,therangeof2050projectionsintheNationalGrid’s2022FES5are:34-47GWonshorewind,89-110GWoffshorewindand57-92GWsolar,andenvisagetheinstallationof10to40GWofdomesticsolarPVwhiletheUKgovernment’sBritishEnergySecurityStrategyproposes2030targetsthatincludeincreasingsolarcapacityfromitscurrentlevelof14GWto70GWandoffshorewindfrom11GWto50GW.aeInNovember2022BEISannouncedfurtherfunding(£32.8millionintotal)forstoragetechnologiesthatwereinitiallyatTRL6/7totakefiveofthemthroughtofirst-of-a-kindfull-systemprototypeshttps://www.gov.uk/government/publications/longer-duration-energy-storage-demonstration-programme-successful-projects/longer-duration-energy-storage-demonstration-programme-stream-2-phase-2-details-of-successful-projects.Thisisawelcomedevelopmentbutdoesnotmeettheneedforlarge-scaledemonstrating/constructingsystemsathighTRLwhichcouldprovidemulti-TWhscalestoragein2050.Hydrogenrelatedprojectsaredescribedinthenextfootnote.afInApril2023,theGovernmentpublishedaHydrogenNetZeroInvestmentRoadmaphttps://www.gov.uk/government/publications/hydrogen-net-zero-investment-roadmap.Thisiswelcome,buttheRoadmapdoesnotrecognisetheneedforhydrogenstoragetosupportelectricitygeneratedbywindandsolar,andthethreeexamplesofhydrogenstores(onpage13)wouldonlyprovideasmallfractionofthestoragethatwillbeneeded.On30/3/23thegovernmentpublishedashortlistofprojectsinvolvingelectrolyticallyproducedhydrogen,totallingupto250MW,withtheintentionofawardingcontractsinthelastquarterof2023–https://www.gov.uk/government/publications/hydrogen-production-business-model-net-zero-hydrogen-fund-shortlisted-projects/hydrogen-business-model-net-zero-hydrogen-fund-shortlisted-projects-allocation-round-2022.SSE’sAldbroughHydrogenPathfinderprojectistheonlythatinvolvesstorageinadeepsalt-cavern(previouslyusedtostorenaturalgas)andisoneofthethreeexamplesofstoragegivenintheRoadMap:itisunclearwhether/howtheothertwomightbefunded.82LARGE-SCALEELECTRICITYSTORAGEChapterten10.3Demonstrators,deploymentandBuildinglargescalehydrogenstorageopportunitiesfacilitiesah,whichUKcompaniesarewellDemonstratorsareneededbeforelarge-positionedtodo,wouldprovidetheUKwithscaleenergystoragesystemscanbewidelyanopportunitytotakealeadingroleinthedeployed,toidentifyandsolveengineeringandenergytransition.However,theconstructionintegrationissuesae.oflargecavernsiscurrentlynotjustifiablecommercially,andtheywillnotbebuiltuntilInthecaseoflarge-scalehydrogenstorage,mechanismstorewardinvestorsareinplace.suppliedbyelectrolyserspoweredbywindandsolarenergy,enoughisknowntostartOthercountrieshaveambitiousplanstoconstructionnowaf,asishappeningelsewhereag.develophydrogenstoragestartingnow.IfHowmuchhydrogenstoragewillultimatelytheUKdoesnotemulatethem,theelectricitybeneededtosupporttheelectricitysystemstoragenecessarytoensurelowcarbon,willdependonwhatotherformsofsupplyandreliableandaffordableenergysupplywillnotstoragearebuilt,butitwillbeTWhs,andtherebeavailablewhenitisneeded.areexpectationsthatgreenhydrogenislikelytoplaymanyroles.Constructionofalargegreenhydrogenproductionandstoragefacilitywouldappeartobeano-regretsoption.ItwouldprovideamuchbetterideaofwhathydrogenwillcostandsetGBontheroadofcostreductionthroughlearning.Theconstructionofothersshouldfollowquickly.agOneexampleinarapidlydevelopingspectrumofprojects:ACESDelta(https://aces-delta.com/)isdeveloping‘theworld’slargestrenewableenergyhub’toproduce,store,anddelivergreenhydrogeninUtahwiththesupportof$500millionofdebtfinancingfromtheUSDepartmentofEnergyhttps://www.energy.gov/lpo/articles/innovative-clean-energy-loan-guarantees-gathering-momentum-new-conditional-commitment.Itwilleventuallyuseasaltcaverntostore5,500tonnesofhydrogen,providedatarateofover450t/daybyover1GWofelectrolysers.Moreconstructionisneededonthisscale,whichisthatofjustoneofthetencavernsintheclustersthattheH21NE26consortiumhasdesignedforconstructioninEastYorkshire.ahElectrolysers:INEOSareconsideringthemanufactureofalkalineelectrolysersforhydrogenproduction,buildingonlongexperienceofmakingandusingthemtoproducecausticsodaandchlorine.ITMpowerisaleadingmanufacturerofProtonElectrolyteMembrane(PEM)electrolysers.CeresisaworldleaderinthedesignofSolidOxideElectrolysers.Undergroundstorage:TheH21NEconsortiumhasdesignedclustersof10300,000m3saltcavernsinEastYorkshire.INOVYNhasplanningpermissiontobuildaclusterof17350,000m3saltcavernsinCheshiretostorenaturalgasandisapplyingforpermissiontousethemtostorehydrogen.SSEisreadytoconvertsomenaturalgasstorageatAldbroughtohydrogenstorage,andCentricahasplanstoconverttheoffshoreRoughgasstoragefacility.Powergenerationfromhydrogenusingfuelcellsorfour-strokeengines:JohnsonMattheyandmanyotherUKcompaniesareinvolvedinthesupplychainforPEMfuelcells(astheyareforelectrolysers).CeresdesignSolidOxideFuelCells,whichhavethepotentialtoworkalsoaselectrolysers.JCBhaveproducedaprototypefour-strokehydrogenenginewhichlooksasifitcouldbescaleduptoprovidearelativelycheapandefficientwayofgeneratingpower.LARGE-SCALEELECTRICITYSTORAGE83AnnexesANNEXAGlossaryandabbreviationsAdvancedcompressedairenergystorageCarboncaptureandstorage,(ACAES)orsequestration(CCS)Advancedcompressedairenergystorage,inCaptureofcarbon-dioxideandthenburyingitwhichtheheatofcompressionisstoredandunderground.usedtopreventfreezingwhentheairexpands.ItisoftencalledAdiabaticcompressedairCarnotbatteryenergystoragealthoughtheaircompressionisAsystemthatusesaresistiveheateroraheatclosertoisothermal.pumptoturnelectricityintoheatthatisstoredandlaterusedtogenerateelectricity.AdiabaticOccurringwithoutlossorgainofheat.ContractforDifference(CfD)CfDsaretheUKgovernment’smainmechanismBaseloadforsupportinglow-carbonelectricitygeneration.AtermusedinthisreporttomeanelectricitySuccessfuldevelopersofrenewableprojectssuppliedataconstantrate.enterintoacontractwiththegovernment-ownedLowCarbonContractsCompanyBasicdemand(LCCC).WhenthemarketpriceforelectricityDemandforelectricity,beforetransmissiongeneratedbyaCfDGenerator(thereferenceanddistributionlosses,excludingdemandprice)isbelowtheStrikePricesetoutinthefortheelectrolyticproductionofhydrogencontract,theLCCCpaystheGeneratortothe(forstoringelectricityorotherpurposes).Thedifference.WhenthereferencepriceisabovecorrespondingquantityafterlossesisknownbytheStrikePrice,theGeneratorpaysLCCCthetheNationalGridas‘customerdemand’.difference.ACfDprovidesadegreeofcertaintyforthegenerator.BioenergywithCarbonCaptureandStorage(BECCS)CurtailmentTheextractionofenergyfrombiomass,Describestemporarilystoppingasourceassumedinthisreporttobebyburningitofelectricity(egawindorsolarfarm)andgeneratingelectricity,followedbytheexportingpower.captureandburialofthecarbon-dioxidethatisproduced.DiabaticInvolvingthetransferofheat.Compressedairenergystorage(CASE)Thisterm,whichisoftenusedforallformsofDiscountratecompressedairenergystorage,butisonlyTheinterestrateusedtoconvertfuturecashusedheretodescribecasesinwhichfossilflowsoroutputsintoanequivalentone-offfuelsareburnedtopreventfreezingwhenupfrontsum,knownastheNetPresentValue.theairexpands.SeeACAES(advancedInestimatingthelevelisedcostofelectricitycompressedairenergystorage).(LCOE)thediscountrateistypicallytakentobeanestimatesoftheinvestor’sWeightedCapexaiAverageCostofCapital.Capitalinvestmentinmachineryandinfrastructure.aiForanintroductiontoissuesrelatedtothecostofcapitalseehttp://CO2economics.blogspot.com/2022/08/bluffers-guide-to-cost-of-capital.html.Formorecompletedefinitionsofthetermsinvolvedseehttps://www.investopedia.com/financial-term-dictionary-4769738(accessed18May2023).84LARGE-SCALEELECTRICITYSTORAGEAnnexesDispatchableaiGridservicesDispatchablesuppliesofelectricityarethoseVariousservicesthatkeepthefrequencyandthatare(normally)fullyunderthecontrolvoltageoftheelectricitygridstable.oftheoperator.Higher(orupper)heatingvalue(HHV)ElectrolyserTheamountofheatreleasedbyaspecifiedAsystemthatuseselectricitytosplitwaterquantity(initiallyat25°C)onceitiscombustedintohydrogenandoxygen.Thisprocessandtheproductshavereturnedto25°C.Itiscalledelectrolysis.includesthelatentheatofvaporisationthatisreleasedwhensteamcondenses.SincenotEnergyarbitrageallcombustiondevicescantakeadvantageofShiftingelectricalenergyfromlow-valuetimesthislatentheat,ithasbecomeconventionaltoorlocationstohigh-valueones.defineefficienciesintermsoflowerheatingvalues.However,insomeregions,suchastheFlowbatteryUSandtheUK,naturalgasissoldbyitshigherArechargeabledeviceinwhichenergyisheatingvalue.providedbyactivecomponentsdissolvedinliquids,storedintanksthatarepumpedthroughInterconnectorsacellbetweenelectrodesonoppositesidesConnectionsbetweenelectricity(orgas)ofamembrane(seefigure22).Astheyinvolvetransmissiongridsindifferentcountriesoxidation-reductionreactions(inwhichelectronsorregions.aretransferredbetweentwospecies)theyareoftencalled‘Redox’flowbatteries(RFBs).TheIsobariccompressedairstoragecapacityofthebattery,whichisdeterminedbyUsesafluidtomaintainthecompressedairatasizeofthetanks,isdecoupledfromthepowerconstantpressure.ofthebattery,whichisdeterminedbytheactiveareaoftheelectrodes/cell.IsothermalChanges(eginthevolumeand/orpressureofFrequencyregulationagas)thattakeplaceatconstanttemperature.TherapidandoftenautomaticadjustmentofinputsorwithdrawalsofelectricalenergyKilowatt(kW)byabalancingauthoritytomaintaintheAunitofpowerequaltoathousandWatts.oscillationfrequencyofthealternatingcurrentinanelectricpowersystemwithinaspecifiedkWetoleranceofthescheduledvalue.Kilowattofelectricalpower.Gigawatt(GW)AunitofpowerequaltoabillionWatts.GWeAgigawattofelectricalpower.LARGE-SCALEELECTRICITYSTORAGE85AnnexesLevelisedcostofelectricity(LCOE)1LCOErepresentswhatfirmsthatinvestinAmeasureoftheaveragecostofgeneratinggeneratingcapacitythinkwillhavetobepaidelectricitygivenbydividingthe(discounted)forelectricityinordertoprovidethereturnlifetimecostsbythelifetimeoutput(discounteddemandedbyholdersofsharesandbondsatthesamerate),asspelledoutbelow.LCOE(whatisactuallypaidwilldependonmarketenablescomparisonofdifferentgeneratingconditions).Theappropriatediscountratefortechnologies(egwind,solar,naturalgas,calculatingtheLCOEisthereforetheinvestor’snuclear)withdifferentlifespans,capacities,WeightedAverageCostofCapital.capitalandoperationalcosts,risks,andratesofreturn.ItdoesnottakeaccountofthedifferentLevelisedcostofstorage(LCOS)systemvaluesresultingfromguaranteedorThecostofaunitofelectricitydischargednon-guaranteedavailabilityandreliability.fromastoragedevice,accountingforallcostsincurredandtheenergyproducedthroughoutFormally:itslifetime(seeSI1.5).LCOE=(NetPresentvalue[NPV]ofcosts)/Lithium-ion(Li-ion)battery(NPVofelectricitygeneration),where:RechargeablebatterythatusessolidcompoundsatboththenegativeandpositiveNPVofcosts=∑n(totalcapexandopexelectrodesashostsforreversiblelithium-ioninyearn)/(1+discountrate)nstorage.Duringdischarge,lithiumionsmovethroughanelectrolytefromthenegativeNPVofelectricitygeneration=∑n(netelectrodetothepositiveelectrode,whilegenerationinyearn)/(1+discountrate)nelectronsmoveinthesamedirectionthroughanexternalcircuit,poweringthedevicetoInthecaseofastoragesystem,whichthebatteryisconnected.Duringcharge,netgeneration=energyoutput.theprocessisreversed,withlithiumionsmigratingfromthepositivetothenegativeInmostofthisreportanumberofsimplifyingelectrodeundervoltagesuppliedbyanexternalassumptionsandapproximationsarepowersource.made,including:LoadfollowingAssumingthatallcapitalcostsoccurinAnincreaseordecreaseinthelevelofyearzero.dispatchablegenerationand/orthenetwithdrawalfromdispatchableenergystoragetoIgnoringdecommissioningcosts.matchchangesinelectricitydemand.AssumingconstantannualoutputthroughLowerheatingvalue(LHV)thefacility’slifetime,beginninginyearoneTheamountofheatreleasedbycombustinga(anexceptionismadeforbatteries,whosespecifiedquantity,initiallyat25°C,andreturningperformancedeteriorateswithage).thetemperatureofthecombustionproductsto150°C,assumingthatthelatentheatofAssumingthatopexisafixedannualvaporisationofwaterinthereactionproductsisamountand/oraconstantλtimesnetnotrecovered.Manufacturersofturbines,fuelannualgeneration.cellsandelectrolysersnormallydefinetheirefficienciesintermsofthelowerheatingvalueInthiscase:ofthefuelconsumedorproduced.LCOE=(capex/‘DiscountFactor’+annualopex)Megawatthour(MWh)/(netannualgeneration)+λEnergygeneratedbyonemillionWattsofpoweroperatingcontinuouslyforanhour.Wherenrunsfrom1totheNyears(thefacility’slifetime),andthe‘DiscountFactor’=MWhe[1–(1/(1+d)N]/dAmegawatthourofelectricalenergy.(notethatasthediscountrated→0,thediscountfactor→N)86LARGE-SCALEELECTRICITYSTORAGEAnnexesMWhthPhotovoltaicAmegawatthourofthermalenergy.Thedirectconversionoflightintoelectricalenergy,ormoregenerallythegenerationofMWhLHVavoltagewhenradiantenergyfallsontheAmegawatthourofthermalenergycontentboundarybetweendissimilarsubstances,measuredwiththeLowerHeatingValue.typicallytwodifferentsemiconductorsofasolarpanel.NorthAtlanticOscillation(NAO)ReferstochangesintheatmosphericPumpedhydropressuregradientovertheNorthAtlantic,UseoftwowaterreservoirsatdifferentlevelswhichinfluencesweatherinEuropeandwithwaterpumpedfromthelowertotheNorthAmerica.ItisdrivenbyatmospherichigherattimesoflowelectricaldemandandpressuredifferentialsbetweentheAzores,excesselectricitygeneration.Attimeswhenwhichhavehighatmosphericpressure,anddemandexceedselectricitygeneration,waterisIceland,whichhaslowpressure.Whentherereleasedfromthehigherreservoirtoflowtotheisagreater-than-usualpressuredifferencelowerreservoirthroughapenstockandturbinesbetweentheregions(apositiveNAOphase),generatingelectricity.Europetypicallyexperienceswarmer,windier,andrainierconditionsthanusual.WhenthePumpedthermaldifferenceisweaker(anegativeNAOphase),StoragethatusesexcesselectricalenergytoEuropewillexperiencecooler,calmer,andchargeawell-insulatedheatstoreusingaheatdrier-than-usualconditions.pumpwhichislaterdischargedthroughaheatenginetogenerateelectricity.Operationandmaintenance(O&M)ThecostofO&MmaybeeitherFixed(FOM)Redoxflowbattery(RFB)orVariable(VOM),dependenton(generallySeeFlowbattery.proportionalto)use.RegulatedAssetBase(RAB)OpexAmethodusedintheUKtofinancelarge-scaleThecostofOperationandmaintenance.infrastructureassetssuchaswater,gasandelectricitynetworks,underwhichacompanyOverprovision/overcapacityreceivesalicencefromaneconomicregulatorAtermusedbysomeauthorstodescribetochargearegulatedpricetoconsumerssituationsinwhichtheaveragesupplyofinexchangeforprovidingtheinfrastructurevariablerenewableelectricityisgreaterthaninquestion.Themodelenablesinvestorsdemand(renewableenergyissometimetosharesomeoftheproject’sconstructionrestrictedtojustwindandsolar).Othersuseitandoperatingriskswithconsumers,therebytodescribesituationsinwhichitisgreaterthansignificantlyloweringthecostofcapital.demandminusbaseloadsupply.Intheabsenceofdispatchablegeneration,overprovisionisRenewableenergyrequiredtooffsetinefficienciesinstorage;Energyfromnaturalsources(wind,solar,provisiongreaterthanrequiredtocompensatebiomass,hydro,geothermalandtheocean)forinefficienciesreducesthesize(andcost)thatarereplenishedatahigherratethanofthestoragesystemthatisneeded.Withtheyareconsumed.constantbaseload,someauthorsdefineandquantifyoverprovisionrelativetodemand;Residualdemandothersrelativetodemandminusbaseload.Demandforelectricity(basicdemandinthisreport)minusdemandmetdirectlybyvariablerenewables(usuallymeaningwindandsoarinthisreport).LARGE-SCALEELECTRICITYSTORAGE87AnnexesResidualenergy/powerThermalenergyDemandmetdirectlybyvariablerenewablesTheinternalenergyofsystem(inastate(usuallymeaningwindandsoarinthisreport)ofthermodynamicequilibrium)byvirtueof–demandforelectricity(basicdemandinthisitstemperature.report),whentheformerislargerthanthelatter.VolumetricenergydensityResistiveheatingAvolume-basedmeasureofenergydensity,Productionofheatbypassinganelectricoftenexpressedinwatt-hoursperlitre.currentthrougharesistiveelement/conductor.WeightedAverageCostofCapital(WACC)aiSpecificenergyRepresentsafirm’saverageafter-taxcostof(orgravimetricenergydensity)capitalfromallsources(shares,bonds,andAmass-basedmeasureofenergydensity,oftenotherformsofdebt).WACC,whichistheexpressedinwatt-hoursperkilogram.averagerateacompanyexpectstopaytofinanceitsassets,expressesthereturnthatSMRbothbondholdersandshareholdersdemandSmallModular(nuclear)Reactor,orSteaminordertoprovidethecompanywithcapital.AMethaneReformationofnaturalgastomakefirm’sWACCislikelytobehigherifitsstockishydrogen.relativelyvolatileorifitsdebtisseenasriskybecauseinvestorswillrequiregreaterreturns.TechnologyReadinessLevel(TRL)WACCisnormallyexpressednetofinflation.TRLsaredefinedbytheEuropeanCommissionasfollows:WholesaleelectricitymarketTRL1–Basicprinciplesobserved;Thebuyingandsellingofpowerbetweengeneratorsandresellers.ResellersincludeTRL2–Technologyconceptformulated;electricityutilitycompanies,competitivepowerproviders,andelectricitymarketers.TRL3–Experimentalproofofconcept;ExchangeRatesTRL4–Technologyvalidatedinlab;Costestimatesinthereportarefirstquotedin$sor€swhenthatwasthecurrencyusedinTRL5–Technologyvalidatedinrelevanttheoriginalsource,andthenconvertedat£1.00environment(industriallyrelevantenvironment=$1.35=€1.18inthecaseofkeyenablingtechnologies);TRL6–Technologydemonstratedinrelevantenvironment(industriallyrelevantenvironmentinthecaseofkeyenablingtechnologies);TRL7–Systemprototypedemonstrationinoperationalenvironment;TRL8–Systemcompleteandqualifiedand;TRL9–Actualsystemproveninoperationalenvironment(competitivemanufacturinginthecaseofkeyenablingtechnologies;orinspace).88LARGE-SCALEELECTRICITYSTORAGEAnnexesANNEXBContentsofsupplementaryinformationThereferencesbelowaretothesectionnumbersinthereport.NotethatthesupplementaryinformationisnotaRoyalSocietypublicationandisprovidedonlineasbackgroundinformationonly.Visitroyalsociety.org/electricity-storageSI1Inroduction1.2SupplyanddemandinanetzerocontextPlotsrelatedtoFigures1Aand1Bthattakeaccountofinefficiencies.1.3StorageEnergystoredingasinthetransmissionanddistributiongrid.1.4CostconsiderationsLevelisedcostofstorage.Annex1Keyquestionsaboutstoragetechnologies.SI2Electricitydemandandsupplyinthenetzeroera2.2FutureelectricitydemandinGreatBritainDailyprofileofelectricitydemand.2.3.Weather,windandsunWindvariations.Extremeweathereventsandperiodsoflowsupply.Weathercorrelations.Sitingofwindfarms.Correlationsbetweenweather,windandsolarsupply,anddemand.Winddroughtsandperiodsofhighdemand.Climatechange.Useofhistoricalweatherdata.2.4.MatchingdemandanddirectwindandsolarsupplyOptimisingthewind/solarmix.2.5Residualdemand,energyandpowerResidualenergy.Residualpower.Periodsofhighdemand.UCLESTIMOmodel.2.6GeneratingcostsWindandsolar.Complementarygeneration–nuclear,gaswithCCS,bioenergywithCCS,otherrenewablesources,bluehydrogen,ammonia,gaspeakingplants:comparisonofflexibilityofdifferentsources.CO2LeakageinCCS,Methaneleakage,andDirectaircapture.Interconnectors.2.7DemandmanagementResidentialandindustrialdemand.Imposedandemergencyreductionsindemand.Annex1Supply/demandcorrelationsinasimplemodelofwithhighelectrificationofheat.Annex2InputprovidedbytheEnergySpaceTimegroup,UCLEnergyInstitute.SI3Modellingtheneedforstorage3.1IntroductionKeyFactors(sizeofthegrid,lengthofweathersequence,solar/windmix,efficiencies,timescales,interplayofchargingrates,storagecapacitiesandthelevelofwindandsolarsupply,scheduling).Selectedestimatesoftheneedforstorageindifferentregions(includingtheUSA,Europe,GermanyandGreatBritain).EstimatesofthecostofpoweringGreatBritainwithhighlevelsofwindandsolarandstorage.3.2ModellingandcostingwithasingletypeofstoreConstructingfigure12.Findingtheminimumaveragecostofelectricity.Surpluses.3.3ModellingandcostingwithseveraltypesofstoreScheduling.Annex1MITReport.Annex2AFRYreports.LARGE-SCALEELECTRICITYSTORAGE89AnnexesSI4Greenhydrogenandammoniaasstoragemedia4.1IntroductionDefinitionoflowerandhigherheatingvalues.4.2HydrogenandAmmoniaProductionElectrolysers–alkaline,polymerelectrolytemembrane,solidoxide,anionexchangemembrane,hightemperatureceramic,reversible,flexiblyfuelled,methanewithCCS.OffshoreElectrolysis.AmmoniaProduction.4.3Transport4.4Storage.Hydrogen.Ammonia.4.5ElectricitygenerationHydrogenoptions–fuelcells(protonexchangemembrane,phosphoricacid,solidoxide),combustion(turbines,4-strokeengines).Ammonia–fuelcells,combustion.Powergenerationoptionsin2050.4.6Safety4.7ClimateimpactAnnexConcludingremarks.SI5Non-chemicalandthermalenergystorage5.1IntroductionRemarksoncosts.5.2AdvancedCompressedAirEnergyStorageExistingsystems.UndergroundstoragecapacityinGB.ModellingACAES.Charginganddischarging.Costofcompressorsandexpanders.5.3ThermalandpumpedthermalenergystorageSensibleandlatentheatstorage.Carnotbatteries.5.4Thermochemicalstorage5.5LiquidAirEnergyStorage5.6GravitationalstoragePumpedhydro.Othergravitationalstorage.5.8ConclusionsComparativecharacteristicsandareasforfurtherresearch.Annex1WindIntegratedStorage.Annex2CompressedCO2storage.SI6Syntheticfuelsforlong-termenergystorageCoversthesamegroundasChapter6inthereportbutinverymuchgreaterdepthSI7Electrochemicalandnovelchemicalenergystorage7.1ElectrochemicalstorageMaterialavailability.Costs.Grid-connectedbatteriesinelectricvehicles.Flowbatteries.7.2ChemicalstorageChoiceofredoxprocessandmetals.Choiceofoxidationprocess.Routestolongterm,large-scalenovelchemicalstorage.Otherpotentialoptions.AnnextoSI7Novelchemicalstorage.90LARGE-SCALEELECTRICITYSTORAGEAnnexesSI8PoweringGreatBritainwithwindplussolarenergyandstorage8.1IntroductionSI9Costofammoniastorage.AnnexA8.3ProvisionofallflexiblepowerbyasingletypeofstoreCalculationofcosts.Sensitivitytoelectrolyserandgenerationefficiencies.Differentwind/solarmixes.Withnuclearbaseload.Nuclearco-generation.8.4MultipletypesofstoreCombiningACAESwithhydrogenstorage.8.5UseofnaturalgaswithCCSMethaneemissions;availabilityofgas;flexibility;cost;asbaseload;toprovideallflexibly;toprovideflexiblyincombinationwithstorage;possibleuseofbluehydrogen–asbaseload,toreplenishhydrogenstores.8.6Possibleuseandvalueofsurpluses8.7ContingenciesagainstperiodsoflowsupplyDemandmanagement.Addingothersourcesofsupply.8.8Differentlevelsofdemand8.9OtherstudiesoftheneedforandcostofstorageinGreatBritainAnnexMulti-yearUKrenewableenergysystemswithstorage–costInvestigation(TRoulstoneandPCosgrove).Thegrid,electricitymarketsandco-ordinationCoversthesamegroundaschapter9inthereportbutinverymuchgreaterdepth.GlossaryLARGE-SCALEELECTRICITYSTORAGE91AcknowledgementsAcknowledgementsTheRoyalSocietywouldliketoacknowledgethecontributionofthefollowingindividuals.ReportleaderSirChrisLlewellynSmithFRS,UniversityofOxfordMajorcontributorsProfessorMarkBarrett,UniversityCollegeLondonProfessorKeithBell,UniversityofStrathclydeDrPaulCosgrove,UniversityofCambridgeProfessorPhilipEames,LoughboroughUniversityProfessorSeamusGarvey,UniversityofNottinghamProfessorIanMetcalfe,NewcastleUniversityDrMikeMuskett,IndependentConsultantDrRichardNayak-Luke,UniversityCollegeLondonDrJohnRhys,UniversityofOxfordTonyRoulstone,UniversityofCambridgeProfessorNilayShah,ImperialCollegeLondonProfessorPaulShearing,UniversityCollegeLondonProfessorAgustinValera-Medina,CardiffUniversityContributorsDrHannahBloomfield,UniversityofBristolProfessorNigelBrandonFRS,ImperialCollegeLondonTrevorBrown,AmmoniaEnergyAssociationJamesCox,AFRYProfessorBillDavidFRS,UniversityofOxfordProfessorMatthewDavidson,UniversityofBathProfessorYulongDing,UniversityofBirminghamProfessorNickEyre,UniversityofOxfordDrAlexandraGormally-Sutton,LancasterUniversityStephenGifford,TheFaradayInstitutionProfessorGeoffHammond,UniversityofBath92LARGE-SCALEELECTRICITYSTORAGEContributors(continued)AcknowledgementsProfessorStuartHaszeldine,UniversityofEdinburgh93ProfessorCameronHepburn,UniversityofOxfordDrNigelHolmes,ScottishHydrogenandFuelCellAssociationEdwardHough,BritishGeologicalSurveyDrWentingHu,NewcastleUniversityProfessorGrahamHutchingsFRS,CardiffUniversityAnthonyKitchener,KDRCompressorsPtyLtdProfessorAnthonyKucernak,ImperialCollegeLondonProfessorYongliangLi,UniversityofBirminghamProfessorNiallMacDowell,ImperialCollegeLondonDrKeithMacLean,UKEnergyResearchInstituteProfessorChristosMarkides,ImperialCollegeLondonDrMikeMason,GreenAmmoniaWorkingGroupDermotNolan,FormerlyOfgemDrRichardPearson,BPProfessorRachaelRothman,UniversityofSheffieldDanSadler,EquinorDrMarkSelby,CeresPowerProfessorGoranStrbac,ImperialCollegeLondonDrHazelThornton,MetOfficeProfessorKarenTurner,UniversityofStrathclydeProfessorDuncanWass,CardiffUniversityJamesWatt,FormerlyWoodPLCJohnWilliams,BritishGeologicalSurveyDrGrantWilson,UniversityofBirminghamDrStanleyZachary,Heriot-WattUniversityLARGE-SCALEELECTRICITYSTORAGEAcknowledgementsRoyalSocietystaffManystaffattheRoyalSocietycontributedtotheproductionofthisreport.Theprojectteamarelistedbelow.RoyalSocietySecretariatPaulDavies,SeniorPolicyAdviserLeonardoMarioni,PolicyAdviserJamesMusisi,PolicyAdviserGeorgiaPark,SeniorProgrammeManagerElizabethSurkovic,HeadofPolicy,ResilientFuturesRichardWalker,SeniorPolicyAdvisorDaisyWeston,ProjectCoordinatorTheconclusionsofthisreportdrawheavilyonastudyofstorageneedsinGBbyPCosgroveandTRoulstone(2021WorkingPaperonEnergyStorage–Multi-YearStudiesRoyalSocietyWGWorkingPaperonEnergyStorage–PreliminaryMulti-YearStudies.doi:10.13140/RG.2.2.12555.41760),whoalsolaidthefoundationsfortheanalysisofweathereffectsinchaptertwo.ThemodellingdescribedinchapterthreeandusedtocoststorageinchaptereightwascarriedoutbyCLlewellynSmithandRNayak-Lukeforsingletypesofstore,andSGarveyformixturesoftypesofstore.94LARGE-SCALEELECTRICITYSTORAGEReferencesReferences1DepartmentforBusiness,EnergyandIndustrialStrategy.2020ElectrictyGenerationCosts2020.Seehttps://www.gov.uk/government/publications/beis-electricity-generation-costs-2020(accessed11May2023).2O’CallaghanB,HuE,IsraelJ,WayR,LlewellynSmithC,HepburnC.2023CouldBritain’senergydemandbemetentirelybywindandsolar?UniversityofOxfordSmithSchoolofEnterpriseandtheEnvironment.WorkingPaper23-02,ISSN2732-4214.3AhluwaliaR,PapadiasD,PengJ,RohH.2019SystemLevelAnalysisofHydrogenStorageOptions.2019DOEHydrogenandFuelCellsAnnualMeritReview.Seehttps://www.hydrogen.energy.gov/pdfs/review19/st001_ahluwalia_2019_o.pdf(accessed11May2023).4BrananC.2002RulesofThumbforChemicalEngineers.GulfPublishing.5NationalGridESO.2022FutureEnergyScenarios2022.Seehttps://www.nationalgrideso.com/document/263951/download.(accessed11May2023).6DepartmentforBusiness,EnergyandIndustrialStrategy.2020Modelling2050:ElectricitySystemAnalysis.Seehttps://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/943714/Modelling-2050-Electricity-System-Analysis.pdf(accessed11May2023).7BettP,ThorntonH.2016TheclimatologicalrelationshipsbetweenwindandsolarenergysupplyinBritain.RenewableEnergy.87,96–110.(https://doi.org/10.1016/j.renene.2015.10.006).8MetOffice.2019WeatherandclimaterelatedsensitivitiesandrisksinahighlyrenewableUKenergysystem:aliteraturereview.Seehttps://nic.org.uk/app/uploads/MetOffice_NIC_LiteratureReview_2019.pdf(accessed11May2023).9BloomfieldH,SuittersC,DrewD.2020MeteorologicaldriversofEuropeanpowersystemstress.JournalofRenewableEnergy.2020.(https://doi.org/10.1155/2020/5481010).10Renewables.ninja.Seehttps://www.renewables.ninja/(accessed15May2023).11PfenningerS,StaffellI.2016Long-termpatternsofEuropeanPVoutputusing30yearsofvalidatedhourlyreanalysisandsatellitedata.Energy114,1251-1265.(https://doi.org/10.1016/j.energy.2016.08.060)12BloomfieldHetal.2021QuantifyingthesensitivityofEuropeanpowersystemstoenergyscenariosandclimatechangeprojections.RenewableEnergy,164,1062-1075.(https://doi.org/10.1016/j.renene.2020.09.125)13KayG,MaidensA,ThorntonH,DunstoneN,ScaifeA,SmithD.2020PreliminaryassessmentoflowwinterwindsovertheNorthSea.Unpublishedprivatecommunication.14IEA.2020WorldEnergyOutlook.See:https://iea.blob.core.windows.net/assets/a72d8abf-de08-4385-8711-b8a062d6124a/WEO2020.pdf(accessed11May2023).15RuhnauO,QvistS.2021Storagerequirementsina100%renewableelectricitysystem:Extremeeventsandinter-annualvariability.Seehttp://hdl.handle.net/10419/236723(accessed11May2023).16InternationalEnergyAgency.2005SavingElectricityInAHurry:DealingwithTemporaryShortfallsinElectricitySupplies.Seehttps://iea.blob.core.windows.net/assets/4cb1d29e-1ecc-4f5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