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LiquidAirMediaCoverage2012132January2013NewScientistIntothinairStoragesalvationforgreenenergy-Page1ExcessenergyfromthepowerstationisusedtopoweragiantfridgeImageJezCoulsonHighview1moreimageIfrenewableenergyistosucceedweneedtofindabetterwaytostoreit.LiquidairbatteriescouldbetheanswerEditorialTimetonailthenumberoneproblemofgreenenergyITHASbeenanunusuallycooldayintheflatlandsofwesternTexas.Aseveningrisesoverthesprawlingwindfarmthetemperaturecontinuestodropandwithitthewind.Farabovethebladeofatoweringturbineglidesslowlytoahalt.Afewhoursagotheseturbineswerechurningsufficientelectricityintothegridtorivaltwonuclearpowerplantsenoughtokeepthelightsonin5percentofTexas.Thestatespowermanagersknewadropwascomingbutthespeedhastakeneveryonebysurprise.Thetimingcouldnotbeworse.AllacrossthestatepeoplearecominghomefromworkflickingonlightsTVsandkettles.Thepowerauthoritydeclaresanemergency.Engineersrequest30megawattsofemergencypowerfromMexico.Supplytolargeindustrialusersiscutformorethananhour.Ittakesthreehoursbeforethesystemisfinallystabilised.Thisisntagooddayforrenewableenergyanditillustratesonereasonwhyevenmodesttargetsconsistentlygounmetallaroundtheworld.In2009intermittentrenewablesaccountedforapaltry3.3percentofworldenergygeneration.Windsunandwavearesimplytoofickletobecountedon.Butthatmaybeabouttochange-andsalvationcouldliterallycomeoutofthinair.Itsnotthatwedonthaveenoughenergysources.IndeedeveryminuteenoughsolarradiationhitsEarthtomeetglobalenergyneedsforayear.Windcouldalsosingle-handedlytakecareoftheentireworldsdemandsaccordingtoresearchpublishedlastyearatStanfordUniversityinCaliforniaPNASvol109p15679.Thereasonitdoesntisdowninparttothemismatchbetweenwhentheenergycanbeobtainedandwhenwecanuseit.Gridoperatorshavetouseback-uppowerstationswhichforcesupthecostofrenewables.Thatspartofthereasonwhylastyearrenewablesourcesaccountedforonly9.4percentoftheelectricitygeneratedintheUKand13percentofelectricityintheUS-wellshortofprevioustargetsseediagram.Itmightseemobviousthattheansweristostoretheextrapowerwhensupplyishighanddemandislowandtotapitwhentheoppositeistrue.Indeedtheconventionalpowerindustryhasdonethisfordecadesparticularlytosalvageextraenergyproducedbynuclearpowerstationswhicharetooexpensivetoshutdownwhendemanddips.Onemethodiscalledpumpedstorage.AttheDinorwigpowerstationintheUKforexamplewaterispumpedupintoareservoirontopoftheElidirFawrmountainduringperiodsoflowdemand.Whenenergydemandspikesthewaterisreleaseddownthemountaintodriveturbinesthatfeedtheelectricitygrid.Itsanextraordinaryengineeringachievementhousedin16kilometresoftunnelsthreadedthroughthemountainandcapableofsupplying1300megawattsin12seconds.Thatpowerspeedandefficiency-about80percent-iswhypumpedstorageaccountsfor99perMyNewScientistHomeIn-DepthArticlesBacktoarticleIntothinairStoragesalvationforgreenenergy02January2013byJimGilesMagazineissue2898.SubscribeandsaveForsimilarstoriesvisittheEnergyandFuelsandClimateChangeTopicGuidescentoftheworldsenergystoragecapacity.Ifeverywindandsolarfarmhaditsownmountainreservoiritmightbepossibletomakewindenergya247resource.AmbitiousdesignsInIrelandathinktankcalledSpiritofIrelandisworkingonjustsuchaprojecta3.6billionundertakingthatwouldusepumpedstoragetotakefulladvantageofthecountryscopioussupplyofintermittentwinds.Wrong-timeenergyfromitslargewindfarmswoulddriveseawatertoacliff-topreservoir.Butnoteverycountrycanrelyonpumpedstoragewhichcruciallydependsonexistinggeographicalfeatures-orawillingnesstoshoulderthecostofbuildingamountain.Sothesuccessofrenewableenergywilldependoneasierstoragemethods.Developingthesehoweverhasbeenfarfromstraightforward.Batteriesmightseemtheobviouschoicebutscalingthemupforgridstoragehasprovedtricky.TheLaurelmountainwindfarminWestVirginiauseslithiumbatterieshousedinshipping-container-sizedstructurestomopupunwantedelectricityduringlowdemandandsend32megawattsbackintothegridathighdemand.Theyarehighlyefficientandhaveasmallfootprint.Buttheyhavedrawbacks.Notonlydotheyuseexoticmaterialssuchasrareearthelementsbutlithiumbatterystorageisatleast10timesasexpensiveaspumpedstorageoverthelietimeoaplantaccordingtoa2010analysisbytheElectricPowerResearchInstituteinPaloAltoCalifornia.SomeplantshaveturnedtoairsuchasanaturalgasplantoperatedbyE.ONKraftwerkeinHuntorfGermany.Insteadofusingexcesselectricalenergytodrivewaterupahilltheyuseittocompressandstoreairinsaltcavernsabout500metresbelowground.Whentheyneedtheenergyoncemoretheyreleasetheairtodriveaturbine.Theproblemwiththismethodisitsefficiencywhichrarelyexceeds50percent.Pressurisingaircausesittoheatupwhichcarriesawayalotoftheoriginalenergy.Thentoexpandthecompressedairitmustbeheatedasecondtimeusingupevenmoreenergy.TheheatproblemisbeingaddressedinGermanywherea90-megawattdemonstrationplantisplannedtobeoperationalby2019.Butthatwontsolvetheproblemthatcompressedairstoragereliesonthepresenceoflimestonecavernsaquifersorsaltcaves.Howeverairmayyetholdthekeytoenergystorage-inliquidform.ForthepasttwoyearsonapatchoflandnotmuchbiggerthanabasketballcourtinSloughUKaliquidairpilotstorageplanthasbeenquietlygeneratingelectricityusingtheexcessenergyfromaneighbouringbiomassplant.Thistangleofgleamingwhitepipesandtankshasenoughadvantagesoverrivaltechnologiestohavebeenhailedasacriticalpartofourenergyfuture.ThiscouldsavetheUKbillionssaysTimFoxheadofenergyandenvironmentattheInstitutionofMechanicalEngineersinLondon.AirapparentTheplantcombinesexistingtechnologiesinanewway.Thepowerstationsexcessenergyisusedtorunagiantfridgethatcreatesandstoresliquidair.Wrong-timeenergypullsambientairoutoftheatmosphereandcoolsitto-196Catemperatureatwhichbothoxygenandnitrogenareliquid.Onceliquefied700litresofaircanbecompressedinto1litreandstoredinatank.Whenthelocalgridneedsatop-upsomeoftheliquidisexposedtoambienttemperatureandtheresultingexpansionpacksenoughpunchtodriveaturbine.Bestofallbecausenitrogenboilsat-195.8Ctheprocessofreturningittoambienttemperaturerequiresverylittleenergy.AccordingtoHighviewtheLondon-basedcompanythatoperatesthepilotplantthistechnologywillbecapableofsupplyingtensorevenhundredsofmegawatts.Asingle50-tonnetank-astandardpieceofkitwidelyusedinthechemicalindustry-couldstoreenoughliquidairtopoweraround15000homesforanhoursaysHighviewsTobyPeters.Themechanismisfunctionallyequivalenttoabatterythatrunsonair.Addmoretanksandliquidairplantscanservicemorehouseholdsforlongerperiodsperhapsevenreplacingtheoutputofamedium-sizedpowerstationforseveralhoursatatime.Liquidairbatteriescouldbedeployedanywherebecausetheyrequireneitherareservoirnorgravity.Whilethecostsarestillbeingdeterminedtheyarelikelytobemuchcheaperthanpumpedstorageasnomountainsneedbeexcavatedandthanlithiumbatteriessincetheequipmentrequiredisalreadywidelyused.AllthecomponentsareavailableofftheshelfsaysYulongDinganengineerattheUniversityofLeedsUKwhohasstudiedliquidair.Theonlycurrentdrawbackisefficiency.Noprocesscanstoreandreleaseenergywithoutwastingalittle-evenbatterieslose10percenttoheat.Buttheprocessofliquefyingairisevenlessefficientthancompressingittheenergyyougetbackisanabysmal25percent.TheSloughpilotplantfaresevenworse.Thedemonstrationprojectwasnotbuiltwithefficiencyinmindanditshows-efficiencyisjust12percent.Thatsaidsimplyscalinguptheplanttocommercialsizeandoptimisingitforefficiencywillpushthatnumberto50percentHighviewpredictsbecauselargerturbinesaremoreefficientthansmallerones.ButHighviewengineersalsohaveacouplemoretricksuptheirsleevestofurtherimproveefficiency.Thefirstistorecycletheliquidairafterithasbeenreturnedtoambienttemperaturebyusingittoheatuptheliquidairthatisjustabouttoentertheturbine.Thissimplemanoeuvretheengineerssaywillbumpefficiencyto55or60percent.Aslightlymoreadvancedtrickmakesuseofthermodynamics.Thebiggerthetemperaturedifferencebetweentheliquidairandthegasasithitstheturbinethemoreexplosivetheexpansionandthereforethemoreenergygoesintothegrid.Highviewengineersnowpumptheexhaustgasesfromtheneighbouringbiomassplantintotheturbinetomeettheliquefiedair.Inacommercialplantthiswillcausetheefficiencyoftheprocesstojumpto70percentpredictsPeters.Theseexhaustgasesareconsideredlow-gradeheatbecauseataround100Ctheyarenothotenoughtobeusefulanywhereelse.Wasteheatiseasytocomeby.ThetotalheatwastedbyindustrydatacentresandpowerplantsintheUKisequivalenttothatneededtoheateverybuildinginthecountrysaysFox.Simplylocatingliquidairplantsadjacenttothesefacilitieswouldtranslateintoextraelectricityhesays.RenewablefutureButwasteheatcanplayanevenbettertrickonethatatfirstglancemayappearimplausiblebumptheefficiencyoftheairbatteriespast100percent.Usingreallyhotexhaust-say150Cor200C-willtransferextraenergyintothegasificationprocesssaysDingandsalvagingsomeoftheheatfromthewastegaseswhichisnormallylosttotheatmospherecanturnitintoevenmoreelectricity.Therecouldbealotofmoneyinthecommercialisationofairbatteries.Butallofthisdependsonaclearpathtowardrenewableenergyandthatrequiresmorethanjustinventiveengineering.Anuncertainfutureforrenewableenergycanderailevenpromisingprojects.ForexampleAirProductsalargeengineeringfirmbasedinAllentownPennsylvaniarecentlystoppedworkedon