Energy Storage Technology Comparison953046/FULLTEXT01.pdf · most commonly used energy storage technologies. Also, the work aimed to collect numeric values of number of common parameters

Bachelor of Science ThesisKTH School of Industrial Engineering and Management

Energy Technology EGI-2016SE-100 44 STOCKHOLM

Energy Storage TechnologyComparison

- A knowledge guide to simplify selection of energystorage technology

Johanna Gustavsson

Reference: http://www.greenenergystorage.eu

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Bachelor of Science Thesis EGI-2016

Energy Storage Technology Comparison

Johanna GustavssonApproved

DateExaminer

Viktoria MartinSupervisor

Saman Nimali GunasekaraCommissioner Contact person

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AbstractThepurposeofthisstudyhasbeentoincreasetheunderstandingofsomeofthemost commonly used energy storage technologies. Also, the work aimed tocollect numeric values of a number of common parameters used to analyzeenergy storage. These numeric values could then be used as basis for a firstevaluation of the energy storage technology that is best suited to a givensituation.Themethodwasdivided intothreemainphases.The firstphasewastogatherinformationonthedifferenttechnologiesandtoassesswhichoftheinformationthat was relevant to present in a technical survey called Energy StorageTechnologyMapping. This partwas done to achieve the goal of increase theinsightofdifferentenergystoragetechnologies.Thefollowingphasewas,onthebasisofthenumericvaluespresentedinthetechnicalsurvey,todevelopatooltofacilitate the choice of energy storage technologies indifferent situations.Thefinalphase consisted of a case study thatwasdone todemonstrate the tool’sutilityandevaluateitsperformance.Withoutcomparingthestudiedtechnologieswithaspecificapplicationinmind,the following was stated regarding the four categories of energy storagetechnologies:

· Electrochemical:highefficiency,shortstorageperiod· Mechanical: large capacity andpower,high initial investment costsand

geographicallylimited· Chemical:verylongstorageperiod,lowefficiency· Thermal: long lifetime and high efficiency, variable depending on the

mediumstudiedFromtheliteraturestudyandtheresultsanumberofconclusionsweredrawn.Amongotherthings,itwaspossibletoconcludethatenvironmental-,social-andethical aspects should be taken into account aswell as the geographical- andgeological conditions. It was also possible to conclude that the technologiescomparedwere foundatdifferent stages in termsofmaturityand commercialuse, which was reflected in the ability to find more general numeric valuesrelativetothevalueslinkedtoaspecificapplication.

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SammanfattningSyftetmeddennastudieharvaritattökaförståelsen förnågraavdevanligasteenergilagringsteknikerna.Utöverdetsyftadearbetettillattsamla innumeriskavärden förettantalgemensammaparametrar somkananses relevanta förattanalysera energilagring. Dessa numeriska värden kunde sedan användas somunderlag vid en första bedömning av vilken energilagringsteknik som är bästlämpadiolikasituationer.Metodenvaruppdeladitreolikahuvudfaser.Denförstafasenbestodiattsamlain information om de olika teknikerna samt bedöma vilken av informationensom var lämplig att presentera i en teknisk kartläggning vid namn EnergyStorageTechnologyMapping.Dennadel gjordes för attuppnåmålet omökadförståelsefördeolikaenergilagringsteknikerna.Denefterföljandefasenbestodiattutifråndenumeriskavärdenasompresenteratsidentekniskakartläggningenta fram ett redskap för att underlätta valet av energilagringsteknik vid olikasituationer. Den sista fasen bestod av en fallstudie som gjordes för attdemonstreraverktygetanvändbarhetsamtutvärderadessprestanda.Utanattjämföradestuderadeteknikernamedettspecifiktanvändningsområdeiåtanke kunde följande konstateras gällande de fyra undergrupperna avenergilagringstekniker:

· Elektrokemiska:högeffektivitet,kortlagringstid· Mekaniska: stor kapacitet och kraft, stora investeringskostnader och

geografisktbegränsade· Kemiska:mycketlånglagringstid,lågeffektivitet· Termiska: lång livslängd och hög effektivitet, varierande beroende på

studeratmediumFrånlitteraturstudienochresultatetkundeettantalslutsatserdras.Blandannatvardetmöjligtattdraslutsatsenattmiljö-,sociala-ochetniskaaspekterbörtasibeaktan liksom geografiska- och geologiska förutsättningar.Det gick också attdra slutsatsen att teknikerna som jämfördes befanns sig på olika stadier vadgällermognadochkommersielltbrukvilketåterspeglades i förmåganatt finnamer generella numeriska värden i förhållande till värden kopplade till ettspecifiktanvändningsområde.

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List of contentAbstract...........................................................................................................................iii

Sammanfattning............................................................................................................ivListofcontent.................................................................................................................v

Listoffigures.................................................................................................................viListoftables..................................................................................................................vii

Nomenclature..............................................................................................................viii

1.Introduction................................................................................................................12.Background.................................................................................................................2

2.1Problemdefinition..........................................................................................................22.2Purpose..............................................................................................................................22.3Limitations........................................................................................................................3

3.Methodology...............................................................................................................3

4.EnergyStorageTechnologyMapping..................................................................44.1ElectrochemicalStorage................................................................................................5

4.1.1LithiumIonBattery..........................................................................................................................54.1.2SodiumSulfurBattery.....................................................................................................................74.1.3LeadAcidBattery..............................................................................................................................84.1.4RedoxFlowBattery.......................................................................................................................10

4.2MechanicalStorage.......................................................................................................114.2.1CompressedAirEnergyStorage.............................................................................................114.2.2PumpedHydroEnergyStorage...............................................................................................13

4.3ChemicalStorage...........................................................................................................154.3.1Hydrogen.............................................................................................................................................154.3.2Methane...............................................................................................................................................17

4.4ThermalStorage............................................................................................................184.4.1SensibleHeatStorage...................................................................................................................184.4.2LatentHeatStorage.......................................................................................................................194.4.3Thermo-ChemicalEnergyStorage.........................................................................................20

5.TechnologyComparison–Resultsanddiscussion........................................215.1Comparisonofdifferentenergystoragetechnologies........................................215.2Casestudy:energystoragecomparisonatthreedifferentcases.....................24

5.2.1Casenr1–Voltagesupport.......................................................................................................245.2.2Casenr2-Arbitrage.....................................................................................................................255.2.3Casenr3–Wasteheatutilization..........................................................................................25

5.3Otheraspectsandoveralldiscussion......................................................................266.Conclusionsandfuturework...............................................................................28

6.1Conclusions.....................................................................................................................286.2Futurework....................................................................................................................29

References.....................................................................................................................30

AppendixA....................................................................................................................36

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List of figuresFigure1:SchematicillustrationofthefourcategoriesandassociatedEST.................3Figure2:Graphicdemonstrationoftheworkflowandpurposeofeachpart..............4Figure3:Figuredemonstratingthetechnologyreadinesslevel(TRL)ofthe

differenttechnologies [16]........................................................................................................5Figure4:SchematicdiagramdescribingthedesignofaLIB[17].....................................6Figure5:SchematicdiagramdescribingthedesignofaSSB [17]....................................7Figure6:Leadacidbatterywithsixcells:outputvoltage≈12V[2].................................9Figure7:BasicconceptofaRedoxFlowbattery.Basedon[19]....................................10Figure8:Schematicdiagramof(a)diabaticand(b)adiabaticCAESsystem[47].12Figure9:SchematicofPHESwithacombinedturbineandelectricgenerator.

Redrawnbasedon[51]............................................................................................................14Figure10:Theelectrolysisofwater;showingwherethehydrogenandoxygenare

producedaswellasthesemipermeablediaphragmbetweenthetwohalf-cellsthatallowstheseparationofthetwogases[58]..........................................................16

Figure11:Hotwatertankconnectedtoasolarcollector,commonapplicationforSHSsystems.Basedon[68].....................................................................................................18

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List of tablesTable1:NumericvaluesofcriticalparametersforLIB.........................................................7Table2:NumericvaluesofcriticalparametersforSSB.........................................................8Table3:NumericvaluesofcriticalparametersforLAB........................................................9Table4:NumericvaluesofcriticalparametersforRFB.....................................................11Table5:NumericvaluesofcriticalparametersforCAES..................................................13Table6:NumericvaluesofcriticalparametersforPHES..................................................15Table7:Numericvaluesofcriticalparametersforhydrogen..........................................17Table8:Numericvaluesofcriticalparametersformethane...........................................17Table9:NumericvaluesofcriticalparametersforSHS.....................................................19Table10:NumericvaluesofcriticalparametersforLHS..................................................20Table11:NumericvaluesofcriticalparametersforTCES................................................21Table12:Energystoragetechnologycomparisontable....................................................22Table13:Commonapplicationsintheenergysystem,includingsomecharacteristic

parameters.Basedon[55]......................................................................................................36

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NomenclatureAbbreviation DenominationCAES CompressedAirEnergyStorageCES ChemicalEnergyStorageECES ElectrochemicalEnergyStorageEST EnergyStorageTechnologiesLAB LeadAcidBatteriesLHS LatentHeatStorageLIB LithiumIonBatteriesMES MechanicalEnergyStoragePCM PhaseChangeMaterialsPCT PhaseChangeTemperaturePEM Proton-ExchangeMembranePHES PumpedHydroEnergyStorageRFB RedoxFlowBatteriesSHS SensibleHeatStorageSSB SodiumSulfurBatteriesTCES Thermo-ChemicalEnergyStorageTES ThermalEnergyStorageTRL TechnologyReadinessLevel

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1. IntroductionBeforetheindustrialrevolutionduringthe19thcentury,theneedofenergywasmodestcomparedwithtoday’ssituation.Theenergyneed inthe industrializedworld increase in line with the technology advances made during theindustrialization.Oneofthemostimportanttechnicalinventionsisthediscoveryofelectricity. Eversinceelectricity,inthe20thcenturybecomeamatterofcourseinmanyindustrializedsocieties;theenergyneedhaveincreasedsignificantly[1].Today, comforts like hot water, air conditioner and outlets provided withelectricity is taken forgranted.Historically, thesourcesconvertingenergy intoelectricity,heatandcoldhavebeenmainlynon-renewable.Fossil fuelssuchasoil,petroleumandnaturalgashavefilledourneedsforalongperiodoftime [1].Production ofheat, cold and electricity from these sourceshave the ability toadapt to demand, hence the need of supplementary energy storage is low.However, these energy sources are finite and have shown negativeenvironmentalimpact.Apartfromglobalwarming,theincreaseinthedifferentgreenhouse gases contribute to ocean acidification, smog pollution, ozonedepletionaswellaschangestoplantgrowthandnutritionlevels [2].Based on increased demand, the price of fossil fuels has firmly risen and anumberof“crises”havehadbigeconomicimpact.E.g.thefirstoilcrisisin1973more than doubled the price of oil over night and led to great reactionsworldwide [3]. Among other things, France then embark on a major nuclearpowerprogram to ensure its energy independence.Ever since,nuclearpoweraccounted for thebulkof theelectricityproduced inFrance, corresponding to75%of theelectricity [4].As a resultof thedecision,Francehas today (2016)almostthelowestcostofelectricityinEuropeandishighlyenergyindependent.Also, the country has extremely low level of CO2 emissions per capita fromelectricity generation because of the high proportion of nuclear power.Nevertheless,nuclearpowerhascausedanumberofseriousaccidentsthathasledtodevastationresultsduetodangerouslyhighconcentrationsofradioactivesubstances [2].NomajoraccidentshaveoccurredinFrancebuttheradionuclidesspreadhasaffectedlargepartsoftheworld,notonlywithintheareawheretheaccidenthappened.Nuclear accidents and globalwarming aswell as the rising price and limitedamountoffossilfuelshasincreasedthenumberofdifferentenergysourcesandatthepresenttimetheproportionofrenewableenergysourceshaveincreased[5].Renewableenergysourcessuchassun-andwindpowerarelessharmfultotheenvironmentand inexhaustible.However, theyareunpredictableandmoredifficult tocontrol.Therefore,oneof today’s largestchallenges is tomatch theavailable energywith the energydemand in time,place and quantity [6].Thisappliesnotonlyelectricitybutalsothermalenergyintheformofheatandcold.Forexample,ifitispossibletostoretheenergygenerated fromthesunduringsunnydaysorsummerseasonstotimeswithlesssunitcanminimizethelossinheat from production to consumption. In that way it is possible to use theresidualheatlateroninsteadofusinge.g.additionalelectricitytogenerateheatfromanelectricalsourceofheatduringtimeswithlesssun.

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Presently there is a great number of Energy Storage Technologies (EST)available on the market, often divided into Electrochemical Energy Storage(ECES),MechanicalEnergyStorage (MES),ChemicalEnergyStorage (CES)andThermal Energy Storage (TES). All the technologies have certain design andoperationalparametersthatputconstraintstowheneacharesuitabletouse.Allofthetechnologieshavetheiradvantagesanddisadvantagesthereforewhichareideal in different situations and applications. The more mature technologiescurrentlyusedarepumpedhydroenergystorage (mechanical),somebatteriese.g. lead-acid-andsodiumsulfurbatteries(electrochemical)aswellassensibleheatstorage(thermal) [7] [8].Eventhoughtheconventionaltechnologiesallarewellknown,thedevelopmentinthefieldisvastandfast.Thiscreatesaneedtoamore in-depth knowledge of each technology to be able to find the onemostsuitableforeachsituation.

2. BackgroundRenewableenergysourcesisahottopicduetoglobalwarming,severalnumbersofnaturaldisastersetc.Inordertooptimizeitsuse,energystoragehavebecomeinterestingandthereisquitealotofongoingresearchinthearea.Researchandmanyof theprevious studiesonlyexamineand compareESTwithin the samecategory(electrochemical,mechanicaletc.).Thishasbeendone instudiessuchas:[9],[10]and[11].Also,manystudiescomparedifferentESTwithaparticularapplication in mind or conversely, comparing different applications with aparticular EST. This is exemplified in following studies: [12], [13] and [14].However,therearegapsregardingmorecomprehensivecomparisonthatmakesit possible to analyze and compare the storage technologies independently ofapplications or category. This project is focusing on a bigger perspective andwithinthissectiontheproblemdefinition,thepurpose,thescopeoftheprojectandthelimitationsencounteredispresented.

2.1 Problem definitionEnergystorageisarelativelynewtopicforresearchandmanyESTareimmatureandnotcommerciallyusedatpresent(2016).ThismakesthelackofknowledgeforseveralnumbersofEST [15].Theoften-limitedknowledgemakes itdifficulttounderstand the advantages anddisadvantages ofdifferent technologiesbutalso to decide which storage technology that is most suitable for whatapplication.Currently,thesearethetwomajorproblemswithinthissubject.

2.2 PurposeThepurposewith thisstudy is to increaseunderstandingof themostcommonEST.Itisalsotogatherandpresentinformationandnumericvaluestodevelopatool for facilitating a first evaluation of the type of the EST that is themostsuitableforparticularapplicationsandgeographicallocations.Byfulfillingthesepurposestheresultaimtoanswerthequestion“whichofthepresentedESTaremostsuitableforagivenapplication?”.

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2.3 LimitationsThenumberofESTavailabletodayismanyandtobeabletopresentaprofoundanalysissomelimitationshavebeennecessary.Thetechnologiestreatedwithinthisthesisarelimitedtoanumberofeleven.ThenumberofmethodsforfurthercategorizationofESTismany.Inthisstudyoneofthemostwidelyusedmethodhavebeen applied.Thatmethod isbased on the formof energy stored in thesystem [15].The technologies treated in thisstudyhavebeendivided into fourcategories.ThesecategoriesandincludingtechnologiesarepresentedinFigure1that aims to clarify the categorization.The choice of technologies isbased onavailabilitybutalsoonthetechnology’spotentialandvariationpossibility.Someoftherathercommontechnologies,e.g.flywheelshavebeenexcludedsincesomeof itsdisadvantagesmakes ituseful inonlya limitedrangeofapplication.Also,manyofthetechnologiesareavailableindifferentvariantsbutsincethisprojectaims to facilitating a first evaluation, the technologies are limited to its basicdesign.Thestudy isnotgeographically limited toFrancebut ithasbeenmadewith the country’s conditions and currently energy storage situation inmind.Meaning, thepurposehas been toprovide a knowledge guide and a tool thatcouldbeusedworldwidebutexamplesanddiscussionhavehadfocusonFrance.

Figure1:SchematicillustrationofthefourcategoriesandassociatedEST.

3. MethodologyThemethodology canbedivided into threemainphases. Initially, informationabout different EST were retrieved from various sources including scientificliterature and publications but also relevant information found onweb pagesbelonging to different organizations and companies. After enough data wasgathered,thefollowingphasewastocriticallyanalyzethedataobtainedandsortoutrelevantinformationtopresentintheliteraturestudynamedEnergyStorageTechnologyMapping.Themainapproachwastomapalloftheapplicationsand

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storage technologies based on a number of important parameters that thetechnologieshadincommon.ThesetwophasesmainpurposewastocollectandpresentrelevantinformationinordertoincreasetheknowledgeofdifferentEST.

Oncethecriticalanalysisandmappingwasdone,theterminativephasebegun.Thisphasewasacomparisonofthetechnologiestreatedintheliteraturestudy.This comparison was based on the numeric values for each of the commonparameters.Thepurpose of thisphasewas topresent substrate and a tool tofacilitating a first evaluation ofwhat kind ofEST thatwasmost suitable for agiven application. To finally demonstrate the tool’s function and be able toevaluate itsperformanceasmallcasestudywasdone.Agraphic illustrationoftheworkflowandeachpart’spurposesarepresentedinFigure2.

Figure2:Graphicdemonstrationoftheworkflowandpurposeofeachpart.

4. Energy Storage Technology MappingThis part of the thesis is designed on the basis of the divisions presented inFigure 1. It therefore consists of sections (4.1 Electrochemical Storage, 4.2MechanicalStorage,4.3ChemicalStorageand4.4ThermalStorage)representingthefourcategoriesoftechnologies:ECES,MES,CESandTES.Furthermore,everysectionconsistsoftwotofourdifferentsubsections(4.1.1LithiumIonBattery,4.1.2SodiumSulfurBatteryetc.)dependingofthenumberoftreatedESTineachsection.ThenameandnumberoftechnologiestreatedineachsubsectionisalsoillustratedinFigure1.

Withineach sectionpresentinganEST the technology’s technical constructionincludingmajorcomponentsaredescribed.Also,commonlyusedapplicationsatthe present time (2016) and the most crucial conditions and design andoperational criteria are considered. Every section presenting an EST (4.1.1LithiumIonBattery,4.1.2SodiumSulfurBatteryetc.)lastlycontainsatablewithnumericvaluesofcriticaldesignandoperationalparameters,presentedat theendofeachsection.Thispartaimstoprovidein-depthknowledgeofeachEST.Inorder to increase theunderstanding of each and every technology’s readinesslevel, already at this point, Figure 3 is presented before the following subsections.Theratingisbasedontheextenttowhichthetechnologyisappliedandusedindailylife.

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Figure3:Figuredemonstratingthetechnologyreadinesslevel(TRL)ofthe

differenttechnologies [16].

4.1 Electrochemical StorageECES is agenericname forbatteriesbeingused to storeenergy.Batteriesareelectrochemicaldeviceswiththeabilitytoreadilyconvertthestoredenergyintoelectrical energy. Since they are portable and often quite small they can belocated anywhere without geographical considerations [16]. Batteries can beeither non-rechargeable (primary) or rechargeable (secondary), onlyrechargeablebatteriesareofinterestforlarge-scaleenergystorage[2].Batteriescanalsobeeithersolid-statebatteriesor flowbatteries.Thissectionpresent anumberofECEStechnologies,includingbothflow-andsolidstatebatteries.

4.1.1 Lithium Ion BatteryLithium Ion batteries (LIB), in theirmost common form, consist of a positiveelectrode (cathode)of lithiumoxides, anegativeelectrode (anode)ofgraphiteandanelectrolyteofalithiumsaltandorganicsolvent [2].Figure4isintendedtoclarifythetechnicaldesignofthebattery.

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Figure4:SchematicdiagramdescribingthedesignofaLIB[17].

Lithium has low density and large standard electrode potential resulting inbatterieswithlowweightandhighoperatingvoltage[2].FurthermoreLIBhaveno memory effecta, low self-charge and one of the best energy-to-mass ratiowhichmakesthemthemainenergystoragedevicesforportableelectronicssuchas mobile phones, TVs and iPads [18]. Table 1 includes numeric values forseveralparameters inordertoenablecomparisonbetweenLIBandotherEST.The properties have proven to be advantageous also for electric traction ofvehicles,power toolsandstorageof intermittentlyavailablerenewableenergyhenceLIB is increasinglycommon intheseapplicationareas [17].AlthoughLIBareextensivelyused inportable electronicdevices andare themain focus forelectricalvehicleapplications,theyareatpresent(2016)tooexpensiveforlarge-scalegridstorage.However, theresearch isextensiveand in theUnitedStatesthere isanumberoflithium-ion-baseddemonstrationsthathaverecentlybeeninstalled and tested.These systemswouldbe capable ofproviding short-termpoweroutputstabilization forwindturbinesbut,comparedwithotheroptionsLIB are still too costly to use for application in longer term storage ofwindenergy [19].Francehas one of the strongest economies inEurope andmost of theFrenchcitizenshavetheabilitytoownportableelectronics,includingLIB.Therefore,thenumberofLIBisquiteextensiveinthecountry[20].Furthermore,thenumberofplug-inhybridandelectricalvehiclehas increaseddramatically inFranceoverthe last couple of years [21]. The plug-in hybrid cars often use Nickel-metalbatteries(NiMH)butallofthemostboughtelectricalcars,suchasNissanLeafandFordFocusEVuseLIB[22] [23].

aNomemoryeffect–thecapacityisnotreducedeventhoughthebatteryisnotfullydischargedbetweenchargecycles.

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LIBhasalargeimpactonmetaldepletionandthelithiummining’stoxicityandlocationinnaturalenvironmentcancausesignificantenvironmental-,social-andhealthimpacts.Thereforeitscontinueduseneedstobemonitoredevenifthereis no immediate shortage of lithium at present (2016). Although, LIB areconcededlylesstoxicthanmanyotherbatteries,e.g.lead-acidbatteries[24].

Advantages: Disadvantages:Highefficiency[8] Expensive[25]Lowweigh,smallbattery[26]

Table1:NumericvaluesofcriticalparametersforLIB

Power Capacity StoragePeriod

SpecificEnergy

EnergyDensity

Efficiency Lifetime PowerCost

EnergyCost

[MW] [MWh] [time] [kWh/ton] [kWh/m3] [%] [#cycles] [$/kW] [$/kWh]

0.001-0.1[27]

0.25-25[28]

Day-month[29]

75-200[8]

300[30]

85-100[27]

1000-4500[31]

175-4000[16]b

500-2500[16]c

4.1.2 Sodium Sulfur BatterySodiumSulfurBatteries (SSB)consistof twoactivematerials;moltensulfurasthepositiveelectrodeandmoltensodiumasthenegativeelectrode.ThebatteryisoftenreferredtoasNaSbatteryduetothechemicalabbreviationsof itstwomaincomponentssodium(Na)andSulfur(S).Asolidceramic,sodiumalumina,separates the electrodes and serves also as the electrolyte [32]. A SSB ispresentedinFigure5thataimstoclarifythebattery’stechnicaldesign.

Figure5:SchematicdiagramdescribingthedesignofaSSB [17].

Thesematerialshavetheadvantagesoflowdensityandcost.ThespecificenergyofaSSBishigh,thecyclelifetimeislongcomparedtomanyotherbatteriesandthechargeefficiencyishigh [2].BecauseoftheseadvantagesSSBareconsideredanattractivecandidateforlarge-scaleenergystorageapplications [16].Evenso,bothsodiumandsulfurhaveacommoncharacteristicofbeinghighlycorrosivebFrom2015cFrom2015

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whichmight cause corrosive problems. Combined with the fact that the SSBoperatesat a temperatureofaround300°Cmakes thebatteries,asmentionedmost suitable for large-scale energy storage such as for the power grid [2].Numeric values for several parameters are presented in Table 2 that aims toenableacomparisonbetweenSSBandotherEST. ReunionIslandPegaseProjectisaprojectwhereSSBhavebeenusedtofacilitateloadlevelingandrenewableintegrationattheReunionIsland,aninsularregionofFrancelocatedintheIndianOcean. TheSSBhaveapowerlevelof1MWandcan provide the average usage of 2000 households [33]. Also, over the lastdecade SSB has seen the largest number of demonstrations and field testsglobally,e.g.over190sites in Japan.Although, furtheruptakeappears tohavesloweddownduetorecentsafetyconcerns [19].

Advantages: Disadvantages:Longlifecycle[8] Highly corrosive behavior [8] Highproductioncost [34]

Highoperatingtemp. [35]

Table2:NumericvaluesofcriticalparametersforSSB


SpecificEnergy

EnergyDensity


EnergyCost


1-50[36]

£300[28]

Day[37]

150[2] 150-250[15]

75-90[8]

2500[16]

1000-3000[16]d

300-500[8]e

4.1.3 Lead Acid BatteryLeadAcidBatteries (LAB)was inventedby theFrenchphysicistGastonPlantéalready in1859andwas the firstpracticalrechargeablebattery.LABnormallyconsistsofleadoxide(PbO2)cathodesandlead(Pb)anodesimmersedinsulfuricacid (H2SO4), with each cell connected in series [38]. The technical design isillustratedinFigure6includingthemaincomponentsjustmentioned.

dFrom2015eFrom2015

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Figure6:Leadacidbatterywithsixcells:outputvoltage≈12V[2].

Comparingwith other solid statebatteries, thedensity isquite lowbut it canprovide a largecurrent that is agreatadvantage inmanyapplicationssuchasstartingacar [2].LABiswidelyusedevenwhensurgecurrentfisnotimportantandotherdesignscouldprovidehigherenergydensities.ThisisbecauseLABischeapcomparedtonewertechnologies.ThereforeLABisalsousedforstorageinbackuppowersuppliesaswellas forwheelchairs,golfcars,personnelcarriersand emergency lighting [39]. LAB emits lead,which is toxicheavymetalwithsevereimpactsontheglobalbioaccumulation,alsowithpotentialriskstohumanhealth.However,LABcanberecycledseveralhundredtimesandarecurrentlythe most recycled consumer product. Given that the LAB is recycled thesebatteries’ disposal is extremely successful from both cost- and environmentalperspectives [40].Table 3 includesnumeric values for severalparameters andaimstoenablecomparisonbetweenLABandotherEST.

Advantages: Disadvantages:Canprovidehighcurrent[2] Containstoxicsubstance[8]Maturetechnology[8] Shortlifetime[8]Highlyrecycled[40]

Table3:NumericvaluesofcriticalparametersforLAB


SpecificEnergy

EnergyDensity


EnergyCost


0-40[8]

0.25-50[41]

Day-month[29]

20[2] 70 [30] 70-90[8]

500-1000[16]

300-600[16]g

200-400[8]h

fSurgeCurrent-asuddenincreaseincurrent.gFrom2015hFrom2015

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4.1.4 Redox Flow BatteryIn Redox Flow Batteries (RFB), two liquid electrolytes are pumped to theopposite sides of the electrochemical cell. The two liquid electrolytes containdissolved metal ions as active masses and they stay dissolved in the fluidelectrolyte, hence no phase change of these active masses takes place. Thenegativeandthepositiveredoxspeciesarecontainedinseparatestoragetanksand are separated by an ion-selective membrane. Redox-active ions undergoreduction- or oxidation reactions when they are in contact or very near thecurrentcollector.However,themembraneallowsthetransportofnon-reactionions to maintain electrolyte balance and electro neutrality [27]. Figure 7representsthebasicprincipleofaRFBwiththeintenttoenhanceunderstandingofthebattery’sappearanceandfunction.

Figure7:BasicconceptofaRedoxFlowbattery.Basedon[19].

Unliketraditional,solidstatebatteriesthatstoreenergywithintheirelectrodes,RFB store their electrical energy within one or more electro-activeispeciesdissolvedintoliquidelectrolytes.Thesizeanddesignoftheelectrochemicalcelldefines thepowerdensitywhile the energydensity or outputdependson thesizeofthetanks[42].SomeoftheadvantagesoftheRFBarehighefficiency,longcycle life, flexible layout and an ability to store large amount of energy [43].Although, compared with other batteries their density is rather low and thedesignmightbecomplicatedduetothefactthatitoftenincludespumps,sensors,control units etc. To enable comparison between RFB and other EST somenumericvaluesforseveralparametersarepresentedinTable4.Foranumberofreasons, including the relatively bulky size ofRFB, they aremost suitable forhighpowerrechargeablestorage.Thus,mostofthebatteriesarecurrentlyusedforgridenergystorage,suchasbeingattachedtoelectricalgridsorpowerplants.Francehas,atthepresenttime(2016)noRFBplantsusedforgreateramountofenergystorage [44].iElectro-active-exhibitingelectricalactivityorresponsivetoelectricalstimuli.

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Advantages: Disadvantages:Shorttimetofullycharge[8] Lowspecificenergy[8]Highdesignflexibility[19] Electricalcurrentleakage[8]Fullycharged/dischargedwithoutlossofcapacity[19]

Table4:NumericvaluesofcriticalparametersforRFB


SpecificEnergy

EnergyDensity


EnergyCost


0.03-7[27]

<10[8]

Day-month[29]

10-30[8]

25-35[15]

75-85[27] [8]

12000[45][16]

600-1500[16]j

150-1000[8]k

4.2 Mechanical StorageTostoremechanicalenergy,kineticenergyisconvertedintoelectricalenergybyusing physical movements. Two of today’s most common technologies;compressed air and pumped hydro storage are describedwithin this section.BothofthesetwoECEStechnologiesarelocationlimitedthatmakesitdifficulttostore energy over longer distances [8]. The MES technologies have howevermanyotheradvantages thatwillbementionedwithinthissection.Thesectionincludes technical descriptions of the two MES technologies include generalinformationandtechnicaldesignaswellasnumericvaluesofsomeofthemostimpactingparameters.

4.2.1 Compressed Air Energy StorageCompressed Air Energy Storage (CAES) is based on air being pumped by anexternal electricity source to a high pressure into a large reservoir duringperiodsof lowdemands (off-peak)and isreleased laterduringperiodsofhighdemands(peak-load)[2].

Regarding large-scale energy storing CAES systems can store the air eitheradiabaticallyordiabatically.Anadiabaticprocessoccurswithoutgainorlossofheat,whereforadiabaticprocesstheoppositeistrue[46].Rathertechnically,ina diabatic CAES system, a compressor driven by amotor compresses the airduring the chargingprocess.During the compressionprocess the airheatsupand a radiator removes the heat. The energy is stored as compressed air in acavern. During discharging, the air cools down due to its expansion and has tobe heated up by burning conventional fuel or biofuel. After being heated, theair drives a turbine/generator unit, which feeds power into the grid. However,when the CAES is adiabatic the heat generated during the compression processis stored. The stored heat is then used to heat up the air while it expands in thedischarging process. Therefore amuch higher efficiency, increased by around20% can be achieved if the heat of compression is recovered and storedadiabatic.Also,theoperation isthencompletelyCO2-freeasno fuel isrequiredwhichisdesirableinanenvironmentalperspective[47]. Allpartoftheprocessis

jFrom2015kFrom2015

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illustratedforbothadiabaticandanadiabaticsysteminFigure8thatdepictsaschematicofaCAESsystem.

Figure8:Schematicdiagramof(a)diabaticand(b)adiabaticCAESsystem[47].

At present time there are only two CAES plants in operationworldwide. Theoldest one was put in operation 1978 and is located in Huntorf, Germany(320MW) and the newer one was put in operation 1991 and is located inMcIntosch,USA (110MW).Bothof theseCAESsystemstore theairdiabaticallyandusenaturalgasasaheatsourceforthedischargingprocess,whichreducedthe overall efficiency (current efficiency: 42% respectively 54%) [47].Nevertheless,adiabaticstoredairisasubjectofongoingstudies,withnoutilityscaleplantsattheyearof2016[48].

13

Duetothelowstoragedensityverylargestoragesarerequiredindependentoftheairbeingstoredadiabaticordiabatic.Saltisself-sealedunderpressureandconsequentlysaltcavernsarepracticallysuitableforCAES.Itisalsopossibletouse natural aquifers if no suitable salt formations are present [2]. The usedstoragemedia is inexpensive leading to theadvantageof a lowenergycost forCAES.Otheradvantagesarequickstart-up (typically10minutes), longstoragecapabilityand largestoragecapacity [49].Numericvalues forsomeparametersarepresentedinTable5inordertobeabletocompareCAESwithotherEST.

Oneof the reason there isnoCAES systemoperating inFranceat thepresenttime (2016) is due to the fact that CAES systems need certain geologicalrequirements (e.g. salt caverns) for their installation. These requirements arelimitedworldwideandpotential locations inEuropeare located in theUnitedKingdom,northernGermanyandintheNetherlands;henceFrancenotincluded.Nevertheless,severalconceptsareunderdevelopmentforairtankssothatitwillbepossibletoovercometheserestrictions[47].

Advantages: Disadvantages:Largestoragecapability[28] Geologicalrequirement[47]Longlife(reservoir,compressor,turbine)[47] Highinvestmentcost[47]Smallfootprintonsurface(undergroundstorage) [47]

Table5:NumericvaluesofcriticalparametersforCAES


SpecificEnergy

EnergyDensity


EnergyCost


5-300[50]

£250[28]

Day[29]

30-60[50]

2-6at70-200bar[47]

60-79[16]

8000-12000[7]

1250[47]l

50-100[8]m

4.2.2 Pumped Hydro Energy StorageInPumpedHydroEnergyStorage(PHES)systems,waterispumpedtoanuphillreservoir from a low-level reservoir during periods of low demands. Thisprocessisfollowedbydischargingthestoredwaterbacktothelowerreservoirduringperiodsofpeakdemands.Thedischargedwaterthendrivesthegeneratorto produce electricity when needed. The same generator is being used forpumpingthewateruphill,consequentlyusedasareversiblepump-turbine [2].AdetailedlayoutofaPHESsystemisillustratedinFigure9.

lFrom2014mFrom2015

14

Figure9:SchematicofPHESwithacombinedturbineandelectricgenerator.

Redrawnbasedon[51].

PHEShelputilitiestoavoidusingexpensivebackuppowerplantsandcanmakethepowernetwork lessvolatile.Compared tootherEST,PHEShas the largeststorage capacityandefficiencyofaround70-85% [34].Becauseof itsability toprovidehighpowerandcapacitythetechnologyisfavoredbyhighdemand.Itishowever stationary and have geographical restrictions which makes itsflexibility rather low [52].PHEShave short start-up timeand can continuouslyrespond to fluctuations and to a sudden surge in demands,which is amajoradvantage [2]. The technology has however geographical restrictions andrequires height differences and major quantities of water [47]. A number ofparameters including numeric values for PHES are presented in Table 6 thataimstoenablecomparisonbetweenPHESandotherEST.

This storages technology is often combined with nuclear power production,sincethenuclearreactorneedstoproduceasteadyoutputinordertominimizeageingeffectsandtomaintainreactorstability [2].DuetothefactthatFranceisone of the world’s biggest nuclear producer and also has hilly areas in thesoutheast this is an advantageous storage technology for France. Currently,France has a dozen plants in operationwith Grand’Maison Dam as themostpowerful [53].Grand’MaisonDamwithan impressivedropof950metersandastoragecapacityof140millionm3ofwaterislocatedintheRomanchevalley,notveryfarfromtheItalianborder.Thepowerstation,including12turbinesetshasa total output of 1820MW and an annual production of 1420GWh [54].Also,globallyPHESisthemajorenergystoragetechnologyatpresent(2016)andwasset in operation already in the early twentieth century. These systems arenormallyusedasmedium-termstoragesystems,typicallyabletostorebetween2and8hours.Besidesbeingthemostwidelyusedtechnologyforenergystorage,PHESisalsoaverydevelopedandmaturetechnology[47].

Advantages: Disadvantages:Maturetechnology[8] Geographicalrestrictions[47]Verylonglifetime[47] Longconstructiontime[8]

Lowenergydensity[47] Highsurfacefootprint [55]

15

Table6:NumericvaluesofcriticalparametersforPHES


SpecificEnergy

EnergyDensity


EnergyCost


<3100[55]

Small:£5000Large:£140000[41]

Day-month[47]

0.28at100m[30]

0.28at100m[30]

65-82%[56][47]

10000-30000[7]

600-2000[52]n

80-200[8]o

4.3 Chemical StorageEndothermic chemical reactions require energy to build chemical bonds in ahigh-energy product while exothermic reactions release energy, forming alower-energyproduct.Thismakesitpossibletodevelopenergystoragesystemsthatstoreelectricityandheat inthebondsofchemicalcompounds(atomsandmolecules) to use them for a future energy supply. The following sectiondescribestwodifferenttechnologiesofstoringenergychemically.

4.3.1 HydrogenHydrogen can be produced by reforming of natural gaswith steam or by theelectrolysisofwater intooxygenandhydrogen.Presently,reformingofnaturalgas is more common but electrolysis of water is more convenient in anenvironmentalperspective.Thatisduetothefactthatelectrolysisofwatercanbedonedirectlyfromrenewablepower.Theefficiencyislowerusingelectrolysisof water but carbon dioxide, which is a by-product during the reforming ofnatural gas, is absent [57]. The electrolysis operates as follows: Water (H2O)consists of hydrogen (H) and oxygen (O) and by using electrical energy theelectrolysis can split water into these two basic elements. Technically, twoelectrodes in abasicelectrolysisareconnected to adirectcurrent (DC)supplyand once a sufficient high cell voltage is applied to the cell, a redox reactionoccurs. The redox reactionproduces oxygen at the anode (positive electrode)andhydrogenat thecathode (negativeelectrode) [58]. Inorder toseparatethereactioncompartments forhydrogenandoxygen aprotonconductingpolymermembrane isused.Themembrane iscalledProton-ExchangeMembrane(PEM)andbesidesfromseparatingthecompartmentsitalsoprovidestheioniccontactbetweentheelectrodes,which isessential fortheelectrochemicalprocess [30].Figure10showshowtheproductionoftheactualgastakesplaceonthesurfaceofthetwopreciousmetalelectrodes.

nFrom2014oFrom2015

16

Figure10:Theelectrolysisofwater;showingwherethehydrogenandoxygenareproducedaswellasthesemipermeablediaphragmbetweenthetwohalf-cellsthat

allowstheseparationofthetwogases[58].

Independent of production technique small amounts of hydrogen has to beeither compressed intopressurizedvesselsor liquefied inorder toget stored.Also,nanotubesorsolidmetalhydridescanserveasstorageunitsforhydrogenwith averyhighdensitywhileman-madeunderground salt caverns can storetruly great amounts of hydrogen. This enables long-term storage; hence thistechnologypermits levelingduring longerperiodsof flawsorexcess/deficitofwind-andsolarproductionandcanevenbalanceseasonalvariations [59].Afterstoring, hydrogen can be converted back to heat or electricity in an internalcombustionengineorafuelcell.Atpresent(2016),thistechnologyplays only aminor roleintheenergysectorandcanbeusedasafuelforportables(vehicles)suchasrockets[30].Although,inrecentyearsenergystoragesystemsbasedonhydrogen are receiving increasing attention; the reason is particularly thetechnology’spossibilitytointegraterenewableenergysources [50].Tobeabletocompare hydrogen storage with other EST a number of numeric values forseveralparametersarepresentedinTable7.

Francehas aratherunique testplatformwith thiskindofenergystorage.Theplatform was commissioned 2012 and is called the MYRTLE platform. Theplatformconnectssolarpanelstoahydrogen-basedenergystoragesystem.Thesystem is joined with the power grid, which gives the opportunity to solveproblem of intermittency. The system also offers greater flexibility for gridoperations. Using this unique system the research team at the University ofCorsicaassociatedwithCNRS(Centrenationaldelarecherchescientifique)andCEA (Commissariat à l'énergieatomiqueetauxénergiesalternatives)have theopportunitytoplanandtestvariousenergymanagementscenarios[60].

Advantages: Disadvantages:Canstorelongtime [34] Lowefficiency [55]Noemission(coupledtorenewablesources) [34]Requirecostlycomponents [34]Environmentallybenignoperatingcharacteristics [8]

17

Table7:Numericvaluesofcriticalparametersforhydrogen


SpecificEnergy

EnergyDensity


EnergyCost


Varies Varies Hours-months[31]

33330[61]

2.7-160at1-700bar[29]

20-50[8]

6-20[8]p

4.3.2 MethaneMethane can be created in a multi-step process. The process starts withelectrolysiswherewaterisdividedintohydrogenandoxygen(seesection4.3.1Hydrogen) followedbyamethanationreactionsuchastheSabatierprocess. Inthe Sabatier process methane and water are being produced by letting thehydrogenreactwithcarbondioxide (CO2).Theproducedmethanecan thenbestored in gas caverns or more ideally in the natural gas grid and usedtemporarily and spatially, adaptably for balancing power by producingelectricityduringperiodsofhighdemand [6].TheSabatierprocessisnowadaysoftendiscussedas“PowertoGas”approach [62].Theinterestofmethane-basedenergystoragehasrisenbecauseofitsabilitytoeffectivelyreducegasemissions[63].Methaneiseasytostoreandinmostcountriesaroundtheworld,includingFrance there are existing infrastructures for domestic transport andinternationaltrade[64].Thetwoby-productsofthisprocess;waterandcarbondioxidearebothbeingrecycledforfurtherelectrolysisandasmeanstoboosttheSabatierprocessrespectively.Duetothefactthatitispossibletostoremethaneinthealreadyexistingnaturalgasgridandthattheby-productsareallrecyclablethistechnologyisfavorableforbothsocialandenvironmentalaspects.Aresultofboththeelectrolysisandthemethanationisexcessheat,providinganadditional area ofuse for this technology.By supplementing theprocesswithheat storage devices to take care of the excess heat this technology cancontributeconditionsforbalancingtheneedforheataswell.

Advantages: Disadvantages:Canstorelongtime[65] Lowefficiency [6]Easytostore [64]Longdistancetransportavailable[64]

Table8:Numericvaluesofcriticalparametersformethane


SpecificEnergy

EnergyDensity


EnergyCost


Varies Varies 10000[61]

360-1200at200bar[31]

28-45[6]

pFrom2015

18

4.4 Thermal StorageByusingTES technologies it ispossible to store thermalenergybyheatingorcooling a storage medium. The stored energy can then be used later on forcooling-andheatingapplicationsaswellasforpowergeneration.Sensibleheat,latent heat and chemical reactions are the three primarywaysmaterials canreserveheat[66].Thesethreedifferenttechnologieswillhereafterbeexplainedbypresentingtechnicalprocess,generalinformationaswellasnumericnumbersforseveralcriticalparameters.

4.4.1 Sensible Heat StorageSensibleHeatStorage(SHS)isamaturetechnologyandisaboutstoringthermalenergybycoolingorheatingeitheraliquidorasolidstoragemedium [67].ThenameSHSisoftenusedregardlessofitisheatingorcoolingthatisbeingapplied.The storage is based on the temperature difference in the material. Thetechnology offers a capacity that is limitedby the specificheat of the storagemedium [11]. Comparedwith other SHSmedia,water has the highest specificheat, which currently (2016) makes it the most favorable material for heatstorage in residential applications. Two of the most common water-basedstoragesystemsarewatertanksandaquiferstoragesystems.Figure11showsahotwatertankusedtostorethesolarenergycollectedviaasolarcollector.Asseen inthe figurecoldwaterentersatthebottomofthehotwatertank.Whilepassing the collector, the cold water gets heated by the thermal energyconverted from solar energy emitted from the sun. Finally thewater deliversheat at the top portion of the water tank. Regarding the water tank, waterstratifies naturally because the density increases at lower temperature.Therefore, thehotwater flows to the topwhile the coldwater remainsat thebottom,andtheintermediateregionisthethermocline[68].

Figure11:Hotwatertankconnectedtoasolarcollector,commonapplicationfor

SHSsystems.Basedon[68].

19

In order to minimize the thermal losses during storage, the heat transfermedium is usually kept in storage tanks with high thermal insulation. Forcustomarily large-scale applications of storing sensible heat in both solid andliquidmediaunderground storage isbeingused.SHS requires largequantitiesandvolumesofmaterials,aswellasproperdesignduetolowenergydensityandthe possibility to discharge thermal energy at constant temperatures. Thestorage capacity and the efficiency are quite variable as they depend on thespecific heat of the storagemedium and thermal insulation technologies thatcouldbequitevarying [11].ToenablecomparisonbetweenSHSandotherESTnumericvaluesforseveralparametersarepresentedinTable9.

Advantages: Disadvantages:Simpleapplicationwithavailablematerials [8] Largevolumeneeded [8]Longlifetime [8] Geologicalrequirements [68]Cost-effectively [11] Heatlosstotheambient [68]Canstorelongtime [11]

Table9:NumericvaluesofcriticalparametersforSHS


SpecificEnergy

EnergyDensity


EnergyCost


0.001-10[11]

Day-year[11]

10-50[11]

25 [11] 50-90[11]

0.1-13[11]q

4.4.2 Latent Heat StorageLatentHeatStorage(LHS)involvesstoringthermalenergyinamaterial,knownas aphasechangematerial(PCM).PCMchangephaseatacertaintemperaturecalled the phase change temperature (PCT). Rather technically, the chemicalbondsinthePCMwillstarttobreakupwhenthetemperatureincreaseaboveacertain point, the PCT. Also at that point, thematerial changes from solid toliquidduetothe factthatthematerial, inanendothermicreaction,willabsorbthe heat. Similarly, as the temperaturedecrease, thematerialwill return to asolidstatesincethePCMdesorbsheatinanexothermicreaction.Bycontrollingthetemperaturewithinaspecificrate it ispossibletostoretheenergyusedtoalterthephaseofthematerial[69].Inordertostorecold,theprocessisreversedbutthenameofthetechnologyusuallyreferstothesamename,LHS.

ThestoragecapacityofaPCMisequaltothephasechangeenthalpyatthePCTplus thesensibleheat/coldstoredover/under thewhole temperaturerangeofthestorage.ThereforethestoragecapacityisgreaterforthistechnologythanforSHS. This is due to the additional storage capacity associatedwith the latentheat/cold of the PCT, per mass or volume of material. Numeric values forcapacity and several otherparameters arepresented inTable10 that aims toenable comparisonbetweenLHSandotherEST.Byusing this technology it isalsopossibletodetermineatarget-orienteddischargingtemperaturethatissetby thealmost constantPCT [11].Beyond, thesolid-liquid state thereare threeotherstatesthatcanclassifythechangingofthematerial:solid-solid,gas-solidqFrom2013

20

andgas-liquid[66].Thetechnologyiswellsuitedfortemperatureregulationasaresult of the sharp change in the storage capacity at a point of a singletemperature,thePCT.E.g.mixingPCMintoabuildingmaterialcouldincreasethethermal capacity of a wall manifold [70]. Using a variety of techniques andmaterials, LHScanbeused forbothshort-term(daily)and long-term(seasonal)energystorage[11].

Advantages: Disadvantages:Smallvolumes [8] Lowthermalconductivity [8]Highstoragedensity(withinasmalltemp.) [71] Corrosivenatureofmaterial [8]

Table10:NumericvaluesofcriticalparametersforLHS


SpecificEnergy

EnergyDensity


EnergyCost


0.001-1 [11]

Hour-week[11]

50-150[11]

100[11]

75-90[11]

10-56[11]r

4.4.3 Thermo-Chemical Energy StorageThermo-Chemical Energy Storage (TCES) is based on storing thermal energyusing chemical reactions. The basic principle of TCES is following; the initialcondition is twoormore components combined in achemical compound.Thecompoundisthanbrokenbyaddingheatandthedividedcomponentsarethenstored separately until a demand arises. During periods of high demand thecomponentsarereunited into achemicalcompoundandheat isreleased. Thereleasedheat fromthereactionconstitutesthestoragecapacity [11]. BothSHSandLHSaremostoften limited intimeduetoheat losses.TCESdifferssince itenables to bridge long duration periods between demand and supply. ThismakesTCESparticularlysuitableforlarge-scaleelectricitygenerating [29].

Thermo-chemicalreactions canbeused toaccumulateanddischarge coldandheatondemandbutalsotoregulatehumidityinavarietyofapplicationsusingdifferentchemicalreactants.Theefficiencyofthistechnology is intherangeof75%tonearly100%andtheTCESmaterialshaveamongthehighestdensityofall storagemedia,hence this technologyhasgreatpotential.However, storagetechnologiesbasedonTCESaremostlyunderdevelopmentanddemonstrationandfurtherimprovementsarenecessarytomakethistechnologycommerciallyavailable [11].Table11includesnumericvaluesforseveralparametersthataimstoenablecomparisonbetweenTCESandotherEST.

Advantages: Disadvantages:Longdistancetransportavailable[8] Expensive[8]Highefficiency[11] Technicallycomplex[8]Highlycompactenergystorage[8] Highcapitalcost[72]

rFrom2013

21

Table11:NumericvaluesofcriticalparametersforTCES


SpecificEnergy

EnergyDensity


EnergyCost


0.01-1 [11]

Hour-week[29]

120-250[11]

120-250[29]

75-100[11]

5. Technology Comparison – Results and discussionIt is well recognized that no single EST can meet the requirements for allapplications,whichcreatesaneedforacomprehensiveanalysisofthedifferentEST. This section presents the results of this study to enable a comparisonbetween the technologies and be able to answer the question “which of thepresented EST are most suitable for a given application?”. The section alsoincludesacasestudyandanoveralldiscussion.

5.1 Comparison of different energy storage technologiesIntheliteraturestudy,insection4.EnergyStorageTechnologyMapping,valuesdescribing the characteristics of each EST included in the study have beenexplored.TheresultcanbeseeninTable12,whichgivestheabilitytocompareandanalyzethedifferentESTinasimplifiedmatter.Table12isalsothebasisofthe following case studies and the overall discussion. The numeric values forPowerCostandEnergyCostarefromyear2015ifnothingelseisspecified.

22

Table12:Energystoragetechnologycomparisontable

sFrom2014tFrom2014

StorageTechnique

Output Power Capacity StoragePeriod

SpecificEnergy

EnergyDensity


EnergyCost

Maturity


LIB Electricity[55] [72]

0.001-0.1[27]

0.25-25[28]

Day-month[29]

75-200[8]

300[30]

85-100[27]

1000-4500[31]

175-4000[16]

500-2500[16]

Commercialized[7]

SSB Electricity[55] [72]

1-50[36]

£300[28]

Day[37]

150[2] 150-250[15]

75-90[8]

2500[16]

1000-3000[16]

300-500[8]

Commercialized[7]

LAB Electricity[72]

0-40[8]

0.25-50[41]

Day-month[29]

20[2] 70 [30] 70-90[8]

500-1000[16]

300-600[16]

200-400[8]

Mature [7]

RFB Electricity[55] [72]

0.03-7[27]

<10 [8] Day-month[29]

10-30[8]

25-35[15]

75-85[27] [8]

12000[45][16]

600-1500[16]

150-1000[8]

Demo/earlycommercialized[41]

CAES Electricity[55] [72]

5-300[50]

£250[28]

Day[29]

30-60[50]

2-6at70-200bar[47]

60-79[16]

8000-12000[7]

1250[47]s

50-100[8]

Demo/earlycommercialized[41]

PHES Electricity[55] [72]

<3100[55]

Small:£5000Large:£140000[41]

Day-month[47]

0.28at100m[30]

0.28at100m[30]

65-82%[56][47]

10000-30000[7]

600-2000[52]t

80-200[8]

Mature [7]

Hydrogen Electricity[55] [72],Thermal

Varies Varies Hours-months[31]

33330[61]

2.7-160at1-700bar[29]

20-50[8]

6-20[8]

Developing/demo[15]

Methane Electricity[63]

Varies Varies 10000[61]

360-1200at200bar

28-45[6]

Developing [73]

23

uFrom2013vFrom2013

[31]SHS Thermal

[55]0.001-10[11]

Day-year[11]

10-50[11]

25 [11] 50-90[11]

0.1-13[11]u

Commercialized[8]

LHS Thermal[55]

0.001-1 [11]

Hour-week[11]

50-150[11]

100[11]

75-90[11]

10-56[11]v

Commercializedforsometemperatureandmaterials [8]

TCES Thermal[55] [72]

0.01-1[11]

Hour-week[29]

120-250[11]

120-250[29]

75-100[11]

Developing/demo[8]

24

ReviewingtheresultsinTable12itisnotedthattheECEStechnologies(LIB,SSB,LABandRFB)ingeneralhavethehighestefficienciesbutareexpensiveandhavefairly limited storage periods. Based on that it is possible to say that thesetechnologies are themost suitable for short-term energy storage applicationssuch as frequently regulations, voltage support and variable supply resourceintegration.The two MES technologies (CAES and PHES) have the highest power andcapacitybutare lesseffective.Bothof these two technologieshavehigh initialinvestment costs and long lifetime that make them profitable mainly in themid/long-termperspective.Thatisreflectedalsoincolumns10andcolumn11in Table 12, the cost is rather low despite the large initial investment cost.Therefore, these technologies can be considered the most suitable forapplicationssuchasarbitrage,blackstartandoff-grid.The EST with the lowest efficiency is linked to the two CES technologies(HydrogenandMethane).Although,aspresentedincolumnfivetheybothhavethe ability to store energy during long time periods, which is an advantagecompared to theother technologies.Due to thevery longstorageperiod thesetwo technologies can be considered the most suitable technologies forapplicationssuchasseasonalstorage.TheTEStechnologiesaremoreproblematictodirectlycomparewiththeothertechnologies since they have a different output. Also, since the results of thethree TES technologies differ rather significantly it is more difficult to makeconsiderationslinkedtotheTEStechnologiesingeneral.However,theyhavetheadvantage of long lifetimes and high efficiency. It must be noted that, asmentionedinsection4.4ThermalStoragetheefficiencydependsonthestoragemediumandisthereforequitevariable.Thesetechnologiesarethemostsuitableforapplicationssuchascombinedheatandpower,wasteheatutilizationsincetheirdesiredoutputmatchestheoutputoftheTEStechnologies.Withouthaving aparticular application inmind, it isdifficult tomake furthercomparisonbasedontheresultspresentedinTable12.Therefore,anumberofapplicationswillbe studied in a case study in order tobe able to answer thethesis’smainquestion“whichofthepresentedESTaremostsuitableforagivenapplication?”.

5.2 Case study: energy storage comparison at three different casesThissubsectionpresents acasestudybasedonthreedifferentcases.ThecasestudyisbasedonthreedifferentkindsofapplicationsthatarefurtherdescribedwithinAppendixA.Other commonapplicationsarealsodescribedwithin thatappendix so that similar studies can be done in the future using otherapplicationsbutstillbasedontheresultspresentedinTable12.

5.2.1 Case nr 1 – Voltage supportFromAppendixAitispossibletofindfollowingconditionsforgivenapplication:Output:ElectricitySize:1-40MWStorageperiod:1second-1minute

25

Cycles:10-100perdayFrom the first condition (output) it is possible to exclude all three TEStechnologiessincetheiroutputisthermal.Fromthesecondcondition(size)itispossibletoexcludethetwoMEStechnologiesbecausetheyprovidesignificantlymorepower.Also, twoof the fourECES technologiescanpossiblybeexcludedsince theirpower is rather limitedand thepricehigher,namely,LIBandRFB.The thirdcondition (storageperiod)makes itpossible toalsoexclude the twoCEStechnologiessincetheyaremoreidealintermsoflong-termenergystorage.Thismeansthatitremainsonlytwopossibletechnologies:SSBandLAB.Theirefficienciesandabilitytoprovidepowerisratherequal.IfchoosingSSBitcanbeassumedthatthe lifetimewouldbemorethandoubledthan ifchoosingtheothertechnology.SSBalsohavetheadvantageofhighercapacityaswellashigher specific energy and energy density. LAB, on the other hand is amorematuretechnologyandhasalowerpowercost.However,SSBhasalowerenergycostand it is thereforerelevant toassume thatSSB is thebest solution in thiscase. In summary: SSB is themost suitableESTwhen the given application isvoltagesupport.

5.2.2 Case nr 2 - ArbitrageFromAppendixAitispossibletofindfollowingconditionsforgivenapplication:Output:ElectricitySize:100-200MWStorageperiod:8-24hoursCycles:0.25-1perdayFrom the first condition (output) all three TES technologies can be excludedsince their output is thermal. The second condition (size) gives the ability toexcludeeverytechnologyexceptfortheMEStechnologiessincetheyaretheonlytwo technologies that can provide enough power. Regarding the two otherconditions, both of the remaining technologies can be considered suitable.Meaning,eitherCAESorPHEScanbeconsideredmostsuitableinthiscase.Tobeginwith, thereareonly twoactualplantsofCAESoperating todaywhilePHES is amoremature technologywith severalplats inoperationworldwide.ThePHESsystemscanbedesigned toprovidebetween a fewMWup toabout3000MW,whichofcoursemakesthenumericvaluesoftheparametersdiffer.InordertomakethetwotechnologiescomparableitwillbeassumedthatthePHESsystemwillberathersmall.Thatofcoursewilldecreasethepowerandcapacityas a result.Nevertheless,PHEShave theadvantageofhigherefficiency, longerlifetime and lower costs. This makes PHES the most suitable EST when theapplicationisarbitrage.

5.2.3 Case nr 3 – Waste heat utilizationFromAppendixAitispossibletofindfollowingconditionsforgivenapplication:Output:ThermalSize:1-10MWStorageperiod:1hour-1dayCycles:1-20perday

26

From the first condition (output) it is possible to exclude every technologyexcept for the three TES technologies. The second condition (size) gives theabilitytoexcludetwoofthethreeTEStechnologies,namelyLHSandTCESsincenoneof them canprovideenoughpowerat thepresent time (2016).Theonlyremaining technology, SHS also meets the two remaining requirements. Insummary: SHS is the most suitable EST when the application is waste heatutilization.

5.3 Other aspects and overall discussionItisimportanttounderstandthatalloftheparametersinteractandaffecteachother.Therefore,theparametershavetobesetinaholisticperspectiveinorderto find the most suitable energy storage solution for a certain application.Similarly,itisimportanttounderstandthatothernone-technicalaspectsshouldbe considered when choosing an EST. Other aspects such as environmental-,social-andethicalaspectsshouldbetakeninaccount.Alsoshouldgeographicalandgeologicalconditions.Thisstudyaimstodevelopaknowledgeguideonlyforafirstevaluation,thereforethesenone-technicalparametersarenotconsideredinthecasestudy.Theywillhoweverbediscussedwithinthissectioninordertounderstanditspossibleimpactofthefinaldecision.Itmustbenoted that consciousness to the environment, seldom leads to lessexpensive solutions, at least in the short term. Nevertheless, it is difficult toignorethedrasticenvironmentaltransformationthathasoccurredoverthelastdecades. The climate is changing and the changes have led to an increasednumber of natural disasters. Phenomenon such as floods, tidal waves anddroughts presently occurswith an increased frequency. In order to avoid anescalation of the climate change it is important to carefully consider theenvironmentalaspectwhencomparingdifferentEST.Forexample,asmentionedin section 4.1 Electrochemical Storage all of the ECES technologies containsubstancesthatare,moreorless,harmfultotheenvironmentandthepeopleinits vicinity. The two chemical storage technologies presented in this thesis,hydrogenandmethane,onlyconsistofnaturalprocessescontainingsubstancesthat are natural for the environment.Thatmakes these two technologies lessharmfulfortheenvironmentandthesocialdemographic,whichshouldbekeptinmindwhilecomparingthesedifferenttechnologies.Regarding social-andethicalaspects it is important to setenergy storage in ahumanandsocialperspective.Itisnecessarytoconsiderquestionssuchas:

· Whatisthegood/rightthingtodo?· Howshouldonebehave?

E.g.,asmentionedinsection4.2.2PumpedHydroEnergyStoragePHESrequirescertain height differences and access to water. This is regardless of thesurrounding area and the peoplewhomight live there.Meaning, in order toinstallaPHESsystemthepeoplewhomighthaveusedthisareaandwaterwillbeforcedtorelocatethemselves.Evenifthissystemwouldfillagreatfunction,it

27

is relevant to consider if it is the right thing to do in a social- and ethicalperspective.Correspondingly, SSB could provide rather inexpensive energy storage withrelativelyhighpowerandcapacity.Asmentionedinsection4.1.2SodiumSulfurBattery, it is thereforeoften consideredanattractive candidate for large-scaleenergystorageapplications.However,itmustbeconsideredthatthesebatteriesconsistofmaterials that shouldbe recycled toavoiddamage theenvironmentandthepeoplewholivethere.Itisreasonabletoassumethatthereisariskthebatterieswillneverbe recycled.From a social-,ethical-andanenvironmentalperspectivethepossibilitytorecyclethecomponentsofthesystemsshouldalsobe evaluated. Furthermore, many of these materials found in the ECEStechnologiesare limitedand tomaintain thenaturalbalance it isnecessary toputtheconsumedamountinproportiontotheavailable.Ifthisisnotcompliede.g.leadwillbeexpendedwithinaperiodof20years[7].InordertochoosethemostsuitableESTforagivenapplicationitisnecessarytoconsiderthegeologicalandgeographicalconditionsintheareawheretheneedofenergystorageareaskedfor.Differentareashavedifferentassetsthatcanbeeither an advantage or a disadvantage depending on the most favorableconditionsfortheEST.Asmentionedinsection4.2MechanicalStoragePHESandCAEScanprovidehighpowerandcapacitybutarelocationlimitedwhichmakesitdifficult to transfer the storedenergyover longerdistances.Therefore, theyare favoredbyhighdemandwithina limitedarea.Hence, ifthestudiedarea islimited and with high demands, the MES technologies are favored but if thestudiedareainsteadisfairlysmall,isolatedandwithoutmajordemandstheMEStechnologiesareunfavorable.AnotherexampleisSHSandLHS.Ifcompareacountryhavingaccesstosunlightfor an increased portion over the year and constantly high temperaturewithanothercountryhavingalotofsnowandratherlowtemperaturestheneedsandassetsaredifferent.Thewarmcountrycaneasilystoreenergy fromthesun inordertoprovideheatwhilethecoldcountrycanstorecoldfromthesnow(ice)inordertoprovidecold. Ifthesetwocountriesshouldbeabletoexchangeandtake advantage of each other’s differences it is necessary to find an energystorage solution that storeandenable transportation rather than storeenergyoveralongerperiodoftime.Itisalsoreasonabletoexaminewhetheritismoreeffective to use the stored energy from the sun to generate electricity, ascompared to a turbine-based generation system.Maybe one solution ismoreefficientfinanciallywhiletheothersolutionismoresuitableinanenvironmentalperspective. Instead,ifthereisanareawithratherdifferentclimate-conditionsdependingontheseasonthechallengeistofindanESTthatcouldprovidelong-termstorage.Itisalsomostoftenimportanttoseeenergystorageinafutureperspective.Theresearch within this subject is rather new when it comes to many of thetechnologies and thepossibilities aswell as the conditionsmight change overtime.E.g.theonlyCAESsystemsinusetodayareusingsaltcavernstostorethecompressed air. France, at the present time (2016) does not have rather

28

favorable conditions since the country lacks large salt deposits. However, asmentioned in section 4.2.1 Compressed Air Energy Storage there is a lot ofongoingresearch.MuchofthenewresearchandprototypesbeingmadewithinCAESisaboutfindingnewstoragecontainersindependentontheavailabilityofsaltdeposits.TherearepromisingconceptswithsubmarineairtanksandsinceFrancehasboththeEnglishChannel,theBayofBiscayandtheBalearicSeatheconditionsareremarkablydifferent ifthatresearchcanbesuccessfullyapplied[47].Therefore, it is important tounderstandboth the futureand thehistoricperspective (earlier tryouts, failuresetc.)of thestorage technology inorder toconsideritsuitableornot.TosummarizetheprospectsforenergystorageinFrance,certainthingsshouldbementioned:thecountry’shillyareasinthesoutheastcombinedwiththemanynuclearpowerplantsadvocatingwideuseofenergystoragebyusingPHESwhilethe lack of salt caverns unfavorable energy storage by using CAES.However,CAESsystemsmightbemoreconvenient if theongoingresearchmentioned insection 4.2.1 Compressed Air Energy Storage could provide possibilities tosuccessfully use alternative storage tanks. The unique test plant called theMYRTLEplatformthatwasmentionedinsection4.3.1Hydrogenprovidesgoodconditions for progress in hydrogen-based energy storage. Furthermore, thecountry,particularlythesouthparthasmanyhoursofsunduringsummer.ThatcreatesthepossibilitytouseTEStechnologiesmorewidelybutsincethepriceofelectricity, as mentioned in section 1. Introduction, is among the lowest inEurope the cost for theTES technologiesprobablyhas todecrease inorder tofullycompetewithheatsystemsgeneratedbyelectricity.

6. Conclusions and future workEvenwith a comprehensive evaluation,with the limited time and resources athesisalwayshassomeaspectsremainingthatcancomplementthestudywithfuture work. This section therefore includes conclusions from this study andfutureworkforcomingstudiesonthesubject.

6.1 Conclusions· Section 4. Energy Storage Technology Mapping includes information

regardingallofthe11technologiesandcanbeusedtofulfillthepurposetoincreasetheknowledgeofdifferentEST.

· Table12 that aims to facilitate the first evaluation ofwhatEST that ismostsuitableforgivenapplicationcanbeusedfortheECEStechnologiesand theMES technologies.However,Table12has somegaps regardingthe CES technologies and the TES technologies leading to certainrestrictions.Asanexample,numericvaluesforcostaremissingforsomeoftheCESandTEStechnologies.Thatmakesitdifficulttocomparethesetechnologies inaneconomicperspective.Although, it is stillpossible tocomparethetechnologiesbasedonmanyotherparameters(e.g.storageperiod, density, efficiency), which should facilitate the choice at leastpartly.

· Thestudycanbeusedasaknowledgeguidetofacilitateafirstevaluationofthemostsuitabletechnologyforagivenapplicationbutotheraspects,

29

suchasenvironmental,socialandethicalhavetobeconsideredinordertomake the final decision. Also, this study only includes a number oftechnologies and in itsmostbasic technicaldesign. In order tomake afinaldecisionitmightberelevanttoexamineadditionaltechnologiesandspecificvariantsofthetechnologiesstudiedwithinthisstudy.

· Thisstudy isbasedon theFrench-contextand thereforeadaptedby thecircumstancesandthecurrentsituationwithinthecountry.Thestudycanbeusedinothergeographicareasbutitisreasonabletostudythatarea’sspecificconditionsandsituation inordertopresentsimilarexamplesofcurrentlyusedapplicationsetc.thathasbeenmadewithinthisstudy.

· The ability to find relevant andprovennumeric values of thedifferenttechnologies inmany casesgoes in linewith the technology’s readinesslevel.Thenumericvalues for thedeveloping technologies (e.g.methaneand TCES) is often linked to a certain research example or so, whichmakes the values differ rather widely. In order not to present amisleadingresult,thesevalueshavenotbeenpresentedwithinthisstudy.

6.2 Future workFuture studies should continue were this study ends. The gaps in Table 12shouldbe filled inordertocompletethecomparisontool.Mostofthegapsarebased on the fact that the given EST is still rather undeveloped and notcommerciallyused.However, there is a lotofongoingresearch,mostcertainlywithin these undeveloped technologies. Namely, there will most likely benumericvaluestofillthegapswithinanearfuture.ThetechnologiesmentionedabovearemainlyCESandTES.Thesewillneedtobe further investigated. Especially the more recent technologies; hydrogen,methane and TCES should be studied in-depth in order to getmore accuratevaluesbutalsogreaterunderstandingofitspotentialandpossibleapplications.Thisstudytreatssomeofthetechnologiesontoday’smarket,butfarfromall.Itwouldbeinterestingtoexamineadditionaltechnologiesinfuturestudies.Inthatway one can make the knowledge guide even more useful. It would also beinteresting todevelopanelectronicprogrambasedon thisstudy. Itcouldbe aprogramwhereonefillinthegivenconditionsanddesiredapplicationandbasedonthismodelgetoneorseveralpurposedEST.Acomputerizedprogramcouldalsoenabletheabilitytocontinuouslyfillthegaporchangecertainvaluesbasedonnewadvances.

30

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36

Appendix ATable13:Commonapplicationsintheenergysystem,includingsomecharacteristicparameters.Basedon[55].

Application Output

Size Storageperiod

Cycles Definition

[MW] [time] [#cycles]

Seasonalstorage

Electricity,thermal

500-2000

Daystomonths

1-5peryear

Compensationforlongersupplydisruptionorforhigherandlowerdemandsdependingondifferentseasons

Arbitrage Electricity 100-2000

8hours-24hours

0.25-1perday

Storingenergywhenthedemandislowandthepriceischeaptosubsequentlysellitduringperiodsofhighpricedenergy,atradebetweentwoenergymarkets

Frequencyregulation

Electricity 1-2000

1minute-15minutes

20-40perday

Tobalanceshiftinginsupplyanddemandthathappenscontinuously,thebalancingwillbeinacontrolareaundernormalconditions

Loadfollowing Electricity,thermal

1-2000

15minutes-1day

1-29perday

Dealingwithsystemfluctuationseithermanuallyorthroughautomaticgenerationcontrol,atimeframebetweenacoupleofmin.to24hours

Voltagesupport Electricity 1-40 1second-1minute

10-100perday

Injectorabsorbreactivepowerinordertomaintainvoltagelevelsinthetransmissionanddistributionsystemundernormalconditions

Blackstart Electricity 0.1-400

1hour-4hours

<1peryear

Allowelectricitysupplyresourcestorestartwithoutpullingelectricityfromthegridincasethepowersystemandallotherancillarymechanismshavecollapsed

Demandshifting&peakreduction

Electricity,thermal

0.001-1

Minutes-hours

1-29perday

Tomatchenergydemandwithsupplyandtoassistintheintegrationofvariablesupplyresourcesenergydemandcanbeshifted.Bychangingthetimeatwhichcertainactivitiestakeplacetheseshiftsarefacilitated.Thisalsogivestheopportunitytoactivelyfacilitateareductioninthemaximumenergydemandlevel

Off-grid Electricity,thermal

0.001-0.01

3hours-5hours

0.75-1.5perday

Tosupporthigherlevelsoflocalresourcesuseandmostlytoensurereliableoff-gridenergysupplies,storagecanbeusedtofillgapsduetodifferencesindemandandsupplyresources

Variablesupplyresourceintegration

Electricity,thermal

1-400 1minute-hours

0.5-2perday

Tooptimizetheoutputfromvariablesupplyresources,mitigatingchanges(rapidorseasonal)inoutputandinordertoincreasesupplyqualityandvaluebridginggaps(temporalorgeographic)betweensupplyanddemand

Wasteheatutilization

Thermal 1-10 1hour-1day

1-20perday

Temporallyorgeographicallydecouplingheatsupplyanddemandbyusingpreviouslywastedheat

Documents

Energy Storage Technology Comparison953046/FULLTEXT01.pdf · most commonly used energy storage technologies. Also, the work aimed to collect numeric values of number of common parameters