Techno-economic modelling of a Power-to-Gas system based on SOEC electrolysis and CO2 methanation in a RES-based electric grid

Renewableenergysources(RES)aregrowingrapidlyasanalternativetofossilenergysourcesinordertodisjoin thesocietyfromcarbonsources.Windandphotovoltaicpowergenerationisintermittentduetoweatherconditions.Therefore,remarkablecentralityisgiventothestorageoftheelectricexcessofproduction,andPowerto-Gas (P2G) systems seem to be one of the most promising technologies to achieve this purpose. In the case analysedinthisresearch,ahightemperatureelectrolyserbasedonsolidoxidecellstechnologywasconsidered, coupledtocatalyticreactorsforthehydrogenationofcarbondioxideintomethane.Theproductisasynthetic naturalgas(SNG)whichcouldbydirectlyinjectedintothenaturalgasdistributionnetwork. ThisworkinvestigatesthecouplingbetweenacompletelyRES-basedelectricprofileinafuturescenarioanda P2Gplanttoperformacomprehensivetechnical,managementalandeconomicassessmentofthesystem.AP2G modelwasbuiltonMATLABenvironmenttoexaminetheP2Gplantbehaviourwhenitwascoupledwiththe RES-based intermittent electric profile. Firstly, the P2G plant arrangement has been discussed by varying the P2Gplantcapacitywhichhasbeencoupledtotheelectricprofile;theP2Gcapacitywasthenselectedbasedon thelevelized cost ofproduct (LCOP).Secondly,the electrochemicalstoragehasbeenintroduced toperform a continuing operation also when excess of electricity is not available, thanks to the storage of electric energy. Finally,chemicalstoragetanksofhydrogen(feedforthemethanation)andsteam(feedfortheelectrolyser)were consideredtoreducethenumberofshutdownsoftheP2Gplant.Anassessmentofthelong-termgasstoragein thegasdistributionnetworkwasadditionallyperformed. Anoptimalplantcapacitywithrespecttotheinvestigatedscenariooflocalelectricresidualprofilewassized, beingequalto7MW,witharecoveryequalto70%ofthetotalavailableelectricenergyfromthegrid.Moreover, theP2Gsystemcouldbeeconomicallycompetitive,becausetheLCOPvariesbetween60.2€/MWhand224.9€/MWh (LHV basis), which suits with current levelized natural gas prices. The overall efficiency of the plant reachedaround77%,withaplantutilizationfactorofabout30%.Theaccumulatorsandtheelectrolyserarethe mostexpensivetechnologies,andtheLCOPstronglydependsontheirsize(ifthebatteriesareconsidered).For thisscenario,theSNGyearlyproductivityreachedavalueof18.5GWh/y(LHVbasis):inthehypothesisofusing SNGtorepowertheelectricgrid(efficiency45%),suchaP2Gplantcouldcompensatethe29.6%oftheamount ofdeficitenergy,withaconsequentreductioninCO2 associatedemissions.