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Energies2018,11, 1948 valveis installedatthehydrogenoutlet,hydrogenisproducedonlywhentheelectrolyzerpressureexceeds thecylinderpressure,withaproductionrateofabout1.14SLPMbyconsumingabout413W.Thehydrogen ispurgedevery350stopreventwaterfloodingthatcoulddisturbtheelectrochemicalreactions.Theoutput hydrogenenergycanbecalculatedusingthefollowingequation: H2+ 1 2 O2→H2O(g) (3) The total enthalpychangeofa reactionat1atm,25 ◦C, referred toas thestandardstate, is the lowheatvalueofhydrogen,which is equivalent to241.32kJ ·mol−1 (or 120MJ ·kg−1). Therefore, thehydrogenproductionefficiencycanbedefinedas follows: ηLHV= Efuel,production Egenerator = HExp2 ·LHV Egenerator (4) whereEgenerator andEfuel,production represent theratioof inputelectricenergyandtheoutputhydrogen energy, respectively,andHExp2 is theproducedhydrogen. Forexample, inoneexperiment, the input electric energywas Egenerator = 0.0372 kWh, and the output hydrogen volumewas H Exp 2 = 6.233 L. The standardmolecularweight anddensity of hydrogenwas 2.0158 g/mole and 0.08228 g/L, respectively. Therefore, theoutputhydrogenenergycanbecalculatedas follows: Efuel,production= 6.233×0.08228×241.32 2.0158×3600 =0.01705 (kWh) Hence, thehydrogenproductionefficiencywas: ηLHV= Efuel,production Egenerator = 0.01705 0.0372 =45.83% Thehydrogenproductionefficienciesinalltheexperimentswereabout45%.Basedontheexperimental results, thehydrogenproductionratewassetasfollowstoconvertrenewableenergytohydrogenstorage: H2= ηLHV LHV ·E=0.0465 (L/kJ) As the electrolyzer consumes an average power of 410 W during the production period, thehydrogenelectrolyzermodulewasset toproducehydrogenatarateof1.14L/minbyconsuming redundantrenewableenergyataconstantpowerof410W. 7LPH V 7HVW RI +\GURJHQ 3URGXFWLRQ ZLWK / +\GURJHQ 6WRUDJH &\OLQGHU 3UHVVXUH %DU 0DVV )ORZ 6/30 7LPH V ,JHQHUDWRU $& 7LPH V 3JHQHUDWRU : :DUP XS 3URGXFWLRQ 6WDQGE\ Figure5.Experimental responsesof thehydrogenelectrolysis system. 200