Page - 93 - in Short-Term Load Forecasting by Artificial Intelligent Technologies

Energies2019,12, 57 i.e., thebattery ischargedbytherenewableenergyso that itsfinalSOCisgreater thanthe initialSOC. Fourth, thecostsof thesolarpanels,battery,andthePEMFCsystem(includingthechemicalhydrogen production system, PEMFC, andNaBH4) are about 40%, 25%, and20%, respectively, for all loads. That is, thecost distributions are almost the same for all systemsafter optimization. Finally, solar energyprovidednearly100%of therequired loaddemandsbecause thecurrenthighcostofhydrogen requires that thesystemavoidusingthePEMFCunlessnecessary. Thecurrentoptimalcostsare0.794, 0.660, and 0.791 for the household, lab, andoffice loads, respectively. Although the costs cannot competewith thegridpower, thesystemprovidesaself-sustainablepowersolutionfor remoteareas andislandswithoutgridpower. Theenergycostcanbegreatlyreducedwhenthecomponentprices are reducedwithpopularity. Forexample, theanalyses in [33] indicated that thecriticalhydrogen price isabout10NT$/batch (onebatchconsumes60gofNaBH4 toproduceabout150Lofhydrogen). That is,morehydrogenenergywillbeused inanoptimalhybridpowersystemif thehydrogenprice is less than1/15NT$/L. Table8.Costandenergydistributions for theoptimalsystems. House Lab Office Dailyaverage (kWh) 19.96 30.41 22.32 Optimalcost ($/kWh) 0.794 0.660 0.791 Optimalsizes (b, s,w) (23,15,0) (27,21,0) (26,17,0) CostDistribution(%) Lead-acidbattery 25.34% 23.50% 25.72% Powerelectricdevices 10.59% 11.72% 11.41% Windturbine 0 0% 0% Solarpanels 39.72% 43.91% 40.41% Chemicalhydrogenproduction 13.56% 10.71% 12.18% PEMFC 7.63% 6.03% 6.85% Sodiumborohydride (NaBH4) 3.16% 4.13% 3.43% EnergySupply Distribution(%) Wind 0% 0% 0% PEMFC 1.27% 1.35% 1.36% Solar 100.65% 100.30% 98.50% Battery −1.92% −1.65% 0.14% 3.5. SafetyAnalyses Theoptimizationdesigns illustrated inTables5–7werebasedonhistoricalweatherdata,where thesolarandwindenergyco-assistedthesustainabilityof thepowersystem.Because theaimof the hybridpowersystemis toprovideuninterruptedpower,wefurther investigated itsability toperform inextremeweatherconditionswhennosolarorwindenergy isavailable. Weapplied theoptimalsettings inTables5–7 to thehybridpowermodelandrecordedthe lowest batterySOCduringthe61-daysimulation tocalculate the lowest remainingenergyandsystemsafety byEquation (9). The results are illustrated inFigure 9 andTable 9,where the lowest SOC (stored energy) for thehousehold, laboratory,andoffice loadswere29.99%(11.03kWh),26.04%(7.83kWh), and27.18%(8.97kWh), respectively. Therefore, theequivalentsustainableoperationperiodsof the systemare0.49,0.23,and0.36days, respectively, consideringtheaveragedailyenergyconsumption showninTable3andassumingabatteryefficiencyof90%. Ifa longersustainability isrequired,wecan adoptsub-optimalsettings. Forexample, theminimalsettingsandcosts tosustain1dayor2daysare labeledinFigure9. Supposethesafetyrequirement is1day; then, the lowestsystemcosts toguarantee 1dayofoperationare0.8952USD/kWh,0.7603USD/kWh,and0.8735USD/kWh,respectively, for the household, laboratory,andoffice loads. Thecorrespondingcomponentsizesare (b, s,w)= (33,26,0), (b, s,w)= (40,24,0), and(b, s,w)= (40,17,0), respectively. Anotherway to extend theguaranteed systemsustainability is touse the chemical hydrogen generation system to produce hydrogen for the PEMFCas ameans of providing back-uppower. Referring to [36], onemoleofNaBH4 cangenerate fourmolesofhydrogen, so20kgofNaBH4 can produce4.16kgofhydrogen,whichwouldprovide63kWhofelectricity for thesystem.Therefore, a furthersustainabilityguarantee ispossiblebystockingmoreNaBH4with theauto-batchingsystem 93