Page - 83 - in Short-Term Load Forecasting by Artificial Intelligent Technologies

Energies2019,12, 57 ofPEMFCsystems. For instance,WooandBenziger [3] tried to improvePEMFCefficiencyusinga proportional-integral-derivative(PID)controller toregulatethehydrogenflowrate.Vega-Lealetal. [4] controlled the air and hydrogen flow rates to optimize the PEMFCoutput power. Parketal. [5] considered load perturbations and applied a slidingmode control tomaintain the pressures of hydrogen andoxygen regardless of current changes. Wang et al. [6] designed a robust controller to regulate theairflowrate toensure that thePEMFCprovidedasteadyoutputvoltage. This idea was further extended to amulti-inputmulti-output (MIMO) PEMFCmodel to reduce hydrogen consumptionwhileprovidingasteadyvoltage [7]. Reduced-orderrobustcontrol [8]androbustPID control [9]werealsoproposedforhardwaresimplificationandindustrialapplications. A PEMFC can supply sustainable power as long as the hydrogen supply is continuous; therefore, the PEMFC has been widely applied in transportation [10–19] and stationary power systems [20–29]. APEMFC can also supply sustainable energy regardless ofweather conditions, makingitareliablepowersourcewhensolarandwindenergyareunavailable.However, theprice of hydrogen energy is generally highwhen compared to other green (e.g., solar) energy, so the PEMFCis typically integratedwithotherenergysourcesandstoragesystemsto formhybridpower systems. Forexample,Zervasetal. [30]presentedahybridsystemthatcontainedphotovoltaics (PV), aPEMFC, and an electrolyzerwithmetal hydride tanks. Rekioua et al. [31] considered a hybrid photovoltaic-electrolyzer-fuel cell system anddiscussed its optimization by selection of different topologies.Nizeticetal. [29]proposedasystemforhouseholdapplicationthatusedahigh-temperature PEMFCtodriveamodifiedheatpumpsystem,withacostof less than0.16euro/kWh. Theroleof thePEMFCinhybridpowersystemsisunique,because it canactasbothanenergy sourceandanenergystoragesystem. It servesasanenergysource toprovidebackuppowerwhen the loadrequirement isgreater thantheenergysupplyfromotherenergysourcesandasanenergy storagesystemtostorehydrogenelectrolyzedbyredundantenergywhentheenergysupply isgreater thantheconsumption[32]. Somehybridpowersystemshaverecentlybeen implemented inpractice. For instance, Singhet al. [22] presentedaPEMFC/PVhybrid system for stand-alone applications in India. Das et al. [23] introduced the PV/battery/PEMFCandPV/battery systems installed in Malaysia. Al-Sharafi et al. [24] considered six different systems in theKingdomof SaudiArabia. Martinez-Lucasetal. [25] demonstrated a systembased onwind turbine (WT) andpump storage hydropowerontheCanaryIslandofElHierro,Spain.Kazemetal. [27]evaluatedfourdifferenthybrid powersystemsonMasirahIsland,Oman. Because of the influence ofweather conditions and loads, the costs of these hybrid systems can be optimized by changing the system configurations. For example, Ettihir et al. [26] applied theadaptive recursive least squaremethod tofind thebest efficiencyandpoweroperatingpoints. Singhetal. [22]appliedafuzzylogicprogramtocalculatesystemcostsandconcludedthat thePEMFC andbatteryare themostsignificantmodules formeeting loaddemands lateatnightandintheearly morning.Kazemetal. [27] showedthat thataPV/WT/battery/dieselhybridsystemhadthe lowest cost forenergyproduction.Cozzolinoetal. [28]analyzedtheTunisiaandItaly (TUNeIT)Projectand showedthat thisalmostself-sustainingrenewablepowerplant,consistingofaWT,PV,battery,PEMFC, anddieselengine, ranatacostof0.522€/kWh.Wangetal. [33]studiedahybridsystemthatconsisted ofaWT,PV,battery,andanelectrolyzerandconcludedthat thecostsandreliabilityofhybridpower systemscanbegreatly improvedbyadjusting thecomponent sizes. Theyalso showed thatpower managementcanhelptoreducesystemcosts [32]. Thepresentpaperextendsthese ideasbydiscussing the impactsof loadprofilesontheoptimizationofsystemcosts.Weappliedthree typical loadprofiles toahybridsystemanddiscussedthecostandenergydistribution.Wealsoevaluatedtheguaranteed operationdurations (calledsystemsafety)ofhybridsystemsanddiscussedtheapplicationsof two methods toextendsystemsafety. Theremainderof thispaper isarrangedas follows: Section2 introduces thegreenbuildingand itshybridpowersystem.Basedonthesystemcharacteristics,webuildageneralhybridpowermodel consisting of solar cells,WTs, batteries, a PEMFC, hydrogen electrolysis, and chemical hydrogen 83