Page - 89 - in Short-Term Load Forecasting by Artificial Intelligent Technologies

Energies2019,12, 57 Wecalculatedthe initial costs Jki(b, s,w) andtheoperationcosts J l o(b, s,w) as follows: Jki(b, s,w) =Ck·nk·CRFk (5) Jlo(b, s,w) =Cl·nl (6) inwhichCandnare thepriceperunit and the installedunits, respectively, for eachcomponent k. CRF representedthecapital recoveryfactor thatwasdefinedas [32,33,39]: CRF= ir(1+ ir)ny (1+ ir)ny−1 (7) where ir is the inflationrate,whichwassetas1.26%inthispaperbyreferringto theaverageannual changeofconsumerpriceindexofTaiwan[39],andny is theexpectedlifeof thecomponents. Theprice andexpected lifeof thecomponentsare illustrated inTable4wereusedtocalculate thesystemcosts in the followingexamples. Table4.Component lifeandprice [32,33,39]. Component Life (year) Price ($) Hybridsystem 15 N/A Windturbine (3kW) 15 9666 PVarrays (1kW) 15 1833 Powerelectronicdevices (6kW) 15 1666 ChemicalH2generation 15 10,666 NaBH4 (60g) N/A 0.33 Electrolyzer (2.5kW–500L/h) N/A 10,666 PEMFC(3kW) N/A 6000 Battery (48V–100Ah) N/A 866 (2) Systemreliability: thereliabilityof thehybridsystemwasdefinedas the lossofpowersupply (LPSP)as follows[32,33,39]: LPSP= ∫ LPS(t)dt∫ P(t)dt (8) inwhichLPS(t)was theshortage (lost)ofpowersupplyat time t,whileP(t)was thepowerdemandof the loadprofileat time t. Therefore, ∫ LPS(t)dt indicatedthe insufficientenergysupplyand ∫ P(t)dt represented the total energydemand for the entire simulation. If the power supplymet the load demandatall times, (i.e.,LPS(t)=0,∀t), thenthesystemwascompletelyreliablewithLPSP=0. (3) Systemsafety: systemsafetywasdefinedas theguaranteed sustainableperiodof thehybrid powersystemunderextremeweatherconditionswhennosolarorwindenergywasavailable. Suppose theenergystored in thesystemwasEstoreandtheaveragedailyenergyconsumption wasEday; then, thesystemsafetycanbedefinedas follows: Safety= Estore Eday (9) For example, averagedaily energydemand is 19.96, 30.41, and22.32kWh for thehousehold, laboratory, and office, respectively (see Table 3). Therefore, if the energy stored in the battery and hydrogen is 60 kWh, the system safety is 3.01, 1.97, and 2.69 days for the laboratory, office, andhousehold, respectively.Whenconsideringtheefficiencyof thebatteryandinverterbothas90%, thenthesystemsafety is2.70,1.78,and2.42days, respectively. 89