ACTA TECHNICA CORVINIENSIS - Bulletin of Engineering

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ACTA TECHNICA CORVINIENSIS – BULLETIN of ENGINEERINGway to compare the energy produced by PVsystems of differing size.The specific plant losses are describedthrough L C - capture losses, losses that arecaused by obfuscation, temperature grown,mismatching, limitation through dust, lossesgenerated by energy conduction in thephotovoltaic modules and L S – system losses,caused by inverter, conduction and loses ofpassive circuit elements.The reference yield Y r is the total in-planeirradiance H divided by the PV’s referenceirradiance G. It represents the under idealconditions obtainable energy. If G equals 1kW/m 2 , then Y r is the number of peak sunhours or the solar radiation in units ofkWh/m 2 . The Y r defines the solar radiationresource for the PV system. It is a function ofthe location, orientation of the PV array, andmonth-to month and year-to-year whethervariability:E PVY A = (2)PmaxG,STCTo compare on different locations mountedgrid connected PV systems, the performanceratio is a decisive value [2]. The performanceratio is the Yf divided by the Yr. Bynormalizing with respect to irradiance, itquantifies the overall effect of losses on therated output due to: inverter inefficiency,wiring, mismatch and other losses whenconverting from d.c. to a.c power, PV moduletemperature, incomplete use of irradiance byreflection from the module front surface,soiling or snow, system down-time andcomponent failures.E PV,ACY f = (3)Pmax G,STCPerformance ratio PR values are typicallyreported on a monthly or yearly basis. Valuescalculated for smaller intervals, such asweekly or daily, may be useful for identifyingoccurrences of component failures. Becauseof losses due the PV module temperature, PRvalues are greater in the winter than in thesummer and normally fall within the range0.6 to 0.8. If the PV module soiling isseasonal, it may also impact differences in PRfrom summer to winter. Decreasing yearlyvalues may indicate a permanent loss inperformance. Considering the increasingdegree of effectiveness, the performance ratioPR factor can reach ideal annual valuesbetween 0.8 and 0.84.The PR being a dimensionless quantity thatindicates the overall effect of losses [5] on therated output, does not represent the amountof produced energy, because a system withlow PR in a high solar resource locationmight produce more energy than a systemwith a high PR in a low solar resourcelocation. However, for any given system,location and time if a change in componentor design increase the performance ratio PR,the final yield Yf increase accordingly. PRvalues are useful for determinations if thesystem is operating as expected. Largedecrease in PR indicates events thatsignificantly impact performance, such asinverters not operating or circuit-breakertrips. If the PR decrease moderate or small, itindicates that a less sever problem exists. Theperformance ratio PR can identify theexistence of a problem, but not the cause. Toidentify the cause of the existing problem, aresearch at the site is needed.GRID CONNECTED PHOTOVOLTAIC PLANT ATTHE UNIVERSITY ‘EFTIMIE MURGU’ RESITAThe grid connected photovoltaic system [3]mounted at the ‘summer theater’ of theUniversity `Eftimie Murgu` Resita, sincemiddle of may 2008, is putted together fromfour high performance standard solarmodules of type Multisol 150, manufacturedby Scheuten Solar – Germany [6], with a totalcapacity of 600W/h. The system is completedwith a Sunny Boy 1100 inverter and acompletely online monitoring system of thePV, made from a Sunny Webbox and theSunny Sensorbox. This monitoring system [4],build up like in figure 1, allows a detailedsupervision of the PV plant, produced energy,measuring and saving values of solarradiation, ambient and module temperature,wind speed and direction.The measured values and the current energyyield are visualized and archieved in theInternet, through the sunny web portal [7], figure2.642010/Fascicule 2/AprilJune /Tome III
ACTA TECHNICA CORVINIENSIS – BULLETIN of ENGINEERINGdetailed, daily, overview of the yield factor in theanalyzed period is given in table 1.Table 1 Daily Specific Yield FactorFigure 1 Complete scheme, photovoltaic andmonitoring systemSPECIFIC YIELD FOR THE SOLAR PHOTOVOLTAICGRID CONNECTED SYSTEM AT THE EFTIMIEMURGU UNIVERSITYThis paragraph allows us an overview of thespecific yield factor Y A for the grid connectedphotovoltaic system, for a time period of almostone year, from middle of May 2008 until the endof March 2009.Figure 2 Sunny web portal on-line monitoringkWh, 180kWh/kW 160140120100806040200Energy production and Specific Yieldmay 08jun 08jul 08aug.08sep.08oct.08nov 08dec.08jan 09feb.09mar.09MonthEnergy prduction[kWh]YA [kWh/kWp]Figure 3. Energy production and array yieldFigure 3 represents the energy production andthe specific yield factor for this period. A more160,00140,00120,00100,0080,0060,0040,0020,000,00Specific Yield FactorkWh / kW 180,003130may2008jun.2008jul .2008aug.2008sept .2008oct .2008nov.2008dec.2008jan .2009febr.2009mart.2009Figure 4 Daily yield factor, May 2008 – March 2009CONCLUSIONSAnalyzing the specific yield factor, thephotovoltaic plant owner can have apermanent look of the time, in hoursexpressed, that the system works in STC andobtains indicate or a higher energy29282726252423222120191817161514131211109876543212010/Fascicule 2/AprilJune /Tome III 65
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