Bucher, K.
November 1997
Fuel and Energy Abstracts, vol 38-6, p. 416
Standard test conditions (STC) are taken into consideration when optimizing solar cells and modules. These conditions are an irradiation of 1000 W/m2, a module temperature of 25°C and the standard spectrum AM 1.5, but they do not correspond to real operating conditions of Photovoltaics: in Freiburg, Germany, 50% of the total irradiation is in the interval below 600 W/m2, but in Sudan, Africa, this amounts to only 20%, for example. As a result, PV modules under real conditions may perform up to 30% (on a monthly scale) lower than at STC, depending on the weather and the module/cell design. Means to derive a rating of outdoor performance from indoor module measurements are presented, and the variation of the module performance ratio with yearly or monthly irradiation sums and average temperatures is given. A linear correlation between performance ratio and the yearly average daytime temperature at a site is observed.
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