Abstract
Today, solar cells and modules are optimised and rated with respect to standard test conditions (STC), i.e. for an irradiation of 1000 W/m 2, a module temperature of 25°C and the standard spectrum AM 1.5. However, these conditions do not correspond to real operating conditions of Photovoltaics: In Freiburg, Germany, 50% of the total irradiation is in the interval below 600 W/m 2, but in Sudan, Africa, this amounts to 20% only. Module temperatures vary between −20°C and 80°C, light incidence angles between 0° and 90°. As a consequence, the performance of PV modules under real conditions can be 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 will be 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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