Site dependence of the energy collection of PV modules
Solar Energy Materials and Solar Cells, (1997)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.