PVsyst's forum

During the sizing time, the overload estimation results of a very quick and coarse calculation, using the histogram representation of the output of the array along the year. This histogram involves global parameters like an average array temperatures for each power class, and doesn't take all losses into account. Moreover, it is based on the monthly irradiation values of the project's site, which may not be the same as the Meteo file's values. Therefore, the loss estimation of this sizing tool is not quite accurate, and is often overestimated.

The "exact" value can only be obtained with the detailed hourly simulation. This gives usually lower overload losses, as all the the losses of the array are correctly taken into account.