Dear Mr. Mermoud, on Fri Aug 17, 2012 4:58 you posted at "Simulations : results" following: Now if you start from Meteo data in monthly values, the synthetic hourly data file is constructed using a stochastic process: with 2 different executions you will have completely different years (sequences of days and or hours in a day). This may lead usually to discrepancies of the order 0.5 to 1% in the yearly result. These are indeed unavoidable uncertainties due to the stochastic models used. Therefore if you want to perform a quite identical simulations as a colleague, you have to share the exact hourly meteo file used (*.MET). Former i have used the programm WetSyn for creating hourly meteofiles. By using the program WetSyn it was possible to fix the stochastic factor. When different users have used the same factor the same values have been calculated. Could it be possible to do the same in PVsyst. Maybe two different versions. One like now by using a random variable and another version by choosing the variable to fix it?