Meteorological, Optical and Thermal Histories for Energy Rating in Photovoltaics (MOTHERPV): This is still an experimental method in development by CEA. It allows the prediction of the performance ratio (PR) for sites with a good knowledge of the frequency distribution function of the incoming energy and the module back temperature as functions of irradiance. This prediction requires a short campaign of measurements in a given site with enough irradiance and temperature levels. For each level of irradiance, the module efficiency is translated from the efficiency measured during the reference period, according to the formula in equation 3: