The present work has been performed at Politecnico di Torino and at the Univeristy of Jaen. The rated power of a PhotoVoltaic (PV) module is provided by the manufacturer in Standard Test Conditions (STC), corresponding to cell temperature Tc=25 °C and irradiance G=1000 W/m2. However, PV generators generally work in very different conditions and, in order to assess their performance, several models have been developed in literature. The Osterwald Model (OM) is the most used, in which, generated power is proportional to irradiance and dependent on temperature by the γ coefficient, provided by the manufacturer. Even if this model is one of the most accurate, it presents a not negligible error regarding the estimation of the maximum power and the productivity of a PV module (3%-6%).