Photovoltaic (PV) systems have been successfully used for over five decades. The output characteristics of PV cell depend on the environmental conditions. For any solar cell, the model parameters are function of the temperature and the irradiance values of the site where the panel is placed. In this paper the performances of PV cells are analysed related to the different irradiance level by using the circuit sensitivity. Therefore the model parameters of the equivalent circuits for typical PV cell are characterized by first-order sensitivity relations. LabVIEW and MatLab applications are implemented to prove the theoretical models. Numerical examples taken from real case on PV cells are provided.