In this paper, we have presented the results of the characterization and the fine modelling of the electric characteristics current-voltage and power-voltage of the photovoltaic (PV) panels. We have analyzed the electric parameters of PV cells and the optimal electric quantities of PV panels (voltage and power) according to the meteorological conditions (Temperature, solar irradiation). The obtained results show that the diode parameters of the PV cells depend on solar irradiation: the saturation current increases with solar irradiation. This induces a decrease of the optimal voltage with solar irradiation: when the solar irradiation varies from 300W/m² to 900W/m², the optimal voltage decreases by 11 %. These results are confirmed by the measures of the manual regulation of the maximum power point (MPP) during one day. Also, we have analysed qualitatively the performances of the associated panels in parallels and in series.