In a photovoltaic power plant, cells and panels often work under non-standard conditions due to mismatch between modules or due to non-uniform sun irradiation. These working conditions are at the origin of electrical and thermal stresses creating hot spots that can go as far as the complete degradation of the module. In this contribution, we analyse the influence of the combined electrical and thermal stresses generated under dark and light conditions on the electrical efficiency and functional parameters of silicon based photovoltaic modules. To simulate the effect of the stress that can occur under standard working conditions, various reverse currents were injected under various temperature levels and irradiation powers in standard low-power commercial modules based on these experimental characterizations, changes in the efficiency and parameters of the cells and modules exposed to shadow effects are compared to that in normal working mode. Based on punctual I-V measurements, the characterization of the changes of the series and parallel resistances of PV modules produces good indicators of the aging, the health and local degradations as hot spots and allows to evaluate the effect of electrical stress under a given temperature on the performance of PV solar modules. Indeed, whatever is the temperature, the electrical stress created by a reverse current under light induced greater changes in both series and parallel resistances than applied in dark. This work points the huge degradation of performances of photovoltaic modules in abnormal working mode