Impedance Spectroscopy for Diagnosis of Photovoltaic Modules Under Outdoor Conditions

This work is aimed at detecting degradation phenomena on photovoltaic (PV) panels working under real outdoor conditions by using the impedance spectroscopy technique. The impedance is measured by leaving the PV panel in the real-operative status corresponding to the maximum power point without altering its power production. Since variations on the series resistance are associated with multiple degradation phenomena, this study seeks to estimate changes in this parameter using a dynamic model fitted to the experimental impedance measurements. An external resistor is added in series to the PV panel for emulating the degraded conditions. Hence, the PV panel impedance measurements are compared in nominal and degraded conditions. The results show that the dynamic model provides higher accuracy in comparison with the series resistance variation identified through the single-diode model, which is the most usual approach. Thus, it is demonstrated the feasibility of detecting degradation effects by using the dynamic model of PV panels working under outdoor conditions.