Identification of Series Resistance from the Measured PV Panel Electrical Characteristics

The condition of a solar PV panel can be evaluated by its measured electrical characteristics. The singlediode model parameters extracted from a measured current-voltage curve may indicate the possible presence of degradation. Aging of PV cells is a common source of degradation and manifests itself typically in increased series resistance values, causing a decline in the voltage characteristics of a PV panel. However, the current and voltage characteristics of a PV panel change considerably with changing environmental conditions, especially with changing irradiance and temperature. Accordingly, the single diode model parameter values change along variations in the surrounding environmental conditions, making the comparison of any two distinct current-voltage curves measured in outdoor conditions difficult. This gives a reason for converting the identified single diode model parameters of a measured curve from actual operating conditions to common reference conditions. In this light, we study the relation between the PV panel voltage and series resistance under different environmental conditions. We also investigate the feasibility of parameter reversion back to standard test conditions.