Detection of Series Resistance Degradation in PV Modules Using Measured Current-Voltage and Frequency-Domain Impedance

Model-based parameter identification methods are widely used to monitor the condition of photovoltaic (PV) modules. Series resistance is a key parameter for detecting PV module aging, as it typically increases with degradation. This paper compares three parameter identification approaches for tracking changes in series resistance: the Single Diode Model (SDM), the recently proposed Double Single Diode Model (D-SDM), and a dynamic model based on the Constant Phase Element (CPE). Measured current-voltage and frequency-domain impedance data from a commercial PV module under uniform irradiance conditions are used to fit the corresponding models. The series resistance of the PV module is estimated in both its nominal state and with an additional series resistor to simulate degradation. The results indicate that while the standard SDM captures resistance changes, it exhibits greater fluctuations across varying irradiance levels. In contrast, the D-SDM and CPE-based approaches provide more stable and reliable resistance estimates, making them better suited for accurate degradation detection.