Experimental Assessment of Partial Shading Detection in PV Panels Using Impedance Spectroscopy

This article investigates the use of Impedance Spectroscopy (IS) to identify mismatches in Photovoltaic (PV) panels/string/array, particularly for detecting partial shading effects. The findings confirm IS as a promising tool for on-field applications, especially in small-scale urban power plants where partial shading is a common issue. An analysis of several experimental impedance spectra measured with PV panels operating at their Maximum Power Point (MPP), with controlled partial shading conditions, reveals that partial shading induces a characteristic double-arc deformation. This feature could be leveraged in a diagnostic tool for mismatch detection. The key advantage of this approach is its ability to perform IS measurements at MPP, preserving the normal operating conditions of the PV panels/string/array. Additionally, IS requires minimal modifications to the system's architecture and integrates easily into existing power electronics interfaces. To validate the consistency of impedance spectra under partial shading, experimental data were compared with two models: a Constant Phase Element (CPE) model adapted for PV strings in non-uniform conditions and an enhanced Single-Diode Model (SDM) developed for SPICE3-based simulations. The results confirm that IS successfully adjusts the models and detects mismatches in both experimental and simulated scenarios, demonstrating its scalability and effectiveness as a state-of-the-art PV diagnostic tool.