Reliable diagnostic methods are essential for assessing the condition of photovoltaic (PV) panels and detecting early-stage degradation. Conventional methods such as I–V measurements and electroluminescence imaging are widely used but often fail to capture subtle changes before noticeable power loss occurs. Electrochemical impedance spectroscopy (EIS) has emerged as a complementary approach, capable of analyzing resistive and capacitive processes associated to material and contact degradation. However, traditional EIS implementations typically rely on analyzers and conditioning circuits that are bulky and unsuitable for portable diagnostics. To address these limitations, this work presents a portable PV impedance measurement system developed using the STEMlab 125-14 platform in combination with a dedicated conditioning circuit for utility-grade panels. The approach was demonstrated on a 200 W monocrystalline PV panel, and the extracted impedance parameters were validated against measurements from a Solartron 1260 frequency response analyzer (FRA). Quantitatively, the comparative study showed that Rp values deviated by less than 2%, while Cp differences remained below 1%.
