Characterizing photovoltaic module power degradation through impedance spectroscopy: Transitioning to outdoor applications

Impedance spectroscopy (IS) shows strong potential as a diagnostic tool for Characterizing degradation in photovoltaic (PV) modules, yet its application in real-world systems remains challenging. This study investigates the critical differences between individual cells and PV modules, as well as the impact of environmental factors on IS characterization, enabling its transition from laboratory settings to outdoor environments. Cell mismatch in PV modules causes non-uniform voltage distribution under forward bias, but at zero bias and near open-circuit voltage, voltage allocation becomes uniform, making zero bias a promising diagnostic point. And a novel metric the ratio of the imaginary peak impedance to parallel resistance was introduced to quantify non-uniformity, promising quantitative identification of PV module degradation. Bypass diodes significantly interfere with impedance measurements at zero bias, while PV modules are highly sensitive to ambient lighting. To address these challenges, an illumination compensation model was developed and validated through testing Al-BSF modules under nighttime outdoor conditions. Finally, testing four PV modules with varying power degradation levels confirmed IS as an effective diagnostic tool. These findings bridge the gap between laboratory research and real-world applications, offering actionable insights for the deployment of IS as a reliable, non-invasive diagnostic technique for PV systems.