Diagnosing PID in Field Electroluminescence Inspections of PV Modules Using Multilevel Forward Current Biasing

Potential-induced degradation (PID) in photovoltaic (PV) modules can be identified using electroluminescence (EL) imaging by comparing the luminescence of degraded cells to that of healthy cells. In nondegraded modules, cells exhibit consistent radiative recombination and luminescence properties, whereas PID alters these, creating measurable differences. This work presents a methodology to quantify relative changes in luminescence between degraded cells and a reference cell within the same module by acquiring EL images at two distinct current injection levels. The resulting metric enables automatic PID characterization and reduces reliance on subjective visual interpretation. The approach was further adapted for daylight field EL inspections using a multibias modulation technique, which introduces an intermediate current bias between high-current injection and open-circuit voltage (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub>). This adaptation mitigates variability from changing irradiance, allowing effective PID characterization under low irradiance conditions. Validation in both field and lab environments confirmed the robustness of the method, with module luminescence differences exceeding 2.5% even at 50% current bias. These results highlight the potential of the proposed metric for reliable PID diagnosis in PV modules.