Dry Pass, Wet Fail: Ground Impedance Testing of Field-Aged PV Modules—Implications for Repowering/Revamping Within 5–10 Years and for Environmental Sustainability

The ground impedance (insulation resistance Risol) of photovoltaic (PV) modules is usually measured only in the dry state, even though arrays frequently operate under dew-wet or rain-wet conditions, when leakage paths can change. We measured dry insulation resistance Rdry and IEC 61215 MQT 15 wet leakage resistance Rwet for N = 37 field-aged crystalline-silicon modules from utility-scale plants and related the results to the IEC 40 MΩ·m2 criterion (Rwet × A ≥ 40). The measurements used 1000 V DC and a 2 min dwell; Rwet was obtained in a salted bath with a solution resistivity < 3500 Ω·cm. The median Rdry was 42.4 GΩ, whereas the median Rwet was 462.5 MΩ, resulting in a median Rdry/Rwet ratio of ~110×. Three modules (8.1%) failed the 40 MΩ·m2 limit already in the dry state, whereas eight modules (21.6%) failed under IEC-wet conditions; five were dry-pass/wet-fail cases that would have passed dry screening. For a representative area A = 1.8 m2, a practical conservative dry triage threshold of approximately 55.5 GΩ identifies modules needing IEC-wet verification rather than serving as a stand-alone limit. Overall, combining dry and IEC-wet measurements improves safety and supports sustainability through resource-efficient repowering/revamping and end-of-life decisions in large PV fleets, particularly in hot climates.