Can Regular String IV Measurements Complement MPP Monitoring Data?

Existing operation and maintenance strategies for PV farms rely on maximum power point (MPP) monitoring data. Meanwhile, current-voltage (IV) curve measurements deliver additional diagnostic information about the state of health of the PV system and inverter based IV scanning enables recording large data at minimal labor and monetary cost. In this work, we investigate the additional value of string IV-curve measurements complementing MPP monitoring to enhance the accuracy for fault detection strategies. We record MPP data along with frequent IV scans from PV strings in Denmark with and without faults such as PID, cell cracks, ribbon damage and bypass diode failures. Observing the IV scan function of a string inverter with high-frequency measurement equipment, we observed an initial sharp power drop, followed by a period of open circuit operation, sequential IV sweeps on each MPPT and slow ramping back to normal operation. The entire IV scan event lasts about 23 seconds for a 4-MPPT inverter. An energy loss estimation shows a maximum 0.087% energy loss per year for daily IV scans. Comparing fault detection accuracy of IV versus MPP monitoring-based features, the IV showed superior accuracy of 96% compared to 82%. Minimal data requirement analysis showed that even at minimal data set size, the accuracy did not fall below 91%, which is still significantly better than the MPP based fault detection. The findings suggest that regular inverter based IV scans can enhance current O&M strategies for improved fault detection at very little energy loss.