Performance ratio (PR) is the primary operational performance metric for solar PV systems. A PR of 100% would mean zero system losses; in practice, well-designed and maintained commercial systems achieve PR values of 75 to 85%. Losses contributing to sub-100% PR include temperature derating of panels, inverter conversion losses, cable losses, soiling, and downtime.
For operational solar assets, declining PR over time indicates increasing system losses attributable to panel degradation, soiling, or electrical faults. Thermal imaging drone surveys and electrical inspections are used to diagnose the source of PR deterioration. Lenders and asset managers use PR as a key performance indicator for operational solar portfolios.