What is Performance Ratio?

Performance Ratio (PR) is the most universally used metric for assessing the health of an operating solar plant, independent of location-specific irradiance.

Formula

PR = Actual yield (kWh) ÷ Reference yield (kWh)
Reference yield = in-plane irradiation (kWh/m²) ÷ 1 kW/m² × installed capacity (kW).

What PR tells you

PR accounts for all losses: temperature, wiring, inverter inefficiency, soiling, shading, mismatch, downtime, and clipping. PR = 0.80 means the plant delivers 80% of what it theoretically could.

Typical PR values

• New well-designed plant: 0.80–0.85
• Operational after 2–3 years: 0.75–0.82
• Poor maintenance / heavy soiling: <0.70

Temperature-corrected PR

Raw PR appears lower in hot months because temperature losses increase. Temperature-corrected PR (IEC 61724-1:2017) adjusts for cell temperature deviation from 25°C, enabling fair seasonal comparison.