Performance Ratio (PR)
Measured plant PR and specific yield per IEC 61724-1.
PerformanceInputs (SI units)
Negative values are not allowed
Results
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Engineering Formula
- Y_f = E_AC / P_DC (specific yield, kWh/kWp)
- Y_r = H_POA / 1 kW/m² (reference yield, h)
- PR = Y_f / Y_r
- PR_temp-corrected = PR / [1 + γ (T_cell − 25)]
PR compares the plant's actual specific yield with the yield it would deliver at STC efficiency under the measured irradiation. It isolates losses (soiling, thermal, wiring, inverter, downtime) from weather variation, so PR is comparable across sites and seasons. Temperature correction removes the thermal component so that only controllable losses remain.
Design Assumptions
- • Irradiation measured in the plane of array with a calibrated pyranometer or reference cell.
- • Energy meter at the AC point of delivery over the same interval.
- • No curtailment or grid outages during the measurement window.
Engineering Tips
- ◆Healthy rooftop plants run PR 0.75–0.82; well-kept ground-mount reaches 0.80–0.85.
- ◆Track PR monthly — a steady decline usually means soiling or string failure.
- ◆Temperature-corrected PR is the fair metric for comparing summer against winter.
Warnings
- ▲PR above 0.90 usually indicates a sensor calibration or metering error.
- ▲A short measurement window (< 1 week) gives statistically unreliable PR.
Standards & References
Related Solar Calculators
Annual Energy Yield
Daily / monthly / annual yield from CUF and PR.
Azimuth Deviation Loss
Annual energy loss vs deviation from true south (N-hem).
Shading Loss
Annual generation loss from partial shading.
Temperature Loss
Power derating from cell temperature above STC 25 °C.
Irradiance → Energy
PV energy produced from measured irradiance.
Peak Sun Hours
Convert daily insolation to Peak Sun Hours.