About the Performance Ratio (PR)
Performance Ratio (PR) measures how effectively a solar plant converts the sunlight actually falling on its modules into grid energy, after every loss (temperature, soiling, wiring, inverter, downtime). It is the IEC 61724 quality metric — independent of plant size and irradiance, so it compares any two plants fairly.
Formula
PR = Actual specific yield (kWh/kWp) ÷ Reference yield
- Reference yield
- In-plane insolation (kWh/m²) ÷ 1 kW/m² STC irradiance
How to calculate it
- 1Measure the plant's actual energy and divide by installed kWp to get specific yield.
- 2Get the plane-of-array insolation for the same period (kWh/m²).
- 3Divide that by the 1 kW/m² STC reference to get the reference yield.
- 4PR = actual specific yield ÷ reference yield, expressed as a percentage.
Worked example
A plant delivering 1,500 kWh/kWp/year at a site receiving 1,900 kWh/m²/year in the array plane has PR = 1,500 ÷ 1,900 ≈ 79% — a healthy figure for India.
What you can calculate
- IEC 61724
- Grade bands
- Energy loss kWh
- Period select
Standards & references
Frequently asked questions
What is a good performance ratio for solar in India?
A well-designed grid-connected plant typically achieves a PR of 75–85%. Modern plants with good thermal management and low soiling reach the top of that range; a PR below ~70% points to soiling, shading, high module temperatures, or inverter/availability losses.
What is the difference between PR and CUF?
PR is normalized for the actual sunlight received, so it isolates system quality. CUF is normalized only for installed capacity and time, so it mixes system quality with the site's irradiance. A desert and a coastal plant can share the same PR but have very different CUF.
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