Performance Ratio (PR)
Actual generation divided by the generation theoretically available from the irradiation that fell on the array — the measure of how much of the available sunlight the plant converted.
What a good PR looks like
A well-designed Indian plant runs at 78-84% PR in year one. Below 75% something is wrong: soiling not being cleaned on the right cycle, string outages nobody noticed, inverter derating, shading, or cable losses from undersized conductors.
Why we guarantee PR, not generation
Generation depends on the weather, which neither party controls. PR normalises it out, so an O&M guarantee written on PR holds us responsible for what we actually control — availability, cleaning, and fault response.
Related terms
Where this applies
Operations & Maintenance, Utility-Scale Solar EPC
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