Technical explanation
Define period, measurement point and reference power. Temperature, shading, conversion, downtime and grid limits can affect PR. For bifacial systems, also specify treatment of rear irradiation.
Definition · Measurement
Performance Ratio (PR)Performance normalized by capacity and solar resource
TL;DR
Performance Ratio compares final yield with reference yield based on received irradiation. It is not cell conversion efficiency.
Definition
PR = Yf ÷ Yr. Yf = final energy ÷ rated power; Yr = in-plane irradiation ÷ STC reference irradiance of 1 kW/m². Both yields have the dimension of time.
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PR formula
Yf ÷ Yr
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Reference irradiance
1 kW/m²
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Period
Same for the data
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Solar measurement
In the module plane
Swiss context
Compare simulation and measurement with the same conventions and period weather. One threshold for all Switzerland cannot grade an installation or diagnose a fault.
Related terms
Related guides
FAQs — Performance Ratio (PR)
Why is my installation producing less than expected?+
First check weather, period, measurement and assumptions. Then compare availability, shading, dirt, settings and components. An output gap alone does not establish its cause.
What PR should we aim for for a good installation?+
Request expected PR for your configuration and its loss components. Compare it with consistent measurements; neither 82–86 % nor another range is a universal rule.
Sources & method
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