Performance ratio

Performance ratio measures how efficiently a PV system turns the available sunlight into energy. It is the ratio of the energy actually produced to the energy the system could theoretically produce. For a manual calculation, divide the measured annual plant output in kWh by the calculated nominal annual plant output in kWh. The inputs are irradiation values measured at the site by a sensor such as a Sunny SensorBox, the module area of the plant, and the module efficiency from the module data sheet. Because the metric is largely independent of a plant's location, orientation and incident irradiation, it can be used to compare plants in different places. PR is reported as a unitless value or as a percent. The closer it is to 1, the more efficiently the system is running. The calculation uses module ratings at standard test conditions, so real operating conditions can push PR above 100 percent. PR can be affected by module temperature, shading or soiling of the modules or the irradiance sensor, conduction losses, module and inverter efficiency, the recording period, and the sensor's orientation and cell technology. If you track PR at regular intervals from a commissioning baseline, values that fall below the normal range can flag a possible fault early.

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• sentence 4: support check: partial - Passage says PR is largely independent of orientation and irradiation, and so can be used to compare plants at different locations; it only says location-independent in u14, which is close enough, but 'largely independent of location' is slightly different from the stated wording. -->