Performance ratio (PR)
How much of a solar system's theoretical output it actually delivers after real-world losses — usually expressed as a percentage around 75–85%.
Performance ratio (PR) compares actual energy output to the maximum a system could theoretically produce in perfect conditions. A PR of 80% means real losses — heat, wiring, inverter conversion, soiling, and shading — eat about 20% of the ideal.
PR is the headline number that bundles all the individual derate factors. Designers use it (alongside peak sun hours and array size) to forecast how many kilowatt-hours a system will actually generate each year.
Put it to work
See also