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Specific yield in kilowatt-hours per kilowatt-peak per year already embeds irradiance and system losses, so annual generation is capacity times specific yield. Modules degrade at 0.3-0.7% a year, so lifetime generation is a geometric series over the project life rather than 25 times year one.
Annual generation
Generation (MWh) = capacity (MWp) x specific yield (kWh/kWp)
Degradation
Year n = year 1 x (1 - degradation)^(n-1); lifetime = year 1 x (1 - (1-d)^n) / d
Performance ratio is the fraction of theoretical output actually delivered, capturing temperature, soiling, inverter and wiring losses. Specific yield is the resulting energy per unit capacity, which already includes it.
78-84% for a well-designed utility plant in a temperate climate, lower in very hot climates where module temperature losses are larger.