PV cells have a lower efficiency at low irradiance. The irradiance loss with respect to 1000 W/m² may vary for different PV modules brands and manufacturers. A typical specification is, for example:
The typical efficiency at 200 W/m2 in relation to 1000 W/m2 (25°C, AM 1.5) is at least 97% of STC efficiency.
Typical solar simulations calculate the low irradiance efficiency hour-by-hour. The results vary case-by-case. Assuming 97% efficiency at 200 W/m2 and 100% at 1,000W/m2, a typical average Low Irradiance Performance loss is around 1%.