Not to be confused with an hour of daylight, one peak sun hour is one hour’s worth of sunshine at an irradiance of 1 kilowatt per square meter (kW/m²). Peak sun hours, measured as kilowatt-hours per square meter (kWh/m²), are influenced by the time of day, the season, the presence of clouds, and geographic location. Even though solar panels may receive eight hours of partial sunlight in a given day, that may average out to only three or four peak sun hours.