1 Peak Sun-hour = 1000 Wh/m or 1kWh/m.
The Sun provides approximately 1000 Watts of power per square meter of area at Earth’s radial distance from the Sun. For every 1 hour the Sun provides that power, the Energy applied to that square meter is equal to 1000Wh. (Energy = Power x Time) Due to the Earth’s curvature and rotation, 1 square meter of the Earth’s surface does not always get the full 1000W of power the Sun is providing. For simplicity of calculations specifically for solar system performance, we add up all of the Solar Energy provided to 1 square meter in a specific location over the course of a day, or average day of a year, and divide it by the standardized power of 1000W/m.
This provides an easy to deal with unit of Average Solar Energy Irradiance per day in a location… or Peak Sun Hour. So, even though sunrise to sunset may be 12 or more hours… the Sun at 5 to 6 PM is not nearly as strong as the sun from 11AM to 12PM. Peak Sun-Hours allows us to mesh all those bits of energy together to 1 average unit for easier calculations for energy production.