Insolation (INcident SOLar radiATION) is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter (W/m²) or kilowatt-hours per square meter per day (kW·h/(m²·day)), or in the case of photovoltaics it's commonly measured as kWh/kWp•y (kilowatt hours per year per kilowatt peak rating). Sometimes, as in the text below, a long-term average intensity of incoming so… (More on Insolation)