average daily irradiance
Jan 152012. Solar insolation, what is it? Solar insolation 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 (kWâ¢h/(m2â¢day)) (or hours/day). In the case of photovoltaics it is commonly measured as kWh/(kWpâ¢y) (kilowatt hours per year per kilowatt peak rating).