Insolation

Insolation is the accumulated solar energy received on a defined surface over a stated period. In solar PV documents it is usually expressed as kWh/m² for a day, month or year, and may refer to a horizontal surface, a tilted roof plane or the plane of the PV array. It is related to irradiance, but irradiance is an instant power-per-area value in W/m² (watts per square metre) while insolation adds that sunlight over time. The value helps compare solar resource, shading and expected PV output, but it is not the same as solar yield, kWp (kilowatt peak), a generation guarantee, DNO acceptance, SEG eligibility, MCS certification, roof suitability or proof of installation quality.