Global radiation is an important parameter for determining the solar energy of photovoltaic systems. It is the solar radiation incident on the earth's surface, consisting of direct, indirect and diffuse light radiation.
The global radiation refers to an area of one square meter. Global radiation is attenuated by the air mass( AM) of the atmosphere and depends on the angle of incidence and thus on the time of year and day, and is less than the solar constant. At our latitudes, global radiation is about 100 W/m2 to 130 W/m2, with perpendicularly incident solar rays. This results in an irradiation energy of 900 kWh/m2 to 1,200 kWh/m2 over the year in Germany. For comparison, the irradiated value at the equator is about 2.2 times as high.