INSOLATION

Insolation is a measure of solar radiation energy received on a given surface area in a given time. A common measure of this energy is kWh/m² and year, or per day. Insolation consists of both direct and diffuse radiation: with the sun in the zenith, the angle of incidence is 90° and direct insolation is at a maximum. Direct insolation is reduced in the atmosphere by dust and clouds, changing it to diffuse insolation. If the sky is completely cloud covered, all insolation is diffuse. In Sweden, about 45–65 % of insolation over the year is diffuse. However, even diffuse insolation contains energy, which means that it is possible to capture solar energy even on cloudy days. However, the type of insolation affects the choice of solar collector and its siting: read more on this in the following chapters.