Relationships between diffuse and global solar radiation in southern Africa : research letter

Diffuse solar radiation, which is not routinely measured at weather stations, has been estimated empirically, from global solar radiation, around the world but not in southern Africa. We report here empirical relationships describing the components of solar radiation at eight locations throughout the subcontinent. Data on diffuse and global solar radiation were collected at weather stations, at latitudes between 22° and 34°S and at altitudes from 0 to 1725 m, representing various climate zones. A simple linear equation is proposed relating the ratio of diffuse to global solar radiation to the ratio of global to extraterrestrial solar radiation for the subcontinent, including both semi-arid / arid and warm temperate climate zones.