Solar radiation is the driving force which most directly influences the surface water balance and crop yields. In South Africa this variable is measured at a limited number of sites. In order to determine the geographic distribution of monthly mean daily totals of incoming solar radiation, an elementary model for solar radiation in terms of sunshine duration was used. It was found that summer solar radiant energy varied from 20 to 30 MJ m−2 d−1 and that the summer—winter differential is in the order of 15 MJ m−2 d−1 throughout the country. While data are available for each month of the year, the geographical distribution of monthly mean daily radiant energy received for only January, April, July and October are presented here. These are representative of summer, autumn, winter and spring. Irrespective of season, maximum incoming solar radiation occurs in the western and north-western interior, indicating that within these areas highest crop yields, coupled to highest water requirement, can be expected.