The solar resource in South Africa is among the best in the world. South Africa has seen an increase in local and international investment in solar power. The optimum angles at which a solar collector should be fixed are often debated. Similar publications on this topic often rely on mathematical models of solar resource rather than measured data. Measured data is preferred since the effects of pollution and weather are included. In this work, recently measured data from nine measuring stations in the Southern African Universities Radiometric Network (SAURAN) equipped with pyranometers and pyrheliometers are considered. The data is used to calculate the annual solar insolation on fixed collectors at all possible installation angles. SolTrace, a ray-tracing software, is used for validation. Relative to horizontally-fixed collectors, the annual solar insolation is 10% more for optimally-fixed collectors and 45% more for solar tracking collectors. The effects of tilt and azimuth angles are presented on contour plots, which are convenient for cost analysis and the determination of the annual insolation on building surfaces. The optimum azimuth angle is a function of the longitude angle minus the absolute latitude angle, which suggests that frontal and convective precipitation effects influence the optimum azimuth angle. (C) 2016 Elsevier Ltd. All rights reserved.