Solar radiation over Sudan—Comparison of measured and predicted data

Abstract Measurements of global solar irradiance on a horizontal surface at 14 meteorological stations in Sudan are compared with predictions made by two independent methods. The first method is based on Angstrom formula which correlates relative global solar irradiance H H 0 to corresponding relative duration of bright sunshine n N . Regional regression coefficients are obtained and used for prediction of global solar irradiance. The agreement with measurements is better than 7.5 per cent. In the second method an empirical relation due to Barbaro et al. which uses sunshine duration and minimum air mass as inputs is employed. An appropriate regional parameter is determined and used to predict solar irradiance at all stations with an accuracy better than 8 per cent. A comparison of the two methods is presented. Estimation of diffuse solar irradiance by Page's as well as Liu and Jordan's correlations is also performed and the results are examined.