On the estimation of global and diffuse solar radiation over Egypt

Abstract

Measurements of global, H, diffuse, D, solar radiation on a horizontal surface and sunshine duration, n, at nine meteorological stations have been used to examine the validity of some methods of the estimate global and diffuse solar radiation. In order to improve the obtained results, for prediction purposes, the investigated area of Egypt has been divided into five regions represented by the nine selected stations (in cold and hot seasons). An appropriate regional parameter, K, of an empirical relation of Barbaro et al. has been determined for each region. The agreement between measurement and estimated values is remarkable. The maximum possible error of estimated values does not exceed 9.6%. It is seen that the modified formula gives precise estimations for global solar radiation at any Egyptian locality. Relation between the diffuse fraction, D/H, and the relative duration of sunshine, n/N, are also determined for each region. Good agreement between the measured and estimated values applying the obtained relations has been found. Therefore, the relations are recommended for use at any location in Egypt. A comparative study for the global and diffuse solar radiation over different sites in Egypt has been made.