Comparison of models for estimating solar radiation in arid and semi-arid regions

The purpose of this study is to compare statistically correlations for estimating the monthly average daily global radiation incident on a horizontal surface for arid and semi-arid regions and to recommend one or more models which are simple and accurate. Our study shows that the correlation of Bahel et al. (1986) yields the best estimates for these regions; the universal models proposed by Sayigh (1977) and by Rietveld (1978) also produce satisfactory results.