Sunshine and global solar radiation estimation at different sites in Egypt

A simple non-linear method is proposed for estimating relative sunshine duration based on monthly mean daily maximum and minimum air temperatures and cloud cover fraction at six sites in Egypt, where long-term period (9-15 years) data were recorded. This method gives low errors (mean bias error is about −0.4% and root mean square is about 2.3% for pooled data), so it can be used in case of unavailability of sunshine duration data. Also, a non-linear equation has been proposed at the same sites to estimate monthly mean daily global radiation based on observed and estimated values of relative sunshine duration. This method was compared with linear Ångström-Prescott and double linear of Garg-Garg equation. These methods were tested seasonally and at different sky conditions (clear, partially cloudy and overcast skies). Also they have been tested against 32 stations dataset, at worldwide sites. The results show that the bias error for the proposed method is low, average values to mean bias error and root mean square error are around 0.1% and 6%, respectively, while they are around 3% and 7% to the other methods at pooled data. Generally, the proposed method preformed better than the others.