“…monthly and annual direct solar radiation, regardless the availability or not of diffuse and GSR measurements. Then, they have found that compared to measurements in Algiers, Ghardaïa and Tamanrasset, the estimated data gave better results than those provided by five spatial databases, especially for the monthly averages values where an RMSE of 0.491 was obtained for the site of Ghardaïa [33]. In [34], 11 empirical models have been studied, correlating the monthly mean daily HGSR with air temperature and monthly mean sunshine duration, at 6 Algerian sites that are Algiers, Oran, Batna, Ghardaïa, Bechar and Tamanrasset (Figure 12).…”