Comparison of several satellite-derived databases of surface solar radiation against ground measurement in Morocco

HelioClim-3v4 (HC3v4), HelioClim-3v5 (HC3v5) and the radiation service version 2 of the Copernicus Atmosphere Monitoring Service (CAMS-Rad) are databases that contain hourly values of solar radiation at ground level. These estimated hourly irradiations are compared to coincident measurements made at five stations in Morocco. The correlation coefficients between measurements and estimates are similar for the three databases and around 0.97-0.98 for global irradiation. For the direct irradiation, the correlation coefficients are around 0.70-0.79 for HC3v4, 0.79-0.84 for HC3v5 and 0.78-0.87 for CAMS-Rad. For global irradiation, the bias relative to the average of the measurements is small and ranges between -6 and -1% for HC3v4, -4 and 0% for HC3v5, and -4 and 7% for CAMS-Rad; HC3v4 and HC3v5 exhibit a tendency to slightly underestimate the global irradiation. The root mean square error (RMSE) ranges between 53 (12 %) and 72Whm(-2) (13 %) for HC3v4, 55 (12 %) and 71Whm(-2) (13 %) for HC3v5, and 59 (11 %) and 97 Wh m(-2) (21 %) for CAMS-Rad. For the direct irradiation, the relative bias ranges between -16 and 21% for HC3v4, -7 and 22% for HC3v5, and -18 and 7% for CAMS-Rad. The RMSE ranges between 170 (28 %) and 210Whm(-2) (33 %) for HC3v4, 153 (25 %) and 209Whm(-2) (40 %) for HC3v5, and 159 (26 %) and 244Whm(-2) (39 %) for CAMS-Rad. HC3v5 captures the temporal and spatial variability of the irradiation field well. The performance is poorer for HC3v4 and CAMS-Rad which exhibit more variability from site to site. As a whole, the three databases are reliable sources on solar radiation in Morocco.