Integration of Meteosat-derived data and digital terrain model into a GIS for local atlases of solar radiation

Abstract : Solar radiation at ground level is a necessary input for several applications as potential solar energy assessment, agronomic or meteorological related studies. Images from meteorological geostationnary satellite, once properly processed, can provide solar radiation maps. Several solar atlases with a wide geographical coverage have been built by this process. These maps are more accurate than those made from interpolations of ground measurements. Nevertheless, their spatial resolution - about 10 km over mid-latitude in the best cases - are not sufficient for taking into account spatial variability of the irradiation due to the orographic effects in a local scale. Among these atlases, HelioClim is a GIS providing daily irradiation maps over Europe, Africa and Atlantic Ocean from 1985 up to now. It was developed from a processing on Meteosat images needing a digital terrain model (DTM) as input. HelioClim use the TerrainBase DTM, its spatial resolution is about 1 km. Irradiation maps produced by HelioClim have a spatial resolution of 10 km in our latitudes. In our work, we integrate a digital terrain model (DTM) of very high resolution (10 m) covering the Ouneine valley (Morocco) with HelioClim outputs into a GIS and we derive solar radiation maps. Spatial resolution of these maps is the same as the DTM. We built 12 maps of monthly mean of daily global irradiation for each month of a year. These monthly means have been computed from daily irradiation between 1997 and 2002. We made comparisons between these maps and ground measurements. We found a relative root mean square error (RMSE) of 7.5 % for July and 5 % for January. HelioClim using TerrainBase presents for monthly mean of daily irradiation a relative RMSE of 10 % for January and 13 % for July. Integration of HelioClim and a high resolution DTM into a GIS permits to produce accurate solar irradiation maps. Spatial variability of terrain elevation is better taken into account. Such GIS are convenient tools for mapping solar irradiation in mountainous area.