Solar energy potential atlas for planning energy system off-grid electrification in the Republic of Djibouti

Abstract Nowadays, energy supply of rural populations is one of the most important challenges in African developing countries, and more particularly in Sub-Saharan Africa. With only one third of the population connected to the grid and the high economical and environmental cost of classical energy resources, the use of renewable energies within the rural energy supply pattern is a reliable alternative solution to improve human development of remote populations. Djibouti is a little poor country of Sub-Saharan Africa which perfectly symbolizes this way of life. Electrification rate is only about 30% and the important scattering of rural peoples throughout the country makes grid extension and fuel transportation unsuitable economic solutions to carry energy. The geographically diffused solar resource can therefore be an interesting mean to produce energy where it is consumed. The aim of this study was the creation of the first Djibouti’s global horizontal irradiation atlas, including assessment and improvement. To realize this atlas, a satellite-derived irradiance model was used (EUMETSAT O&SI SAF). To validate this model over Djibouti, we installed two temporary weather stations during the year 2010 in Djibouti-city and Dikhil and we compared hourly, daily and monthly irradiation estimates against ground-based measurements. Results showed a good agreement between measures and estimates, with a maximum Relative Root Mean Squared Error (RRMSE) over the hourly solar atlas of 12.43% and 15.44%, for Dikhil and Djibouti-city respectively. In order to improve geographic information and accuracy of this solar atlas, we then disaggregated irradiation maps with a 3 arcsec (∼90 m at the equator) Digital Elevation Model (DEM), by taking into consideration terrain-related shading effects and elevation gradient. As current software solutions do not allow downscaling of preprocessed maps, we performed this work by computing our own global model, combination of horizon, elevation correction and irradiance splitting models. The horizon model we developed was assessed and compared with other existing models by using a theodolite in mountainous areas of Corsica. Finally, according to the final computed atlas, during the year 2010, mean irradiation all over the country was around 2100 kW h/m 2 and about 82% of the country received over 2000 kW h/m 2 . Furthermore, the solar radiation reaching Djibouti corresponded to 20,000 times the total yearly energy consumption of the country in 2005. The retrieved irradiation maps can be used to evaluate relevance of the solar resource over rural areas of the country, and implemented within energy models in order to size stand-alone solar systems.