Assessment of solar radiation over Africa: present and future
Résumé
Assessment of solar radiation available at ground level is critical in many aspects, from exploitation of solar energy to climate research. The current means to assess solar radiation over Africa are discussed. There are a few stations in the meteorological networks measuring the global radiation on horizontal plane. Their number decreases in the years due to maintenance costs and other adverse effects. These stations are too few to produce a realistic view of the solar radiation that could be useful for any site located at more than 50 km from a measuring station. A number of efforts were made to produce maps from satellite data since 1980. Satellite images cover the whole Africa and offer a high repetitivity in time, approximately one image every 30 min or 15 min. The MINES ParisTech has recently released the HelioClim-1 database which has been recognised as a critical Earth Observation priorities data set from the International Group on Earth Observation (GEO). HelioClim-1 has been computed from the Meteosat series of European satellites. It offers daily values of solar radiation for a period of 21 years for any site in Africa. Its access is for-free via the SoDa Service website (soda-is.com). The performances of HelioClim-1 compared to coincident ground measurements are discussed. New parameters are currently derived from satellite data that describe the optical state of the atmosphere. These parameters can be input to sophisticated radiative transfer models which in turn provide accurate assessments of the global irradiation and its direct and diffuse components. This is the purpose of the MACC and MACC-2 projects funded by the European Commission. The results of the model for clear-sky cases will be presented. Finally, perspectives for 2015 and beyond will be discussed.