HelioClim: a long-term database on solar radiation for Europe and Africa

An information system, called HelioClim, is available for answering the needs for long-term time-series of solar radiation data. Daily irradiation values are available over Europe, Africa and Atlantic Ocean, from 1985 onwards. This database is accessible through the Soda Web service (http://www.soda-is.com) on a free basis. Meteosat satellites images are used to produce this climatological database. The method Heliosat-2 converts these images into maps of the global irradiation at ground level. A comparison was performed between irradiation values available in HelioClim and those measured by ground stations in Europe. A measuring station is not necessarily contained within a B2 pixel and an interpolation method is needed. The root mean square error (RMSE) increases as the irradiation increases and is less than 850 Wh/m2, that is a relative error of 20 %, a satisfactory result compared to what can be achieved using sparse pyranometric stations only.