COMPARISON BETWEEN 3 YEARS OF DAILY GLOBAL RADIATION MEASUREMENTS IN 3 TUNISIAN SITES AGAINST ASSESSMENTS FROM METEOSAT WEFAX IMAGES

GISTEL is a satellitary methodology based on a simple physical model w ith two components. It is used to estimate global solar irradiance fro m METEOSAT data. The treated images in the present sequel are of Wefax type of the 'visible channel' of METEOSAT. Our method has been applie d in Tunisia. The estimated daily solar global radiation is compared t o the measured values performed in three meteorological stations in th e North of Tunisia during three successive years. The obtained results have shown that the accuracy level of our method is acceptable for en ergy applications. Our results show the convenience of GISTEL method t o METEOSAT-Wefax images. In general, the relative error does not excee d 20% of the global irradiation. The recorded errors between estimated and measured values are, in some cases, linked to the model's paramet ers. They may also arise from the geographical situation of the site, the satellitary data or from the earth-based solar irradiation. (C) 19 98 Elsevier Science Ltd. All rights reserved.