In a lot of sites, at best, only global irradiations on horizontal planes are available. As most systems using solar energy are tilted, it is obvious that these data are not sufficient. The purpose of our work consists in predicting the solar irradiation on inclined surfaces based on horizontal measurements. To reach this goal, two previous studies were performed. They consisted in quantifying the accuracy of various well-known models of the literature: the first type of models (seven correlations) calculated diffuse horizontal irradiations from global ones and the second type (fifteen models) computed global irradiations on inclined planes from diffuse and global components on a horizontal surface. This study combines the two classes of models and calculates the adequacy of each association for experimental hourly data collected on the French Mediterranean site of Ajaccio. We compared these combinations with the Olmo model, transforming global irradiations directly onto tilted planes from horizontal ones. (c) 2005 Elsevier Ltd. All rights reserved.