Hourly global irradiations on tilted planes are required in various engineering calculations for solar systems. In many sites, at best, only global irradiations on horizontal planes are available. The final purpose of our work consists in calculating the global irradiation on inclined surfaces from horizontal global irradiation. In a first step, we estimated several correlations between the horizontal diffuse component and the global irradiation. The second step, which is the objective of this paper, is to test various models to compute hourly global irradiations on tilted planes from horizontal diffuse and global irradiations using solar data collected on the French Mediterranean site of Ajaccio. (c) 2005 Elsevier Ltd. All rights reserved.