Comparison of the Olmo model with global irradiance measurements on vertical surfaces at Madrid

The recently published Olmo model estimates global irradiance on inclined planes. It only requires the horizontal global irradiance and the sun’s azimuth and elevation as input parameters. As a consequence, it does not contain empirical coefficients that need determination for each location. Olmo and co-authors found a good agreement between predicted and experimental values obtained at their measuring site when a factor accounting for ground-reflected radiation was introduced in the model. In the present paper, the Olmo model is assessed in Madrid for vertical planes facing north, south, east and west. The model gives a root mean square error of ≅27%, when all data are used. With the data for the north-facing plane it becomes worse, i.e. ≅52%.