Accuracy assessment of models estimating total irradiance

The accuracy of estimating total in-plane irradiance is investigated for the UK climate. Several models, which differ in essence in an assumed diffuse irradiance distribution at different levels of sky cloudiness, were used to calculate solar irradiance on inclined planes from horizontal irradiance data. The accuracy of this calculation was validated against measured data. It transpires that there is not massive difference between the various methodologies, but on average the Reindl model seems to be slightly better than other methods, followed by Perez et al. model