The optimal utilization of solar energy requires a thorough characterization of the solar resource. The most accurate way is to measure that resource in situ. However accurate measurements are not a common commodity, especially over longer time spans. To circumvent the lack of ground-based measurements, models can be applied to estimate solar irradiance components. A fundamental component is the clear sky irradiance. In particular, clear sky irradiance is used as the normalization function in models that convert meteorological satellite images into irradiance. This paper presents the results of a validation of models that evaluate solar irradiance based on satellite images spanning up to 8 years. The validation relies on high quality measurements from 24 sites in Europe and Africa. After a thorough assessment of the ground measurements, clear conditions are selected in the data banks to evaluate the performance of seven clear sky models. Finally, seven satellite all-weather models are validated against the ground data.