Figure 6: Frequency of gradients of the global irradiance in Lindenberg, Germany (2005). The model quality in lower gradient ranges of up to 10 W/m² is similar in all models. In the range of 10 to 100 W/m², significant deviations can be detected for the models of Aguiar and Skartveit (grey), whereas the new method (blue) shows good congruence. For gradient values of more than 100 W/m², the model of Aguiar underestimates the frequency significantly, while the new method and the method of Skartveit feature similar frequency values compared to the measurement data (black).