Figure 5: Lindenberg, May 14, 2005. The temporal course of the measured global irradiance (a) on a day that was rated as a day with overcast sky is compared to values generated by the new algorithm (b), the algorithm by Aguiar (c), and the algorithm by Skartveit (d). The mean variability, that is, the mean irradiance change from one minute to the next, of the measured irradiance of 7.0 W/m² shows good congruence with the new algorithm (8.2 W/m²), while the usage of the algorithms by Aguiar and Skartveit leads to higher variability values of 13.1 W/m² and 16.6 W/m².