Mean differences in (%) of model derived hourly GHI relative to measurements at each station of HNSE for the whole period of study, separately for clear skies (upper panel)
and all skies (middle panel). Different symbols are used for each SW radiation scheme. Vertical bars in the upper panel correspond to one standard deviation of the data entering the
mean. For all skies, the standard deviation is very large and is shown separately as a bar chart (lower panel).