Thanks guys! Yes, the sky is not perfect. I tried about 140000 different cloud formations
and was a bit fed up with it eventually. But I might find a better one.
Dirk, do you mean broken up clouds to the right or additional illuminating from the right side?
I won't use additional light sources. It might look very odd, since the right part is in the shadow, because the sun is more or less at 3 o'clock position.