Vienna isn’t even the worst place for solar power. Consider places like Ireland, Scotland or Sweden for example. No wonder why wind, hydro or even tidal power suddenly begins to make a lot more sense. IMO, solar really begins to make sense in Spain, Italy, Greece and Turkey. Those places actually get some decent sunshine. Using solar power in Austria should be ok, but it’s not great by any means.

Nearby mountains probably get in the way of building large solar facilities. Maybe you could combine solar power with farming. The panels can provide some shade to more sensitive plants.
See also: solar atlas
Sidenote: Iceland and the northern half of Norway, Sweden and Finland aren’t even on the map. I guess you don’t need fancy a solar map to know that building solar in places like that is a waste of money.