There's nothing wrong with going the solar route, infact access to solar or hydel power should be a key criteria in selecting a location to setup a farm.
It is however not very wise to spend money setting up a solar farm for the express purpose of mining, simply because you could be spending that money on expanding hash instead.
Sure the running costs will be lower with solar, and unlike what people seem to be speculating, it should pay for itself in 5 years, but you are adding one more variable to a delicate mix.
Can't say much about Vosk case but for me it's a necessity to build a solar mining farm because in my country we have less electricity every 24 hours we normally have electricity for 6 to 7 hours per day and that is not enough to power mining rig 24/7 so I just have to go solar in the end it's even more better because now I can run my mining rigs 24/7 without having to rely on GRID power