There's nothing wrong with going the solar route, infact if you access to solar or hyder 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.