I was pre'talking already in case "your don't have" =)
But yeah... using the sun to capture heat for the night and better isolation techniques are of course way better. Lots of them.
Although... I would use Electrical solar panels to use miners... =) just in case the power goes down.
Is this feasible? Solar panels for miners? In winter?
Not a very good ROI if you just consider them to gain profits from the miner. But if you are in remote locations where you don't have alternatives, then it becomes the only choice.
The ratio is always between the amount of sun (like you are guessing) and the price of the panels. Here in NZ for example, it's not very cheap, therefore not wildly adopted. Only used if you want to be independent of the network.