You could run cables down the roof and the outside outside of the wall which not particularly rare. Actually that's the case for one of the aerials on my roof. And piercing roofs isn't exactly uncommon. Aircon vents, chimneys, mountings for aerials etc. The thing with something like this is that it doesn't have to be an optimal solution which instantly solves all our problems, which is what a lot of people seem to demand when it comes to anything which is even vaguely green, it just needs to be cheap and easy and move us away from our reliance on fossil fuels. This, along with traditional solar, hydro, onshore and offshore wind, nuclear etc. all have their place.