there was/is some small neigbourhood  pilot project (state sponsored IIRC) in germany that uses panels as defacto roofing so it is possible.

That idea comes from neccessity, I want to optimize both angle and size for winter. Yes it will generate less overall but with oversized installation summer is over kill anyway. 

 That's cool. I think that it could be a useful technology, but, if I ever roof mount panels, I'd want to space them off the roof and use bifacials to help increase off-peak power capture.