Seriously, I don't get the weird obsession with rooftop PV as if it's the only way to be green. PV is great, but, it doesn't work for every house. Personally, I have big oaks out front helping block passive solar windows in the summer, and the peak of my roof runs north-south so cell mounting would be tricky. That doesn't mean I can't get clean energy, it just means I buy it from a utility company, who are buying it from my neighbor's house where the orientation and canopy placement makes sense to do PV.