For single family residences, yes this is true. The roofs of commercial buildings are often littered with HVAC equipment, antennas, patios, lots of other things

For single family residences, yes this is true. The roofs of commercial buildings are often littered with HVAC equipment, antennas, patios, lots of other things. Plus the more stories you have in a building the smaller the ratio of roof area to building area, so you have less space to generate power for more people. There's definitely a lot of room for growth for solar, but it's not a panacea. I'm looking forward to what we can come up with.