Or, you could just put them on the roofs of existing buildings. I mean, that's where you need the power right? All you need then is a grid so you can off load

Or, you could just put them on the roofs of existing buildings. I mean, that's where you need the power right? All you need then is a grid so you can off load excess power (you're going to have a lot of excess power, if you cover even one in ten roofs in a city) to some kind of storage method and draw back from that when the sun isn't shining. I would think the environmental difference between a ceramic tile or metal roof and a solar panel roof is pretty minimal.