Please note, I copied/pasted (and linked) Karl Denninger's article on this. My daughter first brought the proposal to my attention.
I might think using parking lots as solar electricity generation plants -- at least in areas without significant snow, like the southern portions of the country -- possibly could be useful. However, solar really is NOT "ready for prime time" and as an industry cannot exist without significant subsidies BECAUSE IT IS NOT ECONOMICALLY FEASIBLE. At least at this time, and possibly not for a long time. That said, those who can afford it (individuals, towns, companies) and who choose to participate help - by their purchases - to drive the innovation that makes the industry less inefficient. Today's panels are less than 20% efficient -- but a decade or so ago, they were just under 10% efficient. Some (very expensive, hard to produce) test panels today are in the mid-30's for efficiency.
For the same reason that Lasik became better and more affordable ($20K/eye down to $1.5K/eye, with better outcomes), those willing to pay drive the innovation that benefits others in later years. That's how a free market operates.