It's a nice theory, but for the cost of research/development, installation and maintaing the cells nationally, we could probably perfect cold fusion. We're talking about hundreds of billions of dollars to do something like this. There is also the little problems we have with current solar technology. Solar cells have about a 20-30 year life expectancy and decrease their output each year until eventually they produce nothing. So with our current technology we would have to replace all of the solar cells every 20 years.
Having said that, I can see where this idea would be very cool for homeowners replacing driveways, decks and sidewalks with solar cells if the cost was less than putting them on a roof. It all comes down to affordability regardless if you are a homeowner or the US government.