Great idea! If you get one of the new Ford Focus Electrics, you can get a rooftop solar array permitted and installed for only $10k!
With the 10k tax credit for buying an electric this whole thing is actually quite attractive: an average driving family will have saved back the $10k in electricity bills in 5 years, and after that you are practically driving for free! Also, if your family drives less than average, like mine, you will be selling your excess electricity back to the grid and powering most of your household needs from the roof.
So you have a nice new Ford Focus which costs about $30k after the credit, a modern solar array on your house (hello resale value!), and very well might be the bees knees in 5 years after your investment is recouped.