If you look at the book "Sustainable Energy without the hot air" you will find it chock full of data. Problem is, it's for the UK, not the US. But FWIW, I think the UK is more north than the continental US.

http://www.amazon.com/Sustainable-Energy-Without-Hot-Air/dp/...

Also wanted to add the invaluable http://www.amazon.com/Sustainable-Energy-Without-Hot-Air/dp/...

The amount of energy we can usably harness from the sun is a lot less than is radiated to the earth. Its useful to drive at night and on cloudy days. People also demand similar performance from their future vehicles as they get now.

If you're interested in these sort of questions, I highly recommend the following book which I got a few days ago. I'm finding it both sobering and exciting:

http://www.amazon.com/Sustainable-Energy-Without-Hot-Air/dp/...