Renewable Energy Credit - REC's

Hello,

Looking for information from whoever knows about Renewable Energy Credits aka REC's. I just went to a green energy expo, interested in getting a solar sytem on my house. They talked about REC's as another bonus to green energy providers. For each KWH of green energy you produce you can sell one REC. In NJ they sell for over two hundred dollars each. In NJ the REC has to be produced in NJ. Is there a place to sell these independent of the state you are in? Any other easy to understand info would be nice, Especially about Delaware, PA and NY.