Sunroof is intended as a "treasure map" for future green energy projects, telling you how much of a saving you'd make and how long it'd take to make back your initial outlay.
To begin with, Project Sunroof will only be available in three locations: Boston, San Francisco and Fresno. If it turns out to be successful, however, then Google will roll the service out to the rest of the country and, possibly, the world. Once you've put in your address, you'll be told how much you're likely to save in energy costs, and then be put in touch with a local installer.