"So it's welcome news that Google wants to make this all much, much simpler with its brand new Project Sunroof tool. Plug in your address, and Google uses its aerial imagery capabilities to help you figure out whether solar power might be a worthwhile idea. (The project is still in its early stages; here's Google's announcement from Monday.)
For now, data is only available for selected parts of the country. But let's look at a sample address given in Redwood City, California. The tool first calculates both how big the roof is and how much sun it gets per year."