Google/Alphabet’s mapping tech is powerful enough to start minor wars, so it’s nice to see the plex putting its best tech to sustainable use. Thanks to the newly launched Project Sunroof, Google can provide a free calculation of how much money you’d save if you installed solar panels on your home. The program, which is rolling out in Fresno, San Francisco, and Boston, aims to demystify solar — the energy source President Obama is banking will make America more sustainable over the next decade.

The program works by combining the information Google Maps keeps on your home with information like how much sunlight hits your roof, a 3D modeling of your roof, shadows from nearby structures and trees, cloud coverage, and all variations of sun position over the course of a year.

When everything is calculated, you get a recommendation for what panel size you need to install to get close to 100 percent of your electricity use.

The project is an outgrowth of engineering lead Carl Elkin’s “20 Percent Project,” an initiate born of a directive asking employees to devote 20 percent of their time to working on ideas that could benefit Google long term. Solar demand has been rising lately, especially in residential settings, so this seems like a growth area for a company with an eagle’s eye view of Earth.

It remains unclear how fast Project Sunroof will expand to other corners of the country, but if it’s a hit with Silicon Valley and New England Tech Corridor commuters, you better believe it will get big.