A new fund from solar installer SolarCity would help install solar panels on residential rooftops, and tech giant Google wants in on the action.

SolarCity plans to raise a $750 million fund to invest in installing solar panels on the rooftops of home owners, and $300 million of that fund will come from Google. The deal shows the momentum behind the booming solar panel industry in the U.S. Solar energy represented over a third of all new electricity in the U.S. in 2014, and that could grow to 40 percent in 2015, which would be a new record. The solar industry is now a major U.S. employer, employing twice as many workers as the coal industry; SolarCity employs more workers in California than the state’s three large utilities combined, said SolarCity CEO Lyndon Rive at the ARPA-E Summit earlier this month.

Gigaom answers the question "What's in it for Google?"

Google wants to invest money into funds like SolarCity’s because it can provide a return (8 to 12%) on the investment. The deals with homeowners tend to generate pretty reliable revenue over time because homeowners — particularly the kind getting solar installed — tend to pay their utilities. But because these financing deals are becoming more mainstream as solar becomes more of a commodity, the returns have been slipping in recent years.