By 2020, solar will prove a better deal than regular electricity in more than half of the U.S.

Solar in the U.S. is booming. According to new data from GTM Research, America just set another quarterly record for solar installations, with 1.3 gigawatts-worth of photovoltaic systems coming online in Q3, a 41 percent jump from the same quarter in 2013. It’s also the second-best overall quarter of all time.

The growth is unlikely to slow much. In fact, by 2020, solar will actually prove a better deal than regular electricity in more than half the country, according to new calculations by Shayle Kann, the senior vice president for research at Greentech Media.

Kann released a map this week showing which markets will soon reach not only “grid parity”— the rate at which solar electricity becomes as cheap as whatever you’re paying now— but also where electricity users can expect to see meaningful savings through using solar.

By 2020, he calculates, power customers in 28 states will find that regular electricity will prove more expensive than solar. And customers in 14 of these states can expect to see savings of at least 10 percent.

This calculation even assumes no government incentives, something many markets current rely on to get solar installed. That is mostly because it is larger, utility-scale solar projects, and not home rooftop systems, that see the biggest economic boost from them.

Instead, Kann said, costs are being driven downward by high installation volumes, which allow installers to purchase more hardware in bulk and spread overhead costs over a larger installation base. For the first time in a decade, more rooftop solar will have been installed in one year than at the utility scale.

We can catch a glimpse of which states are on their way to joining the 2020 club by looking at their installation rates for Q3 2014:

Though their solar buildouts are relatively small now, states like Pennsylvania and New Hampshire can expect to be cost competitive with solar within the next five years thanks to already-high regular electricity prices, lower solar installation costs, and attractive electricity rate structures, Kann said.

Rob covers business, economics and the environment for Fusion. He previously worked at Business Insider. He grew up in Chicago.