The coming of solar grid parity offers an opportunity for millions of Americans to go solar affordably. But it also means a potential transformation, a democratization of an electricity system long dominated by centrally-controlled utilities and centralized ownership and production of electricity. When solar can undercut grid electricity prices, it may also undercut this 20th century system of centralized ownership, bringing economic sunshine and self-reliance to communities along with solar electricity.

We used the following assumptions to calculate the residential solar rooftop potential for each metropolitan area:

Only non-vacant, owner-occupied properties were considered. Nationally, about two-thirds of homes are owner-occupied and not vacant, with major metropolitan areas varying from 50 to 70 percent.
We estimated approximately 1,000 square feet of total roof space per home.
We assumed that only 27 percent of this space (in the aggregate) would be suitable for solar, based on national studies of rooftop solar potential.
We assumed that 1 kW of solar could be installed for every 100 s.f. of suitable roof space.