A new U.S. National Renewable Energy Laboratory report claims that covering every suitable rooftop in the U.S. with solar panels could generate 39% of the country's total electricity supply, according to Fast Company staff writer Ben Schiller. Previously, the lab thought the limit was 664 gigawatts (GW) of installed capacity, but now the estimate has jumped to 1,118 GW.

In some specific states the rooftop solar potential is much higher because the rooftops and landscape are more suitable, like in California, where rooftops could generate a whopping 74% of the electricity sold by utilities in 2013. Florida and New England could get 47% and 45% of their needs met, respectively. Even Washington could have 27% of its needs met with rooftop solar, and it has the worst solar resource in the country.

Co-author Robert Margolis, a NREL analyst, says "actual generation from PV in urban areas could exceed these estimates by installing systems on less suitable roof space, by mounting PV on canopies over open spaces such as parking lots, or by integrating PV into building facades." And, indeed, there's plenty of solar potential beyond rooftop space. Soon solar is likely to be installed in more places, including on the sides of walls and as windows.

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