Study: California could get 74% of power from rooftop solar

The National Renewable Energy Laboratory, had estimated in 2008 that rooftop solar could generate 800 terawatt-hours per year, supplying about 21 percent of the country’s current demand. Now they’ve upped their estimate to 39 percent, in an analysis sure to be embraced by clean-energy advocates.
It’s unlikely the United States will tap all the sunlight at its disposal, at least not soon. The study focuses only on rooftop solar’s theoretical potential, without considering which systems would make financial sense for the owners of homes, businesses and other commercial buildings. Dramatically scaling up rooftop solar would also require big investments in the electric grid, which was built to accommodate large, centralized power plants.
But even if the United States never reaches the 1,432 terawatt-hours of annual rooftop solar generation that NREL estimates is possible, the study gives policymakers a starting point for discussion, said Pieter Gagnon, an engineering analyst and the study’s lead author.
"It doesn’t speak to whether or not that’s something that should be supported through policy or not. That’s ultimately up to whatever institutions are making those decisions," Gagnon said. "But they can do it in light of the understanding of how much electricity could conceivably come from rooftop solar."
NREL researchers estimated the country’s rooftop solar potential by examining specialized aerial images, known as light detection and ranging, or LiDAR, for 128 cities, including Los Angeles, St. Louis and Buffalo, and then extrapolating their results to the rest of the country.
The research lab didn’t have access to LiDAR data during its previous analysis of rooftop solar potential, which is one of the reasons the estimates changed so much from 2008, Gagnon said. The estimates also went up because solar panels are much more efficient now than they were a decade ago, and because there are more buildings now than there were then.
Researchers estimated that "small buildings", homes, for the most part, account for 65 percent of the country’s rooftop solar generation potential. In California, that number is 59 percent.