U.S. rooftop energy potential 80% more than thought — study

Source: Christa Marshall, E&E reporter • Posted: Friday, March 25, 2016

U.S. rooftops could generate 80 percent more energy from solar panels than previously thought, according to a new analysis from the National Renewable Energy Laboratory.

Using a combination of aerial surveys, on-the-ground counting and supercomputing, researchers found rooftop solar holds the potential to generate 1,432 terawatt-hours of annual energy, up from the estimated 800 terawatt-hours in 2008. The amount of possible installed capacity from rooftop solar photovoltaics also jumped from 664 gigawatts to 1,118 GW. The three-year analysis projected the level of energy that could be generated in theory if PV systems were installed on all suitable U.S. business and residential rooftops.

Pieter Gagnon, an engineering analyst at NREL and lead author of the report, said an accurate estimate of the “technical potential” of rooftop solar provides a critical baseline for regional and city planning.

“Armed with this new data, municipalities, utilities, solar energy researchers and others will have a much-improved starting point for PV research and policymaking,” he said.

The numbers increased for a variety of reasons, including that a given amount of solar panel space can generate more power than it could eight years ago because of technology improvements, he said in an interview. Researchers also found higher overall estimates of buildings suitable for solar. “There has been a trend of both more buildings as well as larger buildings over the past three decades,” Gagnon said. Within those buildings, a higher percentage of space was determined to be suitable for solar PV as well.

That’s partly because computer modeling of factors such as shading near homes is more accurate than it used to be, he said.

The researchers assessed 128 cities — which hold about a quarter of U.S. buildings — and then extrapolated the results nationwide. The results break down solar potential by state and ZIP code. Light detection and ranging (lidar) data from the Department of Homeland Security informed the results, as well as data from the U.S. census, Gagnon said.

Small buildings, including private homes, hold about 65 percent of the country’s total potential for rooftop solar, even though about a quarter of their rooftops is typically suitable for the power source, according to the report. Their large overall number allows them to hold the greatest solar potential. The actual potential for solar PV in urban areas could be larger than the estimates because of non-rooftop locations like canopies over parking lots, the report said.

The analysis comes as rooftop solar set a record last year in the United States, according to data released yesterday from the Energy Information Administration. Declining costs, improved technology, and federal and state policies are driving the growth, according to analysts (Greenwire, March 23).