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Rooftop Solar Could Provide up to 40% of US Energy Sales, NREL Report

The U.S. could generate nearly 40 percent of its electrical sales via its rooftops according the latest analysis from the Department of Energy’s National Renewable Energy Laboratory (NREL). That’s almost double its previous analysis!

"This report is the culmination of a three-year research effort and represents a significant advancement in our understanding of the potential for rooftop PV to contribute to meeting U.S. electricity demand," said Robert Margolis, NREL senior energy analyst and co-author of the report. "It is important to note that this report only estimates the potential from existing, suitable rooftops," he added. The report doesn’t include the potential for solar parking lots, less suitable roofs or building facades, all of which are potential sites.

The new report, "Rooftop Solar Photovoltaic Technical Potential in the United States: A Detailed Assessment,” estimates that 1,118 gigawatts of solar power could be installed on U.S. rooftops. If the potential was achieved the rooftops would produce 1,432 terawatt-hours (TWh) of annual electric generation—equivalent to 39 percent of the nation’s current electricity sales.

Those figures are also likely to be increased in the future as photovoltaic efficiency continues to increase. For instance, the lab previously estimated that U.S. rooftops could host 664 gigawatts of solar panels. The previous estimation also was made in 2008, since then photovoltaics have made strong strides in energy conversion efficiencies. Other recent studies also hint that U.S. rooftops have more potential than previously thought.

"An accurate estimate of PV's technical potential is a critical input in the development of regional deployment plans," said Pieter Gagnon, an engineering analyst of solar policy and technoeconomics at NREL and lead author of the report. "Armed with this new data, municipalities, utilities, solar energy researchers, and other stakeholders will have a much-improved starting point for PV research and policymaking, both regionally and nationwide."

The researchers used detailed light detection and ranging (LiDAR) data for 128 cities across the nation. They employed GIS methods and PV-generation modeling to determine the viability of solar rooftops on residential and commercial buildings since doing the estimation manually for each rooftop would be too time consuming.

Researchers calculated “the suitability of rooftops for hosting PV in 128 cities nationwide-representing approximately 23 percent of U.S. buildings-and provide PV-generation results for 47 of the cities. The analysts then extrapolated these findings to the entire continental United States. The result is more accurate estimates of technical potential at the national, state, and zip code level,” NREL stated.

Interestingly the report found that 83 percent of small buildings, like homes, are suitable for solar power. But only 26 percent of their individual rooftops are suitable, on average, for solar. That’s because of things like rooftop angles and which way the angles surfaces face.

“Because of the sheer number of this class of building across the country, however, small buildings actually provide the greatest combined technical potential. Altogether, small building rooftops could accommodate up to 731 GW of PV capacity and generate 926 TWh per year of PV energy-approximately 65 percent of the country's total rooftop technical potential,” the report explained. “Medium and large buildings have a total installed capacity potential of 386 GW and energy generation potential of 506 TWh per year, approximately 35 percent of the total technical potential of rooftop PV.”

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