Solar on all U.S. roofs would supply 39% of power

California alone could generate 74% of its electricity

A federal study has revealed that if Americans installed solar panels on every roof, it would supply 39% of the total power used by the U.S.

Researchers from the National Renewable Energy Laboratory (NREL) used light detection and ranging (lidar) data, geographic information systems and photovoltaic (PV) generation modeling to calculate the suitability of rooftops for hosting solar panels in 128 cities nationwide, representing about 23% of U.S. buildings.

The total national potential of rooftop solar power is 1,118 gigawatts (billion watts or GW) of installed capacity and 1,432 terawatt-hours (trillion watt hours or TWh) of annual energy generation. That equates to 39% of total national electric-sector sales last year.

Solar power generation Source: National Renewable Energy Laboratory

Within the 128 cities studied, researchers found that 83% of small buildings have a suitable location for PV installation, but only 26% of the total rooftop area on those buildings is suitable for development. Even so, the potential for power generation is enormous.

The study revealed a significantly greater capacity for energy generation than a previous NREL estimate of 664GW of installed capacity and 800 TWh of annual energy generation, the report stated.

"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.

An earlier federal report showed rooftop solar panel installations could cut utility profits by 15% or more over the next eight years based on current installation trends. The study predicted that rooftop solar panel installations will grow from 0.2% market penetration today to 10% by 2022.

Margolis noted NREL's research estimated the potential only from existing, suitable rooftops, and not the "immense potential of ground-mounted PV."

"This amount... could take a large burden off our reliance on fossil-fuel-based power, but obviously, it'd be a massive undertaking to fit out all that available roof space," Margolis wrote in the report.

Solar power generation rooftop Source: National Renewable Energy Laboratory

California has the greatest potential to offset electricity use through rooftop PV. The Golden State could generate 74% of the electricity sold by its utilities in 2013.

New England states could generate more than 45% of their energy needs because they have a low per-capita electricity consumption that offsets their below-average solar resource.

Washington, with the lowest population-weighted solar resource in the continental United States, could still generate 27% of its needs through rooftop solar. Some states with below-average solar resources (such as Minnesota, Maine, New York, and South Dakota) have similar or even greater potential to offset total sales compared to states with higher-quality resources (such as Arizona and Texas), the study showed.

SolarCity solar PV installations Source: SolarCity

Workers for SolarCity install rooftop solar on a house.

Florida can offset 47% of its total energy consumption despite having an average household electricity consumption of 130% of the national average. "This is largely explained by significantly below-average electricity consumption outside of the residential sector, which makes the state's total per-capita electricity sales slightly lower than the national average," the report stated.

By comparison, the other South Atlantic states range from a potential 23% to 35% of electricity offset owing to lower average rooftop suitability, slightly lower quality solar resource and higher per-capita total electricity sales.

"An accurate estimate of PV's technical potential is a critical input in the development of regional deployment plans," said Pieter Gagnon, an NREL engineering analyst 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."

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