The total potential for solar energy production on the roofs of low- to moderate-income households by county. (Source: NREL)

A recent report from the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) finds that pairing solar PV with rooftops of low- and moderate-income (LMI) housing represents an opportunity to help modernize the U.S. electric grid and improve energy affordability.

The report breaks down the total potential for solar energy production on the roofs of LMI households by county. Though existing rooftop solar adoption in the U.S. has primarily been concentrated in middle- and upper-income households, falling technology costs and market expansion are enabling access by previously underserved market segments, says NREL.

U.S. Census Bureau data has provided an understanding of the share of LMI households in the U.S. (approximately 43%), but the new NREL analysis reveals two other important attributes of these households: the proportion living in buildings suitable for rooftop solar and the share of their total electricity needs that could be met through rooftop solar.

The report, Rooftop Solar Technical Potential for Low-to-Moderate Income Households in the United States, integrates the estimated rooftop solar technical potential of residential buildings with census tract statistics by income, building type and tenure. The report is accompanied by a web application that enables users to assess solar technical potential for their communities.

“We designed the study and associated tool to provide quality, objective data to help inform the decisions of all key stakeholders,” says Benjamin Sigrin, NREL researcher and report author. “The findings can help communities make informed decisions that best meet their needs as they address long-term solar adoption targets across demographic categories and building type.”

Sigrin and fellow NREL researcher Meghan Mooney applied data analysis techniques to U.S. Census data and newly acquired data from 128 U.S. cities. With the assistance of LiDAR scans, the team mapped rooftops of LMI and non-LMI buildings in sample cities and developed an identifying footprint. NREL’s PVWatts tool simulated the energy generated based on each roof’s characteristics. These simulation results were merged with socioeconomic and building stock data from the U.S. Census to gain a better understanding of solar technical potential across building types. Finally, the team developed a statistical model to estimate rooftop potential for the rest of the country.

Based on this analysis, the report estimates that rooftop solar technical potential for the entire residential sector is about 1,000 terawatt-hours of generation, or about 75% of current residential electricity consumption. The report also finds that rooftop solar can significantly contribute to the achievement of long-term solar adoption targets, such as those set by states and city governments – though to do so requires deployment on multifamily and renter-occupied buildings. However, traditional-deployment business models have not sufficiently enabled access to rooftop solar for LMI groups and building types, says NREL. The report analyzes alternative solutions to increasing solar access, such as oversizing PV systems on buildings owned by nonprofits – such as schools and houses of worship – to share energy generation with nearby households.

“Understanding the potential size of the LMI market in detail offers new insights and opportunities to serve these communities,” Mooney says. “The potential electric bill savings from the adoption of rooftop solar would have a greater material impact on low-income households compared to their high-income counterparts.”

GRID Alternatives provided consultation to NREL on the project. GRID’s experience in low-income solar program implementation and development provided real-world context to ensure that the technical potential assessment would be relevant to both solar providers and policymakers. In addition, GRID’s program data provided researchers with a critical understanding of existing national low-income solar deployment, says NREL. In the next phase of the project, GRID will work with the research team to identify approaches to lowering costs associated with customer acquisition and to address other barriers to increased adoption in the LMI market.

“Solar can have tremendous benefits for low-income communities, in addition to diversifying and decarbonizing our national energy mix,” says Tim Sears, chief operating officer at GRID Alternatives. “We hope this research will give more states the data they need to develop effective low-income solar programs and build a more equitable clean energy economy.”

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