by Brianna Crandall — April 15, 2016 — Analysts at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) have used detailed light detection and ranging (LiDAR) data for 128 cities nationwide, along with improved data analysis methods and simulation tools, to update its estimate of total U.S. technical potential for rooftop solar photovoltaic (PV) systems. The analysis reveals a technical potential of 1,118 gigawatts (GW) of capacity and 1,432 terawatt-hours (TWh) of annual energy generation, equivalent to 39% of the nation’s electricity sales.
This current estimate is significantly greater than that of a previous NREL analysis, which estimated 664 GW of installed capacity and 800 TWh of annual energy generation. Analysts attribute the new findings to increases in module power density, improved estimation of building suitability, higher estimates of the total number of buildings, and improvements in PV performance simulation tools.
The analysis appears in Rooftop Solar Photovoltaic Technical Potential in the United States: A Detailed Assessment. The report quantifies the “technical potential” for rooftop PV in the United States, which is an estimate of how much energy could be generated if PV systems were installed on all suitable roof areas.
To calculate these estimates, NREL analysts used LiDAR data, Geographic Information System methods, and PV-generation modeling to calculate the suitability of rooftops for hosting PV in 128 cities nationwide — representing approximately 23% 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.
Within the 128 cities studied, the researchers found that 83% of small buildings have a suitable location for PV installation, but only 26% of those buildings’ total rooftop area is suitable for development. 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% of the country’s total rooftop technical potential. Medium and large buildings have a total installed capacity potential of 386 GW and energy generation potential of 506 TWh per year, approximately 35% of the total technical potential of rooftop PV.
Robert Margolis, NREL senior energy analyst and co-author of the report, points out:
It is important to note that this report only estimates the potential from existing, suitable rooftops, and does not consider the immense potential of ground-mounted PV. Actual generation from PV in urban areas could exceed these estimates by installing systems on less suitable roof space, by mounting PV on canopies over open spaces such as parking lots, or by integrating PV into building façades. Further, the results are sensitive to assumptions about module performance, which are expected to continue improving over time.
Technical potential is an established reference point for renewable technologies, notes NREL. It quantifies the amount of energy that can be captured from a particular resource, considering resource availability and quality, technical system performance, and the physical availability of suitable area for development — without consideration of economic factors like return on investment or market factors such as policies, competition with other technologies, and rate of adoption.
NREL’s work was supported by funding from the DOE’s Office of Energy Efficiency and Renewable Energy (EERE) in support of its SunShot Initiative, which supports efforts by private companies, universities, and national laboratories to drive down the cost of solar electricity to $0.06 per kilowatt-hour.
