The National Renewable Energy Laboratory (NREL) has conducted a new study to find exactly how much solar power potential the nation's rooftops contain and they found that it's far greater than once thought. The study set out to find how much electricity could be generated if every suitable roof area was covered with solar photovoltaic panels.
Using LiDAR (light detection and ranging) data, improved simulation software for solar PV generation and data analysis methods for 128 cities across the country, NREL updated their rooftop solar power estimate to 1,118 gigawatts (GW) of capacity and 1,432 terawatt-hours (TWh) of annual energy generation -- that's 39 percent of the country's current electricity demand.
The new study's findings almost doubled the results from NREL's last estimate, which was 664 GW of capacity and 800 TWh of annual energy generation. The researchers say the huge increase comes from a combination of better survey methods and calculations and improved solar technology.
The study used the data from the 128 cities, which represented about 23 percent of the country's buildings, to extrapolate the potential of the entire continental U.S. The researchers were then able to come up with estimates of rooftop solar power potential down to the zip code level.
A significant finding of the study was that small buildings actually have a greater combined potential than medium to large buildings because there are just far more of them across the country. About 83 percent of small buildings had an area suitable for solar installation and could potentially generate 926 TWh per year of electricity -- 65 percent of the total potential.
These findings go to show that every rooftop installation helps, even if it's small, because it adds up to something much greater.
NREL also points out that this study is actually just a slice of the country's total solar energy potential.
"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," said said Robert Margolis, NREL senior energy analyst and co-author of the report. "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 facades. Further, the results are sensitive to assumptions about module performance, which are expected to continue improving over time."
You can read more details about the study in NREL's official report (PDF).