DOE/National Renewable Energy Laboratory
Analysts at the Energy Department'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 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 percent 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 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.
"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.
Within the 128 cities studied, the researchers found that 83
percent of small buildings have a suitable location for PV installation, but
only 26 percent 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 percent 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
percent of the total technical potential of rooftop PV.
"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."
"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 Margolis.
"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."
Technical potential is an established reference point for
renewable technologies.
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.