A US study has found almost 40% of the nation’s current electricity consumption could be provided by rooftop photovoltaic systems.
The US Department of Energy’s National Renewable Energy Laboratory (NREL) used detailed light detection and ranging (lidar) data, Geographic Information System (GIS) methods and PV-generation modelling to assess the suitability of rooftops in 128 cities. This represented 23% of buildings – the analysts then extrapolated these findings to the entire continental US.
The findings are detailed in a report, which 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.
NREL senior energy analyst and report co-author Robert Margolis says the report, which is the culmination of a three-year research effort, represents a significant advancement in understanding the potential for rooftop PV to contribute to meeting US electricity demand.
Within the cities examined, researchers found 83% of small buildings have a suitable location for installation of solar panels. But when they analysed each building's capacity to hold a PV system on their roof, only 26% passed the grade. While only about a quarter of most small buildings' roofs could practically be used for solar panels, the sheer volume of them means this type of building could actually provide the greatest combined technical potential compared to other kinds of structures.
However, Margolis stresses the report does not take into account PV sources outside rooftops.
"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," Margolis says. "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."