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NREL: California has greatest potential to offset electricity use with rooftop solar

California has the greatest potential out of all of thestates in the continental U.S. to offset electricity use with rooftop solarphotovoltaic systems, according to a new report from the National Renewable Energy Laboratory.

The report, "Rooftop Solar Photovoltaic TechnicalPotential in the United States: A Detailed Assessment," released March 24,said California's rooftop solar photovoltaic could generate 74% of the electricitysold by its utilities in 2013. The report examined rooftop PV's technicalpotential, which NREL said is an estimate of how much energy could be generatedif PV systems were set up on all "suitable" roof areas.

Analysts for NREL used light detection and ranging data, orLiDAR data, geographic information system methods, or GIS, and PV-generationmodeling to determine the suitability of rooftops for accommodating PV panelsin 128 cities, representing roughly 23% of U.S. buildings.

Despite having "below-average" solar resources,New England states could generate more than 45% of the electricity sold by itsutilities in 2013, because these states' low per-capita electricity consumptionoffsets their below-average solar resource, according to the report.Washington, with the lowest population-weighted solar resource in thecontinental U.S. could still generate 27%, the report said.

The top six states — in terms of potential PV generation asa percentage of total state sales — all have substantially below-averagehousehold consumption, "suggesting the role an energy-efficientresidential sector could play in achieving a high penetration of energy fromrooftop PV," the report said.

Wyoming and Washington, D.C., have the lowest and secondlowest potential for offsetting electricity sales with rooftop PV at 14% and15%, respectively. Wyoming's offset potential is so low because it has thehighest per-capita electricity sales out of all of the states at 30.3 MWh peryear per person, or 250% of the national average, due to very high industrialsector electricity use, which accounts for 60% of retail electricity sales,NREL said in the report.

The report's authors called Washington, D.C., "unique"and said its low percentage is mostly due it being an almost entirely urbanarea, with a much smaller-than-average developable roof area per capita.

On a national level, the report's authors found the totaltechnical potential of rooftop PV is 1,118 GW of installed capacity and 1,432TWh of annual energy generation, which is equal to 39% of total nationalelectric-sector sales, and is considerably greater than the NREL estimate of664 GW of installed capacity and 800 TWh of annual energy generation from aprevious analysis.

The change can be linked to increases in module powerdensity, improved estimation of building suitability, higher estimates of thetotal number of buildings, and improvements in PV performance simulation tools,NREL said in the report.

Robert Margolis, a senior energy analyst for NREL and aco-author of the report, said NREL's findings the understanding of rooftop PV'spotential to contribute to meeting electricity demand in the U.S.

Margolis also noted the report "only estimates the potential from existing, suitablerooftops, and does not consider the immense potential of ground-mounted PV."Actual generation from PV in urban areas could exceed these estimates byinstalling systems on less-suitable roof space, by mounting PV on canopies overopen spaces such as parking lots, or by integrating PV into building facades,he said.