GenOn Energy’s Potomac River Generating Station might not be necessary to keep the lights on in the Washington region, according to a recent report.

The coal-fired plant in Alexandria formerly owned by Mirant operates on a limited basis and provides about 5 percent of the area’s electricity, said a July report by Analysis Group, a national engineering and utility research firm. If local utilities complete expected infrastructure upgrades in the next year, there would be enough reliable power that the plant would be unnecessary, the report said. Greenhouses gases, such as carbon dioxide and nitrogen oxide, would also decrease substantially, it said.

Analysis Group said a second assessment of power needs is scheduled be completed by PJM Interconnection, a regional transmission organization that coordinates the movement of electricity in the mid-Atlantic region.

“Once ongoing transmission and substation upgrades are completed, which should happen in 2012 at the latest, there do not appear to be any reliability issues related to this plant,” said Gregory C. Staple, chief executive of American Clean Skies Foundation, which advocates for natural gas and other clean energy sources. The foundation commissioned the report.

The GenOn plant, which has come under fire from the Alexandria community for failing to meet environmental regulations in the past, operates during peak hours when people use much more electricity, the report said.

“Increasingly, more and more of the peak-load needs within the region are being met by ‘demand-side resources,’ that is, users . . . who are willing to reduce demand during peak periods,” Staple said, explaining why the plant’s generation would be unnecessary.

If the plant shuts down, greenhouse gas emissions from the plant would be greatly reduced, based on modeling done by the report’s authors.

But Misty Allen, a GenOn spokeswoman who disagreed with the report, said the plant is needed to ensure there is enough power to handle high-usage days, such as when additional air conditioners are used in extremely hot weather.

“The report conducted and released by the natural gas industry is a one-dimensional analysis of a multi-dimensional, complex issue that comes to an overly simplistic conclusion,” Allen said. “There is not an environmental issue with the plant, or it would not be able to operate. We are in full compliance with state and federal regulations and have invested millions to improve air quality at the plant and continue to demonstrate operational excellence.”

Paul Hibbard, vice president of Analysis Group and co-author of the report, said the plant is expensive to run, and peak days drive the price of electricity up, making economic sense for GenOn Energy to run the plant at that time.

“The fact that it operates on peak days does not necessarily mean that the plant is needed for reliability,” Hibbard said.

The Potomac River Generating Station was shut down in 2005 by the Virginia Department of Environmental Quality to reduce pollutants emitted from the plant. The U.S. Department of Energy and the District government ordered the plant back on to ensure there was enough electricity to power the District.

The plant’s owners are working to install several million dollars’ worth of equipment to reduce the pollutants as part of a settlement agreement with the City of Alexandria.

“If it has to operate, we want it to be as clean as possible,” said Rich Baier, director of the city’s transportation and environmental services. “Our overriding long-term goal is for the plant to close,” he said. Baier welcomed the report as information that will lead to that goal.

The national environmental advocacy group Sierra Club has worked to shut down coal-fired plants across the country, including the Alexandria plant. The local chapter reports that harmful emissions, including sulfur dioxide and mercury, are being spewed over Alexandria and the District and absorbed by fish in local waterways.

Concerned over the emissions, D.C. Mayor Vincent C. Gray (D) and D.C. Department of the Environment chief Christophe A.G. Tulou are considering petitioning the Environmental Protection Agency to shutter the plant.

The District’s Public Service Commission requested that PJM do an analysis of the plant and determine whether it is necessary in the District.

“We need to look at it and see if it affects system stability, among other things. What happens when you take it out of the mix?” said Ray Dotter, a PJM spokesman. “If there is an effect, we’d identify what needs to be done.”

A complete report is expected in the fall, Dotter said.

The report “answers an essential piece of the puzzle — that this energy is not needed in D.C.,” said Phillip Ellis, an Alexandria field organizer for the Sierra Club. “If the plant is not needed and not wanted by the community, why is it still operating?”