A study published by the Union of Concerned Scientists, considered a left-leaning group, said more than 350 coal generators in 31 states may no longer be considered economically viable.
The study said those coal plants, which represent as much as 6 percent of U.S. power capacity, should be closed in favor of renewable energy programs.
"Our analysis shows that switching to cleaner energy sources and investing in energy efficiency often makes more economic sense than spending billions to extend the life of obsolete coal plants," Steve Frenkel, a Union of Concerned Scientists member and co-author of the report, said in a statement.
The UCS report said generators outlined in the study are "well beyond" the typical 30-year life span for coal generators, which suggests they're less efficient and more polluting than newer facilities.
By contrast, the report said, as much as 55 gigawatts of new renewable energy could be on the U.S. grid by 2020.
"Regulators should require utility companies to carefully consider whether ratepayers would be better off by retiring old coal plants and boosting electricity generation from natural gas and renewable energy sources like wind," said Frenkel.