“This is a much higher fraction of economic vulnerability than has previously been reported,” he said of the study published in the journal Environmental Science and Technology.

A decade ago, coal provided more than half of U.S. power, but in 2012 it was down to roughly 37 percent, while gas and renewables have risen. Gas provided more than 30 percent of U.S. power last year, according to the federal Energy Information Administration.



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Under existing standards and prices, 9 percent of U.S. coal plants are more expensive to operate than a median-cost natural gas plant, the Duke researchers say.“However, with tougher emissions standards the EPA would enact and enforce, another 56 percent of U.S. coal plants would become as costly to run as natural gas plants. The regulations would make 65 percent of coal plants nationwide as expensive as natural gas, even if gas prices rise significantly,” according to a Duke summary of the paper.The study looks at the economics of generating power with coal and gas, and finds that the EPA rules will have a considerable effect because of coal’s greater emissions of certain pollutants.The study explores air pollution rules and planned regulations on cooling water and certain waste products from coal plants.“The tighter air-quality standards alone will require upgrades to emission control systems (ECTs) at many natural gas as well as coal plants. But whereas the affected natural gas plants typically produce only NOx [nitrogen oxide] emissions in excess of the new thresholds, the affected coal plants may also be exceeding new SO2 [sulfur dioxide], PM [particulate matter] and mercury (Hg) limits making it more expensive for these plants to come into compliance,” it notes.

The Duke researchers caution, however, that other factors could mitigate the decline in coal-fired power.



“The possibility of generating electricity from natural gas at a competitive cost is certainly a strong factor in favor of retiring coal plants instead of retrofitting them, but it may not be the determinant factor. An extreme shift to natural gas for electricity generation requires the development of necessary infrastructure to transport and store the gas in a way that guarantees its reliable supply to power plants,” the study states.

