Producing renewable electricity is cheaper than running old coal plants, a new report from investment firm Lazard shows.

Lazard reports that new wind farms in the U.S. can produce power for $29 to $56 per megawatt-hour, compared to $27 to $45 for existing coal-fired powerplants, according to a report last week in the British Financial Times (subscription required.) 

The overlapping numbers represent production without existing subsidies for renewable power generation, which can reduce costs for renewables by an additional $15 per megawatt-hour.

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Along with lower prices for power generation from natural gas, the dropping prices for solar and wind put pressure on coal-powerplants, which have been on the decline since 2008. Coal produced more than half of the electricity in the United States in 2001 and dropped to about 30 percent of the nation's electricity in 2016.

The decline of coal—which effectively makes driving electric cars cleaner—looks set to continue indefinitely. Building any new coal facilities would cost even more than running existing ones, which are being undercut by cheap natural gas and now even by renewable energy sources, the Lazard report shows. 

More electricity in the U.S. is now produced using natural gas, and wind and solar are on the rise. These renewable sources produced a negligible percentage of U.S. electricity in 2001 and now account for more than 7 percent.

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As an example of the efficiency of new renewable energy sources, the Financial Times cites a Colorado project in which regulators approved a move by Xcel Energy to save customers $200 million by shutting down a 660-megawatt coal plant and replacing it with 1.1 gigawatts of wind power, 700 megawatts of solar and 275 megawatts of battery storage—all of which until recently were considered prohibitively expensive.

In a speech at the Edison Electric Institute's annual convention in June, Xcel CEO Ben Fowke, said, "It's not a matter of if we're going to retire our coal fleet in this nation, it's just a matter of when.”