The U.S. power grid couldbecome less reliable if too much electricity comes from renewable energy and natural gas, according to a study from the Department of Energy.

But not everyone is buying it. Environmentalists suspect the Trump administration is just trying to prop up an ailing coal industry.

Energy Secretary Rick Perry called for the study in the spring. The report doesn't say there is a grid reliability problem now — only that one could develop if more coal and nuclear power plants shut down.

Those plants are having trouble competing with cheaper natural gas and renewable energy at a time when the country is using less electricity.

The Energy Department study points out that coal and nuclear generate power whenever it's needed, while solar and wind can be less predictable.

This echoes an argument that traditional utilities and power generators have made for years.

"The most reliable and resilient grid is the type that will balance traditional base load sources of power with renewable power," says Scott Segal, director of the Electric Reliability Coordinating Council.

Segal says renewable forms of electricity got a lot of focus during the Obama administration, but now he thinks it's time for the pendulum to swing back.

The Sierra Club's Mark Kresowik sees something else entirely in the Energy Department's report.

"Coal and nuclear interests are making a last-ditch attempt to try and preserve their market share, that is being taken up by fast-growing, clean, reliable, affordable resources like wind and solar," he says.

Kresowik and other renewable energy advocates believe the Trump administration is laying the groundwork to justify subsidies for coal and nuclear power plants.

"It will cost consumers more, and ultimately we will all be paying the price — whether in increased electricity costs or by breathing dirtier air," Kresowik says.

Nuclear plant operators already have won subsidies in some states, and coal companies have lobbied the Trump administration for help.

But Segal says, "Any real bold policy changes require major regulatory change or legislation or both."

The Department of Energy is now accepting public comments on its grid report. Early indications are that the agency is about to get an earful.

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