Jeff Brady, NPR

NPR National Desk Reporter

Think "renewable energy" and the wind and sun come to mind, but someday it may be possible to add ocean energy to that list.

The U.S. power grid could become 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.

Renewable energy like solar and wind is booming across the country as the costs of production have come down. But the sun doesn't always shine, and the wind doesn't blow when we need it to.

This challenge has sparked a technology race to store energy — one that goes beyond your typical battery.

Heat Storage: Molten Salt And A Giant Solar Farm

Batteries are often used to store solar power, but it can be a costly endeavor.

The U.S. wind power industry is celebrating after reaching a new milestone in November: 70 gigawatts (GW) of generating capacity.

"That's enough to power about 19 million homes," says Michael Goggin, senior director of research at the American Wind Energy Association (AWEA).

There are more than 50,000 wind turbines operating across 40 states and Puerto Rico, according to the AWEA.

A natural gas drilling boom in Pennsylvania is helping the economies of Rust Belt cities long accustomed to bad news. Drilling requires steel — lots of it — and that has manufacturers expanding and hiring new workers.

While much attention has been paid to the environmental risks of drilling into the Marcellus Shale, the economic benefits have been less prominent in the national discussion. But in Youngstown, Ohio, locals have been watching an old industry come back to life.

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