New York (CNN Business) America's clean energy revolution is on the verge of a tipping point.

The renewable energy sector is projected to generate more electricity than coal during the month of April, according to a recent report published by the Institute for Energy Economics and Financial Analysis. That's never happened before.

"Five years ago this never would have been close to happening," Dennis Wamstead, research analyst at IEEFA, said in an interview. "The transition that's going on in the electric sector in the United States has been phenomenal."

Even a decade ago, America's renewable energy had little presence other than hydro power. But a wave of investment — first into wind, and then solar — has made these new technologies far cheaper.

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