Large U.S. utilities are taking advantage of government subsidies to buy and produce more renewable energy in anticipation of tougher new regulations on carbon emissions.

Duke Energy Corp., Southern Co. and the energy unit of Warren Buffett’s Berkshire Hathaway Inc. are among the utility companies that are investing more in solar and wind farms and ramping up purchases of clean power, spurred by renewable-energy mandates in more than half the nation’s states and expected federal limits on greenhouse-gas emissions.

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