Duke Energy and Progress Energy committed to energy-efficiency targets in the Carolinas and to shut down old coal-fired power plants in an agreement Monday with advocacy groups that had raised concerns over their merger.

The agreement was announced in Columbia, where the S.C. Public Service Commission began a hearing on one portion of the merger, the utilities' plan to jointly operate their power plant fleets.

The settlement breaks relatively little new ground, accelerating existing energy-efficiency programs and requiring a shutdown of power plants the utilities had already announced they would close. Among them are Duke's Riverbend plant on Mountain Island Lake west of Charlotte and older units at its Cliffside plant in Rutherford County.

But the advocacy groups said it injects a voice for efficiency and green energy in a merger that would create the nation's largest utility.

"When you become the largest utility in the country, people are going to be looking at you to make the right decisions," said Greg Andeck of the Environmental Defense Fund.

"We see replacement of (power plant) generation as fundamental business decisions, and we hope a lot of it will be replaced by energy efficiency and renewable energy."

The Southern Environmental Law Center negotiated the agreement on behalf of the Environmental Defense Fund, Coastal Conservation League and Southern Alliance for Clean Energy.

Duke spokesman Tom Williams called the agreement "another step in the merger approval process. We continue to get intervenors on board in support of the merger."

Duke and Progress hope the Federal Energy Regulatory Commission will approve a merger plan that is on the commission's schedule for Thursday. The merger still needs approval by Carolinas utility commissions.

Under the agreement announced Monday, Duke and Progress will:

Adopt an annual energy-efficiency savings target of 1 percent of retail sales, starting in 2015. It sets a cumulative target of 7 percent from 2014 to 2018. Utility commissions in both Carolinas will have to approve the programs.

Both Duke and Progress have existing energy-efficiency targets in North Carolina. "We've made some good progress and we feel we can achieve them," Williams said of Duke's N.C. save-a-watt program, approved in 2009, which sets a goal of achieving 1 percent in energy efficiency savings by 2015.

Contribute $1 million a year for two years to Palmetto Clean Energy Inc., an S.C. nonprofit that promotes renewable energy.

Commit to retiring older, higher-polluting coal plants totaling more than 3,000 megawatts by 2015.

Duke had already planned to shut down, by 2015, about 2,000 megawatts of plants in the Carolinas that can't meet new environmental standards. Progress has said it would retire about 1,500 megawatts by the end of 2015.

Despite those announcements, company plans sometimes change, said Andeck of the Environmental Defense Fund. "We see this as an insurance policy," he said.