RALEIGH, N.C. – After two years of debate, Duke Energy on Wednesday received approval from the state of North Carolina Utilities Commission to build one of the two coal-fired power plants it has proposed to build west of Charlotte.

The commission voted 5-1 to grant Duke a “certificate of public convenience and necessity” to construct one 800-megawatt plant. But even that decision comes with restrictions.

Those requirements include the “retirement” of the four existing power-generating units at the Cliffside Unit near the South Carolina border “no later than the date of the commercial operation” of the new unit.

Additionally, Duke must “invest” 1 percent of its annual retail revenues from electricity and energy sales in energy efficiency and energy demand programs.

Duke reported $4.07 billion in revenues for the quarter ending on Dec. 31.

The Charlotte-based energy firm supplies power to some 3.9 million customers. Duke has argued that the two plants are necessary to meet growing demands for energy.

Opponents have argued aggressively against Duke’s plan on environmental grounds, saying the new plants would increase pollution.

Duke also recently increased its costs projections for the plant to $3 billion.

Commissioner Robert Owen Jr. dissented, saying the proposal should have been rejected.

The Utilities Commission decision is not the final word on the project. Duke has argued that to build only one plant would be uneconomical. Also, a regulatory permit is still required from the Environmental Protection Agency.

Duke has argued against building either a plant fired by natural gas or nuclear power.

"We view Cliffside as a hedge on any delay in building a nuclear plant, and we also view it as a hedge in never building a nuclear plant," Duke Chief Executive Officer Jim Rogers told Dow Jones Newswires in an interview earlier this month.