On Friday Duke announced that the settlement was related to “technical issues” surrounding permits issued by the Indiana Department of Environmental Management to Duke for the construction and operation of the plant.

Duke said the settlement did not affect the permits, leaving them “approved with no changes”

However, under the terms of the settlement Duke agreed to retire or convert a total of 668 megawatts of power at its Wabash River coal-fired power plant in Vigo County.

The Sierra Club, one of the groups in the settlement, announced that Duke would cease burning coal at four units and convert one unit to gas by June 1, 2018.

The other groups involved include Citizens Action Coalition, Valley Watch and Save the Valley.

Duke said it had been exploring converting unit 6 to gas and the 2018 deadline did not rule out the possibility of converting the unit to natural gas earlier.

Duke Energy Indiana president Doug Esamann said the company was glad to resolve the issues.

“Our new, cleaner Edwardsport plant modernizes our fleet and enables us to retire older, coal-fired generation," he said.

"The new plant replaces the old Edwardsport units, which date back to the 1940s and 1950s and were retired in 2011.

“In addition, we retired two older units at our southern Indiana Gallagher plant in 2012."

Duke Energy also agreed to pursue either a new feed-in tariff program to purchase at least 30MW of solar power from its Hoosier customers or to purchase or install at least 15MW of wind or solar generating capacity from new facilities built in Indiana.

A feed-in tariff enables customers to earn money from their own solar panels by selling excess power back to electric utilities.

The Sierra Club said the settlement did not resolve the parties’ parallel case before the Indiana Court of Appeals to overturn Indiana Utility Regulatory Commission decisions regarding the Edwardsport plant.

In July, mechanical problems at the plant caused it to cease operation just six days after being declared “in-service” by Duke Energy.

Shortly following this, Citizens Action Coalition, Save the Valley, the Sierra Club and Valley Watch appealed the IURC’s December 2012 approval of additional rate increases tied to the Edwardsport coal gasification plant and the Sierra Club said they would file briefs by September 9 in the case pending before the Indiana Court of Appeals.

"Citizens Action Coalition is certainly pleased that Duke has committed to permanently mothballing a dirty coal-fired power plant,” Citizens Action Coalition executive director Kerwin Olson said.

“However, we and our allies will remain diligent in continuing our fight against the scandal-ridden Edwardsport IGCC [integrated gasification combined cycle] power plant.

“Ratepayers should not be forced to pay one more penny for that fiasco.”

In Duke’s statement it says the “advanced technology Edwardsport plant is one of the world's cleanest coal-fired power generating facilities”