Duke decided not to follow through on an agreement to buy energy from Benton County Wind Farm, prompting a lawsuit in 2013. A circuit court ruled that Duke violated its contract with the wind farm and has to pay $29 million in damages.

Duke Energy spokesman Lew Middleton says $29 million represents the cost customers would have paid if they had bought from the farm. He says just like any other fuel, wind energy prices fluctuate.

"Our aim was to try to minimize costs to customers as much as possible by just buying the power from the wind farm that we wanted to buy and that we could use," Middleton says.

The Indiana Utility Regulatory Commission allowed Duke Energy to recover the cost from ratepayers starting in October 2017 through September of this year. That triggered another lawsuit.

Retired attorney and McKinney School of Law professor Mike Mullett and his wife argue that the utility is owned by investors and so investors should foot this bill.

"Customers should be responsible for paying for service - not for the mistakes, not for the misjudgements of utility management," says Mike Mullett.

But the Indiana Court of Appeals disagreed this week and ruled in Duke Energy's favor. The average additional cost to Duke Energy residential rate payers per month is less than a dollar.

Indiana Environmental reporting is supported by the Environmental Resilience Institute, an Indiana University Grand Challenge project developing Indiana-specific projections and informed responses to problems of environmental change.