The 615MW Duane Arnold Energy Center (DAEC) is majority-owned by US firm NextEra and is due to be decommissioned in late 2020. It also provides power to Iowa utility Alliant Energy.

NextEra will instead supply Alliant with wind power from four repowered Iowan wind farms with a combined capacity of 340MW, it stated.

Alliant Energy, meanwhile, will make a $110 million buyout payment to NextEra in September 2020 to cover the cost of shortening the term of its power purchase agreement (PPA) for DAEC from 2025 to 2020.

The utility also plans to add 1GW of wind capacity in Iowa by 2020.

The DAEC’S operating license runs until 2034, but earlier this year, NextEra’s CFO John Ketchum said the power plant was unlikely to run beyond 2025, Platts reported.

Alliant, meanwhile, has a PPA for the plant, which is due to expire in 2025.

Alliant Energy CEO Patricia Kampling said: "The Duane Arnold Energy Center has provided reliable energy to Alliant Energy’s Iowa customers for decades.

"Partially replacing energy from Duane Arnold with NextEra’s additional wind investments in Iowa will bring significant economic benefit to our customers."

Windpower Monthly has asked Alliant what other sources of power it will use to replace output from the DAEC.

Alliant also plans to add 1GW of wind capacity before 21 December 2020 "to qualify for production tax credits", a spokesman for the utility told Windpower Monthly.

The company owns and operates 568MW of wind power capacity in Iowa, Minnesota and Wisconsin, and partly owns a 225MW project in Oklahoma, according to its website.

Alliant applied to the Iowa Utilities Board for approval of the buyout payment on 27 July.

NextEra plans to invest about $650 million in existing and new renewable energy projects across Iowa by 2020, including $250 million for the four repowering projects.

The electricity supplier also stated it plans to notify the Midcontinent Independent System Operator and the Nuclear Regulatory Commission of its intention to decommission the DAEC "at the appropriate time".