One of the largest single investments in Alliant Energy’s multiyear plan to create cleaner and more efficient ways to generate electricity will be a $1-billion expansion of an Iowa wind farm, adding 500 MW of capacity to the 200 MW now in place. Details of the expansion, announced July 27, are still being worked out, a spokesman for the Wisconsin-based utility says, but the project is scheduled for commercial operation in 2020—in time to earn the renewable-energy tax credit.

Alliant Energy’s Iowa utility, Interstate Power & Light Co. (IPL), is seeking regulatory approval to expand its Whispering Willow Wind Farm in Franklin County, Iowa, and possibly develop wind energy in other areas of the state. The new wind project is part of Alliant’s clean energy vision. The company aims to achieve a 40% reduction in carbon dioxide emissions below the 2005 level by 2030. This project, with several others, is being prosecuted under the terms of a July 15, 2015, settlement agreement with the U.S. Environmental Protection Agency, the Sierra Club, Linn County and the State of Iowa.

Since 2011, when negotiations began with EPA and its co-plaintiffs, Alliant has completed or planned most of the projects included in the settlement agreement, company officials say. The agreement requires IPL to install new pollution control technology at its two largest plants in Lansing and Ottumwa, and to retire or convert to natural gas its remaining five plants in Burlington, Cedar Rapids, Clinton, Dubuque and Marshalltown. The new pollution controls are expected to cost approximately $620 million.

The three largest construction projects include a $150-million installation of selective catalytic reduction at the Columbia Energy Center, a $700-million combined-cycle natural gas plant at the Riverside Energy Center scheduled for commercial operation in 2019 and the similarly sized Marshalltown Generating Station nearing completion in 2017. An SCR installation at Ottumwa Generating station estimated at $75 million to $100 million is in regulatory approval, with completion expected in 2018 or 2019.

Alliant issued an RFP for the entire 500-MW Whispering Willow expansion about June 1, but has not yet decided whether all of the new wind capacity will be built in the Franklin County location. “A lot of that comes down to the land we’re able to acquire through land rights and easements with landowners,” says Justin Foss, spokesman. The company probably won’t have answers until late this year, he says. Alliant is building natural-gas generation to serve as reserve capacity for the system instead of building energy storage facilities. “Our combined-cycle station being built in Marshalltown is state-of-the-art and will be able to supplement and complement the fluctuation in wind,” Foss says.