Two Iowa utilities are investing a combined $4.6 billion to build 2,500 megawatts of new wind energy in the state over the next four years.

On Wednesday, Alliant Energy announced a $1 billion, 500-megawatt expansion of its 200-megawatt Whispering Willow Wind Farm in north-central Iowa, while MidAmerican Energy announced that it had settled a rate agreement that would allow its Wind XI project, a $3.6 billion, 2,000-megawatt wind farm, to proceed.

Both projects are aimed at meeting energy demand in a state that is a national wind power leader. Iowa had 6,365 megawatts of wind power capacity at the end of June, according to the American Wind Energy Association—second only to Texas’ 17,911 megawatts. “Iowa has the most of their electricity generated from wind than any other state—about 31 percent” on average, said John Hensley, manager of data and analysis for the trade group. “Some months it’s much higher than that: In April they got more than 50 percent of their power from wind.”

Iowa Gov. Terry Branstad has set an informal target of getting 40 percent of the state’s energy from wind power by 2020. “In fact, wind energy observers believe Iowa could produce enough wind energy by 2030 to achieve complete energy independence and export excess energy to other U.S. states,” Branstad wrote in an op-ed for The Iowa Gazette last year.

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The moves by Alliant and MidAmerican are part of a surge in wind power projects around the country, propelled by the renewal of the federal production tax credit at the end of 2015. Three thousand megawatts’ worth of wind power projects started construction between April and June, Hensley said, while another 5,800 are in advanced planning stages. “To give you a sense of the scale, 2,000 megawatts is the largest project that’s been announced to move forward in the U.S.,” he said, while Alliant’s 500-megawatt plant is more than twice the size of the average wind farm built in 2015.

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Projects must begin construction by the end of the year, or otherwise invest about 5 percent of total anticipated costs, to qualify for the full tax credit, which drops by 20 percent a year until it expires at the end of 2019.

“I do think that this is a very good opportunity for utilities across the country to execute on that value and take advantage of that 100 percent production tax credit,” Hensley said. “It’s also a product that’s really popular with the American people: Over 70 percent of people like wind energy and want to see it added to their mix.”

According to the Federal Energy Regulatory Commission, the nation is adding solar and wind power capacity at a faster pace than any other source, including natural gas.

At the end of 2015, the U.S. had 75,000 megawatts of available wind power capacity, according to the American Wind Energy Association, and wind supplied about 4.7 percent of the nation’s electricity.

Alliant’s wind farm expansion is part of its target of reducing its carbon dioxide emissions 40 percent below 2005 levels by 2030. The company, which operates utilities in Iowa and Wisconsin, sourced 42 percent of its energy supply from coal, 15 percent from natural gas, 5 percent from wind, and 1 percent from a combination of oil, hydropower, solar, and biogas in 2015, according to its annual filing with the federal Securities and Exchange Commission, and purchased 37 percent from providers with a mix of sources including nuclear power.

“Over the last several years, we have already retired or announced the intention to retire about one-third of our coal-generating fleet,” said company spokesperson Justin Foss. “We are steadily moving toward a cleaner energy future, with everything from installing emissions controls on existing coal-fired generation to using more natural gas” to increasing investments in wind and solar.

“What we’re finding with renewable energy, especially with wind energy, is that while it will cost more to build the asset, the fuel costs associated with operating that are zero,” Foss said. “So it comes out even or better for customers over the life of the project.”