Allete Clean Energy, the renewable energy affiliate of Duluth-based Minnesota Power, said Thursday it has acquired an Iowa wind farm for $15 million, the company’s second major acquisition this year.

With the purchase of the 144-turbine wind farm near Storm Lake, Iowa, Allete Clean Energy in one year has gone from having no wind farms to owning four of them. The others are in Lake Benton, Minn., Condon, Ore., and on an adjacent site near Storm Lake.

“We will continue to explore opportunities to add to our portfolio,” Steve Peluso, vice president for project origination at Allete Clean Energy, said in an interview.

The company, established in 2011, operates independently of Minnesota Power, a regulated utility that has separately developed four North Dakota wind farms to serve its 143,000 Minnesota customers. Both are units of Allete Inc., the publicly traded holding company based in Duluth.

Allete Clean Energy develops, owns and operates wind farms, and sells power under long-term contracts to other utilities in Iowa, Wisconsin, Oregon and Minnesota, including Minneapolis-based Xcel Energy Inc., the state’s largest electric utility.

Peluso said that some of those contracts expire in a few years, and the company will look at extending the deals or finding new buyers for the electricity, possibly after repowering the wind farms with newer turbines. The Iowa and Minnesota wind farms were built in 1998-1999 with 750-kilowatt turbines, less than half the output of current models.

He said the company is considering other clean-energy acquisitions, including two that “we are looking at very seriously.” He did not identify the projects, but the company has said it holds an option to acquire a 101-megawatt Armenia Mountain wind farm on the Pennsylvania-New York border.

In 2015, Allete Clean Energy also plans to begin construction of a 43-turbine, 107-megawatt wind farm near Hettinger, N.D., about 100 miles southwest of Bismarck, Peluso said. In November, the company said it had finalized a deal to sell the project for $200 million to MDU Resources Group, a multifaceted utility and energy company based in Bismarck.

Allete Clean Energy’s latest wind farm acquisition from NRG Energy is known as Storm Lake I. It is adjacent to Storm Lake II, a smaller wind farm it acquired in a $26.9 million deal from AES Corp. last January. That deal also included the wind farms in Buffalo Lake, Minn., and Condon, Ore.

The push into renewable energy represents a major shift for Allete and Minnesota Power, which long relied heavily on coal to generate power. The strategy, called Energy Forward, includes wind investments, an emissions control upgrade now underway at the utility’s largest coal-fired generator, conversion of a two-unit coal power plant to natural gas and retirement of one coal unit at another plant in 2015. Minnesota Power also plans to build a large solar power project at Camp Ripley near Little Falls.