A rapidly growing clean-energy affiliate of Duluth-based Minnesota Power on Wednesday said it is buying a large wind farm in Pennsylvania, its seventh wind energy investment in the past 15 months.

Allete Clean Energy said it will acquire Armenia Mountain Wind from the AES Corp. and a minority shareholder for $108 million, plus assumption of debt.

Allete Clean Energy, formed in 2011, has acquired five other wind farms in Iowa, Minnesota and Oregon and is developing one in North Dakota for another utility.

The newest wind farm, near Troy, Pa., in north central Pennsylvania, will be Allete Clean Power's largest, generating 100 megawatts of electricity from 67 turbines installed in 2009. Allete said the power is sold under 25-year power purchase agreements.

Allete Clean Energy, a unit of Allete Inc., has grown from three employees to 60 in four years, including 15 in Duluth, Eric Norberg, president of the clean energy unit, said in an interview.

"We are going to keep adding projects at one or two or maybe, in a busy year, three projects a year," Norberg said. "Allete has a pretty conservative diversification strategy, and we evaluate projects looking for the right fit."

Future investments, he said, could include other forms of clean energy like utility-scale solar power, he said. So far, the acquired projects are wind farms whose original owners have captured each project's federal tax benefits and were willing to sell at a fair price, he added.

Minnesota Power, a regulated utility that operates separately from Allete Clean Energy, also is moving into renewable energy and retiring some coal-fired generators, on which it still relies for most of its electricity. Minnesota Power has completed three wind farms in North Dakota since 2012.

"This latest transaction reinforces our belief that a more sustainable energy future relying less on carbon will mold the North American energy landscape over the long haul," said Allete Inc. CEO Al Hodnik in a statement.

Allete Clean Energy's earlier wind acquisitions include a $47.5 million deal announced in April for 97.5-megawatt project near Lake Benton, Minn., from EDF Renewable Energy. Other acquisitions include three projects in Iowa, Minnesota and Oregon that closed in January 2014 and another in Storm Lake, Iowa, in December.

David Shaffer • 612-673-7090 • Twitter: @ShafferStrib