Minnesota Power will pay a $1.4 million penalty and invest in clean energy products in a Wednesday agreement with state and federal regulators that settles the Duluth-based utility's alleged violations of the U.S. Clean Air Act.

The U.S. Environmental Protection Agency disagreed with the utility's upgrading of its coal-fired plants without installing the best available emissions controls, according to the Star Tribune. Minnesota Power officials haven't admitted to any wrongdoing, the Bemidji Pioneer reported.

Minnesota Power agreed to setting stricter emissions limits at three of its plants, the Star Tribune said.

The agreement, which was praised by environmentalists, comes after six years of negotiations, according to MPR.

Ten years ago, the utility was almost entirely dependent on coal to deliver electronic power to the region, but now it gets 20 percent of energy from the wind, MPR reported.