Xcel Energy Inc. says it is willing to install $50 million in emissions controls on its Sherco coal-fired power plant to help reduce haze over Voyageurs National Park and the Boundary Waters Canoe Area.

The Minneapolis-based utility also said in a letter Friday to the Minnesota Pollution Control Agency that it supports plant-specific curbs on emissions at the power plant near Becker, Minn., the largest electric generating station in the state.

Environmental groups this week criticized Minnesota and other states that propose to opt out of plant-by-plant haze-reduction enforcement under U.S. Clean Air Act.

An alternative, cap-and-trade approach favored by some states could leave many coal power plants without retrofits. It also faces a legal challenge, leaving enforcement uncertain.

Frank Prager, Xcel's vice president of environmental policy and services, said the utility has begun and intends to complete "reasonable" emission-control upgrades at the two oldest Sherco units.

Xcel has long supported those retrofits, which at $50 million don't include expensive technology being required at some other plants. The coal-burning Big Stone power plant in South Dakota, for example, is being required to install more-advanced controls that will cost an estimated $489 million.

Prager said Xcel's more-modest Sherco retrofit is on top of the utility's earlier $1 billion investment in environmental improvements at metro-area coal power plants.

David Shaffer • 612-673-7090