MDU is preparing to retire three of its coal-fired electrical generation units.

Two of them are at the Heskett Plant, north of Mandan – the other is the Lewis and Clark plant at Sidney, Montana. Together, the three units represent 144 megawatts. The natural gas peaking plant is 88 megawatts.

MDU plans to replace the Heskett units with a natural gas peaking unit. The coal fired units were “baseload” units.

MDU President and CEO Nichole Kvisto said the utility is working on an “integrated resource plan” to submit to the North Dakota and Montana Public Service Commissions. She said it will outline the plans to replace the 144 megawatts that will be retired.

"In the interim, we would be looking at purchasing power off the MISO (Midwest Independent System Operator) market," Kvisto said. "Today, that price is very favorable."

Kvisto said MDU's analysis showed retiring the coal fired units and replacing some of the generation through the natural gas plant, it would be at about half the cost to customers.

"Then we would look ahead to the forecast, and evaluate what the options are into the future," Kvisto said.

As for MDU adding more wind power, Kvisto said there are no concrete plans at the present time.

"We just finished the expansion of Thunder Spirit wind, to 150 megawatts from that plant near Hettinger," Kvisto said. "That's been very good for our customers."

Kvisto said with the completion of that expansion, there is nothing on the horizon -- yet.

"But time will tell," Kvisto said.

The Sidney station will be retired at the end of 2020, and the two coal fired units at Heskett will be retired by the end of 2021.