The company took the decision to close down the old coal-fired and gas-fired facilities after evaluating the cost of upgrading the facilities as per the new environmental standards.

The investment for the upgrade of these facilities was not economically viable to the company.

Black Hills Corp. chairman, president and chief executive officer David R Emery said, "After a thorough analysis of new environmental regulations, coupled with changing market and operating conditions, we identified an opportunity to make changes to our resource portfolio by suspending operations at some of our older generating facilities in advance of permanently retiring those plants."

Colorado Electric will suspend the operations at its 42MW W.N. Clark coal-fired power plant located in Cañon City, Colorado on 31 December 2013. It will also shut the natural-gas-fired steam units 5 & 6 in Pueblo, Colorado at the end of 2012.

Black Hills Power’s 25MW coal-fired unit at the Ben French power plant in Rapid City, South Dakota, will be shut down on 31 August, 2012.

The suspension of operations at the 34.5MW Osage and 22MW Neil Simpson 1 coal-fired power plants is scheduled on 21 March, 2014.

The company is expecting to use the units to generate electricity to meet the peak demand during the summer season.