The Colstrip steam electric station (CSES) is a 2,094MW coal-fired power plant located near Colstrip, Rosebud County, Montana, US.

It is operated by Talen Montana, a subsidiary of Talen Energy, which is a privately-owned independent power producer based in Pennsylvania.

The Colstrip power station comprises four coal-fired units commissioned between 1975 and 1986.

The first two units of 307MW capacity each are scheduled for permanent shut down by the beginning of 2020, while the units three and four of 740MW capacity each are expected to be operational at least until 2025.

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Colstrip power station ownership details

The Colstrip units one and two are owned by Talen Energy (50%) and the Washington state energy utility, Puget Sound Energy (PSE, 50%).

Unit three is owned by Talen Energy (30%), PSE (25%), Avista Corporation (15%), Portland General Electric (PGE, 20%), and PacifiCorp (10%).

Talen Energy doesn’t have any ownership interest in the Colstrip unit four, which is owned by the South Dakota-based utility NorthWestern Energy (30%), PSE (25%), PGE (20%), Avista (15%), and PacifiCorp (10%).

The total generating capacity shares held by the six co-owners of the facility are PSE (32%, 677MW), Talen Energy (25.2%, 529MW), PGE (14%, 296MW), Avista (10.6%, 222MW), NorthWestern Energy (10.6%, 222MW), and PacifiCorp (7%, 148MW).

NorthWestern Energy announced that it plans to buy an additional 25% stake in Colstrip unit four from PSE in December 2019. Its total generating capacity at the facility will be increased to 862MW after the acquisition.

Colstrip power plant decommissioning plan

The six co-owners of the Colstrip power plant were sued by Sierra Club and the Montana Environmental Information Centre for the violation of the US Clean Air Act in 2013.

The plant owners agreed to retire the two older units by 2022 as part of a settlement reached in July 2016.

In June 2019, operator Talen Energy, however, announced its plan to close units one and two by the end of 2019, citing poor economics to operate the units as the reason.

Changing environmental laws and increasing operating costs have also led other co-owners to plan for exiting units four and five as early as 2025, approximately nine years ahead of previous estimates.

Colstrip power plant details

Construction of the Colstrip coal-fired power facility was started in 1972, while units one and two were commissioned in 1975 and 1976, respectively. Unit three came online in 1983, followed by unit four in 1985.

Consuming up to ten million tonnes (Mt) of sub-bituminous coal from an adjacent coal mine, the Colstrip power station generates more than 13,000GWh of electricity a year.

All units of the plant are fitted with flue gas desulphurisation (FGD) system to control sulphur dioxide (SO2) emissions.

Colstrip transmission system

The electricity generated by the Colstrip power plant is evacuated through a twin 386km-long, 500kV transmission line connecting Townsend, in central Montana.

The twin-lines further extend for 346km from Townsend for interconnections with the Bonneville Power Administration (BPA) transmission system in Washington and Idaho.

Coal supply from the Rosebud mine

Colstrip is a mine-mouth power plant that receives coal supply from the adjacent Rosebud coal mine through a 6.7km-long conveyer belt.

Rosebud is a 25,000-acre surface coal mine owned and operated by Western Energy Company, a subsidiary of Westmoreland Coal of Colorado.

The US Department of the Interior approved an expansion of the Rosebud coal mine in June 2019. The expansion plan involves 69Mt of coal production from 6,700 acres of additional mining area that allows for extending the operational life of the mine through 2038.

A coalition of environmental groups led by the Western Environmental Law Centre filed a lawsuit in a federal court challenging the proposed coal mine expansion in November 2019.