Five local utilities have signed agreements to build a second electric generating unit on the site of the existing Big Stone Plant near Milbank, South Dakota.
Based on increasing demand and studies that point to a potential energy shortfall, the companies began working together in 2003 to resolve their mutual need for baseload energy. Studies included:
- a cost and performance comparison of state-of-the-art coal combustion and emissions technologies in various size ranges,
- estimates of air emission rates, and
- an evaluation of designs to provide a reliable quantity of cooling water from Big Stone Lake while minimizing impacts and costs.
The result of these efforts was an agreement to develop an electric generating plant that would be:
- approximately 500-580 megawatts;
- coal-based;
- designed with the best available emission-control technologies at the time of purchase, and
- available to serve the customers of the investing utilities.
The five utilities
Based in Minnesota, North Dakota, and South Dakota, the five participating electric utilities serve more than a million people in five states in the Upper Midwest.Otter Tail Power Company, lead developer
Central Minnesota Municipal Power Agency
Heartland Consumers Power District
Missouri River Energy Services
Montana-Dakota Utilities Co
Project timeline
While plant construction is contingent on approval of all necessary permits, this is the proposed timeline:- Initial announcement - October 2004
- Permitting and public comment - Early 2005 through spring 2008
- Construction begins - Mid-2009
- Plant commercially available - Mid-2013
Project impact
Big Stone II represents the largest investment of private and public capital ever made in South Dakota. The electricity it produces will flow to customers in Minnesota, North Dakota, South Dakota, Montana, and Iowa. During its four-year construction period, the plant would employ an average of 625 construction workers, with a peak workforce of 1,500. Once online, Big Stone II would likely employ 35 to 40 operational workers at the site. Learn more about the project's economic impact.Project cost
Early cost estimates for the power plant were at about $1 billion, with an additional $200 million for the transmission line project. These costs estimates have increased, however, largely due to higher costs for construction materials and labor. Other factors include market pricing by vendors as well as design changes made by project participants to increase output and improve efficiency. Based on the most recent design refinements, the project, including transmission, is expected to cost $1.6 billion. Efforts continue to maximize efficiencies and minimize costs.Advantages of the proposed site
The South Dakota site has important economic advantages. Otter Tail Power company has operated Big Stone Plant, which it owns jointly with Montana-Dakota Utilities and NorthWestern Energy, for more than 32 years. The site contains much of the expensive infrastructure needed to support a second unit. A well-trained staff is in place, as are a railroad line and a water supply. In addition to having some existing transmission corridors, it's close to load centers where demand is high.This reduces—by tens of millions of dollars—the expense of building additional transmission from sites farther removed from load centers. Some transmission upgrades or new construction will be necessary to deliver the power generated by the proposed new plant at Big Stone. Also, it is possible that the transmission upgrades could provide opportunities for the development of renewables, such as water, wind, and biomass. The transmission studies will first determine what is needed for the plant, and then what would be available for renewable or other generation. For the transmission project, two corridor options now appear most beneficial. In addition, while Big Stone II's primary fuel source would be Powder River Basin coal, biomass is also being investigated.
The Big Stone site was selected after Burns & McDonnell conducted a study to identify a preferred site, along with alternate sites, for a new coal-fired generating unit.
Site details
The existing Big Stone Plant is two miles northwest of Big Stone City, which is near Milbank, South Dakota. The new generator will be located adjacent to the 450-megawatt Big Stone Plant, which began operating in 1975 on the 2,200-acre site.
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