Generating power

When Otter Tail Power Company became an operating utility in 1909 it was strictly a hydroelectric company. The water power came from the Wright and Dayton Hollow dams on the Otter Tail River. 

During the first year of operation, the company had more generating capacity than it needed, so Vernon Wright offered to sell the surplus to the city of Fargo. The  Fargo city council accepted his offer and plans were made to build a transmission line from Dayton Hollow to Fargo in 1910.

But 1910 turned out to be a very dry year and the flow in the Otter Tail River was far below normal. Low water generated less electricity. Not only was there no surplus, there was a shortage. During the last three months of 1910, Otter Tail Power Company's customers received electric service from 5:00 p.m. to 11:00 p.m. and no more.  That scuttled the transmission line to Fargo. It is interesting to speculate about what the situation would be today if that transmission line had been built.

Hydro units were built at the new Hoot Lake Plant in 1914 and 1916, another was installed at the Pisgah Dam in 1918, and the last one was installed at the Taplin Gorge Dam in 1925 -- the last place on the Otter Tail River with a natural reservoir and a good site for a dam.

As Otter Tail Power Company expanded and new towns were added to the system, the hydro units could no longer carry the peak load. To meet that deficit the company installed a generator at the Hoot Lake Plant in 1921 that was driven by a steam turbine rather than a hydraulic turbine. The steam was produced by a coal-fired boiler. A second unit was added in 1923.

After 1923 the company built more steam-powered generating stations to serve a growing load. With each addition, the output of the hydro units became a smaller percentage of the company's total generating capacity. Today they provide less than one percent of the kilowatt-hours the company generates in a year.

In 1930 the company installed the first generators driven by large diesel engines, two units at Appleton and one unit at Langdon. They were called peaking units because they ran only during peak load periods. The diesels had a higher operating cost per kilowatt-hour than a base load plant but a lower capital cost per kilowatt.

No new diesel units were added until after World War II when the company didn't have enough generation to carry the peak load. Eleven large diesels and many smaller ones were installed in towns spaced around the system to fill that generation deficit.

By 1950 Otter Tail Power Company had nine coal-fired steam generating stations in operation: Washburn, Jamestown, Devils Lake, Crookston, Ortonville, Bemidji, Wahpeton, Hoot Lake, and Canby.

Washburn was retired in 1969 because it was obsolete. Jamestown, Devils Lake, Crookston, Bemidji, Wahpeton, and Canby were retired in 1975 when the Big Stone Plant in eastern South Dakota came on line. Ortonville did not run after 1983 but it was not officially retired until 1988. Replacing those six small plants with a larger and more efficient one at Big Stone brought a large reduction in labor and operating costs.

Otter Tail Power Company was a pioneer in the use of lignite coal for fuel in power plants. Lignite has a lower Btu content than other types of coal, but it was the fuel of choice because it was low in cost and readily available in western North Dakota.

The first plant on the Otter Tail system to use lignite for fuel was Washburn, which was located on the Missouri River. It was completed in 1926, specifically designed to burn lignite.

Other electric utilities were slow to use lignite for fuel because of its high moisture, high sulfur, and high sodium content, which can create operating problems. Otter Tail Power Company was able to work through those problems and burn lignite successfully for many years. This gained the company national recognition in the electric utility industry.

In 1988 Hoot Lake Plant was converted to western coal to reduce transportation costs. Western coal has a higher Btu content per pound than lignite, so even though the haul distance was greater, the transportation cost per million Btus was less.

In 1995 the company converted Big Stone Plant to low-sulfur western coal for two reasons: to increase the output of the plant and to meet the federal emission requirements for sulfur dioxide. Coyote Plant in western North Dakota continues to burn lignite. Completed in 1981 it is a newer plant designed with equipment to remove sulfur dioxide from the stack emissions.

In 1976 the first combustion turbine peaking unit was installed at Jamestown. A combustion turbine has many times the capacity of a diesel unit. Today four combustion turbines are on the system: two at Jamestown, one at Lake Preston, South Dakota, and one at Solway, Minnesota. All the diesel peaking units were retired in 1982.

Today Otter Tail Power Company operates three baseload steam power plants: Hoot Lake Plant, Big Stone Plant, and Coyote Station. Big Stone and Coyote are jointly owned with other utilities. These three stations account for most of the kilowatt-hours the company generates in a year. The remaining amount is produced by hydro, combustion turbines, and wind generators. 

Written by Myron Broschat, Otter Tail Power Company retiree
References:  Otter Tail Power Company Historical Data by Caroline Bale, The Way it Was by Walter Doebbert, and  correspondence with Ward Uggerud