Siemens will maintain 149 turbines across four of the cluster's projects.
Bison 1 phase 2, Bison 2 and Bison 3 were completed between 2010 and 2012. They comprise a total 85 Siemens 3MW turbines. Bison 1 phase 1 is also powered by Siemens turbines.
Siemens will also service the Bison 4 project made up of 64 Siemens 3.2MW turbines, which was completed in January 2015. It was one of the first projects to use the 3.2MW Siemens machine after its launch in early 2014.
Power from the Bison complex is sold to Minnesota Power and transmitted to the state of Minnesota.
In April 2014, Minnesota Power submitted plans to regulators to build a 750MW transmission line to cross the Minnesota-Manitoba border carrying power from wind into Canada for storage through pumped hydro.
The company said the line would allow it to "substantially expand its energy storage opportunities" and the expansion of Bison Wind project was central to the plans.