Hennepin Island Hydroelectric Plant hums with a century of untold stories. The Hennepin Island Hydroelectric Plant stands as a testament to ingenuity. This plant has harnessed the Mississippi’s power for over a century. It is located at St. Anthony Falls in Minneapolis.
The Hennepin Island Hydroelectric Plant is part of St. Anthony Falls Hydroelectric Development. The plant is operated today by Northern States Power. Xcel Energy manages the facility. It is situated on Hennepin Island near the Pillsbury “A” Mill. St. Anthony Falls is the river’s only major waterfall. This waterfall once powered the city’s early sawmills. It also powered grist mills.
The current structure was built in 1908 for electric power. William de la Barre was the architect. The Hennepin Island Hydroelectric Plant is one of 99 contributing properties. These properties belong to the St. Anthony Falls Historic District. The district is listed on the National Register of Historic Places.
The plant has five generating units. Each unit produces 2.4 or 2.5 megawatts. The total output is about 12 megawatts. It initially produced power at 35 Hz. The original capacity was 9.9 megawatts. Four horizontal shaft direct drive generators were used. Minneapolis General Electric leased the total output. They then subleased it to the streetcar system.
In 1955, streetcars were replaced by buses. The Hennepin Island Hydroelectric Plant was converted to 60 Hz. A fifth generator was added. This increased the total capacity to 12.4 megawatts. The fifth generator was vertical shaft. The turbine was placed below the generator. This design allowed better use of the available head. Vertical shaft installations became practical. This was due to the development of bearings. These bearings could bear the weight of the generator rotor.
The rotating turbine runners were replaced. Generators were rewound. This was completed in 2013. The historic turbine outer shells were not affected. These changes raised the capacity. It went from 12.4 megawatts to 13.9 megawatts. The maximum flow increased. It went from 4025 cfs to 4366 cfs.
Northern States Power renewed its license in March 2004. The Federal Energy Regulatory Commission authorized it. The license required a recreation area. This area would show the evolution of St. Anthony Falls. A part of the island was made into Water Power Park. This allows close approaches to the falls.
In 2008, NSP/Xcel worked with the University of Minnesota. They collaborated on “StreamLab”. This is an experimental stream channel and floodplain system. It improves existing flood bypass channels. It helps study the site’s ecology and hydrology.
This is the only historic plant still operating. The Hennepin Island Hydroelectric Plant stands as a symbol. It represents the city’s history. It continues to generate power for Minneapolis. It is a reminder of the city’s industrial past.