Historic Hydroelectric System Revived

The A-Mill Artist Lofts Hydroelectric System is an exciting renewable energy initiative bringing back hydroelectric power to the historic Pillsbury A-Mill. Originally built in 1881, this building represented the largest flour mill in the world. Today, the function and use have drastically changed from a working mill to live/work housing. However, just as nearly 135 years ago, when occupants of the A-Mill Artist Lofts turn on their lights; residents can thank our team, as much of their electricity will be powered by the Mississippi River. The Weis Builders’ task included installation of a 600-kilowatt turbine generator capable of powering 50% of peak demand. The Project team utilized a pre-existing concrete and stone masonry intake structure, which is over a century old.

The Hydroelectric System consists of three major sections:

1. The Intake

  • The existing concrete and stone masonry intake which has been completely tailored to the modern system, while still maintaining the original aesthetic appearance has been revitalized to feature a new fish-friendly (low inlet velocity) trash rack.
  • Our Team coordinated the historic masonry, which required temporary steel bracing from the inside throughout construction, and was permanently reinforced with nearly 250 CY of heavily reinforced concrete.
  • An existing concrete bulkhead that was installed in the 1950s to seal off the headrace tunnel will be removed by the project team and replaced with a new concrete bulkhead with a rectangular to round transition segment and a cast-in fitting to connect with a new steel penstock.

2. The Headracetunnel-small

  • A new 616-foot-long, 5-foot-diameter, steel penstock (a pipeline which carries the water from the intake to the turbine) was brought in and installed with imbedded anchors along the existing limestone floor of the primary tunnel under Main Street. This piping terminated at the drop shaft (a drop where the water falls 50 feet within the vertical turbine assembly).

3. The Dropshaft & Dischargeturbine-small

  • Next, Weis workers installed a new vertical axis, 600-kilowatt turbine/generator has been placed at the bottom of the 50’ deep drop shaft.
  • A steel elbow type draft tube segment will be embedded in concrete at the bottom of the former drop shaft and transition to a new concrete outlet conduit that was installed on the floor of the existing concrete tailrace canal at which point the tailrace channel to merge with the Mississippi River; and (6) appurtenant facilities.

Combining modern generating equipment and controls with existing millrace and drop shaft infrastructure the Hydroelectric System will generate clean, renewable energy for on-site use. The A-Mill Artist Lofts Hydroelectric Project presents a unique opportunity to restore the power generating capability untapped for more than 50 years.