Hydropower: Increasing the efficiency of an Archimedes screw

Minster Mill is a hotel in Minster Lovell, a small village 11 miles from Oxford and on the border of the Cotswolds. The village sits alongside the Windrush River and boasts many historical attractions including the ruins of a 15^th Century manor house and a medieval dovecote.

Historical records show a mill stood by the bridge at the modern village’s west end by 1197, which harnessed the power of the River Windrush and this ancient practice has now been modernised by The Minster Mill hotel with the use of an Archimedes screw.

An Archimedes’ screw, also known as the Archimedean screw is one of the earliest hydraulic machines on record and is named after Greek mathematician Archimedes who first described it around 234 BC, it is even thought that an Archimedes’ screw was used to water the Hanging Gardens of Babylon.

Essentially it is a reversible hydraulic machine and is used for lifting water by turning a screw-shaped surface that’s inside a pipe. Run in reverse, Archimedes screw turbines act as a form of small hydroelectric powerplant in a wide range of flows, it replaces high-performance technologies and so is suited to generate 10kW of power for the hotel.

SWJ Consulting was asked by hydropower specialist Hallidays to help with the task of making this process more efficient, to generate more power by focusing the river’s power more effectively. We designed changes to the earth retaining structures, so in effect, we modified the riverbank to focus the wide channel into a narrower channel to draw more water into the screw.

This involved the design of a concrete retaining wall and an apron. These two concrete structures also provided the foundation for a generator house to house all the mill’s hydroelectric plant.

One of the critical concerns in our design of the concrete retaining walls and apron was to prevent scour – the effect of erosion on the retaining walls, existing pond and riverbank where the focused, more powerful water course now hits. We needed to look at this very carefully to ensure our design would not cause any damage to the environment.

Once approved we were able to provide designs to the contractor and the client implemented all the changes.

If you have an alternative energy project that needs some structural engineering advice then give us a call on Witney (01993 225085) or Southampton (02381 920656). We can not only help with hydropower projects like the one detailed above but have extensive experience with projects with close proximity to water and the challenges that it brings.