Archimedes Screw (turbine)

Archimedes screws are an OLD idea (attributed to Archimedes of Syracuse in the 3rd century BC), but until recently, they have always been used to pump water UP.  By letting water drop via an Archimedes screw it is possible to generate electrical power.

An Archimedes Screw is consists of either a single or multiple helix shaped blades mounted on a central shaft.  This shaft/blade assembly is put into a trough and rests at an angle with the bottom in a fluid.  As the screw is turned, fluid is scooped up by the screw and lifted in a moving “bucket” to the top.  This is how they work as a PUMP and as a generator, the flow is simply reversed.

Archimedes Screw type turbines are especially suited to sites with high flows (200 liters/sec to 6000 liters/second) and work economically with head levels from 1 to 10 meters (i.e. very low is still useful).

They are technically very simple with significantly lower installed costs than comparable low head Kaplan turbines.

Other great benefits of Archimedes screw type turbines include:

• A very flat efficiency curve which means that even dramatic changes in flow levels or head levels do not significantly impact the efficiency of the system (and without the mechanically adjustable blades of a Kaplan turbine).

• Extremely fish friendly – many studies have been performed in which fish suffer no damage traversing the Archimedes screw generators.  In fact, Archimedes screws are used in some areas as PUMPS to move fish from tank to tank (Pescalator is an example).

• Trash and debris tolerant – Because of the design of the screws and how they work (essentially buckets of water being lowered), all sorts of sticks, leaves, branches, etc… can travel through them without any ill effects.  This along with their fish friendly nature make fine guards in the water unnecessary, greatly lowering maintenance costs.

• Ruggedness – Because the design and construction is so simple, because the design is so tolerant of trash, etc…  Archimedes screw type systems are extremely robust and can be expected to last 40 years or more with a minimum of maintenance.

Many potential “run-of-river” hydropower sites (low weirs, disused mill sites, etc…) are low head sites of only a couple of meters head.  Because of this and the advantages listed above, Southeast Power Engineering feels that Archimedes Screw type installations are the ideal solution for small and medium (up to several hundred kW) hydropower development.