Archimedes Screws

 

Archimedian Screw

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 turbine consists 3 or more helix shaped blades mounted on a central shaft. This shaft/blade assembly is put into a trough and is set an angle between 20 and 35 degrees typically (relative to horizontal).

Water enters the top of the screw, filling it to about the midpoint of the diameter. As the water flows downhill it creates torque on the screw and causes it to turn.  The screw is connected to a gearbox to step up the rotation speed and turn the generator.

Archimedes Screw type turbines are especially suited to sites with high flows (200 liters/sec to 10,000 liters/second) and work economically with head levels from 1 to 10 meters (i.e. very low head is still useful).  They are technically very simple with significantly lower installed and operational 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).
  • High efficiency – Water-to-Torque: up to 87% and Water-to-Wire of up to 77%
  • They can be operated down to as low as 5% of design flow and still generate electricity
  • 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).
    • Open to atmosphere – no pressure changes to harm fish swim bladders
    • Large chambers for fish between screws
    • Slow rotation
    • Smooth flowing water so there is no fish disorientation
    • No fish screening required – eliminating associated hazards
  • 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.
  • No complex control system required as speed is regulated by available flow (level sensor typically)Fine fish screening required – fish can get stuck on screens (if not designed carefully)

See the Products Page to understand the "configurations" of Archimedes Screw systems offered and recommended by 3Helix Power.


Fish Passage Studies

A number of studies have been carried out in Europe and by Mann Power Consulting in the UK on the impact of archimedes screw hydropower systems on fish.  Copies of some of these studies are in the "Research" section of this site.

Thousands of fish passages have been monitored using cameras at the intake, within the screw and at the outflow of screw systems.  Trials have included salmonids (smolts and kelts)), brown trout and eels and have been carried out over a range of fish sizes and turbine speeds.

No adverse effects were noted for fully grown fish or kelts while "at most" 1.4% of the smolts observed suffered limited and recoverable scale loss.  This is "at most" since the wild fish that were observed were likely to have have some minor scale damage before their passage.  Of 160 eel passages, 0.64% suffered "minor and recoverable" pinching to the tail.