LONDON: Harnessing tidal power around the UK’s coast has so far been limited by the cost of the large dams and barrages required and unpredictable results.
A British company, in conjunction with Oxford University researchers, believes it has devised a way to overcome this obstacle by creating a new type of horizontal axis turbine that can be used underwater at depths of up to 30 meters, at an economical cost.
Conventional propeller-type turbines are like underwater wind turbines and the number of suitable sites for them are vastly reduced by the size of their large blades, limiting their use to waters at least 30 meters deep. The THAWT (Transverse Horizontal Axis Water Turbine) technology, by contrast, is designed for deployment in shallower, lower velocity, tidal waters.
Developed by Oxford University’s Department of Engineering Science in conjunction with Kepler Energy, THAWT uses a stressed truss configuration with carbon composite hydrofoil blades.
Put simply, as the water flows past the fence a head of water is produced that increases the turbine’s efficiency. The phenomenon is called a ‘blockage’ of the turbines and gets larger in proportion to the length of the fence.
Guy Houlsby, professor of civil engineering at Oxford University, says their design is an improvement on the vertical Darrieus wind turbine used in some turbine systems.
The original Darrieus turbine has blades that are parallel to the axis of rotation, and that means that the loads in the blades are carried entirely by bending of the blades. That results in very high stresses,” said Houlsby. “The re-design that we’ve done changes the blades so that they form this triangulated structure, and that’s a very stiff and very strong structural form. And that means that the loads in the blades are principally carried by axial forces and that means that the stresses are much lower.”
