Tidal Current Devices
Tidal generation exploits the movement of powerful sea currents caused by the gravitational attraction of the Moon and Sun. The most powerful of these tend to occur in narrow straits bounded by topological features such as islands or headlands. Tidal devices can be described by 6 generalised models [1]:
- Horizontal Axis Tidal Turbine (HATT)
- Vertical Axis Tidal Turbine (VATT)
- Oscillating Hydrofoil
- Enclosed Tips (Venturi)
- Archimedes Screw
- Tidal Kite
Horizontal Axis Tidal Turbine (HATT)
HATT's operate in a very similar manner to Wind Turbines. As the water flows over the blades, a perpendicular lift force is generated. This causes the rotor to spin and thus generating power through an electric generator. An example of this device is shown as developed by Atlantic Resources Corporation.
Vertical Axis Tidal Turbine (VATT)
VATT's are drag devices. As the flow reaches the blades, they are rotated by the force of the water impacting the blades. The rotation of the rotor drives an electrical generator. An example of this technology is shown.
Oscillating Hydrofoil
Oscillating Hydrofoils operate using the principles of lift forces on a hydrofoil. As flow passes over the hydrofoil, lift forces are generated, rotating the device around a horizontal axis. This motion is used to drive a hydraulic fluid through a hydraulic motor. An example of this technology is the Stingray Tidal Stream Energy Converter under development by the Engineering Business as shown.
Enclosed Tips
Enclosed tips tidal turbines utilize the Venturi (narrowing and then expanding) geometry to create a low pressure area behind the turbine. This pressure differential drives the turbine. An example of an Enclosed Tidal Turbine is shown.
Archimedes Screw
As water flows past the Archimedes Screw, it forces it to rotate due to drag forces. The spinning motion results in electric power by means of an electrical generator. An example of this technology is currently under development by Flumill.
Tidal Kite
Tidal Kites use a wing and turbine assembly tethered to a fixed point on the sea bed. As the water approaches the assembly, it creates a lift force, allowing the wing and turbine to move through the water. Due to the relative motion, the turbine is forced to rotate, generating electricity. This is a novel technology developed by Swedish company Minesto.
[1] European Marine Energy Centre. Tidal Devices. 2013.
Photo Credits (from top):
Atlantis Resources Corporation via EMEC, 2012. AR-1000 Tidal turbine [online]. Atlantis Resources Corporation. Available from:
http://www.emec.org.uk/about-us/media-centre/gallery/ [Accessed 6th March 2013].
University of Strathclyde, 2011. Vertical Axis Tidal Turbine [online]. University of Strathclyde. Available from: http://www.esru.strath.ac.uk/EandE/Web_sites/05-06/marine_renewables/technology/vertaxis.htm [Accessed 6th March 2013]
IHC Engineering Business Ltd, 2011. Stingray Tidal Device.
EU Infrastructure, 2010. OpenHydro [online]. EU Infrastructure. Available from:
http://www.euinfrastructure.com/news/tidal-power-openhydro/ [Accessed 6th March 2013]
Teknisk Ukeblad, 2013. Flumill [online]. Teknisk Ukeblad. Available from: http://www.tu.no/energi/2012/03/27/far-bygge-tidevannskraftverk [Accessed 6th March 2013]
Minesto via Centre for Energy, 2010. Minesto [online]. Centre for Energy. Available from: http://www.centreflow.ca/2010/06/16/making-waves-with-tidal-kites/ [Accessed 6th March 2013]
Photo Credits (from top):
Atlantis Resources Corporation via EMEC, 2012. AR-1000 Tidal turbine [online]. Atlantis Resources Corporation. Available from:
http://www.emec.org.uk/about-us/media-centre/gallery/ [Accessed 6th March 2013].
University of Strathclyde, 2011. Vertical Axis Tidal Turbine [online]. University of Strathclyde. Available from: http://www.esru.strath.ac.uk/EandE/Web_sites/05-06/marine_renewables/technology/vertaxis.htm [Accessed 6th March 2013]
IHC Engineering Business Ltd, 2011. Stingray Tidal Device.
EU Infrastructure, 2010. OpenHydro [online]. EU Infrastructure. Available from:
http://www.euinfrastructure.com/news/tidal-power-openhydro/ [Accessed 6th March 2013]
Teknisk Ukeblad, 2013. Flumill [online]. Teknisk Ukeblad. Available from: http://www.tu.no/energi/2012/03/27/far-bygge-tidevannskraftverk [Accessed 6th March 2013]
Minesto via Centre for Energy, 2010. Minesto [online]. Centre for Energy. Available from: http://www.centreflow.ca/2010/06/16/making-waves-with-tidal-kites/ [Accessed 6th March 2013]