Tidal stream turbines represent a renewable (‘green’) source of power generation. They utilise the movement of the ocean tides to generate electricity. Tidal barrage and tidal stream plants belong to the hydropower category of power plants.
Tidal stream generation is still in its infancy concerning commercial development, but significant technological progress has been made over the past decade. In appearance, a tidal stream generator looks very similar to a wind turbine, but that is where the similarity ends.
Water is approximately 800 times heavier than air, so it is not possible to have huge rotors similar to those used by a wind turbine, the operational stresses placed upon the underwater turbine blades would be too great. However, with an increase in density, comes the possibility for an increase in power output. A typical tidal stream generator turbine requires blades 12 metres in length to generate approximately 600 kW, a wind turbine would require blades approximately 45 metres in length to generate roughly the same power.
Another advantage for tidal generators is that tides –unlike wind and sunlight- can be predicted, thus its possible to have a reliable cyclic means of power generation.
Each hydroelectric turbine consists of a nacelle, blades, rotor hub, hydraulic brake, gearbox and generator. Because water is approximately 800 times more dense than air, the opportunity to convert potential and kinetic energy into electrical energy is far greater than for a wind turbine.
How Tidal Stream Generators Work
As water passes over the turbine blades, a pressure differential is created across the blades. This pressure differential causes lift, which is applied as rotary torque to the rotor hub. A primary shaft connects the rotor hub to the gearbox. A secondary shaft connects the gearbox to the generator rotor. The generator rotor rotates within the generator stator and induces current flow. At this point, the process is complete and electricity can be dispatched via the electrical grid.
Note that it is the blades that convert the kinetic and potential energy of the water to mechanical energy and that this energy is then converted to electrical energy by a generator.
All tidal barrage and tidal stream plants rely upon Kaplan turbines due to the large flow and low head of pressure in which they operate.
3D Model Details
This 3D tidal stream generator model is animated to show the yawing motion of the turbine and the rotary motion of the blades. The turbine used in the model is a three blade, lift type, hydro turbine.
This 3D model shows all major components associated with a typical tidal stream turbine, these include:
- Rotor Hub
- Control Unit
- Electrical Transformer
- Various motors for yawing and pitching etc.