Horizontal axis turbines

The horizontal axis turbine, or propeller turbine, comprises a propeller with two or more blades. The turbine can either be mounted on a tower fixed to the seabed or it can be deployed below a floating support. The former method is most suitable for shallow waters whereas that floating support can be deployed in deeper water. In order to increase the efficiency of a horizontal axis system, water flow around the turbine can be controlled using a shroud.

As a result of the high-energy density, water turbines are much smaller than wind turbines. A unit with a diameter of 10-15 m can produce between 200 kW and 700 kW. Prototypes include a 15 kW unit tested in a Scottish Loch and a 300 kW unit deployed off the coast of southern England in 2003.10

Water level

(b)

!

Seabed J

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/

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Figure 14.4 Horizontal and vertical axis ocean current energy converters. (a) Horizontal axis turbine (axial flow) and (b) Vertical axis turbine (cross flow)

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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