It is not necessary to build a dam (or barrage) to extract energy from the tides. An alternative is to install one or more slow-turning turbines in an area of naturally high tidal current flows. For example, many of the narrow passes and inlets in the area between Vancouver Island and the mainland have tidal currents that are as good as those anywhere else in the world.
At present there are no commercial tidal-current generating installations, but at least one is under construction in the UK.
Tidal current installations that have been tested or envisioned are of three types:
- a column embedded in the sea floor fitted with propeller type turbines (see below),
- a fully submerged vertical-axis turbine (Davis turbine), or
- a bridge-type structure across the top of a series of submerged turbine units.
Because tide flows are not constant, a tidal-current generation system should only be relied on to generate at about 50% of its rated capacity.
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Artist conception of a Marine Current Turbines Seagen tidal generator embedded in the sea floor © Marine Current Turbines TM Ltd., used with permission, http://www.marineturbines.com |
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Single Seagen rotor at the Marine Current Turbines assembly plant. This is just part of the twin-turbine installation shown in the other diagram. © Marine Current Turbines TM Ltd., used with permission, |
