Page 77 - Fundamentals of Ocean Renewable Energy Generating Electricity From The Sea

Tidal Energy Chapter | 3 69

FIG. 3.21 Constructing a tidal ellipse by adding two rotating vectors in opposite directions. Note
that the sense of rotation of velocity is the same as the larger vector (i.e. W I ).

● horizontal axis turbines
● vertical axis turbines
● oscillating hydrofoils
● venturi effect devices
● tidal kites

3.12.1 Horizontal Axis Turbines
These devices are similar in principal to the operation of conventional wind
turbines. A turbine is placed in a tidal stream, which causes the turbine to
rotate about a horizontal axis. In the horizontal plane, horizontal axis turbines
can either be fixed, or include a yawing mechanism. However, in contrast to
wind, because tidal flows are highly predictable and highly energetic rectilinear
flows are much sought sites for development, most devices being developed do
not include a yawing mechanism. This has the added advantage of reducing
complexity in an environment where simplicity is clearly beneficial. Examples
of horizontal axis turbines are the 1.2 MW twin rotor Marine Current Turbine
(MCT) SeaGen device, which was deployed in Strangford Narrows, Northern
Ireland, and the Tidal Energy Limited DeltaStream device installed in Ramsey
Sound, Wales (Fig. 3.22). Recent developments have seen companies looking