Evopod is a unique tidal energy device being developed by a UK-based company Oceanflow Energy Ltd for generating electricity from tidal streams and ocean currents. It can operate in exposed deep water sites where severe wind and waves also make up the environment.
The flow speed in tidal streams and ocean currents tends to be fastest near the surface and falls off in speed as one descend in the water column. As the power that can be extracted from the free flowing water is proportional to the velocity cubed, then a 10% increase in flow speed equates to a 33% increase in power per unit swept area of the turbine.
The flow is generally more consistent in the top 1/3 of the water column as it is well away from disturbances created by the seabed topography.
The drag force on turbines of the same power output is proportionally less for a turbine in faster flow (positioned in the upper part of the water column) than a turbine in slower flow (positioned in the lower part of the water column).
A floating device does not require a flat seabed as the pile anchors require relatively little space and there is no structure on the seabed.
Turbines supported by floating platforms are more readily accessible for maintenance than those on the seabed.
Maintaining watertight seals is less problematic for devices positioned higher in the water column as they are not subject to such extreme static pressures.
Floating devices that are fitted with navigation lights and markings are more readily identifiable under international navigation regulations than unmarked submerged turbines.
Floating devices are subject to ocean wave action which can induce motions that will impact on the performance of the turbines they support; semi-submerged devices such as Evopod are designed to be a stable platform in waves so that they can operate for longer and extract more energy from the wave particle velocity. Waves large enough to have an adverse effect on Evopod would affect turbines in all parts of the water column.
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