04 Dec 2010
UK ABB and Scottish and Southern Energy's ventures are commended for their contribution to develop renewable energy aquamarine oyster’s system.
For the unit to work it needs a minimum water depth of 12 meters and the moveable hinged flap should have a minimum height of 11 meters (8m wave height + 3m for sea level variations + 1m for lower section thickness).
Water particles move in circular motion in a vertical plane and in line with the incoming wave. The velocity vector at the sea bed is zero and increases linearly to a maximum at the water surface.
The unit works using horizontal wave force at the sea shore, which are minimal at 0.5 km offshore. Near shore installation would damage the coral reef and make the shore line useless for recreation.
As the wave approaches the unit with the upper flap inclined in the wave direction, part of the kinetic energy is deflected downward and by-passes the unit. When the flap is vertical at 90 degrees, the water shoots up into air, and at more than 90 degrees the water overtops the flap. Both situations result in wasting valuable wave energy, thus reducing wave energy extraction.
Offshore installation in deep water, necessitates fixing to the sea bed by means of a catenary flexible line. Water particles accelerating upwards impinge on the moveable flap and the whole unit is subjected to a horizontal force which forces it to trace an arc in the downward direction, that is; it sinks downward. This action wastes wave energy to sink the unit against the buoyant force required to keep the unit afloat. This results in wasting valuable wave energy.
The unit is heavy and weighs in the order of tons. Then it needs submerged floats. How are they provided, and how the lower flap is kept in best position?
As the wave approaches the unit water accelerating upward lifts the unit upward. Part of the wave energy is again wasted in accelerating the high inertia of the unit upward and overcoming water resistance. This is wasted wave energy.
Can the movable flap return into position in less than approximately 4.5 seconds to be ready for the next wave cycle?
What are the effects of inline and cross currents?
What is the lowest wave height for proper operation of the unit?
What is the output of the unit and total efficiency of the unit for different wave heights?
What is being proposed to level the power output during the whole wave cycle?
These questions are raised in the interest of providing a viable system and to protect share and stock holders’ interests, as the funds provided are public property.