Ocean wave energy
Ocean waves are a renewable form of energy generated by wind currents going back and forth in open water. Scientists have recently demonstrated that collecting this form of energy offshore was technically doable. Numerous technologies have been tested to capture the energy from the waves. Here are the main ones.
Terminator devices
The Terminator devices way to capture the wave’s energy is the only one mainly designed to be installed onshore or nearshore. However, floating prototypes were conceived for offshore applications.
The device is settled perpendicularly to the direction of the waves travel and capture or reflects their power. The oscillating water column –the tide - enters through an opening below the surface level into a chamber and therefore traps air above it. The wave’s up and down move pushes the captured water in turn to move up and down exactly the way a piston would do and doing so forces the trapped air through a turbine itself connected to a generator which would finally produce electricity form the tide.
Attenuators
Attenuators devices are composed of different elongated sections linked together which eventually form a floating structure oriented in the same direction as the wave travel.
The working principle is quite easy to understand, the device take advantage of the heights differences generated by the waves between the different sections which causes flexion at the segment connections. This activates hydraulic pumps or other converters at the liaison between segments.
The actual most advanced attenuators are the McCabe and the Pelamis. The first one, the McCabe wave pump has three pontoons hinged together in a line and pointed parallel to the wave direction. On this device, the central pontoon is connected submerged thanks to a damper plate. This keeps the middle section at the same level relatively to the fore and aft segment. Therefore hydraulic pumps between the sections are pushed and pulled successively as the waves force the pontoons up and down.
The Pelamis uses a similar concept, with floating cylindrical pontoons connected by three hinged joints. Wave’s action flexes these joints and eventually drives hydraulic pumps into the joints.
Point absorber
Point absorbers are small device when talking about their width compared with their length. They use wave’s rises and falls at a single point for the wave energy conversion. Like for the attenuator device there are actually two devices whose technologies are far ahead from the others.
The first one is the PowerBuoy developed by the company Ocean Power Technologies. It consists in a floating structure with the bottom component remaining relatively still while a second part moves driven by wave motion. The moving part is a floating buoy fixed inside a cylinder. This motion is used to drive an electromechanical or a hydraulic converter.
The other one named AquaBuOY is developed by the AquaEnergy Group. It is a third generation point absorber engineered by two Swedes. The device utilizes the wave energy to increase the pressure on a fluid used to drive a turbine generator.
The upsides down buoy movement drives a disk pushing like a water piston contained in a long tube under the buoy. The disk movement successively stresses and distresses a pipe filled with seawater, and the change in the hose volume acts the same way as a pump to pressurize the seawater.
Classical
The other classical means of producing energy from the wave are basically wind turbine but under the sea. To learn more about the working principle of a turbine, please refer to the wind turbine article or have a look at the following video.
