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Water for Energy and Fuel Production
13.3.3.1 Wave energy Converters
In its basic design, WEC utilizes the principle of motion of two or more bodies
relative to each other [50,51]. One body, called displacer, is acted on by the waves.
The second body, called reactor, moves in response to the displacer. While there are
a number of designs and configurations of WECs, the four most common ones are
graphically depicted in Figure 13.2a through d [50,51].
In the oscillating water column, waves enter and exit in a partially submerged collector from below, causing the water column inside the collector to rise and fall. The
changing water level acts as a piston as it drives the trapped air in the device above
the water into turbine. The turbine movement generates electricity via a coupled
generator. This device is graphically illustrated in Figure 13.2a [50,51].
In overtopping device, shown in Figure 13.2b, a floating reservoir is formed as
waves break over the walls of the device. This reservoir creates a head of water
higher than that of the surrounding ocean surface. The pressure necessary to
turn hydroturbine is provided by this head of water. The water leaves the bottom
of the device to return back into the sea [50,51]. The device can be used in tidal
currents.
In an attenuator WEC (shown in Figure 13.2c), long, multiple sectioned, floating structures, which are joined and anchored at each end, are aligned parallel to
the wave direction and they generate electricity by riding the waves. These heavysurge devices utilize the passing waves to set each section into the rotational motion
relative to the next segment. This relative motion, which is concentrated at the joint
between the two consecutive segments, is used to pressurize a hydraulic piston that
drives fluids through a motor. The hydraulic piston in turn drives the coupled generator and produces electricity [50,51].
Finally, the point absorber depicted in Figure 13.2d drives a turbine by using
waves from all directions at a single point by using the vertical motion of the waves to
act as a pump that pressurizes seawater or an internal fluid. While this type of device
has many configurations, one of which is the hose pump point absorber that consists
of a surface-floating buoy anchored to the seafloor with the turbine as a part of the
vertical connection. The wave-induced vertical motion of buoy causes the connection to expand and contract, thereby producing pumping action. The captured energy
and the resulting electricity generation by this device can be optimized [50,51] by
operating the device and wave in resonance.
13.3.3.2 Commercial applications of WeC
A brief summary of commercial applications of various types of WECs outlined
above is given in Table 13.3 [60]. Locations of the devices outlined in Table 13.3 can
be shoreline, nearshore, and offshore. Types of power takeoff include hydraulic ram,
elastomeric hose pump, pump to shore, hydroelectric turbine, air turbine, and linear
electrical generator [60]. Some of these designs incorporate parabolic reflectors to
increase the wave energy at the point of capture. These capture systems use the rise
and fall of motion of waves to capture energy. Once the energy is captured, power is
transmitted to its use or to the electrical grid by transmission power cables [60]. More
details on each device outlined in Table 13.3 are given in Ref. [60]. A more detailed