Wave energy technologies extract energy directly from surface waves or from pressure fluctuations below the surface. However, wave energy cannot be harnessed everywhere. Wave power-rich areas of the world include the western coasts of Scotland, northern Canada, southern Africa, and Australia as well as the northeastern and northwestern coasts of the United States. In the Pacific Northwest alone, it is feasible that wave energy could produce 40–70 kilowatts (kW) per 3.3 feet (1 meter) of western coastline.
Wave energy can be converted into electricity by offshore or onshore systems.
Oscillating Water Columns
These are partially submerged structures that house a column of air above a column of water. Waves are then funneled into the structure below the waterline, forcing the water column to rise and fall like a piston. This movement both pressurizes and depressurizes the air column, moving a bidirectional turbine with the resulting “push/pull” force.
The overtopping device generally is constructed on shore or on a levee. There is a collector that funnels waves over the top of the structure and into one of the device’s reservoirs positioned below the waterline. The water is then run back out to sea through one or more turbines. As the water spins the turbine rotors, electric current is generated.
The point absorber is a floating structure that captures energy from the vertical motion of the waves. This up-and-down motion of the device drives generators that create an electric current.
This style of device harnesses wave energy directly from the surging and swelling motion of waves. It uses the oscillation between a float, flap, or membrane and a fixed point. That movement creates a usable form of mechanical energy. Similar devices are also being developed that utilize pitching, heaving, and swaying motions.
This device is long and multi-segmented and floats on the surface. The attenuator is anchored in place with a mooring line and positioned perpendicularly to incoming waves. Some attenuators tap only the heave (vertical motion); others tap both heave and surge. The device captures energy as the motion of the wave causes it to flex where the segments connect. This movement then drives hydraulic pumps or generators.