Wave power is a renewable energy technology that captures the natural energy contained within ocean waves to generate electricity. This process relies on both the potential energy associated with the height of the wave crests and the kinetic energy of the water’s movement. As it converts the mechanical energy of moving water into power, wave power is categorized as a form of marine hydrokinetic energy.
Harnessing Wave Motion
Ocean waves are energy carriers, transferring power across the water’s surface without a significant net movement of the water itself. The energy within a wave is fundamentally divided between gravitational potential energy and kinetic energy. Potential energy is stored in the water displaced above the average sea level, such as the height of the wave crest. Kinetic energy is present in the orbital motion of the water particles beneath the surface as the wave passes. This motion is not purely vertical; water particles move in small, circular paths, which creates both a vertical rise and fall and a horizontal surge. Wave energy converters (WECs) are designed to capture one or both of these primary movements.
Classifications of Wave Energy Converters
Wave energy is captured using three main categories of devices, each designed to interact with the wave’s physical characteristics in a distinct way.
Point Absorbers
Point Absorbers are floating structures that are typically much smaller than the wavelength of the waves they encounter. These devices are moored in place and capture energy from the vertical rise and fall of the ocean surface, acting like a large, specialized buoy. Because of their compact size, Point Absorbers are able to absorb energy effectively from waves approaching from all directions.
Attenuators
Attenuators are long, multi-segmented floating structures that are oriented parallel to the direction of wave travel, effectively riding the waves. As a wave passes along the length of the device, the connected segments flex and hinge in response to the varying heights of the wave crests and troughs. This relative movement between the sections is captured by the internal conversion system.
Terminators
Terminators are devices positioned perpendicular to the wave direction, designed to capture the full force and height of the incoming wave front. One common type is the Oscillating Water Column (OWC), a fixed or floating structure with a partially submerged chamber that traps air above the water surface. Another type is the Overtopping device, which channels waves up a ramp and into a reservoir positioned higher than the surrounding sea level.
Turning Mechanical Motion into Usable Power
The process of converting the captured physical motion into usable electrical power is handled by the Power Take-Off (PTO) system. The exact components of the PTO are determined by the type of motion the device is designed to capture.
In devices that rely on mechanical flexing, like attenuators or certain point absorbers, the PTO often utilizes hydraulic systems. The wave-induced motion drives hydraulic pistons, which pressurize a fluid that then spins a hydraulic motor. This motor is directly connected to an electrical generator, producing electricity.
Terminator devices, particularly Oscillating Water Columns, employ pneumatic conversion methods. The rising and falling water column compresses and decompresses the air trapped above it, forcing this air through a bidirectional turbine. This specialized turbine is designed to spin the generator in the same direction regardless of the airflow direction, ensuring continuous power production. Overtopping devices use a more traditional hydroelectric approach, where the water collected in the reservoir is released through a low-head turbine to generate power. Regardless of the conversion mechanism, the electricity produced is conditioned and transmitted via subsea cables that run along the ocean floor back to a substation on shore, where the power is connected to the existing electrical grid.