Wave

Capturing energy from waves with a point absorber buoy, surface attenuator, oscillating water column, or overtopping device.

Waves are a result of the interaction between the wind (a result of temperature differentials created from the sun) and the water’s surface. The energy potential for waves is greatest between 30° and 60° latitude in both hemispheres on the west coast due to the global direction of the wind. Additionally, waves will increase in size when there is a greater distance for them to build up.

 

Environmental effects will vary between the five most common approaches: point absorber buoys, surface attenuators, oscillating water columns, overtopping devices, and oscillating wave surge converters.

 

Point Absorber Buoy

 

This device floats on the surface of the water and is held in place by cables connected to the seabed. Point absorber buoys use the rise and fall of swells to drive hydraulic pumps and generate electricity.

 

The presence of these buoys may affect fish, marine mammals, and birds as they pose a minor collision risk or they may either attract organisms to the device or cause them to avoid the site. As with all electricity generation, there is some concern that electromagnetic fields generated by power cables and moving parts may affect animals that use Earth's natural magnetic field for orientation, navigation, and hunting. Likewise, chemicals such as anti-corrosion paint and small amounts of oil and grease may enter the waterbody during spills, though some device designs do not require lubrication. Large-scale wave energy removal (from arrays) may disrupt natural physical systems to cause degradation in water quality or changes in sediment transport, potentially affecting the ecosystem. Alternatively, devices absorbing wave energy may positively act as shoreline defense.

Surface Attenuator

 

Surface attenuators have multiple floating segments connected to one another and are oriented perpendicular to incoming waves. Similar to point absorber buoys, they use the rise and fall of swells to create a flexing motion that drives hydraulic pumps to generates electricity.

 

Concerns about collision, attraction or avoidance, electromagnetic fields, chemicals, and energy removal are similar to that of a point absorber buoy, with an additional concern that organisms could be pinched in the joints.

Oscillating Water Column

 

Oscillating water column devices can be located onshore or in deeper waters offshore. With an air chamber integrated into the device, swells compress air in the chambers forcing air through an air turbine to create electricity.

 

Significant noise is produced as air is pushed through the turbines, potentially affecting birds and other marine organisms within the vicinity of the device. There is also concern about marine organisms getting trapped or entangled within the air chambers. When located offshore, concerns about collision, attraction or avoidance, electromagnetic fields, chemicals, and energy removal are similar to that of a point absorber buoy; located onshore these concerns are no different than for a standard shoreline structure.

Overtopping Device

 

Overtopping devices are long structures that use wave velocity to fill a reservoir to a higher water level than the surrounding ocean. The potential energy in the reservoir height is then captured with low-head turbines. Devices can be either onshore or floating offshore.

 

There is some concern regarding low levels of turbine noise, marine organisms getting trapped within the reservoir, or collision with the slow-moving turbines. It should be noted that these turbines spin much slower than propellers on ships. When located offshore, concerns about attraction or avoidance, electromagnetic fields, chemicals, and energy removal are similar to that of a point absorber buoy; located onshore these concerns are no different than for a standard shoreline structure.

Oscillating Wave Surge Converter

 

These devices typically have one end fixed to a structure or the seabed while the other end is free to move. Energy is collected from the relative motion of the body compared to the fixed point. Oscillating wave surge converters often come in the form of floats, flaps, or membranes.

 

Environmental concerns include minor risk of collision with the moving component or attraction, such as artificial reefing near the fixed point. Concerns about electromagnetic fields, chemicals, and energy removal are similar to that of a point absorber buoy.

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