Ocean wave energy is captured directly from surface waves or from pressure fluctuations below the surface. Waves are caused by the wind blowing over the surface of the ocean. In many areas of the world, the wind blows with enough consistency and force to provide continuous waves. There is tremendous energy in the ocean waves. Wave power devices extract energy directly from the surface motion of ocean waves or from pressure fluctuations below the surface.
Wave power varies considerably in different parts of the world, and wave energy can’t be harnessed effectively everywhere. Wave-power rich areas of the world include the western coasts of Scotland, northern Canada, southern Africa, Australia, and the north-western coasts of the United States.
Ocean mechanical wave energy is quite different from ocean thermal energy. Even though the sun affects all ocean activity, tides are driven primarily by the gravitational pull of the moon, and waves are driven primarily by the winds. As a result, tides and waves are intermittent sources of energy, while ocean thermal energy is fairly constant. Also, unlike thermal energy, the electricity conversion of both tidal and wave energy usually involves mechanical devices such as turbines. See illustrations below.
• The energy is free – no fuel is needed and no waste is produced
• Inexpensive to operate and maintain
• Can produce a significant amount of energy.
• Depends on the waves – variable energy supply
• Reeds a suitable site, where waves are consistently strong
• Some designs generate noise
• Must be able to withstand very rough weather
• Costly to develop
• Visual impact if above water or on shore
• Can disturb or disrupt marine life – including changes in the distribution and types of marine life near the shore
• Poses a possible threat to navigation from collisions due to the low profile of the wave energy devices above the water, making them undetectable either by direct sighting or by radar
• May interfere with mooring and anchorage lines with commercial and sport-fishing
• May degrade scenic ocean front views from wave energy devices located near or on the shore, and from onshore overhead electric transmission lines.
Ocean Wave Technologies and Methods
While all wave energy technologies are intended to be installed at or near the water’s surface, they differ in their orientation to the waves with which they are interacting and in the manner in which they convert the energy of the waves into other energy forms, usually electricity. The following wave technologies have been the target of recent developments.
• Wave Terminator devices extend perpendicular to the direction of wave travel and capture or reflect the power of the wave. These devices are typically onshore or nearshore. The oscillating water column is a form of terminator in which water enters through a subsurface opening into a chamber with air trapped above it. The wave action causes the captured water column to move up and down like a piston to force the air though an opening connected to a turbine.
Wave Terminator device
• A point absorber is a floating structure with components that move relative to each other due to wave action (e.g., a floating buoy inside a fixed cylinder). The relative motion is used to drive electromechanical or hydraulic energy converters.
• Attenuator Wave Energy Devices are long multi segment floating structures oriented parallel to the direction of the waves. The differing heights of waves along the length of the device causes flexing where the segments connect, and this flexing is connected to hydraulic pumps or other converters.
Attenuator Wave Energy Devices
• Overtopping devices have reservoirs that are filled by incoming waves to levels above the average surrounding ocean. The water is then released, and gravity causes it to fall back toward the ocean surface. The energy of the falling water is used to turn hydro turbines. Specially built seagoing vessels can also capture the energy of offshore waves. These floating platforms create electricity by funnelling waves through internal turbines and then back into the sea.
To be continued in Part 8 Ocean Thermal Energy
Part 6 – Solar Power
Part 5 – Tidal Energy
Part 4 – Geothermal Energy
Part 3 – Concentrated Solar Power
Part 2 – Wind Power
Part 1 – Introduction