The range of ocean energy technologies is huge and varied for a number of reasons:
1. There are a number of different forms of ocean energy
2. There are many different ways to extract energy from seawater
3. Ocean energy technologies are at an early stage of development and a wide range of experimentation is continuing.
Because there is a wide range of options for energy extraction and no dominant technologies, it is unlikely that ocean energy technologies will converge on a single device type, equivalent to the monopole tower, horizontal axis wind turbine generator with an upwind three-bladed rotor, which characterize the majority of wind turbines.
Seawater is approximately 830 times denser than air at sea level. Consequently devices which seek to extract potential or kinetic energy from seawater movements are likely to be substantially smaller and more robust than wind turbines. The forces exerted by seawater are much greater than forces exerted by the wind.
Presently the only nominally commercial ocean energy technology is the tidal barrage, which is effectively an existing technology—a hydroelectric plant—which utilizes the tidal range in river mouths, estuaries or embayments to generate a hydraulic head during either or both the ebb and flood tides, which can be used to generate electricity.
All other ocean energy technologies have, at best, reached the pre-commercial demonstration phase and have yet to become commercial. However, considerable investment and research effort is being expended worldwide and new technologies are approaching commercial deployment, particularly wave and tidal stream technologies.
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