Ocean energy conversion

The development of ocean energy has continued to gain momentum, with several commercially significant projects being successfully operated, although the sector is still in early evolutionary phases. The United Kingdom, more specifically Scotland, with the largest ocean energy resources in Europe and some of the largest in the world, is fast becoming the global leader in ocean energy research and development. The British government, a strong protagonist of renewable energy, is an enthusiastic supporter of ocean energy.
More than 25 countries are involved in developing relevant conversion technologies for harnessing ocean renewable resources for electricity generation and/or other purposes, such as desalination, air conditioning, heating for aquaculture and other uses.
Over 300 wave and tidal devices have been envisioned, but very few of these are in an advanced stage of development. Ocean energy is mostly in an experimental stage and early prototype stages, apart from, perhaps most significantly the tidal barrage at La Rance in France commissioned in 1966.
Energy can be harvested from the oceans in five basic ways, with a multitude of variations:
1. Tides – Potential energy contained in tides can be harnessed by building barrage or other forms of construction across an estuary.
2. Waves – Kinetic and potential energy in ocean waves can be harnessed using modular technologies.
3. Tidal or marine currents – Kinetic energy in tidal (marine) currents can be harnessed using modular systems.
4. Temperature gradients – Thermal energy due to the temperature gradient between the sea surface and deep-water can be harnessed using different Ocean Thermal Energy Conversion (OTEC) processes.
5. Salinity gradients – At the mouth of rivers where fresh water mixes with salt water, energy associated with the salinity gradient can be harnessed using pressure-retarded reverse osmosis process and associated conversion technologies.
Wave energy is the largest resource, followed by power from the salinity and thermal gradients. Tidal and marine current energy are by far the smallest in potential capacity.

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