Development of Ocean, Tidal and Wave Energy

Ocean energy is mostly in an experimental stage. Many ideas have been generated, and a lot of experimental projects are being funded both by governments and commercially. These range from technologies and schemes which produce small amounts of energy for local, often dedicated use, to large-scale projects which can or will be capable of supplying energy in quantities sufficient to feed into a grid. The ocean can produce two types of energy: thermal energy from the sun's heat and mechanical energy from the tides and waves. Energy can be harvested from the oceans in four ways.

As the ocean energy technology develops, the industry is finding that synergies and expertise exist in the offshore wind power and hydropower industries. In the same way, the wind power industry found that the offshore oil and gas industry had a valuable contribution to make in helping with design of offshore wind plants.

Most countries which have investigated the potential exploitation of tidal energy have concentrated on the use of tidal barrages that can be used to control the natural tidal flow, which is directed to drive turbines. Only around 20 sites in the world have been identified as possible tidal power stations. Three countries have tidal energy schemes in operation: France, with the 240 MW tidal barrage at Rance, the largest tidal power station in the world and the only one in Europe, built in 1966; Canada, with the 20 MW Annapolis tidal barrage; and China, with an 11 MW scheme of small tidal plants.

Experimental tidal energy projects are being tested in Russia, UK, Australia, USA, Argentina, Canada, India, Korea, and Mexico.

Potential sites for tidal energy stations are few and far between, but a number have been identified in the UK, France, Eastern Canada, the Pacific coast of Russia, Korea, China, Mexico, and Chile. Other sites have been identified along the Patagonian coast of Argentina, Western Australia, and Western India.

Tidal ranges along the west coast of England and Wales are unusually large, averaging 7 to 8 metres on the spring tides in several estuaries and as much as 11 metres in the Severn. The Severn estuary is the site for the most ambitious tidal barrage that has been proposed for the UK so far, and it has been discussed for many years.

Tidal energy is expensive to install, costing UK£1.5 /US$2.4 million per megawatt, compared with about US$1 million per megawatt for wind turbines. It also has environmental problems including effects on tidal waters and ecosystems. On the positive side, it is cheap to maintain once installed and the electricity output is completely predictable.

Tidal energy barrages would modify existing estuarine ecosystems to varying degrees, and environmental considerations are some of the barriers which have to be overcome to develop them.

Over 300 wave and tidal devices have been suggested to date, but of these, very few are in an advanced state of development. A study in early 2005 identified that one technology, Ocean Power Delivery's “Pelamis,” was leading in terms of development, and a further 4 systems were following closely behind. There are many different wave energy devices on the drawing board or undergoing tests.

Wave energy is within sight of being able to provide commercially viable electricity. The experience of onshore wind energy costs, which have been seen to fall by a factor of five over 12 to 15 years, supports predictions that the cost of wave energy will fall to 3-4 cents/kWh in five to eight years.

Wave energy is generated by the movement of devices, stationary or floating on the surface of the ocean and moved by waves, as opposed to a large volume of tidal water that is used to drive motors.

The highest energy waves are concentrated off the western coasts in the 40°–60° latitude range north and south, in the Atlantic SW of Ireland, the Southern Ocean and off Cape Horn. The capability to supply electricity from this resource is such that, if harnessed appropriately, 10% of the current level of world supply could be provided.

Development is proceeding vigorously, and while little generating capacity has yet been created, the technology is being explored with many new ideas.

Experimental wave energy projects are being tested in Australia, UK, USA, Argentina, Canada, China, India, Portugal, Sweden, Denmark, Greece, Indonesia, Ireland, Japan, Maldives, and Norway.

Benefits would undoubtedly be gained from greater international collaboration on as many as possible of the pre-competitive aspects of R&D. At present, the EU funding opportunities provide a major incentive to encourage collaboration, but there is room for other mechanisms to bring the international wave community closer together and avoid duplication and waste.