Although easier to exploit, tidal power suffers in two ways from periodicity: the direction of the current changes four times a day in most places, and the amount of energy available at spring tides is considerably greater than at neaps. Whereas the effect of the first can be minimized by using generators at different places along the coast, the second means that less power is generated for a period of a week or more.
By contrast, ocean currents flow relatively steadily throughout the year and in some cases the flow is very considerable. An example is the Straits of Florida where the Gulf Stream flows out of the Carribean Sea and into the North Atlantic on its way to northern Europe. The speed of the current is around 4 knots (2m/s) at the surface although less towards the bottom. There is a potential extractible power of 1KW/m2 near the surface.
A 300 kW full scale plant has been operating at Lynmouth, Devon (UK) since May 2003. Although a prototype for tidal systems such as Seagen, MCT has also been planning deep sea marine current systems, which could be constructed in large farms and thus use economies of scale both in construction and maintenance and in the infrastructure for bringing the electricity to shore.
Another approach which has identified the potential of the Gulf stream is the Gorlov helical turbine. This is a vertical axis turbine which is being currently prototyped in South Korea.
Damage to seabed flora is also potentially dangerous and designs are being explored which are anchored to the seabed but operate at a distance, rather than having towers built on the bed. Since there are at present no firm plans for deployment of these devices, it is difficult to evaluate whether this will be a serious problem.
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Jul 07, 2011; GENEVA, July 7 -- Publication No. WO/2011/076313 was published on June 30. Title of the invention: "CASING FOR RECEIVING AN...
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