Marine current power, is a form of power based on the harnessing of the kinetic energy of marine currents. It includes both tidal power and energy derived from ocean currents such as the Gulf stream. A report from the US government agency, the Department of the Interior in 2006 states: "It has been estimated that capturing just 1/1,000th of the available energy from the Gulf Stream, which has 21,000 times more energy than Niagara Falls in a flow of water that is 50 times the total flow of all the world’s freshwater rivers, would supply Florida with 35% of its electrical needs."
Although not yet widely used, marine current power has an important potential for future electricity generation. Marine currents are more predictable than wind energy and solar power.
Although not yet widely used, marine current power has an important potential for future electricity generation. Marine currents are more predictable than wind energy and solar power.
Comparison with Tidal stream energy
Tidal stream energy systems are currently in development in places such as the United Kingdom, the Bay of Fundy and South Korea where the tides run often in excess of 7 knots (3.6 m/s) in relatively shallow water. Since the power generated from any turbine such as a wind generator varies both with the density of the fluid and the cube of its speed, it's important to find places where this movement is fast enough. Ocean water is about 800 times denser than air, so speeds of about one-tenth of that of the wind speed can generate the same power.
Although easier to exploit, tidal power suffers in two ways from periodicity: the tidal current strength oscillates 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 — in different phases of the tidal wave — the second means that power generation oscillates with a fortnight period.
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 Caribbean Sea and into the North Atlantic on its way to northern Europe. The speed of the current is around 4 knots (2.1 m/s) at the surface although less towards the bottom. There is a potential extractable power of 1 kW/m2 near the surface.
Although easier to exploit, tidal power suffers in two ways from periodicity: the tidal current strength oscillates 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 — in different phases of the tidal wave — the second means that power generation oscillates with a fortnight period.
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 Caribbean Sea and into the North Atlantic on its way to northern Europe. The speed of the current is around 4 knots (2.1 m/s) at the surface although less towards the bottom. There is a potential extractable power of 1 kW/m2 near the surface.
Technical challenge
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.
The challenge of marine current power is quite new. If you are designing a wind turbine which operates at maximum efficiency at, say, 50 km/h (14 m/s), then you have to consider what happens in a storm, when the speed might be 100–200 km/h (28–56 m/s) or even higher. This places severe constraints on the approaches. If you are dealing with a marine current of 1 m/s (1.9 kn) then you can be reasonably certain it will never exceed 1.5 m/s (2.9 kn). Consequently, totally new approaches might be possible.
One of these that is already being realised in tidal systems is the Venturi effect.. You can funnel a large area of water through a small aperture because you know you don't have to worry about abnormal conditions (though you may have to worry about environmental effects). Radically different turbine designs might be possible, such as the Gorlov turbine, or oscillating devices such as the Stingray. On the other hand, the cost of getting the power back to shore, dealing with the marine environment, or the cost of servicing may make the whole thing uneconomic.
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.
The challenge of marine current power is quite new. If you are designing a wind turbine which operates at maximum efficiency at, say, 50 km/h (14 m/s), then you have to consider what happens in a storm, when the speed might be 100–200 km/h (28–56 m/s) or even higher. This places severe constraints on the approaches. If you are dealing with a marine current of 1 m/s (1.9 kn) then you can be reasonably certain it will never exceed 1.5 m/s (2.9 kn). Consequently, totally new approaches might be possible.
One of these that is already being realised in tidal systems is the Venturi effect.. You can funnel a large area of water through a small aperture because you know you don't have to worry about abnormal conditions (though you may have to worry about environmental effects). Radically different turbine designs might be possible, such as the Gorlov turbine, or oscillating devices such as the Stingray. On the other hand, the cost of getting the power back to shore, dealing with the marine environment, or the cost of servicing may make the whole thing uneconomic.
