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Marine current power
 
 
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Marine current power, is a form of power based on the harnessing of the kinetic energy
Kinetic energy

The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the mechanical work needed to accelerate a body of a given mass from rest to its current velocity....
 of marine currents. It includes both tidal power
Tidal power

Tidal power, sometimes called tidal energy, is a form of hydropower that converts the energy of tides into electricity or other useful forms of power....
 and energy derived from ocean current
Ocean current

An ocean current is continuous, directed movement of ocean water. The currents are generated from the forces acting upon the water like the Earth's rotation, the wind, the temperature, salinity differences and the tide....
s such as the Gulf stream
Gulf Stream

The Gulf Stream, together with its northern extension towards Europe, the North Atlantic Current, is a powerful, warm, and swift Atlantic Ocean ocean current that originates in the Gulf of Mexico, exits through the Straits of Florida, and follows the eastern coastlines of the United States and Newfoundland and Labrador before crossing the At...
. 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
Niagara Falls

The Niagara Falls are massive waterfalls on the Niagara River, straddling the Canada?United States border between the Provinces and territories of Canada of Ontario and the U.S....
 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
Electricity generation

Electricity generation is the process of converting non-electrical energy to electricity. For electric utility, it is the first process in the delivery of electricity to consumers....
.






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Marine current power, is a form of power based on the harnessing of the kinetic energy
Kinetic energy

The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the mechanical work needed to accelerate a body of a given mass from rest to its current velocity....
 of marine currents. It includes both tidal power
Tidal power

Tidal power, sometimes called tidal energy, is a form of hydropower that converts the energy of tides into electricity or other useful forms of power....
 and energy derived from ocean current
Ocean current

An ocean current is continuous, directed movement of ocean water. The currents are generated from the forces acting upon the water like the Earth's rotation, the wind, the temperature, salinity differences and the tide....
s such as the Gulf stream
Gulf Stream

The Gulf Stream, together with its northern extension towards Europe, the North Atlantic Current, is a powerful, warm, and swift Atlantic Ocean ocean current that originates in the Gulf of Mexico, exits through the Straits of Florida, and follows the eastern coastlines of the United States and Newfoundland and Labrador before crossing the At...
. 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
Niagara Falls

The Niagara Falls are massive waterfalls on the Niagara River, straddling the Canada?United States border between the Provinces and territories of Canada of Ontario and the U.S....
 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
Electricity generation

Electricity generation is the process of converting non-electrical energy to electricity. For electric utility, it is the first process in the delivery of electricity to consumers....
. Marine currents are more predictable than wind energy and solar power
Solar power

Solar energy is the radiant light and heat from the Sun that has been harnessed by humans since ancient history using a range of ever-evolving technologies....
.

Comparison with Tidal stream energy

Main article: Tidal stream generator


Tidal stream energy systems are currently in development in places such as the United Kingdom
United Kingdom

The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom , the UK or Britain,is a sovereign state located off the northwestern coast of continental Europe....
, the Bay of Fundy
Bay of Fundy

The Bay of Fundy is a Headlands and bays on the Atlantic Ocean coast of North America, on the northeast end of the Gulf of Maine between the Canada Provinces of Canada of New Brunswick and Nova Scotia, with a small portion touching the United States U.S....
 and South Korea
South Korea

South Korea, officially the Republic of Korea , ), often referred to as Korea and the "names of Korea#Revival of the names", is a Semi-presidential system republic in East Asia, located in the southern half of the Korean Peninsula....
 where the tides run often in excess of in relatively shallow water. Since the power generated from any turbine such as a wind generator
Wind generator

A wind generator is a device that generates electrical power from wind energy.Wind generators have traditionally been wind turbines, i.e. a propeller attached to an electric generator attached to appropriate electronics to attach it to the electrical grid or to battery charger....
 varies both with the density
Density

The density of a material is defined as its mass per unit volume. The symbol of density is ....
 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
Periodicity

Periodicity is the quality of occurring at regular intervals or periods and can occur in different contexts:In timing devices:* A clock marks time at periodic intervals....
: 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
Straits of Florida

The Straits of Florida, Florida Straits, or Florida Strait is a strait located south-southeast of the North American mainland, generally accepted to be between the Gulf of Mexico and the Atlantic Ocean, and between the Florida Keys and Cuba....
 where the Gulf Stream
Gulf Stream

The Gulf Stream, together with its northern extension towards Europe, the North Atlantic Current, is a powerful, warm, and swift Atlantic Ocean ocean current that originates in the Gulf of Mexico, exits through the Straits of Florida, and follows the eastern coastlines of the United States and Newfoundland and Labrador before crossing the At...
 flows out of the Caribbean Sea
Caribbean Sea

The Caribbean Sea is a sea of the Atlantic Ocean situated in the mid-latitudes of the Western Hemisphere, bounded to the south and west by the Americas, with the North Atlantic Ocean proper to the northeast and the Gulf of Mexico to the northwest....
 and into the North Atlantic on its way to northern Europe
Europe

Europe is, conventionally, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural , the Caspian Sea, and by the Caucasus Mountains to the southeast....
. The speed of the current is around 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
Gorlov helical turbine

The Gorlov helical turbine , evolved from the Darrieus wind turbine design by altering it to have Helix blades/foils. The GHT is a water turbine, however its design is similar to some air turbines presently on the market, such as the Turby wind turbine and the Quietrevolution wind 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, , then you have to consider what happens in a storm, when the speed might be or even higher. This places severe constraints on the approaches. If you are dealing with a marine current of then you can be reasonably certain it will never exceed . Consequently, totally new approaches might be possible.

One of these that is already being realised in tidal systems is the Venturi effect
Venturi effect

The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe. The fluid velocity must increase through the constriction to satisfy the Derivation of the Navier?Stokes equations#Conservation of mass, while its pressure must decrease due to conservation of energy: the gain in kin...
.. 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
Gorlov helical turbine

The Gorlov helical turbine , evolved from the Darrieus wind turbine design by altering it to have Helix blades/foils. The GHT is a water turbine, however its design is similar to some air turbines presently on the market, such as the Turby wind turbine and the Quietrevolution wind 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.

Environmental considerations

Concerns have been expressed about the danger to fish and other marine life, both directly from the turbines and through the disturbance to the sea floor by construction, anchorages and supply cables. In general the turbines would be relatively slow moving and it is believed that fishes will detect the pressure changes and avoid being caught. This is a contrast to the turbines on barrage tidal systems where 15% mortality of fish passing through the turbines is observed. To confirm this, a monitoring programme has been established at Strangford Lough
Strangford Lough

Strangford Lough is a lough in County Down, Northern Ireland, separated from the Irish Sea by the Ards Peninsula. It is a popular tourist attraction noted for its fishing and the picturesque villages and townships which border its waters....
.

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.

See also

Ocean energy
Ocean energy

The oceans have a tremendous amount of energy and are close to many if not most concentrated populations. Many researches show that ocean energy has the potentiality of providing for a substantial amount of new renewable energy around the world....


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