Tidal power
Overview
 
Tidal power, also called tidal energy, is a form of hydropower
Hydropower
Hydropower, hydraulic power, hydrokinetic power or water power is power that is derived from the force or energy of falling water, which may be harnessed for useful purposes. Since ancient times, hydropower has been used for irrigation and the operation of various mechanical devices, such as...

 that converts the energy of tide
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....

s into useful forms of power - mainly electricity.

Although not yet widely used, tidal power has potential for future electricity generation
Electricity generation
Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...

. Tides are more predictable than wind energy
Wind energy
Wind energy is the kinetic energy of air in motion; see also wind power.Total wind energy flowing through an imaginary area A during the time t is:E = ½ m v2 = ½ v 2...

 and solar power
Solar power
Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...

. Among sources of renewable energy
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...

, tidal power has traditionally suffered from relatively high cost and limited availability of sites with sufficiently high tidal ranges or flow velocities, thus constricting its total availability.
Encyclopedia
Tidal power, also called tidal energy, is a form of hydropower
Hydropower
Hydropower, hydraulic power, hydrokinetic power or water power is power that is derived from the force or energy of falling water, which may be harnessed for useful purposes. Since ancient times, hydropower has been used for irrigation and the operation of various mechanical devices, such as...

 that converts the energy of tide
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....

s into useful forms of power - mainly electricity.

Although not yet widely used, tidal power has potential for future electricity generation
Electricity generation
Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...

. Tides are more predictable than wind energy
Wind energy
Wind energy is the kinetic energy of air in motion; see also wind power.Total wind energy flowing through an imaginary area A during the time t is:E = ½ m v2 = ½ v 2...

 and solar power
Solar power
Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...

. Among sources of renewable energy
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...

, tidal power has traditionally suffered from relatively high cost and limited availability of sites with sufficiently high tidal ranges or flow velocities, thus constricting its total availability. However, many recent technological developments and improvements, both in design (e.g. dynamic tidal power, tidal lagoons) and turbine technology (e.g. new axial turbines, cross flow turbines), indicate that the total availability of tidal power may be much higher than previously assumed, and that economic and environmental costs may be brought down to competitive levels.

Historically, tide mill
Tide mill
A tide mill is a water mill driven by tidal rise and fall. A dam with a sluice is created across a suitable tidal inlet, or a section of river estuary is made into a reservoir. As the tide comes in, it enters the mill pond through a one way gate, and this gate closes automatically when the tide...

s have been used, both in Europe and on the Atlantic coast of North America. The earliest occurrences date from the Middle Ages
Middle Ages
The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

, or even from Roman times
Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

.

The world's first large-scale tidal power plant (the Rance Tidal Power Station) became operational in 1966.

Generation of tidal energy

Tidal power is extracted from the Earth's oceanic tides; tidal forces are periodic variations in gravitational attraction exerted by celestial bodies. These forces create corresponding motions or currents in the world's oceans. The magnitude and character of this motion reflects the changing positions of the Moon and Sun relative to the Earth, the effects of Earth's rotation
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

, and local geography of the sea floor and coastlines
Bathymetry
Bathymetry is the study of underwater depth of lake or ocean floors. In other words, bathymetry is the underwater equivalent to hypsometry. The name comes from Greek βαθύς , "deep", and μέτρον , "measure"...

.

Tidal power is the only technology that draws on energy inherent in the orbital characteristics of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 system, and to a lesser extent in the Earth–Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 system. Other natural energies exploited by human technology originate directly or indirectly with the Sun, including fossil fuel
Fossil fuel
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...

, conventional hydroelectric
Hydroelectricity
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...

, wind
Wind power
Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships....

, biofuel
Biofuel
Biofuel is a type of fuel whose energy is derived from biological carbon fixation. Biofuels include fuels derived from biomass conversion, as well as solid biomass, liquid fuels and various biogases...

, wave
Wave power
Wave power is the transport of energy by ocean surface waves, and the capture of that energy to do useful work — for example, electricity generation, water desalination, or the pumping of water...

 and solar energy. Nuclear energy
Nuclear power
Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...

 makes use of Earth's mineral deposits of fissionable elements, while geothermal power
Geothermal power
Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. Earth's geothermal energy originates from the original formation of the planet and from radioactive decay of minerals...

 taps the Earth's internal heat
Internal heat
Internal heat is the heat source from the interior of celestial objects, such as planets, brown dwarfs, and stars, caused by gravity, nuclear fusion and decaying radioactive materials. The amount of internal heating depends on mass; the more massive the object, the more internal heat it has...

, which comes from a combination of residual heat from planetary accretion
Gravitational binding energy
The gravitational binding energy of an object consisting of loose material, held together by gravity alone, is the amount of energy required to pull all of the material apart, to infinity...

 (about 20%) and heat produced through radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...

 (80%).

A tidal generator converts the energy of tidal flows into electricity. Greater tidal variation and higher tidal current velocities can dramatically increase the potential of a site for tidal electricity generation.

Because the Earth's tides are ultimately due to gravitational interaction with the Moon and Sun and the Earth's rotation, tidal power is practically inexhaustible and classified as a renewable energy
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...

 resource. Movement of tides causes a loss of mechanical energy
Tidal acceleration
Tidal acceleration is an effect of the tidal forces between an orbiting natural satellite , and the primary planet that it orbits . The "acceleration" is usually negative, as it causes a gradual slowing and recession of a satellite in a prograde orbit away from the primary, and a corresponding...

 in the Earth–Moon system: this is a result of pumping of water through natural restrictions around coastlines and consequent viscous
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 dissipation at the seabed
Seabed
The seabed is the bottom of the ocean.- Ocean structure :Most of the oceans have a common structure, created by common physical phenomena, mainly from tectonic movement, and sediment from various sources...

 and in turbulence
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...

. This loss of energy has caused the rotation of the Earth to slow in the 4.5 billion years since its formation. During the last 620 million years the period of rotation of the earth (length of a day) has increased from 21.9 hours to 24 hours; in this period the Earth has lost 17% of its rotational energy. While tidal power may take additional energy from the system, the effect is negligible and would only be noticed over millions of years.

Generating methods

Tidal power can be classified into three generating methods:

Tidal stream generator

Tidal stream generators (or TSGs) make use of the kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...

 of moving water to power turbines, in a similar way to wind turbines that use wind to power turbines.

Tidal barrage

Tidal barrages make use of the potential energy
Potential energy
In physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. The SI unit of measure for energy and work is the Joule...

 in the difference in height (or head
Hydraulic head
Hydraulic head or piezometric head is a specific measurement of water pressure above a geodetic datum. It is usually measured as a water surface elevation, expressed in units of length, at the entrance of a piezometer...

) between high and low tides. Barrages are essentially dam
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...

s across the full width of a tidal estuary.

Dynamic tidal power

Dynamic tidal power (or DTP) is a theoretical generation technology that would exploit an interaction between potential and kinetic energies in tidal flows. It proposes that very long dams (for example: 30–50 km length) be built from coasts straight out into the sea or ocean, without enclosing an area. Tidal phase differences are introduced across the dam, leading to a significant water-level differential in shallow coastal seas – featuring strong coast-parallel oscillating tidal currents such as found in the UK, China and Korea.

US and Canadian studies in the twentieth century

The first study of large scale tidal power plants was by the US Federal Power Commission in 1924 which would have been located if built in the northern border area of the US state of Maine
Maine
Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...

 and the south eastern border area of the Canadian province of New Brunswick, with various dams, powerhouses and ship locks enclosing the Bay of Fundy
Bay of Fundy
The Bay of Fundy is a bay on the Atlantic coast of North America, on the northeast end of the Gulf of Maine between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine...

 and Passamaquoddy Bay
Passamaquoddy Bay
Passamaquoddy Bay is an inlet of the Bay of Fundy, between the U.S. state of Maine and the Canadian province of New Brunswick, at the mouth of the St. Croix River. Most of the bay lies within Canada, with its western shore bounded by Washington County, Maine. The southernmost point is formed by...

 (note: see map in reference). Nothing came of the study and it is unknown whether Canada had been approached about the study by the US Federal Power Commission.

There was also a report on the international commission in April 1961 entitled " Investigation of the International Passamaquoddy Tidal Power Project" produced by both the US and Canadian Federal Governments. According to benefit to costs ratios, the project was beneficial to the US but not to Canada. A highway system along the top of the dams was envisioned as well.

A study was commissioned by the Canadian, Nova Scotian and New Brunswick Governments (Reassessment of Fundy Tidal Power) to determine the potential for tidal barrages at Chignecto Bay and Minas Basin – at the end of the Fundy Bay estuary. There were three sites determined to be financially feasible: Shepody Bay (1550 MW), Cumberline Basin (1085 MW) and Cobequid Bay (3800 MW). These were never built despite their apparent feasibility in 1977.

Current and future tidal power schemes

  • The first tidal power station was the Rance tidal power plant
    Rance tidal power plant
    The Rance Tidal Power Station is the world's first tidal power station and also the world's second biggest tidal power station. The facility is located on the estuary of the Rance River, in Brittany, France. Opened on the 26th November 1966, it is currently operated by Électricité de France, and is...

     built over a period of 6 years from 1960 to 1966 at La Rance
    Rance River
    The Rance is a river of northwestern France. It flows into the English Channel between Dinard and Saint-Malo.Before reaching the Channel, its waters are barred by a 750 metre long dam forming the Rance tidal power plant....

    , France. It has 240 MW installed capacity.
  • 254 MW Sihwa Lake Tidal Power Plant
    Sihwa Lake Tidal Power Plant
    Sihwa Lake Tidal Power Station is the world's largest tidal power installation, with a total power output capacity of 254 MW, surpassing the 240 MW Rance Tidal Power Station after 45 years....

     in South Korea is the largest tidal power installation in the world. Construction was completed in 2011.
  • The first tidal power site in North America
    North America
    North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

     is the Annapolis Royal Generating Station
    Annapolis Royal Generating Station
    The Annapolis Royal Generating Station is a 20 MW tidal power station located on the Annapolis River immediately upstream from the town of Annapolis Royal, Nova Scotia, Canada. It is the only tidal generating station in North America. The generating station harnesses the tidal difference...

    , Annapolis Royal
    Annapolis Royal, Nova Scotia
    Annapolis Royal is a town located in the western part of Annapolis County, Nova Scotia. Known as Port Royal until the Conquest of Acadia in 1710 by Britain, the town is the oldest continuous European settlement in North America, north of St...

    , Nova Scotia
    Nova Scotia
    Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...

    , which opened in 1984 on an inlet of the Bay of Fundy
    Bay of Fundy
    The Bay of Fundy is a bay on the Atlantic coast of North America, on the northeast end of the Gulf of Maine between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine...

    . It has 20 MW installed capacity.
  • The Jiangxia Tidal Power Station
    Jiangxia Tidal Power Station
    The Jiangxia Tidal Power Station is the third largest tidal power station in the world, located in Wuyantou, Wenling City, Zhejiang Province, China...

    , south of Hangzhou
    Hangzhou
    Hangzhou , formerly transliterated as Hangchow, is the capital and largest city of Zhejiang Province in Eastern China. Governed as a sub-provincial city, and as of 2010, its entire administrative division or prefecture had a registered population of 8.7 million people...

      in China
    China
    Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

     has been operational since 1985, with current installed capacity of 3.2 MW. More tidal power is planned near the mouth of the Yalu River.
  • The first in-stream tidal current generator in North America (Race Rocks Tidal Power Demonstration Project
    Race Rocks Tidal Power Demonstration Project
    The Race Rocks Tidal Power Demonstration Project is a joint project of the Lester B. Pearson College, EnCana Corporation and Clean Current Power Systems Incorporated to use tidal power at Race Rocks near Victoria, British Columbia in Canada...

    ) was installed at Race Rocks on southern Vancouver Island
    Vancouver Island
    Vancouver Island is a large island in British Columbia, Canada. It is one of several North American locations named after George Vancouver, the British Royal Navy officer who explored the Pacific Northwest coast of North America between 1791 and 1794...

     in September 2006. The next phase in the development of this tidal current generator will be in Nova Scotia.
  • A small project was built by the Soviet Union at Kislaya Guba
    Kislaya Guba Tidal Power Station
    The Kislaya Guba Tidal Power Station is an experimental project in Kislaya Guba, Russia.The station is the world's 4th largest tidal power plant with the output capacity of 1.7 MW. Construction on the project began in 1968, but was later suspended for 10 years until December 2004, when...

     on the Barents Sea
    Barents Sea
    The Barents Sea is a marginal sea of the Arctic Ocean, located north of Norway and Russia. Known in the Middle Ages as the Murman Sea, the sea takes its current name from the Dutch navigator Willem Barents...

    . It has 0.4 MW installed capacity. In 2006 it was upgraded with a 1.2MW experimental advanced orthogonal turbine.
  • Jindo Uldolmok Tidal Power Plant
    Uldolmok Tidal Power Station
    Uldolmok Tidal Power Station is a tidal power station in Uldolmok, Jindo County, South Korea. The plant was commissioned in by the South Korean government. The plant cost US$10 million and has an installed capacity of , generating annually, sufficient to meet the demand of 430 households...

     in South Korea is a tidal stream generation scheme planned to be expanded progressively to 90 MW of capacity by 2013. The first 1 MW was installed in May 2009.
  • A 1.2 MW SeaGen
    SeaGen
    SeaGen is the world's first large scale commercial tidal stream generator. It is four times more powerful than any other tidal stream generator in the world....

     system became operational in late 2008 on Strangford Lough
    Strangford Lough
    Strangford Lough, sometimes Strangford Loch, is a large sea loch or inlet in County Down, Northern Ireland. It is separated from the Irish Sea by the Ards Peninsula. The name Strangford is derived ; describing the fast-flowing narrows at its mouth...

     in Northern Ireland
    Northern Ireland
    Northern Ireland is one of the four countries of the United Kingdom. Situated in the north-east of the island of Ireland, it shares a border with the Republic of Ireland to the south and west...

    .
  • The contract for an 812 MW tidal barrage near Ganghwa Island
    Ganghwa Island
    Ganghwa Island is an island in the estuary of the Han River, on the west coast of South Korea. Ganghwa Island is separated from Gimpo, on the mainland, by a narrow channel, which is spanned by two bridges. The main channel of the Han River separates the island from Gaeseong in North Korea.About...

     north-west of Incheon has been signed by Daewoo. Completion is planned for 2015.
  • A 1,320 MW barrage
    Incheon Tidal Power Station
    The Incheon Tidal Power Station is a large tidal power station currently proposed to be built at the Incheon Bay, South Korea. The facility is expected to top 1,320 MW in generating capacity with the help of 44 water turbines rated at 30 MW each, making this facility one of the largest of...

     built around islands west of Incheon is proposed by the Korean government, with projected construction start in 2017.
  • Other South Korean projects include barrages planned for Garorim Bay, Ansanman, and Swaseongho, and tidal generation associated with the Saemangeum
    Saemangeum
    Saemangeum is an estuarine tidal flat on the coast of the Yellow Sea in South Korea. It was dammed by the government of South Korea's Saemangeum Seawall Project, completed in April 2006, after a long fight between the government and environmental activists, and is scheduled to be converted into...

     reclamation project. The barrages are all in the multiple-hundred megawatts range.
  • The Scottish Government has approved plans for a 10MW array of tidal stream generators near Islay
    Islay
    -Prehistory:The earliest settlers on Islay were nomadic hunter-gatherers who arrived during the Mesolithic period after the retreat of the Pleistocene ice caps. In 1993 a flint arrowhead was found in a field near Bridgend dating from 10,800 BC, the earliest evidence of a human presence found so far...

    , Scotland
    Scotland
    Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

    , costing 40 million pounds, and consisting of 10 turbines – enough to power over 5,000 homes. The first turbine is expected to be in operation by 2013.
  • The Indian state of Gujarat is planning to host South Asia's first commercial-scale tidal power station. The company Atlantis Resources is to install a 50MW tidal farm in the Gulf of Kutch on India's west coast, with construction starting early in 2012.

See also

  • Hydroelectricity
    Hydroelectricity
    Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...

  • Ocean energy
  • Thermal energy
    Thermal energy
    Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....

  • World energy resources and consumption
    World energy resources and consumption
    ]World energy consumption in 2010: over 5% growthEnergy markets have combined crisis recovery and strong industry dynamism. Energy consumption in the G20 soared by more than 5% in 2010, after the slight decrease of 2009. This strong increase is the result of two converging trends...


External links

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