Renewable energy
Biofuels Biomass Geothermal Hydro power Solar power Tidal power Wave power Wind 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. Renewable energy is Energy generated from Natural resources mdashsuch as Sunlight, Wind, Rain, tides and geothermal Biomass refers to living and recently dead Biological material that can be used as fuel or for industrial production Geothermal power (from the Greek roots geo, meaning earth and therme, meaning heat is energy generated by heat stored in the earth or the collection Hydroelectricity is electricity generated by Hydropower, ie the production of power through use of the gravitational force of falling water Solar energy is the Light and radiant heat from the Sun that powers Earth 's Climate and Weather and sustains Life Wave power refers to the Energy of Ocean surface waves and the capture of that energy to do useful work — including Electricity generation, Wind Power is the conversion of wind energy into a useful form such as electricity using Wind turbines At the end of 2007 worldwide capacity of wind-powered generators was Hydropower, hydraulic power or water power is power that is derived from the Force or Energy of moving water which may Characteristics A tide is a repeated cycle of sea level changes in the following stages Over several hours the water rises or advances up a beach in the flood

Although not yet widely used, tidal power has potential for future electricity generation. Electricity generation is the process of converting non-electrical Energy to Electricity. Tides are more predictable than wind energy and solar power. Wind Power is the conversion of wind energy into a useful form such as electricity using Wind turbines At the end of 2007 worldwide capacity of wind-powered generators was Solar energy is the Light and radiant heat from the Sun that powers Earth 's Climate and Weather and sustains Life Historically, tide mills have been used, both in Europe and on the Atlantic coast of the USA, the earliest occurrences dating from the Middle Ages, or even from Roman times. A tide mill is a specialist type of water mill driven by tidal rise and fall Ancient Rome was a Civilization that grew out of a small agricultural community founded on the Italian Peninsula as early as the 10th century BC ^[1][2]

Generation of tidal energy

Variation of tides over a day

Main articles: Tide and Tidal acceleration

Tidal power is the only form of energy which comes from the tidal forces produced by the relative motions of the Earth-Moon system. Characteristics A tide is a repeated cycle of sea level changes in the following stages Over several hours the water rises or advances up a beach in the flood Tidal acceleration is an effect of the Tidal forces between an orbiting Natural satellite ( i The tidal force is a secondary effect of the Force of Gravity and is responsible for the Tides It arises because the gravitational acceleration experienced Other sources of energy originate directly or indirectly from the Sun, including fossil fuels, conventional hydroelectric, wind, biofuels, and solar. The Sun (Sol is the Star at the center of the Solar System. Fossil fuels or mineral fuels are fossil source Fuels that is Hydrocarbons found within the top layer of the Earth’s crust. Hydroelectricity is electricity generated by Hydropower, ie the production of power through use of the gravitational force of falling water Wind Power is the conversion of wind energy into a useful form such as electricity using Wind turbines At the end of 2007 worldwide capacity of wind-powered generators was Solar energy is the Light and radiant heat from the Sun that powers Earth 's Climate and Weather and sustains Life nuclear and geothermal come from radioactive material in the Earth. Nuclear power is any Nuclear technology designed to extract usable Energy from atomic nuclei via controlled Nuclear reactions Geothermal power (from the Greek roots geo, meaning earth and therme, meaning heat is energy generated by heat stored in the earth or the collection Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation.

Tidal energy is generated by the relative motion of the Earth, Sun and the Moon, which interact via gravitational forces. The Sun (Sol is the Star at the center of the Solar System. Gravitation is a natural Phenomenon by which objects with Mass attract one another Periodic changes of water levels, and associated tidal currents, are due to the gravitational attraction by the Sun and Moon. The magnitude of the tide at a location is the result of the changing positions of the Moon and Sun relative to the Earth, the effects of Earth rotation, and the local shape of the sea floor and coastlines. In physics the Coriolis effect is an apparent deflection of moving objects when they are viewed from a Rotating frame of reference. Bathymetry is the underwater equivalent to Hypsometry. The name comes from Greek βαθυς deep, and μετρον measure.

A tidal energy generator uses this phenomenon to generate energy. The stronger the tide, either in water level height or tidal current velocities, the greater the potential for tidal energy generation.

Tidal movement causes a continual loss of mechanical energy in the Earth-Moon system due to pumping of water through the natural restrictions around coastlines, and due to viscous dissipation at the seabed and in turbulence. Tidal acceleration is an effect of the Tidal forces between an orbiting Natural satellite ( i Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. "Ocean Floor" redirects here For the 2001 song by Audio Adrenaline, see Lift (Audio Adrenaline album. In Fluid dynamics, turbulence or turbulent flow is a fluid regime characterized by chaotic Stochastic property changes This loss of energy has caused the rotation of the Earth to slow in the 4. 5 billion years since formation. During the last 620 million years the period of rotation has increased from 21. 9 hours to the 24 hours ^[3] we see now; in this period the Earth has lost 17% of its rotational energy. Tidal power may take additional energy from the system, increasing the rate of slowing.

Categories of Tidal Power

Tidal power can be classified into two main types:

• Tidal stream systems make use of the kinetic energy of moving water to power turbines, in a similar way to windmills that use moving air. The kinetic energy of an object is the extra Energy which it possesses due to its motion This method is gaining in popularity because of the lower cost and lower ecological impact compared to barrages.

• Barrages make use of the potential energy in the difference in height (or head) between high and low tides. Potential energy can be thought of as Energy stored within a physical system Hydraulic head is a specific measurement of water pressure or Total energy per Unit weight above a Geodetic datum. Barrages suffer from very high civil infrastructure costs, a worldwide shortage of viable sites, and environmental issues.

Modern advances in turbine technology may eventually see large amounts of power generated from the ocean, especially tidal currents using the tidal stream designs. Tidal stream turbines may be arrayed in high-velocity areas where natural tidal current flows are concentrated such as the west and east coasts of Canada, the Strait of Gibraltar, the Bosporus, and numerous sites in south east Asia and Australia. Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page The Strait of Gibraltar ( Arabic: مضيق جبل طارق Spanish: Estrecho de Gibraltar) is the Strait that connects the Atlantic The Bosporus or Bosphorus, also known as the Istanbul Strait, (İstanbul Boğazı (Βόσπορος is a Strait that forms the boundary between the For a topic outline on this subject see List of basic Australia topics. Such flows occur almost anywhere where there are entrances to bays and rivers, or between land masses where water currents are concentrated.

Tidal stream generators

A relatively new technology, tidal stream generators draw energy from currents in much the same way as wind turbines. A wind turbine is a rotating machine which converts the Kinetic energy in Wind into Mechanical energy. The higher density of water, 832 times the density of air, means that a single generator can provide significant power at low tidal flow velocities (compared with the wind speed).

Similar to wind power, selection of location is important for the tidal turbine. Wind Power is the conversion of wind energy into a useful form such as electricity using Wind turbines At the end of 2007 worldwide capacity of wind-powered generators was Tidal stream systems need to be located in areas with fast currents where natural flows are concentrated between obstructions, for example at the entrances to bays and rivers, around rocky points, headlands, or between islands or other land masses. The following potential sites have been suggested:

• Pentland Firth in Scotland
• Channel Islands and Pembrokeshire^[4] in the United Kingdom
• Cook Strait^[5] in New Zealand
• Strait of Gibraltar
• Bosporus in Turkey
• Bass Strait in Australia
• Torres Strait in Australia
• Strait of Malacca between Indonesia and Singapore
• Bay of Fundy^[6] in Canada. The Pentland Firth ( Scottish Gaelic: An Caol Arcach, meaning the Orcadian Strait which is actually more of a Strait than a Firth, separates Scotland ( Gaelic: Alba) is a Country in northwest Europethat occupies the northern third of the island of Great Britain. The Channel Islands ( Norman: Îles d'la Manche, French: Îles Anglo-Normandes or Îles de la Manche) are a group of Islands Geography Pembrokeshire is a maritime County, bordered by the sea on three sides by Ceredigion (Cardiganshire to the northeast and by The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Cook Strait is a Strait between the North and South Islands of New Zealand. New Zealand is an Island country in the south-western Pacific Ocean comprising two main landmasses (the North Island and the South Island The Strait of Gibraltar ( Arabic: مضيق جبل طارق Spanish: Estrecho de Gibraltar) is the Strait that connects the Atlantic The Bosporus or Bosphorus, also known as the Istanbul Strait, (İstanbul Boğazı (Βόσπορος is a Strait that forms the boundary between the Turkey (Türkiye known officially as the Republic of Turkey ( is a Eurasian Country that stretches Bass Strait (bæs is a sea Strait separating Tasmania from the south of the Australian mainland ( Victoria in particular For a topic outline on this subject see List of basic Australia topics. The Torres Strait is a body of water which lies between Australia and the Melanesian island of New Guinea. For a topic outline on this subject see List of basic Australia topics. The Strait of Malacca is a narrow 805 km (500 mile stretch of water between Peninsular Malaysia (West Malaysia) and the Indonesian island of Sumatra The Republic of Indonesia ( (Republik Indonesia is a Country in Southeast Asia. Singapore Tides Folklore in the Mi'kmaq First Nation claims that the tides in the Bay of Fundy are caused by a giant whale splashing in the water Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page
• East River^[7] in New York City
• Vancouver Island in Canada
• Strait of Magellan south of mainland Chile
• Golden Gate in the San Francisco Bay^[8]
• Piscataqua River in New Hampshire^[9]

Prototypes

Several prototypes have shown promise with many companies making bold claims, some of which are yet to be independently verified, or operated commercially for extended periods to establish performances and rates of return on investments. The East River is a tidal Strait in New York City. It connects Upper New York Bay on its south end to Long Island Sound on its north end The City of New York Vancouver Island is a large Island in British Columbia, Canada, one of several North American regions named after George Vancouver, the British Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page The Straits of Magellan (rarely referred to as the Magellanic Straits) comprise a navigable sea route immediately south of mainland Chile and north of Isla Grande Chile, officially the Republic of Chile ( Spanish:) is a country in South America occupying a long and narrow Coastal strip wedged between the The Golden Gate is the North American Strait connecting San Francisco Bay to the Pacific Ocean. San Francisco Bay is a shallow productive Estuary through which water draining from approximately forty percent of California, flowing in the Sacramento The Piscataqua River, in the northeastern United States, is a long tidal Estuary formed by the confluence of the Salmon Falls and Cochecho New Hampshire ( is a state in the New England region of the northeastern United States of America.

Trials in the Strait of Messina, Italy, started in 2001^[10] and Australian company Tidal Energy Pty Ltd undertook successful commercial trials of highly efficient shrouded turbines on the Gold Coast, Queensland in 2002. The Strait of Messina ( Strittu di Missina in Sicilian) is the narrow section of water between the eastern tip of Sicily and the southern Italy (Italia officially the Italian Republic, (Repubblica Italiana is located on the Italian Peninsula in Southern Europe, and on the two largest For a topic outline on this subject see List of basic Australia topics. This article is about the Australian city Gold Coast For other uses see Gold Coast. Tidal Energy Pty Ltd has commenced a rollout of their efficient shrouded turbine (the turbine resembles a jet turbine engine and is capable of converting 60% of the kinetic energy in the flow) for a remote Australian community in northern Australia where there exist some of the fasted flows ever recorded (11 m/s, 21 knots) – two small turbines will provided 3. 5 MW. Another larger 5 meter diameter turbine, capable of 800kW in 4m/s of flow, is planned for deployment as a tidal powered desalination showcase near Brisbane Australia in October 2008.

The SeaGen rotors in Harland and Wolff, Belfast, before installation in Strangford Lough

SeaGen , the world's first commercial tidal stream generator in Strangford Lough. Harland and Wolff Heavy Industries is a diversified heavy industrial company specialising in Shipbuilding, Ship breaking, Offshore construction Strangford Lough ( describing the fast-flowing Narrows; and Loch Cuan in Irish meaning the calm Lough describing the gentle Waters Strangford Lough ( describing the fast-flowing Narrows; and Loch Cuan in Irish meaning the calm Lough describing the gentle Waters The strong wake shows the power in the tidal current.

During 2003 a 300 kW Periodflow marine current propeller type turbine was tested off the coast of Devon, England, and a 150 kW oscillating hydroplane device, the Stingray, was tested off the Scottish coast. Devon is a large county in the South West of England. The county is also referred to as Devonshire, but that is an entirely unofficial name England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Scotland ( Gaelic: Alba) is a Country in northwest Europethat occupies the northern third of the island of Great Britain. Another British device, the Hydro Venturi, is to be tested in San Francisco Bay. ^[11]

Although still a prototype, the world's first grid-connected turbine, generating 300 kW, started generation on November 13, 2003, in the Kvalsund, south of Hammerfest, Norway, with plans to install a further 19 turbines. Electricity distribution is the penultimate stage in the delivery (before retail) of Electricity to end users Events 1002 - English king Ethelred orders the killing of all Danes in England, known today as the St Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. Kvalsund ( Kven language; Valasnuora) is a municipality in the county of Finnmark, Norway. is a city and municipality in the county of Finnmark, Norway. Since the discovery of North Sea oil in Norwegian waters during the late 1960s exports of oil and gas have become very important elements of the Economy of Norway. ^[12][13]

SeaGen, a commercial prototype has been installed by Marine Current Turbines Ltd in Strangford Lough in Northern Ireland in April 2008. Strangford Lough ( describing the fast-flowing Narrows; and Loch Cuan in Irish meaning the calm Lough describing the gentle Waters The turbine is expected to generate 1. 2MW and is being connected to the grid. It is the currently the only commercial scale device to have been installed anywhere in the world. ^[14]

RWE's NPower announced that it is in partnership with Marine Current Turbines to build a tidal farm of SeaGen turbines off the coast of Anglesey in Wales, though strictly speaking this is not a prototype, but a commercial farm. The company RWE is not related to Ralph Waldo Emerson. RWE AG (until 1990 Rheinisch-Westfälisches Elektrizitätswerk History There are numerous Megalithic monuments and Menhirs present on Anglesey testifying to the presence of mankind in prehistory ^[15]

British Columbia Tidal Energy Corp. plans to deploy at least three 1. 2-MW turbines in the Campbell River or in the surrounding coastline of British Columbia by 2009. Campbell River may refer to Campbell River British Columbia, a city on Vancouver Island, Campbell River (Vancouver Island ^[16]

In November 2007, British company Lunar Energy announced that, in conjunction with E. On, they would be building the world's first tidal energy farm off the coast of Pembrokshire in Wales. It will be the world's first deep-sea tidal-energy farm and will provide electricity for 5,000 homes. Eight underwater turbines, each 25 metres long and 15 metres high, are to be installed on the sea bottom off St David's peninsula. Construction is due to start in the summer of 2008 and the proposed tidal energy turbines, described as "a wind farm under the sea", should be operational by 2010.

Verdant Power^[17] is running a prototype project in the East River between Queens and Roosevelt Island in New York City. Verdant Power is a maker and installer of Tidal power and Hydroelectric systems The East River is a tidal Strait in New York City. It connects Upper New York Bay on its south end to Long Island Sound on its north end Roosevelt Island, formerly known as Welfare Island, and before that Blackwell's Island, is a narrow island in the East River of New York The City of New York

OpenHydro an Irish based company, exploiting the Open-Centre Turbine turbine developed in the US, has a prototype being tested at the European Marine Energy Centre (EMEC), in Orkney, Scotland. Nova Scotia Power has selected their turbine for a tidal energy demonstration project in the Bay of Fundy, Nova Scotia, Canada and Alderney Renewable Energy Ltd for the supply of tidal turbines in the Channel Islands. Open Hydro

Shrouded tidal energy turbines

An emerging tidal stream technology is the shrouded tidal turbine enclosed in a Venturi shaped shroud or duct producing a sub atmosphere of low pressure behind the turbine, allowing the turbine to operate at higher efficiency (than the Betz Limit ^[18] of 59. The Venturi effect is the fluid pressure that results when an incompressible fluid flows through a constricted section of pipe Wind turbines are designed to exploit the wind energy that exists at a location 3%) in one case nearly 4 times higher power output ^[19] than the same minus the shroud.

The Race Rocks Tidal Current Generator before installation.
This working example of a shrouded turbine in the photo was deployed by Clean Current Power at Race Rocks in southern British Columbia in 2006. Race Rocks Lighthouse is the second Lighthouse to be built on the west coast of Canada. It operates bi-directionally and has proven to be efficient in contributing to the integrated power system of Race Rocks.

Considerable commercial interest has been shown in shrouded tidal stream turbines due to the increased power output. They can operate in shallower slower moving water with a smaller turbine at sites where large turbines are restricted. Arrayed across a seaway or in fast flowing rivers, shrouded turbines are cabled to shore for connection to a grid or a community. Alternatively the property of the shroud that produces an accelerated flow velocity across the turbine allows tidal flows formerly too slow for commercial use to be used for energy production.

While the shroud may not be practical in wind, as the next generation of tidal stream turbine design it is gaining more popularity and commercial use. Tidal Energy Pty Ltd^[20]in Australia make use of the design and Lunar Energy (http://www.lunarenergy.co.uk/duct.htm) use a double ended shroud. The Tidal Energy Pty Ltd tidal turbine is multi directional able to face up-stream in any direction and the Lunar Energy turbine bi directional. All tidal stream turbines constantly need to face at the correct angle to the water stream in order to operate. The Tidal Energy Pty Ltd is a unique case with a pivoting base. Lunar Energy use a wide angle diffuser to capture incoming flow that may not be inline with the long axis of the turbine. A shroud can also be built into a tidal fence or barrage increasing the performance of turbines.

Types of shroud

Not all shrouded turbines are the same - the performance of a shrouded turbine varies with the design of the shroud. Not all shrouded turbines have undergone independent scrutiny of claimed performances, as companies closely guard their respective technologies, so quoted performance figures need to be closely scrutinised. Claims vary from a 15%-25% [4] to a 384% [5] improvement over the same turbine without the shroud. Shrouded turbines do not operate at maximum efficiency when the shroud does not intercept the current flow at the correct angle, which can occur as currents eddy and swirl, resulting in reduced operational efficiency. At lower turbine efficiencies the extra cost of the shroud must be justified, while at higher efficiencies the extra cost of the shroud has less impact on commercial returns. Similarly the added cost of the supporting structure for the shroud has to be balanced against the performance gained. Yawing (pivoting) the shroud and turbine at the correct angle, so it always faces upstream like a wind sock, can increase turbine performance but may need expensive active devices to turn the shroud into the flow. Passive designs can be incorporated, such as floating the shrouded turbine under a pontoon on a swing mooring, or flying the turbine like a kite under water. [6] One design yaws the shrouded turbine using a turntable [7].

Advantages

• A shroud of suitable geometry can increase the flow velocity across the turbine by 3 to 4 times the open or free stream velocity allowing the turbine to produce 3 to 4 times the power than the same turbine without the shroud.
• More power generated means greater returns on investment.
• The number of suitable sites is increased as sites formerly too slow for commercial development become viable.
• Where large cumbersome turbines are not suitable, smaller shrouded turbines can be sea-bed-mounted in shallow rivers and estuaries allowing safe navigation of the water ways. ^[21]
• Hidden in a shroud, a turbine is less likely to be damaged by floating debris.
• Bio-fouling is also reduced as the turbine is shaded from natural light in shallow water.
• The increased velocities through the turbine effectively water-blast the shroud throat and turbine clean as organisms are unable to attached at increased velocities. ^[22]
• Described as 'eco-benign', the slow r. p. m. of tidal stream turbines does not interfere with marine life or the environment and has little or no visual amenity impact.

Disadvantages

• Most shrouded turbines are directional, although one exception is the version^[23] off Southern Vancouver Island in British Columbia. One-direction fixed shrouds may not capture flow efficiently - in order for the shroud to produce maximum efficiency to use both flood and ebb tide they need to be yawed like a windmill on a pivot or turntable, or suspended under a pontoon on a marine swing mooring allowing the turbine to always face upstream like a wind sock.
• Shrouded turbines need to be below the mean low water level.
• Shrouded turbine loads are 3 to 4 times those of the open or free stream turbine, so a robust mounting system is necessary. However, this mounting system needs to be designed in such a way as to prevent turbulence being spilled onto the turbine or high-pressure waves occurring near the turbine and detuning performance. Streamlining the mounts and or including structural mounts in the shroud geometry performs two functions, that of supporting the turbine and providing a net benefit of 3 to 4 times the power output.
• Shrouded turbines may be hazardous to marine life, as fish or marine mammals can get sucked into the turbine blades, through the venturi. Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Marine mammals are a diverse group of roughly 120 species of Mammal that are primarily Ocean -dwelling or depend on the ocean for food The Venturi effect is the fluid pressure that results when an incompressible fluid flows through a constricted section of pipe

Energy calculations

Various turbine designs have varying efficiencies and therefore varying power output. If the efficiency of the turbine "Cp" is known the equation below can be used to determine the power output.

The energy available from these kinetic systems can be expressed as:

• P = Cp x 0. 5 x ρ x A x V³ ^[24]

where:

Cp is the turbine coefficient of performance

P = the power generated (in watts)

ρ = the density of the water (seawater is 1025 kg/m³)

A = the sweep area of the turbine (in m²)

V³ = the velocity of the flow cubed (i. e. V x V x V)

Relative to an open turbine in free stream, shrouded turbines are capable of efficiencies as much as 3 to 4 times the power of the same turbine in open flow. ^[25]

Price calculations

Prices paid for electricity varies around the globe. The kilowatt price can be 10-15 British Pence in the UK, or 30-40 US cents or more in remote areas.

The following equation can be used to calculate the revenue from a tidal stream turbine. By substituting variables such as the efficiency, size of the turbine, flow velocity and price into the equation it is possible to accurately predict an annual return.

Keeping in mind this equation does not include the cost of civil infrastructure which would vary with manufacturer and from site to site.

In order to calculate the revenue that a tidal stream generator would return the following equation can be used as a guide only. Assuming 1000 meters of cabling then the following would be a close approximation.

Annual Revenue = Cp x 0. 5 x ρ x A x V³ x Hr x LL x GGL x $ x Y (x 3 for shrouded turbines)

Where:
Cp = the turbine coefficient of performance (say 20% for free stream turbine - up to 60% for a shrouded turbine)
ρ = the density of the water (seawater is 1025 kg/m³ or 998 kg/m³ for fresh water)
A = the sweep area of the turbine (in m²)
V³ = the velocity of the flow cubed (i. e. V x V x V)
Hr = the number of hours per day that the turbine would operate at maximum efficiency (12-22 hours for tidal and 24 for run of river)
LL* = x . 95 line losses (multiply by . 95 )assuming a 5% loss in a cable run of 1000 meters. This may vary by manufacturer.
Gearbox and Generator Losses* = x . 95 (multiply by . 95) assuming 5% for gearbox and generator losses
$ = the price per kilowatt hour that would be paid (prices vary with location)
Year = 350 days (allowing 15 days per year for maintenance if necessary)

Shrouded turbines can produce 3 to 4 times as much revenue as a free stream turbine.

For example, a tidal stream turbine with a sweep area of 1m² at a site with a 3 m/s flow velocity, operating at maximum output for 12 hours, and earning 10 cents per kilowatthour would earn

Annual Revenue = Cp x 0. 5 x ρ x A x V³ x Hr x LL x GGL x $ x Y

Annual Revenue = 0. 20 x 0. 5 x 1025 x 27 x 12 x 0. 95 x 0. 95 x 0. 10/1000 x 350

Revenue Revenue = $10,490. 22 (or $31,470. 62 for a shrouded turbine)

Keeping in mind this is only a 1m² sized turbine, in 3m/s flow velocity for only 12 hours per day. Many commercial turbines are 20-30 times or greater in size, in faster flow velocity, at 20 or more hours per day. A run of river turbine would operate for as long as the river flows, which is obviously 24 hours per day. For example a commercial sized turbine with a 100m² sweep area would therefore return $1,049,022. 00 per annum (or $3,147,062. 00 for a shrouded turbine with 60% efficiency)

From the above equation it can be demonstrated that the predictability of tidal power holds very great potential and interest for renewable investment dollars. Wind and solar are unpredictable by nature, but tidal stream can be predicted years in advance, allowing businesses to plan years in advance.

As the flow velocity doubles, the revenue increases by 8 times (as power is a function of the velocity cubed). The same commercial turbine given in the example above, if installed in a 6 m/s velocity flow, would return $8,392,000 (or $25,176,000 for a shrouded turbine) for every square meter of sweep area of the turbine. It's not hard to see the commercial attraction of tidal stream turbines.

Source of the energy

Because the Earth's tides are caused by the tidal forces 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 source. Characteristics A tide is a repeated cycle of sea level changes in the following stages Over several hours the water rises or advances up a beach in the flood The tidal force is a secondary effect of the Force of Gravity and is responsible for the Tides It arises because the gravitational acceleration experienced Gravitation is a natural Phenomenon by which objects with Mass attract one another The Sun (Sol is the Star at the center of the Solar System. A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation Renewable energy is Energy generated from Natural resources mdashsuch as Sunlight, Wind, Rain, tides and geothermal

Barrage tidal power

Rance tidal power plant

An artistic impression of a tidal barrage, including embankments, a ship lock and caissons housing a sluice and two turbines. The Rance tidal power plant ( Usine marémotrice de la Rance in french Stankell vordredan ar Renk in Breton is the world's first electrical generating

Artist's impression of the Severn Barrage and road link proposed in 1989. The Severn Barrage is the name of a number of ideas for building a barrage from the English Coast to the Welsh coast over the The scheme would have generated 6% of the UK's electricity supply

With only three operating plants globally Rance River, Bay of Fundy and Kislaya Guba the barrage method of extracting tidal energy involves building a barrage as in the case of the Rance River in France. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located For Government policy see Energy policy of the United Kingdom Energy use and conservation in the United Kingdom has been receiving increased The Rance is a River of northwestern France. It flows into the English Channel between Dinard and Saint-Malo. Tides Folklore in the Mi'kmaq First Nation claims that the tides in the Bay of Fundy are caused by a giant whale splashing in the water Kislaya Guba is a Fjord on the Kola Peninsula near Murmansk, Russia. WEIR (1430 AM) is a Radio station broadcasting a News Talk Information format The Rance is a River of northwestern France. It flows into the English Channel between Dinard and Saint-Malo. The barrage turbines generate as water flows in and out the estuary bay or river. These systems are similar to a hydro dam that produces Static Head or pressure head (a height of water pressure). Pressure head is a term used in Fluid mechanics to represent the Internal energy of a Fluid due to the Pressure exerted on its container When the water level outside of the basin or lagoon changes relative to the water level inside, the turbines are able to produce power. The largest such installation has been working on the Rance river, France, since 1966 with an installed (peak) power of 240 MW, and an annual production of 600 GWh (about 68 MW average power). The Rance tidal power plant ( Usine marémotrice de la Rance in french Stankell vordredan ar Renk in Breton is the world's first electrical generating The Rance is a River of northwestern France. It flows into the English Channel between Dinard and Saint-Malo. This article is about the country For a topic outline on this subject see List of basic France topics.

The basic elements of a barrage are caissons, embankments, sluices, turbines and ship locks. In Geotechnical engineering, a caisson is a retaining watertight structure used for example to work on the foundations of a Bridge pier, A sluice is a water channel that is controlled at its head by a gate A water turbine is a rotary Engine that takes energy from moving water Sluices, turbines and ship locks are housed in caisson (very large concrete blocks). Embankments seal a basin where it is not sealed by caissons.

The sluice gates applicable to tidal power are the flap gate, vertical rising gate, radial gate and rising sector.

Barrage systems are affected by problems of high civil infrastructure costs associated with what is in effect a dam being placed across estuarine systems, and the environmental problems associated with changing a large ecosystem.

Ebb generation

The basin is filled through the sluices until high tide. Then the sluice gates are closed. (At this stage there may be "Pumping" to raise the level further). The turbine gates are kept closed until the sea level falls to create sufficient head across the barrage, and then are opened so that the turbines generate until the head is again low. Then the sluices are opened, turbines disconnected and the basin is filled again. The cycle repeats itself. Ebb generation (also known as outflow generation) takes its name because generation occurs as the tide ebbs.

Flood generation

The basin is filled through the turbines, which generate at tide flood. This is generally much less efficient than ebb generation, because the volume contained in the upper half of the basin (which is where ebb generation operates) is greater than the volume of the lower half (and making the difference in levels between the basin side and the sea side of the barrage), (and therefore the available potential energy) less than it would otherwise be. This is not a problem with the "lagoon" model; the reason being that there is no current from a river to slow the flooding current from the sea.

Pumping

Turbines are able to be powered in reverse by excess energy in the grid to increase the water level in the basin at high tide (for ebb generation). This energy is more than returned during generation, because power output is strongly related to the head. If water is raised 2 ft (61 cm) by pumping on a high tide of 10 ft (3 m), this will have been raised by 12 ft (3. 7 m) at low tide. The cost of a 2 ft rise is returned by the benefits of a 12 ft rise.

Two-basin schemes

Another form of energy barrage configuration is that of the dual basin type. With two basins, one is filled at high tide and the other is emptied at low tide. Turbines are placed between the basins. Two-basin schemes offer advantages over normal schemes in that generation time can be adjusted with high flexibility and it is also possible to generate almost continuously. In normal estuarine situations, however, two-basin schemes are very expensive to construct due to the cost of the extra length of barrage. There are some favourable geographies, however, which are well suited to this type of scheme.

Environmental impact

The placement of a barrage into an estuary has a considerable effect on the water inside the basin and on the ecosystem. Many governments have been reluctant in recent times to grant approval for tidal barrages.

Turbidity

Turbidity (the amount of matter in suspension in the water) decreases as a result of smaller volume of water being exchanged between the basin and the sea. This lets light from the Sun to penetrate the water further, improving conditions for the phytoplankton. Phytoplankton are the Autotrophic component of the Plankton community The changes propagate up the food chain, causing a general change in the ecosystem. Food chains, also called food networks and/or trophic networks, describe the feeding relationships between species within an Ecosystem. An ecosystem is a natural unit consisting of all plants animals and micro-organisms( Biotic factors in an area functioning together with all of the non-living physical (

Salinity

As a result of less water exchange with the sea, the average salinity inside the basin decreases, also affecting the ecosystem. "Tidal Lagoons" do not suffer from this problem.

Sediment movements

Estuaries often have high volume of sediments moving through them, from the rivers to the sea. The introduction of a barrage into an estuary may result in sediment accumulation within the barrage, affecting the ecosystem and also the operation of the barrage.

Fish

Fish may move through sluices safely, but when these are closed, fish will seek out turbines and attempt to swim through them. Also, some fish will be unable to escape the water speed near a turbine and will be sucked through. Even with the most fish-friendly turbine design, fish mortality per pass is approximately 15% (from pressure drop, contact with blades, cavitation, etc. Cavitation is defined as the phenomenon of formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure ). Alternative passage technologies (fish ladders, fish lifts, etc. Fishways, most commonly called fish ladders but also known as fish passes and in Australia also referred to as fish steps, are structures on or around artificial ) have so far failed to solve this problem for tidal barrages, either offering extremely expensive solutions, or ones which are used by a small fraction of fish only. Research in sonic guidance of fish is ongoing. The Open-Centre turbine reduces this problem allowing fish to pass through the open centre of the turbine. Recently a run of the river type turbine has been developed in France. This basically is a very large slow rotating Kaplan type turbine mounted on an angle. Testing for fish mortality has indicated much lower mortality figures, less than 5%. This concept seems very suitable for adaption to marine current/tidal turbines also VLH TURBINE

Energy calculations

The energy available from barrage is dependent on the volume of water. The potential energy contained in a volume of water is :

E = Mgh

where:
h is the height of the tide
M is the mass of water = 1025 kg per cubic meter (seawater varies between 1021 and 1030 kg per cubic meter)
g is the acceleration due to gravity = 9.81 meters per second squared at the Earth's surface. Potential energy can be thought of as Energy stored within a physical system Standard gravity, usually denoted by g 0 or g n is the nominal acceleration due to gravity at the Earth's surface at sea level

Mathematical demonstration of a sample Tidal power generation

Assumptions:

• Let us assume that the height of tide at a particular place is 32 feet = 10 m (approx)

• The surface of the tidal energy harnessing plant is 9 sq km (3 km * 3 km)= 3000 m * 3000 m = 9 * 10⁶ m²

• Specific gravity of Sea water = 1025. A foot (plural feet or foot; symbol or abbreviation ft or sometimes &prime – the prime symbol) is a non-SI unit The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International 18 kg/m³

Mass of the water = volume of water * specific gravity

               = (area * height) of water * specific gravity
               = (9 * 106 m2 * 10 m) * 1025. 18 kg/m3
               = 92266 * 106 kg (approx)

Energy content of the water mass = Mass of water * g * height

               = 92266 * 106 kg * 9. 81 m/s2 * 10 m
               = 9051 * 109 J (approx)

Now we have 2 high tides and 2 low tides every day.

Therefore the total energy generation potential per day = Energy for a single tide * 4

               = 9051 * 109 J
               = 36 * 1012 J

Therefore, the power generation potential = Energy generation potential / time in 1 day

               = 36 * 1012 J / 86400 s
               = 419 MW

Since we have assumed the power conversion efficiency to be 30%, The power generated = 419 MW * 30%

               = 126 MW (approx)

A barrage is therefore best placed in a location with very high-amplitude tides. Suitable locations are found in Russia, USA, Canada, Australia, Korea, the UK. Russia (Россия Rossiya) or the Russian Federation ( Rossiyskaya Federatsiya) is a transcontinental Country extending The United States of America —commonly referred to as the Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page For a topic outline on this subject see List of basic Australia topics. Korea is a geographic area composed of two sovereign countries a civilization and a former state situated on the Korean Peninsula in East Asia. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Amplitudes of up to 17 m (56 ft) occur for example in the Bay of Fundy, where tidal resonance amplifies the tidal range. Tides Folklore in the Mi'kmaq First Nation claims that the tides in the Bay of Fundy are caused by a giant whale splashing in the water In Oceanography, a tidal Resonance occurs when the Tide excites one of the resonant modes of the ocean

• Simple Approximation: P=hrk, where P is power in watts, h is height in meters, r is rate in cubic meters per second, and k is 7,500 watts (assuming an efficiency factor of about 75 percent).

Economics

Tidal barrage power schemes have a high capital cost and a very low running cost. As a result, a tidal power scheme may not produce returns for many years, and investors may be reluctant to participate in such projects.

Governments may be able to finance tidal barrage power, but many are unwilling to do so also due to the lag time before investment return and the high irreversible commitment. For example the energy policy of the United Kingdom^[26] recognizes the role of tidal energy and expresses the need for local councils to understand the broader national goals of renewable energy in approving tidal projects. For energy use in practice see Energy use and conservation in the United Kingdom The current Energy Policy of the United Kingdom is set The UK government itself appreciates the technical viability and siting options available, but has failed to provide meaningful incentives to move these goals forward.

Mathematical modelling of tidal schemes

In mathematical modelling of a scheme design, the basin is broken into segments, each maintaining its own set of variables. Time is advanced in steps. Every step, neighbouring segments influence each other and variables are updated.

The simplest type of model is the flat estuary model, in which the whole basin is represented by one segment. The surface of the basin is assumed to be flat, hence the name. This model gives rough results and is used to compare many designs at the start of the design process.

In these models, the basin is broken into large segments (1D), squares (2D) or cubes (3D). The complexity and accuracy increases with dimension.

Mathematical modelling produces quantitative information for a range of parameters, including:

• Water levels (during operation, construction, extreme conditions, etc. )
• Currents
• Waves
• Power output
• Turbidity
• Salinity
• Sediment movements

Energy efficiency

Tidal energy has an efficiency of 80% in converting the potential energy of the water into electricity, which is efficient compared to other energy resources such as solar power or fossil fuel power plants. Turbidity is the cloudiness or haziness of a fluid caused by individual particles ( suspended solids) that are generally invisible to the Naked eye Salinity is the Saltiness or dissolved salt content of a body of Water. Solar energy is the Light and radiant heat from the Sun that powers Earth 's Climate and Weather and sustains Life A fossil fuel power plant burns Fossil fuels such as Coal, Natural gas or Petroleum (oil to produce Electricity.

Global environmental impact

A tidal power scheme is a long-term source of electricity. A proposal for the Severn Barrage, if built, has been projected to save 18 million tonnes of coal per year of operation. The Severn Barrage is the name of a number of ideas for building a barrage from the English Coast to the Welsh coast over the This decreases the output of greenhouse gases into the atmosphere. Greenhouse gases are gaseous constituents of the atmosphere bothnatural and anthropogenic that absorb and emit radiation at specific wavelengths within the spectrum of thermal infrared

If fossil fuel resource is likely to decline during the 21st century, as predicted by Hubbert peak theory, tidal power is one of the alternative source of energy that will need to be developed to satisfy the human demand for energy.

Operating tidal power schemes

• The first tidal power station was the Rance tidal power plant built over a period of 6 years from 1960 to 1966 at La Rance, France. The Rance tidal power plant ( Usine marémotrice de la Rance in french Stankell vordredan ar Renk in Breton is the world's first electrical generating The Rance is a River of northwestern France. It flows into the English Channel between Dinard and Saint-Malo. ^[27] It has 240 MW installed capacity.
• The first tidal power site in North America is the Annapolis Royal Generating Station, Annapolis Royal, Nova Scotia, which opened in 1984 on an inlet of the Bay of Fundy. The Annapolis Royal Generating Station is an 18-MW Tidal power plant located on the Annapolis River immediately upstream from the town of Annapolis Royal Annapolis Royal ( 2006 Population 444 is a Canadian town located in the western part of Annapolis County Nova Scotia (ˌnəʊvəˈskəʊʃə ( Latin for New Scotland; Alba Nuadh Nouvelle-Écosse is a Canadian province located on Canada 's Tides Folklore in the Mi'kmaq First Nation claims that the tides in the Bay of Fundy are caused by a giant whale splashing in the water ^[28] It has 18 MW installed capacity.

• The first [(in- stream tidal current generator in North America)]^[29] was installed at [(Race Rocks)]^[30] on Southern Vancouver Island in September 2006, The [(next phase in the development)]^[31] of this tidal current generator will be in Nova Scotia.

• A small project was built by the Soviet Union at Kislaya Guba on the Barents Sea. Kislaya Guba is a Fjord on the Kola Peninsula near Murmansk, Russia. The Barents Sea (Barentshavet Баренцево море is a part of the Arctic Ocean located north of Norway and Russia. It has 0. 5 MW installed capacity. In 2006 it was upgraded with 1. 2MW experimental advanced orthogonal turbine.
• Another 12MW project at Kislaya Guba in Russia with orthogonal turbines is under construction. Kislaya Guba is a Fjord on the Kola Peninsula near Murmansk, Russia.
• China has apparently developed several small tidal power projects and one large facility in Jiangxia.
• China is also developing a tidal lagoon near the mouth of the Yalu. The Yalu River ( Chinese) or the Amnok River ( Korean) is a River on the border between China and North Korea. ^[32]
• Scotland has committed to having 18% of its power from green sources by 2010, including 10% from a tidal generator. The British government says this will replace one huge fossil fuelled power station. ^[33]
• South African energy parastatal Eskom is investigating using the Mozambique Current to generate power off the coast of KwaZulu Natal. This article is about the South African electricity utility For the similarly-named German computer company see Escom. The Mozambique Current is an Ocean current in the Indian Ocean, usually defined as warm surface waters flowing south between the African east coast in the vicinity KwaZulu-Natal (kwɑːˌzuːluː nəˈtɑːl often referred to as " KZN " is a province of South Africa. Because the continental shelf is near to land it may be possible to generate electricity by tapping into the fast flowing Mozambique current. ^[34]

Tidal power schemes being considered

In the table, "-" indicates missing information, "?" indicates information which has not been decided

See also

• Category:Energy by country
• Run-of-the-river hydroelectricity
• Damless hydro
• Wave power
• World energy resources and consumption

References

• Baker, A. The Republic of South Africa (also known by other official names) is a country located at the southern tip of the continent of Africa The Mozambique Channel is a portion of the Indian Ocean between the island of Madagascar and southeast Africa, namely Mozambique. Run-of-the-river hydroelectricity is a type of hydroelectric generation whereby the natural flow and elevation drop of a river are used to generate electricity Damless hydro or Damless hydro-electric is a renewable technology based on capturing the kinetic energy of rivers channels of chutes spillways irrigation systems tides and Wave power refers to the Energy of Ocean surface waves and the capture of that energy to do useful work — including Electricity generation, C. 1991, Tidal power, Peter Peregrinus Ltd. , London.
• Baker, G. C. , Wilson E. M. , Miller, H. , Gibson, R. A. & Ball, M. , 1980. "The Annapolis tidal power pilot project", in Waterpower '79 Proceedings, ed. Anon, U. S. Government Printing Office, Washington, pp 550-559.
• Hammons, T. J. 1993, "Tidal power", Proceedings of the IEEE, [Online], v81, n3, pp 419-433. Available from: IEEE/IEEE Xplore. [[[July 26|26 July]] 2004]. "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again "
• Lecomber, R. 1979, "The evaluation of tidal power projects", in Tidal Power and Estuary Management, eds. Severn, R. T. , Dineley, D. L. & Hawker, L. E. , Henry Ling Ltd. , Dorchester, pp 31-39.

Notes

External links

• Climate Change Chronicles -- Article about new tidal power technology
• Location of Potential Tidal Stream Power sites in the UK
• University of Strathclyde ESRU -- Summary of tidal and marine current generators
• University of Strathclyde ESRU-- Detailed analysis of marine energy resource, current energy capture technology appraisal and environmental impact outline
• Coastal Research - Foreland Point Tidal Turbine and warnings on proposed Severn Barrage
• The British Library - finding information on the renewable energy industry
• Independent Online - information about South African ventures into coastal current power
• State explores renewable energy powered by tides
• Sustainable Development Commission - Report looking at 'Tidal Power in the UK', including proposals for a Severn barrage
• World Energy Council - Report on Tidal Energy