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Although not yet widely used, tidal power has potential for future electricity generation. Tides are more predictable than wind energy and solar power. Historically, tide mills have been used, both in Europe and on the Atlantic coast of the USA. The earliest occurrences date from the Middle Ages, or even from Roman times.
 Generation of tidal energy
Tidal power is the only form of energy which derives directly from the relative motions of the Earth-Moon system, and to a lesser extent from the Earth-Sun system. The tidal forces produced by the Moon and Sun, in combination with Earth's rotation, are responsible for the generation of the tides. Other sources of energy originate directly or indirectly from the Sun, including fossil fuels, conventional hydroelectric, wind, biofuels, and solar. Nuclear is derived using radioactive material from the Earth, geothermal power uses the heat of magma below the Earth's crust.
Tidal energy is generated by the relative motion of the Earth, Sun and the Moon, which interact via gravitational forces. 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.
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. 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  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 over the next millions of years.
 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. 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. 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. 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
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A relatively new technology, tidal stream generators draw energy from currents in much the same way as wind turbines. 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. 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
- Dee estuary in Wales
- Pembrokeshire in Wales 
- River Severn between Wales and England 
- Solway estuary (Morecambe Bay) in England
- Humber estuary in England
- Mersey river in England
- Channel Islands in the English Channel, off the French coast
- Cook Strait 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 in Canada.
- East River in New York City
- Vancouver Island in Canada
- Strait of Magellan south of mainland Chile
- Golden Gate in the San Francisco Bay
- Piscataqua River in New Hampshire
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.
Trials in the Strait of Messina, Italy, started in 2001 and Australian company Tidal Energy Pty Ltd undertook successful commercial trials of highly efficient shrouded turbines on the Gold Coast, Queensland in 2002. 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 fastest flows ever recorded (11 m/s, 21 knots) – two small turbines will provided 3.5 MW. Another larger 5 meter diameter turbine, capable of 800 kW in 4 m/s of flow, is planned for deployment as a tidal powered desalination showcase near Brisbane Australia in October 2008.
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. Another British device, the Hydro Venturi, is to be tested in San Francisco Bay.
A commercial prototype, called SeaGen, has been installed by Marine Current Turbines Ltd in Strangford Lough in Northern Ireland in April 2008. The turbine is expected to generate 1.2 MW and was reported to have fed 150kW into the grid for the first time on July 17, 2008. It is currently the only commercial scale device to have been installed anywhere in the world. 
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.
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.
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  of 59.3%) in one case nearly 4 times higher power output  than the same minus the shroud.
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 Ltdin 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%  to a 384%  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.  One design yaws the shrouded turbine using a turntable .
- 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. 
- 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. 
- 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.
- Most shrouded turbines are directional, although one exception is the version 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.
 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 
- 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)
- P = the power generated (in watts)
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. 
 Price calculations
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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)
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.
 Barrage tidal power
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With only three operating plants globally a large 240 MW plant on the Rance River, and two small plants, one on the Bay of Fundy and the other across a tiny inlet in Kislaya Guba Russia, the barrage method of extracting tidal energy involves building a barrage across a bay or river as in the case of the Rance tidal power plant in France. Turbines installed in the barrage wall generate power as water flows in and out of the estuary basin, bay, or river. These systems are similar to a hydro dam that produces Static Head or pressure head (a height of water pressure). 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 basic elements of a barrage are caissons, embankments, sluices, turbines, and ship locks. Sluices, turbines, and ship locks are housed in caissons (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.
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 (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. The changes propagate up the food chain, causing a general change in the ecosystem.
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 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.). Alternative passage technologies (fish ladders, fish lifts, etc.) 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
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.
 Mathematical demonstration of a sample Tidal power generation
- The surface of the tidal energy harnessing plant is 9 km² (3 km * 3 km)= 3000 m * 3000 m = 9 * 106 m2
- Specific gravity of Sea water = 1025.18 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. Amplitudes of up to 17 m (56 ft) occur for example in the Bay of Fundy, where tidal resonance amplifies the tidal range.
- 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).
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 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. 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.)
- Power output
- 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.
 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. This decreases the output of greenhouse gases into the atmosphere.
If fossil fuel resources decline during the 21st century, as predicted by Hubbert peak theory, tidal power is one of the alternative sources 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. 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. It has 18 MW installed capacity.
- The first in- stream tidal current generator in North America (Race Rocks Tidal Power Demonstration Project) was installed at [(Race Rocks)] on Southern Vancouver Island 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 on the Barents Sea. 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.
- 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.
- 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.
- South African energy parastatal Eskom is investigating using the Mozambique Current to generate power off the coast of KwaZulu Natal. Because the continental shelf is near to land it may be possible to generate electricity by tapping into the fast flowing Mozambique current.
 Tidal power schemes being considered
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In the table, "-" indicates missing information, "?" indicates information which has not been decided
|Country||Place||Mean tidal range (m)||Area of basin (km²)||Maximum capacity (MW)|
|United States||Passamaquoddy Bay, Maine||5.5||-||?|
|Knik Arm, Alaska||7.5||-||2900|
|Turnagain Arm, Alaska||7.5||-||6501|
|Golden Gate, California||?||-||?|
|Penzhinskaya Bay  ||6.0||20,500||87,000|
|South Africa||Mozambique Channel||?||?||?|
|New Zealand||Kaipara Harbour||2.10||947||200+|
 See also
- Category:Energy by country
- Run-of-the-river hydroelectricity
- Damless hydro
- Wave power
- World energy resources and consumption
- Baker, A. 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].
- 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.
- ^ Spain, Rob: "A possible Roman Tide Mill", Paper submitted to the Kent Archaeological Society
- ^ Minchinton, W. E. (Oct. 1979). "Early Tide Mills: Some Problems". Technology and Culture 20 (4): 777–786. doi:10.2307/3103639.
- ^ George E. Williams. "Geological constraints on the Precambrian history of Earth's rotation and the Moon's orbit". Reviews of Geophysics 38 (2000), 37-60.
- ^ Builder & Engineer - Pembrokeshire tidal barrage moves forward
- ^ Severn balancing act
- ^ NZ: Chance to turn the tide of power supply | EnergyBulletin.net | Peak Oil News Clearinghouse
- ^ Bay of Fundy to get three test turbines | Cleantech.com
- ^ Verdant Power
- ^ http://deanzaemtp.googlepages.com/PGEbacksnewstudyofbaystidalpower.pdf
- ^ Tidal power from Piscataqua River?
- ^ A.D.A.Group
- ^ San Francisco Bay Guardian News
- ^ First power station to harness Moon opens - 22 September 2003 - New Scientist
- ^ First connection to the grid
- ^ · Sea Generation Tidal Turbine
- ^ RWE plans 10.5 MW sea current power plant off Welsh coast - Forbes.com
- ^ Tidal Power Coming to West Coast of Canada
- ^ a b Verdant Power
- ^ Betz Limit
- ^ Brian Kirke's published article Developments in Ducted Water Turbines
- ^ Tidal Energy
- ^ Brian Kirke's PhD Thesis
- ^ deployed at Race Rocks
- ^ a b http://www.cyberiad.net/library/pdf/bk_tidal_paper25apr06.pdf tidal paper on cyberiad.net
- ^  (see for example key principles 4 and 6 within Planning Policy Statement 22)
- ^ L'Usine marémotrice de la Rance
- ^ Nova Scotia Power - Environment - Green Power- Tidal
- ^ Race Rocks Demonstration Project
- ^ Tidal Energy, Ocean Energy
- ^ Information for media inquiries
- ^ China Endorses 300 MW Ocean Energy Project
- ^ [dead link]
- ^ Independent Online Article
- ^ Potential Power Source: The Ocean?
- ^ http://www.elektropages.ru/article/4_2006_ELEKTRO.html
- ^ Russian power plants soon to utilize tidal energy :: Russia-InfoCentre
- ^ http://www.severnestuary.net/sep/pdfs/managingtidalchangeprojectreport-phase1final.pdf
 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