View source for Tidal stream generator

{{Short description|Type of tidal power generation technology}}
[[File:Evopod in Strangford Lough 2008.jpg|thumb|Two types of Tidal Stream Generators [[Evopod]] - A semi-submerged floating approach tested in [[Strangford Lough]] with [[SeaGen]] in the background.]] 
A '''tidal stream generator''', often referred to as a '''tidal energy converter''' ('''TEC'''), is a machine that extracts [[energy]] from moving masses of water, in particular [[tides]], although the term is often used in reference to machines designed to extract energy from the run of a river or tidal estuarine sites. Certain types of these machines function very much like underwater [[wind turbine]]s and are thus often referred to as '''tidal turbines'''. They were first conceived in the 1970s during the oil crisis.<ref name="ASAP. Web. 8 October 2009">Jones, Anthony T., and Adam Westwood. "Power from the oceans: wind energy industries are growing, and as we look for alternative power sources, the growth potential is through the roof. Two industry watchers take a look at generating energy from wind and wave action and the potential to alter." The Futurist 39.1 (2005): 37(5). GALE Expanded Academic ASAP. Web. 8  October 2009.</ref>

Tidal stream generators are the cheapest and least ecologically damaging among the [[Tidal power#Methods|four main forms]] of [[tidal power]] generation.<ref>{{cite web|title=Tidal power|url=http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/Tidal%20Power.htm#streams|access-date=1 November 2010|archive-date=23 September 2010|archive-url=https://web.archive.org/web/20100923194654/http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/Tidal%20Power.htm#streams|url-status=dead}}</ref>

== Similarity to wind turbines ==
[[File:Basic diagram of tidal stream power generation.svg|thumb|The kinetic energy of a water current is converted into electricity by a turbine-generator system]]
Tidal stream generators draw energy from water currents in much the same way as [[wind turbine]]s draw energy from air currents. However, the potential for power generation by an individual tidal turbine can be greater than that of a similarly rated wind energy turbine. The higher density of water relative to air (water is about 800 times the density of air) means that a single generator can provide significant power at low tidal flow velocities compared with similar wind speeds.<ref>{{Cite web|url=http://www.time.com/time/magazine/article/0,9171,457348,00.html|title=Has Welsh Firm Caught The Tide? - TIME|date=January 20, 2011|archive-url=https://web.archive.org/web/20110120194729/http://www.time.com/time/magazine/article/0,9171,457348,00.html |archive-date=2011-01-20 }}</ref> Given that power varies with the density of medium and the cube of velocity, water speeds of nearly one-tenth the speed of wind provide the same power for the same size of turbine system; however, this limits the application in practice to places where tide speed is at least 2&nbsp;knots (1&nbsp; m/s), even close to [[neap tide]]s. Furthermore, at higher speeds in a flow between 2 and 3&nbsp;meters per second in seawater, a tidal turbine can typically access four times as much energy per rotor swept area as a similarly rated power wind turbine.

== Types of tidal stream generators ==
No standard tidal stream generator has emerged as the clear winner among a large variety of designs. Several prototypes have shown promise, with many companies making bold claims, some of which are yet to be independently verified, but they have not operated commercially for extended periods to establish performance and rates of return on investments. Some of the many companies and turbines tested are summarised in [[development of tidal stream generators]].

The [[European Marine Energy Centre]] recognizes six principal types of tidal energy converters. They are horizontal axis turbines, vertical axis turbines, oscillating hydrofoils, venturi devices, Archimedes screws and tidal kites.<ref>{{cite web | url=http://www.emec.org.uk/marine-energy/tidal-devices/ | title=Tidal devices : EMEC: European Marine Energy Centre}}</ref>

=== Axial turbines === <!-- [[Tidal power]] points to this section -->
{{update|section|date=March 2022}}
[[File:Bottom Mounted Turbines.png|thumb|Bottom-mounted axial turbines]]
[[File:Cable Tethered Turbine.png|thumb|A cable-tethered turbine]]
These are similar in concept to traditional windmills but operate under the sea. They have most of the prototypes currently under design, development, testing or operations.

The SR2000, a prototype 2MW floating turbine developed by [[Orbital Marine Power]] in Scotland, was operated at the [[European Marine Energy Centre]], [[Orkney]], from 2016.  It produced 3,200 MWhs of electricity in 12 months of continuous testing. It was removed in September 2018 to make way for the Orbital O2, the production model, completed in 2021.<ref>{{cite web|title=ScotRenewables SR2000 at EMEC|url=https://tethys.pnnl.gov/project-sites/scotrenewables-sr2000-emec|access-date=26 November 2020|website=Tethys}}</ref><ref>{{cite press release |last= |first= |date= |title=Orbital Marine Power Launches O2: World's Most Powerful Tidal Turbine |url= https://orbitalmarine.com/orbital-marine-power-launches-o2/|location= Edinburgh|publisher=Orbital Marine Power |agency= |access-date=2021-04-29}}</ref>

Tocardo,<ref>{{cite web|url=http://www.tocardo.com |title=Tocardo home |access-date=2015-04-17}}</ref> a Dutch-based company, has been running tidal turbines since 2008 on the Afsluitdijk, near Den Oever.<ref name="tocardo.com">{{cite web | url=http://www.tocardo.com/projects_and_showcases/den_oever.html | title=Projects | date=23 October 2023 }}</ref> [https://web.archive.org/web/20160201023122/http://www.tocardo.com/siteAssets/assets/uploads/typical_day.png Typical production data of tidal generator] shown in the T100 model as applied in Den Oever.<ref name="tocardo.com" /> Currently, 1 river model (R1) and 2 tidal models (T) are in production, with a 3rd T3 coming soon. Power production for the T1 is around 100&nbsp;kW and around 200&nbsp;kW for the T2. These are suitable for tidal currents as low as 0.4&nbsp; m/s.<ref>{{cite web|url=https://www.tocardo.com/tocardo-t1/|title = Tocardo T-1}}</ref> Tocardo were declared bankrupt in 2019.<ref>{{cite web|url=https://marineenergy.biz/2019/10/11/tocardo-declares-bankruptcy/|title = Tocardo Declares Bankruptcy|date = 11 October 2019}}</ref> QED Naval and HydroWing have joined forces to buy tidal turbine business Tocardo in 2020.<ref>{{cite web|url=https://www.energylivenews.com/2020/01/08/new-eu-tidal-joint-venture-formed-with-dutch-acquisition/|title=New EU tidal joint venture formed with Dutch acquisition|date=8 January 2020}}</ref>

The AR-1000, a 1 MW turbine developed by Atlantis Resources Corporation, was successfully deployed at the EMEC facility during the summer of 2011.  The AR series are commercial-scale, horizontal-axis turbines designed for open ocean deployment. AR turbines feature a single rotor set with fixed-pitch blades. The AR turbine is rotated as required with each tidal exchange. This is done in the slack period between tides and held in place for the optimal heading for the next tide. AR turbines are rated at 1 MW at 2.65&nbsp;m/s of water flow velocity.<ref name="ieeexplore.ieee.org">{{Cite journal|doi=10.1109/ACCESS.2018.2795708|s2cid=4110420|title=Attraction, Challenge and Current Status of Marine Current Energy|year=2018|last1=Chen|first1=Hao|last2=Tang|first2=Tianhao|last3=Ait-Ahmed|first3=Nadia|last4=Benbouzid|first4=Mohamed El Hachemi|last5=Machmoum|first5=Mohamed|last6=Zaim|first6=Mohamed El-Hadi|journal=IEEE Access|volume=6|pages=12665–12685|bibcode=2018IEEEA...612665C |doi-access=free}}</ref>

The [[Kvalsund]] installation is south of [[Hammerfest]], [[Energy in Norway|Norway]] at a 50-meter depth of sea. Although still a prototype, the HS300 turbine, with a reported capacity of 300&nbsp;kW was connected to the grid on November 13, 2003. This made it the world's first tidal turbine delivering to the grid. The submerged structure weighed 120 tonnes and had gravity footings of 200 tonnes. Its three-blades were made in glass fibre-reinforced plastic and measured 10 metres from hub to tip. The device rotated at 7 rpm with an installed capacity of 0.3 MW.<ref>{{cite web|url=https://tethys.pnnl.gov/project-sites/kvalsund-tidal-turbine-prototype|title = Kvalsund Tidal Turbine Prototype &#124; Tethys}}</ref>

[[Seaflow]], a 300&nbsp;kW periodflow marine current propeller type turbine, was installed by [[Marine Current Turbines]] off the coast of [[Lynmouth]], [[Devon]], England, in 2003.<ref>{{cite web|url=http://www.reuk.co.uk/Worlds-First-Open-Sea-Tidal-Turbine.htm |title=Read about the first open-sea tidal turbine generator off Lynmouth, Devon |publisher=REUK |access-date=2013-04-28}}</ref> The 11-meter-diameter turbine generator was fitted to a steel pile which was driven into the seabed. As a prototype, it was connected to a dump load, not to the grid.

In April 2007, [[Verdant Power]]<ref name="autogenerated1">{{cite web |url=http://www.verdantpower.com/what-initiative |title=Verdant Power |publisher=Verdant Power |date=2012-01-23 |access-date=2013-04-28 |archive-date=2013-04-20 |archive-url=https://web.archive.org/web/20130420150859/http://verdantpower.com/what-initiative/ |url-status=dead }}</ref> began running a prototype project in the [[East River]] between [[Queens]] and [[Roosevelt Island]] in New York City; it was the first major tidal-power project in the United States.<ref>[http://www.technologyreview.com/Energy/18567/ MIT ''Technology Review'', April 2007] {{Webarchive|url=https://web.archive.org/web/20101112195622/http://www.technologyreview.com/energy/18567/ |date=2010-11-12 }}. Retrieved August 24, 2008.</ref> The strong currents pose challenges to the design: the blades of the 2006 and 2007 prototypes broke and new reinforced turbines were installed in September 2008.<ref>{{cite news | title=N.Y. Tests Turbines to Produce Power. City Taps Current Of the East River | author=Robin Shulman | date=September 20, 2008 | newspaper=Washington Post | url=https://www.washingtonpost.com/wp-dyn/content/article/2008/09/19/AR2008091903729.html | access-date=2008-10-09}}</ref><ref>{{cite news | title=Power From the Restless Sea Stirs the Imagination | author=Kate Galbraith | date=September 22, 2008 | work=New York Times | url=https://www.nytimes.com/2008/09/23/business/23tidal.html?em | access-date=2008-10-09}}</ref>

Following the Seaflow trial, a full-size prototype called [[SeaGen]] was installed by Marine Current Turbines in Strangford Lough in Northern Ireland in April 2008. The turbine began to generate at full power of just over 1.2&nbsp;MW in December 2008,<ref>{{cite web|url=http://www.marineturbines.com/3/news/ |access-date=November 8, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100925061709/http://www.marineturbines.com/3/news/ |archive-date=September 25, 2010 |title=SIMEC Atlantis Energy {{pipe}} Turbines and Engineering Services }}</ref> is reported to have fed 150&nbsp;kW into the grid for the first time on July 17, 2008, and has now contributed more than a gigawatt hour to consumers in Northern Ireland.<ref>[http://www.marineturbines.com/3/news// First connection to the grid] {{webarchive |url=https://web.archive.org/web/20100925061709/http://www.marineturbines.com/3/news// |date=September 25, 2010 }}</ref> It is currently the only commercial-scale device to have been installed anywhere in the world.<ref>{{cite web|url=http://www.marineturbines.com/18/projects/19/seagen/ |title=· Sea Generation Tidal Turbine |publisher=Marineturbines.com |access-date=2013-04-28}}</ref> SeaGen is made up of two axial flow rotors, each of which drive a generator. The turbines are capable of generating electricity on both the ebb and flood tides because the rotor blades can pitch through 180˚.<ref>{{Cite web | title=Tidal Stream | publisher=SAE | url=http://www.marineturbines.com/21/ | access-date=2024-08-11}}</ref>

[[File:Evopod lighter.jpg|thumb|A 3D model of an Evopod tidal turbine]]
A prototype semi-submerged floating tethered tidal turbine called [[Evopod]] has been tested since June 2008<ref>{{Cite web | url=http://www.oceanflowenergy.com/news-details.aspx?id=6 | title=First Testing of Evopod at Strangford Narrows... | archive-url=https://web.archive.org/web/20090511020140/http://www.oceanflowenergy.com/news-details.aspx?id=6 | archive-date=2009-05-11 }}</ref> in Strangford Lough, [[Northern Ireland]] at 1/10 scale. The UK company developing it is called Ocean Flow Energy Ltd.<ref>{{cite web|url=http://www.oceanflowenergy.com/ |title=Ocean Flow Energy company website |publisher=Oceanflowenergy.com |access-date=2013-04-28}}</ref> The advanced hull form maintains optimum heading into the tidal stream and is designed to operate in the peak flow of the water column.

In 2010, Tenax Energy of Australia proposed to put 450 turbines off the coast of [[Darwin, Australia]], in the [[Clarence Strait (Northern Territory)|Clarence Strait]]. The turbines would feature a rotor section approximately 15&nbsp;metres in diameter with a slightly larger gravity base. The turbines would operate in deep water well below shipping channels. Each turbine is forecast to produce energy for between 300 and 400 homes.<ref>{{cite web | title= Tidal power project could run all homes | author= Nigel Adlam | date= 2010-01-29 | publisher= [[Northern Territory News]] | url= http://www.ntnews.com.au/article/2010/01/29/119431_ntnews.html | access-date= 2010-06-06 | archive-date= 2011-12-24 | archive-url= https://web.archive.org/web/20111224165457/http://www.ntnews.com.au/article/2010/01/29/119431_ntnews.html | url-status= dead }}</ref>

Tidalstream, a UK-based company, commissioned a scaled-down Triton 3 turbine on the Thames in 2003.<ref>{{cite web|url=http://www.tidalstream.co.uk |title=Triton Home |publisher=Tidalstream.co.uk |access-date=2013-04-28}}</ref> It can be floated to its site, installed without cranes, jack-ups, or divers, and then ballasted into an operating position. At full scale, the Triton 3 in 30–50 m deep water has a 3 MW capacity, and the Triton 6 in 60–80 m deep water has a capacity of up to 10MW, depending on the flow. Both platforms have man-access capability both in the operating position and in the float-out maintenance position.

European technology and innovation platform for ocean energy (ETIP OCEAN) Powering homes today, Powering nations tomorrow report 2019 makes note of record volumes being supplied through tidal stream technology.<ref name="Home">{{cite web |url=http://www.emec.org.uk/ |title=Home |website=emec.org.uk}}</ref>

=== Crossflow turbines === <!-- [[Tidal power]] points to this section -->
Invented by [[Georges Darreius]] in 1923 and patented in 1929, these turbines can be deployed either vertically or horizontally.

The [[Gorlov helical turbine|Gorlov turbine]]<ref>[http://www.gcktechnology.com/ Gorlov Turbine] {{webarchive |url=https://web.archive.org/web/20090205181838/http://www.gcktechnology.com/ |date=February 5, 2009 }}</ref> is a variant of the Darrieus design featuring a helical design that is in a large-scale, commercial pilot in South Korea,<ref>{{cite web |url=http://www.worldchanging.com/archives/002383.html |title=Gorlov Turbines in Koreas |publisher=Worldchanging.com |date=1999-02-22 |access-date=2013-04-28 |url-status=dead |archive-url=https://web.archive.org/web/20130511010214/http://www.worldchanging.com/archives/002383.html |archive-date=2013-05-11 }}</ref> starting with a 1 MW plant that opened in May 2009<ref>{{cite web|url=http://www.hydroworld.com/index/display/article-display/2336952618/articles/hrhrw/hydroindustrynews/ocean-tidal-streampower/south-korea_starts.html|title=South Korea starts up, to expand 1-MW Jindo Uldolmok tidal project|publisher=Hydro World|year=2009|access-date=2010-11-08|archive-url=https://web.archive.org/web/20100901093154/http://www.hydroworld.com/index/display/article-display/2336952618/articles/hrhrw/hydroindustrynews/ocean-tidal-streampower/south-korea_starts.html|archive-date=2010-09-01|url-status=dead}}</ref> and expanding to 90MW by 2013. Neptune Renewable Energy's Proteus project<ref>{{cite web|url=http://www.neptunerenewableenergy.com/ |title=Proteus |publisher=Neptunerenewableenergy.com |date=2013-02-07 |access-date=2013-04-28}}</ref> employs a shrouded vertical axis turbine that can be used to form an array in mainly estuarine conditions.

In April 2008, the Ocean Renewable Power Company, LLC (ORPC) successfully completed testing its proprietary turbine-generator unit (TGU) prototype at ORPC's [[Cobscook Bay]] and [[Western Passage]] tidal sites near [[Eastport, Maine]].<ref>{{cite web | url=http://www.masshightech.com/stories/2008/07/28/weekly9-Tide-is-slowly-rising-in-interest-in-ocean-power.html/ | title=Tide is slowly rising in interest in ocean power | publisher=Mass High Tech: The Journal of New England Technology | date=August 1, 2008 | access-date=2008-10-11 | url-status=dead | archive-url=https://web.archive.org/web/20081226061813/http://www.masshightech.com/stories/2008/07/28/weekly9-Tide-is-slowly-rising-in-interest-in-ocean-power.html/ | archive-date=December 26, 2008 }}</ref> The TGU is the core of the OCGen technology and uses advanced design cross-flow (ADCF) turbines to drive a permanent magnet generator located between the turbines and mounted on the same shaft. ORPC has developed TGU designs that can be used for generating power from river, tidal, and deep water ocean currents.

Trials in the [[Strait of Messina]], Italy, started in 2001 of the [[Kobold turbine]] concept.<ref>{{Cite web|url=http://www.dpa.unina.it/adag/eng/renewable_energy.html|archiveurl=https://web.archive.org/web/20090325101125/http://www.dpa.unina.it/adag/eng/renewable_energy.html|url-status=dead|title=A.D.A.Group|archivedate=March 25, 2009}}</ref>

=== Flow augmented turbines ===

[[File:Sea Bed Turbine.png|thumb|A shrouded turbine]]

Using flow augmentation measures, for example a duct or shroud, the incident power available to a turbine can be increased. The most common example uses a [[Shrouded tidal turbine|shroud]] to increase the flow rate through the turbine, which can be either axial or crossflow.

The Australian company Tidal Energy Pty Ltd undertook successful commercial trials of efficient [[shrouded tidal turbine]]s on the [[Gold Coast, Queensland]] in 2002. Tidal Energy delivered their shrouded turbine in northern Australia, where some of the fastest recorded flows (11&nbsp; m/s, 21&nbsp;knots) are found. Two small turbines will provide 3.5&nbsp;MW. Another larger 5&nbsp;meter diameter turbine, capable of 800&nbsp;kW in 4&nbsp; m/s of flow, was planned as a tidal-powered desalination showcase near Brisbane Australia.<ref>{{cite web|url=http://tidalenergy.com.au/index-subpage-2.html|title = Tidal Energy - the Tidal Energy Advantage}}</ref>

=== Oscillating devices ===
Oscillating devices do not have a rotating component, instead making use of [[aerofoil]] sections that are pushed sideways by the flow. Oscillating stream power extraction was proven with the omni- or bi-directional Wing'd Pump windmill.<ref>{{cite web|url=http://econologica.org/watermill.htm |title=Wing'd Pump Windmill |publisher=Econologica.org |access-date=2013-04-28}}</ref> During 2003 a 150&nbsp;kW oscillating hydroplane device, the [[Stingray tidal stream generator]], was tested off the Scottish coast.<ref>{{cite web|url=http://www.engb.com/ |title=Stingray |publisher=Engb.com |access-date=2013-04-28}}</ref><ref>{{Cite web | url=https://tethys.pnnl.gov/sites/default/files/publications/Stingray_Tidal_Stream_Energy_Device.pdf | website=tethys.pnnl.gov | title=Stingray Tidal System Energy Device - Phase 3}}</ref> The Stingray uses hydrofoils to create oscillation, which allows it to create hydraulic power. This hydraulic power is then used to power a hydraulic motor, which then turns a generator.<ref name="ASAP. Web. 8 October 2009"/>

Pulse Tidal operate an oscillating hydrofoil device called Pulse generator in the [[Humber Estuary]].<ref>{{cite web|url=https://www.youtube.com/watch?v=z07OV0d9NS4  |archive-url=https://ghostarchive.org/varchive/youtube/20211221/z07OV0d9NS4 |archive-date=2021-12-21 |url-status=live|title=BBC Look North "A tidal power project in the Humber has generated its first batch of electricity" |publisher=Youtube.com |date=2009-08-06 |access-date=2013-04-28}}{{cbignore}}</ref><ref>{{cite web |url=https://cordis.europa.eu/project/id/239533 |title=Full scale demonstration prototype tidal stream generator |publisher=[[Community Research and Development Information Service]] (CORDIS)}}</ref> Having secured funding from the EU, they are developing a commercial-scale device to be commissioned 2012.<ref>{{cite web |author=Don Pratt |url=http://www.theengineer.co.uk/pulse-tidal-receives-eu-grant/1000213.article |title=EU Grant reported by The Engineer |date=3 December 2009 |publisher=Theengineer.co.uk |access-date=2013-04-28 |archive-date=2012-03-14 |archive-url=https://web.archive.org/web/20120314015858/http://www.theengineer.co.uk/pulse-tidal-receives-eu-grant/1000213.article |url-status=dead }}</ref>

The bioSTREAM tidal power conversion system uses the [[biomimicry]] of swimming species, such as sharks, tuna, and mackerel, using their highly efficient [[Thunniform]] mode propulsion. It is produced by Australian company BioPower Systems.<ref>{{Cite news|url=https://news.mongabay.com/2006/11/shark-biomimicry-produces-renewable-energy-system/|title=Shark biomimicry produces renewable energy system|newspaper=Mongabay Environmental News |date=November 2006}}</ref>

A 2&nbsp;kW prototype relying on the use of two oscillating hydrofoils in a tandem configuration called [[oscillating wing tidal turbine]] has been developed at Laval University and tested successfully near Quebec City, Canada, in 2009. A hydrodynamic efficiency of 40% has been achieved during the field tests.<ref>{{cite web |url=http://hydrolienne.fsg.ulaval.ca/en |title=HAO turbine |publisher=Hydrolienne.fsg.ulaval.ca |access-date=2013-04-28 |archive-date=2012-03-14 |archive-url=https://web.archive.org/web/20120314193408/http://hydrolienne.fsg.ulaval.ca/en |url-status=dead }}</ref><ref>{{Cite web | url=https://www.lmfn.ulaval.ca/fileadmin/lmfn/documents/poster_pdf/TKinsey_INORE_SYMPOSIUM_HAO_2010.pdf | title=Oscillating-wings Hydrokinetic Turbine | access-date=2024-08-11 | first=Thomas | last=Kinsey}}</ref>

=== Venturi effect ===
{{See also|Venturi effect}}

Venturi effect devices use a shroud or duct in order to generate a pressure differential which is used to run a secondary hydraulic circuit which is used to generate power. A device, the Hydro Venturi, is to be tested in San Francisco Bay.<ref>{{cite web |author=Seth Wolf |url=http://www.sfbg.com/38/43/news_tidal.html |title=San Francisco Bay Guardian News |publisher=Sfbg.com |date=2004-07-27 |access-date=2013-04-28 |archive-date=2010-11-02 |archive-url=https://web.archive.org/web/20101102161747/http://www.sfbg.com/38/43/news_tidal.html |url-status=dead }}</ref><ref>{{cite web|url=https://www.verderg.com/hydro|title = Hydro &#124; VerdErg Renewable Energy}}</ref>

===Tidal kite turbines===
A '''tidal kite turbine''' is an underwater kite system or [[Paravane (water kite)|paravane]] that converts [[tidal energy]] into electricity by moving through the tidal stream. An estimated 1% of 2011's global energy requirements could be provided by such devices at scale.<ref name=g1103>{{cite web|last=Carrington |first=Damian |url=https://www.theguardian.com/environment/damian-carrington-blog/2011/mar/02/underwater-kite-turbine-green-electricity |title=Underwater kite-turbine may turn tides into green electricity {{pipe}} Damian Carrington {{pipe}} Environment |publisher=theguardian.com |date=2011-03-02 |access-date=2013-12-03}}</ref>
;History
Ernst Souczek of Vienna, Austria, on August 6, 1947, filed for a patent [https://patents.google.com/patent/US2501696 US2501696]; assignor of one-half to Wolfgang Kmentt, also of Vienna.  Their water kite turbine disclosure demonstrated a rich art in water-kite turbines. In similar technology, many others prior to 2006 advanced water-kite and paravane electric generating systems. In 2006, a tidal kite turbine called the [[Deep Green Kite]] was developed by Swedish company Minesto.<ref>{{cite web|url=https://minesto.com/our-technology|title = The future of renewable energy &#124; Minesto}}</ref> They conducted its first sea trial in Strangford Lough in Northern Ireland in the summer of 2011. The test used kites with wingspan of 1.4m.<ref name=g1103/> 
In 2013 the Deep Green pilot plant began operation off Northern Ireland. The plant uses [[carbon fiber]] kites with a wingspan of 8m (or 12m<ref>{{cite web|url=http://phys.org/news192784124.html |title=Deep Green underwater kite to generate electricity (w/ Video) |publisher=Phys.org |access-date=2013-12-03}}</ref>). Each kite has a rated power of 120 kilowatts at a tidal flow of 1.3 meters per second.<ref name=iee1311>{{cite web|last=Tweed |first=Katherine |url=https://spectrum.ieee.org/underwater-kite-harvests-energy-from-slow-currents |title=Underwater Kite Harvests Energy From Slow Currents - IEEE Spectrum |publisher=[[IEEE]] |date=2013-11-14 |access-date=2013-12-03}}</ref>
;Design
Minesto's kite has a wingspan of {{convert|8|-|14|m}}.  The kite has neutral buoyancy, so doesn't sink as the tide turns from ebb to flow. Each kite is equipped with a gearless [[turbine]] to generate which is transmitted by the attachment cable to a transformer and then to the electricity grid. The turbine mouth is protected to protect marine life.<ref name=g1103/>
The 14-meter version has a rated power of 850 kilowatts at 1.7 meters per second.<ref name=iee1311/>
;Operation
The kite is tethered by a cable to a fixed point. It "flies" through the current carrying a turbine. It moves in a [[figure-eight loop]] to increase the speed of the water flowing through the turbine tenfold. [[Force]] increases with the cube of [[velocity]], offering the potential to generate 1,000-fold more energy than a stationary generator.<ref name=g1103/>
That maneuver means the kite can operate in tidal streams that move too slowly to drive earlier tidal devices, such as the [[SeaGen]] turbine.<ref name=g1103/>
The kite was expected to work in flows as low {{convert|1|-|2.5|m}} per second, while first-generation devices need over 2.5s. Each kite will have a capacity to generate between 150 and 800&nbsp;kW. They can be deployed in waters {{convert|50|-|300|m}} deep.<ref name=g1103/>

== Tidal stream developers ==
{{See also|Development of tidal stream generators}}
There are many individuals and companies developing tidal energy converters across the world, although few have progressed beyond the concept on initial testing stage. A database of tidal energy developers can be found on the EMEC website at [http://www.emec.org.uk/marine-energy/tidal-developers/ Tidal energy developers]<ref>{{Cite web|url=https://www.emec.org.uk/marine-energy/tidal-developers/|title=Tidal developers : EMEC: European Marine Energy Centre}}</ref> 

Tidal stream developers with turbines in the water {{As of|2023|lc=y}} include:<ref name=":0">{{Cite report |url=https://www.ocean-energy-systems.org/publications/oes-annual-reports/document/oes-annual-report-2023/ |title=OES Annual Report 2023: An overview of ocean energy activities in 2023 |last=IEA-OES |date=29 Feb 2024 |publisher=The Executive Committee of IEA Ocean Energy Systems}}cite</ref>

* [[HydroQuest]], France
* [[Development of tidal stream generators#LHD New Energy Corporation|LHD New Energy Corporation]], China
* [[Development of tidal stream generators#Magallanes Renovables|Magallanes Renovables]], Spain
* [[Minesto]], Sweden
* [[Nova Innovation]], Scotland, UK
* [[Ocean Renewable Power Company]], Maine, USA
* Orbital Marine Power, Scotland, UK, with the [[Orbital O2]]
* [[SAE Renewables]], Singapore/UK develop the [[MeyGen]] project, although turbine development was spun out to Proteus Marine, England, UK
* [[Development of tidal stream generators#Tocardo|Tocardo]], Netherlands

== Tidal stream testing ==
The world's first marine energy test facility was established in 2003 to kick start the development of the wave and tidal energy industry in the UK. Based in Orkney, Scotland, the [[European Marine Energy Centre]] (EMEC) has supported the deployment of more wave and tidal energy devices than at any other single site in the world. EMEC provides a variety of test sites in real sea conditions. Its grid connected tidal test site is located at the [[Fall of Warness]], off the island of [[Eday]], in a narrow channel which concentrates the tide as it flows between the Atlantic Ocean and North Sea. This area has a very strong tidal current, which can travel up to 4&nbsp;m/s (8 knots) in spring tides.<ref>{{Cite web |title=Grid-connected tidal test site |url=https://www.emec.org.uk/facilities/tidal-test-site/ |access-date=2024-10-06 |website=European Marine Energy Centre |language=}}</ref> Tidal energy developers that have tested at the site include Alstom (formerly Tidal Generation Ltd), ANDRITZ HYDRO Hammerfest, Atlantis Resources (now [[SAE Renewables|SAE]]), Nautricity, [[OpenHydro]], Orbital Marine Power (formerly Scotrenewables Tidal Power), and Voith.<ref>{{Cite web |title=Tidal clients |url=https://www.emec.org.uk/about-us/our-tidal-clients/ |access-date=2024-10-06 |website=European Marine Energy Centre |language=}}</ref>

The [[Fundy Ocean Research Center for Energy]] (FORCE) Test Site was set up in 2009 in the [[Bay of Fundy]], Canada, to test tidal devices inn one of the strongest tidal currents in the world. The site has grid-connected test berths, and developers who have tested there include OpenHydro and Sustainable Marine Energy.<ref>{{Cite web |title=Fundy Ocean Research Center for Energy (FORCE) Test Site |url=https://tethys.pnnl.gov/project-sites/fundy-ocean-research-center-energy-force-test-site |access-date=2024-10-06 |website=tethys.pnnl.gov}}</ref> 

In 2023, the Zhoushan Tidal Current Energy Demonstration Project was set up in [[Zhoushan]], [[Zhejiang]] province, China, by the [[China Three Gorges Corporation]]. It has included grid-connected tidal power demonstration.<ref name=":0" />

{{As of|2023}}, two more tidal test sites are under development in Asia; the Korea Tidal Current Energy Centre (KTEC) in [[Jindo (island)|Jindo]], southwestern [[South Korea]], and the Sentosa Tidal Test Site in [[Sentosa]] island, [[Singapore]].<ref name=":0" />

== Commercial plans ==
In 2010, The Crown Estate awarded an agreement for lease to MeyGen Limited, granting the option to develop a tidal stream project of up to 398&nbsp;MW at an offshore site between Scotland's northernmost coast and the island of Stroma. {{As of|2024}}, [[MeyGen]] the largest planned tidal farm project worldwide. The first phase of the MeyGen project (Phase 1A) is operational, with four 1.5&nbsp;MW turbines, and subsequent phases are under way.<ref>{{cite web|url=https://simecatlantis.com/projects/meygen/|title=MeyGen - Tidal Projects|access-date=2020-10-07|archive-date=2020-12-27|archive-url=https://web.archive.org/web/20201227084335/https://simecatlantis.com/projects/meygen/|url-status=dead}}</ref><ref name="ieeexplore.ieee.org" /> SIMEC Atlantis Energy, now [[SAE Renewables|SAE]], was awarded [[Contracts for Difference (UK electricity market support)|Contracts for Difference]] totalling 59&nbsp;MW for the next phases, to be built by 2029.<ref>{{Cite web |date=2024-09-05 |title=SAE secures CfD for MyGen site |url=https://www.energyglobal.com/other-renewables/05092024/sae-secures-cfd-for-mygen-site/ |access-date=2024-10-06 |website=Energy Global |language=en}}</ref>

Also in 2010, the West Anglesey Demonstration Zone off [[Anglesey]], North Wales was designated for tidal stream generation. This project is now called [[Morlais]], and was consented in December 2021, with up to 240&nbsp;MW  proposed. This will be from multiple developers, with the first turbines expected to be installed in 2026. {{As of|2024|}}, a total of 38&nbsp;MW of capacity has been awarded [[Contracts for Difference (UK electricity market support)|Contracts for Difference]] to supply power to the GB grid by 2029.<ref>{{Cite web |last=Maksumic |first=Zerina |date=2024-09-05 |title=Industry welcomes boost to tidal stream projects following latest UK renewables auction results |url=https://www.offshore-energy.biz/industry-welcomes-boost-to-tidal-stream-projects-following-latest-uk-renewables-auction-results/ |access-date=2024-10-12 |website=Offshore Energy |language=en-US}}</ref><ref>{{Cite news |last=Ungoed-Thomas |first=Jon |date=2022-04-24 |title=Could Anglesey's tidal energy project drive a new energy revolution? |url=https://www.theguardian.com/environment/2022/apr/24/could-angleseys-tidal-energy-project-drive-a-new-energy-revolution |access-date=2024-10-12 |work=The Observer |language=en-GB |issn=0029-7712}}</ref>

[[Magallanes Renovables]], [[Nova Innovation]], and Orbital Marine Power have all been awarded Contracts for Difference to install a total of 24&nbsp;MW grid-connected tidal power at the EMEC Fall of Warness site.<ref>{{Cite web |last=Perry |first=Mathew |date=2024-09-04 |title=AR6 delivers six tidal stream projects with UK pipeline 'confidently growing' |url=https://www.energyvoice.com/renewables-energy-transition/wave-tidal/uk-wave-tidal/559251/ar6-delivers-six-tidal-stream-projects-with-uk-pipeline-confidently-growing/ |access-date=2024-10-12 |website=Energy Voice |language=en-US}}</ref>

In France, two projects are proposed at [[Raz Blanchard]]. The 17.5&nbsp;MW FloWatt project developed by [[HydroQuest]] and Qair is expected to be commissioned in 2026.<ref>{{Cite web |last=Akella |first=Surya |date=2023-07-10 |title=France approves €65m for FloWatt tidal energy project |url=https://www.power-technology.com/news/france-funding-tidal-project/ |access-date=2024-10-12 |website=Power Technology |language=en-US}}</ref> Normandie Hydroliennes is planning a 12&nbsp;MW project with four Proteus Marine Renewables AR3000 turbines.<ref>{{Cite web |last=Maksumic |first=Zerina |date=2024-10-04 |title=Proteus Marine Rewables' tidal energy system on track to slash costs, EIB confirms |url=https://www.offshore-energy.biz/proteus-marine-rewables-tidal-energy-system-on-track-to-slash-costs-eib-confirms/ |access-date=2024-10-12 |website=Offshore Energy |language=en-US}}</ref>

=== Historical plans ===
There have been many abandoned or postponed tidal stream projects, a selection of which are summarised here.

In November 2007, British company Lunar Energy announced that, in conjunction with [[E.ON]], they would be building the world's first deep-sea tidal energy farm off the coast of Pembrokeshire in Wales; expected to provide electricity for 5,000 homes. Eight underwater turbines, each 25&nbsp;metres long and 15&nbsp;metres high, were to be installed on the sea bottom off St David's peninsula. Construction was due to start in the summer of 2008, operational by 2010.<ref>{{Cite news |date=2007-10-31 |title=Underwater power plan for coast |url=http://news.bbc.co.uk/2/hi/uk_news/wales/south_west/7070821.stm |access-date=2024-10-06 |work=BBC News |language=}}</ref>  Lunar Energy was dissolved in 2019.<ref>{{Cite web|url=https://find-and-update.company-information.service.gov.uk/company/SC369583|title=LUNAR ENERGY POWER LIMITED overview - Find and update company information - GOV.UK|website=find-and-update.company-information.service.gov.uk}}</ref>

Alderney Renewable Energy Ltd was granted a licence in 2008 and is planning to use tidal turbines to extract power from the notoriously strong [[tidal race]]s around [[Alderney]] in the [[Channel Islands]]. It is estimated that up to 3&nbsp;GW could be extracted. This would not only supply the island's needs but also leave a considerable surplus for export,<ref name="arel">{{cite web |url=http://www.are.gb.com/index.php |title=Alderney Renewable Energy Ltd |publisher=Are.gb.com |access-date=2013-04-28 |archive-url=https://web.archive.org/web/20120423233801/http://www.are.gb.com/index.php/ |archive-date=2012-04-23 |url-status=dead }}</ref> using a [[Channel Islands Electricity Grid|France-Alderney-Britain cable]] (FAB Link) which was expected to go online by 2020. This agreement was terminated in 2017.<ref>{{cite web|url=https://marineenergy.biz/2017/05/25/turbulent-tides-hit-alderney/|title = Turbulent tides hit Alderney|date = 25 May 2017}}</ref>

In 2010, [[RWE]]'s [[npower (UK)|npower]] announced that it is in partnership with [[Marine Current Turbines]] to build a 10&nbsp;MW tidal farm of SeaGen S tidal turbines off the coast of [[Anglesey]] in Wales,<ref name="renewableenergyfocus.com">{{cite web|url=http://www.renewableenergyfocus.com/view/11843/norwegian-1-mw-tidal-turbine-to-scotland/|title = Renewable Energy Focus - Journal - Elsevier}}</ref> near [[The Skerries, Anglesey|the Skerries]], with planning permission given in 2013.<ref>[https://web.archive.org/web/20240522020719/https://www.rwe.com/web/cms/en/309778/rwe-npower-renewables/sites/projects-in-development/marine/skerries/the-proposal RWE npower renewables Sites > Projects in Development > Marine > Skerries > The Proposal : Anglesey Skerries Tidal Stream Array]. Retrieved February 26, 2010.</ref> The array was expected to be fully operational by 2015, however the project was shelved in 2016 after Marine Current Turbines was acquired by SIMEC Atlantis Energy.<ref>{{cite web|url=https://www.dailypost.co.uk/business/business-news/70m-anglesey-tidal-project-shelved-11078552|title = £70m Anglesey tidal project is shelved - again|date = 22 March 2016}}</ref>

In 2015, Welsh companies Tidal Energy Ltd (TEL) and Eco2 aimed to deploy a commercial scale demonstration project, with nine turbines at St Davids Head.<ref>{{Cite web |last=Kelsey |first=Chris |date=2015-12-14 |title=Tidal energy device DeltaStream installed in the sea |url=https://www.walesonline.co.uk/business/business-news/radical-new-tidal-energy-device-10594709 |access-date=2024-10-06 |website=Wales Online |language=en}}</ref> However, TEL went into administration less than a year after developing and testing the 400&nbsp;kW DeltaStream turbine in 2015.<ref>{{Cite news|url=https://www.bbc.co.uk/news/uk-wales-south-west-wales-37752750|title = Administrators seek buyer for Tidal Energy Ltd|work = BBC News|date = 24 October 2016}}</ref>

In March 2014, the [[Federal Energy Regulatory Committee]] (FERC) approved a pilot license for Snohomish County PUD to install two [[OpenHydro]] tidal turbines in [[Admiralty Inlet]], WA. This project is the first grid-connected two-turbine project in the US; installation is planned for the summer of 2015.  The tidal turbines will use are designed to be placed directly into the seafloor at a depth of roughly 200 feet, so that there will be no effect on commercial navigation overhead.  The license granted by the FERC also includes plans to protect fish, wildlife, as well as cultural and aesthetic resources, in addition to navigation.  Each turbine measures 6 meters in diameter, and will generate up to 300&nbsp;kW of electricity.<ref>{{cite web |url=http://tethys.pnnl.gov/blog/admiralty-inlet-pilot-tidal-project |title=Admiralty Inlet Pilot Tidal Project &#124; Tethys |access-date=2014-05-07 |archive-date=2014-05-26 |archive-url=https://web.archive.org/web/20140526013535/http://tethys.pnnl.gov/blog/admiralty-inlet-pilot-tidal-project |url-status=dead }}</ref> In September 2014, the project was cancelled due to cost concerns.<ref>{{cite web|url=http://www.seattletimes.com/seattle-news/snohomish-county-pud-drops-tidal-energy-project/|title = Snohomish County PUD drops tidal-energy project|date = 30 September 2014}}</ref>

[[Nova Scotia Power]] selected OpenHydro's 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.<ref>{{cite web |url=http://www.openhydro.com/ |title=Open Hydro |access-date=2010-11-08 |archive-url=https://web.archive.org/web/20101023225456/http://www.openhydro.com/ |archive-date=2010-10-23 |url-status=dead }}</ref> OpenHydro was liquidated in 2018.<ref>{{cite web|url=https://marineenergy.biz/2018/07/26/tides-wash-away-openhydro/|title = Tides wash away OpenHydro|date = 26 July 2018}}</ref>

[[ScottishPower|ScottishPower Renewables]] planned to deploy ten 1MW HS1000 devices designed by [[Hammerfest Strom]] in the [[Sound of Islay]] in 2013.<ref name="Islay Energy Trust">{{Cite web|url=https://www.islayenergytrust.org.uk/|title=Islay Energy Trust Home|website=www.islayenergytrust.org.uk}}</ref><ref name="renewableenergyfocus.com" />

== Energy calculations ==

=== Turbine power ===
Tidal energy converters can have varying modes of operating and therefore varying power output. If the power coefficient of the device "<math> C_P</math>" is known, the equation below can be used to determine the power output of the hydrodynamic subsystem of the machine. This available power cannot exceed that imposed by the [[Betz limit]] on the power coefficient, although this can be circumvented to some degree by placing a [[Shrouded tidal turbine|turbine in a shroud or duct]]. This works, in essence, by forcing water which would not have flowed through the turbine through the rotor disk. In these situations it is the frontal area of the duct, rather than the turbine, which is used in calculating the power coefficient and therefore the Betz limit still applies to the device as a whole.

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

:<math>P = \frac{\rho A V^3}{2} C_P</math>

where:
:<math> C_P</math> = the turbine power coefficient
:''P'' = the power generated (in watts)
:<math>\rho</math> = the density of the water (seawater is 1027 kg/m<sup>3</sup>)
:''A'' = the sweep area of the turbine (in m<sup>2</sup>)
:''V'' = the velocity of the flow

Relative to an open turbine in free stream, ducted turbines are capable of as much as 3 to 4 times the power of the same turbine rotor in open flow.<ref name="autogenerated2">{{cite web |url=http://www.cyberiad.net/library/pdf/bk_tidal_paper25apr06.pdf |title=Developments in ducted water current turbines |access-date=2013-04-28 |url-status=dead |archive-url=https://web.archive.org/web/20120913202219/http://www.cyberiad.net/library/pdf/bk_tidal_paper25apr06.pdf |archive-date=2012-09-13 }}</ref>

=== Resource assessment ===
While initial assessments of the available energy in a channel have focus on calculations using the kinetic energy flux model, the limitations of tidal power generation are significantly more complicated. For example, the maximum physical possible energy extraction from a strait connecting two large basins is given to within 10% by:<ref>Atwater, J.F., Lawrence, G.A. (2008) Limitations on Tidal Power Generation in a Channel, Proceedings of the 10th World Renewable Energy Congress. (pp 947–952)</ref><ref>Garrett, C. and Cummins, P. (2005). "The power potential of tidal currents in channels." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol. 461, London. The Royal Society, 2563–2572</ref>
:<math> P = 0.22\, \rho\, g\, \Delta H_\text{max}\, Q_\text{max}</math>
where
:<math>\rho</math> = the density of the water (seawater is 1027 kg/m<sup>3</sup>)
:''g'' = gravitational acceleration (9.80665 m/s<sup>2</sup>)
:<math>\Delta H_\text{max}</math> = maximum differential water surface elevation across the channel
:<math>Q_\text{max}</math>= maximum volumetric flow rate though the channel.

== Potential sites ==
As with wind power, selection of location is critical 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 are under serious consideration:

* [[Pembrokeshire]] in Wales<ref>[http://www.builderandengineer.co.uk/news/general/pembrokeshire-tidal-barrage-moves-forward-934.html Builder & Engineer - Pembrokeshire tidal barrage moves forward<!-- Bot generated title -->] {{Webarchive|url=https://web.archive.org/web/20110911110108/http://www.builderandengineer.co.uk/news/general/pembrokeshire-tidal-barrage-moves-forward-934.html |date=2011-09-11 }}</ref>
* [[River Severn]] between Wales and England<ref>{{Cite web|url=https://www.walesonline.co.uk/news/|title=News: The latest news, sport, weather and events from WalesOnline|website=Wales Online}}</ref>
*[[Cook Strait]] in New Zealand<ref>{{Cite web|url=http://www.energybulletin.net/6046.html|title=EnergyBulletin.net &#124; NZ: Chance to turn the tide of power supply &#124; Energy and Peak Oil News|date=May 22, 2005|archive-url=https://web.archive.org/web/20050522083514/http://www.energybulletin.net/6046.html |archive-date=2005-05-22 }}</ref>
* [[Kaipara Tidal Power Station|Kaipara Harbour]] in New Zealand<ref name="Energy NZ">{{cite news|url=http://www.contrafedpublishing.co.nz/Energy+NZ/Harnessing+the+power+of+the+sea.html|title=Harnessing the power of the sea|publisher=Energy NZ, Vol 1, No 1|date=Winter 2007|url-status=dead|archive-url=https://web.archive.org/web/20110724192201/http://www.contrafedpublishing.co.nz/Energy+NZ/Harnessing+the+power+of+the+sea.html|archive-date=2011-07-24}}</ref>
*[[Bay of Fundy]]<ref>[http://media.cleantech.com/2269/bay-of-fundy-to-get-three-test-turbines Bay of Fundy to get three test turbines] {{Webarchive|url=https://web.archive.org/web/20080704205027/http://media.cleantech.com/2269/bay-of-fundy-to-get-three-test-turbines |date=2008-07-04 }}</ref> in Canada.
*[[East River]]<ref>{{Cite news |first=Robin |last=Shulman |issn=0740-5421 | title = N.Y. Tests Turbines to Produce Power | newspaper = [[The Washington Post]] | access-date = 2008-09-20 |date = September 20, 2008 | url = https://www.washingtonpost.com/wp-dyn/content/article/2008/09/19/AR2008091903729.html?hpid=topnews&sub=AR}}</ref><ref>{{Cite web|url=http://verdantpower.com/what-initiative|archive-url=https://web.archive.org/web/20101206210601/http://verdantpower.com/what-initiative/|url-status=dead|title=Verdant Power<!-- Bot generated title -->|archive-date=December 6, 2010}}</ref> in the United States
*[[Golden Gate]] in the [[San Francisco Bay]]<ref>{{Cite web|url=https://accounts.google.com/v3/signin/identifier?continue=https%3A%2F%2Fsites.google.com%2Fsite%2Fsites%2Fsystem%2Ferrors%2FWebspaceNotFound%3Fpath%3D%2Fdeanzaemtp2%2FPGEbacksnewstudyofbaystidalpower.pdf&followup=https%3A%2F%2Fsites.google.com%2Fsite%2Fsites%2Fsystem%2Ferrors%2FWebspaceNotFound%3Fpath%3D%2Fdeanzaemtp2%2FPGEbacksnewstudyofbaystidalpower.pdf&ifkv=AVQVeywksc0E-xLS5BTfSiEwfirGrlhbda-TAEbFLoo8pYkn1W75Eq6stAzlT_DGNpa892VmJ6BpJA&passive=1209600&service=jotspot&flowName=WebLiteSignIn&flowEntry=ServiceLogin&dsh=S1728960695%3A1698127357735863|archive-url=https://web.archive.org/web/20090318230558/http://deanzaemtp.googlepages.com/PGEbacksnewstudyofbaystidalpower.pdf|url-status=dead|title=Google Sites: Sign-in|archive-date=March 18, 2009|website=accounts.google.com}}</ref>
*[[Piscataqua River]] in [[New Hampshire]]<ref>{{Cite web|url=http://www.seacoastonline.com/apps/pbcs.dll/article?AID=/20070519/NEWS/705190344|title=Tidal power from Piscataqua River?<!-- Bot generated title -->|access-date=2010-11-08|archive-date=2012-09-27|archive-url=https://web.archive.org/web/20120927032145/http://www.seacoastonline.com/apps/pbcs.dll/article?AID=/20070519/NEWS/705190344|url-status=dead}}</ref>
*The Race of [[Alderney]] and [[The Swinge]] in the [[Channel Islands]]<ref name="arel" />
*The Sound of Islay, between [[Islay]] and [[Jura, Scotland|Jura]] in Scotland<ref name="Islay Energy Trust"/>
*[[Pentland Firth]] between [[Caithness]] and the [[Orkney]] Islands, Scotland
*[[Humboldt County, California]] in the United States
*[[Columbia River]], [[Oregon]] in the United States
*[[Plaquemines Parish, Louisiana]] in the Southern United States <ref>{{cite web| url = http://www.nola.com/business/index.ssf/2011/04/funding_paperwork_slow_ambitio.html| title = Funding, paperwork slow ambitious plans to produce power using underwater turbines in Mississippi River {{!}} Business News {{!}} nola.com| date = 24 April 2011}}</ref>
* [[Isle of Wight]], England <ref>{{cite news| url=https://www.bbc.co.uk/news/uk-england-hampshire-26647962 | work=BBC News | title=Isle of Wight tidal energy demonstration site plans unveiled | date=2014-03-20}}</ref>
* [[Teddington and Ham Hydro]] at Teddington on the River Thames in the London suburbs, England

Modern advances in [[turbine]] technology may eventually see large amounts of power generated from the ocean, especially tidal currents using the tidal stream designs but also from the major thermal current systems such as the [[Gulf Stream]], which is covered by the more general term [[marine current power]]. 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 [[Southeast 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.

== Environmental impacts ==

The main environmental concern with [[tidal energy]] is associated with blade strike and entanglement of marine organisms as high speed water increases the risk of organisms being pushed near or through these devices. As with all offshore renewable energies, there is also a concern about how the creation of [[Electromagnetic field|EMF]] and acoustic outputs may affect marine organisms. Because these devices are in the water, the acoustic output can be greater than those created with [[offshore wind energy]]. Depending on the frequency and amplitude of sound generated by the tidal energy devices, this acoustic output can have varying effects on marine mammals (particularly those who echolocate to communicate and navigate in the marine environment such as [[dolphin]]s and [[whale]]s). Tidal energy removal can also cause environmental concerns such as degrading farfield water quality and disrupting sediment processes. Depending on the size of the project, these effects can range from small traces of sediment build up near the tidal device to severely affecting nearshore ecosystems and processes.<ref>{{Cite web|url=https://tethys.pnnl.gov/|title=Tethys &#124; Environmental Effects of Wind and Marine Renewable Energy|website=tethys.pnnl.gov}}</ref>

One study of the Roosevelt Island Tidal Energy (RITE, Verdant Power) project in the East River (New York City), used 24 split beam hydroacoustic sensors ([[scientific echosounder]]) to detect and track the movement of fish both upstream and downstream of each of six turbines. The results suggested (1) very few fish using this portion of the river, (2) those fish which did use this area were not using the portion of the river which would subject them to blade strikes, and (3) no evidence of fish traveling through blade areas.<ref>{{Cite web|url=https://tethys.pnnl.gov/publications/roosevelt-island-tidal-energy-rite-environmental-assessment-project|title=Roosevelt Island Tidal Energy (RITE) Environmental Assessment Project &#124; Tethys|website=tethys.pnnl.gov}}</ref>

Work is currently being conducted by the Northwest National Marine Renewable Energy Center ([[NNMREC]]<ref>{{cite web | url=http://depts.washington.edu/nnmrec/ |title = PMEC| date=22 August 2022 }}</ref>) to explore and establish tools and protocols for assessment of physical and biological conditions and monitor environmental changes associated with tidal energy development.

== See also ==
{{Portal|Renewable energy}}
* [[Marine energy]]
* [[Renewable energy]]
* [[Tidal power]]
* [[Wave power]]
* [[Wind turbine]]

== References ==
{{reflist|colwidth=30em}}

== External links ==
* [https://openei.org/wiki/PRIMRE Portal and Repository for Information on Marine Renewable Energy] A network of databases providing broad access to marine energy information.
* [https://openei.org/wiki/PRIMRE/Basics/Current_Energy Marine Energy Basics: Current Energy] Basic information about current energy.
* [https://openei.org/wiki/PRIMRE/Databases/Projects_Database Marine Energy Projects Database] A database that provides up-to-date information on marine energy deployments in the U.S. and around the world.
* [https://tethys.pnnl.gov Tethys Database] A database of information on potential environmental effects of marine energy and offshore wind energy development.
* [https://tethys-engineering.pnnl.gov Tethys Engineering Database] A database of information on technical design and engineering of marine energy devices.
* [https://mhkdr.openei.org/ Marine and Hydrokinetic Data Repository] A database for all data collected by marine energy research and development projects funded by the U.S. Department of Energy.

{{DEFAULTSORT:Tidal Stream Generator}}
[[Category:Tidal stream generators| ]]