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{{short description|Technology to convert the energy from tides into useful forms of power}}
[[File:Sihwa Lake Tidal Power Station 01.png|right|thumb|[[Sihwa Lake Tidal Power Station]], located in [[Gyeonggi Province]], South Korea, is the world's largest tidal power installation, with a total power output capacity of 254  MW.]]
{{Renewable energy sources}}
{{Sustainable energy}}
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Historically, [[tide mill]]s have been used both in Europe and on the Atlantic coast of North America. The incoming water was contained in large storage ponds, and as the tide goes out, it turns waterwheels that use the mechanical power to mill grain.<ref>{{cite web|author=Ocean Energy Council|title=Tidal Energy: Pros for Wave and Tidal Power|url=http://www.oceanenergycouncil.com/index.php/Tidal-Energy/Tidal-Energy.html|archive-url=https://web.archive.org/web/20080513175027/http://www.oceanenergycouncil.com/index.php/Tidal-Energy/Tidal-Energy.html|url-status=dead|archive-date=2008-05-13|date=2011}}</ref> The earliest occurrences date from the [[Middle Ages]], or even from [[Ancient Rome|Roman times]].<ref>{{cite web |url=http://www.kentarchaeology.ac/authors/005.pdf |title=Microsoft Word – RS01j.doc |access-date=2011-04-05 |url-status=live |archive-url=https://web.archive.org/web/20110517013738/http://www.kentarchaeology.ac/authors/005.pdf |archive-date=2011-05-17 }}</ref><ref>{{cite journal| author=Minchinton, W. E. | title=Early Tide Mills: Some Problems | journal=Technology and Culture | volume=20 | issue=4 |date=October 1979 | pages=777–786 | doi=10.2307/3103639| jstor=3103639| s2cid=112337062 }}</ref> The process of using falling water and spinning [[turbine]]s to create electricity was introduced in the U.S. and Europe in the 19th century.<ref>{{cite book|last=Dorf|first=Richard|title=The Energy Factbook|url=https://archive.org/details/energyfactbook00dorf|url-access=registration|date=1981|publisher=McGraw-Hill|location=New York}}</ref>
 
Electricity generation from marine technologies increased an estimated 16% in 2018, and an estimated 13% in 2019.<ref>{{Cite web|title=Ocean power – Tracking Power 2020 – Analysis|url=https://www.iea.org/reports/tracking-power-2019/ocean-power|access-date=2020-08-25|website=IEA|language=en-GB|archive-date=2020-06-19|archive-url=https://web.archive.org/web/20200619154701/https://www.iea.org/reports/tracking-power-2019/ocean-power|url-status=dead}}</ref> Policies promoting R&D are needed to achieve further cost reductions and large-scale development. The world's first large-scale tidal power plant was France's [[Rance Tidal Power Station]], which became operational in 1966. It was the largest tidal power station in terms of output until [[Sihwa Lake Tidal Power Station]] opened in South Korea in August 2011. The Sihwa station uses sea wall defense barriers complete with 10 turbines generating 254 &nbsp;MW.<ref>{{Cite book|title=Guinness world records 2014|last=Glenday|first=Craig|year=2013|isbn=978-1-908843-15-9|url-access=registration|url=https://archive.org/details/guinnessworldrec0000unse_r3e7}}</ref>
 
== Principle ==
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== Methods ==
[[File:SeaGen installed.jpg|right|thumb|The world's first commercial-scale and grid-connected tidal stream generator &nbsp;– [[SeaGen]] – in [[Strangford Lough]].<ref>{{Cite journal
| doi = 10.1243/14750902JEME94
| volume = 222
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{{Main|Dynamic tidal power}}
[[File:DTP T dam top-down view.jpg|thumb|right|Top-down diagram of a DTP dam. Blue and dark red colours indicate low and high tides, respectively.]]
Dynamic tidal power (or DTP) is a theoretical technology that would exploit an interaction between potential and kinetic energies in tidal flows. It proposes that very long dams (for example: 30–50&nbsp;km length) be built from coasts straight out into the sea or ocean, without enclosing an area. Tidal [[phase difference]]s are introduced across the dam, leading to a significant water-level differential in shallow coastal seas – featuring strong coast-parallel oscillating tidal currents such as found in the UK, China, and Korea. Induced tides (TDP) could extend the geographic viability of a new hydro-atmospheric concept 'LPD' (lunar pulse drum) discovered by a Devon innovator in which a tidal 'water piston' pushes or pulls a metered jet of air to a rotary air-actuator &and generator. The principle was demonstrated at London Bridge June 2019. Plans for a 30&nbsp;m, 62.5kwh5&nbsp;kWh 'pilot' installation on a (Local Authority) tidal estuary shoreline in the Bristol Channel are underway.
 
=== Tidal lagoon ===
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A study was commissioned by the Canadian, Nova Scotian and New Brunswick governments (Reassessment of Fundy Tidal Power) to determine the potential for tidal barrages at Chignecto Bay and Minas Basin – at the end of the Fundy Bay estuary. There were three sites determined to be financially feasible: Shepody Bay (1550 &nbsp;MW), Cumberland Basin (1085 &nbsp;MW), and Cobequid Bay (3800 &nbsp;MW). These were never built despite their apparent feasibility in 1977.<ref>{{Citation |first=Jen |last=Chang |title=Hydrodynamic Modeling and Feasibility Study of Harnessing Tidal Power at the Bay of Fundy |publisher=University of Southern California |location=Los Angeles |date=2008 |section=6.1 |type=PhD thesis |url=http://digitallibrary.usc.edu/assetserver/controller/item/etd-Chang-20080312.pdf |access-date=2011-09-27 |url-status=dead |archive-url=https://web.archive.org/web/20121122141719/http://digitallibrary.usc.edu/assetserver/controller/item/etd-Chang-20080312.pdf |archive-date=2012-11-22 |bibcode=2008PhDT.......107C }}</ref>
 
== US studies in the 21st century ==
The [[Snohomish County Public Utility District|Snohomish PUD]], a public utility district located primarily in Snohomish County, Washington State, began a tidal energy project in 2007.<ref>[https://www.snopud.com/PowerSupply/tidal/tidalnext.ashx?p=1513“Project Overview,”]{{dead link|date=January 2019 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> In April 2009 the PUD selected OpenHydro,<ref>[https://www.snopud.com/PowerSupply/tidal/tidalbg/tidalopenhydro.ashx?p=1511“OpenHydro Selected,”]{{dead link|date=January 2019 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> a company based in Ireland, to develop turbines and equipment for eventual installation. The project as initially designed was to place generation equipment in areas of high tidal flow and operate that equipment for four to five years. After the trial period the equipment would be removed. The project was initially budgeted at a total cost of $10 &nbsp;million, with half of that funding provided by the PUD out of utility reserve funds, and half from grants, primarily from the US federal government. The PUD paid for part of this project from reserves and received a $900,000 grant in 2009 and a $3.5 &nbsp;million grant in 2010 in addition to using reserves to pay an estimated $4 &nbsp;million of costs. In 2010 the budget estimate was increased to $20 &nbsp;million, half to be paid by the utility, half by the federal government. The utility was unable to control costs on this project, and by October 2014, the costs had ballooned to an estimated $38 &nbsp;million and were projected to continue to increase. The PUD proposed that the federal government provide an additional $10 &nbsp;million towards this increased cost, citing a [[gentlemen's agreement]].<ref>[https://www.heraldnet.com/news/pud-claims-gentlemens-agreement-over-tidal-project-funding/ “PUD claims 'gentleman's agreement over tidal project funding',”] Everett Herald, Oct 2, 2014,</ref> When the federal government refused to pay this, the PUD cancelled the project after spending nearly $10 &nbsp;million from reserves and grants. The PUD abandoned all tidal energy exploration after this project was cancelled and does not own or operate any tidal energy sources.
 
== Rance tidal power plant in France ==
In 1966, [[Électricité de France]] opened the [[Rance Tidal Power Station]], located on the [[estuary]] of the [[Rance River]] in [[Brittany]]. It was the world's first<ref>{{cite web|title= Wyre Tidal Energy|url= http://www.wyretidalenergy.com/tidal-barrage/la-rance-barrage|url-status= dead|archive-url= https://web.archive.org/web/20150204062904/http://www.wyretidalenergy.com/tidal-barrage/la-rance-barrage|archive-date= 4 February 2015|df= dmy-all}}</ref> tidal power station. The plant was for 45 years the largest tidal power station in the world by installed capacity: Its 24 [[turbines]] reach peak output at 240 [[watt|megawatts]] (MW) and average 57 &nbsp;MW, a [[capacity factor]] of approximately 24%.
 
== Tidal power development in the UK ==
The world's first marine energy test facility was established in 2003 to 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 {{cvt|4|m/s|mph kn km/h}} in spring tides. Tidal energy developers that have tested at the site include: Alstom (formerly Tidal Generation Ltd); ANDRITZ HYDRO Hammerfest; Atlantis Resources Corporation; Nautricity; OpenHydro; Scotrenewables Tidal Power; Voith.<ref>{{cite web|url=http://www.emec.org.uk/|title=EMEC: European Marine Energy Centre|website=emec.org.uk|url-status=live|archive-url=https://web.archive.org/web/20070127094922/http://www.emec.org.uk/|archive-date=2007-01-27}}</ref> The resource could be 4 &nbsp;TJ per year.<ref>{{cite journal | last1 = Lewis | first1 = M. | last2 = Neill | first2 = S.P. | last3 = Robins | first3 = P.E. | last4 = Hashemi | first4 = M.R. | year = 2015 | title = Resource assessment for future generations of tidal-stream energy arrays | doi = 10.1016/j.energy.2015.02.038 | journal = Energy | volume = 83 | pages = 403–415 | url = http://e.bangor.ac.uk/4613/1/32174..pdf | doi-access = free }}{{Dead link|date=October 2022 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Elsewhere in the UK, annual energy of 50 &nbsp;TWh can be extracted if 25 &nbsp;GW capacity is installed with pivotable blades.<ref>{{cite web|url=http://www.tu.no/artikler/norske-oppfinneres-turbinteknologi-kan-bli-brukt-i-britisk-tidevannseventyr/367589|title=Norske oppfinneres turbinteknologi kan bli brukt i britisk tidevannseventyr|website=[[Teknisk Ukeblad]]|date=14 January 2017|access-date=15 January 2017|url-status=live|archive-url=https://web.archive.org/web/20170115165731/http://www.tu.no/artikler/norske-oppfinneres-turbinteknologi-kan-bli-brukt-i-britisk-tidevannseventyr/367589|archive-date=15 January 2017}}</ref><ref>{{cite web |url=https://hendryreview.files.wordpress.com/2016/08/hendry-review-final-report-english-version.pdf |title=Archived copy |access-date=2017-01-15 |url-status=live |archive-url=https://web.archive.org/web/20170118062135/https://hendryreview.files.wordpress.com/2016/08/hendry-review-final-report-english-version.pdf |archive-date=2017-01-18 }}</ref><ref>{{cite web|date=2017-01-12|title=Tidal Lagoon May Be Cheaper Than Hinkley, Government Report Says|url=https://www.bloomberg.com/news/articles/2017-01-12/swansea-tidal-lagoon-should-go-ahead-says-u-k-government-review|url-status=live|archive-url=https://web.archive.org/web/20170116181010/https://www.bloomberg.com/news/articles/2017-01-12/swansea-tidal-lagoon-should-go-ahead-says-u-k-government-review|archive-date=2017-01-16|access-date=2017-01-15|website=Bloomberg.com}}</ref>
 
== Current and future tidal power schemes ==
{{Main|List of tidal power stations}}
[[File:VerdantPower 22Oct2020 RooseveltIsland.jpg|thumb|Roosevelt Island Tidal Energy (RITE) installation of three Verdant Power underwater 35-kilowatt turbines on a single triangular base (called a TriFrame) off the coast of New York City's Roosevelt Island on October 22, 2020.<ref>{{cite news |last1=Deign |first1=Jason |title=New York City Is About to Get an Injection of Tidal Power. Is This Time Different? |url=https://www.greentechmedia.com/articles/read/how-new-york-could-snag-a-piece-of-upcoming-tidal-action |access-date=22 October 2020 |publisher=Greentech Media |date=20 October 2020 |archive-url =https://web.archive.org/web/20201022225156/https://www.greentechmedia.com/articles/read/how-new-york-could-snag-a-piece-of-upcoming-tidal-action |archive-date=22 October 2020}}</ref>]]
* The [[Rance tidal power plant]] built over a period of 6six&nbsp;years from 1960 to 1966 at [[Rance river|La Rance]], France.<ref>[http://membres.lycos.fr/chezalex/projets/rance/sommaire_rance.htm L'Usine marémotrice de la Rance] {{webarchive |url=https://web.archive.org/web/20050408052145/http://membres.lycos.fr/chezalex/projets/rance/sommaire_rance.htm |date=April 8, 2005 }}</ref> It has 240&nbsp;MW installed capacity.
* 254 &nbsp;MW [[Sihwa Lake Tidal Power Plant]] in South Korea is the largest tidal power installation in the world. Construction was completed in 2011.<ref name=korea>{{cite web |url=http://www.newsworld.co.kr/cont/article2009/0909-52.htm |title=Hunt for African Projects |publisher=Newsworld.co.kr |access-date=2011-04-05 |url-status=dead |archive-url=https://web.archive.org/web/20110719135526/http://www.newsworld.co.kr/cont/article2009/0909-52.htm |archive-date=2011-07-19 }}</ref><ref>{{cite web|url=http://engsales.yonhapnews.co.kr/YNA/ContentsSales/EngSales/YISW_PopupPhotoPreview.aspx?CID=PYH20110411088100341|title=Tidal power plant nears completion|website=yonhapnews.co.kr|url-status=live|archive-url=https://web.archive.org/web/20120425235816/http://engsales.yonhapnews.co.kr/YNA/ContentsSales/EngSales/YISW_PopupPhotoPreview.aspx?CID=PYH20110411088100341|archive-date=2012-04-25}}</ref>
* The [[Jiangxia Tidal Power Station]], south of [[Hangzhou]] in [[China]] has been operational since 1985, with current installed capacity of 3.2 &nbsp;MW. More tidal power is planned near the mouth of the [[Yalu Jiang|Yalu River]].<ref>{{cite web |url=http://www.renewableenergyworld.com/rea/news/article/2004/11/china-endorses-300-mw-ocean-energy-project-17685 |title=China Endorses 300 MW Ocean Energy Project |date=2 November 2004 |publisher=Renewableenergyworld.com |access-date=2011-04-05 |url-status=live |archive-url=https://web.archive.org/web/20120715035036/http://www.renewableenergyworld.com/rea/news/article/2004/11/china-endorses-300-mw-ocean-energy-project-17685 |archive-date=2012-07-15 }}</ref>
* 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.<ref>{{cite web |url=http://www.cleancurrent.com/technology/rrproject.htm |title=Race Rocks Demonstration Project |publisher=Cleancurrent.com |access-date=2011-04-05 |url-status=dead |archive-url=https://web.archive.org/web/20080705173021/http://www.cleancurrent.com/technology/rrproject.htm |archive-date=2008-07-05 }}</ref><ref>{{cite web |url=http://www.racerocks.com/racerock/energy/tidalenergy/tidalenergy2.htm |title=Tidal Energy, Ocean Energy |publisher=Racerocks.com |access-date=2011-04-05 |url-status=live |archive-url=https://web.archive.org/web/20110612142255/http://www.racerocks.com/racerock/energy/tidalenergy/tidalenergy2.htm |archive-date=2011-06-12 }}</ref> The Race Rocks project was shut down after operating for five years (2006–2011) because high operating costs produced electricity at a rate that was not economically feasible.<ref>{{Cite news|url=http://www.racerocks.ca/tidal-energy-turbine-removal/|title=Tidal Energy Turbine Removal|date=2011-09-18|work=Race Rocks Ecological Reserve- Marine mammals, seabirds|access-date=2018-09-09|language=en-CA}}</ref> The next phase in the development of this tidal current generator will be in Nova Scotia (Bay of Fundy).<ref>{{cite web |url=http://www.cleancurrent.com/media/index.htm |archive-url=https://web.archive.org/web/20070603100529/http://www.cleancurrent.com/media/index.htm |url-status=dead |archive-date=2007-06-03 |title=Information for media inquiries |publisher=Cleancurrent.com |date=2009-11-13 |access-date=2011-04-05 }}</ref>
* A small project was built by the Soviet Union at [[Kislaya Guba Tidal Power Station|Kislaya Guba]] on the [[Barents Sea]]. It has 0.4&nbsp;MW installed capacity. In 2006 it was upgraded with a 1.2 &nbsp;MW experimental advanced orthogonal turbine.
* [[Uldolmok Tidal Power Station|Jindo Uldolmok Tidal Power Plant]] in South Korea is a tidal stream generation scheme planned to be expanded progressively to 90 &nbsp;MW of capacity by 2013. The first 1 &nbsp;MW was installed in May 2009.<ref>[http://www.korea.net/news/News/newsView.asp?serial_no=20090518009&part=101&SearchDay=2009.05.18&page=1 Korea's first tidal power plant built in Uldolmok, Jindo] {{dead link|date=June 2016|bot=medic}}{{cbignore|bot=medic}}</ref>
* A 1.2 &nbsp;MW [[SeaGen]] system became operational in late 2008 on [[Strangford Lough]] in [[Northern Ireland]].<ref>{{cite news | url=http://news.bbc.co.uk/2/hi/uk_news/northern_ireland/7790494.stm | work=BBC News | title=Tidal energy system on full power | date=December 18, 2008 | access-date=March 26, 2010 | url-status=live | archive-url=https://web.archive.org/web/20100826022612/http://news.bbc.co.uk/2/hi/uk_news/northern_ireland/7790494.stm | archive-date=August 26, 2010 }}</ref>
* The contract for an 812 &nbsp;MW tidal barrage near [[Ganghwa Island]] (South Korea) north-west of Incheon has been signed by Daewoo. Completion was planned for 2015<ref name=korea /> but project was retracted in 2013.<ref>{{Cite web|date=2011-06-29|title=Tidal Power in South Korea|url=https://saveinternational.org/saveinaction/tidal-power-in-south-korea/|access-date=2021-10-11|website=SAVE International|language=en}}</ref>
* A 1,320 &nbsp;MW [[Incheon Tidal Power Station|barrage]] built around islands west of Incheon was proposed by the South Korean government in 2009. Project halted since 2012 due to environmental concerns.<ref>[https://web.archive.org/web/20100107103634/http://ecoseed.org/en/general-green-news/green-politics/green-policies/asia-pacific/3457 $ 3-B tidal power plant proposed near Korean islands]</ref>
* The Scottish Government has approved plans for a 10 &nbsp;MW array of tidal stream generators near [[Islay]], [[Scotland]], costing 40 &nbsp;million pounds, and consisting of 10 turbines &nbsp;– enough to power over 5,000 homes. The first turbine was expected to be in operation by 2013<ref>{{cite news |url=https://www.bbc.co.uk/news/uk-scotland-glasgow-west-12767211 |title=Islay to get major tidal power scheme |publisher=BBC |access-date=2011-03-19 |date=March 17, 2011 |url-status=live |archive-url=https://web.archive.org/web/20110318115244/http://www.bbc.co.uk/news/uk-scotland-glasgow-west-12767211 |archive-date=March 18, 2011 }}</ref> but as of 2021 was not operational.
* The Indian state of [[Gujarat]] was planning to host South Asia's first commercial-scale tidal power station. The company Atlantis Resources planned to install a 50 &nbsp;MW tidal farm in the Gulf of Kutch on India's west coast, with construction planned to start 2012,<ref>{{cite news | url=https://www.bbc.co.uk/news/science-environment-12215065 | work=BBC News | title=India plans Asian tidal power first | date=January 18, 2011 | url-status=live | archive-url=https://web.archive.org/web/20110119045601/http://www.bbc.co.uk/news/science-environment-12215065 | archive-date=January 19, 2011 }}</ref> later withdrawn due to high costs.<ref>{{Cite web|date=2021-08-20|title=India's tidal power potential hampered by high costs and environmental risks|url=https://india.mongabay.com/2021/08/indias-tidal-power-potential-hampered-by-high-costs-and-environmental-risks/|access-date=2021-10-11|website=Mongabay-India|language=en-US}}</ref>
* Ocean Renewable Power Corporation was the first company to deliver tidal power to the US grid in September, 2012 when its pilot TidGen system was successfully deployed in [[Cobscook Bay]], near Eastport.<ref>[http://www.cbsnews.com/8301-505245_162-57512964/1st-tidal-power-delivered-to-us-grid-off-maine/ "1st tidal power delivered to US grid off Maine"] {{webarchive |url=https://web.archive.org/web/20120916223233/http://www.cbsnews.com/8301-505245_162-57512964/1st-tidal-power-delivered-to-us-grid-off-maine/ |date=September 16, 2012 }}, CBS MoneyWatch, September 14, 2012</ref>
* In New York City, Verdant Power successfully deployed and operated three tidal turbines in the East River near Roosevelt Island, on a single triangular base system, called a TriFrame™TriFrame. The Roosevelt Island Tidal Energy (RITE) Project generated over 300MWh of electricity to the local grid, an American marine energy record. The system’s performance was independently confirmed by Scotland’s European Marine Energy Centre (EMEC) under the new International Electrotechnical Commission (IEC) international standards. This is the first instance of a third-party verification of a tidal energy converter to an international standard. .<ref>{{cite web|title=Turbines Off NYC East River Will Create Enough Energy to Power 9,500 Homes|url=http://energy.gov/articles/turbines-nyc-east-river-will-create-enough-energy-power-9500-homes|publisher=U.S. Department of Energy|access-date=13 February 2012|url-status=live|archive-url=https://web.archive.org/web/20120211073710/http://energy.gov/articles/turbines-nyc-east-river-will-create-enough-energy-power-9500-homes|archive-date=11 February 2012}}</ref>
* A turbine project is being installed in [[Ramsey Island|Ramsey Sound]] in 2014.<ref>Macalister, Terry. "[https://www.theguardian.com/business/2014/sep/25/tidal-power-electricity-edf-energy-marine-pembrokeshire Tidal power firm signs deal to sell electricity to EDF Energy] {{webarchive|url=https://web.archive.org/web/20161012132608/https://www.theguardian.com/business/2014/sep/25/tidal-power-electricity-edf-energy-marine-pembrokeshire |date=2016-10-12 }}" ''[[The Guardian]]'', 25 September 2014.</ref>
* The largest tidal energy project entitled [[MeyGen]] (398 &nbsp;MW) is currently in construction in the [[Pentland Firth]] in northern Scotland <ref>{{cite news |url=https://www.ft.com/content/d197308a-7826-11e6-97ae-647294649b28 |title=Scotland unveils world's largest tidal stream power project |newspaper=Financial Times |date=12 September 2016 |access-date=2016-12-01 |url-status=live |archive-url=https://web.archive.org/web/20161202040709/https://www.ft.com/content/d197308a-7826-11e6-97ae-647294649b28 |archive-date=2016-12-02 }}</ref>
* Construction of a 320 &nbsp;MW tidal lagoon power plant outside the city of [[Swansea]] in the UK was granted planning permission in June 2015, however it was later rejected by the UK government in 2018. If built it would have been the world's first tidal power plant based on a constructed lagoon.<ref>{{cite news|url=https://www.bbc.co.uk/news/uk-wales-south-west-wales-44589083|title=£1.3bn Swansea Bay tidal lagoon project thrown out|date=25 June 2018|work=BBC News website|access-date=27 May 2022|url-status=live}}</ref>
 
== Issues and challenges ==
 
=== Environmental concerns ===
Tidal power can affect marine life. The turbines' rotating blades can accidentally kill swimming sea life. Projects such as the one in Strangford include a safety mechanism that turns off the turbine when marine animals approach. However, this feature causes a major loss in energy because of the amount of marine life that passes through the turbines.<ref>{{cite web|title=Tidal Energy Technology Brief|url=http://www.irena.org/DocumentDownloads/Publications/Tidal_Energy_V4_WEB.pdf|publisher=International Renewable Energy Agency|access-date=16 October 2015|url-status=live|archive-url=https://web.archive.org/web/20151122225322/http://www.irena.org/documentdownloads/publications/tidal_energy_v4_web.pdf|archive-date=22 November 2015}}</ref> Some fish may avoid the area if threatened by a constantly rotating or noisy object. Marine life is a huge factor when siting tidal power [[energy generator]]s, and precautions are taken to ensure that as few [[marine animal]]s as possible are affected by it. The [[Tethys (database)|Tethys database]] provides access to scientific literature and general information on the potential environmental effects of tidal energy.<ref>{{cite web|title=Tethys|url=http://tethys.pnnl.gov/wiki/index.php/Tethys_Home|url-status=dead|archive-url=https://web.archive.org/web/20141110141934/http://tethys.pnnl.gov/wiki/index.php/Tethys_Home|archive-date=2014-11-10}}</ref> In terms of [[global warming potential]] (i.e. carbon footprint), the impact of tidal power generation technologies ranges between 15 and 37 &nbsp;gCO<sub>2</sub>-eq/kWhe, with a median value of 23.8 &nbsp;gCO<sub>2</sub>-eq/kWhe.<ref>{{cite journal |last1=Kaddoura |first1=Mohamad |last2=Tivander |first2=Johan |last3=Molander |first3=Sverker |title= life cycle assessment of electricity generation from an array of subsea tidal kite prototypes |journal=Energies |date=2020 |volume=13 |issue=2 |pages=456 |doi= 10.3390/en13020456 |doi-access=free }}</ref> This is in line with the impact of other renewables like wind and solar power, and significantly better than fossil-based technologies.
 
==== Tidal turbines ====
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