Editing Tidal power (section)

== 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
| issue = 1
| pages = 1–12
| last1 = Douglas
| first1 = C. A.
| first2 = G. P.
| last2 = Harrison
| first3 = J. P.
| last3 = Chick
| title = Life cycle assessment of the Seagen marine current turbine
| journal = Proceedings of the Institution of Mechanical Engineers, Part M: Journal of Engineering for the Maritime Environment
| date = 2008
| bibcode = 2008PIMEM.222....1D
| s2cid = 111126521
| url = https://www.research.ed.ac.uk/portal/files/49243203/MCT_Seagen_Audit_Post_print.pdf
| hdl = 20.500.11820/935cdfa5-aeed-423c-aa52-f51c5e5753ef
| hdl-access = free
}}</ref> The strong [[Wake (physics)|wake]] shows the power in the [[tidal current]].]]
Tidal power can be classified into four generating methods:

=== Tidal stream generator ===
{{Main|Tidal stream generator}}

Tidal stream generators make use of the [[kinetic energy]] of moving water to power turbines, in a similar way to [[wind turbine]]s that use the wind to power turbines. Some tidal generators can be built into the structures of existing bridges or are entirely submersed, thus avoiding concerns over aesthetics or visual impact. Land constrictions such as straits or inlets can create high velocities at specific sites, which can be captured using turbines. These turbines can be horizontal, vertical, open, or ducted.<ref name="Tethys">{{cite web|title=Tidal – Capturing tidal fluctuations with turbines, tidal barrages, or tidal lagoons|url=http://tethys.pnnl.gov/technology-type/tidal|website=Tidal / Tethys|publisher=[[Pacific Northwest National Laboratory]] (PNNL)|access-date=2 February 2016|url-status=live|archive-url=https://web.archive.org/web/20160216190319/https://tethys.pnnl.gov/technology-type/tidal|archive-date=16 February 2016}}</ref>

=== Tidal barrage ===
{{Main|Tidal barrage}}

Tidal barrages use [[potential energy]] in the difference in height (or [[hydraulic head]]) between high and low tides. When using tidal barrages to generate power, the potential energy from a tide is seized through the strategic placement of specialized dams.  When the sea level rises and the tide begins to come in, the temporary increase in tidal power is channeled into a large basin behind the dam, holding a large amount of potential energy.  With the receding tide, this energy is then converted into [[mechanical energy]] as the water is released through large turbines that create electrical power through the use of generators.<ref>{{cite book|last=Evans|first=Robert|title=Fueling Our Future: An Introduction to Sustainable Energy|url=https://archive.org/details/fuelingourfuture00evan_0|url-access=registration|date=2007|publisher=Cambridge University Press|location=New York}}</ref>  Barrages are essentially [[dam]]s across the full width of a tidal estuary.

=== Tidal lagoon ===
A new tidal energy design option is to construct circular retaining walls embedded with turbines that can capture the potential energy of tides. The created reservoirs are similar to those of tidal barrages, except that the location is artificial and does not contain a pre-existing ecosystem.<ref name="Tethys" />
The lagoons can also be in double (or triple) format without pumping<ref>{{cite web |url=https://www.youtube.com/watch?v=lnHwb8BKJzU |title=Hydrological Changing Double Current-typed Tidal Power Generation |website=[[YouTube]] |date=23 September 2012 |format=video |access-date=2015-04-15 |url-status=live |archive-url=https://web.archive.org/web/20151018074420/https://www.youtube.com/watch?v=lnHwb8BKJzU |archive-date=2015-10-18 }}</ref>  or with pumping<ref>{{cite web |url=http://www.inference.phy.cam.ac.uk/sustainable/book/tex/Lagoons.pdf |title=Enhancing Electrical Supply by Pumped Storage in Tidal Lagoons |access-date=2014-03-13 |url-status=live |archive-url=https://web.archive.org/web/20150924034732/http://www.inference.phy.cam.ac.uk/sustainable/book/tex/Lagoons.pdf |archive-date=2015-09-24 }}</ref> that will flatten out the power output. The pumping power could be provided by excess to grid demand renewable energy from for example wind turbines or solar photovoltaic arrays. Excess renewable energy rather than being curtailed could be used and stored for a later period of time. Geographically dispersed tidal lagoons with a time delay between peak production would also flatten out peak production providing near baseload production at a higher cost than other alternatives such as district heating renewable energy storage. The cancelled [[Tidal Lagoon Swansea Bay]] in Wales, United Kingdom would have been the first tidal power station of this type once built.<ref>{{cite web|url=http://www.renewableenergyfocus.com/view/42607/green-light-for-worlds-first-tidal-lagoon/|title=Green light for world's first tidal lagoon|author=Elsevier Ltd, The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1&nbsp;GB, United Kingdom|website=renewableenergyfocus.com|access-date=26 July 2015|url-status=live|archive-url=https://web.archive.org/web/20150818213310/http://www.renewableenergyfocus.com/view/42607/green-light-for-worlds-first-tidal-lagoon/|archive-date=18 August 2015}}</ref>

=== Dynamic tidal power ===
{{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.