Tidal power

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Renewable energy
Wind turbine

Biofuel
Biomass
Geothermal
Hydroelectricity
Solar energy
Tidal power
Wave power
Wind power

Tidal power, also called tidal energy, is a form of hydropower that converts the energy of tides into useful forms of power - mainly electricity.

Although not yet widely used, tidal power has potential for future electricity generation. Tides are more predictable than wind energy and solar power. Among sources of renewable energy, tidal power has traditionally suffered from relatively high cost and limited availability of sites with sufficiently high tidal ranges or flow velocities, thus constricting its total availability. However, many recent technological developments and improvements, both in design (e.g. dynamic tidal power, tidal lagoons) and turbine technology (e.g. new axial turbines, cross flow turbines), indicate that the total availability of tidal power may be much higher than previously assumed, and that economic and environmental costs may be brought down to competitive levels.

Historically, tide mills 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 went out, it turned waterwheels that used the mechanical power it produced to mill grain. [1] The earliest occurrences date from the Middle Ages, or even from Roman times.[2][3] It was only in the 19th century that the process of using falling water and spinning turbines to create electricity was introduced in the U.S. and Europe.[4]

The world's first large-scale tidal power plant (the Rance Tidal Power Station) became operational in 1966.

Contents

Generation of tidal energy

Variation of tides over a day

Tidal power is extracted from the Earth's oceanic tides; tidal forces are periodic variations in gravitational attraction exerted by celestial bodies. These forces create corresponding motions or currents in the world's oceans. Due to the strong attraction to the oceans, a bulge in the water level is created, causing a temporary increase in sea level. When the sea level is raised, water from the middle of the ocean is forced to move toward the shorelines, creating a tide. This occurrence takes place in an unfailing manner, due to the consistent pattern of the moon’s orbit around the earth. [5] The magnitude and character of this motion reflects the changing positions of the Moon and Sun relative to the Earth, the effects of Earth's rotation, and local geography of the sea floor and coastlines.

Tidal power is the only technology that draws on energy inherent in the orbital characteristics of the EarthMoon system, and to a lesser extent in the Earth–Sun system. Other natural energies exploited by human technology originate directly or indirectly with the Sun, including fossil fuel, conventional hydroelectric, wind, biofuel, wave and solar energy. Nuclear energy makes use of Earth's mineral deposits of fissionable elements, while geothermal power taps the Earth's internal heat, which comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%).[6]

A tidal generator converts the energy of tidal flows into electricity. Greater tidal variation and higher tidal current velocities can dramatically increase the potential of a site for tidal electricity generation.

Because the Earth's tides are ultimately 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 resource. Movement of tides causes a loss of mechanical energy in the Earth–Moon system: this is a result of pumping of water through natural restrictions around coastlines and consequent 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 its formation. During the last 620 million years the period of rotation of the earth (length of a day) has increased from 21.9 hours to 24 hours;[7] in this period the Earth has lost 17% of its rotational energy. While tidal power may take additional energy from the system, the effect is negligible and would only be noticed over millions of years.

Generating methods

The world's first commercial-scale and grid-connected tidal stream generator – SeaGen – in Strangford Lough.[8] The strong wake shows the power in the tidal current.
Top-down view of a DTP dam. Blue and dark red colors indicate low and high tides, respectively.

Tidal power can be classified into three generating methods:

Tidal stream generator

Tidal stream generators (or TSGs) make use of the kinetic energy of moving water to power turbines, in a similar way to wind turbines that use wind to power turbines. Some tidal generators can be built into the structures of existing bridges, involving virtually no aesthetic problems. Likewise, “tidal bridging” is a relatively new advancement that is gaining recognition as a more practical and beneficial way to generate tidal power. Blue Energy Canada is a company that is focused on building bridges to match today's demands. [9]

Tidal barrage

Tidal barrages make use of the potential energy in the difference in height (or head) between high and low tides. When using tidal barrages to generate power, the potential energy from a tide is seized through 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 though the use of generators. [10] Barrages are essentially dams across the full width of a tidal estuary.

Dynamic tidal power

Dynamic tidal power (or DTP) is an untried but promising technology that would exploit an interaction between potential and kinetic energies in tidal flows. It proposes that very long dams (for example: 30–50 km length) be built from coasts straight out into the sea or ocean, without enclosing an area. Tidal phase differences 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.

US and Canadian studies in the twentieth century

The first study of large scale tidal power plants was by the US Federal Power Commission in 1924 which would have been located if built in the northern border area of the US state of Maine and the south eastern border area of the Canadian province of New Brunswick, with various dams, powerhouses and ship locks enclosing the Bay of Fundy and Passamaquoddy Bay (note: see map in reference). Nothing came of the study and it is unknown whether Canada had been approached about the study by the US Federal Power Commission.[11]

There was also a report on the international commission in April 1961 entitled " Investigation of the International Passamaquoddy Tidal Power Project" produced by both the US and Canadian Federal Governments. According to benefit to costs ratios, the project was beneficial to the US but not to Canada. A highway system along the top of the dams was envisioned as well.

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 MW), Cumberline Basin (1085 MW) and Cobequid Bay (3800 MW). These were never built despite their apparent feasibility in 1977.[12]

Current and future tidal power schemes

Tidal power issues

Ecological

Tidal power can have effects on marine life. The turbines can accidentally kill swimming sea life with the rotating blades. Some fish may no longer utilize the area if they were threatened with a constant rotating object.

Corrosion

Salt water causes corrosion in metal parts. It can be difficult to maintain tidal stream generators due to their size and depth in the water. Mechanical fluids, such as lubricants, can leak out, which may be harmful to the marine life nearby. Proper maintenance can minimize the amount of harmful chemicals that may enter the environment.

See also

Notes

  • 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, 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.

References

  1. ^ Ocean Energy Council (2011). "Tidal Energy: Pros for Wave and Tidal Power". http://www.oceanenergycouncil.com/index.php/Tidal-Energy/Tidal-Energy.html. 
  2. ^ "Microsoft Word - RS01j.doc" (PDF). http://www.kentarchaeology.ac/authors/005.pdf. Retrieved 2011-04-05. 
  3. ^ Minchinton, W. E. (October 1979). "Early Tide Mills: Some Problems". Technology and Culture (Society for the History of Technology) 20 (4): 777–786. doi:10.2307/3103639. JSTOR 3103639. 
  4. ^ Dorf, Richard (1981). The Energy Factbook. New York: McGraw-Hill. 
  5. ^ DiCerto, JJ (1976). The Electric Wishing Well: The Solution to the Energy Crisis. New York: Macmillan. 
  6. ^ Turcotte, D. L.; Schubert, G. (2002). "4". Geodynamics (2 ed.). Cambridge, England, UK: Cambridge University Press. pp. 136–137. ISBN 978-0-521-66624-4. 
  7. ^ George E. Williams (2000). "Geological constraints on the Precambrian history of Earth's rotation and the Moon's orbit". Reviews of Geophysics 38 (1): 37–60. Bibcode 2000RvGeo..38...37W. doi:10.1029/1999RG900016. 
  8. ^ Douglas, C. A.; Harrison, G. P.; Chick, J. P. (2008). "Life cycle assessment of the Seagen marine current turbine". Proceedings of the Institution of Mechanical Engineers, Part M: Journal of Engineering for the Maritime Environment 222 (1): 1–12. doi:10.1243/14750902JEME94. 
  9. ^ Blue Energy Canada (2010). "Tidal Power: Blue Energy". http://www.bluenergy.com/technology_method_tidal_bridge.html. 
  10. ^ Evans, Robert (2007). Fueling Our Future: An Introduction to Sustainable Energy. New York: Cambridge University Press. 
  11. ^ "Niagra's Power From The Tides" May 1924 Popular Science Monthly
  12. ^ Chang, Jen (2008), Hydrodynamic Modeling and Feasibility Study of Harnessing Tidal Power at the Bay of Fundy (PhD thesis), Los Angeles: University of Southern California, http://digitallibrary.usc.edu/assetserver/controller/item/etd-Chang-20080312.pdf, retrieved 2011-09-27 
  13. ^ L'Usine marémotrice de la Rance[dead link]
  14. ^ a b "Hunt for African Projects". Newsworld.co.kr. http://www.newsworld.co.kr/cont/article2009/0909-52.htm. Retrieved 2011-04-05. 
  15. ^ Tidal power plant nears completion
  16. ^ "Nova Scotia Power - Environment - Green Power- Tidal". Nspower.ca. http://www.nspower.ca/en/home/environment/renewableenergy/tidal/annapolis.aspx. Retrieved 2011-04-05. 
  17. ^ "China Endorses 300 MW Ocean Energy Project". Renewableenergyworld.com. http://www.renewableenergyworld.com/rea/news/article/2004/11/china-endorses-300-mw-ocean-energy-project-17685. Retrieved 2011-04-05. 
  18. ^ "Race Rocks Demonstration Project". Cleancurrent.com. http://www.cleancurrent.com/technology/rrproject.htm. Retrieved 2011-04-05. 
  19. ^ "Tidal Energy, Ocean Energy". Racerocks.com. http://www.racerocks.com/racerock/energy/tidalenergy/tidalenergy2.htm. Retrieved 2011-04-05. 
  20. ^ "Information for media inquiries". Cleancurrent.com. 2009-11-13. http://www.cleancurrent.com/media/index.htm. Retrieved 2011-04-05. 
  21. ^ Korea's first tidal power plant built in Uldolmok, Jindo[dead link]
  22. ^ "Tidal energy system on full power". BBC News. December 18, 2008. http://news.bbc.co.uk/2/hi/uk_news/northern_ireland/7790494.stm. Retrieved March 26, 2010. 
  23. ^ $ 3-B tidal power plant proposed near Korean islands[dead link]
  24. ^ "Islay to get major tidal power scheme". BBC. March 17, 2011. http://www.bbc.co.uk/news/uk-scotland-glasgow-west-12767211. Retrieved 2011-03-19. 
  25. ^ "India plans Asian tidal power first". BBC News. January 18, 2011. http://www.bbc.co.uk/news/science-environment-12215065. 
  26. ^ "1st tidal power delivered to US grid off Maine", CBS MoneyWatch, September 14, 2012
  27. ^ "Turbines Off NYC East River Will Create Enough Energy to Power 9,500 Homes". U.S. Department of Energy. http://energy.gov/articles/turbines-nyc-east-river-will-create-enough-energy-power-9500-homes. Retrieved 13 February 2012. 

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