Tidal power

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Tidal power, also known as ocean tidal power and tidal energy, is a form of hydropower that converts the energy of tides into electricity or other useful forms of power. Because the Earth's tides are caused by forces due to gravitational interaction with the Moon and Sun, and the Earth's rotation, tidal power is practically inexhaustible and classified as a renewable energy source.

Generation of tidal energy

Tidal power is the only form of energy which derives directly from the relative motions of the Earth–Moon system, and to a lesser extent from the Earth–Sun system. The tidal forces produced by the Moon and Sun, in combination with Earth's rotation, are responsible for the generation of the tides. Other sources of energy originate directly or indirectly from the Sun, including fossil fuels, conventional hydroelectric, wind, biofuels, wave power and solar. Nuclear energy is derived using radioactive material from the Earth, geothermal power uses 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%). Tidal energy is generated by the relative motion of the water which interact via gravitational forces. Periodic changes of water levels, and associated tidal currents, are due to the gravitational attraction by the Sun and Moon. The magnitude of the tide at a location is the result of the changing positions of the Moon and Sun relative to the Earth, the effects of Earth rotation, and the local shape of the sea floor and coastlines.[1]

A tidal generator uses this phenomenon to generate electricity. The stronger the tide, either in water level height or tidal current velocities, the greater the potential for tidal electricity generation. Tidal movement causes a continual loss of mechanical energy in the Earth–Moon system due to pumping of water through the natural restrictions around coastlines, and due to viscous dissipation at the seabed and in turbulence. This loss of energy has caused the rotation of the Earth to slow in the 4.5 billion years since formation. During the last 620 million years the period of rotation has increased from 21.9 hours to the 24 hours we see now; in this period the Earth has lost 17% of its rotational energy. While tidal power may take additional energy from the system, increasing the rate of slowdown, the effect would be noticeable over millions of years only, thus being negligible.[2]

Generating methods

Tidal power: how it works

Tidal power can be classified into three generating methods:[3]

  • Tidal stream systems make use of the kinetic energy of moving water to power turbines, in a similar way to windmills that use moving air.
  • Barrages make use of the potential energy in the difference in height (or head) between high and low tides. They are created at the mouth of a river or other choke point that connects to the ocean, much like a dam.
  • Dynamic tidal power exploits a combination of potential and kinetic energy: by constructing long dams of 30–50 km in length from the coast straight out into the sea or ocean, without enclosing an area. Both the obstruction of the tidal flow by the dam – as well as the tidal phase differences introduced by the presence of the dam (which is not negligible in length as compared to the tidal wavelength) – lead to hydraulic head differences along the dam. Turbines in the dam are used to convert power (6–15 GW per dam).


The following are companies either currently involved in or which have applied for the development of tidal energy projects.



Watchdog and Opponent Groups

U.S. Legislation

Related SourceWatch Resources

External links



  • Peter Clark, Rebecca Klossner, and Lauren Kologe, "Tidal Energy," CAUSE 2003: Final Project, College of Earth and Mineral Sciences, Penn State, November 13, 2003.

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Articles & Commentary








  • Turcotte, D. L.; Schubert, G. (2002). "4", Geodynamics, 2, Cambridge, England, UK: Cambridge University Press, 136–137. ISBN 978-0-521-66624-4. 
  • George E. Williams (2000). "Geological constraints on the Precambrian history of Earth's rotation and the Moon's orbit". Reviews of Geophysics 38: 37–60. doi:10.1029/1999RG900016. 
  • "How Does Tidal Power Work?" Renewable Energy Resource, accessed September 2010.