Tidal power

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.

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.

Generating methods
Tidal power can be classified into three generating methods:


 * 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).

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


 * Aqua Energy Group International (Web), Washington, U.S.
 * Blue Energy Canada Inc. (Blue Energy) (Web)
 * Bourne Energy, California, U.S.
 * BWEA (British Wind Energy Association) (Web), U.K.
 * Crest Energy, New Zealand
 * Finavera Renewables, Inc. (Finavera), Vancouver, British Columbia, Canada (purchased AquaEnergy Group, Ltd. in June 2006)
 * Focus Environmental, Inc., Canada
 * Hammerfest UK (ScottishPower (utility), Scotland and Hammerfest Strøm (technology), Norway)
 * Independent Natural Resources Inc. (INRI), U.S.
 * Maine Tidal Energy Co., Maine, U.S.
 * Marine Current Turbines (MCT) (Web), U.K.; SeaGen and SeaFlow devices
 * New Energy Corporation, Canada
 * NH Tidal Energy Co., New Hampshire, U.S.
 * Norsk Hydro ASA (Web), Norway
 * North Atlantic Energy Structures Inc. (Web), Canada
 * Ocean Power Delivery Ltd. (OPD), Scotland
 * Ocean Power Technologies Inc., New Jersey, U.S.
 * Ocean Renewable Energy Group (OREG), Canada
 * Ocean Renewable Power Company (Web), Florida, U.S.
 * Oceana Energy Co., U.S.
 * OpenHyro Group Limited (Web), Ireland (with Miami, Florida operation)
 * Renewable Energy Holdings (REH), Australia
 * Seacore Ltd. (Web), U.K.
 * SyncWave Energy Inc. (SEI), Canada (previously known as Sieber Energy)
 * Tidal Energy Australia
 * Tidewalker Associates, Maine, U.S.
 * TRC Environmental Corp., U.S.
 * Verdant Power LLC (Web), New York, U.S.
 * Wavebob Limited (Web), Ireland
 * Wavegen (Web), U.K.

Organizations

 * Aotearoa Wave and Tidal Energy Association (AWATEA) (Web), New Zealand
 * Electric Power Research Institute (EPRI) (Web), California, U.S.
 * European Marine Energy Centre Ltd. (EMEC) (Web), Scotland
 * European Ocean Energy Association (EUOEA)
 * National Hydropower Association

Lobbyists

 * Ocean Renewable Energy Coalition

Watchdog and Opponent Groups

 * American Fisheries Society
 * Friends of the Earth (FOE) (Web), U.K.
 * Hydropower Reform Coalition, U.S. (Web)
 * MARINET, U.K.
 * The Ocean Conservancy, U.S.
 * Oceans Public Trust Initiative
 * Orca Network

U.S. Legislation

 * Marine and Hydrokinetic Renewable Energy Promotion Act of 2007 (introduced April 24, 2007, in U.S. House of Representatives by Rep. Jay Inslee (D-Wash.) to "provide financial support for research and development (R&D) of energy sources based in oceans, rivers, lakes, streams and other waterways." )

Related SourceWatch Resources

 * climate change / global warming
 * Duke Energy
 * Energy Policy Act of 2005
 * European Forum for Renewable Energy Sources (EFRES) (Web)
 * Federal Energy Regulatory Commission
 * National Commission on Energy Policy
 * National Energy Policy
 * National Renewable Energy Laboratory (NREL) (Web)
 * production tax credit (PTC)
 * U.S. Department of Energy
 * U.S. National Oceanic and Atmospheric Administration (NOAA)

General

 * EPRI Ocean Energy Web Page.
 * "Ocean Tidal Power," Energy Efficiency and Renewable Energy, U.S. Department of Energy (Last Updated September 12, 2005).
 * "Tidal Energy" (Alternative Energy), ThinkQuest.org.
 * "Tidal Energy," United Nations Atlas of the Oceans.
 * "Tidal Energy," World Energy Council, 2001.
 * Directory: Ocean Wave Energy, PESWiki.com.
 * tidal power in the Wikipedia.

Reports

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

Conferences & Meetings

 * 2007 First Tidal Energy Conference, Alaska Tidal Energy Conference, Alaska Energy Authority, January 23-24, 2007.
 * 7th European Wave and Tidal Energy Conference (EWTEC2007), Porto, Portugal, September 11-14, 2007.

News Archives

 * Tidal Energy News published in Energy Bulletin.
 * Tidal Power Archives, Alternative Energy News.

Websites

 * ThinkTidal.com.

Blogs

 * Alternative Energy Blogspot.

2000

 * "Making waves to generate cash" (Scotland), BBC News, November 16, 2000.
 * "How it works: Wave power station," BBC News, November 20, 2000.

2001

 * "Wave power hope for Scotland," BBC News, June 3, 2001.
 * "Cash for wave power scheme" (Scotland), BBC News, September 11, 2001.
 * "Q&A: Wind and wave power," BBC News, November 12, 2001.

2003

 * Mary Gahan, Analysis: "Changing the face of energy," BBC News, February 24, 2003.
 * "Tidal energy project rests on weather," BBC News, April 30, 2003.
 * "Tidal energy turbine launches. Energy pioneers have launched the world's first offshore tidal energy turbine off the Devon coast," BBC News, June 16, 2003.

2004

 * "Wave energy test centre launched," BBC News, August 10, 2004.
 * "Warning over tidal energy impact," BBC News, August 20, 2004.

2005

 * "Manchester develops new wave energy device: The Manchester Bobber," innovations report, September 9, 2005.
 * "Scotland set to harness tidal power," Reuters (RedOrbit.com), September 9, 2005.
 * Rep. Cynthia Thielen, "Hawaii: Catch a Wave Energy," Hawaii Reporter, September 21, 2005.
 * Keith Doucette, "Tidal power study considers Bay of Fundy," Canadian Press (The Globe and Mail), October 21, 2005.
 * Joel Gallob, "Wave energy proponent a hit at conference," Newport News Times, November 4, 2005.
 * "Wave power could provide 20 pct of Portugal's eletricity - study," AFX News Limited (Forbes), November 10, 2005.
 * "Ocean Energy Devices Deployed in Two Oceans," RenewableEnergyAccess.com, November 15, 2005.

2006

 * "GE invests in world's first offshore wave farm project," OilOnline.com, April 18, 2006. Also see CarbonFree article re General Electric funding Ocean Power Delivery, Ltd. (OPD)
 * Aubrey Gibavic, "Tidal energy farm proposed for Vineyard Sound," The Martha's Vineyard Times, June 8, 2006.
 * Stephanie Ebbert and Beth Daley, "As some talk wind farms, others want to harness the tides. Nantucket Sound considered as site," Boston Globe, June 13, 2006.
 * Cecilia M. Vega, "Tides around Golden Gate are potential energy source," San Francisco Chronicle, September 19, 2006.
 * Jeannette J. Lee, "Tidal energy companies stake claims," Associated Press (USA TODAY), November 4, 2006.
 * "Tidal Energy Boom," Alternative Energy News, November 8, 2006.

2007

 * Michael Burnham, "Entrepreneurs start testing waters for offshore hydropower," Greenwire (EENews.net), March 22, 2007.
 * Shannon Moneo, "Turning to the tide for green energy," The Globe and Mail, March 27, 2007. Subscription or purchase required.
 * Paul Davidson, "Marine energy can be forecast," USA TODAY, April 18, 2007.
 * Peter Fairley, "Tidal Turbines Help Light Up Manhattan. Turbines are being submerged in the East River to generate electricity from rapid tidal currents," Technology Review/MIT, April 23, 2007.
 * "PUD gets grant to study 7 tidal-energy sites," Seattle Times, May 2, 2007.
 * Wojciech Moskwa and Daniel Fineren, "Scottish Power to develop tidal energy," Reuters (The Scotsman), May 14, 2007.
 * "New boost for Tidal Energy in the UK," OilVoice.com, May 14, 2007.