Tidal energy is produced by the surge of ocean waters during the rise and fall of tides. Tidal energy is a renewable source of energy.
During the 20th century, engineers developed ways to use tidal movement to generate electricity in areas where there is a significant tidal range—the difference in area between high tide and low tide. All methods use special generators to convert tidal energy into electricity.
Tidal energy production is still in its infancy. The amount of power produced so far has been small. There are very few commercial-sized tidal power plants operating in the world. The first was located in La Rance, France. The largest facility is the Sihwa Lake Tidal Power Station in South Korea. The United States has no tidal plants and only a few sites where tidal energy could be produced at a reasonable price. China, France, England, Canada, and Russia have much more potential to use this type of energy.
In the United States, there are legal concerns about underwater land ownership and environmental impact. Investors are not enthusiastic about tidal energy because there is not a strong guarantee that it will make money or benefit consumers. Engineers are working to improve the technology of tidal energy generators to increase the amount of energy they produce, to decrease their impact on the environment, and to find a way to earn a profit for energy companies.
Tidal Energy Generators
There are currently three different ways to get tidal energy: tidal streams, barrages, and tidal lagoons.
For most tidal energy generators, turbines are placed in tidal streams. A tidal stream is a fast-flowing body of water created by tides. A turbine is a machine that takes energy from a flow of fluid. That fluid can be air (wind) or liquid (water). Because water is much more dense than air, tidal energy is more powerful than wind energy. Unlike wind, tides are predictable and stable. Where tidal generators are used, they produce a steady, reliable stream of electricity.
Placing turbines in tidal streams is complex, because the machines are large and disrupt the tide they are trying to harness. The environmental impact could be severe, depending on the size of the turbine and the site of the tidal stream. Turbines are most effective in shallow water. This produces more energy and allows ships to navigate around the turbines. A tidal generator's turbine blades also turn slowly, which helps marine life avoid getting caught in the system.
The world's first tidal power station was constructed in 2007 at Strangford Lough in Northern Ireland. The turbines are placed in a narrow strait between the Strangford Lough inlet and the Irish Sea. The tide can move at 4 meters (13 feet) per second across the strait.
Barrage
Another type of tidal energy generator uses a large dam called a barrage. With a barrage, water can spill over the top or through turbines in the dam because the dam is low. Barrages can be constructed across tidal rivers, bays, and estuaries.
Turbines inside the barrage harness the power of tides the same way a river dam harnesses the power of a river. The barrage gates are open as the tide rises. At high tide, the barrage gates close, creating a pool, or tidal lagoon. The water is then released through the barrage's turbines, creating energy at a rate that can be controlled by engineers.
The environmental impact of a barrage system can be quite significant. The land in the tidal range is completely disrupted. The change in water level in the tidal lagoon might harm plant and animal life. The salinity inside the tidal lagoon lowers, which changes the organisms that are able to live there. As with dams across rivers, fish are blocked into or out of the tidal lagoon. Turbines move quickly in barrages, and marine animals can be caught in the blades. With their food source limited, birds might find different places to migrate.
A barrage is a much more expensive tidal energy generator than a single turbine. Although there are no fuel costs, barrages involve more construction and more machines. Unlike single turbines, barrages also require constant supervision to adjust power output.
The tidal power plant at the Rance River estuary in Brittany, France, uses a barrage. It was built in 1966 and is still functioning. The plant uses two sources of energy: tidal energy from the English Channel and river current energy from the Rance River. The barrage has led to an increased level of silt in the habitat. Native aquatic plants suffocate in silt, and a flatfish called plaice is now extinct in the area. Other organisms, such as cuttlefish, a relative of squids, now thrive in the Rance estuary. Cuttlefish prefer cloudy, silty ecosystems.
Tidal Lagoon
The final type of tidal energy generator involves the construction of tidal lagoons. A tidal lagoon is a body of ocean water that is partly enclosed by a natural or manmade barrier. Tidal lagoons might also be estuaries and have freshwater emptying into them.
A tidal energy generator using tidal lagoons would function much like a barrage. Unlike barrages, however, tidal lagoons can be constructed along the natural coastline. A tidal lagoon power plant could also generate continuous power. The turbines work as the lagoon is filling and emptying.
The environmental impact of tidal lagoons is minimal. The lagoons can be constructed with natural materials like rock. They would appear as a low breakwater (sea wall) at low tide, and be submerged at high tide. Animals could swim around the structure, and smaller organisms could swim inside it. Large predators like sharks would not be able to penetrate the lagoon, so smaller fish would probably thrive. Birds would likely flock to the area.
But the energy output from generators using tidal lagoons is likely to be low. There are no functioning examples yet. China is constructing a tidal lagoon power plant at the Yalu River, near its border with North Korea. A private company is also planning a small tidal lagoon power plant in Swansea Bay, Wales.
Photograph by James A. Sugar
DTP
Dynamic tidal power (DTP) is one of the newest proposals to harness the power of tides. Using DTP, enormous dams (as long as 50 kilometers (31 miles)) would extend straight from the shore into the open ocean.
having to do with water.
a low dam.
body of water partially surrounded by land, usually with a wide mouth to a larger body of water.
a manmade wall rising from the sea floor that protects a harbor or beach from the force of waves.
outer boundary of a shore.
having to do with the buying and selling of goods and services.
complicated.
to build or erect.
person who uses a good or service.
marine organism (mollusk) related to squid and octopuses.
structure built across a river or other waterway to control the flow of water.
to lower.
having parts or molecules that are packed closely together.
to interrupt.
useful or able to perform a task.
set of physical phenomena associated with the presence and flow of electric charge.
area surrounded by a wall, fence, or other physical boundary.
capacity to do work.
person who plans the building of things, such as structures (construction engineer) or substances (chemical engineer).
strip of the Atlantic Ocean between southeast England and northwest France.
excited.
incident or activity's total effect on the surrounding environment.
very costly.
to try or test an idea.
no longer existing.
material that is able to flow and change shape.
water that is not salty.
material that provides power or energy.
to work or work correctly.
to create or begin.
machine that converts one type of energy to another, such as mechanical energy to electricity.
to promise or confirm.
environment where an organism lives throughout the year or for shorter periods of time.
to control or guide for a specific purpose.
water level that has risen as a result of the moon's gravitational pull on the Earth.
very early stages.
small indentation in a shoreline.
a person or organization that gives money in order to gain a future advantage.
allowed by law.
water level that has dropped as a result of the moon's gravitational pull on the Earth.
having to do with the ocean.
to move from one place or activity to another.
the lowest or least.
to plan and direct the course of a journey.
to push through.
possibility.
industrial facility for the generation of electric energy.
animal that hunts other animals for food.
regular or able to be forecasted.
money earned after production costs and taxes are subtracted.
logical.
energy obtained from sources that are virtually inexhaustible and replenish naturally over small time scales relative to the human life span.
natural substance composed of solid mineral matter.
saltiness.
harsh.
important or impressive.
marine animal (cephalopod) with eight arms and two tentacles.
steady and reliable.
to put underwater.
sudden, strong movement forward.
the science of using tools and complex machines to make human life easier or more profitable.
to develop and be successful.
force that helps create a tide.
machine for turning tidal energy into electricity humans can use.
gravitational pull exerted by one object, such as the sun or moon, that raises tides on another object, such as the Earth.
pool of ocean water that is partially cut off from the ocean by a barrier. Often used as a source of hydroelectric power.
the difference in height between an area's high tide and low tide.
river whose flow is affected by ocean tides.
an ocean current produced by the tide.
rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.
machine that captures the energy of a moving fluid, such as air or water.
kinetic energy produced by the movement of air, able to be converted to mechanical power.
