• tidal energy
    Tidewater swirls into a turbine.

    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.

    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.

  • Term Part of Speech Definition Encyclopedic Entry
    aquatic Adjective

    having to do with water.

    barrage Noun

    a low dam.

    bay Noun

    body of water partially surrounded by land, usually with a wide mouth to a larger body of water.

    Encyclopedic Entry: bay
    border Noun

    natural or artificial line separating two pieces of land.

    Encyclopedic Entry: border
    breakwater Noun

    a manmade wall rising from the sea floor that protects a harbor or beach from the force of waves.

    coastline Noun

    outer boundary of a shore.

    commercial Adjective

    having to do with the buying and selling of goods and services.

    complex Adjective

    complicated.

    construct Verb

    to build or erect.

    consumer Noun

    person who uses a good or service.

    current Noun

    steady, predictable flow of fluid within a larger body of that fluid.

    Encyclopedic Entry: current
    cuttlefish Noun

    marine organism (mollusk) related to squid and octopuses.

    dam Noun

    structure built across a river or other waterway to control the flow of water.

    decrease Verb

    to lower.

    dense Adjective

    having parts or molecules that are packed closely together.

    disrupt Verb

    to interrupt.

    ecosystem Noun

    community and interactions of living and nonliving things in an area.

    Encyclopedic Entry: ecosystem
    effective Adjective

    useful or able to perform a task.

    electricity Noun

    set of physical phenomena associated with the presence and flow of electric charge.

    enclosure Noun

    area surrounded by a wall, fence, or other physical boundary.

    energy Noun

    capacity to do work.

    engineer Noun

    person who plans the building of things, such as structures (construction engineer) or substances (chemical engineer).

    English Channel Noun

    strip of the Atlantic Ocean between southeast England and northwest France.

    enthusiastic Adjective

    excited.

    environmental impact Noun

    incident or activity's total effect on the surrounding environment.

    estuary Noun

    mouth of a river where the river's current meets the sea's tide.

    Encyclopedic Entry: estuary
    expensive Adjective

    very costly.

    experiment Verb

    to try or test an idea.

    extinct Adjective

    no longer existing.

    fluid Noun

    material that is able to flow and change shape.

    freshwater Noun

    water that is not salty.

    fuel Noun

    material that provides power or energy.

    function Verb

    to work or work correctly.

    generate Verb

    to create or begin.

    generator Noun

    machine that converts one type of energy to another, such as mechanical energy to electricity.

    guarantee Verb

    to promise or confirm.

    habitat Noun

    environment where an organism lives throughout the year or for shorter periods of time.

    Encyclopedic Entry: habitat
    harness Verb

    to control or guide for a specific purpose.

    high tide Noun

    water level that has risen as a result of the moon's gravitational pull on the Earth.

    infancy Noun

    very early stages.

    inlet Noun

    small indentation in a shoreline.

    investor Noun

    a person or organization that gives money in order to gain a future advantage.

    legal Adjective

    allowed by law.

    low tide Noun

    water level that has dropped as a result of the moon's gravitational pull on the Earth.

    marine Adjective

    having to do with the ocean.

    migrate Verb

    to move from one place or activity to another.

    minimal Adjective

    the lowest or least.

    navigate Verb

    to plan and direct the course of a journey.

    ocean Noun

    large body of salt water that covers most of the Earth.

    Encyclopedic Entry: ocean
    penetrate Verb

    to push through.

    potential Noun

    possibility.

    power plant Noun

    industrial facility for the generation of electric energy.

    predator Noun

    animal that hunts other animals for food.

    predictable Adjective

    regular or able to be forecasted.

    profit Noun

    money earned after production costs and taxes are subtracted.

    reasonable Adjective

    logical.

    renewable energy Noun

    energy obtained from sources that are virtually inexhaustible and replenish naturally over small time scales relative to the human life span.

    rock Noun

    natural substance composed of solid mineral matter.

    salinity Noun

    saltiness.

    severe Adjective

    harsh.

    significant Adjective

    important or impressive.

    silt Noun

    small sediment particles.

    Encyclopedic Entry: silt
    squid Noun

    marine animal (cephalopod) with eight arms and two tentacles.

    stable Adjective

    steady and reliable.

    strait Noun

    narrow passage of water that connects two larger bodies of water.

    Encyclopedic Entry: strait
    submerge Verb

    to put underwater.

    surge noun, verb

    sudden, strong movement forward.

    technology Noun

    the science of using tools and complex machines to make human life easier or more profitable.

    thrive Verb

    to develop and be successful.

    tidal constituent Noun

    force that helps create a tide.

    tidal energy Noun

    energy produced as ocean waters surge in and out with tides.

    Encyclopedic Entry: tidal energy
    tidal energy generator Noun

    machine for turning tidal energy into electricity humans can use.

    tidal force Noun

    gravitational pull exerted by one object, such as the sun or moon, that raises tides on another object, such as the Earth.

    tidal lagoon Noun

    pool of ocean water that is partially cut off from the ocean by a barrier. Often used as a source of hydroelectric power.

    tidal range Noun

    the difference in height between an area's high tide and low tide.

    tidal river Noun

    river whose flow is affected by ocean tides.

    tidal stream Noun

    an ocean current produced by the tide.

    tide Noun

    rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.

    Encyclopedic Entry: tide
    turbine Noun

    machine that captures the energy of a moving fluid, such as air or water.

    wind energy Noun

    energy produced by the movement of air, and converted into electricity.

Tell us what you think