Waves and Tides

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Wave and tidal energy are renewable energy sources receiving
attention in research and development due to the abundance of the
resource, and the ability to decarbonise. Wave energy is a derivative of
wind energy, where the wind interaction with the water surface over
large distances causes the propagation and growth of waves that
transfer energy across the water surface. Tides are driven by the
gravitational pull from the moon, sun, and other celestial bodies,
resulting in the natural rise and fall of ocean tides, and

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 Wave and Tidal Energy • Waves, driven by the winds, make the
water oscillate in roughly circular
Water in the oceans is constantly in orbits extending to a depth of one half
motion due to waves and tides, and of the wavelength of the wave
energy can be harvested from these (distance between peaks).
kinds of motions. • Tides, related to the gravitational
pull of the Moon and Sun on the
oceans, are like very long-
wavelength waves that can
produce very strong currents in
some coastal areas due to the
geometry of the shoreline.

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In terms of power generation technologies, wave and tidal power
have both similarities and differences. Both refer to the extraction of
kinetic energy from the ocean to generate electricity (again, by
spinning a turbine just as hydroelectric dams or wind farms do), but
the locations of each and the mechanisms that they use for
generating power are slightly different.

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Wave energy projects extract energy from waves on the surface of
the water, or from wave motion a bit deeper (a few 10s of meters) in
the ocean. Surface wave energy technologies capture the kinetic
energy in breaking waves; these provide periodic impulses that spin
a turbine.

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 Tidal Energy Generators

There are currently three different ways to get tidal energy:

• tidal streams,
• barrages, and
• tidal Lagoons/inlets.

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 Tidal Streams
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.
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• Wave and tidal are both proven technologies that can help to offer
predictable renewable energy from the UK’s abundant coastline.
The UK is currently a leader in tidal stream, with world leading
projects operational around the country and a total of 50MW of
developments in the pipeline.
• While currently more expensive than other renewables, tidal
stream is on a cost-reduction journey and could be cheaper than
nuclear by 2035. With the right support, tidal energy could provide
11% of the UK's electricity by 2050.

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 Environmental Implications

• 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.

• 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.
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 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.

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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.

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 Environmental Impacts
• 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.
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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.

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 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.

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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.

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 Environmental impacts
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.

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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.

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 Past and current status of tidal 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.

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 Future perspective
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.

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