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Tidal Energy and How it Works

What is Tidal Energy, and How Does it Work?

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.1

According to National Geographic, there are currently three different ways to get tidal energy: tidal streams, barrages, and tidal lagoons. The following is taken from the tidal energy encyclopedia post found on the National Geographic website:

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.1

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.1

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.1

Advantages of Tidal Energy

The key benefits of tidal power include the following2:

  • Tides are easily predictable
  • Inexpensive to maintain
  • Reliable and renewable source of energy
  • High energy density than other renewable energy forms
  • It produces no greenhouse gases or other waste
  • Vertical-axis turbines and offshore turbines are inexpensive to build and have less environmental impact
  • Tidal turbines are 80% efficient, which is higher than solar or wind energy generators.
  • Barrages reduce the damage of high tidal surges on the land.

Disadvantages of Tidal Energy

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.1

Some other limitations of tidal power is as follows2:

  • Initial construction cost is very high
  • Formation of silt behind the barrage
  • Effect on animals and plants living near tidal stations
  • Very few suitable sites for constructing barrages
  • Disturbs migration of living creatures in the ocean
  • Water cannot be replenished, and hence dirt gets settled within the coast
  • It produces power for only about 10 h of the day when the tide is moving in and out.

Why Tidal Energy is Important

Tidal energy is a renewable source of electricity which does not result in the emission of gases responsible for global warming or acid rain associated with fossil fuel generated electricity. Use of tidal energy could also decrease the need for nuclear power, with its associated radiation risks.3

How Tidal Energy is Being Used Today

The world’s largest tidal energy project is located in South Korea, called the Sihwa Lake Tidal Power Station. It has an output capacity of 254MW. The world’s oldest and second largest tidal power station is in Brittany, France, called La Rance Tidal Power Plant (240MW).4 There are many more tidal power plants scattered around the world, and we are excited to see this type of renewable energy grow.

References

1National Geographic. (2019). Tidal energy. Retrieved from nationalgeographic.org: https://www.nationalgeographic.org/encyclopedia/tidal-energy/

2Walker, Kris. (January 22, 2013). Is Tidal Power a Viable Source of Energy? Retrieved from azocleantech.com: https://www.azocleantech.com/article.aspx?ArticleID=350

3Ocean Energy Council (2018). Tidal Energy. Retrieved from oceanenergycouncil.com: oceanenergycouncil.com/ocean-energy/tidal-energy/

4(April 10, 2014). Tidal giants – the world’s five biggest tidal power plants. Retrieved from power-technology.com: https://www.power-technology.com/features/featuretidal-giants-the-worlds-five-biggest-tidal-power-plants-4211218/