Tidal Energy

How Does Tidal Energy Work?

By April 24, 2021No Comments
how does tidal energy work

How Does Tidal Energy Work?

Solar and wind have been in the spotlight for many years now touted as the future of renewable energy. However, there is a more energy efficient and predictable source of green power nobody talks about, tidal energy. Tidal energy provides a relatively constant source of power from the tides and oceans compared to other sources of renewable energy such as solar energy, geothermal energy, and wind energy. Although combined gravitational forces of the sun, moon and the earth help produce the tides, the moon’s strength is the most relied upon for this renewable energy. So, how does tidal energy work?

What Causes Tidal Energy?

It is the presence of both the sun and the moon that cause the tides. The moon is responsible for around 2/3 of it only because it is closer to the earth. Their gravitational forces make tides to go out and go in. There are characterized by a bulge(s) on planet Earth. A bulge on planet Earth means another object (moon or sun) is pulling the Earth towards it, creating a high tide. For example, the moon located right above us creates a hide tide.

In other words, the gravitational forces exerted by the sun and the moon on a specific part of the ocean pull water from elsewhere and cause a rise in water (a rise in the tides). When this happens, there will be a drop in water levels in other parts of the ocean.

When the earth rotates, there is a change in the tides. As a result, there are generally two high tides and two low tides each day. This means it takes 12 hours and 25 minutes for the high tide to go in and go out. Conversely, it takes 12 hours and 25 minutes for the low tide to go in and out.

The change in tides produces a natural form of kinetic energy, which can be used to generate electricity. This renewable source of energy can help reduce carbon footprint and decrease the need for coal-burning power plants thus cutting down on emissions.

diagram of tidal turbines and tidal barrage

Diagram of Tidal Turbines (left) and Tidal Barrage (right).

How Does Tidal Energy Work? – Similarities to Wind Turbines

The way tidal energy works is much like the wind turbine but under water. This means tidal energy uses blades, rotor, shaft, (gearbox) and a generator, which ultimately produces electricity.

The tidal strength determines how many times a minute the blades will rotate.  Every movement of the water (tides) results in electricity generation. The larger the tidal range, the more usable electricity will be harnessed.

It is estimated that tidal energy can power turbines between 18 and 22 hours a day thus making it one of the most reliable renewable sources of power.

How Does Tidal Energy Work? – Tidal Technology

There are three types of tidal technology to produce electricity: Tidal Turbine, Tidal Barrage, and Tidal Fence.

Let’s explore how each of them works:

Tidal Turbine

Tidal turbines are quite similar to the wind turbines, with the exception that tidal turbines are installed underwater. The mechanism remains the same, though. The blades are connected to a generator through a shaft to produce energy. Each time the tidal waves push or pull the blades, the shaft rotates and the generator produces energy.

Although large, the blades move slowly thus keeping disruption to the ecosystem around them on the low side. Also, there is no concern for noise pollution with this technology. Some tidal turbines have gearboxes to step up rotation for power generation. However, manufacturers are now trying to do without them to reduce the costs.

Tidal Barrages

Tidal barrages bear a close resemblance to the traditional hydropower dams, although the barrages are bigger. The turbines are positioned at the bottom of the barrages. Whenever tides come and go, the turbines turn and produce energy.

Tidal barrages are constructed using concrete, which makes it costly. Also, with the concrete structure, marine life can be affected. For example, it may not be impossible for marine life to pass through the structure.

They are constructed across tidal rivers, estuaries, and bays. The turbine functions much like a river dam does when harnessing power. Whenever the water level on one side of the tidal barrage is higher than the water level on the other side, this creates an imbalance. In other words, there is a pressure difference between the two sides. For example, when there is a rise in the tide, the barrage gate opens to allow water to flow through a narrow opening, where the turbine is located.

On the downside though, with the gate opening and closing, there is a possibility of marine life getting trapped. And since turbines in the barrage move faster than the ones in the tidal turbine, there is a possibility of harming marine life.

In terms of construction, barrages cost a lot more than tidal turbines. They require constant supervision if the power output is to be maintained.

Tidal Fence

The tidal fence technology is a cross between the tidal turbine and the tidal barrage. A fence-like structure is constructed to generate energy. They spin like a turnstile as opposed to a propeller. The turnstile blades are vertical and each time they are pushed or pulled by moving water, they help generate electricity through a generator connected to the system. The vertical-axis wind turbine works on the same principle.

This technology has little impact on the surrounding ecosystem. It is not completely blocked off as for the tidal barrages and animals can still swim past it. However, there is a question mark over larger animals and what impact this has on them. it is typically installed in-between landmasses where water flows faster. It is also constructed in inlets and fast-moving streams. The turnstiles are completely immersed in the water.

How Does Tidal Energy Work? Advantages and Disadvantages of Tidal Energy

Advantages

  • It is green energy thus limiting the carbon footprint.
  • Tides are easily predictable thus promising reliable energy generation. It is easy to follow tide cycles to produce energy.
  • It can produce plenty of energy thanks to high water density compared to wind density.
  • The barrages can help reduce the damage of high tidal surges on the land. Therefore, it can serve as a flood barrier.
  • The equipment and facilities have a longer lifespan compared to those of other renewable technologies.
  • Although the initial cost is high, tidal energy is cost-competitive with a reliable generation of energy in the long term (For example, the La Rance tidal barrage, which has been producing electricity since 1966).
  • It is capable of producing more energy than other renewable energy sources such as the wind or the sun.

Disadvantages

  • The initial cost is high.
  • Negative impact on plants and animals near the tidal structures.
  • The barrages may prevent migration of marine life.
  • Not entirely efficient as tidal surges happen twice a day. However, this can be said about other green energy sources. The sun does not shine all day and the wind does not blow everyday.
  • With a downtime of about 10 hours, when there are no tides, a need for installing storage systems further makes this expensive.
  • Silt production (tidal barrage) can affect marine life.

 

Is Tidal Energy Renewable?

Tidal energy is seen as completely renewable energy with a plenty of potential. And, considering that its production does not leave a carbon footprint, tidal energy is considered to be one of the cleanest forms of energy.

Notable Tidal Power Stations Around the World

Thanks to the massive size of the oceans, tidal power has a great potential for future power and electricity generation.

Notable tidal power stations include:

  • The Sihwa Lake Tidal Power Station (South Korea-254MW) is by far the biggest in the world and it was opened in August 2011. It has an annual generation capacity of 552.7GWh.
  • La Rance Tidal Power Plant (France-240MW) came into operation in 1966 thus making it the world’s oldest and second biggest tidal power station. It has an annual generation capacity of 540GWh.
  • Swansea Bay Tidal Lagoon, (United Kingdom-240MW) has an estimated annual power generation capacity of 400GWh.
  • MeyGen Tidal Energy Project (Scotland-86MW) is expected to reach the capacity of 398MW.
  • Annapolis Royal Generating Station (Canada-20MW) has an annual generation capacity of 50GWh.