How does tidal power work?
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There are many different types of renewable energy resources. One source with the biggest potential is tidal energy, which relies on changing tides in the ocean to produce electricity.
But how exactly can you get high tide to power a town?
We’ll explore how tidal energy works, where it’s being used, and what we can expect in the future.
Tidal energy is a form of hydropower that works by harnessing the kinetic energy created from the rise and fall of ocean tides and currents, also called tidal flows, and turns it into usable electricity.
The larger the tidal range, or the height difference between sea level at high and low tide, the more power can be produced.
Tides fluctuate thanks to the gravitational pull of the sun and moon. Tidal power is a clean and renewable energy source - it emits no greenhouse gases as it produces electricity. Tidal power is only practical for large, commercial-scale projects.
Tides hold an incredible amount of energy, so much so that the National Renewable Energy Laboratory has estimated that the ocean has the potential to provide one-third of the electricity needed in the United States.
There are three main ways to harness the energy created by tides and currents in a body of water: tidal turbines, tidal barrages, and tidal fences.
Tidal turbines are very similar to wind turbines, except they are below the water’s surface instead of above or on land. The water’s current pushes the blades of the turbine, which is connected to a generator that creates electricity.
Tidal turbines are able to produce much more electricity than wind power plants, mainly because water is much denser than air. However, water’s high density also means that tidal turbines need to be much stronger than wind turbines, making them more expensive to manufacture.
Tidal turbines are large, but they create relatively little disruption to the ecosystem around them. They could cause collision damage, like wind turbines, however, with marine life, but the blades tend to move slowly so it isn’t that much of a concern. They also emit low level noise, which can impact marine mammals.
Tidal barrages are low-walled dams, usually installed at tidal inlets or estuaries.
Similar to traditional hydroelectric dams, sluice gates are used to create a reservoir on one side of the barrage. The barrage is secured to the sea floor, while the top of the barrage is just slightly above where the water level hits during the highest tide.
Tidal turbines are located towards the bottom of the barrage, inside a tunnel, which allow water to flow through.
Tidal barrages look like traditional hydropower dams. Turbines located along the bottom of the barrage are turned with the incoming and outgoing tides.
During an incoming high tide, water flows over the turbines as the water rises. Then, the water flows back through the turbines as it becomes low tide. The turbines are connected to a generator which produces the electricity.
Tidal barrages are the most efficient way to harness tidal energy, but they’re also the most costly.
They require an entire concrete structure to be built, which can cost a pretty penny. Barrages also have a larger environmental impact on the surrounding ecosystem than tidal fences or turbines.
Because they are essentially an underwater wall, fish and other sea creatures can’t pass through, causing a myriad of effects on the local ecosystem.
A tidal fence is like a hybrid between tidal barrages and tidal turbines.
The vertical tidal fence turnstiles are installed together in a ‘fence-like’ structure, hence the name ‘tidal fence’. Instead of spinning like a propeller, tidal fences spin like a turnstile.
To create electricity, the energy from tidal currents pushes the turnstile blades, which are connected to a generator.
Tidal fences have vertical blades that are pushed by moving water. These vertical turbines are installed together like a fence, but they don’t require the large, concrete structure that tidal barrages do.
Usually, they will be installed in between land masses in things like inlets and fast-moving streams. They are submerged entirely underwater, and have little impact on the surrounding ecosystem.
Tidal power is not a widely used energy source just yet. There are only nine tidal power stations in operation globally.
However, there are more being planned as tidal power technologies become more fine-tuned. Many of the proposed tidal power plants are solely for research purposes, but the number of commercial energy power plants is increasing.
Testing sites for tidal power generation have been popping up in places in order to learn more about how tidal energy systems work. One of the most notable testing sites is in the Bay of Fundy in Canada.
From what we know now, it seems that tidal power holds a lot of potential to help us move away from fossil fuels in the future.
La Rance Tidal Power Station in France is the first tidal power generating station. Image source: Power Technology
The first large scale tidal power system, La Rance Tidal Power Station, opened in 1966 in Brittany, France.
The power is generated by a tidal barrage, which is composed of 24 tidal turbines. It has an installed capacity of 240 megawatts, with an average annual output of around 600 gigawatt hours per year.
That’s enough electricity generation to power over 50,000 American homes for a year.
The Sihwa Lake Tidal Power Station is the largest power station in the world. Image source: International Hydropower Association
The largest tidal power station in the world is the Sihwa Lake Tidal Power Station in South Korea.
The Sihwa Lake tidal project is also a tidal barrage, which made use of an existing seawall that was constructed for flood mitigation. It has an estimated annual generation of 552 gigawatt hours per year.
Although tidal energy generators aren’t widely used, they have a ton of potential. Some experts estimate that tidal stream energy generation could supply more than 150 terawatt hours of energy per year. That’s more energy than the entire United Kingdom uses annually.
Plus, tidal energy generation is predictable. Unlike other renewables like wind energy, we know exactly when the tides will change, and thus know exactly when power will be generated.
Another bonus is that water is so dense, that even if the tidal current speeds are low, tidal turbines can still generate large amounts of power.
The biggest downfalls to tidal power are that it’s expensive. In fact, a tidal energy project in the United Kingdom, called Tidal Lagoon Swansea Bay, was rejected because of cost factors. Plus, it can have a major impact on the surrounding ecosystem.
The good news is, as tidal energy technology continues to improve, the cost of installing tidal power plants will decrease. Check out our article on the pros and cons of tidal power for more information.
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