A guide to tidal energy: how does it work, and what are the advantages?
By Aimee Tweedale Friday 15 January 2021
Here in the UK, we might moan about our weather – but there’s a big positive to life on our blustery shores. Not only does being the windiest country in Europe mean we can take advantage of wind power, but it means we can capture the energy of our tides, too.
Tidal power is a giant on the horizon of renewable energy. Here’s everything you need to know about how it works, the pros and cons, and what the future of tidal energy looks like.
What is tidal energy or tidal power?
The clue’s in the title – but to silence any doubt, tidal energy, or tidal power, is energy created by the tides of the sea.
Like other forms of renewable energy, like wind and solar, it involves using equipment to capture one of Earth’s natural energy sources. In this case, barrages or lagoons (more on those later) are used to catch the power of the waves. That power is then used to generate electricity, which is then sent to the grid – and eventually, your home!
The idea of using tidal power to turn wheels and grind grains dates back as far as the Romans. More recently, the very first barrage designed to capture tidal energy and generate electricity was built in France in the 1960s1.
Compared to wind and solar energy, tidal energy has yet to be adopted in a major way. There aren’t many tidal power plants, because they’re expensive to build (there are other drawbacks, too, which we’ll explore later in this guide). But with the government predicting it has the potential to deliver 20% of the UK’s energy needs2, tidal energy’s expected to surge over the coming years (pun intended).
Want to learn more about renewable electricity? Read our guide to different types of green energy, and where it comes from.
How does tidal energy work?
The natural surge of ocean water, during both the rise and the fall of the tide, produces energy. And because it happens twice daily, we have 4 chances to harness that energy, each and every day.
How is it harnessed? There are 3 main methods:
Most tidal energy is generated in tidal streams.
A tidal stream is a fast-flowing current created by the tide. To capture its power, turbines are placed on the ocean floor. Turbines are like wheels, or rotors with blades, which are pushed around by the movement of water. They work similarly to wind turbines.
Placing these turbines on the ocean floor can be really difficult, because they’re usually really big. In fact, their size can actually disrupt the tides – which can defeat the point of putting them down there! They can also potentially have an impact on marine life, and on ships.
A tidal barrage is like a huge dam that’s placed in the ocean to capture tidal energy. Water flows through tunnels inside the dam. When the tide goes in and out, it pushes the turbines hidden inside these tunnels.
Like tidal streams, barrages can also have a big impact on the environment around them, as they create an area that’s cut off from the rest of the ocean. This could trap fish and other sea life, along with sewage.
There’s a tidal power plant that uses barrages in Brittany, France, where it’s been successfully harnessing renewable energy since 1966.
Tidal lagoons work in a similar way to barrages. They also capture part of the ocean inside a man-made structure, and use its energy to move turbines. The turbines spin as the lagoon fills up with water, and then empties out.
Lagoons are constructed a bit differently to barrages. A barrage cuts across an estuary in a straight line, like a dam. But a tidal lagoon is usually built along the natural coastline, and can be constructed to minimise the impact on local wildlife.
Is tidal energy renewable?
Yes! Tidal energy is a renewable source of energy, because it comes from the natural rise and fall of the ocean – a resource we won’t run out of.
What are the advantages and disadvantages of tidal energy?
Advantages of tidal energy
It’s green: as we mentioned above, tidal energy is renewable – because we’ll never run out of the natural power of the sea! It also doesn’t emit any carbon.
The tides are predictable: unlike the wind and sun, the power of the tide is predictable – so much so, you could practically set your watch by it. We know the cycles that the tides follow, so it’s easy to guess how much energy a tidal power plant will generate in a day.
Tidal power plants last a long time: the equipment used to capture tidal power is built to last around 4 times longer than wind and solar farms. Concrete tidal barrages can have lifespans of 100 years3.
High power: because water is so dense, tidal power plants can generate a lot of energy even at low speeds. An underwater turbine can generate energy at 2.2mph, while a wind turbine would need speeds of 7-9mph to start generating power4.
Disadvantages of tidal energy
The cost: building tidal power plants is currently pretty expensive. This is because they need to be incredibly sturdy to withstand the force of the sea. Tidal barrages are usually built from concrete, for example, which makes the upfront cost high.
Effects on the environment: tidal power plants aren’t always good for the environment around them, even though the energy they produce is environmentally-friendly. Fish and other critters can get caught in the turbines, and the barrages can prevent sea life from migrating. It’s also thought that the electromagnetic emissions of some power plants could disrupt underwater life.
Gaps between the tides: tidal power is not constant. We know that the tide goes in and out twice a day. This means there’s only about 10 hours per day when power can be generated by the sea. So, we need large-scale battery energy storage to make the most of tidal power.
Where are tidal energy plants located around the world?
There are still fairly few tidal power plants around the world. This is because they’re expensive to build – plus they work better in some countries than others (mainly small countries with lots of coastline). The UK has the potential to be a hydro hotspot, because of its big coastline, and the fact that strong winds and fast tides give the eastern shores of the world’s oceans the edge.
The biggest tidal energy plant in the world is the Sihwa Lake Tidal Power Station in South Korea, which opened in 2011.
The 5 largest tidal power stations to date are:
South Korea: Sihwa Lake Tidal Power Station
France: La Rance Tidal Power Plant
Wales: Swansea Bay Tidal Lagoon
Scotland: MeyGen Tidal Energy Project
Canada: Annapolis Royal Generating Station
Other tidal plants are based within Alderney, China, India, the Philippines, Russia, the Netherlands and the UK. And there’s likely more on the way, as global interest in tidal energy – and funding – amps up.
How much electricity in the UK is generated using tidal energy?
While the goal is to generate 20% of the UK’s power using the tides, right now, we have enough plants in place to generate around 12%5.
The UK is the ideal place for tidal energy: our island is small, windy, and has a lot of coastline. The weather in the Scottish Isles in particular creates the right conditions for the largest production of tidal power in the UK. All we need to do now is build the power stations that can make the most of it.
What is the future of tidal energy?
Tidal energy is still in its infancy, but it has the potential to make a huge impact on the world. You can see how important it’s poised to become by how much it’s worth: valued at $487million in 2014, experts expect the tidal energy market to be worth $11.3billion by 2024.
Can tidal energy replace fossil fuels? Not alone it can’t – but with the combined power of the wind, sun, and tides, and with dedicated energy storage systems, we could make our way to a renewable future in the UK.
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Sources and references
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7 OVO Energy's Green Gas is made up of 15% green gas, with the remaining 85% offset to make your gas carbon-neutral. As of 31st July 2020, the proportion of biogas offered vs. the amount offset was higher than all other providers who share details of their green gas offering, except Green Energy UK - and that's something we're pretty proud of. The green gas we sell is backed by renewable certificates (Renewable Gas Guarantees of Origin (RGGOs)). See here for details on Renewable Gas Guarantees of Origin and how these work. We offset the remaining emissions by supporting UN REDD+ carbon reduction projects that are certified to the Verified Carbon Standard.