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Tidal energy explained

What is tidal energy?

The clue’s in the title – but to silence any doubt, tidal energy, or tidal power, is energy created by the tidal power of the sea.

How was tidal energy discovered?

Unsurprisingly, people cottoned onto tidal energy pretty early on. Tidal-powered dams and waterwheels that grind grain into flour, existed as early as 900AD. While Roman ruins of ancient tidal mills, dating from 700AD have also been found in Europe.

The world’s first commercial plant came later, in 1966 when the gigantic La Rance Tidal Barrage was installed near St. Malo in Brittany. It was groundbreaking at the time – and more than half a century later, it’s still producing 100% clean electricity.

How does tidal energy work?

It’s the surge of ocean water, during both the rise and the fall of the tide that produces the energy. And because it happens twice daily, we have 4 chances to harness its energy. 

Chaucer famously stated that, "Time and tide wait for no man” – so, knowing precisely when and where tide water comes and goes makes tidal energy a truly dependable form of hydropower. It’s predictable. And being a natural daily (and nightly) occurrence, it’s also completely renewable.

Can tidal energy be stored?

It sure can, and as it’s created around the clock, tidal energy will always be available – if we want to be. So far, the 2 main storage options are via pumps or batteries:

Pumped storage

Pumped storage hydropower is the more established system, which pumps water from a lower reservoir up into a higher one. The water stored at height then passes through a turbine on its way back down to the lower reservoir – this creates electricity whenever it’s needed. And because it’s super efficient, it doesn’t waste a drop.

Battery storage

Now that new battery storage projects have been given the green light in the UK, lithium ion batteries (Li-on or LIB), among others, are being explored as tidal energy storage options.

It’s an exploration that’s set to continue as renewable energy demand grows, and as tech firms step up to get a piece of the action. In short, watch this space. We’re going to see a huge variety of batteries being developed.

Where are tidal energy plants located?

You’ll find tidal plants in key locations around the planet. The 5 largest to date are:

  1. South Korea: Sihwa Lake Tidal Power Station

  2. France: La Rance Tidal Power Plant

  3. Wales: Swansea Bay Tidal Lagoon

  4. Scotland: MeyGen Tidal Energy Project

  5. Canada: Annapolis Royal Generating Station

Other tidal plants are based within Alderney, China, India, the Philippines, Russia, the Netherlands and the UK. Oh, and there’s plenty more on the way, as global interest in tidal energy – and funding – amps up.

Although tidal energy can, in theory, be produced anywhere along a coastline, only a small number of places on the planet are suitable for the really large plants. Strong winds and fast tides give eastern shores of the world’s oceans the edge – making both the UK and the Northwest US, hydro hotspots.  

Tidal energy: the pros and cons

Pros

  • Renewable.

  • Predictable (we know the tide times).

  • Long-lasting power plants.

  • Works on a large scale.

  • Zero carbon.

Cons

  • Hydro power can’t be generated everywhere.

  • The transition from existing power sources will take a while.

  • Infrastructure is pricey (it’s hoped costs will come down).

  • Storage batteries need developing (and time is money, for investors).

  • Can disrupt wildlife.

Tidal energy in the UK

We might moan about our weather – but the strong winds and seas off our little island allow us to fully embrace tidal power. Scotland is leading the charge – with enough potential tidal power to generate half the country’s electricity – and you might have clocked in the news recently, the giant tidal lagoon that’s coming soon in Wales.

Can tidal energy replace fossil fuels?

Some say it can, some say it can’t. It’s being debated relentlessly right now in  scientific, political, and public forums.

Professor Mark Jacobson, director of Stanford's atmosphere and energy programme, feel that it can – along with other renewables like wind and solar power. And many researchers who feel the same.

“Both individuals and governments can lead this change. Policymakers don’t usually want to commit to doing something unless there is some reasonable science that can show it is possible,” he says.

“Our findings suggest that the benefits are so great that we should accelerate the transition to wind, water and solar as fast as possible, by retiring fossil-fuel systems early wherever we can.”

On the other hand…

Many say it can’t (or rather won’t) happen because of economic reasons. Lots of governments and big energy companies say that renewables aren’t viable yet. And until they are? Yep, they’ll keep burning fossil fuels.

Tidal energy limitations

Only 40 sites have been chosen around the world so far, as conditions need to be just right before you create a tidal power plant. Also, surging tides happen in a window of around 10 hours out of 24. Or, 40% of the time. So energy storage is vital if we’re going to provide power when the ocean goes quiet.

Another setback? Well there are a couple…

Many areas with great potential for ocean energy, happen to be regions with low population – and weak electricity networks, which could limit how much power gets delivered to the grid – a costly problem to fix.

How efficient is tidal energy?

Tidal energy is 80% efficient when it comes to converting water energy into electricity. Compare that to burning coal (which scores a pretty useless 33% efficiency) and you can see why it’s such a good option.

It even beats wind power – which, according to 'Betz's law', has its limits. One of the reasons tidal energy is more effective than wind power is because water is around 1000 times denser than air. So, when water pushes those turbines, even slowly, it does so with more force, with the full power of the ocean behind it.

But as you can imagine, we humans are never going to rest at 80% efficiency. A lot of work has gone into maximising tidal efficiency.

Oxford University Professor Richard Willden’s research reveals how tidal turbines are best arranged in a 'cluster' (unlike wind turbines) – and perpendicular to (or facing) the direction of the tides. Apparently this jigging around of the turbines can boost the kinetic energy created by more than 20%.

How can tidal energy be improved?

To be honest, it’s about those two little words: ‘new technology’. Tidal energy has all the power we need – it’s harnessing it that needs to be improved.

In 2017, the European Marine Energy Centre (EMEC) took steps in the right direction – producing hydrogen gas using electricity generated from tidal power. A world first.

They achieved this by harnessing tidal energy at their test site in Orkney using prototype energy converters that fed power into an electrolyser. This then used the electricity to separate water (H2O) into both hydrogen (H2) and oxygen (O2).

EMEC’s test site and several others are all busy collecting data to improve the technology, so it shouldn’t be long before tidal energy is really firing on all cylinders.

Can hydropower be used for transportation?

Yes! Neil Kermode, EMEC’s Managing Director says that – using hydrogen – it certainly could.

“One of the most promising uses of hydrogen is as a fuel for transport as it emits no carbon when it’s consumed and, providing it’s generated by clean renewable energy sources, it becomes a carbon neutral fuel source.”

He also said that, “We could see green hydrogen, over time, replace polluting fuels in our cars, vans and ferries.”

Ecosystems and the environment

Hydropower itself doesn’t pollute, but the creation and eventual dismantling of a power plant will. That’s why the onus is on us to weigh up what’s best for the planet in the long term.

Take migrating fish and bird populations as an example. We know that dams and power plants are forcing them to adapt their lives. So in the UK, new sonar systems are tracking them to study the way they relate to tidal power plants.

And that’s not all. There’s concern around the creation of reservoirs, where the flooding of land can harm the immediate environment. Some studies have revealed a reduction in wildlife during the construction of tidal devices. But there’s also evidence of wildlife bouncing back to original numbers once the plants are in operation.

The conclusion?

Tidal energy is consistently proving its worth as an energy source with the potential to change the world for the better.

Sure, it’s not perfect. But with minimal carbon dioxide emissions being released into the atmosphere, hydropower won’t harm the planet anywhere near as much as most energy sources. And that can only be a good thing.