Raphael Thys
Photo by Johannes Plenio on Unsplash
Here’s a question: What is the world’s cleanest energy? The answer is actually quite shocking. It isn’t solar, which is rated at 48g of life-cycle carbon dioxide emissions per kWh (g/kWh), though that is much better than coal at 820 g/kWh. It isn’t wind or nuclear either, which both sit at 12 g/kWh. No, the cleanest energy in the world blows them all out of the water at only 1.8 g/kWh. That’s 26 times lower carbon emissions than solar, which is currently leading the renewable revolution! What’s more, this remarkable energy source isn’t based on some far-off sci-fi technology. Instead, it is just simple tidal power, which, thanks to a recent breakthrough from Scotland, could be on the verge of breaking into the mainstream and taking its rightful place as a planet-saving technology. But why hasn’t tidal power been more widely adopted? And how can this breakthrough change that?
Let’s first go over the basics. What on Earth is tidal power?
As the Moon and Sun pass overhead, their gravity pulls on the Earth and its oceans, which causes the oceans to rise and fall twice a day. In some places, this causes ocean water to flow gently, but in other places, it causes a torrent. All tidal power does is place a turbine underwater where the tidal flow is particularly strong and produce electricity in the same way as a wind turbine does.
But, if that is the case, then how can tidal power have a substantially lower carbon footprint than wind power? Well, it has all to do with the weight and viscosity of water.
The blades of a turbine are far more efficient in water than in air. This is because water’s viscosity and weight allow higher pressure differentials to be built over their surface without creating too much energy-wasting turbulence, creating more force over the blades. As such, a tidal power turbine is a whopping 80% efficient, whereas a wind turbine is at most 40% efficient. This allows tidal power to pull far more energy from the tides than wind turbines can from the wind.
However, water weighs nearly a thousand times more than air. The equation for kinetic energy is K.E. = 1/2 m v², which means water can carry a thousand times the kinetic energy of air for the same flow rate! This means a typical 2 mph tide will contain the same kinetic energy as 2,000 mph winds (for the same flow measured in volume per minute).
These factors combined mean that a single tidal turbine can produce far more power than a single wind turbine. Therefore, less carbon-intensive mining, manufacturing, or construction needs to take place, giving tidal power its brilliantly low carbon emissions. This is further aided by the fact that the energy produced by tidal is consistent and predictable. In other words, it requires far smaller grid batteries to meet demand than wind or solar, which can lag behind energy demand for days at a time. These batteries are carbon-intensive and environmentally dubious to produce, so using fewer of them has a massive overall impact on tidal’s carbon footprint.
Despite this, tidal power has faced some significant challenges.
You see, while the turbines are far more efficient and powerful, they are also hideously expensive, so much so that tidal power costs up to $280 per MWh. In comparison, wind energy costs as little as $26 per MWh. This expense is necessary because these turbines need to be far tougher than wind turbines to survive years in the harsh marine environment. But it isn’t just cost; there have been plenty of worries about environmental impact. These underwater turbines can negatively impact animal and plant life under the waves. They can even change the environment around them, as the slower speed of the tides downstream of them causes the water to drop any sediment it is carrying, causing silt to build up on the sea floor. Both of these factors (combined with how hard it is to engineer instruments to last for years underwater) made tidal power incredibly unreliable, as turbines could be regularly taken out of commission.
These issues must be fully ironed out before tidal power can be rolled out worldwide as a genuine energy solution. But remember, tidal power is location-specific, and there are not many places where the sea is shallow enough and the tide runs fast enough for it to function properly. This means that few people have been willing to pour money into developing tidal power, as it has an inherently limited market reach.
But luckily, SAE has been mad enough to develop this astonishing technology. Their MeyGen experimental tidal power farm in Scotland is a world leader. It became fully operational in 2017 and has been delivering power to the grid via its three 1.5 MW turbines ever since. However, it doesn’t end there, as they plan to expand this site to a whopping 312 MW over the coming years. This site aims to develop tidal power, demonstrate to the world how good it can be, and deliver genuine power to nearby towns.
This is where the breakthrough comes in. You see, recently, MeyGen tipped over 50 Wh of total energy production, setting a new record for tidal power miles ahead of anyone else. For some idea of how much energy that is, it can power 17,241 average UK homes for a year! That is a lot of energy from only three turbines.
This shows that they have ironed out many of the problems, like reliability and ecological impact, as they wouldn’t have been able to stay operational if they hadn’t.
What’s more, it turns out the price issue isn’t as bad as many thought it would be. For example, MeyGen sells its energy for £178.54/MWh. Now, admittedly, that is a lot of money, but it is paying for the development and expansion of the site. What’s more, unlike wind energy, these turbines have no off-the-shelf parts. They are all practically custom-made. So if tidal were to expand, economies of scale would come into play, and the price per turbine would drop. But compared to other tidal projects, MeyGen is about half the price per MWh, showing just how far they have developed this technology. It might take a few years, but it seems certain that tidal power will soon cost about the same as nuclear power.
But how much of an impact can tidal energy really have? After all, it will always be limited by the locations that can use it. Well, the EU estimates that the global potential for tidal energy is 800 TWh per year. For some comparison, the US uses around 3,900 TWh per year. So, it’s unlikely to become anyone’s primary source of energy, but at the same time, it can still make a difference. And if we can harness that 800 TWh rather than building 800 TWh of solar power, we will save 46,200,000 kg of carbon dioxide emissions per year. When you look at it like that, you can see that tidal energy can still significantly impact our fight to save the planet. Ultimately, it is incredible that SAE is on the path to finally unlocking it.
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