What is tidal power, why is it important and when will we see more of it?
We’ve been drawing power from the tides since the Dark Ages, yet this highly predictable form of renewable energy barely gets a mention in any serious discussion about the energy transition. Let’s dig into why this is and whether that’s set to change. First up, here’s a quick overview of the technology.
A tidal power explainer
Tidal power takes advantage of the regular movement of tides in areas where either the current is strong or the tidal range (the difference between high and low tides) is significant. Take a look at this map to see all the global tidal hotspots:
In places like the Mediterranean, where the water is enclosed past the straits of Gibraltar, tides are low and the sea is calm. On the west coast of Britain, by comparison, the full might of the Atlantic forces itself against land and you get some of the highest tides in the world. This effect is heightened in specific areas like estuaries and narrow sea passages, where tides are squeezed between two stretches of shoreline. The Severn Estuary between England and Wales, for example, boasts the second-highest tidal range in the world and produces tidal surges large enough to surf right up the river on!
Once you’ve found your tidal hotspot, you then need to find the best way to harness all that power.
Tidal technologies
Whether you’re looking to take advantage of the tidal range or tidal currents, there’s a technology already in operation or being developed as a pilot project. Here’s a quick overview of the most common forms.
Tidal barrages
These effectively create a physical barrier across an estuary to trap water on one side, to be released through turbine-filled sluicegates at the other end to produce power.
The oldest working example of this is a tidal barrage across the Rance river in France. Built in the 60s it is still in operation today and generates some of the cheapest electricity in Europe. A similar barrage in South Korea was built on an existing dam to remedy an issue of water flow and pollution but there aren’t a lot of new barrages in development because of their impact on local ecosystems.
Tidal lagoons
Projects like the Swansea Bay lagoon are being developed to overcome the environmental impact of barrages.
By enclosing a bay area, rather than bisecting a waterway, the ecological impact can be kept to a minimum, waterways remain open and added amenities can be included in the design of the landscape, encouraging a multi-use approach.
Both barrages and lagoons take advantage of high tide differentials, so can only be deployed in large bays and estuaries where the range is high enough. Where these features aren’t present there’s still an opportunity to generate power if the tidal currents are strong enough.
Tidal stream generators
In places where water is squeezed between two landmasses and the seafloor conditions are right, the force of water can be harnessed by freestanding bidirectional turbines sitting on the seabed in the direction of the current flow.
The world’s largest tidal power project is currently under phased construction in the Pentland Firth, a treacherous sea strait separating the Scottish mainland from the Orkney Islands. Scores of heavy-duty 24-metre high turbines are being submerged in a 2-mile stretch where the currents are strongest. When complete, the power station will have a peak capacity of 384MW, enough to power 175,000 homes.
Smaller versions of these turbine types are being tested and deployed in New York Harbour. At 1MW capacity, these projects are much smaller in scale yet can be installed in busy shipping lanes next to built-up urban areas.
Floating barrages
The final technology I’ll mention in this post is the most adaptable, designed to emulate an outboard motor boat’s rotor blades and could be deployed in a huge range of waterways.
The Grand Passage floating tidal energy array consists of six turbines hung from a platform sitting in one of the world’s fastest flowing currents in the Bay of Fundy. Launched in early 2021, the current platform connects to the mainland Canadian power grid using undersea cables and, when combined with a further two platforms, will generate enough electricity to power 3,000 homes.
Why is tidal power so important?
Apart from developing some awesome turbine technology, what’s so great about tidal power? Don’t we have enough renewables already with wind and solar?
As predictable as the tides
Firstly, it’s the regularity of tides that makes this form of renewable energy so attractive. Tides move in an extremely predictable pattern, unaffected by what’s going on above the water. Whereas wind and solar power generation are intermittent, underwater turbines can make use of the 4 tidal differentials a day to provide a constant pattern of power to the grid. This presents a real opportunity to replace baseload power currently provided by fossil fuels.
As old as time
Longevity is the next factor in tidal power’s favour. Solar panels and wind turbines have an expected lifespan of 25 years; gas-powered turbines wear out at around 30 years; the average nuclear plant lasts for 40 years and coal-fired units top this list at an average of 45 years.
The world’s oldest tidal power station is fast approaching 60 years of operation, with no signs of slowing down. The latest tidal power plant to gain approval has an estimated lifespan of 120 years.
Cheap at twice the price
Finally, the levelized cost of energy (LCOE) for tidal power plants, compared to their fossil-fuel counterparts, is really low: $40/MWh compared to $124/MWh for US combustion turbines. So while the upfront cost of these projects is high, the payback period is so long it more than makes up for this.
Tidal power is awesome. Why aren’t we using more of it?
So, let me get this straight. We have a cheap form of predictable energy that can replace fossil-fueled baseload power generation and last over a century.
What the hell is stopping us?
Alberto Boretti, a mechanical engineer from Saudi Arabia, sums the problem up perfectly:
“These technologies are still in their infancy, as apart from their theoretical performance, every other aspect of a submerged power plant operation needs further developments.”
— Trends in power development
Scaling up new forms of technology requires a huge amount of R&D, supply chain evolution, project financing and economies of scale to kick in. It took decades for solar power to gain momentum and tidal power just isn’t at the same stage in its development trajectory.
To provide the momentum required for a tidal power revolution, there needs to be enthusiastic support for projects at the local and national stages. Local people, regional authorities, national politicians and global leaders need to understand the potential of tidal energy and get behind it as the awesome renewable force it is!
Tidal power is the unloved, overlooked child of the energy transition.
Both innovative pilot projects and well established 20th-century power plants provide working examples of what’s possible and prove that tidal power is a booming new industry waiting for its time to come.
