As predictable as the sun rising and setting every day, tides will always go in and out. This unerring twice-daily rhythm has the potential to generate 313 GW globally each year, yet there are only a handful of viable projects harnessing this great force around the world. Why is that?
Let’s take a closer look at some of these projects to find out.
First up, the grandmother of them all.
La Grand-Mère de la mer
La Rance Tidal Power Plant
Location: Brittany, France
Operational since: 1966
Peak capacity: 240MW
Annual generation capacity: 540GWh
Enough to power: 130,000 homes
Built right across the mouth of the Rance river estuary in the early ‘60s, this tidal barrage has an unbroken operational history spanning seven decades and generates some of the cheapest power in Europe.
Constructing the barrage involved damming the entire river for several years while the intricate engineering work took place. Here’s a wonderful archival film showing parts of the work, including the installation of one of the 24 ginormous reversible turbines that are still in operation today:
EDF, la construction de l'usine marémotrice de la Rance
Dans les années 1960, EDF lance la construction de l'usine marémotrice de La Rance, en Bretagne, est lancée. Cette…
While the project has more than paid for itself and scores points for longevity, La Rance’s environmental record is less than exemplary. Studies have shown that ecological damage incurred during the construction phase of the project still affects the river today, with a depleted ecosystem existing in a fragile state.
A combination of eye-wateringly high upfront costs, complex stakeholder needs and increasingly rigorous environmental impact assessments make these large-scale infrastructure projects hard to push past the planning phase.
Unless it’s a case of cake or death, that is…
Snatched from the jaws of death
Sihwa Lake tidal power station
Location: Gyeonggi Bay, South Korea
Operational since: 2011
Planned capacity: 254MW
Annual generation capacity: 553GWh
Despite being the largest tidal barrage in the world, the Sihwa Lake power station came about as an opportunistic afterthought.
Looking to secure agricultural water and reclaim land next to three large coastal cities in South Korea, the authorities built a giant freshwater lake by sealing off a sea inlet. What they unfortunately overlooked was that if you create an inland lake right next to polluting industrial sites, there’s nowhere for industrial run-off to go, except into the now not-so-fresh water.
Rapidly dubbed The Lake of Death, Sihwa became an unusable polluted sewer, until the authorities opened a sluicegate in the reservoir wall to let the sea back in.
Technology case study: Sihwa Lake tidal power station
The west coast of South Korea, with its winding rias, many-sized inlets and wide tidal range, is a rich repository of…
Flustered civil servants looked to the South Korean governmental water authority for a solution to this rather embarrassing predicament. Their response was to suggest a tidal power barrage, allowing 60 billion tons of seawater to circulate through the system annually to flush out all the nasties and produce a staggering amount of electricity in the process.
The reintroduction of seawater into the lake has restored local ecosystems, while two eco-parks have been integrated into the power station’s design. The success of Sihwa has spawned further projects that look to harness powerful tides in the Yellow Sea and a nascent tidal power industry in South Korea looks set to take off.
While tidal barrages look like heavy hitters, there’s a new kid in town taking advantage of advanced engineering and crazy currents to build the biggest tidal power project yet.
Bring out the big guns
MeyGen Tidal Power Project
Location: Pentland Firth, Scotland
Operational since: 2016
Planned capacity: 398MW
Enough to power: 175,000 homes
The Pentland Firth, a narrow strait dividing the Scottish mainland from the Orkney Islands, is dark, stormy and dangerous, experiencing some of the fastest tidal streams in the world. While this presents challenges to sailors, it presents opportunities for tidal power production.
The MeyGen project, when complete, will be the largest tidal energy project in the world, boasting a peak capacity of 398MW. With the initial stages of the project underway, the tidal turbines are being tested, improved, and just seem to be getting bigger!
While the basic principle of using a bidirectional turbine to harness tidal power is the same, these SIMEC Atlantis machines are generations beyond La Rance in terms of power and efficiency.
They stand unanchored to the seafloor on extremely heavy platforms in water at least 30 metres deep. That minimum depth is necessary for clearance above, as each unit stands at 24 metres high at the top of the turbine blade’s rotation.
Now, while these bad boys look huge, when you compare the rotor blade size and speed to onshore wind turbines (9 metres vs 40 metres and 9mph vs 40mph), they produce the same amount of electricity from a smaller area at slower speeds. This is good news for both marine ecosystems and the lifespan of each turbine unit.
MeyGen Tidal Power Project, Pentland Firth
The total capacity of the project is planned to be increased to 252MW and 398MW respectively through MeyGen Phase 2 and…
While this is an incredibly exciting project in terms of its scale, there are only so many places in the world where this can be replicated. What would a tidal project look like in a city with complex planning regulations and a shallower seafloor?
Cosmopolitan / bijou
Roosevelt Island tidal energy (RITE) project
Location: East River, New York City, USA
Operational since: 2012
Planned capacity: 1MW
Annual generation capacity: 2.4GWh
As the Hudson River disgorges freshwater into the East River, it meets the saltwater pushback from the Atlantic. Tides trapped between the banks of Manhatten and Brooklyn are further constrained by the shallow riverbed and the bulk of Roosevelt Island, providing ideal conditions for tidal power generation.
Verdant Power has been testing turbine designs at this project site since 2002, with the fifth generation now installed. You can see from the image below that while they are far smaller than the Simec behemoths churning under the Pentland Firth, the design principles are the same:
This is the first project of its kind in the States to connect directly to the grid and so far, so good as a proof of concept goes. Crucially, the Federal Energy Regulatory Commission (FERC) approved Verdant’s pilot license application, paving the way for new sites. Other locations pegged for future development include the St. Lawrence and Niagara rivers.
The final example of tidal power generation in this article is even smaller than the RITE project, yet has adopted a radically different design in response to environmental conditions, proving that when the going gets tough, the tough get floating…
Grand Passage floating platform
Location: Bay of Fundy, Canada
Operational since: 2018
Planned capacity: 0.28MW
Despite boasting the largest tidal range in the world and a generating capacity of at least 2.5GW, the Bay of Fundy has yet to provide tidal energy on a significant scale.
Part of the problem lies in the sheer size of the forces at play. A large turbine project was shredded by strong currents in 2009, with all 12 of the installed rotor blades destroyed within 3 weeks by 10-knot tide speeds. While a similar design is being trialled in a calmer part of the bay, a new floating platform is being trialled in the Minas Passage, facing the strongest tidal forces present in the area.
The hope is that the rotating blades, designed like outboard motors on a boat, will generate energy without being overwhelmed by the underwater forces.
What can we learn from all of this?
Tidal power is predictable, clean and plentiful in many regions across the world. We have viable power stations still in operation from the 1960s and a new generation of turbine designs aimed at harnessing power from both wide-open rough seas and tight urban waterways.
So why aren’t there more tidal power stations in operation?
I’ve answered this partially with the examples above, showing that, in essence, it's complicated. Each area identified as a possible site for tidal power generation presents its own unique set of engineering and design challenges, even before you look at environmental impact and planning permission.
To answer this more fully, I’ve written an additional piece on tidal power and tidal technologies: