A tidal power ‘mega project’ in one of Europe’s iconic waterways could power 1 million homes. But costs are huge

The River Mersey is one of Europe’s most iconic waterways. On top of being a major hub for shipbuilding and industry, it’s been a source of inspiration for a host of writers, artists and musicians over the years.

If all goes to plan, the Mersey could also play a major role in the U.K.’s sustainable future.

Authorities in Liverpool want the river to be home to a huge tidal power project which, they say, could power as many as 1 million homes, generating thousands of jobs for the region in the process.

If built, the facility would have a capacity of at least 1 gigawatt and make use of the Mersey’s tidal range, which is the U.K.’s second highest.

Speaking to CNBC, Martin Land, director of the Mersey Tidal Power Project, outlined how the system would work in practice.

The idea, he explained, is to center it on the creation of “a structure to hold back the tide, or to contain the tide — we let the height build up on one side, and the other side has a low level.”

“And then we let that water, that seawater, pass through turbines and generate electricity,” he added. “So it’s using the potential energy, which is the height difference of the tide.”

This setup is different from installations that use tidal stream turbines, which, in very simple terms, can often look a bit like underwater wind turbines. 

Land told CNBC that the project is coming to the end of its concept phase, with a number of scenarios on the table.

“We still have an option for a barrage location, which would cross from the Birkenhead side … the left bank of the Mersey, to the right bank, the Liverpool side,” he said. “Or, alternatively, it could be a lagoon.”

Spanning a body of water, a tidal barrage resembles a dam. The International Renewable Energy Agency describes tidal lagoons as being similar to a barrage, but adds that “they are not necessarily connected to the shore” and are able to “sit within the ocean.”

Tidal barrage systems in operation today include EDF’s 240 megawatt La Rance tidal power plant in France, and South Korea’s 254 MW Sihwa Lake tidal power plant, currently the world’s largest.

Initial proposals for a tidal barrage spanning the Mersey were formulated in 1924. The current project has taken a number of steps forward in recent times. 

In December 2022, an agreement with the Korea Water Resources Corporation — the owner and operator of the Sihwa Lake facility — was signed.

In a statement at the time, the Liverpool City Region Combined Authority said K-Water had agreed to “share tidal power knowledge.”

The agreement, it added, would see “K-water and the Combined Authority working closely together to explore possibilities for tidal power.”

The Combined Authority in Liverpool is bullish about the prospects for its tidal power project, stating on its website that “tidal power’s time has come” thanks to technological improvements and the climate emergency.

In a statement sent to CNBC, Steve Rotheram, mayor of the Liverpool City Region, struck a similar tone.

“Once operational, Mersey Tidal Power would have the potential to become the world’s largest tidal power scheme,” he said.

Tidal power facilities have been around for decades — EDF’s La Rance dates back to the 1960s — but a number of projects have made great strides in recent years.

In February 2023, for example, an Edinburgh-headquartered firm said its tidal stream array had achieved a world first by producing 50 gigawatt hours of electricity.

And back in July 2021, a tidal turbine weighing 680 metric tons started grid-connected power generation at the European Marine Energy Centre in Orkney, an archipelago located north of mainland Scotland.

In October of the same year, plans for a £1.7 billion (around $2.05 billion) project incorporating technologies including underwater turbines in waters off Swansea, a coastal city in Wales, were announced.

Cheshire Wildlife Trust, for instance, states it is “keen to support renewable energy schemes in the right place” but adds that “a barrage scheme in the Mersey Estuary has the potential to cause significant environmental damage.”

More generally, the U.S. Energy Information Administration notes that one “potential disadvantage of tidal power is the effect a tidal station can have on plants and animals in estuaries of the tidal basin.”

“Tidal barrages can change the tidal level in the basin and increase turbidity (the amount of matter in suspension in the water),” it adds. “They can also affect navigation and recreation.”

As previously noted, at the moment it’s still to be decided if the scheme planned for the Mersey will be a barrage or lagoon.

For his part, the Mersey Tidal Power Project’s Martin Land sought to emphasize that there was “well developed guidance for the environment impact assessment that you have to perform for mega projects … for big infrastructure projects.”

“We know that in developing project options we need to consider the impact of a scheme on the river and estuary and also whether this can help with the regional issue of rising sea levels,” he added.