Tidal fights for its share

Liverpool may one day be home to the world’s largest tidal energy project: a giant tidal barrage stretching across the River Mersey, powering over 1 million homes. The £3.5 billion, 700 MW Mersey Tidal Power Project received preliminary approval from the city’s local authority last month.

“Mersey Tidal Power has the potential to generate clean, predictable energy for 120 years, create thousands of green jobs and apprenticeships – and all but seal our area’s status as Britain’s renewable energy coast,” said Liverpool Mayor Steve Rotheram.

“Beyond the banks of the River Mersey, this is a national infrastructure asset that could position the UK as a global leader in the renewables race and help to turbocharge our net zero ambitions.”

The UK has been interested in the development of tidal energy for some time. Despite the technology’s early hype, the cost of production has remained stubbornly high. As a result, the sector has remained relatively dormant.

One of Scotland’s leading tidal developers has led a groundbreaking European project, EnFAIT (Enabling Future Arrays in Tidal). This has set out ways in which to reduce the cost of tidal energy by as much as 40%. Findings from the projects could redefine the boundaries on what can be achieved by tidal power globally. But will it ever become a key component in the UK’s energy transition?

Harnessing the power of the ocean

Tidal energy harnesses the power of the sea and ocean’s tides to produce renewable electricity.

The technology is split into two segments. Tidal stream uses ocean currents to turn underwater turbines to generate power, while tidal range uses barrages or dams to capture water at high tide. It then releases it slowly through turbines to produce electricity.

“Tidal stream has proven more popular than tidal range as it’s modular and less expensive, with much less environmental impacts,” said AbuBakr Bahaj, professor of sustainable energy at the University of Southampton.

The UK has one of the best tidal energy resources in the world. It also has some of the leading companies developing tidal stream technology, according to Magnus Harrold, senior marine energy technical manager at Offshore Renewable Energy (ORE) Catapult. 

There are no tidal range projects operational in the country. The UK has just over 10 MW of deployed tidal stream capacity, which have provided over 60 GWh of renewable electricity. There are, though, plans to deliver over 100 MW of projects by 2028.

Companies like Nova Innovation and Orbital Marine Power have deployed projects. These have over 80% UK supply chain content in projects across Scotland, Orkney and the Shetland Islands.

“Tidal is where offshore wind was 15-20 years ago,” said Simon Cheeseman, ORE Catapult’s Wave & Tidal Energy sector specialist.

As well as the environmental impacts of its vast dams or barrages, a need for more subsidies, and for longer, has put tidal range’s development at a disadvantage to stream, according to Cheeseman.

The lifespan of a range project is around 120 years, compared to stream’s 25 years.

Wavering support

Excitement around the potential of the UK’s tidal power resource started in the mid-2000s. The industry went mysteriously quiet in the late 2010s, and it is fair to say that the technology has still yet to have its breakthrough moment.

“The lack of a consistent route to market has significantly hampered development,” explained Richard Arnold, policy director of the UK Marine Energy Council (MEC).

“Prior to 2016, tidal stream could access support via the Renewables Obligation scheme. The shift to the contracts for difference (CfD) mechanism with a focus on the levelised cost of energy (LCOE) meant that tidal stream projects could not compete against wind, solar and other more established technologies.”

The fortunes of tidal stream changed, however, when the government introduced a technology specific ring fence in its energy auction process for tidal stream in 2022. This led to several pre-commercial projects in Wales and Northern Scotland receiving CfDs.

The government awarded further CfDs in 2023. Harrold expects the pipeline to grow this year as the government has already confirmed it will keep the ringfence in place.

“The UK government has demonstrated international leadership in setting a tidal stream ringfence,” said Arnold. “Others are now following, with French President Emmanuel Macron announcing last year the introduction of commercial tenders in France.”

The technology is now very much proven, according to Harrold. The next stage for the industry is going from pre-commercial small arrays to installing tens of turbines at a site to reach commercial scale.

A complementary role

Over the past six years, the 20 million euro (£17mn) EnFAIT project brought together seven partners. These included Nova Innovation, ORE Catapult, IDETA, RSK, SKF, Wood and The University of Edinburgh.

As well as the 40% cost reduction, the project was able to generate power for an impressive 95% of the time. It extended the time between turbine maintenance periods from six months to two and a half years.

Studying the tidal steam’s environmental impacts, it also revealed no evidence of adverse effects on marine wildlife – corroborating other research on the matter. “Research projects like EnFAIT, ELEMENT and TIGER have really put the sector back on the map,” said Harrold.

As the UK’s energy system transitions from fossil fuels to renewables, the intermittency of wind or solar power threatens the reliability of the grid to match demand.

Tidal’s inherent predictability and flexibility will allow it to play an important role backing up the grid for when sun fails to shine and the wind blow, in a similar role to nuclear energy or energy storage systems.

“With tidal, within 20 minutes you know exactly what your energy output will be,” said Bahaj. “And you can predict the energy over the next 30-40 years due to the tides being dependent on the movement of the moon and the earth. We did the analysis for certain sites around the UK and found the predictable nature of the tides provides unsurpassed opportunities for power purchase agreements that, unlike solar and wind, are not weather dependent.”

Extrapolating the data

The cost of tidal stream energy is a relatively expensive £200 per MWh. But Cheeseman believes that – with government support – it could eventually come down to £47 per MWh. That would make it extremely cost competitive with nuclear’s £90 per MWh today.

But not everyone’s convinced. Mike Hogan, senior adviser at the Regulatory Assistance Project, an energy research NGO, believes EnFAIT is the “usual exercise in projecting – rather optimistically – from experience with very small pilot projects”. The Mersey project, coming online in the mid to late 2030s, will be too late to make a contribution to the UK’s target to decarbonise the electricity system by 2035, he said.

Even if industry’s “rosy projections” are realised, Hogan pointed out that technology has a relatively modest capacity factor of 25-30%. This is comparable to solar, although the latter is vastly cheaper.

Tidal has much smaller technical potential, and is typically fixed in fairly remote locations relative to major load centres, he added.

Hogan also doesn’t believe technology’s costs will come down as EnFAIT forecasts. He said it was “for the same reason it’s never worked for large commercial nuclear technology: the accumulation of experience is far too slow, too characterised by unique project-by-project conditions, and too widely dispersed, for the well understood phenomenon of technology and manufacturing learning to ever have much effect”.

Tidal power is a “much smaller, much more expensive, much more geographically constrained version of solar”, he concluded.

Powering net zero

Nonetheless, there is still optimism around tidal energy, particularly stream, for the UK. A 2021 study found the UK and British Channel Islands could generate 11% of their shared electricity demand each year using tidal stream turbines. This would require installing 11.5 GW of energy in the strongest tidal streams – roughly the same as the installed capacity of offshore wind in the UK to date, which took 20 years to reach that level.

MEC advocates for the UK government to set a 1 GW by 2035 target for the industry, which ORE Catapult endorses. “That would provide clear pipeline visibility and allow the sector to reduce costs,” said Harrold. Once the cost comes down to below nuclear’s, projects should start to ramp up, he added.

“A secure transition to net zero will require a diverse energy mix,” said Arnold. “Following a similar cost reduction pathway as wind and solar, tidal stream can get to below £50/MWh. Securing this requires consistent support from the UK policy environment to help harness private investment in the technology.”

Research from the University of Edinburgh found deployment of 6 GW of tidal stream power would deliver a saving of £1 billion per annum in energy system costs. It would also provide £17 billion in gross value added (GVA) to the UK economy by 2050.

Developing the tidal stream industry, Arnold said, would create jobs in coastal communities and beyond. Furthermore, the UK could export technology and expertise around the world – with France, Canada, the US, and South-East Asia representing large potential markets. 

High LCOE

But Hogan simply isn’t buying the 11% forecast. He pointed out the IEA’s Net Zero Energy projection of the share of global electricity production coming from marine energy sources – tidal and wave energy combined – in 2050 rounds out to 0%.

“That may be overly pessimistic and the UK could in theory see more development of marine energy than the global average because of the larger number of potentially developable sites around the UK’s shores. But there are sound reasons why it’s not ever likely to be much more than that, reasons that can’t be overcome by more development.”

Bahaj, for his part, saw both sides of the argument. He believes the 11% target is technically achievable, but it will be commercially difficult to justify without a huge reduction in LCOE.

“But [stream’s] costs are currently higher than offshore wind due to the lack of scale-up,” he said. “So, we need appropriate support mechanisms to achieve the scale-up of the technology.”

To achieve this, the government needs to fund the sector to transition it to commercial viability – as it did with wind and solar. With sufficient support, Bahai believes tidal stream will become an important flexible power source. It can play a useful complementary role in supporting the UK’s renewables-oriented grid.

Export potential

“And the export potential of the sector is not something the UK should take for granted,” adds Bahaj. “The UK currently has the lead in the technology, and it could be exporting it to other countries,” he said.

“But China and other countries have also been doing a lot in the same space recently, and they could catch up quickly if the UK government doesn’t support the technology’s development.”

Perhaps inspiration can be taken from the development of Denmark’s much-heralded wind power sector.

In the 1980s, Denmark invested early in its wind energy industry, delivering projects with high levels of local content and developing its domestic market.

In the process, it gained first-mover advantage. Its wind sector exports now generate over £7 billion annually for the Danish economy.

By contrast, the UK’s wind sector, Europe’s largest generator of wind energy, exports less than £0.5 billion per year. It is a net importer of wind technology – principally from Denmark. 

“The UK can be the leader in tidal stream, exporting its technology and expertise around the world,” concludes Arnold.

“By 2050, UK content should be embedded in tidal stream projects deployed here and in other countries, ensuring UK households and communities benefit from the net zero transition and the jobs and opportunities it will create.”