Turn the tide: is it time for tidal stream energy?

What the harbour porpoises, razorbills and recreational kayakers will make of the whirring turbines beneath the surging seas around Anglesey is largely unknown. But a patch of ocean off the coast of North Wales is now the focus of an emerging and under-exploited source of energy – tidal power. If all goes to plan, it could become one of the largest tidal energy sites on the planet.

Beneath the iconic lighthouse of South Stack on Anglesey’s Holy Island – so called for its ancient standing stones and burial chambers – some of the fiercest tides in the UK funnel around the sheer Welsh cliffs at speeds of up to seven miles per hour (11km/h). These are busy waters – ferries shuttle two million passengers a year to and from Ireland, and Holyhead is the UK’s second busiest roll-on roll-off port after Dover. Year-round, surfers and sailors enjoy the rugged inlets and broad sandy beaches that make the area one of the country’s best-known watersports locations.

Here, across 13 square miles (35km2) of Irish Sea in depths of up to 50m, companies will begin harnessing the kinetic energy of the tidal stream in an experiment to put tidal devices through their paces for longer and at a larger scale than before. This is the Morlais project – a halfway house for proven tidal technology seeking to demonstrate both its commercial worth and its impact upon sea life and the ocean. This zone is one of several around the UK earmarked by authorities in order to encourage tidal energy.

Tidal energy works when the Sun doesn’t shine and the wind doesn’t blow. It’s utterly predictable; in 2050, whether or not the UK has met its commitment to achieve net zero by then, tides around Anglesey will be ebbing and flowing twice a day with the same intensity, pulled across the planet by the Moon and Sun’s gravity.

Tidal energy could eventually supply 11 per cent of the UK’s baseline electricity demand according to a report released in 2021 by the Royal Society – but to reach this, some 11.5GW-worth of generation capacity must be installed in the strongest tidal currents.
We need to get our skates on, say those in the tidal sector. Nearly a decade ago the government estimated that wave and tidal combined could provide up to 20 per cent of the UK’s electricity needs. For now, tidal energy is relatively immature and still too expensive. However, marine energy could be worth £76bn to the UK economy by 2050, according to an assessment by the Carbon Trust – and the country could capture nearly a quarter of the global market for wave and tidal technology, the report predicts. Experts in the sector believe this is too good an opportunity to miss.

An island nation, the UK has half of Europe’s tidal energy, and seas surge most forcefully around the UK’s west coasts and up, from the Channel Islands and Isle of Wight to the far north of Scotland. This would sit well against offshore wind farms mainly situated to the east of the country in the North Sea. “You get a balancing effect in terms of energy distribution onto the grid,” says Sue Barr, chair of the UK Marine Energy Council.

Anglesey also has a history of intensive electricity generation with a former nuclear power station. “Not only are there good tidal resources, but there are also good grid connections in Anglesey, which isn’t the case in other tidal sites in the UK,” says John Jenkins, Morlais’ project director.

“We are leaders in tidal stream technology,” adds Barr. “We’ve been looking at this for a very long time in the UK and we’ve seen more technology deployed here than anywhere else in the world.” To date, tidal technology has produced about 48GWh onto the grid in the UK, she says. “So, we’ve got technology that works.”

And the technology – roughly an underwater version of wind turbines – can harvest kinetic energy of strong currents. This differs from the likes of tidal barrages and dams, which harness the rise and fall of the water and tend to be more intrusive to the environment.  

Currently the UK’s largest commercial tidal project, MeyGen, is in the far north of Scotland in the Pentland Firth off Caithness, where tides flow at up to 11 miles per hour (18km/h). This has eventual capacity for nearly 400MW. Scientists are assessing how marine mammals are reacting to seabed-anchored turbines first installed in 2016, and the hefty cabling to the mainland – early research found that porpoises have tended to steer clear of the rotating turbine blades.

With some 6MW of operational capacity, the project benefited from a recent government funding round and is expanding with a target of becoming the world’s first commercial-scale tidal array. It has produced most of the UK’s tidal energy to date. “The industry is at the really early stage of commercialisation,” says Jenkins.

To the south-west, ten companies are interested in lowering their turbines into the Welsh site, which developers describe as a kind of ‘campsite’ for proven tidal technologies. They will take up a ‘pitch’ and benefit from the plug-and-play infrastructure – the cabling and connection to the national grid that the project offers. A Spanish developer will begin deploying technology at Morlais in 2026, to be joined by up to four more the following year. For now, local contractors are busy digging up roads on the island and building infrastructure in preparation for ushering renewable power onto the grid. EU structural funds are contributing to onshore infrastructure and must be spent by the end of next year.

Technologies to take up residence in Anglesey have already passed their nursery tests – this is a project to test them in a larger scale to understand their maintenance needs, impact, and viability in the longer term.

“Morlais is providing a step between the very small-scale single devices in the water and the very large scale – the multi-megawatt generating stations,” says Barr. “Developers can come in at a commercially attractive rate because all the grid infrastructure is in place – it’s a key project for the UK.”

This is the only UK tidal project which is being managed by a social enterprise, Menter Môn, which aims to divert all benefits back into local communities in North Wales. In total the site, granted consent and a marine licence in 2021, has capacity for up to 240MW of electricity generation from installed tidal stream technology – enough for 180,000 homes – but this won’t happen quickly. Developers must take a softly-softly approach, as environmental concerns mean that each stage will be closely observed for any impact on marine and bird life and the surrounding sea before expanding, and it will be decades before it could reach capacity.

‘We are leaders in tidal stream technology. We’ve been looking at this for a very long time in the UK and we’ve seen more technology deployed here than anywhere else in the world.’

For the first time ever, the government has earmarked cash worth £20m a year to help commercialise a portion of the UK’s tidal energy and guarantee a price for 15 years – meaning tidal hasn’t had to compete with the likes of cheaper wind and solar for funding as it bids for government contracts to supply low-carbon energy.

Tidal energy remains pricey, with costs similar to wind energy some 15 years earlier. Analysts don’t expect costs to fall as low as wind – operating underwater is more expensive than on the surface, and available space is constrained by the water depth; environmental surveys are lengthy and costly. In the last government funding round the strike price was £178/MWh, compared to around £40 for offshore wind. But in the early days of wind power, prices were higher than tidal for the same installed capacity. And tidal could become cheaper than nuclear if it achieves a 1GW deployment. “Once you scale up, the value of tidal stream becomes interesting,” says Barr. Observers also point out the Danish government invested millions in wind technology. With UK demand for electricity expected to more than double by 2050, this development is timely.

“Clearly tidal operators are going to have to drive out some of the cost,” says Barr, “but the way we are moving towards decarbonisation and electrification of the energy system, we will need all technologies for a resilient sector.”

With tidal turbines, it’s as much about their location as how they work. A range of experimental turbines floating on the surface, at mid-depth or anchored to the seabed with heavy structures have already been put through their paces at the pioneering European Marine Energy Centre in the Orkney Islands. While fixed seabed turbines are less vulnerable to storms, floating turbines – such as Scottish firm Orbital Marine Power’s model – can be more easily repaired and maintained. Mobile submersible turbines can be more easily installed and raised for maintenance, says QED Naval, which is developing a platform that can be made to rise and fall by tweaking its ballast.

Barr believes there’s room for a range of technologies and doesn’t foresee a convergence on a single design. “I think we need all of them,” she says. “Different technologies suit different environments, and the sea is so different in different places.” Waters flow fastest on the surface where there’s less friction, and technology here must be sturdy. Waves can also add to the energy mix. But there are more ‘low-flow’ tidal sites in the world – these are the beneath-the-surface currents, which are less dynamic. “They all have a different cost profile, and they will all be deployed in slightly different receiving environments,” explains Barr.

Engineers compare running a tidal turbine to trying to fix a wind turbine in a hurricane – water is about 800 times denser than air – and this means blades can be smaller than aerial counterparts. The industry is so young, engineers have yet to know how turbines will behave in the longer term in a wet and salty environment.

One of the first companies to begin operations in Anglesey is the Spanish firm Magallanes Renovables, which has been developing prototypes for two decades and previously tested in the Orkney Islands. The company says it aims to make use of tried and tested technology developed by naval and wind sectors – its robust design sees twin turbines fixed to a floating ship via a vast underwater mast designed to withstand the extreme pressure of the tides.

This project is timely too for Anglesey, amid ongoing uncertainty around a potential new nuclear power station at Wylfa since backers withdrew in 2020, five years after the original 1963 station shut down. Through the Morlais project, Menter Môn says some 100 ‘well-paid’ jobs will be created in the first decade and there will be training and apprenticeships, and supply chain opportunities for local businesses. More widely, tidal energy has the potential to create tens of thousands of UK jobs, say supporters, with a potential to export evolving technology worldwide.

This, says Barr, is a race we can’t lose. “The market is driving collaboration, but other countries (France, South Korea, Japan) are moving closer to supporting tidal stream in a way that could see us lose our lead.” Scottish firm Sustainable Marine Energy is now deploying its technology in Canada’s Bay of Fundy, which has the highest tides in the world, to take advantage of financial support on offer.

Getting over the hump of capital investment required to move tidal energy towards commercial viability is the challenge. “We do marine energy here in the UK better than anywhere else,” says Barr. “We just need more of it in the water to make it cheaper and enable the supply chain.” 

How it works: MeyGen tidal energy plant, Scotland

• Steel nacelle with composite blades.
• Total weight (inc foundations) – 1,000t.
• Each 1.5MW turbine can generate enough electricity to power around 1,400 homes.
• Each nacelle takes approximately 90 minutes to install onto a pre-installed foundation, offshore.
• The turbine is mounted on a foundation structure and set on the seabed. No drilling is necessary as its weight secures it in place.
• Tidal currents cause the blades to rotate, powering a generator that produces electricity. The output varies with the tides and is predictable.
• Underwater cables carry the electricity to an onshore substation.
• The substation is connected to the national grid, which distributes the electricity.

Why underwater?

• Space saving, no visual pollution.
  An underwater turbine generates the same power as an onshore wind turbine with 30m blades. Low environmental impact with slow rotor speeds.
• More predictable.
  Unlike wind and solar energy, tidal energy is predictable as tidal currents can be accurately forecast years in advance. This makes for a more reliable source of electricity generation.
• Large untapped resources.
  Water covers about 70 per cent of the world’s surface, and every continent has potential sites for harnessing the power of tidal currents.

In the UK, there is a huge estimated energy resource of 29TWh per year available in tidal currents.