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Alternative Energy | Tidal power

swansea barrage

With around 60 sunny days per year, “the UK” and “solar power” do not make for a natural co-location. And although we are not short of wind, many see it as an unreliable energy source.

But Britain does have something else in its favour. With roughly 17,820km of coastline, it has an energy source that the government thinks could provide 50% of Europe’s tidal power resources. It is entirely renewable and, unlike wind and solar energy, it is completely reliable.

“As long as we have a moon in a sky, we’ll always have tides and we can predict 1,000 years ahead exactly when our tides will be,” says Tidal Lagoon Power (TLP) director of engineering and construction Mike Unsworth.

TLP aims to capitalise on our country’s high tidal ranges – the Severn Estuary has the second highest tidal ranges in the world, beaten only by the Bay of Fundy in Canada. This natural advantage puts the UK in a strong position to develop world-leading expertise in a new tidal power industry.

10 to 12 UK hotspots

The Tidal Lagoon team has identified between 10 and 12 tidal hotspots around the UK that are perfectly placed for tidal power plants. It has projects in the pipeline for six of those, but Unsworth stresses that if other developers take an interest, the potential is great.

“We think if 10 of those 12 projects were built over, say, the next 20 years, then that would contribute 12% of UK electricity demand,” he says.

Back in 2011, TLP began plans for a pathfinder project in Swansea, a chance to prove the technology and the market potential for tidal power.

155,000 homes

Once complete, the £1.3bn Swansea Bay Tidal Lagoon will power around 155,000 homes – equivalent to 90% of Swansea Bay’s domestic energy use, or around 11% of Wales’ needs.

The Swansea concept is being scaled up for a much bigger barrage at Cardiff.  This project had its first formal planning document submitted in 2015 and is estimated to produce enough electricity to power more than 1.3M homes – putting its installed capacity on a par with Hinkley Point C.

“It is a nuclear scale power station, but clearly it’s acting on the tides so it’s purely renewable, 100% renewable,” says Unsworth.

Tidal

Tidal

There is another advantage to a tidal power plant – it has double the lifespan of a nuclear plant at 120 years compared to 60. In comparison, solar photovoltaic power sources have a life expectancy of 25 years and offshore wind turbines, a mere 22 years.

Of course, the technology planned for the Swansea Bay tidal lagoon project is not new. Tidal barrages are well established. French energy company EDF – also the client behind Hinkley’s expansion – completed the tidal barrage across the Rance river in Brittany, in 1966, achieving a world first.

Biggest barrage

The Sihwa tidal barrage in South Korea has since overtaken it, becoming the world’s biggest tidal barrage plant in 2010 with a capacity of 254MW compared to the Rance barrage’s 240MW.

Tidal barrages create a breakwater, across a river or estuary. Turbines are housed inside the breakwater and as the tide comes in, water is funnelled through them, creating energy.

But the 320MW Swansea Bay project is different. Although the breakwater will span from one spot of land to another, it has less impact as it creates a lagoon rather than cutting across a water flow.

First of a kind

“While the technology associated with building breakwaters and the technology associated with the turbines is not novel, it’s not new, bringing those aspects together into a lagoon is the first of a kind element,” says Unsworth.

The 9.5km breakwater consists of a mixture of sand and gravels protected by rock armour. In its mid-section, a concrete housing holds 16 conventional hydro turbines.

The turbines are bi-directional, and their blades can be positioned according to the direction of water flow. It means the cycle can be repeated four times a day with each tide, and the tidal lagoon can generate electricity for 14 hours out of 24.

Subisdy decision

But before it can begin construction, the TLP team has a few barriers to overcome. It has already received planning permission but is now waiting for a Contract for Difference (CfD) from government.

At the same time, the Hendry Review, which has been examining the potential for tidal power in the UK since May 2016 could give the project a boost.  

It is led by industry expert and former energy minister Charles Hendry with a brief to decide whether there should be a pathfinder tidal power scheme. A decision that there should be one and that it should be Swansea would give the project a further boost.  

Contract for Difference

The Contract for Difference is expected to be agreed shortly, as is the outcome of the review. In the meantime, Laing O’Rouke has been named as preferred bidder for the civils structures, and a JV between General Electric and Andritz Hydro is in place for electrical work.

But the team has retendered the marine works after deselecting its preferred bidder, Chinese company China Harbour Engineering.

“We felt that the solutions, and the designs, and the methodologies of how you would build the breakwaters – they weren’t delivering us with what we considered to be value for money,” explains Unsworth.

New opportunities

So does this present new opportunities for the UK? According to Unsworth, the top four marine dredging companies in the world are in Europe and each has subsidiaries in the UK. The team at Tidal Lagoon Power has set a benchmark for their projects to create 65% of spending on the project in the UK supply chain. If they achieve it, this could be a massive boost to British business, making it a world leader in a technology still in its infancy.

“We are really keen that the technology and the knowledge, the design, the intellectual property, the expertise, is all developed within the UK, on the UK projects, using a UK-focused supply chain, ” says Unsworth. As he explains, there are several key places around the world – including France, China, and India – which have similar tidal ranges to the UK.

Export potential

If a British supply chain can establish itself on home-grown projects, it has a good chance of exporting its world-leading design and capability successfully.

Unsworth stresses that “the time has come” for innovative renewable technology, and points to the Paris Agreement on emissions reduction as evidence that climate change is a global priority. Developing technologies like tidal lagoons will also create jobs in a low carbon economy – a popular prospect for any career-minded politician.

“The renewables sector – be it wind farms, be it floating wind, be it tidal lagoons – they will continue to thrive as more and more reliance is placed on low carbon and renewable technologies,” says Unsworth.

Readers' comments (2)

  • Double Tidal Lagoon Baseload Scheme

    I propose a renewable energy scheme where a tidal lagoon is partitioned into a ‘high’ lagoon and a ‘low’ lagoon by a dividing wall, which houses turbines which continuously generate power as sea water flows from the high lagoon to the low lagoon.

    Operation

    At high tide, the sea-gates of the high lagoon are opened and the high lagoon is filled up to high tide level.

    When the ebb tide begins, the sea-gates of the high lagoon are closed and remain closed until the next high tide.

    At low tide, the sea-gates of the low lagoon are opened and the low lagoon is emptied to low tide level.

    When the flood tide begins, the sea-gates of the low lagoon are closed and remain closed until the next low tide.

    The sea-gates are functionally identical to one-way flap valves and may be engineered as such.

    Baseload

    The Double Tidal Lagoon Baseload Scheme delivers a genuine baseload generation capability which can’t be delivered by inferior single tidal lagoon schemes as proposed by Tidal Lagoon PLC, as explained in the critical review in Energy Matters, “Swansea Bay Tidal Lagoon and Baseload Tidal Generation in the UK”.

    Reference

    A couple of days after posting this, a comment was kind enough to provide a reference to David J C MacKay’s “Sustainable Energy – without the hot air”, pages 320/321 – “Getting “always-on” tidal power by using two basins”

    “These toppings-up and emptyings could be done either passively through sluices, or …” – David J C MacKay

    So MacKay’s “passively through sluices” “two basins” scheme is indeed absolutely equivalent to my double lagoon proposal here.

    Scotland

    The Solway Firth

    The Solway Firth is the best location for Scottish tidal lagoon plans because that’s where Scotland’s highest tides are.

    Almorness Tidal Energy Scheme

    The Almorness Tidal Energy Scheme is my outline design concept intended to serve only as an example of possible Double Tidal Lagoon Baseload Schemes. Points to note are

    * the River Urr empties into the high lagoon, adding to generation capacity.
    * dredging the estuary mud out of the lagoons, especially the low lagoon and around the turbine house would likely be necessary for satisfactory performance
    * there should be a drainage canal to redirect water flow to prevent drainage into the low lagoon
    * the lagoon walls would obstruct sea-going navigation to the Urr estuary harbour unless a lock for boats was built into the high lagoon sea wall to enable (admittedly delayed) navigation.

    Sea Lochs

    Whilst the tides on Scotland’s north-west coast aren’t so high, there do seem to be quite a number of suitable sea-lochs there that could relatively easily be barraged to exploit tidal energy, somewhat in the style of a tidal lagoon but without having to build much in the way of lagoon walls, nature having done most of the work already.

    Simple.

    More -
    https://scottishscientist.wordpress.com/2017/01/16/double-tidal-lagoon-baseload-scheme/

    Scottish Scientist
    Independent Scientific Adviser for Scotland
    https://scottishscientist.wordpress.com/

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  • You are quite right, tidal energy appears to be the only certain "renewable" source; there is some geothermal but this seems not to have moved beyond Southampton. Whilst one can accept the idea of using the natural power of the wind and the sun, we will always have uncertainty - will the wind blow, will the sun shine. I accept that bright sunshine is not a necessity, but as someone who has had PV on the roof for 6 years, I know that a dull summer seriously reduces generation. Tidal power will always be available, and if it isn't, we don't have a problem.
    I have devised a use of the tide which, rather than generating electricity,reduces existing and potential future power use. In my book, if I can show that the power use is essential, then using the tide to obviate it, is as good as generation.
    My idea is quite simple. Water companies have to cease freshwater abstraction at times of low flow in the river and the water be allowed to flow down into the estuary. The Environment Agency regard it essential that this Minimum Residual Flow is allowed to keep the estuary wet at low tide in order to maintain the environment. To continue water supply, the companies pump water at times of high flow up into reservoirs and then use it at times of low flow in order keep supplying the public.
    In effect they are storing water at the top of the river in order to solve a problem at the bottom.

    I propose the installation of a removeable or retractable weir in the estuary, just downstream of the final weir. With two tides per day it would be placed so that when raised at high tide it would temporarily store at the top of the estuary, half of what the water company wishes to abstract from the freshwater part. Then, during the low tide period, the temporarily stored water would be steadily released, returning the flow to natural but still allowing freshwater abstraction. At low tide the temporary reservoir would be empty, the moveable weir could be moved out of the way, and the process repeated.
    The beauty of the idea is the twice daily return of the tide with no dependence on the weather. If the regulators can assure the power boys that the use of the water supply system is "essential" then the electricity saved should be recognised as the same as a non fossil fuel generation.

    My recent correspondence with Ministers makes the point that current ideas for large scale increases in water resources, such as pumping it from the north to the south or, building new reservoirs, cannot be completed this decade (or if planning is anything to go by the end of the next decade). We are about to start the post Brexit trade negotiations, hoping to get more investment into the UK. Much of this would be aimed at the South East and this has a recognised water supply uncertainty. My idea would solve this uncertainty inside a couple of years, not a couple of decades.
    Despite many letters and unsuccessful meetings, I am still hopeful someone else will see the benefits of this innovative tidal power idea.

    Bill Cutting. Retired Member

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