Skip to content

Swansea Bay Tidal Lagoon and Baseload Tidal Generation in the UK

January 18, 2017

By Paul Homewood


Tidal lagoon

The project would see energy produced for 14 out of every 24 hours, according to TLP


We are well aware of the problems of intermittency with the proposed tidal lagoon at Swansea Bay. Even the developers, TLP, admit it can only supply power for 14 hours a day.

But they also propose to build a chain of other lagoons, which they claim overcome this problem because of differences in high tide times around the coast.

Euan Mearns has tested this claim by carrying out a detailed study of tides at the sites likely to be developed. His verdict is that even with staggered tide times, the issue of intermittency remains, with four spikes separated by four periods of zero production every day.

He writes:



Charles Hendry, former energy secretary, published his long awaited report on the Swansea Bay tidal lagoon power station last week coming down in favour of the project. Hendry’s report is comprehensive but has one key omission. It does not ask if tidal lagoons can provide renewable base-load power in the UK as is often claimed. I set out in a positive frame of mind to show that it could, but failed miserably in that attempt. Facts defeated me.

The timing of high and low tides are staggered around the coast of Britain. Hence, the ideology says that combining output from several sites can provide smooth base-load supply. Indeed, the main company peddling this technology in the UK, Tidal Lagoon PLC, makes this claim.

I built a generation model based on 7 lagoons spread along the English coast in areas with the highest tides. The model shows that the ideology does not work in practice. In fact, UK tidal lagoons will produce more intermittent electricity than any other form of renewable generation providing four spikes separated by four periods of zero production each day. It is often claimed that the predictability of tides is a virtue. This also means we can predict with certainty that this energy source will be a disaster for the public as well as the environment.


This is the key graph:


Figure 10 Summing the generating opportunities shown in Figure 9 creates this picture of tidal lagoon generation for 7 power stations distributed along the best sites on the English coast. The chart is for two days. Rather than showing anything remotely like base-load generation, it shows the most extreme form of intermittency of any renewable generation source with 4 large spikes in generation separated by 4 periods of zero generation each day. By way of comparison, solar has just one spike each day.


Euan’s post is well worth reading in full here.

  1. AlecM permalink
    January 18, 2017 1:13 pm

    Hendry is a Rugby School educated fool, bent on enriching his mates. His degree (Edinburgh) was in commerce.

    His knowledge of utility systems and the consequences of their intermittency is limited to imagining that when you are asleep, you don’t need to pee.

  2. Jack Broughton permalink
    January 18, 2017 1:13 pm

    Euan’s assessment is a really beautiful bit of applied common sense that finds the real worry about the tidal project that is hidden or even omitted from the hype in Hendry’s report. The need for it and costs are obviously not proven, but the issue of the 6-hour cycle puts the lie to the claimed security of supply if more are built.

    It is analogous to the claim that “The wind is always blowing somewhere” that was used to justify the wind-powered white elephants that are making our electricity uncompetitive and putting supply at risk.

  3. Max Sawyer permalink
    January 18, 2017 2:12 pm

    I suppose it is too much to hope for government scientists to have carried out this research. On the other hand, perhaps they did and filed the results under “inconvenient”.

  4. Robert Christopher permalink
    January 18, 2017 2:18 pm

    The Swansea Bay Tidal Lagoon project isn’t the worst of his interests 🙂 :

    “In July 2013, it became known that Hendry had secured a job as adviser to the Atlantic Supergrid Corporation which plans to import power to the UK via an undersea cable from Iceland. Hendry had signed an energy pact with Iceland while he was Minister of State at the Department of Energy and Climate Change.”

    • AlecM permalink
      January 18, 2017 2:30 pm

      The Man is a typical elitist *rook.

    • It doesn't add up... permalink
      January 18, 2017 8:37 pm

      He is also Chairman of Forewind, which hopes to milk £3bn a year in subsidies from the Dogger Bank. In fact, that was the role he first took having resigned as energy minister, replacing Lord Deben/JohnSelwyn Gummer when he took over the Climate Change Commitee.

  5. Mike Jackson permalink
    January 18, 2017 2:39 pm

    It’s those bloody facts again, Euan! Do it to you every time! Many thanks for the work you have put into this though I doubt you’ll get much applause or even acknowledgment from those in power.

    I had hoped that May and her advisors, being a bit less starry-eyed than Cameron and his, might be more amenable to reason and I suppose we can still hope though the decision on Hinkley does not bode well for an outbreak of sanity.

    As usual Booker makes the point fairly well. Whatever the benefits to be gained environmentally from Swansea Bay — and frankly all I can see are disbenefits — for the relatively paltry amount of electricity expensively generated, the intermittency, and the cost of the entire project (not forgetting the cost in financial and environmental terms of quarrying and transporting the stone) we could have half-a-dozen CCGT stations generating considerably more electricity 90% of the time instead of a variable 60%.

    And why is anyone listening to Hendry? An ex-minister at DECC shoots through the revolving door, produces a report on a highly complex matter in an area in which he has no professional expertise to please the Green Blob … and we describe that as “independent”??

    “When I use a word,” Humpty Dumpty said, in rather a scornful tone, “it means just what I choose it to mean—neither more nor less.”
    “The question is,” said Alice, “whether you can make words mean so many different things.”
    “The question is,” said Humpty Dumpty, “which is to be master—that’s all.”

    Knew a thing or two did Lewis Carroll.

  6. January 18, 2017 2:59 pm

    Thanks for this Paul. The post had some good comments, the main points being:

    1) There is good published academic work on this exact issue which shows that my main conclusions are generally correct though not in detail – which is what I expected.
    2) Tidal stream has maximum flow at half tide height and can therefore be used to fill in the troughs a bit – so long as you don’t mind paying for it.
    3) The spring / neap problem cannot be got rid of no matter what you do, spring generation about 3* neap – this remains the main obstacle to ever turning tides into base-load.
    4) There has to be concern about seabed stability around the wall where strong currents may cause scour.
    5) The large lagoons may actually impact tides on a semi-regional basis.

    The academic who published the work acts as a consultant to Tidal Lagoon plc. So they have access to the best information that shows tides can never provide base-load and yet continue to pretend that it does.This is typical Green thinking. Make believe that tides can provide base-load and continue to push that myth regardless of facts that emerge. I’ll have a follow up post Friday.

  7. January 18, 2017 3:08 pm

    So ‘Swansea Bay Tidal Lagoon and Baseload Tidal Generation in the UK’ don’t belong in the same sentence.

  8. Joe Public permalink
    January 18, 2017 3:13 pm

    “We are well aware of the problems of intermittency with the proposed tidal lagoon at Swansea Bay.”

    Readers of the Beeb’s original version of the story didn’t have that fact drawn to their attention.

    The initial story and image caption failed to mention intermittency at all

    The Beeb had to be informed that there was a major flaw in their fawning sycophancy of which the public had a right to be informed.


  9. Athelstan permalink
    January 18, 2017 4:19 pm

    Mr. Jackson gets it, to which, humbly………………….. I can only add to, Mike.

    The Swansea deposition lake, you can feel it know wot I mean?

    It is tangible – a folly to beat the others! if birdmincers don’t do it for Joe and Joanna public, then perhaps their green taste buds can be tantalized by a boondoggle which is spectacular in all that it does, can be utilized by part time sea farers, grockles galore, looks shiny and significant [of what we know not]……….. like the ‘Angel of yon Northern tribe’ – wow and could be artualized by Damian or Tracy – just think! …………………modern art, is a movement in, of and for the people innit, who cares about the cost or efficacy, shower them in shiny shite, it shows that [for the authorities] you care and definitely that – yers don’t.

    Didn’t tony once shout, a computerized NHS records system for all!, regime change, MAD, saddam must go whatev – for all!, Education, Education and more EU bogoff to prudence MacRuin it was always – boondoggles, boondoggles, Boondoggles for all!

    Art imitating art for the arts only and the people: one way or another will be buggered.

  10. January 18, 2017 4:45 pm

    Of course one of the environmental impacts of tidal lagoons that is never mentioned is coastal erosion, particularly adjacent to cliffs (the White Cliffs of Dover are only white because of continuous erosion). This would be of particular concern for the lagoon proposed in Bridgewater Bay.

  11. ANdrew Tull permalink
    January 18, 2017 7:35 pm

    I am always staggered at the white washing of green issues applied by the general media. The public are continually brainwashed so that the scientific community can dine out. When I’m told the science is settled I just know I’m being bullshitted.
    To my un-educated eye the world isn’t about to fry but we probably have at most 100 years of realistic fossil energy, two to three generations of power generation before we will have to rely of some other form energy creation. In 100 years time energy storage might just be at a useful stage in which case 14 hours of reasonably secure generation sounds pretty good to me and worth investing in.
    Unless this forum recognises that we do actually need a way forward for the future then.its no more than a collection of tossers just like the ones on the otherside of the fence!!
    …bet you don’t publish this!!!!

  12. It doesn't add up... permalink
    January 18, 2017 7:41 pm

    The real picture looks more like this:

    • Jack Broughton permalink
      January 18, 2017 8:47 pm

      Is this based on Euan’s report, as I thought that his peak was 6GW, but this is even worse in terms of the back-up plant regime. We would need to have about 10 GW of fast response plant such as pumped storage able to supply the lost power for several hours – where will this come from?

    • Jack Broughton permalink
      January 18, 2017 8:49 pm

      Sudden thought, maybe Mr Knut Hendry can command the tides and avoid the problem!

    • January 19, 2017 9:53 am

      IDAU, what you have posted is ebb only generation – 2* / day. What it shows is that the Severn is out of phase with the Irish Sea – which is what we already said. The dual – ebb + flood 4* / day generation – that is favoured looks like this.

      • It doesn't add up... permalink
        January 20, 2017 3:02 pm

        I don’t think it is clear what is favoured, or perhaps more to the point, how tidal schemes will be optimised in the light of economic incentives. Given a guaranteed high price for MWh produced the incentive is to maximise energy produced. Reverse turbining on flood tides produces the alternating lower power pulses. The models suggest that more total power is produced by ebb only operation, where extra hours of ebb operation and a greater maximum head more than compensate for the loss of flood generation.

        Neither of those schemes consider additional pumping, which produces negative power spikes in between the gaps, as well as more output (creating even bigger ramping problems for the rest of the grid’s power suppliers, which could be made a lot worse when a solar peak coincides with peak tidal output). The first tranche of additional pumping may add net output – 100MWh invested in pumping shifting additional quantities of water that have already been mainly lifted by the moon’s gravity might produce 200MWh of additional output. However, the next 100MWh of pumping might only produce an additional 50MWh of output, so it becomes energy negative on a net basis. However, if they’re being paid £123/MWh and the pumping only costs £40/MWh, they make a profit of £50×123-40×100= £2150 out of destroying energy. That’s why I think it could be like the RHI cash for ash scandal in Ulster. The only limit is when additional pumping eats too far into generation time, resulting in loss of output, or when the additional pumping power costs more than the value of marginal output.

        Since tide cycle time becomes a constraint, the incentive is to over-invest in turbine capacity to harvest the generous subsidy on pumping, by pumping faster, and producing more.

    • January 19, 2017 10:07 am

      I guess I should clarify that with Severn and Irish Sea ~ 6 hours out of phase gives 4 * day generation with 2*day in Severn staggered with 2* / day in Irish Sea.

  13. duker permalink
    January 18, 2017 10:39 pm

    Was there any thought to making the tidal lagoon partly storage as well to be able to generate on demand? Those gates that rise out of the seabed would do nicely, even if it was to only partly reduce the outflow

    • It doesn't add up... permalink
      January 19, 2017 1:18 am

      Swansea is pretty puny for storage (in theory on a high spring tide, perhaps 1 GWh might be behind the sea wall provided you can accept it will not provide anything until the tide has dropped at least a couple of metres, and power will tail off significantly as it empties), and it would not be able to add much (or even any) power back to the grid on demand, unlike Dinorwig, which has the big advantage of a big drop between its top lake and the bottom one, allowing it to offer up to 1.7GW from its 9GWh maximum storage. Swansea might need to be producing power in the middle of the night depending on the tide, instead of buying it to pump water uphill. Rush hour could then be at slack water. Building up the sea wall to increase capacity becomes very expensive – wall costs scale with the square of height (triangular cross section to diffuse waves) – with a poor return. They will be able to buy some power at market prices close to high tide to pump in some extra water – and sell it again at three times as much under their CFD – particularly during lower neap tides.

  14. January 19, 2017 10:22 am

    La Rance tidal power station has a capacity factor of 28%. Unlikely Swansea could do much better, if at all?

  15. Jack Broughton permalink
    January 22, 2017 7:15 pm

    A lot of great comments about the issues of tidal power and the back-up, following Euan’s excellent analysis. I just looked at the wiki site mentioned by IDAU and it does state that the UK has 20 GW available, however, the secure generators in hospitals etc. are there to cover for grid failures and then operate in island mode. So far as I am aware they do not have export meters (G59), even though they can easily be added. There will be a conflict between the security duty and the exporting duty as the stand by set will be tripped by a grid voltage dip.

    It would be desperate to use these small generators for long periods as they burn premium fuels as is appropriate when in security mode; they are not usually suited to continuous generation.

    The intermittency coupled with the comment about Rance by Denise Bowes should be enough to get this proposal filed in the round cabinet.

Comments are closed.

%d bloggers like this: