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Swansea Bay–The Basic Facts

June 26, 2020

By Paul Homewood


Given the renewed interest in the Swansea Tidal Lagoon, it is worth republishing a post I published in June 2018. It still seems as valid now as it did then:


This letter appeared in the Telegraph the other day:




Leaving aside the question of HS2, the writer shows a total lack of understanding about Swansea Bay, which is probably due in turn to the wholly amateurish way it has been treated by most of the media.

So, for Tess’ benefit, here are a few basic calculations:

  • Cost of lagoon – £1.3bn
  • Electricity produced – 532 GWh pa, which is 0.15% of UK generation
  • This is enough to supply on average 40,000 homes
  • Therefore the cost per household is £32,500
  • There are an estimated 107,500 households in Swansea, so the lagoon could not even supply half of the town.
  • Even after the capital costs, ongoing costs will be substantial, for instance dredging and maintenance and replacement of turbines.

If Tess thinks that sounds like a good deal, heaven knows what a bad one looks like!

  1. Stewart Herring permalink
    June 26, 2020 11:01 am

    On the other hand.
    The generation of electricity will be predictable, unlike other renewable sources.
    What are the savings generated by reduced flooding further upstream?
    There will be jobs created.
    Another source of income could come from putting a railroad on top of the polder/dam (that would also help reduce maintenance costs).
    There is the possibility of bird life being harmed by loss of habitat. Such habitats can be recreated nearby utilising by products from the polder.
    It’ll be a huge project.
    Just because it’s difficult doesn’t mean we shouldn’t do it.

    • Harry Davidson permalink
      June 26, 2020 12:15 pm

      You seem to be thinking of the Severn Barrage, which IMHO would be a good idea. The Swansea lagoon would have no effect on up-stream flooding, you couldn’t put anything on top because it doesn’t go anywhere. You are right it would be a huge project, but one that gives very return on investment.

      • Stewart Herring permalink
        June 26, 2020 12:43 pm

        You are correct.
        My mistake.
        I think I’ll sit on the naughty step and keep quiet

      • It doesn't add up... permalink
        June 26, 2020 8:59 pm

        Not quite no effect… The barrage would go right up to the mouth of the River Tawe. I suspect the construction would also affect the mouth of the River Afan which emerges at Port Talbot. Changes in the water circulation would likely lead to silting of channels into both ports (there is a scouring circulation around the bay from the Mumbles that performs some natural dredging).

    • Harry Davidson permalink
      June 26, 2020 2:17 pm

      Nope, you can’t have the naughty step. I’ve got it booked long term.

    • Ray Sanders permalink
      June 26, 2020 7:44 pm

      “The generation of electricity will be predictable, unlike other renewable sources.”
      Predictability is not a virtue. Knowing my car will not start tomorrow morning is still rather annoying.
      “What are the savings generated by reduced flooding further upstream?”
      This is a tidal lagoon… “upstream” at all.
      “There will be jobs created.”
      Sweeping the street is also a job……so what.
      “Another source of income could come from putting a railroad on top of the polder/dam (that would also help reduce maintenance costs).”
      Where on earth do you think this “railroad” will be going from and to?
      “There is the possibility of bird life being harmed by loss of habitat. Such habitats can be recreated nearby utilising by products from the polder.2
      What habitat is being lost? This is a tidal lagoon around a bit of sea.
      “It’ll be a huge project.
      Just because it’s difficult doesn’t mean we shouldn’t do it.”

      Is your name Tess Samuelson?

      • Harry Davidson permalink
        June 26, 2020 9:09 pm

        Nope, he has already admitted that he had confused it with the Severn Barrage. You would have known this had you followed the sound principle of “read before rant”

    • It doesn't add up... permalink
      June 27, 2020 4:01 am

      I dug out a PhD thesis I referred to when I was helping Roger Andrews and Euan Mearns with assessing tidal projects. This one dates from 1988, but is actually much more informative than some of the other papers and prepared to discuss some of the real practical problems. It provides a solid underpinning for the modelling used – the entire model is listed (in FORTRAN!) – a lesson for one N Ferguson, along with data and output for a Severn barrage, which was assessed as capable of generating some 12.8TWh/year. Those who want to dig for themselves can find it here:

      Click to access 381648.pdf

      I charted up the various water levels and generator output for a peak spring tide and a low amplitude neap tide to show what the optimised output would look like. There is a lot of waiting time after high tide before generation starts. Starting to generate earlier means that the head (difference in water levels) starts low, generating less power, and chases the tide level down, reducing the maximum output, and running out of head altogether as the tide starts rising again. There is almost a tenfold difference in energy output between the spring tide and the neap tide. Maximum power in the neap tide is barely a quarter of that in the spring tide, and the duration of generation is much shorter. Switching in 3GW of supply at the start of generation in a spring tide is no easy matter for the Grid to handle: in practice there would be a limit on ramp rate of say 100MW/min. Losing the 7GW peak output due to a fault would be a nightmare likely to result in blackout.

      Predictable – more or less, give or take storm surges, which can change timings as well as tide levels. But horribly gap toothed, and a grid nightmare, requiring extensive backup both to cover the gaps and spinning reserve to avoid blackout trips.

  2. June 26, 2020 12:04 pm

    These exchanges tend to get emotional and the more factual and data oriented you get the worse it gets because then it appears that you “don’t care”.

    Something most deniers may not appreciate is that the climate change thing is an emotional issue.

    • June 26, 2020 12:47 pm

      Bill McKibben for example. Even the scientists. Kate Marvel for one and that lady from Texas. Also that lady from Ireland shedding tears for the oceans being acidified. What is another science driven by emotion and legitimized by brandishing the word science?

    • Bertie permalink
      June 26, 2020 12:58 pm

      I cannot agree that it is an emotional ‘issue’. The issue is surely one of scientific fact – the emotions are overlaid on various premises. For some obscure reason the progenitors get much more animated than the ‘deniers’ who deal in facts.

      • MrGrimNasty permalink
        June 26, 2020 5:02 pm

        It shouldn’t be, but it is. Climate science has been co-opted by political operatives/social justice warriors, not credible scientists, and turned into an ism/ology.

      • June 26, 2020 5:02 pm

        Thank you for your input

  3. Mad Mike permalink
    June 26, 2020 12:37 pm

    chaamjamal, you could apply that to virtually anything in life from vegetarianism to fishing in the North Sea etc.

  4. Mr N Moore permalink
    June 26, 2020 12:52 pm

    Looking at it from an investment perspective, the annual 532GWH equate to around £21.3m (at £40/ MWH). So knocking off some running costs and a sinking fund to replace plant I’d guess at a ‘return on investment’ of around £15m, or 1.15%. Most infra investors would be looking for a ROCE of
    10-12%. It’s just not an ‘investable’ deal.

    • A C Osborn permalink
      June 26, 2020 5:10 pm

      Ho, dondn’t worry they want a lot more than £40/ MWH, at least 3 times as much

      • It doesn't add up... permalink
        June 26, 2020 9:04 pm

        Their original bid was for £168/MWh in 2012 money, guaranteed and indexed for 90 years. That would already be worth £194.84/MWh if they started generating tomorrow.

  5. Robert Jones permalink
    June 26, 2020 5:26 pm

    My memory is dusty but isn’t the businessman pushing the Swansea Lagoon project a little bit of a chancer?

    • Harry Davidson permalink
      June 26, 2020 9:10 pm

      Almost right. You should not have included “little bit of”.

  6. tom0mason permalink
    June 26, 2020 5:44 pm

    From 4 years ago is this paper Wave and tidal current energy – A review of the current state of research beyond technology.
    ( )

    The conclusion is very interesting —

    8. Conclusions
    This study has reviewed the state-of-research in ocean energy, focusing on wave and tidal current, not directly associated with improvement to ocean energy technology and identified areas where future research efforts should be directed to.

    Modelling approaches for resource assessment and forecasting are already very advanced and have been performed for many regions of the world. However, this should be widened to accommodate conflicting or competing use of the marine environment such as fishing, shipping, offshore wind, habitat protection and also technical limitations (e.g. grid connection).

    Comprehensive Life Cycle Assessments of ocean energy arrays that would also include areas like fluctuation of power output, storage, or grid integration are still missing and for a number of individual WEC types, no Life Cycle Assessments are available so far. Another area which merits further research is the field of regulatory and legal affairs to define an adequate and optimal legal framework for ocean energy.

    In terms of grid integration, the impacts of increasing demands on power quality of renewable energy to contribute to system reliability and stability should be discussed. Further research in the area of control strategies is needed since it offers a great potential for cost reduction due to increased absorbed energy while allowing meeting grid codes requirements. No long-term experience with devices is available concerning commercial operation and maintenance and few articles try to assess the resource needs for installation (e.g. time, cost). Array design parameters such as device spacing might have an impact on operation and maintenance activities and costs: this is not very well understood so far and should be addressed.

    The most important areas, however, where future research should be focussing on are the economic and social impacts of ocean energy. A broad cost benefit analysis of ocean energy incorporating aspects such as grid integration and energy security could be very important. Economic aspects of ocean energy including predictions of future costs of ocean energy have been addressed but improvements are needed, especially in the area of operation and maintenance costs. Cost–benefit analyses that include also aspects such as grid integration, energy security, and ecosystem services are missing. Social impacts are not well understood, when it comes to impacts beyond job creation. In particular, studies on the effects on national and EU level are needed.

    They call for a “broad cost benefit analysis” of these systems, now that would be new for so called ‘sustainable’ or ‘renewable’ technology!

  7. Stuart Brown permalink
    June 26, 2020 6:58 pm

    Has anything much changed since the late Roger Andrews skewered this 5 years ago? Sadly the site that hosted many of his diagrams folded, but you can see them on the wayback machine if you go here:

  8. Thomas Carr permalink
    June 26, 2020 8:52 pm

    Yes there will be plenty of siltation to be cleared regularly before the turbines are compromised .
    Before a letter goes to the Telegraph to bring Tess up to speed should we not be able to say what the feed tariff income will be as a return on the £32,500 capital cost per household.
    And then there is the cost per dwelling of the zero carbon enhancements.
    Its all a bit complicated but I’m sure that a Telegraph reader will relate to stats. expressed on a per household basis.

  9. It doesn't add up... permalink
    June 27, 2020 4:09 am

    I think 13.3MWh per home is rather high for electricity (2.5-4+, depending on who is claiming…), but probably a bit low for overall household energy consumption. The “home” is one of the most flexible units of energy known to man. MTOE would be better!

  10. Nordisch geo-climber permalink
    June 27, 2020 10:33 am

    This is Euan’s analysis of tidal, comments below are informative:

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