Renewable Energy - Double Tidal Lagoon Baseload Scheme

Discussion in 'Architecture & Engineering' started by Scottish Scientist, Jan 17, 2017.

  1. Scottish Scientist Registered Member

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    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.

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    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”.
     
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  3. exchemist Valued Senior Member

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    Very good idea. The snag with almost all renewables is their intermittency and this seems a very reasonable way to address the problem with tidal power. Nice.

    I hope you got your patent application in before posting your message!
     
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  5. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

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    I'm sure I've seen a paper on this before from a while ago, not specific to double lagoons but using multiple lagoons in general, starting from the same point that tidal power provides intermittent, if predictable, supply.

    But good stuff. It's certainly a pertinent discussion given the recent news.

    Okay, so following your notes (and please do not take this as anything other than me trying to get my head round what you have proposed... any perceived slight is utterly unintended):

    At high tide the high lagoon is open to the ocean, so is at high level, and water is flowing into the low lagoon which is closed to the ocean. At what point in the cycle does the high lagoon close its gates after high tide? If left open too long both sides of the lagoon will be at the same relatively high level, right - depending on volume flow through the turbine.
    So let's say it is closed at high tide.
    Water flows from high to low lagoon... There must come an equilibrium point at which they are the same level. Is this timed to match the low tide?
    Okay, so when the low lagoon - now at the same equilibrium level as the high lagoon - is opened to the ocean, the level of both lowers... So why not generate power with that?
    Likewise, when the high lagoon is being filled by the ocean, why not generate power then?
    Then you would be generating power during the high lagoon filling up, during the transfer from high to low, then to emptying both.

    What you seem to be suggesting, though, if I have understood correctly, is a system whereby the generating capability barely touches on the maximum capability of the tides, where the flow through the central turbine is relatively low such that the lagoons never reach equilibrium during the tide cycle. Before it reaches equilibrium, the high lagoon is topped up, the low lagoon is emptied?
    While the load would indeed seem to be more steady, would the cost per MW not be that much higher, even once the intermittent supply of the original design is averaged?
    And again, why not generate power during those topping up/emptying phases?

    Alternative solution could be lagoon-based storage devices, using the excess supply (beyond a required steady baseload) to actually pump water into another lagoon that can (somehow) be used to generate electricity while the main lagoon is effectively not producing, and thus smooth out the overall supply.

    I'd be interested in comparing the production capability and cost of your proposed solution, though, with the original, taking into account the additional cost for the original in smoothing out the supply.
     
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  7. Scottish Scientist Registered Member

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    MacKay discusses double lagoons (with and without pumps) in Sustainable Energy - without the hot air, pages 320/321.

    The web claims that, in 2000, a three-lagoon proposal was floated by Peter Ullman’s Tidal Electric co. and offers an image (below), though the Tidal Electric website now doesn't, that I can see, explain.

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    Impression of a 3-cell lagoon (Peter Ullman’s Tidal Electric Co, 2000)

    Wikipedia mentions "Tidal Barrage - Two-basin schemes".

    Well it's not my original idea but the news about Swansea Tidal Lagoon and the criticism of that scheme in Energy Matters sparked my interest and inspired my Scottish Scientist blog post of a couple of days ago and this thread.

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    What part of
    don't you understand?

    As the high tide turns to ebb, the high lagoon sea-gates, as per a one-way flow flap valve, close automatically to resist any back-flow of water from the high lagoon.

    The system is designed in normal operation not reach such an equilibrium by limiting, by design, the flow through and the maximum power of the turbines. It is not a question of timing, it is a question of scaling by design the number and power output of turbines appropriately to match the continuous power capacity of the lagoons and the tides.

    In this scheme, the high tide flows through the sea-gate into the high lagoon as soon as there is enough of a head of tide to open the flap valves (or other equivalent engineering). There is indeed generation at that time but through the turbines between the high and low lagoons, as there is continuously.

    This double lagoon baseload scheme offers steady power on demand, sacrificing the inferior single lagoon's maximum peaks of power which come at the terrible price of zero power minimums. So if you understand the baseload scheme why are you asking me to explain it again!

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    Well can I suggest you try to answer your own questions about relative costs per MW of this baseload scheme versus intermittent single tidal lagoon schemes plus the cost of back-up power supplies pumped-storage / batteries etc, to, as you so casually put it "is averaged".

    "Is averaged"? Oh why don't we just "is average" intermittent wind and solar too while we are at it?

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    Storing energy is very expensive!

    In this scheme, power is generated continuously through the turbines between the high and low lagoons. There's no appreciable head between the sea and the lagoon when the sea gates are opened so attempting to generate lots of power there would be futile.

    Yes well, knock yourself out trying to come up with more complex so-called "solutions".

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    That is of interest. Agreed.

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    Last edited: Jan 18, 2017
  8. exchemist Valued Senior Member

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    The interesting point to me in this exchange is that one should compare the cost of this type of scheme against that of conventional (e.g. Rance -type) intermittent tidal generation, plus the electricity storage required to cover the periods around slack water at each end of the tidal cycle.
     
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  9. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

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    I understand that, but it didn't make sense to me until I fully surmised the system you were describing, for which I asked clarification of my understanding.
    Okay.
    Got it. Could there not be benefit from delaying the refill of the high lagoon and outflow of the low lagoon to generate from them as well, without sacrificing the the continuous generation?
    It was a question that sought clarification of my eventual understanding. You may have noticed that throughout my initial reply I did not seem entirely clear of the process being described. I believe your subsequent response has helped clarify, though.
    Rather than simply look to ridicule, perhaps provide some information? Or usefully direct toward where it might be found? A civil response is not too much to ask, is it?
    Are there numbers to support the proposal that you'd care to share? Or that I have missed somewhere?
    One man's complexity is another man's job.

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    My thinking was that there may be more complex solutions that offer a more beneficial power/cost ratio. Having only seen the standard single lagoon before, and now this, I have seen nothing to rule such out, but if you have...?
    Are you aware of any such study in the past? Or know of costs of methods of smoothing supply?
     
  10. Scottish Scientist Registered Member

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  11. Scottish Scientist Registered Member

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    Well any delay to filling the high lagoon / emptying the low lagoon would reduce the head between the two lagoons and reduce power.

    Wikipedia - Energy Storage. https://en.wikipedia.org/wiki/Energy_storage

    I have already shared a reference with you to
    And here's the link in case you missed it -
    http://www.withouthotair.com/cG/page_320.shtml
    Numbers are MacKay's thing but unfortunately, his presentation of this "no pumps" scheme is mixed up with his (in my view misplaced) enthusiasm for "with pumps" two lagoon schemes so his numbers and diagrams aren't all that useful in this context.

    The numbers in the critical review in Energy Matters, “Swansea Bay Tidal Lagoon and Baseload Tidal Generation in the UK”.
    http://euanmearns.com/swansea-bay-tidal-lagoon-and-baseload-tidal-generation-in-the-uk/
    oppose the single tidal lagoon proposal
    http://www.tidallagoonpower.com/'

    No, I don't know of, but I would be interested to find, a good review of the principles of this double tidal lagoon proposal, with calculations of the efficiency versus single lagoons.

    If I or someone else finds a good reference, then hopefully it will be posted here, or perhaps on my blog post -
    https://scottishscientist.wordpress.com/2017/01/16/double-tidal-lagoon-baseload-scheme/

    I invite people to post things that they know either here or on my blog.

    What I don't invite is anyone trying to pump me for information by asking a serious of tedious questions, expecting me to go do a search on their behalf instead of getting onto google and doing their own literature search.

    Please do not ask me any more questions.
     
  12. Baldeee Registered Senior Member

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    817
    To be fair to Sarkus, rather than just post and comment on some interesting article about the benefits of double lagoons, you have posted what you state is a proposal.
    On a science forum.
    Now it may be me, but surely that entitles people to question your proposal, as to the numbers, the benefits, the drawbacks etc, so that they may evaluate the proposal more closely.
    To expect people to do the work for you, when it is your proposal, seems... odd.
    To expect people not to ask you questions about your proposal is also... odd.

    Or is this not really a proposal at all that you posted?
     
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  13. billvon Valued Senior Member

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    It is indeed a good idea, but has been considered on and off for over forty years. So no patents I am afraid.
     
  14. billvon Valued Senior Member

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    I would point out that that picture indicates an anchored structure, not a floating one (you probably knew that.)

    One drawback is that low-head hydro systems are VERY heavy, inefficient and awkward to use, so you want to maximize the head by putting it someplace that sees at least 6' difference in tides. Here's an idea - use a single lagoon to store water. At the change of the tides, use ram pumps (simple mechanical pumps powered by a difference in water pressure) to pump a small amount of water to a small lagoon 50 feet up a nearby hill. Then release the water during times of peak demand. That way you have a lot of (cheap) mechanical hydraulic pump, and one smaller (complex) turbine/generator.
     
  15. exchemist Valued Senior Member

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    That's no problem around the British coasts. We get a tidal range of about 50ft in the Severn Estuary.
     
  16. billvon Valued Senior Member

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    Cool! One problem solved, then.

    I grew up on an island where one shore had 2-3 foot tides and the other had 6-8 foot tides. The 6-8 foot tides _might_ have worked - but 50 feet is obviously a much easier starting point.
     
  17. exchemist Valued Senior Member

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    Yes I think is why tidal power is, or should be, such a serious proposition for us in the UK. We have the tides, and we have a good ratio of coastline to land area as well. Mind you, the engineering for the winter storms needs to be robust.
     
  18. Scottish Scientist Registered Member

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    Well let's take a look at the tidal range of the coastline around Scotland and the north of England.

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    The Solway Firth

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

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    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.

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    Simple.

    Fortunately for tidal lagoon engineers, there seems to be an inverse relationship between "wave height and power" and "tidal range".

    Scotland's Marine Atlas: Information for The National Marine Plan
    http://www.gov.scot/Publications/2011/03/16182005/28
     
    Last edited: Jan 20, 2017
  19. Scottish Scientist Registered Member

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    Almorness Tidal Energy Scheme

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    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.
     

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