[Scottish Scientist (OP)]

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”.

[chris]

Why is your design better? It looks like the sensible and standard way one would approach this problem... What are the other designs proposing?

[Scottish Scientist (OP)]

Why ...

Pardon me Chris for not replying sooner but you appeared to be asking a question to which I had already posted the information you needed.

Why is your design better? It looks like the sensible and standard way one would approach this problem... What are the other designs proposing?

What I had already posted was this.

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”.

You don't seem to have investigated those links I posted. Perhaps you expected me to spoon feed you the information?

However, I will now copy and paste this text from an email I sent to MPs.

Dear MP who has supported the early day motion
"VALUE FOR MONEY AND SWANSEA BAY TIDAL LAGOON"

I am writing to try to outline to you the main scientific, engineering and technical flaw in the Swansea Bay Tidal Lagoon proposal whose primitive and inferior single lagoon design is not appropriate even as a "first of a kind" renewable energy generation project.

The advanced and superior double lagoon design, which I explain below in my emails to government is much more appropriate for generating electricity.

Please be aware that the proposed Swansea Bay Tidal Lagoon inferior single lagoon design does not offer valuable "dispatchable" power, on demand, when it is wanted by customers, when they are happy to pay for power.

Rather, this inferior scheme supplies a lot of worthless power only when it is convenient for the tides and to hell with what power the customer demands and is willing to pay for.

With the inferior single lagoon design there are times during the day when no power whatsoever can be generated, whenever the level of the water inside the single lagoon is the same as the level of the sea outside the lagoon.

Fortunately, the superior double lagoon design (explained below) can dispatch the day's tidal energy at any time in the day or continuously and therefore does, to some extent, offer dispatchable power on demand, though there is still a large variation in how much power can be dispatched from week to week between the high energy spring tides and the low energy neap tides.

In order to smooth this spring / neap variation in generation of tidal energy completely, so that full power can be dispatched on demand to happy customers regardless of the time of the day, week or month then additional back-up energy storage capacity (most likely using pumped-storage technology as is used at Dinorwig but other energy storage technologies exist) will be required and this will have to be constructed (and costed for) as part of a better plan for a double tidal lagoon scheme.

So Tidal Lagoon Plc have blundered fatally in proposing an inferior single tidal lagoon design with no back-up energy storage capacity but whereas Charles Hendry's review concludes “it offers limited dispatchability” regardless of that Hendry nevertheless recommends blundering on with this severely limited design, demonstrating that Hendry is out of his depth and is not competent to review tidal lagoon energy generation schemes.

Unless of course, this lagoon scheme is not really about generating electricity but is really about subsidising developer profits for building a recreational lagoon with dubious energy generation potential?

Anyway, I will leave the politics of it to politicians but at least you should all be forewarned about the half-baked nature of this tidal lagoon proposal as an electricity generating scheme - and have some idea about what sort of redesign (from single to double lagoon) it will take to rescue such flawed tidal lagoon proposals from gathering dust on the shelf.

[alancalverd]

A very good idea indeed.

It doesn't matter if the occasional spring or storm tide overtops the deep lagoon, if you just increase the area of the shallow one - much cheaper than increasing the height of the deep one.

Any figures on the reliability of existing tidal turbines?

[Scottish Scientist (OP)]

A very good idea indeed.

Relatively good, compared to the single lagoon design certainly but "very good" in absolute terms, compared to say simply using the same money that it will cost to build any such lagoon - which I have not accounted for and so I cannot even estimate - instead to buy more wind turbines and other technologies which we have more experience of, still has to be demonstrated.

I would like to see test structures built to prove the technology first - say a test lagoon the size of a large swimming pool to check whether the proposed construction method will work to hold the water in or keep it out as anticipated.

Tidal lagoons are an interesting concept which is promising if it works and can be built cost effectively but it is too unproven to bet the house on it, yet.

It doesn't matter if the occasional spring or storm tide overtops the deep lagoon,

Indeed, one could arrange the high ("deep") lagoon wall to be sea-facing so that waves can lap over it to top the high lagoon up, use wave power as well as tidal. Also it may be possible to arrange for the high lagoon to be topped up from a river, like this.

Almorness Tidal Energy Scheme

Almorness Tidal Energy Scheme – Map

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.

if you just increase the area of the shallow one - much cheaper than increasing the height of the deep one.

I can see why the area of the high ("deep") lagoon which was getting additional inflows from waves and rivers could be smaller than than the larger area of the low ("shallow") lagoon, sure.

However, I am not clear what you mean by "increasing the height of the deep one"? Increasing the height of the high ("deep") lagoon wall? Why would you want to do that, if you wanted waves to lap over it?

Oh it is the height of the low ("shallow") lagoon wall which must be higher, to keep out the highest of storm spring tides and waves. Any water that gets in to the low ("shallow") lagoon other than through the generating turbines is lost power and energy.

I doubt that it would be worth putting a cover over the low lagoon to drain rainwater into the high lagoon but someone should run the numbers on that to check.

Any figures on the reliability of existing tidal turbines?

I don't have those figures Alan no, sorry.

[alancalverd]

The last question is rather the weight of the elephant, I fear! There should be data available from the Rance barrage at least. Problem is that you can't extrapolate from a freshwater turbine as the water speeds will be much lower, there's a lot more flora and fauna in seawater, and the stuff is inherently more corrosive.

You will run into ecopolitical problems if you start damming estuaries and upsetting the treehuggers, but the system will work just as well a mile or so offshore.So here's a thought: three long, narrow parallel concrete strips in the Thames estuary, separated by say a quarter of a mile between each and joined at the ends, to form two lagoons, a runway, a taxiway and a service road. Airport and power station in one unit!

[Petrochemicals]

Must say i disagree, a double lagoon will half the catchment area, and quater the generation. And from the figures i have seen the tidal pool system is not worth the effort. It costs 1.3 billion, takes up a lqrge ammount of natural habitat and only powers 130,000 homes. Im sure useless solarphotovolcaic and wind will provide better value.

If the thames has a barrier on it already, surely closing the barrier for low tide and letting the water run through the already present pumps will generate alot of energy, or the same with the severn mouth. I think the problem is the storing of the energy, so some sort of water pump up th the mountains above swansea seems obvious.