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The proposed Swansea Bay tidal lagoon

These notes from a presentation to the Campaign for the Protection of Rural England (CPRE) at Taunton on 13th January 2015 were taken by Phillip Bratby.


Tidal Lagoon Swansea Bay (TSLB)[1] was founded by its CEO Mark Shorrock in 2012.  He has a long history of involvement in renewable energy (CEO of Shire Oak Energy, Low Carbon Group, Low Carbon Investors Ltd and Wind Energy Ltd).

Finance of the initial phase of tidal lagoon development is being funded by Mark Shorrock to the tune of about £20m.  Thereafter it is expected that institutional investors would fund the construction and would become shareholders.

CPRE was invited to a presentation on the proposed Swansea Bay Tidal Lagoon on 13th January 2015 at Taunton.  It was attended by the CPRE Senior Energy Campaigner from London and representatives from CPRE Devon, CPRE Somerset, CPRE Gloucestershire and CPRE Avonside.  The interest of CPRE is not directly in the proposed Swansea Bay Tidal Lagoon, but on possible future tidal lagoons on the English side of the Bristol Channel.

The presentation was given by Eva Bishop of TLSB.  We were promised a copy of the presentation, but after over 3 months, we were presented with a reduced set of slides because of "the sensitivity over certain information and figures within the slides presented" and the slides that we did receive were "not for wider circulation".

The Swansea Bay Tidal Lagoon

The proposed Swansea Bay Tidal Lagoon is intended to be the first of a series of much larger tidal lagoons.  As an 'offshore generating station' and being of >100MW, a 'nationally significant infrastructure project' (NSIP), the planning process is managed by the Planning Inspectorate and the decision to grant a 'Development Consent Order' (DCO) is made by the Secretary of State for Energy and Climate Change following a recommendation by the Planning Inspectorate.  The process requires an Environmental Impact Assessment, public consultation, public hearings and examination by the Planning Inspectorate leading to a recommendation to grant or refuse by the Planning Inspectorate.  The process began in 2010.  The decision will be made by Amber Rudd by 10th June 2015 and if a DCO is given, construction will start at the end of 2015 with completion and connection to the grid expected in 2019.  A marine licence (to allow dredging and construction is required from the Marine Licensing Team of Natural Resources Wales (NRW) on behalf of the Welsh Government.  Other permits, such as from the Crown Estate and Swansea Docks, are also required.  The Planning Inspectorate issued a report of recommendation to the Secretary of State on 10 March 2015.  The Secretary of State has 3 months in which to issue a decision.  The decision letter of the Planning Inspectorate will not be made public until after the decision has been made by 10th June 2015.  A 6 week period is available after the decision for any legal challenges to the decision..

All the documentation can be seen at the National Infrastructure Planning website[2].

As is the norm with renewable energy schemes, there is a great deal of confusing, contradictory and misleading information given in the project description and application documents.  Based on past experience, it is very unlikely that the Planning Inspectorate will realise this and will have taken the information provided by the TLSB as being factually correct.  I will explain the most important of these below.

Project description

The project would consist of a 9.5km long breakwater enclosing a lagoon of area about 11.5km² in the Swansea Bay area of the Bristol Channel, a location chosen because of the high tidal range.  Two designs of breakwater are being examined, but both would include a considerable quantity of dredged material/rubble enclosed in rock armour and capped with concrete. 

Its lifetime of the Swansea Bay tidal lagoon is about 120 years and it will be funded for about 35 years at a strike price of about £168/MWh[3][4].  After that period it will produce unsubsidised electricity.  If the scheme is permitted, it will be considered as a first-of-kind test bed for the concept of tidal lagoons.  Note that £168/MWh is about 3 to 4 times the wholesale price of electricity (see chart below[5] which shows wholesale electricity prices fairly stable since 2009 at around £40 to £50/MWh) and would probably make the Swansea Bay tidal lagoon the most expensive generator in the UK, exceeding Hinkley C by 80% and offshore wind by 20%.  Notwithstanding this fact, TLSB state that it is "low cost".

The electrical output is uncertain and TLSB don't like to use the term capacity factor.  It will produce electricity four times a day during each ebb and flow tide, roughly 14 out of 24 hours.  The installed capacity of the 16 x 20MW bi-directional turbines is 320MW, but the rated capacity at 4.5m head is 240MW.  [Note the tidal range is between 4.1m (neap)  and 8.5m (spring)]  The actual output is optimised by operating for longer at lower output, based on the head difference between the water levels inside and outside the lagoon.  Basically, the output is intermittent but predictable, being roughly 14 hours per day (3.5h per ebb and flood tide, with 2.5h between), with water flow controlled by sluice gates.  Because the subsidy is a flat-rate, based on total MWh produced, not when it is produced or based on maximum demand, it is evident that the output profile will be managed to produce as much electricity as possible. 

TLSB repeatedly state in the application documents that the scheme will produce baseload electricity, but that is clearly false.  The total estimated annual output is variously given as 400GWh and 495GWh.  Thus based on an installed capacity of 320MW, the load factor is 14.3% or 17.7% and based on the rated capacity of 240MW, the load factor is 19.0% or 23.5%.  This is roughly equivalent in output to a conventional power station of about 60MW operating at a load factor of 90% (in other words, a tenth of the size of a typical 600MW turbogenerator).At a strike price of £168/MWh and a production of 495Gwh, the annual income would be £83m.

The capital cost of the scheme is obviously commercially sensitive, but has variously been estimated at between £750m and £1,000m.  For this capital investment one could build a 600MW CCGT power station which would produce 10 times as much electricity and which would not need a subsidy.

TLSB variously claim that the scheme will produce enough electricity to power 120,000 to 155,000 homes and will reduce (or save) the emission of 236,000 te CO2 per year.  Based on these figures it can be deduced that TLSB assume an emissions displacement factor of 0.477 kg CO2 /kWh.  No reference is given for this figure of 0.477 kg CO2 /kWh.  The correct displacement factor to use is given by DECC.  The Government approach to CO2 emissions savings from renewable electricity is specified in its progress report to the EU 'First Progress on Promotion and Use of Energy from Renewable Sources for the United Kingdom'[6] where it is stated that the savings from renewable energy electricity deployment are "calculated by multiplying the amount of renewable electricity generation by DECC's marginal emissions factor".  The marginal emissions factors are given in a joint HM Treasury/DECC report entitled ‘Valuation of energy use and greenhouse gas emissions for appraisal and evaluation’, June 2010.  This report was updated in September 2013.  The conversion factor for 2015 is 0.312 kg CO2 /kWh and the figure falls with time as the UK electricity generation is de-carbonised such that by 2050 it is 0.030 kg CO2 /kWh.  Over a 35 year period beginning in 2019, the average factor is less than 0.175 kg CO2 /kWh.  TLSB have exaggerated the emissions of CO2 displaced from other generating plant by a factor 2.7 over the 35 years that the scheme would be subsidised.  The CO2 emissions displaced over the 35 year period would be no more than 87,000 te per year.  This exaggeration of displaced emissions is typical of renewable energy companies. 

However, the CO2 displaced is only part of the story.  The 'carbon footprint' of the scheme has to be considered, together with the impact of the intermittent and variable output on the operating efficiency of other generators on the grid.

A 4-year payback time was stated (the carbon footprint).  However, this figure would be based on the exaggerated CO2 displacement ffigure, which is a factor 2.7 too high.  Hence the payback time would be at least 10 years.

The impact of the intermittent production of up to 240MW of electricity upon the efficiency of despatchable fossil-fuel power stations required to balance supply with demand and maintain grid stability is not known.  However, the ramping of power up and down to mirror the output of the tidal lagoon would reduce the efficiency of the despatchable power station(s) and would result in increased CO2 emissions. 

Taking account of the carbon footprint and the increased emissions of despatchable plant, the CO2 emissions saved by the proposed tidal lagoon would be considerably less than 50,000 te per year.  Compared to the UK 2025 target of an annual reduction of 296Mt of CO2, the contribution of the proposed tidal lagoon would be less than 0.02% of the target, i.e. an insignificant amount.  The Government has repeatedly made it clear that the renewable energy targets for 2020 will be met without any further renewable energy schemes and there are no renewable energy targets beyond 2020.  CO2 targets beyond 2020 should be met by the cheapest and most effective generators.

The breakwater/embankment will be built of millions of tons of gabbro rock from a re-opened Dean Quarry in the Lizard Peninsular in Cornwall.  The quarry is now owned by Shire Oak Quarries, a sister company to TLSB.  It has been selected due to its proximity (when compared with shipping from outside the UK), suitability (in terms of rock density and particle size) and volume of rock available.  The site is consented to extract rock and the company is preparing a planning application to replace the existing jetty with two new jetties plus a protective breakwater to enable the transport of all rock by sea, avoiding rail or road traffic for construction.  The proposed jetties and breakwater would be located within the Manacles Marine Conservation Zone (MCZ).  This has understandably created controversy[7].  TLSB says that it considered alternative sources of rock from as far away as Norway, but it seems to have overlooked, for example, the suitable rock available from an existing and operational super-quarry at Glensanda in Scotland, where, subject to contract, the required particle size could be obtained.

A CPRE geologist raised the issue of silting, stating that he would expect rapid silt deposition such that it would become an issue within a few years of operation.  Silting up of the lagoon received very little attention in the application documents.  A brief search found this:

Dredging works will also be carried out as part of the continued maintenance of the Project. During the Project's operation, limited siltation will occur within the impoundment, which will eventually affect the level of head that is able to build.  When this occurs, TLSB will undertake maintenance dredging. 

We have been subsequently informed that:

...for Swansea Bay TLP will bring in a transportable dredger and place it into the lagoon.  This will dredge while the lagoon is in operation and has no effect on power output.  It will pump over the wall and into barges outside the lagoon.  Then tug boats will take this to a disposal site 3 to 5km from Swansea (an existing site).  Other lagoons are likely to have ship access, which is generally more efficient.  This would enable TLP to bring in a dredging vessel e.g. a small hopper or a cutter so we do not have to pump over the wall.

It is not known whether dredging will be a continuous operation, 24 hours a day throughout the year and there is no indication of the amount of fossil fuel used in the dredging operation or the noise created.  The benefits in terms of assumed tourism and recreational use could be seriously impacted by dredging operations.

Future tidal lagoons

The major CPRE concern is for possible future tidal lagoons along the English coast, with several large schemes being looked at which it is claimed could produce up to 8% of the UK electricity (in the Bristol Channel and between Colwyn Bay and Cumbria).  Three of the schemes being examined are in the Bristol Channel, two on the Welsh side (Cardiff scheme and Newport scheme) and one on the English side (Bridgewater scheme).  The Bridgewater scheme (stretching from possibly Minehead to Weston-Super-Mare and completed by 2027) was of huge concern to CPRE on the grounds of impact on tourism, landscape, wildlife, farming (Somerset levels) and on the natural processes of coastline erosion, beaches and mudflats.  In particular it is noted that the Somerset coastline to the west of Hinckley Point is an erosional coastline.  The land is gradually eroded to form the cliffs that produce the attractive coastline of significant tourism and recreational value.  If the erosion was halted by the coast being enclosed within a lagoon, then the cliffs would become overgrown and degraded, and the coastline would become less attractive.  Silt deposition and the need for dredging would also be an issue.


The proposed Swansea bay tidal lagoon is a nationally significant infrastructure to be decided by the Secretary of State for Energy and Climate Change.  It is likely that the Secretary of State will have been given a recommendation by the Planning Inspectorate, based upon incorrect evidence because the application documents contain misleading and incorrect information.

The proposed tidal lagoon would produce an insignificantly small amount of very expensive (unaffordable) and intermittent electricity, it would have an insignificant effect on CO2 emissions and it would adversely impact on the operation of despatchable power stations required to balance supply with demand and maintain grid stability.

Logically, the proposed tidal lagoon should not go ahead.

Post script

If the Secretary of State for Energy and Climate Change decides in favour of the Swansea Bay Tidal Lagoon it will indicate several things:

  1. The Conservative Government is continuing with the Labour and LibDem energy policy of command and control, in which business decisions are taken by politicians..  It will signal that it is not in favour of a free market in electricity generation.  It will indicate that it has not learnt the lessons of history showing that free and competitive markets picks winners and that Governments pick losers.
  2. The Conservative Government is happy to see the continued destruction of the nuclear industry, the closure of the cheapest electricity generators (coal-fired power stations), the future unprofitability of gas-fired power stations, the construction of intermittent and unaffordable renewable energy schemes and the continued construction of dirty and expensive diesel  generators.
  3. The Conservative Government is not concerned about 'the lights going out' on its watch.
  4. The Conservative Government is happy to continue to force electricity consumers to subsidise intermittent and inefficient renewable technologies that do not reduce CO2 emissions.
  5. The Conservative Government is happy to allow electricity prices to rise rapidly and thus increase fuel poverty and reduce industry's competitiveness.

The electricity industry will note these indicators and will not invest in much-needed new despatchable power stations to replace those closing down, unless they too are guaranteed massive subsidies.



[3] 'Levelised cost of power from tidal lagoons'.  Poyry, March 2014.



[6]  URN: 11D/943  First Progress Report on the Promotion and Use of Energy from Renewable Sources for the United Kingdom  Article 22 of the Renewable Energy Directive 2009/28/EC


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Reader Comments (51)

The pricing structure of green energy really gets up my nose. In my village we have a BP petrol station and they charge 9-10p/Litre more than our usual supermarket five miles away. By choice I tend to go to the supermarket for my fuel and save well over £5 when I do so.
Under a green energy government I cannot exercise choice for electricity: I have to pay what they tell me is the rate and shopping around is pointless. What would happen if they did the same for petrol?

Jun 9, 2015 at 4:18 PM | Unregistered CommenterHarry Passfield

"no indication of the amount of fossil fuel used in the dredging operation"

Obviously not, as they will be using moonbeams, as usual...
(Or maybe a long piece of wire, although that will limit the times they can actually do it.)

Jun 9, 2015 at 4:21 PM | Registered Commenterjamesp

"This exaggeration of displaced emissions is typical of renewable energy companies."

I suppose the silver lining is that the bigger the porkies that are told, the fewer the number of boondoggles that need to be built to wave around as a claim that we are 'doing something' to save the planet (again). Christiana Figueres et al are probably fooled by that, leaving other people relatively freer to get on with the important things in life.

Jun 9, 2015 at 4:23 PM | Unregistered Commentermichael hart

Given that environmentalists have been making much of surrendering coastlines to the sea, this seems the exact opposite. From past experience they know that man made structures can either increase coastal erosion or decrease beach deposition, what will these schemes do? The sea is notrious for not wanting to let mankind change the coastline in a way that suits.

However, I can see that this sort of thing is the lastest 'great idea' and only experience will dissuade them. Thanks for writing this up PB.

Jun 9, 2015 at 4:43 PM | Unregistered CommenterTinyCO2

I used to be a Master of a 5000t dwt ( we could load 5000 tonnes) marine aggregate dredger. Which is not a big dredger by today's standards. We used to burn about 11tonnes of gas oil a day.
Thier proposed maintenance dredging using a transportable "mini" dredger, tugs and barges would probably be in this ballpark figure.
And it's going to need maintenance dredging as anyone who has sailed in the Bristol Channel will know. It's not pristine, clear sea water flowing in and out on every tide. At times it resembles liquid mud; especially over the English side of the Bristol Channel!
From an old, salty seadog's point of view; it's just another money making scheme being foster on us poor plebs that pay the bills.

Jun 9, 2015 at 4:45 PM | Unregistered Commenterseasick ricky

Somewhere in Brussels, in a lavish suite of offices, an over-paid bureaucrat is reading this and exploding with a hearty "MUHAHAHA!!!"

Jun 9, 2015 at 4:45 PM | Unregistered Commenterjorgekafkazar

I have just learnt that Amber Rudd has given it the go-ahead:

Planning consent was given today for construction of the world’s first tidal lagoon, in a boost to moving towards a low carbon, home grown energy mix.

If built, turbines in the proposed six-mile horseshoe shaped sea wall around Swansea Bay in Wales could generate around 500GWh per year of low carbon electricity.

Energy and Climate Change and Wales Office Minister Lord Bourne said:

“We need more clean and home-grown sources of energy, which will help to reduce our reliance on foreign fossil fuels. Low carbon energy projects like the tidal lagoon in Swansea Bay could bring investment, support local jobs and help contribute to the Welsh economy and Swansea area.”

Separately from the planning consent, the project is still subject to Contract for Difference (CfD) negotiations to establish whether a tidal lagoon at Swansea Bay is affordable and value for money for consumers. Any decision to offer a CFD for the Swansea Bay Tidal Lagoon project would be subject to strict value for money considerations and affordability, and to State aid approval.

Swansea Bay Tidal Lagoon project gets green light on planning

Value for money and affordability should rule out a CfD offer.

Jun 9, 2015 at 5:07 PM | Registered CommenterPhillip Bratby

There's a new article on BBC Wales online about the lagoon:

It makes a few interesting points; the cost of the project has already almost doubled, the developers want another five lagoons along the west coast of the UK to make the project economically viable, and, they are asking for a strike price for the energy generated higher than wind, solar and nuclear.

Jun 9, 2015 at 5:10 PM | Registered CommenterSalopian

It seems the BBC have agreed to the scheme and passed it already.

I look forward with eager anticipation to paying CEO Mark Shorrock's wages for the next 20 years from my electricity bill

Jun 9, 2015 at 5:14 PM | Unregistered CommenterIvor Ward

"Christiana Figueres et al are probably fooled by that, leaving other people relatively freer to get on with the important things in life."

Au contraire. That little Oscar winning (whining) tear-jerking drama-queen won't be satisfied until she's in her 6 taxpayer funded star hotel room lying on her super-king-sized bed counting out her wads of £20s ready to put into her bank accounts, that she has extracted from the rest of us! Ghastly woman! Crooks the lot of them.

Jun 9, 2015 at 5:20 PM | Unregistered CommenterAlan the Brit

I probably ought to remain tactfully silent here having proposed that the new M7(E) goes across the mouth of the Clyde estuary: Proposed Scottish Motorway System

Jun 9, 2015 at 5:24 PM | Registered CommenterMikeHaseler

Is this to be the biggest, most expensive and economically disastrous green/white elephant ever built?

Britain leads the world again.

It may attract tourists for thousands of years, wondering why primitive cultures ever thought to build it.

Local roads may get a bypass sooner than Stonehenge

Jun 9, 2015 at 5:47 PM | Unregistered Commentergolf charlie

"...It may attract tourists for thousands of years, wondering why primitive cultures ever thought to build it...." --golf charlie

Then perhaps Swanhenge would be an appropriate name to bestow upon the project.

Jun 9, 2015 at 6:01 PM | Unregistered Commenterjorgekafkazar

And, BTW, the £300 million contract to build the lagoon wall has been awarded to a Chinese company - China Harbour Engineering Company.

Jun 9, 2015 at 6:15 PM | Registered CommenterSalopian

Is there a forecast for the likely cost over run that the taxpayer will have to fund, with zero chance of any financial return? Minor details like these tend to get left out of glowing 'get rich quick' schemes.

Silting up will be a problem, so dredging will be required. Where will the dredged silt be dumped? Environmentalists will object to dumping silt dredged from the sea, back into the sea, somewhere else.

Wasn't it lucky that the only bit of rock suitable for crushing into concrete for the seawall, was also owned by a sister company, it helps keep nepotism within the family.

Jun 9, 2015 at 6:16 PM | Unregistered Commentergolf charlie

And, BTW, the £300 million contract to build the lagoon wall has been awarded to a Chinese company - China Harbour Engineering Company.

And therein, lies the real reason for the construction of this concrete folly - Dave's quid pro quo for begging kowtowing to the PRC for access to it's markets - sorry to say Phil [Mr. Bratby] - that despite your noble and valiant efforts: this monstrous idiocy was a done deal a long time ago.

Jun 9, 2015 at 6:22 PM | Unregistered CommenterAthelstan.

they are guessing, with our money, but it is so simple too look at an existing one, the Rance tidal station

just have a look at wiki, not a very honnest description
they say


Le barrage de la Rance perd 1 % de sa capacité par an du fait de l’envasement qu’il provoque18. L’envasement est si important qu’il menace la navigabilité de la Rance 19;20. Les accumulations de vase ont transformé les plages de sable blanc en vasières21. Elles sont recouvertes d’une épaisse couche de vase pouvant atteindre 3 m


the power station loose 1 % off capacity every year

note also that the Rance projet can be use als a TEP, but even so, the charge factor is 24 %

the pricing is absolutely "crazy"
just see what EDF is quoting, based on an long production

EDF : ". Pendant 30 ans, les 24 turbines de la Rance ont fait preuve d'une remarquable fiabilité, l'usine a fonctionné sans incident ni panne majeurs pendant 160 000 heures et produit 16 milliards de kWh au prix de 18,5 centimes le kilowattheure, un prix très compétitif et inférieur à la moyenne des coûts de production d'EDF".

the greens... an absolute cancer

Jun 9, 2015 at 6:34 PM | Unregistered Commenterjoletaxi

Athelstan: There were no noble or valiant efforts. I have been too busy with proposals this side of the Bristol Channel to get involved in it. However. I will study the Planning Inspectorate report and use it as a learning process for when (if) the proposed tidal lagoon on this side of the Bristol Channel is applied for.

Jun 9, 2015 at 6:41 PM | Registered CommenterPhillip Bratby

golf charlie Jun 9, 2015 at 6:16 PM
"Where will the dredged silt be dumped? "

Just ask anyone from the Somerset Levels. They are experts in this area of EU law.

Jun 9, 2015 at 6:50 PM | Registered CommenterRobert Christopher

Athelstan :
re the Chinese contract- I posted this a couple of days ago on Unthreaded; copied here.

The Great Wall of Swansea, as a nalopkt commenter wrote

Maybe it's encouraging that this prospective white elephant is to built by a company who have apparently committed fraud, as it may result in this mad fool idea never being completed

Jun 9, 2015 at 6:55 PM | Unregistered CommenterMessenger

Tidas occur when they do , they cannot be linked in anyway to demand .
So like many renewables their ability to supply when there is need will be hit and miss.
Second the energy this will take out of the tide movement is energy that already has an effect on the natural environment. the effect of taking energy out of the environment is unknown, however it is clear that there will be some effect
Thirdly, it is already clear that is idea goes nowhere without big subsidies to make it profitable for the companies involved.
And it is worth remembering that this is not a new idea at all, using tidal changes to obtain power is nothing new at all. mills etc have used this approach for years , the reason they stopped, is becasue it simply could not supply power in a reliable and consistent manner required. This idea gives no indication of overcoming that very old difficulty.

Jun 9, 2015 at 7:17 PM | Unregistered Commenterknr

It is interesting that most of the presentation slides went missing, especially the technical ones. for the simple reason their calculations are very 'pie in the sky'.

Any generated output will follow a bell curve with peak output being between high and low water (the turbines are being driven by the difference in height of the water either side of the wall and as the height differential gets smaller the output tails off). Bearing that in mind they might get about 4 hours of usable output per 24 hours - not a very good return on investment unless you get the shortfall and profit paid by the taxpayer.

Jun 9, 2015 at 7:26 PM | Unregistered Commenterivan

A problem with tidal power, generally not understood by the green blob, is that tides do not follow a consistent 24/7 pattern.

In the UK, there are usually two tide cycles per day, but the period from one high (or low) is usually around 12.5-13 hours. Similarly, the variation between high and low tides is periodic dependent on whether the sun and moon are aligned (highest) or at right angles (lowest), on a lunar monthly cycle.

In addition, sea levels and tidal variations in onshore areas are affected by air pressure, wind direction and, in estuaries, by variations in downstream water flows.

In fact, tidal energy is probably more unpredictable than wind or solar.

Jun 9, 2015 at 8:06 PM | Registered CommenterSalopian

"the world’s first tidal lagoon" (A Rudd)

Only if you ignore the others. I expect the rest of her statement is just as accurate.

Jun 9, 2015 at 8:45 PM | Registered Commenterjamesp

seasick ricky is right about dredging and emissions. But forget about that.

Two things can make this project a winner.

1) Put gates on the barrage so as water is released (as required to meet demand). This does need plastic sheets dropped inside the barrage to make segments. No need for permanent concrete segments as they should be adaptable for market changes.

2) Use this contained area to farm shellfish. Crabs, lobster, oysters and mussels - food for the future. This will boost the profitability of the project. And this technology can be sold to Japan.

This is not wind or solar. It need not be an unreliable.

Let's experiment and try it. I'm in favour.
(It even boosts the Cornish economy to build it).

Jun 9, 2015 at 8:49 PM | Registered CommenterM Courtney


I presume that EdF quote is pre-euro (Rance was built in 1967, and 30 years later is 1997). At 6.56 FF/€ that 18.5 centimes is 2.82 eurocents, or about 2.1p/kWh.

There is a very useful presentation on Rance here (with a coy mention of silting):


Swansea tide tables can be found here:

The tides are reasonably predictable (storm surges etc. aside), but the variation in timing and range is considerable over each month. Roger Andrews had a go at looking at this here:

The actual output patterns will be a sawtooth: if they add in pumping capacity (see the Rance slides on p 12/13/14 of that presentation), that could be aggravated by drawing on the grid before each production cycle commences. There is a minimum head below which the turbines will not operate, and turbine efficiency is also a function of the head. At La Rance it appears that they concentrate on ebb generation:

Ebb generation (direct turbining): 60%
•Reverse pumping (reservoir towards sea): 0%
•Flood generation (reverse turbining): 2 to 6%
•Direct pumping (sea towards reservoir): 15 to 20%
•Free flow through the turbines orifices (mainly sea
towards reservoir): 20% (when 0.3 m < Head < 1.2 m)
•No pumping required when tidal range is above 7 or 10 m

All of which suggests there are some "interesting" questions to be asked about the planned operation. Valuing the output at balancing mechanism prices per half hour window might be instructive, as would looking at the cost of the necessary backup generation. We might then get a handle on the true level of subsidy.

Jun 9, 2015 at 9:21 PM | Unregistered CommenterIt doesn't add up...

Apparently the immediate effect on climate will be to turn the UK's wettest city into a cloudless tourist magnet for people wanting to push baby strollers on a 10 km footpath across the bay...according to the "artist's impression" on Swansea City council.

Perhaps a deposit covering the full costs to remove the structure and remediate possible environmental damage would be appropriate?

Jun 9, 2015 at 9:29 PM | Unregistered Commenterbetapug

In 1607 the Bristol Channel suffered a major flood, possibly a Tsunami. See Wikipedia. If it happens again, will it be due to the tidal lagoon, global warming or something that just happens every 500 years or so?

Tidal "mill ponds" still exist in the UK. Emsworth near Portsmouth being one I know. Have any been reused to generate electricity?

The tidal range (difference in height between high and low tide) in the Bristol Channel is one of the greatest in the world, and I can see the appeal of it, to tidal power enthusiasts, but I don't think it makes any economic logic at all. But it is nice to know how the Green environmentalists can keep their marching boots off estuarine mud if it is for a Green approved project, that WILL actually change the natural environment and do permanent damage.

Jun 9, 2015 at 10:02 PM | Unregistered Commentergolf charlie

golf charlie: the Severn Estuary is not only a very important, and sensitive natural environment.; it is also a very critical British archaeological site of interest, particularly when it comes to the prehistoric, roman and early medieval history of south Wales and south-west England. Hopefully any draft consent to this project will involve a full archaeological assessment that could potentially scupper it.

Jun 9, 2015 at 10:15 PM | Registered CommenterSalopian

It doesn't add up...: Thanks for the detail. As far as I'm aware (please correct me if I'm wrong); there is no pumping element in the Swansea Bay proposal, it simply involves reversible turbines generating power from the tidal ebb and flow. Surely this means it is less efficient than a barrier like La Ranche that has a pumped element?

Jun 9, 2015 at 10:49 PM | Registered CommenterSalopian

Athelstan: There were no noble or valiant efforts. I have been too busy with proposals this side of the Bristol Channel to get involved in it. However. I will study the Planning Inspectorate report and use it as a learning process for when (if) the proposed tidal lagoon on this side of the Bristol Channel is applied for.

Noted sir. Sufficed to say, that, I hope if and when the Bristol Channel effort is erm...... 'floated' - that its blueprint, can be left, gathering dust in some [Avon] local council archive.

Jun 9, 2015 at 11:03 PM | Unregistered CommenterAthelstan.

Salopian, any project that Team Green don't like is always scuppered by history, archaeology and most importantly, environmental considerations that can be made up, as necessary to obstruct whatever, whenever.

I gave up history in favour of geography at school, and have no regrets, as in later life, it has given me the opportunity to study the history I am interested in. As a yottie, I have not sailed in the Bristol Channel, but Seasick Ricky's assessment is not one I would argue with.

From memory, the biggest tidal ranges are Bay of Fundy (Nova Scotia), Channel Islands, then Bristol Channel, hence the obvious attraction of this scheme, and double standards from the Greens.

Bristol grew from shipping, the UK end of the slave trade was there. The Kennet and Avon canal linked Bristol to the Thames at Reading, and Brunel's Great Western Railway was about linking London to Bristol and then to south Wales. I do not doubt the Roman links and other archaeology, yet to be uncovered.

Jun 9, 2015 at 11:16 PM | Unregistered Commentergolf charlie

Salopian, don't want to seem pedantic but, ... !

The ebb and flow of the tide relates to the water flowing, ie how fast a turbine would spin if you dangled it beneath Tower Bridge due to the tide. The Bristol Channel does have relatively high flows of water, it is the tidal range, ie total difference between high tide height and low tide height, that excites tidal power enthusiasts.

If high ebb and flow was what you were after, dangling a turbine around the Channel Islands, or Cherburg peninsular would be ideal. The French haven't.

Jun 9, 2015 at 11:47 PM | Unregistered Commentergolf charlie

I suspect that the CfD should kill this, if it doesn't then there is a major problem of the understanding of reality on the part of the government, OH wait a minute, that could be a problem.

Jun 10, 2015 at 1:32 AM | Unregistered CommenterMike Singleton


AFAIK you are correct on both points, although presumably the generators could be used as motors powering the turbines as pumps with only a few modifications.

I discovered that the Strangford Lough tidal race turbines smooth their output by throwing away peak power capability through feathering the blades to maintain a constant maximum blade tip speed in currents of over 2.4m/s. That has consequences. They have a new design for 2MW units: the brochure includes a power curve against current speed:

Of course, these aren't the same units that will be used at Swansea - almost certainly they'll be bulb turbines as at La Rance.

I've just found what is proving to be a very interesting paper on work done in evaluating the Severn Barrage many years ago:

Quite long, but I suspect informative and free of green bias.

Jun 10, 2015 at 2:29 AM | Unregistered CommenterIt doesn't add up...

The dredge could be powered by the power generated by the tidal movement.
The dredge will operate for two undetermined periods each day which will vary from new moon to full moon.

Isn't it exciting? The proponents should be fitted with concrete boots and go for a walk in the Bristol Chanel.

Who is responsible for breeding these imbeciles?

Jun 10, 2015 at 2:41 AM | Unregistered Commentertoorightmate

But doncha realise, DC's boyos are in hock to the Renewables' Corporations, an extension of property, banking and fossil fuel interests via carbon trading, the most vicious attack on the poor since the end of feudalism. Rope and Lamp Posts come to mind once the inner city power cuts start in earnest, early next year and organised crime controls resources.

Jun 10, 2015 at 6:47 AM | Unregistered CommenterNCC 1701E

Having skimmed through the Planning Inspectorate's report recommending the go-ahead, it is clear that the panel of four Inspectors just made a judgement in favour because that is what their political masters wanted. The contents of the 561 page report can be boiled down to a single sentence. They judged that the benefit in terms of (reliable???) renewable energy outweighed the matters weighing against, or in simple terms:

on balance, the matters weighing in favour of the development outweigh the matters weighing against

No evidence needed, no attempt to quantify the benefits (which in terms of intermittent electricity produced are minuscule) just a judgement by four bureaucrats who are no doubt experts in planning law. Just what the Government ordered!

They considered the significant economic benefit to the Swansea area (all based on subsidies) but ignored the adverse economic impacts of the higher electricity prices on the rest of the economy.

Jun 10, 2015 at 7:11 AM | Registered CommenterPhillip Bratby

They considered the significant economic benefit to the Swansea area (all based on subsidies) but ignored the adverse economic impacts of the higher electricity prices on the rest of the economy.

Ah but you get to polish your 'green credentials medals' at big international conferences...................PLUS - and it works at the micro level - showing off your solar panels on your own roof - you can also pop round to a pensioners north facing house [sad no panels see] and shout at the top of your voice - "thanks for the subsidy mate!"

Feed in tariffs concocted by the politicos, green lobby and renewable industry to fleece the - POOR!

Jun 10, 2015 at 8:36 AM | Unregistered CommenterAthelstan.

If it is truly a viable investment private investors will be queuing to back it and good luck to them. I hope they make a buck.

If it is not a viable investment why back it with tax money?

The Wash tidal barrage has been on the cards since 1949, originally as a fresh water reservoir and to make a giant deep water port. More recently electricity generation has been the focus, Environmental impacts will stop that one happening in the foreseeable future I suspect.

Jun 10, 2015 at 9:55 AM | Unregistered CommenterClovis Marcus



Simon Gibbs (Planner by profession, with degrees in Geography and Social Sciences)

Lillian Harrison (Environmental Scientist and a chartered Town Planner)

John Lloyd-Jones (former Chairman of the Countryside Council for Wales)

Peter Widd (Mariner)

Taken from:

It would have been more convincing if Dave had just asked Amber to toss a coin - heads the troughers win, tails the peasants lose.

Trebles all round.

Jun 10, 2015 at 10:53 AM | Unregistered CommenterBrownedoff

Clovis Marcus:

The problem is that the government is awarding a guaranteed price to the project output way in excess of the free market price of power. That is a licence to print money, which deserves no good luck wishes. Moreover, it appears they have chosen who the investor beneficiaries are likely to be - all paid for out of our power bills..

Jun 10, 2015 at 11:09 AM | Unregistered CommenterIt doesn't add up...


I think you're being too pedantic. The plan is to make use of both ebb and flood tides, although the various sources of information I have found suggest that it is difficult to do both well. From the Salford thesis:

At the time of these Severn Barrage studies (1978/79) there was a belief that a tidal power barrage should be developed to extract energy at lowest unit cost and the ebb-generation mode of operation was the way to do this. Comparative studies for the Severn Barrage Committee of the alternative forms of development, to which the writer contributed, confirmed this to be so, although it is true to say that more in-depth studies were carried out for the single-effect ebb-generation mode of operation than for double-effect operation or any of the double-basin alternatives proposed which could provide a degree of firm power.

Jun 10, 2015 at 12:13 PM | Unregistered CommenterIt doesn't add up...

It doesn't add up ... I typed that last night, deliberately deleted it, and then retyped it!

Fast currents caused by tides, are common around the UK, but simply dangling a turbine in the water is not very cost effective partially because they get smashed up by waves. The Bristol Channel does not have a narrow neck, so does not concentrate the flow.

If Strangford Lough is the one I am thinking of, it does have a narrow neck, so there is no need to build an artificial lagoon.

You can make turbines that spin the same way, irrespective of the direction of flow, I can't remember their name!

The 'ebb and flow' of the tide is a regularly used expression, but in terms of generating electricity, it is not relevant, and if I came across as pedantic, I apologise again. It is a bit like the 'wrong sort of rain', but in a discussion about tidal power potential, as a yottie, I know that high 'rise and fall' and high 'flow rates' are not always the same, but can be harnessed in different manners.

A Severn Barrage would harness both, but would be billions. Strangford is making use of the high flow, caused by etc.

The logical extension to this, is why not fit every weir on every canalised river, with a mini water mill generator?

Jun 10, 2015 at 12:46 PM | Unregistered Commentergolf charlie


The answer to your last question is here:

The total potential identified by this study for England and Wales is in the range of
146,280-248,400 kW.

248MW isn't even half a modern CCGT genset. I did a back of envelope calculation on the power available in the Thames a year or two back, looking at flow rates and altitudes at various points along its course: even such simple analysis produces good answers - I concluded a Trent engine's worth was available, which is very similar to the above study.

Jun 10, 2015 at 1:59 PM | Unregistered CommenterIt doesn't add up...

Apparently the Irish gubmint have come up with an economy boosting taxpayer funded grand make-work scheme

Jun 10, 2015 at 2:08 PM | Registered Commentertomo

It doesn't add up.. thanks for that. As a child I loved the idea of hydro electric power, and still do. The Thames and Severn are not suitable for hydro, yet HEP at Fort William could run an aluminium smeltery (?) .

Yotties fit wind turbines to yachts to help power the electrics and electronics. Solar panels are useful to keep batteries topped up in the UK, but not much else. Towed generators are useful when sailing, and can generate whilst anchored, if there is a tidal flow. Otherwise, you need to burn diesel.

I offer the above, as an alternative source of information about unreliable energy, not because it is my expertise!

Jun 10, 2015 at 2:31 PM | Unregistered Commentergolf charlie

Wow - this got suggested, embraced by politicians, and approved, faster than you can say 'carbon footprint'..!

The engineer in me suspects it will all end in (taxpayer-funded) tears - because politicians and green-related energy policies go together like fish and bicycles...

Need I mention: 'low-energy' (i.e. mercury-filled) lightbulbs..?

'Diesel is good. Buy diesel cars. Diesel is bad. We will tax diesel cars out of sight.'

Wind/solar of course - but there are loads more....

Jun 10, 2015 at 2:40 PM | Unregistered Commentersherlock1

Given that the building of new coal fired plants in China and India give rise to the same amount as all the CO2 emissions in the UK every six months, it is ironic that a Chinese firm is to do the work. We are paying the Chinese to make our industry uncompetitive. Rudd does not have any judgment, following diktats rather than logic.

Jun 10, 2015 at 4:38 PM | Unregistered Commentersrga

"Who is responsible for breeding these imbeciles?" --toorightmate

The Germans, who used mutagenic chemicals for gas warfare in WWI. It's the only possible explanation for the Climate Change Act receiving 463 ayes against a handful of nays.

Jun 10, 2015 at 5:27 PM | Unregistered Commenterjorgekafkazar

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