The Swansea Bay Tidal Lagoon

In the news last week was the story that a scoping document has been submitted to National Infrastructure Planning as a first step in the process of getting permission to construct a tidal lagoon at Swansea Bay.

     Multi-million pound tidal lagoon could power all of Swansea
     Swansea Bay tidal power could 'supply 100,000 homes'

As someone who has been quite unequivocal in support of the need for Wales to invest in tidal power, and particularly to invest in tidal lagoons rather than a barrage (here, for example) I decided to look at this proposal in more detail. The scoping document is here:

     Tidal Power Swansea Bay Scoping Document

The first thing to note is that this project is not the same as the previous proposal from Tidal Electric Limited (TEL), details here, which I fully support. It is in roughly the same position, but instead of being an offshore structure built away from the shoreline, it has been modified to become an "attached" tidal lagoon. I've produced this map showing the new proposal from Tidal Power Swansea Bay (TPSB) in blue and the TEL scheme in yellow.

     

 
Environmental Considerations

In general terms, attached tidal lagoons are not a good idea. The point of building tidal lagoons offshore rather than against the shoreline is to minimize any ecological damage to both the sea shore and inter-tidal area. By building the sea wall facing the shore just beyond the lowest low tide line, the inter-tidal marine life is untouched, and the natural tidal flow parallel to the shoreline is not completely blocked, meaning that sand and silt can move normally. In contrast, an attached tidal lagoon will cause exactly the same sort of damage to inter-tidal marine and bird life as a barrage will, and it is for this for this reason I am opposed to the attached tidal lagoons that have been proposed further east, as shown on this map.

However in this particular case the damage will be less pronounced. As we can see from the map, the new sea wall enclosing the lagoon is not built against a stretch of natural shoreline, but against the man-made wall of Swansea docks. This means there will be that much less wildlife to damage ... or at least it won't be any more damaged than it was when the docks were built in the first place. But I'd still be concerned about the triangle between the eastern sea wall, Crymlyn Burrows and the Neath navigation channel.

 
Construction

The second thing to note is that the construction of the sea wall in the TPSB scheme is more massive—and therefore more expensive—than that proposed in the TEL scheme. TEL envisaged the sea wall as a minimal structure designed only to retain water. It therefore only extended marginally above the height of the highest tide, and didn't have a vehicle roadway on top of it. It simply wouldn't matter if waves broke over the top of it in storm conditions. As it happened, this was one of the reasons why the DTI rubbished the TEL scheme (in this report) which contributed to it not going ahead. The DTI made a number of very odd assumptions, one of which was that a more massive sea wall was required, in order to claim that TEL had underestimated the cost. The sea wall accounts for the major part of the overall cost of the project, and because the only practical way of constructing it is by piling up material on the sea bed, any increase in height results in an exponential increase in cost.

But although a sea wall with a roadway on top would not be needed for an offshore tidal lagoon, it actually makes some sense for an attached lagoon. In addition to making maintenance easier, the public can use it as a walkway. It therefore has the potential to become a tourist attraction, the twenty-first century equivalent of a Victorian or Edwardian pier. This is what TPSB are proposing:

The presence of a permanent connection to the shore would also open up tourism, recreation or educational opportunities for the Lagoon during its lifetime.

In addition to this, located adjacent to the O&M facilities it is proposed that there will be visitors’ facilities. The exact details of these will be determined during the EIA process and could include:

•  Watersports and activities facilities – potentially incorporating a clubhouse, toilets/changing facilities, café, boat or equipment storage units, additional slipways – one inside and one outside the lagoon;

•  Cycle hire points for public equipment use;

•  Parking provision, public transport pick-up/drop-off and landscaped circulation space suitable for 70-100k visitors per year; and

•  Safe, secure visitor access between the two seawall landfall points so a complete circuit can be made.

... it is proposed to have a visitor centre building offshore, located near and integrated with the turbine housing area approximately 5km out along the lagoon wall. The exact appearance and facilities within this building are still to be determined but they are likely to include:

•  Architecturally significant design/appearance, with the objective of creating an iconic building

•  Lobby;

•  Café/restaurant/toilets;

•  Permanent renewable energy exhibition space(s);

•  Interactive physical exhibitions for education and interest;

•  Multi-use exhibition/function space; and

•  Navigational lighting as required.

Scoping Document – Pages 8 and 9

For me, the important thing is for a tidal lagoon to produce electricity. If that is the "cake", then the visitor attraction aspects of the scheme are the "icing" put on top of it. But if designed well, I think it could be an exciting part of an expanding and vibrant city, and this could help justify the additional cost of the more massive structure. But we need to be clear that the difference in cost is quite considerable. TEL estimated the cost of their sea wall at just under £50m, the DTI's roadway version cost £137m.

It might also be worth saying that at 9.3km, the round trip will be quite a long walk or cycle ride. To give some idea how big it is, both the maps below are to the same scale. The breakwater at Holyhead is only 2.5km long.

     

     

 
Electricity Generation

One thing that I found rather odd about the TPSB scheme is that the turbines will have an installed capacity of 250-350 MW, but that the TEL scheme had an installed capacity of 60 MW.

Although there is a big difference in installed capacity, it isn't all that significant. The amount of electricity that can be generated from a lagoon depends on the area of impounded water and the height difference between low and high tides. Having more (or bigger) turbines produces more electricity, but over a shorter period, by filling or emptying the lagoon more quickly. In overall terms the total electricity produced is going to be the almost same.

The area of the TPSB scheme is just short of double the area of the TEL scheme, and the tidal range is obviously the same, so it should generate about twice the electricity. But it is harder to figure out why the installed capacity of the TPSB scheme should be so much greater. My best guess is that TPSB are proposing two separate sets of turbines, one set to generate on the ebb tide and one set to generate on the flow. TEL's scheme envisaged bi-directional turbines, and uni-directional turbines might well be more efficient. The question is whether the greater efficiency of two sets of turbines would justify doubling the cost of the turbines and turbine house. It might do, for these are much less significant elements of the overall cost than the sea wall.

TEL estimated the output of their scheme at 187 GWh/yr. So with just under double the area of impounded water but more efficient turbines, TPSB's claim of 400 GWh/yr is probably justified. This equates to about 2% of the 20 TWh of electricity Wales needs to produce each year to meet our current needs. It would be the equivalent of a 130 MW offshore wind farm ... say 36 turbines rated at 3.6 MW each, which is the size of the turbines proposed for Gwynt y Môr.

 
Conclusions

When I first saw looked at TPSB's scheme in detail, I was disappointed to see that the TEL concept had been abandoned. Yet although I have grave reservations about attached tidal lagoons in general, I think that this scheme probably can be justified because no natural stretch of coastline is affected.

In terms of its contribution to our energy needs I have no doubt whatsoever that a lagoon of this sort, generating some 400 GWh of renewable energy a year, is exactly what we need. Given the fact that we are blessed with the second or third largest tidal range on the planet, not to make use of it would be recklessly irresponsible. I would hope that this is the first of many tidal lagoons.

I am a little less convinced by what I described as the "icing" on the cake. Not because I don't like icing, but because a project in which the sea wall is built high enough and strong enough to take a roadway and be safe as a visitor attraction for the public is going to be very much more expensive than a project that is only designed to produce electricity. But if someone can put together a business plan to justify it, why not? It will certainly put Swansea on the map.

I think we should have built the scheme proposed by TEL, and I can't think of any good reason why their offer was refused. But this scheme is an opportunity to build something that, at least in terms of generating electricity, is substantially similar. We must grasp this opportunity.