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Barrage sinks

It’s been a long running saga – over the years there have been many reports and studies on the idea of building a tidal barrage across the Severn Estuary. Most have said it was technically possible, but economically and environmentally challenging – although no final conclusion emerged, just more studies. The most recent study looked not just at the large Cardiff to Weston barrage idea, but also at other options for exploiting the large tidal range in the estuary – smaller barrages and tidal lagoons. However this time a decision emerged – basically they were all too expensive. The government’s ‘Severn Tidal Power Feasibility Study: Conclusions and Summary Report’ in October seems to have finished off tidal range projects in the UK, at least for the moment. Although it did say that the results for other locations around the UK might be different, it is hard to see how they could do better than the Severn – the best site by far in terms of tidal range. Given that most environmental groups strongly opposed large barrages, the government decision not to provide support did not lead to complaints from them about ‘ignoring green options’.

The main conclusions were pretty clear. ‘The Government has concluded that it does not see a strategic case to bring forward a tidal energy scheme in the Severn estuary at this time, but wishes to keep the option open for future consideration. The decision has been taken in the context of wider climate and energy goals, including consideration of the relative costs, benefits and impacts of a Severn tidal power scheme, as compared to other options for generating low carbon electricity. The Severn Tidal Power feasibility study showed that a tidal power scheme in the Estuary could cost in excess of £30bn, making it high cost and high risk in comparison to other ways of generating electricity.’

www.decc.gov.uk/severntidalpower

The report text is a little less abrupt. It says: ‘The Cardiff-Weston barrage is the largest scheme considered by the study to be potentially feasible and has the lowest cost of energy of any of the schemes studied. As such it offers the best value for money, despite its high capital cost which the study estimated to be £34.3 bn including correction for optimism bias. However this option would also have the greatest impact on habitats and bird populations and the estuary ports.’

It went on: ‘A lagoon across Bridgwater Bay (£17.7 bn estimated capital cost) is also considered potentially feasible, as is the smaller Shoots barrage (£7bn). The Bridgwater Bay lagoon could produce a substantial energy yield and has lower environmental impacts than barrage options. It also offers the larger net gains in terms of employment.’ By contrast: ‘The Beachley Barrage and Welsh Grounds Lagoon are no longer considered to be feasible. The estimated costs of these options have risen substantially on investigation over the course of the study’ It added ‘combinations of smaller schemes do not offer cost or energy yield advantages over a single larger scheme between Cardiff and Weston.’

It noted that, in addition, the study funded further work on three proposals using innovative and immature technologies (the Severn Embryonic Technologies study). It said: ‘Of these, a tidal bar and a spectral marine energy converter showed promise for future deployment within the Severn estuary – with potentially lower costs and environmental impacts than either lagoons or barrages. However, these proposals are a long way from technical maturity and have much higher risks than the more conventional schemes the study has considered. Much more work would be required to develop them to the point where they could be properly assessed.’

The spectral marine energy converter (SMEC), which makes use of the venturi effect, tapping off tidal flows to drive a separate generator, certainly looks interesting for the Severn and also, in smaller versions, elsewhere.

See www.verderg.com/.

DECC had previously indicated that if a scheme had been considered viable for the Severn, further consultation would have to continue up to maybe 2014 with construction then between 2015 to 2022, followed by operation perhaps in 2023. But all that is now wiped out. With DECC faced by spending cuts and the capital cost of the big barrage now put at £34.3 bn, it just wasn’t viable as a public project and, with the generation costs of the other options put higher, private-sector interest would be unlikely. So tidal range seems to been written out of the story for some while. Which leaves tidal currents – a much less invasive and rapidly developing approach, with, it is claimed (in the DECC 2050 Pathways study and the PIRC Offshore Valuation), a larger overall UK energy resource than offered by tidal range projects.

Tidal-current turbines can be much more flexible and modular – although there are site limitations. It seems that the Severn estuary isn’t suited to the pile driven support system needed. It does seem tragic to ignore the huge tidal energy potential of the Severn, so a tidal-range project or some other concept may yet be back there (e.g. SMEC), and also elsewhere (there are several proposals for smaller barrages (e.g for the Mersey, Duddon, Solway Firth) but maybe not a for while. A rearguard action is being fought by some of the original backers of the Severn Barrage (see www.corlanhafren.co.uk/. But it seems to be doomed in the current financial and political climate.

I’ll be looking at the tidal-stream options shortly. See also www.natta-renew.org for regular updates.

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