Severn Wye Energy Agency
Severn Tidal Power
NOTE - Severn Wye Energy Agency is not formally involved in the ongoing
Severn Tidal Power feasibility study, nor do we currently take a position on
the merits (or otherwise) of the proposals. However, our work does enable us to cast
an expert eye over the facts and figures as we understand them so far. The exploration of
Severn Tidal Power (or 'The Severn Barrage') is quite rightly generating a
huge amount of interest across South West England and Wales, and the eventual outcome will
have a critical bearing on the UK's wider renewable energy strategy.
Introduction
The idea of tidal power in the Severn has been around since the 19th Century. The current proposals include a revival of some longstanding ideas (with the large Cardiff-Weston barrage remaining the reference option), as well as the inclusion of some more recent alternatives. Of the 10 original proposals, 5 have been shortlisted for more detailed investigation. If built, the largest of the schemes would become the biggest renewable energy projects (as well as the biggest civil engineering projects) in Europe, by some margin.
The Government's official Severn Tidal Power Consultation is embarking on its second phase, which will continue into 2010. The output of this will be a decision on whether the Government will formally support a Severn Tidal Power scheme, and if so which one and on what terms.
Further facts and figures on the Severn Tidal Power proposals, as known at the present stage of the consultation, will be added to this page on an ongoing basis.
The Facts
- The tidal range of Severn estuary is 14m, which is the second highest in the world: this is a very attractive potential clean energy resource.
- In January 2009 five shortlisted schemes to capture this energy resource were announced by DECC, from the original list of 10 proposals.
- The shortlist includes three barrages (the large Cardiff-Weston scheme, the Shoots barrage south of the M4 bridge, and the Beachley barrage north of the M48 bridge) and two lagoons (at Bridgwater Bay and Fleming on the Welsh grounds).
- Other concept studies may continue: a £500k SETS fund (for embryonic technologies) was launched in April to help develop alternative ideas for Severn Tidal technologies (such as the fence and reef) - applications have already closed, and the following were chosen for funding:
- Low head barrage (Rolls Royce / Atkins)
- The tidal fence proposal (STF Consortium)
- New tidal fence proposal (VerdErg), featuring a radical new design
- For the Cardiff-Weston barrage, peak output may be 8.6 GW (14% of UK winter peak demand), but average output would be equivalent to 2GW - or roughly 2 nuclear plants (Sizewell B) or 1 large coal power plant (Didcot A); not some of the much larger numbers touted in the media.
- Total annual output would be 16-18 TWh (using a capacity factor of 22-26%) using ebb-only generation; flood generation represents a much smaller energy resource, due to raw geometry and lower efficiency, and it also causes more silting problems.
- On a year-round basis, the Cardiff-Weston barrage would generate around 5.0-5.5% of annual UK electricity demand.
- Tidal power is highly variable but precisely predictable and fairly controllable, in contrast to wind power.
- The barrage would be the largest UK engineering project since the Channel Tunnel.
- Much uncertainty surrounds the potential costs of any Severn Tidal project, since no comparable schemes on this scale have been attempted before.
- Mechanical and electrical works are expected to form the biggest component of capital costs, exceeding civil works.
- Maintenance costs will be around 1.5x higher than a hydro scheme of equivalent capacity, due to the harsh regime, seawater, silt etc.
- An entire new global supply chain is needed to build the components, including concrete caissons and 'bulb' turbines in larger numbers than ever built before.
Supporters
These include SeBAS (Severn Barrage Association of Supporters), who claim a 'carbon' payback within 6 months; and ICE (Civil Maritime Engineering group), who claim water quality and biodiversity will be greatly improved.
Detractors
These include SOS (Save Our Severn), who focus on major siltation problems; CLA (Country Land & Business Association), who focus on productive land loss; RSPB and WWF, who both believe shortlist is flawed and biased against innovative schemes; WWT (Slimbridge), who also regard the big barrage as 'destructive'; and the Environment Agency chair, who agrees that the ecological impacts of Cardiff-Weston are too great, but supports the smaller/alternative options.