The government has announced its shortlist of ways to exploit the tidal energy of the Severn estuary, potentially one of the richest renewable-energy resources in the world.
The shortlist of five proposals includes the headlining, controversial idea of a massive barrage spanning the Bristol Channel from Weston-super-Mare to Cardiff on the Welsh coast. This plan, according to the government's assessment, would produce 17 terawatt-hours each year: about 4.8 per cent of present-day UK electricity demand, or 0.6 per cent of the UK's total energy requirements as of 2006*. By way of context, a smallish nuclear plant like Sizewell B generates ten terawatt-hours each year.
Some green groups were distressed to see the Cardiff/Weston barrage make the cut, as it would destroy 20,000 hectares of intertidal habitats - home to various ecologies and species, particularly wading birds, which would suffer as a result.
Friends of the Earth, for instance, told the Guardian: "Plans to build a Severn barrage are too big a threat to an internationally important wildlife site and must be scrapped - ministers must focus on developing the estuary's potential for tidal lagoons instead."
Greenpeace says that "the Severn barrage could be a huge resource of carbon free energy, but the jury’s still out on the best way to reap the tidal power of the river without having huge environmental impacts on wading birds".
Green groups generally favour the idea of artificial tidal lagoons rather than a barrage, seen as less damaging ecologically. The more bird-friendly propose that these lagoons be located completely offshore, making no use of the coast - but such schemes are assessed as terrifically expensive, and none made the shortlist.
The government's list of five includes two land-connected lagoon schemes, putting a major impoundment either on the Welsh coast (Fleming lagoon) or the English (Bridgwater Bay). The Fleming layout would produce an estimated 2.3 terawatt-hours annually; Bridgwater 2.6 TWh. This would equate to about a thousandth of the UK's energy requirements, but losses of bird habitat would be only a quarter of what the Cardiff/Weston barrage would cause.
The government also shortlisted two less ambitious barrage schemes, Shoots Barrage at 2.7 TWh/year and Beachley (upstream of the Wye) which would produce just 1.6 TWh annually. The Shoots Barrage would wipe out habitat area to the same tune as the two coastal lagoon schemes; the small Beachley scheme less.
Two more ambitious barrage schemes, further west even than the Cardiff/Weston line, were sidelined. The largest of these would have seen a barrage from Minehead to Aberthaw generating 25.3 TWh each year, almost 1 per cent of all the energy the UK uses. However, its cost was estimated at £35bn, making the energy very expensive: a modern nuclear plant would produce the same energy and cost substantially less than £5bn.
Massive government subsidy would be required for the "outer barrage"; it could never pay its own way. The Cardiff/Weston barrage, at £20bn, would still be very costly in terms of £billions per terawatt-hour produced each year, but not as much so.
Energy and Climate Change minister Ed Miliband, announcing the shortlist, said: "The five schemes shortlisted today are what we believe can be feasible, but this doesn't mean we have lost sight of others. Half a million pounds of new funding will go some way to developing technologies still in their infancy, like tidal reef and fences. We will consider the progress of this work before any final decisions are taken.
"We have tough choices to make. Failing to act on climate change could see catastrophic effects on the environment and its wildlife, but the estuary itself is a protected environment, home to vulnerable species including birds and fish. We need to think about how to balance the value of this unique natural environment against the long-term threat of global climate change."
Detailed specs on all plans, including the sidelined longlist ones, are available from the government here. ®
*We include the total energy usage figures as transport, heating, industry and so on will all need to switch away from fossil fuel energy at some point - either to cut carbon emissions, to avoid dependence on imports from unsavoury regimes, or eventually because supplies have run out. It is very common to see erroneous reporting saying that a Cardiff/Weston barrage could generate "5% of the UK's energy needs", which is of course totally untrue.