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U.K. shortlists five proposals for Severn tidal project

The United Kingdom has shortlisted five proposals from a total of ten schemes to develop a Severn Estuary tidal power project that could have a capacity as high as 8,600 MW.

The Department of Energy and Climate Change said the preliminary short list proposals and the original list of ten schemes would be subjected to a public consultation until April 23 before a final shortlist is chosen.

"A final decision on whether Government could support Severn tidal power generation and, if so, on what terms, will be taken at the end of the feasibility study in 2010, following a second public consultation," the department said.

Tidal reefs, fences to be studied

Also before any decision is made, the department is allotting 500,000 pounds (US$709,000) to further develop "embryonic technologies" such as tidal reefs and fences.

"The progress of these technologies will be considered before decisions are taken whether to go ahead with a Severn tidal power scheme," Energy and Climate Change Secretary Ed Milliband said.

Using conventional hydroelectric equipment and a barrage across the Severn Estuary between England and Wales, it is estimated a proposed project could generate 17 terawatt-hours per year to supply 5 percent of the U.K.'s electricity from renewable sources.

However, project officials sought proposals considering all tidal range technologies, utilizing the vertical distance between high tide and low tide, rather than tidal stream technology, utilizing flows. (HNN 6/13/08) Electricity is generated by impounding water at high tide and releasing it through turbines at low tide. Tides in Severn Estuary range up to 42 feet.

Balance sought between clean energy, habitat

The shortlisted proposals, and the additional look at scaled-down alternatives, reflect concerns about effects on the environment and wildlife habitat in the estuary.

"We have tough choices to make," Milliband said. "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."

Short-listed projects include:
o Cardiff Weston Barrage (also called Middle Barrage), 8,600-MW, crossing the estuary from Brean Down, near Weston super Mare, to Lavernock Point, near Cardiff;
o Shoots Barrage (also called Inner Barrage or English Stones), 1,050-MW, further upstream;
o Beachley Barrage, 625-MW, the smallest barrage on the short list, just above Wye River;
o Bridgwater Bay Lagoon, 1,360-MW, described as a "radical new proposal" to impound a section of the estuary without damming it, on the English shore between Hinkley Point and Weston super Mare;
o Fleming Lagoon, 1,360-MW, an impoundment on the Welsh shore between Newport and the Severn road crossings.

Other proposals submitted in the first phase of the study, and still on the table for consultation, include:
o Outer Barrage, from Minehead to Aberthaw, the largest barrage making maximum use of the Severn Estuary tidal resource;
o Middle Barrage, from Hinkley to Lavernock Point, similar to Cardiff Weston Barrage, but terminating at Hinkley, rather than Brean Down;
o Tidal Fence proposal, constructed over the Cardiff-to-Weston line, with open sections, incorporating tidal stream turbines (rather than tidal range turbines) to capture energy from ebb and flood tides;
o Tidal Lagoon concept, a proposal for a number of tidal lagoons (apparently the source of the shortlisted Bridgwater Bay Lagoon);
o Tidal Reef proposal, a concept that would include floating turbines and caissons;
o Severn Lake Scheme, a kilometer-wide barrage in the Cardiff-to-Weston location, designed to allow construction of additional features such as a wave farm on the seaward side and four marinas.

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