Severn Barrage Outperformed By Tidal Lagoons, Greens Advise Assembly

Friends of the Earth Cymru (FOE Cymru) are calling on the Assembly to support rock walled tidal lagoons (1) rather than a Severn Barrage (2) as a means to generate green electricity from the high tides around Wales. The Assembly is due to debate the Severn Barrage scheme this week (3). The environmentalists say that lagoons would be much more commercially viable than the Barrage and would not pose the shipping or environmental problems either. The group has informed both the Economic Development and Environment Committees of the Assembly of the benefits of tidal lagoons (4).

Neil Crumpton, FOE Cymru energy spokesperson said:

"Tidal lagoons could well generate electricity at less than half the cost of the Severn Barrage scheme and would not require a huge £10 billion lump sum outlay.

The Barrage would also damage the sensitive and heavily designated coastal areas of the Severn Estuary and its lock gates would interrupt shipping to and from Bristol and other busy Severn ports. In contrast, rock walled lagoons would be located a mile or so offshore, avoiding coastal and shipping interests and may actually provide extra wildlife habitat.

The lagoons are more cost and size effective because they are built in shallow water and generate electricity on both the rise and fall of the tide. The Barrage would have to dam the deepest part of the Severn estuary and would generate on the ebb tide only."

The Barrage would cause environmental problems for a number of reasons. There would be a change in salinity, increased depths upstream and non-natural tidal movements across the intertidal zone. The subsequent habitat changes would result in the loss of breeding grounds for a number of bird species.

Lagoon developers Tidal Electric Inc are currently planning a small scheme in Swansea Bay enclosing about one square mile of sea, much larger schemes are entirely possible. A lagoon as big as twenty square miles has been suggested on Rhyl Flats which would generate 260MW (megawatts) on average rivalling the 300MW lifetime average output of the Trawsfynydd nuclear power station. FOE Cymru estimate that the Barrage would meet about 5.3 % of current UK electricity consumption averaging 2,170 megawatts. Lagoons could have a coastal defence and also a tourism role depending on their location.

Notes

1) Tidal lagoons or generators are rock-walled structures which enclose an area of shallow sea, potentially many square miles. The lagoons generate electricity as tidal water fills and ebbs through large water turbines built within its walls. The structures would look like similar to a harbour or marina breakwater with the nearest wall being typically a mile or so offshore. The structures could last 50 to 100 years plus and could be decommissioned by recovering the rock aggregate for subsequent uses.

2) Severn Barrage Scheme as proposed by Severn Tidal Power Group (STPG) 187.5 square miles, average output 2.2 gigawatts.

3) Assembly Economic Development Committee (plus Environment Cttee) Debate on Wednesday.

4) See FOE Cymru Barrage/Lagoons Briefing below.

---------------------------
Friends of the Earth Cymru Briefing for Assembly

Severn Barrage/Tidal Lagoons

The output of the Severn Barrage is often quoted in the press to supply 7% of UK electricity (some papers even print UK energy !).

Barrage consultant Tom Shaw says annual output would be 17-20 TWhrs per year from the proposed 8,640 GW IC scheme (Severn Barrage Report). The Barrage impoundment area would be 187.5 square miles (480 sq km).

So, assuming 19 TWhrs per year, the Barrage output would represent 4.88 % of annual UK 2000 electricity generation (see DTi figures below and also note the difference in generation and consumption due to grid losses and the industry's internal requirements). If the UK consumption figure is used the output is 5.77 %.

So, the Barrage would more likely meet 5.3 % of current UK electricity CONSUMPTION (assuming small internal requirements and normal grid losses).

The Barrage AVERAGE output and load factor (for 19 TWhrs per year) is 2.17 GW (19000/8760 = 2.17), and the load factor would be 25.1 % (2.17/8.64 = 25.1).