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Energy alternatives

What a good idea of Will Howie to bring up the matter of energy policy and the Severn Barrage which could make good use of the most extensive tides that we have around in the UK (NCE 1 October).

Some 10 or more years ago the Government was funding several interesting programmes of research into the use of tidal energy around the shores of the UK. With the increased knowledge of working in deep water which has been accumulated over that period, with many deep oil rigs surviving in quite severe conditions of tide and weather, some of the proposals that were being considered then could well be viable now.

The other point Will Howie brings up is the use of nuclear power, and the difficulty in finding suitable accommodation for the low level waste that is produced. The Swedes seem to have mastered the use of underground space for this purpose. So why don't we try? To build the Severn Barrage will take a mountain of rock either as stone or as concrete. Why don't we dig tunnels out of the existing quarries in the Mendips to produce this rock and concrete? The carboniferous limestone is generally good quality rock and we should have the environmentalists well pleased with the reduced need to extend the existing quarries.

Richard Watts (F), Mayfield House, Shute Lane, Long Sutton, Langport, Somerset, TA10 9LZ.

Small but sustainable

Will Howie is obviously lobbying for a consortium wishing to build a Severn Barrage. His analogy with the Channel Tunnel is unfortunate, since he has obviously forgotten that the construction cost was nearly 100% over budget and it was three years late. It will be well into the next century before shareholders receive dividends to reward their investments in Eurotunnel. Perhaps Lord Howie is proposing that the barrage should be paid by taxpayers like UK nuclear power stations?

Similarly his advocacy of nuclear electricity might be less ardent after reading the eloquent counter arguments of student Mark Swanepoel in Professional Engineering of 2 September. 'My generation does not owe ... any respect [to] ... the engineers and politicians who designed and authorised such power stations.'

The recent World Wide Fund for Nature Survey showed that one third of the natural habitat of the world has been destroyed since 1960. Clearly this is unsustainable. Without forest cover and vegetation, carbon dioxide levels will rise even faster amplifying the greenhouse effect. Rising sea levels will threaten many cities including London.

Civil engineers must promote sustainability but need to be more humble by building small scale projects which can be easily decommissioned at the end of their usual lives. Even better would be to improve the energy efficiency of construction processes and especially of the final projects in use. The UK wastes over 50% of the energy it consumes, not all of which is electricity. Retrofitting the existing infrastructure would be a major engineering challenge. More efficient structures would reduce total energy demand to a point where renewable resources could provide most if not all energy demands. New zero fossil fuel buildings are now the norm in Germany. As Eric Schumacker observed: 'Small is beautiful. He might have added 'and sustainable'.

Professor Lewis Lesley (M), Liverpool John Moores University, School of the Built Environment, 96 Mount Pleasant, Liverpool L3 5UZ.

Wind of change

In the article promoting the Severn Barrage to replace nuclear power, Will Howie has got his facts seriously wrong. For the UK it will be offshore wind power that provides the alternative to building more nuclear power stations. Current state of the art technology is now based on 1.5MW

wind turbines which with an availability factor of 0.33 will generate an average output of 0.5MW each, thus requiring 7,000 turbines to generate 10% of average UK demand, ie 3,500MW. Ian Fells' figure quoted of 26,000 turbines was based on much smaller land based turbines available at that time.

The barrage scheme would cost pounds9bn not pounds900M and the average daily generation would be 1,940MW. The installed capacity of 8,640MW would only be available for a short period each tide and the timing of this peak output would move through the day with the tides so that sometimes output would be zero at periods of peak demand!

For these reasons the value of the Severn Barrage to the Grid is about 1,000MW, ie one half of one 'big power station' and not 'more than four big power stations' as Will claims. This makes the Severn Barrage at pounds4,500/kW of average available capacity the most expensive of all the renewables on offer. Offshore wind will initially cost about pounds3,000/kW of average available capacity.

Peter Chambers (M), Clean Energy Educational Trust, 66 Dartmouth Road, London NW2 4HA.

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