Sir - The Renewable Energy Foundation recently examined just what fraction of their rated powers the 500 or so serious wind turbines in the UK actually delivered (Sunday Times, November 6, 2006). Even the best ones in the Hebrides delivered less than one third of their rated power. Inland wind turbines did far worse.

That outside the Renewable Energy Systems site at Kings Langley delivered only 7.7 per cent of its rated power, a figure accepted by this wind turbine manufacturer. Fashion toys, like David Cameron's, are likely to do worse still, because local roof structures have substantial effects on air currents. I have no knowledge of the wind patterns at Midshires Co-operative's Botley site. Probably they have not been measured. It is very possible that the proposed windmill, over its lifetime, will not even pay off its carbon costs for manufacture and installation.

Prof Marshall Stoneham FRS, Dorchester-on-Thames