Letter: The rumble of wind turbines

MALCOLM SMITH'S 'Tilting at wind turbines' (Review, 27 March) was marred by two errors, one explicit the other implied. First, it is not true that '35-45 decibels . . . is twice as high as the background level of 19 decibels typical of a still night in the countryside'.

Each 3 decibel increase constitutes a doubling of sound power, so that an increase from 19 to, say 40 decibels (a rise of 21 or 7 x 3 decibels) represents seven doublings. This amounts not to a twofold but a 128-fold increase in sound output.

Second, the reference in the penultimate paragraph to conventional power stations operating 'at little more than a third of peak efficiency', with its clear implication that the stations could (by getting their act together perhaps?) operate much more efficiently, is not fair.

The concept of 100 per cent thermal efficiency, while useful in thermodynamic theory, is not remotely approachable in the real world where wholly intractable and quite fundamental practical constraints impose limits on thermal efficiency which exceed those actually attained in power station practice by very little.

Alan Lewis

Thornbury, Bristol