MIKE ASTON noted that wind turbines required back-up from conventional power stations, which must be kept warmed up and wasting fuel.

In fact, the problem is much greater than he suggests.

Only coal-fired power stations can provide back-up because nuclear power stations and gas-fired power stations must run at full power all the time.

We sometimes have the insane situation, when electricity demand is very low, of the power companies having to pay wind farm operators for not taking their power because nuclear and gas power stations are providing all that is needed.

RICHARD DURRANT, Sea Road, Boscombe