ROBIN Ball (Letters, August 5) has been a victim of the wind-energy deceivers. Those sails in Germany were not producing any energy at all. Industrial windmills are fitted with an automatic decoupler, which comes into action at 10mph. That means that with winds up to 10mph, although the sails are turning, there is no electricity. If the wind speeds up to 14mph, then only one out of eight customers has any electricity. At the much stronger speed of 20mph, four out of10 have electricity. The wind has to be about 27mph before the claimed power is produced. I can assure Mr Ball that 10mph occurs more than 27mph. It is the big money that pays off. Windfarms are not renewable electricity; they are unreliable electricity.

Robert Pate, Willowbank, Old Edinburgh Road, Minnigaff, Newton Stewart.
 
ROBIN Ball reports the vast number of wind generators working "with almost no discernible movement of air". This production of electricity from almost nothing would be wonderful if it were true.

As the electricity produced is in the ratio of the cube of the windspeed, a fall in that speed leads to a dramatic loss of output. Assume for illustration that the speed he reported was one-tenth of the design speed, which would seem reasonable. The output would be one-tenth times one-tenth times one-tenth, namely one thousandth of the rated output. Thus a huge two-megawatt machine over 100 metres high would be reduced to a mere two kilowatts, enough to power one electric fire.

The truth is that the machines are locked into the grid, and at very low windspeeds the generator will act as a motor, extracting energy from the grid system. This is a convenience to the operators, as they do not require to stop the blades and later restart them. The publicity benefit is that the uninformed public are conned into believing they are doing good and reducing carbon dioxide emissions, when they are doing no such thing.

The average power output over the year from a two-megawatt machine is around 500 to 600 kilowatts. This leads to the wasteful expense of having to construct massive power transmission lines in order to carry the full output, when the average is 25% to 30%.

William D Brown, Dunvegan, Achscrabster, Thurso.