The coming of wind power

Press, 10 February 1981, Page 17

The coming of wind power

By

NIGEL HAWKES,

“Observer,” London

The windmill makes a comeback: 150 feet high (almost as tall e.s Nelson’s Column), the Orkneys wind generator will produce three megawatts of electricity. The outer fifth of each blade (A) can adjust to different wind speeds, and the entire superstructure (B) can turn on its concrete tower (C) to follow changes in wind direction. It will be under remote control from Kirkwall.

Britain's first big wind power generator will be built on. top of a hill in the Orkneys, where the wind speed averages close to 30 miles an hour.

The generator, announced fay Mr David Howell, the Energy Secretary, will cost about $l2 million and generate three megawatts of electricity to be fed into the Orkney grid. Together with a smaller 250 kilowatt machine, it is expected to supply about a seventh of Orkney’s electricity when it comes into full operation in the winter of 1983-84.

To go almost straight for a machine of such a large size — it will be almost 250 feet high from

base to rotor tip, and the blades and machinery at the top of the tower will weigh 195 tons — is a brave step. The United States, which ha- led the way into big wind power machines, has increased in size more modestly, little by little. However, Dr David Lindley, general manager of the Wind Energy System Group, which has designed the machine, is confident it will work. Many of the design solutions the Americans had reached by trial and error had already been worked out by calculation by the British group.

One is to use steel for the twin-bladed rotor. Since wind speed increases with height, the blade is under greater pressure at the top of its travel. than at the bottom, inducing a flexing motion as it goes round. This means that the material chosen must have a long fatigue life, and steel is the best choice. The Americans, after building one generator with aluminium blades, and flirting with wood, fibreglass, and even concrete, have come to the same conclusion.

To control the power delivered by the wind, the outer 20 per cent of each blade can be rotated so that it can be “feathered.” The exact angle of this part of the blade will be controlled by a silicon chip fed with information about the speed of the wind.

The machine is designed to produce full power at wind speeds between 37 and 60 m.p.h. It will operate at slower wind speeds but is automatically stopped when wind speeds rise above 60 m.p.h. This is done by feathering the tips to provide reverse thrust, and applying a huge disc brake, based on the same technology used to stop mine cages. Why stop it at all? If the machine had to be designed to run in all wind speeds, it would be very much over-designed for the conditions it. will experience for most of the time. And throwing away the energy available in winds of more than 60 m.p.h. is a fairly small sacrifice; such winds are not too common, even 600 feet up in the Orkneys. Dr Lindley estimates by operating at full power between 37 and 60 m.p.h., the machine will in fact capture 70-80 per cent of the total wind energy available. The machinery for swivelling the blades round into the wind and keeping them there will . also be controlled by microprocessor. Mounted on top of a 150 foot concrete tower, the “cap” — consisting of blades, generator, and gears — will be held in place by four pads which will grip the outside of the tower.. When the wind veers by

more Elan ? degrees —• not very often in a- good breeze — the pads will “walk” their way around the tower, carrying the cap with them. The smaller machine, with blades 66 feet in diameter, should come into operation in the winter cf 1981-82, in time to provide some experience which could still be used to modify the design of the bigger. Dr Lindley believes that in export markets tne smaller machine may well sell in larger number-5 than the bigger one. This is because wind power will never amount to more than about 20 per cent of the generation .n any grid system, unless expensive storage systems are built (none is planned for Orkney). If wind power took any larger share, there would inevitably be power cuts when calm days coincided with high electricity demand. Many - electricity systems on islands or in isolated communities, are quite small. A few 250 kilowatt fenerators might be all they could take. ' Britain, on the other hand, with total installed capacity of more than 60,000 megawatts, could probably take up to 12,000 MW of wind power, or 4000 of Dr Lindley’s - big machines. Qn Orkney, the two generators will replace electricity generated by expensive diesel engines. The diesels will have to be detained in case the wind either falls to nothing or exceeds 60 m.p.h., but for most of the time one or more of them can be shut down, saving fuel. That should be good news for the North of Scotland Hydro Bdard, which has been making heavy losses in Orkney for the past few years. It is contributing $2.3 .million towards the cost of * the machines. . ! -