The potential for using the wind to generate electricity is huge. A recent study for the European Community estimated that there were sufficient sites in Europe for about 400,000 big machines – enough to provide three times Europe’s present needs.
Modern wind generators are very different from the old windmills. They are more like giant propellers with two or three blades, called rotors, mounted on top of tall towers of steel or concrete. The rotors turn a shaft which drives an electric generator.
The size of the blades and the height of the tower determine how much electricity the machine can generate. Wind generally gets stronger as you go higher, and the power of the wind you capture depends on the swept area of the blades. Double the length of the blades and the power increases four-fold. More important still is the speed of the wind, for the power that can be extracted goes up as the cube of wind speed – if it blows twice as hard, there is eight times as much power to be had.
However, wind generators do not need, or want, stormy weather. Most machines are designed to operate at wind speeds between Force 3 and Force 10 on the Beaufort Scale – 13 to 60mph (21 to 97km/h). above Force 10 the machines automatically shut down to save themselves from flying apart.
Most machines are designed to produce much the same power throughout their working range, the blades automatically ‘feathering’ as the wind increases so that the machine does not accelerate too much. It is better to have a steady output over a wide range of wind speeds than to be able to take advantage of the few really strong gusts.
Wind generators must point in the right direction, either directly towards the wind or directly away from it. For this reason th rotor is mounted on a turntable and controlled by an electric motor connected to sensors which tell it which way to face.
This problem of wind direction can be avoided completely if the blades are mounted on a vertical rather than horizontal axis. Then it does not matter where the wind is blowing from.
These vertical machines, called Darreius Turbines, have other advantages. The heavy generating machinery that converts the power into electricity can be placed on the ground, rather than at the top of a tower. The rotor is, therefore, subjected to less stress than in the horizontal-axis generators. A disadvantage is that they often need a push to get started, either by hand or by an electric motor.
One of the main problems of using wind turbines is environmental. While people like the idea of wind power, they are less keen on having every hill crowned with a whirling turbine.
Serious examination has been given to placing the turbines out at sea. But there would be problems anchoring them and in transmitting the power back to land. The British Department of energy has estimated that clusters of wind turbines built in shallow water around the coast could produce one and a half times Britain’s present electricity demand, but engineers first want to study the performance of land-based machines.
The people of Fair Isle, off the north coast of Scotland, have already been making use of wind power. They installed a small wind generator in the early 1980s and have cut electricity bills by more than three-quarters from the old diesel engines.
Picture Credit : Google