WIND farms, those green-but-ugly blots on the rural landscape, could soon be
banished far offshore or placed high up mountains thanks to a new type of
hyper-efficient wind turbine invented in Sweden.
In conventional wind turbines, the rotating blades are attached to an
internal generator by an axle. The generator normally needs to turn at high
speed, so a gearbox is used to increase the speed of the axle from around 18
revolutions per minute to 1500. But gearboxes are expensive and can wear out
quickly, so wind farms must be built where the turbines can easily be reached
for maintenance.
This isn鈥檛 their only disadvantage. Traditional wind turbines can only
produce a low voltage that is 鈥済enerally too low for transmission over any
distance鈥�, says David Infield, director of the Centre for Renewable Energy
Systems Technology at Loughborough University. The alternating current produced
is boosted with a transformer (see Diagram)
but this doesn鈥檛 solve the problem
entirely. AC is harder to pump over long distances because it prefers to
transmit along the skin of a conductor, which increases the
resistance鈥攃ausing more energy to be lost as heat. This limits the
distance today鈥檚 AC-generating wind farms can be floated offshore.
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Now, Mats Leijon of Swedish engineering firm ABB has developed a turbine he
thinks will overcome many of these problems. Instead of using a small generator
that turns at high speed, Leijon鈥檚 Windformer turbine drives a large rotor
ringed with permanent magnets that works at whatever low speed the blades rotate
at鈥攕o it doesn鈥檛 need a gearbox. Leijon鈥檚 generator also produces a high
voltage, so it doesn鈥檛 need a transformer either. Having fewer components has
distinct advantages, he says. 鈥淭he reliability is much higher, so we reduce
maintenance costs.鈥� And without a conventional gearbox and transformer, the new
turbine is more energy efficient鈥攂y around 20 per cent, says Leijon.
A simple way to transmit the electricity over long distances from the turbine
was next on Leijon鈥檚 list. 鈥淲e take the AC from the turbine and convert it to
DC鈥攖his can then be passed down a long, high-voltage cable,鈥� he says. 鈥淪o
the wind turbine can be in an area where it鈥檚 difficult to get access鈥攍ike
high mountainous regions鈥攐r up to 100 kilometres offshore,鈥� says
Leijon.
鈥淭he big issue with wind power is the public acceptance in terms of
visibility and noise,鈥� says Michael Graham, an expert in wind energy at Imperial
College, London, so being able to hide wind farms could be useful. 鈥淚t鈥檚
certainly an intelligent direction to go in,鈥� says Infield.