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’t their only disadvantage. Traditional wind turbines can only
produce a low voltage that is “generally too low for transmission over any
distance”, 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’t 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—causing more energy to be lost as heat. This limits the
distance today’s 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’s Windformer turbine drives a large rotor
ringed with permanent magnets that works at whatever low speed the blades rotate
at—so it doesn’t need a gearbox. Leijon’s generator also produces a high
voltage, so it doesn’t need a transformer either. Having fewer components has
distinct advantages, he says. “The reliability is much higher, so we reduce
maintenance costs.” And without a conventional gearbox and transformer, the new
turbine is more energy efficient—by around 20 per cent, says Leijon.
A simple way to transmit the electricity over long distances from the turbine
was next on Leijon’s list. “We take the AC from the turbine and convert it to
DC—this can then be passed down a long, high-voltage cable,” he says. “So
the wind turbine can be in an area where it’s difficult to get access—like
high mountainous regions—or up to 100 kilometres offshore,” says
Leijon.
“The big issue with wind power is the public acceptance in terms of
visibility and noise,” says Michael Graham, an expert in wind energy at Imperial
College, London, so being able to hide wind farms could be useful. “It’s
certainly an intelligent direction to go in,” says Infield.