The Guardian, Ian Sample, Wednesday 29 February 2012
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| Hywind floating windmill being towed to its trial site in deep water off Norway. Photograph: Oyvind Hagen |
Six miles
off south-west Norway, the first full-scale demonstration of a floating wind
turbine heaves and sways in the North Sea. The depth of water, at 200 metres,
rules out driving piles into the seabed, or mounting the turbine on a
submersible tower.
Instead, it
sits on a buoyant steel cylinder, kept upright with ballast, and tethered (not
too tightly) to the seabed by a three-point mooring.
Hopes are
running high for the Hywind project which ends this year. Since 2010, the
turbine has generated 15MWh of energy. If it survives the battering waves and
driving winds, floating offshore wind turbines will shift from the plausible to
the probable.
Though
turbines on land still dominate the field, offshore sites are expected to grow
rapidly, especially if floating turbines can make electricity cheaply enough to
compete.
With
floating platforms, wind could be tapped over the deeper seas of the
Mediterranean, and off Japan and off both coasts of the US, says Peter Jamieson, of energy consultants GL Garrad Hassan, the author of Innovation in
Wind Turbine Design.
Offshore
gives higher wind speeds and smoother conditions. "We are now at the stage
where there are a few floating prototypes, but the technology is not yet
established," he said.
The
economics of offshore wind favour fewer, larger turbines. In new projects, 5MW
and 7MW turbines range from 126-metre to 164-metre spans, with some ambitious
designs nearing 200 metre diameters. The largest turbines on land are around
half that size.
The push
for profitable new sites has run alongside advances that have transformed early
turbine designs into direct drive, or gearless, models that use permanent
magnet generators. These have fewer parts so, theoretically, are more reliable,
with some firms claiming they are also quieter and more efficient.
While the
major suppliers, including Vestas, Enercon and Nordex, have focused on larger
wind turbines, scores of smaller companies are developing models for local use,
for farms, schools and urban centres, emphasising appearance and noise
reduction.
"There
have been successes and failures, but this is a major market with a lot of
activity. The challenge for them is to be fully economic," said Jamieson.
More
distant are airborne systems that tap into high-altitude winds, which according
to Ken Caldeira, a climate scientist at Stanford University, hold enough energy
to power civilisation.
Though much
derided, tThe technology for making and controlling them is steadily becoming
established. The German companyfirm SkySails has drawn on its experience of
designing enormous kites to tow cargo ships, to develop offshore wind systems
that generate electricity as the kite pulls cable from a drum. When the kite is
fully deployed, it is steered automatically into an area where the pull is very
low, and reeled in again.
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