Industrial strength wind energy


As reported in The Generator in December, a new approach to wind
generation harvests more of the available wind energy through the use
of a vertical axis turbine. This approach achieves better performance
by capturing more energy in the first place and, as a consequence
having smaller blades resulting in a lighter turbine, thus wasting less
energy. The Economist this week reports that UK electricity generation
companies are planning to use the technology at sea.

TMA, a company based in Cheyenne, Wyoming, announced last November that
its first vertical-axis wind turbine (VAWT) would soon be ready for
commercial production, reported The Economist (11 March 2006, p.3).

Pressure differential is created: The TMA system has two sets of
vertical blades. The two inner blades, each shaped like a
half-cylinder, catch the wind and rotate about a central axis, while
the three outer blades, shaped like aircraft wings, are fixed. The
interaction between the two sets of blades causes a drop in pressure in
front of the rotating blades’ leading edges, which further increases
the rate of rotation.

Big efficiency gains claimed: TMA claims that its system
harvests 43-45 per cent of the wind’s available energy; conventional
propeller-style turbines, in contrast, have efficiencies Of 25-40 per

High wind capability: Furthermore, in winds of more than 80kph
(50mph) the blades and gearboxes of conventional turbines cannot cope
with the strain, and they have to be shutdown. TMA says its
vertical-axis design can still work even at wind speeds as high as
110kph, however.

Quieter and less obstrusive, too: The ability to harvest
high-speed winds is particularly valuable, since each doubling of wind
speed results in an eightfold increase in available energy. TMA also
claims that its design is quieter and less visually obtrusive than
conventional turbines.

Giant offshore turbines in offing?: A British consortium,
Eurowind Developments, which includes VT Group, a shipbuilding and
engineering company, and Mott Macdonald, a consultancy, believes VAWTs
could be the best design for giant offshore turbines. Such a turbine,
with a capacity of 10MW, would be able to power around 10,000 homes.

Sheer scale of today’s blades is a problem: Today’s largest
horizontal-axis turbines produce around 5MW, and are proving difficult
to scale up. Each blade has to be more than 60 metres long, and the
bigger the blade, the greater the stress it experiences as it turns:
the blade’s own weight compresses it at the top of the cycle and
stretches it at the bottom.

Cost, efficiency penalties: As a result, blades must be made and
transported in one piece, which is expensive. Reinforcing the blade to
enable it to withstand these forces further increases cost and reduces

The Economist, 11/3/2006, p. 3


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