POWER April 2011 - 42

FUTURE POWER
9. Maglev. When Chinese developers unveiled
the magnetic levitation wind turbine
at the 2006 Wind Power Asia Exhibition, it
was hailed as a breakthrough in the evolution
of wind technology. The technology is today
used to power streetlights in Shenzhen and
is available in ranges from 300 W to 1 kW.
Courtesy: Shenzhen TIMAR Wind-Solar Energy
Technology Co., Ltd.
12. The quietrevolution. London-based
quietrevolution's qr5 VAWT is designed to
eliminate noise and vibration. Courtesy: quietrevolution
fication
applications from small wind turbine
makers just last year.
The second type of VAWT-the Savoni13.
KiteGen. Arranged in a " carousel " or
" stem " configuration, Italian company KiteGen's
power kites are tethered to a power
plant and flown over a predefined flight path.
Courtesy: KiteGen
10. Windspire. Nevada-based Windspire's
Giromill generates power when the wind
blows against the vertical airfoils, causing
them to spin. Courtesy: Windspire
us-uses a rotor, formed by cutting a cylinder
into two halves along the central plane
and then moving the two semi-cylindrical
surfaces sideways along the cutting plane
so that the cross-section resembles the letter
" S. " One much-cited modern-day example of
a Savonius turbine is the Helix system from
Helix Wind (Figure 11). The company says
that as the wind blows (at speeds as low as 10
mph), the long helical blades catch wind from
all directions, forcing it through the turbine.
The turbine and generator assembly are currently
being tested for UL listing, with which
the turbine would be eligible for rebates under
all state renewable energy programs.
To gain traction in the competitive market,
other VAWT makers have chosen to address
HAWT shortcomings. UK firm quietrevolution
claims its qr5, a helical VAWT designed
to increase demand for wind turbines in environments
close to people and buildings, is
said to virtually eliminate noise and vibration
while generating 7,500 kWh per year (Figure
12). So far, more than 100 turbines have reportedly
been installed across the UK, Austria,
and Germany.
11. The Helix. California firm Helix Wind's
system is a Savonius, drag-based vertical-axis
wind turbine. Courtesy: Helix Wind
14. The Joby. California firm Joby Energy
is evaluating a 30-kW multiwinged kite,
while simultaneously designing and building
100- and 300-kW systems. Plans are to fly
initial commercial systems between 500 and
2,000 feet high and to begin manufacturing
commercial systems in 2012. Courtesy: Joby
Energy
Airborne Turbines
Meanwhile, wind turbine design is also taking
off in an entirely new direction-skyward.
Prompted by suggestions that there is
an estimated 870 TW of power potential in
high-altitude tropospheric winds, and that the
four-decades-old idea is finally technically
feasible, several developers around world
(including research labs and private industry)
are testing prototypes that use kite-like attributes
to harness wind energy. The concept
is so close to reality that the Federal Aviation
Administration has administered limits
restricting airborne turbines to flight at altitudes
below 600 meters.
One prominent example is the KiteGen
power plant (Figure 13), which comprises several
" Kite Steering Units " that pilot an array
of " power kites " over a predefined flight path.
KiteGen is typically arranged in a " carousel "
or " stem " configuration. Modular approaches
could allow developers to build plants up to
100 MW with costs of energy produced lower
than €0.03/kWh, KiteGen says.
Joby Energy takes another approach. It
is testing a 30-kW system (Figure 14) that
looks like a multiwinged kite supporting an
array of turbines. Thrust for the kite's vertical
takeoff is supplied by motor generators connected
to the turbines, and the orientation is
controlled by a computer system that differentially
adjusts rotor speeds to keep it flying
in a circular path.
42
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POWER April 2011

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