[ExI] kite power?
thespike at satx.rr.com
Fri Jun 19 22:14:05 UTC 2009
Kites could power world 100 times over
Friday, 19 June 2009
by Kerensa McElroy
SYDNEY: High-flying Kites could harness enough
energy to power the world 100 times over,
according to a survey of high-altitude winds.
Published in the journal Energies, the study
reports that areas well suited to harvesting high
altitude winds fall over some of the world's
major cities such as New York and Tokyo.
"The wind energy aloft is phenomenal. Energy
densities unthinkable near the ground are common
in the upper levels of the atmosphere," said
Cristina Archer, lead author and a meteorologist
at California State University in Chico, USA.
"It's like a perpetual source of free energy."
Fast and furious
"These winds blow much more strongly and steadily
than near-surface winds, but you need to go get
up miles to get a big advantage. Ideally, you
would like to be up near the jet streams, around
30,000 feet," added coauthor Ken Caldeira, a
climate scientist at the Carnegie Institution's
Department of Global Ecology in Stanford, California.
Jet streams are moving belts of furious winds,
shifting seasonally at altitudes between 6,000
and 15,000 metres. To get a global picture of the
energy these jets hold, the researchers compiled
28-years-worth of data from both the U.S.
National Centres for Environmental Prediction and the Department of Energy.
Archer and Caldeira looked at both wind speed and
air density at different altitudes, concluding
that extraordinary amounts of energy exist above
Japan, eastern China, the eastern coast of the
U.S., southern Australia and north-eastern Africa.
Average wind power densities in these locales
"are greater than 10 kilowatts per square metre.
This is unthinkable near the ground, where even
the best locations have usually less than one
kilowatt per square metre," said Archer. New York
clocked up a whopping wind power density of 16
kilowatts per square metre, the study found.
Kite-driven generators have been suggested as one
method of capturing this energy. In principle,
they work by using the strong pull of the wind to
drive a land-based turbine, tethered to the kite via a cable.
When the cable reaches its full extension, the
angle of the kite is shifted so that the wind no
longer pulls and the cable can be rolled in
again, before the cycle repeats. A prototype kite
designed by Dutch former astronaut Wubbo Ockels,
now at the Delft University of Technology in the
Netherlands, was able to generate 10 kilowatts of
power - or enough electricity to supply 10 homes.
"This approach has the advantage that the heavy
generator stays on the ground" said Pavel
Trivailo, an aerospace engineer from the Royal
Melbourne Institute of Technology, in Australia.
He said he has recently applied for funding to
develop Ockels' technology further, using radio-controlled gliders.
Like kites, gliders would only be useful on their
way out into the wind whilst winding back in,
no electricity is generated. Trivailo imagines
paired systems of kites, where one travels out as
the other returns, likening the system to the
paired action of a piston engine.
Gaps in the grid
He points out that cables capable of safely
coping with large forces - such as those
generated by wind - already exist, thanks to the
'space tethers' used to join sections of satellites.
Some challenges of high-altitude wind power are
still to be met, however. "While there is enough
energy in these high altitude winds to power all
of modern civilisation, at any specific location
there are still times when the winds do not blow," said Caldeira.
The study predicts wind may still fail about 5%
of the time. "This means that you either need
back-up power, massive amounts of energy storage,
or a continental or even global scale electricity
grid to assure power availability," he said.
Trivailo agrees much work needs to be done. "How
you deploy the gliders or kites at high altitudes
is still an open question," he said.
high altitude wind power - Sky Windpower Corporation
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