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High-flying Kites Could Light Up New York 
In the future, will wind power tapped by high-flying kites light up New
York? A new study by scientists at the Carnegie Institution and
California State University identifies New York as a prime location for
exploiting high-altitude winds, which globally contain enough energy to
meet world demand 100 times over. The researchers found that the
regions best suited for harvesting this energy match with population
centers in the eastern U.S. and East Asia, but fluctuating wind
strength still presents a challenge for exploiting this energy source
on a large scale.
Using 28 years of data from the National
Center for Environmental Prediction and the Department of Energy, Ken
Caldeira of the Carnegie Institution's Department of Global Ecology and
Cristina Archer of California State University, Chico, compiled the
first-ever global survey of wind energy available at high altitudes in
the atmosphere. The researchers assessed potential for wind power in
terms of "wind power density," which takes into account both wind speed
and air density at different altitudes.
"There is a huge amount
of energy available in high altitude winds," said coauthor Ken
Caldeira. "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."
Jet streams are meandering belts of fast
winds at altitudes between 20 and 50,000 feet that shift seasonally,
but otherwise are persistent features in the atmosphere. Jet stream
winds are generally steadier and 10 times faster than winds near the
ground, making them a potentially vast and dependable source of energy.
Several technological schemes have been proposed to harvest this
energy, including tethered, kite-like wind turbines that would be
lofted to the altitude of the jet streams. Up to 40 megawatts of
electricity could be generated by current designs and transmitted to
the ground via the tether.
"We found the highest wind power
densities over Japan and eastern China, the eastern coast of the United
States, southern Australia, and north-eastern Africa," said lead author
Archer. "The median values in these areas are greater than 10 kilowatts
per square meter. This is unthinkable near the ground, where even the
best locations have usually less than one kilowatt per square meter."
Included
in the analysis were assessments of high altitude wind energy for the
world's five largest cities: Tokyo, New York, Sao Paulo, Seoul, and
Mexico City. "For cities that are affected by polar jet streams such as
Tokyo, Seoul, and New York, the high-altitude resource is phenomenal,"
said Archer. "New York, which has the highest average high-altitude
wind power density of any U.S. city, has an average wind power density
of up to 16 kilowatts per square meter."
Tokyo and Seoul also
have high wind power density because they are both affected by the East
Asian jet stream. Mexico City and Sao Paulo are located at tropical
latitudes, so they are rarely affected by the polar jet streams and
just occasionally by the weaker sub-tropical jets. As a result they
have lower wind power densities than the other three cities.
"While
there is enough power in these high altitude winds to power all of
modern civilization, at any specific location there are still times
when the winds do not blow," said Caldeira. Even over the best areas,
the wind can be expected to fail about five percent 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. So, while high-altitude wind may ultimately
prove to be a major energy source, it requires substantial
infrastructure."
--------------------------------------------------------------------------------
Journal reference:
Archer et al. Global Assessment of High-Altitude Wind Power. Energies, 2009; 2 (2): 307 DOI: |
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