[LINK] NASA Power Kites
stephen at melbpc.org.au
stephen at melbpc.org.au
Fri Jul 6 20:54:13 AEST 2012
Good old NASA. Here they are looking at wind power-generation with kites.
Lots of advantages. Eg cost (and flying at 2000 feet) efficiency, visual
and sub-sonic pollution. Thus, simple, cheap, almost-base-load renewable
energy, which would be almost free after you buy some $10-20,000 kites :)
By Bob Silberg, NASA Jet Propulsion Laboratory
The faster a wind turbine's blade spins, the more energy you can get from
it. And the farther you get from the hub, the faster that part of the
blade is traveling.
So the tips of the blades generate most of the turbine's poweras much as
90 percent, according to David North, an engineer at NASA's Langley
Research Center in Virginia.
"What if I had a machine that was just the tip of the blade?" North
said. "That's really the idea of airborne wind energy get rid of 400
tons of tower and concrete, and just fly the blade tip. Basically, it's
flying kites to create power."
A wind turbine that's flying at the end of a tether instead of fixed to a
concrete foundation has big advantages.
For one, it's highly portablean attractive feature for potential users
such as the military, which is eyeing the technology for war-zone bases
where importing fuel comes with great risk and expense.
Another huge advantage is that an airborne system can go much higher, up
to altitudes where the wind blows faster and more steadily. And with
greater speed comes much greater energy. Moving twice as fast produces
eight times the power. Moving three times as fast produces 27 times the
According to North, most tower turbines are about 80 to 100 meters
(roughly 300 feet) high, which he says is "pathetically down in the
boundary layer of Earth." The boundary layer is where friction from
Earth's surface keeps the wind relatively slow and turbulent.
The sweet spot for wind energy starts around 2000 feet up. To use wind at
that altitude to generate electricity, youd have to build a turbine
tower taller than the Empire State Building. Or you can fly a kite.
There are two basic types of airborne wind-energy systems. One, known
as "flygen," is literally a flying generator, with turbines built into
the kite. The resulting electricity travels by tether to a storage or
distribution device on the ground.
In the other kind of system, the generator sits on the ground, powered by
the reeling out of the tether as the wind catches the kite. By
maneuvering the kite like a sailboat tacking upwind, the periodic reeling-
in phase can take only about 10 percent of the energy produced by the
reeling-out phase, for a 90 percent net gain.
Several private companies are trying to get airborne wind energy ready
for market. NASA's contribution focuses on two aspects of the technology:
autonomous flight control and aerodynamics.
"A lot of the systems that are flying have pretty cruddy aerodynamics,"
North said. He explained that companies under deadline pressure from
investors arent able to spend much time on the difficult challenge of
optimizing the kites efficiency. "Here at NASA," he said, "we have the
luxury of focusing very specifically on problems and not have to worry
about getting a commercial product fielded by a certain date."
Autonomy the ability to set it and forget it for long stretches of time
is crucial to the airborne wind industry. It's fun to fly a kite
manually, but 24/7 for months at a time is a little much to ask of a
human operator, even if he or she could manage the precise maneuvers that
are required over and over again. And the likelihood that airborne wind
farms would be located far offshore, where air traffic tends to soar high
above the altitude where these kites would fly, makes autonomy all the
The companies that have demonstrated autonomous flight so far have relied
on sophisticated onboard electronics and flight-control systems,
comparable to autopilot systems for commercial aircraft, according to
North. "Our goal is to simplify the whole thing," he said, "especially if
we are only flying at 2,000 feet, which is in most cases below the
On March 1, 2012, North and his colleagues at Langley achieved the
world's first sustained autonomous flight using only ground-based
"The breakthrough we've made," North said, "is we are basically using a
cheapo digital webcam tied into a laptop computer (on the ground) to
track the motion of the kite and keep it flying autonomously."
Langley's system operates much like Microsofts Kinect gaming system,
which tracks the body movement of players. "It's pattern recognition
software," North said. "The software is basically determining where the
kite is, how the kite is oriented and how fast the kite is going, and
using all that data to feed into the flight-control system."
The Langley prototype was small, with a wingspan of about 10 feet. But
the devices the industry ultimately produces are likely to be much
bigger. "Some people are talking very large, like wings the size of
Boeing 747 airliners," North said.
Ironically, the biggest challenge the Langley team faces is having their
test flights limited to low altitudes, to avoid interfering with
aircraft. They are currently trying to work out a deal that would enable
them to fly at 2,000 feet for long periods of time in the restricted
airspace reserved for NASA above Wallops Island, Virginia.
Given a chance to develop this technology, who knows? We might see a day
when those who scoff at green energy alternatives could be given this
friendly piece of advice: Go fly a kite!
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