IEEE Spectrum December, 2012 - 48

to fund product development
is never easy, as any tech entrepreneur will tell you. But I've had
to grapple with a unique complication: My company, WindLift,
is developing a kite-based system that generates electricity. The
prototype, designed to put out 12 kilowatts, could save tons of
money for some people now using diesel generators. But when
I pitch the business to potential investors, it often seems as if
all they can remember is their childhood struggles with those
cheap stick-and-string fliers, making it impossible for them to
envisage what my company aims to achieve.
The problem isn't so much that most people view kites as
toys-it's that most people have no idea how sophisticated those As far back as the early 19th century, some kites
toys have become! Take kiteboarding. Since the mid-1990s, a were used as a power source-to propel buggies. But the first
growing number of enthusiasts have been using large kites to rigorous technical analysis of kites for generating electricity
enjoy an experience similar to that of waterskiing or skimming began in about 1980. Miles Loyd, a researcher at Lawrence
over the water on a wakeboard while being pulled by a motor- Livermore National Laboratory, in California, investigated the
boat. With kiteboarding, you dispense with the boat and are physics of the problem, publishing his results in a journal artiinstead pulled across the waves by a good-size kite.
cle titled "Crosswind Kite Power."
The kites designed for this sport measure up to 20 square
Loyd showed that by flying a tethered wing back and forth
meters, almost as big as a small billboard. With them, expert across the wind, you could get considerably more power than
kiteboarders can really fly: In 2010, the world's speed-record you could from a kite that just hovered in one spot. According
holder, Rob Douglas, hit 103 kilometers per hour (64 miles per to Loyd's calculations, if you used a wing as big as the one on a
hour)-faster than the fastest sailboat. And skilled kiteboard- Lockheed C-5A military transport (68 meters long), you could,
ers can leap 15 or more meters into the air and then glide back at least in principle, extract a few megawatts from a 10-metergently to the water's surface.
per-second wind. That's comparable to what you might get
A kite capable of such feats isn't anything like the ones you from the biggest of modern wind turbines.
played with as a kid-it's an ingeniously engineered airfoil. And
Loyd considered two ways to get electrical energy out of a
by the way, it has high-tech tethers that are 15 times as strong as tethered wing. One is to outfit the wing itself with propellersteel. A lot of research has gone into designing such kites and their like turbine blades that generate power as it zooms through the
rigging so that they can be turned on a dime with a gentle tug on air. That power would then be sent down an electrically conthe control lines. They can also be instantly adjusted to reduce the ductive tether. This is now known as the flying-generator, or
power they deliver, an important feature that allows a kiteboarder "flygen," approach. The other technique he considered was to
to negotiate strong, gusty winds safely.
exploit the force that the wing exerts on its tether to generate
Given these advances in kite engineering, it should come as electricity using equipment on the ground.
little surprise that several companies are now trying to deploy
Loyd's analysis didn't examine yet another possibility:
this technology for something more than recreation. A few to generate electricity using turbine blades that serve as both
have attached large kites to cargo ships and motor yachts as a lifting surfaces and energy-harvesting devices. That's the techway to reduce their fuel consumption. My company is looking nique Australian engineer Bryan Roberts began experimentto use these airfoils to offset fuel use, too, but in a different set- ing with in 1979-something he calls a gyromill, which he conting-for electrical generators in remote locations where the tinues to work on with California-based Sky Windpower.
diesel fuel to run them is a scarce commodity. Diesel in these
Beginning in the 1990s, other groups around the world
places is so expensive that supplementing conventional gen- also began devising various ways to generate electricity with
48

NA * iEEE SpEctrum * dEcEmbEr 2012

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previous pages, from left: makani power; altaeros energies; DaviD schneiDer; altaeros energies

Raising money

erators with power produced from the wind makes good economic sense.
Mine is just one of several ongoing efforts to use kites to
generate electrical power from the wind. Such airborne windenergy systems offer many advantages over standard wind
turbines, most notably that these tethered airfoils can tap the
relatively strong and steady winds found higher up. In addition, the area the airfoil can sweep isn't limited by the diameter
of the turbine, so these airborne systems are inherently more
efficient. Finally, the massive pylon needed to support a very
large rotating blade can be eliminated, slashing construction
costs and setup times.
Of course, generating electricity with a kite has some challenges you don't have with a standard wind turbine. Turbines
can't crash, for example. To avoid such mishaps, you must
be able to control the kite so that it crisscrosses the sky in an
orderly fashion, despite the vagaries of the wind. You also need
to automate this piloting and to make the whole system robust
and reliable. So far, nothing that meets all those requirements
has emerged on the commercial market, and it will probably
be several years at least before anything is available that does.
I view the present situation as being akin to the pioneering days of flight, where nobody knew what configuration of
wings and control surfaces would serve best-or whether the
whole enterprise would prove practical at all. But if the engineers now working on this technology are persistent and clever
enough, using tethered wings to generate electricity from the
wind will surely progress just as quickly as early aviation did.

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Table of Contents for the Digital Edition of IEEE Spectrum December, 2012