ROTOR POWER: These rotors serve as both turbines and propellers. Each of the four rotors on the Wing 7 contains a permanent magnet that spins in the breeze to generate electricity. Those electrons travel back to the earth via a tether that connects the kite to land or to a floating platform. AUTOPILOT: An onboard computer housed just behind the nose cone makes adjustments to allow the Wing 7 to generate the most power in flight. Carbon fiber throughout the kite makes it light but strong: the 120-pound device can pull more than three tons. “It can pull your car away,” says Makani Power's Corwin Hardham.
The powerful thrust of ocean-spawned winds can zip a kite surfer across the sea's surface at up to 55 miles per hour. Engineers are now trying to harvest the power in that wind to generate electricity. The Wing 7 airborne wind turbine pictured here is a prototype of a leading contender for the job. The autonomous, lightweight device is tethered to land or to a floating platform; when wind speeds pick up, four rotors fly it up above 820 feet in a circle perpendicular to the wind. As the air rushes across the carbon-fiber wing, the rotors generate electricity by spinning permanent magnets. “The rotors are both propellers and turbines,” notes mechanical engineer Corwin Hardham, CEO and co-founder of Makani Power, which created the Wing 7. An onboard computer makes constant adjustments.
The idea of generating power with kites, to avoid the fickleness of winds closer to the earth, is centuries old; modern iterations—including schemes for harvesting energy by flying into jet streams—date back to at least the 1970s. Makani intends to meet that challenge by designing its kite to work over the ocean, where the wind blows fairly constantly, and to cover a wide expanse of sky in its circular flight. Even relatively light winds that fail to stir traditional turbines can speed the light, tethered aircraft at more than 100 miles per hour and allow it to generate power.
This article was originally published with the title Kinetic Kite.
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19 Comments
Add CommentStill, having flown much less sophisticated kites a couple of times, they are likely to fall to Earth when the wind does die down. Operating over water would reduce the potential for kite damage (if they float), but it seems the hard part would be recovering and re-launching them...
Reply | Report Abuse | Link to thisIf you have light wind you will get light power generation. I am not disparaging the idea necessarily, just the reporting. Also, the higher you go the less the air density & the faster the wind must blow to produce a given amount of power. It does not matter how clever the design might be, it can not extract more energy then is available in the energy source. As a mater of fact a little over 59 percent is the maximum possible theoretically. This system will in fact lose much of its efficiency just in supporting itself with its tether & electrical cable plus the resistance in a necessarily thin cable.
Reply | Report Abuse | Link to thisSee: http://en.wikipedia.org/wiki/Betz'_law
oh bull
Reply | Report Abuse | Link to thisI would assume the tether would measure the tension and reel it in if the pressure from the wind drops. If it just reels out enough cable to balance the wind pressure and the weight of the kite plus cable, the kite should stay up.
Reply | Report Abuse | Link to thisI think the opposite would also have to be taken into account. Too high of a wind speed could damage the kite as well or snap the cable.
That sounds like a reasonable approach, but still the kite may crash if winds die down or are gusty. At least that's the experience of this 'intelligent controller'. No doubt current computers are more capable...
Reply | Report Abuse | Link to thisThe consistent low energy density of most renewables make them a non-starter for significant or practical energy generation. Notably the concentrated energy of high temp geothermal or conventional hydro remain the only practical renewables but both are severely limited by geography. Fact is, renewable energy can only be a bit player, and will be virtually eliminated by Nuclear once the roadblocks to Nuclear development are removed. I've read that in private even Big Oil executives recognize that after 2030 Nuclear will begin to dominate all Energy production - but don't tell anyone. Sooner we get started on the Nuclear Transformation and get over these Pixie Power Fantasies the less suffering there will be for future generations and the less ecological destruction there will be.
Reply | Report Abuse | Link to thisMy comment was meant in reply to Carlyle's.
Reply | Report Abuse | Link to this"... they are likely to fall to Earth when the wind does die down."
Reply | Report Abuse | Link to this"The rotors are both propellers and turbines", says the article, which means that the plane can stay airborne with no wind at all, switching its generators to motors, and by reversing the propeller's blade pitch -- which however poses a problem:
A propeller cannot work as a turbine, and vice versa, because this implies not only reversal of blade pitch, but also of blade twist -- and to my knowledge variable/reversible pitch blades aren't yet state-of-the-art!
An there's another point to be made: the day such blades are industrially produced, the tilt-rotor concept will become feasible as an ultra-light electric personal air vehicle deemed to replace the motorcar outside town (note that in its actual state of development it isn't eligible for civil certification, as it cannot autorotate).
And from then on, massively popularized airborne individual intercity mobility would get seriously obstructed by the presence of tether cables in the lower airspace -- although when operating over water, even large wind-farms of this type might pose no problem!
Anyway, humanity's future is in the air...
Your enthusiasm is only exceeded by your ignorance.
Reply | Report Abuse | Link to thisCarlyle:
Reply | Report Abuse | Link to thisI sincerely apologize for having polluted this thread with my disobliging reaction to your comment!
All I might pledge is the following, i.e. about your statement "... the higher you go the less the air density & the faster the wind must blow to produce a given amount of power.":
I must have found it utterly upsetting that anyone could even mention the irrelevant difference in air density at the low operating altitudes of these kites... and so much the more being told further on that the theoretical maximum yield is 59%, since this limit applies to all other types of wind-energy converters as well.
Thanks nevertheless for having read my enthusiastic comment!
Yet somehow, after this outburst of hot temper, I feel in trouble remembering G.-B. Shaw's prophecy: "The future belongs to cold-blooded enthusiasts..."
So tell us again about propeller direction of rotation when generating power as opposed to generating thrust.
Reply | Report Abuse | Link to thisSo much verbosity, so little knowledge.
Direction of rotation being assumed the same in both blower and turbine configurations, switching from thrust to torque generation needs both blade pitch AND twist reversal (not to be confused with direction of rotation reversal!) -- whereby the rate of blade pitch variation from tip to root is increasing exponentially.
Reply | Report Abuse | Link to thisThe NASA has recently issued a call for submissions by private US companies for the development of a variable/reversible twist rotor blade for the V22-Osprey because the military want to use it for less risky missions than combat front missions flown exclusively by the Air-Force and the Navy where the risk peak of fatal crash in case of total power failure (since it cannot autorotate) is blended with a forest of risk peaks anyway.
Hence my guess: what's good and safe for the military will sooner or later be so much the better and safer for the civil society...
BTW, blade twist variation is also known as a potential performance booster for large HAWTs!
To prevent any misunderstanding: my assumption of same direction of rotation for both thrust and torque generation isn't referring to kite planes, as these do indeed need their rotors to spin in respectively opposite directions for this purpose, together with hub pitch reversal (relative to the rotor axis, i.e. leading/trailing edge reversal) and blade twist reversal.
Reply | Report Abuse | Link to thisKite plane rotors spinning in the same direction for both operation modes would actually need blade profile camber reversal -- which is a much tougher technological challenge despite unchanged blade twist.
My example refers indeed only to helicopter rotors when switching from powered flight to autorotation -- whereby currently neither mode is optimized, due to a compromising nearly flat blade design.
And there's still another application my example refers to, called DDFTTW (Direct-Downwind Faster Than The Wind).
Ever heard of wind-driven road-vehicles running faster than the wind blowing directly from stern into a thrust generating, road-wheel-driven propeller?
It works -- yet when used in the turbine mode to drive the wheels for initial acceleration, the rotor is operating with wrongly twisted blades, thus yielding very little torque so that an initial push may be needed to reach rated speed.
But once cruising, they're incredibly fast -- with current world-record set at 2,7 times wind speed!
@dwbd: If we manage a few more Fukushimas, we may not make it to 2030.
Reply | Report Abuse | Link to thisGet an electric fan. Put it in a breeze & note the direction of rotation. Now switch the power on. Get an electric fan & place it in a breeze. Note the direction of rotation. If it is a DC powered fan it will be generating power. Now switch the power on.
Reply | Report Abuse | Link to thisDirection of rotation is the same. I think you will find that by referring to reversible twist your sources are simply referring to going from coarse pitch to fine pitch & back again as in a light aircraft with a variable pitch prop. If you totally reversed the pitch your prop would be trying to push your aircraft backwards. Some aircraft in fact have this ability which is used on the ground to aid braking.
If you dispense with the abuse, you may learn something. By the way, a sailboat can go faster than the wind if it travels at a tangent to the wind. Not directly towards or away from the wind direction. Same with a land yacht or any other wind powered land craft. The other claims are false perpetual motion garbage.
"The other claims are false perpetual motion garbage."
Reply | Report Abuse | Link to thisThis last sentence of your last comment demonstrates that a person who is notoriously wrong in some objective aspects, can be perfectly right in some other, rather subjective aspect, without even knowing he (or she) is -- do you realize that false garbage is the exact opposite of true garbage?
Sorry, Carlyle, your last reply disqualifies you as a serious discussion partner in rotary-wing technology (plus probably other related fields) -- guess you are a teacher or professor... right?
However, I'm quite surprised that no other commentators are reacting to my attempts to have you understand the fundamentals of aerodynamic rotors -- or at least to confirm the official DDFTTW world record...
This said, I feel sorry for the author and the editors, who deserve a higher participation rate in this challenging discussion.
And in the meantime, dear readers, I'll still be waiting patiently for responses likely to contribute to a peer-review of my comments -- though not likely from Carlyle!
"...a few more Fukushimas, we may not make it to 2030..."
Reply | Report Abuse | Link to thisOh, so now its a few more Fukushima's, first you told us Fukushima will destroy the World and there would be two-headed people walking around all over. And here I was looking forward to that 2nd head that you promised me after Fukushima #1, I could get twice the work done in half the time. But now you are telling us we have to wait for a few more Fukushima's to destroy the World and give everyone two heads. What a disappointment you are.
Hi All!
Reply | Report Abuse | Link to thisMiles L. Loyd from Lawrence Livermore National Laboratory published a very nice article about the basics of High Altitude Wind Energy (HAWE) in 1980. I recommend it to everybody who are interested about this.
There are also many ways to extract power from stronger and more sustaining high altitude winds, the one that Makani has chosen is not the only option!
If only the anti-renewable crusaders and spewers of bunk would go fly a kite!
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