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Energy from High-Altitude Kites
maddmike writes "High altitude kites could produce energy equal to some power stations at a comparable cost without polluting. The technique uses a thing dubbed a 'Laddermill' - a chain of kites attached together to create a loop in the sky more than 5 miles long."
Flying kites at high altitude isn't as easy as it seem: pretty soon you get a lot of problem from the line(s), chiefly the weight of the line, but also line drag.
The former problem is essentially a strength vs. weight problem that even high tensile lines made of dyneema won't solve easily (above 400/500m, a 6m parafoil can very well sit there and refuse to climb with standard lines).
The latter problem introduces a problem of angle, since the line becomes curved under the wind drag, which makes the section right under the kite more and more vertical as it climbs, which in turn "flattens" its incidence angle and reduces its lift. It's always possible to modify the incidence on the ground to compensate, but takeoff can get dicey then. And of course, the wind drag on the line also tends to pull the kite down, and it's not negligible with a lot of line up.
So yes, it should be possible to use kites to generate power, but there will have to be a great deal of electronic magic to regulate everything, down on the ground and up in the air, if high altitude flying is to be more than stunts performed by enthusiasts on good days with (semi-)controlled conditions.
Kite trains, or stacks, readily soar to heights greater than what can be attained with a single kite.
The record, set back in 1969, is 10,830 m abg. So the 30,000 ft mark has already been surpassed.
The single kite record stands at around 13K feet.
Have a look at some of the plans and protoype pics of this behemoth, and it becomes clear (if not in the article) that the intention is for the ladder to be ground-originated, not just ground-anchored. This means the kites are travelling up from the ground to 5 miles and back again. The volume occupied by such a structure - especially one as non-static as this - would be monumental, not to mention the massive safety margin required to have more than one in operation within a few miles of any other ladder.
So if we're looking at 400 ladders to generate enough to power a city, we're look at a good 3000+ square miles of land if we're to be sure that no ladder is to collide with another. Not practical on any scale, I suspect.
Now if we're to be sure the things don't come down every time there's a spot of bad weather, we are looking at getting them up above the common cloud-cover atmospheric strata. In that case, why the hell not just use bigger kites, no ridiculous ladder-arrangement, and use the kite-wing surface-area to convert solar-energy? If the kites are well-engineered and -controlled enough to be able to operate in such a stringently unified fashion, I'm sure the same technology could be used to keep solar-kites in the air. True, the strain on the cables would be even greater if they have to be reliable electrical conduits as well, but that's really only one of several major flaws in this project.
Frankly, we'd be better off burning drug-addled research-scientists as fuel. They're renewable, at least.
Meta will eat itself
Check out http://www.laddermill.com/. I think it will be awesome to see these generating a city's power one day.
Side note. Kinda funny how it is being developed for high altitude in the Netherlands.
Zoeith
This is a really interesting concept. The designers say they won't fly the kite except in good weather so they won't have to worry about electrical storms etc. but I wonder if they have considered the atmosphere's natural electric field as well... It is estimated that the natural electric field potential between the earth's surface and the ionosphere is in the hundreds of thousands of volts range. While the current is usually very low for small but rather tall structures (regular kites, radio towers etc.) I would imagine that having a huge 5 mile wide kite 30 thousand!! feet up would make an immense difference in the current transmitted through a conducting wire to the ground. We may be talking about tens or perhaps even hundreds (??) of watts here. This will have to be dealt with and I imagine it could actually be used to perhaps, power some backup or secondary control equipment way up there.
- "Hear that?! The percolations are imminent! Cease your ingress!"
The idea of tethered high altitude wind power generation has been around for a long time. The people behind Sky Wind Power Corporation (http://skywindpower.com) have been developing their technology since 1979.
They do not use kites but a tethered electrical generator, like a helicopter with 2 fifteen foot rotors and no cabin. The documentation on their site seems to cover a lot of questions that would come up here, especially about the tether etc.
It is just sad to see another australian inventor having to go overseas to try and get their idea noticed.