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Science Technology

Harvesting Energy in the Sky 261

Posted by ScuttleMonkey
from the pie-in-the-sky dept.
withoutfeathers writes "The Economist magazine has an article on Flying wind farms. Mind you, we're not talking about ordinary, terrestrial windmills here. We're talking about actual airborne — up to 10km in the sky — wind farms intended to harvest the immense supply of energy in the jet stream. On the surface, the idea seems a little eccentric but, in fact, San Diego (California, US) based Sky WindPower has, apparently, thought their concept through pretty thoroughly and believes they can not only make this work, but do so profitably. The article discusses several other ideas for high-flying wind farming including a Dutch proposal to use pairs of kites to drive a generator."
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Harvesting Energy in the Sky

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  • Hmm (Score:5, Funny)

    by Lithdren (605362) on Wednesday April 04, 2007 @06:33PM (#18613089)
    Hope they tell the FAA before they put one up...

    Somehow, putting up tons of windfarm hardware in the jetstream, strikes me as a great way to disrupt airtravel.
    • Re:Hmm (Score:5, Interesting)

      by Tatisimo (1061320) on Wednesday April 04, 2007 @06:41PM (#18613199)
      I do wonder: if one of those fell to the ground, what would happen? With the recent stories of space junk falling to earth, could we someday be troubled by power stations falling on us?
      • Re: (Score:2, Funny)

        by Anonymous Coward
        ...could we someday be troubled by power stations falling on us?

        Hmmm nice hypothesis Mr. Little....
      • Re:Hmm (Score:4, Insightful)

        by gardyloo (512791) on Wednesday April 04, 2007 @07:29PM (#18613751)

        With the recent stories of space junk falling to earth, could we someday be troubled by power stations falling on us?
        SOMEday?!? I'm troubled now.
      • Falling to the ground is rather unlikely. If the unit can still be controlled, the best scenario is to just let it autorotate down and lay its cable down gently as it goes.
        • by bytesex (112972)
          Or have the cable on a large pully. And create a redundant subsystem on top of it, that throws out a parachute in case of an emergency. And have an independent computer monitor its position and vector, and throw the emergency switch when one of those values falls outside of safe parameters.
    • Re:Hmm (Score:5, Funny)

      by creimer (824291) on Wednesday April 04, 2007 @06:46PM (#18613269) Homepage
      I think the neighbors would have a problem with the 10km-long orange extension cord hanging from the sky.
    • by BrewerDude (716509) on Wednesday April 04, 2007 @07:10PM (#18613541)
      The cable that is tethering it to the ground will be a hazard to aviation and all altitudes below the generator. Not only would the cable be very hard to see, but, unlike power cables and guy wires for antennas, it would also be hard to chart, since I imagine that the generator will move around quite a bit as the jetstream fluctuates.
    • by njh (24312)
      But that's the whole point - by disrupting air travel they will get great reductions in GHG emissions! The wind turbine bit is just a cover story :)
    • by MightyYar (622222)
      Use the length of cable as a radius and make a cylindrical no-fly zone. A few 10km circles in low-traffic areas shouldn't cause too much of a disruption. For non-commercial pilots, you could mark out the radius with visual aids - though the really dangerous area would be pretty small at low altitudes, and it probably would not be too cost prohibitive to have regular markings for the first few thousand feet of cable.
  • by khasim (1285) <brandioch.conner@gmail.com> on Wednesday April 04, 2007 @06:34PM (#18613095)
    If we take the kinetic energy out of the wind and transform it into electrical energy, will this cause any problems? If we do so on a major scale?

    Is it even possible for us to tap enough power from the jet stream (or other high altitude winds) to cause problems?
    • by pilgrim23 (716938) on Wednesday April 04, 2007 @06:37PM (#18613159)
      But what of Global Calming?
      • Re: (Score:3, Funny)

        Well since Global Warming is just a matter of too much energy in the system, maybe Global Calming would mitigate some of the weather pattern effects. (yes I know you being humorous)
    • by 2short (466733) on Wednesday April 04, 2007 @06:45PM (#18613249)
      "Is it even possible for us to tap enough power from the jet stream (or other high altitude winds) to cause problems?"

      No. The total power we could possibly harvest with systems like those in the article is not worth mentioning in the scale of the total energy in the jet stream. Windmills take a few percent of the energy of the wind that actually passes over them, wich would only be a tiny fraction of the wind in the jet stream.
      • The total power we could possibly harvest with systems like those in the article is not worth mentioning in the scale of the total energy in the jet stream.

        Perhaps you are neglecting the Butterfly Effect. [wikipedia.org]
        • by 2short (466733) on Wednesday April 04, 2007 @10:44PM (#18615617)
          "Perhaps you are neglecting the Butterfly Effect."

          I am not. I have a degree in Mathematics in which I made a particular study of chaotic dynamical systems. I've written papers about the Butterfly effect; I've constructed physical models that demonstrate it. Let me tell you about the Butterfly Effect, so that you can refrain from bringing it up in discussions such as this in the future:

          In a system which exhibits sensitive dependence on initial conditions (such as the weather), you cannot predict the details of long-term behavior (will there be a tornado in Iowa exactly 1 year from today) because tiny variations, well below what your measurement of the system could possibly account for (such as the breeze generated by the flapping of butterfly wings) will cause reality to drift further and further out of synch with your model until there is no resemblance on the detail level.

          So the butterfly effect makes it impossible to ever predict what day it will rain months in advance, for example. But it does not prevent predictions about the aggregate, macroscopic behaviour of the system as a whole. In Meterological terms, long term weather prediction is impossible, but short-to-mid term climate prediction is easy.

          Lets be ridiculously generous, and say this system takes a thousanth of a percent of the wind energy in the jet stream out. Is it reasonable to suppose this might cause significant changes in the world climate that will make a huge difference in its suitability for humans? No; it is not remotely reasonable. It's just not enough energy to make much difference.

          Would it mean sometime in the future there will be a thunderstorm one day and not another? Absolutely. Whether you exhale the next breath you take slowly or forcefully means exactly the same thing; the minute difference in the velocity of a few thousand molecules of air your breathing pattern makes will eventually mean the difference in what day you get a thunderstorm.

          The relevance of the Butterfly Effect in deciding whether to build this wind farm is the same as its relevance in deciding how forcefully to exhale your next breath. It means that the exact effect of either cannot be predicted, and that's it. It's not a reason to not do anything. (Well, except things like attempting long term prediction of weather detail.)

          Hope that helps.
          • Butterflies (Score:4, Interesting)

            by umbrellasd (876984) on Thursday April 05, 2007 @12:13PM (#18622153)
            I am also a mathematician and I can tell you that the concern is whether or not our "minute" impact will tip the system over a threshold and toward a chaotic attractor which represents an undesirable state (e.g. a shift of the jetstream to a lower potential state which results in altered rainfall or temperature patterns in agricultural areas of the world).

            What you said about the Butterfly Effect is correct but deals with the impact of small random fluctuations on a chaotic system. In this situation the planned alteration is highly non-random (a consistent reduction in energy potential of the jetstream), and the inevitable consequence of success is a gradual and significant increase in the magnitude of the change. The Butterfly Effect is not the correct model for non-random state changes of increasing magnitude.

            In other words, the quoted person is thinking about a valid concern, but used the wrong model to express it. The concern is still valid however. Will our actions disturb a delicate balance in nature of which we are not yet aware? We just don't know. Experiments of this scope are not the ones that you want to go the wrong way, so I sincerely hope that this company and the government spends as much time determining how to calculate the limit of what we allow ourselves to pull from the jetstream as we do figuring out how to do it.

      • by Ungrounded Lightning (62228) on Wednesday April 04, 2007 @10:25PM (#18615441) Journal
        Windmills take a few percent of the energy of the wind that actually passes over them, wich would only be a tiny fraction of the wind in the jet stream.

        Even of the wind that actually passes through the area "swept" by the blades, the max it can harvest is about 59.3%. This is the "Betz Limit", the aerodynamic counterpart of the Laugher Curve of government revenue versus tax rates:

          - Extracting power slows and deflects the air.
          - Slowing and deflecting the air reduces the amount of moving air you can extract power from.
          - Don't slow/deflect it and you get no power, stop it completely and you get no air - and thus no power. Zero at both ends, non-zero between. Somewhere there's a maximum.
          - The maximum (for compressible fluids in free space) is where you extract 16/27ths of the energy from the air you affect (which is essentially the stream of air that passes through the area swept by the blades).

        Real turbines can get very close to that, and most of the shortfall is a bit of energy left as rotation and turbulence in the wake.
        • by 2short (466733)
          Hmmm, I was under the impression real turbines didn't get very close to the theoretical maximums at all. But OK, let's call it 60% of the air that passes through the swept area, and let's call that swept area something ridiculously big, like 100,000 square meters (about 25 football fields). With just the core, fastest winds of the jet stream being about 300 miles wide by 3 miles thick, that will extract, by my calculations, 0.0026% of the total energy. I'm not worried.
        • Re: (Score:3, Informative)

          You're thinking of the Laffer Curve, and it's been mostly discredited in the economics world AFAIK
    • by CorSci81 (1007499) on Wednesday April 04, 2007 @07:35PM (#18613807) Journal
      I'd honestly be more concerned with global warming killing the jet stream than this. The jet stream is largely the result of low-altitude/surface-level thermal gradients (ie the equator to pole temperature difference). Given that most climate models predict the poles will warm significantly more than the equator, if they turn out to be correct I'd say that's far more troubling to the jet stream than a few big kites.
  • by Anonymous Coward on Wednesday April 04, 2007 @06:35PM (#18613119)
    The SHPEGS [shpegs.org] project is an initiative to design and build a system that uses a combination of direct and indirect solar collection to generate electricity and store thermal energy in an economical, environmentally friendly, scalable, reliable, efficient and location independent manner using common construction materials.
  • Be careful (Score:5, Funny)

    by UbuntuDupe (970646) * on Wednesday April 04, 2007 @06:36PM (#18613133) Journal
    I once had a similar idea: to pull energy right out of the air. Here's what I would do: separate a sealed chamber into two subchambers with a little door between them that could be opened. Have some kind of monitor determine *just* the right time to open it so as to increase the pressure in one side. When the pressure difference is large enough? Have one side expand against the other, drawing out useful work. End result? Both chambers have the same pressure *which is less than atmosopheric*! So to recharge, I just open it up to the atmosphere, and start over again.

    Go, me, right?

    After a few days of this, I woke up to find a severed horse's head in my bed. A note attached to it said. "You're depressurizing the atmosphere. Stop."

    That settled it for me :-/
    • by markana (152984)
      Mr. Maxwell - is that you???

      (and they're calling them "monitors" now?)
    • by cdrguru (88047)
      Reminds me of a story about the Shortstack. The idea is you build a very, very tall tube that ends where the air pressure is significantly lower. Unsealing the bottom of the tube at ground level than causes the higher pressure air to be sucked upwards where it is a near vacuum. This would introduce an entirely new cycle of circulation and clear polluted cities where the air is trapped by ground features.

      Of course, the original proponent seemed to miss out that the air in the tube might be affected by gra
  • by RM6f9 (825298) * <rwmurker@yahoo.com> on Wednesday April 04, 2007 @06:36PM (#18613141) Homepage Journal
    Gather 3 wives and their mothers in front of these devices: output to be rated at MW/cup of coffee.
  • "The Economist magazine has an article on Flying wind farms. Mind you, we're not talking about ordinary, terrestrial windmills here.

    You're kidding? Flying wind farms aren't ordinary, terrestrial windmills? You learn something new every day!
  • Well (Score:3, Funny)

    by RobertM1968 (951074) on Wednesday April 04, 2007 @06:38PM (#18613171) Homepage Journal
    It will be really sad when this idea comes crashing down... ;-)
    • Re: (Score:2, Interesting)

      by Clever7Devil (985356)
      Yeah, talk about Vaporware.
  • Great (Score:2, Insightful)

    by demonbug (309515)
    Hey, lets put a bunch of aircraft up at 10km, with cables that tie them to the ground! Excellent idea! Why didn't anyone think of this before?

    Oh, that's right - they did. They used them to prevent aircraft from flying over towns/cities/military targets (it sort of worked).

    It also doesn't seem to make a whole lot of sense to stick a bunch of obstacles up in the jet stream. You know, where airliners tend to like to fly (at least when going west to east).

    Oh, and doesn't the jet stream tend to be rather dyn
    • Re:Great (Score:5, Funny)

      by Migrant Programmer (19727) on Wednesday April 04, 2007 @07:10PM (#18613543) Journal
      You know, where airliners tend to like to fly

      Don't worry, they've planned for this. Air cowboys are ready to rassle up those wild airliners and keep them out of harm's way.
      • by bigpat (158134)

        Don't worry, they've planned for this. Air cowboys are ready to rassle up those wild airliners and keep them out of harm's way.
        air traffic controllers = air cowboys?
    • But don't planes at that altitude stick to well-defined air corridors?
    • by 2short (466733)
      "They used them to prevent aircraft from flying over towns/cities/military targets (it sort of worked)."

      Yes, very large numbers of balloons each of which had very large numbers of unmarked trailing cables, which were moved around a lot without telling the enemy where they were, were vaugely successful in making aircraft that wished to attack specific small targets fly at a different altitude. (those balloons were not at 10Km, but low to the ground, and only made the attackers fly a bit higher, where they co
  • In the Jet Stream... (Score:5, Interesting)

    by Radon360 (951529) on Wednesday April 04, 2007 @06:50PM (#18613305)

    You know what else tends to reside in the path of the jet stream? Storm systems.

    I bet that these things would make excellent conductors for lightning. Take them down when storms approach and put them back up afterwards? Probably not feasible.

    Then again, they would probably build up a heck of a static charge themselves just with the wind flowing over them.

    Oh yeah, would ice build-up be a problem? Maybe not at the windmill itself, but on the tether, perhaps.

    Seems to me there's a few (obvious) technical hurdles to address, first./p.

    • Any chance to actually use that lightning for energy as well?
      • Well, the technical hurdle is capturing the energy from a massive electrical discharge and then releasing it in a controlled form. You can't just send it through some super transformer to knock down the voltage because, even if you could, the voltage rise/fall time is so fast that the inductive impedance of the transformer would probably make it quite ineffective. Even if you could down convert the voltage of the lightning, you'd have difficulty building a device that could accept such a large inrush of

        • Re: (Score:3, Interesting)

          Well, the technical hurdle is capturing the energy from a massive electrical discharge and then releasing it in a controlled form

          Build a very large capacitor with it's positive pole at the anchor point. If you build it large enough you might be able to keep it from melting. Large glass Leyden jars? A cap is a cap (you should see the ones I used to build my Interociter) but the methods, conductors and dielectrics can differ widely. Surround the base with induction coils to grab lumps of current that lea

      • by glittalogik (837604) on Wednesday April 04, 2007 @07:16PM (#18613609)
        All 1.21 Jiggawatts of it!
      • by CorSci81 (1007499) on Wednesday April 04, 2007 @07:26PM (#18613721) Journal
        Yes, I believe a DeLorean connected to a large cable and going precisely 88 mph does the trick...
      • YES! I have seen video demonstrating lightning as a power source for a time machine built out of a Delorian. Seemed to work perfectly. Especially if you know where lightning is going to strike.
      • by ArcherB (796902) *
        Any chance to actually use that lightning for energy as well?

        Worked for Doc Brown and Marty McFly!
      • Re: (Score:3, Interesting)

        A typical lightning strike is around a thousand kWh. That'll keep a 100W light bulb lit for a few months, but given that your air turbine gizmo will likely only get a few strikes per month, it's hardly worth the effort to capture considering how much wind energy it'll be capturing during that time.

        It's best to just treat the lightning a like a nuisance and try to dissipate it safely.

    • by 2short (466733) on Wednesday April 04, 2007 @07:10PM (#18613539)
      The jet stream is instumental in pushing storm systems around, but is itself a fairly stable, continuous flow at a higher altitude than the storms.

      The tethers will keep these continuously grounded, so any static is just some bonus power. The teathers will be great lightning rods, which will probably be more power at once than can be made usable, but it is entirely possible to design them so it's not destructive either.

      Ice build up would have to be dealt with, but, hey, it's a power station, if nothing better, heat the cable.

      There are definitely technical hurdles to overcome; this is at the conceptual daydreaming stage so far. But the obvious problems seem entirely doable to me.

      I'd say the big issue is if you can get reliability good enough that maintenance costs don't kill your cost effectiveness.
      • Re: (Score:2, Interesting)

        by MadnessASAP (1052274)
        They are stable in that there are always jet streams and they follow predictable patterns and don't suddenly drop off. Unfortunately they do move quite a bit. IIRC they tend to start at the poles and head toward the equator making them pretty much unusable for flying a big metal kite.
    • by Shag (3737)
      You know what else tends to reside in the path of the jet stream? Storm systems.

      Seems like 10km up would also be right about... ah yes, cruising altitude for jetliners! What fun!
      • by Jeremi (14640)
        Seems like 10km up would also be right about... ah yes, cruising altitude for jetliners! What fun!


        Not to mention all altitudes below 10km that would have tethers hanging down through them...


        But of course this problem has already been solved -- you just mark the affected areas as "no fly zones" on the air navigation maps.

        • Re: (Score:2, Funny)

          by maxume (22995)
          Do you have any idea how small Nebraska is? Marking maps could never work.
    • by MobyDisk (75490)

      I bet that these things would make excellent conductors for lightning. Take them down when storms approach and put them back up afterwards?
      Don't do that! That's 1.21 jigawatts of electricity you are throwing away!
    • You need to send them a email right now! Those are some very important things I'm sure haven't been considered! You could save lives!
  • by Anonymous Coward

    On the surface, the idea seems a little eccentric but, in fact, San Diego (California, US) based Sky WindPower has, apparently, thought their concept through pretty thoroughly and believes they can not only make this work, but do so profitably.

    Translation:

    This is a totally fucked up idea that has no hope of becoming reality. However, certain venture capitalists that have the ears of certain elected officials, retired milirary leaders, and recent political appointees think that this is certainly worthy of (1) government contracts, (2) earmarks in military spending bills, and (3) "grants" from the DOE, Military, and any other government agency that has a large amount of government gave-a-way cash to burn.

    Thankfully, these cash infusions will allo

    • by Jeremi (14640)
      This is a totally fucked up idea that has no hope of becoming reality. However, certain venture capitalists that have the ears of certain elected officials, retired milirary leaders, and recent political appointees think that this is certainly worthy of (1) government contracts, (2) earmarks in military spending bills, and (3) "grants" from the DOE, Military, and any other government agency that has a large amount of government gave-a-way cash to burn.

      I remember back when Americans were known for their "can

  • Profit (Score:4, Insightful)

    by Haxx (314221) on Wednesday April 04, 2007 @07:19PM (#18613651) Homepage
    It's a good thing it might be profitable, otherwise we would have to forget about the idea forever.
  • by Adeptus_Luminati (634274) on Wednesday April 04, 2007 @07:23PM (#18613685)
    According to this public disclosure meeting in 2001, whereby high ranking government officials, very senior ex-military, black project staff, and ex-NASA employees pointed out... Zero point energy (aka. free energy) devices already exist, and have for decades, but are hidden by secret black project government programs due to the massive economic impact it would have on the world (i.e. no more need for OIL).

    VIDEO: http://www.youtube.com/watch?v=uCLOIcFTSlE [youtube.com]

    It's time USA citizens wrote their congress men and appealed for all of these senior government etc officials to have a chance to testify under oath as they have promised to do. To date the disclosure project has over 400 such officials willing to testify. This is not wacko conspiracy theorists coming up with crazy theories... it's about the largest government cover up in the history of the modern world.

    Adeptus.

    PS. If the above is not enough to motivate you, think about how a world without burning fossil fuels would end the global warming impact nearly overnight! The evidence is simply overwhelming. See the video for yourself.
  • Keeping airplanes and birds from hitting the tether could be an issue -- the former an aviation safety problem, the latter a reliability problem for the power station.
  • Forget the tether... (Score:4, Interesting)

    by skelly33 (891182) on Wednesday April 04, 2007 @07:41PM (#18613875)
    ... what about the power transfer cable? I can't imagine a cable that can carry 10MW of juice over 10KM of distance could possibly considered a lightweight matter. This little helicopter contraption will need to generate power AND have enough energy to remain aloft under the weight of that cable. I think it's an interesting concept, but the solution to all our future power woes? Enh. While we're dreaming big, I'd be more interested in this Energy Island [soton.ac.uk] concept being built out.
    • by skelly33 (891182)
      On second thought, if anyone here has the knowledge to calculate the cable size to carry 10MW and can figure the cable weight per meter and multiply by 10,000 of those... to determine how much weight this device must suspend, I think you have to double it because the ground line has to be able to carry the same amount of power. This isn't an issue for terrestrial power plants because they're ON the ground. But something up in the sky will need to be connected to ground to complete the circuit... is this cra
      • by florescent_beige (608235) on Thursday April 05, 2007 @11:13AM (#18621061) Journal

        It just so happens I have a bit of experience designing aluminum and graphite aircraft parts, and my brother is an EE so by osmosis I know enough electrical stuff to fake some calculations.

        Thing is, for a constant-diameter cable of a given density and a given strength, the length that can hang under it's own weight is an intrinsic property. For example, I would guess electrical grade (fairly pure) aluminum has a strength of at most 10,000 psi, and a density of .1 lb/in^3. The maximum hanging length would be 1.6 miles. If you taper it you might double that.

        That doesn't even include the pulling loads from the monster at the top, which would be large. So aluminum is out.

        Carbon nonotubes are hocus-pocus for real-world stuff right now, so forget about that.

        However, graphite fibers conduct electricity not too bad, they might work, and they have fabulous strength in tension.

        You could probably load a carbon fiber cable up to at least 100,000 psi, and it's density is .06 lb/in^3. That gives a hanging length of 26 miles. That looks better.

        Let's fake an electrical calculation to see if it has a chance to work as a transmission cable.

        If we use 10KV then for 10MW we have 1000A. The resistivity of graphite fibers is about 4 micro ohms-in. So lets say we make a 1 in^2 section cable, the resistance would be 4 micro-ohms/inch. A 10 mile length would have a resistance of 2.5 ohms and the power dissipation would be 2,500 watts. Surely we could dissipate that over about 10 miles without it overheating the cable.

        The weight of the cable would be 1*10*5280*12*.06 = 38,016 lbs (19 tons). Since you need two of them, the total cable-weight load on the monster would be 38 tons.

        Add to that the air loads of the horizontal windmill action (which is the whole point of the stupid thing) and what I'll call the catenary multiplier effect for lack of a better term, and the actual load on the cables will probably be something on the order of 100 tons. Since the cables were only stressed to about half their capabilities by the hanging load, it might work.

        But you see why I call it a monster. The rotors have to genterate 100 tons of (inclined) lift.

        (I used a 10 mile cable length throughout because while the altitude is about 6 miles, the monster is blown sideways and the cable hangs in a catenary shape.)

    • Re: (Score:3, Funny)

      by edwardpickman (965122)
      You could always use microwaves. It would also eliminate the problem of birds hitting the cable. Any flying through the microwave stream would be cooked and ready to eat.
  • NAMBY (Score:2, Funny)

    I can see the protests now: "Not above my back yard".
  • October 10, 2006, Wired: Generating Power From Kites [wired.com]

    "KiteGen [sequoiaonline.com]", a kite-driven rotating carousel generating electricity. The kites, at altitudes up to 2Km, could be quickly maneuvered to avoid aircraft, even individual birds. An initial cost of 360,000 euros for a 100m model could generate .5Gw of electricity. A 2 Km version could generate 5 Gw. A proposed initial site is the former Trino Vercellese [keyhole.com] nuclear power plant, already a no-fly zone.

  • This doesn't mesh well with the personal flying cars we will all be flying in the future. The Jetsons and Futurama never had to deal with these flying windmill contraptions.
  • by BenEnglishAtHome (449670) * on Thursday April 05, 2007 @11:08AM (#18620953)
    Interesting ideas, all, but access to the jet stream is a big deal requiring big bucks. I'm wondering about small projects.

    When I was a kid, I got one of those big, plastic "bat" kites. (They were new on the U.S. toy market at the time, so that tells you how old I am.) I found it horrifically unstable, so I attached a tail made of torn cloth and other stuff. It was quite long and weighed several pounds, making the kite a pain to launch. Once it had gained some altitude, though, it was stable and pulled steadily. I ran out of kite twine, so I drove a stake in the ground and tied it off. Then I rooted around in the garage and found a giant spool of 100lb test fishing line. (Why we had it since it had been years since we'd lived near the Gulf Coast and gone offshore fishing, I didn't know.) I attached this new line to the kite string and let it play out. Quick as a wink, that kite was hundreds of yards high, just hanging there, pulling hard and steady. My older sis had a party that night and all the high school boys wanted to show off how manly they were, so they pulled in the kite for me. They had to work hard for over an hour, pulling it in as fast as they could, to get it to the ground. They were tired, sweaty, and pissed at me by the time they were finished.

    I haven't thought about that episode in years. I wonder, though, if it would be possible to put up a fairly large kite to an altitude of just a few hundred yards and keep it aloft (semi-)long term with some sort of small wind generator hanging from it (I know that kite I launched in my youth could have held up 20 or 30 pounds, easily, once it was in the air.) and a small cable leading back to the ground. I live in a fairly mild climate and could pull it in if the weather got bad. I'm just wondering if this could produce enough energy to bank to some batteries that the exercise would be worthwhile.

    I know lots of people have tried to go off the grid using power generated from small, often home-built terrestrial windmills. Because the wind at ground level is capricious, they need to feed big battery banks to tide them over the inevitable down time. I'm just wondering if putting a small windmill up at an altitude where air movement is more reliable could actually be a workable approach to the problem.

    Of course, this is all just an unformed idea from someone who knows nothing about this stuff. For all I know, the wind at 1000 feet is no more reliable than the wind at ground level and that's why TFA is talking about getting up into the jet stream. Still, it's an intriguing idea to me.

    So who wants to be the first to shoot it down?

    (Yes, I love bad puns, too.)

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