High altitude wind power II: the reactions

Tall ships are the embodiment of the fascination we feel for the free and abundant energy of the wind. Already at the time of the sailing ships, it was recognized that it was important to catch the wind at the maximum possible height. So, the main mast of a tall ship could go up to 30 meters. Modern wind turbines reach heights of a hundred meters or more. But Airborne Wind Energy (AWE) can tap winds at heights up to thousands of meters. The present post is a more in depth examination of AWE after a previous post that I wrote on The Oil Drum and which generated a lot of comments and of reactions. (Image from the Imperial College Yacht Club.) .

I came in contact with the idea of AWE (*) (Airborne Wind Energy) for the first time - I think - six years ago when someone named Massimo Ippolito wrote to the mailing list of ASPO-Italy proposing the concept on which he was working. It was a wind power system based on remotely controlled kites. I remember that I wrote back saying that the concept didn't violate any physical law, but that it seemed to me rather difficult to transform it into something practical.

As I followed the development of the idea, which later became known as "kitegen", I saw it growing from just a qualitative concept to a full fledged project, refined in all details. I tried many times to find faults in it, but I never succeeded. Whatever objection I could raise, Ippolito always had a good answer to it. Eventually, I ran out of objections and when Ippolito tested a working prototype, in 2008, I had to count myself among the believers. In the process, I learned a lot about aerodynamics; for instance what is the difference between a "drag machine" and a "lift machine". The latter is much more efficient in terms of energy generation and is the way the kitegen works. Here is the basic concept of kite power.

Image from M. Canale, L. Fagiano and M. Milanese, "Power Kites for Energy Generation" IEEE control systems Magazine, Dec. 2007, p. 25

The last doubt I had on AWE was related to the environmental impact of high altitude turbines or kites. The recent paper by Archer and Caldeira was a small epiphany that dissipated my doubts. We can obtain plenty of energy from high altitude winds with a minimal environmental impact. So, I decided to write a post for The Oil Drum, summarizing what I knew and the perspectives of the idea.

Passing the "meat grinder" which is the comments section of The Oil Drum is quite scary. AWE (and, in particular, the kitegen) came out of it somewhat ruffled but, on the whole, it survived the ordeal. Because of the many questions and comments received (more than 260), I think it could be interesting to examine AWE more in depth. I apologize for this post being "kitegen-centered" and I have no intention of disparaging other ideas and projects which are being developed in the world. There is a lot of atmosphere over there and there is plenty of space for AWE in many forms. It is just that the kitegen is the project I know best.

So, first of all, let me summarize how a kitegen works in the configuration called "stem" or "yo-yo". Here "KSU" stands for "kite steering unit".

Trajectories of a kitegen in the "Stem" configuration. From M. Canale, L. Fagiano and M. Milanese, "Power Kites for Energy Generation" IEEE control systems Magazine, Dec. 2007, p. 25

As you can see in this simulation, in the simplest configuration a single kite is attached to a power generator on the ground, where also the control system (KSU) is located. During the "traction phase" the kite moves sweeping the wind (green lines) as it pulls on the generator. When it has reached a maximum distance from the generator, the kite is placed in a "stall" position and pulled back (red line). In this phase, very little energy is expended. In the paper by Fagiano et al. you can see also the results of practical tests that confirm the results of the simulation. This system is at present being built in Italy in a version which is expected to produce a maximum power of 3MW.

Now, let's go to the questions and the comments to my previous post. These can be divided in 4 groups (I apologize if I forgot someone's comments - there are just too many of them).

1. Does it work? ("It won't work because the lines will snap off, kites will get entangled with each other, etc..")
2. Is it safe? ("Kites will fall on people's heads, will destroy planes, etc.")
3. How efficient is it? ("Wont you affect atmospheric wind circulation?, etc..")
4. What is it for? ("Do we really need all that energy? What problems will it solve?")

1. Does it work? Here, commenters correctly identified some critical points of the kitegen system. In particular, the strain on the cables is an important issue and so is the control of the kites. These problems have been studied in detail and - in my opinion - solved. The kites are continuously controlled by a sophisticated positioning system that avoids collisions and entanglement of the cables. About the cables ability to withstand the strain, there have been both theoretical studies and experimental tests. As a consequence, the winch control system has been designed in such a way to maintain a nearly constant load; which will reduce the fatigue problem. It is estimated that cables will need to be replaced every six months of operation but will actually be replaced more often for safety. That is not a problem for the efficiency of the system and, on this point, Ippolito wrote in the "comments" section that:

Let me say, a coal power plant burn 300 tons of coal to produce 1 GWhe. A KiteGen to produce the same amount of energy will wear about 100kg of tether. Then the rope will be recycled and only the 20% of the ply will be discarded because too short.

One point that was raised is that, if it was so easy, it would have been done already. I think the answer is that it is not easy, and so it took some time to produce a working concept. AWE is not something that came out of the blue (although, in a literal sense, it does). It is the evolution of a technological line that started with the sailboats of Sumerian times and that has arrived today to giant wind towers, a hundred meters tall. Technology goes step by step and we shouldn't be surprised if, to have high altitude wind power, we had to wait the maturing of the conventional wind tower technology.

2. Is it safe? It was somewhat surprising to see so much importance given to the concern that kites could fall onto something or on someone. Certainly, this is an important point, but also one that shouldn't be overstated. So, first of all, in normal conditions, a loss of lift won't bring a kite to the ground because it can be retracted faster than it can fall.

Then, of course, we can think of a series of failures that might bring the kites down. In case of total failure of the mechanical system on the ground, the kites will lose lift and fall. Other possible causes of kites reaching the ground will be cable failure. That could occur as the result of fatigue or of a sudden gust of wind. The problem of fatigue has been extensively studied and modeled, and the cables have been designed in such a way to minimize the problem. In any case, they will be replaced at regular intervals - as I said in the previous section. About sudden gusts of wind, in case of bad weather, the system can be quickly shut down by retracting the kites. At 25 m/sec retraction speed, it takes always less than one minute to completely retract a kite operated by a stem system. There would be plenty of time to avoid the occasional twister passing by, although one might try (perhaps) to fly the kites into it to slow it down.

I think we may consider kites falling as very infrequent events if the system is carefully designed, as it should be. Take into account, also, that the kites won't be flown over densely populated areas. Even so, there would always be a small chance of falling kites hitting people or something valuable. In such case, the damage is expected to be small. The cables will fall at a speed of 4 m/sec, being slowed down by aerodynamic drag. A stalled kite should fall at an even lower speed. One meter of cable of a 1MW stem weighs less than half a kg while a kite weighs something like 10 kg per square meter. The cables are made of soft materials, while the kite is mostly fabric. If a kite or a cable falls on a roof, the most we can expect are a few shingles broken or displaced. Of course, hitting a person would surely hurt, but it wouldn't necessarily kill.

Here commenters have correctly raised the problem of the "snapping" of a suddenly broken cable. That could considerably increase the speed of the cable and do much more damage. However, snapping is a typical feature of a sudden fracture, as it happens - for instance - for steel cables under stress. But the kitegen cables are made out of multi-strand dyneema fiber. Experimental tests have shown that these cables don't break all of a sudden but tend to "unravel" first and so they dissipate a lot of energy in that process. No snapping worth noticing was observed in these laboratory tests. The cables, therefore, should normally fall "flat" on the ground.

In the end, there exists a worst case hypothesis that someone may get badly hurt or even killed by kites or cables crashing down in an extensive failure of the kitegen system. The data we have show that this possibility is very unlikely and so it can be controlled by known risk management techniques, as it is done practically in all fields of technology. In ordinary commercial aviation, for instance, we don't require zero risk of planes falling from the sky, but we strive to reduce this risk to a minimum. The same approach would work for the kitegen or for any AWE system.

Other safety issues were raised in the discussion, such as the kites interfering with plane traffic and the possibility of damage from lightning. The first problem does not seem to be difficult to solve. The atmosphere is crowded with all sorts of flying objects and we seem to be very good in managing air traffic: collisions are very rare. Kites will have their reserved flying area and active avoidance can be practiced by the control system on the ground, which is equipped with a radar. Kites can be rapidly retracted or moved out of the way if an aircraft is detected moving too close to the reserved area. This kind of control could also be used to avoid damage to birds, a point that was not raised in the comments. About lightning, the issue has been studied and it seems to be a modest risk since the cables are not conductive. Of course, in addition, the kites won't be flown into thunderstorms.

3. How efficient is it? I have cited Archer and Caldeira's paper estimates the total energy we can extract from the atmosphere without causing a serious environmental damage. It turns out to be at least 10 times (or perhaps even 100 times) the currently produced primary energy in the world. But can we really reach these limits? According to Archer and Caldeira, in order to generate as much energy as we produce today we would need approximately one kite (or other device) per cubic km of atmosphere. This doesn't seem to be a lot: one cubic km is a very large space for a kite to fly. But we can't reserve the whole atmosphere for kites or rotors. So, we would need more detailed studies to understand exactly how much of the atmosphere we can use for generating energy. We can say that the total amount is probably large, but it will be surely limited.

The main point at present, anyway, is not so much what is the ultimate total energy that AWE can provide. It is how fast we can build up renewable power in the face of dwindling supplies of fossil fuels. That is the critical point, and the one which I emphasized in my previous post. With the kind of energy yield (EROEI) that AWE promises, (over 100 according to estimates) we can have the technology grow quickly and replace fossil fuels before we run out of them. That is by no means demonstrated, so far, but it is at least a reasonable possibility.

4. What do we need it for? Good question and it is one of the points that I was making in my previous post. In the past few years, we have understood that we have an energy problem and we have placed a lot of resources in developing new gadgets that are meant to solve it. But often we seem to have misplaced our aim. One example may be the emphasis we are giving today to biofuels. We may end up with just a meager source of fuel for our cars in exchange for a serious misuse of agricultural resources which we badly need for producing food.

Airborne wind energy should be a good solution for at least one problem: replacing fossil fuels for the production of electric power. But how is it going to impact on everything else? Perhaps the most worrying observation here is that there has been at least one case, that of France, where the availability of cheap electricity from nuclear plants has not caused a reduction of the use of fossil fuels (as described in a post by Eugenio Saraceno ). Electricity "too cheap to meter" may free financial resources that people could use to drive their cars more or to buy SUVs. So, it is not completely obvious that AWE would really cut on the use of fossil fuels and, therefore, mitigate the climate problem. With a bit of luck, however, it would make coal plants obsolete and eliminate at least one of the biggest sources of pollution and greenhouse gases we have.

Nevertheless, it is perfectly clear to me that our problem is not in the availability of energy or resources; it is in the way we use energy and resources. This problem has a name "overshoot" and, in turn, it is related to our tendency of favoring short term returns over long term ones . Over and over in history, we have destroyed the resources that sustained us because of this tendency. Humans are very good at solving one problem at a time; much less at understanding and caring for whole systems. We are excellent gadget builders but terrible planet managers.

AWE can't do much to change the way we think. Nevertheless AWE on a reasonable scale is one of the most benign form of renewable energy I can think of: it is cheap and relatively simple, so that anyone can use it, anywhere in the world. It generates electric power, which is very efficient and non polluting. It has a very small environmental impact; it uses mostly abundant resources (steel and fabric, the latter could be obtained by natural sources). So, it gives us a chance of a smooth transition from fossil fuels to renewables. Whether we'll be able to do that, is all to be seen, but at least it is a chance - better than no chance at all.

In the end, it is obvious that we still need practical tests, but this discussion didn't evidence fatal flaws in the kitegen concept. This conclusion can be probably extrapolated to all AWE systems using kites, although those which use rotors or balloons will need a different analysis. Hence, AWE emerges out as a very promising technology based on sound physical and engineering concepts. Its development could be stopped only by strangling it with red tape; something that, unfortunately, governments are very good at doing. But renewable energy is already changing the world and it is probably impossible to stop it, by now. AWE would be a further step in the right direction.

(*) Thanks to Joe Faust (kitesystems.net) for pointing out to me the "AWE" acronym for Airborne Wind Power.


M. Canale, L. Fagiano and M. Milanese, "Power Kites for Energy Generation" IEEE control systems Magazine, Dec. 2007, p. 25
The kitegen site
"High Altitude Wind Power", a post by Ugo Bardi

Looks very interesting.

- How much does it cost to build a full-scale working model?
- How much do each of the kites and cable cost and how long do they last?
- What would be the target average power output of a full-scale model?
- How much empty land (if any) does it require around it?
- How much empty airspace does it require (how long is the cable)?
- When is the first full-scale working model planned?

kitegen - Google Image Search. Some prototypes have large circular ground stations, all with arches built in - very Italianate. The footprint was what I was chiefly concerned with; ostensibly the kites would be invisible, or barely visible, at 800m. Trying to find out more about that I find this Wired piece: High-Altitude Wind Machines Could Power New York City | Wired Science | Wired.com.

The Department of Energy had a very small high-altitude wind program, which produced some of the first good data about the qualities of the wind up there, but it got axed as energy prices dropped in the 1980s and Reagan-era DOE officials directed funds elsewhere.

The program hasn’t been restarted, despite growing attention to renewables, but that’s not because it’s considered a bad idea. Rather, it is seen as just a little too far out on the horizon.

“We’re very much aimed these days at things that we can fairly quickly commercialize, like in the next 10 years or so,” said National Renewable Energy Laboratory spokesperson George Douglas.

Startups like KiteGen, Sky Windpower, Magenn, and Makani (Google’s secretive fundee) have come into the space over the last several years, and they seem to be working on much shorter timelines.

“We are not that far from working prototypes,” Archer said, though she noted that the companies are all incredibly secretive about the data from their testing.

Drake, for several details I have to refer to Massimo Ippolito, who knows these things better than me. Anyway, for what I can answer.

1. Cost. It depends on the size and the type of the machine. There are several estimations of the pure cost of building a Stem. But the one planned in Italy is the first one of its kind, so its cost doesn't reflect what the cost could be once it is mass produced. So, personally I think it is too early to speak of costs; but, of course, since the machine is lighter and simpler than an equivalent wind turbine of the conventional kind, the energy it produces would cost much less.

2. Duration. As I say in the post, kites and cables should last at least 6 months in normal conditions of operation. Ippolito says that he plans to change them every 4 months.

3. The first full scale model of a stem is planned for a maximum power of 3 MW. The average power is expected to correspond to about 5000 working hours per year.

4 and 5 . A 1-3 MW stem will require a hemisphere of about one km radius. It is not necessary that the land is completely empty. It can be farmland - it could even be suburbs, but for the time being it is not planned. The airspace within the hemisphere must be reserved for the kite(s). It is possible and it is allowed by present regulations.

6. The first working kitegen is planned in an agricultural area in Piedmont, Italy. Ippolito tells me that all the necessary authorizations have been obtained and that construction should start very soon.

Drake, and all interested in exploring rapid development of various AWE methods for small wind and large wind are invited to explore the opportunities at
with its adjoined AirborneWindEnergy
discussion group. There are scores of distinct methods being explored. Several kite labs are perfecting in the small before scaling. Proofs of concepts are announced.
The Kitegen "Stem" is a hybrid "reel-out and reel-in" energy kite system. There are some neat variations in that family. Differently are stems and booms that do not involve reel-in and reel-out cycles that hold promise.
There are identified over 100 energy kite systems researchers shown on one of the public pages. Our net list for special notices is over 70 persons at the moment. The AWE discussion open-to-all group is at 38 members. Let me know of your interests: Notes@EnergyKiteSystems.net
The web is aiming for rapid development in both open and closed source tech.


I LIKE it.

Many thanks for these posts. This is one of the most innovative and intelligent proposals I've seen for providing humans with power.

The rationale for providing with humans with power remains uncomfortably cloudy. Yet it will be attempted, and this is conceptually and aesthetically elegant. If it actually works, so much the better.

I'd love to live under a kite farm.

I can not let KiteGen rest yet ... and I was about to post this Levi-Logo the other day as an input for reflection. But since the KiteGen post grew old and disappeared - I saved it 'till now', so I think I'll just add it here.
I see you're trying to 'push down' the Windturbine on some aspects, whereas you try to 'lift up' KiteGen via other arguments (eg. under Fig 5).Maybe you have a point - but I suffer from seeing that immediately (as I do not have a full idea of how you efficiently will be able to extract the energy yet ... from KiteGen) - furthermore I have not read this very post, so my reply here is merely as an input for further discussions/reflections regarding KiteGen.

This LeviS Logo illustrates the troubles that 'I see' KiteGen will encounter (- big time IMO)

I foresee alot of forces involved , but I feel most of them end up as statical forces - doing little work, which in turn can be turned into energy.Depeding on how smart and fast your computer logic is , there may even arise (unwanted) statistical negative counter-forces - acting against your wanted/planned for 'directions/movments' ...

Anyway, the two horses in the LeviS Logo are going nowhere - AND they will get exhausted .....BUT NO WORK IS DONE - SEEN FROM OUTSIDE OF THE SYSTEM - KiteGens configuration is not 100% equal, but the similarities are definitely there.

On another note : The wind will a) turn the windturbine (work) and the wind will b) propell the sailboat (work) ---- BUT how much work will KiteGen actually be able to extract compared to the forces involved ? (efficiency )
Remark : this is ment as an positive input - and hopefully I am entirely wrong, but that very issue struck me.

When I see KiteGen - I really 'do see' the LeviS logo in practical termes - (and then some) - namely that I understand that you can pick up energy from it via the winch system

Energy or work is force over a distance. Now if each horse moves a distance and does something useful with that force, even though it is nearly in dynamic tension, you could harness the energy. If the silly mule vs. mule is replaces with a mule pulling a heavy load up an incline, you would have a better picture of what I believe the kite system would be doing.
So it is not 2 mules equally opposed. It is more like one mule pulling to raise a heavy load and using this mgh (mass*gravity accel*height) to generate electricity.

Work is force x distance. Power is work / unit of time, or, for a given force at constant speed, force x velocity, MOL.

You also need to consider how fast the process is working to estimate power output and it's power that we need to produce. Having a kite flying at high altitude where the wind forces are greater may not necessarily produce lots more poser, as there must be a way to capture that mechanical force while the velocity is high. Flying the kite from side to side isn't going to produce lots of (rotational) velocity at the base of the stem...

E. Swanson

Paal, I am sure yours is a positive input. To find an answer to your question, I suggest to read the paper by Fagiano et al. (it is linked at the bottom of the paper). It is a detailed simulation of the forces involved in the operation of a kitegen "yo-yo". The results are very encouraging; the yo-yo is not at all like two horses pulling in opposite directions. But I understand that it takes a while getting used to the idea; it took a while to me, too!

Thanks and sorry Ugo - I forgot entirely about that haul-back procedure when posting this LeviS analogy. SO LET IT BE UNSAID.
And i agree that if 12% of generated energy is all it takes to bring the Kite back for 'a new round' , that is quite encouraging.

The fact that the kite needs to be "re-set" to a position where it can again pull on the cable is not much different from the way a waterwheel needs to ride up and over the axle so that it can again collect some power from the flowing stream.

The power is in the constant high altitude wind (or the flowing stream of water) and the kite or the waterwheel is just harvesting some of it. The fact that part of the harvested energy is used up re-setting the harvesting device doesn't matter as long as a reasonable amount of net energy is collected.

Hopefully KiteGen's future prototypes will prove that a reasonable amount of net energy can be collected in this way.

The waterwheel analogy is apt.

You should, in fact, be able to build a very similar yo-yo device to replace a waterwheel, though it would likely be only drag powered, with no lift-generating mechanism. Makes me wonder if there is a yo-yo application for tidal generation, with the direction of the kite shifting with the currents.

There is a small company developing such a system where a friend of mine works as one of the innovators. The idea is to fly a hydrofoil ancored in the sea floor in a figure 8 almost exactly like the kite and extract the power by an attached water turbine. Unfortunately they got a useless web page. :-(

It is more than a waterwheel. Consider a high performance sailplane wing with a 60:1 lift / drag ratio. It could generate vastly more tension in the cable than a simple kite of equal area.

Back to basics. Air has mass. Moving air has kinetic energy. Wind machines extract the kinetic energy by slowing the air down.

Consider a modern windmill with thin long airfoils at a standstill. The blades intercept perhaps 10% of the air flowing through its disk resulting in a slight reduction in average speed and a modest drag force on the tower. Now spin it up to maximum power conditions. The airfoils slow down all the air passing through its disk producing a much larger load on the tower.

It is that ability to absorb energy from a large mass of air with a small device that is the difference. If the concept succeeds the kites may evolve into rigid wings because their high velocity allows them to absorb energy from a much larger mass of air.

I think the show stoppers are;

1. Large land requirements per MW.

2. Large airspace requirements per MW.

3. Noise. A high performance sailplane at minimum sink speed 3000 feet above the ground is silent. But at high speed it is audible on an otherwise quiet day.

Consider a 1000 lb sailplane at high speed sinking at 250 ft/min. it is converting 7.6 hp of potential energy to maintain that speed.

A 3MW rigid wing machine would be equivalent to 531 such sailplanes flying in formation. They would make considerable noise. A 3MW kite would be slower, much larger and would produce much more noise.

With increasing wind speed the required area would shrink as the wing loading increases, but I would expect the noise level to stay about the same.

Its worth testing even if every one of your objections are correct.
It cant be much wore then the german one wing wind turbine and that one ought to have been an intresting research piece in dynamics.

I think that this is an interesting alternative to rotary wind power, and it does not seem to me like there will be problems obtaining steel and fabric to make the working components.

One question I have about wind energy is the issue of copper to make generator windings out of. Although we clearly have enough copper (in the form of existing generators) to provide us with electricity, once many of the generators are operating on a lower duty cycle than they presently are, more generators will be needed to provide the same amount of power. (However, we do not need all of the power we presently use, so a reduction in available electrical energy might be fine). If we need more generators, where is the copper going to come from? Is there other metals that will work in generator windings besides copper?

Re: copper, you can use aluminium instead. It's electrically and thermally very conductive and there's plenty of it (given the energy neeeded to extract and refine it). Sure, systems would need to be re-engineered as some of its properties are quite different (behaviour under electrical overload, for instance).

Silver works well. At $12.50 an ounce, a ton of silver is $400,000 so it adds 40 cents a watt to the cost of a windmill. After 20 years of operation, the blades and the transmission is junk but the silver is still there. Worldwide production of silver was 680 million oz. last year, so if you corner the market on silver, you can put up 20 gigawatts of windmills.

Wind turbines use about 1tonne copper/MW, or 30,000 tonnes was used last year to build the 30GW of wind turbines. The world production of copper is 15Million tonnes/year, so wind turbine construction could increase 250 fold and still only use half the annual copper production.

This looks a promising system.

One of the main issues with wind as you know is availability and load balancing, as wind (at least at ground level) is one of the least predictable renewable resources. This limits its usefulness even if it does reportedly have a pretty good EROEI.

Apologies if this was covered in the earlier post, but can anyone comment on the extent to which this may be different at elevated altitudes?

An another matter, I've heard of an alternative concept which is a "turbine on a conductive tether" that would be flown into the jet streams. To launch these, power would br drawn from the grid to "fly" the machine to the required position.
How would the kite system be launched?

Go back to the original post and you will see 2 blowers that aim at the kite to launch it.

As an engineer, I must say the AWE kite system is just plain cool. But not cool as in neat technology, but rather as such an interesting test bed for this new energy source. Imagine the first oil wells, all hell would break loose and they really didn't understand what they were doing, but with continuous improvement and learning they have done amazing things with oil drilling.

What AWE needs now is actual testing. The high level system concept looks fairly sound. The potential energy available is amazing. Build the system and run it in an area where if is safe to fail. Perhaps White Sands NM? Sure the cable "should theoretically" last 6 months, it just needs to be flown at this point and iteratively improved.

This would be a fascinating project, I would LOVE to work on it. It seems very "do-able" much like landing men on the moon must have been back in the early 1960's. I also think people who work on high performance sailboats would be top people to involve. Please get the first one flying ASAP & let us know where to apply for jobs to work on it. It is a wet dream of a project for any breathing mechanical engineer...

Meat grinder, eh?

Okay, I know a little bit about mrst grinders. The principles involved with grinders and turbines are very similar, translating linear force to torque.

With a wind turbine the relationship of the blades and the axis around which they turn is fixed. The action of the wind on the blades creates torque which is the roatating force of the wind as leveraged by the blades. Because the blades are rigid and lengthy, there is sufficient torque to force an alternator to remove a lot of energy from the wind.

The tower serves to put the turbine itself high enough to capture the linear force of the wind and convert that force to torque.

With a cable system the force of the wind at high altitudes is absorbed by the cable as it stretches. The longer the cable - the higher the altitude of the kite on the end of it - the more stretch. A lot of energy will be absorbed by the cable and at enough distance, all of it.

At some point the weight of the cable is too much for the witch on the broomstick on the other end to lift. Before that point the line stretch would absorb the wind's linear force.

This would require having the airfoil close to the ground which would constrain the advantage proposed here over rotary turbines.

If the kite turns on the axis of a base station of the ground, there would not be enough angular force on the base to allow it to translate the wind force thousands of feet in the air - into torque on the ground. An airfoil might move hundreds of feet but the angular distance at the base would only be a few degrees. The longer the cable, the less angual disance. At some point the kite would yaw and whatnot all over but the cable at the base would not move at all.

Adding this to the issues of cable stretch and cable weight does not suggest a return of electicity that would be equal to the kinds of machines that are already functioning.

It is the rigidity of the turbine blades and its tower that allows the turbine to work efficiently.

With the kite, the cable is an energy sink. The longer the cable the greater the friction losses within the cable itself.

As for 'alternatives' ... the best and easiest is simple conservation. It always works. It's the cheapest. It doesn't ruin things. You insulate buildings, get rid of automobiles, get rid of industrial agriculture, you get rid of 'adult toys' such as televisions, cell phones, household gadgets, power boats, weed whackers, giant office buildings, super- highways, parking lots, box stores, sprawl, McDonalds ... the list of American- style detritus is endless ...

Get rid of it! All of it. Start over again with a clean slate.

You cut military expenditures. You reform government. You eliminate the oligarchs.

You engage people with an end of connecting them to the real. Believe me, all these things are going to happen and soon. There will be no more cars a long time before the first kite is generating electricity on anything like a commercial scale.

BTW; the tall ships are a great idea! We need a lot more of them!

All the world is impatiently waiting that the American style of life of the Americans will be brought into question, I agree with you.

About the cable i agree again with you, it is an energy sink, but now let me do the math in order to have a quantitative figure and not only qualitative.
The cable elongation at break is 3.8%.
with a yoyo full operative 3MW machine each cycle for each cable will elastically accumulate about 745000 J and the elastical restitution will be the 80% to be conservative.
The KiteGen Stem cycle about 25 times/hours the power dissipated by one cable of 200 kg will be in the order of 1 kW.
The thermal capacity of the material is 1 J/gK that means an initial increment in temperature of 18 Kelvin/hour.
I let you imagine the heat exchange into the forced air at 60 m/s and the resulting temperature balance.
This is a rough estimation, we already built a running model of that.

If the kite turns on the axis of a base station of the ground, there would not be enough angular force on the base to allow it to translate the wind force thousands of feet in the air - into torque on the ground. An airfoil might move hundreds of feet but the angular distance at the base would only be a few degrees. The longer the cable, the less angual disance. At some point the kite would yaw and whatnot all over but the cable at the base would not move at all.

I think you did not fully understand the working principle of the machine, sorry I was confident that the movie and the explications were clear enough.
the yaw and elevations arm movements do not contribute to the electrical energy production.

All the world is impatiently waiting that the American style of life of the Americans will be brought into question, I agree with you.

Prof Ippolito, this is the quote of the week (month) here, and is at heart of these issues.

Like many above, I have been skeptical of many (most) alternative energy schemes but wind has held my interest, at least as having the ability to scale and be long term without seriously degrading environment - the research highlighted in this and last weeks post should be continued/accelerated - it seems very promising.

But as you allude to, unless America (or someone else via example) changes the global carrot away from conspicuous consumption, the extra electricity will only enable a buffet of other scarce resources to be consumed faster. This is not your problem and research should continue apace. Thanks for thinking about these concepts.

The media creates the culture..guess who controls the media?
" It is very difficult to make a man understand something when his salary depends on him not understanding it."( paraphrase Upton Sinclair).

The wrong people are in control.

You might be interested in the following article that illustrates how things work in the US, "the select few who will get it done"


In the US the banks “own” the government through donations and revolving door employment. Already we see banksters lobbying against proposed new controls and working on gaming the system. The Plunge Protection Team is pushing the US market artificially higher, gold is held down, commercial real estate owes USD 3.5 trillion, how much can be made out of cap and trade? The banks are not lending out their cheap money but hoarding it and increasing interest rates on e.g. credit cards to boost their balance sheets and profits hence bonuses.

Thanks, but I already read that article.
The one and only solution is to stop using their money. It has no intrinsic value anyway and we look like fools chasing paper or worse electrons in servers somewhere in cyber space.
It all seems surreal at this point and can't end anyway but badly. Peak Oil is the trigger event.
Are you an American?
I feel ashamed to be one.

This is veering way off topic, but I couldn't help but respond--

Are you an American?
I feel ashamed to be one.

There is no original sin attached to being an American -- who can control the circumstances of his or her birth? The question is, what do you do with your life now that you are there.

This search for low-impact, renewable (as long as the sun shines) power seems like a good beginning to a worthwhile life, regardless of nationality.

I know that everyone on this site understands this but..............an energy based value system/currency would go a long way toward realigning human activity with the best interests of the planet and the species future. Any new carrot must have the feature of maximizing the efficient use of the actual resources and not some phony marker.

Alas Professor, Steve did not assert that the lateral excursions of the kite generated electricity. He proposed that the torsional rigidity of the system was so low that the kite might spin rather than extend the tether.

Whether or not this is true, his was a very intelligent post. It was essentially an attempt to draw a free body diagram accounting not just for the instantaneous static loads, but for the dynamic loads at the extremes of operation, to better understand the operating envelope of the system.

I am skeptical as well. One is reminded of the promised efficiencies of the space shuttle vs. the operational realities.


Steve did not assert that the lateral excursions of the kite generated electricity. He proposed that the torsional rigidity of the system was so low that the kite might spin rather than extend the tether.

The only way to find out whether this idea can perform is build a prototype and try it. I suspect that the energy operating costs are going to be higher than expected. That's largely a 'gut feeling' rather than the child of analysis. Part of that is Murphy's Law.

I've been trying - and will from this point onward - stay out of the technical discussion. There are others here who are far more qualified than I ...

One of the basic problems with technology is that it reinforces the foolish idea that we humans are somehow above the rules; that the operating system that nature bestowed us with is adequate only so far as it can be leveraged in a way that can take (some of) us beyond what we are. Consequences are stuffed either into the past or wished into the future. We don't see the problems because the problems really don't belong to us, only to 'others'.

Then ... the humans themselves are subdivided, there are our betters leaving the rest outside the charmed circles wherein all the benefits of our collective escape from reality converge. In this way, step by step, the entire world becomes a garbage dump, a little at a time, starting at the out-of-the-way corners.

The best people don't go there ... of if they do they refuse to look out the car windows.

We choose not to remain human ... but this is a comforting lie we tell ourselves. We create this elaborate mirage with numbers and gadgets and use the trick of making a few of us extremely 'successful' on terms that we ourselves create as we go ... and ignore everything else.

What is successful? 'Championships'? Numbers on a piece of paper? Toys? Time to waste? Our advancement is advertised as a way for the many to escape poverty- time to pull out the 'Working Man' again. This is a lie, we have simply substituted one form of poverty for another.

Now, the dream is over, equal opportunity poverty for all.

Obviously, the entire 'progress' concept is false. We are embedded in the rulse, they are part of our DNA. We cannot escape them any more than we can escape death. In fact any solution to our human - non human dilemma can only be found by going back in the other direction and embracing our 'nature- ness'. We - ME - am so enmeshed in the lies of machine capitalism I - and I doubt anyone else - knows what that means or what it entails except in the vaguest suggestive way.

Four billion years of evolution (or God(s), if you prefer) have given us everything we could possibly think of to use to make our time here as blissful as can be imagined. As Rilke says, our enemies are what we create ourselves, our gifts which are astounding are such that we cannot imagine them. We instead choose to misrepresent them, we make this rationalization into 'efficiency' or some other nonsense ...

We can go to the stars we need not be in haste - the stars will come to us if we are not so foolish as to ruin ourselves in the meantime.

Where the danger is ... is the lie that there are solutions to whatever it is we call problems. There are no solutions, only coping strategies.


Please forgive me for putting words in your mouth, but in an attempt to make my post as short as possible I see that I did. This was my fault, but the answer you got (that you did not understand how the thing works because the power is not generated by yaw or "elevation arm movements") upset me more than a little since your questions seemed reasonable to me.

Then in my haste to bring up that yaw was certainly a problem as well and that the stability problems were also implicit in your post I neglected to point out that your question on how can the tether be further pulled out with small angle horizontal excursions had not been answered. (I was nervous.) If I had taken my time I might not have come across so badly, but as it was I ended up implying maybe that you or I or both didn't understand the kitegen concept very well, the very point I was trying to rebut. Again, apologies. I am a novice at this, hopefully it won't happen again.

Perhaps my post should have read in part:

It seems to me that Steve did not assert that any of the lateral excursions of the kite generated electricity. He proposed that the power might decrease or stop if the tether got very long. Also his mention of torque leads me to wonder whether the torsional rigidity of the system was so low that the kite might spin rather than extend the tether.

Almost as short but a lot better.

I also was thinking of Murphy's law after I realized that the proposed system seems to be kind of a kludge or compromise and that's why I mentioned the shuttle. I think some dreams were stolen with the space shuttle.

I also need to stay out of technical discussions here. I am an engineer, Civil/Structural, but here there be tigers. Also, what good does it really do?

BTW I think you are pretty much right about the other as well, but I don't know how to express it like you or what else to do but try to cope. So I do my techie stuff and in my spare time try to understand the impending disaster.


... Now, the dream is over, equal opportunity poverty for all.

Obviously, the entire 'progress' concept is false....

Sorry, but that's an unsupported RAPD position. (Rapid Arbitrary Power Down). Where is your evidence that "things would be better" without whatever level of "progress" (?technology, literature, astronomy, theology, written language, invention of the wheel, taming of fire?) you object to? For whom exactly? (It appears, between the lines, to be for you and everyone below you on the totem pole. If so it then becomes relevant for everyone else to know where in the pecking order are you exactly?)

This could go on a long time, but hopefully you "get it".

I always like reading your rants. Very informed and passionate.
What we have is a sick culture.........a culture of consumption. I call it the junk culture.
I think that if we just stopped using the derogatory term "consumer" and replaced it with "utilizer" it would create a different more prudent attitude immediately.
The misallocation of resources must stop and the first step is to put a tourniquet on the bleeder then refocus on the problems created in order to mitigate and create a new paradigm that will improve the human and planet's condition. I just don't know if it is too late.

It ain't gonna happen with the current self-serving political class and oligarchs. Sweeping change comes only at the hands of the people and never at the hands of the bankers or politicians. Which politician is going to vote for a ban on all donations except from individual registered voters?? a ban on going from government/military to suppliers?? a ban on the sale of new gas guzzlers starting 1 Janurary next year??

The trend forecaster Gerald Celents has been predicting riots for some time but i think the MSM has kept a lid on it by pushing the mantra of infinite growth (new opiate of the masses?), green shoots (IMHO weeds or cannabis). Obviously on a finite planet with finite resources that ain't gonna happen, we have taken nearly all the big fish, cleared the jungles, contaminated the soil, are changing the climate...

I think the anger will come once the American people realise they have been lied to and robbed by the oligarchy, banksters and politicians on the make. But when will they realise?

I think that it is past apparent that most Americans know they have been had, they just don't know what to do.
Stuff will start happening when the pain gets bad.
There are a few guys inside the beltway that make noise, Ron Paul, Dennis Kucinich and some others.
Really, a military coup is the typical way things turn over or at least a good portion of the military sympathizing with their families.
That is the one thing those fools at the top keep forgetting that the military is composed of the poor and dispossessed in the first place.
They are not going to point guns at their brothers.

"They are not going to point guns at their brothers."

Really? On which Earth? Who gets the short end of the stick in most military dictatorships most of the time? Oh, and in those cases where your 'poor and dispossessed' do go around and wreck everything, who gets the short end ultimately? Right. There's no simplistic solution to this problem - and maybe no solution at all, unless everyone were all from the same biological and cultural clone.

To replace the word "consumer," you have to replace the business class. It's their self-serving view of product-users, and they aren't going to stop pushing it until they are demoted from their current dictatorial position.

"As for 'alternatives' ... the best and easiest is simple conservation. It always works. It's the cheapest. It doesn't ruin things. You insulate buildings, get rid of automobiles, get rid of industrial agriculture, you get rid of 'adult toys' such as televisions, cell phones, household gadgets, power boats, weed whackers, giant office buildings, super- highways, parking lots, box stores, sprawl, McDonalds ... the list of American- style detritus is endless ...

Get rid of it! All of it. Start over again with a clean slate.

You cut military expenditures. You reform government. You eliminate the oligarchs.

You engage people with an end of connecting them to the real. Believe me, all these things are going to happen and soon. "

Very well put. This needs to be repeated in every medium every day, every hour...

Unfortunately the messages that ARE getting repeated millions of times an hour on nearly every medium is the one that says in various ways, "Your life will be improved if you buy X." The enormous romanticizing of consumption swamps nearly every other message. The ones who create these messages have the best psychologists and sociologists working on keeping us addicted to this earth-destroying culture. I heard a child psychologist say that the people in her field in industry are light years beyond their academic colleagues, and they target kids at ever younger ages, with huge increases in the numbers and sophistication of adds targeting kids under 5 in the last 15 years.

The potential good news is that if this vast propaganda machine could be redirected to motivate people to live well withing their ecological limits, it could have an enormous impact.

The bad news is IANGFH (it ain't never gonna f'n happen).

Mean while the new and old (relatively) wealthy around the world are madly working to emulate the worst of American/Western consumerism.

Regarding birds, I'm surprised this wasn't brought up in the first post; Darwin's Dog must have been busy that day. This would be an issue for siting, taking into account migratory patterns. How Fast and High Do Birds Fly?

Most birds fly below 500 feet except during migration. There is no reason to expend the energy to go higher -- and there may be dangers, such as exposure to higher winds or to the sharp vision of hawks. When migrating, however, birds often do climb to relatively great heights, possibly to avoid dehydration in the warmer air near the ground. Migrating birds in the Caribbean are mostly observed around 10,000 feet, although some are found half and some twice that high. Generally long-distance migrants seem to start out at about 5,000 feet and then progressively climb to around 20,000 feet. Just like jet aircraft, the optimum cruise altitude of migrants increases as their "fuel" is used up and their weight declines. Vultures sometimes rise over 10,000 feet in order to scan larger areas for food (and to watch the behavior of distant vultures for clues to the location of a feast). Perhaps the most impressive altitude record is that of a flock of Whooper Swans which was seen on radar arriving over Northern Ireland on migration and was visually identified by an airline pilot at 29,000 feet. Birds can fly at altitudes that would be impossible for bats, since bird lungs can extract a larger fraction of oxygen from the air than can mammal lungs.

I don't see retracting the kites to make way for a high altitude flock being feasible - you'd find yourself having to paint broad swathes of the countryside with radar as a result, for one thing. In remote areas I don't believe dedicated systems are employed to track such small objects, someone more familiar with ATC should chime in here though. Could the kites be retracted and re-extended fast enough to make way for a passing flock?

You can see a bird flying in one of the movies on the testing of the first prototype of the kitegen. The bird passed near the cables and flew away; probably it was just curious about that strange flying thing. More in general, the reactions of birds to the kitegen are still unknown, nevertheless we can say from experience that birds and kites (intended as common toys) don't interact much with each other. Also, single birds tend to fly at lower heights than those intended for the stem system. The problem might be flocks of birds flying at relatively high altitudes, indeed. Now, the stem comes equipped with a radar which, I think, should be able to detect flocks of birds coming in. As I say in the post, retracting the kites takes just a few tens of seconds - should be enough to make way for flocks.

What altitude was that prototype flying at? You're adding a radar system to each stem - what kind of additional cost will that entail? Having a dedicated station for each farm would be more cost effective - they're not spread out very far, are they? The pics I've seen (and mentioned above) depict a gaggle of kites attached to a circular central station.

Some cursory examination of the main migratory routes for birds should be done - huge flocks descend on the Great Salt Lake in the US for instance, do they follow discrete corridors, or tend to arrive in a whole swath of directions? Seems like this could be problematic for the kites in an area like that.

I don't think bats will have any run ins with the kites; possibly the cables. Are the cables producing much in the way of ambient sound during the testing?

Dude, as far as I understood, things stand as follows:

In the stem configuration, the kite flies to a maximum height of about 1000 m. The minimum height depends on the angle. Some studies indicate that the best efficiency would be obtained for a low angle, but for safety reasons the kite won't be allowed to fly too low. The safe minimum needs to be adapted to the conditions of the area - taking also into account the possibility of birds flying by. A small radar system is planned - indeed - at the level of a kite farm rather than for each stem. Some of the pics labeled "kitegen" depict the "carousel" concept; something much larger than a stem. In that case, kites should flow higher. About migration corridors, it is the same problem encountered with conventional wind farms. There are some areas that are best left to birds but, on the whole, the interaction of birds with wind turbines seems to be extremely rare. Kite farms would not be much different

Concerning cables and safety. Have you taken a look at the safe devices used on WWII barrage baloons? I have no idea what weight the cables were but they needed to be thick enough to take the wing off a plane. Maybe they could be incorperated directly or modified for the kite cables?

Grautr, I am not very expert in barrage balloons, but I am sure that they were made in such a way to damage the incoming planes. That wouldn't be the purpose of the kites; at least for now (I have wondered if the kites could be used as anti-aircraft weapons; but I think there are better methods for that). So, we don't know what would happen if a plane were to hit a kitegen cable. The best, I think, is to make sure that it never happens by using flight control and active avoidance methods.

Incidentally, there has been a case a few years ago, in Italy, when a military NATO plane hit the cable of a cable car (or aerial tramway; i think cable car has a different meaning in American English) in the Alps. The plane severed the cable, the gondola fell to the ground and all the 20 passengers died. Curiously, the plane survived and landed safely. I think it has to do with the fact that it was a fragile fracture - the cable broke neatly and rapidly. I don't know what would happen if a plane were to hit the cable of a kitegen. For one thing, there would be no gondola full of passengers, so no damage in that sense. But the dyneema cable wouldn't be so easy to break in two neat halves as a steel cable can be. So, my impression is that the plane wouldn't survive the hit; but - of course - it is a test that is better not to do.

Uhhh buzzards can be seen flying at very high altitudes. Some are just a speck. And there are lots of buzzards in my area.

But overall your correct.
The buzzards are wind freaks for updrafts. But the Laysan Albatross takes all prizes for soaring and gliding.

I used to watch them track the only navy ship I was on as it crossed the Pacific I found that albatross watching was a very good pastime.


I think I'd put the Iwa birds high over my house up against your Laysan albatrosses for soaring.

They have the lowest wing loading of any bird, and can use even slight updrafts. They look like pterodactyls at the heights I normally see them.

Judging from the KiteGen video, the kite behaves in the same chaotic swerving and diving manner that we are familiar with from toy and stunt kites.

Whilst I really love the principle of high altitude energy generation, is it really possible to continuously generate energy from a chaotic system ? I can´t think off-hand of any other technologically viable source of energy that is so fundamentally chaotic as this.

In particular, how often does it experience a Black Swan event, such as an air pocket, that the the real-time control system can´t cope with, and/or which stresses the fabric and steel components beyond their design tolerances.

As other people on this thread have pointed out, there is a limit to how much you can over-engineer safety margins because of the total weight limitation.
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gernos, the kite movement is not chaotic. It is not a simple kite of the kind used as a toy - it is controlled by acting on the two cables that hold it: it is the same kind of control that is used in modern parachuting. In this case, it is controlled from the ground. I suggest you to read the paper by Fagiano et al. (linked at the bottom) to understand how the concept works.

About the black swan, yes, it is always possible. But the kitegen seems to be a rather resilient system, not easily subjected to sudden breakdowns.

After a quick look at Fagiano et al., I noticed that they appear to have a mistake in their equations. Their claim that CL and CD are constant is not likely to be correct as both depend on the angle of attack between the airfoil shape and the relative wind. This would be a big problem during the so-called "passive phase" of the "carousel" design, where the kites must attain high altitude during the period of motion of that side of the carousel while advancing against the wind. Also, the rotational speed of the carousel is limited by the time required to perform the climb and dive maneuver during the passive phase. I still think the carousel design is a drag turbine.

Furthermore, the flow volume of air impinging on the kite is not simply a projection of the kite's area, as the streamlines from upstream diverge as the air is slowed in passing the kite. The same is true for a typical horizontal axis wind turbine and results in a theoretical maximum efficiency called the Betz Limit. That fact would likely be reflected in the values for CL and CD while the kites are operated during the power phase with high angles of attack.

And I must repeat that the carousel design is not resilient, since lack of control for any one of the kites would result in entanglement of all the kites within one rotation after failure, which would likely result in catastrophic consequences.

E. Swanson

We decided to disclose the KiteGen Stem design because we just start to build the industrial scale machine, this is done after a complete research and test activity on the scaled prototype and we very confident about our assertions but it is not easy to explain everything due the absolute novelty.

An esplication of the very complex behaviour of the KiteGen Carousel is not published yet.
There are a lot of published scientific paper that try to guess the detailed functioning of the Carousel, but up to now, all of them are more or less based on simplified assumptions, and they generally miss the main or recent KiteGen research and design achievements.
The Carousel is a very big design project and it is still in progress.

Currently, based on design dimensioning and simulation activity I can assert:

The Carousel, in a specific base, is at least 5 times more efficient than the Stem design;
The KG Stem is a propaedeutical development to the KG carousel;
the energy specific extraction is limited at few tens W per square metre, it is a light load machine, ie. a 120m rotor wind turbine push the limit to 500W/square_metre;
the energy production is balanced more on speed conversion than in force;
there are no passive phases, all the flying parameter of the kite are stabilized during the full cycle;
The traction force on the ropes is constant in the full path;
The apparent wind speed on the kite is a constant;
The CL/CD is maintained retroactively constant on an optimized value;
The Carousel work well below the Betz limit, in any case the Betz law is specific for rotors and propellers and is unproperly applicable to free flying Kites;
It intercepts a huge wind front in a double fashion;
The drag of the ropes, due to a special design, is a negligible phenomena;
The carousel is dynamically a full dampened machine;
The carousel can be quickly and freely adjusted in energy production;
The theoretical power limit is several tens GW with diameters suitable for offshore or desert installations;
The power progression is a function of the diameter elevated to fourth power;
In specific power ranges cost progression is a linear function of the diameter;
The carousel is definitively a lift machine;
when it is fully operative, excluding catastrophic failures, it cannot loose the precise and robust control of each kites;

I disagree completely.

For example, the Betz Limit is in reality just a statement of the basic physics. The energy in the moving air is a function of the difference in speed between the air and the relatively stationary wind device, such as a turbine. To capture the energy from the wind, the speed of the air flow must be slowed down as the air passes the device. As a result of conservation of mass, at maximum power, the area of air flow upstream which later passes the device will be smaller than the area of the device, say, the "disk" of the turbine. Therefore, the maximum energy available as a function of intercepted area (the area of the disk) will be lower than simply that of a similar area of air flow elsewhere in the free stream. The aerodynamic efficiency further reduces the available maximum power, which is often a function of wind speed in turbines, since they are usually optimized for a narrow speed envelope.

In the single kite design, the power available is the product of the force on the cable at the stem multiplied by the speed at which the cable is allowed to reel out. Maximum power would be achieved a cable release speed of less than half the wind speed, as the force on the kite is reduced in direct proportion to the relative wind speed. If the cable were released at the wind speed, there would be no power produced as the aerodynamic force on the kite would drop to zero. The "figure 8" maneuver does not increase the average force on the cable and may even reduce it, as energy is likely to be wasted as the kite moves laterally (see figure 12 for the variation in force). Flying the "figure 8" pattern does not increase the area of air flow intercepted by the device, as that is simply the area of the kite itself.

Also, once the cable is fully deployed, the kite must maneuver in pitch to produce the vertical forces which move the kite to the high altitude from which the cable may be rewound during the "passive phase". In that orientation, the aerodynamic drag on the cable would become important as it would tend to keep the kite flying away from the vertical, thus increasing the force needed to return the kite to low altitude to begin the cycle again. Also, your calculations do not appear to include the effects of the mass of the cable, which would weigh down the kite and require more "lift" as the cable is extended.

The simulation results are also off scale considering available wind energy. In figure 6, average wind speed is shows to be about 11 m/s at an altitude of 2600 m. That's only 39.6 km/hr, but in the simulation results, figure 17, the effective wind speed shown is about 250 km/hr during the traction phase. Obviously, when the wind is blasting along at 250 km/hr, there's going to be lots of energy available. But, that's not normal, is it?

E. Swanson

I disagree completely

So do I - but with you Black_Dog.

The simulation results are also off scale considering available wind energy. In figure 6, average wind speed is shows to be about 11 m/s at an altitude of 2600 m. That's only 39.6 km/hr, but in the simulation results, figure 17, the effective wind speed shown is about 250 km/hr during the traction phase. Obviously, when the wind is blasting along at 250 km/hr, there's going to be lots of energy available. But, that's not normal, is it?

I think you need to check out aerodynamics or fluid dynamics 101. You do not need the wind to be blasting along at 250 km/hr for the kite to experience a wind speed of 250 km/hr - 40 km/hr is quite enough if your kite is pointing the right way. I think that if you check out my comparison with the gyrocopter explanation below as that might make things slightly clearer

Here's a bit of calculations to show how limited the single kite system would be.

Consider a simple system at ground level, perhaps a sail attached to a rail car such that the car could move along with the wind. No need for "lift" and assume the wheels are friction less. The car pulls the cable from the drum at various speeds and drives a generator. Assume an axis with the "X" direction horizontal along the track with "Z" upwards. A similar situation would apply to a sailing craft moving with the wind astern.

The force on the kite/sail/cable would be:

1) Fx = 1/2 * rho * Cx * Area * (Vwind - Vx)2

2) Power = Vx * Fx

3) Energy from wind = 1/2 * rho * Area * Vwind3

4) Efficiency = Eq(2) / Eq(3)

Assuming a Cx = 1.2 gives results as seen in this graph:

KiteGen Test 1

Notice the fact that the peak power production occurs at a speed of the car much below the speed of the wind. That's rather like the calculations of the Betz Limit and points out a basic flaw with the KiteGen concept, IMHO. Of course, the peak depends on the actual value of Cx and I used the value for Cl from the report linked above. But, then, it all gets worse if some of the wind energy is required to counter the pull of gravity to keep the kite and the rope aloft. If those effects were included, the upper end of the curves would hit zero at a lower speed...

E. Swanson
Research Engineer

Dear Swanson
with your math, you well described a parachute pulled by the wind, certainly not a flying wing.
Don't worry it is a very common error starting to think about KiteGenerators.

Sorry, a couple of questions,
Alfred just put you in the right direction to understand, why you totally ignored him?
Internet is rich of scientific publications on this issue, as research engineer, why not start reading this material?

Black Dog,
I would like to give you an example, from the real world that should, according to the Bernoulli equation that you quote, be quite impossible:

Australian Macquarie Speed Sailing Team with their wonderful boat Macquarie Innovation(formerly known as Yellow Pages Endeavour) has crushed this friday the World Speed Sailing Record powering down the 500m Sandy Point course at an average speed of 50.43 knots. With only 24 knots of wind, Macquarie Innovation managed to reach a whopping maximum speed of 54.23 knots (100km/hr) and became the first sailing boat in the world to complete an official 500m run in excess of 50 knots.

There is nothing wrong with the Bernoulli equation, it is based on a different set of conditions that is all. Please do some research and you will find the applicable equations for these conditions. The important point is that this boat has been clocked doing 2.3 times the wind speed.
The basic premiss behind KiteGen is correct. It may be counter-intuitive but that is not their fault. We all have a lot to learn.


I think you are missing the entire point. Your example in no way applies to the situation I described where the kite or sail is moving in the same direction as the air flow. Your example is a different case, where the vehicle is moving across the wind. Look at the spray from the wake behind the craft. The KiteGen system has the kite operating a bit differently, but the characteristic I was attempting to demonstrate is that the force on the cable will decrease as the speed of the cable as it exits the winch increases.

It's important to sort out the terminology, for example, what coordinate system should be used. AS THIS NOTE points out: "The lift is the component of the aerodynamic force which is perpendicular to the original flow direction of the gas." the definition of lift and drag in the referenced paper uses a body fixed coordinate system, which fails to directly account for the angle of attack of the wind (although the vector equations should handle this transformation).

If you are suggesting that the "figure 8" motion causes an increase in the tension in the cable over a static pull from a kite with no lateral motion, consider that the forces thru out the maneuver are not constant, thus one must consider the average force, not the maximum. I used to water ski when younger and I usually followed an "S" shaped track, as I traversed across the wake and back. The speed and the pull on the rope when crossing the wake were both higer than that of simply training behind the boat. However, at each end of the track, the speed dropped briefly and the pull on the rope was greatly reduced as I changed direction, because I had moved ahead of the position that I would have been at directly behind the boat. To produce power, one must consider the average power, not the instantaneous value.

So, tell us, what does the power output look like when graphed as I did? Remember that the speed of the cable detracts from the effective wind speed at the kite.

E. Swanson

I have followed your arguments here Mr. Research Engineer Swanson - and I feel you have alot of valid points. You have not been refuted by the KiteGen establishment - thus far. The more I think of the Kite-shape (Lift/ wingshape) for this concept - well the more I "feel" it's wrong - B/C it is 'alot of random motions in all sorts of directions' without generating the instant maximum force in the correct direction ,which is : ==>> along the tethers ==>> and away from the winch.

My preliminary conclusion is -

    KiteGen (airfoil version) waste a lot of time and in this regard wasted time is wasted potential energy --- never to be ---

I think a modified "Para sail" (drag type) will 'cut through this cheese' - proven and done. IT will immediately be 'taken by the wind' during the spool-out-sequence and MOST NOTABLY at ALMOST MAXIMUM (possible) force and always in the WANTED direction. Hefty versions of these are used to stop the Space shuttle and more.

The "KiteGen project" or others ... need to simplify the entanglement-factors "up there" - but a drag-type shute could easily be embedded in their general thinking regarding their ground station and their 2 tether-system. I can mentally easier see their multi-station work with drag-shutes, cus' these will need a fraction of air-volume to play in - compared to the flying wing-version.
Some 'new' thinking has to be added in for the 'ground-to-air lift up' procedure. A sort of reuasble Pilot-ballon with helium is up for that task ... add a tether-spool to that one also and spool it back in when deployment is done. - Next ! -

Whatever happens in this picture is 100% equivalent to the forces KG will face - the "round shute is flying ...." ... and do you see the tethers direction ?

Some modifications here --- and GO !

My math isn't up to the task these days, but the head-scratching part of the project for me is exactly what Black Dog and Paal have described. My own rough designs for systems like this were all based around straight drag, since the vector "away from" the ground pull point is what's salient. I would be delighted to understand that this is wrong and am intrigued by KiteGen's arguments that you can significantly beat drag by zooming around.

No, no, no!
A wing is not a parachute ... the equations which E. Swanson has provided above apply only if the force along the lines are purely drag forces. This is the case for a parachute, but not for a wing.
The very fast movement of the wing(kite) perpendicular to the direction of the wind leads to a force (lift) in the direction of the tether. This force is much stronger than the pure drag forces due to the wind.
The only point in which I agree with you, Paal, is that a kitegen certainly would not work if only drag forces were in play.
I am a bit puzzled why you guys, regulars on TOD, and usually rather stringent in your arguments, seem to refuse the difference between a parachute and a wing, or between lift and drag.
But, hey, physics is not based on consensus, but on experimental evidence. And while of course many things can still go wrong for the kitegen, it will in the least show the difference between lift and drag and close this argument ...

Speaking for myself, I'm not disagreeing, simply noting that I haven't worked it out in my head yet. My other posts here are strongly supportive of KiteGen and its proposal, and as I say, I'll be delighted to see it work.

And I'm not an engineer, certainly, just a generalist at this point. best.

EDIT: and fifteen minutes after I posted this, with a bit more thought, I agree with KiteGen. I think the force limit limit set by drag can be significantly exceeded by an airfoil. They already know this, but I like to work things through in my non-rigorous way.

My understanding of aerodynamics is that increasing the relative speed at the kite would tend to increase the force on the kite, other things being equal, thus the "Figure 8" maneuver would increase the forces with the cable stationary. But, the "other things" are not equal and the kite cable is being released as the maneuver is performed.

An airfoil which produces a certain quantity of lift at low speed may enter flow separation at higher speeds, thus reduced lift. That's why airfoils designed for higher speeds tend to be thinner than those intended for operation at lower speeds. The kite pictures I've seen so far show what appears to be a thick airfoil, which would work fine at low speeds, but would suffer as the speed is increased. Also, we don't know what angle of attack the kite is to operate at, if it is set high to maximize the forces during low speeds the angle may be to great for the higher speeds resulting from a maneuver. And a kite is not a airplane wing, which usually has a smooth surface, indeed aircraft suffer from dirt, bugs or ice which become attached to the surface.

My imperfect mental model thinks that the lift component of force in actual operation will be small and the drag component will be large. Lacking more information on the characteristics of the kite's airfoil or the angle of attack during flight, I remain very skeptical...

E. Swanson

The data are you looking for, can be summarized in the aerodynamic efficency of the arieal part of the kiteGen, wing+cables.
Up to now we operated with 8-12 efficent systems and our foreseeable target is about 28.

This value mainly affect the minimun wind speed requirement needed to produce the full (130% of nominal) power of the KiteGen Stem.

based to the current design, an efficency of:
8 require a wind of 23,8m/s to reach the machine full power
here follow the list:

efficency / min wind speed m/s
8 / 23,8
12 / 13,3
16 / 9,7
20 / 8,0
24 / 7,1
28 / 6,5
32 / 6,2

with an efficency over 24 the KiteGen Stem supply about 8760 MWh/MW

To clarify or confuse a little bit more -
Let it be said : I can see that the airfoil may (will) generate more power outwards , but my main trouble is the rinse/repeat factor regarding the 24/7/365 paradigm as described for KiteGen.
A modified "Parasail" - with some more of the "Square shut's" lift properties combined with drag - is my best "understanding" for this kind of concept. Drag / lift ==>> straight outwards ... so to speak.

Line stretch will not be a problem w/ the system as sailors for years have been using lightweight/super strong/virtually non stretch lines. These new materials are stronger than wire rope of the same diameter. I suppose cantanary could allow for a small decrease in efficiency at highest operating altitude, but not enough to prohibit power generation in useful amounts.
The same type kites/wings have been affixed to ocean going freighters/tankers in experiments/trials for a couple years & have shown reductions in fuel usage.

Hate to have to keep saying this but "free and abundant" doesn't mean that using it is without risk. Oil was abundant and in essence free - or at least as free as wind. (while the wind is not on people's property, the location of wind mills is). We thought we could just use oil coal and the only consequence would be that taking it out of the ground would leave empty holes in the ground. But it turned out that all that fossil fuel was sequestering Carbon and that although free and abundant using it has had huge consequences. How can we know what consequences using vast amounts of wind will have for weather, wildlife etc. We can't. We won't unless we start using vast amounts of wind energy. When we use wind energy we remove its current use. It is doing something all the time right now. We cannot use it without changing what it is currently doing.

Oxidatedgem, you are right; in principle. But there is a LOT of wind up there and tapping just a little of it is a large amount for our needs. See the paper by Archer and Caldeira that I link at the bottom of my post.

Ugo yep, and their was just a little bit of chloroflorocarbons released relative to the huge up their atmosphere and yet it almost destroyed our ozone layer because we just didn't know exactly how they might work up there. Scale is relative. If we had only used them in one type of spray bottle that was used by folks relatively infrequently we would not have an ozone hole, but we used them in lots of spray bottles, and air conditioners and fridges. Still the atmosphere was so big and this was so little compared to it and .... we still don't know if we have saved our ozone...

And lets see we are at 380 PPM of CO2 - that is PARTS PER MILLION - not much not much....and yet we may have destroyed the environment we need to live with those tiny little parts per million.

SO yes there is lots of wind, but right now we don't have lots of windmills. If we put up lots and lots more it may do something we really don't like and it is not something we will really know until we do it. Maybe we will like what it does, but it will do something and maybe we really really won't like what it does. Willing to take another chance with the environment we have already messed up.

BTW I didn't think this up myself - see http://www.livescience.com/environment/041109_wind_mills.html

Couldn't we just kiss the energy intensive life goodbye and return to the life lived by most humans who ever lived and most humans alive today. Are we so special that we deserve to party on?

It is the usual problem: we are excellent gadget builders, but we don't know when to stop using them. AWE will give us another chance after we missed the one we had with fossils. If we miss it; it is probably the last one.

There are multiple large scale chances, for some regions it is hydro power, in sunny regions it is solar power, breeder nuclear power is sustainable in advanced societies, ocean current power could work in some regions and this high altitude wind power could work in manny places.

But no solution will work for all of humanity since it is unikely that all societies will be able to prioritize long term investments and manny of the solutions depend on the siting.

My guess is that the handling of the financial crisis will give indications on regions likely to turn into some kind of Zimbabwe where authorities fucks up the ability to use the local resources.

" 'free and abundant' doesn't mean that using it is without risk."

Oh, please. This life carries 100% mortality. What is "without risk"? The delusion that life can be completely free of risk seems to motivate many doomer commenters especially in the American threads. Too bad: those who expect all things to be "without risk" have simply chosen the wrong universe in which to live.

Exactly. I second that.

Pauls, Hmm well the risk of releasing all the carbon sequestered in fossil fuels seems to be that of quite possibly changing the world so that few if any humans can survive on it but heck I guess it was worth that risk....perhaps the next generation will not agree.

That's a dishonest reply. Pauls did NOT say that releasing the carbon sequestered in fossil fuels was "worth the risk" at any point in his post. You're using illegitimate debating tactics.

Thanks for addressing the line snapping issue.

You'll still want to keep an eye on such issues as you scale up the systems since the failure characteristics of the line are not necessarily consistent as it scales, but it appears to be adequately considered for now.

You did not address the issues of downdrafts and clear air turbulence that I raised. Turbulence in the lee of mountains is a real threat (one a/c was brought down by Mt Fuji).

And you unfairly linked the safety of KiteGen to civil aviation safety. You do not have the mindset (from your writings) that created the superb safety record of civil aviation after over a half century of effort, billions of $ and millions of man-hours.

And you do not have the track record.

It is certainly possible that KiteGen will have a safety record comparable to that of civil aviation from 1910 to 1920 as you learn from your mistakes. Modern engineering (not available in 1910-1920) may, or may not, reduce that risk, but claiming to achieve civil aviation safety levels of 2009 with fresh technology is simply hubris.

Current wind turbines cannot be (in most jurisdictions, India is an exception I think) located within "falling distance" of permanent human habitation. There is no reason that rule should not be applied to KiteGen until a better safety record has been conclusively proven.

By conclusively proven, I would suggest thousands of KiteGens for a decade of operation at hundreds of locations in a wide variety of climates and wind regimes with a perfect safety record. Until then, no permanent human habitation within "falling distance".

Another economic issue is acquiring air rights to produce power over someone else's land.


"And you do not have the track record."

Now, now. Nothing new ever has a "track record". So life is not 100% free of risk. We knew that. Of course there's always the incessant nagging of the Safety Nazis, who want everybody to spend $1000 for $1 of "safety", who want to strap everybody in bed for life lest they should ever fall, or at least force people to rent scaffolding just to change the bulb in an ordinary ceiling fixture. But so what?

Given the size of the population, and the dependencies in modern food, medicine, and so on, not having electricity would pose far greater risks than anything likely to be posed by these guys - especially when they're tiptoeing on eggs through the lawyer-infested USA. And given that the overwhelming majority of us (in OECD countries anyway) are already "safe" enough to well outlive both our minds and bodies, how much more do we need to overpay for "safety" anyhow?

Actually, I think much of the modern fuss over insignificant risks is nothing more than another channel for rage against "bigness" - corporations and so on. But that's futile: with nearly 7 billion people, far too many to live au naturel as beasts in the manner seemingly desired by doomers, bigness is not avoidable, it just is. The fuss is also often counterproductive, witness our Congresscritters imposing new food "safety" rules that guarantee an even tighter monopoly for problematically huge producers, higher costs, and no improvement in "safety" for as long as food continues to be grown in open fields where birds and animals make random disease-laden "deposits" anytime, anywhere. Sometimes we really need to consider the greater good of the greater number, instead of being totally ruled by the whining of the few.


There is safety,and then there is the WORSHIP of safety.On the last big construction job I ever worked,I needed to do a little work over a penetration (large hole in the floor) five floors up in hundred degree high humidity heat.

The safety man insisted that we carry scaffolding up the steps,erect it ,do the job,and carry it back down,rather than just work off a couple of boards and wearing a safety harness.

Fortunately the engineer in charge quickly saw when I got him aside that the likelihood of somebody having a heart attack or stroke toting the scaffolding up five floors was higher than the probability of my falling wearing a harness.He found an "emergency job" for me till quitting time and he and I stayed a few minutes over after every one else was gone and took care of that little problem.

That seems to be a strangly contradictory position for someone who has often railed that the world is drastically overpopulated and needs a significant, fast population reduction. Or was that "fast population reduction in other people's countries only"?

Alan, where did your slogan go ? "Best hopes for .... ehh say KiteGen"..?

You are attacking this system from the wrong side of the pipe - you see first the Tech stuffs have to be sorted out and proven - there after, years from now, your 'political and practical initiatives' will arise as a subject. Also and eventually the first pilot KiteGen farms will not be mounted in the 'middle of town'-

My take is : If KiteGen can deliver power at a fairly competitive pricetag and in a resonable sceduled manner - it will succeed, simple as that. There are only SO FEW WAYS - without fossil-fuels ! And Windturbines will be hard to make 'after fossils...' - KG not so. IMO.


Alan, like others, I am a bit surprised by your insisting on the safety aspect. Especially the comparison with aviation seems far fetched: If an airliner crashes, hundreds of people might die.

The consequences of a kite crash are, fortunately, not particularly scaring, as I witnessed myself just the other day: Being on vacation, I was swimming off the beach here in Italy, sharing the shore with some kite-surfers. All of a sudden one of the kites crashed down right on my head ... I was admittedly not very happy about this, but in the end, nothing serious happened at all.

If the risk of falling kites are really the major obstacle for the kitegen, then this technology has a bright future!

I'm not worried so much about aircraft safety, but I haven't seen the issue of power lines addressed. I know the cables aren't conductive, but can a slightly conductive cable short out a 230 kV line? Are the kite and cable heavy enough to damage power lines?

This is again a worst case hypothesis: the cables are not conductive, but you could imagine a kite falling on power lines during a thunderstorm, and so the cables are wet - that is not enough, because rain is not conductive, but let's say it is acid rain, or polluted rain. I think that wouldn't make the cables conductive enough, but just as a possibility, that could - perhaps - short circuit high voltage lines and cause a power outage. In 2003 most of Italy went in total blackout for 12 hours because a tree fell on a power line in Switzerland. Extreme events are always possible, "Black Swans", indeed. But I think this one is not something we should consider a major problem for AWE.

In 2003 most of Italy went in total blackout for 12 hours because a tree fell on a power line in Switzerland.

There is more to the story, one of the reasons for the inadequate redundancy were "protect the alps" efforts made by environmentalists that blocked new high tension lines.

Another major reason for the large electricity flows were Italys abandonment of nuclear power that were partly replaced by importing nucler electricity from France. It were not that bad from an efficiency standpoint since the French has a night and week end surplus of electricity, the worst effect of the decision were probaby the larger day time CO2 emissions and a need for lots of imported fuel.

You must have sufficent redundancy in the grid to get 24/7 power, the scary thing is that people wont notice an erosion of margins until something breaks and several years can pass before something breaks down.

You are right, Magnus, there was more than just a falling tree that caused the blackout. But complex systems, such as the power grid, tend to collapse starting at their weak points.

Power plants need to be built near transmission lines, so it may or may not be such an extreme event. There are relatively few long distance transmission lines, and the solution could be as simple as no Kitegen upwind of them. What remains are the smaller lines feeding Kitegen power into the grid. Are they vulnerable to a cable falling across, and do they carry enough power to destabilize the grid if cut?

I really like this concept. It makes a lot of sense to an engineer. I like flying kites on the beach near here (on the Isle of Wight) when the weather is right and I am familiar with their peculiarities and aerodynamics.

I believe that you are aiming to produce a prototype that is as advanced as current technology will allow. Personally, I would be much more interested in something low tech but still using the most advanced materials, controls and software. The additional cost of these items would be easily offset by the improvement in performance.

I think all this talk of birds, radar lightening, black swans, effect on planetary climate and so on is a distraction. If the Wight brothers operated like that, human flight would have been seriously delayed.

In case you didn't notice, energy wars started some time ago and that should be taken into account when looking at the cost/benefits of this proposal. Loads of peoples are living in remote areas where the only resource readily available is wind.

I would love to make a much smaller and very much less expensive prototype to produce, say, a maximum of 5KW and to ramp it up from there.

By the way, I studied at Imperial College many years ago and I was wondering what the connection between the Imperial College Yacht Club and the author might be.

Alfred, I chose that picture of tall ships because I liked it. I just found it surfing at random over the Internet. ABout the Imperial College, I have been there many times, but I never suspected that they had a Yacht Club, somewhere. But I do love sailboats and I have sailed many times on small boats - alas, never on a tall ship!

Ah.... Alfred, about the 5 kW prototype, Ippolito has built a 1 kW kitegen using as generators parts of a Chinese electric bicycle. He says it was a lot of fun to do it, but that it is not the right scale. To produce energy that can be sold, it has to be bigger, on the MW scale.

So Imperial College has nothing to so with this proposal. I must say that I am not surprised as it is full of rather self-satisfied and very clever clowns who could never come up with anything as original as this (harsh words, but true) :=)
The reason I am interested in a 5KW prototype is that it should be do-able for someone with limited resources. Also, the power is enough for a family or a small group of people living far from the electric grid.
I have been giving this concept some thought and I realized that there was a different approach that I am sure was considered and dropped before this version was taken up. I would like to know why this other version was discounted.
This "Alfred" version would have been as follows:

  • The kite would be a rigid flying wing rather than a foil / parafoil (banana shaped)
  • The kite would be tethered by one cable to the base-station
  • The base-station would be responsible for releasing the cable - to extract power - and rewinding the cable in the second stroke
  • The kite / flying wing would be radio-controlled. The roll, pitch and yaw could be controlled by adjusting, dynamically, the three cables that connect this kite to the main cable.
  • The kite, during the first power-generating stroke, would fly in a large circle and gain distance (and some altitude)
  • During the second stroke, when the cable is rewound, the kite would fly in a smooth glide back towards the base-station.
  • At the beginning of the following first stroke, the kite would be made to rotate in the opposite sense - so that the cable would unwind.

For those who had problems visualizing the kitegen.com video (like myself), I suggest that they think of this kite / flying wing as the tip of the rotor of a gyrocopter Some of you may have seen the James Bond film "You Only Live Twice", well that is what a gyrocopter looks like. If you have not seen this film, I would recommend it as it is one of the better Bond movies.
The forward motion of the gyrocopter makes the wind turn the rotor and this turning results in the lift that makes the machine fly. The girocopter has been flying for 90 years so it is not something brand new. It is quite different to the helicopter - and an awful lot simpler.
It would seem to me that:

  • Pretty well all the components for building such an apparatus already exist "off the shelf" and are tested and proven - except for the base station
  • The base station should be a lot simpler - a clutch would be needed to change between the first and second strokes plus a little motor to rewind the single cable during the second stroke
  • The power transmitted along the cable would be a good deal steadier (during the first stroke) as the kite is rotating in a large circle of, say, 300m diameter at a distance of 800-1200m from the base station. It is not oscillating and it never stalls. Obviously, it create more power when it is high and falling than when it is low and rising so there still would be some periodicity.
  • I expect that, in suitable wind conditions, the kite would be moving at an airspeed of 200 hundred km/hour - just imagine the lift.
  • The kite would have some basic telemetry and a transmitter to let the base-station's computer send the appropriate control signals.
  • It was not clear from the information provided what sort of kite is proposed by kitegen.com but I would guess that my proposal probably has a weight disadvantage.

I am sure that I am missing some important factors (please don't mention birds/black swans/lightening/global effects/hurricanes etc. in your critique as that has already been brought up above and the responses would be similar)

Well, I won't make any comment about the Imperial College, but it is true that large and highly rated institutions have often problems in being creative. Anyway, your scheme, as far as I understand it, doesn't seem to be much different than the kitegen "stem" scheme, except for having a rigid wing tethered with a single cable instead of two. I don't see much the advantage of flying a large circle rather than a smaller "8" figure, but that doesn't seem to me a big difference, either. I know that Ippolito started with the idea of kites from the beginning, but I am sure he has considered many possible alternatives. Personally, I would say that kites have the advantage of being light and inexpensive, but I am sure that there is space for different kinds of technologies. I know that rigid wings are being proposed by other companies, so there are plenty of possibilities for those who come up with a better mousetrap!

Yes, I am sure he checked out lots of different combinations. Anyway, I do wish Ippolito buona fortuna with his endeavour.

Some people of the Imperial College helped us to prepare a comprehensive environmental impact assessment on the KiteGen technology.
We are currently presenting on this document base to obtain authorization.

About the one, two or more cable design, we chose the two cable for security reasons. As humans have doubled organs (like eyes) also the kitegen can rely on a double control chain, on two ropes etc.

With a single cable it is possible to obtain slight more power due the reduced drag, but each strong wind gust guarantee destructive effect because the onboard actuator are not fast enough to flagging or drastically change the attitude of the wing, the limited power available aboard, and the needed weight limits make difficult to implement reliable, powerful and recoverable mechanism.

In the KiteGen stem design the sideslip maneuver is functional to close the productive cycle and also to safeguard the machine, so the absolute maximum force excerpted on the machine is chosen by design and not by the wind.


Thank you for your explanation. I liked the comparison with humans having two eyes and so on.

In theory, it should be possible to change the cross-section of the kite that I proposed so as to optimize its shape with respect to prevailing wind speed. A Rogallo wing might be appropriate - there are other approaches though.

Hugo, thanks for the clear explanations.
I am still sceptial if this new concept will work under real world conditions. But as it would be stupid to discard this idea based only on theoretical concerns now a practical litmus test is needed:
Who can build the first prototype for a long-term scientific evaluation?
(The prototype shown on the video at http://www.kitegen.com/pages/faq_eng.html only looks like a normal kite without power production)

Drillo, the first prototype is being built in Torino by Massimo Ippolito's company. It is a complete unit, designed to deliver power to the grid. I called Massimo just one hour ago and he told me that he will spend this August working at the prototype. I told him that if he needs help, I can go there, too. At least, I can paint the housing of the generators! Barring sabotage from bureaucracy, it should be up and running before the end of the year.



Thanks for this article!

Not sure if it's been brought up yet or not, but what would the output variation range be for various numbers of kitegens in a wind farm? For example, is it possible in a configuration of 10 kitegens that conditions could exist that have 5 or more kitegens retracting at the same time? Or are all of the kitegens in a farm controlled as a scheduled system, instead of optimizing for individual kitegen efficiency? In a perfectly balanced farm of 10 kitegens where they are all orchestrated centrally, I would assume no more than 2 would be in the retraction phase at any one time; what are the plans for individual vs. central control? Or will there be a modest amount of local storage?

Will, the "retraction" phase lasts only about 10% of the time in a single stem. So, if you have 10 stems, on the average one out of ten will be retracting at any given moment. The whole farm should be centrally controlled but, of course, the power generated will not be perfectly constant - it will be smoothed by a battery of supercapacitors in the short term. It will also depend on winds; the estimate is 5000 equivalent hours.

That answers the question fully, thanks.

My main question is what sort of energy density (megawatts per square kilometer) is envisioned? Because of fears of
entanglement, I suspect that the minimum distance between stems may be a not insignificant fraction of a kilometer. So roughly how many kites/stems per KM**2 makes sense. I suspect this spacing requirement is probably independent of kite size (or very nearly so), so I suspect the main way to scaleup will be to make the kites bigger.

....so I suspect the main way to scaleup will be to make the kites bigger

I echo this , that Central-station looks like it is begging for troubles.
Also if they need (can) make really large kites, they could embedd some fix-volumed cells containing gas (helium, argon ... what have you) to ensure 'automatic lift', no Fans needed - thus simpler ?
The gas should only make the kite -slightly lighter than air- so that it would be easy enough to haul back. The gas-cells could also self evacuate (self empty throug a pressure valve) when in operation, if seen necessary for a better operation.

These gas-celles would also by and large 'eradicate' all troubles concerning Plunging Kites ... and so forth. (Oh sure, you are welcome!)

That's a good idea it can be called a kiteloon.

Let's see, enemy, if I can try a little calculation in a worst case hypothesis. Let's assume that a 3MW stem needs a free bubble of 1 km radius. That's very pessimistic, but it means a density of about 1 MW/km2 (max power). Now, let's take Germany as an example. Peak power in Germany is about 70 GWe (I cite from the february issue of "Photon Magazine"). To produce that much power with stems only, you'd need 70,000 km2; let's say 100,000 km2 considering that stems wont work at full power all the time. The total area of Germany is 357,000 km2. Obviously, you'd need to appropriate a large fraction of it for AWE but, in principle, it is not impossible to do it, since kites only flight over the area, they don't occupy it and so it is free for other uses.

But this is just a worst case hypothesis. In practice, stems would be clustered in stem farms and the density would be considerably higher. Finally, the next step in kite power is the configuration called "carousel" which is more efficient. And Germany is also a worst case hypothesis because it is a highly industrialized and populated region. You don't need to place the kites exactly over where electricity is consumed: the 9 million km2 of the Sahara desert would be a nicer target for AWE.

In the end, as I said in my post, we don't have yet an estimate of the total power that could be extracted in practice by AWE from the atmosphere. That will have to wait for the technology to mature. I'd say that perspectives are very good but, of course, there are practical limits. My impression is that we'll arrive at some form of integration of direct solar technologies (PV and CSP) and AWE. But that is just a guess.

How do go from say 15 rpm to say 3600 for a generator?

The generator is not syncronous, it is a direct drive torque motor/alternator.
with static convertion to go to the grid.

What is the expected noise footprint? When skydivers swoop at high velocity their chutes make a lot of noise. I would expect a 3 MW kite system to produce far more noise than a 3MW windmill with streamlined laminar flow blades.

Consider a wind farm of say 20 three MW windmills. Compare the land requirements, airspace requirements and noise footprint of an equivalent kite farm.

Yes, but they have to be very close to the ground for people to hear the noise. In normal conditions, the kites will be up in the sky and the kitegen should be basically noiseless.

With a bit of luck, however, it would make coal plants obsolete and eliminate at least one of the biggest sources of pollution and greenhouse gases we have.

Amend "luck" to "political groundwork" and you have a statement I can agree with, at least as concerns the US and China, for example. There may be a bit of luck involved with technological issues, but the real obstacles don't involve luck at all.

I posted an artical up about kite generated power over at peakoil.com a few weeks back but it didnt get much interest.

How much would it cost to make one functioning unit? and how much of that unit is made from petroleum products? (with its potential for a rapid increase in price)

Does the system make economic sense when taking into account the replacement cost of the cable and kite 2-3 times a year?

I'm not familiar with the cost of the kite, but cable is very expensive, and the price escalates quickly at thicker diameters. What is the cost per foot of the cable diam. needed, x the length required, x 2.5 avg. replacement times a year?

Thousands of meters is mentioned as a height for the kites. So let's take 3 thousand meters = more than 9,000 feet, (rounding down to make the math easy). Now let's say the cable is 5 bucks a foot. 9,000 x 5 = 45,000 dollars. Now we multiply that times our average replacement per year (2.5) and just the cable itself costs 135,000 dollars.

Now take the cost of the kite, multiply by 2.5 and add that to 135,000 dollars. Then take the initial cost for the base system including the land, then add the replacement costs, divide by the kilowatts generated and figure a cost per kilowatt. Does it make economic sense?

I think it'd be interesting to see some serious research effort put into creating synthetic spider silk. There's no question that it's strong, that it can be produced with a number of different attributes by the same spider, that it can be eaten and recycled by the spider, and that it is within the spider's energy budget to use and replace frequently. Without any exotic materials inputs.

Now that would be useful technology.

To replace the cable every 6 months or so seems like overkill to me. Wouldnt it be possible to just test the cable for faults and if none were found reuse it? that would cut down costs drasticly.

Testing in place is likely to be prohibitively difficult.

If I recall from the original article they have a recycling plan for the lines, which would doubtless include an inspection and return to service for lines that pass a sufficiently strict test.

..and with that, there will also grow the actual experiential data which will help them adjust this timing, which is more than likely a little loose at this point.

The cost of the cables is - of course - accounted for in the cost estimations. I have been discussing at length with Ippolito about the economic issue. They have made extensive estimates, but it is very difficult to come up with just a number: price per kWh. One thing is to estimate the EROEI, which is based on physical factors. Another is to estimate the cost of the energy produced, which will come down considerably as the technology goes up the learning curve. Even more difficult, almost impossible, is to estimate prices, which will depend on market factors, on the interplay of demand and offer, and of the obvious fact that whoever produces something wants to make money out of it. I know that Ippolito is sure that he'll be making a profit from the plant they are building in Northern Italy. I tend to trust him on this!

So, the price of AWE energy will vary as a function of the penetration of the technology; I mentioned in my post the possibility of energy "too cheap to meter" and I think that, in the long run, we could really arrive to that.

As an engineer who has dealt with large mechanical systems and is at least somewhat conversant in the field of aerodynamics, from what I've gathered so far from the material presented, this whole concept is based on some possibly shaky assumptions that raise some doubts in my mind. To wit:

- We have the claim that due to the higher wind velocities at higher altitudes and due to the rapid movement of the kite in that wind, that the 'tip speed' of the kite is far higher than the tip speed of a typical large wind turbine. I say this is comparing apples and oranges, because the kite really doesn't have a tip speed in the same sense as a turbine, due to the simple fact that it is not directly rotating a shaft. Whether the kite is bobbling about rapidly is of little relevance ... what really matters is how much force it exerts on the unwinding cable and how rapidly the cable unwinds.

- While obviously there has to be lift to get the kite up in the air in the first place, the system in the 'yo-yo' configuration is largely extracting energy due to drag forces, rather than lift forces, i.e., how much force is exerted on the cable as it unwinds. So in this regard, I think the important question are i) how much drag can a given area of kite cause to be exerted on the cable over the period of the unwind phase?, and ii) how does that compare the amount of torque produced by a wind turbine operating under equivalent conditions (fully allowing for the high altitude advantage in wind velocity).

- Little if any mention is made of the fact that during the 'retrieval' phase, no power is being extracted, and, in fact, a small amount of power is actually being expended in retrieving the kite. Question: Is the length of time required to retrieve the kite roughly the same as the power-producing 'unwind phase"? If these two phase are roughly the same length of time, then the power absorption of the system is roughly cut in half, thus cutting into the advantages of operating at high altitude.

- Cable wear should not be taken lightly. It is one thing to have a more or less constant stress on a cable, such as in towing a vessel (and even that is not really constant, but rather slightly oscillating). However, with the kite system in the yo-yo configuration, there is a continual winding and unwinding of the cable upon a drum. This is inherently a very high-wear application. Furthermore, there can be enormous stresses induced in situations where the wind suddenly drops and then just as suddenly picks up again.

- As far as the 'carousel' configuration is concerned, this makes even less sense to me. Based on the video animation, the basic idea appears to be to essentially have a rotating arm on a vertical shaft and to have the kite attached to the end of the rotating arm. As the kite yaws back and forth (presumably due to various vortex effects), the arm is moved through an arc which appears to be something like 60 to 90 degrees. In this configuration, the driving force is no longer the drag on the kite, but rather whatever aerodynamic forces are causing the kite the yaw back and forth. Being that the kite is at the end of a very long tether, I fail to see how much side-to-side force can be generated, given the apparent geometry. (This may be explained in the paper presented, but unfortunately I don't know Italian.)

In closing, the fundamental problem I see with this kite system is that it relies on trying to extract energy from the somewhat unstable movement of an object suspended in mid-air by a delicate balance of drag and lift forces. Plus, it relies on an oscillating movement rather than a continuous smooth movement as in a wind turbine. As I said previously, to me the inherent drawbacks appear to far outweigh the claimed advantages.

Having said that, if the backers of this system can build a commercial scale prototype (say something in the 1 MW size range) that works as intended over an extended period of time and does experience any of the problems I've mentioned, then I will have been proved wrong.

Also in the yoyo configuration the lift force come into play for the energy extraction. Imagine the cross wind motion of the kite: it will have a large component almost parallel to the apparent wind and another smaller component perpendicular, that unrolls the rope. The lift force is produced by the apparent wind, and is almost perpendicular to its direction, and multiplied by the rope unrolling speed will produce the power.

mmarchitti -

Perhaps it is a misunderstanding of terminology on my part, but it would seem just the opposite to me.

As I see it, the cross wind motion of the kite would have a SMALL rather than a large force component parallel to the apparent wind, whereas the force component parallel to the wind is the one doing most of the work as the rope unwinds from its drum.

Yes, the force on the rope is the vector sum of the components of lift and drag in the general direction of the rope. But I'm not sure I understand what you mean by being 'multiplied by the rope unrolling'. ????

Yes, maybe there is misunderstanding of terminology in both parts. I would have specified that a "velocity" component of the kite is almost parallel and similar to the apparent wind. The apparent wind produces the lift force that is perpendicular to it, therefore parallel to the other kite velocity component, which is also the velocity of the rope unrolling.

A financial operation to promote the project, addressed to medium/small investors, came into life last year. It is a sort of financial holding, Wind Operations Worldwide srl.


This idea struck me as a very good one from the moment I saw it- quite a while ago.

I am appalled by the naivety of so many of the objections here, not what I would have thought would be the case where so many people are engineers.

But I shouldn't have been surprised, after all, my business is thinking up new things related to energy, and I have been at it for a long time. ALWAYS there are such objections, objections that sound flat-out stupid to me, but shouldn't, since the doubter usually has not given the subject much, if any, thought.

A few examples.

A while ago I proposed here that rather than spend time charging batteries in an EV, we simply replace them just as we do in a power tool. People immediately jumped all over this one as "unsafe", "hard to do", or the really stupid one-- " Batteries are heavy, most people wouldn't be able to lift them" !

Then of course, people started making businesses based on this idea, incidentally a pretty obvious one, and then it got raves as clever, original, etc. Ah, well.

Then there was a favorite of mine- the vacuum tube train. Super speed, no energy ( or very little) and so on and so on, and to curtail the expected flood of criticism and usual attacks on my sanity, I remarked that the idea was over 100 years old and was a favorite of science fiction, much of it written, as we know, by highly qualified scientists. To no avail. Still the floods of all that, my favorite
super-stupid one being :

"Vacuum tube? Passenger train? My god, how would you breathe?".

Anyhow, great idea, people, and thanks for being so patient and effective in countering criticisms, some of them not worth the bits and bytes they are written on.

If I only had the time, I would go out in the back yard and make a little one- maybe a kilowatt or something. To hell with the airplanes- or the neighbors, they being threatened, as you said, by being clobbered by a sheet.

So your advice is to not question it, simply plunk down a big wad of cash and go for it. Well, please do as you suggest and try it, then come back here and tell us how it went. How did you handle the lawsuit when a small plane got tangled up in the cable and the pilot plunged to Earth at terminal velocity? What trouble did you encounter replacing the cable? Was it expensive? Did you hold your head out of anguish for having spent so much on something not thought all the way through? Are the environmentalist still angry about the flock of geese that got stuck in the kite? Or, was the it the breakthrough that made all other forms of energy production obsolete, and you won a Nobel for the work. I'd love to know how it turns out.

There's such a thing as being paralyzed by a list of perceived risks that sounds long, but are very unlikely even in aggregate.

Of all the things one could do, flying a kite from one's backyard is pretty low on the scale of destructive human activities; arguably less than posting to an internet blog.

Really, everybody, go fly a kite. It's a good meditation and it's darn near sure to use less energy and cause less damage than whatever you might be doing otherwise.

Then there was a favorite of mine- the vacuum tube train.

Well this does sort of exist (just without the expensive infrastructure): A passenger aircraft flying at 36'000 feet is kind of a tube which travels in a 80%-vacuum.

And I also hope that the kitegen succeeds:
But the promotion of kitegens should be done without badmouthing wind turbines, because that will not only reduces acceptance of wind turbines, but also acceptance of kitegens.

A standard 2-MW wind turbine has a mean production of 4000 MWh/year. To attain a mean generation of 9 TWh/year, which corresponds to almost 1000-MW mean power, 2250 such towers are required, with a land usage of 300 km2 and an energy production cost of about 100–120 €/MWh.

Feed in tariffs are lower than 100–120 €/MWh for wind power in most of Europe. So if this statement was true, wind turbines wouldn't exist and yet Europe has already about 60 GW of wind power installed. Also wind turbines hardly use any land. Cows actually appreciate the shadow of a wind turbine and don't mind that they're missing 10 m2 of a grass patch on a large field. And 2250 towers is a small number considering the fact that Europe has several Million of transmission poles.

Ahem. That tube at 36,000 ft is exactly what I was arguing to replace with a vacuum tube train. The train uses next to no energy compared with that Mach. 0.8 missile punching a hole thru the stratosphere. And yes, I do know how much it takes to make the tube and the vacuum. But that is for another day. For this one, wind is great, kites are great, and I like the advice to go fly a kite. I still remember the rope burns I got from flying mine.

I live in Chicago and am an experienced static tow hang glider pilot. I also have a couple four line power kites, the kind which some people use to tow themselves on 3 wheeled kite buggies.

The idea of trying to fly a multi line kite at thousands of meters of altitude seems daunting. The longer the control lines the more difficult it is to deal with rapid changes in windspeed or direction. I expect the biggest challenge for scaled up power kites with super long lines is going to be finding locations with steady enough conditions.

However, we routinely towed hang gliders with several thousand feet of line in raucous air with booming thermals. While it will surely be more expensive and complicated, I would be strongly inclined to explore single line systems with a kite more like a hang glider or a sail plane.

Bravo SpeedEBikes - This is a great contribution !
Your few sentences here are pinpointing the Operational Challenges KiteGen may (or definitely WILL ?) endure ...

I too have deep problems to see this system do well in other weather conditions than near perfect laminar winds. Being a hanglider pilot many years back myself - the thermal boom difference from one wingtip ... to the other would easily tilt the entire glider for a whole new direction .. little or no time to counter-act upon thoses 'bursts', new direction there is -
And the 1000 meters altitude that KiteGen-promotors are talking about is just the perfect level for these dense thermal-differences to take place . 1000 meters is 'turbulence land' - at least in spring / summer northern lattitudes.

Agreed, they may be underestimating the control problems of 1000+ meter kite lines. But it seems logical to me that that can be overcome with a small intelligent package carried just below the kite and using a small propellor to generate enough power to manage some control flaps / etc. on the wing based on some sensor data and logic algorithm. Or how about a small patch of flexible solar cells and a LION battery pack laminated to the top of the kite surface right at each control vent / flap, with a central logic unit?

You are doing a quite good brainstorming.
In the beginning of our project, we had the same heavy concerns as yours, and we got the answers since the year 2006 during the test campaigns thanks the prototype's flights.
It is really curious that our professional experience and our intuitive physics, work so badly with stuff like this.
May be in our evolutionary ancestors we never had birds or flying animals :-).
That's exactly the opposite, the higher the kite flies the easier its control and the more predictable its behavior.
About the power supply aboard you are right, thin film flexible solar cells, small wind turbine and ultra capacitors buffers are the chosen components to power the sensors and the radio link, but we do not need any mechanical actuator.

here you can see the flexisolar applied to the wing.

Can I, politely, ask you, in yours incipits, to be more cautious in assuming that we missed something or we underestimated something else. More than 100 people linked to KiteGen are working, studying, experimenting on the concept since more than 6 years, either youngs ones and professionals. I let you imagine the number of effective brainstorming already occurred.

If we underestimated anything, that is the global indifference about energy (+ demographic and environmental) issues.

Your picture is interesting, but do you have one which includes a horizontal reference? I doubt a kite would "fly" with the cables vertical as the picture suggests. The word "Hype" comes to mind...

E. Swanson

Sorry Massimo. You are right, it was very arrogant of me to assume you hadn't though of such an obvious item. Just in my own defense, I am strongly in favour of you're group's efforts succeeding, and to this point have seen no reason why they shouldn't. Andiamo.

you say:
"So, the main mast of a tall ship could go up to 30 meters."
The mainmast of Flying Cloud was 164 ft.
She was built in 1851, there were taller ships later.

and Mirabella V has a mast height of 292 ft (88.5m)

Ouch.... that shows I am not a real expert on tall ships..... Thanks for the info.

Cool stuff Urgo, I couldn't help but immediately connect the controlled kite concept to the tall ships. It seems cargo (and passenger) vessels might be able to greatly benefit from some variation of such a system. Any significant work being done in that realm these days?

That's being done, Luke!

The system could readily provide ship power as well as the motive force of a static kite or sail. Perhaps you could vary the line angle to vary the power split between the two aspects.

Excellent, sorry I botched your handle Ugo.

A small unit would make a very neat onboard power generator for a yacht.

No comments about Kitegen, just a memory. When I was a kid I had a lot of trouble trying to get a regular kite up and flying, it usually crashed. One day I read that some life rafts for ocean-crossing ships had box kites, to pull up a wire for emergency radio SOS antenna. So I bought a toy box kite. It was the simplest to launch, the easiest to fly, and in strong wind it pulled much harder. It would fly until my ball of string was completely played out, where the regular kite would not. But it was boring, once it was up, it just sat there in the sky, while the regular kite would bob and weave, you had to fight the tailed kite.

My brother and I built a pretty large box kite back in the mid-'60's, about 8' tall, and it was indeed quite stable and pulled strong. In order to get that much stability out of a diamond-shaped kite we generally had to add quite a bit of tail.

Which reminds me of an old joke. A man's kite is repeatedly crashing. A woman from a nearby house calls out to him and says "I think you need a piece of tail". He yells back "That's what I said an hour ago, and you told me to go fly a kite."

Would the ideal location for the base be atop a mountain or on high plateaus (Tibet)?

This is a brilliant concept that could evolve to incredible power-generating flying machines. E.g., instead of a kite, could it be a flying wing with it own guidance/navigation controller with sensors that enable it to avoid other flying wings (and their cables)? The wing could glide itself down without need for power from the base, and could land and take-off from a nearby strip.

The resulting scene would look like a flock of vultures soaring on thermals.

Thanks for posting this Ugo.

I hope Mr. Ippolito has not forgotten to check in with the kitesurfing crowd. We have been tethering ourselves to these types of kites and generating power for about a decade now. If you are close to the wind/water combo - you have seen these things out on the water. They're beautiful to watch. As with most things that tap into the natural energy of the planet, there is a cult-following. Dense energy sources are incredibly addictive. Kitesurfing has gone through a learning curve with this type of thing. Would could shed some light on some of the issues kitegen will run into.

In any event, when you are flying your kite with a surfboard on your feet and you want to generate more power from your kite, you fly a figure-8 that Kitegen describes. This is called sine-ing your kite. A stationary observer on land sees the kite in a sine wave pattern, where the surfer sees the figure eight pattern. You can generate smooth consistent power with this technique.

If anyone wants to gain a little hands on experience with a power kite just fork over about $100US and you're in business. Small traction kites used for honing your flying skills are great fun. You can find one here: http://www.slingshotsports.com/s.nl/it.A/id.265/.f?sc=45&category=12714
but there are many others around.

Knowing a little about this kite power, just from surfing around on the ocean, I have to hand it to kitegen - to make the leap to high altitude is fascinating and bold. The subtle changes you make on the control bar when you're cruising in the ocean is complex. I couldn't imagine writing a computer code to do it. Often, when I'm getting pounded in a shore break, I wish a computer was controlling the kite instead of me. I often wonder what it would be like to have 10,000 foot kite lines. Would it be smoother power? Kiters are always talking about the responsiveness of the kite - how quickly you can turn it,how it deals with gusts etc...

Here's a TED TV talk about the big kite thing:

Good luck kitegen.

Looks to me like an unstable money hole project fishing for financing from suckers.

The whole notion stinks of overengineered nonsense that cant compete with a simple tower and turbine.

That's awesome.

The developers of this prototype provide detailed, point-by-point answers to the many objections (some specious) to their project that have been pitched on this site, and you weigh in to say it's 'overengineered'.

BTW, modern wind turbines are far from 'simple'......

Its a rube goldberg machine; Getting one to work is a chore enough in itself, compared to getting something that is competitive.

No way are these silly things ever going to command market share of ordinary wind turbines, let alone significant fractions of the grid.

Best to be silent and thought a fool, than open your mouth and remove all doubt.

Nice repartee', Dez.

I hope everyone understands Ugo stands to financially gain from kitegen's success, he can not be objective.

Global wind energy amounts to a total of ~5tw. Global electric demand is ~13tw. Kitegen's fractional efficiency will never scale past even microhydro. Has anyone run calcs on the geographic requirement to just maintain 13tw of production in the face of expanding populations and economies?

Out of curiosity, how many proponents have ever flown a traction kite? You need intuition in addition to logic to succeed.

This commercially biased drivel does not belong on TOD.

Are you expecting not to see business proposals?

And forget 13tw.. they're looking at this idea to see if it works. What if it does and they just build up a couple GW and have a nice business to run? Ultimately, it's Alt. Energy.. and as such is safe to see as one of any number of BB's.

"I don't want to buy 'Happiness'.. just a boat and some other stuff." -C. Barra

"Are you expecting not to see business proposals? "

Not on TOD biofool.

Myself I prefer openly subjective people over people who claim that they are objective.
True objectivity is a very rare beast and even a truly objective person will probably not give the complete truth since the ability to know things is limted, even the truly objective needs to state the basis for his and her knowledge so that it is possible to know the limits of the persons knowledge.

When discussing solutions I dont care if they will scale to fill the whole market. There might somewhere be a unique waterfall where a one-off water turbine design is the perfect one and newer will scale to a second site, thats fine, lets build it if it gives a good ROI and EROEI.

We got to use every solution that makes sense and then we will se how far they will carry us. If we fuck up or it realy is impossible it will provide a larger sustainable resource base for the people and culture that survives a population crasch. And we do right now have more resources and knowledge then ever before, today is the right day for testing all kind of ideas and then pass down the raw data and our conclusions to the following generations. Its ok to reserach extreme solar cells, one winged wind powerplants, prototype fusion reactors, odd schemes for gathering wind power, every reasonable design for breeder reactors and so on as long as we regard it as a quest for knowledge and save the data and we can also hope we get lucky that some of it scales well.

What I like to se on ToD is analysis of what happens, testemonies of peoples experiences and new ideas and I have no problem with reading about commercial ideas. We are on the right track if ToD ideas become big business.

I, too, am amazed by the weird objections.

Apparently birds and aircraft pilots are incapable of avoiding things in the air. Yes, flying at half the cable height would be challenging but Pilots already keep away from open pit mines, nuclear plants, fur farms, rifle ranges and nature reserves. Birds would have a slightly harder time avoiding the (moving) tether than they do avoiding (stationary) power lines. I guess this would be the last straw.

Yes, they will slow down the wind, like forests, mountains, cities, & ocean waves.

Yes, there are mountain wave effects, but where this happens the glider pilots already know the baselines - if a kite works well in wave, or needs to avoid it, we already have a very good understanding.

Kite surfing kites are semi-rigid (inflatable), and it is unpleasant to be hit by one 'falling' I would not be surprised if someone has managed to be killed by one. The pictures I have seen of Kitegen and ship-borne kites appear to be non-rigid, and would probably be like being hit by falling loose fabric. Ouch. The line might drape over something. Power lines do this regularly at x thousand volts and are still accepted in society.

I think Kitegen uses a two-stranded control line. If one line breaks the airfoil collapses, tension goes to ~0 and the other one can bring in the kite. The broken falling line will probably also be wound in as fast as it falls, like a glider winch. That uses a tiny parachute to keep line stability, but I suspect it is not necessary in an 'emergency' windup.

There seems to be confusion between 'drag' and 'lift'. If it were a drag device a parachute would work equally well. It is not. Modern horizontal axis wind turbines are lift devices, those weird rotating advertising signs at petrol stations are drag devices. That's why barrel shaped wind generators don't get funded.

A windmill is by no means simple technology - 100 years of airfoil research and composite /steel technology are hidden in those delicate white blades. For example, why are they always white? I'll give you a hint, it is not a fashion statement. Both systems would use similar generators but the structural difference between a fabric kite & 1 km of line vs tons of steel tower and carbonfibre/wood blades seems significant. If we can accomplish the same job with 1% of the material why not try?

The spacing issue reminds me of discussing boat anchoring - each boat has 100 feet of line out so they have to all be at least 250 feet apart? Or can we put them 50' apart; expect them all to behave roughly the same so all lie with the wind and/or tide? Since the kites will always be 'downwind' ignoring wind shear with altitude it might be theoretically possible (but not terribly likely) to fly synchronized and space them one kite-width apart.

A large number of modern aircraft are built dynamically unstable - a human being cannot fly them, all control input is filtered through a computer. ABS allows average car drivers to brake 95% as well as professional race car drivers. I can imagine a possibility that even a simple analog computer could outperform most humans (except perhaps very good kite surfers) in keeping constant tension and a constant flight pattern.

Yes, we should all use less. But right now that equates to living in a cave. I can see a use for a slightly complex electrical generating system, even if it is not 100% available.

I would love to see a couple go up, then find out what the problems are. I have this feeling it is a helluva lot more believable and cheaper than coal CCS.

I don't know what's scarier, running out of fossil fuels or finding a near infinite source of energy.
Either way we're going to continue running amok and creating a big mess. As Nate Hagens posted earlier, the biophysical limits of earth have been reached, we are clearly in overshoot. Finding a new energy source just means we use up some other critical component/ input faster.

You can't say that without stating exactly what level of energy use per capita you consider appropriate? Two wood fires per month? Except for you and your hench, who "must have" your own nuclear reactor for administrative purposes?

Dyneema fiber is made from polyethylene, and you indicated only 80% of it will be recycled when the cable needs replacement. Polyethylene degrades in sunlight which might place a limit on the number of times the cable can be recycled. Polyethylene is made from crude oil or natural gas.

What is the replacement for Dyneema fiber when there is no more crude oil or natural gas available as feedstock? Is this system sustainable?

By volume 2000m of 1 cm2 tether = 200 liters of fuel, which I burn at work in 30 minutes, with no current means of recovery. I think this will last an average American automobile about a month.

Assuming we can recycle it 5 times we only have enough petroleum on earth to produce 10 trillion km of tether, say to Neptune and back. YMMV. Then we'll be right back to the same problem, so there's no point trying, right?

Is plastic rope sustainable? No. Is it a more rational use of natural gas than lighting it on fire to heat your house? Yes.

Also consider the transportation fuel needed to move all of the Dyneema fiber cables to recycling plants and the volume of waste produced from the portion that will not be recycled. If there are tens of thousands of Kitegens spread out across the country side, replacing the cables every 4 months would require a massive amount of maintenance. Other materials could be used for the cable, but they all have trade-offs in price, weight, durability and likely other factors. If the production of the cables relies on vast amounts of methane and the frequent servicing relies on crude oil to power vehicles and make asphalt, both peak oil and peak methane would be disastrous for Kitegen.

Thus my first question remains: what other materials can be used to make the cable?

If a truck only carries one roll cable out and one used roll back to the factory every workday it adds up to about 20 rolls per month and 80 kitegens per truck.

The used fibers will be fairly cleen and a very uniform material wich makes them easy to recycle into something that is more valuble then burning for energy or synthesis gas.

If I were workig for Kiegen I would concentrate on developig light cabels with long service times over optimizing the cable manufacturing since the cable performance is central for the systems economy and should drive the develeopment of manufacturing and recycling methods.

Your problem example is a common objection that is correct if oil deliveries stops cold and no road maintanance is done but that is a very unlikely scenario. The likely versions of such scenarios should be contered by civil defence stockpiles and not mmassive use of sub-optimal energy systems.

Good point, Blue Twilight, I have been thinking to that, too. How could we make a kitegen (or generally an AWE) system that is totally independent from oil? I was thinking that silk could do almost as well as dyneema, it doesn't have the same strength, but it could be usable. There is a problem here: my experience in archery tells me that the natural materials that you can use for bow strings are good in terms of strength, but suffer humidity. But I figure it would be possible to find a remedy. All that made me think that some kind of kitegen-like technology could have been invented long ago - much before the fossil era. Who knows? We might have skipped the oil age altogether.

But, more seriously, I suppose that if can manage to keep the industrial society running, it will not be a big problem to make a kitegen-suitable fiber starting from biological materials.

Ugo and the guys from Kitegen,

I'm convinced that your system can work from a technical point of view.
Where I see a possible problem is in the economics, not because of the need to replace a tether every 4-6 month but because of the need to bring the kite down in case of a thunderstorm.
I have some experience in airship design and operation. The typical size of the ground-crew of a Goodyear blimp is 15 people, Zeppelin has a semi-automated landing system which still needs 3. They only operate in fair weather.
Scaling up your figure of a 10m^2 kite for the 40kW system, I get 750m^2 for a 3MW system. Let's say 12m x 60m. The size of a very large blimp. If a understand you correct, you intend to bring the kite down in case of an approaching thunderstorm, which, during an average german summer, may be every third day. But you never know when, it may happen every day.
How many men do you recon will you need to bring the kite down safe in the gusts of an approaching thunderstorm?

5000 hours/year times 3MW times 150€/MWh (0.15€/kWh ~german feed-in tarif for wind) gives an anual return of 2,250,000€. You can't afford to have a sizable ground crew on stand-by without severly eating into your profits.

So, to make your system a success, you have to keep the number of men on the ground to an absolute minimum, which means either:

A semi- or better fully-automated and *reliable* recovery and relaunch system. Not a simple engineering task.
A kite and tether strong enough, and a controll system sophisticated enough to leave the kite up in the air all the time and have it survive an once-per-decade thunderstorm.

Your thoughts on this?


Never having been to northern Italy I can't say what bearing this economic angle has and I certainly doubt the people involved would want to deal with what follows, but I will throw it out anyway. If a prototype Kitegen operation were up and running say in Healy, Alaska (not far from Denali Park, quite windy and the site of a mothballed for underperformance prototype clean coal plant) tour busses would route it right in, tours and souveniers could be quite lucractive and would do more to put the seed of awareness in diverse and unsupecting portions of the populace than one might imagine. I don't think a Kitegen 'plant' has quite the potential for tourism the local hot springs operation does (it uses relatively low temp hot spring water to refrigerate an ice castle a few hundred yards from its toasty and sizeable mineral pool) but tourism buck potential the first Kitegen 'plants' have.

Rainer, I think I understand the problem with airships: I have seen movies and I see that it isn't easy to manage one of those things when wind is blowing. That's too bad, because I would love to see airships coming back. But, about the kitegen, that kind of problem is minor or non existing. With the kite, you don't have to work against the wind, you use the wind to do the work. And launching and retreating the kite is fully automatic. No crew at all is needed. Of course, some more experience will be needed, but I think that Ippolito's tests have already shown that this is not a major problem.

Great thread Ugo,

KiteGen is really coming along. Readers may want to review the recent work by KiteLab & others as announced on Joe Faust's email ring & web site ( energykitesystems.net ). A stem-like variant called a "tipping boom" does true crosswind power without reeling in/out. A driven tripod-tether can cheaply perform the function of a massive carousel. A hot kite can be constrained to fly loops or eights passively without aerospace robotics. Good news, various AWE prototypes are working well & small scale systems are easy to build.

Hello to Ippolito. Lets all work together & get AWE established as a practical reality worldwide.

Dave Santos

Ilwaco, WA
Austin, TX