The ERoEI of High Altitude Wind Power

For several weeks I have been researching and writing a review post on high altitude wind power. It has grown into a 6000 word monster that should hopefully fly on Monday. While doing this it has been difficult to find time to write other posts. Hence this is a preview of one section on Energy Return on Energy Invested (ERoEI) which makes a nice post in its own right.

KiteGen have presented a back of the envelope style ERoEI calculation for their 3 MW stem indicating a value of 562 which is incredibly high. I have done my own calculation using a variant of their methodology and my own input variables. The idea is to try and estimate the energy intensity of a wind turbine structure and to interpolate that into a KiteGen stem. This involves making many weak assumptions but should be good for arriving at a ball park number.

I will begin with estimating the energy intensity of a wind turbine based on the mass of the superstructure. According to Vestas, their V112 3 MW turbine contains 372 tonnes of metal in the tower and nacelle (I will ignore the 947 tonnes of steel and concrete in the foundations for the time being).

I am going to make the following assumptions:

ERoEI = 18 [1]
Capacity factor = 0.3
Lifespan = 20 years
Power = 3 MW
Mass of superstructure = 372 tonnes

Energy produced during life time = 3*24*365.25*20*0.3 = 157,788 MWh

Energy required to create and maintain machine = 157,788 / 18 = 8,766 MWh for an ERoEI of 18.

Energy intensity = 8,766 MWh / 372 tonnes = 23.6 MWh / tonne

In his PhD thesis, Lorenzo Fagiano provides the following table for the theoretical capacity factors for a KiteGen [2]:

The average is 0.54 which is used in the calculation below. The capacity factor is higher than a turbine because high altitude winds (500 to 2000 m) blow more steadily than at the surface. Assumptions for a 3 MW KiteGen stem:

Capacity factor = 0.54
Lifespan = 20 years
Power = 3 MW
Mass of superstructure = 20 tonnes

Energy produced during lifetime = 3*24*365.25*20*0.54 = 284,018 MWh

Energy required to create and to maintain machine = 20 tonnes * 23.6 MWh / tonne = 472 MWh

ERoEI = 284,018 MWh / 472 MWh = 602

This is an astonishingly high and difficult to believe number but it is born out of the much lighter weight and higher capacity factor for the KiteGen. In his calculation, Massimo Ippolito got a number of 562 using an energy intensity of 40 MWh / tonne. Using that figure, my ERoEI estimate falls to 355 which is perhaps more realitsic.

It is this aspect of the KiteGen and high altitude wind that really caught my attention. Many years ago when I first began looking into global energy issues I believed the problem may be easily solved by a combination of wind power and partial conversion of surplus power to an energy store such as hydrogen. Unfortunately there are many who still believe this is a solution. The problem with this approach and conventional turbines is the low ERoEI of wind turbine electricity, that makes it expensive combined with round trip energy losses in going to storage such as hydrogen that are typically of the order 70%. With 70% losses, the ERoEI of a wind turbine – hydrogen system falls to 5.4 (ERoEI of 18 * 0.3) and we drop off the net energy cliff (Figure1). In other words, with a wind turbine – hydrogen system you take expensive electricity and waste 70% of it to mitigate for intermittency. Consumers and economies don’t like this!

Figure 1 The estimated ERoEI for a 3 MW KiteGen plotted on the Net Energy Cliff. The electrical output from a KiteGen is not smooth. This is partly mitigated by on-board super-capacitors that can store and discharge power to smooth out the supply. To convert the output to dispatchable power a very conservative approach would be to convert all the electricity to an energy carrier like hydrogen and then combust the hydrogen in a gas turbine to generate electricity. This will consume about 70% of the available energy, but even doing this leaves an ERoEI > 100. In reality some of the output power can be sent direct to the grid while some can be stored to mitigate for intermittency. For explanation of the net energy cliff see ERoEI for Beginners.

The KiteGen stem is a complex machine, but it is light weight and cheap to build and to install. IF it works according to expectation then it may produce large quantities of cheap, unsubsidised electricity. A KiteGen – hydrogen generator would still have ERoEI of 355*0.3 = 107 which is still huge compared to most other forms of electricity generation today. A KiteGen may also be used to make synthetic fuels. An important point is that a KiteGen may be able to make the liquid fuel to mine materials and make the electricity to manufacture more KiteGens with ample energy left over for the rest of society to use. But all this depends on the assumptions made above holding true and the machines actually working to specification.

[1] Charles A.S. Hall n, Jessica G. Lambert, Stephen B. Balogh: EROI of different fuels and the implications for society: Energy Policy 64 (2014) 141–152

[2] LORENZO FAGIANO PhD thesis 2009. Control of Tethered Airfoils for High–Altitude Wind Energy Generation

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53 Responses to The ERoEI of High Altitude Wind Power

  1. Have you seen that one already?

    Also Siemens’s assessment of energy payback time for onshore wind is 4.5month here which would yield an EROEI above 50.

    I believe the is vastly superior but 18 sounds awfully low for modern wind.

    • @Jenny,
      The discrepancies are due the methods and the bounders, If KiteGen adopt the same Siemens method to calculate the ERoEI, the result will be much over 1500. Raugei invented a method to inflate the ERoEI of solar PV, expressing production in primary energy terms; all other renewable sources evaluation adopted the same wishful concept. As you probably knows, this give rise to heated debate about the KiteGen right to adopt the same other renewable metrics: [in Italian].
      I suppose those intimidation often directed at KiteGen, have an official position in the “Club of Rome” which belongs Bardi, the reason could descend by another heated debate of the past around the “Ultimate Resource” of the ostracised Julian Simon.

    • Euan Mearns says:

      Jenny, as Massimo points out, ERoEI depends on where the boundaries are set. I’ve read a number of papers on this over the years and the numbers usually fall between 10 and 20. The number I use comes from Hall et al (2014). So I’d take the manufacturers number with a pinch of salt. But lets do the sum using 50:

      Energy produced during life time = 3*24*365.25*20*0.3 = 157,788 MWh

      Energy required to create and maintain machine = 157,788 / 50 = 3156 MWh for an ERoEI of 50.

      Energy intensity = 3156 MWh / 372 tonnes = 8.5 MWh / tonne

      And for the KiteGen:

      Energy produced during lifetime = 3*24*365.25*20*0.54 = 284,018 MWh

      Energy required to create and to maintain machine = 20 tonnes * 8.5 MWh / tonne = 170 MWh

      ERoEI = 284,018 MWh / 170 MWh = 1671

      The KiteGen has much higher ERoEI than a turbine because it catches more wind and is much lighter. Eugenio had an alternative calculation which also came out at about 300 which I hope he may post.

    • Al Mizar says:

      Massimo Ippolito,
      Euan Mearns wrote here above:

      … I am going to make the following assumptions:

      Capacity factor = 0.3

      Power = 3 MW

      As you could already know, Mr. Giancarlo Abbate, Kitegen’s “Consigliere Scientifico” (scientific Advisor) [1], wrote in 2012 [2]:

      “All’idea originaria sono seguiti 10 anni di ricerche scientifiche e tecnologiche, culminati con la realizzazione di alcuni prototipi industriali, funzionanti da oltre un anno, che producono effettivamente energia a piccola scala (circa 0,5-1 MW)”.

      As I translate it, “The [Kitegen] original idea was followed by 10 years of scientific and technological research, culminating with the creation of some industrial prototypes, working for over a year, that actually produce small-scale energy (about 0.5-1 MW)”;

      it appears from that, that at least two Kitegen “prototipi industriali” have been working for at least one year, so I do imagine it should be possible to get actual data by now, about the Maximum Power and Mean Power attained, along with data about the Energy produced by those plants in a given time span, and the observed Capacity Factor..
      It would be interesting to know other relevant data too, i.e. the number of consecutively performed cycles, the continuous-flight time achieved, and the maximum altitude reached.
      If showing actual data is not possible right now, please could you at least confirm (or disprove) the correctness of E. Mearns’ assumptions?

      Thank you.

      Al Mizar


      • Why you asking always the same questions everywhere?
        You always received reasonable answers from many interlocutors.
        Ok, in this case could be useful here, but you are adding confusion because the scaled up KiteGen isn’t an “off the shelf” product but, as clearly stated in our site, it is under industrialization and batch production, sorry you have to wait for the new version fully operative for track records.

        Now you could be fully satisfied with the previous versions outcomes that are fully significant. Moreover, perhaps, if you are aware of the gravity and dimension of the energetic problem, instead to ask us insistently the last minute performances, please ask for public policies in favor of the innovation instead the insane deployment of energetically unproven technologies.

        Said that, I confirm everything, is quite easy reach huge power with altitude wind, less easy to have an equipment able to resist such powers.

        Typically, the behavior expose force increases that follows the fifth power of the wind speed, because the wind (a cube law) plus the increasing flying speeds of the wing itself (a square law).

        For that reason professor Giancarlo Abbate talk prudentially of power and not of energy because he is aware of all the effort we are spending to align the strength of all the kinematic chain in order to avoid breakages, that is a technological/material issue nor any more conceptual.

        KiteGen was fully aware of this problem from the beginning of concept experimentation because I have personally assisted tens of wing explosion with an impressive thunder. After that, we headed the research to investigate ultra-strong materials and dynamic behaviors not any more flying or maneuvering the wing in the air space that is quite trivial.

        The project appeared dead locked until we asked for help to one of the biggest chemical companies in order to develop a very light and semi-rigid wings with the 500kN of tensile strength that is required by the project and also prepare the production of the special UHDPE ropes we adopted.

        The wind gust could suddenly increase the force flowing in the ropes and the heavy drum hosting the reeled ropes have to follow the spin with the same dynamic in order to limit or clamp those forces. The motorized reeling out pulse applied to the drum, to limit the force on the ropes, could reach the full nominal power and a duration of 100ms.

    • Eugenio Saraceno says:

      Some old calculations of mine match with the results reported by Euan even if the calculation logic is a bit different:

      Comparision between windmills and KiteGen stem: approximatively the emergy of the two struttuctures is calculated from their weight , assuming they are made of steel. Moreover it is to be considered the concrete foundation, needed only for the windmill
      3 MW Kitegen is about 30 tons (mainly steel and plastics) + say 10 tons for supports (micropiles to fix on ground, auxiliary buildings and so on). 3 MW windmill is about 250 tons of steel and 1500-2000 tons of concrete.
      One ton of concrete costs 1,76 MWh one ton of steel costs 4,4 MWh. If both materials are produced using petcoke fuel with a 5% overhead due to transport and refination we must consider 4,62 MWh for steel and 1,85 MWh for concrete. Energy intensity of labour is inferred by the per capita energy consumption (3 toe per capita per year in Italy and similar in Europe). 1 toe =11,6 MWh so every maintenance labourer enbeds 35 MWh or 700MWh throughout 20 years. Assuming 8 hours per day of maintenance and operations for both and neglecting the labour energetic cost for construction (by the way windmill construction needs much more labour than a Kitegen):
      Emergy windmill
      250*4,62+1500*1,85+700=4630 MWh

      Emergy kitegen stem
      40*4,62+700=885 MWh


      * lifetime: 20 years for both
      * productivity: 5000 MWh/MW for KiteGen and 2000 MWh/MW for windmill
      * nominal power 3MW for both
      * availability KiteGen: 95%
      * energy needed for plant services KiteGen 5%


      20 y cumulative kitegen net production= 20*5000*3*0,95*0,95=270750 MWh

      Energy Input = 885 MWh

      KG EROEI=305

      Windmill EROEI =16

  2. Peter Lang says:

    In your main article (to come) have you calculated the ERoEI including buffering (energy storage necessary to make the power fully dispatchable)? I suggest, if you don’t include buffering, the ERoEI calculated for KiteGen is misleading and should not be compared with other technologies (this applies to all weather-dependent technologies).

    I doubt KiteGen can become a realistic option for supplying much power, certainly not in densely populated countries with significant air traffic. Occasionally airliners get into trouble and the pilots are so engrossed in trying to solve the problem they fly outside the allotted corridors. It seems inevitable, that sometimes air liners will be brought down by flying into the cable. What’s the EROEI when you include a probability for loss of passenger aircraft? I can’t offer any suggestions on how to calculate this, but it seems it needs to be included.

    • Euan Mearns says:

      Peter, this article includes a 70% hit for round trip to H2 and back to dispatchable electricity. Have you read it?

      • robertok06 says:

        70% is WAY too high!… 70% is probably even too much just for the generation of H2 via hydrolisis, then you have to burn the H2 (alone or mixed with NG) in a conventional thermal unit, which may have a 50-60% max thermodynamic efficiency… so 0.7×0.5=0.35.
        I think this was already debunked back then when the Audi H2 thing was discussed… on this very same blog.


      • Peter Lang says:


        yes, I read it before replying. I saw this:

        A KiteGen – hydrogen generator would still have ERoEI of 355*0.3 = 107

        However, with such an enormous discrepancy from other ERoEI estimates and no attempt to explain the reason for the enormous discrepancy I simply dismissed it. I was trying to, nicely, encourage you to do proper reality checks before posting.

        Regarding the snide comment about “did you read it?”, a similar comment could be made to you and Roger regarding many of your responses to comments.

        • Euan Mearns says:

          Peter, I say that the calculation is based on a number of weak assumptions. But for the reality check:

          Mass of 3 MW turbine = 372 tonnes
          Mass of KiteGen stem 20 tonnes

          Wind speed at ground level = 3 m/s (thats too slow to drive a turbine)
          Wind speed at 2000 m = 9 m/s

          Power increases by the cube of wind speed!

          [2] Power = 1/2*r*A*V1^3

          r = density
          A=area of the kite
          V1 = wind speed

          Wind front for a fixed turbine ~ 8000 m^2
          Wind front for a kite flying the sky ~ 1,000,000 m^2

          With these numbers, its not too difficult to see that the ERoEI may scale up by many factors. The amount of energy and power available is immense. But the challenge is taming and controlling it. An H bomb will also have huge ERoEI but its not normally much use.

    • Charles 16 says:

      Commercial airplanes fly at around 30,000 to 40,000 feet. These kites will go (I believe) 2,000 to 3,000 feet.
      Planning these high altitude kites in areas that are not around commercial and private airports shouldn’t be too difficult.

  3. Willem Post says:


    How many hundred thousand of these 2000 to 3000 ft high kites would we need?
    Based on airline travel, as soon as one gets near the clouds, it becomes turbulent.
    An approaching hurricane on the US east coast would mean reeling in almost all of the kites?
    Having wind turbines is bad enough. Let us not make it worse.
    I think folks will eventually realize about 70% of all energy, not just electrical energy, will need to come from nuclear, including fast breeders, and thorium, with the rest from hydro, wind and solar. Here is a perspective on bio-energy.

    Plant Material Replacing Crude Oil?

    Efficiently harvesting corn requires modern machinery, good soils, fertilizers, various chemicals and adequate rainfall. To replace the Btu value of the world’s annual crude oil production with the same Btu value as corn kernels, about 3.04 billion acres would be required of the 12.14 b acres currently used for food production, of which about 3.40 b acres are in annual crop production, i.e., about 3.04/3.40 = 89% of the world’s cropland would be required for corn. Corn replacing coal and gas would require additional acreage. Also, there is no equivalence, as crude oil, coal and gas require much less energy to produce chemicals for many purposes, than corn kernels to produce, for example, ethanol.

    For the past 200 years, we have lived like kings courtesy of our fossil fuel inheritance. Transitioning to biofuels is like having to get a real job and work for the annual yield, year after year. No more freebees from nature that were just lying around for millions of years waiting to be scooped up.

    Corn crop: 160 bu/acre/y x 56 lb/bu x 7000 Btu/lb x 0.85 = 53,312,000 net Btu/acre/y, equivalent to 9.6 barrels of oil/acre/y.
    World crude oil production replaced by corn = 80 million/d x 365 d/y = 29,200 million barrels/y.
    Land area in corn = 29,200 million/9.6 = 3.040 b acres.
    World land area for food production = 18,963,881 sq mi x 640 acre/sq mi = 12.14 b acres, of which 28%, 3.40 b acres, is in annual crop production.

  4. gweberbv says:

    Too good to be true. But even if the KiteGen system would achieve only 10% of the ERoEI calculated here, it would still be superior to most wind turbines. I really wonder why not one of the crazy billionairs around the world did not already invest a few millions in this technology. Just for the fun of it.

    • Euan Mearns says:

      Google just bought Makani, a KiteGen competitor for $10 million. And Bill Gates is interested in the general technology class.

      • Google bought Makani back in May 2013. It’s part of Google X under Alphabet now.

        I don’t think KiteGen is really interested in selling out to some Billionaire but for X-Wind, E-Kite, Skysails Power and the odd 20 other kite type high altitude startups the best buyer would be Richard Branson if you ask me.
        He’s a kiteboarder, talking about RE for Caribbean islands…would be rather fitting.

        • @Jenny,
          the first things that possible buyers look for, is the full patent coverage and knoe-how. So no hope for newbie.
          KiteGen has successfully completed his planned path in both conceptual and technological sides, the status of the art is that the KiteGen scientist-designers have finalized their technological package with an impressive amount of validated idea-development loops, focused on fully featured sub-assemblies and pushed deeply towards the industrialization and production needs.
          The productive investment part require very small funds if computed in material, production processes and machinery.

          Instead the investment to proceed firmly: the needed human resources; skill recruitment; specific formation and technology update and spreading. Is still the heaviest part and unfortunately it is not only money that would be easy, but also time.

    • GeoffM says:

      Perhaps because it would need fewer turbines to meet govt. targets therefore the big capitalists would receive fewer subsides.

    • John says:

      This looks like a promising technology, I too don’t understand why it struggles so much to find some financial partners (if money are the problem).

  5. Eugenio Saraceno says:

    @Wilem Post
    You forgot the energy subsidy needed to grow the corn crop and the energy input to the biofuel manufacturing process; it is a figure greater than the energy embedded in the crop itself, especially if we consider high yeld corn crops. Thus the EROI is <1 it is an energy sink, not a source.
    There is a famous paper of Pimentel's on biofuels EROI. I just cite a statement from it:
    "The total energy input to produce a liter of ethanol is 7,474 kcal. However, a liter of ethanol has an energy value of only 5,130 kcal"
    Please find the complete paper at

    • Willem Post says:


      I am familiar with Pimental. He is an outlier.

      EROEI = 1.25 is more realistic. Again, it depends on the boundaries. If one adds CO2 emitted by disturbing the land, and other such factors, then it becomes closer to zero.

      A modern, industrial society, with all the bells and whistles, needs an EROEI of about 14 to sustain itself.

      Under- and undeveloped countries can get by with an EROEI of about 7

      • Eugenio Saraceno says:

        @Wilem Post
        I agree it depends on a number of constraint as the climate and the fertility (wet climate fertile soil=less irrigation and fertilizer=less energy subsidy and so on)
        I agree that even if >1 no civilization can exist on such low EROI

  6. Javier says:

    Do these things crash from time to time? I mean everything that goes up must come down. That could certainly affect the ERoEI calculation.

    • Euan Mearns says:

      As you will see in Mondays article there are two main classes of kite power. One where the generators are in the air. The other where the generators are on the ground (KiteGen). In the former if you crash you lose a lot. The KiteGen kite is cheap and light.

      I believe one of the enabling technologies today is solid state motion sensors that greatly enhances flight control. But this new generation of kite still needs to be tested. It works in Massimo’s flight simulator.

  7. stone100 says:

    I’m very enthusiastic about kite power. My guess is that the economics may not be as fabulous as the EROI simply because they may be very labour intensive (lots of sewing etc). BUT much of what people cheer about with Green stuff is jobs -so perhaps this is no bad thing.

    • Rather glueing than sewing.
      It’s a composite wing, somewhat semirigid in the case of KiteGen.
      Ampyx says their rigid wings need about 10% of the material of one turbine blade from a matching turbine. So there are more jobs in blade manufacturing today.

  8. Pingback: Kite Wind / KiWiGen (generatore eolico alimentato dal movimento di aquiloni): QUI TUTTE LE DOMANDE E DUBBI - Pagina 51

  9. Phil Chapman says:

    1. The net energy payback time (NEPT) is a fraction of the useful life equal to the inverse of the ERoEI. If a system has a useful life of 25 years and an ERoEI of 50, the NEPT is 6 months – i.e., you have to wait 6 months after it is in service before it generates any net energy. The important metric is however the project energy payback time (PEPT) – i.e. how long you have to wait from the time the project starts before the system energy output exceeds the energy invested. The PEPT includes the time taken to organize the project, raise the money and build the system. Since this is likely to be more than 6 months, I don’t understand why it is worth striving to achieve ERoEIs much above 50 (including any losses in energy storage). Your Fig 1 leads to a similar conclusion.

    2. I am no fan (pun intended) of wind energy, but if you are going to compare the KiteGen to terrestrial windpower by estimating the ERoEI on the basis of mass, you need to consider what could be done to make terrestrial wind turbines and towers less massive (and thus presumably less energy intensive).

    Here is a fanciful idea (pun intended): let’s attach the wind turbines to trees instead of steel towers, eliminating most of the (artificial) energy invested. As an example, the Colombian wax palm Ceroxylon quindiuense grows to a height of 45 m (and sometimes 60 m) and has no branches except the topknot. See for pictures of this amazing plant. It is native to the high Andes and thrives in cool but not freezing climates (e.g. Northern CA). It would do OK in UK Plant Hardiness Zone 9 (the west coast of Scotland and especially Cornwall).

    There may be better trees for the purpose (and we could probably genetically engineer optimal trees for wind-turbine support) but the wax palm will do for a rough estimate.

    This tree could not support the 3 MW Vestas V112 you use for comparison, both because the blades are too long (54.7 m) and because the drag in any significant wind might knock it over. For an estimate, I assume blades 10 m long.

    For the same wind, the power produced is proportional to the swept area (i.e., the square of the blade length), so my guess is that the 10 m. system would produce 100 kW. The three glass fiber/carbon blades of the V112 together weigh 11.9 metric tons (MT) and the mass is probably proportional to some power of the length (greater centrifugal force, increased bending moments, etc.) so the combined mass of three 10 m. blades is probably less than 1 MT.

    Yuneec International in China (whose principal products are small drone multicopters) claim ( that they produce a brushless DC electric motor meant for light aircraft that puts out 60 kW and weighs 30 kg (or 2 kW/kg). It is probably possible to build a generator with a similar power to weight ratio, so my guess for the mass of an optimized generator producing 100 kW, including the housing, is only of order 100 kg.
    With the addition of wiring, etc, it looks as if this tree-mounted system might weigh less than 2 MT.

    Matching the output of the V112 would require 30 of them, for a total mass of less than 60. This is a lot better than your quoted figures of 372 MT and an ERoEI of 18. Other factors being equal, it suggests an ERoEI >110 (or >33, including losses in hydrogen storage). That’s still not great, but it’s better than your estimate.

    3. Now consider the KiteGen. First, it will never be built on any significant scale because it would be an unacceptable hazard to aviation. Second, it might conceivably be possible to control a single kite string, 10 or 20 km long, by aerodynamic controls on the kite, but flying a number of them in relatively close proximity (as in the KiteGen Carousel) in any kind of turbulence is the stuff of nightmares.

    Even if we neglect those problems, the Fagiano ERoEI makes no sense.

    a. On average, the wind at altitude is more constant than at ground level, but “average” is not the right measure. Energy storage can even out brief fluctuations, but wind systems must be designed to handle days, weeks or maybe months of calm. The fact that such outages may be less frequent in a KiteGen than in a ground-level system doesn’t help because the system must still handle the worst-case doldrums.

    b. There is surely no doubt that the generating equipment on the ground would be heavier than the generator in a conventional wind turbine.

    c. It is inconceivable (at least to me) that the kite and the long strings in a system generating 3 MW would be lighter than the 11.9 MT of the blades on a Vestas V112.

    Thus it appears that the only possible reason for a higher ERoEI for a KiteGen is that it avoids support towers. In the carousel version, how much energy must be invested in building the track and the maglev systems it needs, compared to that in support towers for conventional wind turbines? Trees, anyone?

    My conclusion is that KiteGen is yet another wind fantasy (pun intended), not worth further consideration.

    • Trees? Really?
      We build 150m timber towers for wind turbines though.

      C. makes no sense at all. The kite emulates only the fast tip of the turbine.
      The wing of Ampyx is 10% of one blade of a similar rated turbine.

      Planes can be avoided . When something flies along the lines drop to under 200m or get reeled in completely.

    • Euan Mearns says:

      Phil, you sound rather sceptical 😉 I have never paid much attention to high altitude wind before believing the concept to be rather bonkers. But after Massimo asked me to look into it there are number of reasons I believe to at least give the technology a hearing.

      The first is that power increases with the cube of wind speed:

      [2] Power = 1/2*r*A*V1^3

      r = density
      A=area of the kite
      V1 = wind speed

      So there is an enormous advantage managing to catch more KE at altitude. The second is that the devices that catch that energy are much lighter, smaller and cheaper than turbines (less embedded energy). Combined these features lead to the high ERoEI.

      You say that a more sensible approach is to reduce the mass of conventional turbines, while in fact the exact opposite has happened as they have tried to reach that extra power that lies a little higher up.

      Figure 3 The evolution of hub height with time.

      Setting aside the environmental considerations, the main problem with conventional wind is a combination of cost and intermittency. If it was dirt cheap and intermittent then the low price could be used to solve the latter. As things stand, wind is parasitic.

      There are some political and social realities to consider (although the political reality in the UK just blew up and might do so also in the USA this fall). We live in a world where the majority of world leaders believe that CO2 emissions need to be reduced. The options we have are rather limited. Solar or supernova power. There’s also a load of billionaires out there, whizzing around in private jets, who believe the same. High altitude wind will be tested to prototype “power station” level.

      You have a long association with space based solar which I also think is bonkers. But you have in the past laid out the energy balance argument for pursuing it. If the entry level cost wasn’t so high, I’m quite sure that it too would be tested one day.

      Meanwhile, in the UK we are happily closing down coal fired power stations, our oil and gas industry is going to the wall and we discuss the high cost of nuclear.

    • @Phil Chapman

      c. It is inconceivable (at least to me) that the kite and the long strings in a system generating 3 MW would be lighter than the 11.9 MT of the blades on a Vestas V112.

      our data:
      the Wing weight is 250kg@130sqm and the suitable ropes full extended are 1000kg@2500m.(500kg each rope)
      The developed wing traction is by design 500kN (250kN each rope)

  10. John Harrison says:

    Has anyone thought of the problem of bringing 3MW of power down to ground level. The electrical cables could have a mass of 50 metric tonnes. Work it out! Start with #2 AWG for 200A. The diameter of #2 AWG is 6.5 mm.

    • OpenSourceElectricity says:

      Siple: you don’rt bring it down, in case of kitegen and similar. The generator is on the ground. But even with a flying generator – with different mass etc involved than in this discussion, there is the air as insulator between, and you could use some m distance between the two wires holding the flying generator in place. So you can choose the voltage to transfer freely up to 400kV. (3,2m distance between wires required)
      So with 10kV there would be 300A to be transported, with 100kV 30A would be required. Since the flying generator would include a variable speed turbine, it would also include a inverter which can transform voltage at high frequency (>>10kHz), which aoloows 3MW to be transformed in a tiny transformer.
      30A would reqire less tha 2,5mm² of copper in such a arrangement. Equivalent something around 15mm² of Iron, a higher diameter will be needed anyway to keep the generator in place. So it should be possible to dimension the wires to hold the generator in place, choose a appropriate voltage, and transfer the power down the holding wires without any further wires needed for power transfer.
      The mass of 2x 15mm² Iron would be 250g/m so with 1500m height this would be 400kg. It will be more heavy to keep the generator in place.

    • I was wondering about this as well though I have no idea how to calculate the thickness of the cable.

      For me though the weak point is probably the insulation.

    • Euan Mearns says:

      With the KiteGen, the generators are on the ground so the ropes are non-conducting. The ropes are made of Dyneema, a very strong and light fibre. 10 mm rope can stand 11 tonnes of force and the weight is about 200 kg / km.

      In terms of mass and drag, the ropes are a significant component of what is up in the air. More on this on Monday.

    • Eugenio Saraceno says:

      @John Harrison
      Good point but it is not an issue for KiteGen as it has a ground based generator. It is an issue for Makani.

  11. Olav says:

    Have been looking around and still do not know how this thing work..
    A winch on ground connected to a generator/motor which reels in and out I would assume?
    Only reeling out can produce power. As cable lenght is limited so reeling in is part of the operation.
    Producing 3 MW while reeling out at 1m/s requires a very strong cable.

  12. Leo Smith says:

    I am one of the people who attended the first Isle of wight festival.

    I took with me an ex miltary signals* kite and around 300 meters of line, with the original rotted linen replaced with yellow nylon.

    For 3 days it hovered over the campsite.

    Then the wind fell overnight.

    I got the kite back but the line was ruined forever.

    Does anyone really think that the modern equivalent of barrage balloons, with high voltage wires reaching up thousands of feet would be allowed in civilian airspace? Or that a structure big enough to generate reasonable power would not represent a very dangerous hazard if the string broke? Or as deliberately cut? Or the wind dropped?

    IN the end EROEI is only one of many criteria a viable energy project has to meet.

    All one can say about EROEI is that if it fails to exceed unity, the technology is not even worth analysing any more for mainstream power production..

    The real issue is can it succeed commercially? And is it acceptable to an informed public? Because that tends to incorporate EROEI and many many other things in the equation.

    *used to pull an antenna up high

    • Euan Mearns says:

      For 3 days it hovered over the campsite.

      Well that’s encouraging 🙂 And if you had a weather forecast you could have reeled it in and saved your string 🙂

      • This is a common misunderstanding, wind is important for the energy production not for the wing control, the rope tension provide the power to fly the wing in all conditions. If the wind fall to zero the robot slowly reel-in the ropes in order to maintain enough lift and flying speed. The wing behavior is always precise and fully deterministic, no solution of continuity between no-wind to strong wind. If the loss of wind is permanent the wing descend navigating smoothly up to be hanged to the robot arms without touching the ground. When somebody ask us about the frequency of wing crash is because he is joining the wind losses with a loss of control. really, it is a wrong prejudice.
        The specific reliability of a technological mature machine is much better than civil aviation, because the KiteGen wing performs with a tethered fly and the stall condition, that is a plague in aviation, is unlikely with KiteGen.

  13. John Oneill says:

    Bringing the kite down in light winds shouldn’t be too much of a problem. The hard bits would be getting it up when there’s enough wind at altitude but not much on the ground, and getting it down when it’s too strong at altitude, and the turbulence at ground level is really kicking in. Both those scenarios are going to happen a lot – the wind at altitude varies by about two orders of magnitude, from ‘ Not enough to lift the gear ‘ to ‘ Enough to break just about anything ‘ – bearing in mind that the power of the wind scales with the cube of the velocity. Usually in light winds there’s a bigger difference between ground level velocity and high altitude, than when it’s strong – the wind gradient gets less, exactly the opposite of what a Kitegen operator would want. The great majority of air accidents happen on take-offs and landings.
    Comparing the mass of a kite to that of a conventional turbine is misleading – most of the bulk of a Danish-style WT is steel and concrete, with a cost per kilo comparable to a bridge, whereas a high percentage of the Kitegen gear is more like high-tech aircraft technology, with cost to match. If it is achieving near-baseload capacity factors, the hours of airtime will be even higher than a passenger jet – much higher than general aviation has to do – and the constant high frequency cycling between pulling up and getting pulled down would stress it more like an aerobatics plane than a GA flying taxi.
    If climate change is seen as being enough of a problem to mandate 100% zero carbon energy, general aviation will have to justify its emissions. As the wartime ads said – ‘ Is your trip really necessary ?’
    Advanced nuclear also promises to give results ~100 times better ( per kilo of uranium or thorium ) than the current light water reactor, but renewables advocates scoff at this as unproven pie in the sky. There’s a bit of truth to that argument, but sodium cooled fast reactors have demonstrated far more power production historically than any of the high-altitude pioneers, and so did the molten salt reactor experiment.
    Off topic, that palm tree looks like one crazy freak of nature. The canopy of a sequoia forest, a hundred metres up, gets the same sun per hectare as a flat paddock, but evolution forces them all to go giraffe. The palm trees, though, look to be more spread out – what’s making them get so lanky?

    • Euan Mearns says:

      John, I agree with most of this. I think the KiteGen is comparable to the nacelle. The support tower is more like a bridge and I didn’t include the foundations. Some of this is accounted for by going from 24 to 40 MWh/tonne.

      And I agree that air traffic considerations should be addressed down the line. Lets find out if the technology works and if it does, then decide on humanity’s priorities.

      Palm trees – and interesting question that I’ll allow someone else to answer.


      • KiteGen intend to convert the wind kinetic energy in active power, nor statically fly an uncontrolled kite. The strong wind Is useful, will be exploited to produce more energy, it cannot break about anything, because the system is designed to reel-out the ropes maintain constant the force and the wing itself “see” always the same reasonable wind.

        To lift the wing, about 3 m/s of wind are sufficient that is less than the European mean, this allows to safely takeoff 50% of the time. The wing can fly for months in altitude.

        In Italy, we obtained the full permission to fly up 5000m, aircraft recently moved above the 8000m.

        The wind gradient is welcome, is the reason to go high, however it is not the only kiteGen advantage, the huge wind front the other opportunity

        Turbulence is meaningless without a phenomena dimension, ground wind rotors could affect the wing but are rare and localised were the ground shape allows them, i.e. mountain crest.

        The composite wing weight is only 250 kg, the Wind turbine blades 30-60 tons. The rest of the KiteGen could be compared appropriately to the wind turbines.

        Yes, I think this trip is highly necessary because the coal is the last remaining source of energy available with an ERoEI suitable for civilization.

        The comparison with molten salt fast reactors I hope it is a joke, the initial cost of Superphoenix was about €10billion for more or less 10TWh of total production €1000/MWh. It was clearly an energy sink not a source. French and Italians to earn €10billion consumes 40TWh, according the countries energy intensity.

        The fast reactors have a cooling system constantly over the thousand degree the more optimistic expected design life is less than 5 years, insufficient to reach both the energetic and economic breakeven.

  14. Eulenspiegel says:

    The main wear I see here is the wear of the cables. I think they have to be replaced in regulary intervals.

    I know only the cables from tower cranes, they have a strong weardown. With non-steel-cables you have additional weardown with UV-radiation. Running at full power the strain at the cable drum should be very high – I think here is the key to the reliability of this technique. I don’t think a cable can work the 20 years lifetime of this interesting concept.

  15. Volvo740 says:

    1. It seems like, since electricity generation is not the problem – it’s an eventual lack of liquid fossil fuels that is – this stuff is solving the wrong problem.

    2. My second thought is that – let’s wait until we have 1000 in production. At that point this technology has perhaps started to replace 1 nuclear reactor. Only 400 to go.

    3. Scale. Land costs………….

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