High Altitude Wind Power Reviewed

This post reviews the weird and wonderful world of high altitude wind power. It looks into the reasons for wanting to go high, explains tethered flight and explores the main competing technologies of 1) airborne generation (Google Makani) and 2) ground based generation (KiteGen) and compares their strengths and weaknesses.

Executive Summary

  • High altitude (500 to 2000 m) wind power machines are still at a relatively early stage of development with the first tests run about 12 years ago.
  • Over most of the land surface of The Earth, average wind speeds at surface are below 5 m/s, well below the velocity required for conventional ground-based wind turbines to operate. Hence traditional wind turbines can only be deployed in selected areas where surface winds regularly blow strongly and steadily.
  • 250m above the surface winds blow more strongly and steadily providing usable wind speeds over most of the land area of The Earth. As a rule, the higher you go the wind speed increases. The challenge is how to access this wind to generate electricity.
  • Many companies are engaged in developing prototypes. Most are based on the principle of tethered flight where an aerodynamic kite flies at altitude tethered to the ground by ropes. The wind keeps the kite aloft where the flight speed is related to the aerodynamic efficiency and wind speed. In turn, power is linked to flight speed.
  • These kites fly cross wind, that is in a direction that is transverse to the wind direction.
  • There are two main families of tethered kite. One where a simple kite flies a figure of 8 pattern in the sky drawing rope from a ground-based drum that turns a generator. The second is based on kite-like gliders that carry generators on board where the flight movement turns rotors generating electricity that is transmitted to ground via a conducting tether.
  • There are three obvious risks associated with this technology 1) the risk of crash, 2) the risk to aviation and 3) the risk to birds. Much of the current research and development is going into flight control systems to mitigate the risk of a crash. If the technology can be proven to work then it promises to deliver cheap, subsidy free renewable energy in which case governments may clear selected air space for technology deployment.

These risks are balanced by a number of clear benefits of accessing high altitude wind:

  1. Wind power can be accessed at altitude where wind speed at surface is insufficient to drive a traditional turbine.
  2. The wind blows more steadily at altitude reducing intermittency.
  3. Power increases by the cube of wind speed. Thus going a little higher may produce a lot more power.
  4. High altitude devices are significantly less massive (20 tonnes for 3 MW) than traditional turbines of equivalent rating (417 tonnes of steel and 902 tonnes of concrete). Hence, high altitude devices will be significantly cheaper to make and may produce subsidy free electricity.
  5. The low mass translates into less energy used to create high altitude wind capture systems. Back of the envelope style calculations suggest ERoEI >300 for a KiteGen stem device. This is massive compared to other forms of renewable energy apart from hydro and offers scope to mitigate for intermittency by sending some of the power to chemical energy storage.
  6. The wind front of a ground-based turbine is defined by the area swept by the turbine blades. A 3 MW turbine may sweep 8000 m^2. This limits the amount of kinetic energy a turbine can extract from the wind defined by Betz’ law to be 59.3% of the available kinetic energy. In comparison, because a kite flies across the sky, a massive wind front of about 1,000,000 m^2 is available (1500 m rope length, 50 degree elevation).


Several weeks ago I received an email from Massimo Ippolito, the founder of KiteGen, enquiring about advertising on Energy Matters. KiteGen are a world leader in the development of high altitude wind technology. While I was delighted at the prospect of selling some advertising space, the enquiry came with some strings attached. Massimo wanted me to write an article on high altitude wind power. I explained I knew nothing about this having not followed the technology, believing it to be a bit ‘bonkers’. Massimo confided that everyone thought that to begin with.

And so I did a little research and found some information that caught my attention. For starters, there are many companies active in this arena and one of them, Makani, had recently been bought by Google for $10 million. Secondly KiteGen claimed that high altitude kites had high energy return on energy invested (ERoEI) >300. This was the real hook, because if true, this would make high altitude wind power dirt cheap and this could substantially ease, or remove altogether, issues with intermittency (see Appendix 1 on ERoEI). And finally I came across a very unkind article called Airborne Wind Energy: It’s All Platypuses Instead Of Cheetahs that was published in Clean Technica. It struck me as rather odd that a Green Tech blog should publish an article that focussed only on the potential weaknesses of high altitude wind, totally ignoring the strengths. Could there be any truth in the notion that Green Tech does not want a cheap renewable solution?

This post provides an overview of high altitude wind covering basic principles, the main types of competing technologies, ERoEI and some of the basic physics.

Why Go High?

The primary reason for seeking wind at high altitude is that the wind tends to blow faster and more constantly the higher you go (Figure 1)(see also Figures 6 and 7). Add to that the nominal power increases with the cube of wind speed and you will understand the attraction of reaching for the sky.


r=air density
A = area
V= wind speed

The reason for lower wind speeds at surface is wind shear between the circulating atmosphere and the surface of The Earth. Surface topography and features break up the circulation. It is useful to imagine the flow of a river that will normally be much slower at the edge than in the middle where the main volume of water can flow unimpeded by boulders and branches etc.

Figure 1 Average Dutch wind speed with altitude. At 2000 m the wind blows on average three times as fast as at ground level and given that power increases with the cube of wind speed, 27 times the power is available 2000 m up. High altitude wind devices are all about trying to access that additional high altitude power. While there is often talk about accessing wind in the Jet Stream 10,000 m high, the focus at present is to tap into the layer between 500 and 2000 m. Data for chart provided by Massimo Ippolito.

This is the reason that ground based turbines have grown taller and taller as they reach upwards to access that better wind resource (Figure 2). But this has also been the Achilles heel of wind turbines since as they have grown taller they have grown more massive and ever larger quantities of steel and concrete (embedded energy) are required in their construction. A three MW turbine (Vestas 3112) contains 417 tonnes of metal in the tower and nacelle and 902 tonnes of concrete in the foundations.

This provides the second reason to reach for the sky since the designs of the high altitude devices are much lighter than turbines they promise to deliver much higher energy return (ERoEI) and lower cost electricity. Hence the opportunity is to access greater power using lighter and cheaper devices.

Figure 2 The evolution of wind turbine size. In 1995 the hub height of a 750 kW machine was 50m. In 2015, the hub height of a 6 MW machine had grown to 120 m. Image from Makani.

Figure 3 The evolution of hub height with time.

Figure 4 The evolution of wind front (area swept by rotor) and power rating with time.

Ground based turbines have an operational wind speed range of approximately 3.5 to 25 m/s (these numbers will vary with turbine size and design). 3.5 m/s is the cut-in speed where the rotor is turning with sufficient force to drive the actuator (the generator) and 14 m/s the speed at which the turbine reaches its maximum power rating (Figure 5). Turbines may continue to operate beyond 14 m/s but will not produce any more power. And when it gets too windy at say 25 m/s the turbine needs to be shut down. These features define the all too familiar intermittency issue with wind. No wind – no power, too much wind – no power.

Figure 5 Wind speed versus power for a “typical” turbine.

14 m/s = 50.4 km/h = 31.3 miles / h

Makani has produced a couple of nice wind speed maps of the Earth (Figures 6 and 7). I live in windy Scotland and take wind for granted and was therefore surprised to see that windy places are the exception rather than the rule. Bearing in mind an operational range of 3.5 to 14 m/s for ground based turbines, Figure 6 shows that ground-based turbines are quite simply not viable in most areas. Climb to 250 m however and a useful wind resource can be found over most of the inhabited land mass of the planet.

Figure 6 Areas of Earth where a sufficient wind resource to drive wind turbines are found at surface (hub height 100 m). Map from Makani Power.

Figure 7 Areas of earth where a useful wind resource is found at an altitude of 250 m. Map from Makani Power.

However, these average wind speed maps do not tell us how steady the wind is blowing. In his PhD thesis, Lorenzo Fagiano [1] provides an estimate for capacity factors at 500 m altitude in Italy and Holland which average to 0.54 (Appendix 1). Altitude therefore reduces but does not solve intermittency alone. To solve intermittency completely depends upon the argument made for high ERoEI (Appendix 1) where a portion of production can go to chemical storage, for example hydrogen or synthetic fuel, that can be used for generation when the high altitude winds drop. The round trip efficiency of storage is of the order 30%, hence a significant portion of production may be lost, but that is the price of dispatch. The anticipated lower cost of high altitude wind makes this acceptable.

The Competing Concepts

Exploiting high altitude wind power is an innovation space still at a very early stage of development. For example major player The Kite Power Research Group of Delft University of Technology initially tested a first experimental prototype of 3 kilowatts (kW) traction power in 2007. While KiteGen tested their first 30 kW prototype a year earlier in 2006. This is only 10 years ago.

Figure 8 Some of the main players and sponsors of high altitude wind power technology. Image credit KiteGen.

These innovators have filed dozens of patents and this has driven innovation in a number of bizarre directions as new entrants seek to secure a toehold in what may develop into a multi-billion dollar industry. This reminds me of the early days of aviation (see video 6 at the end of the post).

All of the main-stream electricity generation concepts involve tethering a high altitude airborne device to the ground. The basic physics principle is to harness the kinetic energy of the wind and convert some of this kinetic energy to electricity. With dozens of players I’m going to summarise the three main concepts:

  1. Lighter than air devices that lift a turbine to altitude using a helium-filled balloon (Air Gen) (The Altaeros Blimp)
  2. Kites that fly through the air with rotors and generators attached making more electricity the faster they fly (Air Gen) (The Makani Kite)
  3. Kites that fly through the air with ropes that uncoil from a drum on the ground that rotates and drives an actuator (Ground Gen) (The KiteGen Stem)

The blimps are not serious contenders for grid-scale generation but are more intended for niche applications. The kites (2 and 3) are both serious contenders with different strengths and weaknesses.

The Altaeros Blimp

I will kick off with one of the most unlikely entrants which comes from US company Altaeros. Their concept is to simply lift a rotor-based turbine into the sky using a helium filled balloon. The balloon is tethered to a ground station by two tethers one of which must obviously be conducting to transfer power.

Figure 9 The Altareos lighter than air generator.

Figure 10 Altareos reaching for the sky.

Video 1 2 mins 19 secs

I have not found any detailed presentations from Altaeros nor have I found the power rating of their turbine, but it doesn’t look very large. Somewhat confusingly they call their balloon a BAT which I have to guess means Balloon Airborne Turbine?

This concept does not really capture the power of the wind in the way that a kite does (see the Makani and KiteGen videos below) and one can envisage in a strong wind that the device would get blown towards the ground losing any advantage that altitude might offer.

Reading the Altaeros web site I get the feeling that this is not a serious entrant for full scale power generation but it may instead have niche applications:

  1. Power to remote communities
  2. An elevated platform for telecommunications systems
  3. An elevated platform for defence surveillance systems

The Altaeros BAT has the advantage of being simple, and mobile and it may turn out to be the first commercial generator of high altitude wind but I don’t see it replacing nuclear power baseload any time soon.

The Makani “Quadracopter” Kite

Makani is Hawaiian for wind and was founded in 2006 by Saul Griffith, Don Montague, and Corwin Hardham. Makani is interesting, partly because of their technology concept but also because long-term supporter, Google, acquired the company into Google-x in 2013 for an undisclosed sum rumoured to be $10 million. If you are a tech company committed to reducing CO2 emissions through renewable energy innovation, then high altitude wind power is at the top of most investor’s shopping list.

Makani won the competition for the most avantgarde device that is a hybrid kite / glider (Figure 11). Makani have a simple but informative web site and several informative videos two of which are linked below. Make no mistake, this is a serious high tech venture aiming to capture industrial scale energy from high altitude winds. Whether or not it can be made to work is of course another question. You just have to watch the Makani kite whizzing round in giant circles to get a feel for what might go wrong (Video 3).

Figure 11 The Makani kite. For take off and landing, the generators turn into propellors enabling the kite to hover like a helicopter.

Video 2: 5 mins 23 secs

Video 3: 6 mins 17 secs

The Makani concept is a glider tethered to the ground and so when the wind blows across the aerofoil this produces lift that may keep the glider aloft indefinitely for so long as the wind blows strongly enough. At this point I need to introduce the concept of flying cross wind. To understand this you really need to watch the video linked above where you will see the Makani flying at high speed in giant circles in the sky transverse to the wind direction. Electricity is generated by the rotors linked to actuators and is transmitted to the ground via a conducting tether. It is conceptually easy to understand how flying faster will generate more power. And at this point it is worthwhile introducing a second equation that links flight speed to wind speed and aerodynamics:

flight speed = wind speed * aerodynamic efficiency

The aerodynamic efficiency is the ratio of lift to drag of the aerofoil + tether rope. The drag of the Makani kite is also increased by rotors that will slow the flight speed and reduce power but it is the braking of the flight that at the same time produces power.

Figure 12 The Makani concept emulates that of a wind turbine but can reach much higher altitude and generate more electricity using a lighter device.

The Makani system is comparable to the motion described by the tips of a turbine blade but has the advantage of being much lighter. And not being constrained by the height of the tower it can fly higher to access faster winds.

Some vital stats gleaned from the videos includes a 1 MW Makani will weigh about 1/10th of an equivalent turbine (10 tonnes versus 100 tonnes) and will cost about 1/2 as much. The flight speed is 100 mph (67 m/s).

Saul Griffith, one of the founders, provides an audacious vision in Video 2.

Figure 13 A 230Kw Makani would be the size of a Cessna.

Figure 14 A 1.3 MW Makani would be the size of a Gulfstream.

Figure 15 A 6MW Makani would be the side of a Jumbo Jet.

Figure 16 Plans for a 600 kW Makani armed with 8 turbines.

Conceptually I have problems imagining a kite the size of a jumbo jet whizzing around the sky but can easily imagine the mess and loss of capital that would follow should it crash. But one of the big plusses for Makani is that the rotors can quickly be turned into propellers providing the option of powered conventional flight and the ability to hover giving control over take off and landing.

The KiteGen Stem

KiteGen was founded in 2007 by Massimo Ippolito. The venture began as a hobby flying kites to see if electricity could be generated. In 2006 the first prototype was tested. This was a truck mounted with 30 kW nominal output using a fabric sports kite at low altitude. The first patent application was filed in 2003 jointly with others including the University of Delft and the first patent granted in 2009.

The essence of the patent that underpins KiteGen technology today was a kite or aerofoil attached by two ropes to a control system on the ground where varying the forces on the two ropes both controlled the kite and drove an electrical generator located on the ground.

Figure 17 One of several patents linked to high altitude wind power owned by KiteGen.

Figure 18 provides a simplified view of the basic technology comprising a kite, two ropes that wrap around two drums located on the ground. As the kite is pulled up and away by the wind, the drums rotate individually generating electricity. Figure 18 shows that the kite is fitted with motion sensors that communicate with the kite steering unit (KSU) on the ground.

Figure 18 Simplified view of the KiteGen showing a kite attached by two ropes that are individually wrapped around drums anchored to the ground. When the kite flies away from the ground station the ropes spool out turning the drums that turn a generator. Graphic from ref 1 figure 2.3.

Alert readers will grasp this simple concept but will wonder how the kite is recovered when it reaches the end of its ropes. The answer to this is given in Figure 19.

Figure 19 The KiteGen flies across the sky and away from the ground station tracing figures of 8 patterns. The power produced is a function of the force on the ropes and the speed at which the ropes unwind the drums. The KiteGen is designed to maintain a uniform force on the ropes and so power varies with wind speed and reel out speed (Appendix 3). Graphic from ref 1 figure 4.12.

Figure 20 Schematic layout of the KiteGen stem showing the main components.

Figure 21 Turin, 26th April 2016. Rope drums and actuator on a real KiteGen. The actuator (generator) is the black drum to the right of the yellow label. This prototype is being used to perfect the layout design and components testing.

In keeping with most groups testing kite power systems, the KiteGen flies in a cross wind pattern figure of 8. The aerofoil shape of the kite generates “lift” as it flies with tremendous forces transmitted to the two ropes (up to 20 tonnes per rope). The kite flies away from the ground station tracing out figures of 8 in what is called the power or traction phase (Figure 19). At the end of its ropes, the kite is manoeuvred into an aerodynamic neutral position where it loses all of its lift and the ground generators turn into electric motors to recover the kite at tremendous speed to its starting position in what is called the recovery phase. Recovery consumes only a small fraction of the energy used in the power phase (Figure 22, sideslip recovery).

Figure 22 Left electrical output (kW), right rope length (m) from a 42 minute test flight. The first half of the test shows the kite gaining altitude, but also generating electricity as the ropes unwind. The kite then reaches its target altitude of 1400 m for a rope length of 2000 m (45˚ elevation) and switches to the yo-yo operational mode, flying out to 2,500 m before being pulled back in. In pink is power consumption used to pull the kite back and shows the difference between doing so in full power wing mode and using the side slip manoeuvre. Clearly pulling the kite back without losing lift will consume as much energy as is produced. Click chart for a large version.

The KiteGen is furled into a wind neutral position using a side-slip manoeuvre that is also patented by KiteGen. This is best understood watching Video 4 below.

Video 4 4 mins 47 secs. Note this video switches between animation and real flight footage. The sideslip demonstration comes in at about 2 mins 20 secs.

Video 5 6 mins 28 secs. Flying figures of 8 and generating electricity.

It is only the patented two rope system that can perform the patented side-slip. Competing systems that use one rope have developed their own manoeuvres that are aerodynamically less efficient. In other words more energy is required for the recovery phase.

This operational mode is called the yoyo configuration and produces electrical output as shown in Figure 20. With several KiteGens operating together the yoyo cycles can be adjusted to eliminate the intermittency.

One aspect of this operational mode that it is important to grasp is that most of the power is generated by the aerodynamic lift of the kite. The faster the kite flies in its figure of 8, the more lift is generated transmitting more power via the ropes to pulleys, drums and generators on the ground (Figure 19). Equally the aerodynamic efficiency of the kite determines how much force is transmitted through the tethers to the ground.

Figure 23 The operational mode of the KiteGen aims to maintain a constant force on the ropes (the nominal force) (another KiteGen patent). As shown here 250 kN total for a 50 m^2 kite. For the 120 m^2 power wing (see below) the nominal force is 300 kN (150 kN per rope). For the 120 m^2 power wing to reach the nominal force a wind speed of 5 m/s is required. When that wind speed is exceeded the ropes begin to reel out and electricity is generated. The reel out rate continues to increase with wind speed until a reel out rate of 10 m/s is reached (wind speed = 15 m/s) at which point the KiteGen has reached its nominal power rating of 3 MW. The system aims to maintain the nominal force and power rating by adjusting the position of the kite in the sky.

Aerodynamic efficiency is defined as the ratio of lift / drag, some examples are given below.

Sport kite ~ 6
Jumbo jet ~ 12
KiteGen power wing ~ 28
Glider ~ 70

All of the tests conducted to date by KiteGen, and other groups pursuing similar concepts, have been made using small fabric kites. But fabric wind surfers kites are not suited to commercial power generation. KiteGen are now at the stage where they have designed and built a 120 m^2 semi-rigid composite material power wing that is enormously more powerful than the sports kites used before. The prototype is nearing completion awaiting first test flights in 2017 (Figure 22).

Figure 24 The 120 m^2 power wing prototype manufactured on-site by KiteGen. It is a semi-rigid composite construction designed to be light and strong. The core is honeycomb paper covered in fibreglass. The leading edge is milled by a robot from a large block of polystyrene and then coated in fibreglass. The sections are connected using high performance zippers. Production models will use Kevlar instead of fibreglass (lighter and stronger) and the leading edge of the aerofoil will be made of carbon fibre instead of polystyrene. The kite is studded with motion sensors that provide on-board communication describing the shape of the kite and communication between the kite and the ground. Massimo Ippolito (right), Eugenio Saraceno (left) leaving me in the centre.

One final aspect of the operational aerodynamics is the impact that the drag of the ropes has on the wing. The aerodynamic efficiency is the ratio of lift / drag. The ropes provide only drag that increases with altitude as more rope is deployed, compensated by faster winds the higher you go. Calculations show that the aerodynamic efficiency of the power wing falls to roughly 18 when the ropes are included.

The ropes used by KiteGen are made of Dyneema, an extremely light and strong polyethylene fibre. 9 mm ropes are able to withstand 10 tonnes of force.

Risks: The Makani and KiteGen Compared

The Makani quadracopter can quickly change from a kite into a powered glider that offers clear advantages over the KiteGen in take off, landing and flight control. But on the opposite side of that same coin with the Makani quadracopter most of your money is in the sky and one must expect to lose devices. And the Makani studded with 8+ rotors flying at 67 m/s does not appear to be avian friendly, although I’m unsure what bird life is found at the planned operational altitude.

The KiteGen kite is simple, lightweight and cheap and may almost be viewed as a consumable item. Thus in the event of a crash significant financial loss is not incurred. But technical challenges remain in achieving automated take off and landing of a large kite. The KiteGen power wing is huge and should be clearly visible to birds. But seen from a distance it will appear as the size of a bird soaring in the sky. Near ground level, the ropes do not move very fast. Eugenio tells me that at operational altitude it would mainly be large flocks of migrating birds that may be encountered. These can be detected by radar and avoided.

To become serious contenders in the commercial power generation market, both technologies need to prove reliability through extended field trials. These alas are not cheap to conduct.

The Other Players

I don’t have time and there is little need to review all of the players on the high altitude wind field. But three other companies / concepts merit a brief mention.


KitePower headed by Dr. Roland Schmehl at the University of Delft (The Netherlands) is one of the early entrants to this field a little over 10 years ago. Their kite flies from a single rope and the kite therefore needs a control box that flies below the kite. The box creates drag compensated by the single rope creating less drag. But the kite control unit needs the muscle to fight large forces via the bridle system. And this also requires a conducting tether to transmit electricity from ground to the kite.

Figure 25 The components of the KitePower set up has a lot in common with the KiteGen stem. Though note the single rope and kite control unit that flies below the kite.

Kite Power Solutions

Kite Power Solutions are actually based in Scotland. Their concept, as far as I can tell, is very similar to KitePower with a single rope and a kite control unit flying beneath the kite. Figure 26 gives a feel for the bridal control system.

Figure 26 Detail of the bridal ropes of the Kite Power solutions kite.

Ampyx Power

Ampyx Power is a hybrid concept between the KiteGen and the Makani using a glider to fly figures of 8 with a single tether that unspools cable from a ground based drum / generator.

Figure 27 The Ampyx “glider” flies figures of 8 similar to the conventional kites.

Concluding Thoughts

Is trying to access high altitude wind energy using tethered kites that fly cross wind driving generators a crazy idea? Maybe!

But one just needs to read the 6 benefits I list in the Executive Summary to understand that this is an energy resource that Mankind will pursue and that a range of technology concepts must be given the opportunity of commercial scale field trials. And trials must be afforded the opportunity to fail in pursuit of eventual success.

Conceptually, I find it impossible to conceive that this technology could be deployed in windy, blustery Scotland. But this technology is not intended for windy areas but for those vast areas of the globe where wind speed at ground level is low but a few hundred meters up there is this steady but invisible flow of 10 m/s wind (Figure 7).

Ten years ago I did not believe that the commercial deployment of high altitude kite power would have been feasible. The enabling technologies today are the huge advances made in solid state motion sensors combined with GPS and computing power that in theory enables automated control of kite geometry and flight.

When I visited KiteGen at the end of April, I was impressed by their engineering and physics skills that spans aeronautics, mechanical engineering, electrical engineering, automation and simulation. When I asked Massimo what drove him, his reply was simply this:

To solve the global energy problem.

I think it is fitting to conclude with this video of the Wright brothers first flight at Kitty Hawk in 1903. It took a long time for Man to reach this point. 102 years later the Airbus A380 took to the sky.

Video 6 2 mins 46 secs. Classic footage of the Wright Brothers first flight at Kitty Hawk, 1903. Its well worth watching 😉


The 4 appendices go into greater detail about the physics and engineering of the KiteGen system that may only be of interest to those with physics and engineering backgrounds. I personally have struggled to grasp and understand all the concepts. Parts are copied from KiteGen documents.

1) An Estimate of ERoEI for a KiteGen Stem

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 borne 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 realistic.

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 (Figure 28). 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 28 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 lightweight and cheap to build and to install. IF it works according to expectations 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

2) The Physics of Kite Flight and Power Generation

The various aspects of the Kite power system can be described by 5 basic equations. Wind power systems operate on a basis of extracting kinetic energy from moving air and the equations therefore are rooted in the equation for kinetic energy.

[1] KE = 1/2 mv^2

m = mass of air
v = velocity of air, in this case wind speed.

From this one can see that the area of the wind front will determine the mass of moving air. And since the KiteGen is operating at different altitudes the density of the air is an additional variable that will control the mass of air. These variables combine to give the equation for power.

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

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

We see here a crucial factor in that power increases by the cube of wind speed.

[3] flight speed = wind speed * aerodynamic efficiency

As mentioned previously, much of the force on the ropes is generated by the efficiency of the aerofoil. Flight speed increases with wind speed and the aerodynamic efficiency.

We end with two equations that describe the force on the ropes. Equation 4 uses the lift coefficient of the wing. Equation 5 uses the aerodynamic efficiency.

[4] force on the ropes = 1/2 * flight_speed ^2 * lift coefficient * area of the wing * air_density (lift coeff. CL = 1.2 -:- 1)

[5] force on the ropes= 1/2 * wind speed^2 * aerodynamic efficiency^2 * area of the wing * air_density (aerodynamic efficiency E=8-:-60 KiteGen wing =28)

3) The Different Modes of the Operational Cycle.

KiteGen have some excellent internal documentation that helps one further understand the physics of kite based power generation.

“In a groundgen concept such as that of KiteGen Stem, the reel-out velocity and the cables tension are fundamental factors for determining the power output. It is possible to show that when the reel-out speed is zero the tension is maximum and when the reel-out speed is maximum, i.e. equal to the absolute wind speed, the tension is zero. Since a first assessment of the power output is given by the product of the cables tension by the reel out velocity, zero reel-out speed means zero power output and maximum reel-out speed means again zero power output. Therefore, the KiteGen Stem must operate with a non-zero reel-out speed and a non-zero tension. It is possible to find an optimal reel-out speed that maximizes the power output. In his article, Miles L. Loyd demonstrated the optimal power output is achieved at 1/3 of the wind speed. In this scenario, having a greater absolute wind speed means achieving greater power by increasing both the reel-out speed and the cables tension.

Despite the physical optimality of the Loyd’s model [2], KiteGen chose to follow a different practical approach in order to both manage practical design and operations and decrease the cost of energy. What happens when the absolute wind speed is increased is shown in Figs. 1 to 4 (summarised in Figure 29) which represent the Kitegen Stem power curve in four different hypothesis. The power curves look similar to those of conventional windmills, however, whereas windmills can only regulate their power, the KiteGen Stem regulates both force and power. Note that this curve is valid during the reel-out phase only and therefore does not take account for the duty cycle of the machine.”

Figure 29 The four phases of KiteGen operation. Upper panel is power, middle panel is force and the lower panel reel out velocity. The key feature is “stage B” where reel out and power production are zero as the system builds to the nominal force, in this example 200,000 N in each rope (middle panel) achieved at wind velocity of 5.42 m/s. Upon reaching nominal force, the ropes begin to unwind and power is produced (stage C) and power continues to rise with wind speed (compare upper and lower panels) while maintaining uniform force on the ropes. At 16.97 m/s the nominal power of the machine is reached, in this case 4 MW. Note that the reel out velocity is wind speed minus 5.42 m/s. 

The KiteGen Stem power curve is divided into four zones depending on the absolute wind speed.

– Zone A: The machine is switched off because the absolute wind velocity is below the cut-in velocity.

Zone A and Zone B are separated by the cut-in velocity

– Zone B: The machine does not reel-out the cables, the force in the cable is below the nominal force.

Zone B and Zone C are separated by the full-force velocity

– Zone C: Full Force Zone: the absolute wind speed is above the full-force-wind-velocity. The machine operates with nominal tension in each cable. Power generated varies and is below the maximum power. The machine is regulated in order to maintain a constant nominal force in the cables.

Zone C and Zone D are separated by the full-power velocity

– Zone D: Full Power Zone: the absolute wind speed is above the full-power-wind-velocity. The force in the cables is maintained equal to the nominal force and the generated power is equal to the maximum power. The machine is regulated by positioning the kite outside the power zone.

In this approach the cables operate at their nominal tension and the generators operate at the nominal torque and/or power.

4) Betz’ Law

Wind turbines function by extracting some of the kinetic energy of the wind moving through the turbine blades. We can imagine a cylinder or pipe of air flowing through the blades that extract some of the kinetic energy. Let us imagine we could extract all the kinetic energy, then the exit velocity of the wind would be zero and no air would pass across the blades, hence energy production would be zero. This tells us that we cannot extract all the energy. Similarly, at the other end of the scale, if the wind blows straight through we extract no energy. It is clear that somewhere between these end members there may be an optimum amount of energy that a turbine can extract from air flowing through the blades.

Betz law from 1919 defines this optimum amount of energy a wind turbine can extract from the wind. It turns out that 59.3% of the kinetic energy of the wind can be extracted when the outlet velocity of the air flow is equal to 1/3 of the inlet velocity.

M. Ippolito has claimed that Betz’ law does not apply to the KiteGen and I believe he may be correct. Betz’ calculation is applied to the flow of wind across a turbine blade. The removal of kinetic energy applies only to the cylinder or pipe of air flowing through the turbine defined by the circular area of the rotating blades more commonly known as the wind front.

For a Kite flying circular or figure of 8 paths through the sky there are two ways to define the wind front. The first is the area of the kite and the second is the area of the sky that is swept by the flight pattern. Because the kite is moving continuously it is always sampling fresh wind that has maximum kinetic energy. The area swept is vast compared with the area of the kite that will never notice the slowing of the wind caused by its flight path. With a rope length of 1500 m and 50 degree elevation the swept area is approximately 1,000,000 m^2. That is 125 times larger than the area swept by an equivalent turbine rotor. I believe it may be the case that a kite should never manage to extract more than 59.3% of the energy in the swept flight path area. But in practice, a kite will only ever manage or need to extract a fraction of 1% of the kinetic energy of the wind that is available to it.

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

[2] Miles L. Loyd (1980) J. Energy: Crosswind KitePower

[Note added 18th August 2016: After 45 days the comments are closed on all Energy Matters posts. Hence the comments closed here today just as interesting commentary was emerging. I am proposing to open a new commentary thread on High Altitude Wind Power (HAWP) in a week or so.]

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186 Responses to High Altitude Wind Power Reviewed

  1. David Ellard says:

    Thanks for an interesting and I think rather fair-minded article.

    Although not strictly airborne wind power, I was wondering about exploiting high-altitude winds by (conceptually, in its most basic form) stringing up a cable between two mountains and hanging a wind turbine from it i.e. downwards.

    I’m not sure this is any apparently crazier than the ideas in this article.

    Has anyone come across this idea?

    • OpenSourceElectricity says:

      No, but you could ask a company like this which obstacles they see: https://www.doppelmayr.com/
      It is usefull only in special locations, but it could produce really a lot of wind power there.
      If it is economical would require some calculations. Maybe the generators are too heavy at the moment for this purpose.

  2. Jonathan Madden says:

    Euan, thank you for this interesting and detailed post.

    I have to say my initial reaction is pretty sceptical, but then it often is when it comes to renewable generation.

    The atmosphere and the sun are harsh. Dust, ice particles and hail, and freezing rain incident upon the flying structure at speeds of 10’s m/s, and perhaps up to 50m/s, will over time cause abrasion and damage. Finding locations where particulate wear is sufficiently minor or uncommon may limit its application.

    The degrading effects of continuous UV light on anything that is not glass or metal will induce brittleness over time. An electric storm may cause power surges down the conducting cables of the Makani-type airborne generation system. The tether cables themselves, thought of as machines in the ship science world, will need regular checks and occasional renewal.

    I assume that full production scale versions of these systems will be fully automated and designed to cope with all weather conditions. One can imagine operators wrestling with a set of wayward kites or planes in a gathering storm!

    Overall I suggest that the anticipated lifetime of moving components will be less than that of, say, conventional wind turbines, which will increase cost and reduce ERoEI.

    • Replacing and recycling lines every few month (3-4?) is already folded in the maintainance calculation if I am not wrong.

    • Euan Mearns says:

      The ropes and kites are light and cheap and as Jenny points out are scheduled to be replaced on a regular basis. The resilience of drums, actuators and electrical engineering equipment I imagine is similar to a turbine.

  3. Nice article though there is nothing new for people that have been following KiteGen.
    Did Massimo talk about the carousel configuration?
    There are other advantages you left out. The Stem units can be placed much denser than wind turbines, they aim to built farm called KiteGen campus iIRC.
    In an Italian article I once read that the engineering limit of the carousel is somewhere around 60GWe.

    While not trivial I am quite bullish on that the launching and other hard parts will be solved eventually. There are hundreds if really smart people working on AWES now.
    To bad conventional turbine makers are not jumping in.
    A multinational AWES project would also be neat (like ITER but a little less money would probably suffice)

    • Euan Mearns says:

      I’m familiar with the carousel and will give it some attention once I see a prototype production model stem in operation.

      This industry is fragmented and spread thinly. And so I believe resources need to be focussed at the cheap end on the more easily attainable goals.

      I think Massimo is interested to try and draw some of the existing groups together to form a larger project. And I think he would also be quite pleased by the prospect of substantial government assistance.

      The sums invested in this so far are really quite trivial.

      • I’m familiar with the carousel and will give it some attention once I see a prototype production model stem in operation.

        Euan, this sentence seem reasonable, but the Carousel operations are easier, more powerful with less forces, the takeoff is straightforward, the cut-in is significantly at lower wind speeds. This without any needs to add further base research or to address unknown issues to build the big generator ring.

        We early understood that the Carousel concept was quite impossible to explain and communicate in order to obtain support, mobilise resources and allies, despite the efforts:

        Then we were obliged to focus to a single module of the Carousel that is the exactly the single wing KG-Stem, thus adding new challenges. Now seen from KiteGen all issues are solved and well addressed even in the Stem version, but it took several years of additional creativity, work and experiment planning, to conceive and validate the methods to take-off and to quickly and effectively recall the wing in the pumping cycle.

        This resulted, perhaps a loss of project image due the delays, without easing the understanding difficulties that are unexpectedly persistent outside our work and community.
        Additionally, downgrading the project from the Carousel to the Stem added some confusion and didn’t improved the perception of stakeholder, they seems still blocked despite the several successful demonstrators.

        • heavyweather says:

          Hi Massimo,

          I guess you have to be a kiteboarder to understand the genuine of the carrousel concept. From my experience I know that a kite can operate very smoothly (with a very continuous force in the lines throughout) in all conditions even going upwind.
          The data in the video confirms what I have imagined for the carrousel, the kite needs very little energy and only about 20° to dive through the negative power phase.

          I have to side with Jenny on this…the perfect investor would be Branson. He knows kites and aeronautics (and spacecrafts)…you should go straight for the carrousel.
          But I read from your other answer here that you have no intention to sell (the IP?).
          May I ask what is the plan instead? Is there some official timeline? Find investors, industrial partners?

          • Hi Marcus,
            Thank you.
            I hope you noticed that the kite is piloted by an AI that invented alone the sinusoidal kite path and the gybe.
            Nobody wrote line of code to provide experience to AI.

            I could be happy if Branson would join the mission, but let me say, I’m looking for professionals, I foresee 100000 workers, starting with 200 people initially fulfilling all the needed functions to start the production would be great.

            Branson what can do, pay for the people selection and recruiting, pay the salary to this people for one or two year? before the selling activity and revenues takeoff?
            ok are 16 M€, we really need involve Branson for this amount?
            I’m looking for industrial partners, to setup the machine supply chain, we have now good ones for minor part of the machine, the rope and the wing, is missing some for electronic board industrialisation, mechanic productions. and system integration.

            I (hopelessly) looking for High End pros able to learn all KiteGen in less than 1 month. for reference a PHd take 2 year to catch all.

          • OpenSourceElectricity says:

            Alternatively, from the technical point of view (generators, inverters, mivoltage equipment, Alois Wobben could be the right person. But I don’t know if he has the right midset to disrupt his existing business he controlls completely by a alternative technology he will control only partly.
            To make the system a reiliable workhorse for utilitys the mindset of his company would be perfect.

    • oldfossil says:

      Thanks for raising this Jenny. I was about to ask what is the energy density. I watched part of Massimo’s youtube video but even with advanced positioning systems, won’t the kites interfere with each other in turbulent conditions?

      As far as the million m² swept area goes, there’s a time element that Euan seems to have ignored, in other words the swept area per second.

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

  5. Alex says:

    Excellent article and promising technology.

    This is indeed a harsh operating environment, which gives advantages to any concept where the mechanics are on the ground. Also, there will be a weight penalty to transmitting lowish voltage current from the kite to the ground.That would favour Kite Power and Kite Gen.

    One of the questions raised is whether you can or can’t have buildings or people normally within the radius of operation. If not, then these will require a lot of empty space. To avoid entanglement risks, and wind shadowing, I assume base stations would also have to be perhaps 1000m apart for a 5MW design. That’s a lot of country side taken up.

    One potential solution would be shallow waters in the North Sea, perhaps using standard, or decommissioned wind turbine foundations, The kite-gen arm captures the kite above ground level, so it wouldn’t land in water. It could even share a platform with a conventional wind turbine.

    One other thought – I’ve seen videos of people in Scotland skiing uphill behind a kite/parachute. They can slow down by pulling another cable which opens a hole in the middle of the parachute, spilling most of the force. Wouldn’t this be an an easier way of reeling in? (Patent not pending)

    • The ground stations are supposed to be placed much denser. Like every 100m.
      See page 2 in that document.

      Taking power out of the kite is called depowering in Kitesurfing/Kiteboarder. You basically change the angle of attack so that the kite floats on the wind above you.You can always fly it out of the wind window.

      On that Facebook page somebody is collecting everything about highaltitudewind right back to the old oildrum ones. The first about the EROEI was also posted already.

      • Alex says:

        Thanks – page 22 – Putting them 100m apart will require all to be perfectly synchronised. Positioning them to 10m tolerance, at the end of a 3,000m cable, 100% of the time, might be a challenge. (That said, I found out last year I’m not too good at flying kites).

        For standard turbines, it’s generally reckoned that you can get about 10MW of capacity per square kilometre, before you start to have shadowing losses. In an “infinite plain windfarm”, the energy lost in the wind is replenished from above.

        Double the wind speed, and you have 80MW of capacity/km2. The wind is however being replenished from above and below, so maybe 160MW/km2? That could go up to the 360MW/km2 claimed in the document for a “finite wind farm”.

        Anyway, get them working perfectly 1,000m apart before going for 100m apart.

        • OpenSourceElectricity says:

          You could also seperat them by height, so one flying at 1200m the neighbour flying at 1700m, as a example, so 100m distance at ground, 500m distance in the sky. as a example to think how it could be solved.

          • Alex says:

            You would rather have to separate them out by pitch (angle of cable to the ground) rather than altitude – so spreading out like porcupine spikes. There will be an optimum pitch for performance but I suspect a few degrees either side of optimum will be OK.

  6. Graeme No.3 says:

    Obviously the best sites are away from populated areas leaving the losses from transmission higher.
    The ropes? cables are HDHMWPE. Fabrication OK? Not the sort of material I would like to extrude. Are they monofilament or multi-strand? In the latter case will there be frictional problems? (Twist and untwist action).
    Also creep must be a problem with cables under tension for long periods.
    How are the cables protected from UV degradation?

    • Jonathan Madden says:

      Here is a quick spec. for various diameter UHMPE rope:


      Generation at 3MW, and assuming 10m/S spool runout speed, gives a total force of 30 tonnes, 15 tonnes per kite tether.

      With a safety margin of, say, 10 compared to breaking load, this would mean a rope diameter of 44 – 48mm and weight of 1 – 1.5 kg/m. With a total deployed rope length of 2km, and without a pronounced suspension catenary, this would give somewhere around a total of 5 tonnes of rope for the kite.

      I presume the aerodynamic characteristics of the rope can be controlled so as to minimise vibrational instability.

      This particular rope has a polyester jacket and spools well.

      • The safety factor of 10 is good for cranes, in the KiteGen application a safety factor 2 is enough, because:
        1) the ground robot supervise the ropes force, precisely clipping all overshoots, that are plaguing cranes.
        2) we tested the ropes having in mind our specifications, and 1 million cycles endurance is normal with a 0.7 breaking load.
        3) As you argued the part of the rope that deal with the pulleys is protected by a jacket.

        • Jonathan Madden says:

          Thank you, Massimo. So a lot less rope weight than I thought.

          If I am anywhere close to estimating each spooling cycle, then for a full scale system at 10m/S spool rate and a 1.5 – 2km run-out would give a per cycle generation time of 150 – 200 seconds. Combined with respooling, say taking the same again, gives 300-400 seconds per cycle. 1 million cycles endurance would therefore come to about 10 years usage. Pretty good!

      • robertok06 says:

        You should ot forget the possibility of ice formation on said rope… could add several tons of weight while changing the aerodynamic characteristics of the rope/conductor.

        • Alex says:

          Ice rain could be a problem in some locations. At altitude it could be an issue and would probably ground the kites.

          • Euan Mearns says:

            Alex, in Denmark flat terrain worries me about any proposal to deploy hydroelectric power. But I guess that’s why the Danes have decided to not pursue it even though they are renewable crazy. Horses for course.

          • Alex says:

            The Danes are powered by hydroelectric power! Norwegian hydro electric.

            I think ice rain will be a problem like too much wind for wind turbines. It happens, but not too often.

            Summer thunderstorms might be an issue. We get a lot of those, complete with very strong thermals.

    • EHV lines transport energy up to 2000km before being noneffective.
      one KiteGen needs 1 km radius of land, 100 KiteGen 1.5 km radius.
      (20 minutes walking)

      the ratio D/d (Diameter of the pulley/diameter of the rope), is the important parameter to address the bending effect and extend the rope life, the Diameter we chosen align the rope bending endurance with the pumping cycles.

      The production is ok, no problems at all, our chemicals partner is happy to take care of supply in large qty.

      UV degradation is well addressed by common chemicals, available off the shelf, it wasn’t a research issue.

      • Alex says:

        Massimo, I think this is a great concept. As mentioned above, I think there will be big control and risk issues in trying to stack these in close formation, but I think that’s a problem to solve for later,

        Have you looked at UK testing? There is Government funding for this sort of thing, and wind conditions are better than most places.

        Although there are more environmental issues to overcome – particularly with regard to bird strike, near shore mud flats could be a good location. Float in at spring high tide, and ballast down. Strong and regular ground winds and ultra flat terrain make launch easy, though corrosion of anything metal can be an issue. No neighbours to complain about risk or noise.

        You could also classify it as offshore wind and get a good strike price. Even if Brexit has pushed down the pound.

    • Greg Kaan says:

      From the images and the quoted strength, I would assume kernmantel construction for the cables as used by climbers, yachties and window cleaners. The allowance for periodic replacement of the cables and flying wing plus the location of all the machinery at the ground station is a rather elegant design solution for a seemingly bonkers concept. It may literally actually fly!

      Most frequent visitors to this site would view wind turbines as a dead end in terms of potential improvements while these high altitude concepts are still in their infancy. I’m actually excited by their potential and hope they prove my inherent scepticism to be incorrect.

      The Kitegen design (and presumably the other kites as well) has the launch issue but perhaps balloons could be used for this purpose – a single tethered balloon could serve a cluster of surrounding kite stations if control of the kites is sufficient.

      • Jonathan Madden says:

        One could use a winch, as per glider launch, to get the kite wing up. Put it on a runway skid and just reel it in. You should be able to get it up to 500m or so before release on a 1500m towing cable.

      • There are two approaches as far as I know (maybe more). The motorised stem and actuators can swing the kite to launch it in relatively light wind.
        The other idea are lifting drones. You’d probably have a drone for up to 10 kites on standby. Should be quite doable.

      • Eugenio Saraceno says:

        Dyneema fiber is produced by Dutch DSM and the ropes are manufactured by a number of sport and marine equipement brands.
        Balloons launch system has been tested in 2012 at KiteGen’s but discarded as they are very difficult to manage and helium is to be replaced continuously at a huge cost.

  7. John Oneill says:

    I read the article ‘ It’s all platypuses instead of cheetahs ‘, and would like to strongly protest this specist attitude – the platypus is considered to have a conservation status of ‘least concern ‘, whereas in most of its range the cheetah is hanging on by one non-retractable toenail. Apart from that, the author is on the money. I spent twenty years trying to milk free energy out of mother nature in the altitude band the kite power guys want to use – mostly in hang gliders ( lift/drag ratio up to about 12/1 ), with a few forays into paragliders ( 9/1 ) and sailplanes ( 70/1 and better ). Conventional wind turbines have blades similar in construction to a sailplane wing, but even longer and skinnier – they might manage 120/1 – so the range of conditions they can operate in is wider. You could build a similar kite, but the kilometre of tether it’s hauling around would make a bigger fraction of the drag the faster it flew. Then the direct conversion of the standard tower wind turbine to smooth power is incomparably better than the seesaw, positive- then negative- output of the Kitegen type systems, and better than Makani’s too, always slowing on the way up then diving down the other side.
    Makani at least has a demonstrated system for getting up to the wind. Kitegen’s simulation of a couple of jet-engine style fans blowing their product aloft is unconvincing – there’s often an inversion layer at five hundred metres or so, with still air below it. Actual videos of their machine all show reasonably strong winds, which would work just as well for a tower mounted turbine.
    Kitegen’s simulated – not demonstrated – capacity factors average about double those – demonstrated – for conventional turbines. That means they’re still pathetic throughout Italy, and would have sizeable power gaps even in windy Holland. Even if they reached 90% CF – the nuclear industry standard – the fact they would all shut down simultaneously would still make far more backup mandatory.

    • Euan Mearns says:

      John, no denying that there are problems launching the kite in calm conditions. And other technical issues which testing to date has thrown up and Massimo and his team are systematically working through and solving.

      But you forget the ERoEI and intermittency argument. Wind turbines cannot power a grid today unaided by the support given by FF generation to balance the grid and to provide back up during calm. Wind turbines may seem great, but they are parasitic. And so unless we are prepared to pay sharply higher electricity prices wind turbines will remain parasites and we will have developed a long-term dependency on natural gas.

      Part of Massimo’s vision is to have a self perpetuating cheap energy source and to be rid of subsidies and high prices that are having adverse impact on many throughout Europe and beyond.

      • Alex says:

        ” there are problems launching the kite in calm conditions.”

        Could spin it out?

        Though I suspect, like conventional wind turbines, it’s not designed for continuous rotation through the vertical axis.

        • Euan Mearns says:

          Could spin it out?

          What exactly do you have in mind Alex. The KiteGen stem has much in common with a fishing rod (and a yacht) and I’ve been thinking about casting the kite like a spinner – an overhead sling shot.

          • Alex says:

            I was thinking of some proposals for launching cargos off the surface of the moon. Basically an arm rotates through a vertical axis, on a mountain top. Out of this arm, a cable is deployed on the end of which is the cargo. Once it reaches orbital velocity (and a couple of g of acceleration) the cargo is released (and the shock wave destroys the launch pad – but that’s a detail).

            The trouble is, any casting or rotovator launch of this will encounter drag, which you want after launch, but not during launch.

            I can think of a few other outlandish launch schemes, but I think a lifting drone or lifting balloon (tethered to a Land Rover) might be best. After all, I assume these things are meant to stay airborne for months at a time, so one lifter can handle a whole farm

      • robertok06 says:

        “John, no denying that there are problems launching the kite in calm conditions. ”

        How about recoverable small blimps, taking the wing at a sufficiently high altitude where there’s enough wind speed for it to deploy?
        Modern remotely-controled drone technology would/could make it without too much hassle, maybe?

      • John Oneill says:

        In saying nice things about standard wind turbines, I only meant how good they are in comparison to kites. As a way of reducing greenhouse gases I think they really only have a place on a hydro dominated grid, like New Zealand’s, and even there should only be a minor player.

    • I agree the tips of a wind turbine is 1/120 as efficiency, not the full blade, also the KiteGen wing adopt a profile of more 1/120 limited at the moment to manufacturing imprecision and roughness. However wind turbines are limited by the Betz law, so a very high glide factor would have the only effect to spin faster, and this worsen the noise problem.
      About the rope drag we will soon publish a document, one of the last KiteGen main achievements, that demonstrate that is not affecting the production potential, and that the system efficiency (wing +ropes) is a wrong assumption.

      We are used to a lot reciprocating machines, like cars engines that smoothly provides traction. Our pumping cycle of the Stem is enough effective to provide the highest ERoEI available and the grid is totally unaffected from the pulsation, only three machines operating in counter-phase fade it.

      I agree that the KiteGen Carousel is more elegant it expose even a better ERoEI that is more than 1500.

      We also demonstrated the takeoffs, sorry if it is less spectacular but it is quite deterministic and safe, including the case of very slow winds.
      I hope this is more convincing, the fans is one of the seven methods conceived to supplement the takeoff and it ask for 1.5kWh to send the wing at 200m in altitude.

      The capacity factor is obviously extrapolated, because we are fighting now to gain the right to deploy the technology and it could easily reach the base-load as explained here:

      Electrons are quite easy to transport for long distances, Italy could be pathetic but authorities gave us the right to fly up to 5000m ASL, and this altitude is better than Holland, I hope to involve, for this occasion, a lot of professional ready to support the deployment worldwide.

      • OpenSourceElectricity says:

        Would a automatic cargo quadrocopter be able to support launching from above (so kite hanging from a cable, releasing the kite and return to the base to lift the next kite be reasonable?
        It would have to connect to the kite automatically wich will be a challenge to find thr right idea for this – maybe magnetic sine there should be low wind during launch?
        Just for brainstorming.

  8. Thinkstoomuch says:

    Thank You Euan and all commenters!

    Going to take me some time to think about. I had previously read the KiteGen links provided through this page. Per usual I did not really understand most of the things to consider.


  9. Leo Smith says:

    Can someone explain to me, given that the ground based systems extract energy on ‘letting out the string’ as the kite ascends higher, where the energy comes from to reel them back in once they have got up there?

    So you can do it all over again?

    • Alex says:

      As the kite is let out, it puts electricity into the grid. As it pulls back in, it takes energy from the grid. However, by changing the orientation of the kite (side slips), it can be pulled in with significantly less force and hence less energy. (The power both ways = Force x Velocity, less inefficiencies)

      For an array of these systems, that will have to be managed – say 25% pulling in at any one time, and 75% pulling out.

    • Jonathan Madden says:


      I think of the kite as a wing, that can behave in an analogous manner to a sailing boat. By adjusting the angle of attack the wing can derive ‘lift’, even it is actually going sideways while reeling the line out.

      Once maximum extent is reached on the line the tethers are rebalanced to permit pulling back in again, but with comparatively low force. A bit like tacking. Some work will need to be done while respooling the line, but only a fraction of that generated while the kite is running out.

    • Euan Mearns says:

      Figure 22 Leo, compare full power recall with sideslip recall. Watch video 4 to see sideslip animation and for real.

  10. robertok06 says:


    Nice piece of research Euan, thanks.

    I only have one comment…

    “These innovators have filed dozens of patents and this has driven innovation in a number of bizarre directions ”

    … normally “patents” and “innovation” should bot be written in the same sentence. Once someone patents something then that patent is either going to be used to farbicate/commercialize a product or it is dead for development, as nobody who’s trying to develop a new device will resort to using another device or process which has already been patented by someone else.
    Only “open source” type of research, typically publicly-funded research works.
    The place where I work is the classic and best example: can you imagine if the world wide web would have been patented by, let’s say, Microsoft of Apple?… nowadays we wouldn’t be here on this blog.
    Patents are a brake to development of new technologies… they are good only to guarantee/maintain the status quo and/or advantage positions on the market… lots of money, for sure, but not fast development of new technologies.
    Look at semiconductor technology: the basis of it has been developed under public funding and (sort of) free for all research… had it been under industrial research we wouldn’t have it the way it is today.

    • Euan Mearns says:

      Interesting comment Roberto. I think I agree. KiteGen have the patent to the two rope system. So new entrants have to go a one rope route that is likely inferior and make do. And the patent holders can end up in disputes with others etc. And with so many patents already awarded in this area its virtually impossible for new groups to get involved.

      Interested to hear what Massimo has to say on this.

      • Giancarlo Abbate says:

        First of all, congratulations to Euan for this very clear and informative post. I read (almost) all the comments and the whole discussion seems to me quite constructive and sometimes even proactive, no matter whether the comment comes from the skeptic or from the enthusiastic side. Coming to Roberto’s comment, and Euan’s reply, I agree that this is an interesting theme, however at the same time it is also a complex one, dealing more with ideology than with technology. I tend to disagree with Roberto’s position, even though I can understand well the basis from which it moves (and I can share this basis). He made some examples supporting his idea, but it’s quite easy finding counter-examples supporting the opposite one (Microsoft and Apple that he mentions may be a couple of them). It’s of no use demonizing “patents” as opposed to open products and public research. I work in a scientific Department of a public University and our findings are public, by definition. However, my University, and most other Universities all along Italy and Europe, encourage us to patent every result that may have a potential practical application. I believe that this policy is not driven by economic interest, by the way rightful, or worse by greed; instead, it’s a way to increase the value of the public support to scientific research. For Massimo Ippolito and KiteGen Company, patenting has been the only way, or better the most important one, to gain the attention of many national and international stakeholders. At least in this particular case, ie MI and KG, it’s very hard to state that existing patents has been a brake for the innovation. Ask to him, and you’ll discover that many of the present players in the HAWE field have started with him, or have collaborated with him, or have started after visiting him, when the first fundamental concepts of KG stem and Carrousel were already patented.

        • Euan Mearns says:

          Giancarlo, I think that both you and Roberto are correct. It to some extent is a matter of scale. I don’t know how much of the technology developed during the Manhattan project, Apollo program and the Large Hadron Collider was actually patented. But I very much doubt that if Oppenheimer had patented the design of an atomic bomb that the Russians would have paid much attention to it.

          At a different scale it is equally clear that patenting technology is vital to a company like KiteGen. This only becomes problematic if KiteGen choses to not exploit its patents. It is positive that Massimo says he wants this to be an open project. Perhaps more difficult to create the conditions where this can happen. I’m quite sure the innovators and entrepreneurs at Kite Power Solutions and Delft are accustomed to independence. And drawing people like that into a team is a challenge.

    • I have already, and early announced to the community that KiteGen IS an open project, if somebody bring good original and feasible concept that match with the current IP, we could consider the relative patent an asset to eventually buy or exchange with the company shares, we consider also the know-how invested in the project a very valuable asset.
      I agree that the patents have sent in dozen bizarre directions alternative concepts introducing a lot of confusion. I think this is a limit of the human nature; it is easier to be spectators of a lot greedy attitude toward our IP, instead to look for collaborative and win-win relationships, with a simple accords it is possible to be part of an international initiative.
      Magenn, with the rolling blimps, was in condition to collect a big amount of money from little investors, exploiting the altitude wind concept, I was upset with them for the fraudulent, uneducated but sounding approach, and I had pointlessly met their COO Mc.Brown in order to find a synthesis/synergy recognizing him a great marketing ability. Now Magenn seems disappeared from the scenery.
      We are often exposed to infringement tentative conducted by thirds, but without a granted patent nobody consider them as credible interlocutors. So all the initial enthusiasm on the concept results very misplaced. It could much easier to talk with us, and perhaps obtain the rights to inherit the big work already done, join the mission and further develop and finally commercially exploit under an agreement.
      We avoid giving perpetual right or exclusivity without enough counterbalances: creative, operative or financials are all good. Ventures claim full rights on our IP proposing only and shaming investments amounts, Makani proposed to join them with all the KiteGen IP provision, I was very positive to the idea to join with my group, Saul Griffith, Corwin, Don Montague, unfortunately Google require all the patents in the funded/participated company as precondition.

      At the beginning of the project, we founded an interdepartmental (Physics; Aerospace; Energetic Eng.; Control and Electrical Eng.) laboratory at the Turin Polytechnic with Giovanni Del Tin rector, It was a public institution contractually holding the IP right, about KiteGen. We called it the RESPIRA lab, which in Italian means “breathe”, and the acronym is Renewable Energy Sources Piedmont Innovation Research Advocacy. This lab was eligible for public funding through the Piedmont Region, unfortunately politics, officers belonging Kyoto club/protocol strongly opposed the initiative, and the lab never started the activities. I had immediately understood that only a private initiative free from the pervasive international “green” organisations should be in conditions to advance the project, and even in this case, we have to defend ourselves.

      • Alex Terrell says:

        Massimo, good to get inter-disciplinary input. I think “innovative” parts of the design are not where the problems will be. It will be on boring stuff like drum unwinding and coupling to generators, and power management.

        Some more thoughts:
        – As asked about, have you looked at UK Innovation funding. That could pay 50% of the cost of a full scale prototype in the UK.
        – The igloo looks very cool. But it might be better to package the whole thin in an ISO container or a standard truck platform (with drop down support legs and anchors to withstand 30 tons). Then the whole thing can be made in one factory, driven to the site, and set up in a matter of hours.
        – What is the noise and hazard profile for flying over semi-populated areas? There is a 300m hill near me in southern Germany, which, for 6 months, had a test mast. In the end, they decided not to build a wind turbine (for one thing, hills create wind shear and turbulence which is bad for turbines). It might be a good site for some Kite Gens. A village is 1000m away and a farm house would be under the zone.
        – Are you now looking for an industrial company to partner? I’d suggest a company not in energy, but with useful know how and design skills (i.e synergies), prepared to put these into a new market.

      • Alex says:

        One other point on the igloo design. The legs at the base are vertical and therefore taking the entire lateral thrust as a bending moment. It would be better to have straight beams at 45 degrees, meaning the igloo becomes a squat tepee.

        • @Alex
          sorry, a little delayed answer.

          The igloo represent the spring side of a damping system, FEM computed.
          Previous analysis shown localized peak forces on the main bearing of 2m diameter and also possible deformation over the specification, the dome solved all issue and provide enough room for the ropes drums, that slide laterally during the spinning. A teepee structure it would worsen the behavior

          • Alex says:

            Massimo, we discussed the igloo – tipee offline.

            Whilst a tipee would be stronger, the igloo is strong enough, and if it adds a dampening function, all the better. It also make more room under the dome.

            Perhaps most important – the igloo looks better and cooler. This may not matter to you or most engineers, but will be important for public acceptability.

            Speaking of which, should the kites be painted sky blue to reduce visual impact? Or a dull grey colour for use in Scotland 🙂

  11. Dave Ward says:

    My first thoughts on reading this were “I’m glad I learned to fly 25 years ago”. I certainly wouldn’t want to be embarking on such a pastime now. Like John Oneill I spent a good proportion of my time “In the altitude band the kite power guys want to use”, except I had an engine to get me off the ground, and keep me there. He mentioned “An inversion layer at five hundred metres or so, with still air below it” – I often found inversions at altitudes of as little as 4-500ft near the East Anglian Coast where I was based. Furthermore they usually resulted in an abrupt (sometimes 180 degrees) change in wind direction, and temperature. Climbing/descending through this is one thing in an autonomous aircraft, but in a tethered kite of the types described here – particularly one being reeled out and back in again? Whilst the winds may be far more predictable over the sea, they most certainly are not over land. Here you have hills, valleys, forests & buildings creating turbulence as well as sources of heating to generate thermals. Add to that the network of overhead power & telephone cables as well as roads, railways and airports found in any developed country, and I simply can’t see large kites being practical (or even permitted) except in the more remote areas already being targeted. Perhaps in 50 years (if fossil fuels are becoming scarce/very expensive) the situation will be different, but by then so will everyday life…

    • @Dave Ward

      Sorry, I’m not in condition to understand the perception of needs of remote areas, atmosphere thickness is described to the kids, assuming the world as an apple, is the apple peel, so very tiny, a tethered flight at 1500 m in altitude require a small territory often available in dense populated zones. I prefers installations in little forests or compact woods so all concerns are over, if the wing really fall down as you fear, will be a service of tree climbers to get it down from the top, very happy to do so as job.

      Usaf Captain Cahoon found a lot of places in the USA despite the dense airr traffic:

      Wind inversion, turbulence, ascending or descending winds are all good to produce energy. The wing fly at 80 m/s pulling with 30 tons is not wind disturbances even strong that change its behavior.

      • John Oneill says:

        ‘The wing fly at 80 m/s pulling with 30 tons ..’
        That’s far higher performance than the ragwings on your videos. One question is, will a semi rigid wing like your more advanced prototype just flutter on the pullback, like your collapsed fabric ones do, or will it spin and tangle the two cords together? Also, what do you figure will be the minimum wind to keep the wings airborne ? An ordinary aircraft has a fixed load, but can vary the airspeed by changing the angle of attack. Your device looks to have a fixed angel of attack, but can presumably change the airspeed by varying the load on the lines. If you reduced that load to the minimum required for control, there would be no power generation, but the kite might stay aloft till hopefully the wind picked up. What wind strength do you estimate would be needed for that? At the other extreme, in very strong winds you’d have to let the wing shoot up to the maximum operating altitude with low line tension, then slip it and try to haul it back down fast before the lines were blown flat downwind. Again, no power production, some power use for the return winch. All this assuming steady winds with no sink or turbulence, which, as Dave Ward and ROM point out, is not the world we live in.
        I stopped flying mainly because of the quantities of fossil fuel it was taking to get me up there, but another factor was the length of time I’d spent sitting on top of mountains waiting for the wind to pick up to a useful speed. Most of that was in New Zealand’s South Island, which on the world wind map is shown as one of the better places for windpower. A country trying to rely on wind will have both these problems – long periods of no power, or fossil power.

    • @David Ward,
      I really have difficulties to figure out the perception you have of a kite flying at 1500m.
      Why do not need remote areas, dense populated lands still have 1 km radius available, I prefer little forest or compact woods, So if the fear to see the kite falling is over.
      In case will be a service of tree climbers to recover

      Here USAF capitain Cahoon found a lot of available sites in USA:

      Thermals, inversions, ascending or descending winds are all good to produce energy.
      The wing fly at 80 m/s developing a traction of 30 tons, it cannot change its behavior with wind events including the abrupt ones.

      • Dave Ward says:

        “I really have difficulties to figure out the perception you have of a kite flying at 1500m. We do not need remote areas, dense populated lands still have 1 km radius available”

        Even a fixed kite flying at 1500m will be tethered to a cable significantly longer (2000m or more, depending on the angle), so a 1km radius is no use if a fault resulted in it coming down – even if it remained attached to the tether. You have to consider a worst case scenario where a structural failure or loss of control AND some failure of the winch prevents it from being reeled in.

        “Here USAF capitain Cahoon found a lot of available sites in USA”

        I had a quick look through the linked PDF, and it appears to be based on USAF sites that could be used for wind generation. The “Airline Route Mapper data” is largely irrelevant, as most of those aircraft are well above your target altitudes. The USAF sites will already have restricted lower level airspace, so privately owned light aircraft / helicopter traffic won’t be a problem. And the US is a far less congested country than the UK, for example. The vast majority of private aircraft operate at lower levels, along with most helicopters, both private and commercial. Even in the crowded UK much of this airspace is uncontrolled, and pilots are free to fly where they want, mostly between 500 and 5000ft, or lower when landing or taking off. The increasing number of large wind turbines both here, and in other countries are already a risk to pilots, particularly in poor visibility, and have resulted in collisions and fatalities. I don’t believe that the UK Civil Aviation Authority will accept large numbers of tethered kites or turbines, and public opposition would apply in more densely populated areas. You might find places in the UK with no power lines in a 1km radius, but 2km or more would be very difficult!

        “it cannot change its behaviour with wind events including the abrupt ones”

        If that is true you have just solved the biggest risk to flying since man first took to the skies! I would love to see what happens when a kite starts ascending in a light (5kts) Easterly wind, then suddenly (within 50ft) encounters a brisk (15kts) Westerly. These are typical conditions I have experienced many times at altitudes of around 500ft. I wonder if you have ever flown in a light aircraft or microlight?

        • I’d say this is an insurance issue and best left to the insurer. They will asses the risk when it gets necessary. Maybe KiteGen has already looked in that issue anyways, they probably have a good idea of the reliability of their machines. We take other risks and they are insurable too. Every sort of aircraft can come down over a city, cut a power line or hit anything in it’s path. Hot air balloons are still not prohibited, guess they are just appropriately insured.
          We operate hydro plants, some dams have a huge potential of destruction. Nuclear plants…well we banned them because the puplic doesn’t want to take the risk.
          You could operate the KiteGen offshore or on the coast.

          There will always be people opposed to anything.

          • “I’d say this is an insurance issue and best left to the insurer.”

            Hmm. It is a can of worms to some extent in that your risk is predominantly off site. That is a regulatory issue, not insurance. That comes after.

            “They will asses the risk when it gets necessary. ”
            No. Kitegen or whoever is running the power plan will conduct the risk assessment. The regulator aka competent authority will review such and see if they believe it.

            “Hot air balloons are still not prohibited, guess they are just appropriately insured.”
            No. the credible risk is low enough so that the benefit outweighs the risk. It is not insurance.

            What i see for Kitgen is a need for redundancy. You have tow cables with both tethered together to some extent. If one breaks, you reel in. If one breaks, it is not failing all over the place as it is anchored to the other cable.

          • And that is only for cable breakage. I am not sure how I would deal with the issues Dave Ward brings up. He is correct. There would need to be conclusive proof that changing conditions would not result in a nose dive other than near off shore. Swansea bay perhaps?

            In any case, it is the responsibility of the power plant owner to provide a safe system. Insuring the systems yields no protection or validity in case of failure with the competent authority if they decided to prosecute.

        • Euan Mearns says:

          Dave, if like me you are in the UK, then your view of the climate and wind is shaped by Atlantic cyclones, summer thunderstorms and sea and land breezes. I think in the first instance the kites will be tested in much less windy and less turbulent areas than the UK. Massimo has told me that after getting the control system sorted out that the majority of test flights last all day, apart from on those days when a technical hitch means the kite has to be recalled. The idea about building prototypes and testing them is to discover design faults and weaknesses and to then eliminate them.

          I don’t think the air traffic risk is worth contemplating seriously at this stage. 3 MW prototypes must and will be tested somewhere and if they work, or can be made to work, then commercial deployment will take place somewhere. The rest of the world will then look on and decide.

          Lets imagine a world in 20 years time where oil costs >$200 / bbl. Airlines are on their knees. And KiteGens can manufacture syn-fuel for $50. Do you not think that the airlines (and everyone else) would be agreeable to clearing some air space?

          • Dave Ward says:

            “Dave, if like me you are in the UK, then your view of the climate and wind is shaped by Atlantic cyclones, summer thunderstorms and sea and land breezes”

            @ Euan – Indeed I am, (East Anglia) and I spent 20 years flying from a small airstrip near the coast, hence my frequent exposure to most of the above. Thunderstorms are a definite NO-NO for any small planes, and the thought of hundreds of kites airborne during a typical summer afternoon like we had last week is not one I favour! Personal circumstances meant I had to give up flying a few years back, but I remain keenly interested in the subject.

            Kites are no different to any other flying machine, be it the 340kg microlight that I flew, or a 400+ tonne airliner, and I simply can’t accept Massimo’s claim: that “It cannot change its behaviour with wind events including the abrupt ones”. There have been thousands of crashes over the years due to low level turbulence and windshear. A sudden loss of airspeed at 50ft when landing, one (apparently) calm evening, nearly finished me off. And there are numerous YouTube videos showing commercial aircraft being thrown around in gusty winds whilst landing. A rigid wing/turbine(s) should avoid most of this, but a kite being repeatedly reeled out and the back in won’t be so lucky.

            There would seem to be merit in locating kites at sea, where wind conditions are much more predictable, but they would be subject to the same difficulties with access and corrosion as current wind farms. And you would still have many occasions when there was little or no wind over large areas – yes, even at 1500 metres! On land I agree that in the current situation there would not be a problem with a limited number of test sites, but in 20 (50?) years? Yes, by then things could be very different, and it wouldn’t just be the airlines on their knees…

            I made my initial comment based on hands-on experience of our “interesting” weather and the air traffic situation, in a crowded country – it seemed to me that this had not been taken into account in the rest of the discussion. I hope Massimo and others are successful, as the present situation with “renewable energy” clearly isn’t going to keep the lights on.

            “There will always be people opposed to anything”

            @ Jenny – Indeed there will, and I am simply looking at this from a pilots perspective, which will naturally be rather different to yours.

        • @David Ward
          This is most important aspect to mind the right picture of the wing behavior.
          The kite is linked to the base station that provide or maintain the axial (ropes) force constant.
          Therefore the wing itself is not a light aircraft it is always better comparable to an airliner, the figures are similar.
          The flight parameters of the kite are constant in local coordinate as the apparent wind is.
          If the wind conditions vary abruptly or not, the reeling in/out react in feedback according. Perhaps a sort of jump downward.
          The only effect will be a temporary instability of the rope length and reeling speed, recovered after the transient.

          Another feature is that KiteGen do not need a machine sprawling, few big and dense wind farms could supply a country. This ease the site finding and permitting.

          The pro-capita peak net energy is a past event, perhaps before the 2000 resulting a loss of out living standards, and impeding access to energy to the rest of world. All economies are in irrecoverable bad shape for this reason.

        • Mike Mellor says:

          Dave Ward, the wind shear problem will only arise on launching and retrieval, and there is technology to detect it.

          But as you say, airspace in the UK (and in Europe as a whole) is very limited and that could make it difficult to find suitable sites.

  12. OpenSourceElectricity says:

    I just saw, while searching for the weight of the kite, that makani wants to opertate in heights of just 310m. This sounds unreasonable, because Max Bögel already told that their hybrid tower can be deliverd for 200m hub height at any time this is requested ( 160m hub height is standard for new projects in south germany resulting in 230m tip height), this hub height is expected here for the next generation ow wind turbines, with 140-170m Rotor diameter, resulting in tip heights of 270-285 meters. The towers produced in series are astonishing cheap.
    What is limiting them from flying higher?
    (And a stupid question : would it be possible to launch a kite from the top of a wind turbine, thus sharing place and power cables, since the turbine is running luv and the kite running lee, this might work – and a starting point >150m above ground might make it quite easy to start at lower winds – especially sinse wind up there is already stronger.
    Different wind directions in different heights naturally would makt this not work. Just for brainstorming.

    • Why lift the structure on top of a turbine? Turbines are spaced further apart. This is not worth the hassle and the kite and groundstation become much less reachable for service and frequent line changes.
      Ideally the kite stays aloft for month until a line change is in order.
      This is the only concern I have about the carrousel approach but maybe I am wrong and it can be serviced while running or the temporary loss of some kites would not be a problem and stopping to service could be postponed until xx kites need service at once.
      Maybe I am wrong and kites/lines failing in the carrousel will be much less common because of the smaller, more constant forces and less strain on individual stations.

      Massimo, are the individual anker points on the carrousel built like the Stem units? Are they supposed to generate power by reeling out also or are there only drums to control the kite? How does the carrousel generate power? A central hub or generators along the track?
      Is the whole “wheel” turning or rather running linked trains around a track? I am much more curious about the carrousel.

      I guess the iglo is built to take the weight of the groundstation, there shouldn’t be much lateral forces and those would be in an angle upward anyways. The unit will be shipped in containers anyways but to house something permanent in containers is just unnecessary engineering imho. Other, smaller kite based projects seem to go that way though (enerkite?).

      There is also one group with a two kite approach (had that idea myself about 10 years ago when I first saw the laddermill concept – an infinite loop with kites going up and down but no crosswind flying). With alternating passive and active phases. I am not sure if that is better than the side slip approach, probably not that efficient but takes some of the high spike forces out of the system and generates more evenly. The depowered kite will take more energy to bring down than a slipped one.
      Again…the carrousel would be the best thing to do in the first place.

      • OpenSourceElectricity says:

        This is why it is “only brainstorming” . The idea was to possibly solve the problem with starting the kite.
        IT adds the problem that to get to the kite the use of the elevator in the turbine is neccesary.
        On the other hand, power lines (mid voltage, so several MW), telecommunication, road infrastructure, etc are already present at the wind turbine. This infrastructure is often more expensive than the tower of the wind turbbine, and might also conribute to significant costs of the kite system, although this should benefit from allowing smaller distances.

        One question would be: how about black starting a kite-generation site? My belly tells me black starting could become a problem unless there are strong winds available at 0m. A Wind turbine park can do black start, if a little wind is present, and the software of the wind turbines is designed for black start. The only initial energy needed is to turn the nacelle in the wind, so the rotor starts rotating – equivalent to opening the valves of a hydropowerstation.
        With a kite generation system it would require enough wind to start the kite without support, and several sites started with some time offset, so that some sites generate power while others pull in the kite with this power.

      • Alex says:

        One reason to put it on wind turbine towers is that out at sea, they are there. Though this could equally be put on a ship, anchored or grounded.

        I see in the presentation the igloo: “Tethering : designed for 60 ton max traction, 20 ton working conditions”.

        60 tons – that might be resolved as 40 tons upwards and 40 tons down wind. That’s quite a bit.

        I agree about shipping – as the hub seems a bit big to fit in one container. However, a tepee structure will be a stronger and cheaper than an igloo.

        The two kite approach? Is that like an elevator with its counterweight?

      • @Jenny
        We studied the KG carousel with tires/annular road , rail/steel wheels and finally the passive levitation that is very simple and require few magnetic material. the generators into the final design, are in the track, having the rotor carrying the permanent poles and the stator is the coils side allowing the electrical connection to power servo drive on the steady part.
        The linear generator tend to attract and additional band are repulsive. The control of the air gap could be inside a distance feedback loop acting on the local torque control, so is the generator itself that provide the sliding stability and centering on track.
        With a little radial, about 600mm, magnetic coupling all control and suspension functions are assured including the power generation.
        Our idea of the rotor is monolithic, composed by easy to manufacture segments in concrete, the rotor weight is useful as a big flywheel to re-phase the grid. The rotor is to consider a wide annular platform suitable to install an array of Stem, The Stem only control the flight of the wing, a little energy will be produced aboard and it is in common to all stems to provide the power to adjust or recall the wing.
        We were concerned about the Neodymium-iron-boron magnet sustainability then we successfully studied an alternative reluctance equipment composed only by silicon-steel and aluminum coils.

        here an old presentation of the KiteGen Carousel:

    • Mike Mellor says:

      OpenSouce, the problem with the generation-at-altitude model is the weight of the power cable. My rough calculation for a 10mm copper cable says 1.4kg/meter so with a 300m kite that’s 420kg, not allowing for the natural sag of the cable. Already that’s quite a lot of work gone into keeping the kite aloft, work that could have gone into energy generation. The cable has to be over-engineered to handle all the flex and stress and will need regular replacement. You need a larger, heavier, more expensive and less maneuverable kite.

      Massimo’s KiteGen by comparison needs only to lift its tethers. Being so light it can maneuver instantaneously. I foresee that at sites with high kite densities, each kite may be fitted with ailerons to avoid collisions with other kites in turbulent conditions, and this will increase the weight.

      It’s somewhat ironic that a kite intended to reduce carbon emissions may be built from carbon fiber… CCS taken to the max?

      • We were strongly advocating the CCU (carbon capture and utilisation), but recent publications and satellite data about the high beneficial effects of extra carbon dioxide in atmosphere without evidence of side effects requires to rethink all the topic.

      • OpenSourceElectricity says:

        Te brainstorming Idea was to put Massimos Kite-Gen Equipment on top of the wind power tower. The coalculation in detail of cost rises in tower construction got lost again as it seems, th extra costs in the tower would be around 50.000€ as back of a envelope calculation, the major costs for first versions would surely be engineering costs of the nacelle.
        Benefit would be to double energy production per site, without needing more infrastructure per site.
        So from this point the economy of scale should be similar when placing a 3MW Kite Gen on top of a 3 MW usual Wind power generator, as if there would be a scale op of the wind power generator from 3 to e.g. 7,5 MW with a 150% higher swept area for the rotor. (so 200m Rotor).
        Might be useful if this could solve the problems to start the kite, and so to remove one of the last remaining problems.
        If there is a mass production of 10.000 Kite gen systems per year perfectly working, this is most likely not useful any more, if it is useful at all.

        • @OpenSourceElectricity
          I agree, I think will be better a platform for the KiteGen at the tower half height, in order to be more compatible with the tower bending resistance. The platform need to be always downwind. a virtual axis link to the nacelle.

          • OpenSourceElectricity says:

            yes, this could be a better idea. less due to the bending forces – they would add just a few dozend tons of steel even to a 200m tower, they are quite strong, but to avoid changing construction of the nacelle, and also in some other points.
            Changing construction of the concrete tube should be far more easy. With a 160m hub height, and a 140 rotor, placing the kite equipment at 80m height wuld make it stay just below the rotor, so with no kate out it is sure with the rotor in any position.

  13. Pingback: High Altitude Wind Power Reviewed | Patents and...

  14. Euan Mearns says:

    @ Dave Ward

    I’m starting a fresh thread down here where it is less crowded. Scepticism provides fertile ground for discussion. I share your scepticism about deployment of kites in the turbulent skies over the UK. But on the other hand, Massimo has unshakable belief in maintaining constant force on ropes by reeling in and out to maintain stable flight. For me, the proof is in the pudding of test flight data. You can’t say it can never work until this is proven to be the case.

    One of the problems to overcome are the enormous forces. In one email exchange I was working through data and the equations (Appendix 2) and was apparently an order of magnitude out (on the high side), and felt I must have made a mistake. But I hadn’t. There is a huge amount of energy to harness, it simply comes down to working out the best way of harnessing it.

    Else where there is talk of mounting kites atop wind turbines etc. The problem with turbines is they sit on top of a stick more commonly known as a lever. The longer the lever and the greater force applied to it creates the need for the stick to become ever stronger and heavier.

    The KiteGen is attached to an anchor.

    • Alex says:

      I’m not sure whether the skies over the UK are especially turbulent. Winds are stronger – yes, but turbulence tends to be generated by hills/mountains below, and the UK is pretty flat, and the North Sea flatter still. I’d be more worried about freezing rain which is an issue in northern Europe (and maybe elsewhere at 1,500m) https://en.wikipedia.org/wiki/Freezing_rain#Aircraft.

      The forces can be up to – if I read correctly – 300KN, or 600KN. I’m sure a constant force on the rope can be maintained at the drum end, but the rope itself has a mass and if the kite decides to change force, could the inertia in the cable cause it to exceed its design load? If the rope weighs 1 ton, then an acceleration of 10g will add 100KN to the load, no matter what is done at the drum end. However, I’m sure Massimo has modelled the transient response.

      There’s a mundane problem that if the speed of draw out varies, the RPM of the drum will vary and that will cause the output frequency to change. It might be easiest to use a DC generator and worry about AC conversion later.

      • Mike Mellor says:

        I flew a glider in wave lift of 10m/sec over mountains near Aberdeen and wow. On that day we abandoned the flight at 5000m but other hardier pilots were climbing to over 6000m. That’s a heck of a lot of energy.

    • @Euan,
      perhaps our current wing is too wide for Scotland, However when the wind is very strong we could equip the machine with a “storm jib” equivalent kite. And everything come back into the specs.

    • Eric Swanson says:

      Euan (and Massimo Ippolit), having studied aerodynamics a bit, I find the claim that the Betz’ Law does not apply to the KiteGen system to be incorrect. The calculation in the Appendix which shows that the kite must be reeled out at some speed between 0 and the wind speed at altitude to produce maximum power is just another version of what the Betz Law says. The force on the kite will be the result of the RELATIVE wind speed, not the free stream wind speed. Also, the area of the wind intercepted by the kite applies only to the wing area transverse to the flow, not the area of the entire curved surface. Think of it as a flat wing with a cord equal to the width of the kite attached between the “Y’s” at the the end of each tether at the base of the kite as shown in Figure 18.

      The force on the tethers is the vector combination of the lift plus the drag, using conventional terms. For the wing on an aircraft, the “angle of attack” is defined relative to the cord of the wing (that is, the line from the leading edge to the trailing edge of the airfoil) and the coefficient of lift and drag are only valid within a relatively narrow range. At high angles of attack, the flow separates form the top surface and the lift force drops, while the drag may increase. From the geometry shown, the kite is being operated at a high angle of attack, so most of the force is the result of drag, not lift. I suggest that your presentation is seriously flawed when you add a term to your equations which you call “aerodynamic efficiency”, what ever that means. The “figure 8” mode of operation implies a diving and climbing operation, where the tether force will increase during dive, but decrease during climb. It’s not clear to me that this mode will result in increased power output from the generator. Indeed, the requirement for reeling in the kite to complete the cycle requires energy input, which would reduce the net output. Your calculations don’t include that negative power period. One must look at the total power output over time, not just an instantaneous force which does not include the entire cycle, such as indicated in Figure 22.

      I submit that the tethered glider concept from Ampyx Power could offer better aerodynamic performance, given the ability to control angle of attack, if only because the tether force can be minimized during the reel in period. Time will tell which is the superior concept.

      • Euan Mearns says:

        Eric, to a certain extent here I am a messenger of a very complex message. But I do have physics to first year university and so have some qualification to draw my own judgements. It struck me that Betz’ Law applied to a static structure that could only extract a certain % of the KE of the air moving through the turbine blades. A kite does not slow the wind in any appreciable way. So there is a philosophical point to discuss.

        Including aerodynamic efficiency in the equations seems logical to me. Whether or not it is included correctly is another issue. If force is dependent on aerodynamic lift then the efficiency of that lift linked to kite speed has to be included somewhere in the equation.

        Of course the power used in recovery needs to be taken into account in the gross calculation. I’ll let Massimo answer here. But I think he did tell me that the kite in side slip mode had less air resistance than Ampyx glider that is after all still a glider when it is being drawn back in.

        • Alex says:

          I think Betz’s law applies, but it’s not a constraint. I remember a discussion with a wind energy exec explaining why turbines have three blades.

          Three blades gets about 95% of the way to Betz’s law. Two blades would get about 90%, and one blade 80%. There’s no reason to go to more blades. Two blades – or even one blade, would be more cost effective, except for balance issues causing wear.

          The Kitegen gets the same power, from “125 times the area” of a 3MW turbine. Hence it is not even 1% of the way to reaching to Betz’s “limit”. As such – it’s not constrained by Betz’s law.

          Betz’s law says it’s not worthwhile having a 4 or more blade wind turbine – IIRC, you go to 97% the way to Betz’s law. With KiteGen, in principle, you could have multiple units in the same “orbit”, and Betz’s law is not a limitation. Put 100 in the same “orbit”, and Betz’s law will start to apply.

          • Alex

            Put 100 in the same “orbit”, and Betz’s law will start to apply.

            This single sentence it is enough to reveal your full and superior understanding. Sometime a satisfaction!

            The risk is that if is so rare the ability to catch the basics, and worst, the more advanced topics of this powerful and ultimate solution, we will dive inexorably in a perennial societal decline up to the full loss of the technology capability available in industrial communities. We already experiencing this trend in Italy.
            KiteGen represent a singularity: 500 of ERoEI it is the only hope, up to now, to recover the world economy, unfortunately only a restricted and insufficient to be a critical mass place correctly this opportunity in the scenery.

      • @Swanson
        Wing area
        Yes, the projected area of a C shaped wing is about 70% lesser than a flat wing, however the flat wing require an heavy longeron to support the axial (rope) forces worsening the area/weight ratio.
        Or alternatively it require a fanout of bridles that heavily affect the flight attitude (angle of attack) at high speed.
        You are missing the story of the concept the early designs were including the kiteplanes, like the Wubbo Ockels’s Laddermill:
        This discussion belongs to the past, with a simple structural check the flat wing, with tens tons forces, is highly unpractical.
        Ampix Power is working on the tethered glider, that is an old and abandoned concept, without any IP.

        Angle of Attack
        You are contradicting yourself!
        This angle is calculated with the cord and the apparent/relative wind, the wing fly at 80m/s so the natural wind is only minor vector component composing the flow that involve the wing. It seems you have in mind a mere parachute inherently without relative wind. Hundred of scientific publications on the issue tried to explain this very recurrent and primordial evaluation error.

        Negative cycle
        the power exposed is already a mean between active and passive phases. Fig 29 shows the power in active phase.

        Alex, just provided the right answer about Betz

        It is quite frustrating, no one of the of the sentences you proposed reveal an even minimum understanding of the base concept, despite you are claiming to have studied aerodynamic. In addition you mix minor issues with “seriously flawed” accusations.
        I suspect you are making an unfair tentative to add mess to the discussion.

        • Eric Swanson says:

          Massimo, please see my reply below which did not end up in the proper order.

          I think we are using the same definition of “angle of attack”. I used a coordinate system which is based on the Earth, that is, x = horizontal and y = vertical. The angle of attack would then be roughly the angle between the airfoil cord and horizontal, with the wind vector assumed to be horizontal. Thus, the terms “lift” and “drag” refer to the vector force components in the vertical and horizontal. Some fraction of the lift force counters the gravitational pull on the kite (or glider) and the tether(s), the remainder when combined with the drag component produces the tension at the top end of the tether(s). At what effective angle of attack does your kite system operate and what are the coefficients of lift and drag which you find for this system?

          As for the Betz Limit and the notion of the device slowing the wind, as noted, it’s relative speed which produces the force on the kite (or glider). As the kite is allowed to move away from the base, the effect is a slowing of the air speed over the airfoil, which is analogous to the slowing of the airflow thru the disk area a ground anchored turbine. The fact that the kite can be maneuvered over a larger area than it’s cross sectional area has nothing to do with the net power produced, IMHO. Please provide some real time data (or a reference which does), which shows wind velocity, force and power over several cycles of operation, so one might calculate the average power produced.

          • heavyweather says:

            Betz law is effected by the swepted area. It’s a maximum theoretical percentage of the power that is inherent to the wind flowing through the given area.
            If you extend the area you also extend the total power that can be extracted before hitting the limit.
            Alex’s explanation was spot on. The kite would be just a part of a huge turbine blade (70℅ of the 150m2 wing?) with a rotor diameter of 500-1000m? whatever the effective wind window is.
            That’s a huge area and you have to use this area to calculate how many kites could sweep that area before hitting Betz limit. The Stem after all is only extracting 3MW out of that huge area (maybe a little more when the windows are overlapping). The kite would have to cover a much bigger percentage if the area or fly at insane speeds before you would ever think about Betz (like the disc that is sometimes used to describe Betz law).
            The KiteGen is a lift machine.

            I wouldn’t even worry about hundreds of kites flying at lower speeds in a joint area like proposed in the carousel.

            Besides most of the data from KiteGen has been evaluated in real testing compared against physical simulations. I believe KiteGen is past proving that the KiteGen is possible like intended.

          • heavyweather says:

            Did you have the same conversation almost on the day 7 years ago?

          • Euan Mearns says:

            I’m absolutely amazed that you have had the memory for and ability to find this old conversation 🙂

          • heavyweather says:

            I also have it archived offline in case those old articles/discussions get lost some day…

          • Eric Swanson says:

            heavyweather, Yes, I was part of a similar discussion back in 2009, which I also archived. The assertion that sweeping the kite over a larger area results in greater power misses the fact that the only important point of view is the forces produced on the kite by the wind. And, as noted, the maximum power point is such that the relative wind speed is less than the free stream speed, which is what Betz found more than 100 years ago. Don’t forget that the tip speeds of wind turbine blades are quite high, on the order of hundreds of miles per hour (for readers in the US).

            To claim grandiose power production requires extraordinary proof. Where’s Massimo’s data???

            Oh yeah, just to remind any other Oil Drumers out there, Global Warming is not a hoax.


          • Again, the same pattern!, A climate alarmist that is deadly against KiteGen, that is the sole concept with a potential leading to the definitive solution. Climate alarmists endorse always, and only, initiatives that worsen the problem. Evidently they are scared to loose the incomes coming from their catastrophic story telling.

  15. Dave Ward says:

    “You can’t say it can never work until this is proven to be the case”

    Absolutely, and I’m sorry if I gave that impression, just pointing out that actual wind conditions in the first few thousand feet above ground can be very different to forecasts, and that the skies over any developed country are complex 3 dimensional maps, as far as aviation (both private, commercial & military) are concerned. I’ve raised the subject of low level inversions on other threads about the latest (and tallest) breed of wind turbines – the same abrupt change in wind direction & speed applies to blade tips. The difference is those machines are bolted to the ground, whereas a kite will want to follow the wind direction, regardless of how high the effective wing loading and airspeed is. I cannot see how you could operate a multi-kite carousel in such conditions without them all becoming tangled!

    “Talk of mounting kites atop wind turbines etc”

    When I drive past a local turbine in strong winds the “lever” effect is clear from the degree of blade bending! I suspect what those suggestions really mean is to just use the bases once the current turbines have reached the end of their life?

  16. @Alex
    During the test we never met icing conditions. I suppose the frequency of this weather condition particularly rare, suggesting that prohibitively weather conditions could be simply avoided without flying at all, having the overall availability pretty unaffected.
    In any case the wettability and the adesivity of the wing surface could be controlled with special long lasting silicon additives, as the icing point that could moved in order to extend the operative conditions.
    The wing isn’t fully rigid, during the cyclic side-sleep the wing segments bends enough to likely break the tiny Ice formations.
    yes, the wing could accelerate the climbing for extra lift, and the ropes propagate axially the pulse at 2700 m/s, a fraction of second for the wave to reach the base.
    However we have two mitigating effects: The wing own weight that smooths the pulses; and the rope young module, that is 3% at breaking load. This allows tens of meters of elongation, avoiding the rigid body behavior you worry about.
    Drums and pulleys are driven by direct drive alternators, this is mandatory for the precise and quick rope tension-length feedback.

  17. ROM says:

    I am a now retired Australian grain farmer and glider pilot who both has watched and studied the weather and atmospheric systems over my life time both as a part of trying to earn a living by taking on Nature in its own realm and as my sport of gliding and power flying.

    I started power flying in Tiger Moths in late 1959.

    Then onto flying gliders or sailplanes in 1963, a sport which after some 3000 hours gliding time and 600 hours power flying time I finally gave up a couple of years ago due to at a now 78 years of age I am having some DOB induced problems. [ DOB = Date Of Birth. ]

    I am with Dave Ward on the constant atmospheric physical instabilities in the height range of 500 to 2000 metres, the height range in which I did almost all of my glider flying over those 55 years of my gliding over south eastern Australia.

    One of the strong impressions I have got from the various posts above is that the promoters of these Kite type power generating systems is that those same promoters of these systems have NO direct first hand experience or have accumulated long hours of direct experience with the real world of the lower levels of the atmosphere where they are proposing to establish their kite power generating arrays.

    It almost appears that they are establishing and promoting their systems on the basis of an idealised and modelled atmosphere without an real time knowledge of the immense range of and highly variable and frequently quite unstable and unpredictable, often highly turbulent micro conditions that can and do change quite dramatically within a couple of hundred metres distance and within a few tens of seconds in the height bands they are proposing..
    Such conditions exist just about everywhere over the global land masses at the low altitudes they intend their Kites to operate in.

    First as Dave Ward has pointed out are inversions and the change in wind directions above and below those inversions which if the Kite cable anchoring drums were only a hundred metres apart will lead to a glorious entangling of kite cables if there were abrupt and different wind direction changes at low level during the launch of a number of kites.

    Then there are the thermals which can extend to 12000 or 14000 feet [ 4000 mteres ] on a very good day but in our conditions regularly extend to 2500 metres.
    Thermals often have strong shears between the fast rising thermal air mass and fast sinking air mass vertical air flows that exist over a couple of tens of metres near the thermal’s edges.

    The fast rising thermal airmass which has vertical velocities of anywhere from a couple of hundred feet per minute in winter [ in southern Australia ] and up to 1500 feet per minute plus in our summer thermals, often have a fast rotating column of air, a willy willy in Australian country parlance which on a few ocassions has almost inverted me when I have flown into a particularly strong willy willy under a cloud at 8000 or 9000 feet altitude.

    When one of those down wind drifting thermal air masses which are highly variable in spacing, in strength and in the actual duration of the thermal structure which can be from a minute or so, a “bubble of lift” in a glider pilot’s vocabulary , to a half and hour or so, would pass through the area that a Kite or array of Kites is operating in then the sometimes severe shears would in seconds twist the Kite into an uncontrollable attitude leading to a probable loss of that Kite.
    And if other Kites were in close proximity to the out of control Kite as it seems to be proposed, it would likely tangle the lines and bring down a whole array of Kites.

    Of course where air goes up, air also goes down and again I regularly have experienced sink rates right down to a couple of hundred feet above the ground of a 600 to 1000 feet per minute extending over many kilometres as I have tried to fly out of the area at speed in a glider.

    Such large area, slow moving long duration high sink rate air mass allied with a slow wind speed aloft, a fairly common summer time occurrence in most gliding regions of the world, would likely bring down the whole of any Kite array within that area.

    There are any number of times during the year when one can stand on the ground and just watch the clouds and their shadows moving across the countryside to get some idea of the wind speed at height .
    And it is frequent during the many days long periods when a high pressure system settles down over an area that can cover a quarter of the continent for those wind speeds as measured by the cumulous clouds shadow speeds across the countryside to be only perhaps some 15 or 20 at most kilometers per hour.

    Then there are the regular and sometimes frequent frontal and trough line passages across the land scape, all of which introduce areas of high turbulence into the lower levels of the atmospheric air mass.
    There are the unpredictable effects of hilly or mountainous terrain in generating abrupt wind changes at height plus turbulence in any down wind air mass particularly so when a small and undefined trough line or very weak frontal systems moves through the area.

    There is the probability of thunder storms which with their very high vertical air mass flows both into and out in front of a thunderstorm as the very cold air from inside of the thunderhead some thousands of feet above literally falls to the ground creating severe turbulence and very strong winds at the thunderstorm face .
    Plus of course the potential to wreck the electrics of the entire Kite system if and when the very high voltages from the electrical currents ie lightning gets crackling.
    In winter the freezing levels  even here in southern Australia can get down to a few hundred metres altitude.

    Any such turbulence and the possibility of Kite anchoring ropes being rapidly adjusted to cater for the gyrations of the Kite during severe or moderate turbulence seems to have avoided the problems of the inertia of the heavy duty rope winding drums as they are accelerated and decelerated which would need huge pulses of very high power for the fast acceleration of those drums to stabilise the Kite as it gets buffeted by turbulence.

    Where those very large, seconds in reaction time, pulses of high power to accelerate and decelerate those highly loads and heavy duty winding drums would come from particularly when a whole array of Kites is hit by a line of frontal wind change turbulence is just another of the many unanswered questions about these types of highly speculative power generation systems .

    The idea that the Kite anchoring cable drum systems can be located within a couple of hundred metres of one another is utterly fanciful and thats being polite.

    A far more rational spread of Kite anchoring points would be perhaps a minimum at least of some 300 or 400 hundred metres apart but more pragmatic would be at least a half a kilometre spacing on twin cabled Kites each with say 3000 metres of extended cables which would allow Kites to avoid entanglement in turbulent conditions and allow individual Kites to be deployed or landed in height related variable wind directions and strengths..

    The energy generating density on this spacing then becomes very low and highly inefficient plus taking up huge areas of land extending over hundreds of square kilometres for any meaningful industrial category sized generating capacity from which all aviation activity, particularly those aircraft of the light aircraft category that normally operate within the height band the Kites are proposed to operate within would have to avoid as a complete no-go area.
    Given a bit of low cloud and bad weather it would be inevitable that a number of crashes and deaths in both light and medium sized aircraft would occur if the Kite arrays were allowed to extend over large areas of any nation.

    There is much more I could add but to sum up.
    One or even a few such power generating kites would be an interesting experiment to carry out.

    But an array or many arrays of hundreds of such Kites as any sort of substitute for the present big fossil fueled power stations and hopefully of future fusion power generators is an utter fantasy from the aspects of reliability of power supply, from the economics of such a scheme and from the sheer levels of the utter impracticability of trying to generate reliable power by trying to impose such a Kite based system on a highly variable, unpredictable [ as I can well testify to with 50 plus years of gliding and flying in my log books.] frequently unstable at the micro atmospheric scales operating environment.

    With all the atmospheric variables and the irregular and unpredictable generating outs due to the highly variable and unpredictable atmospheric effects on the Kite arrays, like the grossly overrated and extremely socially costly wind turbines, such Kite arrays would still need that minimum 80% plus of their actual generating output as back up in the form of rapid reaction, low efficiency gas and fossil fueled generators.
    And THAT just means we are not back at the start economically but are economically and financially quite a lot worse off as individuals and a nation than if we just continued to rely on the increasingly efficient fossil fueled centralised power generators..

    Kites like Wind turbines would NOT REPLACE conventional fossil, and nuclear fueled generators.
    They, like Wind turbines, would merely DISPLACE conventional fossil fueled and nuclear generators and to no advantage whatsoever to the populace but to to that populace’s ultimate and great economic, financial and increasingly, its increasingly serious and deleterious social costs.

    • Alex says:

      The important point about a kite is that it is self stabilising once it gets through the turbulence – as long as it hasn’t entangled with another kite – which is why I’d agree on the spacing, at least until more real world testing is done.

      I’m not a pilot but as a passenger – I’ve noticed that airliners don’t want to take off through a thunder storm. It may be that the kites have to reel in under such storm conditions. As that takes only 2 minutes, they can do that when the storm arrives, with no human intervention. In Europe, this is more commonly an issue in summer evenings, when net electricity demand might be quite low.

      Note Maasimo’s point about the elasticity of the cable – 3% at braking load – would deal with the fastest transients (subject to some modelling)

      What are the consequences of a glider crashing? I’d think we can’t take the risk of flying these over villages (there’s also the noise issue), but farm land and park land? Farm houses? Roads? Generally if one’s brought down by a thunder storm, there aren’t many people out an about.

      That’s a risk – consequence trade off. A falling kite could damage a person or livestock, but maybe not if they’re indoors. 500m spacing of these devices still gives the same energy density as conventional wind turbines, with a fraction of the visual and noise impact. Plus the fact that you can put this in a cheap boat, provide a strong anchor, and you have an offshore solution.

    • @Dave Ward and ROM

      I cannot see how you could operate a multi-kite carousel in such conditions without them all becoming tangled!

      Ok, speaking with Einstein “If you cannot explain it simply, you do not understand it well enough”, So let me retry, but please a little effort also from your side.

      It seems you, DAVE and ROM, have in mind merely a kid kite, instead of a huge “Mazinger-z” robot flying a wing with a tensor-structural resistance of more than 500kN. Your concerns are a positive confirmation of the powerful nature of the phenomena, and our scaling up of the concept was precisely to deal with such winds intense behaviors, fruitfully exploitable it in most weather conditions.

      Contour conditions:
      1) I am talking about the C and D conditions depicted in the graph above (fig 29), because very low winds of B imply lower forces and longer reactions. I could admit here some tricky conditions appearing just during the takeoffs and very close to the ground.

      2) We are talking about possible wide turbulent wind phenomena, because the micro, mini and meso scale turbulence are well dominated and flattered by the wing itself.

      3) We focus on wide gusts suddenly varying direction and intensity, considering that in storms and typhoon condition we easily avoid flying. Slightly affecting the overall availability.

      Ok, I try to give another representation, consider the wing, that is only 250kg, trusted by an engine of 200 horsepower, the wing is equipped of bilateral aero-brakes allowing the U turns could completed in less than 60m diameter at 80 m/s, it is like a fighter in dogfight.
      The wing fly in the own reference air volume having constant local parameters (vectors), including speed, axial (ropes) forces, lift, and drag. The wing aerodynamically processing this volume is well tensioned, like a drum skin, therefore gaining high stiffness and a well deterministic behavior.
      The wing moves precisely as it is firmly steered by a three-dimensional virtual “rollercoaster” railway in the sky.
      Only inertial transients could briefly diverge the control setpoint with the real position, but the very low system inertia limit to milliseconds and inches the unwanted bending ranges of the possible disturbances. The wing aeroelasticity features is obviously designed and dimensioned accordingly.
      Now we could introduce that the wide enveloping air volume is randomly wobbling, oscillating, gusting in all possible directions and intensity. As you already pointed out, we could meet 5knots in one direction followed by 15 knots in the opposite direction in few meters.
      Now we can move to the world coordinates, in order to evaluate what it means. The described air volume transient is 20knots, also said 10 m/s. applied to a flying wing at a speed vector of 80 m/s, resulting in world coordinate a possible fast variation that ranges from 70 to 90m/s, without affecting the aerodynamic and slightly the inertial dynamic.

      The light and very stiff drums, hosting the ropes, are linked to a MW alternator that occasionally could operate as motor of the same power; a typical figure is 25ms for 10m/s variation of the tangential and rope speed. Additionally the wing itself, through the onboard accelerometers continuous monitoring, early announces the impelling need of those reactions (at light speed of the radio communication link).
      By the way, you seem proud to tell us to entrust your life to those very harsh conditions and getting out alive, our less bold presumption is to send there only a wide chunk of kevlar and carbon fibers composite, were 50 g are not blooding out the onboard microprocessors brain.
      It is bizarre that a farmer of a no-man-land is concerned about the occupation of territory; also, the concerns for rare intermittency is overstated, as Euan has here shown that even if transforming all the electricity to hydrogen and back, the ERoEI stands well over 100. The quick dismissal and qualitative economics about social usefulness worthiness utility of such a high EROEI opportunity reveals a misconception of the magnitude of the energetic matter, which is far more important than allowing hobbyist pilots exclusive use a resource that can save humankind from the decline due to energy poverty.

      • Alex Terrell says:

        “, through the onboard accelerometers continuous monitoring”

        I was wondering about that. How do you power these? I’ve worked with a company that uses energy harvesting – piezio electric forces from the fabric vibrations – to power positioning devices.

        “The wing moves precisely as it is firmly steered by a three-dimensional virtual “rollercoaster” railway in the sky.”

        Are you still not trying to control the kite with elastics? I say that because any 2km cable is elastic.

        The fundamental control question might be: If the control ropes twist round each other due to a spin, will it then correct when it stops spinning?

        I like your analogy of a fighter pilot. 2g forces will probably rip a glider apart and 5g will make the pilot lose concentration. 50g is trivial for a kite.

        I think thunder storms and freezing rain are two conditions to avoid – but as you can reel in in 2 minutes, the actual down time would be very small. (Though if you reel in in freezing rain, you won’t be able to launch again until the ice has been removed).

        I would like to see ONE Kitegen operating for a year before we put them into clusters 100m apart.

        Can I e-mail you with a suggested development and manufacturing partner?

        • On board power Supply:
          We discarded the piezo solution because it work on delta forces and we are stabilising all, we developed instead a micro-turbine carried by the wing a sort of aircraft RAM air.

          Elasticity of Cable:
          when the rope force is stabilised by the ground station the elastic behavior is pretty cancelled or unexploited.

          Wing spinning:
          We demonstrated that about 10 twist is the limit before loosing the roll control of the wing.
          The control detect and maintain updated the spinning turns in order to choose the untwisting path.

          Suggesting Partners:
          Yes, please, this is the main reason of my public apparitions :-).
          We met hundred of companies with the scientific, technical and commercial side enthusiast to deal with us and our project, then after a while our dossier go to the table of M&A lawyers and the CFO, COO, CEO often economists. The two human categories that make me sick, so the negotiations epilogues often risks to be creepy. I always hope and eager to met companies leaded at the top by smart guys nor dumb and greedy MBA international champions.

          enermatt(_a-t }kitegen.com

      • For more clarity, the cited 200 horsepower engine is virtual, It is the aerodynamic lift vector component that trust the flight. And it is a little percentage of the power that the wing provide to the base generators.

  18. Thank you Massimo Ippolito for a brilliant concept. Full marks for perseverance. I am not surprised the “Greens” are not interested. Their money comes from elsewhere and they have their own agenda.

    I was wondering whether it is really essential to always use your concept for generating electricity. Here are two alternatives:

    1- Pulleys could directly turn reciprocating pumps that raise water. The water could run turbines when electricity is required.

    2- The reciprocating motion is perfectly suited to raising heavy loads of minerals from open cast mines. At the moment, huge trucks have to be driven long winding roads circling the excavation. Obviously, the bins would need rails to guide them. Currently, vast amounts of waste material has to be removed in order for the mine to go deeper. If the digging were better targeted, that would save a lot of money. Here are some examples of these mines.


    Also, these mines are frequently in isolated locations where fuel and maintenance of the trucks is very expensive. One tyre may cost $50,000+


    • Euan Mearns says:

      Alfred, I don’t know why your comment went to moderation. Every now and then one of my own comments gets sent there too 🙁

      While I’m sure Massimo will be interested to read this, remember that a vital part of system operation in yo-yo mode is the ability to send electricity to actuators to recall kite and to maintain constant force on ropes.

      • I think that the kite can have some controls. You don’t need to pull an aircraft down to the ground so I don’t see why it should be any different for a kite. These controls could manipulate it by changing the angle of attack, for example. Anyway, being able to change the angle of attack (like for some propellors and most wind turbines) allows better adaptation to wind conditions.

        Massimo explained how the kite generated its own electricity (“we developed instead a micro-turbine carried by the wing a sort of aircraft RAM air.”) so the power is there. I appreciate that the two-cable approach is his preferred one, but it does not have to be so.

        With appropriate telemetry (Wi-Fi? optical fibre?), it should be possible to automate all of that. If the lift from the kite suddenly changes, the water pump would adjust by itself as would the ore bin’s rate of ascent/descent – stabilising negative feedback.

        I am just making the point that this is an entirely newish field and all sorts of options are up for grab. There is not such thing as one perfect solution for all conditions.

    • The Greens agenda is scaring!

      I think that to go electrical, and the use it for other applications is the most elegant and effective. i.e. pumps needs high and constant RPM to be effective, and an electrical motor is less expensive than a geared mechanical power link.

  19. Kite Gen concepts look constantly less complicated than competing ideas,
    and so result usually elegant too.
    I am not engineer but I suspect they’ll be also the most efficient.

    I come to guess Massimo Ippolito shaves himself regularly by Occam’s razor!
    Ad maiora!

  20. Alex says:

    How does the Kitegen compare to a traditional wind turbine in terms of visual impact and noise?

    In the UK, onshore wind turbines are pretty much blocked as too many people object to the visual and noise impact, and this feeds through to Government planning policy.

    How much noise does a Kitegen make?

    I assume the cables are invisible from a few hundred metres away, but will people accept their distant hills covered in kites? At what distance do they become visually insignificant?

    This is a famous image used to knock wind turbines.
    It’s actually taken with a high zoom lens so is misleading, but reducing visual impact is very important.

  21. Eric Swanson says:

    Euan, you wrote: “ A kite does not slow the wind in any appreciable way.”

    Actually, any flow around a solid within the flow will cause a disturbance, so your statement is false. The concept of a “stream tube” (or, multiple parallel divisions of the entire flow field) is used to describe the flow past a fixed turbine. In that situation, the disk area intercepts some of the flow and in the process, the flow slows. What this means is that the conceptual “tube” which delivers this air to the disk has a smaller diameter at a distance up stream from the turbine and as the flow continues downstream, the tube widens further. Thus, the mass of air flowing thru the disk is less than the mass which would flow thru a similar size disk without the turbine blades. The result is that at maximum power, the the most power available is defined by the Betz Limit. Furthermore, other effects, such as surface roughness, reduce that actual power output, which can be described as an overall efficiency term as a fraction of the power at the Betz Limit..

    A similar effect is used to visualize the flow over a wing in 2 dimensions using “streamlines” and these are easily demonstrated in a wind tunnel. The resulting single aerodynamic force is divided between the two terms, which depend on the coordinate system used for the specific design. In the end, the force on the tether is a combination of lift and drag. But, without specifying the coordinate system, the use of terms like “Lift” and “Drag” are meanless. Usually, “Lift” is the vertical component, which keeps an aircraft aloft, but the KiteGen device may not follow that convention. Adding three dimensions and maneuvering just adds more complexity, such as yawing torques, which causes instabilities.

    The Ampyx glider has full 3-axis pitch, roll and yaw control, which allows it to “fly” down toward the base of the tether while descending. This process would reduce the force on the tether as it is reeled in, which would minimize the required power to recover the tether. The KiteGen can not do that as it has no pitch control, IMHO. With 3-axis control, the Ampyx glider could be recovered if there were a broken tether or other problems, such as sudden drop in wind speed or a down burst from a storm.

    • heavyweather says:

      The Kite is depowered during the reel in phase. It is “slipped” to minimize the profile. When one theather snaps the kite is automatically depowered and can be reeled in at high speed to bring it down.
      The glider concept is also interesting though but I believe the gliders operating speed is much higher. There is also just one theather.

  22. Eric Swanson,

    If the kite were performing a figure-of-eight, or simply circling, the diameter of the “wind tunnel” would be such as to make the statement “A kite does not slow the wind in any appreciable way.” a reasonable one. Wind-turbines are another matter.

    The terms “lift” and “drag” are quite clear when one considers the kite as the centre of the coordinate system. The same thing is true with aircraft – where is the airspeed is much more meaningful than groundspeed insofar as the aerodynamics are concerned.

    However, I do agree with you that the Ampyx seems to present an elegant solution. Essentially, the controls would be shifted from the ground to the kite – it needs one cable plus telemetry.

    I am wondering how long it will take the various armed forces to work out that a rapidly-moving and oscillating kite would make an excellent cheap platform for directing artillery. The siege warfare in Syria (e.g. Aleppo) would be a perfect testing ground. If the thing were made of cloth and bamboo, and equipped with a video camera, it would not matter much if it were shot down. Keep in mind that doubling the accuracy of a shell leads to a four-fold increase in its effect. Who would need satellites and GPS in such an environment?


    Sorry. I forgot that my ex-employer would not be very happy

    “Currently in low initial rate production, the Excalibur shells are coming in at around US$140,000 each, but once full production begins, the new Excalibur XM982 rounds will cost roughly 30 times more than existing unguided artillery shells which costs around US$1000 each, but are only accurate within 200 metres”


  23. The terms “lift” and “drag” are quite clear when one considers the kite as the centre of the coordinate system. The same thing is true with aircraft – where is the airspeed is much more meaningful than groundspeed insofar as the aerodynamics are concerned.

    exactly, no need to reference the coordinate system, because it is always the aircraft.

    At the beginning of the concept wasn’t enough documentation, now it is plenty and available, I consider a pure provocation spreading uninformed doubt or asking us to teach base concept that are in common with aeronautic science, Google scholar report hundred of papers on the issue, done by hundred of authors that explain at best the concepts.

    In case of a discussion about the nuclear power opportunity, I think should be fruitful avoid to enter again and again in the detail of the cross sectional behavior of thermal neutron, It is better to push ahead the thinking,and project the technology in the reference economic and societal scenario.

    The case of KiteGen is the same, from the theoretical, experimental and technological point of view everything was successfully done. We are now looking for a critical mass of professional, companies and good planning to give concreteness to the new opportunity in order to put it at the service of our society wealth.

    This critical mass is quite small compared to the impact, no needs to persist explaining the concept to who is unable to go deeper, it is a waste of time.

  24. good news!

    KiteGen always maintained a very low profile, pretty absent, in scientific publications and congress proceedings, because it is a private research company, and it could arise the suspect to endorse the technology for commercial purposes only.
    KiteGen striven for allowing independent and uncorrelated academy works, in order to provide the concept itself of the best provision of thought and well educated publications on the great opportunity for mankind.
    Our understatement strategy was partially successful because we could now read hundred of papers explaining in detail this unimaginable good and novel source, in the meantime some works, obeying mainly to the climate/subsidies bandwagon, pointed out non existent concerns and dismissal tentative, that provoked harmful interruption of support and delay to this powerful engine for the word economy and ultimate solution for the human ecological footprint.

    The intrusion of huge economical interests inside the scientific and academic institutions is becoming worrisome and is leading to a flourishing of ideologically biased papers, especially in the field of solar and wind renewable energies, where many scholars are committed to producing papers with the aim of artificially boost the low efficiency of these energy sources and introduce topics to increase unreasonably the climate alarm in order to enforce the call for government subsidy support for them. These forces are also acting against any concept that might raise the suspicion that there are ways other than subsidized low efficiency and expansive energy sources.
    One of the worst and recent conceptual attach to KiteGen was about the role of the ropes drag and weight in the energy production performances of the high wind, limiting the possible operative height of the wing stating a deep loss of power.

    As happen in settled climate science , were oversimplified models and omissive assumptions, leads to wrong and scaring results, we too were the victim of the same, well trained strategy, consisting in publications adopting a wing-rope rigid body model, obliging us, to suspend the engineering activities in order to revise this mayor “no-go” theoretical obstacle.

    Our working group, including physicist and master degree in energy engineering is investigating the mismatch between the real behaviour and all the papers and theoretical works done on the rope drag and system drag. (Argatov and others).
    We already discovered several errors all-detrimental for the concept, but of minor importance like the propagation speeds of the forces on the ropes.
    The propagation speeds are in two directions and very different, one is the fast axial propagation and the other a much slower wave propagation, that imply that each kite movement is perceived with an important delay by the ropes, so the wing flight speed is always much higher than the mean rope speed divided by two, greatly reducing the drag.
    Today we have finally focused the main problem arising from all the publications, which is geometrical; it is related to the use of the aerodynamic wing barycentre point of application of the additional rope drag.
    This is clearly an error because imply again a rigid behavior of the system wing-rope that is obviously non-true having a joint with only one Degree Of Freedom (DOF) blocked: the distance.
    The rope drag fall in the axial force with a progressive bending of the rope itself that expose a tangent vector that could be divided in the axial force and a tiny drag, node by node in the discrete representation adopted.
    So the novelty is that we could consider now in computations the full aerodynamic efficiency of wing without any reductions effects, instead the rope delay/drag acts on the wing imposing a slight angle change that has effects only in the cosine part of the formula much less disadvantageous than the efficiency cut.
    We will publish soon the document and the findings.
    The bad news is that now we clearly know that the wing will be able to develop additional forces that go well over the current specifications.
    For me this is a paramount achievement because this issue was the worst well educated critics against the concept without having a good answer to offer.

    • Hello Massimo,

      It is obvious to me that the fundamentals of this concept are sound.

      I would try not to pay too much attention to detractors who are using computer models that are not based on reality, or formulae that are inappropriate. I would go ahead and publish actual _experimental_ data. Preferably raw data that people can try to model with software that gets close to reality.

      The “climate scientists” have a lot of expertise in producing fake data from skewed computer models. Kindly ignore them.

      Luckily, you do not have to wait for decades (or centuries) to prove that their models are fake. You should already have enough data to skewer them. Just put it online and watch them squirm.

  25. @Alfred Nassim
    Obviously we are eager to show the data of the new wing, but after the geometrical validation we are currently dealing with its production, including multimillionaire investment contracts on a huge autoclave and carbon mold for the wing composite curing. The new tests take several months to be performed, then the new data will be available. The raw data of the old test (research prototypes) are in my opinion superfluous and harmful. The most important parameter is the wing aerodynamic efficiency that play a quadratic role in overall power, thus economy. The inflatable edge sport kites have inherent low efficiency, as they have to safeguard the hanged people. A sport kite has a typical 4 efficiency only, instead our new composite wing is 7 times better, this implies 50 times more power with same area and conditions.

    By experience, most people consider only the wing area as a boost factor to figure out the performance improvement, so our old raw data are misleading without a deep knowledge of the theory. The area of our new wing is 8 times larger, combined with the previous x50 gives a 400 times improvement.

    If you want to fight with those data, they are available here:
    Be careful that I have heavily low-pass filtered and decimated in order to graph fig22 nicely, so the values are smoothed.

    However I want to stress that KiteGen, a design and engineering company, is not trying to sell (or oversell) machines. By the contrary, it is gathering around the project a full organization of individuals and companies in order to manage all the aspects of the industrial development, from the production to the deployment. The involved partners will have mandatory enough skills to distinguish the relevant issues. For the moment, our message is addressed to a restricted number of aware and active people. Everybody who believes to be in that number is warmly invited to join us.

    • Euan Mearns says:

      Thanks for posting that Massimo. So how long do you think it will take Roger and I to chart this? Eyeballing the data one thing I notice is that the current on the two alternators is normally the same but in short intervals different, presumably where flight adjustments are being made?

      • Yes, the kite behavior to the respect of the ropes is like a far-away free pulley. Typically the two ropes force and the currents are always the same, excluding transients and/or servo-drive tuning inaccuracy.
        Note, that due a log setup error during this test the rope differential is the set-point (command) not the actual data, but very close.
        This data were collected in one of the numerous field test sessions, to give an idea of the experimental setup, here a film:
        There is also the audio track but checking with my browser is mute, let me know .

    • Euan Mearns says:

      (Click chart for large readable version).

      Here is my first pass on plotting some of the data. The data are recorded at 0.1 second intervals resulting in 25000 lines for this 42 minute’s worth of test flying. I’m plotting the current on alternators A and B. The black line plots the differences. I’ve plotted current and not power, but the voltage is held constant at about 324 V, giving a power output of 6.5 kW at 20 A on each alternator.

      The chart plots the first 5000 lines equal to 8.4 minutes of flying.

      There are a number of simple observations which I’m sure Massimo accepts as routine, but for those of have not had access to these data may find enlightening. I hope Massimo calls by to conform or correct my non-expert interpretations.

      1. dA-B is normally zero which I presume = same reel out speed on ropes A and B? Or is it = force on ropes? 🙁
      2. Power output is normally positive but with negative spikes that I presume reflects transient flight control recalls. A possible next stage is to look at cumulative power production.
      3. There are two longer recalls lasting about 3 seconds which align with Massimo’s chart (below).

      One of the interesting things for me here is the challenge of charting and presenting the data. Massimo has smoothed and decimated the data in his chart – something I am quite accustomed to doing with Gridwatch data. The challenge is to not lose the detail. 8 hours at 0.1 seconds = 288,000 lines of data.

      • Alex Terrell says:

        Modelling the data I get a similar curve using a 50 Moving Average of Power:
        It would be interesting to see a longer experiment, but:
        – Without the Full Power wing recalls, which confuse things a bit.
        – A parallel measurement of ground wind speed – and ideally where we can get some variability in this – so if the forecast says “winds picking up during the day”.

        Regarding the sideslip:
        > At 2329.64 seconds, for 4 records (0.4 seconds), the current on A goes negative (c -70A) and that on B goes highly negative (c -160A). So B is pulled in faster than A. Then B-A goes back to it’s normal 0.1.
        > At 2412.06 seconds, for 4 records, the currents go to -170A and -70A. So basically the reverse for 0.4 seconds, and then it starts to power again.

        They might get the same effect, with less force, by making the currents -100A and 0A? i.e. free-wheel on rope and apply force on the other.

        Incidentally, this is a ~10KW system. It will be useful for testing sites before a 3MW system is deployed – just like they put up wind speed towers for a year or so before building large wind turbines.

        • @alex
          Please, let imagine the work flow.
          Monday: test on field, the airport was reserved to us.
          The rest of the week to wrote the software code and fix the hardware issues, to test the next Monday.
          So, all the Mondays were overcharged of test plannings.
          The side-sleep was tested with different strategy and spread in months, I do not remember to what version belongs this data, likely an early one, because the final was done with different delays starting the reeling in.

          Your idea to test (and certify) sites in advance with the little systems is great and could have a very interesting business model. I never mind this opportunity.

          • Alex Terrell says:

            Test; Evaluate; Reprogram; Repeat.

            Finally get some where, and then decide to make an improvement, or a supplier change.

            Test; Evaluate; Reprogram; Repeat.

            Tedious – but I suspect your testing is more fun than most.

            It gets easier when you can actually do real life testing, which in Kitegen’s case is leaving the kite running for weeks.

      • @Euan,
        the 3 sec kite recall, are certainly a kite speed boost, perhaps who was piloting get out from the wind power spot, and decided to come back with the power provided by the generator instead the wind.
        Yes, my data decimation loosed details and peaks.

  26. Massimo Ippolito, I really appreciate the fact that you went out of your way to put together such good documentation based upon what you know — or rather what you think you know. At the first international conference on high altitude wind power generation in Chico California I was honored as being the Father of Modern TetheredWing Technology (my name for it now). If you are among the few who have not received a copy of the paper I now call TetheredWings please email me at zain(AT)soaren(Dot)com. I now focus almost all of my attention on flying without fuel by sailing in air alone. But I would be glad to give you some pointers you should find most useful. Since you went way out of your way to help everyone know TetheredWing technology (the name I coined for it). I would like you to take up the ball to help the “Airborne Wind Energy” folks on both sides of the Atlantic focus on what is far better though at odds with what people think, do, and say now. I will give you the best clue that should motivate you to focus on what is real rather than what people think or suppose. That clue is the existence of “low level jets” where the wind power at 1000 to 2000 feet. can often be as much as 5 times as great as the winds at the tallest of wind turbines. With a lighter-than-air wing high enough to just be within the bottom of such a jet — tethered to another such wing just below the low level jet then the tether could be short — but you could now sail in air alone — and tack to go anywhere and arrive even faster than the wind blows. For example, if the winds are blowing from Tokyo to Portland Oregon (God’s country) then you could tack from Portland to Tokyo and arrive at Tokyo in less time than the wind would take to leave Tokyo and arrive in Portland.

    Massimo, I could tell you far better ways to generate power from high altitude winds, and I might decide to do so just between the two of us, but I would like to know that it would be used to help low income people have their needs met first and foremost. I also own the KiteEnergy and TetheredFlight domain names which is far better than …Airborne Wind Energy …. because it does not even imply that tethers are virtually always used to extract energy from winds to provide practical power on earth or in flight.

    P.S. What I know is so far beyond what people know now that I very rarely take the time to see what others come up with. But I could not help but be greatly impressed with this presentation of yours. I appreciate this article in that it helps people come together and focus together. I have lost patience with the ….AWE… organizations because they do little besides bicker for morsels. And they accept projects based on drag just as much as those based on lift.

    I was a project leader at the Flight Research Institute (FRI) — a non-profit offshoot of Boeing — and the retired Chief of Product Development at Boeing and his right hand man, a retired Supervisor of Aeronautical Architects both came out of retirement and offered to help me voluntarily because they say the potential that could be developed. It was there twenty five years ago that I first came disclosed the prospects of flying without fuel — thereby potentially making all forms of transporting people and cargo obsolete and vastly less expensive — with just a couple inflated gas bags in the shape of wings — and making it possible to extract power from the “Roaring Forties” where the winds are so powerful — below Tasmania — that few ships consider going there — yet it would be about the most abundant wind resource of all — allowing anyone to drop sea anchors — and convert vast wind power to hydrogen — to take to Japan to sell for three or four times as much — to generate clean power during times of peak demand — and gladly pay three to four times as much rather than let people die in the smog.

    Let’s talk privately. You seem entirely reasonable and willing to promote what is right rather than that which merely makes affluent people ever more affluent — with little or no regard for those who need such technologies most.

    By the way, I think it is Google that is flying helium gas bags to make the internet accessible for everyone. They have some success because they can direct the gas bags to sail almost anywhere by the amount of compressed air they make. The winds go in different directions in strata at different altitudes. They can fly anywhere — to some degree — by having the gas bags merely float at different altitudes. Your meterological aspects of this paper need to be brought up to date — winds are not just blowing one direction overhead as people erroneously want to believe. Last thing, I am busy, but if anyone wants to discuss things please do so directly at zain(AT)soaren(DOT)com. Zain is my super-secret pseudonym.

    Thanks, Wayne German

    P.S. I would be pleased if we were to work together to make such documents together. I would like to toss outlines to you to add your things to — then make great documents like this that people might choose to take to heart.

    • Eugenio Saraceno says:

      Dear Mr.German

      At KiteGen we are very pleased to hear news from you.
      As you noticed in your message KiteGen has for a long time maintained a very low profile in communication. We preferred to focus on the technical work and validation of the 80+ components of the first industrial scale KiteGen Stem 3 MW and reached the Technology Readiness Level 8 (working prototype at final scale).
      Recently we decided to go ahead with a new work phase aiming to gather as many concerned experts as to reach a critical mass to help support the industrialization and the step up to TRL9 and the first productive kite farms.
      We will send you soon a email with further details

      Best Regards
      Eugenio Saraceno

      KiteGen JDA Project Manager

    • @Zain
      Hi, I missed to thank you when you rescued me time ago in the hot discussion about patents with the AWE people. So thank you very much.

      Massimo, I could tell you far better ways to generate power from high altitude winds

      German, I’m perhaps interested to a bit worst way to generate power! Because an ERoEI of 500 imply directly an IRR greater to 120% in 4 years. It is so amazing and lucrative that nobody trust us without having a deep understanding of energy issues and technology.
      I’ve tried in any way to domesticate the balance sheet of the machine production activity in order to reduce the expected return, but finally appear clearly the artifacts.

      Our TRL8 -> TRL9 financial plan follows:


      Balance sheet description:
      The machine selling price projection is based on the actual productivity of the generator (MWh/MW) that is foreseen to start by low values and grow steeply in few years as the technology is now ramping up the learning curve. The feasible technical productivity level of 6800 MWh/MW (paretian saturation of the learning curve or 80% of the target reached by the 20% of the effort) is foreseen to be reached after seven years and about 20 GW installed. Then the productivity increase is envisaged to continue up to the theoretical limit of 8000 MWh/MW at a very slow rate towards the maturity of the product. Please note that the projected IRR for the investor is targeted at less than a one third of the envisaged productivity rate
      The machine projected production cost is based on real market surveys provided by our supply chain on the basis of the scale scale (discounts on number of items to be produced). The cost evaluation reached the best maturity as several prototypes at industrial scale were already done
      The easy logistic (generator units lower than 20 tons) allows doubling each year the machine production as in the projection.
      One of the factors helping high revenues is that the commercial structure costs are negligible, having available hundred deployers looking for novel RES.
      Though the astounding IRR is appropriate for balancing a high-risk investment, a proper technical due diligence can easily show that the most of the perceived technical risk of the project has been mitigated by careful design and methodology for validation. We are aware that is a cost a new concept with the highest potential like KG has to pay.

    • Euan Mearns says:

      Dear Wayne, thank you for your kind words. Would you believe that I knew nothing about high altitude wind and tethered flight 5 months ago? Massimo is either a good teacher or I am a fast learner 😉 (a geologist by training).

      I visited Massimo in Turin in April. He has a small team achieving huge things. In fact I couldn’t quite work out how so few have managed to deliver so much.

      We are discussing at present the best way to support this effort going forward. I know that Massimo is frustrated seeing huge sums in subsidies going to support solar PV in countries where it is dark or cloudy most of the time and an evident reluctance to support HAWP. But I suspect this is partly down to how the message is delivered. I think it may be the case that a single $50 million internationally funded strategic project may deliver a lot more than 5* $10 million spread among small groups.

      My wife tells me I have to go eat dinner. More later.

      Best Dr Euan Mearns (blogger)

  27. jim moore says:

    Hey KiteGen folks,

    I was thinking about the drag caused by the cables that you use. Have you thought about changing the cross sectional shape of the cables to reduce the drag? If you are using cables with a circular cross sectional shape, you might reduce the air resistance by giving the cables a tear drop cross sectional shape.

  28. The carousel concept should work fine. I fly a rotary network of kites for AWES without any control input. It should prove “easy” with control. Networks of lift kites (as well as kite speed) can alleviate many of the meteorological instability concerns in this thread.

    • Hello Rod,
      I recognize in you a precious live memory of the concept evolution, I think is arrived the good moment to internationally joint the efforts…
      About the Carousel, I agree with you, I hope that enough culture was spread on the concept, in order to propose with more chances such projects to communities.

  29. Serphin says:

    I think one easy/big boost that Eaun could provide would be proof reading of English texts. While Massimo’s English is far better than my Italian will ever be, when trying to present new and strange concepts, it is better to remove as much friction as possible.

    • @Serphin, I agree with you, the most important problem KiteGen is facing is the complexity of the technical and sophisticate message (however in Italian too).
      Our risk is to waste it due our language barrier, leaving to believe that we have invented a hammer , and now everything looks like a nail. Instead there are a lot of nails out there (energy poverty, dwindling resources, decreasing returns…) and we have made ​​efforts to find the hammer suitable.
      The international communication, where English is hegemonic, is particularly important due the few people aware of the big picture worldwide, that could appreciate the potential impact of High Winds.

      I know how complex is to build in mind the good images of a novel concept, I fear we will never be able to render the expression quality required to spread the opportunity. That’s pity because a deep understanding is urgent and a common interest, and at this pace we will in delay to make the needed critical mass.

      • Euan Mearns says:

        @ Serphin and Massimo:

        There are communication issues at a number of levels. The Italian – English language one is the least important and easily overcome. But the way Italians and Anglo Saxons (or Scots) express themselves requires an additional layer of understanding. Figures of speech and the way we express things differ. This requires a little more work.

        And then at level 2 there is how to understand the physics and engineering of HAWP (high altitude wind power). Translating that from Italian to English is not such a great problem since it is written in the language of science.

        At level 3 we have the problem of translating why the world needs HAWP and explaining this to global institutions and national governments. At this point we have the challenge of explaining complex energy production technology to solve energy problems few understand. Over the last 10 years Massimo has invested a vast amount of his effort to develop an energy production technology aimed at solving cheap energy scarcity problems that the world does not know it has and is trying to explain this in English from an Italian language perspective.

        I’m hoping that Massimo agrees with this so far. But at the next level I think our views may diverge. My view is that KiteGen stem must absolutely be given the opportunity for full-scale commercial field tests – which are not cheap – but beyond that the multi-polar energy market will decide which options are best for global energy production and security and climate policies.

        • OpenSourceElectricity says:

          For the last point one has to keep in mind that market forces are perfect to find a local minimum of prices, even if this is continuously moving due to new developments. It is not good in getting from one local “hole” of prices to another hole which might be even significant deeper, if the barrier in between is too high. A market will then remain at the local minimum. A state could then decide to force at least a part of the market on the other side of the barrier and let it start it’s optimisation work there, to see how deep the new hole is.
          When doing this is a good idea is always a big and difficult to answer question, as well how to do this best. But it is known that opportunities which can not be made pay out with a maximum of a low two digit number of billion Euro’s or pounds will not be considered by market forces. Even if they are attractive. OFten private investment hesitates at even lower sum.

          • Too rational thinking, around I see only peak prices not holes. my “too high barrier” explanation is that Kyoto protocol bandwagon knows very well HAWP and is scared from it. They fear to make the same end of Montreal protocol were industry quickly solved the problem with the R410 series. Kyoto protocol’s agent are everywhere, including the EU DG research, the National departments of climate change, Bloomberg, IEA and banks (eib, db, world etc).
            They approve and sustain only energetic presidium worsening the emission balance, in order to maintain the alarm (and consequently their undemocratic power) at the highest level.

      • Sorry Euan,
        I think you missed the point.
        Over the last 10 years, I have invested an amount of my effort to advocate and teach basis of a novel, abundant, reliable, feasible and sustainable energy production technology that require an investment aimed at building around the project a critical mass of awareness, professionals and partners companies. All those must involved to take care of all needed brand new components to develop and mass-produce, including set-up the deployment and maintenance teams, protocols and strategy. In brief, a so-called detailed industrial and business plan and supply chain set-up.

        45 years after the moon landing I do not think that a big robot flying a big kite is worse than such rocket science. I have also invested part of my effort to publicly provide and register detailed description of all technical solutions needed to serve and launch the industrial initiative; I wrote almost 40 proposal aimed to obtain public support due the highest societal importance of such solution. The proposals, was one of two awarded but incredibly only one of 40 effectively funded.
        In the meantime and during some WE, I have craft-worked some small 40kW prototypes able to produce energy and to show the main achievements, like the side-slip and the automatic flight.

        The multi-polar market could decide to use for a while parasitic energy technologies, but not forever. Seeing at the economic brilliant results is become urgent to switch on real source of energy, that currently only the long proven coal and the short proven HAWP could provide.

        The full-scale demonstrator is precisely the full-scale industrial generator, no differences.

  30. “They approve and sustain only energetic presidium worsening the emission balance, in order to maintain the alarm (and consequently their undemocratic power) at the highest level.”

    Absolutely correct. IMHO, the problem with this site is that it is engineer-rich. However, the people who are pulling all the strings and making the decisions are “politicians”. They are all in it to maintain their power – at all costs. They don’t care about anything else.

    Right now, for an academic, the best way to get research funded is by somehow helping these people maintain the “global warming” agenda. They know that only by scaring people can they maintain their grip on power. They do not want any efficient alternative to the status quo. They want all solar panels and wind turbines to plug into the centralised grid. They are perfectly aware of the intermittency of solar and wind in the UK, but keep on plugging it. Glasgow is an extreme case.

    “Revealed: how Glasgow will be Scotland’s first Solar City”


    A hilarious piece of fiction which shows how this process works is “Solar” by Ian McEwan. It is not only funny, but makes a serious point at the same time.


  31. Euan Mearns says:

    Massimo, it is with some trepidation that I reply 😉

    The full-scale demonstrator is precisely the full-scale industrial generator, no differences.

    This statement is only true if the full scale demonstrator works. Now I believe you believe the statement is true which implies you have 100% confidence in success. While it is perhaps necessary for the inventor to be confident in his own abilities, I don’t think anyone else reading these pages will share the same level of confidence that you have. It is in fact a dangerous precept with investors to say there is no risk. They won’t believe it and will be scared away.

    100% confidence among investors, customers for KiteGen and consumers will only follow successful testing of industrial scale prototype. Industrial scale trials are an essential step on the way to full scale production. You may not see things that way but I assure you that everyone else in the game will see things from my perspective. That won’t stop investors who will weigh risks against the potentially large rewards.

    The greater challenge is to create the critical mass of expertise required to advance this project through trials to manufacturing. The way I see things is that money comes first (that’s the easy part), people follow, then successful trials, then orders and a lot more money that can be invested in establishing both technical and engineering courses at colleges and universities. There is a sequence of events that have to occur. In my opinion it is impossible for all of these things to happen simultaneously.

  32. I feel compelled to comment again. To be as dismissive as you are, you are not cultivating a position based on objectively analyzing our history, experience and our industrial plan – but on pragmatic skepticism. A pragmatic skeptic never shaped the future. I would prefer a more “industrial and systems engineering’s approach”.
    You seem to immediately associate anything that is little more complex as risky or non-viable. Look into the future, when and if this deadly energetic crisis would be overcame (thanks HAWP), don’t you agree that the future is going to be filled with highly complex systems, that are also far more effective that simpler systems? Being a light and intelligent system is the absolute superiority of KiteGen.

    This statement is only true if the full scale demonstrator works.

    Yes obviously, but here the good news for investors and partners: The working full-scale demonstrators are very close to the mass production machines, which are quite cheap to duplicate.
    The overall approach is like a brand new aircraft. Before it takes off for first time testing, it has to be completed technically and operationally. The full-scale generators manufacturing, here is the challenge, must approach the final quality in order to reliably perform the wing maneuvers, thus involving a full factory or a supply chain able to provide the numerous components and sub-assemblies of the machines at the highest level, respecting design and specifications. A supply chain involvement is hopefully a lighter solution than a full factory. We are in hurry to complete the partners panel, because the first five companies have started to work on the project, and some important role isn’t still covered, despite we meet many including Chinese ones. The risk we are facing is the missing ring of the chain at the coming operative milestone.

    Said that, KiteGen is much easier to set-up and test compared to an aircraft:
    – No test pilot safety issues;
    – No destructive or particularly harmful or dangerous failures.
    – Thanks to the big robot, we could perform brief sequential takeoff and landing in order to progressively set-up and tune the control reactions up to the full operative flights, without the risks to crash the big wing in this early phase. We are currently physically validating our wing features through aborted take-off while cross characterizing our multi-body dynamics simulation. This has already led us to rework the big wings 3 times for geometrical and materials adaption and optimization; it seems to be enough perfected now.
    -The more expensive part is currently the wing, but it is a consumable. However, the most time consuming activity is the installation and setup of the robot itself, including the generators connected to the grid, which fortunately are stable and well fixed at ground.

    Now I believe you believe the statement is true which implies you have 100% confidence in success. While it is perhaps necessary for the inventor to be confident in his own abilities, I do not think anyone else reading these pages will share the same level of confidence that you have.

    Obviously, I am 99% confident, as are my collaborators, the good as the wrong experiences during test and design loops, built us this strong confidence; we never met somebody able to satisfactorily argument his own criticisms or skeptic attitude about KiteGen or HAWP.
    In the optics of collaboration we are open for deep explanation and discussions, starting by looking in detail the technical basis for what could appear to be the arbitrary in our detailed FMECA documents and scaling up strategy,

    It is in fact a dangerous precept with investors to say there is no risk. They won’t believe it and will be scared away.

    No hope here, it is a brand new concept so the risk perception is there by default, thus inescapable. Good practices of professional investors and partners is to perform a competent technical diligence; my aim is to make them aware of the risks of missing the opportunity to be main actors in the new economic renaissance. Which consequently imply a large reward too. We need, I think, a good narrative behind the project, in order to start the technical dialog and the procedure.
    I have witnessed huge capitals being applied in several wrong directions, i.e. The Hydrogen Economy, supported by the Jeremy Rifkin’s book, which was, and is, clearly a dead loss. After such errors committed by investors I hoped that at least some competence in what really matter in energy would arise; unfortunately it is not the case, investors still put attention to well exposed and wider pictures or fashionable trends, instead energy balances.

    100% confidence among investors, customers for KiteGen and consumers will only follow successful testing of industrial scale prototype. Industrial scale trials are an essential step on the way to full scale production.

    Conquering such confidence after the demonstrators is no longer interesting for us and for the project, too late. Because the successful completion of the industrial scale machines will be enough to trigger the auto-breeding evolution of the technology, this is an advantage of its highest ERoEI. The full scale production is simply the duplication of the debugged full scale demonstrators, no difficulties no more risky investments. At this point banks could assist for the ordinary cash flow.

    You may not see things that way but I assure you that everyone else in the game will see things from my perspective. .

    I really do not hope so, your perspective here appears short sighted, and far away from the special machine industrial culture that we have developed in a life of work.

    That won’t stop investors who will weigh risks against the potentially large rewards.

    I’m looking also for investors who could share our vision, the large reward could be obviously financial but the aim must be a superior understanding in the problems affecting our time.
    Our commitment:
    KiteGen received the commitment to study all aspects, develop, advocate and deploy the novel concept able to convert the energy that the world needs. Providing accessible, affordable energy not only helps to make modern – day life possible in the developed world, it offers hope of progress and opportunities for many in the undeveloped world who have none. We are naturally committed to supplying energy in a sustainable and environmentally friendly manner.

    The greater challenge is to create the critical mass of expertise required to advance this project through trials to manufacturing. The way I see things is that money comes first (that’s the easy part), people follow, then successful trials, then orders and a lot more money that can be invested in establishing both technical and engineering courses at colleges and universities. There is a sequence of events that have to occur. In my opinion it is impossible for all of these things to happen simultaneously. .

    Ok, this part was already done, at least the first round trip; hundreds of publications, IEEE papers, Phd masterworks, awards, trial tests now we are focused to build a critical mass of operative actors around the project in order to go straight as possible to the deployment.
    No more research, doubt or uncertainty, only somehow a lack of good, smart and independent interlocutors. The main problems and difficulties are currently all outside KiteGen is strenuous to work having against us an established system of political and institutional power based on energy subsidies.

  33. Joe Faust says:

    Good start, Euan Mearns. However, there is much more that has not found it way into your first coverage. EnergyKiteSystems.net http://www.energykitesystems.net

    • Euan Mearns says:

      Joe, I’m aware I did not cover all and my focus was on theory and the current generations of MW scale generators that are being developed. What additional technologies and systems would you have liked to have seen included.

    • Joe, Your link leads nowhere. Why the mystery? Is it top secret? 🙂

    • @Joe Faust
      In my opinion, with your well-known big directory you have acted like a sort of hobbyist stamp collector never looking at the real value.
      In such case, I fully agree with Wayne German:

      I have lost patience with the ….AWE… organizations because they do little besides bicker for morsels. And they accept projects based on drag just as much as those based on lift.

      This shows a complete lack of understanding and a willingness to add noise above a sophisticated and complex topic to disseminate, causing damage to the great opportunity of quickly achieve a significant and destined to grow, complement to fossil fuels.

      • Joe Faust says:

        There are very many real values being traced. And the tracings are open for study and advance by anyone interested. Down selects will yet need to compete with one another; we are infants in the matter of open field comparison testing/competing; holding such activity back will cost the realm dearly; investments made without having the clarity from competition have a high chance of being lost; enough of such experience by investors will slow matters. It is hoped that each AWE team will open budget to achieve fair competing; such would aid scientists studying our technologies.

  34. kitedog says:

    Hi Folks,

    Kite energy is real, but the problems are operational and aviators have the right-stuff; the same basic skills and safety culture as other aircraft, when conditions are right. Reliable flight automation is a distant goal. Meanwhile, the FAA is requiring a PIC and VO (Pilot in Command and Visual Observer) of an “AWES” to do “sense-and-avoid” of stray air traffic.

    None of KiteGen’s patents are seen as blocking by competitors, since there is plenty of prior art. Payne’s seminal 1975 patent is now public domain. There needs to be broad comparative simulation and fly-off to reduce investment uncertainty.

    A new AWE design paradigm is emerging in the form of vast “rag & string” metamaterial structure with inherent topological stability ensured by many-connectedness of the latticed sail units and anchor field. A single control thread would thus suffice for GW scale production, and collminated lattice-waves could drive the largest legacy power plants, as kite-hybrids. When the wind lulls, fossil-fuels pick up the gap.

    Kite energy only works in global macroeconomic and ecological models by going really big. There are designs on the drawing-board for kite sails 1000-7000m2 that would just be single “kixel” units in vast multi-km-scale arrays. The kite design part is fairly easy, building on validated soft-wing design. The sheer megascale industrial competence and audacity required to go all the way, without killing anyone, is harder.

    Its going to be a very grand adventure to replace fossil fuels and nukes with kites. Welcome to all the wonderful new talent in AWE.

    dave santos


    • @KiteDog

      Reliable flight automation is a distant goal

      False, we already demonstrated and tested the automatic flight automation with two different methods:
      -One quite muscular with thousandth processors running physical and fluid-dynamic engines in real time providing the model based multi-predictive control;
      -the other with an artificial intelligence running on analytical models and algorithms.

      However, those are not the most complex part of the development as mostly could think, in my experience dealing mechanically with high energy and huge dynamic forces was the true challenge we faced.

      in addition, for who isn’t still available to trust the automation, a KiteGen stem could be able to gain at 20$/MWh about $500,000/year, enough room to pay, the loan the maintenance and 7 human pilots, as shift workers 24/7. Thus fulfilling the PIC – VO US requirements. No problems at all. In KiteGen we have chosen the pilot-autopilot paradigm, exactly as the aircraft.

      None of KiteGen’s patents are seen as blocking by competitors

      Good, as I already explained you several times, we conquered our full freedom to operate; we are not interested to block anybody else. Being the first movers I am very attentive to others good ideas and experience.
      Currently the most valuable patents are those focusing the industrial applicability the general concepts are quite status of the art, so worthless.
      Unfortunately, up to now I am able to recognize, in a worldwide scope, only little valuable novelties.
      Instead, I saw big efforts to bypass our IP with sub-optimal concepts. I could tell at length our approaches and the stories behind Makani, SkySails, KiteNRG, NTS, KPS and others, both the good and the bad.
      I would be eager to do a joint venture, sharing the knowledge, with somebody that expose a real and effective focus; in fact, we tried to work several times with TuDelft, with EU research proposals and exchanging internships. Only recently, I have discovered a political commitment to impede HAWP to emerge.

  35. Euan Mearns says:

    Dave, you say quite a lot in this short comment and I dare say Massimo will have something to say. A note on energy transitions:

    Many commentators discuss energy transition as if it was substitution. It is popular to talk about FF being replaced by wind and solar (wind a solar are too small to register on my chart). In fact energy transition is about addition, not substitution – at least that is how it has always been. We are still using wood and I dare say we will still be burning coal and using nuclear power in 2050. Only in the event of a truly disruptive energy technology coming along will humanity select that in favour of all other sources.

    The sheer megascale industrial competence and audacity required to go all the way, without killing anyone, is harder.

    Do you have any ideas about how this might be achieved?

    • Euan,
      Here we are coming back at the origin and rationale of the KiteGen project. The transition from fossil fuel is mandatory, as it is the renewable nature of the coming source.
      I agree that the timing and the urgency could depend of the analysis we could perform.
      My well-informed opinion is that we are in dramatic delay, let me analyze the last 10 years, the 100EJ increment is simply a fake signal. The wholesale price payed for such additional energy was about $7T in the meantime the global debt increase of $55T. Historically energy leaded the real economy leveraging from 10 to 20 times, since 2005 appears to be the opposite.
      The effectiveness of the quantitative easing as stimulus to the growth disappear when all the main world economies applied the same recipes concurrently; the main losers are the emerging ones. Therefore, our destiny will be to assist a perennial global recession, also evident with the current figures if we cancel the polluting role of QE on GDPs.
      We need inexpensive replacements for both oil and electricity, and KiteGen could fulfill both.
      We must avoid parasitic methods to convert energy like sea energy, solar PV & CSP and most wind turbines.
      We must avoid wasting resources for climate change, understanding that is only a pretext to advertise parasitic sources and promoting undemocratic organizations.
      We must understand that the fable of energy slaves is severely overrated, including the energetic cost of devices converting energy in services and taxes the slaves disappears.
      We need to understand the cost of energy clearly shows an absolute usefulness threshold, after which muscle strength returns competitive. In addition, according to Angus Maddison the GDP of a muscle based society is forced down to less of $4000/year per capita in a 2 billion people world, perhaps lower in a 8 billion people world.
      This forcing to the dark times is what is precisely happening now.

      • Euan Mearns says:

        Massimo, I have been sitting here reading your comment over and over for over an hour. The problem is the Spanish wine – no decent Italian wine to hand. Your comment deserves a comprehensive response which I cannot give right now. And I’m not sure I will fare better tomorrow.

        Its clear we have many problems – Aleppo, Greece, Niece, Turkey, Brexit and US elections. But to reach a conclusion on the root cause of these problems is not easy.

        My belief is that political correctness and Greenthinking lies at the roots. It is imperative that energy policy returns to be rooted in true science.

      • Euan Mearns says:

        Massimo, 24 hours on and I’m still struggling to formulate a proper response. The variables 1) population, 2) the economy, 3) currencies and monetary policies, 4) politics, 5) energy, 6) environment, 7) innovation, 8) the media and propaganda. It is beyond hard for any individual or group of individuals to understand how all these interact.

        You are playing in the energy and innovation groups calling on politics, the economy and media for support.

        There are those who try to understand how all these forces are going to pull together in the future. I have decided that is an impossible task. For example should Donald win in the US we will see a huge realignment of energy and social policies in the USA that may be emulated in many other countries.

        A couple of points you make where I disagree – it is the way of the world and science to pick on the points where disagreement exists!

        The transition from fossil fuel is mandatory, as it is the renewable nature of the coming source.

        This excludes nuclear and breeders from the mix. That decision will be made by the market. All KiteGen needs to worry about is being a competitor in that market.


        We must understand that the fable of energy slaves is severely overrated

        I don’t agree with this at all.

        I see the energy slave concept as central to our society. Man leverages wealth and prosperity from the energy we master and the efficiency with which we master it. In energy production systems, efficiency is ERoEI.

      • It is imperative that energy policy returns to be rooted in true science.

        Right here it is where lurks the issue, too often pursuing the real science is confused with an oversimplification and visions too partial, isolating one by one the various aspects.
        I was lucky enough to study and write software about the multivariate statistical methods, with Chuk Tilly of the New School in New York within a social research program.
        I have seen for many years, TOD included, a large production of analysis around energy, but never crossing of some independent variables, such as for example the cost of extraction, amount of investments and production quantity, which would be very enlightening.

        A healthy economy could avoid to generate problems like Aleppo, Greece etc, you cannot exchange the causes with effects.

        I see the energy slave concept as central to our society

        To date, there are about 150 years that these aspects are discussed: Jevons, rebound effect, Tainter, Resher, metabolic needs of a complex society etc.
        I think both you and me discuss this issue for several decades, I cannot understand your attempts to bring it back to the beginner level.

        The news is that today we have the opportunity to gather all the elements to figure out which was the best description of reality.

        At least 3 billion people have no access to energy slaves and much less than 2 billion fully enjoy the benefits, which shows the strong non-linearity of the enabling conditions.

        Energy poverty is spreading among us, leading us to a dramatic regression. In this scenario, KiteGen adds important novelties to be analyzed responsibly.

        This excludes nuclear and breeders from the mix.

        I was definitely a fan of nuclear power, but it also requires the maintenance of a complex society, and the growth of the plants number is still lagging despite it is a mature and replicable technology.
        Look at your chart.

        • Euan Mearns says:

          I cannot understand your attempts to bring it back to the beginner level.

          Massimo, one of the declared objectives of this blog is to educate. The readership here is hopefully far better informed on energy matters than most, but even here the concept of energy slaves is perhaps understood by 10% of readers (I put myself in the 90% who don’t properly understand it).

          Ban Ki Moon doesn’t understand what energy is let alone the concept of energy slave. The only thing he understands are $US that runs his organisation that is over seeing catastrophe after catastrophe around the world.

          In my mind you are contradicting yourself here. You want to diminish the concept of energy slaves while at the same time highlighting their importance:

          At least 3 billion people have no access to energy slaves and much less than 2 billion fully enjoy the benefits, which shows the strong non-linearity of the enabling conditions.

          There will be many readers of this blog who will be mighty pissed off at the actions of the UN to deprive developing countries access to cheap energy upon which their future prosperity lies.

          It has to be an assumption that the anointed leaders of Planet Earth have the best interests of its population uppermost in their minds. The Greens don’t. The Greens want the population of Earth to collapse below 1 billion. And yet the UN, most if not all OECD countries and their international institutions and corporations parade the Earth’s media extolling Green virtues without understanding at all what it is they are supporting. The only conclusion we can draw at the moment is that it is not going very well ( I may now need to go into hiding).

          As for nuclear power. I have listened to Green arguments for 10 years saying that it is too late to go the nuclear route. Fukushima turned George Monbiot into a nuclear supporter, while it made me more sceptical. Its quite obvious if you have a massive natural disaster that having a nuclear problem in the mix would be best avoided.

          Nuclear power provides the clearest path to avoid collapse in the OECD. The false argument is to shut down nuclear, cause collapse and leave a future population with an “unmanageable” nuclear legacy – that probably wouldn’t be that dangerous. But the nuclear route is a treadmill. Once your on you got to keep going to maintain society and controls. But we are already on it.

          So where does this leave HAWP? Its clear to me that your endeavour of the last several years must be afforded the opportunity to be tested and to succeed or fail and to be modified and tested again …. until it eventually succeeds or fails. Massimo my friend, that is the way the World works.


        • Bad news for KiteGen and for the hope of an economic recovery. Even if Euan Mearns, who has dedicated many years to the energy popularization does not address in depth the role of energy in the economic scenario, then right there is no hope, we will see you again to all the errors that have already been made, without no one can warn in advance.
          Yet there seems to be someone who understands such Gail the actuary who in his blog is patiently arguing the issue in various aspects:

  36. kitedog says:

    Hi Massimo,

    The rough AE metric of acceptable reliability in UAS flight is less than one major mishap per hundred thousand hours. No one outside of KiteGen thinks you have shown this. We are still waiting just to see all-modes flight of any prototype, and sustained flight of the SuperWing.

    Alex is right that a “tee-pee” structure is structurally more rational for the Stem cuppola. I have made that point before, and raised many such detail issues. KiteGen simply avoids answering specific technical questions posed from Open-AWE, by the secretive venture culture under your leadership.

    If you do finally open up KiteGen to do transparent engineering science, as suggested here, then you will have many collaborators from Open-AWE. Start by attending conferences and freely allowing outside observers at KiteGen test sessions (especially since you claim reliable operation).

    Hi Euan,

    The scaling strategy for megascale AWE was proposed by Chris Carlin [Boeing Ret.] and consists of reviewing megascale COTS for similarity cases for AWES adoption. So in open-AWE, we have closely studied everything from giant trawling nets to mining cableways, and the mechanical interfaces to the largest generators. While this is not the format to go into great detail, the research engineers involved are now confident an end-to-end development path is feasible.

    So now we are in discussions and recruiting megascale engineers as consultants, and in our field work scaling-up, we are preferring career “rough-neck” “roustabout” talent from industries like oil drilling and commercial fishing. I have industrial rigging in my background as well as aviation.

    Great discussion you have going, and you are learning faster than a gaggle of GoogleX kids 🙂


  37. The tether is the radius of a huge land area.

    So beside calculations of the efficiency per wing area, one could add the efficiency per used land area and per used space volume.

    Example: a 3 MW crosswind kite system has a 1 km tether. The used land area is 3.14 km² without people due to the risk of a moving tether having several tons of tension. And due to possible different wind directions spacing should be high enough within a farm of AWES, perhaps a tether length.

    3 MW/3.14 km² is not enough by far.

    So sweeping the biggest possible area of wind within the available area of frontal airspace delimited by the tether is required in order to achieve economic viability. So the flying body should be roughly as big as the tether(s) is (are) long.

    • heavyweather says:

      Or you are just very late to the party and have not done your homework at all 😉

      Seriously, look at the documentation.

    • Pierre.

      I think you should read this in order to understand better the aerodynamics:

      “Sailing faster than the wind”


      Because the kite is tethered, it can sail much faster than the wind. A sailing boat needs a large keel that performs a similar function.

    • Pierre Benhaïem says:

      On https://collegerama.tudelft.nl/Mediasite/Play/2e1f967767d541b1b1f2c912e8eff7df1d there is a description of a farm in the end of Ampyx presentation.

      Unities are represented with the same wind direction. What happens when wind directions are suddenly different from a unity to the other one? And in case of failure of the automated management?
      The whole available frontal airspace of wind is far from being maximized. And a great area of land can be expensive even if the system itself is cheap.

      In my opinion as the concept of farm of conventional wind turbines works, its transposition for airborne wind energy systems (AWES) seems more difficult because of the length of the tethers which are in permanent and not always predictable movement.

      So each AWES-unity should be far more significant in term of power, involving in scalability concerns.

      • I am pleasantly surprised that the Ampix Power people have finally realized that the flat wing necessarily leads to the unacceptable masses. Both Wubbo Ockels (kiteplanes of laddermill) and I immediately abandoned the flat wing idea in 2003.
        For comparison, a DC9 airplane has 90 square meters of wing area supporting up to 50 tons, which are suitable for HAWP. The DC9 wing itself weighs 13 tons as it hosts a thick spar (longeron), which acts as a cantilever. This, also, must be dressed aerodynamically leading to much lower aerodynamic efficiency when compared with the rigid and tiny C-shaped wing.
        I really wonder how anyone can think to keep flying wings over 10 tons to produce 3 MW. This with a single rope that does not offer a security backup. The wing that KiteGen studied, instead, with only 200kg is able to withstand tensor structurally the great forces of several dozens of tons, taking advantage of the new light materials and fibers.

        I find it an insult to the intelligence, the emergence of contradictory initiatives not regarding at the experience, the state of the art and the intellectual property of others. To avoid wasting work, I highly recommend to Ampix to find a synthesis of such situation.
        Of course, it seems easier to set up a glider model rather than a C-shaped wing, KiteGen has been a pioneer in the C-shaped wing concept in order to accumulate knowledge in this direction and approximate the industrial scale having always in mind a common interest. Viewing at the confirmation trends clearly appear the only viable.

        • Pierre Benhaïem says:

          http://www.dariopiga.com/Papers/Conference/EU2009.pdf you well know Massimo.
          Two observations. For the unities settled inside I think 300m spacing is not enough due to possible and sudden variations of wind. For the uni5ties settled outside taking account of tethers lengths covering an area neighboring to the reference area of 1 km ², making a complete area of several km².
          It is interesting that many measures ignore tethers, even http://homes.esat.kuleuven.be/~highwind/wp-content/uploads/2013/08/Diehl2013a.pdf mentioned above: “…theoretical power output of P = 40 kW per m2 of wing area…”. And the tether ?
          Certainly a tether is very lightweight in regard to a tower. Nevertheless the mobile ropes of several tons of tension are mobile guillotines of 1 km. So the tethers should be included in all the measures.
          Another interesting fact is the absence of consensus, it after years of R&D. Soft or rigid wings? Groundgen or Flygen? So one can says Ampyx’s choices are not appropriate. But Ampyx can tell the same for others. Who is wrong? Who is right? Answer: Makani, Ampyx, KiteGen, etc. etc.
          So instead of hearing the settled speech for years (high altitude winds are better, taking only the “tip of blades” and other generalities, then the expected lack of consensus from all sides) we should study other designs, taking account of expected positive and negative features in AWES.

        • Pierre Benhaïem says:

          A possible design avoiding some bending moment in spite of the implementation of flat wings in https://www.nasa.gov/sites/default/files/files/Moore_EternalFlight.pdf. This is a “Centrifugally Stiffened Rotor”. An adaptation as airborne wind energy system can be studied, making some changes.

        • Pierre Benhaïem says:


          I have to change my point of view as your statement about the C-shaped wing as it is well supported.
          Congratulations for your Power Wing I just studied more last time. It looks as a new standard for airborne wind energy systems, gathering advantages from both fabric wings as lightness, and from rigid wings as aerodynamical efficiency and durability. C-shape avoids a too big bending moment and is specially adapted for wind force.

        • @Pierre
          A 80m distance between the generators is more than enough for a KiteGen farm, who is concerned with collision and entanglement between ropes knows too little about avionic equipment and reaction timing of these wings. the territorial power density of HAWP is nearby 250MW/km2

          There is definitely a lack of education and deep understanding I would not say consensus.
          Patents filing statistic say a lot more: http://www.scopeknowledge.com/downloads.aspx?did=27
          There is an exponentially growing number of patent applications that seek to complement our concept of groundgen.

          In any case, no doubt that the Carousel with the rigid wings is the overall winner concept, has been calculated several times and by different and independent authors that exposes a LCOE $3/MWhe including capex and opex.

          Nuclear and Coal fuels are currently at nearby $7/MWhe (only fuel-opex). PV was considered being at $200-300/MWhe (only capex), now with the disruptive and very last news we must considered at minimum $900/MWhe of cost. (Italy PV production decline 14% Y2Y)

          By the way, this topic of photovoltaics decline at the European level would be an important topic that should deserve much attention, because the EROEI PV depends primarily on the aging rate. Ferroni and Hopkins got a sub-unit EROEI with a forecast of 17 year endurance, the reality check suggests less than half.

          I want to reiterate here, that in the 80’s I had been involved in photovoltaics research, alongside the RCA laboratories and Albert Rose who invented the aSI_PV for the cameras and transferred it to the domain of energy production. So my relationship with photovoltaics is much more complex, than anyone can imagine, KiteGen is a consequence.

          • Pierre Benhaïem says:


            Please can you announce the launch of a program of tests and simulations of the Power Wing?

  38. kitedog says:

    A common fallacy in AWE is to reason from constraints inherent to tower-based wind farms. Kitefarms based on the same unstable “brush” topology as HAWTs, of many small AWES units each on its own tether, is economically and operationally marginal. AWE must be more than a poor imitation of “the tips of a turbine rotor”.

    The FAA is giving us 2000ft high to start us well beyond towers. Atmospheric scientist, Dr. Cristina Archer has identified around 1000m high as a sort of sweet spot of “wind speed maxima” (WSM). Compare with a wind farm I was visit regularly, even just the other day, the 2000+ HAWTs around Sweetwater, Texas, roughly 10km square (~100km2). Therefore consider a kite farm airspace more than twice as high, but on the same footprint. The far better wind is in the added airspace.

    In principle, an AWES with the reliability of transport aircraft could operate over the Sweetwater wind farm, in the better wind. A bunch of single tethered units would be either too sparsely spaced or foul too easily (topological entropy). Instead, a there are classes of more ordered cellular topologies such as kite “trains”, “arches”, and “domes”. The latest is a topological “foam” of “rag-and-string” to in effect polymerize the sky as a megascale metamaterial.

    What is needed are huge kite units assembled from standard pieces at the maximum practical scale. GoogleX/Makani has estimated a soft wing must be to about 10x larger to rate equally with a rigid wing, but they seem to overlook that soft kites promise to scale >100x, being less subject to square-cube scaling law, for a >10x rated advantage.

    kPower has already flown a dirt cheap and easy 300m2 kite, “Mothra”, made of 50 tarps rigged along rope load paths, as a roughly 1/20 scale precursor study to the 7000m2 power kite being designed by Reinhart Paelinck. If quality kixel sail units (not just ordinary tarps) were made at high-speed from roll-stock, one factory could power the world. Quality rope production is highly automated already.

    The idea is simply to scale up the archetypal successful power kite to the AWE airspace provided and master megascale flying by methods of passive control and inherent stabilities known to us in current practice at a handy scale. Rod Read, a commentator here, is author of a chapter in the new AWE textbook being published by Springer, that covers more of this sort of thinking.

    • Euan Mearns says:

      KiteDog, I’d be interested to know a little bit more about you and how you fit into the global HAWP scene. I’d also be interested to hear your views on what needs to be done to consolidate what appears to be a fragmented “cottage industry” into something with a more solid capital base and common sense of purpose to commercialise this resource.

      The way this technology / industry has developed is for me a bit strange. No one seems to have been content with designing a 100 kW machine and deploying 100 of them in a demonstration project in order to gain credibility and visibility.

      Massimo, in my opinion, is trying to take a gigantic step for Man going from small fabric sports kites to the 120 m2 power wing (which I’ve seen) where one of the main challenges is to harness and control the enormous forces and energy. The latter comment tells us that this is a resource that must be pursued.

      But you have come with even more extreme and for me hard to understand comments. Is there any documentary evidence of the 300 m^2 kite flying and the forces it generated. And how on Earth does anyone plan to launch a 7000 m^2 kite. I can see that if it stays permanently airborne once launched then elaborate and expensive launch procedures can be sanctioned. But what force does a device this size generate?

      • Pierre Benhaïem says:

        SkySails http://www.skysails.info/english/ develops 320 m² kites and more for towing cargos. http://www.awesco.eu/esr10.html mentions 1000 m² kites as a target. Even far bigger flying elements are expected to reach a possible economic viability. One of the main reasons I mentioned above is the tether length (about 1 km). And a tether can move in a not always predictable way, above all by the implementation of crosswind kite systems with their moving tethers. A farm of small unities would be a forest of cables moving in possible different directions, and can get tangled .
        And it is unlikely an active control would be sufficient enough during a long time if unities are not spaced enough. If unities are spaced enough, the maximization of the used land and space is not reached.
        Possible solutions can be scaling-up or multiple wing systems (see http://homes.esat.kuleuven.be/~highwind/wp-content/uploads/2013/08/Diehl2013a.pdf) with also possible multiple anchors, or networks of relatively small kites mixing elements for lift and that for power.

      • No one seems to have been content with designing a 100 kW machine and deploying 100 of them in a demonstration project in order to gain credibility and visibility.

        Simple, just ask the right guys, those who have already done the testing, an intermediate step to 150-200 kW or more, cannot exist.
        In KiteGen we looked for a path without interruption, from 40kW to the largest, but obviously emerges the wing problem.
        Here is the take-off of a fabric wing of 50 square meters, as you can see, as soon as it picks up speed comes to breaking.


        KiteGen have already realized several fabric wings by 50 – 100 square meters, but are increasingly inefficient with the area, making pointless the scaling effort. As you know from the formulas, which describe the power of the system, the aerodynamic efficiency counts to the square, while the wing area is linear.
        Talking about wings 300 or 7000 square meters and likely 2 of efficiency is a sign of absolute ignorance in the matter, much better to take care of the aerodynamic. As already said by Wayne German, We have lost the patience to explain the differences between Drag and Lift machines to such parvenus.

        Why KiteGen was forced to go to 100sqm for his rigid wing?
        The wing is necessarily a composite, with a core of honeycomb and Kevlar skins.
        While choosing the thinner skins available on the market was not possible to design and dimension smaller wing. Scalability sometimes show discretization constrains, smaller wing would have had an unfavorable ratio of weight to surface. Our big power wing is an absolute success, 28 of efficiency, designed for 80m/s and 200kg the full weight including ailerons, ropes hooks, on-board generators and electronic.

        As a reference, a fabric wing to equal the performance of our rigid 100 sq.m. should be 30000 square meters, what are we talking about?

        • heavyweather says:

          It’s because most people don’t fly power kites. It’s easier to understand when you hand them the lines of a 5m² power kite and let them fly a kiteloop…then a 5m² box kite for comparison.
          Some educational videos maybe comparing how much power lift generates vs. drag.
          I bet you never met a kiteboarder that wasn’t instantly sold on the KiteGen?

        • Pierre Benhaïem says:

          Very interesting comment as scability concerns of fabric wings are not well known, comprising by me. Does SkySails produce a similar return of experience from tests?
          The C-shaped Power Wing looks to be a great innovation, and could be used in a way described on http://flygenkite.com/ (here a fabric C-shaped wing carrying turbines on a stick settled below between the two lines I built) among the other expected methods. I quote from http://www.sciencedirect.com/science/article/pii/S1364032115007005 p. 1467: ” They are composed of multiple short rigid modules that are hinged to each other. The resulting structure is lighter than straight rigid wings and more aerodynamically efficient and durable than fabric kites.”
          And perhaps more scalable. So waiting for results from tests.

          • Pierre Benhaïem says:

            I precise the very interesting comment is from Massimo, just before: “No one seems to have been content with designing a 100 kW …” as it is almost (I believe this is also on KiteGen website) an information about the lack of efficiency of fabric wings as they scale up.

        • Euan mearns says:

          This is a great reply Massimo! Folks reading this will learn a lot! I don’t think the difference between drag and lift kites was ever properly explained to me. If it was I’ve forgotten. Pls remember I’ve only been studying this for 4 months and still learning.

  39. Pierre Benhaïem says:

    The structure of the C-shaped Power Wing allows to restrain drastically the bending moment encountered in a (rigid) flat wing tethered by its center. So, adding other advantages, it looks as a possible standard in airborne wind energy.

  40. kitedog says:

    Massimo is correct that KiteGen will not be able to scale its rigid wing greatly, nor do LEI kites scale very well. kPower predicts such KiteGen wings will tend to dangle from their “stem” in most-probable-wind, without launching readily. That is the supposed explanation why we are not seeing videos of the KiteGen SuperWing in flight, even after two years since the first one was built. The tearing LEI trailing edge of the 50m2 LEI was simply poorly reinforced, and should have been easily corrected.

    Euan asked about my background in AWE, which is quite different from Massimo’s experience. I was recruited by KiteShip in 2006 to work on revolutionary “single-skin” (SS) ship-kites which do scale greatly. There is in fact a revolution in hot SS sport power kites lately (including paragliders) and the top designers are confident that nothing else will scale so well, to match real-world wind conditions.

    “Double-skin” parafoils have been flight validated >1000m2. There is the MegaFly that delivers massive military payloads, and the largest wing ever made was a >1500m2 parafoil sewn by community-college students, that fired up “like a 747 taking off”, and killed a leading kite figure within two minutes. Soft kites want to fly, and getting them down is harder than launching them.

    Let a serious AE AWE fly-off decide what kite wing designs win by LCOE, and whose predictions were correct.

    • @kitedog a.k.a. Dave Santos

      The large wings used in the military have as main objective to dissipate the high potential energy of launching equipment, the aim is to fly slowly and to safely land these massive weights carefully, avoiding to transform the potential energy into kinetic energy.

      For this type of service the interest is to maximize the lift coefficient to the detriment of the drag coefficient, which is usually harmful to increase, but in this case providential.

      This is exactly opposite needs in power generation, where the wings have to increase both the speed and the wind front intercepted in order to harness effectively the wind energy. This sound like a further argument in favour of what I just (little above) told you about wing scalability.

      I suggest you less enthusiasm in publicly asserting your merits and if you really want to talk properly of HAWP a bit more theoretical study, and while we’re at, even some experiments in the real world that are very enlightening.
      I am aware of your advocacy of a tensile structural system on the ground that theoretically is inspired and is a variation of the Persian spinning Panemone:
      I do not understand why poison the thoughts and discussions of other people who work on a new concept focused well over the 600m of altitude and not correlated to your.

      HAWP, despite my opinion, is a strange and complicated field. I find further heavy having to deal with the narcissism of those who simply want to pointlessly impose himself. I have already repeatedly stated that the concept of your wobbling and waving Panemone, do not find it interesting because it is hopelessly a drag machine dealing with weak ground winds. If we make an analysis of patents, 98% of filed patents in the wind sector, they belong ideally again and again to the Persian Panemone, which, regulary rejected, reveals a real and widespread difficulty in acquiring the necessary aerodynamic cognition. In any case I’m working on a different concept.

      • Giancarlo says:

        Massimo, I understand from your comment that, for military purpose, the wing must fly “slowly”, but then you say “the interest is to maximize the lift coefficient to the detriment of the drag coefficient” and that for power generation “This is exactly opposite”. Now, given that KiteGen efforts are clearly towards reaching the maximum aerodynamic coefficient, namely maximize the lift coefficient to the detriment of the drag, it’s not clear tome to what “This is exactly opposite”?

        • Euan Mearns says:

          [Note added 18th August 2016: After 45 days the comments are closed on all Energy Matters posts. Hence the comments closed here today just as interesting commentary was emerging. I am proposing to open a new commentary thread on High Altitude Wind Power (HAWP) in a week or so.]

  41. Renato says:

    I am very curious to read the answer of Massimo to the interesting question of kitedog

  42. kitedog says:


    You are confusing the work of several different persons. The kite photo linked shows Ed Sapir’s mini-Mothra kite, which I did not work on. My old overlaid concept for Aerotecture was a schematic, now obsolete. The current Aerotecture prototype is a 132m2 composite arch of six 22m2 Peter Lynn Pilot-lifters, under active development in on the US NW Coast (WSIKF 2016). This is specific airborne habitat research by a large team of top kite pros, architects, and BASE jumpers.

    kPower’s AWE WECS research is a separate track. There has never been any “panemone” aspect. My collaborators and I over many years have tested dozens of different AWES ideas, including the flapping wings, which have a very high power-to-weight pumping, and are conceptually just a self-tacking sail. We have also tested many kinds of flygens and turbines, even marginal ideas, as due diligence. If you do not cross-test all major concepts, why condemn those who do so, for your benefit?

    Another major difference in our AWE theory and practice is that my circle is counting on cheap modular kite lift with inherent stability to lift WECS of any kind, including your wing, for earlier launch and crashproofing. We focus on pure crosswind motion, without the downwind-upwind cycle-loss that KiteGen tolerates. See Joe Hadzicki’s concept in [Lang, DF, 2004] to get a correct idea of kPower’s load-motion.

    KiteGen only seems interested in electrical generation, while others see the kite as a broad tool for all kinds of direct mechanical work on a megascale. For example, the Chinese Three Gorges Dam can in principle become a kite hybrid by using giant kites to power reverse-pumped hydro, both enhancing electrical production and conserving water. Lifting water for irrigation and wildfire-fighting are also current experimental tracks. This is high-value research that your SABIC investor should be aware of, particularly for direct-pumping desalination.

    kPower above all represents traditional AE test-engineering and operational-research ethos, not the stealth-venture marketing-hype culture that has raised many millions, with scant technical prowess. We await seeing just how well KiteGen and all other serious players fare in a serious fly-off vetting process across major contending AWE concepts. kPower will stand with whoever wins that vetting process, rather than sink by a premature design down-select.

    Good luck to you, and thanks for fairly understanding kPower and other fine AWE R&D teams on their factual merits and flaws, rather than so much mistaken supposition. Similarly, understand that KiteGen is overdue to show its new power-wing performing as long claimed. Enough claiming already; its 2016, and you have had many years and many millions to prove your concept,


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