License: All rights reserved. Credit: Zachary Boren

The wind turbine rises: Is high-altitude the future of wind energy?

Zachary Davies Boren
Reporter for Energydesk
License: All rights reserved. Credit: SkySails

Last month, we examined the nascent sector of Wave and Tidal Energy. In the second feature in an Energydesk series, we look at High-Altitude Wind Energy, a potential reserve second in size only to sun radiation.

Wind energy as it is today, both onshore and offshore, has a problem. It misses most of the wind.

Most of the energy which flows around the planet in the form of wind isn’t near the ground, or even above the ocean, it’s in the sky. Where  some research suggests  constant winds could meet the world’s energy needs and cut the cost of power.

It’s not surprising people are trying to use it.

According to the Airborne Wind Energy Group, there are nearly 50 commercial high-altitude wind energy projects in development, chief among them Google’s Makani Power from the same Google X labs which brought us Google glass.

A couple of months ago a video of an airborne wind turbine in Alaska caught the internet’s imagination. All it took was a few hundred extra metres and some flashy video production to make wind energy sexy.

It sounds just a bit 'out there'  like something out of of science fiction  so how close are we to putting the ideas into practice?

An apparently much more straightforward technology, offshore wind, is running into well documented problems  with the logistics of operating in deep waters putting up costs.

But the reward could make the complexity worthwhile.

Not only would airborne technology do without the concrete foundations which drive up the cost of offshore wind but winds at high-altitude have, on average, twice the velocity of those near ground level, with up to eight times the power density.

“There is enough energy in high altitude winds to power civilization 100 times over,” wrote Professor Ken Caldeira of Stanford University in his research paper. Other peer-reviewed papers estimate it could reduce the cost of wind energy ten-fold. So if this technology arrives in earnest, it will make a serious impact on the global energy market.


The runners

Many of world’s AWE projects started in the mid-2000s and are now entering the testing stages ahead. So does the future of wind energy look like Altaeros, the lovechild of a sports stadium blimp and a doughnut?

Perhaps not. Whilst the Altaeros BAT is arguably the best known (it shows up top on Google, ahead of even Google’s own high-altitude wind project), it is only one of a several technologies in the sector.

All this innovation, will it fly?

Balloon – It’s under the banner of balloon technology that Altaeros falls. A turbine, designed to be much lighter than those on traditional towers, is lifted by a balloon or blimp to the higher reaches of the sky and kept in place by tethers on which the generated power travels.

Kite – Lifted into the higher skies via a kite steering unit, the kite is moved to optimum wind conditions as it sends the acquired kinetic energy to a ground generation station.

Kytoon – The fantastically named cross of a heavier-than-air kite and a lighter-than-air balloon. The key benefit of this hybrid is stability; it is lifted by its kite components and maintains its position due to balloon buoyancy.

Tethered Autogen – Largely patented by Google, the Autogen is a contraption akin to a wind copter.

Firstly let’s visit Fairbanks, Alaska, where Altaeros Energies is partnering with Golden Valley Electric Association to launch a 18-month product test in 2015.


"We're really leaping beyond what you can get with the traditional tower based turbines, and because of that we're able to produce energy at a much higher capacity factor,” said Ben Glass, the MIT graduate who co-founded Altaeros.

Capacity factor, the bane of renewable energy, is a techy way of saying the wind only blows some of the time requiring investment in interconnected grids and backup power. A 2009 report put the average factor for renewables at 33%.

“We often compare the BAT against a 100 kilowatt wind tower turbine that's fairly popular, and which has a capacity factor in the 20 to 25% range. We're producing energy at a capacity factor of 50 to 65%, which is twice as much.” Indeed, it’s almost as much as some fossil fuel plants.

How exactly does the Altaeros BAT work?

The balloon, filled with helium, lifts the turbine placed in its centre to about 600 metres. The structure is held in place by three tethers, one of which is electro-mechanical and used to transfer the power from the turbine to the ground station. The turbine itself is a lot like the big horizontal axis turbines we’re used seeing to on towers, with the key difference is that it’s much lighter.

Remote areas 

Glass says Altaeros has a specific market in mind for the BAT: “We’re developing the product pretty focused on the remote power market, basically any place that’s using diesel gen sets. This can be remote communities like you have in Alaska, it can be disaster relief where your main power infrastructure is knocked out, or it could be remote industrial areas.”

In those areas high altitude wind will be competing with diesel and Glass says it could prove to be more than three times cheaper.

Whilst cost is always a key consideration, for these remote areas so is access. Part of the Altaeros balloon design is for portability.

“For this system, because it’s a large inflatable structure, it actually packs down very small and we’re able to ship it in a couple of standard shipping containers basically to any site in the world and set up within a day or two.”

Over in California, there is Makani Power, last year acquired by Google X, the tech giant’s top secret innovations division.

Image: Makani Power, Google

The Makani technology is essentially a tethered aircraft, a sophisticated kite-wing with built-in wind turbines. As is their MO, X wouldn’t talk to me about their tech.

“The Americans are more focused on airborne generation,” said Marcello Corongiu, Programme Manager of Italy’s KiteGen, “whilst in Europe, we are mostly committed to on-ground generation.”

He theorised that American companies tend towards air generation because of the abundance of patents already issued for on-ground generation technology.

'Future of electricity'

“Is high-altitude the future of wind energy?” Corogniu asked, “I would go one further and say it is the future of electrical production.”

“High-altitude wind is an enormous reservoir of energy, the second biggest energy flow after sun radiation. It also highly exploitable without causing environmental issues, as a recent study found 1800 terrawatts can be generated without impacting the climate.”

Another study, however, claims that extracting any more than 7.5 terrawatts could cause a climate catastrophe.

The German researchers concluded that “jet stream wind power does not have the potential to become a significant source of renewable energy.”

But let’s get back to KiteGen. It is one of the world’s kite tech big-wigs, with more patents than any other company in the sector (37).

Image: KiteGen

A recent partnership with Saudi Arabia Basic Industries (SABIC) has seen the development of two industrial generators ready for testing this autumn.

Whether that will happen, however, hinges on KiteGen’s ability to navigate the country’s bureaucratic labyrinth.

The KiteGen technology was conceived as a clever (we hope) generator that controls kites extended on multi-function cables. The system uses climate sensors to inform its management of the kites – optimising speed and torque, and also the flight path.

The last year has seen a major redesign - after the firm ran into some problems.

“We asked a manufacturer to make a kit for us of about 50 square metres, but we broke it in 10 minutes. The material is not robust enough for bear the high-altitude forces. Our new wing, which has aeronautical and structural integrity, is about 100 square metres.”

Mike Barnard of Cleantechnica earlier this year poked holes in kite-tech, writing that the system  is “fraught with failure conditions.”

And according to Barnard, the semi-flex wing to which KiteGen have moved “increases complexity and weight in the air” which then increases chances of failure and reduces efficiency.

Low cost

The kite model, says Corongiu, is designed work with the particular conditions of high-altitude where stationary turbines cannot - because it would be too expensive to build them that high.

The success of the sector will be measured in what it does to energy costs, and KiteGen, like its rivals is astoundingly optimistic: “We expect a levelised energy cost of less than €20 per megawatt per hour, much less than all present energy technology except for some hydroelectric.” Less, in fact, than coal.

And finally, over in Germany, there’s SkySails, which is looking towards high-altitude offshore. Using the kite method, SkySails, which is in the design phase of its 1 MW unit, is building its stations to float.

“Wind in higher altitudes is more stable and stronger, so there’s more to harvest,” explained Stephan Wrage, Managing Director of SkySails, “And the floating AWE turbines are much easier and cheaper to produce and install than conventional wind turbines.”

In his brutally comprehensive assessment of the sector, Barnard said it suffered for lack of harmonious design: “As soon as you start engineering an airborne solution to harvest that energy, the compromises strip away the potential bit-by-bit until it just isn’t viable in any incarnation so far attempted.”

But the wind energy sector has grown more than any other renewable in recent years. These projects have yet to arrive, and they certainly won’t be the finished article when they do. There is great potential for the sector in the years ahead; that vast expanse of energy gold above our heads is waiting to mined, and there is an ever-growing number of people and organisations committed to doing just that.

Update: Using data from AWEC, this article orginally estimated the number of projects at over 100, but has since changed that figure and infograph to reflect the 46 commercial and academic projects in operation according to a study from Springer Berlin Heidelberg.

Update 2: KiteGen has responded to the study from the Max Planck Institute that warned against AWE, calling it "superficial and substantially wrong"

Comments Add new comment

Great article and very exciting. Am just aware a little bit that thinking of renewable energy in terms that relate to fossil-derived finite energy could be limiting. I think such terms as 'reserves', or 'mined/mining', or indeed 'gold' takes away from the potentially relatively infinite use of these 'resources' (this term would seem right), into the human future. I think the materialistic nature of conventual energy 'resources' has led to adopting these terms, and I think linguistically the green movement towards a different notion of 'energy' would seem to benefit by adjusting this language?

I feel that the government should back this up.

The title alludes to Kaze Tachinu directed by Hayao Miyazaki.

The film tells of the dream of Jiro Horikosi's dream to design and build a perfect aeroplane. He achieved his dream in the Mitsubishi Zero. However his dream turned sour with the realisation of total war. Horikoshi lived to agonise about his part in the war machine and died unhappy.

The green dream is for free wind power. This will turn sour on you too.

It is not clear which "Airborne Wind Energy Group" is referred to here but the YahooGroups AirborneWindEnergy Group will not be fairly served without the mention of KiteLab Group/kPower llc of Austin, Texas; KitePower Cooperative (UK), WOW of Italy, and amongst others. Certainly, Makani Power does not best represent the open, free-access Airborne WInd Energy Group.

Hi Zachary,

thanks for your article and pointing out the simple logic of Ariborne Wind Energy (AWE) to harness the stronger and more consistent wind at higher altitudes.

Please note that the AWE-community meets at the Airborne Wind Energy Conferences (AWEC). Starting with a meeting at the University of California in 2009 with approx. 30 people the German Airborne Wind Energy Association (BHWE
Bundesverband Höhenwindenergie e.V.) welcomed over 200 participants from 21 countries last September at AWEC 2013 at Berlin. In 48 talks and 21 poster
presentations the current development status and the next steps for serial
production have been presented.

More information at

Best wishes


Guido Luetsch

German Airborne Wind Energy Association

Thanks Scott55, will update (again)

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Decent overview. I like the term "brutally comprehensive". It's not a bad description of my style. ;)

That said, I've looked at most of the technologies referenced more specifically, so here are a few links for those interested.

On the Altaeros BAT:

On Makani's device:

On an early player in the field, Sky Windpower:

It's worth also pointing that average capacity factor of modern wind turbines is 40.35% according to NREL. Wind turbines are getting taller while FAA regulations and tether challenges are limiting the height of AWES approaches. Wind turbines are seeing 80% wind velocities of current AWES designs while also being scaled up much more and being much cheaper per KWH. AWES is suffering the law of diminishing returns, but in most cases seem to think that ground-based wind turbines are stuck in the 1980's. 

AWES is a side bet, and a fairly poor one.


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