Airborne wind turbines to generate power from high winds (w/ Video)

Jun 04, 2010 by Lin Edwards report
Image credit: Joby Energy

(PhysOrg.com) -- Airborne wind turbines may soon be generating power from high-altitude winds to provide consistent, clean, cheap, and abundant energy for a power-hungry world.

Mr Bevirt of airborne wind turbine company Joby Energy, said wind is a great source of energy, with an estimated 870 terawatts being carried in the tropospheric winds. This potential is considerably greater than the 17 terawatts of current global demand.

The idea of using winds at high altitudes to generate power was first suggested around four decades ago but at the time was not technically feasible. Now, with new materials and more advanced computers, electronics and sensors, and the development of , the concept may be viable, and several companies are investigating the best ways to tap into the resource to generate renewable energy cheaply. Joby Energy is one of these, and its design looks like a multi-winged kite supporting an array of turbines.

This video is not supported by your browser at this time.
Depiction of our 2 MW upper boundary layer system. Video: Joby Energy

The thrust required for the kite's vertical take-off is supplied by motor-generators connected to the turbines, and the orientation of the kite to the wind is controlled by a computer system that differentially adjusts rotor speeds to keep it flying in a circular path. The winds flowing through the turbines spin the generators at high speed, so there is no need for gearboxes. The electricity generated by the turbines is transmitted to the ground via the reinforced composite tether that anchors the kite to the ground.

The airborne turbines would initially fly at a height five times higher than conventional wind turbines, and this would increase access to higher wind speeds and better wind consistency, giving more reliable power supplies. If the turbines were flown higher the power generated could be even greater because the tends to increase at higher altitudes.

The US Federal Aviation Administration has restricted the altitude initially to 600 meters or less, even though the airborne turbines can in theory fly at altitudes over 10,000 meters, and they are designed to operate in the upper troposphere and upper boundary layer.

After testing over 20 designs the company has selected a 30 kW system for evaluation and testing. If the tests are successful the company plans to test a 100 kW prototype, and then an initial set of turbine arrays generating 300 kW, enough to supply power to about 150 homes. The generated DC electricity transferred to the ground via the tether would then be converted to AC power to be fed into the power grid.

Bevirt said the system is designed to withstand strong winds, and in gale-force winds or periods of no wind at all the array would be programmed to land itself and take to the air again when the wind conditions are more suitable. The kite is also designed to be landed safely even if the tether is broken, using batteries to power its motors. The design includes a high degree of redundancy in the array, which means it can remain in the air even with multiple points of failure.

This video is not supported by your browser at this time.

The eventual goal of Joby is to develop farms with several arrays to develop consistent power, but it will first need to demonstrate the system is safe and the control systems are reliable. Bevirt said the ultimate aim is to deploy the around the world to produce an abundant global supply of cheap and clean electricity.

Explore further: Imaginative ideas for a 'greenlight district' in Amsterdam

More information: Joby Energy: www.jobyenergy.com/tech

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antialias
4 / 5 (6) Jun 04, 2010
Better let these things fly high or the greens are going to go nuts about all the birds being shredded at low altitudes.
magpies
1 / 5 (7) Jun 04, 2010
Oh joy some more things that will cause climate change ya!!
HeloMenelo
1 / 5 (7) Jun 04, 2010
How does these turbines land themselves? Do they have
energy stored somewhere to turn the blades and work like helicopters with perhaps a gyro system to land? I'd like to see the process.
antialias
3.7 / 5 (3) Jun 04, 2010
Well, once airborne they would stay up as long as possible. But since they get airborne under their own power they can land under their own power (Or to be more precise: under the power through the cable. The connection can go both ways. )

Landing such a contraption is not hard. Here's an awesome video of how stable/manouverable a multi-blade helicopter contraption can be.
http://www.youtub...ujjP5J-k
GSwift7
3.7 / 5 (6) Jun 04, 2010
They conspicuously fail to mention the estimated cost per kWH. Also, the construction of such a complicated machine with so many moving parts under continuous loads, made from expensive synthetic composite materials, has proven to be prohibitive for similar ventures. Ground-based wind turbines are so complicated that they require a permanent professional maintenance staff to keep them running. These machines will be much more difficult to maintain than a ground-based wind turbine and will require complete shut-down and landing whenever you want to work on them. This article is nothing more than an advertisement to attract investors.
freethinking
2.3 / 5 (3) Jun 04, 2010
If I understand this right, they say that (if you crunch the numbers give) if we harvest just 2% of the wind power we could power the whole world. Two things, I think that the potential wind energy should be much higher, but if it isn't wouldn't disrupting 2% of the earths high altitude wind flow have significant affect on weather.

My guess this is going to be another dream energy source that never will be practical, but which governments will spend a lot of money on or if it is successful, just like bio-fuels, will do more harm than good.
GSwift7
3 / 5 (5) Jun 04, 2010
One more thing: The land space required for just one of these things would be enormous. You couldn't put two of these things anywhere near each other and you can't have anything near it that could foul the tether in a 360 degree arc around the base station unless you could guarantee that the wind will only blow in one direction. Keep in mind that the video they provide isn't really accurate. The tether cable will sag in the middle under it's own weight, so the lower part of the cable will be close to the ground for a good sized radius away from the base station. You would have to clear all the trees and everything else I would imagine.
antialias
not rated yet Jun 04, 2010
You couldn't put two of these things anywhere near each other

You could daisy chain them. Have several of these units riding at different altitudes on the same tether. That way they don't get in each other's way.

but if it isn't wouldn't disrupting 2% of the earths high altitude wind flow have significant affect on weather.

Don't worry - the amount of units one would have to put up to gather 2% of the wind would be enormous (i.e. completely unrealistic). But I could see it working in particularly windy places.

Like many alterantive energy sources this is a niche product. But that is not to say that it's a bad idea. We have to become less monolithic in our ideas of where our energy comes from. Mix and match where sensible.
GSwift7
2.5 / 5 (4) Jun 04, 2010
"You could daisy chain them. Have several of these units riding at different altitudes on the same tether. That way they don't get in each other's way."

I don't think the engineering for that would work. Remember that they fly in a continuous loop perpendicular to the tether, so you have to have a high strength rotary joint to connect the kite to the tether or you'll twist the tether to failure point quickly. If you daisy chain more than one on the same tether then you multiply the complexity of that connection exponentially, as well as the difficulty of synchronized takeoff/landing and synchronized loop flying, especially when the wind at each kite on the same tether could vary wildly. The wind at different altitudes may not even blow in the same direction, much less the same speed.
rsa
5 / 5 (3) Jun 04, 2010
"They conspicuously fail to mention the estimated cost per kWH." Who is "they", the reporters?

http://www.jobyen...m/impact

"the construction of such a complicated machine with so many moving parts"

So many moving parts? Which, exactly? It is essentially a turbine on a glider on a tether. Very few moving parts compared to, say, a car. Construction costs are much *lower* than tower based turbines because you replace tons of steel in a tower with a relatively cheap tether.

"Ground-based wind turbines are so complicated that they require a permanent professional maintenance staff to keep them running."

Natural gas plants don't? Coal plants don't? What is the disadvantage here exactly?

And what are these "similar ventures" you are talking about?
rsa
5 / 5 (1) Jun 04, 2010
"One more thing: The land space required for just one of these things would be enormous."

Land requirements per kW are comparable or favorable to ground based turbines. Most of what you say is reasonable except the 360 deg requirements. Most good sites will have wind that blows in one direction, and the system can be brought down in adverse conditions. Remember that you are accessing wind power of significantly higher power density per square meter of swept area at higher altitude.
rsa
5 / 5 (1) Jun 04, 2010
"wouldn't disrupting 2% of the earths high altitude wind flow have significant affect on weather."

The best climate models say no, and if they did, it would be a net cooling effect. Besides, you would need just absolutely enormous scale deployment to approach 2% intercept of energy in wind. It is extremely unlikely that you would power the world on wind, due to intermittency and transmissions issues. That figure is just to put a scale on the power available on the wind - it's very large compared to most renewable sources.

rsa
not rated yet Jun 04, 2010
"How does these turbines land themselves?"

It's just the reverse of the launch process - they draw power rather than generate it during launch/land, and the turbine blades work like helicopter blades to land it vertically.
HeloMenelo
1 / 5 (3) Jun 04, 2010
I agree with Antialias and rsa, I get the idea, something like a "draganfly" Just the giant version wow!

Then indeed you are right they are very stable, and the system is basically a direct drive unit. Not too much complexity, i suppose the blades will be fixed and the landing controlled precisely by a multi axis gyro system. (If the blades are fixed, complexity is minimum)

This is really interesting, i wish i was involve in anything that has to do with it. And regarding space, windfarms usually are out in the sticks anyway, there should be plenty of space wherever they put it. Of Course if it lands like a heli, (meaning one has precise control over the system) they can programme them to land in close proximity.
rsa
5 / 5 (1) Jun 04, 2010
And now for the real issues I'm aware of:

The control systems for this type of device are, as far as I know, unproven. Seemingly feasible, but unproven. Makani Power has done something very similar but they share extremely little about either their successes or failures. They have shown some pictures/video of autonomous tethered flight, but it appeared not to be generating power, but rather free-flying.

Second, I gather that tether drag is an issue that is not entirely solved, and attempting to solve it with aerodynamic fairings creates its own problems. You can see some of Makani's patents in this area, they look pretty sketchy and conceptual to me.

All of this will hinge on what kind of robustness can really be achieved in the autonomous operation of the system, in my opinion. And while I'd love to see it, we'll have to wait and see how far along towards that goal these folks and a few others really are. As for me, I think there is too much potential to ignore.
Djincs
1 / 5 (1) Jun 04, 2010
that totally beats the japanese moon project!
It seem promising to me.
PinkElephant
not rated yet Jun 04, 2010
Short of space elevators, I'd expect this type of system to be benefit handsomely from strong, thin cables woven out of carbon nanotubes. You kill four birds with one "stone", so to speak:

1) extreme strength of cable (unlikely to snap)
2) high electrical conductivity (so, tether is also the conductor)
3) small cable cross-section (low wind loads on cable)
4) small cable mass (less sagging, less wind wasted just counteracting cable weight)

Maybe in 10-15 years, when CNT cables are a reality and at a reasonable price, this concept will be viable.
frajo
3 / 5 (2) Jun 04, 2010
I'd expect this type of system to be benefit handsomely from strong, thin cables woven out of carbon nanotubes.
If there were such a cable it would already be in use for overhead power lines.
The overhead power lines currently in use (steel and aluminium for 110 KV) typically have a mass of roughly 1000 kg per 1000 m. Without winter ice.
Feldagast
1 / 5 (1) Jun 04, 2010
Wonder how long before a airplane collides with one of them.
PinkElephant
not rated yet Jun 04, 2010
@frajo,

I don't know if CNT cables will ever be cost-competitive with steel or aluminum. And I don't know if their bulk conductivity will be competitive either. Individual CNTs can be excellent conductors, but a cable woven from them might not be as good due to the discontinuities involved between molecules. I expect it would still conduct, but perhaps with higher losses than a pure steel cable might...
DGBEACH
1 / 5 (1) Jun 04, 2010
Couldn't matching resonant coils be used, both up in the turbine, and on the ground, in order to harvest the power "wirelessly"? The power would first be modulated onto the coil, from DC to a carrier frequency, right at the turbine. Next, ground-based coils would transfer the resonant energy into something useable (like 10kV AC), right onto the grid...let's just say I'm a little skeptical that they could transfer all that DC current down to the ground through their "magically-thin" cables.
MarkyMark
not rated yet Jun 05, 2010
An interesting idea with some problems, but not insurmountable ones. Also i would imagine that they would have some proximity warning system for any nearby aircraft. In time say 10 years i see this venture with the right funding being a real alternative energy source.
DaveMart
5 / 5 (1) Jun 05, 2010
I'm not sure what some people here have against reading the links etc before criticizing, but most of the points raised are either trivial or dealt with.
You can watch actual prototypes taking off and landing at the Joby website, so there is no mystery there.
No need for carbon nanotube cables, commercially available dyneema will do the job just fine, even at 10,000ft, so the drag at 600 meters is trivial in comparison.
As for the first part hanging close to the ground, if the landscape requires if is is trivial to run the cable from the top of a 20 meter tower, so the sag happens higher up.
Initially areas like Montana where there is plenty of space would be most suitable, as large areas are indeed needed, but once the concept is got working at megawatt scale then versions for deployment at sea are planned.
The article specifies that there will be batteries aboard to enable landing in the unlikely event the cable breaks.
sender
not rated yet Jun 05, 2010
balloons with microwave oscillators seem more feasible for space requirements
antialias_physorg
5 / 5 (1) Jun 05, 2010
Balloons are no good (unless you tether them) because they'll otherwise just be...erm...gone with the wind.

And if you use a tether you might as well conduct the electricity up/down it.

emember that they fly in a continuous loop perpendicular to the tether

Yes, that is a problem - though I'm not sure if they actually need to fly in a loop. If you design them more like a kite then they'd be more or less stationary.

As an aside: there are multi-kites (stunt kites) which are effectively daisy-chained single kites and they do seem to fly very well without twisting their tethers to the point of failure.

(example : http://farm3.stat...jpg?v=0)
frajo
not rated yet Jun 05, 2010
No need for carbon nanotube cables, commercially available dyneema will do the job just fine, even at 10,000ft, so the drag at 600 meters is trivial in comparison.
It's indeed very lightweight, but I didn't find any information about its electrical conductivity.
DaveMart
1 / 5 (1) Jun 05, 2010
Flying in a loop generates much more power. Multi kites might be a possibility, but add a lot to the complexity so obviously would come in at a much later stage, if at all.
Balloons as in the Magenn system use helium, which is a really, really bad idea in my view as this is very valuable and essential for many industrial uses.
It is so light that it escapes from the atmosphere so it leaves the earth forever so there is no question of recycling.
Hydrogen is a possibility but safety concerns may well limit it's use.
CSharpner
not rated yet Jun 05, 2010
It is so light that it escapes from the atmosphere so it leaves the earth forever so there is no question of recycling.

What??? Not unless the weight of the helium + the weight of the balloon material are lighter than empty space (not). A balloon CANNOT float out into space! It can only reach the upper atmosphere until it gets to where the atmosphere equals the combined weight of the balloon + helium per volume. At that point, it's impossible for it to go any higher.
PinkElephant
not rated yet Jun 05, 2010
@CSharpner,

Helium molecules are so small that they seep out through the walls of balloons. DaveMart is right: just like hydrogen, helium will tend to rise to the top of the atmosphere, where it will be exposed to ionizing radiation and solar wind, and eventually stripped away into space. Unlike hydrogen, helium is a noble gas, and it won't react with anything else (e.g. oxygen) to form a heavier compound that might keep it in the atmosphere...

@DaveMart,

I think multi-kites would put too much strain on a tether. But I also think there's a way to better utilize the space overhead: instead of flying just one kite in a loop, put several of them in the same loop, evenly spaced apart. Depending on how stable and precise the kites' maneuvering capability is, you could space them let's say 45 degrees apart on the loop, which would let you fly 8 kites in the same space, for example...
CSharpner
not rated yet Jun 05, 2010
I thought he was talking about the balloon itself escaping.
fhtmguy
not rated yet Jun 06, 2010
As we should all remember, the law of conservation of energy states that energy may neither be created nor destroyed. Therefore the sum of all the energies in the system is a constant. So taking energy from the jet stream or high altitude winds must have an effect on the total global energy needed to regulate climate and the current system of evaporation/rain around the globe. I would guess that the weather patterns will change dramatically if this type of power generation is implemented on a large scale. Does anybody ever think of these effects?
CSharpner
5 / 5 (1) Jun 06, 2010
I would guess that the weather patterns will change dramatically if this type of power generation is implemented on a large scale. Does anybody ever think of these effects?

Yes. I think of it every time I read an article like this, but I am immediately satisfied that no such effect would happen: Think of how much physical matter you'd have to have in air space to significantly effect the wind itself. Look at the videos on this article. Compare how minuscule these things are compared to the whole volume of atmosphere. Back away a little and you can barely see them. Take 10 cubic miles of atmosphere in a 10 mile high column. How much of that volume is occupied by wind energy harvesting devices? It's an infinitesimal amount. But, your intuition is right: To harvest energy from the wind, you do slow it down a bit, but it's so little, it's not worth worrying about until we build solid walls of wind mills tall enough and wide enough to effect actual weather patterns.
CSharpner
not rated yet Jun 06, 2010
... and I don't think that'll happen anytime soon. Before our civilization gets to THAT level of need, I'd guess we'd probably have mastered nuclear fusion by then. If not, we'll tackle that problem then. Right now, it's nothing to fret over at all.
antialias_physorg
5 / 5 (1) Jun 06, 2010
You're right. We should really realize that we (humans) are but a 2meter high biofilm on a very small fraction of this globe whose atmosphere extends 50 thousand(!) meters up and 6 million meters down to the center. We are not _that_ central to things.

Now we can (and do) affect the climate but by harvesting a little bit of wind over a few square meters (or even hundreds of square kilometers) isn't going to do all that much.

With more CO2 in the atmosphere and a heating up of the climate we should expect stronger winds - so if we harvest a _lot_ and actually did manage to change the windflow a little bit then it will be for the better.
fhtmguy
not rated yet Jun 06, 2010
Good point, Csharpner!
GaryB
5 / 5 (1) Jun 07, 2010
Hmm, killing the fly space over huge swaths of land. Maybe better to put out at sea which might work if the kite part were inflatable so it could float.

But still, all this uses so much area for not very much power. A thorium breeder reactor would consume, including its mine, a small fraction of the space for many many times the power production. And that produces heat which can be often used directly rather than converted to electricity, such as in desalination via boiling.
antialias
3.5 / 5 (2) Jun 07, 2010
You can have your thorium reactor in your back yard (and you can also dispose of its radioactive remains there - or don't you want that?)

I'll take something like this kite-generator over a nuclear reactor any time.
rsa
5 / 5 (1) Jun 07, 2010
Does anybody ever think of these effects?


Of course. And the possible effects have been modeled, and found to be trivial with tons of headroom for any realistic deployment scenario. Google "Archer and Caldeira".
rsa
not rated yet Jun 07, 2010
though I'm not sure if they actually need to fly in a loop. If you design them more like a kite then they'd be more or less stationary.


Flying in a loop is central to these lower boundary layer designs. A dynamic crosswind kite generates about (lift/drag)^2/2 times as much power as a static kite. With realistic L/D about 20, that's 200x more power in the crosswind kite. It's the key to the whole thing.

snapoli
not rated yet Jun 11, 2010
As with the Japanese proposal to gird the moon with a solar panel (which will provide all the energy needs for the WHOLE WORLD!!!!!), again, only stupid and naive people would believe that 'the people' of the world will ever see any easing of life's struggle. The uberclass of the world will control and pocket 95% of the energy/value of any such technology.
Quantum_Conundrum
1.7 / 5 (3) Jun 12, 2010
Why not use tethered airships to hoist the turbines into the air, instead of just gliders?

I think these systems would be most practical on top of skyscrapers where they are unlikely to interfere with surrounding terrain, and get even more elevation boost. (i.e. 600-800meters extra from the newest, tallest skyscrapers.)
Javinator
not rated yet Jun 13, 2010
I'll take something like this kite-generator over a nuclear reactor any time.


It'd be interesting to see what the overall footprint of these kites would be (at ~300kW a pop) vs. a nuclear plant (at say ~2400MW). Not that I'm against these wind turbines. They definitely show promise and could do well in some specific areas.
Javinator
not rated yet Jun 13, 2010
I think these systems would be most practical on top of skyscrapers where they are unlikely to interfere with surrounding terrain, and get even more elevation boost. (i.e. 600-800meters extra from the newest, tallest skyscrapers.)


That might be a tough sell given that in a worst case scenario falling from a skyscraper would have it landing in the middle of a city.
antialias
not rated yet Jun 14, 2010
And also that it would be a serious strain on the skyscraper (given the leverage involved I'd say that attaching these suckers to skyscrapers is not a good idea)