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Kite power getting off the ground in Germany

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November 1, 2012

A kite makes its maiden voyage at the test site in Mecklenburg-West Pomerania (Photo: © Fr...

A kite makes its maiden voyage at the test site in Mecklenburg-West Pomerania (Photo: © Fraunhofer IPA)

Despite offering numerous advantages over its rotating brethren, most notably the ability to reach the high-speed winds found at higher altitudes, kite-based energy systems are yet to really get off the ground in a meaningful way. But things are looking up. Earlier this year, NASA revealed it is investigating ways to improve the aerodynamics and autonomous flight control of kites for power generation applications, and now Berlin-based wind energy developer NTS GmbH has teamed with the Fraunhofer Institute for Manufacturing Engineering and Automation (IPA) to make their own kite energy system concept a reality.

The team’s “kite power station” would see kites attached to cables measuring around 700 meters (2,297 ft) long, which would allow the kites to fly at heights of 300 to 500 meters (984 to 1,640 ft). Unlike the “Flygen” systems that have the turbines built into the kite, the NTS system would tether the cables to vehicles on the ground that are pulled around a circuit on rails by the power of the wind. The kinetic energy of the vehicles is then converted into electricity by way of a generator.

The ground vehicles would also contain the measuring and control technology with a horizontal and vertical angle sensor located in each cable line and a force sensor within the cable distributor enabling precise control of the kite’s movements. The developers of the system say a kite flying in a figure-eight or sine-wave flight pattern can generate a pulling power of up to 10 kilonewtons (kN), which would give a kite with a surface area of 20 m2 (215 ft2 the capacity to pull one ton.

Fraunhofer claims that at a height of 100 meters (328 ft), wind speeds are around 15 meters per second (49 ft/s), while at a height of 500 meters (1,640 ft) they exceed 20 m/s (66 ft/s).

“The energy yield of a kite far exceeds that of a wind turbine, whose rotor tips turn at a maximum height of 200 meters. Doubling the wind speed results in eight times the energy,” says IPA engineer Joachim Montnacher. “Depending on wind conditions, eight kites with a combined surface area of up to 300 square meters (3,229 ft2) can equate to 20 conventional one-megawatt wind turbines.”

But it’s not just the ability to reach the higher wind speeds found at higher altitudes, but also the consistency of the wind at these heights that offers kite-based systems an advantage over conventional wind turbines. According to Fraunhofer, figures for the past year show that there is a 35 percent chance of wind speeds reaching 5 m/s (16 ft/s) at a height of 10 meters (32.8 ft), but the likelihood increases to 70 percent at heights of 500 meters (1,640 ft).

This greater wind consistency provides the potential for locations that are unsuitable for conventional wind turbines to be considered as sites for kite power systems. Fraunhofer also claims that such kite-based systems will be cheaper to build than large tower-mounted wind turbines.

NTS and IPA researchers have already begun trials at a test site in Mecklenburg in the north of Germany. A kite was flown along a 400-meter-long (1,312 ft) track manually controlled with a handheld remote control, however, the kite will eventually be flown autonomously under computer control. The team also plans to reconfigure the test track into the loop for further testing. Initial investors are already on board and the team is confident further testing will verify results seen in computer simulations.

“According to our simulations, we could use an NTS track running a total of 24 kites to generate 120 gigawatt hours a year (GWh/year). To put this into perspective, a two-megawatt wind turbine produces around 4 GWh/year. So an NTS system could replace 30 two-megawatt turbines and supply power to around 30,000 homes,” says Guido Lütsch, managing director of NTS GmbH.

Source: Fraunhofer

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.   All articles by Darren Quick
25 Comments

How does the kite pull a vehicle around a figure eight track, given a constant wind direction?

capiti
2nd November, 2012 @ 06:38 am PDT

"vehicles on the ground that are pulled around a circuit on rails by the power of the wind"

The kite can pull the vehicle only half the circuit, what will bring the vehicle around the second half?against the wind.

jochair
2nd November, 2012 @ 07:00 am PDT

I believe the article explained that.

"The developers of the system say a kite flying in a figure-eight or sine-wave flight pattern can generate a pulling power of up to 10 kilonewtons"

And the kite can be controlled in its movement as noted below

"The ground vehicles would also contain the measuring and control technology with a horizontal and vertical angle sensor located in each cable line and a force sensor within the cable distributor enabling precise control of the kite’s movements"

So the kites can fly in figure eights and probably can pull the cars in either directions.

brahmo
2nd November, 2012 @ 09:13 am PDT

It can pull around a track because it is not a parachute.

Stewart Mitchell
2nd November, 2012 @ 09:40 am PDT

I would think somthing like a tacking manuver, like a sailboart, adjusting the tension on the lines would allow for a complete "circuit" of the track...

Lou Digilio
2nd November, 2012 @ 09:41 am PDT

This works like 'tacking' in sailing. The angle of the kite is changed to pull the vehicles around the circle. See "sail karts" for example of this.

William Volk
2nd November, 2012 @ 09:44 am PDT

The kite may be doing a figure 8, much like a stunt kite, but I am guessing the track will be more like a hot dog or ellipse shape rather than circular. The kite can be feathered when the cart reaches the ends, maintaining enough kinetic energy to get around the curve, then off we go again, like a wind surfer. And the rail/cart interface might be like a modern rollercoaster with a captured rail. How the kinetic energy is converted to power a generator is unanswered, maybe a friction wheel on the rail. I wonder if inductance is a viable option? And how does the electricity get from the cart to the grid? A video simulation would have been nice. Still, way cool.

Bruce H. Anderson
2nd November, 2012 @ 09:50 am PDT

Sail powered craft manage to move against the wind, and a kite is only a form of sail.

Techtwit
2nd November, 2012 @ 10:00 am PDT

To answer your question: by a steering maneuver. Just imagine a kid standing on the beach flying a figure eight. The kid doesn't move yet the kite does. Conversely, a steered kite under strong wind pressure will pull a vehicle through a figure eight or round track continuously. Trust me, if Fraunhofer is involved, it works.

moreover
2nd November, 2012 @ 10:18 am PDT

Anyone notice "Sine Wave" Or "Figure 8"?

Zappenfusen
2nd November, 2012 @ 10:29 am PDT

Is this some kind of sisyphean contraption, where a kite pulls the wheeled generator on rails up slope, then reduces lift for gravity to complete the cycle?

steelengine
2nd November, 2012 @ 11:04 am PDT

And then the wind quit blowing for a week. The kites came down, several getting their lines tangled in the ground tracks and cars. Others had tears in their fabric and needed repairs - in all the confusion the cold front moved in with a blast of 40 knot winds and freezing rain.

Richard Chesher
2nd November, 2012 @ 02:05 pm PDT

@capiti

How does a boat sails against the wind? Same thing. It is definitely a slower process, but would be possible, I guess.

Personally, I think it would have been more convenient (and more romantic) to do this out at sea, on a boat, with a water turbine dipped into the water. I was going to do my thesis on that, but alas, none of the advisers were interested in green energy.

Savin Nay Wangtal
2nd November, 2012 @ 04:53 pm PDT

@Bruce One easy way of getting power from the moving cart to stationary lines would be through metal wheels on the cart to metal track, having one positive, and one negative of each. Brushes would work pretty well also.

Electrothump
3rd November, 2012 @ 12:03 am PDT

Interesting idea. projected yield is quite impressive indeed. I think in reality, this has NIMBY all over it. Funny how just about everyone wants clean, alternative power generation... just not near THEM.

Burnerjack
3rd November, 2012 @ 02:10 pm PDT

re; Richard Chesher

I am not a fan of wind power and I think that rigid wings would be better but you must think that the operators are blindingly stupid.

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re; Savin Nay Wangtal

Your windjammer sounds beautiful but how were you planning on getting the electricity to land?

Pikeman
3rd November, 2012 @ 09:18 pm PDT

That's quite clever. It's safer for birds, bats and other wildlife as well. Plus, you can always reel the kite in for a storm -- not exactly something you can as easily do with a turbine.

Stradric
3rd November, 2012 @ 09:34 pm PDT



Why not replace this vehicle with a horizontal bar (seen as vertical here)

that is constructed in such a way that its always able to slide to a perfect angle and lock up -you need a full 360° circle for that!

All you then need to do is find a way to generate electricity with a vehicle that´s "sliding" across the bar, pulled by the kite. Something as shown in the video perhaps, without thoese people sitting on it ofcourse. ;)

Pieter Voorhans
4th November, 2012 @ 10:38 am PST

Kites need wires, so it makes a lot more sense to me to have the generator up in the kite in the wind, moving power to the ground through the wire: it should be possible to generate 10kw from a 2.5kg unit with a suitable prop, mounted on or below a kite (think: paramotor)

(see: http://www.hobbyking.com/hobbycity/store/__25413__Turnigy_RotoMax_150cc_Size_Brushless_Outrunner_Motor.html for source of my guesstimate)

In fact - imagine a massive "box kite", except using cylinders instead of boxes, and put the generator and prop inside the cylindrical "duct" - that kind of design should be really good?

christopher
4th November, 2012 @ 07:15 pm PST

re; christopher

The generators are very heavy look out below.

Pikeman
5th November, 2012 @ 01:29 am PST

If you use a figure of 8 track, the crossover point limits you as to how many of these vehicles can be pulled by kites round the same track. To get best value out of it you'd really need to pack them in to the point that the whole thing is covered in a train of these vehicles with no beginning or end, and you need to get rid of the crossover point to avoid the cables getting tangled with each other. There will be a part of the track where the vehicles aren't powered forwards, but they will be pulled forward simply by being part of the train. You now have two lines of kites moving at slightly different altitudes in different directions along long straight paths with tight turns at the end, the track being lined up at 90 degrees to the prevailing wind. An ideal site would enable the train to switch onto different tracks depending on the wind direction, all of which would be exactly the right length to enable the train to link front to back once its made the transition from one circuit to another. It may be better to have more than two different lines of kites such that no kite would be close enough to another to be affected by turbulance from the one ahead of it, but I'm sure it can all be done under computer control.

David Cooper
5th November, 2012 @ 12:46 pm PST

Kite-surfers have known for quite some time now that the power of the wind increases with altitude. The main problems for land-based kite power are trees and man made obstacles... power lines, wind turbines...

nutcase
6th November, 2012 @ 06:06 am PST

That sounds fun and certainly Fraunhofer can do.

Emdenfahrer
8th November, 2012 @ 10:06 am PST

For more information on the NTS method, see "NTS" in the KiteEnergy main glossary in page "n" with links to the patent and drawings.

The method of sailing wings for energy around a closed loop is an ancient technique. Roads, waterways, cableways ... in closed loop let the ground vehicle be a site for generator; in case of a waterway, a hull-held water turbine could generate; in case of wheel or railed-wheeled vehicle, the axle could be the driver for standard generators. NTS seems to involve drag-based and lift-based tactics using the ancient-closed-loop choice; they seem intent also on having the downwind sails be higher while the upwind sails are somewhat feathered and perhaps lower in lower winds in order to reduce the "cost" of the upwind struggle.

Joe Faust
19th November, 2012 @ 02:47 pm PST

The problem with kites is, that the higher wind speeds are per definition translated into forces perpendicular to its natural motion - meaning those larger forces do not support energy conversion. Also, slow cyclic linear motion will always struggle to gear-up to the constant 50/60Hz rotational motion our grids are based on.

francm
23rd November, 2012 @ 02:04 am PST
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