Engineers in Germany believe the aerial movements of stunt kites can be harnessed to generate electricity.
Berlin-based wind energy developer NTS and experts from the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in Stuttgart are now working on a project to harness the power of winds at altitudes of up to 500m.
Joachim Montnacher, an engineer at the IPA, said: ‘The kites fly at a height of 300–500m, perfectly positioned to be caught by strong winds. Cables, about 700m in length, tether the kites to vehicles and pull them around a circuit on rails.
‘A generator then converts the kinetic energy of the vehicles into electricity. The control and measuring technology is positioned on the vehicles.’
Compared with conventional wind farm technology that relies on rotors, this technology is said to offer a wide range of advantages: at a height of 100m wind speeds are around 15m/sec while at 500m they exceed 20m/sec.
‘The energy yield of a kite far exceeds that of a wind turbine, whose rotor tips turn at a maximum height of 200m. Doubling the wind speed results in eight times the energy,’ said Montnacher. ‘Depending on wind conditions, eight kites with a combined surface area of up to 300m² can equate to 20 conventional 1MW wind turbines.’
According to Fraunhofer, figures for the past year show that at a height of 10m there is only an approximately 35 per cent chance of wind speeds reaching 5m/sec, but at 500m that likelihood goes up to 70 per cent.
This makes any number of new low-land sites viable for the production of wind energy. Another advantage is that it costs less to build a system that, among other things, does not require towers.
High-altitude wind farm
NTS will design the kites and construct the high-altitude wind farm, and the researchers from the IPA will develop the control and measuring technology, which includes the cable winching mechanism and cable store.
One of the jobs of the control unit is to transmit the measuring signals to the cable control and kite regulation mechanisms. A horizontal and vertical angle sensor located in each cable line and a force sensor within the cable distributor guarantee precise control of the kite’s movements as it follows either a figure-of-eight or sine-wave flight path up above.
These flight manoeuvres are claimed to generate a high pulling power of up to 10kN — meaning that a 20m² kite has the capacity to pull one ton. Each vehicle is pulled by a different flight system.
At a test site in Mecklenburg-West Pomerania, IPA researchers and NTS sent a remotely controlled kite on its maiden voyage along a 400m-long straight track.
The team now want to reconfigure the test track making it into a loop and computers will eventually be used to achieve fully automatic control of the kites.
Guido Lütsch, managing director of NTS, said: ‘According to our simulations, we could use an NTS track running a total of 24 kites to generate 120GWh/year. To put this into perspective, a 2MW wind turbine produces around 4GWh/year.
‘So an NTS system could replace 30 2MW turbines and supply power to around 30,000 homes.’
After successful test flights on the demonstration track, the project partners are confident that their computer simulations will hold up in reality. The first investors are already on board.
I fly stunt kites as a hobby and i know that traveling directly upwind can be tricky. Given that that the generator ‘cars’ are running on a loop they will have to run upwind for half of each loop. Can this be done entirely by the kite or will the ‘cars’ have assistance for going up wind. Also, i wonder what diameter the track needs to be. They claim to be able to replace 30 turbines but what is the relative amount of space required for each system?
Its certainly and interesting idea. I look forward to seeing how well it works.
Fascinating concept.
The return loop I presume would be a non-generating part during which the unit would require some power to drive it back to the start. A bit like the unproductive strokes of an internal combustion piston engine. The kite would then turn to a neutral position or be lowered??
The track does not neccesarily need to be round. Two parallel tracks could also work if there is a predominant wind direction plane.
I wonder how they control the kite to maintain optimum pulling power?
I have been involved in “conventional” Wind Energy R&D from 1984 to 2000, at ENEA, Italy. A similar idea (kites for Wind energy) has been yet proposed and is under development in Italy since 2006, at least before 2009. See “kitegen” on the web, e.g. http://kitegen.com/2012/04/ (in italian) or http://www.kitegen.com/en/ (in english).
As far as I know there has not been yet official interest from the “institutional” side of R&D and industrial sectors, even if the kitegen has been recently proposed to feed an aluminium factory undere economic stress (Alcoa, in Sardinia). The Key point is to proceed from a prototype to a “Demo” application with significant size, that could be seen as pre-commercial or fully commercial depending on degree of mayurity. In my opinion the key points to thoroughly evaluate such systems (after a demonstration that they “work” at a sufficient level of prototyping) are durabiliyty, environmental (visual) impact, impact on aero navigation; I am not able to judge from an engineering point of view since a specific assessment should be made on specific situations (this requires time and effort). Good luck for now.
Good idea, if they have a loop probably does not make sense to have half of the track lost, they could just have a linear track.
Put a sail on the cart for the upwind segments….