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Delft explores kite power for rural Africa


July 11, 2013

The current wing is an inflateable wing specially built by a kitesurfing manufacturer for the Delft team

The current wing is an inflateable wing specially built by a kitesurfing manufacturer for the Delft team

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The University of Delft has a program devoted to kite-based generation systems, with 20 years of research and development under their belt since Wubbo Ockels, the first Dutch astronaut, established it. Now, members of the team are exploring practical niches where kite-based power might pay off. One has just completed a trip through Kenya, Tanzania and Senegal seeking opportunities for kite generation in rural Africa.

Christopher Grete, a member of the Delft KitePower curriculum focusing on deployment of kite generation, has just returned from an extended trip through Africa where he was drumming up interest in using kite-based generation in rural Africa. This is an area typically poorly served by the national grids and with significant logistical challenges for major construction. Delft has been researching kite-based generation since 1993 when the first Dutch astronaut into space, Wubbo Ockels, established the program. The faculty has several professors and students engaged in simulating, prototyping and assessing all aspects of the field, but are just starting to seriously consider commercialization.

Innovative wind generation systems have a tendency to focus on the technology instead of a target business niche, and the Delft team is no exception. They have advanced three different types of kites over the years, including inflated tube kites similar to those used by kite surfers, inflated airplane-style kites and airfoil kites.

They have stayed with fabric kites which typically have an advantage for deployment, crashes and recovery of airborne generation while giving up top-end power to rigid wings. The inflated and airplane kites they use have greater speed and hence power advantages over airfoils, but of course depend on either ground-based repressurizing, or as yet unbuilt airborne repressurization systems. This is a similar challenge to their counterparts at TwingTec, who use a unique, inflated structural member of high-strength.

The Delft staff have tried a mixture of control systems over the years. For some of their prototypes they have used radio controls, while for others they use ground-based tether controls just as any traction- or stunt-kiter is familiar with. They have settled on an airborne, radio-controlled system positioned in the bridle of the kite that hauls in and releases the control tethers for the kites using microwinches. This increases airborne complexity, but eliminates multiple lines running all the way to the ground and multiple ground winches for control. It also allows easy depowering of the kite for the upwind pull. This is a very reasonable compromise, and the solution allows intelligence of automated control to be ground-based or in the control unit itself in the future.

At present, they are flying their kites manually with a ground-based pilot and winch operator team, but this is an area that they are focusing on automating. It's also an area where they are behind the front runners in this space, Makani and SkySails. Both of those companies have built automated launch, flight and recovery systems that are robust and work today, Makani for its hard-body wing, and SkySails for their cargo-ship towing airfoils.

Because of their airborne control system, their ground station is relatively simple, with a single winch. What's missing is a roost mechanism for automated launch and return of the kite to the ground station. This is necessary for both very high and very low wind scenarios which will occur, and the lack of attention to this to date is indicative that they have been focused on research into specific areas of kite energy rather than into creating a commercial system. SkySails has this solved for fabric kites with their proven commercial solution today.

Onshore high-altitude wind rapidly runs into problems with flying effectively invisible cables potentially kilometres long into airspace where small planes and helicopters fly. And it rapidly runs into problems with downwind ranges in the event of a failure situation which might drape very thin but very strong cables over power lines, roads and buildings. Delft's soft-structure kites virtually eliminate danger from the kite itself if the cable snaps, but overall potential liability is higher compared to alternatives, which is why most high-altitude companies looking to commercialize target offshore or niche remote situations.

That's where Christoph Grete's recent trip comes in. He traveled to the capitals and countryside of Kenya, Tanzania and Senegal on the coasts of Africa. He met with governmental agencies, research institutions, university departments and companies engaged in power in Africa. He experienced several power outages even in the developed parts of the countries, and heard clearly that many rural areas were completely disconnected from the national grid and dependent on fossil fuels that were trucked in to generators at substantial expense. Small-scale renewables in these circumstances can have very advantageous price points for specific areas and applications. One suggestion was providing power for long-lasting UHT-milk processing, a virtuous combination.

Rural Africa has large spaces and low existing technical infrastructure and air traffic to disrupt. This makes a potential siting of kite power have lower concerns. However, the combination also increases the challenges of getting more complex technical and electronic equipment serviced. He has identified several research and deployment opportunities for the Delft technology and is working to get them funded and moving forward to address concerns.

It's possible that at least some of Africa's next wave of rural electricity will come from the sky.

Source: Delft University of Technology

About the Author
Mike Barnard Mike Barnard is Senior Fellow - Wind, with the Energy and Policy Institute. He has been a deeply interested observer of energy systems for three decades. His work as a business and technical architect on large initiatives in a variety of domains gives him the systems thinking perspective and stakeholder analysis skills to engage effectively with an area as complex as the grid. He’s regularly asked to peer-review academic and non-academic publications related to wind energy by journals, organizations and individuals. Through the Energy & Policy Institute, his blog barnardonwind.com and other venues, he focuses on bringing data-centric reality to bear in policy, siting and social license discussions related to wind around the world. All articles by Mike Barnard

I have seen tarps unravel in a few hours at under 40 mph. What is the life expectancy of one of the kites?


You bring up an excellent question I hadn't considered previously. Certainly lower than most components of a three-blade HAWT. At present, I haven't seen a lifespan estimate for any of these generation kites and since none are in production, there isn't historical data.

SkySails has been towing cargo ships since early 2008 with their 160 m2 and 300 m2 kites. In general, these are not expected to operated day and night year round as would generation kites, but they are subject to different stresses with the ships plowing through swells and would certainly have much more annual usage than the average kitesurfer wing. The overall system was projected to last 16 years according to one reference, but with expected kite replacement. Skysails does not make lifespan information on the kite component of their system public.

From another domain, paragliding, lightweight wings capable of flying a hundred or more kilometers have a safe lifespan of 400 hours of flying or so. One vendor used very UV resistant fabric and saw much slower degradation due to that factor. A heavy-duty traction kite expected to fly in much more powerful winds than the average kitesurfer or paraglider would typically fly in for much longer periods would be built of UV resistant, heavier duty fabric. Given the expectation of 95% flight time or so per year, it wouldn't be unreasonable to expect potentially annual replacement of the kites at a currently unstated price. Expectation of kites being much costlier than retail kitesurfers or paragliders is reasonable given size and MTBF expectations, so a $100K kite isn't out of the question.

You bring up a different good point than just lifespan of the wing, of course. The Delft system uses inflateable kites, and inflation membranes typically have lower lifespans than airfoil membranes because the porosity demands are different. Delft doesn't publish information on lifespan of their kites, but they are using standard kitesurfer fabric and construction techniques at present, customized for their needs by a kitesurfer manufacturer. Their lifespan is 250-300 hours. However, as the system moves to commercial viability, once again much more robust fabrics and techniques would be expected for heavier duty kites, extending the lifespan.

Mike Barnard

Can you really confirm that Makani can do an automated flight from end to end just about anytime the wind is good? The lifespan of soft kites might approach the decades of inflated stadium roofs. There's a tradeoff for performance, but the bean counters will have a long range to pick from. If I had a power kite, I'd try using it to haul water up to a raised reservoir, so I'd have electricity on demand. The initial generation and integrated storage can be pretty low-tech. Africa can certainly produce a fine canvas tent; once it is working well, much of the technology may then be adapted for local and organic materials. A low kite is still higher than a tall tower, and not a long-range liability.

Bob Stuart

Anyone who has ever flown a hang glider in lift conditions will tell you the awe of the power in nature. I've been in lift conditions going up at 3,000 ft/min that moving 400 #s straight up in air that's about 40 mph that is a lot of power and to have an automatic guided kite doing the same over and over again could harvest that energy into a source of alternate power.

Bryce Guenther
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