Some said AWE was all about replacing hardware with software. Well they have had 14 years to write the software. Now people are stepping back to take “the view from 30,000 feet”, and saying there is no place to run an AWE system, etc.
So nobody knew wind energy requires space until now?
I still maintain that for AWE to catch on in any meaningful way, someone will have to demonstrate a useful configuration that does something for someone, generating useful amounts of power, in some useful way, rather than just generating more excuses.
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Kiwee meets the conditions you describe. It will be difficult to do better in this range unless you have a fully automated drone system, even in the search for sites.
AWE requires far more space. Imagine that there are MW-scale AWES (SkySails later?) like some installed wind turbines, and these AWES would work not too badly. Now replace HAWT with these hypothetical AWES. I bet it would be a miracle if you managed to replace a tenth of them.
Hi Pierre:
Well, my point is we’re just noticing this now? After 14 years of hype? So why did we ever start pursuing AWE? I am not arguing your point, that it would appear, without a working AWE system to use as an example, that it would be difficult to match a regular windfarm as far as density. But so far AWE targets remote islands, ships, offshore, single installations, shipping-container systems for “disaster-relief”, etc. AWE arguments seem to want to pick and choose whether they compare against standard wind turbines, depending on which discussion they are in. If we are talking about windfarms, you (as an example) point out how we don’t know how we could pack the same density of AWE systems into a windfarm space. But then people developing the typical shipping-container AWE systems will cite remote islands where it is expensive to import diesel fuel to run a generator, never mentioning they are still in competition with regular wind turbines, since a regular wind turbine is also an option for a remote island. Meanwhile, if there were an AWE system that could compete with a regular wind turbine, THEN remote islands, single residences and farms, etc., WOULD be a place where you could run an AWE system without entanglement with neighboring systems. So, to me, worrying about how close you could pack AWE systems is relevant, but a future problem. Cart before the horse. First you need an AWE system that someone would WANT to pack together in a windfarm. As it is now, there is no such problem. And like the three blind me trying to describe an elephant, it is hard to say how we would pack many AWE systems together if we don’t know what they would look like.
Yeah and they are selling systems and nobody is worried about how to pack them into a windfarm.
I will be attended IFA Berlin from september 2 to 6. So If anyone wants to come along, it will be a great pleasure.
I will showcase Kiwee and also our Molding injection process
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POIDS 10 kg DIMENSIONS 100 × 40 × 40 cm POWER OUTPUT 100 Watts @ 28 km/h , up to 400 Watts @ 50 km/h FLIGHT ALTITUDE Between 30 and 60 meters, depending wind speed Wind speed range : starting at 20 km/h up to 60 km/h continuous. Gust up to 120 km/h INTERNAL BATTERY Li-ion, 10S, 40 V, 2200 mAh, 80 Wh CONNECTORS – Cigar lighter receptacle 12 / 24 V, 100 W Max – 2 x USB socket 5V – Terminal block 12/ 24 V, 100 W Max PROPELLER DIAMETER 1.05 m
400 W at 50 km/h (about 14 m/s). What an achievement! Indeed, progress has been made to be able to produce more with more wind, or I missed something.
that 's it @pierre. more with more wind ! Your numbers are about right, It was done at around 50km/h constant wind. At start kiwee was planned to be 50W. then we discovered it could do more. We design it to hold 120 km/h winds. It ended up on molene Island last year to make some records at 400W generated power. We were forced to lower production at that moment because power output capability and battery charge current where limiting our power production. Also I think generator was a bit overheating 
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The Kiwee system is truly different from all the other AWE designs. The basic principle is to use a lifter kite to suspend a conventional horizontal axis turbine at a high altitude to capitalize on increased wind velocity and wind consistency. If we combined this with a cable drive we can eliminate the onboard generator and the electric cable transferring power to the ground. With the Kiwee system the primary functions of the parts are separate. The function of the turbine is for creating power only and the function of the lifter kite is for creating enough lift to suspend the whole system and maintain altitude. In the system the turbine is optimized for power and the lifter kite is optimized for lifting. The Kiwee system is the only system that eliminates the problem of cosine cubed losses. In all other systems, the tether is connected directly to the kite and so the greater the tether angle, the more cosine cubed losses are accrued. This effect becomes progressively more severe when the tether angle is greater than 45°. See attached drawing.
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I think this is one of the most impressive “pseudo” flygens out there, it’s truly a rotary AWES but the the tether cleverly acts like a transmission method. Quite an elegant design (for a flygen heh). Personally I don’t prefer rotor and cables next to each other… (could be solved with a ducted approach). I don’t know what else to say other than if the wind is blowing, this system works at any scale.
There is no conflict of interest in my assesment here, I am more partial to multiline control systems… But as a pure AWES… it’s hard to beat Kiwee in terms of cost, weight, and efficiency.
I think we need a standard test for all of these AWES or a scoring method.
Say we have a nominal speed of 15k of wind
We consider the weight to power ratio
and the cost
Well yes and no.
If you only look at the horizontal axis blades, you can analyze like this. But dig a little deeper I think you must also take into account that the lifter is also a wing integral to the design, and must be included in the analysis.
The bigger an angle wind to tether, the more lift you need in the lifter kite. I think this is quite close in effect to cosine losses.
Also to make things worse, the lifter is not moving crosswind, so the wing area of the lifter must be relatively large compared to the area of the turbine blades that are spinning.
So you can choose fast spinning turbine blades and a lot of downwind pull, and a lot of power. A huge downwind pull then requires a large lifter if you want to maintain a steep tether angle.
Or - you can make the turbine blades rotate slower, decreasing downwind pull, and use a relatively smaller lifter, but that means you need to increase turbine blade area to get the same power output.
I’d say the situation wrt cosine losses in this design are probably in the same magnitude as other AWE systems. Actually I prefer a Daisy kind of arrangement but with no lifter (maybe more a «The Pyramid» arrangement really) because the blades themselves are providing bouyancy, and the blade speed would be the same for bouyancy and power generation, making analysis easier and also making the system maybe act more uniformly in the face of changing wind speed
To forward the discussion about lifter kite designs, maybe a number like ratio swept area vs lifter area could be useful to describe «cubic» losses in these designs. This makes sense I guess if you assume that the optimal design of the turbine blade is more of less settled on based on HAWT design…
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This is very hard because AWE systems are very different. So many metrics could apply; LCOE, mass, power curve, maintenance costs, installation costs, etc. The truth is I think no actor in AWE can provide all these numbers accurately.
So for now, careful judgement must be applied to every design, considering stated specs along with the maturity of the project and how much you trust the metrics provided.
I do think the Kiwee is an interesting and great design though.
I would be careful stating «at any scale» for anything airborne. Small things fly easier than large ones. If you see no scaling limit, you probably just didnt do enough analysis
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Tallakt,
Excellent analysis. While I don’t perceive the tether angle as a significant problem, I do concur with the noticeable absence of crosswind power. This system is inherently stable, which makes it simple and safe. However, stability can be a disadvantage in a dynamic system dependent on crosswind/apparent wind. I’m also intrigued about how the two-line transmission is reeled in - it’s likely straightforward, but I’m still curious.
Regarding a competition (has this topic been discussed before?), I’m interested in whether a somewhat equitable system can be established. We could compare the feasibility of different renewable energy sources and their worth in terms of economic and power ratios. In sailing, there are various classes and scoring methods. I firmly believe that it’s possible to devise a similar system…
Is there are AWES park where formative tests can be done?
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I think that Kitewinder’s Kiwee is by far the most operational of the rotary systems you mention. In fact, it’s the only one to fly at any altitude (in the first place thanks to its rope drive transmission system), which is what enabled it to be commercialized.
The reason you give seems to be relevant as part of the rotary AWES you set, but the positive consequences of an optimized (not tilted) wind turbine are even more important.
Beforehand if Kiwee flew at a lower elevation angle, for example 30-35 degrees instead of 60 degrees, the lifter could be much smaller and comparable to the lifters of other rotary systems you mention.
Thus the [power-elevation angle / lifter area] ratio is probably comparable to that of other rotary systems, I would even say certainly higher, because the wind turbine is optimized for production, being not tilted, as is the lifter for its task, while tilted turbines are not optimized at the same level for generation, leading to the requirement of more material per unit of power, and from the ground due also to the torque transfer transmission, leading to more weight (although TRPT Daisy remains light) and more catenary sag effect.
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The rotor(s) are always downwind of the cables and there should be no interference. If the cables become slack, then the kite must be immediately landed.
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This kind of talk has been going on since the mythical “flyoff” promoted by one of the people running the previous forum. As though wind energy is some sort of game for people to play. Imagine real wind turbine people talking about all flying to the same place to set up their wind turbines for some sort of in-person competition - why? Who would bother? As though people have nothing better to do than ship systems around the world to go temporarily set them up and “prove” they even work? This is the sort of thinking that shows the whole field of AWE is in a fantasy-land.
To have an effective AWE system, is the same as any other successful energy system - it has to BE successful in terms of showing promise as an economical energy solution worth the trouble to set up and run. Simple. It’s like if you want to have a successful lemonade stand you need to get some lemons and some sugar and water and pitchers and glasses, and quench peoples’ thirst. No you don’t need to set up a formal competition where everytone ships a bunch of crap to the same location to see if someone can set up a lemonade stand.
People are always looking for some formal “approval”. You can’t get formal approval from anyone until you have something worth being approved. For that, it has to be useful, reliable, convenient enough for someone to want to bother using. Build it and they will come. Don’t build it and you sit around talking about organizing some “competition”. It’s like talking about organizing a car race when there is no car that can make it around the track. And of there were, people would simply be driving it, no race required.
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“It is cool but too restrictive in term of space where you can set up the device.”
Perhaps not, if the power generated becomes commensurate with the space used.
That said, we can’t ignore the feedback from a rotary device which works.
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The Kitewinder system has two basic advantages, firstly it eliminates the cosine cube losses and secondly it operates at a higher elevation at higher wind velocity . Because of the increase in the tether angle at altitude, a slightly larger lifter kite might be required but this is more than compensated for by having a much smaller turbine system to generate the same amount of power. My analysis using the wind profile that I have selected shows that there’s an increase of 250% in power when elevating from 50 m to 1000 m. (See graph)
I think Kitewinder did a great job of executing their design. As to whether the gearing interface is just as heavy as a generator would be, or how far (long distance) one could go with a “grandma’s clothesline” drive, and many other aspects, a lot remains unknown. It’s common in small wind efforts to come up with something that seems to work OK in the short run, given favorable winds, etc. But how long does it last?
I have a similar size 2-rotor ST here that’s been running for ten years, wearing out one set of blades (replaced), but the overall unit still functions like new. This might be unlikely for a gear drive - maybe not - who knows, but also, one might rightly point out that a Kitewinder would be unlikely to be run all day and night for years, but more likely deployed as a brief demo or used to have a fun time on a weekend, maybe demonstrating usefulness by charging a phone, etc.
I have people who see my 3-foot diameter, dual-rotor ST in the front yard and say “I’d like one of them to add to my solar”. But I have to let them know, they will probably never notice the amount of extra power from one small turbine like that. It’s just too small to make a difference in an electric bill. And that’s with it running continuously.
Since the kite-borne turbine needs extra attention, requiring an intentional launch when winds are favorable, it won’t see as much wear as a dedicated installation. So it’s not an apples-to-apples comparison to place a fun demo turbine up against a permanent installation that must perform in all weather conditions, including severe storms, throughout every day and night, even in hail, snow, thunderstorms, sustained high winds, etc.
There is real wind energy, and there is fooling around and fantasiy. I really like Kitewinder though, and it shows a lot of talent.
Doug: I’d like your opinion on an autonomously launched industrial Kitewinder system which I proposed, involving a fully restrained lifter kite which only launches when the conditions are favorable. The system autonomously lands the kite when the tension in the cable drive system is too low or too high.
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This what is desperately needed, an automatic reel in low winds and a way to really store the kite… preferably change the kite if necessary