I am wondering why not more companies are pursuing a soft-wing ground-gen AWE system without a pumping cycle. In my limited experience, it has become clear that the reel-in and reel-out phases introduce several complexities, here is a non-complete list:
As energy is needed during the reel-in phase, some type of energy storage is required. (maybe when operating multiple AWE systems off-phase, this could change)
The flight pattern is rather complex, making controller design more difficult and the system in general more error-prone.
Developing a design that must be optimized for generating both maximal and minimal force is challenging and leads to suboptimal performance in both phases.
Implementing tether drag reduction add-ons is more difficult when a large portion of the tether must be reeled in and out.
etc.
If, instead one would fly only figures of eight or circles (assuming here that a solution for the cable twisting problems can be found) and find a way of generating energy from that motion, e.g. a linear actuator that swings left and right, the problems mentioned above would be resolved.
Curious about your opinions, as I am likely overlooking something crucial.
Welcome to the forum, Jelle There is also a rocking arm design implemented by some teams. WPI was particularly active in pursuing this. The kite flying figures-of-eight maneuvers is pulling this rocking arm left and right. This motion can be converted into electricity. Below are some references from WPI. But, as @PierreB puts it, while this concept solves the reeling problem it has its own challenges.
Yeah Roddy, I remember telling you, if you want to make real power, you will need to use rigid blades.
That was during the old forum and constituted one of the many daveS/DougS “debates”, if you can call correcting an inexperienced person who doesn’t know any better, “a debate”. As I was saying at the time, except they deleted my message, you were listening to the wrong people.
Any real wind energy person already knew about hard blades versus soft - it was never in question. Pretty-much figured out 1000 years ago, like so much of wind energy.
Anyway, it might be nice to give credit where credit is due once in a while.
Not that I’m not as attracted to kites (of any kind - soft or hard) as the next person.
I DO think the whole rocking arm idea, as well as several related possible configurations, MIGHT find some success in AWE, and have always been surprised that we have not seen more of them tried.
And when I say “success in AWE”, it could be pumping water, for example, still what most windmills are used for today.
Currently the most powerful AWES by far is SkySails’ wing, with an average of 92 kW, wind speed of 12 m/s. And it is a flexible kite, flying in yo-yo (pumping) mode. It is a fact.
Touche` Pierre. Pumping, pulling boats, yes I can see performance coming from soft kites. I was talking about regular wind turbine configurations, sometimes referred to as “rotary” in AWE (in regular wind energy, the word “rotary” doesn’t need to be said because that is how wind energy is done 100% of the time).
Here’s the last time soft cloth airfoils were used in a rotary wind turbine: (1000 years ago)
Well, I have to say, today’s parafoils might work better than these cloth triangles! Just imagine the tip losses with these things!
As to whether a soft-kite apparatus can ever compete for economical power (such as electricity) generation against hard blades, we have yet to see it. But you make a great point, and I’m not one to argue with facts. If someone can make soft airfoils work in a wind turbine, I’m all for it, and I would be the biggest fan. (Of course when we use the term “biggest fan” in wind energy, we have to be careful about puns!)
As much as I point out the suboptimal nature of various alternative forms of wind energy, I have many many “inadvisable” ideas that include soft kites, vertical-axis turbines, etc. In that way I’m just like every other brainstorming tinkerer/inventor, but when people really want to know what really is proven to work well, I’m happy to share the basic knowledge I’ve accumulated since the 1970’s. Most of that has not changed much.
Welcome, @jellepoland
Being new to the forum you might want to check out old posts by @kiteghost /@kitefreak for his Soft-wings including NASA POWER WINGS derivatives Applications over the years at kpower now JAL.
He is not available on the forum for now but you can easily reach him directly via his email - santos137@yahoo.com
My position has been mostly aligned with his.
Something like W&I rotating designs already exists and also something like «The Pyramid» could easily be implemented using soft kites.
I think the question is slightly wrongly worded. You always want the best possible performance. So the quedtion is rather; why would a soft wing be better suited for a certain application.
From where I stand, soft wings have lower aero efficiency but this may largely be offset by tether drag anyway to an extent where it doesnt matter much. Next you have handling issues, if said soft kites are maybe bigger and harder to «catch» than a comparable soft kite. On the positive side though, you may get more energy for a given mass, and it may scale to bigger sizes.
These are all quite fuzzy subjects so its hard to say which is the better choice.
Even for a system without a pumping cycles it’s still necessary for the system to be able to reduce the power and forces once rated power / rated loads is reached.
A guy from Alaska called me yesterday, looking for a turbine that would do well in his normal super-light winds, and also in his occasional super-heavy sustained 40 MPH winds coming down his canyon. He thought my SuperTwin™ might fit the bill.
It does seem that a turbine needs to target a certain zone of performance. A powerful generator, for high winds, may not start so easily in light winds. Really, the stupid thing about this whole topic is that light winds have so little power they are usually not worth pursuing. On the other hand, even a turbine built for light winds, if permanently mounted, will need to be able to survive very high winds. So we end up with the standard wind turbine, made to harness productive winds, with little emphasis on light winds, except the occasional “people-pleaser” modification (like a voltage boost) that can let it reach down to squeeze a little juice out of light winds, as a symbolic “at least it’s making SOMETHING” tip-of-the-hat to the anxious owner who just wants to see it making some power, no matter what.
Today’s “low wind speed” turbines are usually just a standard utility-scale wind turbine fitted with longer blades, but of course that means the bearings etc. will be overworked in higher winds since the platform was not designed for blades that long. But some area with maybe a class 3 or 4 wind resource instead of a 5 or 6 will choose that turbine and hopefully it can keep out of trouble in high winds.
So, while some adjustment is possible, really, wind turbine design has honed in on the productive speed zone and there’s no point in deviating too much from that, since there is so little power in light winds, and so comparatively rare to have super-high winds.
There is also a rocking arm design implemented by some teams. WPI was particularly active in pursuing this. The kite flying figures-of-eight maneuvers is pulling this rocking arm left and right. This motion can be converted into electricity. Below are some references from WPI. But, as 
