166 comments on High altitude wind power II: the reactions
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166 comments on High altitude wind power II: the reactions
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I can not let KiteGen rest yet ... and I was about to post this Levi-Logo the other day as an input for reflection. But since the KiteGen post grew old and disappeared - I saved it 'till now', so I think I'll just add it here.
I see you're trying to 'push down' the Windturbine on some aspects, whereas you try to 'lift up' KiteGen via other arguments (eg. under Fig 5).Maybe you have a point - but I suffer from seeing that immediately (as I do not have a full idea of how you efficiently will be able to extract the energy yet ... from KiteGen) - furthermore I have not read this very post, so my reply here is merely as an input for further discussions/reflections regarding KiteGen.
This LeviS Logo illustrates the troubles that 'I see' KiteGen will encounter (- big time IMO)
I foresee alot of forces involved , but I feel most of them end up as statical forces - doing little work, which in turn can be turned into energy.Depeding on how smart and fast your computer logic is , there may even arise (unwanted) statistical negative counter-forces - acting against your wanted/planned for 'directions/movments' ...
Anyway, the two horses in the LeviS Logo are going nowhere - AND they will get exhausted .....BUT NO WORK IS DONE - SEEN FROM OUTSIDE OF THE SYSTEM - KiteGens configuration is not 100% equal, but the similarities are definitely there.
On another note : The wind will a) turn the windturbine (work) and the wind will b) propell the sailboat (work) ---- BUT how much work will KiteGen actually be able to extract compared to the forces involved ? (efficiency )
Remark : this is ment as an positive input - and hopefully I am entirely wrong, but that very issue struck me.
When I see KiteGen - I really 'do see' the LeviS logo in practical termes - (and then some) - namely that I understand that you can pick up energy from it via the winch system
Energy or work is force over a distance. Now if each horse moves a distance and does something useful with that force, even though it is nearly in dynamic tension, you could harness the energy. If the silly mule vs. mule is replaces with a mule pulling a heavy load up an incline, you would have a better picture of what I believe the kite system would be doing.
So it is not 2 mules equally opposed. It is more like one mule pulling to raise a heavy load and using this mgh (mass*gravity accel*height) to generate electricity.
Work is force x distance. Power is work / unit of time, or, for a given force at constant speed, force x velocity, MOL.
You also need to consider how fast the process is working to estimate power output and it's power that we need to produce. Having a kite flying at high altitude where the wind forces are greater may not necessarily produce lots more poser, as there must be a way to capture that mechanical force while the velocity is high. Flying the kite from side to side isn't going to produce lots of (rotational) velocity at the base of the stem...
E. Swanson
Paal, I am sure yours is a positive input. To find an answer to your question, I suggest to read the paper by Fagiano et al. (it is linked at the bottom of the paper). It is a detailed simulation of the forces involved in the operation of a kitegen "yo-yo". The results are very encouraging; the yo-yo is not at all like two horses pulling in opposite directions. But I understand that it takes a while getting used to the idea; it took a while to me, too!
Thanks and sorry Ugo - I forgot entirely about that haul-back procedure when posting this LeviS analogy. SO LET IT BE UNSAID.
And i agree that if 12% of generated energy is all it takes to bring the Kite back for 'a new round' , that is quite encouraging.
The fact that the kite needs to be "re-set" to a position where it can again pull on the cable is not much different from the way a waterwheel needs to ride up and over the axle so that it can again collect some power from the flowing stream.
The power is in the constant high altitude wind (or the flowing stream of water) and the kite or the waterwheel is just harvesting some of it. The fact that part of the harvested energy is used up re-setting the harvesting device doesn't matter as long as a reasonable amount of net energy is collected.
Hopefully KiteGen's future prototypes will prove that a reasonable amount of net energy can be collected in this way.
The waterwheel analogy is apt.
You should, in fact, be able to build a very similar yo-yo device to replace a waterwheel, though it would likely be only drag powered, with no lift-generating mechanism. Makes me wonder if there is a yo-yo application for tidal generation, with the direction of the kite shifting with the currents.
There is a small company developing such a system where a friend of mine works as one of the innovators. The idea is to fly a hydrofoil ancored in the sea floor in a figure 8 almost exactly like the kite and extract the power by an attached water turbine. Unfortunately they got a useless web page. :-(
It is more than a waterwheel. Consider a high performance sailplane wing with a 60:1 lift / drag ratio. It could generate vastly more tension in the cable than a simple kite of equal area.
Back to basics. Air has mass. Moving air has kinetic energy. Wind machines extract the kinetic energy by slowing the air down.
Consider a modern windmill with thin long airfoils at a standstill. The blades intercept perhaps 10% of the air flowing through its disk resulting in a slight reduction in average speed and a modest drag force on the tower. Now spin it up to maximum power conditions. The airfoils slow down all the air passing through its disk producing a much larger load on the tower.
It is that ability to absorb energy from a large mass of air with a small device that is the difference. If the concept succeeds the kites may evolve into rigid wings because their high velocity allows them to absorb energy from a much larger mass of air.
I think the show stoppers are;
1. Large land requirements per MW.
2. Large airspace requirements per MW.
3. Noise. A high performance sailplane at minimum sink speed 3000 feet above the ground is silent. But at high speed it is audible on an otherwise quiet day.
Consider a 1000 lb sailplane at high speed sinking at 250 ft/min. it is converting 7.6 hp of potential energy to maintain that speed.
A 3MW rigid wing machine would be equivalent to 531 such sailplanes flying in formation. They would make considerable noise. A 3MW kite would be slower, much larger and would produce much more noise.
With increasing wind speed the required area would shrink as the wing loading increases, but I would expect the noise level to stay about the same.
Its worth testing even if every one of your objections are correct.
It cant be much wore then the german one wing wind turbine and that one ought to have been an intresting research piece in dynamics.