I think the second option could be feasible for JoJo as well… return phase would remain the really large obstacle though. I dont see any reason why our current kite could not do it though (even practical issues related to launching and landing are possible using VTOL).
I believe the dancing kites/Y tether was mentioned in the first revision of the AWE book.
Kiteswarms are working on a system utilizing this. https://twitter.com/kiteswarms
https://www.youtube.com/watch?v=x05yNwG1x80
Indeed the second option could be feasible as pumping mode (= yo-yo = reel-out/in = also lift power device). But the management of reel-out and reel-in phases looks to be a complex task for several wings.
And the abstract of “The Betz limit applied to Airborne Wind Energy” on https://www.sciencedirect.com/science/article/pii/S0960148118304427 indicates: “Another contribution is to show that Loyd’s lift power AWE devices during the reel-out phase can harvest up to 4/27≈15%
of usable power available in the wind, i.e. exactly 1/4 of the theoretical limit of the horizontal-axis turbines and AWE drag power systems with ideal airfoils”.
As the wings are spaced due to flight and safety requirements it can be pratically insignificant. But rotating AWE systems like Daisy or Rotating Reel could reach a real maximization of the space use combined with reaching Betz limit (before cosine loss like for all systems) instead of 1/4 Betz limit. One price for it is a high level of tethers drag. Another price is the big structure of the ground ring.
It is in the second option mentioned by tallakt, here in pumping mode if I am right.
The present topic is relevant as now we can put side by side several crosswind multi kite systems: in the second option are Kitewarms and other “dancing kites”; in the third option are Daisy, Rotating Reel, KiteGen carousel…
I think that using the Betz limit may be relevant sometimes and sometimes not so relevant. The betz limit is relevant if airspace is a limited comodity. Think about last time you flew a plane - there are vast areas of unused airspace, at least here in Norway, and at sea in general.
Now look at material cost vs generated power. I am pretty sure no AWE can ignore this parameter. If the wings are not working at their optimum parameters, those materials are partially wasted. This is why Im thinking that we need to make sure that losses such as tether drag are minimized and wings are not flying in the wake of another wing.
Reaching the Betz limit will be a story of diminishing returns. The further you approach the limit the more it will cost. And lets face it, energy is not particularily expensive.
AWE’s potential is in getting access to more wind resources, not extracting all energy out of a particular airspace.
That being said, there could be made arguments for extracting more energy from a given airspace given constraints such as grid access and distance to buildings and roads. Perhaps there will be markets for many kinds if AWE, who knows.
A serious problem is the huge area use where the tether length is the radius, preventing secondary uses like farming or fishing, at least when they exist. Using Betz limit is only a mean to go towards a better maximization of the space/land use in order to limit AWES areas, allowing more secondary uses for the same power.
I never got that argument. The crops and fish don’t care and once it’s safe enough even fieldwork and fishing are possible.
(I believe we’ve already had that argument on twitter)
I don’t think people can work or live in complete safety under highly tense ropes going fast.
In my alternative reply using more atmosphere like you suggest can also allow to improve the capacity factor. For that options 1 or 2 can be more suitable as the potential of the wing is better exploited.
They don’t have to live under it, to make secondary land use possible. Awes can be landed for fieldwork etc.
The elevation angle is low in order to minimize the cosine loss. But as it is low, the tether is not far from the ground. As tether traction is very strong and as it goes fast, secondary uses below the tether are quite impossible.
I remember the safety directive from Enerkite during AWECBerlin 2013: nobody under the tether. And the kite power was only in kW-range.
A device like KiweeOne could better allow secondary use as its tether is stationary and has an elevation angle high enough.
At todays AWE evolution, using the land under the kite is probably not recommended, but that will improve once/if AWE has had years of operational time. In the end its just a matter of frequency and consequence. If we can get frequency low enough, people wont mind going inside the area under the kite.
Looking at how large area a AWE rig of height 500 m may land in, I think AWE will not be feasible at a larger scale if we dont solve this.
Actually this is a very good thing about the canopy/production mesh split, the canopy acts as retention if you have a failure in the production mesh… and the canopy will probably have redundant lifters
Land use does not require people under the awes. (I’m repeating myself here)
Just land the damn thing during fieldwork and do maintenance on the awes.
That might not be possible for giant meshes like Rod envisions, but all standard kite/winch aka jojo systems as well as airborne gen / makani can be landed and launched.
If the schedule of maintenance of the AWES coincides with the schedule of the fieldwork, it is a possibility.
But in sea scheduling the passage of ships with the maintenance of the AWES would be difficult, if even possible.
Does the thing on the ground need to be a circle? Does it need to have a hub at its center? What do you lose by it not being a circle but a loop stretched between two points for example? Or a loop stretched around a triangle or square or higher order polygon?
If I were a landowner I’d sooner give the thing a try if I didn’t need to clear a circle with a radius of 500 meters for it. I’d sooner have a long strip of land available also.
The circular area is the result of the tether length as radius by taking account of all wind direction changes.
Thanks for the questions @tallakt
There are a few options for hoisting networked kite rotors, especially where we assume the rotors are combined with lifting kite lines.
So far, for simplicity, I have tested by just laying the rotor network out, stretching it downwind then attaching it to a lifting line. This has worked fine with both a static and a rotary lifting line running down through the centre of the rotor and torque tube set. This method has the advantage of having a line attached above and downwind of the turbine on the lift line. Thus it is safer and easily avoids spinning the lifting kite line.
However… Those advantages will be nullified by lift kite networks… Where “redundant” top lines will not allow any torque transmission to the top kites. (have also tested workable top kite steering by being mounted on a tilting hub)
So… This works fine for a single lift and rotor system… There should be 360 clearance anyway in the case of long term deployment.
But when we use lifting networks that’s when hoisting will really make sense. A few methods…
1 reel out the lift line from the ground station through a hollow power take off hub and any thrust bearing lifting hubs you need. Attach the thrust bearing hubs to the line with clamping. Continue to release lift line to raise the rotor.
In initial launching state the rotor will be small radius and the PTO will be a large powerful alignable wheel.
Ok
2 since we can already run the rotors around a fixed (non rotating) line, almost any block and tackle arrangement under the lifting bridle will suffice to lift a rotor or release a rotor upwards from inside the rotor under the rotor lift point.
I don’t follow. The wind is never in line with the direction of motion of the rotor (your idea) or loop (my idea) anyway. Can you estimate what is lost when you change the circle to a 10 or 20-sided polygon for example?
The idea behind the question is my assumption that stretching a wire between pulleys is very much cheaper and more achievable than the alternative (I don’t know how you plan to build the rotor). So you would have to have a very good reason to not do it like that.
Ah also, where there is no need for a centre line. Modularly releasing more and more kite and later attaching torque tube rings as you feed torque lines out… Should be workable… Eventually with a good bit of control