Safety management in a kite-farm allowing more density

Lounge
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We will assume that the flight management difficulties are resolved for an unit.

We will also assume that the collisions between the kites are not very serious and even possibly avoidable by control: at first we will be confined in flexible wings flying relatively slowly.

The problem of entanglement between units has already been mentioned. Indeed the direction of the wind can vary very quickly and asymmetrically, even in a small area. One solution is to space more. Another possibility would be to manage the control systems in such a way as to allow untangling by pair of units, then the whole if necessary. Then check if the tethers are still in good condition.

An example: a wing and its tether wraps around its neighbor. In this case, the programmer tells it to turn around in the opposite direction. In the event of failure, the programmer of the other wing is automatically activated, resulting in redundancy. These maneuvers can be experienced.

Another case: the tether of a wing is broken. The other wings flying downwind are piloted in order to intercept the wing, and therefore used as dam kites.

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As a programmer solving this seems very difficult. Also; If kites tangle you may also have secondary catching up of the tether and other parts of the kite, such as the wing.

I think sufficient space and muliti kite synchronization is the only way forward.

Kite networks are ok also

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I was talking about single line units like most companies envision.

More space is a possibility, but greater density will always have advantages and is sought after for all power plants.

Syncing is a good thing, but you need to plan how to react in the event of a tangling, which is very likely if AWE occurs at this point.

When it comes to kite networks or multi-kite systems, you have to see how they are laid out. They may not prevent the risk of damage despite proper management. The wind is not predictable.

That’s why you have to think about managing two things: avoiding problems as much as possible with a more favorable architecture, and countering them when they arise.

Of course these are just a little abstract thoughts at the moment.

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I think there are some ways to approach the question of: what is the minimum spacing that makes tangles highly unlikely?

The wind at probable sites may be mapped eg by Lidar or by placing multiple kites in the air. Then use that wind data, which contains information about turbulences, to simulate an array of AWE.

I believe for most parts kite arrays will move mostly in sync. The number to keep track of I guess is the size of the turbulent flows. Eg turbulence with size around 50 m can be bad, but 200 m is not so bad. Much like waves and ship length combining for good or bad effect.

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You’ll be lucky to get a tangle
UHMWPE has a very low melting point.
The lines are very tight and thin.
Two lines clashing will deform and rub at a sharp intersection.

when a single kite line rubs against another single line, it’s often a very quick game over for one of the lines. Usually the one not made of higher melting point sewing thread holding a child’s poly-bag kite.

I’ll argue for networks of course… Being able to spread impact loads of the misalignment by having two points of line clash bending a single line… might help a bit
A net doesn’t tangle much… Think of the many threads in your sock / sleeve. You can twist, and bash them together but it doesn’t change their main topology.

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Good point. Fishing nets and trawls may be a source of investigating behavior in turbulent flow.

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I spent a lot of time around Fish farm cages pulling nets

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The fish could be (Daisy or other) turbines attached to the meshes of the net.

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Hard to market that. People would object to the smell and there are welfare & hygiene concerns

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Vertical Airborne Wind Energy Farms with High Power Density per Ground Area based on Multi-Aircraft Systems
Authors: Jochem De Schutter, Jakob Harzer, Moritz Diehl

It is also a response to the issue of Power to space use ratio.

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Arent we here just saying what everyone knows? That multi kite is more performant than single kite?

But they are not dealing with the main crux; what should the multi kite AWE plant look like? Before stacking 100s of plants in a farm, should we not focus on making a single unit work?

I would rather like to see more work put into this perspective, as I did with «The Pyramid» or Windswept is doing with their designs. Because that is where the challenge lies.

If you built on «The Pyramid», everything in this paper is moot, as tether length is limited. If you went for Windswept’s approach, you need more space (not comparing those two here though). Instead we are left with a very optimistic outlook for multi kite AWE, but no real help on how to build it.

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Below are some quotes from the document.

Page 1/6:

Airborne wind energy (AWE) is an upcoming renewable energy technology which aims at harvesting the steady and strong high-altitude winds that cannot be reached by conventional wind technology, at only a fraction of the resources.

Page 4/6:

• The tether length is bounded from above by a value lt,max = 700 m. For the M-AWES, this constraint is active at the end of the reel-out phase.

To begin with, this paper (and more broadly AWE as indicated in the first quote which makes sense to me), is about devices capable of reaching high altitudes.

Now about your observation Tallak, the table 1 page 6/6 replies in some way:
According to this table, a power density of 7.3 MW / km² is possible by using M-AWES flying a circle radius of 18.4 m, and comprising two aircraft of 5.5 m span each. In contrast only 0.2 MW / km² is possible for a S-AWES (a single aircraft) which flies a circle radius of 46.5 m. The same table indicates a value of (only) 8.4 MW / km² by using far larger aircraft of 26 m span in M-AWES (two aircraft) configuration.

From this a temporary conclusion could be that Scaling by size is not necessarily required. This is rather a case of Scaling in numbers rather than size. The wingspan of Kitemill KM1 is 7.4 m if I’m not mistaken, which is a little over 5.5 m. So if we take the final plant of the paper as a model, KM1 already has the required dimensions. This is an example of a set that can determine the characteristics of a unit. This may give good prospects for the rigid kites that have so much trouble scaling up.

I would like to make a comment on the statement on page 5/6, which may also affect the aforementioned Table 1, concerning a single aircraft:

The dual-aircraft configuration thus allows the system to fly extremely tight circles.

It is also possible with a single soft kite as I experimented it. For a single aircraft I don’t know exactly, but I guess that (as for a soft kite) a far smaller circle radius of flight would be possible for a slightly lesser efficiency. On the other hand, with either a soft or rigid kite, the main tether would wobble a bit, which is noticeable on the video.

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Some thoughts:

  • The authors didnt consider what scaling makes economic sense (thats ok). 7 m wingspan probably is too small, too many moving parts to compete at utility scale
  • These extremely tight loops are very difficult to achieve in practice. The wing should probably not be symmetric.
  • The spacing between the kites is minimal. The assumption of wind uniform in direction and speed does not hold at all
  • The assumptions done to compensate for induction seem simplistic and for me questionable without experimental support.

The net result being I think the resulting numbers are optimistic to the nonsensical.

What would be the value in that?

And no mention of the practical implementation of such a complex plant.

The paper is fine for what it is, my point being just that is is probably not adding tremendous value other than waving a carrot in front of investors and governments

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14

I agree with these thoughts. It is the reason why I considered this paper as a basis to be reworked.

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15

Encouragingly the Freiburg team have been working with @/cb someAWE.org
So they have access to AWES with tight looping blade performance.
And they’re working on steering this rotor too.

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This is great news! …. If they were able to make that work reliably it could be a strong combination

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So the “geniuses” have now “discovered” the wind turbine rotor.
All roads lead to SuperTurbine™. :slight_smile:

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Provided that they do not exceed a few meters in altitude.