# Rotating Reel System

the water viscosity will waste most of the energy harnessed.

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It could be the same for https://minesto.com/, however this system seems to work in spite of the relatively high speed (until about 15 m/s) of the hydro-turbine.

Beside it I wonder if a vortex can be generated by the rotating ring, even if only the hydro turbines are in the water thanks to the foils raising the annular structure. If yes I wonder if such a vortex can generate too much drag.

For the water viscosity issue «it depends». For sure someone should do some calculations to determine the probable outcome. But I can say this:

• Kitesurf hydrofoils have very little drag, perceived relative to other vessels
• The foils need not necessarily run at the same diameter as the kites. As drag scales with v^2 a diameter ratio air:subsea of 3:1 for instance would have a dramatic effect
• I dont think in terms of viscosity much, rather lift-to-drag, and I gather wings work mostly the same in air or in water

The sooner fast kite motion becomes fast coils through magnetic fields the better.
Don’t waste material, effort and energy getting this to happen.
Make kite motion and generator motion fit together.
What’s the most efficient transport? A train on rock solid rail, hard wheels and great bearings. Run it in a hoop for constant motion/output.
A spinning train ring moving magnets past coils… That’s a motor / generator.
Bearings. . Rails. . Same-ish thing. Just align with kite motion. 1st bit of job done.

I can agree.

It is an huge installation comprising a support for the stator (far above water for an offshore plant), a stator then the rotor, so a fixed part and a moving part. With hydro-turbines one can eliminate the fixed part.

How will anchoring impact hydrofoil performance?

Low in my opinion, due to a swivel on the single central anchor.

I’m not a good example for hiding opinions … but I’ll wait for the calculation.
The word Single on such a large system scares me.

The swivel friction should be neglected.

Me too. As (single) advantage a single big anchor installation makes less damage in deep sea.
If the single anchor is broken, the hydro-turbines-ring is still floating (for rotating reel, not for Daisy as a part is in the water). They are too heavy to go in the air by kite lift, but the whole plant could be dragged up the coast.
AWES are expected to be far more dangerous as current wind turbines.

I think forget about the svivel at the bottom of the sea. How will all that torque be transmitted to the bottom of the sea without adding too much drag?

My approach would be to use the hydrofoils to generate necessary forces in 3D to run in a ring, then add a «propeller» (generator?) subsea to generate electricity at the foil. Finally concentrate all energy at the center, above sea level.

The anchor still needs to be there. The swivel is above sea level nominally (may submerge if loaded) and a single wire is fastened to the anchor.

After some thinking I would prefer a “classical” carousel as its use can be easier. It can be anchored in several places. @Massimo provides the dimensions and the weight of the stator and the rotor, page 14, on http://www.kitegen.com/pdf/dossierkitegenen.pdf . The dimensions of the carousel are important but in the same time it is used for take-off and landing. The weight looks to be low in regard to the power.

After studying different AWES I return to the Rotating Reel Parotor as, at least for me, this system accumulates positive features for a successful implementation at high scale:

• It is a stationary device with continuous power.

• There is no insuperable limit for scaling. The large ring helps the flying rotors to scale by holding it by distant anchored points.

• The dimensions between the diameter of the ground and the flying rotors and the length of the peripheral ropes are comparable for a good torque transfer, producing harmonious proportions, and allow to achieve a high power/space use ratio. In other carousels the smaller and numerous kites fly at the same altitude compared to the diameter of the ground ring. A single flying rotor is both simpler and more powerful by sweeping the full area.

• As an example a ground ring (ground generator) of 1000 m diameter can be rotated by a flying rotor of 1400 m outer diameter, 800 m inner diameter, so 1 036 200 m² of swept area, leading to a power about 80 MW with 10 m/s wind speed, a Cp of 0.2 (leading to the possible use of soft wings) and a cosine cubed of 0.65 with an angle of elevation of 30°. Such a rig would use about 4 km² of land by taking account of wind changes, instead of 50 km² for currently envisaged kite-farms of single unities flying in an erratic way, with a risk of entanglement.

• The horizontal rotor allows scaling in all dimensions.

• The secondary mode, now analysed as not productive is simplified and allow variations of the length of the peripheral ropes while the tilted flying rotor rotates the horizontal ground rotor.

• Safe control by multi ropes and complete depower by the central rope.

• The ground ring is used to spread the kite, then takeoff by rotation by the generator as motor, then landing, all being automatable.

• There is no rigid parts between the ground and the flying rotors, as there are only ropes. That facilitates both scaling and safety.

Just to show the principle.

See also the quote on Medium scales for torque transfer systems onshore and offshore.

By using leashes I also noticed the difficulty of the rotation, but I thought it was due to the resistance of the spring when the rope was unwinding. I think a main cause could be the power consumption of the moving tethers under tension. This power is removed from the overall power of the complete system.

https://www.researchgate.net/publication/324135034_Airborne_Wind_Energy_Conversion_Using_a_Rotating_Reel_System : the tension is assumed to be constant and equal for each of the four tethers. When using the direct mode of generation (22.3.2), the main generation is assured by the horizontal ring. Then “The modules are electrically interconnected such that the generated and consumed energy is balanced”, but the generated energy is removed from the overall power of the main generation.

As a result I will study more some other AWE systems.

I would like to thank everyone who participated in this topic. My latest tests and further analysis have shown that there is too much power consumption of the rotating reel system.

But the chapter 22 mentions in the page 566: “This essentially means that the transmission efficiency for the ideal system in steady-state operation is, as expected, 100%.” and in the pages 564 and 565: “The solution is approximative because the residual transverse forces are causing compensating motions which are not taken into account in the analysis. However, the following results indicate that the effect of the compensating motions is minor and can be neglected.”

The “too much power consumption” can be wrong as a 100% transmission efficiency is theoretically possible, and as the physical model is not respected by using leashes (different forces during winding and unwinding) or by using pulleys (forces theoretically equal and constant if the pulleys are well oriented during the operation, but it is not the case). There are also frictions.

The idea was to implement a horizontal conversion system to facilitate scaling and take-off and landing operations.

Nevertheless for the first time a (small) horizontal carousel was rotated by a kite.

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How big of you to share even your disappointments. The video is very nice. For a test, I would redo it with the pulleys being more flexible. Perhaps a chain of the links between the ground and pulley. This would make the geometry better when the elevation angle is reduced and the pulleys need to rotate.

I still think the center line is not a good idea, because it it the tension of the outer lines which is the carrier of power.

Seems a few modifications could yield significant improvement

Its unclear whether Pierre means “too much power consumption” simply for the realistic friction load of the prototype’s recoil mechanisms, or power loss inherent to the architecture. The only considerable inherent power loss I see is typical VAWT phase loss of direct upwind and direct downwind rotation phases.

Unlike my pulley system the leashes allow a good transmission whatever the angle of their respective ropes, but the higher tension of the unwound ropes distort the appreciation.

I would need a multi directional pulley system managed by computer and following the angle of the tethers, or controlled electrical winches assuring an equal and constant tension.

The figure 22.18 provides a value of the transferable torque of 1 when the two rotors are close each other, so a maximal value that is equivalent to a value of parallel and aligned rotors. But I am not sure if the motion of the ropes under traction leads to a significant power consumption, or if my material is not adapted enough.

I was likely wrong by thinking some additional significant power would be needed to assure the move of the ropes under tension when the two rotors are close each other. The chapter 22 does not confirm it (https://www.researchgate.net/publication/324135034_Airborne_Wind_Energy_Conversion_Using_a_Rotating_Reel_System):

Pages 564 and 565: “The solution is approximative because the residual transverse forces are causing compensating motions which are not taken into account in the analysis. However, the following results indicate that the effect of the compensating motions is minor and can be neglected.”

Page 566: “This essentially means that the transmission efficiency for the ideal system in steady-state operation is, as expected, 100%.”

Some last tests are correcting my bad feeling, using better fixations for the pulleys.
A physical model conform to basic principles of the rotating reel system would be using multi directional pulleys, or winches with generators in order to assure a constant and equal tension of the ropes that is not possible with leashes.

A photo of the pulley system:

A video of the pulley system (see the move of the orange marks):

And also a video of the system with leashes to try to show that a same moment is required to rotate the ground ring when the superior rotor is tilted or when it is parallel and also horizontal, that when the rotors are close enough each other. As in all cases the tension of the ropes opposes a resistance to the rotation, I tried to hold the rotor at the same height (the whole parallel rotor then the top of the tilted rotor) in its two positions in order to make a fair enough comparison.

Now by assuming a good material is used, the forces and moments are unbalanced in such a way that a stable mode of operation would be difficult if not impossible to find. Unbalancing is the big issue of the rotating reel system. I do not know if some aerodynamic or mechanic means could correct this.

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Just a dumb question: why cant the generator be mounted on the rotated ring, so that the horizontal ring is not necessary?

By rotated ring… are you meaning the airborne autogyro part?
If so, and it is tethered from only 1 point, (sort of like a spin bol kite) so that the system needs the means to interface a generator to the expanding tethers or to the tensile ring which the kites are mounted on … (There could be many tensile kite rings on a cone form)
In this case, any method is going to drag at the soft line (network or not) so deformation of the turbine and lines is going to happen.
Well maybe you could run a beaded or toothed band (like those beaded curtain reeling control lines) over the top of the tethering and pulled to go round a generator place on the ground, with the band running somewhere between perpendicular to the axis and perpendicular to the effective top of the cone of tethers.
That would be taking power from the top side, Somehow I’d kinda think the best way to avoid compression is to have the generator spread it’s interfacing on the bottom to up-going quarter , from around 6 to 9 o’clock.
So maybe the gen could be a toothed wheel hit round by successive lines
Or the gen is a rail guide holding wheels clamped against an expanded outer ring of soft line… probably best with an outer gen driving band sewn to an inner kite driven band. Sounds kinda hard to do but possible.