Yo-yo Farm versus Loop Carousel

Let us compare the cost and performance of two equivalent systems. The first is a wind farm consisting of 20, 100 kW yo-yo systems. We compare this with a single loop carousel with 20 kites rated at 100 kW each.

Power output
Both systems are operating in crosswind mode. Each kite in the loop carousel has maximum power for 50 to 60% of the cycle whereas each yo-yo kite operates for 85 to 90% at maximum power. For the loop system, the rest of the cycle is operating at zero or slightly negative power, whereas the yo-yo kites operate at large negative power for a short period of time during their retraction cycle . The loop system will give a constant power output at all times (at fixed wind velocity), whereas the yo-yo system will have spikes of reduced power as each kite requires negative power at a certain point in its cycle. Since the retractions are random, the power spikes could be quite large at times. It is difficult to compare these two power outputs, and I am wondering whether the yo-yo system gives intrinsically more power, because with yo-yo, the tension of the tether is pulling directly on a drum, whereas kites in the loop carousel are pulling at an angle to the horizontal loop. Is it correct to assume that the optimum power for the loop system is obtained when the loop is traveling at 1/3 of the wind speed?

Launch & land
To date the only commercial development of autonomous launch and land is the Skysails system. This involves a launching mast, nose line, and furling system. This is clearly not suitable for the loop system but the kites could be launched at a remote location using methods I have proposed and be transferred to the loop. This is clearly not an autonomous method. In the case of the yo-yo, wind farm, each kite can have its own launching station and so operation can be much more automated. It may be possible to operate the loop system in a zero wind condition by driving the loop at approximately 5 m/s so that all kites can remain airborne. The real problem is transitioning back to normal operation when the wind starts blowing again.

Land usage
My feeling is that both systems occupy approximately the same land area. With the loop system, the interior area can be used for alternative purposes although access to this area might be problematic. If remote launching of each kite is used for the loop system, then this might require considerable more land area.

In either system, if a tether breaks, or a control system goes haywire in any kite, we have a problem. The loop carousel system cannot be stopped so we just have to remove the errant kite from the system without damaging other kites. In the yo-yo wind farm we have a similar problem where downwind kites can be affected by the broken kite. Since the kites in a yo-yo, wind farm are individual units, they are intrinsically safer than in the loop Carousel system.

System cost
The loop Carousel has a single large generator/motor which drives the whole system. The yo-yo wind farm has individual reversible windup reels and each one must have a Motor/generater attached. Each unit in the yo-yo wind farm has to have a mast and wind/unwind reel which must be rotated when there are changes in wind direction.

Although the loop carousel has the advantage of continuous output and possible lower cost, it requires much more development to resolve safety issues and methods of autonomous launch and land procedures.


[1], [2], [3], and elsewhere, [citation \ needed].

I don’t think the SkySails launching method is that credible. It is dependent on wind, an expensive mast, the hope it doesn’t tangle, and a very lightweight kite. A linear launch for a loop carousel seems more credible to me, which would have the added benefits of sharing the launching method and generator between more kites.

You mean only they have sold systems [?], so only they are commercial? I don’t think that is a valid criterion for ignoring other launch methods.

The launching method isn’t the difficult thing, controlling the kites is.

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