For discussion:

"There is a confidence that the cable drag issue, that was raised by Ivan Argatov, was a consequence of a wrong assumption: of a cable that oscillates like the windscreen wiper - even taking into account the catenary effect. The geometry of the movement, and consequently its dynamic, is very different: you have to think at the whip tip or the launch of the fishing line, and reverse their tip movement." (Mario Marchitti).

For discussion:

"Also the projects which have the generators on ground are easily distinguished on their effectiveness and efficiency. It should be excluded those which have a rigid wing, like that of a traditional airplane, with ribs and spars. Because the manufacturing of such a device with , for example, one MW of power, with the cables from the wing which unroll at 10 m/s, should withstand 10 tons of pull, which originates on the wing structure. I wonder how that load can be sustained from such a wing, that should be light and efficient. Also the C-shaped kites which carry the actuators in flight, as  pods just below them, are dramatically affected in their aerodynamic efficiency, technical design and control; they also require significant power from the ground to drive the actuators, which cannot produce a swift response, moreover the retraction phase would be difficult and slow." (Mario Marchitti)

I put again but only the extracts concerning flygen energy kite systems for discussion.

"" The projects which carry the generators on board are doomed to industrial failure, even though they are backed by a giant of the financial world, even though functioning prototypes up to 600kW of target power have been built and flown. Here the weaknesses are easily detectable: they lie on three major drawbacks: it is necessary that the wing carries heavy generators, therefore the wing efficiency is thus reduced, moreover it is necessary to transfer the energy produced to the ground, via a cable. Those projects, suggested by Miles Loyd, are just a sort of reversed aircraft, like the turbine which is a reversed compressor. I don’t think they could be more efficient than the traditional wind turbines – on the contrary." (Mario Marchitti)

"Airborne Wind Energy Systems: A review of the technologies" (A. Cherubini), see page 1473, 7.1:

" 7.1.Effectof flying mass

In all AWESs, increasing the flying mass decreases the tension of the cables.Since Ground-Gen systems rely on cables tension to generate electricity,a higher mass of the aircraft and/or cables decreases the energy production [107] and should not be neglected when modelling [109]. On the contrary, increasing the flying mass in Fly-Gen systems does not affect the energy production even though it still reduces the tension of the cable. Indeed, as a first approximation,the basic equations of Fly-Gen power production do not change if the aircraft/cable mass is included and this is also supported bye xperimental data [108]. "

Only the following extract is about the topic:

"Also the C-shaped kites which carry the actuators in flight, as  pods just below them, are dramatically affected in their aerodynamic efficiency, technical design and control; they also require significant power from the ground to drive the actuators, which cannot produce a swift response, moreover the retraction phase would be difficult and slow." (Mario Marchitti)

The Betz limit

On page 206 the Betz law and its limit of 59.3% in mentioned. The mathematical formulations of Betz actually describe the methodology needed to curb the flow of the wind in order to extract energy. They allow us to understand that the wind flow does not have to be fully exploited because it has to flow through the machine without losing all its speed and the energy possessed. A necessary condition to obtain the best result.
However, the Betz’s laws are valuable for wind turbines, which exploit a relatively small wind front limited by the size of the rotating blades, so the wind keeps the residual energy that is not converted by the machine. In the case of high altitude technologies (ground generator), those laws lose much of their importance as the wind front exploitable is dozens of times more than that of wind turbine blades and that the wind speed is reduced only slightly.

The authors of the paper forced the so-called Betz’s law, with the intent to assert that the discovered maximum kinetic power of 7.5 TW is, due to the Betz’s law (59.3%), reduced in 4.5 TW of electric power. This is not true, because if the kinetic power would actually be limited to 7.5 TW, the machines should process wind for 12 TW preserving a flow of 4.5 TW, this absolving the specific that only 7.5 TW Kinetic are subtracted."

I am not sure to understand. Havue you some explains please? Thanks.

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