I provided an example, not assuming it can really work (too large), just to show what is possible to do with Joule loss.The efficiency can be higher, leading to lesser Joule loss. But if the generator is not very efficient or is old, higher Joule loss can occur. And if we do not want produce electricity, heating directly with a brake is a theoretical possibility. For AWES I do not still know how or even if that can work.
A generator of a large wind turbine is too heavy for any AWES. I think about high rpm and density generators like
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Electric machines can be much smaller and have better efficiency when they can operate at a higher speed than the 3,600 rpm limit imposed by 60 Hz power systems.
An example of a power dense machine that we have designed and manufactured is rated at 100 kW and weighs 7.7 kg in a 2.3-liter volume, which is equivalent to a machine power density of 13 kW/kg and 43 kW/liter.
I don’t know the efficiency and the percentage of Joule loss for these generators.
A very high rpm is possible by using a sort of rim drive transmission, or/and by using small wind turbines aloft (Makani style) for a crosswind device flying fast.
On the sketch below:
Fuselage balloon 10 m in diameter, diameter 78.5 m²; with blades of 2.5 m wingspan, 15 m in diameter, diameter 176.625 m². Surface swept by the blades of 2.5 m, 98,125 m². Assuming that the fuselage balloon (3) is 30 m long, for an area of approximately 710 m², a mass of 141 kg with an envelope of 0.2 kg / m², and approximately 500 kg for a double envelope (double layered ETFE film) of 0.7 kg / m², volume about 1000 m³ and U value of 2.6, a power of 182 kW makes it possible to raise the temperature by 100° and to save about 0.33 kg / m³, so 330 kg / 1000 m³, for a mass of 500 kg of double envelope, 500 kg of generators, and 500 kg of wings. If the balloon has a shape comprising a cylinder 40 m long for a total length of 65 m, the surface would be approximately 2130 m², and the volume 4000 m³. A power of 546 kW would be required in order to raise the temperature of 100° and gain 1320 kg, for a mass of 1500 kg of double envelope, 500 kg of generators, and 500 kg of wings, which amounts to roughly the same . With a double envelope of 0.35 kg / m², and a U value assumed to be a little higher, i.e. 2.7, we would have respectively a required power of 189 kW and 567 kW, for masses of the double envelope of 250 kg and 750 kg for the same respective gains of 330 kg and 1320 kg: we gain more with the longest envelope (leading also to more heating power required), in gain of 570 kg against 80 kg. These figures are a rough approximation.
In short, aerostatic thrust will not be enough to lift the assembly but will lighten it by 1/3 or less. That can be interesting to obtain a low cut-in wind speed.
The balloon gives the possibility of implementing the rim drive transmission allowing the use of small generators rotating at high rpm. In this 5 MW (wind speed 12 m/s) example, the diameter of the balloon fuselage is 10 m, the diameter with 2.5 m span blades is 15 m. The two soft wings have a total area of 2000 m². Expected lift-to-drag ratio of 5 without the turbine.
The wind turbine (aloft) surrounding the balloon: