So Skysails announced their power curve with 160 kW at around 14 m/s at the kite. I was wondering about their scalability, and what we can make of this from the information we have.

ChatGPT says:

Skysails are typically used to harness wind power for propulsion, especially in marine applications. The weight of a Skysails kite can vary depending on its size and the materials used. Generally, they range from about 100 kg to 500 kg. For instance, a 160 square meter Skysails kite, suitable for a large vessel, might weigh around 320 kg. This includes the weight of the kite itself and the associated control system components.

It seems a 160 sqm kite coincides quite nicely with their 160 kW output, looking at the generic numbers at their web page.

For a 160 kW producing plant at 14 m/s the pull of the kite should be (reel out 1/3 wind speed assumed) 34 kN (approx the weight of 3.5 ton).

So at this point we have a flying gravity force to lift ratio of

\kappa_{160} = \frac{34k}{320 \cdot 9.81} \approx 10.8

Lets assume they want to scale double wing span, achieveing a power of 640 kW. Also lets assume cubic scaling of mass from here on. Thus we have the square-cube law in action. Power and area scales with the square of the scale, the mass by the cube. That means at this scale, the ratio would be

\kappa_{640} = \frac{4 \cdot 34k}{8 \cdot 320 \cdot 9.81} \approx 5.4

Doubling again to 2560 kW gives us

\kappa_{2560} = \frac{16 \cdot 34k}{64 \cdot 320 \cdot 9.81} \approx 2.7

I think a ratio of 5.4 may still work well enough, but a ratio of 2.7 probably wonâ€™t.

So we can conclude that when Skysails try to scale above 500 kW, they will need to optimize the weight of their kite.