Offshore Comparison : Makani vs HAWT

[PierreB]

I also evoked this concern on

Makani Archives

The big lesson may be the impracticability of the large, rigid and heavy kites, at least by flying in circular figures. An underestimated problem may be the significant kinetic energy as the kite descends, preventing it from ascending. Thus a wing like M600 weighing a ton and flying downwards at 50 m/s produces 1,250,000 Joule, added to gravity. And its speed upwards is lesser, so its kinetic energy is also lesser. Perhaps kinetic energy issue during flying downwards phase can be mitigated by …

I mentioned on the same comment:

@PierreB

Perhaps kinetic energy issue during flying downwards phase can be mitigated by flattening the trajectories, using flat figure-eights kiteKRAFT fly-gen kite flew figure-eights.

Dancing kites (two kites in opposition) could perhaps mitigate the irregularity issue (adding significant control issue) but losses by gravity and resulting higher kinetic energy during down phase would occur in the same way, increasing while scaling up.

To get back to the heart of the problem let us quote again, on page 13, Part I:

● The potential energy swings resulting from large loops forced us into large speed
variations. At low winds, we’re often flying much faster than optimum at the bottom of
the path, and at high winds, we must fly much slower than optimum at the top of the
path to prevent overspeeding at the bottom.

I see a double issue. Even if there was no need to prevent overspeeding at the bottom, the system would undergo loss. Kinetic energy is higher during descent than during climb, the difference increasing by the square of the kite speed, and this energy is more or less directed to the ground, preventing climb. HAWT has an axis supporting the rotor, a crosswind AWES has not.