Thank you for that! I think utilising more of the wind window, and accepting reduced power as being better than parking the kite in certain wind directions would be a valuable step in increasing the system’s usefulness.
The difficulty I see with the net-headwind situation is that the forces on the kite will be determined by the apparent wind, and a headwind will increase those, but if the resulting tether tension can be resolved into the -X direction (in opposition to the direction of the ship), they will act to slow the ship down, requiring energy input from elsewhere to maintain that motion. The kite will be generating more power, but now additional power will be needed from the ship to maintain that ability.
I’m in the process of revising all my maths for this, but so far it seems that we only get a few degrees of apparent headwind where the additional load on the ship’s main engine (at 50-55% maximum efficiency) gives us a net energy benefit over just running an independent diesel generator for the same electrical output. This is what I’ve been thinking of as a kind of “wind-assisted alternator”, where trading-off some increased fuel combustion against additional wind power harvested is still a net ‘win’. I haven’t got this right in my head yet, though.
Something I’m really struggling with on this is how to account for the energy from the kite if the resultant tether tension (in an apparent tailwind) is pulling the ship forward. It feels like double-accounting to say that we can use the reeling out of the tether at constant tension to spin a generator and yield electrical power, but also that this tension multiplied by the ship’s velocity (relative to the ocean) is work the kite’s doing to contribute to the ship’s motion versus the water.
Intuitively, saying that we’re extracting two distinct sets of energy from the wind for the same physical action of the air wind ‘pulling’ on the kite seems wrong. I’ve gone back to the chapters on reference frames in my old University Physics textbooks, and have been digging through discussions of the physics of sailing, and especially on the Downwind Faster Than The Wind project, but all of those are, I think, subtly different situations, and I’m getting more & more confused. Do you have any insight that could clear that up?