In your static example how does the turbine get back to the front of the vehicle? Does the force of the wind push it there? If so, if the wind is blowing at 10 knots but the base of the vehicle is moving at 20 then as far as the turbine is concerned it is actually being pushed backwards, no? Or is the idea that when you lift the anchor the vehicle slows to below wind speed while the turbine gets pushed?
For that 'spherical cow' example, assume that the vehicle has batteries to average out the duty cycle while the turbine is going back to the front. Fold the mast down flat and stow the blades so it has minimal air resistance, assume it has minimal weight, and let an electric motor zip it back to the front of the vehicle at 100 knots ground-speed or 90 knots into the wind, if you're moving forward at 20 knots this gives you an 80% duty cycle.
The critical thing to glean from the example is that when it's anchored, the 10 knot ground speed wind is generating power at the turbine, and this has absolutely nothing to do with the speed of the vehicle.
Yes, in the real world, there are all kinds of problems with actually building such a vehicle, and the folding and weight and efficiency and timing and air resistance and rigidity and friction and so on would make it hard to actually get it to work. But these are all purely engineering problems, the physics obviously work!
