Wind speed typically increases with height and wind direction varies, so you could have a sail or kite that’s in faster wind, but I doubt the difference is large enough in practice.
(in theory, I think a kite up in the jet stream and a fairly large sail near ground level would work for some definition of ‘work’)
Two sail planes on a tether should be able to do it. How the pilots are going to get good at it without getting killed is probably a bigger problem than constructing it.
(in theory, I think a kite up in the jet stream and a fairly large sail near ground level would work for some definition of ‘work’)