[myself248]

I couldn't find a good explanation either, but my guess was different from some others I've seen here:

I think it doesn't generate continuously. I think the plane spends some energy to get up into the fast-moving air, while the tether pays out some of its length easily to let it climb. I think it only does this "once", or as infrequently as possible.

Once the plane is in the fast-moving air, the generators kick up their field current to extract energy from the tether being unreeled further, as the plane turns broadside to the wind to haul the tether out despite this drag. It's generating power as the tether pays out.

Then the tether runs out.

So the plane dives/glides back towards the base, while the generators run in reverse, reeling the slack back in. But it doesn't return so far as to get out of the good wind. So as soon as most of the tether is reeled back in, the plane turns to haul on it, the generators go back to generating, lather, rinse, repeat.

I think it only lands when the wind dies, or if it gets too strong to remain safely in the air.

[brandmeyer]

This is one scheme that runs the generator on the ground. Makani and Ampyx both run generators in the air and transmit power down to the ground on the tether.

Here's an (unkind) summary where the players are: https://cleantechnica.com/2014/03/03/airborne-wind-energy-pl...