The article talks a little about it. It’s more of an unwind+rewind cycle:

The pull from this force then rotates the ground-based drum at a high speed.

This rotation then generates electricity that can be stored in a battery system for deployment wherever and whenever it is needed.

After 45 seconds, the kites are levelled up so that the pull from the wind is momentarily minimised.

This enables the tether to be wound back in, using only a fraction of the electricity generated when it was being spun out.

The result is a net gain in renewable power at the simple cost of flying a kite.

Then the cycle is repeated, again and again, potentially for hours on end.

It makes sense to me. I hope it catches on!