When it reaches the end of the tether, the taut tether pulls a mechanism to open the top and let the hot air out. The mechanism gives it enough weight to come down again. Once it comes down, the top gets shut again (somehow?). A wind powered fan inflates it again, and back up it goes.
I suppose a big one could generate a small amount of electricity, but:
When it reaches the end of the tether, the taut tether pulls a mechanism to open the top and let the hot air out. The mechanism gives it enough weight to come down again. Once it comes down, the top gets shut again (somehow?). A wind powered fan inflates it again, and back up it goes.