Ok, this is definitely a new idea.
[Use] solar energy to fill a balloon with hot air. The rising balloon pulls a tether, which turns a generator on the ground. Once the balloon has floated up to 3 kilometers, air is released and it loses buoyancy. The balloon needs less energy to be pulled down and a net power gain is reached as a result.
The developer estimates a balloon 88 meters in diameter could power 100 homes.