Example embodiments may facilitate altitude control by a balloon in a balloon network in a manner that also can generate power. An example method involves regulating buoyancy of the balloon by solar heating atmospheric air drawn into the balloon through a first opening of an envelope of the balloon and venting heated air in the balloon out through a second opening of the envelope. Atmospheric air heated within the envelope could supply the balloon's buoyancy. The method may further involve capturing a portion of energy of the heated air as it is venting out of the balloon through the second opening, converting a portion of the captured energy into electrical energy, and storing the electrical energy. The balloon could also be configured with a heat engine for converting heat energy into mechanical and/or electrical energy.