Example embodiments may facilitate altitude control by a balloon in a balloon network. An example method involves: (a) causing a balloon to operate in a first mode, wherein the balloon comprises an envelope, a high-pressure storage chamber, and a solar power system, (b) while the balloon is operating in the first mode: (i) operating the solar power system to generate power for the balloon and (ii) using at least some of the power generated by the solar power system to move gas from the envelope to the high-pressure storage chamber such that the buoyancy of the balloon decreases; (c) causing the balloon to operate in a second mode; and while the balloon is operating in the second mode, moving gas from the high-pressure storage chamber to the envelope such that the buoyancy of the balloon increases.