PV Stabilized High Altitude Balloon

There are three kinds of high altitude balloons: Expanding latex balloons, zero pressure balloons and super pressure balloons. The first are large latex balloons that contain the lifting gas and explode at an altitude where the gas expands past the ability of the envelope to contain it. They usually go up until a preset altitude and then burst. The second are envelopes with open bottoms that can vent lifting gas as the ambient pressure drops to allow them to vent lifting gas as ambient pressure drops. They stay up for longer periods of time but loose lifting gas each day as solar heating causes the gas to expand and vent and then drop in altitude as the remaining gas cools at night. The last are closed inelastic envelopes which are made strong enough to contain the gas as it is heated during the day and can stay aloft for weeks or months. My idea is to use a PV array to power a pump to pump lifting gas from the balloon into a small tank and then re-release the gas at night. This would allow you to make a cheap zero pressure balloon with the duration of a super pressure balloon.