lighting strike?
Put a lightning rod on the balloon and collect even more electricity! Problem is that for the energy they carry, lighting bolts are relatively low amperage. Still, it could be used.
As for the helium, it is possible to use hydrogen with a fire suppressant. Alternatively, make a bigger balloon and divert some energy to making hot air, or utilizing the heat generated by the panels.
It was calculated long ago that hot air balloons past a certain size can hold heat for so long they can stay up without a heater.
So, there are lots of options to consider.
As for the carbon footprint crap..Yeah, even balloons that create themselves are going to use up resources, including carbon, in order to be created. It’s so beyond stupid, but this just brings it home.