Al is a major element in the solar system. Most rocks have Al2O3 on the order of 3-10 wt.%. That includes chondrites (the major class of meteorite) which have plenty of feldspar, a mineral that’s like 20 wt.% Al2O3, and calcium-aluminium inclusions (CAIs), which are as their name suggests, Al-rich.

I think they’d be solar powered with some kind of thin film photovoltaic. You don’t need much battery in that case. While some carbon cost is inevitable, the point is they wouldn’t ever compete with something that burns kerosene.

Airships only make sense in a world in which the economy takes into account ecodestruction. Kind of like wind-powered ships. If we didn’t know what GHGs do environmentally, which offset any short-term efficiency gains provided by burning hydrocarons, nobody would ever dream of abandoning these miracle fuels. So you can only examine the efficiency of airships with hydrocarbons off the table entirely.