A nice idea I had was for a personal airship on Venus. About 75 cu.m of helium balloon will lift 100 kilos. An electrical oxygen machine, cracking O2 straight from the air, would take about 470 We to provide one person's needs. On Venus with 50% efficient PVs (a reasonable goal) and 1900 W insolation this requires <0.5 sq. metres of panel. Coating the lifting envelope with PVs would power the oxygen machine and a couple of propellers.

A solar-powered ultralight would have unlimited range, especially if the high energy density supercapacitors I've read about are for real. I'm wondering if tuned thermovoltaic panels couldn't get power from the IR coming up from the ground at night?