Solar Impulse 2 already comes pretty close to perpetual flight -
afaik it's limited by the pilot
It can carry a payload of a few hundred kg I think. Cruises at 27'000 ft though, obviously limited by weather. Also limited by overheating batteries on it's last 76 hour leg... Interesting technology though, people kept saying this has no practical applications, but I'm sure they can be found, and the technology will mature