Recently, Facebook suggested solar powered drones could be used to provide internet coverage in remote areas and they would basically act as low altitude 'geostationary' satellites. The current duration record for a solar drone is 2 weeks using energy stored in batteries during the day, to keep the aircraft airborne overnight. http://www.barnardmicrosystems.com/UAV/milestones/solar_powered.html What is the best way forward to design a drone that can stay up for months or even years? For example another way to store energy during the day is to gain altitude and glide overnight, eliminating the requirement for heavy and expensive batteries. I think the key parameter here is the sink rate rather than the glide ratio as the glider would have to keep itself in the air for roughly 12 hours each night without losing too much altitude. Is wind a problem at the altitudes considered (around 50,000 ft) requiring higher wing loading and glide speed to penetrate into the winds and hold station? What other considerations are there for a long duration solar aircraft with a significant payload and requiring power to transmit internet data? Are flight durations of years feasible?