A really cool idea, but as others have mentioned a tiny bit impractical with only a few dozen minutes of flight time. However, there are actually serious attemp

A really cool idea, but as others have mentioned a tiny bit impractical with only a few dozen minutes of flight time. However, there are actually serious attempts to adress these issues: Cellphone providers are looking into blimps as antennas; A guy I know is working on a autonomous airplane, that can keep itself in air more or less forever (Their goal is acutally to go to mars with this): "The goal of this project is to design and build a solar powered micro airplane for autonomous exploration. This system, named Sky-Sailor, is fully autonomous in navigation and power generation. Equipped with solar cells covering its wing, it retrieves energy from the sun in order to supply power to the propulsion system and the control electronics, and charge the battery with the surplus of energy. During the night, the only energy available comes from the battery, which discharges slowly until the next morning when a new cycle starts." http://www.sky-sailor.ethz.ch/ http://www.sky-sailor.ethz.ch/