ETH Zurich's AtlantikSolar 2 Unmanned Aerial Vehicle during its continuous flight of 2316km and 81.5 hours (4 days and 3 nights) that took place between July 14th-17th 2015 and broke the flight endurance world record for all UAVs below 50kg total mass.
In addition, the fully solar-powered flight is the longest-ever flight of a low-altitude long-endurance (LALE) Unmanned Aerial Vehicle, the second-longest flight among any UAV, and the fifth-longest flight ever shown by any aircraft worldwide. From an applications perspective, the flight proves the central commercially-promising advantage of solar-powered UAVs, i.e. their capability to stay airborne for multiple days while providing telecommunication services in large-scale disaster-scenarios or live-imagery during industrial sensing and inspection missions.
video of their flight