Researchers at the ETH autonomous systems lab have recently successfully completed a continuous solar powered flight that lasted for 81 hours! . The cool this about this is that the UAV was powered by the Pixhawk autopilot (which wold make sense as it was also designed by ETH.
This flight has set a new world record for the longest ever flight of an aircraft that is less than 50Kg. The previous record was 48 hours from a 13Kg SoLong UAV, and is the 5th longest flight ever demonstrated by any aircraft (both manned and unmanned)
You can read more over at moredrone.com