https://www.techradar.com/news/this-solar-powered-drone-will-fly-unaided-for-a-year

At the Farnborough International Airshow, a 35-meter wide black plane with wafer-thin wings is suspended on a wall beside an exhibit of BAE Systems' cutting-edge space technology. This is PHASA-35 – a high-altitude, long endurance unmanned aerial vehicle (HALE UAV), and it could stay airborne for a whole year using nothing but solar power.

The drone on display at Farnborough is a scale model, but real test flights will take place next year and finished aircraft could be shipped to customers in 2020 or 2021.