In 2017, Google’s parent Alphabet decided to end its solar-powered drone program, tasked with developing aerial vehicles that could fly for several days at a time and take images of earth or beam down internet, instead concentrating its efforts on Project Loon, which is delivering something similar, but with the help of high-altitude wind-propelled balloons.

A notable achievement in the field of solar-powered aircrafts took place in 2016 when the Solar Impulse 2 plane, a wingspan wider than a Boeing 747 with more than 17,000 solar cells on its wings, completed the first round-the-world flight using no fossil fuel in 16 legs of the trip that lasted more than 23 days.

During its maiden flight last August, Airbus’ Zephyr S stayed in the air 25 days, 23 hours, and 57 minutes, which qualified as the longest duration flight ever made. The previous longest flight duration record was also logged by a Zephyr prototype aircraft a few years earlier, achieving then more than 14 days continuous flight, which already was ten times longer than any other aircraft in the world.