They ran the 18 day flight test in September, so not the dead of winter, but also not on the longest summer days: A solar-powered aircraft has completed an 18-

They ran the 18 day flight test in September, so not the dead of winter, but also not on the longest summer days: A solar-powered aircraft has completed an 18-day test flight offering hope it could be used to create internet access for billions of unconnected people around the world...The test flight touched down in Arizona on September 13. https://www.thenationalnews.com/world/the-americas/2021/10/11/solar-powered-airbus-zephyr-completes-18-day-test-flight/ https://www.thenationalnews.com/world/the-americas/2021/10/1... Phoenix has about 12.5 hours of daylight on Sept 13th. (compared to ~14.5 hours on June 21st, ~10 hours on Dec 21st.