Solar Impulse 2 was headed from China to Hawaii when its team decided to divert to Nagoya, Japan, because of bad weather ahead.
After landing late Monday, a cover was put over the wing to protect it from the rain and the sun.
"There was so much wind and gusts that this cover started to shake on the wing, and damaged an aileron on the trailing edge of the wing," Bertrand Piccard, the head of the project, said in a video posted on the expedition's website.
The Solar Impulse departed Nanjing, China, on Sunday on what was expected to be the longest leg of the journey, a six-day, 8,175-kilometre flight to Hawaii.
Instead, the plane landed in Nagoya in central Japan to wait out the unexpected bad weather.
Swiss pilot Andre Borschberg is flying without any fuel.