The neatest thing about solar planes is how high they can fly. One got up to about 100,000 feet.
Well, it needs to be that high, because night.
When the sun sets it gets dark and the solar power is no more, and the only electricity they have is from batteries.
So it will consume the batteries until such time as the sun comes up. If they exhaust the batteries before that time they can avoid an early splash down by being high up to begin with.
Still, wonder how long this thing can glide at night? Higher altitude means less lift, no?