Once you can keep the plane up for 24 hours, you can go anywhere
Non-manned solar powered planes is already capable of remaining airborne for many days since a few years ago. The problem with manned planes is twofold - the crew adds considerable weight, and it gets really cold in the night - and there's still not enough capacity in the batteries to fly and heat all the night at the same time. So no heating. And it gets pretty cold up there.