I understand.

The N800 does last a good while on a charge. It takes a while before the first and second bar dim out. Then it seems to drain pretty rapid. If you keep the screen on the dimmer side (N810 has some automatic sensor, not sure what the manual control is) and keep wifi & bluetooth off ... you could go a while between recharging.

I tend to turn mine off entirely if I really need to keep the charge (as in out and about) as I've found certain sites to keep it awake (didn't load completely? certain scripts or flash keep running?) and get activated when there's pressure on the little soft pouch ... in jacket or bag while walking.

So, if you can charge a nano in a day on solar. You can probably alternate day to day. Or top up both with half a day. Weather permitting.