hi again victor ...

yeah, i too like chemical free photography. it works very well and it is a lot of fun. i have wanted to make solar graphs, but we have too many trees near me, and i wouldn't get a good view of the horizon .. so i have settled on normal lenses box cameras and shorter exposures. same idea, but takes less time

i didn't realize you were doing your project in remote areas ...
have you thought of a solar power or dry cell powered "shutter"
using a timer? you can hook up a dry-cell battery to the timer and then have a "shutter" attached to that ... some large format cameras have electric shutters. it won't be technology free, but you could hook up a dry cell ( or solar cell ) to one of these set to "BULB" mounted to your pinhole camera ...

this stuff won't be technology free, but it might help ...

good luck !

john