Is one allowed to go out with a solar powered watch on Shabbos (where they know the watch is in a situation where they will surely benefit from the power produced through the sun?) What could be the possible issur or malachca in this (if any?)
For all practical situations a Rov should be consulted. I'm asking the question to find sources for this, authoritative poskim that discussed it or perhaps "svaras" that people have in order to answer this.