I wonder if, for the stated design goal of a zero-battery solution, something like a solar thermal concentrator + Einstein–Szilard refrigerator would work. Som

I wonder if, for the stated design goal of a zero-battery solution, something like a solar thermal concentrator + Einstein–Szilard refrigerator would work. Something as simple as an icyball or two kept charged via the solar thermal system might work as well. https://en.wikipedia.org/wiki/Einstein_refrigerator https://en.wikipedia.org/wiki/Einstein_refrigerator https://en.wikipedia.org/wiki/Icyball https://en.wikipedia.org/wiki/Icyball