you would probably get a lot more energy in cumulative milliwatt-hours per week/month from having a tiny 2 x 1cm size photovoltaic cell such as from a cheap desk calculator exposed to ambient room light, and something like that has no moving parts.
if we are talking about actual practical IoT things a single "big" solar cell (125x125 or 156x156mm) size is quite cheap, and you'd run the output of the PV cell directly into a tiny battery charge controller circuit configured to keep one 18650 or 21700 size battery at its float voltage.
if we are talking about actual practical IoT things a single "big" solar cell (125x125 or 156x156mm) size is quite cheap, and you'd run the output of the PV cell directly into a tiny battery charge controller circuit configured to keep one 18650 or 21700 size battery at its float voltage.