The basic premise of the project is, that during daytime, there's relatively plentiful source of the primary energy (solar panels can be bought in larger sizes if necessary), but the key issue is to provide enough energy to sustain rudimentary functionality during night. Even if the time is not been indicated during night, storing energy for timekeeping alone may be challenging enough.
The "root" project concluded, that for the given goal it is necessary to omit parts based on "chemical" principles. This largely disqualifies the conventional energy harvesting models, which rely on accumulators and/or supercaps.; even electrolytic capacitors are off. Omitting exotic principles such as mechanical storage, we are left with a short list of "solid-state" capacitors. This project will try to find a way to make the best use of them.
While the discussion in the "root" project identified also other potential issues (e.g. enclosure), for sake of simplicity, we are not going to be bothered by these here.