Gonna shill my project, a 34 key solar powered split keyboard https://github.com/cjshearer/cweep . Each half should end up just a bit wider than a smartphone (114mm x 86mm). I'm still working on the case generation, which is intended to have a metal backplate for magnetic mounting, but I've gotten distracted developing a generic method to convert kicad geometry primitives to cadquery, so others can benefit from this…
What is that battery? It looks like it will last about ten years, wouldn't a solar keyboard need a battery about 1/50th the size?
I acknowledge that that really isn't much of an improvement, so at this point the solar charger mostly exists "because it's cool".