I have this crazy idea about a solar panel and a sensor that starts and stops a SBC when the power exceeds or drops below a specific level.
So if you have a 5v solar panel and your SBC needs 1Amp, you start the SBC at 1.1Amp and stop it at 1.01Amp, or something.
I'm not an electronics person, but I may get to it one day.
I have thought about that as well. But you would need something to measure the Amps as well. If you ever explore further, please let me know :)