The amount of solar energy available indoor is very limited… a very small fraction of outside, I’m sure.
Still, this unit has been running in the house here for a few years now, and not near a window either:
It’s a attractive goal: gadgets which you buy (or build) once and then use essentially forever!
We don’t use the alarm clock mode of this thing, so the beeper never goes off, but it does listen for the DCF77 clock standard transmitter in Germany once a day to stay in sync. It’s also slightly glow-in-the-dark, so this clock remains readable at night.
The fact that this clock works so well tells me that, with proper care, we should be able to run simple nodes inside the house with a solar cell of perhaps a few square centimeters, just like this clock.
And, whether battery- or supercap-powered, that’s precisely what I’d like to get going…
As with the AC-mains connected ultra-low power supply, I suspect that reliable startup will be the hardest part. Such an energy source will have very little spare energy and charge up very slowly, so when the JeeNode comes out of power-up (or brownout) reset, it’ll have to be careful to not cut off the hand that is feeding it, so to speak.