Psst!
Hey, you! Yeah, you -- the nerd sitting in the corner.
You know that solar panel you bought a couple years back "just in case" that's collecting dust in a desk drawer?
And that portable USB battery that you keep forgetting to recharge?
Do yourself a favor and shove 'em both in a south-facing* window.
You're welcome.
* (north-facing for you southern hemisphere weirdos)