I’m only half kidding. I’m a bit of a prepper and I have lots of powerbanks and devices that charge from USB but besides idling my truck I really had no other way to charge any of them in case of a long-term power outage which seemed a bit of an oversight on my part.
Not like this solves the issue. 30 watts (under ideal conditions) isn’t much but it’s a start.
Check out some auctions, estate sales and such for some deep cycle batteries, solar charge controllers and panels. I have fixed my set up a few times over the years on the super cheap that way. The whole system is not bad other then the batteries for cost.