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.
Those backpack folding units arel great for powering a speaker when gardening.
Have a look at solar blankets. More expensive, but same storage footprint when folded and you can get more wattage out of them