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.
Using solar energy directly is also always an option, a fresnel lens or convex mirror are great for heating things. You can even make things cold using an absorption cycle cooler (the kind of things used in “propane powered” camper fridges)