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.
In a situation where you don't have constant access to abundant electricity, you would naturally reduce your use of electronics quite a bit. An e-reader battery lasts a long time, so load it up with a bunch of good and useful books and that panel will be able to power it indefinitely. Winter is tricky, still it would probably be enough to keep it going with sparse use. Or you could rig up a bike-alternator-car battery set up. But you need to think about how much power you can reasonably generate and base your planned consumption off of that. This makes me sound like a big prepper, I'm not, but I have been thinking about this a lot lately. Wonder why...