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.
My strimmer battery charger takes 65w. So 8 hours of 30w to charge a battery is almost 4 hours charging the strimmer battery which would probably fill it's small battery a few times over. If you are not depleting the strimmer battery multiple times a day, that is more than enough power.
You of course do need a battery to store it so many hours of solar are used in several minute short time loads.