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.
To add to my comment, many cheaper portable brands underperform greatly as well.
Get a rigid panel (not flexible) and you’ll see a huge improvement.
The flexible panels are great for keeping weight down, though. Probably the only way to go if you’re hiking or backpacking!