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.
All of the labor has been DIY, and I've got about $9,000 invested in the system components.
Back of the napkin math, at current electric rates, puts my ROI at just under 9 years. If electric rates keep going up, it'll pay back even faster.
Edit: Depending on how you look at it, ROI could be in as few as 1.5 to 2 years. This system is in lieu of a whole house generator that would have cost us about $7,000. Had we gone with that instead, it would never have paid for itself (other than peace of mind) and we would have been perfectly content. So if I'm only considering the price difference between this and the generator, it'd only have to pay back $2,000.