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.
A 30W solar panel is likely going to charge at about 5W, given the inefficiency.
There is some inefficiency in charging a battery but not that much. Main losses would be that the solar panel isn’t actually outputting 30w as you won’t be getting ideal conditions all day.
But it doesn’t necessarily matter either. 65w to charge a battery but you only need it once a week for an hour can easily be managed by 5w all day for a week.
Though planning for an apocalypse is kinda pointless anyway. Preparing for a disaster is more reasonable, such as a storm knocking out power for a while.
I was getting around 12 watts during the sunset when I was testing it. It can probably reach around 20 watts under ideal conditions.