this post was submitted on 18 Jul 2026
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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.

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[–] HerbGrower@slrpnk.net 3 points 2 days ago (1 children)

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.

[–] GoatSynagogue@lemmy.world 1 points 2 days ago (2 children)

A 30W solar panel is likely going to charge at about 5W, given the inefficiency.

[–] HerbGrower@slrpnk.net 1 points 2 days ago (1 children)

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.

[–] GoatSynagogue@lemmy.world 1 points 14 hours ago (1 children)

The inefficiency isn’t the battery, it’s the panel. They run at about 20-25% efficiency at best.

[–] HerbGrower@slrpnk.net 1 points 12 hours ago

The rated wattage should take that into consideration.

[–] Iconoclast@feddit.uk 1 points 2 days ago* (last edited 2 days ago) (1 children)

I was getting around 12 watts during the sunset when I was testing it. It can probably reach around 20 watts under ideal conditions.

[–] GoatSynagogue@lemmy.world 1 points 14 hours ago* (last edited 14 hours ago) (1 children)

Highly doubtful. ~30% efficiency is already pushing the limit of solar panels. No way you’d get over 65%.

[–] Iconoclast@feddit.uk 1 points 10 hours ago

Efficiency means how much of the sunlight hitting the panels gets converted into electricity. How accurately manufacturers report the true output of the panel is a completely different thing. Plenty of reputable brands reach the advertised output.