[GuB-42]

I have tried my luck with portable solar panels, and my conclusion is that in most cases, they suck.

For a solar panel to be useful you need:

- At least a few days without access to electricity, otherwise even at max power, you won't get as much charge as a similarly sized power bank

- Good sunlight, preferably in the summer (more daylight)

- No shade, which is the opposite of what you want in hot and sunny summer days

- Correct placement for your solar panel, for example, having it hanging from your backpack will only work if you have the sun in your back

- A large enough solar panel, these tiny panels you sometimes find on power banks are useless

- Compatible devices. Solar panels have a variable power output, not all devices support it, some of them just shut down charging. Your best bet is to use a compatible power bank, but that information is not often specified. Test it beforehand!

My experience with a solar panel is from two week-long music festivals in the summer, which would be almost ideal conditions. My experience was that over the course of a week, I got about the charge equivalent of a 10Ah battery from my solar panel (rated 10W, 300g), so about half the efficiency of that gummy bear battery, for the reasons cited earlier. Maybe I could have done better with a better panel and better planning, but I'd rather have a battery, much more convenient, and cheaper too. I want to enjoy the festival, not babysit my solar panel.

So I'd say you need at least a week without electricity in the best conditions to make a solar panel worth it, preferably more, which I believe is rather uncommon.

Also, I am talking about these portable <1kg solar panels. The large solar panels that go in your car/van are another story.

[dgacmu]

We did a five day backpacking trip this summer (in Wyoming, with lots of sun) and the solar was great. Kept my wife's iPhone at 80-100% for the trip (some idiot left the usb-c cable for his phone in the car) with mostly only using it after we reached camp. Decided that with two phones we had enough redundancy to leave the paper maps behind. And we used the phone a -lot- for taking photos in addition to navigation.

I've had trips where solar would have mostly failed - 11 days of nonstop rain on the Continental divide trail in Canada, to be specific - but solar has worked for me really well in CA, UT, WY, CO, etc. the places where solar would have failed were pretty obvious in advance, too.

And it doesn't take much direct sun on a 15 or 20W panel to keep two phones and a steripen charged if you're not being crazy with the use.

[GuB-42]

To make it clear, I am not saying that solar panels don't work, of course they do. What I was questioning is using a solar panel over a power bank of the same weight.

A 20 Ah (77 Wh) power bank weight about the same as a 15W solar panel. That about 3 full (0-100%) charges on a typical smartphone. I think that would have kept your wife phone up the whole trip no problem, and no need to worry about the sun.

On a 11 day trek in the sun, yes, by all means take a solar panel. However, most people I know who do such long hikes usually have access to electricity at some point. But if it is not your case, well, you are the reason why these solar panels exist ;)

[addaon]

> So I'd say you need at least a week without electricity in the best conditions to make a solar panel worth it, preferably more, which I believe is rather uncommon.

That's basically my use case. I have a "15 W" panel. I can get about 5 days from my iPhone for navigation, and most of my trips are 5 - 7 days, so really it's opportunistic charging for reading on my phone after dinner. I can generally get an hour or so of reading from just hanging the panel off the back of my pack, and another two hours from setting it in the sun during my ~1 hour lunch break if it's not so hot out that nothing charges. 300 g for ~3 hours of reading at night, indefinitely, is a good trade for me.