Anker Solix 30W USB solar panel (PS30)
I finally did more testing and observation of a solar panel I bought for emergency preparedness, following Hurricane Helene taking out power and water in my brother's neighborhood.
Initial impressions were extremely underwhelming. The product claims to provide 12W USB-A and 15W USB-C charging, but was unable to keep my iPhone SE 2 charging constantly, with only a smidgen of cloud in the July sky. One of the photos showed a person hiking with the product clipped to the top of a backpack, hanging down the back. I'm (still) not sure that can possibly work.
But, further research shows that the "12W" figure for USB-A charging is both minimum and maximum. If the panel can provide 12W, the USB-A will feed the device; if not, it does not. Consequently, if the device cannot take 12W after reaching 80% charge, then it will cut itself off, remaining at 80%. This would be fine if it didn't consume 50-70% of battery a day, and/or low power mode actually consumed observably less power. (To be fair, I haven't tested this in a few years. I guess it's time to rerun it.)
I had really expected it to be able to offer a 5W charge in bad weather. It does not.
Update: In a later test, my iPhone SE charged from 56 to 91% over the course of an hour. It is possible that the original 80% cutoff was affected by optimized charging settings or thermal limits. I wasn't present to watch it, so I don't know if it successfully switched to 5W/trickle charge mode. Benchmarking is hard, let's go to bed. (End update.)
The 15W USB-C port will deliver more power if there is sufficient sun, and the USB-A port isn't in use. The iPhone 16e for work estimates faster charging times when it is plugged in alone. I have not attempted to charge this device above 80%, but I'm pretty sure it would handle it. It's much newer and larger.
The final note about this product is that it is very stiff when cold. When setting it up, one needs to plan for some pretty heavy weights to hold it open, or budget five minutes to do it by hand. The heat of the sun relaxes it quite a bit. This works both ways; leaving it flat and letting it cool makes it resist folding.
Like all solar, it is extremely sensitive to the angle of the sun above the horizon, and the angle between the panel and the incoming sunlight. It's able to output 30W (two phones) on a cloudless summer afternoon, but in can't consistently output 12W in the morning. Again, that's not a fault of the device; that's physics.
Overall, I'm somewhat happy with the device. It could work, under the right conditions. It would be less conditional to have a power bank and bigger solar panels for it, but also far more expensive. A worthy middle ground would be an inverter run by power tool batteries. One of those options is certainly in my future, because I don't think there's enough sun where I live to make the 30W panel viable year-round.