Any experiences with portable power chargers like the solar-outdoor-pads? There are some products but I have no idea if there is a chance to charge a battery pack or batteries for field recording. Would be an interesting thing to have a little solar-powerplant in the backpack to charge things specially on longer trips far away from civilization. But I fear they bring by far not enough power to charge something.
Solar panels (especially affordable ones) haven’t gotten efficient enough to reliably charge without a massive panel or an array. I have a portable 4 panel system that folds down to a backpack. It’s about 5 pounds, plus the battery (panel needs a capacitor to charge to feed a smooth signal to the device you’re charging – otherwise it could burn out the charger due to unstable output – cloud covers the sun, etc…). It takes about 10 – 12 hours of more or less direct sunlight to charge my phone (iPhone 6). If you find a way to convert to 12v, you could theoretically charge through a DC port (7 series, etc…), but it would burn through the panel battery faster than the panel can charge it. Definitely a no-go for AC, at the moment…
If you had an array of panels, you might be able to pull it off, but that’s pushing the boundaries of portable.
With many companies pursuing Solar more actively lately, panels are starting to get much more efficient (small portable panels usually have a 15-25% efficiency rating, meaning they convert more solar energy to heat than usable power). A better solution might be in the near future, but currently, it would be better to carry extra batteries than the amount of gear it would take to charge batteries, as it would be far lighter.
I occasionally use a Sunkingdom portable solar panel to charge or top up the powerbank(s) I use for my recorder. It works OK, but I haven’t given it super extensive testing yet to be honest. It basically charges the battery, but it’s slow going. I have a 39W panel, there’s more powerful ones which in theory should charge faster (as they have more solar cells).