I am doing a couple hikes this summer that are going to be 5-10 days long and think I should probably look into a solar charging system.  What are you guys using?  Which ones work and which ones should I avoid?

ETA: I plan on charging a power bank which I will then use to charge my camera, phone, etc.

I think the folks best able to give you an answer (and that's not me) are going to need to know what it is you're trying to keep charged.

All my stuff is AA and I use Powerfilm 4 AA chargers.  They come in different colors, this is just an example.
https://www.amazon.com/PowerFilm-Foldable-Solar-Charger-Digital/dp/B00G2KVQSW?tag=vglnk-c102-20

7 watt versions are the bare minimum, like most things, more is better.   I have a goal zero 7 watt and the 4 aa power pack.  All day to charge the pack, and that gets me 1-2 full charges on my phone.

Fixed the OP, I plan on using it to charge a power bank.

Any of the popular folding 14w-21w jobbies like Anker, Blitzwolf, or Instapark should suffice.  Get the biggest one you can afford and one that will do 2.1A/2.4A for current.

Get a big power bank, preferably one that lets you replace the cells inside.

This assumes that weight isn't a huge factor.

Chris

Are you base camping and then doing day hikes?  Or do you need to charge while packing all your gear?  How much sun will you have?  How much power capacity in your powerpack?

If you base camp, then you can go with a much bigger setup.  I have a 50W flexible (even a 100W aluminum frame) for certain longer stays (driving my portable fridge/freezer).  You also have to carry a charge controller for the 50 and 100W.  If you need to be charging on the go, you're looking at rigging either across the top or draped down the back.  The size of the foldable is going to be partially determine what you can do here.  Proper orientation is critical for highest output and any of pack method is always going to be non optimal.  Panels have a peak power output in direct sun and in cold temperatures.  All other conditions will lower this.  And orientation is the biggest "controllable" factor.  My experience with my GoalZero 7W is that I probably get less than 3W in a flippy floppy configuration on top of my pack.  I get 5W when fixed almost upright strapped to topside on kayak.  My GZ has only 2 panels to try to orient correctly.  The 14-28W double or triple that, which makes optimal orientation even more difficult in a pack situation.  That said, if you are using in a fixed location with optimal orientation say for an hour each @ lunch and @ camp, you could get what I would get in an 8 hour hike day off my 7w (@ 3W).

I have a 14W - 4 panel (not a GZ), it folds to the same size LxW, but has 4 panels, which unfolds to two feet, so doesn't drape well on a pack.  Each panel is half a page of paper in size, my GZ folds out to a full sheet of paper.  There are major differences in the power modulation/controller built into the panels and the powerpack.  If you aren't actively managing the panels, you want to pay attention to this as you may want to test your panels before you go (and return ones which don't perform well).  Either clouds, a pack flap covering, or your head casting a shadow that causes a output drop that then drops the feed to your pack from say 2.4A to .5A, but because either the panel or the packs controller then stays at .5A rate, will be problematic.

BTW - both my GZ and my non-big brand 14W panel stink in this regard.  My GZ is not the current generation of their panel, so they may have that beat. My Gorilla battery packs can take variable input ok.  I know some of the current Ankers have smart controllers, that don't have this problem.

I really like anker banks and panels. A 16000-200000mah battery plus the 24watt pannel are a great combo. Anker is really good quality items and should they fail they have a 18mo no BS warranty.
I own a few different brands and various wattages of panels and banks. Anker by far out performs. And yes I own some goal zero stuff, but I won't be buying anymore. Ive melted 2 of the goal zero 4 aa/aaa chargers

Brunton solaris 26.

That's a good one--Brunton, Goal Zero Power Film and Global Solar make some nice panels, but most of them are 12vdc and the OP wants to charge up a power bank and most of those are 5vdc USB jobbies.

Chris

I simply love the robustness and simplicity of Suntactics.  A little more expensive than other, but the design is built for rough use/abuse. Their 8W charger is the one I typically choose if backpacking, but their larger 14W charger is extremely efficient and fast for the size.

Regardless, I only pack a 10-13K-mAh charger as anything bigger will take a couple days of full sun for those really large battery banks.  The double port models are nice as I can charge both my battery bank and phone (or other USB charged device).  

Do some research and test what you decide on.  The biggest challenge is how much sun exposure you're going to get and charging while backpacking isn't really that reliable (see why the Suntactics "auto-retry" is some important).  You will need 2-3 hours of stable, full-exposure sun to really take advantage of using a solar charger.  I've found a balance of minimizing my electronics needs and just backpacking with the portable charger for trips as long as 5-7 days.  If we're car camping or kayaking, or setting up a base camp, I'll bring along the larger solar chargers.





ROCK6

EBay is full of voltage regulators for .99 a pop, some of them are even fixed to 5v for this very purpose and have micro USB ports on them.

I use a Powerfilm 10 watt panel to charge a RavPower 26800 power bank when camping and backpacking. I use the power bank to keep cell phones and a 10" Tablet charged and also have a Xtar VC2 Plus charger to charge AA and AAA Eneloops for headlamps and GPS.

It's a great setup that takes up very little room.

If you're going to be on the move daily, you need hours and hours of sun exposure to charge much of anything. I suggest getting one you can drape over the back of your pack like this.