If you're looking into solar panels, read this first. My tried and tested experience.

[Timinator]

I haven't been on this site in a while but I figure since I'm here I might as well throw a bone.

So I hated the idea of having to pull out paper maps every 5 seconds on the CDT. I did long hard research on a way to power a gps permanently, among other gadgets.
The most practical approach was with solar panels.

Let me start by saying that for most practical purposes a panel below 10w just won't work, even 10w is kinda low. Lots of people on these forums have displayed disappointment in panels and yet they use low watt panels. If you want to use panels on the trail and expect to get reasonable power then don't use low watt panels.

The panels I currently own are the old goal zero 13.5w solar panel, two of their new 13w models and a 17w voltaic panel.
I also have the old heavy goal zero sherpa 50 battery pack and the new light sherpa 50 battery pack along with the guide 10 battery pack.

There's two things that people need to know. 1. Goal Zero panels suck. 2. Goal Zero battery packs don't.
I have replaced so many goal zero panels because they broke in damp conditions or because they didn't output as much as they should, even if they don't get a drop of rain on them they can break from humidity, at least for certain models.
That being said the old 13.5w model has never failed me, even though it's best not to expose the control box to water directly.

Now for the shocker. I have a 17w panel from a company called voltaic that weighs 26 oz which is less than half the weight of the 13w panels and can be thrown into a lake and still function. PLUS it's designed to be strapped directly to a pack or whatever you want. The guy on the phone even said he would do everything he could to ship me out a new one asap if it ever did break during my hike. The panel itself is pretty barebones so I was concerned it might break under a certain amount of stress but he assured me it would take a serious beating, which I confirmed for myself during my hike through Montana. The voltaic panel outputs some serious power, the difference is noticeable even over the 13 watt panels.

So in other words if you are going to buy a solar panel voltaic panels are lighter, cheaper, and more powerful panels than goal zero, and they are already designed to strap to things.

As for the battery packs. Goal zero is pretty solid. The sherpa 50 which is a 50wh battery weighs about 1lb and the guide 10 AA charger weighs about 6oz. I haven't seen or used another battery pack that comes close to goal zero durability and reliability. Always make sure that the terminals on the goal zero batteries are dry before powering them on, I learned that the hard way when a slim film of moisture short circuited my sherpa 50, thankfully they have fuses.
I don't remember the specifics but as I recall the sherpa 50 will charge the batteries of the guide 10 at least two times and will keep my gps powered for about 2-3 days. The blindingly bright led lamp on it will last about a month, and about a week on the guide 10.

As the reliability of the new goal zero 13w panels suck, I don't use their guide 10 super charger cables leaving me with only the usb option. This means it's more efficient for me to charge up the sherpa 50 and charge the guide 10 from that, which I then use to keep my gps powered.

The sherpa 50 can take anywhere from a few hours to a day to charge, a few days in overcast conditions.
The guide 10 can take anywhere from 2 hours to a day to charge depending on how you charge it and the conditions.

It's very hard to drain the battery of a sherpa 50 with a 17w voltaic panel. The only time I ever managed to do it was when I was powering my psp and charging my aa batteries and my gps all at once for hours under cloudy weather.

For the average person just trying to keep their phone from dying voltaic has adapters for seemingly everything imaginable so you can plug the panel directly into you're phone, laptop, guide 10, or whatever and their 9w panel should be alright for the weight conscious, as long as they aren't constantly using their phones or whatever.

As for me, as long as I keep my gps on the home screen when I'm not looking at it, I can keep it powered forever along with my uv water purifier, headlamp, phone, and yes, even a psp on occasion :D.

This may not be for everyone. Carrying around 2lb of power sources can be considered a deal breaker for some people.
The convenience factor for me makes it worth it.

[garyp]

I am having trouble believing that the Voltaic panels are cheaper when I am finding them more expensive than the Goal Zero Brands.

[Slo-go'en]

I am having trouble believing that the Voltaic panels are cheaper when I am finding them more expensive than the Goal Zero Brands.

I don't see where he says that the Voltaic were cheaper. He did say the Voltaics were better and more reliable then the Goal Zero, which in long run could make the Voltaic a better deal.

[Damn Yankee]

I don't see where he says that the Voltaic were cheaper. He did say the Voltaics were better and more reliable then the Goal Zero, which in long run could make the Voltaic a better deal.

Now for the shocker. I have a 17w panel from a company called voltaic that weighs 26 oz which is less than half the weight of the 13w panels and can be thrown into a lake and still function

[Harrison Bergeron]

One of the three things in my kit that I didn't use on my recent 3-week section in GA-NC was my 7 oz (that's nearly half a pound!) solar charger/battery pack. I just left my phone in "Airplane Mode" with "Location Services" turned off and invariably I would arrive at the next town with over 60% charge. And that's even with taking pictures all day and reading on the Kindle app for a couple of hours in the evening, plus calling home whenever I could actually get a signal. Next time I'll leave it at home, along with the sunscreen I didn't use either. (Point to ponder -- if there's not enough sun on most of the AT to turn your skin brown, how do you expect to charge a battery with it?)

Well, although I didn't use it, it did get used once. I hiked for a while with a guy who left his iPhone full-on all the time -- I guess so that he could conveniently hunt for Verizon service when we took a break without turning off airplane mode. He borrowed my charger once the day before we hit Franklin, after 5 days on the trail. So I guess you could say it got used, just not by me. But I thought it was interesting that even without managing his phone properly, he still barely needed a spare battery, and certainly didn't need a solar charger.

[Slo-go'en]

One of the three things in my kit that I didn't use on my recent 3-week section in GA-NC was my 7 oz (that's nearly half a pound!) solar charger/battery pack. I just left my phone in "Airplane Mode" with "Location Services" turned off and invariably I would arrive at the next town with over 60% charge.

That is definately true of the AT where you can get to town frequently and the tree canopy makes solar chargers useless. However, the OP used his on the CDT where you can go over a week between towns and your hiking in the sun more often then not. On that trail, a solar charger makes more sense and is more useful.

[Timinator]

I am having trouble believing that the Voltaic panels are cheaper when I am finding them more expensive than the Goal Zero Brands.
The 17 watt voltaic panel is $150 and the 13 watt goal zero panel is $200.
The voltaic panel is lighter and attaches to a pack easier as well.

[Cedar1974]

FRom what I've read, a solar panel is useful, depending on where you are hiking. Places like the Southern ends of the PCT and CDT where it is mostly desert, a Solar panel is a great idea. Most East coast trails have lots of tree cover, and it is hart to get any good sun, so a large power bank or two might be a better option.

[Meriadoc]

Definitely look at outdoor gear lab. They have some very good reviews of solar panels and batteries. A good solar panel is available for about $50 as long as you don't need to charge a laptop. And a good battery can be had for $30. They are lighter too.
http://m.outdoorgearlab.com/Solar-Charger-Reviews

[BrianLe]

"However, the OP used his on the CDT where you can go over a week between towns and your hiking in the sun more often then not. On that trail, a solar charger makes more sense and is more useful."

The same strategy works on the CDT. It's certainly true that on the AT town stops are closer together, more opportunity to recharge. So I carried two spare batteries on the CDT rather than one. And I carried a standalone GPS, separately powered with lithium AA's, very light to carry spares and readily obtainable. That whole kit weighed a whole lot less than two pounds, and the standalone GPS (for that trail) was worth it. For me.

These comments aren't intended to disparage the OP (!). We each analyze our personal situation and preferences and make the trade-offs as we wish. I'm just saying that the CDT or PCT don't somehow mandate a solar charger, and, IMO, far from it. I did carry a solar charger for most of the PCT, something much lighter but also certainly much less effective. I stopped carrying it at the OR/WA border but IMO should have ditched it sooner. Tied to the top of my pack it helped stretch out time between recharges in towns, but again, with experience I could have done fine with a spare battery or two.

I'd also note that the trade-off depends very much just for what and how you're using your various devices; this can span quite a range of use and associated power consumption. I rarely bring a standalone GPS, but do bring a separate MP3 player, in part so it's on its own separate "power budget" (a single AAA battery). Phone for me is used to blog each night, take photos, as a GPS on occasion, infrequently as voice recorder or book reader. The latter only when power budget clearly allows, and, typically, only hiking in relatively early spring or autumn when the nights are long. I say all this just to be clear that the "carry spare battery or two" approach doesn't inherently put you on a severely restricted power budget, so long as you pay attention and know how to run your phone somewhat 'lean'.

[Timinator]

I never had an issue charging with 13+ watt panels on the AT, even under tree cover. If you have good panels they should still do their job well enough.
I don't think panels are quite needed on the AT though.