There is no more irritating dead weight than a bag of batteries in your backpack.  You brought them along because you wanted extras for your GPS or your camera, and that little pocket radio with the emergency weather band that really doesn't take up any space and weighs just an ounce, and the penlite you might need.  Now that you've weaned yourself from civilization none of that seems really necessary.  It's just heavy.  Since you're the ecologically sensible sort, you won't bury the little packets of poison beside the trail.  Pack it in, pack it out.

The only things that sucker me into hauling along batteries are the GPS and the camera.  I'll probably plan to look for a geocache along the way and I'll feel obligated to take the camera just in case I see something neat.  Both of my gizmos devour batteries like a dog eats biscuits.  By the time I get very far I'll realize I could have happily left all of this behind but then it's too late.  Whether I use them or not they are permanent dead weight.

Suddenly there are alternatives.  Some, like the hand cranked generator, have been around as emergency equipment for decades but have been redesigned and are now compact and lightweight.  The best solution to wilderness power needs--the solar panel--was too fragile and too expensive only a few years ago.  Now rollup panels that lash to your pack or stow in a pocket are within the reach of any cost conscious environmentalist willing to crunch numbers and look at the long term.  If you shop for new gear, one of your choices will be a backpack with solar charger built in.  It's a tough idea to pass up.

If you're an ultralight backpacker or at all concerned about extra weight, forget the solar panels for now.  Maybe the technology will improve, but at present you'll probably be carrying more weight in terms of solar panels than you normally would as batteries.  There will only be a weight benefit over the old system if you are heading out for a long time and you're a heavy user.  Recreational hikers will probably be better off with battery packs.  The panels pictured above weigh two pounds apiece.  That's a lot of batteries.

If you buy a backpack with solar panels built in, that's weight you can't leave home.  You'd better be sure you need them.

Not all foldup solar panels are the same. The Sunlinq 6.5 Watt Folding Solar Power Panel is only .45 pounds and capable of recharging four AA batteries with only four to six hours of full sun. That's getting to be more practical. The Coleman Exponent 5 Watt will need an hour or two more, and is a little heavier at 9.5 ounces. Don't get too excited, because either of them will require an additional battery charger device like the iSun 3-way BattPak Charger. The iSun will charge ten ni-cad AA's at once, but adds weight and bulk to what seemed like a frugal system. Add another half pound, plus at least two rechargeable batteries to the total weight cost.   Both types of portable panels use a "cigarette lighter" style adapter as an output; if you have a device with a rechargeable battery built in, and you also have a charging adapter you can hook to your car's lighter socket, you can also use that with the solar panels.  That only adds a little more weight.

For all that trouble, this had better work really well.

At this point it's pretty clear that if you are going on an extended canoe trip to the upper reaches of the Canadian wilderness and you want to keep a video record of the journey, a portable solar panel and charging station makes really good sense--but if you're going on a weekend outing and want to keep your IPod charged, it's only going to make sense if you think of very long term benefits. Actually, it may not be even that good, because in actual use the panels don't do quite what they would do under perfect circumstances--and the charge times listed by the manufacturers do refer to perfect conditions, full sun and correct orientation to the sun for the minimum specified time. If you're hiking with a panel strapped to your backpack it will seldom be working at full efficiency. There will be full sun, indirect sun, shade, and the occasional rainy day. The claims some have made that their backpack units will, for instance, power a laptop computer, seem to be a bit stretched.

So, is there something that does work?

Let's get practical. You'll seldom hike in perfect conditions for a solar panel, but there are ways you can use one to get by. The early versions, which we are just beginning to see fade into expensive obscurity, were lazy designs. Someone built them thinking people would buy them just because they were solar panels, and people did. That's been the mainstay of the solar panel market for most of its history anyway--customers who could afford very expensive alternatives that weren't nearly as convenient as gobbling cheap energy from the power grid. Now there are a few that make a little good sense for the rest of us.

PowerFilm's USB and AA Solar Panel Charger does only those two things. If you have a portable device that runs off a Universal Serial Bus, it will plug directly into the foldable Solar Panel. If the sun shines the panel will provide power. That may not be enough for a full charge, but it will give the device a boost and often that will be enough to keep it running. Built into this system is a compartment for two AA rechargeables. Drap this over the top of your pack and on a sunny day you really do have a chance of building that charge up to nearly full capacity. There's no extra gear to acquire if that's all you want to do, and that is a very sensible system. The Silva SC22-2 Solar Panel Charger will charge either AAA or AA batteries without muss or fuss, but it'll take awhile--ten hours for the AA's. Total weight of either of these systems is about a pound without the batteries, so it's getting down to a reasonable level now compared to a week's supply of batteries for a GPS.

Two other solar chargers, built only for charging batteries, have also gotten pretty good results and are suitable for camping and possibly as emergency units for hikers. They are box type chargers with solar panel lids and would best be used at base camp, not while moving. Hunters, campers, and fishermen would all find them useful and they are not terribly expensive. They would not make good sense strapped to a backpack, however.

SunJia's Four Battery Solar Charger will even recharge C and D batteries. Expect longer charge times. It is obviously more practical for the smaller AAA and AA types. You must charge four batteries at a time, and in backpacker's terms it's pretty heavy, about two pounds by itself. It does have the ability to run other devices directly from a universal connector jack, with a continuous output of 6 to 7 volts in direct sunlight.

The Solar 2 in 1 Folding Panel and Power Supply offers more panel area, more charging capacity, and direct connection capability for rechargeable devices. It seems a little over optimistic but is self contained and if you charge four AAA or AA batteries at once instead of eight, which is the maximum capacity, you'll have much faster results. Too big and too bulky for backpackers, it would be a convenient addition to campground living or traveling by canoe.

The other option, which may really make more sense but does translate into more work, is to make use of human energy instead of solar power.  There are literally dozens of hand cranked generator devices available now and they do not depend on sunshine.  While most are designed for cellphones, they can be adapted as battery chargers or as power sources for GPS systems.  I've included a couple of videos here to show how they work.  While it might not be the sort of thing you'd choose to do around the campfire in the evening, if you really need a couple of batteries charged it is possible to rig something up fairly easily.  This is something you need to do at home with a workbench and a soldering iron handy, not in a tent with nothing to work with but a Swiss Army Knife, but it's a very reasonable approach to emergency power. 

Actually, if I can find a pocket shortwave radio that isn't very heavy, I might rig one up myself.  With the weight I'd save by leaving extra batteries at home, I bet I could make room.  I could listen to the world news at night in comfort in my little tent, during the five minutes of consciousness I usually have before I fall asleep.