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Does anyone know of any solar-powered systems with enough output to charge the average DSLR battery?
I'm considering going to somewhere rather remote and might be away from mains electricity (or even portable generators) for two or three weeks. I have considered taking a film camera and making do with that, but would rather take my digital gear. The cameras I'd be looking to charge are a Nikon D200 and a Canon S90.
Check out the FreeLoader from Solar Technologies in the UK.
I bought the Freeloader Pro online last year, and it's worked okay for me so far, charging the Li-ion "brick" battery for my Canon 350D, although I admit I haven't actually used it that much. Comes with adaptors for different models of mobile phone too.
You can do it; Thom Hogan has a detailed explanation of his solar charging setup.
As D. Lambert says though, it might still be more economical to just take a bunch of batteries. For example, I get 500-1000 frames out of my D90 on one charge in decent weather, so two batteries is more than enough for a week -- and at this rate, one battery corresponds to roughly 15-25 rolls of film. How many rolls of film would you realistically take with you? (The place where this breaks down, of course, is that you don't know exactly how many frames are left on the battery.)
It sort of depends on what sort of charger you can find for your camera batteries, I think. Most popular cameras have aftermarket chargers that'll work with a 12V power supply (a car outlet, for example), but that's a pretty big solar panel. The smaller panels generally put out enough juice to power a USB device, which is 5V.
I considered the same thing, as I take my camera on camping trips for up to two weeks. At this point, though, it's a whole lot easier and more cost-effective to just buy a bunch of batteries. Easier to carry, too, if you're talking about one of the big solar units. If I had other stuff to charge, too (GPS, etc.), I might swing back toward the solar panel solution.
A 7.4 volt lithium ion battery having 860 mAh (my Canon 2000D uses this kind of battery) has 6.36 watt hours of energy. Even after the various voltage conversion and charging losses, charging it won't take more than 10 watts if done in an hour, or 5 watts if done in two hours.
Sun provides 1000 watts / square meter, of which a solar cell can capture perhaps 16% or 160 watts per square meter. For 10 watts, sqrt(10/160) = 0.25, so for 10 watts, 25 cm x 25 cm solar panel will be enough if its normal is facing the sun. At an unoptimal angle, let's say 35 cm x 35 cm will be enough.
For 5 watts, it will be about 18 cm x 18 cm at an optimal angle, or let's say 25 cm x 25 cm at an unoptimal angle.
For my tastes, these chargers are way too large. Not only that, but you get only part of the output when it's cloudy. The 1000 watts per square meter applies only when not cloudy.
I guess you could include let's say 4 solar cells in a foldable system. Then each cell could be small, and you could fold it to an opened form to cover the required area.
Also, very slow charging could perhaps work. The trouble is, most lithium ion batteries are designed to be charged at a rather fast rate. The battery may degrade if you are charging it at an unoptimally slow rate.
Also, unless you can find a charger that accepts DC voltage from the solar panels, you would need a small inverter to convert solar cell voltage to 120-230 volts. That would mean some extra weight and an additional component to carry around.
Buy few extra batteries instead, and if using DSLR, use the viewfinder and turn off the LCD to save the battery from exhausting.
Somebody proposed hand-crank, would that be a good idea? No! Most batteries are not designed to be quick charged, so you would need to crank continuously for at least an hour. My hands would become tired from that. A foot-crank system (similar to a bicycle) would be too heavy to carry around.
Fortunately, typically the supplied charger accepts 120-230 volts of voltage, works anywhere in the world, and usually you won't be out of reach of electricity for multiple days continuously.
AA batteries are your savior here. I use the previous version of this one: http://www.siliconsolar.com/solar-battery-charger-aa-aaa-c-and-d-p-135.html
It takes 6 hours to charge a set of 4 AAs, the docs say less but maybe this didn't test on 2700 mah as I use.
There are two ways to get AAs into your DSLR, either by a Pentax K-x which is an entry-level DSLR with excellent image quality in a light body. You can also often get a battery-grip which takes AAs but that means more weight. BTW, the K-x can take 1100 on 4 AAs! You can also go to a bulk store and by 20 AAs for $20, that's 5500 photos!
