How much silicon cell area you need depends on how much other junk you are carrying. OK, provocative and aggressive - but true.

I use a solar cell to recharge the batteries for my Steripen. Works great. LIGHT too.


Cheers

I have a LGX13 with a 9 cell battery. At the back of the pc it is written 20V.

Could anyone tell me whether the solar roll would do the job. I don't mind to charge it while walking all day. I expect to use the pc maybe 1 or 2 hours per day maximum.

Thanks for help!

Eugene, Hugo,

If you run your battery down by 20% or less a day, the Silva would be a candidate as far as power output goes, but the voltage makes it tough. I don't know of anything you can buy that would do the job. Sorry.

The only thing I can suggest is that you look for a computer that charges from 5 volts, or comes with a solar charger.

Edited by herman666 on 01/12/2010 11:20:24 MST.

Roger,

Do you happen to know the weight and full sun power output of your solar cell?

> Do you happen to know the weight and full sun power output of your solar cell?

Sorry, no. Never bothered measuring.

I found it was able to recharge the two Tenergy CR123R batteries I use with my Steripen in maybe 4 - 6 hours, depending on the sky, after I had treated two litres of water. That took 1 amp for 2*90 seconds.

So ... Steripen power consumption of 180 seconds at 1 amp draw at 6 V nominal: about 1,000 watt-seconds. Assume 50% recharge efficiency: 2,000 watt-seconds required. Spread that over 5 hours or 18,000 seconds: 0.11 watt output required (which is not all that much).

Assume 1 kW per squ metre sun power. The cell is about 0.13 m x 0.06 m or 0.0078 sq m. It should 'see' about 7.8 W under perfect conditions. Assume that the angle of the cell with respect to the sun, my movement, etc, gives 20% solar interception efficiency: about 1.56 W of sun power available. Assume a solar cell efficiency of about 7%: power output of 0.11 W. Matches requirement.

OK, the assumed efficiencies have been slightly fudged, but the numbers are quite realistic.

On the last trip I also used the same solar cell to recharge my mobile phone battery. I used the phone to ring ahead to Refuges a few times - I could have done just as well by taking one spare fully charged phone battery, but the weight of the adapter I made was extremely small.

This works for me. But I do not lug around all sorts of electronic devices when we are walking. I am quite capable of surviving without them - actually I don't own them anyhow. (Yeah - super-techie but no devices!). I have a log book - Rite in the Rain paper.

Cheers

The design goal of my Compact Solar Charger project was to be able to fully charge two AA 2500mAh NiMH batteries in a single day of sunlight. These AA batteries can then be used to keep a GPS charged indefinitely, a camera taking pictures, flashlight working etc.
My calculations showed that it requires about a 1.5 watt solar panel to generate the needed 5000mAh in one day.

Here is my MYOG charger


It uses high efficiency polycrystalline solar cells to keep the panel size small. Clam-shell design to protect the cells when jammed into a pack. The panel puts out (measured) 300mA at 5.5V in full sun. Just over 1.5W.

The unit weighs 5 oz and I usually carry 2 AA batteries (1 oz each) in the unit to rotate with run down batteries.

Nice for thru hikes where you want to power small electronics like GPS or camera indefinitely.

Keith,

I see that the Solio Mag puts out 5-12V. It also has 12V car jack adapter. This seems like it'd be a workable combination with my Fujitsu u820 and its car charger.

Just a comment about some of those large folding commercial solar cell arrangements sold to hang on the back of packs.

In a nutshell, they are useless.

OK, a bold statement, especially considering I carry a solar cell myself sometimes. So Why?

Because hanging the solar cell **down the back of the pack** is stupid. Where's the sun? Up in the sky for most of the day, not down on the horizon. Anyhow, for at least half the time the hanging cells will be in the shade because (on average) half the time you will be facing more towards the sun.

The most viable place is on top of your pack. There is has the best chance of seeing some direct sunlight - and you need direct sunlight to make a solar cell give any significant power output.

Cheers

I am having a real problem with all of this. After all, this is a lightweight backpacking forum. I don't understand why anyone would need a system to recharge electrical equipment, or why they even need the electrical equipment. Okay... I confess I do carry a digital camera most of the time, but along with a spare battery weighing .6 oz I can take 1,000s of pictures. No need to charge this. The .6 oz spare battery is going to be lighter than any charger and take up less room.

Now I am a solar advocate. My tent trailer has a system that I have invested close to $2,000 in. But this type of camping is not UL backpacking.

My 2 cents and I am sure it will bring out the ire of many folks. Sorry for that. We have people thru hiking the PCT, CDT, and AT each year without solar systems. Most of us aren't going to make any of these 3 trips in the near future.

If you need electronics so you don't get lost, then perhaps a comprehensive map and compass course is a solution. I think BPL even teaches this in some of their offerings.

> The most viable place is on top of your pack.
> There is has the best chance of seeing some direct sunlight

Hi Roger,

While agree with your statement that the top of the pack is the best place, the amorphous silicon cells used in the roll up solar chargers are remarkably good at working in diffuse light. Their big drawback is amorphous cells are notoriously low efficiency, requiring much larger surface area.

I looked up the output of the charger hanging down the back of the pack. It is 3.6 V at 400mA which is 1.4W in full sun.

I think solar charger is a good discussion to have on this forum, because some of our lightweight solutions, such as Steripen, are battery powered devices.

Laptops are too power hungry and solar is too inefficient to provide a light weight charging solution today. I just carry a spare high capacity battery and use the laptop (actually a lower power consumption netbook) when I am backpacking (yes I backpack with a netbook for research purposes). With the main and spare battery I can get about 15 - 17 hours of use or about a week in the back country. I use a solar charging station (40W solar panel, controller, deep cycle battery, inverter)to charge the netbook when I get back to base camp. Works great. The base station charges during the day and I can draw off the stored power from the battery at night through the inverter.

There is a solar powered notebook but it makes some serious compromises in computing power to keep power consumption to a minimum.

Al, where did you get that clamshell solar panel?

Hi Al

> I looked up the output of the charger hanging down the back of the pack. It
> is 3.6 V at 400mA which is 1.4W in full sun.

I would want to see that verified by someone other than the vendor.

I have no problem with the power rating quoted when the pack is lying down on the ground and the panel is horizontal, but I have extreme doubts as to whether one would get a fraction of that hanging from the back of a pack while walking. Of course, I may be wrong ...

Cheers

Hi Nick

> I don't understand why anyone would need a system to recharge electrical
> equipment, or why they even need the electrical equipment.

Well, actually, I tend to agree with you!

I carried the solar panel in France and Switzerland for two reasons: we were away for 2 - 3 months straight, and I knew that the small towns we did pass through would not carry the CR123 cells. A few carried AA alkalines, but that was all.

Cheers

> Al, where did you get that clamshell solar panel?

I got it a few years ago on clearance when I was doing a bunch of solar charger MYOG experiments. I gutted the insides and kept the panels and clamshell to make the AA battery charger.

There are a number of similar products available today. A quick web search turned up this clamshell solar panel of about the same physical size and wattage.

http://usb.brando.com/prod_detail.php?prod_id=00304

> I don't understand why anyone would need a system to
> recharge electrical equipment, or why they even need the
> electrical equipment. Okay... I confess I do carry a
> digital camera most of the time

Hi Nick,

It is hard to find someone who doesn't take at least one electrical device with them no matter how SUL -- a flashlight. But your point about needing a recharger vs. a spare battery is valid and a common reply on this thread.

But given that someone asks about solar chargers for a thru hike, it seems reasonable for the folks on this forum to discuss/show lightweight alternatives he may wish to consider.

While bike touring in Europe for 2 months this past summer, I used a SolarMio 31 folding panel. It only has a USB output, but it turns out this is useful for a lot of things. I found a very light 2-AA/AAA USB charger, and a tiny USB->1/8" adapter for my iPod Shuffle, a mini self-coiling cable for my iPhone, and (this was really cool) a universal USB lithium-ion battery charger that charged my camera battery. All these charger / adapters fit inside the tiny mesh webbing on the solar panel. I also brought a mini AC-USB adapter for backup when passing through locales with power.

In the heat of the Italian mid-summer sun, it worked quite well at most these tasks. However, it wasn't up to maintaining my iPhone battery. Even though the unit has an internal battery that can be fully charged, it still isn't enough wattage to start charging a completely dead iPhone.

If I do something like this again, I'll probably spring for a folding 12-watt Sunlinq panel. They actually fold up quite small and light, only a bit larger than a wallet, but unfold with huge surface area. Enough power to do all those kinds of tasks even in poor weather in the off-season. Probably even off the back of a backpack in the shade.

I would also make a DIY supercapacitor to store the charge (supercapacitors are much lighter than batteries and last forever - storage capacity is of course lower).

"In a nutshell, they are useless."

Roger, Orientation has to do with time of day, direction of hike, time of year and cloud cover. Sometimes hanging down the back of the pack is fine.

That said, there's no law that says they have to be hung that way. I keep mine moving for best angle. It's often strapped to my sleeping pad roll across the top of my pack, but not always.

I've been very satisfied with my folding panel charger. It's very light. It keeps all my electrics charged which in my definition of the term at least, is useful.

Edited by herman666 on 01/14/2010 08:27:49 MST.

@Keith,

I have noticed over the years that, as a conversational "style" thing, those from Commonwealth coutries tend to make dramatic-sounding pronouncements as if from authority as a way of emphasizing their opinions. In similar situations an American tends to be much more subdued. (Probably because if an American encounters another American who disagrees strongly enough, he may get shot. :o)

That said, Roger probably CAN speak with some authority about almost any trivial electronic device. Still, I'm also quite certain that he doesn't mean to be as brash as he sounds to American ears. (Otherwise I would pounce on him regularly.)

FYI.

Or, just about anything else that isn't needed when hiking? Well, I think much of the time the answer is that some of us are going not just solely for the hike. Other activities are involved, and sometimes are the primary activity. I recently went and the sole purpose was to shoot some film for a little home movie I'm making. I managed to only take 3.5 lbs of extra equipment, but that wasn't really adequate. Next time it will be more.

Sometimes, some of us are combining other hobbies with backpacking. :^)