Solar solution to recharge laptop, please help.

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.

@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. :^)

From what I recall(looked in to this a while ago) hand crank chargers are cheaper and more efficient. They also give you something to do in your tent.

I looked into hand crank chargers extensively and I really wanted them to be the answer. Unfortunately, they just don't put out enough power for much of anything. The commercially available ones put out enough juice so that 10 minutes of cranking gives you 1-2 minutes of talk time on a cellphone. What they don't tell you is that as soon as you put a load on them (cellphone battery), they get HARD to crank. If you can actually do 10 minutes of hand cranking on one of those things without grasping your wrist / elbow in pain or running out of breath, I'd be very surprised.

And of course, the question is about charging a laptop – no way. Way too hard.

Treadle power looks more interesting (your legs are a lot stronger than your arms, and treadles seem to be more efficiently designed) but the so-called portable units are still huge and very heavy.

I have thought about making a flexible solar charger using something like this. Weight is .8oz but even after you add a cable & voltage regulator it should be quite light. A non flexible crystalline cell would be almost 2x the efficiency but I would have to build a frame to keep it from breaking.

Bradley, that's good to know thanks for the info. I guess there's a market for everything hand cranks are as cheap as 15 bucks (now I know why) while solar can get quite expensive. It would be nice to have a cool solution in place. But personally I like getting away from technology. The only technological comfort I need out there is the cold sidearm resting next to me :)

Hugo, Just a thought… I reread your initial post and noticed you're bringing your laptop for mostly gps mapping software. For the cost of the solar and charger etc. could it not prove to be more cost/weight effective to just get a different GPS system that includes that in its list of features? Then you can just bring extra batteries.

It's just not sounding like charging up a laptop battery is very practical.

I was hiking along a trail one time, and I came up behind another hiker who had some apparatus hanging over his pack. I glanced at it and couldn't figure out what it was, so I asked, and the other hiker told me.

It was a Pelton Wheel. This was a very small-scale hydro turbine generator. This guy knew exactly where he was going to camp by a roaring stream, and he knew exactly where he was going to place the Pelton Wheel, and he had a good idea how many watts it was going to generate. I don't think he was going to run a toaster on it, but he had some ideas with lights and stuff.

The Pelton hiker and I parted ways at the next trail junction, so I never got to see it work. You think a crank or a PV panel are impractical, just go put up your own Pelton Wheel.
–B.G.–

I use this model:
http://store.sundancesolar.com/pow15v100maf.html

to charge this:
http://www.sparkfun.com/commerce/product_info.php?products_id=8484

via this:
http://www.sparkfun.com/commerce/product_info.php?products_id=726

I'm going to be using this setup to maintain my iphone for an upcoming thru hike of the Arizona trail. The panel is overkill in terms of voltage and I regulate it with a 5v regulator but the benefit is that it charges the battery with even the slightest ambient light.

Hi Dean

Yeah, I have that problem. Sorry about that.

But I don't mind if someone wants to contradict me bluntly – it's a free world. I might even be wrong (utterly unlikely of course, but let's not be too dogmatic about it :-) )

About all I can say is that when I do sound like that, I have usually,/i> spent some time checking my facts. Nothing worse than having to eat one's words later :-)

Cheers

"But I don't mind if someone wants to contradict me bluntly – it's a free world. I might even be wrong (utterly unlikely of course, but let's not be too dogmatic about it :-) ) "

Remember, on the Internet, nobody knows that you are a dog.

–B.G.–

Brady how flexible is the encapsulated film cell? I may make a phone charger for bike trips. Hanging it lengthwise on my Camelback would work well for sun position since my back is closer to parallel than it would be hiking.

FYI the SUL backpackers have nothing on the weight freaks over at rcgroups.com :) Can you imagine sub 10g for a solar powered RC plane or non solar planes in the 200-500mg range!

Bender,
It's very flexible, however I have since bought this panel for my wife's charger:
http://www.sparkfun.com/commerce/product_info.php?products_id=7845
and its performance in our particular application is better than the larger panel. Its cheaper too! And plug and play with our charging circuit (no voltage regulator needed).

I just ordered (3) of these:
http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=12269
which I will wire up in series to max out my charger (300mA). I'll report back when I've done some testing.