Watts, Amps, Volts and Solar AA Chargers

Could someone explain to me the relationship between a solar panel's rated watts and its ability to charge 4xAA Eneloops?

I have 2 portable solar battery chargers - the Powerfilm 6 panel, 4xAA, 2.2 watt, 3.6V, (assume that's 600 mah); and the Goal Zero Guide 10 Plus Adventure Kit, which has the Nomad 7 panels which the specs say put out 6 watt, 6V, 1.0A to the 4xAA Guide 10 Plus charger.

Now I've been testing both units side-by-side charging 4 Eneloops. The Eneloops have been discharged in a Maha C9000 prior to the solar charge, and then again after the solar charge to measure the charge capacity. After several attempts in admittedly less than perfect condtions (Dec/Jan, double pane windows, tree branches, etc.) it surprises me that the 6 watt Goal Zero can only muster around 60-80% of the charge that 2.2 watt Powerfilm can for any given length of time. FWIW, the solar collecting surface area between both units appears to be about the same.

Shouldn't the GZ be at least as efficient as the PF in any given light situation? Do you think the GZ would pull away and leave the PF in the dust in perfect sunlight conditions? Is there something wrong with the GZ (I'm thinking about returning it)?

Powerfilm is copper induim gallium selenide, which is a thin film that is best rated for low level light conditions. Its going to absorb lower light levels better since it is thin film. If you have overcast then a amorphous or CIGS panel will do best(only%10-%14 efficient). Its doing a better job of storing energy in lower light levels and this is why you are seeing the powerfilm charge quicker. The goal zero is by far better.

Goal Zero is a mono-crystalline thicker film panel. This is going to do best in direct sunlight to low over cast conditions. since it has a thicker wafer of silicon it can absorb a much higher number of photons. The wavelength capture is lower than a thin film but trades in efficiency(17-20%).

You are going to capture more energy in a mono-crystalline for sure but the guide 10 pack is sensitive is charging. If a cloud passes by when you are charging, then it will reset and restart from the beginning. Also the goal zero products need to be perpendicular to the sun to be most effective. So you have to follow the sun. As to the power film they can absorb just an ambient light source.

On my goal zero nomad 7 I can get 14.9V @ 1.3A from the 12V socket. [email protected] on USB. Then [email protected] on the supercharge port. This is when its 70F out in Arizona. You sould have an under performing panel setup from goal zero and you should takes some measurements.

You need to state :
Location
Weather
Temperature
In Arizona the sun is beating at least 1000W/m^2
The guide 10 doesn't like heat and the cells dont as well. Keep it shaded at all times.

Thanks for the comments ama230, much appreciated.

I'm near NYC and have been testing in Dec/Jan winter sun the weakest sun of the year. Generally it's 3 hrs, hung vertically, in a SE window in the AM, and then another 3 hrs moved to a SW window in the PM. Although I've had some perfectly clear days, my windows are double pane, and there're trees surrounding my house (bare branch shadowing). Looking a the Powerfilm FAQ efficiency chart as a guide, I'd guess that I'm getting at best 50% efficiency (double pane windows, angle to the sun, tree branch shadows). Unfortunately, other than a multi-meter and the C9000, I don't have the necessary tools to test output. I know what the Powerfilm can do, and am satisfied with it's capabilities, so I'm just trying to see if I can do equal or better with the side-by-side testing.

Based on your comments, it sounds like the GZ should catch-up, and then walk away from the PF if I can improve conditions, ie, cloudless day, direct summer sun, and maintaining perpendicular orientation. Unfortunately, I'm not so sure those are realistic charging conditions for me in the heavily-wooded, volatile-weathered Eastern part of the US.

Although my primary purpose is to charge AA Eneloops, I really do like the versatility of GZ (ie, 12V, 1A USB output, etc), but it is several times the weight and size of the PF. I would happily call it even, if the GZ charged AAs as well as the PF in less than perfect conditions. However, if this is just the nature of these two different solar panel types, then I'm going to have to return the GZ.


Anyone else have any experience with these two solar panels?

A thick window like yours is definitely going to cut down on performance a lot. Then again if you have the goal zero panel in moderate light it will do great. If you can get it outside somehow and not behind anything i promise that the goal zero will do better.

Its not as much work as it sounds to track the sun. In a good day you have to move a solar panel 3-5 times ad its being generous. Just have to make sure its facing in the general direction of the sun. The powerfilm you only have to move it twice at most during the day. The days when you have the sun beating down and need to have a set of batteries charged in 2hrs, its hard to find a wall charger to do this without ruining them.

In your case and conditions the powerfilm will do the best. GIGS is the best of the thin films so you aren't buying junk. I have always looked at the powerfilm 4aa charger and just went with the goal zero for the 12v option.

Got it ama230,

It sounds like it's worth trying side-by-side outside, and I'll lean it 45-degrees on plank, and TRY to move it several times w/the sun (really hate doing that part though). I do like the idea of the GZ's versatility and want to make it work. Happy to have both units for different purposes.

Btw, do you know anything about the Brunton Explorer with USB output? I also have one of those I got for $30 on a fire sale, but can't seem to find a single thing that it will charge or power (light blinks though) and I've tried both the Guide 10 charger as well as a Sanyo USB AA charger.

Off to evenly discharge 8 Eneloops and wait for a sunny day.

Thank you again ama230... the advice makes a lot of sense and is greatly appreciated.

The brunton as far as I know use poly crystalline panels and this is to cut corners on budget. This is a good indicator that the panel is not going to adequate at putting out more than 500mA(if even 400mA). I would say that its best suited for charging and ipod shuffle and any other small mp3 device. Maybe even a non-smart phone with it off and it might give it a charge but its the same procedure with a mono-crystalline (thick film panel)setup as you have to have it generally positioned toward the sun(direct light).

That's why windows and clouds are killing the work its producing. With the Powerfilm setup you are using a thin fim(CIGS) that is designed for diffused and works worse with direct sunlight as the sunlight(photons) can easily penetrate the silicon and thus not providing sufficient carriers(+proton) to the holes(-electrons),

If you really want a nice setup. I can sell you a 10 watt fordable mono panel that can charge two guide 10 pluses in 4-6 hours. Each USB port can supply up to 1.5A, which is enough to charge the ipad and charge and iphone at the same time as a wall charger. Its the same size as a nomad 7 but with an extra panel and higher efficiency panels(17%(GZ) Vs 20%(Mine)).

Another company to look at for stored power is Revolve electronics too as they have some nice stuff and a good deal on amazon. This will replace you wall charger for sure.

Glad to help too and if you have any other questions or queries please do not hesitate to fire away.

ama230,

Just wanted to get back to you after getting a chance to run a test outside... short answer is that you're right, the GZ well out performed the PF outside, even still in less than ideal conditions.

GZ - 1.41V, avg of 4 batts, 1756mA
PF - 1.36V, avg of 4 batts, 1068mA

Maha C9000 used to discharge before and after solar charge. Used older Eneloop 2000 mah, avg around 1850-1900 capacity.

Outside 9am - 3pm, repositioned 4 times, first and last 1.5 hrs sun below tree line, and first 3 hrs cloud covered, but still reasonably good sun - enough to shadow well.



So both are definitely going to be keepers with the PF the choice for lightweight backpacking (usually just emergency use anyway), and the GZ as the work horse for a variety of needs.

Really appreciate you explaining all that to me, I never would have guessed that each would perform so differently under different circumstances. Can't wait to test this under ideal summer sun.

Thanks again for the great advice.

Thanks for the kind comments and I also appreciate you taking in my advice. With alternative energy, you have to make do with what it can perform.

Glad you like both the solar setups as I love my goal zero stuff. It does take some work to get them to perform good but then again its like your stealing energy.

I found out that the goal zero guide 10 plus pack can take in about 700mA to charge the batteries. In conclusion I am able to charge two of them( holding 4 eneloops each) in less than 3hours and with less than ideal conditions with a 10watt panel(has two 1a usb ports). In ideal conditions I can charge in less than two hours as It beat the guide 10's supercharger port. I think the guide 10 pack can accept more than the .5A-.7A claims.

So for a 150 shipped I have a setup than can charge 8 aa/aaa in 2-3 hours and each pack can handle 1A out. I can live without the 12v as my goal zero does this.

I feel that its my responsibility to help ease the transition into alternative energies. Nice setup by the way and please tell others as the quicker it catches on the sooner we can advance.

ama230 said:

I feel that its my responsibility to help ease the transition into alternative energies. Nice setup by the way and please tell others as the quicker it catches on the sooner we can advance.

Click to expand...

Now this is a good point.... Perhaps my search skills are lacking, but when I was researching solar panels, I thought there was a surprising lack of information on solar chargers here at CPF. I come here for anything and everything battery/charger/flashlight related and have always found a ton more information than I could ever possibly digest..... except for solar (also as evidenced that you are the only person responding to this thread).

Really odd, cuz this stuff is getting really good now and definitely worth the money and time.

BTW, ran one more test from 10-2pm cloudless, about 3 hrs unobstructed by branches w/2 AAs in PF and 4 AAs in GZ

They all came in at about 1600ma.... I'm happy with that and the PF is just slightly better on a ma/lbs basis.

Just got the GoalZero Plus Nomad 7 kit from Costco(saved about 60 bucks). Included items:Nomad7 solar panel 12v car adapter, Luna Light, guide 10plus battery charger, 4 AA, 4 AAA and short USB to mini USB cable (aprox 10-12inches).
This is the second generation of the solar panel that puts out 5v @ 1000mah for the USB port to handle tablets.

Tried it out this morning on a bright and cloudless day in socal angled toward the sun (ie not flat). Charged a Ultrafire BRC 18650 3600mah batt from 3.29v to 4.18v starting at 9am until green light on charger @ 11:30am.
Used the 4sevens smart charger pluged into the USB port and placed in the shade to keep the batt &charger cool.

Cheers,
Lightsolo

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