Solar Panels??

[Mark Ryan]

Anyone with experience using these? Looking to get one of these for next season.

[Bob Gross]

I have experience with big ones, but I suspect that you are looking for something small. Some of the small ones are OK, but their output wattage is so low that you have to spend a lot of sun time trying to recharge some ordinary batteries. Medium size flexible ones that roll up are better, but they weigh more. Before you start looking, you need to have a firm grasp on the power you need for portable devices.

–B.G.–

[Mark Ryan]

Bob-

Using it for an iPhone or iPod.

[EndoftheTrail]

I think they are more useful in a base camp type set up where the solar charger can sit for hours under the sun — without shade and without risk of theft. OTOH, if you are thinking about hanging the charger off your backpack while you hike — that will be very much suboptimal. Also, as "sexy" as solar charging might be, methinks rechargeable batteries are the way to go for all but the longest trips.

[Bob Gross]

You will need to know how much power you need for an iPhone or iPod.

That means volts and amperage, and for how much time per day.

–B.G.–

[Bob Gross]

I agree with Ben. You can use a small solar charger hung off the back of your backpack if you are headed north. However, few have much power output, so you might have to "solar charge" for lots of hours to power up some load for a very short period. The places where the medium size ones work best is someplace like Everest Base Camp where you carry it in once and set it up, then use it a lot for a month or more, then roll it up and carry it out once.

A few replacement batteries might end up weighing a lot less, and would be less prone to theft, breakage, or cloudy weather.

–B.G.–

[Ceph Lotus]

Can you charge up the IPhone through a USB port? I know of a flashlight (with a hand crank) that can charge up USB devices. It also has a solar cell, but the USB charging is done through the hand crank part.

[Kendall Clement]

My understanding about solar chargers is that they don't require direct sunlight to work properly. Charging them during daylight hours is sufficient. Does anyone have any other info regarding what I've read about them?

[Bob Gross]

You can get up to 50% more output from a solar panel if you have it aimed directly at the bright sun. Exactly how the aiming helps depends on the latitude where you are operating.

They will continue to function a little if they are out in a cloudy-bright day, or if they are aimed off-axis. However, a little bit of output might or might not be sufficient for some loads.

–B.G.–

[Kendall Clement]

Bob,

Wouldn't that also depend on how long you have it hanging from your pack? 8 to 10 hours of hiking for instance?

[Bob Gross]

"Wouldn't that also depend on how long you have it hanging from your pack? 8 to 10 hours of hiking for instance?"

Wouldn't what depend on how long?

The number of watt-hours of output you get from a solar panel will obviously be increased for the number of hours of light it gets.

However, if you run a typical solar panel at a dim light level, sometimes you won't get its output voltage high enough to _start_ driving the load. You can put a DC-DC converter between the solar panel and your load, and sometimes it can convert voltages to make the load run, but that is an extra level of complication that some users won't want to delve into.

The way to start determining your power needs are at the load would be to look at the normal household charger that the load can use. If the output of that charger is 5 volts at 100 milliamperes, that is 0.5 watts. If you normally need to use that charger for ten hours to charge the device up, then that is 5 watt-hours. So, you would likely need something in the ballpark of 5 watt-hours out of your solar panel to charge the device similarly.

–B.G.–

[Kendall Clement]

Bob,

I believe I have interpreted your response correctly. And, I appreciate the explanation, but just to be certain I understand or anyone else reading this, could you restate that in non-technical terms, please?

[Bob Gross]

OK, let me try again. Let's say that you have one flashlight that you want to recharge along the trail, and it has an ordinary home-style charger that you use when you have AC power. Let's say that the home-style charger is marked with its output specs: "5 Volts, 100 milliamperes." That means it puts out (Voltage in volts times Current in amperes) 5×0.1=0.5 watts output power. If you use that charger to charge up your flashlight for 1 hour (and if that gets it done), then that is 0.5 watt-hour that is required. It it is ten hours, then that would be 5 watt-hours that is required. So, the first step is to find the normal charge rate that your flashlight device expects. Your own numbers might be quite different.

If you have a solar panel, it also has output specs in watt-hours that may be similar to the home charger. If those specs are similar, then the solar panel should be able to charge the flashlight in a similar time as the home charger.

My experience with small solar panels is that the manufacturers seldom advertise a full set of specs. If they do (rare), they advertise specs for "full sun." Your guess is as good as mine as to what that means. I guess it means something like full, direct, Southern California sun at noontime. As you get away from noontime by a few hours, often the sun intensity falls off dramatically. Also, as you get clouds in the sky, it falls off dramatically. With some solar panels, a small shadow across the panel will ruin its output significantly, and that could be from something as dinky as a pack strap hanging across it. In defense of the manufacturers, I will say that they don't really know how good the user will be at keeping the solar panel oriented or at keeping it in good sun, so they just omit a few specs to protect themselves.

Also, there is the sun angle. If you were located on the Equator, the sun would pass almost directly over your head at noon, so you would want to have your solar panel relatively flat to the Earth to collect that good noon sun. If you were at the North Pole, the sun would not be anywhere near overhead. Instead, it would be lower toward the horizon, so you would need to point the solar panel much lower. I remember that the correct angle is Latitude (degrees)+ 23 degrees for optimal winter operation in the Northern Hemisphere. For summer, I don't remember, but it is less.

–B.G.–

[Jason G]

T

[Peter Pancake]

Hi Kendall,

What he means is that if the voltage output of the cells is too low (e.g. 2 volts) it won't be enough to even charge your iPhone battery at all (because it will only 'accept' a voltage input of e.g. 2.8 to 3.2 Volts)

So that if the cells are tilted (i.e. not-perpendicular to sunlight) it is possible for sunlight to be shining on the cells all day, yet still do no charging whatsoever, just converting to heat

Bob notes that it's possible to put a converter between the cells and the iPhone to step the voltage up from 2V to 3V (or down from 12V to 3V..) of course with a corresponding reduction/increase in current

I think this issue only matters if you are going make a home-made setup (using a large 12V/20W panel or so) and not the little 'solar chargers' floating around on eBay (which charge a battery inside them, and then after a few hours can be used to charge an iPhone or similar)

[Bob Gross]

(wow, my text got cut off)

[Bob Gross]

Jason, here are some specs from yours:

– Solar panel: 5.5v, 80mA

– High capacity build in polymer battery: 1350mAh

– Output voltage: 5.5V

– Output current: 500-1000mA

– Estimate Charging time when under sunlight : 10-15 hrs

– When under USB : 5 hrs

That 5.5 volt number is probably a maximum number. If the battery gets low, you might get a lot less voltage than that, which might or might not be good for your device to be charged.

Jason, it sounds like your solar panel thing was on your front, hanging by the shoulder straps, as you walked south. What if you hit cloudy weather for a week?

–B.G.–

[Peter Pancake]

Oops, didn't read the 2 fresh posts above mine before posting. Good posts

Yes, if you get a rather large panel for the purpose of charging (say 12V or more) you'll need to do some work to get it functioning (matching the voltage, orientating it correctly, preventing shading, etc.) as Bob recommends

With Jason's charger it should generally be a 'set and forget' system where it charges the internal battery, and whenever your iPhone needs to be charged it will be charged from that battery

Bob (2), is "High capacity build in polymer battery" some kind of slang for just 'lithium battery'?! :-D
I'd say if we expected cloudy weather, or being exposed to direct sunlight only a small %age of the time, one should go with an amorphous charger (browny coloured cells) which absorb diffuse light much stronger than polycrystalline (which appears to be on Jason's charger)

Yeah, if the voltage drops below around 4(?)V it may not charge the battery at all, but it may collect enough residual charge throughout a cloudy day such that energy collected is greater than the energy used by the iPhone – esepcially if the charger is hanging around all day every day for a few days..

Have to admit I don't own an iPhone or one of those solar chargers, but it would be fun to take one apart and see the voltage / charge rate for different lighting conditions (especially when there's one claiming over 15% efficiency on australian eBay!!!)

[Bob Gross]

"Bob (2), is "High capacity build in polymer battery" some kind of slang for just 'lithium battery'?! :-D"

Peter, I believe that you have deciphered market-speak.

"I'd say if we expected cloudy weather, or being exposed to direct sunlight only a small %age of the time, one should go with an amorphous charger (browny coloured cells) which absorb diffuse light much stronger than polycrystalline (which appears to be on Jason's charger)"

Amorphous silicon solar panels are cheaper to buy, and the output tends to be somewhat lower than crystalline solar panels. So, if you are serious about performance, you go with crystalline. If you are serious about costs, then you go with amorphous. I've been running a (big, heavy) Siemens 75-watt crystalline panel for about ten years, but I would never carry it anyplace.

Specifically, the open circuit voltage might be 15 volts on amorphous, and it might be 17 volts on crystalline. That won't seem like a big deal to some people, but with certain loads, it is a big deal.

–B.G.–

[Kendall Clement]

Thanks a bunch guys. I get now. :)

[Dug Shelby]

I've been researching this for several months myself. This is what I've found, ymmv:

Solio makes a little charger that actually has a caribiner top, intended to be clipped onto a backpack/etc. It's called the "Rocster." reviews vary but shown to be solid. Fairly light for what it is. Charge it for a day for one iPhone recharge.

Solio also makes a more efficient (yet slightly heavier by a few ounces) three panel fan shaped charger. Slightly more expensive, but more solar area for a quicker sun charge. Spoken with several people who have used this particular model strapped to the back of their pack the length of the PCT, JMT, CDT, and AT. One said it wasn't much help in parts OR, most of WA, but still worked ok, just not as well as through CA, fwiw. One was sold last month in the Gear Swap as a matter of fact.

Brunton makes two options viable for backcountry use: the heavier, more powerful option weighs just under 16 ounces and can be juiced up primarily by wall socket or car adapter. Said to hold 7-10 recharges for an iPhone. Costs approximately $175.

The smaller Brunton device weighs 5.5 ounces, costs $44, and charges up the same way as the larger Brunton. It holds approximately 3 to 4 complete iPhone recharges. In addition, it can be used in conjuction with a portable solar powered charger ( such as the Solios) to be recharged itself.

Not sure how far or for how long you'd be off the power grid, but a combo of the smaller Brunton along with either Solio would do you alright.

Alot of cool technical jargon being flung about, but the reviews back up the Brunton claims spot on, and they even break it down between iPhone recharges and other device recharges. Even if cloudy, hiking 10 hours will give you more juice than no juice. iPhones have yet to accept AA batteries. :)

Hope that helped a little, happy solar trails!

Dug
http://thf2.wordpress.com/2011-pct-gear-list/

[Kendall Clement]

I just purchased the Solio Classic (3 panel fan) here on Gear Swap and paid about 40% of the retail price for it. The product description looked pretty good to me when I checked their website. The price was good. If it doesn't work as well as Solio claims I'll just put it up on Ebay. Had to look at the product comparisons to get all the info. It weighs about 5.6 oz.

[Mike W]

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[Mike W]

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[James Marco]

I looked at these pretty hard several years ago. They have some strong advantages to backpackers. But the energy density availible through sunlight on a small surface simply is not enough to warent the extra weight. As was said, they can work to keep a set of batteries partially charged. I have a smaller one that came with the Setripen Adventuror Kit. It takes a couple days to get two uses out of a set of batteries. I tried it, it doesn't work all that well. They cannot even maintain enough power to generate the water I needed.

Here in NY, I normally hike through heavy tree cover. Even with the larger sized panels offered by Brunton, it would take about five days to a week to charge a pair of AA batteries. The trade off in weight simply isn't worth it, to me. Like Mike was saying, in my area, I would choose a battery pack over a solar charger. The spare batteries will deliver a lot more wallop over a couple weeks than the solar panels for the weight.

That said, for LONG TERM applications, as was mentioned, they can make sense.

[Author]

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