A very basic understanding of solar panels is pretty easy to get your head around. Sunlight is required for photo-voltaic cells to convert one form of energy to another (radiant energy to electricity). Bigger is (usually) better. They are less effective on grey days so a UK backpacker is pushing it to rely on these. Most important- there is almost always a more effective, quicker, lighter and more reliable method of charging electronic devices. But hey, who doesn’t want to save the world and get off-grid?
Three Points of the Compass first dipped a toe into the uncertain morass that is solar charger land in 2010. The Solio Solar Charger that I used for a couple of years following that was OK’ish, but only on the sunniest of days and I eventually gave up on it for anything UK based. It worked far better overseas in more reliably sunnier climes and at 156g was also pretty heavy. Once I added in all the various leads and jacks (there was nothing universal about phone ports back then) and a mains adapter to charge the Solio’s built in battery from a wall plug, it all totalled 580g.
We have all desperately been waiting for the necessary improvements in this technology. It has to come. Are we there yet? I think not, but we are getting there.
“…ignore anything the manufacturers and sellers tell you. It isn’t true”
I am not going to go into anything in great detail here. This is just a brief glance at three smaller solar panels. There are many other solar panels available, mostly monocrystalline, or the cheaper to make and less efficient polycrystalline. There is also a thin-film type that I have no experience of, that hasn’t, as far as I can see, made serious inroads into backpacking land. Many solar panels you will find are either tiny, perhaps set into the side of a powerbank so therefore too small to catch much sun. Or large folding set-ups with many panels that really are pretty hefty. Certainly too heavy for my liking. The three solar panels I have are amongst the best options for serious consideration for lightweight backpacking purposes.
Output from panels from different manufacturers can vary incredibly and it is almost pointless to believe any given statistics. So, the first thing to remember is to ignore anything the manufacturers and sellers tell you. It isn’t true. They are either quoting optimum conditions, never realised in real life, or they are lying. Some large folding solar panels are actually pretty good, but as said, they are heavy in the extreme and also very bulky. The three I have are all pretty small and light, ranging from 93g-223g.
Orientation of a solar panel to the sun is pretty much crucial. It needs to face it, or nigh on. Anything that can affect the efficiency of a solar panel, will- shade from trees or clouds, a less optimum panel aspect in relation to the sun, poor circuitry, poor connectors, high resistance from a cable (the longer the cable, the more power is lost). Add all these little drops in performance together and an already modest output can drop to almost nothing, or nothing. It is for this reason that most backpackers might briefly consider or experiment with a solar system, only to quickly abandon it as being impractical.
What I show below is not particularly scientific, not by any means. It is purely to offer a suggestion of potential. On a sunny day with clear blue sky, in mid July in the UK, Three Points of the Compass took three solar panels out onto the grass, lay them flat on the ground, plugged each in turn into a power bank with a USB power tester between the two and compared the output from each. A reading was taken having waited five minutes for things to settle down and become consistent. Note that solar panels were not oriented to directly face the sun so were sub-optimum, but my three readings are now directly comparable to each other.
Lixada (model L1613)
This is advertised as a ’10w 6.8v solar panel with 1700mA output, with a photoelectric conversion rate of 20-23%, giving a USB output of 5v 1200mA (or 1.2A)’.
It is a rigid monocrystalline panel measuring 230mm x 145mm x 2mm with a charge port that protrudes 7mm from the back. It weighs 93g despite still being advertised as weighing 80g. That lower weight was close to the weight of an earlier version, now no longer available. The grams increased when the panel was beefed up a little to the present incarnation. There is not a lot to this panel- a rigid sheet containing the silicone crystalline structure, a few holes that would enable it to be clipped into a lever arch file and a square USB outlet on the rear. It comes supplied with suckers to attach it to a window, obviously these are of no use for backpacking.
The single USB 2.1 connector mounted on one side of the back is, in common with the others looked at here, open to the elements, but is given an IP65 protection rating. The holes in the panel enable it to be fastened to the top of a pack with carabiners or have cordage/bungy cord passed through to lash it down.
Duragadget (model- 1882-275).
This is advertised as a- ‘5w 5v solar panel with 1000mA output’, which, again, is a nonsense. It measures 250mm x 190mm x 0.75mm with metal ringed holes at the edges 3mm thick and a charge port that protrudes 14mm. Despite being advertised as weighing 250g, it tips the scales at 161g. The only panel to weigh less than advertised.
This is another rigid monocrystalline panel quite similar to the Lixada one. The five metal ringed holes around its edges may add to the weight but do enable it to be fastened to the top of a pack. A USB outlet is centrally mounted on it’s back. When purchased it comes with two carabiners for fastening it to ‘something’ such as a pack. I immediately disposed of these as they are quite large and poor quality. A short USB-A/Micro USB cable is also provided, a better cable reduces resistance and improves, very slightly, performance.
As with the Lixada, the single USB port is open to the elements. These smaller solar panels are not the most sturdy of products. Which is fine as long as they work. Solar panels have to be mollycoddled a little. But by looking after these products and being careful, a more minimalist panel such as the Lixada and Duragadget can be considered and weight and bulk is reduced a little as a result. Keep it simple, that’s what I say.
Link Solar (model- LS-11.0 (0.5))
This is advertised as an ’11w 6.5v solar panel with USB output of 5.5v, 0-2.1A’. At least Link Solar do add that an 11W output is “peak power” unlike other manufacturers who give the impression high outputs are easily achievable. When open the panel measures 314mm (with a charge port that adds a further 50mm) x 245mm x 1mm. It is roughly twice the size of the little Lixada panel when open and about the same size when closed. The small charging port is 14mm thick. Manufacturer stats have it weighing 198g, this is wildly incorrect as it tips the scales significantly heavier at 223g.
The Link Solar panel is a very well made quality product. Unlike my other two panels, the Link Solar panel has an ETFE (Ethylene Tetrafluoroethylene) laminate with SunPower solar cells. It simply looks and feels the better product. There are four holes, one at each corner so that it can be fastened to the top of a pack. In depth manufacturer efficiency stats and construction can be difficult to tie down for this solar panel but one source suggests efficiency as being >23% which, again, points at monocrystalline, though I would suggest this should more properly be <23%. It folds neatly and the single USB outlet block also acts as the closure mechanism, a small magnet keeps the two folded halves closed. Despite being a foldable panel it is not particularly bulky. I find the manufacturers website complicated to navigate and it could do with a bit of work and some information being added for international customers.
Voltage is what ‘pushes’ a charge into a device. The voltage output of a charger, solar panel or power bank, should be equal to the voltage input requirements of a device (headlamp, phone, power bank etc.). My NB10000 specifies 5v, so with voltages from the three panels varying from 4.63 to 4.74 all panels are just about there. The voltage reader may actually account for the loss shown. The least I would want to be seeing is around 4.2v. What do these three readings tell me? – not a great deal but what there is, is quite interesting.
I am sure you know, but if you don’t- Watts (W ) = Amps (A) x Volts (v)
Lixada= 0.32A x 4.62v = 1.48W (so 63g/W)
Duragadget = 0.61A x 4.66v = 2.84W (so 57g/W)
Link Solar = 1.28A x 4.74v = 6.07W (so 37g/W)
Note that the Lixada is advertised as a 10W solar panel. I got 1.48W. Quite a difference. If I tilted the panel to directly face the sun then I was able to briefly realise 4.6W, but that is optimum, not real world. In the real world I might have had improved readings at another time, or on another day, or less so on a greyer day.
Despite hours of sunlight being from dawn to dusk, the actual optimum period during which a solar panel works with a heightened degree of efficiency is quite small, from around 11.00-14.00, with less efficiency outside that ‘solar window’. Three hours, not a great amount. A panel will still work to a degree outside those hours, just less effectively. Perhaps more important than this is the orientation of panel to sun. As I mentioned above, none of these readings were taken from panels facing the sun, they were flat on their back on the ground, at perhaps fifteen degrees away from optimum. Who has time when hiking to orientate a solar panel to the sun? No-one. Though a panel could be correctly oriented by hand at a mid-day lunch halt. Hanging from the back of a pack while hiking is no use either. There is no way that a panel is pointing anywhere near toward the sun if it is hung vertically. Best thing to do is strap as near to horizontal across the top of a pack so that it is as close as possible to correct orientation when the ‘solar window’ is at its height.
The unfortunate fact of relying on a solar charger to charge electronic devices such as a phone while backpacking is that a solar panel does not do away with the requirement to pack along a battery power bank. Phones just don’t like solar chargers, particularly the smaller solar panels that a backpacker may consider. A phone’s circuitry may not recognise them and altering, unregulated, rates of charge can cause a phone to switch on/off/on or simply stop charging, perhaps unknown if it is sitting six inches behind your head while hiking. Also, a phone screen coming on/off/on while charging can actually use more power than is being received. Charging via a solar panel is a slow and lengthy process. Power banks are more forgiving to being charged by a solar panel. The most to hope for is possibly reducing the size (weight) of the power bank carried. Three Points of the Compass tends to favour the Nitecore NB10000 power bank when backpacking but something smaller and lighter, such as Nitecore’s minimal F21i, which is based around a 21700 series battery, could also be pretty effective.
My Nitecore NB10000 power bank holds 38.5 W/h. My understanding of this is that if I want to fully charge it from empty, it requires inputting at a rate of 38.5 watts for one hour (which isn’t going to happen), or 1 watt for 38.5 hours, or 2 watts for 19.25 hours and so on. So the Link Solar panel, if the rate shown here were sustained, would take around six and a half hours to fully charge the NB10000, while the Lixada would take twenty-six hours and the Duragadget thirteen and a half. It is possible to calculate a three hour ‘solar window’ expectation of mAh from each panel with these figures. There will obviously be an additional power conversion achieved in the many hours bracketing this, just to a lesser degree.
This is really stretching the math now, but for three hours with each panel at the wattage output recorded, I can realise each day:
Lixada= 4.44W = 961mAh (not a lot)
Duragadget= 8.52W = 1828mAh (hmmm…)
Link Solar= 18.21W = 3842mAh (getting there)
To put power requirements into context. My Samsung S20+ has a capacity of 4500mAh. If you are considering incorporating a solar charger into a backpacking electronics system, it is best to look at all devices used and top up any recharge expectation or requirement. I can stretch a phone battery over two, sometimes three days and other requirements, headlamp, ear buds etc. are minimal.
I’ll stop there as to attempt to extrapolate any more would be foolish.
“…charge rates from all of the solar panels is woeful. But woeful isn’t nil”
It is best to keep a device or power bank shaded when charging (or even when not charging). All of the panels get very hot when in direct sun, so much so that plastic can distort. If an airflow around them can be maintained, they will appreciate it.
Both Lixada and Duragadget panels suffer from having had USB outlets hot glued to their backs, this can fail so a little preliminary work applying extra glue to the edges may help stop these coming adrift. I have either run a dob of superglue gel round the edges, or used Sugru, though the latter is pretty heavy stuff. It is also wise to hold the connector block while pulling out the cable.
What I have shown above says little. It reinforces what I already knew- that charge rates from all of the solar panels is woeful. But woeful isn’t nil. There is still potential with every panel to trickle a charge into a powerbank. Unsurprisingly the lightest solar panel demonstrates a very slow trickle, the heaviest solar panel is a slightly faster trickle. What I also haven’t shown here is that the Link Solar is slightly more forgiving as to orientation. Point the Lixada panel directly away from the sun, it halts charging entirely while the Link Solar slows but continues.
Three Points of the Compass is still occasionally experimenting with his small selection of solar panel chargers. Just a couple of weeks ago I took the Lixada panel and a small power bank with me on a four day hike of the Yorkshire Wolds Way. I used the panel on day one to fully top up my power bank. It rained the next day so I had it packed away. On the third day I had it leaning against my shelter, pointing directly at the sun in the afternoon for four hours (outside the solar window). This is fairly typical of the sort of usage you can obtain from a solar panel over the course of a summer hike in the UK. Could I have done without it, almost certainly. I could have simply taken a larger power bank. But it is good to play around with different systems on occasion and see what works and what doesn’t. I am not convinced about solar panels quite yet, especially in the UK. But amongst future hiking plans is completing the GR131 over the next couple of years. A solar charger to enable me to keep charged up and in touch with family while off-grid would very much be a desirable and one of the three panels looked at here will likely be used. This will be more easily achievable on the Canary Islands so if I can obtain any form of success in northerly UK, then further south on the globe will be a doddle.
I wonder why nothing more has been made of movement technology which would seem to be the route that makes the most sense. If you can power a watch why not a power bank.
You also have to wonder about rotational energy so why not some thing you put into a tree and then raise a weight up. It drops and generates energy. The weight could be a water bottle. Or the Bayliss radio without the radio.
Finally I wonder if you could do something with water so have a gravity feed water set up that also generates energy.
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Not sure where the next development will come from but it will definitely not deliver as advertised, will be cranky, expensive and promptly obsolete
(Context: I’m an electronics hobbyist, not a real expert but I’ve been studying this stuff a bit, including considering DIY approaches).
The Lixada panel is quite popular with the ultralight crowd here. They say its real output is around 4W though of course that would mean pointed directly at the sun, e.g. outside of a tent. If worn on a backpack while walking, it would be lower. You can supposedly decrease its weight by trimming off excess material around the solar array. I don’t have one yet so I haven’t tried it myself.
It also seems to me that running a phone nonstop on a long hike is not really in the ultralight spirit. I can see bringing a phone for emergencies and as a navigation tool, but would leave it powered off except when it was needed. So that extends battery life. It is unfortunate that few phones now have removable batteries. Otherwise, bringing some charged ones would get rid of the need for powerbanks, saving some weight.
Finally, the powerbank approach with solar is fairly inefficient. First the solar panel (6 volts) has to charge the powerbank battery (3.7 volts), incurring some inefficiency as the powerbank’s charging circuit is usually designed for charging from mains rather than being optimised for solar. Then the 3.7 volt powerbank battery has to be stepped up to 5 volt USB output (more inefficiency to be plugged into the phone). Then the phone uses the 5 volts to charge its own 3.7 volt battery, another inefficient stepdown. Then there is the extra set of cables (more weight), etc.
What you really want is a phone with a removable battery, that you can charge directly from the solar panel with a solar optimised charging circuit. That gets rid of two steps of voltage conversion and at least one cable. It gets rid of the powerbank too, but you’d want a spare phone battery instead, so you save only part of the powerbank weight instead of all of it.
There is a solar optimised charging circuit here (the small PCB in the picture): https://www.adafruit.com/product/4755 The weight is not specified but it looks like maybe 10g. A 3500 mAH 18650 cylindrical cell weighs around 50g and costs around 4 GBP if you shop around. Plus you need a few grams of contact wires. So my idea is to get the Lixada panel, the solar charging board mentioned above, some 18650 cells (I already have a few of those), and modify my phone to use an 18650 instead of its internal battery, or alternatively bring out contacts from the internal battery to the solar charger. For me this would be more for staying in one place for several days off grid than for hiking, but the same ideas apply.
Note: I’m in the US but have tried to use UK spelling in this post. I hope I didn’t make too many mistakes ;).
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Some interesting ideas there Paul, come back and let us know how you get on with your experimentation
I would be interested to see the numbers if a MPPT (Maximum Power Point Tracking) device was put inline before the volt meter.
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My apologies Corkey, I don’t have a MPPT device so have no stats, but if anyone else does…