I recently picked up a folding solar panel to charge my cell phone & GPS when out and about. It’s a RAVPower (no affiliation) 16W panel with two USB output ports which together top out at 3.2 Amps (full sun, optimum exposure). I really only need one port and 2 Amps max, but those tend to be smaller panels and this gives me a spare port and wiggle room for exposure.

Testing, testing — as I type the panel is laying across a bush in the back yard attached to my flip-phone. If the phone’s estimate is correct it should be fully charged in ~45 minutes or so. Then I do the same with my GPS.

Amazon shows a number of folding solar panels from different manufacturers and of different wattage output, some with two USB ports, others with three. The larger one from this manufacturer has three ports, but since I would need a max of two and normally only one, the smaller of their offerings seemed a better choice. In any case since available power is shared by the two or three ports, more ports is not always an advantage. This one looked to be well built and a good size for hiking.

OutdoorGearLab’s ”The Best Portable Solar Panels and Chargers of 2019” shows this one to be middle of the pack, however my test is running ahead of schedule (that’s a good thing I think), so while it may not be #1, it’s good enough. I initially rejected their Editor’s Choice (BigBlue 28W) primarily because of size, but that doesn’t mean I won’t get it too — objective opinions count and it looks like a great way to recharge a 20,000 mAh power bank.

Done, phone’s charged, test complete.

I have a 20W unit, but noticed one issue in summer heat. The panel has a pocket for a powerbank, but in summer the panel can get hot enough that the powerbank will refuse to charge. So i need to extend the cable and put the powerbank somewhere in the shade.

The pocket on this 16W charger is good to keep the USB ports covered when not in use and you might be able to store an additional 3” USB cable, but it would be too tight to store a power bank. The BigBlue 28W has a zippered compartment and a strap for holding a cell phone. Like you indicate though, in direct sun (where the panel should be) it’s going to heat up so probably not as useful as it appears.

Tjin... if you make a dedicated support for your panel, whose angle to the Sun can be adjusted to match that of your location in relation to the Equator( I use a 2x4 to slide under a piece of 1/4" plywood, to change angle), a nail driven vertically will cast a shadow on itself when the Sun is directly perpendicular to the orientation of the unit.... I then place my cells under the platform to keep them cool

Thanks Les, that’s a great idea for use during/after an event where you can have a dedicated set-up for a portable solar panel. Your nail technique would make it very easy to fine tune a panel’s orientation to the sun.

Fabricating a small shelf in the shadow to place your cellphone or a power bank would keep them cooler and less susceptible to being rained on (for those of you in locales where it rains in the summer).

Russ, thanks for bringing Outdoor Gear Lab to my attention. I note that they did not rank the Goal Zero Nomad panels very high at all. Looking over some of their other ratings, I must say they seem to be a pretty decent outfit and probably a reliable resource.

Portable solar power is indeed a worthwhile technology, especially when the grid is down.

The Goal Zero solar panel I have is a 7 watt unit that’s not much smaller folded up than the 16W unit, and the GZ was considerably more $$. 16W is great for the small electronic gear you’d take on short hikes.

For my GZ Yeti 400, I have a 100W Renogy panel, not exactly portable, but lots more output if I need to set up in the backyard.

For on-the-go charging of a phone or other small device, wouldn't one of the power banks, pre-charged prior to your trip, be more practical? I can recharge my phone (admittedly, a small flip phone) a bazillion times off of one power bank charge.

I've recharged my fliphone several times, my Kindle Fire tablet a couple of times, and my MP3 player once over the last 6 months from a single power bank, and the power bank is still showing 3/4 full (of course that could actually mean 1 second over 1/2 full, since there are 4 LEDs to indicate charge status - 3 of those are currently lit on mine). My power bank is a smallish one, only 12000 mAh and 8.5 oz.

I can see how solar panels would be very handy for extended trips out in the middle of nowhere though. Or if you have a whole lot of power hungry devices that you use frequently (but then, you'd probably spend all your time futzing around with the solar panels and your electronics may become the focus of your trip). And panels are quite a bit more bulky and heavier than a power bank. I would guess they might be more fragile too, but I don't know.

I can see solar panels being a good fallback (backup) if you can handle their space requirements and weight. But unless I'm missing something here, I don't see them as being a very good choice for primary charging.

I have both 10k & 20k mAh power banks with the same four lights as yours (Anker) so I totally get what you are saying, but as big as those numbers seem, a power bank’s energy is finite. While I tested it with my flip-phone,the solar panel’s primary job will be to keep the power banks charged.

Besides camping and hiking, one thing I am gearing for is a major EQ which disrupts the power grid and maybe disrupts our way of life. Hikermor has already been kicked out of his house by a mudslide — unexpected stuff happens. Portable solar is a good way to mitigate — at least with the smaller things. It won’t run a refrigerator, but it will keep cellphones, lights and a radio running.

I see the solar panels as the ultimate, last ditch way to keep small stuff, the phone, lights, GPS running, most likely in an EQ, given my location. Of course, like any good card carrying southern Californian, my wife drives a Prius (a bunch of 18650 batteries on wheels) and I ought to try and hook that up to our fridge. If the gasoline is exhausted, I wonder how long a solar panel would take to fully charge the Prius? Probably too long, but the sun is the ultimate source for juice to run the small stuff.

I have toyed with the idea to get some solar panels for use at home (last ditch backup). I haven't acted on that yet. Prices are definitely coming down these days, and that is making the idea much more attractive then when they first came out. If I buy them, they will probably be fairly large, higher capacity, marginally or non-portable devices for use only at home.

A friend of mine has a setup of some panels permanently mounted to his roof that charge a large bank of deep cycle golf cart batteries. And inverters for getting 120vac out of the batteries if needed. A very enviable setup. But it's not portable. Actually, the batteries and inverters are on large multi-shelved wheeled carts, and those can be moved around (but very heavy, and it isn't going to do well being rolled through the mud). The solar panels are fixed to the roof though. During normal times (when mains power is available) those golf cart batteries are charged off of the mains. The solar panels are a backup charging system for when the power is out. My friend has 12vdc lighting installed alongside the normal 120vac lights so he can run directly off the batteries and not waste power due to inefficiencies inherent to an inverter. This is obviously a hunker down at home setup, not a bug out setup.

I like it. My hunker down at home set-up is a single 100W panel plugged into a Goal Zero Yeti 400 power station. I haven’t needed it yet, but that should power all I need other than a refrigerator. A single 100 watt panel doesn’t seem like much, but most of the year SOCAL has great sun and the panel can easily be moved to optimize its orientation throughout the day - it’s not on the roof.

That said, more panels, a lot more storage in the form of deep cycle batteries and a largish inverter to power a refrigerator would be nice.

Just noticed in my second post above I mentioned storing a 3” USB cable, when I should have said 3’ (tightly wrapped). As it is, I’m keeping a braided 1’ (12”) USB cable in that pocket — small, well built and necessary to move the 5 volts from panel to phone/power bank.

For anyone on the fence regarding buying a small portable solar panel — take a good look at the Renogy E.Flex5 — relatively inexpensive, $23.98 on Amazon — mine arrived yesterday.

The panel is a small, lightweight, simple design with no moving parts. There is a single USB port mounted on the rear with an output of (5 volts x 1 amp =) 5 watts max, which with good sun should be enough to charge most cell phones — when I hooked up my iPhone 6s Plus just now it immediately went into charging mode. I’ll run it up to ~90% and unhook it. Rough charging rate with the iPhone: it charged from 65% to 72% in 20 minutes — ~1% every 3 minutes in good sun. That should be excellent in an emergency.

After I charge the iPhone, I’ll hook up my Anker PowerCore+ Mini, 3350mAh Portable Charger.

The panel is hyper-portable, small, thin & lightweight. It should be great for emergencies, or to have while hiking and sensitive to extra ounces. This may become my primary hiking set-up for small, lightweight power — small solar panel to keep a small power bank charged, or hook-up directly to the cellphone or GPS (if it can take a USB input).

Note: I unhooked the phone at 82%, 50 minutes from 65%. So 17% in 50 minutes is still still about 1% every 3 minutes with an iPhone 6sPlus. The percentage charge should be quicker with the smaller flip-phone I carry when out & about. YMMV

I love solar panels, the idea of basically having a 2.1 amp charger small enough to fit in a backpack pocket makes a world of things possible. Of course I still have battery banks too.

One huge issue to consider is not all the solar panels will automatically start charging again at a fast rate once their charging rate drops due to clouds moving overhead, and most of them don't have that information available on the specs sheet, so it's good to read reviews. Often, even the 2 amp port in full sun isn't a full 2 amps, especially if there was a brief cloud. It'll simply say charging (or not charging) on your device, and it's difficult to tell what it's actually feeding your phone or electronic device without a USB ammeter. One day out on a boat my phone (S7 Active) was actually slowly discharging despite the panels efforts to charge it up (2A port on the Anker) and this was in full sun, where it should have charged fully in a couple hours.

There is one comprehensive review on Youtube where a guy tested a bunch of commercially available panels and put the info in a spreadsheet, but unfortunately it's a little outdated.

I have a Goal Zero 7 watt, and an Anker 21w. I liked that the Goal Zero one had a lot of torture test videos and it seemed to keep working, but it's a bit anemic by today's standards.

Thanks. Since my first post I decided to do some objective testing for myself, so I picked up a couple USB multimeters in order to check voltage and amperes directly while my power banks are charging. One of the objectives will be to compare a solar panel’s name (a number in a name is just a name) with the actual output of the panel under ideal conditions. For that, optimal solar conditions are required — solar noon, clear air, etal. I’ll post my results here. My old GoalZero Nomad 7, the RAVPower 16W, Renogy E.Flex5 and and a recently procured Renogy 21W the will be first since they’re available to me. But that should be enough to see a pattern if one exists.

A couple things gave me the idea to do this, one was the BigBlue 28W specifications:

Make sure the devices you are using to test with will allow input of the current you are trying to measure.

e.g., If you want to test if your solar panel is indeed putting out, say, an advertised current of 2.4 amps, the device you plug it into (the device you are charging) must be able to accept input current of at least that magnitude. Plugging your 2.4 amp solar panel into a power bank that accepts charging at a max current of 1.0 amps will tell you nothing about what you solar panel is capable of putting out.

Yep, covered. My power banks can take up to 2.0 amps each to get that max of 4.0 amps. They’ve been drained to less than 50% to decrease resistance. Weather for tomorrow is supposed to be sunny with nice temps, so I may get some good numbers.

I didn't mean to question you or state the obvious. But then I started thinking, just because it's obvious to me (I have a degree in EE) does not mean it's obvious to the population at large. I just wanted to make sure that since you are volunteering your time to conduct an experiment that we will all benefit from, you would not be wasting your time (in case you didn't know that the load will limit the current the source puts out).

With two power banks at 2.0 amps each you can test for the max 4.0 amp output from the panel (I'm assuming you have two ammeters). Just barely, it would be better if you had power banks that could accept even more current. But I'm assuming you only have two power banks and your power bank only has two outlets. If you had three power banks and three outlets, you could easily test for 4.0 amps max output! But you can't test if a single outlet can reach its advertised 2.4 amps. I guess you could use a USB hub to try and charge two power banks from a single solar panel USB output. I'm not even sure it that would work - I've never researched the internals of a non-powered USB hub, and it may limit current as well.

Thanks, keep it coming, you’re giving me ideas. I have three USB multimeters, two of which I’ll use for the test because they are identical and as luck would have it, they each have two outputs. So I can hook up a power bank to one outlet, watch the current at 2.0 amps, and then hook up the second power bank through the same meter. I’ve already had that panel up to 2.5 amps on two multimeters, so that should be doable.

The two multimeters I’m using have large fonts in color, easily read in daylight. I won’t be using the third multimeter; tested it today and it worked but the display was not easily read in sunlight, dim B&W, small font.

Edit: The multimeters I’m using are:
Two DROK Digital Multimeter USB 2.0
One Eversame USB Digital Power Meter Tester Multimeter

The Eversame is difficult for me to read in daylight. Drok units are easily read in daylight; volts & amperes seem to be consistent between all three.

No affiliation. I wouldn’t know these companies existed were it not for Amazon’s marketing.

Hikermor — don’t toss that GZ Nomad 7 just yet. The testing I’ve done and will complete soon (I need to double check some numbers) show the Nomad 7 doing okay.
Goal Zero Nomad 7: USB: 4.64 volts, .95 amps = 4.41 watts — which is 63% of the number in its name, not bad at all and easily enough to charge a cellphone.

I’ll publish all the numbers later (maybe today).

Almost done. I’m waiting for a solar panel manufacturer to get back (or not) regarding poor performance of their panel. So far they haven’t even acknowledged the email, so I will probably delete the name of the panel in the results summary. I may even just delete that panel from the summary.

Having a portable solar panel would be great to have in a bug-out kit, or during the aftermath of a massive earthquake or other natural disaster that can break the electric grid locally. It would also be very nice to have following a massive solar flare event such as the Solar storm of 1859 aka the Carrington Event, if the solar panel survives the event.

I would just post the results of that panel. If the panel doesn't work as it's supposed to, and the manufacturer doesn't respond, then that is valuable information that people may want to know. No need to editorialize on those particular results. Just post them, and they will speak for themselves.

"Panel XYZ from manufacturer ABC, advertised MNO watts, measured TUV watts. Attempted to contact manufacturer about the apparent discrepancy and testing methods, but received no response."

Posting factual stuff like the above is fine. But editorializing by saying something like, "Manfuacturer ABC is a total *&%^! and I would never buy their piece of ^&*$ product!!!" might get you into trouble.