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.