• Comments (34)

    • 9
      C R DubU - October 25, 2019

      Any chance you’d do an article on home generators for emergencies like power failures? As someone with friends in California’s wildfire areas where the blackouts are *still* ongoing, it’d be nice to get some good recommendations for a care package I’ll be sending their way.

      • 7
        John AdamaStaff - October 25, 2019

        We definitely intend on covering home gennies, just don’t know when. Still working through a lot of the basics (like these portable panels for your go-bags).

    • 4
      WF654 - December 18, 2019

      Nice test! Although would have really appreciated if you addressed these questions, at least informally, as they might affect the real world performance a lot:

      1) Intermittent sun charge recovery – while it can be surmised from the graphs over time, some panels allegedly recover pretty badly from just a short shading (some versions of Big Blue 28W IIRC took longer if ever to get to full charging current after a brief shade, I had to unplug and plug it again usually). Might be just an issue with actual devices and possible USB power renegotiation, not visible on a load tester with power and gnd only?

      2) Both USB ports – would be quite interesting to see how the devices cope with both ports loaded to the max at the probably nice solar flux you had. And people do use both ports simultaneously. The 3A you tested select devices with is still only 13-15W dep. on V, compared to marketing claims of at least 20W with some (not mentioning the likes of 28W, which is purely theoretical I guess).

      3) Did your load tester adhere to any USB power standards (I know, there have been many, incl. proprietary), or just Vbus and GND connected? Could it confuse some panels with ICs to detect a higher draw device like iPad or USB PD or not? Just wondering how some of these spiked so much 🙂

      • 5
        Jon StokesStaff - December 21, 2019

        Thanks for the feedback!

        1) I honestly didn’t find anything in any of the data that looked to me like this intermittent shade issue. I know people write about it and complain about it, but I have yet to see it show up in any of my graphs in real life. My hypothesis is that this phenomenon is either solely about the battery or device plugged into the panel, or it’s an issue somehow with some device plus panel combos. So yeah, I think there is something about the negotiation going on here.

        2) I didn’t test both USB, but in the next version I will try loading two ports at a time and see how that works.

        3) My load tester was pretty “dumb” and didn’t do anything fancy. I think this was a shortcoming of the testing with some of the smarter panels, as it looks like they’re trying to get the tester to talk to them and negotiate, and it doesn’t. Some of the patterns are almost like they’re polling it.

        I think the tests did a pretty good job of pitting the panels against each other as fairly as possible, but I do need a much smarter load tester that supports some of the more popular USB power protocols and can fully exercise the panels. Such testers do exist, but they cost a couple thousand dollars, so were out of reach for this round. But at some point in the future when we can justify the investment, I want to get one of these and redo the tests with it to address these issues.

    • 3
      JBinAZ - January 18, 2020

      Hi and thank you for this article. I live in the Phoenix area, so sun is one natural resource I intend to take advantage of. I went to purchase your top recommendation on Amazon, and they are saying that there is a newer model of this item:

      Ryno Tuff Solar Charger with Built-in Battery Power Bank, 21W Dual USB, Compact, Durable and Waterproof, Portable Solar Panel Battery Charger for Cellphones, Tablets, and Electronics, While Camping

      Can you tell me if this newer version does anything better (or worse) than the version you recommend?  Thanks! Here’s the link for the newer version:

      https://www.amazon.com/Charger-Waterproof-Portable-Cellphones-Electronics/dp/B07MB83DCJ/ref=dp_ob_title_wld

      • 2
        Jay F - March 1, 2020

        Jill did they ever get back to you on the different version??  from what I read the newer version has the Built-in Battery Power Bank and the other has no battery pack.

      • 5
        Dan Ello - March 31, 2020

        They have actually mentioned both models in this review.  Here is what it says:

        > We strongly recommend pairing a solar charger with a separate external USB battery bank so that you don’t have to ruin your gadgets built-in batteries by baking them in the sun during a charge cycle. Many of the products in this guide sell versions with and without a battery built into the solar charger. Although we prefer keeping the charger and battery separate, it’s not wrong if you pick the built-in battery version.

        It sounds like the thinking is that the built-in battery would lose capacity in the sun.  If that’s the only reason, it’s only $5 more for the battery version of the Ryno at the moment, so maybe it’s worth it to still use an external battery but also use the Ryno’s built-in as a backup.

    • 7
      Dan Ello - March 31, 2020

      Another great article, thank you for the free research.

    • 6
      平子温 - April 21, 2020

      Thank you for very accuracy report. I’m refering this report for choosing solar charger.

      I agree “Power output greatly depends on angle to the sun” so I think that solar charger with kick stand is efficient,but most these are high watt(over 60W). however I think it is too high for smartphone but if I will use laptop ,may be appropriate.
      how do you feel it?

      • 6
        John AdamaStaff - April 21, 2020

        If you want to power a “real” laptop (like a Macbook), yes, you’ll want a larger solar panel. These portable ones aren’t strong enough.

      • 3
        平子温 - April 21, 2020

        I appreciate for your reply. I’ll survey reviews of high watt solar charger.

        and, I would be grateful if you could consider to write article of semi-portable solar charger (as written on “Off-grid power 101”).

        thank you.

    • 3
      平子温 - April 25, 2020

      does anyone have idea to adjust angle between soft folding solar charger and sun light?

      “Power output greatly depends on angle to the sun” but if the solar charger is not with kick stand.

      especially I wally that folding directions are horizontal and vartical.

      • 4
        Ef Rodriguez - April 30, 2020

        If your panel does not have a built-in kickstand or some other feature for propping it up at an angle, you just need to get creative by using other gear or random stuff you find around you. You could also try walking with the panel tied to and hanging over your backpack in a way so that it faces the sun, and so on.

    • 6
      SafeHavenEstates - May 1, 2020

      We build & manage off-grid estates in Belize. For one of our watchmen, Fidel, I furnished an RAV system similar to the one you cover here. It worked well for a few years in a very tough high-heat, bright-sun, saltwater environment. The folding solar panel was rugged, but it took some explaining to get Fidel to follow the sun with it – thus achieving maximum charge. It powers the battery pack, which powers Fidel’s cellphone, low-voltage night light, radio, and Fenix UC35 rechargeable flashlight – (the absolute best which we furnish to all our security people).     Be careful flying with the battery pack because it is lithium ion and many have almost the max amount (24,000mAh ??) of capacity legal as carry-on baggage. And FHA battery restrictions may have changed since then, so check with FHA before you buy, if your bugout location require a quick flight like ours does.

    • 4
      IIlIllIlll - June 4, 2020

      You’ve written square meters everywhere instead of square feet.

    • 3
      Sun Yeti - June 15, 2020

      Thanks for doing this testing! A few thoughts/questions:

      1. How did you measure cell area in order to calculate efficiency?

      2. Commercial (non-camping) solar panels are tested at standardized conditions (1000 w/m^2 and 25 degC). That’s pretty close to irradiance you get at a cloudless day around noon in many parts of the world, at the equator it’s more. You lose a bit from the panels typically being warmer, but not that much. So you really should be able to get rated power out of these panels, especially when you first brought them out and they were cool from the AC. It’s honestly a bit disturbing that you can’t; that kind of exaggeration is not tolerated elsewhere in the solar market (if anything, commercial panels usually outperform by a few percent when tested; a 20W panel might actually go to 21w under ideal conditions).

      3. I was curious how my own panel from my own bag would perform by this criteria. I ran a sloppier test, it was still enough to give me a pretty good ballpark. I have the renogy 5w (basically 1/2 of the 10w folding panel you tested). I hooked it up to a usb powerbank, through a datalogging usb meter. Clear day (cloudless for vast majority of the test) temps in the 70’s F, I adjusted the tilt every hour or two, and got a pretty consistent output in the range of 2.8 to 3.3 watts (4.7+ volts, 0.5+ amps) throughout the peak hours of the day ~10 am to ~5 pm. The record of mAh accumulated was consistent with the power staying in that range when I wasn’t watching it. So pretty good, but you’re correct, it’s a bit more than half of what they promised. Still I’m pretty happy overall with the renogy panel; I haven’t field tested it all that much, but it’s built like a tank as you say, and even a 5w panel puts enough into my powerbank in a day to keep my phone topped up for two or three days.

    • 9
      Katie Fire - June 26, 2020

      Does anyone have recommendations (or could you do a whole article???) on “semi-portable” solar panels, ideal for bugging-in instead of out?

      For home use during a prolonged power outage (assuming you are not trying to power big stuff like fridges, toasters, driers, etc), what is the best way to power a family’s worth of phones, laptops, radios, headlamps, and lanterns?

      Is it best to just buy additional BigBlue 28W panels?

      Or do the larger “briefcase” panels from companies like Jackery and Goal Zero make sense price-wise?

      • 6
        John AdamaStaff - June 27, 2020

        We do plan on making a separate roundup for the semi-portable panels. It’s better to have that kind for larger at-home stuff rather than trying to piece together multiple portable panels.

        I’ve been testing a briefcase style 90W panel from Zamp this week, and so far am happy with it. Jackery is likely okay too. Stay away from Goal Zero, as all of their stuff failed our tests pretty badly last year.

      • 6
        Katie Fire - June 28, 2020

        Thanks!

      • 6
        stumps211 - February 7, 2021

        John,

        Are any of these panels capable of being linked together?  If so, how does that affect their performance?  If the renogy is so durable, would two panels linked together be a better option than one big blue, and does the output increase proportionately with the number of panels connected, or are there any losses in efficiency?

        Thanks for all the great reviews and info.

      • 6
        John AdamaStaff - February 9, 2021

        I asked the main researcher for this guide and they believe Goal Zero’s are the only ones particularly designed for daisy chaining. But then you’re overpaying for poor general performance with GZ, so it defeats the purpose.

        Generally speaking, yes, output rises proportionately with panels. 

    • 5
      Jonnie PekelnyContributor - July 8, 2020

      Thanks for this write-up. I wound up getting the Big Blue but for my home, to charge small devices. I have a few questions on this topic. 1) If we’re not supposed to fry our phone battery by putting it in direct sunlight, why is it okay to fry the battery pack? 2) Is it a viable strategy to try to shield the gadget or battery pack from the sun by putting it, for example, under the solar panel or otherwise in the shade? 3) What happens if you plug more than one device into the solar panel? for example, what if you plug in two battery packs. Do they each get charged at half the rate? I’m sure it’s not that neatly broken out, but I’m trying to get the general idea. 4) I am a little bit confused about how to figure out what “perpendicular to the sun” means because the sun is a ball not a plane, to be simplistic about it. Could you explain? Also, what are best practices for propping portable panels up so that they are at the correct angle? .

    • 5
      - August 13, 2020

      Hi guys, great research, really thorough, except for the panel areas. You’ve calculated these incorrectly in your spreadsheets by a factor of 10. One square metre is 10,000cm2, not 1,000cm2 as used in your calculations. This explains the problem you found with the efficiencies. 

    • 5
      Juha Sahakangas - January 20, 2021

      Looks like at least the Big Blue might have actually benefited from multi-port testing given how close it came to matching (or even overcoming) the listed amperage? Would be interesting to know if the larger size does give you anything more than just coping better in less than optimal light conditions. 

      They’re also selling 21W version with listed 3.8A total output, which seems to be higher than any other 21W panel I’ve seen, would be good to see that one tested to see if it is actually more powerful than other 21W panels, might be a great weight/power combo if there’s anything to that.

      • 4
        Gideon ParkerStaff - January 20, 2021

        When I chose a portable solar panel for my bug out bag, I went with the largest one with most wattage that I could find. I want to be able to charge my devices as quickly as possible compared to using a smaller panel. 

        Is the 21W version listed at 3.8A made by Big Blue? If you could share a link to that panel, that would be great for others to see and possibly consider when they are buying a portable solar panel. 

      • 5
        Juha Sahakangas - April 7, 2021

        Yes it’s made by Big Blue, but I managed to dig up some specs for it and turns out it’s actually significantly *heavier* than the 28W version, I don’t know why, maybe it’s older model based on older tech, but whatever the reason, it’s not interesting at all in the end.

    • 4
      Michael - August 1, 2021

      Choetech’s been booted from Amazon! Seems they got in trouble for creating fake positive reviews or something. Looks like you can still get the panel directly from their home page here:  https://choetech.com/products/solar-charger-19w-solar-phone-charger-with-dual-usb-ports

      • 3
        John AdamaStaff - August 17, 2021

        Thanks for the intel. So sad to see a company that didn’t need to do fake reviews still doing them — but good on Amazon for taking action, because fake reviews do nothing but hurt the community.

    • 3
      Bill Masen - August 17, 2021

      So a very good article on PV energy for 5 volt DC device charging, how about one for 12volt DC operations such as running 12 volt water heaters, fridges, freezers, washing machines, cool boxes, vehicle starting and liesure batteries. 12 volt equipment is more likely to be useful in a grid down situation than 5 volt stuff.

      • 2
        John AdamaStaff - August 17, 2021

        Definitely plan on doing more solar guides. We’re halfway through one now on semi-portable “basecamp” models (eg. 100W), and then hope to fill in any other gaps in the coverage. 

        Started with the smallest ones because they’re most appropriate for BOBs, cheapest, and cover the basics for charging phones etc.

        You’re welcome to help get the ball rolling with any tips, research, products, etc!

      • 3
        Bill Masen - August 17, 2021

        I dont have much experience in DOMESTIC 12VDC but I did visit some rural preppers in the midwest who have BOTH 110AC wired homes AND 12VDC wired back ups. They are normally PV panel and micro wind turbine combos connected to battery backs.  But I have built my own 12 volt systems for my DIY RV.

        Some of these folks are on tight budgets so the batteries are often part used Golf Cart or Fork lift truck batteries, one old dude I met was using batteries salvaged from submarines originally. Though these days 110amp deep cycle liesure batteries are much more affordable.

        I have also come across Brits and Americans who salvage the white goods from RVs. Fridges, TVs, Heaters, Microwaves, Electric toilets, LED lights, switchgear, aircon units etc and install them in their homes and cabins.

        Using marine grade PV panels and boat micro turbines or Expedition / Overlander spec kit (sometimes salvaged) is another option

        Two excellent books I can reccomend is

        OFF THE GRID by Duncan Kerridge  9781902175560

        Do it yourself 12 volt solar power by Michel Daniek  9781856230728

         In the UK campers, RVers and some preppers use portable power packs as the power reserve for 12vdc back up systems. like the one below.

        https://www.batteriesandsolar.co.uk/bespoke-portable-power-box/

      • 2
        John AdamaStaff - August 17, 2021

        Speaking of books, I wanted to bring your attention to the best books list we updated yesterday. I bet you have some thoughts! 

      • 3
        Bill Masen - August 17, 2021

        Ok I’ve uploaded my library list of reference and fictional books to the relevent section. I have removed it from this page so as to not go OT on this page.

    • 1
      Scott McNay - May 1, 2023

      Maybe the quoted values are from the equator? Maybe you can calculate the difference in solar radiation between the low 30’s latitudes and the equator, for that time of year?

      I agree with the general theme of some of the other commenters; it’s hard to believe none of them seem to work very consistently.