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I spent roughly 30 hours researching and testing portable solar chargers for this guide on top of the 30 hours that other Wirecutter staffers clocked over the past two years. I've written guides to the best USB power banks for phones and tablets, the best USB power banks for laptops, the best portable power stations, and more, and before working at Wirecutter I was a science writer and fact checker for four years. Plus, during a month-long visit to rural Malawi, I got firsthand experience with a subpar portable solar charger—it was so slow that I gave up on it midway through the trip.

Who this is for

Photo: Rozette Rago

USB solar chargers are a great option if you're taking an extended camping trip or if you're traveling somewhere with an unreliable power grid. They're also good for stashing in an emergency kit. In all those specific situations, a solar charger could charge a phone the size of an iPhone X using a few hours of midday sun. But in most situations, a USB solar charger isn't actually the best portable power source, and you may be better off starting with a USB power bank designed for phones and tablets, USB-C laptops, or AC-powered laptops. Our power bank picks keep a smartphone charged for hours or even days at a time, are the size of a paperback novel or smaller, and are not dependent on the weather.

But whether you choose a solar charger or a battery, it'll work only with USB or USB-C devices, which limits these options' appeal for anyone who needs power for a long-term, off-grid setup. If you're going to be mostly stationary and need to charge or run larger devices like laptops or televisions, or if you need to use more sophisticated communications equipment, you'll probably be more interested in the larger setups that we cover in our guide to the best portable power stations.

How we picked

Photo: Rozette Rago

To decide which solar chargers we wanted to test, we started with a pool culled from Amazon's best-selling and top-reviewed listings, recommendations from authoritative review sites such as OutdoorGearLab, and any mentions on sites that specialize in tech or outdoor gear. Bad overall ratings or poor owner-review scores on Fakespot weren't automatic dealbreakers, but we did axe any models with a pattern of bad reviews—those mentioning problems such as inconsistent and slow performance, warping and bowing, or power-related problems and defects. Before calling in any models for testing, we considered these key features:

Power output and charging

We considered only USB solar chargers rated at 10 watts or higher because with anything less you may not get enough power throughout the day to charge a single phone, which just isn't practical. Although we preferred models that claimed to offer even more power, we didn't want that to come with a major increase in size that would limit the charger's portability.

We skipped any chargers that had only a single USB charging port. We preferred two output ports, a design that lets you charge a second device or share the power with someone else. Any extra ports were a bonus. Each port had to draw at least 1 amp, which is the minimum necessary to fully charge a phone like the iPhone X in three to four hours.

Our pick, the BigBlue 28W USB Solar Charger, is not much bigger than an iPad, and you can easily stow it in most daypacks. Photo: Rozette Rago

Size

A good portable solar charger is sized such that you can easily fold it up and stow it away in a daypack—ideally it should not be much bigger than an iPad. At the same time, more surface area is better at capturing elusive rays on a cloudy day, so we discounted models with fewer than two panels. (In previous tests, we saw poor results from small, brick-style models with a built-in battery—see our last entry in the Competition section.) And since backpackers or hike-in campers are the most likely people to need a solar charger, we didn't want it to add too much weight to a pack. Every model we tested weighed around a pound, and we didn't consider anything over 2 pounds.

Warranty and reliability

We looked at the company websites and contacted customer support to make sure each model was made and distributed by a reputable brand, was readily available to buy, was unlikely to go out of stock quickly, and was under warranty for at least a year.

Extras

If a charger came with any bonus features, we took those into account as well. Features such as a magnetic closure or a built-in kickstand can make a solar charger easier to use, but only if it's already great at its core job of producing power and charging devices. Most of the chargers we tested included a USB–to–Micro-USB cable, but some (like Anker's 3-foot cable) were longer or felt more durable than others. Many included a few carabiners, too. The carabiners themselves were small and chintzy across the board, but we appreciated the added ability to hang the charger from a backpack or tent.

Price

Solar chargers that cost more than $100 either don't offer any notable advantages over sub-$100 models or occupy a completely different size and weight class that would be overkill for the casual camper or the average emergency kit. On the other end of the scale, really inexpensive solar chargers generally can't produce enough power or charge fast enough to be worth bothering with. We've struggled with cheap chargers that produce too little power or have inconvenient quirks like those we outline in the Competition section, and we've concluded that you shouldn't rely on such models regardless of the situation. That left us with just four chargers that hit our sweet spot of maximum-output rating, size and weight, availability, and nice-to-have features. We tested an Anker 15 W charger (our former pick, which has since been discontinued) against three competitors:

In the past, we also tested nine other models; we discuss them further in the Competition section.

How we tested

We tested the most promising models on a smoggy July week in New York City. If you're planning to travel closer to the equator or under clearer skies, you'll get more power than we did in our testing. But since we've tested chargers under ideal conditions in the past—in sunny Southern California—this time we wanted to have a point of comparison for the benefit of urban dwellers a bit farther north. We conducted head-to-head tests to make sure each charger had the same weather conditions, and we measured each model's maximum power output, the total power it produced throughout the day, and how consistent the power production was when the charger was faced with passing clouds.

On a smoggy day in New York City, none of the solar chargers were able to produce the maximum power output their USB ports are capable of.

Maximum output/fastest charge: We set out the panels just before solar noon, which is when the sun reaches its highest point in the sky at a given location. Making sure the panels were facing the same direction and set up at the same angle, we plugged each one into a PortaPow 3-20V Dual USB Power Monitor and a Drok DC 3-21V Load Tester to find out just how much power they could produce during the sunniest part of the day.

We set out the panels just before solar noon, which is when the sun reaches its highest point in the sky at a given location. Making sure the panels were facing the same direction and set up at the same angle, we plugged each one into a PortaPow 3-20V Dual USB Power Monitor and a Drok DC 3-21V Load Tester to find out just how much power they could produce during the sunniest part of the day. Total power: We also set all of our candidates up for a four-hour period in the middle of the day so that each could charge a fully drained Anker PowerCore 20100 power bank. We monitored the cumulative power production with a PortaPow power monitor attached between each solar charger and power bank. When the test was complete, we also drained each power bank using four Drok load testers to double check that our results were accurate. Those numbers helped us understand just how charged a standard phone or tablet would be when left out for the same amount of time.

We also set all of our candidates up for a four-hour period in the middle of the day so that each could charge a fully drained Anker PowerCore 20100 power bank. We monitored the cumulative power production with a PortaPow power monitor attached between each solar charger and power bank. When the test was complete, we also drained each power bank using four Drok load testers to double check that our results were accurate. Those numbers helped us understand just how charged a standard phone or tablet would be when left out for the same amount of time. Consistent power: On a different sunny day, we tested whether each solar charger could return to full power after being shaded—imitating, say, a cloud passing overhead. Using the same setup, we waited for the power meters to reach at least a few watts, and then folded the chargers shut. Once the device readings hit zero, we opened them up again and waited for them to return to full power. All the models in our latest round of testing passed this test, but in past tests some solar chargers (especially the cheapest ones) couldn't bounce back—which is a dealbreaker for us. If you were to leave your phone and solar charger out all afternoon to absorb some juice while you're off hiking, you'd be pretty disappointed to find your phone had charged for only 15 minutes before a cloud passed by.

On a different sunny day, we tested whether each solar charger could return to full power after being shaded—imitating, say, a cloud passing overhead. Using the same setup, we waited for the power meters to reach at least a few watts, and then folded the chargers shut. Once the device readings hit zero, we opened them up again and waited for them to return to full power. All the models in our latest round of testing passed this test, but in past tests some solar chargers (especially the cheapest ones) couldn't bounce back—which is a dealbreaker for us. If you were to leave your phone and solar charger out all afternoon to absorb some juice while you're off hiking, you'd be pretty disappointed to find your phone had charged for only 15 minutes before a cloud passed by. Size, fit, and finish: Beyond analyzing performance, we compared the size and construction quality of each model in person. We measured their dimensions when folded and unfolded, and we used a digital kitchen scale to weigh them with precision. Most solar chargers consist of just two to four solar panels sewn to a woven-nylon backing, with wires hidden between the layers of nylon and a charging component in a pocket on the end. They usually have a Velcro or magnet closure and are designed with riveted holes or loops around the edges to help you hang or mount the charger to a backpack or tent. All the models we examined had roughly the same quality of stitching and nylon. Since the panels themselves are weatherproof, they're simply sewn in at the edges without any additional covering. The size and weight varied a little between the models, but once we had them all in hand, we saw that the basic designs didn't vary enough for us to rule out any or to pick a favorite.

The BigBlue 28W USB Solar Charger is the USB solar charger we'd pack for a week in the woods or a month in Malawi. It produced the most power of the models we tested and offers several standout features—an additional output port, a weatherproof port protector, and an expansive (but lightweight) array of panels to catch every last ray of sunlight.

At the sunniest point of our tests, the BigBlue tied with the X-Dragon 20W SunPower Solar Charger for how much power it produced at any one instant, reaching about 10.7 watts. But over the course of the day, the BigBlue had the highest cumulative wattage: 48.8 watt-hours to the X-Dragon's 43.7 watt-hours. That isn't a huge gain—you could barely charge an iPhone X battery halfway with the additional power—but every watt matters if you're far from an outlet, and the extra power costs little more in size or price.

The BigBlue charger produced more power over the course of a four-hour test day than any other charger we tested.

The BigBlue stood out among the dozens of models we considered in part because it has two 2.4 A ports and one 1 A port so you can charge three devices simultaneously. (Those ratings are based on the assumption that the solar panels are working at full 28-watt capacity, which will rarely happen with any solar charger.) Every other model we tested had just two ports. Plus, the ports on the BigBlue are the most protected from water and dust among all the models we tested, as they're covered by both a cloth flap and a rubber cover. Thankfully the cover is connected by a small tether (unlike the rubber cover on the Eceen charger we tested) so you don't lose it.

The charging ports on the BigBlue are protected from the elements by a rubber flap when they're not in use. Photo: Rozette Rago

The BigBlue looks attractive, feels sturdy, and is well made with a weatherproof synthetic fabric. Along with the X-Dragon, which weighs about the same, it's one of the lightest models we tested; at 1 pound, 4 ounces, it's about as heavy as a can of soup. The BigBlue is also one of the smallest models we tested when folded up—tied with the Anker charger at 11 by 6.3 inches. Yet it's by far the largest when unfolded, with four fold-out solar panels to the X-Dragon's three (the Anker and Eceen both have just two). This size makes the BigBlue a little more cumbersome to use, but the extra surface area is nice for catching every possible ray on a cloudy day.

To power your gear, the BigBlue charger comes with a 2-foot cable, double the length of the X-Dragon and Eceen cables. That extra foot makes a world of difference if you want to look at your phone while it's charging, for example, or if you want to place your power bank safely in the shade while leaving your solar panels exposed to the sun. Also included are four carabiners—they clip onto the fabric loops sewn around the edges of the BigBlue—that you can use to attach it to the outside of a backpack for on-the-go powering or to a tent to charge up your gear while you're enjoying the day.

Flaws but not dealbreakers

The main downside of the BigBlue charger is, as the brand name might suggest, its size. Even though it weighs the same as the X-Dragon, it's a good 10 inches longer when unfolded, making it a little harder to maneuver into just the right position. But the extra size gives it more surface area to collect the sunshine, and it's still relatively sleek and compact when packed—that's when size and weight are most important.

Some models we've tested, such as the Eceen, snap closed with two magnets sewn into the material—making them, quite literally, a snap to pack up and stow away. The BigBlue's single strip of Velcro was wimpier than that of the X-Dragon and came unstuck more easily. We've noticed in past long-term testing that Velcro generally wears poorly in water, mud, and sun in comparison with magnets. Something to keep in mind, but again, not a dealbreaker.

Runner-up: X-Dragon 20W SunPower Solar Charger

Photo: Rozette Rago

If the BigBlue is unavailable, or if the prices change dramatically, the X-Dragon 20W SunPower Solar Charger is another good bet. It generated almost as much power as the BigBlue in our testing—leaving the Anker and Eceen chargers in the dust—and like the BigBlue, it has a Velcro flap to keep the panels folded up and protected from scratches when not in use. But it has fewer (two) USB-A output ports than the BigBlue, and the zip-up mesh pocket covering them is less protective than the BigBlue's rubber flap.

The X-Dragon tied the 28 W BigBlue in terms of peak power output, as both chargers maxed out at about 10.7 W on our smoggy test day in New York. But the X-Dragon was about 5 watt-hours behind on cumulative output—43.7 watt-hours to the BigBlue's 48.8 watt-hours. For reference, you could charge a Galaxy S10 more than a third full with that difference in power.

The X-Dragon produced nearly as much power as our top pick when we tested them at solar noon.

The X-Dragon's two ports are each rated for 2 amps (10 watts), so either one will be almost as fast as a USB-A wall charger when the sun is shining bright. Combined, the ports top out at 3 amps, or 15 watts, so charging two devices at the same time will slow them both down. That's a reasonable rating for 20 watts of solar because there's some standard loss expected in the process.

The X-Dragon's zip-up mesh pocket keeps track of your cords and protects the charger's output ports from wear and tear when they're not in use. Photo: Rozette Rago

Although the X-Dragon doesn't have the BigBlue's rubber port protector, we like that its ports are protected by a zip-up mesh pocket in addition to an outer layer of material. An extra flap of fabric lined with Velcro keeps it closed securely when folded, too—a slightly better example of this design than on the BigBlue. Models we've tested that completely lack such features are more vulnerable to the elements.

The X-Dragon weighs the same as the BigBlue, and it lies a bit flatter, but it's about an inch wider and taller when folded. It's also much homelier, with a neon green stripe and a large logo splashed across the front. Neither factor is a dealbreaker, though.

How to get the most from your solar charger

One of the wonderful things about solar power is how simple it can be. The only care and maintenance most solar panels require is keeping them relatively clean and free of dust. A damp cloth should do the trick most of the time.

To really max out your power output, you should angle the panels correctly. A good rule of thumb is that the panel's angle, relative to flat ground, should be roughly the same as your latitude, with some minor seasonal adjustments. The farther you are from the poles—and from summer—the steeper the angle. For example, the average angle in Winnipeg would be around 41.1 degrees, while in Key West it would be around 22.1 degrees. Even if you don't get the angle exactly right, approximating it could increase your power production by a noticeable amount. If you want to get the most juice, check sites such as Solarpaneltilt.com, PVEducation.org, or Solar Electricity Handbook's Solar Angle Calculator to figure out the best angle before you go, take a photo of the setup on your phone, and try your best to replicate it out in the wild. Pro tip: Use a hiking boot to prop up the panels.

Like most solar chargers, the BigBlue includes a pocket on the top flap to store your device while charging. If it's a hot day, though, that black pocket in direct sunlight is like an oven for your phone. You'd be better off putting your device underneath the panels—in the triangular gap between the ground, the prop, and the angled panel, perhaps—or shading it some other way to prevent it from overheating and shutting down.

The competition

A representative for Anker confirmed that the company is discontinuing Anker's 15W PowerPort Solar Lite, our former pick, along with the 21-watt version.

Eceen's ECC-626 13W Solar Charger (which is no longer available) was light and compact, and it had some nice added features such as a fold-out stand, a magnetic closure, and a neoprene pocket. But it performed significantly worse in our testing than every other model we tested, and we didn't like that the output ports were located on the outside of the charger—completely at the mercy of the elements. Like the BigBlue, it had a rubber flap to cover the ports when they were not in use, but since the flap was not attached by a tether it was potentially easy to lose (and we almost lost it a few times).

We tested the Goal Zero Nomad 7 because the brand has one of the best reputations for product quality and service in this category. The unit is well made, it features USB and DC charging options, and it even has niceties such as a magnetic closure instead of the Velcro that cheaper units use. But it's rated for only 7 watts (a quarter of the BigBlue's maximum-output rating) and has a hefty price tag.

Though compact, neither the Instapark Mercury 10 nor the now-discontinued Poweradd 14W Solar Charger was able to bounce back to the original charging rates after being shaded for 10 seconds.

The RAVPower 15W Solar Charger used to be our runner-up pick, but RAVPower has replaced it with a 16-watt model, which we haven't tested because it costs the same as models with much higher maximum-output ratings.

The Creative Edge Solar-5, the Poweradd Apollo 3, and the ZeroLemon SolarJuice 10,000mAh all-in-one models got up to 60, 60, and 65 percent, respectively, of their advertised ratings in our testing. But even with the built-in battery that these three chargers had, their single small panel charged too slowly to compete with the larger surface areas of fold-up solar chargers.

This guide may have been updated by Wirecutter. To see the current recommendation, please go here.

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