FlexSolar 40W Review

We loved the previous generation, but the new FlexSolar 40W is far and away a major upgrade. The latest version is more than 21 ounces lighter, plus it's far more efficient. In our tests, this updated FlexSolar 40W more than doubled its ability to transform sunlight into electricity for recharging our gadgets.

Direct Solar Charging Speed

The FlexSolar 40W is at its best when charging via USB-C in bright sunshine. It worked well, albeit slowly over USB-A, and it was functionally solid via its DC port. When we tested it over USB-C, however, it collected more energy than some panels rated at higher wattages.

To test each solar charger, we set them out side-by-side and connected them to separate, identical battery banks. After one hour, we measured the amount of energy each solar panel sent to the battery banks by discharging each battery bank on our workbench. We repeated these tests three times and averaged the results.

In midday sun in July in Idaho at 2,400 feet of elevation, the FlexSolar 40W produced 4,302 mAh on our USB-C test battery bank. This outperformed other similarly sized solar chargers we tested. In typical clear-sky summer sunshine in North America, we would trust this charger to collect enough energy to recharge our phones in 1-2 hours. Wattages over USB-C in direct sun sometimes exceeded 30 watts, which is also faster than many USB wall chargers.

Interestingly, when we tested this panel with a DC connection to a small Jackery 300 power station, we generated about the same or slightly less energy in 1 hour of direct sunlight. In general, DC connections usually result in more efficient energy collection, particularly when the size of the panel is rated high enough to outperform USB-C connections. We also noted some high wattage inputs over DC, at one point receiving 33 watts on a relatively cool 65° Fahrenheit day.

The FlexSolar 40W seemed happiest when connected to quality USB-C battery banks where it tended to deliver higher wattages.

Indirect Solar Charging Speed

To test how well a solar charger might work under cloudy skies, we suspend a white sheet above the solar chargers to simulate cloud cover, repeating this test three times and averaging the results.

After the FlexSolar 40W's stunning performance in direct sunlight, we were disappointed to see it drop down to typical results for its rated size. It collected an average of 1,038 mAh in one hour of indirect sunlight.

The FlexSolar 40W may be capable of recharging a phone in 3-5 hours on a cloudy day, depending on the conditions. In addition, you'll likely need to readjust the position and angles of the panels to maximize energy collection when charging for more than a couple hours at a time.

Portability

The new generation of FlexSolar 40W is far more portable than the previous version, which was a full panel longer and weighed nearly twice as much.

Like most powerful portable solar chargers, it uses multiple stiff connected solar panels that fold up to conserve space. When unfolded, it's 44.75" long. When folded, it's just 10 inches by 9 inches by 1.5 inches thick. It doesn't have any clasps to secure it, so it occasionally flops open during travel, so we had to pay attention when grabbing it and stowing it.

Weighing in at just 26.1 ounces, this solar charger is light enough to take backpacking if you have multiple devices you want to charge each day. It's a bit unwieldy to hang from the back of your backpack while walking though, so it's strictly a panel you would set up at camp.

As for durability, we were very impressed. The stiff panels inspire confidence, letting us fold, unfold, and set up the panel on the ground with little concern for wear and tear.

The only minor annoyance we have with the FlexSolar 40W is the lack of port covers to prevent dirt or forest debris from getting inside.

Functionality

The FlexSolar 40W is a basic portable solar charger that does it job well. The most important features we appreciate are its three different output ports: USB-A, USB-C, and DC.

The three ports cover that vast majority of devices and their cables that most people will likely want or need to charge. The USB-A port is good for older devices with smaller batteries and USB-A cables. USB-C is transitioning to a do-it-all port for most new mobile devices. The DC port is most often used with small power stations.

The FlexSolar 40W has four built-in carabiner holes so you can hang it to charge. This works best during morning and evening charging sessions when you're trying to collect low-angle sunlight. The orientation doesn't matter, so you can hang it vertically along a tree trunk or horizontally across a parked bike frame.

Should You Buy the FlexSolar 40W?

The FlexSolar 40W is an easy-to-use solar charger that is surprisingly powerful for its size and weight. If you're looking for a highly portable solar charging option that produces usable wattages for fast-charging devices in off-grid locations, this is a good choice. It's a bit heavy for 1-2 person backpacking trips, but when you want to charge multiple devices, it's worth its weight on the trail.

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