Can the FlexSolar 40W charge a portable power station?

Yes, through the DC port, which outputs up to 19V/2.1A (40W). You need a DC5521 cable, which FlexSolar sells separately but does not include in the box. It will charge small power stations at a meaningful rate in good sunlight, but it will not fast-charge a large station. For stations over 500Wh, a 100W or larger panel is more practical.

Can I use the USB and DC ports at the same time?

You can, but FlexSolar advises against it because charging speed drops significantly when both USB and DC are active simultaneously. The panel's total output is shared across all connected ports. For best results, use one port type at a time: DC for a power station, or USB for phones and power banks.

How does the FlexSolar 40W compare to the BigBlue 28W?

The FlexSolar 40W produces significantly more energy in direct sunlight at a similar weight and adds a DC port the BigBlue lacks. The BigBlue 28W has a built-in ammeter for real-time output monitoring and three USB ports instead of two. In cloudy conditions, the performance gap between them narrows. Choose the FlexSolar when output and DC capability matter most. Choose the BigBlue when the ammeter and a third USB port matter more.

Home Gear Reviews FlexSolar E40 40W

Gear Review · Energy

FlexSolar E40 40W Solar Charger.

The highest output per ounce in independent testing. Here is what 40 watts and a DC port actually deliver, where they fit in a preparedness plan, and who should save the weight and get a smaller panel.

Rated Power

40 watts

Weight

~1.65 lbs

NWS Verdict

Buy it

View on Amazon

Strengths

Produced the highest energy output per ounce of any panel in independent field testing.
DC port charges small portable power stations directly, something USB-only panels cannot do.
USB-C PD and USB-A QC3.0 deliver fast charging to phones and tablets simultaneously.
ETFE-coated monocrystalline cells with IP67 weather resistance on the panel surface.

Limitations

No kickstand means improvising support to aim the panel at the sun.
Performance drops to average in cloudy or indirect sunlight despite strong direct-sun output.
No DC cable included; the cable to connect to a power station must be purchased separately.

What it is

The panel that bridges USB charging and power station territory

The FlexSolar E40 is a foldable 40-watt solar panel with three output ports: USB-C with Power Delivery (up to 18W), USB-A with Quick Charge 3.0 (up to 18W), and a DC5521 port (19V/2.1A, up to 40W). Six monocrystalline panels fold down to roughly 9 by 10 by 1.5 inches and weigh about 1.65 pounds. It unfolds in direct sunlight and charges phones, tablets, power banks, and, through the DC port, small portable power stations.

That DC port is the distinguishing feature. Most foldable USB solar panels in this size range top out at 5V USB output, which can charge phones and power banks but cannot charge a portable power station. The FlexSolar E40's DC port outputs at 19V, which is high enough to charge many small power stations (under ~500Wh) directly. That makes it a bridge product: it does the phone-and-power-bank job that any USB solar panel does, and it also extends into territory that normally requires a much larger (and heavier) 100W+ panel.

The panel surface uses an ETFE coating over monocrystalline cells rated at 24.7% conversion efficiency. The surface carries an IP67 dust and water resistance rating, though FlexSolar is clear that the rating applies to the panel and not to the junction box where the ports live. An LED indicator shows charging status, and an integrated smart IC chip detects connected devices and adjusts output accordingly.

Like all USB solar panels, it has no internal battery. It generates electricity only while deployed in direct sunlight with a device connected. No DC cable is included in the box. FlexSolar sells the compatible DC5521 cable separately, and you will need one to use the DC port with a power station.

Why it works

The testing backs it up

Best output per ounce in controlled testing

In OutdoorGearLab's side-by-side field testing (August 2026), the FlexSolar 40W produced 4,302 milliamp-hours in one hour of direct sun via USB-C, outperforming other panels in its weight class. Ounce for ounce, it out-produced every other panel they tested, including panels rated at higher wattages. They named it their top pick for do-it-all lightweight solar chargers.

Major upgrade over the previous version

OutdoorGearLab noted that the current version is more than 21 ounces lighter than its predecessor and more than doubled its energy collection in their tests. In late afternoon Oregon sunlight, it collected enough energy to match the output of a common USB wall charger. That is a meaningful benchmark: it means the panel, in decent sunlight, charges devices at roughly the same speed as plugging into a wall outlet.

DC port opens a category USB-only panels cannot reach

The DC5521 port outputs up to 19V/2.1A, which is enough to charge small portable power stations directly from sunlight. This turns the FlexSolar E40 into the smallest practical solar input for a power station, a capability that normally requires a 100W+ panel. For a household that owns a small station like a Jackery 300 or similar, this means solar recharging with a panel that fits in a backpack.

Proven over three years of field use

A three-year long-term review documented the FlexSolar 40W holding up through repeated overnight hiking trips, charging an Anker 737 power bank during the day and running a phone overnight from the stored power. The reviewer confirmed the workflow is reliable and the panel has maintained performance over years of use.

What owners actually say

The patterns across thousands of reviews

The FlexSolar 40W has a strong owner discussion base, with thousands of Amazon ratings and coverage across outdoor and preparedness forums. Several clear patterns emerge.

The most consistent praise is about output in good sunlight. Owners who use it in direct sun repeatedly report that it charges phones faster than they expected from a foldable panel, and several compare it favorably to wall-charger speeds. The pairing with a power bank is the dominant use model: deploy the panel during the day, charge the bank, use the bank overnight. Multiple long-term owners confirm this workflow is reliable over months and years of repeated use.

The DC port draws praise from a smaller but committed group of owners who use it to top off small power stations during camping trips. One owner noted that during the Texas winter power crisis, two of these panels paired with a small solar generator could run a heated throw blanket, charge a laptop, and keep lights on. That is an edge case, but it illustrates the versatility the DC port adds.

The most common complaint is the lack of a kickstand. Long-term owners mention it repeatedly: because aiming the panel toward the sun matters for output, and because the panel has no built-in support, you end up leaning it against rocks, trees, pack frames, or whatever is nearby. It works, but it is not elegant, and on flat ground with no props it can be frustrating. This is the one design omission that multiple independent reviewers call out.

A secondary complaint involves the fold joints. In cold weather, the hinges between panel sections stiffen noticeably and require extra effort to unfold. This is a materials issue common to most foldable panels, but owners who use the FlexSolar in cold conditions mention it specifically. A smaller number of owners report that using the DC and USB ports simultaneously produces noticeably slower charging on both, which matches FlexSolar's own guidance to use one port type at a time for best results.

The one thing to know

It is a fair-weather champion

The FlexSolar E40's advantage over competing panels is largest in direct sunlight. OutdoorGearLab's testers found that in cloudy or indirect light, its output dropped to average for its size class. The gap between the FlexSolar and a cheaper 28W or 30W panel narrows considerably once clouds roll in. This makes sense physically: a more efficient panel extracts more energy per square inch when there is abundant light to extract from. When light is scarce, every panel is fighting for the same thin supply.

If you live in a region with consistently overcast skies and are choosing between this panel and a cheaper alternative, the price premium for the FlexSolar buys you less advantage than it would in a sunnier climate. The panel still works in overcast conditions, but its lead over competitors shrinks. Where it truly shines (the word earns its place here) is in strong sunlight, where it collects more usable energy per hour than panels rated higher on paper.

How it fails, and what to do then

What breaks and when

Solar cells degrade under UV exposure over years, the same physics that applies to every panel. The ETFE coating slows this degradation compared to cheaper PET surfaces, but it does not stop it. After several years of regular use, the panel will produce gradually less power than when it was new. Store it indoors when not in use to extend its productive life.

The fold joints are the mechanical weak point. Six panels means five hinges, and each one flexes every time you deploy and store the panel. In cold weather, the joints stiffen and require more force to open, which accelerates wear. Long-term owners report that the joints loosen over time, which is actually an improvement for cold-weather use but may eventually result in panels that do not fold as compactly. Inspect the joints and the fabric connecting the panels before relying on the charger for a trip.

The junction box, where the three ports live, is not covered by the IP67 rating. Water, condensation, or humidity around the port area can damage the electronics. The LED indicator and the smart IC chip are housed here and are the most likely electronic failure points. After wet-weather use, open the panel and dry it completely before folding and storing.

A small number of owners report units that stopped working within the first few uses. FlexSolar offers warranty support, though the warranty duration and responsiveness reports vary. Confirm the warranty terms at the time of purchase. A panel that arrives dead or dies within weeks is a legitimate warranty claim.

What it costs over time

Near-zero ongoing cost

The FlexSolar E40 is in the $40 to $70 range depending on the version, retailer, and promotions. It has been spotted as low as $28 during Amazon sales. There are no consumable parts, no fuel, and no recurring costs beyond replacing USB cables as they wear.

If you plan to use the DC port with a power station, budget for the DC5521 cable, which FlexSolar sells for a few dollars. This is the one accessory that is not optional but is not included. Without it, the DC port is unusable.

If you do not already own a power bank, the pairing is the same as with any USB solar panel: a 10,000 to 20,000 mAh power bank ($15 to $40) turns the panel from a daytime-only charger into a round-the-clock system. Total entry cost for a complete solar charging setup with DC capability: roughly $55 to $115 depending on what you already own.

If the panel dies, replacement is the path. At this price point, there are no repair services. The ETFE coating and upgraded cell design are intended to extend the lifespan meaningfully, but the eventual replacement cost is the panel price again.

Who should skip this

When 40 watts is more than you need

Anyone who only needs to charge a phone and a power bank and wants the lightest possible panel. The BigBlue SolarPowa P25 weighs under a pound, fits in a cargo pocket, and handles the phone-and-power-bank job. The FlexSolar E40 weighs twice as much and is twice the size when folded. If you will never use the DC port or need the extra output, the weight savings of a 25W panel is a real advantage.

Anyone who wants real-time output monitoring. The FlexSolar E40 has no ammeter. You cannot see how many amps it is delivering, cannot confirm the best angle, and cannot diagnose whether a slow charge is caused by clouds, a bad cable, or panel degradation. The BigBlue 28W with ammeter gives you that feedback. If you are the kind of person who wants to know what your equipment is doing, the ammeter is worth the 3-watt tradeoff in rated power.

Anyone in a consistently overcast climate who is choosing on price. The FlexSolar E40's performance advantage over cheaper panels narrows significantly in cloudy conditions. If direct sunlight is rare where you live, a less expensive 28W or 30W panel may deliver nearly the same real-world performance at a lower cost.

Anyone who needs to run a laptop, CPAP, or anything larger than a small power station. 40 watts is not enough for those devices. Look at a portable power station paired with a 100W+ folding panel.

Where it fits in your readiness

The power-priority portable panel

The FlexSolar E40 belongs in the Sustain tier (the 2-week readiness band) and extends into Endure (long-term self-reliance). It is the panel for a household that wants maximum solar charging capability in a backpack-portable package. The DC port extends its usefulness beyond phone charging into the small-power-station category, which means it can contribute to running lights, fans, radios, and small appliances when paired with the right station.

It matters most for power outages, hurricanes, winter storms, and any extended disruption where grid power is out and fuel may be unavailable. The DC port makes it particularly valuable in scenarios where a portable power station is part of the household energy plan.

It contributes to the solar-charging line on the Energy Preparedness checklist and bridges into the portable power station capability. For a pure USB phone-and-power-bank setup, any of the panels in this review series will do the job. The E40 earns its place when DC charging capability or maximum USB output per hour of sunlight is the priority.

Alternatives worth knowing

Other paths to the same goal

BigBlue 28W (~$50 to $70) - the ammeter advantage

The NWS top pick for USB solar chargers. Three ports, a built-in ammeter for real-time output feedback, and a proven track record with thousands of owners. Produces less power per hour than the FlexSolar E40, but the ammeter is a genuinely useful tool for anyone who wants to know what their panel is doing. No DC port. Full review here.

BigBlue SolarPowa P25 (~$55 to $75) - half the weight

Pocket-sized, under a pound, with IP68 on the panel. The right choice when portability matters more than output. No DC port, no ammeter, and less power, but you will actually carry it every day. Full review here.

FlexSolar 60W (~$70 to $100) - more of the same, larger

If the E40 leaves you wanting more output and you have room in your pack, FlexSolar's 60W panel uses the same port layout and ETFE construction at a higher wattage. Heavier and larger when folded, but significantly more DC charging capability for larger power stations.

Maintenance

Keeping it ready

Store the panel folded and indoors when not in use. Even with ETFE coating, prolonged UV exposure degrades solar cells over time. A closet shelf, a kit bag, or a vehicle kit are all fine. Avoid leaving it in a hot car trunk in direct sun for extended periods.

Wipe the panel face with a dry or slightly damp cloth before each use. Dust, pollen, and fingerprints reduce output. The ETFE surface is durable but still benefits from a clean face for maximum light transmission.

In cold weather, open the panel slowly and let the fold joints warm up before forcing them. Stiff hinges that are forced open in freezing temperatures can crack or loosen prematurely. A few minutes in the sun usually loosens them enough to unfold smoothly.

Check the DC5521 cable and connectors periodically if you use the DC port. A loose or corroded barrel connector will reduce power delivery to a power station without any visible warning. The USB cables are standard and easily replaced; the DC cable is less common and worth keeping a spare.

After any rain or moisture exposure, unfold the panel completely and let it dry before folding and storing. Pay particular attention to the junction box area. The panel surface is IP67; the port area is not.

NWS recommendation

The FlexSolar E40 is the USB solar panel for the household that wants maximum charging capability in a portable package. It produces more energy per hour than competing panels at the same weight, and the DC port opens the door to solar-charging a portable power station without carrying a 100W panel. Pair it with a power bank for phone and radio charging, or connect it to a small power station via the DC port for broader capability. If weight matters more than output, get the BigBlue P25 instead. If the ammeter matters, get the BigBlue 28W.