Can a USB solar charger keep a phone running during a multi-day power outage?

Yes, if you pair it with a power bank. The solar panel charges the power bank during daylight hours, and the power bank charges the phone anytime. In direct sun, the BigBlue 28W can refill a 10,000 mAh power bank in roughly a day, which is enough to charge most smartphones twice. Without a power bank, you can charge a phone directly, but only while the sun is shining and the panel is deployed.

Does the BigBlue 28W work through a window?

Poorly. Window glass blocks a significant portion of the UV and infrared spectrum that solar cells convert to electricity, and the angle is rarely optimal. BigBlue's own documentation recommends against using it inside a window or behind a windshield. Place it outdoors in direct sunlight for usable output.

What is the difference between a USB solar charger and a solar power bank?

A USB solar charger is an external panel with no internal battery. It generates electricity only while in direct sunlight and delivers it through USB ports to whatever is plugged in. A solar power bank is a battery pack with a small solar panel built into its surface. The built-in panel on most solar power banks is too small to meaningfully recharge the battery. A dedicated USB solar panel paired with a separate power bank is a far more effective combination for emergency charging.

Home Gear Reviews BigBlue 28W Solar Charger

Gear Review · Energy

BigBlue 28W USB Solar Charger.

The USB solar panel that field testers and thousands of owners keep choosing. Here is what it actually delivers, what to pair it with, and who should buy something else.

Rated Power

28 watts

Weight

~1.5 lbs

NWS Verdict

Buy it

View on Amazon

Strengths

Produced the highest power output of any panel in its class in independent field testing.
Built-in ammeter shows real-time charging current so you can confirm it is working and find the best angle.
Folds to the size of a tablet and weighs about 1.5 pounds, light enough to clip to a pack and forget.
Dual USB-C and one USB-A port charge up to three devices at once.

Limitations

Real-world output is well below the 28W rating in anything less than full direct sun.
Cloud cover can interrupt charging, sometimes requiring you to unplug and replug the device to restart.
The USB junction box is not waterproof despite the panel surface carrying an IP44 rating.

What it is

A real solar panel for charging phones and power banks

The BigBlue 28W is a foldable USB solar panel. Four monocrystalline solar cells unfold from a tablet-sized package and convert sunlight into USB power for phones, power banks, GPS units, headlamps, radios, and other small electronics. It has no internal battery. It generates electricity only while deployed in direct sunlight with a device plugged in.

The current model uses N-type solar cells rated at 25.4% conversion efficiency with a shadow-free surface design (no metal grid lines on the panel face). It carries dual USB-C ports and one USB-A port, each rated at up to 5V/3A, with a combined maximum output of 5V/4.8A. A built-in digital ammeter on one version shows the real-time charging current so you can confirm the panel is working and adjust the angle for the strongest reading.

Folded, it measures about 11 by 6 by 1.4 inches and weighs approximately 1.5 pounds. It includes carabiners for hanging from a pack, clothesline, or branch, and a zippered pocket for stowing cables and small devices.

This is a distinct product category from solar power banks, which are battery packs with a small panel glued to the surface. The integrated panel on most solar power banks is so small that it contributes negligible charge. A dedicated USB solar panel like this one, paired with a separate power bank, is a far more capable system for keeping devices alive during a multi-day outage or off-grid trip.

Why it works

The testing backs it up

Highest measured output in its class

In Treeline Review's side-by-side field testing, the BigBlue 28W produced roughly 950 milliamp-hours per hour in direct sun, the highest output of any panel tested. It outperformed competing panels from multiple brands in the same conditions.

The ammeter changes how you use it

OutdoorGearLab's testers highlighted the built-in ammeter as a genuinely useful feature, not a gimmick. It shows exactly how many amps the panel is delivering, which means you can angle the panel, watch the number climb, and know you have the strongest possible charge angle. On cloudy days, it confirms the panel is still working even when progress is slow.

Proven on month-long trips

A long-term field review documented the BigBlue 28W keeping electronics for two people charged indefinitely across two thru-hikes and a month-long bikepacking trip through Central Asia. Even in shade and intermittent sun, it still contributed a meaningful charge.

Three ports for simultaneous charging

Two USB-C ports and one USB-A port let you charge a phone, a power bank, and a headlamp or radio at the same time. The total output is shared across connected devices, so each charges slower than it would alone, but for a household deploying this during an outage, the ability to top off several devices in one sunny window is practical.

What owners actually say

The patterns across thousands of reviews

With nearly 10,000 Amazon ratings and strong discussion across camping, preparedness, and outdoor gear forums, the BigBlue 28W has one of the largest owner bases of any USB solar panel. Several clear patterns emerge.

Owners consistently praise the real-world charging speed in good sunlight. A recurring theme across forums and retailer reviews is that the panel charges phones and small power banks faster than expected once properly positioned. Owners who pair it with a 10,000 to 20,000 mAh power bank report refilling the bank over the course of a sunny day, then using the bank to charge phones overnight or on cloudy days. That pairing is mentioned so frequently it effectively functions as the standard setup.

The ammeter draws consistent praise, especially from first-time solar users. Owners say it removes the guesswork: you can see immediately whether the panel is working, whether a cable is making good contact, and whether the angle you chose is producing the best result. Several long-term reviewers call it the single feature that separates the BigBlue from competing panels that look nearly identical.

The most common frustration is the gap between the 28W rating and what the panel delivers in practice. Owners measuring actual output report something closer to 15 to 20 watts even in strong sunlight, with significantly less in overcast or partially shaded conditions. This is normal for all solar panels (rated wattage assumes laboratory conditions no real sky matches), but owners who expect 28 watts of phone-charging power are routinely surprised. A smaller number of owners report that passing cloud cover can stop charging entirely, sometimes requiring them to unplug and replug the device to restart the charge cycle.

A handful of reviewers report early failures within the first few uses, though this appears to be a small fraction against the volume of positive long-term reports. BigBlue offers a two-year warranty and, according to owner discussion, their customer service has responded reasonably to defective-unit claims.

The one thing to know

It charges a power bank, not a laptop

The BigBlue 28W is designed for phones, power banks, GPS devices, headlamps, radios, and other small USB electronics. It does not have enough output to charge a laptop or a large portable power station. BigBlue's own product documentation is explicit about this. If you need to run or recharge larger devices during an outage, you need either a much larger solar panel (100W or more) paired with a portable power station, or a generator.

The best use model for preparedness: unfold the panel in direct sunlight during the day, connect it to a power bank, let it charge the bank while you do other things. Use the power bank to charge your phone, radio, headlamp, and other small devices as needed, day or night. That setup keeps a household's communications and lighting running for as long as the sun keeps rising.

How it fails, and what to do then

What breaks and when

Solar cells degrade slowly over years of UV exposure. A panel stored indoors and deployed only when needed will last significantly longer than one left permanently in the sun. You will not notice the degradation from year to year, but after several years of heavy outdoor use, the ammeter will show lower peak readings than it did when the panel was new. There is no repair for this; it is the physics of the material.

The USB junction box and cable connections are the most common failure point. The panel surface has an IP44 weather resistance rating, but the junction box where the ports live is not waterproof. Rain, condensation, or water pooling around the port area can damage the electronics. The rubber port covers help, but they are not a seal. Treat it like you would treat a phone: use it in rain if you have to, but dry it promptly and do not leave it face-down in a puddle.

The fabric and stitching on the folding panels can wear with heavy use, particularly the attachment points where carabiners clip. Inspect these before relying on it for a trip. A torn loop is a panel that blows off a pack.

BigBlue backs this with a two-year warranty. A dead panel within the warranty period, particularly one that stopped charging within the first few months, is a legitimate warranty claim. Owners report that BigBlue's support team has been responsive to DOA and early-failure claims.

What it costs over time

Close to a one-time purchase

The BigBlue 28W is in the $50 to $70 range depending on the version and retailer. There are no consumable parts, no filters, no cartridges, and no fuel. The sun is free. The only ongoing cost is replacing USB cables as they wear out, which is a few dollars every year or two at most.

If you do not already own a power bank, budget for one. A good 10,000 to 20,000 mAh power bank runs $15 to $40 and turns the solar panel from a daytime-only charger into a round-the-clock system. That pairing is the real cost of entry: roughly $65 to $110 total for a complete solar charging setup with no recurring expenses.

Replacement cost if the panel dies after warranty: buy another one. There are no repair services for USB solar panels, and the cost of the unit is low enough that replacement is the practical path. A well-maintained panel stored indoors between uses should last five or more years before output degradation becomes noticeable.

Who should skip this

It is not for every household

Anyone who needs to charge a laptop, run a CPAP, or power anything larger than a phone or tablet. This panel does not have enough output for those devices. Look at a portable power station paired with a 100W+ folding panel instead.

Households in regions with consistently heavy cloud cover for extended periods. The BigBlue 28W needs direct sunlight to produce meaningful charge. A week of solid overcast will leave you with a dead power bank and a panel that is generating almost nothing. In those climates, a hand-crank charger or a generator is the more reliable backup.

Anyone expecting set-and-forget reliability. Solar charging requires some attention: angling the panel toward the sun, repositioning as the sun moves, unplugging and replugging devices when cloud cover interrupts the charge cycle. If that sounds like more involvement than you want, a larger power bank charged from the wall before an outage, or a generator, is a simpler solution.

Where it fits in your readiness

The renewable layer of your energy plan

A USB solar charger belongs in the Sustain tier (the 2-week readiness band) and extends into Endure (long-term self-reliance). It is the piece that keeps working after batteries are dead and fuel is gone. Paired with a power bank, it gives a household indefinite ability to charge phones, radios, lights, and other USB devices for as long as the sun rises.

It matters most for power outages, hurricanes, winter storms, and any disruption where grid power may be out for days or longer. It is also the core of a portable energy plan for evacuation kits and vehicle kits.

It satisfies the solar-charging line on the Energy Preparedness checklist and contributes to the communications and lighting capabilities on several hazard-specific checklists.

Alternatives worth knowing

Other paths to the same goal

FlexSolar 20W (~$30 to $50) - lighter and cheaper

A smaller panel with USB-C and USB-A that costs less and weighs less. The tradeoff is lower output: it will charge a phone, but it will take longer, and it has less headroom for running multiple devices at once. A good choice if weight and budget are the primary constraints.

Nekteck 28W (~$40 to $55) - proven dual-USB alternative

Another well-reviewed 28W panel with dual USB-A ports (no USB-C). It performs comparably to the BigBlue in direct sun but lacks the ammeter and USB-C connectivity. A solid option if USB-C does not matter and you want to save a few dollars.

Goal Zero Nomad 10 (~$50 to $80) - the premium compact option

A smaller, lighter panel from a well-known outdoor brand. It has lower output (10W) but pairs directly with Goal Zero's power bank ecosystem. More expensive per watt than the BigBlue, and considerably slower at charging, but well-built and very compact. Best for someone already invested in Goal Zero gear.

Maintenance

Keeping it ready

Store the panel folded and indoors when not in use. UV exposure degrades solar cells over time even when nothing is plugged in. A closet shelf, a go-bag, or a vehicle glove box 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. Do not use solvents or abrasive cloths.

Check the USB port covers and carabiner loops before relying on it. Replace fraying cables. Test the panel against a phone or power bank once or twice a year to confirm it still charges. If the ammeter shows noticeably lower numbers than when the panel was new under comparable sunlight, the cells are aging.

After any rain exposure, open the panel fully and let it dry completely before folding and storing. Moisture trapped between folded panels can damage connections over time.

NWS recommendation

Buy one BigBlue 28W and pair it with a 10,000 to 20,000 mAh USB power bank. That combination gives your household indefinite phone, radio, and light charging capability during any power outage, for under $110 total and with no fuel or recurring costs. Put the panel in your go-bag, your vehicle kit, or on the shelf next to your other energy supplies. Test it once before you need it.