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Once a portable charger runs out of juice, you have to find an outlet to repower it. Solar power banks, however, help you avoid that problem — they can be repowered by the sun. Like solar chargers, the devices feature built-in solar cells that capture sunlight and convert it into electrical energy to charge devices. But unlike solar chargers, solar power banks are designed with a built-in battery to store generated energy. This means solar power banks do not need to be exposed to the sun while they’re charging your devices (so long as the battery is filled up), giving you more flexibility in terms of when and how you use it.
You can keep a solar power bank in your emergency kit as a backup battery, or bring it with you if you’re heading outdoors for the day. And since a solar power bank stores energy, you can also use it to charge your devices indoors — solar chargers don’t give you this option since they only function when exposed to sunlight. To help you pick a solar power bank, we consulted experts about their benefits and drawbacks, as well as which features matter most — we also rounded up highly rated models in a variety of sizes and power capacities.
What are solar power banks?
Solar power banksare designed with batteries to store generated energy. You can plug your devices into the solar power bank and charge them. Then, you can “refill” the solar power bank’s battery by exposing its solar cells to sunlight. You can also plug some solar power banks into outlets to charge their batteries — in these cases, the sun acts as an alternate source of energy to the battery, explained Sudip K. Mazumder, a professor at the University of Illinois Chicago’s Department of Electrical and Computer Engineering.
As we noted in our guide to solar chargers, many people refer to all charging devices built with solar cells as “solar chargers.” But there is a distinction between solar chargers and solar power banks.
- Solar power banks store generated energy in built-in batteries, so you can charge devices even when there’s no sun.
- Solar chargers are designed without batteries and do not store energy. They have to be exposed to sunlight when they’re charging your devices.
Since solar power banks store generated energy and thus do not need to be exposed to sunlight while charging your devices, they give you more freedom then solar chargers do (so long as you planned ahead, that is).
Best solar power banks
Since we don’t test solar power banks ourselves, we rely on expert guidance and our previous reporting about how to shop for them in order to highlight the best ones. Experts recommended looking at device compatibility, power and size to determine the right model for you. Note that charging capacity is often measured in either milliamp-hours (mAh) or watt-hours (Wh) — all solar power banks we recommend listed capacity in mAh, but only some included capacity in watts. Below, we highlight highly rated solar power banks in a range of sizes with varying capacities that align with expert guidance.
Capacity: 5W, 3,2000mAh
Compatibility: 1 USB-A port
BioLite’s SolarPanel 5+ has a kickstand to prop it up, as well as an integrated sundial to help you align the solar cells with sunlight. It also comes with a battery and charge strength indicator to see the strength of the sun and measure your panel capacity. Additionally, the SolarPanel 5+ boasts a battery status button that tells you how much power is stored in the battery. You can also charge the device’s battery by plugging it into an outlet. If you’re looking for a solar power bank with a larger capacity, BioLite offers the SolarPanel 10+, which can provide up to 10W of usable power
Capacity: 12W, 10,000mAh
Compatibility: 2 USB-A ports
In addition to sunlight captured through the built-in solar cells, the brand said you can also charge this solar power bank’s battery via a 10.5W wall charger. The PowerCore Solar 10000 is designed with an integrated flashlight with three modes: low brightness, full brightness and SOS mode. Anker said the device has a solar efficiency rating of between 21.5 percent and 23.5 percent and is IP64-rated, meaning it's dust and water splash resistant.
Compatibility: 2 USB-A ports
Gordon previously recommended this Hiluckey solar power bank in our guide to solar-powered gadgets. It features solar panels that fold out when you want to use them, and you can also recharge the battery by plugging it into an outlet. The solar power bank features a built-in flashlight with three modes: normal, SOS and strobe.
Compatibility: 2 USB-A ports
In addition to relying on the sun, the battery built into this solar power bank from 4PATRIOTS can be charged using an outlet. The brand said it has an IP67 rating, meaning it’s resistant to rain and splashes. The solar power bank is designed with a LED flashlight with an SOS mode, as well as a battery indicator — when all of the power bank’s four blue lights are lit, it’s fully charged.
How to shop for a solar power bank
While shopping for a solar power bank, experts told us it’s important to think about what’s best for your needs and the devices you own. Keep price point in mind, too — based on our research, we noticed that devices with more or larger solar panels, as well as higher power capacities, often cost more. Some solar power banks feature built-in flashlights, too, which may come in handy during emergency situations like blackouts. Here’s what experts recommend you consider before buying.
Power output and efficiency
Every device is designed with a different size battery, which can help guide your shopping. According to our previous reporting, when it comes to power banks, charging capacity is often measured in milliamp-hours (mAh) or watt-hours (Wh) — all solar power banks we recommend listed capacity in mAh, but only some included capacity in watts.
- Watt-hours (Wh) is one way to measure charging capacity and will give you the best estimate of how much or how many times the charger can charge your device.
- Milliamp-hours (mAh) can be useful when comparing the capacities of different battery packs. For example, a 5,000mAh battery pack will provide fewer charges than a 12,000mAh model.
Generally, devices that are physically larger in size with higher energy demands have larger batteries, and thus require higher capacity chargers to expedite charging, Mazumder said. And if listed, experts told us to compare a solar power bank’s wattage to your device’s charger when shopping.
“If it says ‘works best with a charger that’s rated at 27W and higher,’ then go look for the 27W-and-higher charger,” said Brad Saunders, chairman of the nonprofit USB-IF, in our guide to portable chargers. However, Mazumder said lower capacity chargers may still power larger devices, just at a slower rate than higher capacity options.
As a rule of thumb, Gordon explained, “a typical phone can charge at 5W, but most modern phones contain fast charging capabilities up to 18W. And if you’re charging two devices at once, you’ll need enough wattage for both.” Gordon also suggested checking a solar panel’s efficiency rating when shopping — however, efficiency ratings are not always listed. He said the higher the percentage, the more solar energy you can convert into charging power, and noted that anything above 20-percent efficiency is ideal.
Before you purchase a solar power bank, Mazumder said to make sure its ports are compatible with your electronics. Many solar power banks are built with USB-A ports, while some may come with an additional USB-C port.
Mazumder said people often buy new models of electronic devices and do so at a faster rate compared to buying solar power banks and other charging accessories. Thus, the type of port on your new phone might not match the port on your two-year-old solar power bank, causing you to have to purchase adapters to continue to use it in the future.
Size and solar panels
According to Mazumder, the number and size of solar cells on solar power banks impact how much power they can generate.
When there are more solar cells on a charger — or larger cells — they can generate more power. Gordon noted that some solar battery banks only have one panel, limiting the amount of power they can generate. But more and larger solar cells may mean that the physical size of the solar power bank increases — you may need to decide if you want to prioritize size or power while shopping.