Solar Power Banks: Can They Charge a Phone From the Sun?

A solar power bank can charge a phone from the sun, but slowly. The panel built into the bank is tiny: one 10,000mAh model lists a solar panel rated at 1.8 watts, and a full solar recharge can take several days. Charge the bank from a wall outlet and treat the panel as a backup trickle.

Why the built-in panel is so slow

A solar power bank is a normal battery pack with a small solar panel on its face. The panel can only be as big as the case, and that limits its power.

Choetech’s B658, a 10,000mAh solar bank, lists a 1.8 watt solar panel and calls a wall charger the faster way to refill it. Anker’s support page says solar recharge speed depends on sunlight intensity and the panel’s conversion rate, that a full solar recharge may take a long time, and that a wall charger is the way to recharge quickly. PCWorld, covering a 10,000mAh solar bank, put a full charge in direct sunlight at several days.

A rough check shows why. A 20,000mAh bank at a typical 3.7 volt cell voltage stores about 74 watt-hours. A 1.8 watt panel in perfect sun would need about 41 hours of it to put that much back, before any charging losses, and real sun is rarely perfect.

The table ignores charging losses, clouds and panel angle, all of which add time. Its point is the gap between the two columns.

What a solar power bank is good for

The built-in panel earns its place in a few situations:

• An emergency drawer or car kit. A bank stored by a window or on a dashboard slowly keeps itself topped up, so it is not empty when you need it.
• Long, sunny trips. Clipped to a pack in the open, it adds a little charge every day you are away from outlets.
• Peace of mind in an outage. The battery is the main asset; the panel is insurance after the first full charge runs out.

Most solar banks also have a USB-C input for normal wall charging and often a flashlight. Anker’s PowerCore Solar 20000, for example, lists an 18 watt USB-C port that works as both input and output.

When a foldable solar panel works better

If you really need sun to charge your devices, a folding USB solar panel does the job far better than a panel built into a bank. Panels sold for phones fold out to several sections and are rated in the tens of watts (Anker’s SOLIX PS30, for example, is rated at 30 watts), so they can deliver many times the power of a 1 or 2 watt built-in panel in good sun. Pair one with an ordinary power bank: the panel fills the bank by day and the bank charges the phone at night.

For more than phones, a portable power station with its own solar panel is the next step up. It runs lights, a CPAP or a small fridge, and our guide on how to charge a solar generator explains how panel size, angle and shade change charging time. The solar generator buying guide compares sizes. For trips, the best solar generator for camping sizes a unit by the kind of camping, and renters can read solar generators for apartments.

How to read a solar power bank listing

• Solar input. Look for the panel’s watts or amps. If the listing hides it, assume it is small.
• Battery capacity. A larger mAh figure means more phone charges, and a longer solar refill.
• Wall input. A USB-C input with a stated wattage tells you how fast it fills from an outlet, which is how you will charge it most of the time.
• Outputs. Check that the ports match your phone and cables.
• Water and dust rating. An IP rating matters if it will ride on a pack in the rain.

Some solar lanterns also charge a phone in an outage. Solar banks also make a small add-on gift for campers; see our solar generator gifts guide for bigger ideas. More guides on batteries and solar charging are in our power stations section.