Solar Power Bank vs Folding Solar Panel: Which to Buy in the UK

For real off-grid charging, a folding solar panel beats a solar power bank. A built-in panel is tiny, so it gathers only a trickle of energy. The better plan is an ordinary power bank to store energy, plus a folding panel of 28W or more to fill it. In short, panel area, not battery size, decides how much power you get.

This guide shows the sums for UK sunshine. It also covers the airline limits for power banks and who should buy which. Because we have not tested any product, everything below comes from published specifications and public data.

Why panel area decides everything

Energy equals power multiplied by time. PVGIS data for London gives about 4.1Wh per rated watt of panel on an average June day. In December it falls to about 1.2Wh per watt. However, those figures assume a south-facing panel at a 35 degree tilt. A panel laid flat does about as well in June, but far worse in December.

For example, take a 28W folding panel. It could gather about 115Wh in June (28 multiplied by 4.1). In December it could gather about 33Wh (28 multiplied by 1.17). A built-in panel rated at, say, 3W would gather about 12Wh in June and about 3.5Wh in December.

How much is that in phone charges? EcoFlow’s UK page for its RAPID 20K power bank claims up to 3.87 iPhone 17 charges from 20,000mAh. Multiply 20,000mAh by 3.7V and divide by 1,000 and you get 74Wh. Divide 74Wh by 3.87 and each claimed charge implies about 19Wh from the bank, including losses. So the 28W panel gives roughly six charges on an average June day (115 divided by 19). The 3W panel gives well under one (12 divided by 19 is 0.6).

What a solar power bank does well

A solar power bank is a battery with a small panel on its face. It works as an emergency top-up. However, it is a poor way to charge from the sun. Because its panel is so small, a day outdoors adds little.

Its real value is the battery inside. For example, a 10,000mAh bank holds about 37Wh and a 20,000mAh bank about 74Wh. Therefore, treat the panel as insurance. Charge the bank from the mains before you leave, and use the sun only when you have no other choice.

You can also skip the solar part and buy a plain bank. The EcoFlow RAPID 20K lists 45W USB-C output and a built-in cable. It has no panel at all, so you charge it from the mains or from a folding panel.

What a folding panel does better

A folding panel is large enough to gather meaningful energy. Instead of storing it, the panel sends that energy to a phone directly, or to a power bank for later. EcoFlow describes its 28W panel as keeping phones, power banks and cameras charged. It lists 600g and an IP68 rating, although its UK page showed the panel as sold out when we read it. Jackery lists its SolarSaga 40W Mini at IP68 with a 23% conversion rate.

The catch is that a panel stores nothing. Clouds, shade and low winter sun all cut its output. So pair it with a bank, and let the bank smooth out the gaps. A panel on a rucksack while you walk is the classic use.

In UK weather, aim the panel at the sun and keep it clear of shade. Also, charging through glass greatly lessens charging, according to retailer Festive Lights, so a windowsill is a weak spot. Our portable solar chargers hub covers the basics, and our solar power bank guide lists the picks by role.

How long does a panel take to fill a power bank?

Combine the two figures. A 20,000mAh bank holds about 74Wh. A 28W panel could gather about 115Wh on an average June day, so it could refill the bank in under a day (74 divided by 115 is 0.64). In December the same panel gathers about 33Wh, so a refill takes more than two days (74 divided by 33 is 2.2).

These are long-run averages for a well-placed panel. A single cloudy day gives far less, and shade or a poor angle cuts the yield further. Therefore, treat these figures as rough guides, and treat winter charging as a bonus. A 3W built-in panel needs about six days of June sun (74 divided by 12), which is why it only trickles.

Which should you buy?

Match the kit to the trip. These rules follow the sums above.

• Commuting and everyday carry: A large ordinary power bank. Solar is optional insurance at best.
• A weekend festival or camp: A 10,000 to 20,000mAh bank, fully charged before you leave.
• A multi-day hike: A 28 to 45W folding panel feeding a bank as you walk.
• A power cut at home: A bank charged from the mains. A panel helps only on bright days.
• Laptops, kettles or fridges: Neither option. See our guide to what size portable power station you need, our power station buyer’s guide and the solar generators and power stations hub.

Can you take a power bank on a plane?

Yes, within limits. The UK Civil Aviation Authority allows power banks up to 100Wh in cabin baggage without airline approval. Banks above 100Wh and up to 160Wh need the airline’s approval. The CAA allows no more than two power banks per person. You must not recharge a bank on board. The CAA also says a power bank should not be used to charge a device in flight.

Check the watt-hours on the label. A 20,000mAh bank is about 74Wh, so it falls under 100Wh. A 50,000mAh bank at 3.7V is about 185Wh, which is above the 160Wh the CAA page covers, so ask the airline before you fly with one. Very large mAh claims on unbranded banks are therefore a warning sign.

What about garden lights and home monitors?

Meanwhile, solar garden lights avoid the charger problem, because each light has its own panel. Our solar fence lights buying guide and our guide to solar string lights cover the options. If a set fades, our fix guide for solar garden lights that stop working helps. You can also browse solar garden lighting.

Finally, to see how much power your home really uses before you buy any battery, a monitor helps. Read about home energy monitors. We chose the products we mention from published specifications and have not tested them, as our page on how we choose explains.

Frequently asked questions

Does a solar power bank really work?

Yes, but slowly. The built-in panel adds a trickle, so treat it as an emergency top-up. A folding panel of 28W or more is the better way to charge from sunlight.

Can a solar panel charge a power bank?

Yes. EcoFlow says its 28W panel keeps power banks charged, and the bank can then charge your phone. A panel feeding a bank also means a phone does not depend on patchy light.

How long does a solar power bank take to charge?

It depends on the panel and the weather. At 3W in June, a 74Wh bank needs about six days of good June sun (74 divided by 12). From the mains it is far quicker, so always charge it at home first.

Sources

• What items can I travel with and which are restricted: carry-on only, power banks up to 100Wh, 100 to 160Wh with operator approval, no more than two per person, not recharged on board, should not charge a device in flight. UK Civil Aviation Authority.
• EcoFlow RAPID Power Bank (20K, 45W, built-in cable) product page: 20,000mAh, 45W, up to 3.87 iPhone 17 charges. EcoFlow UK.
• EcoFlow 28W Portable Solar Panel product page: 600g, IP68, keeps phones, power banks and cameras charged; marked sold out when read. EcoFlow UK.
• Jackery SolarSaga 40W Mini product page: IP68, 23% conversion rate. Jackery UK.
• PVGIS photovoltaic estimates: London, PVGIS-SARAH3, 2005 to 2023, 35 degree south-facing, 14% losses; June 4.09 and December 1.17Wh per rated watt per day; a flat panel gives 4.19 in June and 0.46 in December. European Commission Joint Research Centre.
• 8 things to do if your solar lights aren’t working: charging through glass greatly lessens a panel’s ability to charge. Festive Lights (retailer).
• Arithmetic shown in the text: Wh equals mAh multiplied by 3.7 and divided by 1,000; panel energy equals rated watts multiplied by Wh per watt. The 3W built-in panel is an illustration, not a specific product.