A solar power bank is a good power bank with a panel stuck on the back, and the panel is close to ornamental. That is not a criticism of the products - several are excellent batteries at fair prices - but it is the opposite of how they are sold, and it is the single thing worth understanding before you buy one.
The rest of this page is the arithmetic. What a given capacity genuinely charges, what it will never charge, and what to buy if you actually want to generate electricity rather than carry it.
The panel, honestly
The panels built into these banks run from about 1W to 6W. Most listings do not tell you which, and that silence is informative.
A 20,000mAh bank holds roughly 74 watt-hours. At a genuine 2W - which is what a UK reviewer measured on one popular model in bright midday sun - filling it from empty takes about 37 hours of that kind of light. Britain does not supply 37 consecutive hours of bright midday sun, so in practice you are looking at four to six days of leaving it out, assuming you angle it and it does not overheat.
The most telling evidence is not from reviewers, it is from the manufacturers. One brand's own Amazon listing advises using a charging cable and keeping the solar for emergencies. Another's specification sheet quietly states 50 hours to charge fully. They are not hiding it so much as burying it.
Across five different brands the pattern is the same - four and five star reviews praising the battery, one and two star reviews complaining that solar charging did nothing. One UK buyer left a bank in full sun for seven hours and it did not pass 25%. Another reported a bank charged all morning in direct sun managed a single bar. The fairest summary came from a reviewer who called it a trickle charge and said charging it on solar alone would take days.
The wattage trap
Look at a listing titled something like Solar Power Bank 20000mAh 22.5W. The 22.5W is not the panel. It is how fast the bank charges your phone through the USB cable.
This is not quite a lie, because output wattage is a real and useful specification. But it sits in the title next to the word solar, and the panel - which might be 1.9W - goes unmentioned. One of the banks below is unusual in actually disclosing 6W across four fold-out panels. The rest say nothing at all.
The rule is simple. If a listing does not state the solar panel wattage separately from the output wattage, assume the panel is small. Sellers publish the numbers that flatter them.
What it will power
Now the good news, because as batteries these things are genuinely useful. A 20,000mAh bank is about 74Wh on paper, of which roughly 55 to 60Wh survives the conversion to your device.
| Device | Energy per charge | From 20,000mAh |
|---|---|---|
| Phone | 15-24Wh | 3-4 full charges |
| Head torch | 2-5Wh | A dozen or more |
| Handheld GPS | 3-7Wh | 8-15 charges |
| Camera battery | 7-16Wh | 4-7 batteries |
| Bite alarms and bivvy light | ~6W draw | Over a week |
| Tablet | 25-40Wh | 1-2 charges |
For a weekend away, a long fishing session or a festival, that is a genuinely useful amount of electricity in a pocket. The torch, GPS and camera-battery figures are approximate rather than measured, because they vary by model, but they are the right order of magnitude.
What it will not power
A laptop. Laptop batteries hold 50 to 100 watt-hours, which is more than a 20,000mAh bank usefully contains. Even a top-up needs USB-C Power Delivery at 60W or more, which most solar banks do not have. You want a plain high-output bank for this, and there is one below.
A CPAP machine. This comes up often and the answer is a firm no. A CPAP draws around 30W without humidification, which is roughly 280Wh across an eight-hour night, and closer to 375Wh with the humidifier running. That is four to five times what the bank holds. CPAP off-grid is a job for a proper power station, not a power bank.
Anything with a mains plug. These banks have USB sockets, not three-pin sockets. No kettle, no laptop charger with a figure-of-eight lead, no camera battery charger that plugs into the wall.
A fridge or coolbox. A 12V compressor coolbox averages around 45W and runs continuously, so it would flatten a 20,000mAh bank in under two hours.
If you actually want solar
Buy the battery and the panel as two separate things. It costs a little more and works several times better.
A 20W folding panel measured about 6W in hazy conditions in independent testing, and independent lab work suggests these panels deliver roughly a quarter to a third of their rated output in overcast light. That is still three times what a built-in panel manages, and the practical advantage is bigger than the numbers suggest, because a folding panel can be angled at the sun and hung on a rucksack or a car window while the bank itself sits in the shade staying cool.
UK users report filling a 20,000mAh bank to roughly 60% across an eight-hour day on a car windscreen with a 20W panel. That is a real result, and nothing bolted to the back of a power bank comes close to it. Our portable solar panels guide covers the larger folding panels if you need more than this.
What to buy
All confirmed in stock on Amazon UK at the time of writing.
Riapow 20,000mAh Solar Power Bank
The pick if you want one of these, and the one with by far the most UK reviews behind it. A capable 20,000mAh bank with genuine wireless charging and cables built in, so nothing to forget. The panel is a bonus rather than a feature - a reviewer with a wattmeter measured it at 1.9W - but nothing here depends on it working.
amazon Check Price on Amazon →A ADDTOP 20,000mAh Solar Power Bank
Worth singling out because it actually states the solar figure - 6W across four panels that unfold - which is more than most competitors will tell you, and more panel area than a single-face bank. It is still a several-day proposition to fill it by sun alone, and buyers say as much, but at least you know what you are getting.
amazon Check Price on Amazon →INIU 100W 25,000mAh Power Bank
No solar panel at all, and that is the point. One of very few banks that genuinely sustains 100W over USB-C, verified by a reviewer running a gaming laptop from it for 45 minutes while the laptop charged. At 92.5Wh it sits under the 100Wh airline threshold. If your reason for wanting a solar bank was laptop power, this is the honest answer.
amazon Check Price on Amazon →FlexSolar 20W Folding Solar Panel
Pair this with any power bank and you have a setup that genuinely recharges off-grid. Independent measurement put it at about 6W in hazy light against its 20W rating, which is the honest expectation, and UK users report roughly 60% of a 20,000mAh bank across a day on a car windscreen. Light enough at 395g to strap to a rucksack.
amazon Check Price on Amazon →Taking one on a plane
The UK rules changed on 27 March 2026 and are stricter than many people realise.
- Power banks go in hand luggage only - never in the hold
- Two per passenger maximum
- Each must be individually protected against short circuit, so a pouch or tape over the terminals
- Up to 100Wh needs no approval; 100 to 160Wh needs the airline's permission; above that is not allowed
- You cannot recharge them on board
Every bank on this page falls under 100Wh, so none of them needs approval. The catch is that airlines check watt-hours while listings advertise mAh, so do the conversion yourself before you travel - divide the mAh by 1000 and multiply by 3.7. A 26,800mAh bank is about 99Wh, which is close enough to the limit to be worth knowing.
Summary
- Buy it for the battery, not the panel. As power banks these are good; as solar chargers they are not
- A 20,000mAh bank is 74Wh on paper, 55-60Wh in practice - three or four phone charges
- Built-in panels run 1W to 6W, so refilling by sun takes days, not an afternoon
- The wattage in the title is usually the USB output speed, not the panel
- No laptop, no CPAP, nothing with a mains plug - those need a power station
- If you want real off-grid charging, buy a separate folding panel
- Flying - hand luggage only, two per person, under 100Wh, no charging on board
If your honest need is more than a few phone charges, the next step up is a power station rather than a bigger bank, and building one yourself becomes cheaper than buying above about two kilowatt-hours.
Frequently Asked Questions
Does the solar panel on a solar power bank actually work?
It works, but far more slowly than buyers expect. The panels built into these banks are typically 1 to 6 watts, and in real UK light they deliver a fraction of that. Filling a 20,000mAh bank from its own panel takes several days of good sun rather than an afternoon. One manufacturer's own listing advises using a cable and keeping solar for emergencies.
How many times will a 20,000mAh power bank charge a phone?
Three to four times for a typical modern phone. The headline figure of 20,000mAh is about 74 watt-hours on paper, but conversion losses mean roughly 55 to 60 watt-hours actually reach your phone, and a full phone charge costs 15 to 24 watt-hours once losses are counted.
Can a solar power bank charge a laptop?
Most cannot, and even the ones that can will not fill it. A laptop battery holds 50 to 100 watt-hours, which is more than the usable capacity of a 20,000mAh bank. You also need USB-C Power Delivery at 60W or more, which most solar banks do not offer. For laptops, buy a plain high-output power bank instead.
Will a solar power bank run a CPAP machine overnight?
No. A CPAP draws roughly 30W without humidification and more with it, which is about 280 watt-hours across an eight-hour night. That is nearly four times what a 20,000mAh bank holds. CPAP off-grid needs a proper portable power station, not a power bank.
What does the wattage in the product title mean?
Usually the USB output speed, not the solar panel. A bank advertised as 22.5W is describing how fast it charges your phone through the cable. The panel is often a fraction of that and frequently is not stated anywhere on the listing. If the solar wattage is not disclosed, assume it is small.
Can I take a solar power bank on a plane?
Yes, in hand luggage only. Since March 2026 UK rules allow a maximum of two power banks per passenger, each protected against short circuit, and they cannot be recharged on board. Anything up to 100 watt-hours needs no approval, which covers every bank on this page. Airlines check watt-hours rather than mAh, so divide the mAh figure by 1000 and multiply by 3.7 to get it.
What should I buy if I genuinely want solar charging off-grid?
A separate folding panel. A 20W folding panel measured about 6W in hazy conditions in independent testing, which is several times what a built-in panel manages, and it can be angled at the sun while the bank sits in the shade. Buy the bank and the panel as two things rather than one compromised object.