Last September, car boot sale in a village outside Bath. I stumble across a chap selling a "200 watt" solar panel he'd bought online, never taken out of the packaging. He'd paid £150 for it six months earlier. He let me have it for £40. I tested it the next day: 78 W max in full midday sun. The panel was a polycrystalline model sold by a ghost brand, with completely fabricated specs. Forty quid well spent on a lesson: in portable solar, the marketing often lies more than the weather forecast.
A solar panel is a sandwich of doped silicon. When sunlight hits the photovoltaic cells, it knocks electrons free from the silicon atoms. Those electrons flow through a circuit, creating a direct current (DC). This current travels via a cable to your station, passes through the charge controller (MPPT if you've read my article on the subject), and fills up the battery.
No moving parts. No noise. No fuel. Just sunlight and silicon. That's what makes the whole thing feel almost magical when you're in the middle of nowhere with zero infrastructure. Paired with a portable power station, you've got a complete, silent energy system.
The peak power (Wp) shown on a panel refers to standardised test conditions: 1000 W/m2 irradiance, 25 degrees C cell temperature, AM1.5 solar spectrum. In the UK, you'll hit those conditions roughly two to three hours a day in summer, around midday. The rest of the time, you're below it.
In 2026, there's no debate left. Monocrystalline won.
Monocrystalline cells are cut from a single silicon crystal. Their typical efficiency sits around 22 to 24% on good portable panels. Polycrystalline cells, made from silicon melted into a block and then sliced, top out at 16-18%. For the same surface area, monocrystalline produces 25 to 40% more energy.
And the price of monocrystalline has dropped so far that it costs virtually the same as polycrystalline. If you still find polycrystalline portable panels for sale, it's old stock or counterfeit. Move along.
IBC (Interdigitated Back Contact) and HJT (Heterojunction) cells push even higher, to 25-26% efficiency. You'll find these on premium EcoFlow and Bluetti panels. The 15-20% price premium is justified if you want to maximise output from a small surface area -- typically for a setup where deployment space is limited.
Foldable panels account for 90% of the portable market. They fold up like a briefcase, fit in a boot, and unfold in thirty seconds. The ETFE or PET coating protecting the cells resists splashes and dust. It's the go-to format for camping, campervans, and any mobile use.
A foldable 200 W panel weighs between 5 and 8 kg folded, measuring roughly 60 x 55 cm. Unfolded, it stretches between 150 and 230 cm wide depending on the model. It stands up using the built-in kickstand, or lies flat on a campervan roof.
Rigid panels are more efficient at equal wattage. The tempered glass protecting the cells transmits light better than ETFE, and the rigid frame keeps cells perfectly flat without the micro-flexing that degrades efficiency. A rigid 200 W panel produces 5 to 10% more in practice than a foldable 200 W panel.
But a rigid panel doesn't fold. It measures at least 100 x 60 cm, weighs 10 to 15 kg, and needs to be mounted somewhere. For a permanent installation on a campervan or motorhome roof, rigid is superior. For anything mobile and temporary, foldable wins by a mile.
My personal setup: a 200 W rigid panel fixed to the van roof for permanent production, and a 200 W foldable panel I bring out when I'm parked in the shade and can position the foldable in the sun further away. Best of both worlds, but it costs twice as much.
60 to 100 W: the supplement. You keep your small station topped up over a camping weekend. Charge a phone directly. Strictly a backup. A 100 W panel takes roughly 8 to 10 hours to charge a 500 Wh station in real conditions. That's slow going.
100 to 200 W: the campervan standard. Paired with a 1000 Wh station, you can maintain autonomy over several days if you manage your consumption sensibly. It's the most popular format, and for good reason -- it's the best compromise between weight, output, and price.
200 to 400 W: full autonomy. Here, you can recharge a 2000 Wh station in a single day of good weather. This is the setup for long-haul campervan travellers and semi-permanent installations. Weight and bulk increase seriously: a 400 W kit weighs between 15 and 25 kg and takes up proper space once folded.
Beyond 400 W: we've left portable territory. That's fixed installation on a roof or ground-mounted frame.
A classic pitfall: adding up panel wattage without checking whether your station can accept that much input. If your station has a maximum solar input of 200 W, connecting 400 W of panels won't double your charging speed. The station will cap at 200 W and you'll have spent money for nothing. Always check the maximum solar input wattage of your station before buying panels.
A solar panel outputs a voltage and a current. Your station accepts a voltage range and a maximum current. If the two don't match, it won't work. Or it'll work badly.
Let's take an example. Your panel outputs 22V and 9A at peak (that's 200 W). Your station accepts 12-60V input and 10A max. Perfect, everything's within range. But if your station only accepts 12-25V and 8A, your panel at 22V and 9A will be throttled to 8A by the station -- 176 W instead of 200 W. Not catastrophic, but you're losing 12% of performance.
The worst case: a panel whose open-circuit voltage (Voc) exceeds the station's maximum input voltage. Open-circuit voltage is what the panel produces when nothing is connected -- it's always higher than the voltage under load. A panel with a Voc of 48V plugged into a station that accepts a max of 45V can damage the charge controller. It's rare with major brands (they have protections), but it happens with budget stations.
My advice: stay within the ecosystem. An EcoFlow panel with an EcoFlow station, a Bluetti with a Bluetti. Compatibility is guaranteed, the connectors are right, and the voltage ranges are optimised. If you mix brands, check the panel's open-circuit voltage (Voc), the station's max input voltage, and the max input current. That's three numbers to compare -- hardly rocket science, but you do need to check.
The advertised efficiency of a panel is the percentage of solar energy received that gets converted into electricity. 23% is very good for a portable panel. But that figure is measured in a lab, not in a field.
In real conditions, several factors nibble away at your output.
Angle of incidence. A panel produces maximum power when sunlight hits its surface perpendicularly. At 45 degrees of incidence, you lose roughly 30%. Most foldable panels have a kickstand that gives a fixed angle. The cleverer ones (like some EcoFlow models) have an angle tracker in the app that tells you how to orient the panel. In practice, repositioning the panel every two hours makes a genuine difference: I've measured 15-20% more production over a day by manually following the sun.
Temperature. Solar cells lose efficiency as they heat up. The typical temperature coefficient is -0.3 to -0.4% per degree above 25 degrees C. In summer in southern England, a panel lying on the ground in full sun can reach 60-70 degrees C. That's 10 to 15% loss. Propping the panel slightly elevated to let air circulate underneath helps limit overheating.
Partial shading. Just one corner of the panel in shade, and the entire output nosedives. The cells in a panel are connected in series: if one cell is shaded, it becomes a bottleneck for all the others. This is the number one trap when camping: the tree that cast no shadow at 10am is throwing shade across your panel at 2pm. Some panels have bypass diodes that soften the blow, but they don't eliminate it.
Factoring in all of this, a 200 W panel produces on average 120 to 140 W in summer around midday, 60 to 90 W in mid-morning or afternoon, and 20 to 40 W on overcast days. Over a full summer day, reorienting it two or three times, I've measured total production of 800 to 1000 Wh from my 200 W panel. That's roughly 60% of the theoretical maximum. Still impressive for something that fits in a bag.
A portable solar panel needs almost no upkeep. Almost.
Wipe the surface with a damp cloth when it gets dusty. Dust, pollen, and bird droppings can reduce output by 5 to 15%. When camping, a quick wipe each morning takes ten seconds and gets you a few extra watts.
Check the connectors regularly. MC4 connectors (industry standard) are robust, but the seals can wear if you force them. An oxidised or loose connector creates resistance, generates heat, and reduces current.
Store the panel folded, not rolled. Repeated micro-flexing of the cells eventually creates invisible microcracks that gradually reduce efficiency. A foldable panel folds at its intended hinges, not elsewhere.
Don't walk on it. Seems obvious, but I've seen people lay their panel flat and walk across it to get to their van. The cells are fragile under point pressure.
If I were starting from scratch with a single panel for all-round camping and campervan use, I'd go for a foldable monocrystalline 200 W with IBC or HJT cells, ETFE coating, MC4 connectors, and a cable at least three metres long. Budget: £220 to £350 from EcoFlow, Bluetti, or Jackery.
200 W is the sweet spot. Enough to keep a 1000 Wh station in near-complete autonomy through summer. Light enough for one person to carry. Compact enough when folded to stay out of the way. And with a good MPPT controller, you squeeze every last drop from every ray of sunshine. To understand what all this means in concrete energy terms, have a look at my guide on the watt-hour.
If your budget is tight, a 100 W panel from a reputable brand beats a 200 W panel from an unknown one. Wattage means nothing if the advertised watts are hot air.
Yes, but far less effectively. On an overcast day, a 200 W panel produces between 20 and 40 W -- enough to charge a phone or keep a small station ticking over, but not enough to run a fridge. The MPPT controller in your station helps squeeze the most from limited light, but it can't work miracles.
In real conditions, a 100 W panel produces about 60-75 W and a 200 W panel around 120-140 W. Double the output essentially means double the freedom: with a 200 W panel, you can keep a fridge running AND recharge your station during the day. With a 100 W panel, you have to choose.
If you want to get the most from your panel, absolutely. An MPPT controller harvests 20 to 30% more energy compared with PWM, especially in overcast conditions or early morning and late afternoon. The good news is that most recent stations above 500 Wh already have one built in.
A single 200 W panel does the job in summer if you have a full day of decent weather -- you'll recover between 800 and 1000 Wh over the day. In spring, autumn, or mixed conditions, two 200 W panels give you a comfortable margin. It all depends on your daily consumption and the capacity of your station.
Cedric
