A van conversion is the one place where solar genuinely earns its keep in Britain. There is no mains socket, the roof is empty, and the thing you most want to run — a 12V compressor fridge — draws steadily all day and all night. A panel on the roof is what lets you park in a field for three days without the leisure battery dying or the engine having to run.
This guide is about 12V van systems: campervans, self-builds and small motorhomes. It covers what the fridge and lights really cost you in amp hours, what size panel covers that in UK light, and the parts you need between the panel and the battery. If your van is more of a weekend proposition, the folding panel route may suit you better, and there is a separate guide for touring caravans.
From March to October, 100W to 200W on the roof will keep a fridge, lights and phones running indefinitely without hook-up. From November to February it will not, whatever anyone selling you a kit says. Winter vanning runs on the alternator while you drive, with solar as a top-up.
What a campervan actually uses
Everything in a 12V van is measured in amp hours (Ah). A 100Ah lithium leisure battery gives you roughly 100Ah of usable capacity; a 100Ah lead-acid one gives you about 50Ah, because you should not run lead-acid below half. Here is what the usual kit draws over a full day.
| What it is | Typical daily use | Notes |
|---|---|---|
| 12V compressor fridge (50L) | 20-30Ah | The big one. Doubles in a heatwave |
| LED lights | 2-5Ah | Four or five spots, an evening's use |
| Phone and tablet charging | 3-6Ah | Two phones, one tablet |
| Laptop (via inverter) | 8-15Ah | A working day, not an evening film |
| Diesel heater (fan and glow plug) | 5-10Ah | Mostly on start-up; the fan is small |
| Water pump | 1-2Ah | Negligible unless you shower in the van |
A typical weekend van with a fridge, lights and phones lands at 30 to 45Ah a day. Add a laptop and you are nearer 55Ah. That is the number your panel has to replace.
What size panel do you need?
A panel's rating is what it makes in laboratory sunshine, not in Yorkshire in April. As a working rule for the UK, expect a fixed roof panel to deliver around 3 to 4 times its wattage in watt hours on a good summer day, roughly half that in spring and autumn cloud, and a tenth of it in midwinter.
| Panel | Good summer day | April or September | December |
|---|---|---|---|
| 100W | 300-400Wh (25-33Ah) | 150-250Wh (12-20Ah) | 50-100Wh (4-8Ah) |
| 200W | 600-800Wh (50-66Ah) | 300-500Wh (25-41Ah) | 100-200Wh (8-16Ah) |
| 300W | 900-1,200Wh (75-100Ah) | 450-750Wh (37-62Ah) | 150-300Wh (12-25Ah) |
So: 100W if your van is a fridge, lights and phones in summer. 200W if you want shoulder-season weekends without thinking about it. 300W or more if you work from the van, or you have a big fridge and like staying put for a week.
Roof space is usually the real limit. A 100W rigid panel is about 1,050 x 540mm, so most medium wheelbase vans fit two of them around the roof vent and aerial without much argument.
Fixed roof panels vs folding panels
Both work. They suit different ways of using a van.
| Fixed roof panel | Folding panel | |
|---|---|---|
| Best for | Living in it, long trips, no faff | Weekends, vans parked in shade, hire vans |
| Charges while driving | Yes | No |
| Can chase the sun | No | Yes, and it can be angled |
| Security | Bolted and bonded on | Can walk off if you leave it out |
| Roof holes | One cable entry | None |
The trick a lot of people miss is that an angled folding panel can out-produce a flat roof panel of the same rating, because a flat panel on a van roof is pointing at the sky rather than at the low British sun. If you park under trees and walk to the beach, a folding panel on a lead that you set down in the sunshine is genuinely better.
The parts list for a 12V van system
Between the panel and your sockets there are four things, and skipping any of them causes trouble.
- Panel. Rigid for a roof. Flexible panels stick down neatly and look lovely but run hotter, make less, and have a much shorter life.
- MPPT charge controller. This is what makes the panel's variable output safe for the battery, and it harvests 15 to 30 per cent more than the cheaper PWM type in weak light.
- Leisure battery. Lithium (LiFePO4) costs more up front, gives you double the usable capacity for the same rating, and charges faster from solar. It is now the default in new conversions.
- Inverter, only if you need mains. A laptop or camera charger is better run from 12V or USB-C. An inverter is for the hair dryer, the blender and the power tools.
Plus the bits that make it last: MC4 connectors, correctly sized cable, an inline fuse at the battery end, and a waterproof cable gland on the roof. There is more on those in the accessories guide.
Recommended kit
These are the same components we recommend for other 12V off-grid builds on this site, because a van, a tack room and a shepherd's hut want exactly the same things: a panel that tolerates shade, an MPPT controller, a lithium battery and a small inverter.
Renogy 120W ShadowFlux Anti-Shading Panel
N-type cells that keep producing when a roof vent, aerial or branch shades part of the panel, which on a van roof is most of the time. One of these covers a fridge, lights and charging from spring to autumn.
amazon Check Price on AmazonRenogy Rover 20A MPPT
MPPT rather than PWM, which is worth 15 to 30 per cent more from the same panel in British light. Bluetooth means you can check what the roof is making from inside the van without fitting a display.
amazon Check Price on AmazonDCHOUSE 12V 100Ah LiFePO4
Lithium gives you the full 100Ah rather than the 50Ah you would get from lead-acid, charges faster from solar, and weighs about a third as much. It is the single biggest upgrade in a van build.
amazon Check Price on AmazonGiandel 600W Pure Sine Wave Inverter
Enough for a laptop charger, a blender or a small power tool. Run phones and laptops from 12V or USB-C where you can, because an inverter wastes power converting.
amazon Check Price on AmazonIf you would rather not touch the roof at all, a folding panel on a lead does the same job for a weekend van, and packs away when you get home.
EcoFlow 110W / 160W Foldable Solar Panel
Folds away, angles at the sun, and can sit in a sunny spot while the van stays in the shade. For a weekend van, or one you would rather not make holes in, this does the same job as a roof panel.
amazon Check Price on AmazonFitting it without wrecking your roof
Mount it without drilling if you can. Adhesive mounting brackets bonded with a suitable sealant hold a panel on a van roof at motorway speed, and they avoid putting holes in a steel roof that will rust from the inside out. If you do bolt through, use stainless fixings, bed them properly and seal the heads.
Leave an air gap. Panels lose output as they get hot. Brackets that lift the panel 20 to 30mm off the roof keep it cooler and let water run away.
One cable entry, done properly. Use a purpose-made waterproof gland, face the entry backwards relative to travel, and seal it generously.
Fuse at the battery. The short, thick cable from the controller to the battery is the one that can start a fire. It needs an inline fuse within 150mm of the positive terminal.
Watch your height. Panels and brackets add 50 to 80mm. Write the new height somewhere you can see it from the driver's seat, before you meet a height barrier.
Summary — what to buy
Weekend van, fridge and lights, March to October. One 100-120W rigid panel, a 20A MPPT controller and a 100Ah lithium leisure battery. Roughly £350 all in.
Longer trips or a laptop. 200W on the roof, same controller, and consider a 200Ah battery if you are off hook-up for a week at a time.
Weekends, shady pitches, or a van you do not want to drill. A folding 100-160W panel on a lead, with an MPPT controller inside the van.
Winter. Plan to charge from the alternator while driving, or on hook-up. Solar in December is a top-up, not a power supply.
If your van is parked up most of the year and you mainly want the battery kept alive between trips, a small solar trickle charger is a cheaper answer than a full system. And if you are weighing up a van against a static pitch, the static caravan guide covers that side.
Frequently Asked Questions
What size solar panel do I need for a campervan?
For a van with a 12V compressor fridge, LED lights and phone charging, 100W to 200W on the roof is the usual answer. A 100W panel makes roughly 300 to 400Wh on a good summer day in the UK, which covers a fridge drawing 20 to 30Ah a day. If you work from the van on a laptop, or you want to stay out in winter, go to 200W or more.
Will solar keep my leisure battery charged in winter?
Not on its own. A 100W panel might make only 50 to 100Wh a day in December, perhaps a tenth of its summer output. Winter vanning usually means charging from the alternator as you drive, or hooking up to the mains, with solar topping up rather than doing the whole job.
Do I need an MPPT controller or will PWM do?
Use MPPT. It harvests roughly 15 to 30 per cent more from the same panel in weak British light, and the price gap is now small. PWM controllers only really make sense on very small panels such as a trickle charger.
Can I fit solar panels without drilling the roof?
Yes. Most van conversions now bond panels to the roof with adhesive mounting brackets or a bed of sealant, which avoids making holes in a metal roof. You still need one hole for the cable, fitted with a proper waterproof gland and sealed well.
Is a folding panel better than a fixed one?
It depends on where you park. A folding panel can be angled at the sun and moved into a sunny spot while the van sits in shade, so it often beats a fixed panel of the same size. A fixed panel needs no setting up and works while you drive, which suits weekend trips better.