400W Solar Panels: Output & What They Power
A popular size for campervans, boats and off-grid living — and a common home-roof panel too. Here’s what a 400W panel produces, what it runs, and which type to pick.
The short answer
A 400W solar panel generates roughly 1.6–2kWh on a good UK summer day (much less in winter) — enough to charge phones and laptops, run LED lighting, a fridge or cool box, fans, and keep a leisure battery or power station topped up. It’s one of the most popular sizes for campervans, motorhomes, boats and off-grid setups, comfortably covering the basics for one or two people.
It comes in rigid (durable, permanent mounting), flexible (bends to curved roofs) and foldable (grab-and-go portable) types, costing anywhere from ~£80 to £500+. One thing worth knowing: 400W is also the wattage of modern rooftop panels — so if you’re actually researching home solar, that’s a different setup we’ll point you to below. First, the portable picture.
What this guide covers
The 400W panel is a sweet spot in portable and off-grid solar — powerful enough to be genuinely useful, still manageable in size and cost. It’s the go-to for a lot of campervan and motorhome builds. Here’s what it’ll actually do for you, which type suits your use, and how to pick well.
What can a 400W solar panel run?
A 400W panel (with a suitable battery to store what it makes) comfortably handles low-to-medium power needs:
| Will happily run | Won’t run directly |
|---|---|
| Phone & laptop charging | Kettle |
| LED lighting | Electric heater |
| Fridge / cool box | Oven / hob |
| Fans, water pump | Hairdryer |
| Charging a power station / leisure battery | Air conditioning |
The rule of thumb: 400W is great for electronics, lighting, refrigeration and charging, but not for high-power heating appliances (kettles, heaters, ovens) which draw far more than it can supply. Paired with a battery, though, it covers most day-to-day off-grid essentials for one or two people very well.
How much power does a 400W panel produce a day?
| Conditions | Typical daily output |
|---|---|
| Bright summer day | ~1.6–2kWh |
| Average spring/autumn day | ~0.8–1.4kWh |
| Dull winter day | ~0.4–0.8kWh |
The honest headline is the seasonal swing: a 400W panel might make 2kWh on a bright summer day but only a few hundred watt-hours in dull winter, because UK winter daylight is short and weak. A rough way to estimate: panel wattage × effective sun-hours — 400W over ~4–5 good summer sun-hours ≈ 1.6–2kWh. This big summer-winter difference is why off-grid and campervan users often size generously or add a second panel if they use their setup year-round.
Rigid vs flexible vs foldable 400W panels
400W panels come in three main forms, and the right one depends entirely on how you’ll use it:
| Type | Best for | Trade-off |
|---|---|---|
| Rigid (glass + frame) | Permanent campervan/off-grid mounting | Most efficient & durable; heavier, flat only |
| Flexible | Curved van roofs, low profile | Bends to fit; less efficient, shorter life |
| Foldable / folding | Grab-and-go portable use | Packs away; set out each time |
Rigid panels are the most efficient and long-lasting — the default for a permanent campervan roof or off-grid frame. Flexible panels bend slightly to fit curved roofs and sit low, but usually trade some efficiency and lifespan for it. Foldable panels fold up for storage and are set out when needed — ideal for occasional or fully portable use with a power station. Match the type to the job: permanent mount → rigid; curved roof → flexible; pack-away portable → foldable.
400W for campervans & off-grid
Why 400W is a campervan favourite
400W has become one of the most popular sizes for campervans and motorhomes, and for good reason: it comfortably keeps a leisure battery topped up for lighting, a fridge, water pump, and phone/laptop charging — the essentials for one or two people touring, especially spring to autumn. Pair it with a suitable leisure battery and charge controller (an MPPT controller gets the most from it) and it’s a well-balanced off-grid setup. Heavier users — running a compressor fridge year-round, or wild-camping through winter — might step up to 500–600W or a bigger battery, but for typical touring, 400W hits the sweet spot of power, size and cost. It’s enough to be genuinely free of hook-ups for everyday needs, without the bulk of a larger array.
How much does a 400W solar panel cost?
Prices vary a lot by type and brand:
- Standard rigid 400W panel: ~£80–£200.
- Flexible / foldable 400W: often more, especially branded portable kits.
- Premium portable brands (EcoFlow, Anker, Renogy) & foldable kits: £250–£500+.
- Full kit (panel + charge controller, or with a power station): more again.
As always, very cheap panels can cut corners on durability, so balance price against how you’ll use it — a permanent van install is worth spending on for longevity, while an occasional foldable can be more budget-led. Check the panel’s actual specs and reviews rather than wattage alone.
Wait — 400W for a house roof?
Here’s a useful point of confusion to clear up. 400W is also the typical wattage of a modern rooftop solar panel — today’s residential panels are usually 400–450W each. So “400W solar panel” can mean two quite different things:
- A single portable 400W panel — for a campervan, boat or off-grid use (what most of this guide covers).
- One panel within a home rooftop system — where you’d have many 400W+ panels wired together into a full grid-connected array.
If you’re actually researching solar for your house, a single 400W panel isn’t the unit to think about — you’d size the whole system in kilowatts. Our guides on system sizes and how many panels fit your roof are the right starting point, and a free quote gets a home system designed properly. For portable and off-grid 400W use, read on — and see our companion guides on 100W and 200W panels for smaller setups.
400W panels: the honest summary
✓ Great for
- Campervans, motorhomes, boats, off-grid
- Lighting, fridge, charging, power stations
- 1–2 people’s essentials, spring–autumn
- ~1.6–2kWh on a good summer day
- Rigid, flexible or foldable options
✗ Not for
- Kettles, heaters, ovens (too high-power)
- Heavy year-round/winter off-grid use alone
- Thinking of home solar as a single panel
- Relying on winter output (drops sharply)
- Cheapest panels if you need durability
Frequently asked questions
What can a 400W solar panel run?
With a battery: phone/laptop charging, LED lighting, a fridge or cool box, fans, water pump, and topping up a power station or leisure battery. Not high-power appliances like kettles, heaters or ovens. Great for campervan and off-grid essentials for 1–2 people.
How much power per day?
Around 1.6–2kWh on a bright UK summer day, but only ~0.4–0.8kWh on a dull winter day. Estimate as wattage × effective sun-hours (400W × ~4–5 summer hours ≈ 1.6–2kWh). Winter output drops sharply.
Is 400W enough for a campervan?
For many, yes — it’s a popular, often ideal size, keeping a leisure battery topped up for lighting, fridge, pump and charging for 1–2 people, especially spring–autumn. Heavy or winter users might want 500–600W or a bigger battery.
Rigid, flexible or foldable?
Rigid: most efficient/durable, for permanent mounting. Flexible: bends to curved roofs, less efficient. Foldable: packs away for portable use with a power station. Match to your use — permanent, curved, or grab-and-go.
How much does a 400W panel cost?
~£80–£200 for a standard rigid panel; flexible, foldable and branded portable versions (EcoFlow, Anker, Renogy) often £250–£500+. Full kits with a controller or power station cost more. Cheap panels may cut durability corners.
Are these the same as house-roof panels?
400W is also modern rooftop panel wattage, but portable 400W panels differ (flexible/foldable/single units used with a battery). For home solar you’d have many 400W+ panels in a full array — see our system sizes guide.
The campervan sweet spot — pick the right type
The bottom line: A 400W panel is a genuinely useful, popular size for campervans, boats and off-grid living — ~1.6–2kWh on a good summer day, enough for lighting, a fridge and charging with a battery. Pick rigid for permanent mounting, flexible for curved roofs, foldable for portability, and size up if you’re a heavy or winter user. Just remember: for home solar, 400W is one panel of many, not the whole system.
Researching home solar? Get free quotes →The verdict
The 400W solar panel is one of the most useful sizes in portable and off-grid solar — a genuine sweet spot for campervans, motorhomes, boats and off-grid living. It produces around 1.6–2kWh on a good UK summer day, comfortably runs lighting, a fridge, charging and a leisure battery for one or two people, and comes in rigid, flexible or foldable forms to suit permanent, curved-roof or portable use. Size up to 500–600W only if you’re a heavy or year-round winter user.
The one thing to keep clear: 400W is also the wattage of modern rooftop panels, so if you’re really researching home solar, you’re looking at a full multi-panel system, not a single panel — and our roof and sizing guides (or a free quote) are the place to start. For everyone kitting out a van or off-grid setup, a good 400W panel is an excellent choice — just match the type to how you’ll use it.
Important
Going Solar UK is an introduction service for home solar installations, not a retailer of portable panels. Output figures and prices here are indicative 2026 generalisations and vary by panel, brand, weather, angle and location. For home rooftop solar, always get a professional assessment and quotes from MCS-certified installers. Portable and off-grid setups should follow the manufacturer’s guidance and be installed safely.
We may receive a commission when we introduce you to an installer, at no cost to you. Any contract for work is directly between you and the installer.