How Many Solar Panels Do I Need on My Campervan?

Working out how many solar panels you need on your campervan is one of the most common questions in any van conversion, and getting it wrong means either running out of power or wasting money on panels you do not need. This guide walks you through the calculation step by step, tailored specifically for the UK and European climate.

For the full picture on solar system design, see our campervan solar setup guide. And if you want the answer in two minutes flat, our free calculator will size your entire solar system based on your actual daily usage.

The Basic Solar Sizing Formula

The calculation is straightforward once you know three numbers:

Daily energy consumption (Wh) / Peak sun hours / System efficiency = Solar watts needed

Let us break each of those down.

Step 1: Calculate Your Daily Energy Usage

List every electrical device you plan to use in your van and work out how many watt-hours (Wh) each consumes per day.

Your total will vary enormously depending on your lifestyle. A weekend warrior with LED lights and a fridge might use 400 Wh per day. A full-time van lifer working remotely could easily hit 1,200 Wh or more.

For guidance on matching your battery bank to this usage, see how to size your campervan battery.

Step 2: Find Your Peak Sun Hours

Peak sun hours (PSH) represent the number of hours per day when solar irradiance equals 1,000 W/m². This is not the same as daylight hours.

UK averages:

• Summer (June–August): 4–5 PSH
• Spring/Autumn: 2–3 PSH
• Winter (December–February): 0.8–1.5 PSH
• Annual average: approximately 2.5–3 PSH

For detailed data by region, see our peak sun hours by location guide. If you travel to southern Europe in summer, you can expect 6–7 PSH, which nearly doubles your output.

Step 3: Apply System Efficiency

No solar system is 100% efficient. You lose energy at every stage:

• Panel efficiency in real conditions vs lab ratings: 85%
• Charge controller efficiency (MPPT): 95%
• Battery charge/discharge efficiency: 95%
• Cable losses: 97%

Combined system efficiency: approximately 0.73 (73%)

Step 4: Run the Calculation

Using our example of 865 Wh daily usage in the UK with 3 PSH average:

865 Wh / 3 PSH / 0.73 = 395W of solar panels

So you would need roughly 400W of solar panels for this setup.

Quick Reference: Solar Sizing by Usage Level

For a detailed comparison of common configurations, see 200W vs 400W vs 600W solar.

Factors That Affect Your Solar Output

Panel Orientation and Tilt

Flat-mounted panels on a campervan roof produce roughly 10–15% less energy annually than optimally tilted panels. This is already factored into the efficiency calculation above, but it is worth knowing that portable or tilt-mounted panels can help.

Temperature

Solar panels lose efficiency as they get hot — typically 0.3–0.5% per degree above 25°C. On a dark van roof in summer, panel temperatures can reach 60–70°C, reducing output by 10–15%.

Shading

Even partial shading can dramatically reduce output. A single shaded cell in a series string can reduce the entire panel's output by 30–50%. This is one reason parallel wiring is often preferred for campervans. For the full breakdown, see our guides on solar panel shading and series vs parallel wiring.

Panel Age and Degradation

Quality panels degrade at roughly 0.5% per year. A 400W panel will produce around 380W after 10 years. This is minor for campervan use but worth knowing.

UK-Specific Considerations

The Winter Problem

The biggest challenge for solar-dependent campervans in the UK is winter. With only 0.8–1.5 PSH per day in December and January, a 400W system might only produce 250–450 Wh daily — not enough for most setups.

Solutions:

• Install a DC-DC charger to supplement solar with alternator charging while driving
• Size your solar for spring/autumn rather than winter, and accept you will need to drive or use hookup in winter
• Carry a portable solar panel that you can angle towards the low winter sun

For detailed winter data, see how much solar do I need in winter.

Scottish vs Southern England

There is a meaningful difference in solar resource across the UK:

• South coast of England: ~3.2 PSH annual average
• Midlands: ~2.7 PSH
• Scottish Highlands: ~2.2 PSH

If you are based in Scotland, size your system 20–30% larger than the base calculation suggests.

Common Solar Setups for UK Campervans

The Weekend Van: 200W

Two 100W panels or a single 200W panel. Suits vans used primarily on weekends with basic electrical needs — LED lights, phone charging, a small fridge. Expect to need hookup or driving top-ups in winter.

Cost: £200–£350 for panels

The Touring Van: 400W

The sweet spot for most UK campervans. Typically two 200W panels. Handles a compressor fridge, lighting, phone and laptop charging, and moderate use of a small inverter. Works well spring through autumn. Will need DC-DC charger support in winter.

Cost: £350–£600 for panels

The Full-Timer: 600W

Three 200W panels or two 300W panels. For van lifers who work remotely and have higher power needs. Allows generous use of laptops, monitors, and other moderate-draw devices. Still needs DC-DC supplementation in UK winters.

Cost: £500–£900 for panels

Matching Solar to Your Battery Bank

Your solar array and battery bank need to work together. A general rule for the UK is:

Battery capacity (Ah at 12V) should be 2–3 times your daily usage in Ah

So if you use 865 Wh/day (roughly 72 Ah at 12V), you want 150–200 Ah of lithium battery capacity. This gives you a full day's buffer for cloudy weather.

For the full battery sizing methodology, see how to size your campervan battery.

Can You Have Too Much Solar?

Technically, your charge controller limits how much power reaches the battery. Once the battery is full, the controller throttles the panels. So you cannot overcharge the battery by having too many panels, but you can overload the charge controller.

Make sure your controller is rated for the total wattage of your array. See solar charge controller sizing for the calculation.

How Roof Space Limits Your Options

Before planning a massive array, check whether it actually fits. Most panel-friendly campervans can accommodate:

• SWB vans (Transit Custom, VW T6): 200–400W
• LWB vans (Transit L3, Sprinter L2): 400–600W
• Luton/box vans: 600–1,000W

See campervan roof space by van model for exact dimensions. Remember to account for roof vents, satellite dishes, and access to your roof rack.

Frequently Asked Questions

Is 200W of solar enough for a campervan?

For a basic weekend setup with LED lights, phone charging, and a small fridge, 200W can work in UK summer months. It will not be enough for year-round use or higher power needs. Most people upgrading later wish they had started with 400W.

Can I run an air conditioner from solar panels?

Not practically from rooftop solar alone. Even a small campervan AC unit draws 500–1,000W continuously. You would need a very large solar array and battery bank, and it would only work in direct sunlight — exactly when you need cooling most. Shore power is far more practical for AC.

Do I need solar if I have a DC-DC charger?

A DC-DC charger is excellent for topping up while driving, but it only works when the engine is running. If you want to park up for multiple days without driving, solar is essential. Most well-designed systems use both.

How do I know if my solar panels are performing correctly?

A Victron SmartSolar controller with Bluetooth lets you monitor daily yield, current output, and battery state from your phone. In UK summer, a 400W system should produce 1,200–1,600 Wh on a good day. If you are consistently seeing less than 60% of rated output in clear conditions, check for shading, dirty panels, or wiring issues.

What happens on cloudy days?

Panels still produce power on overcast days, but typically only 10–25% of their rated output. In the UK, you should expect multiple consecutive cloudy days, which is why battery capacity and supplementary charging are so important.

Next Steps

1. Calculate your daily usage using our free calculator
2. Choose your panel type — see best solar panels for campervans
3. Size your charge controller — see solar charge controller sizing
4. Plan your mounting — see solar panel mounting guide
5. Wire it up — see solar cables through the roof

Getting your solar sizing right from the start saves you money, roof space, and the frustration of running out of power when you are parked up in your favourite spot.