What Size Solar Panel for a Campervan?

Author: Steve Fairless
Originally Published: 27th May 2024 · Updated: 28th August 2026

For a campervan, solar-panel size should be calculated from daily energy use in watt-hours, realistic seasonal solar harvest, available roof area, battery capacity and the charge controller's voltage/current limits. For light weekend use, 100-200 W can be useful; for a compressor fridge, laptops and longer off-grid stays, 300-500 W or more may be appropriate if the roof and electrical system can support it.

At Sustainable Energy Engineering, our core work is building-mounted solar and battery engineering rather than campervan conversions. However, the same electrical fundamentals apply: energy must balance, voltage and current limits must be respected, cables and protection must be correctly specified, and a panel's nameplate wattage is not the amount of energy it will deliver every day.

This updated guide is therefore written as an engineering sizing guide for owners planning a 12 V or 24 V leisure system. It does not replace a vehicle-specific electrical design or the equipment manufacturer's installation instructions.

Updated: 28th August 2026 with current off-grid modelling tools, charge-controller ratings and real appliance/panel specification examples.

Start with Watt-Hours, Not Panel Watts

The most important number is how much energy the van uses in a day. A 60 W laptop used for two hours consumes about 120 Wh. A 5 W light used for four hours consumes 20 Wh. A compressor fridge cycles on and off, so its daily kWh or Wh figure is more useful than its instantaneous wattage.

Add every meaningful load, then include an engineering margin for conversion losses, hot weather, cloudy periods and the fact that panels rarely operate at their rated power for a whole day.

A Real Fridge Example Shows Why Daily Energy Matters

A current 90-litre compressor refrigerator is published at about 0.4 kWh per 24 hours under its stated test condition. That is about 400 Wh/day before we add lights, water pump, USB charging, laptops, fans or inverter loads.

If we add roughly 20% for conversion and design margin, the planning target becomes about 840 Wh/day. That does not mean an 840 W panel is required; panel watts are power, while 840 Wh is daily energy.

Convert Daily Wh into a Solar Array Size

A rough off-grid calculation divides required daily Wh by the equivalent full-sun hours available to the panel, then adjusts for system losses. Because the UK solar resource changes dramatically through the year, using one annual average can be misleading for a van.

For the 840 Wh/day planning target above:

Why Campervan Solar Is Much More Seasonal Than Most Online Calculators Admit

A fixed panel mounted flat on a van roof is rarely at the optimum angle, and the vehicle may be parked under trees, beside tall buildings or facing any direction. In winter, low sun angle and short days can reduce harvest dramatically. In summer, long days can make the same array feel oversized.

The European Commission's PVGIS tool includes off-grid PV modelling and monthly solar-radiation data, which is much more useful than assuming the same "sun hours" in January and July. For regular off-grid touring, run the model for the locations and months in which the van will actually be used.

Fixed Rigid, Flexible or Portable Panels?

Current Product Examples Show How Different 200 W Can Look

Two products can both be labelled around 200 W yet be completely different physically. A current 200 W flexible monocrystalline product is published at 1,605 x 748 x 3 mm and 4.9 kg. A current 220 W portable folding panel is published at 2,270 x 598 x 26 mm when unfolded and about 5.1 kg.

The flexible product is designed around permanent low-profile mounting. The folding product prioritises portable deployment and adjustable angle. Wattage alone does not tell you which is right for the van.

Your Charge Controller Can Set the Real Solar Limit

An MPPT charge controller has maximum PV voltage, current and recommended power limits. Adding more panels without checking those figures can make the system unsafe or simply waste money.

For example, one current 30 A MPPT controller is specified for nominal PV power of 440 W on a 12 V battery system and 880 W on a 24 V system, with 100 V maximum PV open-circuit voltage and 98% maximum efficiency. That example demonstrates why the same controller model can accept different nominal PV power depending on battery voltage.

12 V vs 24 V Campervan Systems

At the same power, a 24 V system carries roughly half the current of a 12 V system. Lower current can reduce voltage drop and cable cross-section requirements for higher-power loads, but a vehicle may already have 12 V appliances and charging equipment. The best voltage architecture depends on the full conversion, battery and charging system.

For example, 600 W at 12 V is theoretically 50 A before losses, while 600 W at 24 V is 25 A. Real charging current depends on battery voltage, controller efficiency and operating conditions.

How Much Battery Capacity Should Match the Solar?

Battery capacity is the energy buffer. A nominal 12.8 V, 100 Ah lithium battery contains about 1.28 kWh of theoretical stored energy before any manufacturer limits or reserve are considered. Two such batteries would be about 2.56 kWh nominal.

Usable energy depends on chemistry, BMS settings, permitted depth of discharge, temperature and load. We therefore size batteries from required off-grid autonomy rather than assuming "one 100 Ah battery per 200 W panel".

Example: Weekend Van vs Full-Time Off-Grid Van

What About Kettles, Hairdryers and Induction Hobs?

High-power heating appliances are the reason a campervan energy system can escalate rapidly. A 2,000 W kettle run for only six minutes uses around 200 Wh, but the inverter and battery must still deliver roughly 2 kW while it operates. That is a power problem as well as an energy problem.

Induction cooking, electric water heating and hairdryers can require large inverters, high battery current and substantial cable/protection design. It may be possible, but the system should be engineered deliberately.

Roof Area Often Becomes the Limiting Factor Before Energy Demand

Rooflights, vents, aerials, awnings and curved sections can leave less usable area than expected. A fixed panel also needs safe mounting and cable entry, and anything added to a vehicle roof affects height, aerodynamics and potentially load distribution.

Measure the exact clear rectangles available, then compare the current product dimensions. Do not buy panels first and hope they fit around the roof furniture later.

Why a Flat Roof Panel Cannot Be Compared Directly with a Tilted Ground Panel

A flat-mounted van panel is convenient while driving and parking, but its angle to the sun is rarely ideal. A portable panel can often be tilted 30-60 degrees and moved to face the sun while the van stays in the shade. That can materially improve daily harvest in some conditions.

The trade-off is that portable panels work only when you deploy them, and they create storage and security considerations.

Alternator and Mains Charging Still Matter

Solar is only one charging source in a robust campervan system. A DC-DC alternator charger can replenish the leisure battery while driving, and a mains charger can recover the battery quickly on a campsite or at home. Relying on solar alone makes winter autonomy much harder.

A good energy design therefore asks how much energy each source can provide over the actual travel pattern.

Our Campervan Solar Sizing Checklist

When 200 W Is Enough - and When It Is Not

There is nothing inherently "small" or "large" about a 200 W campervan array. If the van uses 250 Wh/day in summer and drives frequently, 200 W can be generous. If a fridge alone consumes around 400 Wh/day and the van is stationary for days in poor weather, 200 W can be inadequate.

The correct panel size is the one that closes the daily energy balance often enough for the way the van is actually used.

Keep Vehicle Solar and Building Solar as Separate Design Problems

Campervans are off-grid/mobile electrical systems with different mounting, vibration, charging and battery constraints from grid-connected buildings. If your project is a house or commercial property rather than a vehicle, our domestic solar PV guidance covers the building-mounted approach we install every day.

You can also read more about our engineering background and experience. For campervan work, use a competent specialist familiar with vehicle electrical systems, battery charging, safe cable routing and the exact equipment being fitted.

If you have a building-mounted solar question, contact Sustainable Energy Engineering and we will be happy to discuss the property-based system.