Van Life Electrical Systems: Batteries, Solar & Wiring for UK Campervans
Introduction
The electrical system is the most intimidating part of a van conversion for most people, and with good reason. Get it wrong and you either blow fuses constantly, run out of power on day two, or set something on fire. Get it right and you never think about power again — lights work, fridge stays cold, phone charges, and the diesel heater runs all night without killing the battery.
The first thing to understand is that a campervan has two separate electrical systems: the vehicle's starter system (12V, runs the engine, lights, dashboard) and the leisure system (also 12V, runs everything in the living area). These must be kept separate. The starter battery is designed for one job — starting the engine. The leisure battery is designed for deep discharge — powering things overnight and recharging slowly.
12V vs 240V in a Van
Almost everything in a campervan can run on 12V DC power. LED lights, water pumps, USB chargers, fans, diesel heaters, and 12V compressor fridges all run directly from the leisure battery without needing an inverter. This is the most efficient way to use power because there are no conversion losses.
240V AC power (mains electricity) is needed for things like laptop chargers, camera batteries, and any appliance that plugs into a wall socket. To get 240V from a 12V battery, you need an inverter. Pure sine wave inverters cost more but produce clean power that sensitive electronics need. Modified sine wave inverters are cheaper but can cause buzzing in audio equipment and may not charge some laptop batteries.
The mistake many first-time converters make is installing a large inverter and running everything through it. This is inefficient because inverters consume power even when nothing is plugged in (standby draw), and converting 12V to 240V and back to DC for a laptop charger wastes about 20% of the power. Better to run DC devices directly and only use the inverter when you genuinely need mains power.
Battery Sizing for UK Conditions
Battery sizing depends on your usage, not your van size. A typical setup runs lights (2-5Ah per day), a fridge (15-25Ah per day in summer), a water pump (1-2Ah), phone charging (3-5Ah), and a diesel heater (5-10Ah per winter night). Total daily consumption is around 25-45Ah depending on season and usage.
A 100Ah leisure battery provides about 50Ah of usable power if it's lead-acid (you should never discharge lead-acid below 50%) or 80-90Ah if it's lithium LiFePO4 (which handles deeper discharge much better). For most UK van lifers, a 100Ah lithium battery paired with 200W of solar is the sweet spot for spring-to-autumn living. Winter living requires alternator charging or a larger battery bank.
Lithium batteries cost more upfront — about £400-600 for a decent 100Ah unit versus £80-120 for a lead-acid leisure battery — but they last four times longer, weigh half as much, and provide more usable capacity. If you plan to live in the van for more than a year, lithium pays for itself.
Solar Panel Basics for the UK
UK solar conditions are not like Australia or California. A 100W solar panel in the UK generates roughly 300-400Wh per day in summer and as little as 50-100Wh per day in December cloud cover. That is enough to keep batteries topped up in summer but nowhere near enough in winter.
Monocrystalline panels are more efficient than polycrystalline, which matters in limited roof space. Flexible panels are lighter and mount flush to curved roofs but are less efficient and overheat more easily than rigid panels. In the UK climate, a compromise is semi-flexible panels bonded to the roof with VHB tape — no roof rack needed, no holes, reasonable efficiency.
MPPT charge controllers are worth the extra money over PWM controllers. In UK conditions with partial cloud cover, an MPPT controller extracts 20-30% more power than a PWM, which makes a real difference on those days when the sun keeps appearing and disappearing.
Alternator charging via a DC-DC charger is essential for UK van life. Solar alone cannot keep up with winter consumption. A DC-DC charger (20-30A) charges the leisure battery while you drive. A 30-minute drive at lunchtime puts about 15Ah back into the battery, which is enough to run a fridge and lights overnight. Without this, you will run out of power by day three of winter camping.
What to Know Before Starting
Plan your system on paper before buying anything. List every device you will run, calculate its daily power consumption in amp-hours, then size your battery and charging sources to match. Oversizing solar is rarely a mistake in the UK — more solar means you can stay parked in one spot longer without needing to drive.
Use proper cable sizes. Undersized cables cause voltage drop, which means devices at the far end of the van don't work properly and cables can overheat. For a typical 12V system, use 6mm² cable for runs up to 3 metres and 10mm² for longer runs. Fuse everything close to the battery. A single short circuit in an unfused system can melt wiring and start a fire within seconds.
Earth bonding is a legal requirement for 240V systems in campervans. All metal exterior panels and exposed metal parts must be connected to the vehicle chassis earth. This is not optional — it prevents electric shock if a mains appliance faults. Get a qualified electrician to inspect your 240V installation.
Conclusion
A well-designed 12V electrical system for a UK campervan is not complicated. One lithium battery, a DC-DC charger from the alternator, solar panels with an MPPT controller, and a small pure sine wave inverter cover almost every need. The key is matching your battery capacity to your actual consumption and accepting that UK winter conditions require alternator charging to supplement solar. Plan it properly on paper first, and the wiring itself is just a matter of following a clear diagram.
