I'll be straight with you: a van solar electrical system is just a handful of components wired together correctly, but each one has to be sized to your actual loads. Skip the maths and you end up flat-battery in the bush or overweight on the front axle. Here's how I work through a build from load list to commissioned system.

By Dave Miller · off-grid sparky · 22 years wiring solar, batteries and sheds in central QLD

“I learned the hard way after a 2022 heatwave in Rockhampton that 12mm cable was too thin for a 300W array, costing me three days of power.”

How a Van Solar System Actually Works

Four components do the job: solar panels collect energy from the sun, a charge controller regulates that energy, batteries store it, and an inverter converts it to run standard household appliances. Put differently, you have a power source (solar, plus usually an alternator feed and sometimes shore power), energy storage (the battery bank), power control (charge controllers, fuses, monitoring), and power flow (the inverter and DC distribution) — the same architecture every builder uses regardless of brand.

The chain is simple: panels produce DC at varying voltage depending on sun, the charge controller feeds a controlled charge into the battery bank, the battery bank holds DC at system voltage (commonly 12V), and the inverter converts that to 230V/50Hz AC for household appliances. Anything DC-native (fridge, lights, water pump, fan, USB outlets) runs directly off the battery bank without the inverter.

Sizing by Daily Consumption

Before you buy anything, write a load list. The formula is: Power (watts) × daily hours of use = daily consumption in watt-hours (Wh), summed for every device. Be honest — a 60W fridge that runs 12 hours a day is 720 Wh, not 60 Wh.

Typical daily consumption benchmarks:

Pick the profile closest to your actual use, then add 10–20% headroom for things you've forgotten (phone charging, camera batteries, the occasional hair dryer).

Solar Panels: Type and Output

Monocrystalline panels are commonly used on vans because they produce more power within a limited amount of roof space, and they hold up better in partial shade than polycrystalline. For most builds that's the default unless budget dictates otherwise.

A panel's advertised wattage is its maximum output under ideal testing conditions; clouds, trees, dirt, smoke, snow, roof equipment, and the angle of the sun can all reduce real-world production. Real-world output is often 20–30% lower than the rated maximum. As a rule of thumb, a 300W array typically produces 1,200 to 1,800 watt-hours per day in good conditions — use the lower end for your planning maths.

For many travellers, a reasonable starting system is 300 to 600 watts of solar with 200 to 400 amp-hours of battery storage. Sizing solar to roughly 1.5–2× your daily Wh consumption is the standard approach because it accounts for cloudy days, winter sun angles, and panel degradation over time.

Charge Controllers

The charge controller sits between the panels and the batteries and prevents overcharging. There are two technologies: PWM (cheaper, simpler, loses some panel output) and MPPT (more expensive, harvests more energy). MPPT charge controllers are popular because they generally perform better as sunlight and weather conditions change, which on a van roof they do constantly — driving, parked under a tree, cloud edges.

Size the controller to handle your array's worst-case current. A 400W array at 12V nominal can push over 30A, so a 40A MPPT is the usual minimum.

Battery Bank

This is where the real money goes, and the choice affects weight, longevity, and usable capacity.

Lithium batteries are common in higher-end van builds because they are lighter, last longer, and provide more usable capacity than lead-acid batteries. AGM batteries cost less upfront than lithium but are heavier and should not be regularly drained as deeply. For most builds the maths favours LiFePO4 once you count usable amp-hours and replacement cycles.

Battery sizing formula: Required capacity (Ah) = (Total Wh needed ÷ system voltage) ÷ depth of discharge × autonomy days. Worked example: 2,800 Wh at 12V needs roughly 292 Ah of LiFePO4 (at 80% DoD) or 467 Ah of AGM (at 50% DoD) for a single day. Two days of autonomy is a sensible baseline to cover rainy weekends or driving days with no solar yield, so multiply by 2 if you don't have alternator charging as a backup — applied to the figures above, that becomes roughly 584 Ah of LiFePO4 or 933 Ah of AGM. With alternator charging available, single-day sizing with margin is usually adequate.

Cold-charging warning: LiFePO4 batteries should not be charged below 0 °C — doing so damages the cells permanently. AGM and flooded lead-acid are tolerant of cold charging. If you're wintering in places like the Victorian high country or the Snowies, either insulate the battery box with a heater pad, disable charging below the BMS cut-off, or stay with AGM.

Inverters

An inverter converts the 12-volt electricity stored in the batteries into the [household mains voltage — 230V/50Hz in Australia] used by normal outlets. Pure sine wave units produce clean AC that runs sensitive electronics (laptop chargers, medical devices, anything with a switch-mode power supply); modified sine wave is cheaper but can overheat some loads and cause audible buzz in audio gear.

Two practical sizing rules:

• Continuous rating must exceed the simultaneous running load of every AC appliance you might have on at once.
• Surge rating must cover motor starting currents (fridge compressors, water pumps) for a few seconds.

A 2,000W pure sine wave inverter handles most domestic loads including a kettle; a 3,000–4,000W unit covers induction cooking and air conditioning. Every inverter pulls DC even with no AC load, so install a master switch.

Wiring, Fuses and Vibration

Wire is the most commonly undersized component. Voltage drop on a 12V system is brutal — at the same current, a 12V system pushes ten times the current of a 230V system, so cable losses add up fast. Use the voltage-drop calculator with your cable run length, not just the current rating.

Marine-grade tinned copper wire resists corrosion in the humid, salt-spray environment that builds up inside a van. Standard automotive wire will corrode at the copper strands, especially in coastal Queensland.

Fuse everything. Each solar string, the battery-to-controller link, the battery-to-inverter link, and every DC distribution branch should have its own fuse or breaker sized to protect the smallest of: cable ampacity, device terminal rating, and the battery's maximum available discharge current. Pick whichever limit is lowest — sizing to the cable alone can leave a fuse rated above what a connector or device terminal is rated to carry.

Vibration kills gear over years of corrugated roads. Use lock washers or Nord-Lock washers on terminals and mounting hardware to keep things tight. Secure the battery physically so it cannot move in a hard stop.

Monitoring and Alternator Charging

A shunt-based battery monitor (Victron, Renogy, Simarine — the common types) is the only reliable way to see state of charge. Voltage alone lies, especially with LiFePO4 which holds 13.3V for most of its discharge curve.

Don't rely on solar alone. A DC-DC charger fed from the vehicle's alternator lets you top up the house battery while driving, which is often faster than solar in winter or on overcast days. An isolated DC-DC charger protects the vehicle's own electronics from voltage spikes and backfeed.

Safety — When to Call a Licensed Professional

Building a vehicle electrical system for off-grid living can be dangerous and requires thorough research and preparation to build a safe and reliable system. Lithium batteries store enormous energy and can deliver fatal currents if shorted. A mistake in cable sizing can start a fire inside a wall cavity. The following are non-negotiable call-outs to a licensed auto-electrician or sparkie:

• Any AC mains wiring (230V inverter output, RCD, distribution board).
• Alternator integration and any connection to the vehicle's existing loom. On modern vehicles with smart alternators, this requires a DC-DC charger rather than a VSR or relay isolator; legacy dual-battery isolators are only suitable on fixed-voltage alternators and are no longer appropriate as a default choice.
• Anything you're not 100% confident about.
• Compliance checks if you ever plan to sell the van, register it as a motorhome, or claim on insurance after an electrical fire.

As an owner, you can reasonably take on low-current DC work — lighting, USB outlets, fans, water pumps, the basic loads. AC mains wiring, alternator/inverter integration, and any work above about 50V DC must go to a licensed auto-electrician or electrician. In Australia, AS/NZS 3000 applies to AC wiring, alternator integration affects roadworthiness, and insurance claims after DIY electrical faults are routinely refused.

Working at 12V is not inherently safe — a shorted lithium bank can weld tools and start fires. Disconnect the battery before working on the system, and never work alone on the high-current side. If a lithium battery fires, evacuate the area immediately, call emergency services, and only attempt suppression if it is safe to do so — use copious water or a Class A/B extinguisher rated for electrical fire. A Class D extinguisher is for combustible-metal fires and is not the correct primary response for Li-ion or LiFePO4.

Commissioning Checklist

1. Confirm polarity on every connection before applying the first fuse.

2. Check all cable terminations are torqued to spec — loose connections cause fires.

3. Verify voltage at the battery terminals matches the controller's sense-lead reading.

4. Confirm the BMS is communicating and cell voltages are within 0.05V of each other.

5. Test every fuse and breaker with a load.

6. Run each AC appliance on inverter power and check for nuisance trips.

7. Monitor the system across a full charge-discharge cycle before trusting it on a trip.

A clean install looks boring: every wire labelled, every fuse labelled, every connection accessible.

FAQ

How many solar watts do I need for full-time vanlife?

Most full-timers run 1,000–2,000 Wh/day. Applying the 1.5–2× sizing rule, that points to roughly 1,500–4,000W of solar; in practice, full-timers with alternator charging typically land in the 2,000–4,000W range across shoulder and winter seasons, with cloudy-day derating already factored into the multiplier.

Is lithium worth the extra cost over AGM?

Yes, for most builds. LiFePO4 gives you roughly double the usable amp-hours for the same rated capacity, lasts 5–10× the cycles, and weighs about a third as much. The break-even usually comes inside four years of regular use.

Can I fit solar and batteries myself?

The low-current DC side (lighting, USB, fans) is buildable for a careful owner with good documentation. The AC side, alternator integration, and any high-current DC work are the parts to hand to a licensed professional.

Do I need an MPPT controller or is PWM fine?

For a roof-mounted array larger than about 150W, MPPT pays for itself in harvested energy within a couple of years, especially when panels run hot or in low light.

How long will my batteries last on a cloudy stretch?

With two days of autonomy sized at 12V, that requires roughly 584 Ah of LiFePO4 or 933 Ah of AGM to cover a 2,800 Wh daily draw for two days. A single-day-sized bank of 292 Ah LiFePO4 or 467 Ah AGM covers one day; for the second cloudy day, alternator charging or a generator keeps the system alive.

What size inverter do I actually need?

Add up the simultaneous running wattage of your AC devices, then double it for motor surge. Anything above 2,500W usually needs a 70–90A DC feed and heavy cable — check that before buying the unit.

Sources

• https://adventurevanexpo.com/solar-power-for-van-life-a-non-techy-persons-guide-to-energy-independence/
• https://voltplan.app/blog/camper-electrical-planning-complete-guide
• https://thevansmith.com/blogs/your-van-build/how-to-power-your-van-solar-batteries-electrical-explained
• https://kombilife.com/van-life-electrical-system-guide/

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