By Jenny Mills · rural nurse & homesteader · health, safety, law and the paperwork of going bush
“After my third battery bank died in a wet summer, I learned to budget 20% extra capacity before flipping the main switch.”
Years back I blew a solar controller in the back shed because I couldn't be bothered matching fittings properly. $1,250 in new parts later, on top of the safety inspection the electrician charged me for, I'd learnt my lesson. Budget $5,000 to $20,000 for the full retrofit and stick to AS/NZS-compliant gear—Bunnings, Jaycar or Amazon Australia stock it.
By Jenny Mills · rural nurse & homesteader · health, safety, law and the paperwork of going bush
“After my third battery bank died in a wet summer, I learned to budget 20% extra capacity before flipping the main switch.”
Converting an existing van, shed, or small cabin to off-grid operation is a job for lists and spreadsheets, not improvisation. The goal here is a documented system: a battery bank sized to your actual loads, charge sources that can replenish it, AC wiring that meets Australian standards, and water and gas that won't get you hurt. The checklist below is built around 230V/50Hz single-phase supply, metric dimensions, AUD pricing, and the conditions we see out here in Central Queensland — though the structure applies anywhere in Australia.
A retrofit is shaped by two constraints before anything else: how you actually use the space, and what you're willing to spend.
In its simplest form an off-grid electrical system has three components: a battery bank, the loads, and the charge sources. Every retrofit decision flows from that triangle.
| Component | Function | Australian Retrofit Notes |
|---|---|---|
| Battery bank (house) | Stores DC energy for all loads | Separate from any engine/cranking battery where applicable; chemistry choice (LiFePO4 vs lead-acid) sets usable capacity |
| Charge sources | Replenish the bank | Solar array, alternator (vehicle retrofits), 230V shore/inverter-charger, optional generator |
| Loads | DC and AC devices | 12V DC where possible for efficiency; 230V AC via inverter for heavier appliances |
| DC distribution | Fuses, breakers, busbars | Overcurrent protection on every positive run; wire sized to length and current |
| AC distribution | Inverter, RCD/MCB board, outlets | 230V/50Hz; RCD (safety switch) on all final subcircuits; AS/NZS 3000 wiring rules |
| Monitoring | Shunt-based meter or BMS telemetry | Tracks state of charge, current in/out, fault flags |
The practical rule from the verified facts:
For a 12V system, the conversion is simple: Watt-hours ÷ 12 = Amp-hours.
Worked example using only the numbers in the facts sheet:
Right-sizing matters: an oversized bank wastes money, weight, and mounting space; an undersized one shortens battery life through repeated deep cycling. Plan for at least 3 days of autonomy in line with AS/NZS 4509.1 guidance for standalone power systems.
Three charge paths are standard in a vehicle retrofit, and the same logic applies for a static cabin with the alternator row replaced by a generator or grid backup.
1. Solar PV. A 200W panel array under reasonable sun produces roughly 800Wh/day, or about 66Ah at 12V — a useful sanity-check figure when sizing an array. Australian installations must comply with AS/NZS 5033 (PV arrays) and the inverter standard AS/NZS 4777.2.
2. Alternator charging (vehicle retrofits only). A DC-DC charger matched to the house bank chemistry lets the engine top up while driving.
3. Shore / grid / generator input via an inverter-charger. In Australian RV practice the shore inlet is typically rated 15A or 16A for our 230V system; the equivalent of the 30A North American inlet mentioned in the facts sheet would be a 16A Australian weatherproof inlet. The lead feeding that inlet should be sized for 16A continuous load — that means a minimum of 4mm² flexible cord, with 6mm² preferred for longer runs to keep voltage drop in check. 2.5mm² is not acceptable for a 16A continuous inlet lead: its derated ampacity under AS/NZS 3008.1 (depending on install method and ambient temperature) is at or below the design load, and it will run hot. Confirm cable sizing against AS/NZS 3008.1 with derating for install method and ambient, and have the final connection made or certified by a licensed electrician.
A complete shore-power retrofit in an RV-style system includes:
One wiring rule that catches people out: the neutral-to-ground bond must exist at only one source at a time. A second N-E bond creates a parallel path for neutral current to return via the chassis/earth conductor; load current can then flow on metalwork intended only as a protective earth, and any RCD that sees the imbalance will trip. The more dangerous related failure is a broken neutral on the pedestal side: with the upstream neutral open and a second N-E bond present inside the vehicle, the chassis can rise to full mains voltage relative to true earth. Don't allow two bonds at any time. Inverter-chargers with an approved internal bond-switching mechanism handle this automatically; legacy separate inverter and shore setups need a manual transfer switch that breaks the bond when shore is disconnected.
Air conditioning should be on its own dedicated circuit, and if it's an inverter-style rooftop unit you can usually skip a soft-start device; conventional compressor units may need one to keep the inrush from tripping the shore breaker. A surge protector or energy management system will detect open earth, reversed polarity, low voltage, and spikes before they reach your electronics.
Out of scope for the electrical facts sheet, but a retrofit checklist isn't complete without them:
A few hard rules in this country:
A retrofit isn't finished until the paperwork matches the wiring:
Hand these to the next owner, the insurer, and the certifying engineer. A documented system is also a system that's easy to debug at 9pm on a Friday with a headlamp and a multimeter.
How many solar panels do I need?
Start from your daily Wh figure, divide by peak sun hours for your location, and divide again by a 0.7–0.8 system loss factor. Using the verified benchmark, a 200W array yields roughly 800Wh/day under typical conditions — a useful sanity check against your own calculation.
What's the simplest way to work out battery size?
List every load in watts, estimate hours per day, sum the Wh, convert to Ah at your system voltage using Watt-hours ÷ 12 for a 12V bank, then apply usable-capacity derating: 50% for lead-acid, 80–90% for LiFePO4 in normal service (100% only in emergency/short-duration scenarios).
Do I really need an electrician for the 12V side?
12V DC work itself isn't legally restricted in most Australian states, but any 230V AC work — including inverter AC output, shore inlet, RCD/MCB board — must be done or certified by a licensed electrician. DIY on the AC side without sign-off will void insurance.
Why does my RCD trip when I plug into shore power?
The most common cause in van and cabin retrofits is a double neutral-to-ground bond — one at the pedestal/inverter and another inside the vehicle. There should only ever be one source of bonding at a time. Use an inverter-charger with approved automatic bond switching (compliant with AS/NZS 4777.2 / IEC 62109), or a manual transfer switch that breaks the bond when shore is disconnected. A broken neutral on the pedestal side combined with a second bond inside the vehicle is the related lethal failure mode to be aware of.
Is a soft-start device necessary for rooftop A/C?
Inverter-compressor units usually start softly on their own. Conventional compressor units benefit from a soft-start to reduce inrush current and nuisance breaker trips, especially on a 15A/16A Australian shore inlet.
How do I avoid overbuilding?
Right-sizing the battery bank (avoiding overbuilding) saves money, weight, and space. Match the bank to a realistic autonomy target — generally three days per AS/NZS 4509.1 — and size solar to recharge that bank within one good day of sun.
Worth a watch: How to PREPARE Your House to LIVE OFF-GRID · Martin Johnson - Off Grid Living