Off-grid power setup for caravans: battery, solar, inverter sizing for Australian touring

Two facts decide whether your caravan’s power system actually works off-grid:

How much energy you use per day (measured in watt-hours, Wh)
How much you can store + replenish in a 24-hour cycle

Get either wrong and the lived experience is the same — battery dies overnight on day three, fridge starts cycling warm, you find yourself running the tow vehicle to top up or hunting for a powered site you didn’t plan to use.

This guide walks the maths in plain English, then gives worked sizing for the two most common Australian touring setups: a couples van for free-camping weekends and a family rig for extended trips.

The four numbers that matter

1. Daily usage (watt-hours per day)

Add up what each appliance draws per day. Fridges are usually the dominant load. A typical 12V compressor caravan fridge (190–220 L) draws about 40–60 Ah per 24 hours in summer — roughly 500–720 Wh at nominal 12 V. Air conditioning, induction cooking and high-draw appliances change the maths entirely; if you’re running aircon off battery overnight, your sizing problem isn’t a sizing problem, it’s a category error (run aircon off mains or a generator, full stop).

A realistic couples-touring 24-hour daily budget without aircon:

Load	Daily draw
12V compressor fridge (220 L)	600 Wh
LED interior lighting (4 hrs)	40 Wh
Water pump (intermittent)	30 Wh
Phone + laptop charging	100 Wh
TV/entertainment (2 hrs)	80 Wh
Diesel heater (cool nights)	100 Wh
Total	~950 Wh

Round up to 1,000 Wh/day for buffer. A family setup with extra lighting, more device-charging and additional fridge load runs closer to 1,400–1,600 Wh/day.

2. Battery capacity (usable, not nameplate)

The number stamped on a battery isn’t the number you can actually use. The depth of discharge (DoD) you can safely take a battery to matters enormously:

AGM batteries: practical DoD is 50%. A 100 Ah AGM gives you 50 Ah usable (~600 Wh at 12 V).
Lithium (LiFePO4): practical DoD is 80%. A 100 Ah lithium gives you 80 Ah usable (~960 Wh at 12 V).

That’s a 60% real-energy advantage for lithium at the same nameplate. Plus lithium typically lasts 8–12 years versus 3–5 for AGM, and weighs roughly half. The upfront price premium (lithium runs about 2–3× the per-Ah cost of AGM) pays back in 2–4 years for any owner doing meaningful off-grid time.

For our 1,000 Wh/day couples target, you want a battery bank that gives you at least 2 days’ autonomy for cloudy-weather buffer:

AGM path: 2 × 100 Ah AGM = 200 Ah nameplate, ~100 Ah usable, ~1,200 Wh usable. 1.2 days of autonomy. Marginal.
Lithium path: 1 × 200 Ah lithium = 200 Ah nameplate, 160 Ah usable, ~1,920 Wh usable. 2 days of autonomy. Solid.
Lithium path generous: 1 × 300 Ah lithium = 240 Ah usable, ~2,880 Wh usable. 3 days of autonomy. Family-grade.

3. Solar input (real-world watts per day)

Manufacturer specs are peak-rated. Real-world solar output averaged across an Australian day depends on season, panel angle and shading. Conservative rule:

Northern Australia / inland (summer): ~5 sun-hours/day equivalent → 1 W of panel = ~5 Wh/day
Southern Australia (winter): ~3 sun-hours/day equivalent → 1 W of panel = ~3 Wh/day

For a couples setup needing to replace ~1,000 Wh/day in winter, you want approximately 350 W of panel as a minimum. In practice, factor in shading from awnings, antennae and roof furniture — most rooftop installs lose 20% to real-world inefficiencies. 400–500 W is the practical floor for free-camping autonomy.

A premium off-grid setup runs 800–1,200 W. Our Lotus Off-Grid catalogue entry ships with 1,000 W standard; the MDC XT19HRT MKIII ships with 1,225 W. That’s the upper end of what’s practical to fit on a caravan roof.

4. Inverter sizing

The inverter converts 12 V DC battery power to 240 V AC for mains appliances. Three numbers matter:

Continuous wattage — the steady AC draw it can sustain (e.g. 2,000 W continuous for a 2 kW inverter)
Surge wattage — peak draw it can handle for a few seconds at startup (typically 2× continuous for inductive loads like fridges and pumps)
Sine wave shape — always pure sine wave, not modified. Pure sine is mandatory for sensitive electronics, modern fridges, induction cooktops and CPAP machines. Modified-sine inverters are obsolete for caravan use; don’t buy one even if cheaper.

For a couples setup running coffee machine, induction cooktop or microwave occasionally: 1,500–2,000 W inverter is the sweet spot. For a family setup running multiple high-draw appliances simultaneously: 3,000 W. Going larger than you need wastes battery on inverter overhead (most inverters draw 1–2 A on standby).

Worked example: couples free-camping setup

Daily budget: 1,000 Wh
Battery: 200 Ah LiFePO4 (~$1,800–$2,200 from REDARC, Enerdrive or BMPro)
Solar: 400 W rooftop (2 × 200 W panels) + Victron 100/30 MPPT charge controller
Inverter: 2,000 W pure sine wave
Total install cost (parts only): ~$4,500–$5,500
Autonomy: 2+ days no sun, indefinite with average AU sun
Suited for: weekend free-camping, the Big Lap, 1–3 weeks between resupply

Worked example: family extended-touring setup

Daily budget: 1,500 Wh
Battery: 300 Ah LiFePO4 + DC-DC charger from alternator (e.g. REDARC BCDC1240)
Solar: 800 W rooftop + 200 W portable for shaded sites
Inverter: 3,000 W pure sine wave
Total install cost (parts only): ~$8,000–$10,000
Autonomy: 3+ days no sun, indefinite with average AU sun + alternator top-up while driving
Suited for: 3+ week trips off-grid, Cape York / Kimberley / Stuart Highway touring

The five most common mistakes

Big battery, small solar. A 400 Ah bank with 200 W of panel will never recharge. The bank’s role is buffer, not endurance. Match solar to daily usage first, battery to autonomy second.
Cheap modified-sine inverter. Will kill modern compressor fridges and damage CPAP machines. Pure sine only.
Wrong DC-DC charger size. A 200 Ah lithium bank needs a 40 A+ DC-DC charger to actually top up while driving. The 25 A unit that came standard on many builds is undersized.
Cable sizing skipped. Long DC runs at 12 V need fat cables. Voltage drop on undersized cabling can leave you with 11.2 V at the appliance even though the battery’s at 13.4 V — and the appliance shuts off thinking the battery’s flat.
Treating “off-grid capable” badges as gospel. Manufacturer “off-grid pack” upgrades vary wildly. Always check the actual numbers — battery type, battery Ah, solar wattage, inverter capacity — before assuming a van is genuinely free-camp ready.