Start with what you actually use
Most caravan power mistakes start the same way: someone guesses. They buy a 100Ah battery because that’s what the salesman recommended. They bolt on whatever solar panel fits the roof. Then they spend their trip monitoring a battery monitor and wondering why the fridge cut out at 3am.
The right way is a load audit. It takes 15 minutes and it’s the only way to size a system that works for how you camp — not how someone else camps.
List every electrical appliance in your caravan, its power draw in watts, and roughly how many hours per day you run it. Then multiply: watts × hours = watt-hours. Sum everything up and that’s your daily consumption.
What a typical caravan draws
| Appliance | Typical draw | Hours/day | Daily use (Wh) |
|---|---|---|---|
| 12V compressor fridge | 40–60W (average, cycling) | 8–12 (compressor running) | 320–720 |
| LED lights (6×) | 30W total | 3–4 | 90–120 |
| Water pump | 50–60W | 0.5–1 | 25–60 |
| Phone/tablet charging | 10–20W | 2–3 | 20–60 |
| Laptop (via inverter) | 60–90W | 1–2 | 60–180 |
| TV (12V) | 30–50W | 1–2 | 30–100 |
| Diesel heater | 15–40W (running) | 4–8 (cold nights) | 60–320 |
The fridge is your biggest consumer — by a long way. A modern 12V compressor fridge cycles on and off, so it doesn’t draw its rated wattage continuously. In warm weather, expect the compressor to run roughly half the time. In hot conditions, more like two-thirds.
A basic setup — fridge, lights, pump, phone charging — might land around 500–800Wh per day. Add a laptop, a TV, and a diesel heater in winter, and you’re looking at 800–1,400Wh. These are the numbers your system needs to support.
Sizing the battery
Once you know your daily consumption, size the battery to cover at least two days. That gives you a full day of autonomy if solar input drops — rain, heavy cloud, or a shaded camp spot.
For a 700Wh daily load: two days is 1,400Wh. At 12.8V nominal (LiFePO4), that’s about 110 amp-hours of usable capacity. Most lithium batteries can discharge to 90% or more without damage, so a 120–150Ah battery would do the job comfortably.
For a 1,200Wh daily load: two days needs 2,400Wh, or roughly 190Ah usable. A 200–250Ah lithium bank covers this with margin.
These are examples using typical numbers. Your actual load audit will give you your real figure. Don’t skip the audit and copy someone else’s — the couple running a 40-litre fridge and LED lights has very different needs from the family with a 90-litre fridge, inverter, TV, and coffee machine.
Worked example: a couple in a 5-metre van
Say you’re two people in a compact caravan. Your gear: a 60-litre 12V fridge (averaging 50W, compressor running 10 hours a day in summer), six LED lights (30W total, 3 hours), a water pump (55W, 45 minutes), two phones charging (15W, 2 hours), and a laptop via inverter (75W, 1 hour).
Fridge: 50 × 10 = 500Wh. Lights: 30 × 3 = 90Wh. Pump: 55 × 0.75 ≈ 41Wh. Phones: 15 × 2 = 30Wh. Laptop: 75 × 1 = 75Wh. Total: 736Wh/day.
At two days’ autonomy, you need 1,472Wh of usable storage. That’s about 115Ah at 12.8V LiFePO4. A 150Ah battery gives you comfortable headroom. For solar, 736Wh/day ÷ 4 effective sun hours = 184W. Pad it to 300W of roof panels and you’re sorted for most conditions — and the alternator charging covers the rest on driving days.
Write your own list and do your own sums. The method is the same regardless of whether your daily total lands at 500Wh or 2,000Wh.
Sizing the solar
Solar panels on a caravan roof need to replace your daily consumption within the available sun hours. In most of Australia, you can count on roughly four to five effective sun hours per day — more in summer, less in winter, and less again if you’re parked under trees.
A simple starting point: divide your daily Wh by four. If your daily consumption is 800Wh, you need roughly 200W of solar. In practice, pad this by 50% because panels rarely deliver their rated output. Flat-mounted panels on a caravan roof lose efficiency compared to angled panels facing the sun. Partial shading from a rooftop air conditioner or roof rack knocks output further.
For 800Wh daily consumption, target 300–400W of solar. For 1,200Wh, target 400–500W. Use a quality MPPT solar controller — it’ll extract more power from the same panels than a cheaper PWM unit, especially in lower light.
A portable solar mat is a smart addition. It lets you park in the shade and run a cable to a panel in the sun. It’s not a substitute for roof panels, but it’s cheap insurance for cloudy stretches.
Charging while you drive
Solar alone isn’t always enough. If you’re moving camp every day or two, alternator charging via a DC-DC charger can top up what solar misses. A 30–50A DC-DC charger will add roughly 30–50 amp-hours per hour of driving, which is significant when you’ve had a few grey days.
The key is matching your charging to your usage pattern. If you base-camp for a week and the vehicle doesn’t move, alternator charging doesn’t help — you need solar sized for the full load. If you drive every second day, a smaller solar array plus alternator charging might be the more practical combination. Our DC-DC charging guide covers the specifics.
An all-in-one system simplifies this wiring. Instead of a separate DC-DC charger, separate MPPT solar controller, separate inverter, and separate battery monitor — each with its own wiring and mounting — everything lives in one housing. One cable to the starter battery covers alternator charging. Solar panels plug straight in. The 240V inverter is built in.
For caravanners who’d rather spend their time planning trips than planning wiring, that’s the appeal. See our Caravan Power solutions page for how this looks in practice.