Find out exactly how much solar power you need for your next trip.
Whether you’re running a 12 V fridge, LED lights, or an inverter for your coffee machine, this step-by-step solar sizing guide helps you calculate the right solar-panel wattage and battery capacity for your caravan, camper trailer, or 4WD setup.
⚡ Why Correct Solar Sizing Matters
An undersized system will leave you with flat batteries, while an oversized setup adds unnecessary weight and cost. Calculating your system size ensures you:
Stay powered day and night without relying on generators
Extend battery life and reduce depth-of-discharge stress
Make full use of Australia’s abundant sunshine
Match panels, regulators, and batteries safely and efficiently
? Step 1 — List Your 12 V Appliances
| Appliance | Watts | Hours / Day | Watt-hours / Day |
|---|---|---|---|
| 12 V Fridge | 60 W | 12 h | 720 Wh |
| LED Lights (4) | 20 W | 5 h | 100 Wh |
| Water Pump | 50 W | 0.5 h | 25 Wh |
| Laptop Charger | 90 W | 2 h | 180 Wh |
| Phone Chargers × 2 | 10 W | 3 h | 30 Wh |
| Total Daily Load | ≈ 1,055 Wh ≈ 1.05 kWh |
? Step 2 — Convert to Battery Capacity
Use the formula:
Example:
( 1,055 Wh ÷ 12 V ) × 2 days ÷ 0.8 (DOD) ≈ 220 Ah
? You’d need around 220 Ah of usable battery capacity (e.g. 2 × 120 Ah LiFePO₄ batteries).
☀️ Step 3 — Size Your Solar Panels
In Australia, average effective solar hours ≈ 5 h / day (varies by region).
Assume 80 % efficiency.
( 1,055 Wh ÷ 5 h ) ÷ 0.8 ≈ 264 W
Round up to 300 W of solar minimum.
To recharge faster or run extra loads, 400–600 W is ideal for touring rigs.
? Typical System Examples
| Setup | Battery Bank | Solar Panels | Notes |
|---|---|---|---|
| Weekend Tourer | 120 Ah LiFePO₄ | 200 W Portable Panel | Basic fridge + LED lights |
| Full-Time Traveller | 240 Ah LiFePO₄ | 400–600 W Fixed Panels | Fridge, laptops, water pump |
| 4WD with Roof Tent | 100 Ah LiFePO₄ | 200–300 W Folding Panel | Compact setup |
| Off-Grid Caravan (Heavy Use) | 400 Ah Battery Bank | 800–1000 W Array + MPPT | Inverter + appliances |
?️ Step 4 — Adjust for Weather & Location
| Region | Avg Peak Sun Hours | Recommended Oversize Factor |
|---|---|---|
| QLD (North) | 5.5–6 h | × 1.0 |
| NSW / VIC Coast | 4–5 h | × 1.2 |
| SA / WA Interior | 5–5.5 h | × 1.1 |
| TAS / Highlands | 3–4 h | × 1.3 |
Multiply your panel wattage by the factor above for reliable year-round charging.
? Pro Tips
Use an MPPT solar controller for 15–25 % more efficiency than PWM.
Size cables correctly (max 3 % voltage drop).
Include a DC fuse or circuit breaker near the battery.
Tilt or reposition portable panels for best sun exposure.
Add battery monitoring (e.g. Victron SmartShunt) to track usage.
? Recommended Products
400 W – 600 W Fixed Solar Panels — for roof or canopy installs
Foldable Solar Blankets 200 W – 400 W — portable off-grid power
LiFePO₄ Batteries (100 Ah – 400 Ah) — lightweight, long cycle life
MPPT Solar Controllers or DC-DC Chargers — maximise energy harvest
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