How this solar panel calculator works
Solar sizing comes down to one sum: your daily energy use in watt-hours, divided by how much sun actually hits your panel each day (peak sun hours) and how efficiently your system turns that into charge. We use Bureau of Meteorology mean daily solar exposure data for about 20 Australian towns, by month, so winter in Hobart and summer in Darwin get genuinely different numbers instead of one national average.
Shading and angle matter as much as panel size. A flat roof panel in Melbourne in June sees a lot less usable sun than the same panel tilted to face the sun on a portable blanket. The shading/angle setting adjusts for how exposed your panel realistically is.
Fixed vs blanket. Roof panels are permanent and need no setup, but take whatever angle your roof gives them. Blankets can be aimed within 15–20° of the sun and moved through the day, often doing more with fewer watts, at the cost of setting them up each time you stop.
MPPT controllers size to the panel watts, not your battery. We calculate amps from panel watts at 12V with a conversion efficiency, then round up to a common controller size.
Common questions
What are peak sun hours?
Peak sun hours are the number of hours per day the sun's energy would need to shine at 1,000W per square metre to deliver the same total energy as the real day. Australia averages about 6–8 in summer in the north and west, and as little as 1.5–3 in winter in the south. We use Bureau of Meteorology solar exposure data by town and month, not a single national average.
Should I get a solar blanket or fixed roof panels?
Fixed roof panels are permanent, wired in and need no setup, but they take whatever angle your roof has, which can lose a lot of winter sun. A portable blanket can be angled and moved to follow the sun, often needing fewer rated watts for the same job, but you have to set it up and it's vulnerable to being left out or stolen. Many vans run both: roof panels for base load, a blanket for shaded camps or top-ups.
MPPT or PWM solar controller?
MPPT (Maximum Power Point Tracking) controllers extract 10–30% more power than PWM, especially on cold mornings, cloudy days and when panel voltage doesn't closely match battery voltage. Almost everything sold for caravans and camping now is MPPT. This calculator sizes an MPPT controller.
Why is my winter solar number so much higher than summer?
Peak sun hours in southern Australia can fall from 6–7 in summer to 2–3 in winter, so the panel size needed to produce the same daily watt-hours roughly doubles. If you travel mostly in winter, size for your worst month, or plan on a generator or extra driving to make up the gap on short, overcast days.
Can I run panels in parallel to add more watts?
Yes. Most 12V systems add panels in parallel (same voltage, amps add up) up to the charge controller's amp rating, or in series (voltages add, for longer cable runs) if the controller and panel voltages support it. Get your stringing and controller sizing checked by whoever installs your gear, since open-circuit voltage limits vary by controller.
Why use Bureau of Meteorology data instead of a flat number?
A single Australia-wide "4.5 sun hours" figure hides huge seasonal and geographic swings: Darwin's sun hours barely change across the year, while Hobart's winter sun hours are a third of its summer figure. Using BOM's mean daily solar exposure by town and month gives a size that actually matches where and when you're travelling.
Assumptions we use
- Peak sun hours come from the Bureau of Meteorology Climate Averages: mean daily solar exposure (MJ/m²), satellite-derived, converted to peak sun hours (kWh/m²/day) by dividing by 3.6 (1 kWh/m² = 3.6 MJ/m²).
- 12V nominal for converting watt-hours to amp-hours.
- Base system efficiency: 75% for a well-mounted fixed panel with MPPT, 70% for a portable blanket, before shading/angle loss is applied.
- Shading/angle loss: 10% (good), 20% (typical) or 35% (poor), multiplied with base efficiency.
- MPPT controller: about 90% conversion efficiency. Common sizes are 10, 20, 30, 40, 50 and 60A.
- Panels are rounded up to common sizes: 100, 120, 150, 200, 300, 400 and 600W, then in 100W steps above that.
- Product prices are approximate and were checked on 17 October 2026.
Guide only. RigMaths isn't an electrician. Always follow the manufacturer's instructions and get high-current 12V and any 240V work done by a licensed professional.
Already sized your battery? Head back to the 12V Power Budget & Lithium Battery Sizer.