A lot of people spec their solar before working out what they actually need it to do. They land on 200 watts because they read it somewhere, or go bigger because bigger feels like a safer margin. Neither of those is a bad outcome — but neither is the right way to start. Work out what you are running first. The wattage follows from there.
Start with What You're Running
I start every solar conversation the same way: a load calculation. Everything electrical that runs on a trip, and an honest estimate of how many hours a day each thing actually gets used. Fridge, lighting, phone and camera charging, a 12V device or two. If a CPAP applies, that goes on the list too.
The numbers are not complicated. A 60-litre compressor fridge draws roughly 3 to 5 amps per hour when it is cycling, but it does not run continuously. In mild conditions it cycles around 40 to 50 percent of the time. Call it 30 to 40 amp-hours per day. LED camp lighting for a couple of hours at night adds 2 to 3 amp-hours. Device charging, a few more. Most touring setups with one fridge land somewhere between 40 and 55 amp-hours per day.
The Fridge Is the Main Draw
In every setup I work on, the fridge accounts for the majority of the daily load. Everything else is secondary. For an accurate number, pull the spec sheet for the actual fridge model and run the calculation on that unit specifically.
Ambient temperature makes a significant difference and it is easy to underestimate. A fridge working hard in summer heat cycles more often and draws considerably more power than the same fridge in mild weather. Building some extra headroom into the estimate is worth doing if the trip involves real heat.
Battery Capacity and Solar Wattage Work Together
The panel charges the battery. The battery runs the gear. Both numbers need to be right, not just one of them.
If the daily draw is sitting around 50 amp-hours, the battery needs to absorb that without being pushed into a range that shortens its life. A 100Ah lithium gives around 80 usable amp-hours before it starts getting into territory I would rather avoid. A 100Ah AGM gives closer to 50 usable amp-hours. That difference matters when sizing the bank.
On the panel side, a 150 to 200 watt panel in Australian sun can realistically recover 40 to 60 amp-hours on a clear day, depending on mounting position, shade, and time of year. In good conditions that covers a standard daily draw. The battery carries the gap on harder days.
What Most Touring Setups Actually Need
For a setup running one compressor fridge, standard LED lighting and device charging, 150 to 200 watts of panel paired with a 100Ah lithium battery handles most situations comfortably. That is the combination we fit on the majority of builds. Not the cheapest option, but the one that works without needing to be managed.
For AGM instead of lithium, size the bank up to get the same usable capacity. Something in the 120 to 150Ah range gets to a similar place. The panel requirement stays roughly the same.
When You Actually Need More
A few scenarios where going bigger genuinely makes sense.
Running a CPAP machine is one. The overnight draw is significant — typically 30 to 40 amp-hours depending on the machine and settings. Add that to the daily fridge load and the total is considerably heavier than a standard setup.
Two fridges, or a fridge and a separate freezer, is another. The total draw increases and the battery and panel need to keep up with it.
Extended time in cloud cover or heavy shade is the third. Several consecutive days where the panel is not getting meaningful sun will drain a bank that is only sized for average conditions. More panel capacity gives a larger buffer to work with.
For most tourers on standard WA tracks and national park stays, 150 to 200 watts is enough. The scenarios above are real, but they are not the majority.
The Honest Answer
In my experience, most touring setups do not need as much solar as people assume going in. A 150 to 200 watt panel and a quality 100Ah lithium battery covers the typical load without requiring daily power management. Some people go bigger because it feels like a safety margin, and I understand that reasoning. But if the calculation is done properly from the start, the right size is usually simpler than the instinct suggests.
Work out the daily draw. Size the battery to carry it. Size the panel to recover it. That is the whole process.