Day three. The fridge has gone quiet. The milk is warm. The headtorch died at 9pm. The auxiliary battery you charged before leaving home is flat — because the "big enough" solar panel you bought is doing maybe 60% of what its sticker promised, and your fridge alone has been sucking down 40 amp-hours a day.

This guide is the maths nobody walks you through at the camping shop. Work out what you actually pull each day, multiply by a fudge factor (because the Aussie sun lies), and back out the panel size you need. Then we'll cover fixed vs portable vs blanket, why MPPT regulators matter, and the three kits we'd actually buy at $300, $700 and $1500.

Photo by Zendure Power Station on Unsplash

Solar sizing is grade-9 maths. Add up your daily amp-hours, multiply by 1.5, divide by sun-hours. Done.

Step 1 — daily amp-hours (Ah/day). Typical Aussie touring loads at 12V:

• 40-litre 12V fridge — 30-50 Ah/day depending on ambient temp and how often you open it. Call it 40 Ah for planning
• LED camp lights (4hrs) — 3-5 Ah
• Phones + tablet charging — 5-8 Ah
• 12V water pump (intermittent) — 1-3 Ah
• Diesel heater (winter, 6hrs) — 6-10 Ah
• Inverter for laptop/coffee machine — add 10-30 Ah depending on use

Worked example — couple, weekend tent setup: 40Ah fridge + 4Ah lights + 6Ah devices = 50 Ah/day.

Step 2 — apply the fudge factor. Cloudy days, panels not perpendicular to the sun, voltage drop in cables, regulator inefficiency. Multiply by 1.5: 75 Ah/day of charge needed.

Step 3 — divide by sun-hours. A "200W" panel makes about 12A in full perpendicular sun. With ~5 average sun-hours per day in summer, that's 60 Ah/day. In winter at 3 sun-hours, it's 36 Ah/day. So a 200W panel just barely covers a 50Ah/day load in summer — and falls 40% short in winter.

The honest answer for that setup: 200W gets you through summer free-camping; 300W gets you through winter; 400W gives you headroom for an inverter or a longer trip.

Three form factors, three jobs. Most regular tourers end up with two of the three.

Fixed roof-mounted panels — set-and-forget. Best for caravans, motorhomes, canopies. Charging the moment the sun's up, no setup, no theft risk. Downside: you can't park in the shade. Pricing: $200-450 for 200W mono panel; $500-900 installed with charge controller.

Folding portable panels (with kickstand) — the touring all-rounder. Carry in the back of the 4WD or boot, set up beside camp, chase the sun through the day. Aluminium-framed, glass face, robust. Pricing: $250-500 for 120W; $400-750 for 200W. Best brands at this end: Hardkorr, Projecta, Renogy, Drift.

Solar blankets — the swag/4WD ultralight pick. Roll up to the size of a beach towel, weigh 3-4kg for 200W, drape over the bonnet or roof rack. Pricing: $400-700 for 200W blanket; the cheap eBay ones are NOT the same product — get a known brand or you'll regret it inside 12 months.

The combo most tourers settle on: fixed 200W on the caravan/canopy as base load + a 200W folding panel for camp. Total ~$700-900, full redundancy, you can park in the shade and still charge.

Browse the lot in our solar panels + blankets collection or the broader 12V electrical + battery range.

The regulator (charge controller) sits between the panel and the battery. It determines how much of the panel's output actually makes it into the battery. There are two types and the difference is real money on bigger panels.

PWM (Pulse Width Modulation) — cheap, simple, 70-75% efficient. Fine for small panels (under 120W) charging a single battery. About $30-80.

MPPT (Maximum Power Point Tracking) — clever, 92-97% efficient. On a 200W panel that's 40-50W more delivered to the battery — roughly an extra 4Ah/day. Pays for itself inside a year of regular use. About $120-300 for a quality 20A unit (Victron, Redarc, Projecta).

The rule: if your panel is over 120W or you ever want to add a second panel later, get MPPT. If you're running a fixed 50W trickle on a caravan battery, PWM is fine.

One more thing — voltage matters. Most folding panels are nominal 18V; battery is 12.6-14.4V. PWM dumps that voltage difference as heat (lost watts). MPPT converts it down — so all the watts make it through. That's the whole reason MPPT exists.

Photo: Jackery Power Station / Unsplash

"Sun hours" is the equivalent number of hours per day at full perpendicular intensity (1000 W/m²). It's NOT how long the sun is in the sky. Annual averages from Bureau of Meteorology data:

• Alice Springs / Pilbara — 6.5 hrs/day average; 7.5 in summer, 5.5 in winter. Solar paradise.
• Brisbane / Gold Coast — 5.4 avg; 6.2 summer / 4.5 winter
• Sydney / NSW north coast — 4.8 avg; 5.8 summer / 3.6 winter
• Melbourne / VIC — 4.0 avg; 5.5 summer / 2.5 winter — the trap zone
• Tassie — 3.7 avg; 5.2 summer / 1.8 winter — undersize at your peril
• Perth + WA south-west — 5.5 avg; 7.5 summer / 3.5 winter

What this means in practice: a 200W panel that pumps 60Ah/day in Alice in summer makes 24Ah/day in Hobart in July. Same panel, less than half the output. Plan for the worst conditions of your trip, not the best.

The sneaky thief: shade. Even one large gum tree shadow over a single cell can drop a panel's output by 50%+ because cells are wired in series. Move the panel — don't trust "near enough."

1. Sizing for summer, camping in winter. Halve your sun-hours November-to-July south of Brisbane. Plan for it.
2. Skinny cables. A 5m run from panel to battery on undersized 6mm² cable can lose 8-12% in voltage drop. Use 8mm² minimum for runs over 4m at 200W.
3. Battery too small for the load. 100Ah AGM gives you 50Ah usable (50% DOD). Daily draw of 50Ah and one cloudy day = flat. Match battery to 2-3x daily load.
4. No way to read state of charge. Voltage alone lies — needs to settle for an hour. Get a battery monitor with shunt (Victron BMV, Redarc, ~$200-350). Worth every cent.
5. Panel angled wrong. Flat to the sky in winter loses 30%. Tilt fixed panels seasonally; angle folding panels every 2-3 hours through the day.
6. Cheap eBay panels. "200W" panels that test at 130W. Buy known brands with proper IEC/CE certification — Hardkorr, Projecta, Redarc, Renogy, Victron. The premium is 20-40%, the difference is double the lifespan.

Photo: Loom Solar / Unsplash

Three real-world setups, scaled to trip type.

Tier 1 — Weekend warrior (~$350-450). Couple, tent, 40L fridge + lights + phones. Two-night max free-camp.

• 120W folding panel with built-in PWM regulator — $300-400
• One 100Ah AGM battery (or a portable power station like a peak power pack for instant plug-and-play)
• Anderson plug, 4m of 8mm² cable

Tier 2 — Long-trip tourer (~$900-1200). Family, swag/camper trailer, fridge + LED strip lights + diesel heater + USB everything. Week-plus free-camping.

• 200W folding solar panel — $500-700
• External 20A MPPT regulator (Projecta, Redarc) — $180-250
• 120-200Ah lithium aux battery — $700-1100 (or 2x AGM at $300)
• Battery monitor with shunt — $200

Tier 3 — Full off-grid touring (~$2000-3500). 4WD + canopy or caravan, fridge + freezer + induction cooktop + inverter for power tools. Indefinite free-camping.

• Fixed 200-300W roof panel + 200W folding portable for shade days
• 30A MPPT (Victron SmartSolar) + DC-DC charger from alternator
• 200-300Ah lithium battery bank (BMS-managed)
• Pure-sine inverter (1500-2000W) for laptops, induction cooktop
• Backup peak power pack for jump-starting and tools

Most people buy Tier 1, want Tier 2 within a year, and end up at Tier 3 by year three. Skip a tier if budget allows — it's cheaper than buying twice.

Solar isn't black magic — it's an Ah/day audit, a fudge factor of 1.5, and 5 sun-hours of sensible Aussie maths. The biggest mistakes are buying once-and-cheap, undersizing for winter, and skimping on the regulator that actually delivers the power.

Get the maths right before you spend a dollar. A $400 well-sized kit beats a $1200 mismatched one every weekend of the year.