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Here’s the uncomfortable truth about solar for camping: the wattage printed on a panel is what it makes in a laboratory under perfect sun, and real life is not a laboratory. A residential solar installation in Melbourne — 19 kilowatts of panels — was observed making just 120 watts on a rainy grey afternoon. That same array produced 76kWh on a good sunny day. That’s not a rounding error; that’s a near-total collapse. If you size your camping rig off a panel’s nameplate number and then get rained in for two days, you’ll come home with warm food and a flat battery.
The fix isn’t just buying more panel. It’s thinking in energy first — watt-hours in, watt-hours out — and treating panel wattage as the last number you pick, not the first. This guide works through the calculation that actually holds up, the loads that actually drive the answer (one appliance above all others), and the battery trap that quietly ruins gear before most people realise what happened.
Start with Energy, Not Panels
The instinct is to ask “how many watts of solar do I need?” but that’s the wrong starting point. Panels produce power; your battery stores energy; your gear consumes energy over time. Work backwards from what you actually use each day, and the panel size falls out at the end.
The core formula is straightforward. For each device, multiply its draw in amps by the hours you run it, then multiply by your system voltage (12V for most camping setups). That gives you watt-hours. Sum everything up and you have your daily load. Then:
Panel watts ≈ daily watt-hours ÷ usable sun hours ÷ 0.8
The 0.8 accounts for real-world losses — wiring resistance, inverter conversion, battery charge/discharge inefficiency — that silently eat around 20% of what your panels harvest. Ignore it and you’ll be undersized from day one.
To make it concrete: if your gear uses 1,745Wh per day and you plan around five sun hours, the math lands at roughly 436W of panel. That’s not a product recommendation — it’s the output of your own numbers plugged in.
The weakest input in that formula is sun hours, and it’s where the whole calculation can fall apart. Five hours is a reasonable conservative figure for decent weather in a moderate climate, but winter shrinks it, high latitudes shrink it further, and clouds can take it down to nearly nothing. The 19kW→120W collapse example isn’t a freak event — it’s what partial overcast does to solar output. Plug in an optimistic sun-hours figure and treat the result as guaranteed, and you’ve already lost the bet.
Build in a buffer on top of whatever the formula spits out. Recommendations vary — some sources say 20%, others say 30–50% — and the right answer depends on how often you camp in poor weather and how much autonomy you need. In practice: if bad weather or shade is a realistic part of your trips, lean toward the larger buffer. The formula gives you a floor, not a target.
The Fridge Is the Load That Decides Everything
You can spend a long time optimising lights, phone chargers, and a water pump. They matter, but they’re not the answer to your question. A compressor fridge is. It’s the single appliance that does more to drive your solar and battery requirements than everything else combined, and any “basic camping” figure that doesn’t mention whether it includes a fridge should be read with that caveat firmly in mind.
Lights, phone charging, and a water pump together can be served by roughly 50–160W of solar. Add a compressor fridge and you’re realistically looking at 150–200W at minimum — and that’s for a modest setup in decent weather. Field observations of a roughly 50L compressor fridge show it averaging around 1A per hour over a full day (at 12V), but pulling closer to 3A while the compressor is actively cycling. That sounds manageable until you remember the compressor runs more in hot weather, the panel produces less on cloudy days, and both things tend to happen at the same time.
Real-world testing with 100Ah of lithium and 200W of solar sustained a 75L dual-zone fridge alongside phones and a pump in good weather — but by day three in poor conditions, that setup needed a top-up from the vehicle’s alternator. A larger rig (300W solar, 240Ah AGM) running an 85L fridge held up indefinitely in good weather and dropped to a couple of days of autonomy in poor weather or shade.
The marketing version of this — “150W runs a modern 60L fridge continuously” — is technically true under ideal conditions, meaning no overcast, full sun, fridge-only mode. It’s best-case, not typical. The field reports are more honest: the panel keeps up on sunny days, the battery covers nights and bad weather, and if either is undersized, the fridge loses.
A few conditions change the fridge equation significantly:
- Dual-zone or freezer mode roughly doubles the draw compared to fridge-only
- Hot ambient temperatures make the compressor run harder and more often
- A gas fridge removes the electrical load almost entirely and dramatically cuts your solar requirement
- Fridge size matters — a 75–85L unit needs meaningfully more panel and battery than a 50L
For planning purposes: if you’re running a compressor fridge, budget at least 150–300W of solar and size your battery for the fridge load plus autonomy through bad weather. The specific numbers depend on your fridge, your climate, and how many sunless days you might string together.
What “Enough Panel” Actually Looks Like by Use Case
With the calculation logic and the fridge load established, rough tiers start to make sense — provided you apply them with conditions attached, not as guarantees.
Minimal camping — lights, phones, small cooler or gas fridge: somewhere in the 50–160W range. The low end assumes no compressor fridge and short trips; the high end assumes a water pump and a few more devices. A 50–100W figure from a panel seller should be read as a floor, not a recommendation.
Standard setup — compressor fridge plus the above: 150–300W of solar with at least 100Ah of usable battery capacity. The 200W + 100Ah lithium field observation is the most credible real-world anchor here; treat it as a starting point for a moderate climate and average weather.
Vanlife / extended trips — laptops, water pump, entertainment: 400W solar with 200–300Ah of battery is the commonly cited standard. Power-hungry setups adding HVAC, a full kitchen, or always-on work gear climb to 600W or more with 400Ah+ of storage. These figures come from blog-tier guidance rather than independent testing — treat them as directional, verify them against your own watt-hour load, and remember that 400W in Arizona and 400W in the Pacific Northwest in November are not the same number in practice.
One figure the guide won’t give you: how many watts “per person.” That framing has no physical basis — your loads scale with devices and the fridge, not headcount.
The Battery Trap That Ruins Gear Quietly
Panel sizing gets all the attention. Battery chemistry gets almost none, and it’s the more expensive mistake.
A lead-acid or AGM battery is rated at, say, 100Ah. That is not 100Ah of usable capacity. Repeatedly discharging a lead-acid or AGM battery past 50% degrades it — quickly and permanently. In practice, a 100Ah AGM battery gives you roughly 50Ah before you’re into the damage zone. Most people don’t know this when they buy. They budget 100Ah of use, they get 50, and they destroy the battery finding out the hard way.
LiFePO4 lithium doesn’t have this constraint in the same way — you can use most of the rated capacity without the same degradation penalty. That difference in usable capacity is a significant part of why lithium costs more and why the field reports running fridge setups tend to specify lithium.
For sizing battery autonomy, the math works off usable capacity, not rated capacity. If your daily load is around 750Wh and you want two days of autonomy without solar input — enough to ride out a stretch of bad weather — that’s roughly 1,500Wh of usable capacity, which at 12V works out to about 125Ah usable. On AGM, that means buying 250Ah rated. On lithium, it’s closer to 125–150Ah rated. The difference in physical size, weight, and cost between those two options is substantial.
Cold weather is also worth flagging: low temperatures reduce effective battery capacity, which matters if you’re winter camping or in high-altitude conditions. This isn’t about damage the same way over-discharge is — it’s a temporary reduction — but it’s another reason to build autonomy margin into your sizing rather than cutting it close.
The One Thing That Should Change How You Shop
The number on the panel box is what it makes in a lab. Your battery’s rated capacity is not what you can use. Manufacturer figures assume ideal conditions; the field reports show what happens when conditions are real. Size your system around energy — watt-hours in and out — with the fridge as your dominant load, a realistic sun-hours figure that accounts for your worst likely weather, and a buffer on top. Then pick panels last. A system built around those constraints will run through a cloudy stretch; one built around a wattage number on a box probably won’t.