By Dave Miller · off-grid sparky · 22 years wiring solar, batteries and sheds in central QLD
“After blowing three inverters in central QLD, I learned a 12-volt fridge needs at least 400Ah of battery to survive a cloudy week.”
By Dave Miller · off-grid sparky · 22 years wiring solar, batteries and sheds in central QLD
“After blowing three inverters in central QLD, I learned a 12-volt fridge needs at least 400Ah of battery to survive a cloudy week.”
Running a fridge off-grid isn't about the box on the front of the catalogue. It's about the battery bank, the panels, the inverter losses, and what the compressor actually pulls over a 24-hour period in Central Queensland heat. This article lays out the verified numbers, the realistic sizing maths, and the gotchas — including the one time I'll bend my own "no colour" rule because shade at 38 °C is genuinely the difference between cold beer and warm regret.
A standard mains fridge runs on 110V/220V AC. When you run one off-grid through an inverter, you lose roughly 10–20% of the power as conversion heat, plus the inverter draws standby power just sitting there. A 12V/24V DC compressor fridge connects directly to the battery bank with no inverter required, which eliminates that conversion loss.
The surge behaviour is the other big win. DC compressors typically use soft-start designs with low startup surge, while AC compressor fridges can spike 3× to 6× their running wattage at startup. An inverter has to handle both the continuous running load and that brief surge — and undersizing the inverter for surge is one of the most common ways a system trips or just won't start the compressor.
The practical off-grid refrigeration system is: solar panels → charge controller → battery bank → DC compressor fridge. An inverter only enters the picture if you're running a standard AC fridge instead.
Solar fridges come in three forms: cooling-only fridge, freezer-only, or a refrigerator/freezer combination unit. A chest-style solar freezer is the most energy-efficient of the three because cold air stays inside when the lid is opened — the same reason a top-loader chest freezer beats an upright freezer for efficiency.
Typical sizing for these units sits in the ranges below. Note these are rough examples, not product recommendations:
| Unit type | Daily draw | Solar array | Battery (lithium) |
|---|---|---|---|
| 30–60L fridge only | 0.35–0.55 kWh/day | 100–200W panels | 100Ah |
| 100–210L freezer only | 0.40–0.55 kWh/day | 150–200W panels | 100Ah |
| 50–165L fridge/freezer combo | 0.55–0.80 kWh/day | 200–300W panels | 150–200Ah |
A 400Ah lithium (LiFePO4) bank is a common off-grid target for a small household. LiFePO4 is appropriate for off-grid refrigeration because of its deep cycle capability — you can regularly use a high percentage of the rated capacity without killing the bank the way you would an AGM.
Sizing has to start from measured daily energy in Wh or kWh, not from the nameplate wattage on the appliance. The right move is to record a normal 24-hour period and a high-use day (think: summer, lots of door opening, warm load going in), and design for the higher number.
The maths from the verified facts:
A 400Ah lithium bank at 12V nominal is 4.8 kWh of nameplate. At 90% usable, you have about 4.3 kWh. For a 1.2 kWh/day fridge that gives roughly 3.5 days of autonomy with no charge coming in. Add solar and that figure is just your worst-case cloud cover buffer.
The standard sizing approach is to plan for the fridge to run without charging for at least 3 days (72 hours). That's a minimum — not a comfortable target. If you're running more than a single fridge, or you're in a low-sun period, or you want to avoid deep-cycling your battery daily, plan for more.
A battery bank is simply two or more batteries connected together: two 120Ah batteries joined give 240Ah; four 100Ah batteries give 400Ah. Wiring configuration (series for voltage, parallel for capacity) depends on whether you're running 12V or 24V. Getting this wrong damages batteries and gear, so it sits firmly in the "when to call a licensed professional" section below.
The facts sheet uses AGM pricing as a reference point: a small 120Ah AGM costs around $400, and a larger 300Ah AGM bank costs $1200 or more. AGM usable depth is typically 50% — meaning that $1200 300Ah AGM bank only gives you about 150Ah of usable capacity before you're hurting the batteries.
LiFePO4 costs more upfront per Ah, but you can use 90%+ of the nameplate. The maths usually works out in lithium's favour over the life of the system if you're cycling daily, which a fridge forces you to do.
If you want a fridge that doesn't need a battery bank at all, an LPG gas fridge doesn't need electricity and can run for weeks or months from a single gas bottle. They work in all climates. The catch is they're designed for freestanding use only — not built into cabinetry without ventilation clearances.
A 2-door LPG gas fridge costs around $2000–$2500. Running cost is mostly the gas bottle exchange, which in a remote setting means either a gas run to your property or planning around bottle swaps.
The honest trade-off: LPG fridges have a flame burning 24/7. In a well-ventilated installation they're fine. In an enclosed space they're a serious hazard. If you go this route, read the installation manual cover-to-cover and follow the clearances exactly.
A solar fridge system can run a generator as backup, but the recommended approach is to power a smart battery charger from the generator to top up a 12V battery bank, keeping the fridge running from the battery bank continuously. Running a generator directly into an AC fridge works, but it's harder on the fridge compressor (frequent start/stop with no soft-start benefit) and harder on your ears.
A pure sine wave generator is recommended for stable power supply — modified sine wave generators can cause some compressor and electronics issues over time. The reference figures from the facts sheet: a small 1000W high-quality 240V generator costs around $1500, and a smart battery charger to pair with it costs around $400.
If you can size your solar array and battery bank correctly, the generator becomes an insurance policy, not a daily driver. That's the goal.
A few non-obvious things affect daily energy use more than people expect:
Some of this work is DIY-appropriate; some of it is not. In Australia, fixed 230V/50Hz wiring, inverter installation connected to fixed wiring, and any work that requires a circuit breaker or RCD on the mains side must be done by a licensed electrician under state electrical safety regulations. Getting this wrong can void insurance and is genuinely dangerous.
Call a licensed professional if any of the following apply:
Battery banks themselves — particularly low-voltage 12V/24V DC battery wiring — can be DIY in many cases, but mistakes cause fires (loose lugs, undersized cable, no fuse or breaker near the battery). Follow the manufacturer's cable sizing and put a fuse or DC breaker as close to the positive terminal as physically possible.
Can I just run a normal house fridge off solar?
Yes, but you'll lose 10–20% to inverter conversion plus inverter standby draw, and the AC compressor startup surge (3×–6× running watts) means you need an inverter rated for surge, not just continuous load. A DC compressor fridge is more efficient end-to-end.
How many panels do I need for a fridge?
It depends on daily kWh and your site's peak sun hours. The verified formula is daily energy use ÷ peak sun hours, plus ~25% margin. A 1.2 kWh/day fridge in a 5 peak sun hour site needs about 290W of panels; in a 4 peak sun hour site (winter, southern exposure), about 375W.
Is 400Ah lithium enough for one fridge?
At 12V and 90% usable depth, you have ~4.3 kWh. For a 1.2 kWh/day fridge that's roughly 3.5 days of autonomy with zero charging. Comfortable for most setups with solar recharging daily.
Do I need an inverter if I have a 12V fridge?
No. The whole point of a DC compressor fridge is direct connection to the battery bank. Only add an inverter if you also want to run AC appliances.
What about running a generator directly into an AC fridge?
It works mechanically, but you're better off running the generator into a smart battery charger and letting the fridge run from the battery. Smoother power, less compressor stress, less noise runtime.
Is an LPG gas fridge a good idea?
It's a valid option — no electricity needed, can run for weeks on a bottle. The trade-offs are ongoing gas cost, the need for proper ventilation, and the fact they're freestanding only.
While many off-grid projects are achievable as DIY, certain situations require licensed professionals:
Always check local regulations and obtain necessary permits before commencing work.
Worth a watch: I tried to run my freezers off grid - and learned a lesson! Solar Reality using My #VTOMAN Jump 1800 · Solar Power Edge