Quick answer: start with 1,450 W of solar
It depends entirely on the mode. On propane, solar only has to keep the 12 V controls alive, and a small panel covers that. On its electric element, even this compact absorption refrigerator uses about 3,240 Wh a day, roughly 1,450 W of solar, which is more than a modern full-size compressor refrigerator needs. That is why most solar owners run absorption units on gas and switch to electric only when the array has a surplus.
Planning result
At 200 W per module, the array target is 8 panels. That count assumes four peak-sun-hours, 75% end-to-end solar yield, 90% conversion efficiency, and a 20% planning margin. Absorption units lose cooling capacity in high outdoor temperatures and need their rear vents clear, so a hot day with the coach or cabin in the sun is the design day.
How a propane refrigerator actually uses power
Planning case: a compact three-way absorption refrigerator of about 95 litres (3.4 cu ft), the size used in vans, small campers, and cabins, switched to AC mode, where a heating element of about 180 W replaces the propane flame and runs about 75% of the day. Dometic rates its 95-litre RM 2356 at 175 W on AC; full-size RV units have larger elements, so read your own label. On propane, a two- or three-way unit still needs 12 V DC for its controls (Norcold lists low DC voltage as a fault that stops propane cooling), while gas-only cabin refrigerators run with no household electricity at all.
An absorption refrigerator moves heat with a heated ammonia, water, and hydrogen loop instead of a compressor. Whether the heat comes from a flame or an element, the element is a plain resistive heater: fully on or off. In hot weather, or with frequent door openings, it stays on for most of the day, which is why the watt-hours are high even though the watts look modest.
Load calculation from running watts and duty cycle
The appliance-class estimate is 180 W running for 24 h/day at a 75% duty cycle, an average of about 135 W across those hours:
Then losses and reserve raise the energy the system must collect to about 4,320 Wh/day.
Typical manufacturer nameplate/manual range for the propane refrigerator class, triangulated with Dometic: Dometic RM 2356 absorption refrigerator specifications and Norcold (Thetford): N611v and N811v installation and owner's manual, then reduced to a conservative planning midpoint; this is not a product specification. Verify the exact unit's nameplate and manual before sizing.
Measure electric mode over a full 24 hours with a plug-in energy meter on the 120 V cord, on a warm day, starting with the box already cold. The first pull-down from warm takes many hours and uses far more energy than steady running.
Solar and battery sizing table
| Design item | Planning value | Basis |
|---|---|---|
| Appliance energy | 3,240 Wh/day | Running W × hours × duty cycle |
| Solar collection target | 1,450 W | 4 peak-sun-hours, 75% yield, 20% margin |
| 200 W panel count | 8 | Rounded up; real modules must satisfy controller voltage/current limits |
| One-day battery allowance | 5,400 Wh | 90% conversion efficiency, 80% LiFePO4 usable fraction, 20% margin |
| 12.8 V LiFePO4 equivalent | 425 Ah | Nominal planning conversion |
| 25.6 V LiFePO4 equivalent | 215 Ah | Nominal planning conversion |
Storing a full day of electric-mode energy is expensive. The practical design keeps propane as the default and treats electric mode as a way to use daytime surplus; the battery allowance above applies only if the element must run overnight.
Build the closest passing wiring-diagram preset
The Propane Refrigerator Planning System preset is an engine-passing starting point whose array, battery bank, continuous inverter rating, and surge rating each meet or exceed this page's stated planning allowances. Adjust it only from measured load data and verified equipment limits.
Inverter and startup current
Use at least 300 W continuous with 300 W surge for this planning case. There is no compressor, so there is no locked-rotor surge; the element draws close to its running power from the first second. What matters is that the inverter can carry 180 W continuously for many hours alongside the other loads.
Because this load draws its full power for long stretches rather than for a moment, the battery-to-inverter cable carries heavy current continuously. A run that is too long or too small wastes energy as heat and can push the inverter to its low-voltage cutoff late in the day, even with energy left in the battery, so use the diagram machine's real run length and keep every fuse within the equipment and conductor limits. The 200 W peak estimate is a planning figure, not the manual's rating.
The common mistake
Ways to cut the load
- Run on propane by default; the 12 V control draw is tiny compared with the heating element.
- Keep the rear vent and flue clear; a hot coil compartment makes the element run longer.
- Pre-cool the box on surplus solar or shore power before a trip rather than pulling it down from warm on battery.
- If propane cost is the reason to go electric, a compressor refrigerator is the solar-friendly replacement; compare it on the refrigerator page.
What to verify before buying equipment
- The exact running watts, startup current, voltage, frequency, and required circuit from the appliance label and manual.
- Actual watt-hours over a representative day; seasonal heating or cooling loads need a design-day measurement.
- Local peak-sun-hours for the worst operating season, plus shade and array orientation.
- Controller maximum input voltage at the coldest expected temperature and maximum output current.
- Battery discharge current, series/parallel permission, terminal torque, low-temperature controls, and overcurrent protection.
- Conductor ampacity, voltage drop, terminal temperature ratings, disconnecting means, grounding, local amendments, and inspection requirements.
For a whole-system load list, use the load and appliance calculator. For the system context around this appliance, continue to the Off-grid refrigeration guide.
Frequently asked questions
How much solar do I need for a propane refrigerator?
For the planning case on this page (a compact three-way absorption unit running on its AC heating element), allow about 1,450 watts of solar at four peak-sun-hours per day. That covers an estimated 3,240 Wh daily load plus conversion, temperature, and recharge margin. On propane, a single small panel usually keeps the control board and its battery topped up.
What size inverter should I use for a propane refrigerator?
Plan on at least 300 W continuous and 300 W surge. There is no motor surge, so the continuous rating is what matters; the inverter must carry the element for hours without derating in a warm compartment.
What battery size keeps a propane refrigerator running for one day?
The one-day planning allowance is about 5,400 Wh nominal usable design capacity, roughly 425 Ah at 12.8 V or 215 Ah at 25.6 V for LiFePO4. Most owners avoid that cost by running on propane overnight and using electric mode only with daytime surplus.