Quick answer: start with 6,700 W of solar
A walk-in cooler is a refrigerator the size of a room, and its energy shows it: about 15.0 kWh a day in this planning case, which needs roughly 6,700 W of solar. Insulation, door openings, and how warm the product is when it goes in decide most of that, so the box matters as much as the cooling unit.
Planning result
At 200 W per module, the array target is 34 panels. That count assumes four peak-sun-hours, 75% end-to-end solar yield, 90% conversion efficiency, and a 20% planning margin. Summer is the design case: high outdoor temperatures and harvest or processing loads arrive together, although long days help.
How a walk-in cooler actually uses power
Planning case: an 8 x 8 ft insulated walk-in held at refrigerator temperature for meat, produce, or dairy, cooled the common homestead way: a CoolBot controller driving a 14,000 BTU/h window air conditioner (the LG unit in Store It Cold's 8 x 8 kit is rated 1,250 W, 11.8 A at 115 V), running about 50% of the day, the top of the 30 to 50% that CoolBot reports.
The cooling unit cycles on a thermostat like a refrigerator, but the box is far larger and is opened far more often. Each door opening dumps cold air, and warm product, such as a fresh carcass or field-hot produce, adds a heavy pull-down load for hours. A well-insulated box with a strip curtain can run at a much lower duty cycle than this planning case.
Load calculation from running watts and duty cycle
The appliance-class estimate is 1,250 W running for 24 h/day at a 50% duty cycle, an average of about 625 W across those hours:
Then losses and reserve raise the energy the system must collect to about 20,000 Wh/day.
Typical manufacturer nameplate/manual range for the walk-in cooler class, triangulated with U.S. Department of Energy: Walk-In Coolers and Walk-In Freezers and Store It Cold (CoolBot): 8 x 8 walk-in cooler kit specification sheet, then reduced to a conservative planning midpoint; this is not a product specification. Verify the exact unit's nameplate and manual before sizing.
Log a full day with an energy monitor on the cooling unit's circuit in hot weather, and note the door openings and any warm product loaded.
Solar and battery sizing table
| Design item | Planning value | Basis |
|---|---|---|
| Appliance energy | 15,000 Wh/day | Running W × hours × duty cycle |
| Solar collection target | 6,700 W | 4 peak-sun-hours, 75% yield, 20% margin |
| 200 W panel count | 34 | Rounded up; real modules must satisfy controller voltage/current limits |
| One-day battery allowance | 25,000 Wh | 90% conversion efficiency, 80% LiFePO4 usable fraction, 20% margin |
| 12.8 V LiFePO4 equivalent | 1,955 Ah | Nominal planning conversion |
| 25.6 V LiFePO4 equivalent | 980 Ah | Nominal planning conversion |
A thickly insulated cold room stores cold itself: running the cooling harder during the day and coasting overnight shifts energy onto the array and reduces the battery needed.
Build the closest passing wiring-diagram preset
The Walk-In Cooler 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 1,600 W continuous with 4,000 W surge for this planning case. Every thermostat cycle restarts the compressor, which is what the 4,000 W surge allowance covers; a soft starter or an inverter-driven cooling unit reduces it.
The 3,600 W startup estimate is not a substitute for the manual's locked-rotor, compressor-start, or motor-start requirements, and an inverter's surge rating usually lasts seconds, not minutes. A battery-to-inverter cable that is too long or too small can pull the DC input below the inverter's low-voltage threshold during that start even when the battery has plenty of energy, so use the diagram machine's real run length.
The common mistake
Ways to cut the load
- Build to CoolBot's own sizing assumptions: an airtight room with at least R25 rigid foam and fewer than six door openings an hour, including insulation under the floor.
- Fit a strip curtain and keep door openings short and planned.
- Pre-chill warm product elsewhere before it goes into the cooler.
- Run the cooling harder during sun-hours so the box coasts overnight.
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 walk-in cooler?
For the planning case on this page (an 8 x 8 ft homestead walk-in cooled by a window air conditioner and a CoolBot), allow about 6,700 watts of solar at four peak-sun-hours per day. That covers an estimated 15,000 Wh daily load plus conversion, temperature, and recharge margin. Better insulation and fewer door openings reduce this more than any equipment change.
What size inverter should I use for a walk-in cooler?
Plan on at least 1,600 W continuous and 4,000 W surge. Plan for the compressor start on every cycle, and confirm the cooling unit's voltage.
What battery size keeps a walk-in cooler running for one day?
The one-day planning allowance is about 25,000 Wh nominal usable design capacity, roughly 1,955 Ah at 12.8 V or 980 Ah at 25.6 V for LiFePO4. A well-insulated box can coast overnight, which reduces the battery the system needs.