Quick answer: start with 1,750 W of solar
The useful answer starts with watt-hours, not panel count. This worked example turns a typical EnergyGuide/nameplate/manual planning range into a daily energy budget, then adds explicit system losses and reserve.
Planning result
At 200 W per module, the array target is 9 panels. That count assumes four peak-sun-hours, 75% end-to-end solar yield, 90% AC conversion efficiency, and a 20% planning margin. Winter, shade, heat, snow, and battery recharge after cloudy days can require more.
Load calculation from running watts and duty cycle
The appliance-class estimate is 750 W running for 8 h/day at a 65% duty cycle:
Then losses and reserve raise the energy the system must collect to about 5,200 Wh/day.
Typical manufacturer EnergyGuide/nameplate/manual range for the window air conditioner class, triangulated with ENERGY STAR Heating and cooling product guidance (https://www.energystar.gov/products/heating_cooling) and Midea Product support and manuals (https://www.midea.com/us/support), then reduced to a conservative planning midpoint; this is not a product specification. Verify the exact unit's EnergyGuide, nameplate, and manual before sizing.
A plug-in energy meter is better than a single watt reading for cycling loads. Measure for at least 24 hours under the hottest or busiest conditions you expect. For hard-wired equipment, use a qualified person and a suitable meter rather than opening energized equipment.
Solar and battery sizing table
| Design item | Planning value | Basis |
|---|---|---|
| Appliance energy | 3,900 Wh/day | Running W × hours × duty cycle |
| Solar collection target | 1,750 W | 4 peak-sun-hours, 75% yield, 20% margin |
| 200 W panel count | 9 | Rounded up; real modules must satisfy controller voltage/current limits |
| One-day battery allowance | 6,500 Wh | 90% inverter efficiency, 80% LiFePO4 usable fraction, 20% margin |
| 12.8 V LiFePO4 equivalent | 510 Ah | Nominal planning conversion |
| 25.6 V LiFePO4 equivalent | 255 Ah | Nominal planning conversion |
One day of storage is a comparison point, not a universal recommendation. Multiply the battery value by the desired autonomy days, then check the battery maker's continuous current, low-temperature charging limits, and series/parallel rules.
Build the closest passing wiring-diagram preset
The Window Air Conditioner 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 1,000 W continuous with 2,500 W surge for this planning case. The 2,200 W appliance surge estimate is not a substitute for the manual's locked-rotor, compressor-start, heating-element, or power-supply requirements. The inverter must also be compatible with the battery voltage and provide the waveform the appliance requires.
Startup problems are often wiring problems. A battery-to-inverter cable that is too long or too small can pull the DC input below the inverter's low-voltage threshold even when the battery has adequate energy. Use the diagram machine's actual run length and keep every fuse or breaker within the equipment and conductor limits.
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 heating and cooling guide.
Frequently asked questions
How much solar do I need for a window air conditioner?
Using the planning case on this page, allow about 1750 watts of solar at four peak-sun-hours per day. That covers an estimated 3900 Wh daily appliance load plus conversion, temperature, and recharge margin. Measure the exact unit before buying equipment.
What size inverter should I use for a window air conditioner?
The conservative starting point is at least 1000 W continuous and 2500 W surge. The exact nameplate and manual govern, and motor or compressor loads may need a larger short-duration surge rating.
What battery size keeps a window air conditioner running for one day?
The one-day planning allowance is about 6500 Wh nominal usable design capacity, roughly 510 Ah at 12.8 V or 255 Ah at 25.6 V for LiFePO4. Add autonomy for cloudy weather and keep the manufacturer's temperature limits in view.