How this is calculated
Energy per day is running watts × hours switched on × the compressor duty cycle — the thermostat cycles the compressor, so a unit that’s “on” for 8 hours typically compresses for about 5 of them. At the defaults (8,000 BTU, 710W, 8h, 60%) that’s roughly 3.4 kWh/day: as much as a fridge, lights, laptop and TV combined.
The surge figure is what makes or breaks AC off-grid. A fixed-speed compressor slams on at about 3× running watts — over 2,000W for even a small unit — and the inverter has to clear that peak or the whole system trips. A soft-start kit (~1.8×) or an inverter-type unit (~1.3×, ramps up smoothly and modulates instead of cycling) turns a marginal system into a working one; if you’re buying new for off-grid, buy inverter-type.
Panel wattage divides one day’s Wh by your region’s average peak-sun-hours with the 25% system derate used across Grid CEO’s sizing guides. AC has one thing going for it: peak cooling demand and peak solar arrive together.
- Shade the unit’s outdoor side and seal the window mount — both cut the duty cycle for free.
- Cool one room, not the house: close the door and let the calculator’s numbers stay small.
- If the numbers land past a 3.6 kWh station, this is mini-split territory — a mini-split heat pump on solar cools (and heats) far more per watt-hour.
Sizing the whole system? Run the full load calculator, then the solar sizing calculator.
Quick answers
How many watts does a window AC use?
About 460W at 5,000 BTU, 710W at 8,000 BTU, and 1,100W at 12,000 BTU while compressing — with a start-up spike of roughly 3× those figures on fixed-speed units.
Can a power station run one?
A 2–3 kWh station runs a small unit roughly 4–8 cycled hours — enough for a night’s sleep — provided its inverter clears the start-up surge.
How much solar for daily AC?
An 8,000 BTU unit cycled 8 h/day needs around 1,000–1,300W of panel in average US sun — the array’s biggest single customer in most builds.