Can I run an air conditioner on an inverter and solar?
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Yes, but air conditioning is the single biggest thing most homes ask a backup system to do, and it can double or triple the size and cost of the system. Here is how to work out what you need, and how to keep it affordable.
How much power an air conditioner uses
Common sizes in homes, as a rough guide:
| Size | Cooling capacity | Typical running power |
|---|---|---|
| 1 HP | about 9,000 BTU/h | roughly 750–1,000 W |
| 1.5 HP | about 12,000 BTU/h | roughly 1,100–1,500 W |
| 2 HP | about 18,000 BTU/h | roughly 1,600–2,200 W |
Your unit’s label or manual gives its real figure, usually as rated input power in watts. Efficient models can be well below these ranges.
Two different problems: starting and running
Starting. A conventional (fixed-speed) air conditioner’s compressor draws several times its running power for a moment as it starts. On an inverter this surge, not the running load, is often what trips the system. The inverter must handle the surge on top of everything else that is running. See kVA vs kW for surge ratings.
Running. Energy is power × hours. A 1,000 W unit running 8 hours overnight uses about 8 kWh. That is more than many backup batteries hold in total.
Inverter-type air conditioners make a big difference
“Inverter” air conditioners (variable-speed compressors) are a different thing from your backup inverter, despite the name. They:
- start gently, without the big surge, so a smaller backup inverter can cope;
- slow down once the room is cool, so their average draw over a night can be far lower than their maximum.
If you are choosing a new air conditioner and want to run it on backup power, an inverter-type unit is usually the best single decision you can make.
Sizing an example
Say you want one 1 HP inverter-type unit for 8 hours a night, plus lights, a fridge and fans (about 300 W average), with a lithium battery.
- Air conditioner, assuming it averages around 600 W once the room is cool: 600 × 8 = 4.8 kWh
- Everything else over the same 8 hours: 300 × 8 = 2.4 kWh
- Total: 7.2 kWh, divided by 0.9 inverter efficiency and 0.8 depth of discharge: about 10 kWh of lithium battery
- Inverter: the combined maximum draw is about 1.3 kW; with 25% headroom that is about 1.6 kW, so 2 kW or more
Run the same evening without the air conditioner and the battery shrinks to about 3.3 kWh. That gap is the real cost of cooling on backup power.
Ways to make it affordable
- Cool one room, usually the bedroom, rather than the whole home.
- Set the thermostat a little higher, around 24–26 °C (75–79 °F), and use a fan as well.
- Run it on solar during the day when panels are producing, and limit night-time use.
- Close curtains and doors to the cooled room, and seal gaps.
- Consider a soft starter for a fixed-speed unit, fitted by a technician. It reduces the starting surge.
Put the air conditioner into the calculator with your real running hours to see the battery, inverter and panels it needs where you live.