Can You Run Aircon on Solar or Inverter Backup?
Plenty of Gauteng homes now have panels, batteries or both, and the obvious next question is whether you can run aircon on solar. Often you can, but it depends on the aircon, the backup system and how you use them together.
An air conditioner is one of the heavier loads in a typical home, so it's usually the appliance people are told to leave off when the grid goes down. That advice made sense with older units and small backup systems. With a modern inverter aircon and a properly sized solar setup, the picture is different.
This guide explains what actually matters in plain terms. It won't give you a kW figure for your system, because that depends on your specific equipment and belongs with your solar installer. It will help you ask the right questions.
Two numbers that matter: starting power and running power
Every compressor-driven appliance has two power demands. Running power is what it draws once it's up and working. Starting power is the brief surge it needs to get the compressor moving from standstill.
A fixed-speed (non-inverter) aircon starts its compressor at full speed every time the thermostat calls for cooling. For a split second it can pull several times its normal running current. A backup inverter has to handle that peak, not just the running load, or it may trip, shut down or alarm. On a sunny afternoon the unit might cycle on and off many times, and each restart is another surge.
An inverter aircon works differently. Its electronics ramp the compressor up gradually, so there's no hard start, and once the room is at temperature it slows down rather than stopping. The draw is smoother and generally lower on average, which is much easier on a battery system.
Why inverter aircons suit solar and battery systems
| Inverter aircon | Fixed-speed aircon | |
|---|---|---|
| Start-up | Soft start, compressor ramps up | Hard start at full speed, high momentary surge |
| Once the room is cool | Slows down and keeps running gently | Switches off, then restarts with another surge |
| Load on a battery | Steadier, easier to plan around | Spiky, harder for smaller inverters |
| Daytime solar use | Can follow available solar output more smoothly | Draws full power or nothing |
Still running an older fixed-speed unit and want it to work alongside solar? Replacing it with an inverter model is often the most practical change. Our comparison of inverter and non-inverter aircons goes into the differences in more detail.
Sizing the backup is the solar installer's job
Whether your inverter and batteries can carry an aircon is a question about the whole system: inverter rating, battery capacity, how much else is connected and how long you expect to run things during an outage. That calculation should be done by the company that designed or installs your solar system, using the actual specification of your aircon.
If you want to run aircon on solar and batteries during outages as well as on sunny days, here's what to give them:
- The make and model number of each aircon. These are on the rating plate on the side of the indoor and outdoor units.
- Rated power input and maximum current. From the rating plate or the specification sheet, for both cooling and heating modes.
- Whether each unit is inverter or fixed speed. This affects how the backup inverter sees the load.
- How you want to use it. Daytime only on solar, or also from batteries at night and during outages.
Many installations deliberately put aircons on the non-essential circuit, so they run from the grid and solar but not from the batteries when the power is off. That's a reasonable design choice, not a fault, and it protects the battery for lights, fridges and Wi-Fi.
When to run aircon on solar: pre-cooling during the day
On the Highveld, late morning and early afternoon usually bring the strongest sunshine, before summer thunderstorms build later in the day. Running the aircon in that window, while the panels are producing well, lets you cool the house using solar power instead of grid electricity. By the time the sun drops, the rooms are already comfortable and the aircon can slow down or switch off.
A few habits help:
- Use the timer. Start cooling before the hottest part of the day rather than waiting until the house is already hot.
- Set a moderate temperature. Every degree lower means more work for the compressor and more power drawn.
- Close curtains on sunny windows. Less heat coming in means less to remove.
- Keep filters clean. A clogged filter makes the unit work harder for the same cooling.
For more ways to cut consumption, see our tips on lowering aircon running costs.
Load shedding, outages and protecting the unit
Load shedding taught most South Africans that the moment power returns can be harder on electronics than the outage itself. Voltage spikes and dips when supply is restored can damage an aircon's control board. A few sensible precautions:
- Switch off before a scheduled outage. Then wait a few minutes after power returns before switching back on.
- Ask your electrician about surge protection. Protection at the distribution board helps shield the aircon and everything else.
- Check your backup inverter's output. Aircons should run on a pure sine wave supply. Most solar hybrid inverters provide this, but some older or budget backup units don't, so confirm with your installer.
- Don't keep resetting a tripping unit. If the aircon repeatedly trips the inverter or breaker, have it checked.
If your aircon stopped working properly after an outage or a switch to backup power, book an aircon repair or call 0861 995 092. We diagnose on site, including control board faults.
Planning a new aircon around your solar system
Installing a new unit and want to run aircon on solar from day one? Choose an efficient inverter model in the right size and share its specification with your solar installer before both jobs are finalised. We handle the aircon installation side, from choosing the unit to commissioning it, and regular servicing keeps it drawing no more power than it should.
Solar and aircon questions
With a grid-tied or hybrid system, the aircon runs on whatever mix of solar and grid power the inverter provides. Without grid power or batteries, output rises and falls with every passing cloud, so a standard aircon should not rely on panels alone. Your solar installer can explain how your particular system behaves.
The most common reason is that the start-up surge of a fixed-speed compressor exceeds what the inverter can supply, or the aircon plus other loads exceeds its rating. A fault in the aircon can also cause it. Have the aircon checked and ask your solar installer to confirm the inverter rating.
Often yes, especially an inverter aircon used mainly during sunny hours. Whether it can also run from batteries during outages depends on your inverter and battery capacity, which your solar installer should assess using the aircon's specification sheet.
Make your aircon a better fit for solar
Talk to us about efficient inverter units, or have an existing system checked after an outage.