How to integrate solar energy air conditioning

By On Dec 27, 2025

If you want to properly control your air conditioning with solar, it helps to understand how things actually work. As a former control systems engineer, this is perfect for me. Let’s break it down.

How air conditioners regulate temperature

Old school “bang-bang” control

Previous air conditioners used a simple method called “bang-bang control.” You set a temperature (so-called setpoint) on the remote control.

In cooling mode: When the room is hotter than the set value, the compressor turns on at full power. As soon as the room falls below the set value, it switches off.
In heating mode: same idea, but reversed.

It’s literally all or nothing.

Modern inverter control

Nowadays air conditioners use inverter control. Instead of being 100% on or off, the compressor can run anywhere between 0 and 100% power. That means:

Better temperature stability
Greater efficiency
Longer lifespan (less hammering motor switching on and off)

The brain behind it: PID control

So how does the air conditioner know how much power to draw at any given time?

It uses a bit of math called the PID algorithm. I won’t bore you with the equations (I’ve literally written three books about them), but here’s what you need to know:

Not all PIDs are created equal. Bad implementations don’t behave better than bang-bang. Good models use gentle adjustments to ensure that the temperature in the room remains constant.
The algorithm reacts to “errors”. The error is simply the difference between the set point and the actual room temperature. The larger the error, the more current the system draws.

Example: Your room is 12°C and you want 22°C. The system starts at full power, then gently lowers the temperature by around 20°C so that it doesn’t go too far, and finally keeps the room at a constant 22°C. For example, it could settle at 63% performance.1

Electrical vs. thermal energy

This is where confusion often creeps in.

A device could be marketed as a “14kW air conditioner.”
This number refers to thermal performance (how much heat or cold can enter a room).
The actual electricity requirement is much lower thanks to the efficiency of the heat pump.

For example:

A 14 kW air conditioner with a coefficient of performance (COP) of 3 only requires about 4.7 kW of electricity to pump out 14 kW of thermal energy.
If the COP is closer to 4, it is even better – about 3.5 kW of electrical input for 14 kW of thermal output.

When sizing your solar system, always base it on the nominal electrical output, not on the flashy marketing number.

Solar air conditioning cover

Let’s say your air conditioner uses 7 kW of electricity at full power.

On a perfect day, a 7kW solar system doesn’t reach its peak until midday.
Losses (shading, inverter limits, module alignment) further reduce this.
So if you want your air conditioner to always be powered by solar energy, you’ll need a lot more than 7kW on the roof.

The good news:

With good PID control, your system won’t run at full speed all day.
As soon as the room is at the right temperature, the electricity requirement drops significantly.
A well-sized battery can also help – by filling the deficit when the air conditioning starts up strongly or clouds gather. Remember that you need to consider the following:
- Battery power: Kilowatts (kW) to cover initial power (and surge currents if you want to operate off-grid)
- Battery energy capacity: Kilowatt hours (kWh) to get you through the evening at a consistent temperature.

Smarter usage: pre-cooling and timing

Since the sun’s rays are strongest during the day, it makes sense:

Pre-cool (or heat) the house while the sun is shining.
Make sure the temperature remains stable until late afternoon.
Then let your battery endure the evening.

This will prevent your battery from dying right after sunset when the air conditioning is at full load.

Unfortunately, most Australian homes have such a poor thermal envelope that pre-cooling does not last long. To improve the thermal envelope of your home, contact:

gaps
Glazing,
Insulation.

Then, unless you live in the tropics, add thermal mass to your home. Use dense materials like brick inside and swap out your plasterboard for something more solid for bonus points.

Bricks inside for thermal mass and lime plaster instead of gyprock are a boon.

What you should discuss with your installer

If you are seriously interested in adding solar power to your air conditioner, sit down with your installer and discuss the following:

Electrical size of your air conditioner (not the heat output on the packaging).
Your usage profile. Cooling down in summer is easy – there is plenty of sun. Heating is more difficult in winter (particularly in South Australia), so you should have a generous solar system.
Your habits. Do you want the device to run all night or just until you go to bed? Do you blow it up in the morning before sunrise?
Data. If you have smart meter data (5 minute resolution) you can usually clearly see the load on the air conditioning system. If not, consider having your own meter on the circuit.

From there it’s all about size:

Solar system large enough to cover daily loads.
The battery is sized so that coverage lasts into the evening or early morning.

Summary

These are the basics of combining solar energy and air conditioning. In summary:

Do not confuse thermal and electrical performance values.
Expect higher demand at launch, but lower demand once the space stabilizes.
Solar power covers most of the daytime needs, batteries smooth out the rest.

To assess which air conditioners are worth it and which brands are best to avoid, check out our new air conditioning review hub.

Footnotes

An air conditioner with a good, well-tuned PID algorithm does not need to be set at 16°C to cool down faster. The algorithm initially knows that it has to run at full speed. But good luck explaining that to the rest of the family. ↩