For many Sydney homes, air-conditioning is the largest single electricity load in summer, and it is becoming a big winter load as households replace gas heating. If you have solar, a modern inverter reverse-cycle system can run largely on your own daytime production, particularly if you cool or heat the house before the sun fades. The upgrade pays off best when the new unit is efficient, correctly sized for the space and controlled so that most of its running hours fall within your solar hours.

Reading the energy rating label

Air-conditioners sold in Australia carry an energy rating label. The current zoned label shows separate star ratings for cooling and heating across hot, average and cold climate zones, because the same unit performs differently in each. Find your area on the label's map and read the ratings for that zone. When comparing models, look at:

• The star ratings for your zone, for cooling and heating separately if you use both.
• The estimated annual energy use in kWh, which is easier to turn into dollars than stars.
• The rated cooling and heating capacity in kW, which is output, not the electricity drawn.
• Indoor and outdoor noise levels, which matter for bedrooms and neighbours.

Behind the stars is efficiency: how much heating or cooling you get per unit of electricity. Modern inverter reverse-cycle units commonly deliver roughly 3-5 kW of heating or cooling for every 1 kW of electricity they draw. Older fixed-speed units generally do worse, partly because they cycle hard on and off instead of adjusting their speed.

Sizing: bigger is not better

An undersized unit runs flat out and still struggles on hot days. An oversized unit costs more to buy, switches on and off more often and can leave rooms feeling clammy because it does not run long enough to remove humidity. The right size depends on floor area, ceiling height, insulation, window size and orientation, and whether the room is open to other spaces. As a very rough starting point only:

Ask each installer how they calculated the size. A quote that names a capacity without asking about insulation, windows or which way the room faces is a guess. West-facing living areas with large windows usually need more capacity than the floor area alone suggests.

Running costs with and without solar

A simple worked example shows why timing matters as much as efficiency. Suppose a mid-sized split system draws about 1.5 kW while working hard and runs for four hours on a hot afternoon. That is about 6 kWh.

Over a summer of hot afternoons, that gap adds up. It also shows why a large air-conditioning load can change how you size a solar system. Production drops away through the late afternoon, which is exactly when many homes switch on cooling, so some west-facing panels or a slightly larger array may help. If you are adding air-conditioning, recheck your needs with our system sizing guide and our guide to how many panels you need.

Pre-cooling and pre-heating on solar

1. On hot days, close blinds and curtains on west- and north-facing windows in the morning.
2. Start cooling in the early afternoon while production is strong, at a moderate setting in the mid-20s.
3. Close doors to rooms you are not using, so you only condition the space you live in.
4. As solar falls away, let the setting rise a degree; the cooled rooms and furniture carry you into the evening.
5. In winter, warm the main living area in the early afternoon, then hold the heat with curtains and draught sealing.
6. Automate it with the unit's timer, its app or a home energy management system, so it happens even when you are out.

A battery can stretch this into the evening, but air-conditioning can drain a battery quickly. Running it directly from daytime solar is usually the most valuable use of that energy.

When replacing an old unit makes sense

• It is an older fixed-speed model that cycles noisily on and off.
• It uses R22 refrigerant, which has been phased out, making re-gassing difficult and costly.
• It needs repeated repairs, or it cannot keep the room comfortable on hot or cold days.
• It cannot heat efficiently, so you still rely on gas or plug-in heaters in winter.

If an existing unit works well and is reasonably efficient, replacing it only because you now have solar rarely makes sense; change when it runs first. Installation needs a licensed electrician for the electrical connection and a technician holding a refrigerant handling licence. The market lists Efficient Air-Conditioning from $2,990 for a supplied-and-installed split system and Smart Home Energy Controls from $690, both indicative and confirmed after an on-site assessment.

Questions to ask an air-conditioning installer

• Where will the outdoor unit sit? Shade and good airflow help efficiency, and a spot away from bedroom windows, yours and the neighbours', keeps noise down.
• How will the condensate drain be run, and where will it discharge?
• Is Wi-Fi or app control included, or an extra module? Without it, scheduling around solar hours is harder.
• What are the warranty terms for the compressor and for the installation work, and who handles claims?
• Does the price include removing the old unit and recovering its refrigerant properly?

Next steps

Check the age, refrigerant and performance of your current units, then look at last summer's and last winter's bills to see what air-conditioning costs you today. Compare efficient split systems and smart controls on the energy market page. If you would like new air-conditioning and your solar planned together, request a free assessment from Blue Energy Solar.

Frequently asked questions

Is ducted or split-system air-conditioning better for a solar home?

It depends on how you live. Split systems condition only the rooms you use, which usually keeps energy use down in smaller homes. Ducted systems are convenient for whole-house comfort, and zoning lets you shut off unused areas. Either can run well on solar if it is controlled to start during production hours. Compare the annual energy use figures on each label for your climate zone.

Should I leave the air-conditioner running while I am out?

Not all day. A better approach is to use a timer or the app to start it in the early afternoon, when solar production is strong, at a moderate setting. The house is then comfortable when you arrive, and most of the energy comes from your panels. Running it all morning in an empty house mainly adds wear and uses energy the home does not need yet.

Does a new split system need its own electrical circuit?

Larger units typically need a dedicated circuit, and a licensed electrician should check that your switchboard has capacity and suitable safety switch protection. Older switchboards sometimes need upgrading before new air-conditioning, solar or battery work can be added. Ask for this to be assessed and included in the quote, so you do not face an unexpected extra cost on installation day.