Running Your Reverse Cycle Air Conditioner Off Rooftop Solar Instead of the Grid

Most Australian homes with rooftop solar are quietly giving away their cheapest electricity. The panels peak between roughly 10am and 3pm, nobody's home, and the surplus goes to the grid for a feed-in tariff that is now often only a few cents per kilowatt-hour. In NSW, IPART's benchmark for solar exports in 2026-27 is 3.4-6.5c/kWh. In Victoria, the Essential Services Commission no longer sets a minimum feed-in tariff. Since 1 July 2025 retailers set their own, which can be as low as zero. Meanwhile the reverse cycle air conditioner - the single hungriest appliance in the house - gets switched on at 6pm when you're buying power back at three to seven times that rate.

The fix isn't a battery. It's timing.

Why the maths works so strongly in your favour

The value of running your aircon on solar isn't the solar itself, it's the gap between what you'd have been paid for exporting and what you'd have paid to import.

Both rates vary by state, retailer and tariff type, so take yours from your bill. As energy.gov.au puts it, if you are new to solar your feed-in tariff will be much lower than the retail rate you pay to buy electricity. For a sense of the spread, IPART's May 2026 survey of NSW offers found solar feed-in tariffs ranging from 0c to 12c/kWh. You can compare plans and feed-in tariffs on Energy Made Easy (ACT, NSW, south-east Queensland, SA and Tasmania) or Victorian Energy Compare in Victoria. Every kilowatt-hour of solar you self-consume instead of export is worth the difference between the two. For example, that is 25c on a plan that charges 30c/kWh to import and pays 5c/kWh for exports, not the 5c the export would have earned.

A 7.1kW (cooling capacity) split system is typically rated at around 2kW of electrical input when cooling at its rated capacity - Mitsubishi Electric's AP71, for example, lists 2.01kW. It draws considerably less once it's reached setpoint and the inverter compressor throttles back. Check your own unit's specification sheet or look it up in the Energy Rating Calculator. Run it for four midday hours and you might consume 4-6kWh. Shift that from grid to solar and, at the example 25c difference above, you're saving roughly $1.00-$1.50 a day, every day you'd have run it anyway. Multiply your own kilowatt-hours by your own rate gap for the real figure.

That's the whole idea. You're not using less energy. You're using the same energy at a much better price.

Pre-cooling and pre-heating: the core tactic

A well-sealed, reasonably insulated Australian home behaves like a slow thermal battery. You can charge it with solar.

In summer: start the aircon around 11am-midday while the array is producing, and pull the house down to 21-22°C rather than the 24°C you'd normally accept. By late afternoon when solar output falls away, the building fabric is already cold and the unit needs far less run time to hold a comfortable temperature through the evening peak.

In winter: the same trick in reverse. Reverse cycle heating is also dramatically more efficient in the middle of the day, because heat pump performance drops as the outdoor temperature falls. Heating at 1pm when it's 16°C outside costs meaningfully less per unit of heat delivered than heating at 7am when it's 4°C - so a solar-timed schedule wins twice.

How well this works depends entirely on your building. A double-brick or well-insulated home with decent window coverings might hold pre-cooling for four or five hours. A 1970s brick veneer with single glazing and no ceiling insulation top-up may bleed it in ninety minutes. Test it before you commit to a schedule: set a temperature logger in the living area and watch how fast the room drifts back after the unit stops.

Getting a smart controller onto a dumb split system

Most split systems in Australian homes have no cloud connectivity at all - just an infrared remote. An IR bridge controller solves this without touching the wiring, which matters enormously if you're renting.

These devices sit in line of sight of the indoor head unit, learn its IR command set, and expose the aircon to your phone, to voice assistants, and critically to schedules and automations. Sensibo's controller is the most established option in this category and includes its own temperature and humidity sensing, plus geofencing and climate-based scheduling. Pairing your AC schedule with one of the best smart fans in Australia can help distribute cooled air efficiently without lowering the thermostat.

A note on plug-in smart switches: don't try to control a split system with a standard 10A smart plug. Reverse cycle units are typically either hardwired or on a dedicated 15A circuit, and cycling power at the plug is a poor way to control a compressor anyway. Any change to hardwired circuits, isolators or dedicated aircon wiring is a job for a licensed electrician. They work to the Wiring Rules (AS/NZS 3000:2018, the current edition at the time of writing) and your state's requirements. Check with your state's electrical safety regulator if you're unsure what counts as electrical work where you live.

Triggering on actual solar production, not just the clock

A fixed 11am-3pm schedule is a fine start. Triggering on real export is better, because it survives cloudy days, dirty panels and the days you left the pool pump running.

The approach: measure net grid flow at the switchboard, and only allow the aircon to run its solar-priority schedule when the house is exporting more than, say, 1.5kW. A whole-home energy meter with current transformer clamps gives you that signal in real time.

This class of device reports per-phase power and direction over Wi-Fi and integrates with Home Assistant, which is where the logic lives. A basic automation looks like:

• If grid export > 1.5kW for 10 minutes and indoor temp > 23°C and time is between 10:00 and 15:30 → set aircon to 21°C
• If export drops below 300W for 15 minutes → raise setpoint to 24°C or turn off

The delay timers matter. Without them, a passing cloud makes your compressor short-cycle, which is hard on the equipment and inefficient.

Important: CT clamps go around live conductors inside the switchboard. Fitting them means working inside the switchboard, so have a licensed electrician do it - this is not a DIY job regardless of what an overseas installation video shows. Energy Safe Victoria, for example, warns that doing your own electrical work is illegal and can be deadly; rules differ between states, so check with your state's electrical safety regulator.

If you have a hybrid inverter or battery system, check whether your inverter brand already exposes production and export data to Home Assistant. Support varies by brand. Home Assistant's official Fronius integration polls the inverter locally and reports grid import and export when a Fronius smart meter is fitted. The official Enphase Envoy integration reads the Envoy over your local network, with net grid flow available when it has a consumption CT. The official SolarEdge integration is cloud-based and updates only every 15 minutes, which is slow for export triggers. Sungrow has no official Home Assistant integration; community-built Modbus and cloud integrations exist. Any of these can save you buying a separate meter.

What this doesn't fix

Be realistic about the limits.

Evening peaks still cost money. Pre-cooling reduces evening run time; it doesn't eliminate it. On a 40°C Adelaide or Western Sydney day, you'll still be importing after sunset.

Oversized systems behave badly. An aircon much larger than the room needs will satisfy the thermostat quickly and then cycle, which is inefficient and uncomfortable. Solar timing won't rescue a badly specified install.

Export limits apply. In most areas your local distribution network sets limits on how much your system can export, and some networks use dynamic export limits that only restrict exports when the grid is under pressure. Some states also require new and upgraded solar systems to support remote curtailment in an emergency. In Victoria, for example, the solar emergency backstop applies to new, upgraded and replacement systems of 200kW or less from 1 October 2024. Check your connection agreement, or ask your installer or distribution network, for the limits that apply to you. Self-consumption becomes more valuable, not less, under those conditions - which strengthens the case here.

Draughts undo everything. Before spending on controllers, spend twenty dollars on door seals and check your ceiling insulation. Pre-cooling a leaky house is like filling a bath with the plug out.

A sensible order to do this in

1. Read your last four quarterly bills and find your actual import rate and feed-in tariff. Everything downstream depends on that gap.
2. Seal draughts and check insulation.
3. Add a temperature sensor in your main living area and log how fast the room drifts after the aircon stops. That tells you how long pre-cooling will hold.
4. Add an IR controller and run a simple time-based schedule for two weeks. Compare bills or meter readings.
5. Only then invest in switchboard-level monitoring and export-triggered automation.

Steps one to four cost very little and deliver most of the benefit. Step five is for people who enjoy the optimisation as much as the savings - and if you're reading a smart-home site, that's probably you.