How it works in your home
Rooftop solar feeds the circuits in your house. Whatever's running at the time, the aircon included, uses that power first, and anything left over goes out to the grid. When the panels aren't producing enough, the shortfall comes from the grid, or from a battery if you have one.
So running aircon on solar doesn't usually need a special kind of air conditioner. It's about running the one you have while the panels are producing.
Check whether your panels can carry it
Find the aircon's input power
It's in the manual or the specifications, in kW, and it's different for cooling and heating. Mitsubishi Electric says input power is what the unit draws, separate from the capacity it delivers.
Watch your solar output
Your solar inverter's display or monitoring app shows what the panels are producing right now. Check it at the times you'd usually run the aircon.
Compare the two
If the panels are producing more than the aircon draws, plus everything else that's switched on, the aircon is running on your solar. If they aren't, the difference comes from the grid.
Work out the daily use
Input power times hours gives kWh. The running cost tool does the sums for you, and our running costs guide explains the method in full.
Move the hours into daylight
Use the unit's timer to start cooling earlier in the afternoon, while the sun's still on the panels, instead of all at once after dark.
Summer cooling: the good match
Hot, sunny afternoons are when the panels are producing and the aircon is working, so the two line up naturally.
Inverter units help, because they don't run flat out the whole time. Daikin says an inverter keeps adjusting its output to the temperature in the room. Set it between 25 and 27 degrees, as the Energy Rating calculator suggests, and it needs less of your solar to hold the room.
On the very hottest days, expect it to work harder for the same comfort. ActronAir says an air conditioner loses cooling capacity once it's above 35 degrees outside.
Winter heating: where solar falls short
Heating demand peaks on cold mornings and evenings, outside the hours panels produce well, and winter days are short. Expect a bigger share of winter heating to come from the grid than summer cooling does.
Reverse cycle stretches whatever solar you do get: the ACT Government puts its output at 3 to 6 units of heat per unit of electricity. Warming the main room in the early afternoon, then letting a lower setting hold it, uses more of the day's solar.
Overnight, a lower setting trims the load. Mitsubishi Electric's i-save mode, as one example, sets the temperature 2 to 3 degrees cooler when heating rooms that are empty or while you sleep.
Batteries
A battery stores surplus daytime solar so you can use it after dark. Without one, solar can't run your aircon at night.
Sizing a battery is a job for a solar and battery installer. They'll want your aircon's input power and the hours you run it, which a heating and cooling installer can help you pin down.
In the ACT, the Sustainable Household Scheme offers low-interest loans for eligible products, including household batteries and electric heating and cooling systems. It's a loan, not a rebate. Our ACT Sustainable Household Scheme guide has the detail.
Make each kWh go further
Solar or not, an efficient, well-sized unit uses less. Don't buy a bigger unit to soak up spare solar: Rinnai says an oversized system short cycles, takes less moisture out of the air and wears faster.
Small habits add up. Daikin says swapping a blocked filter for a clean one can cut an air conditioner's energy use by 5% to 15%, and it says to keep the outdoor unit clear of leaves and debris.
Older systems are the bigger leak. Solar Victoria's 2021 buyers guide puts anything over 15 years old at more than three times the energy use of a modern reverse cycle air conditioner, which is worth knowing before you plan your solar around an old unit.
Plenty of households are in this position. In Western Australia, about 36% of customers on the network around Perth, the SWIS, have rooftop solar.
Leave the solar and the switchboard to electricians
Don't open or rewire the solar inverter, its isolators or the switchboard. Switching an air conditioner off is fine; anything more is licensed electrical work. Energy Safe Victoria says you need a licence it issues to do electrical work in Victoria, and Mitsubishi Electric says an air conditioner needs a dedicated power supply and must be earthed correctly.
What you can do, and what needs a licence
You can
- Read your solar monitoring at the times you'd run the aircon.
- Set the timer so cooling starts while the panels are producing.
- Find the unit's input power in the manual.
- Keep the thermostat in the suggested ranges and the filters clean.
Leave to a licensed installer
- Checking the switchboard and running a dedicated circuit for a new unit.
- Sizing a new unit for the room, not for the solar system.
- Three-phase upgrades, which the ACT guide says large ducted or multi-head systems may need.
- Battery and solar work: a solar installer and a licensed electrician.
What we'd do
Our take
If you have solar, we'd use the timer to do the cooling while the sun's up, keep the setting at 25 degrees or a little above, and never upsize a unit just to use more solar. For heating, reverse cycle is the efficient way to use what winter solar you get. And if you're buying new, we'd have a heating and cooling specialist size it for the room first, then check its input power against what your panels actually produce.
