08/10/2026
Solar Changes the Sums, But It Doesn’t Make Cooling Free
WA has one of the highest rates of rooftop solar in the country. Here’s how that actually interacts with running an air conditioner during the day and where the “free power” idea falls apart.
This is the part of the equation that makes WA genuinely different from most of the country, and it’s why a series about air conditioning in Western Australia can’t really avoid talking about what’s happening on the roof.
Western Australia’s own State of Energy data shows 41% of homes connected to the main grid already have rooftop solar installed which is one of the highest adoption rates anywhere, and a big part of why the old “just switch it off” logic deserves a second look.
On a sunny WA afternoon, a lot of these systems are generating more power than an empty house is using, and that surplus has to go somewhere: either back out to the grid for a modest return, or put to use running something at home.
What the numbers actually say
Under Synergy’s Distributed Energy Buyback Scheme, exported solar earns 10 cents per kilowatt-hour during the 3pm–9pm window and roughly 2 cents per kilowatt-hour outside it. Those aren’t throwaway numbers, they matter to this question, because they mean the “free” power sitting on your roof at 3pm actually has a real, if modest, alternative value if it’s exported rather than used at home. Whether it’s worth more running an air conditioner or heading out to the grid isn’t obvious at a glance, and depends on your specific export arrangement.
If the sun is already paying for the power, does the old advice even apply?
Sometimes, yes, it still does. The answer depends on the size of the solar system, how much the rest of the household is drawing at the time, the specific tariff and export arrangement on the account, how efficient the air conditioner itself is, and simply how hot that particular day is. A 6.6kW system on a mild 28-degree day with nobody drawing much power is a very different situation to a smaller system on a 38-degree scorcher with a pool pump also running.
Solar doesn’t remove the cost of running an air conditioner. It changes where some of that cost sits, and by how much varies household to household. Treating “we’ve got solar” as a blanket green light to run the aircon all day skips over all of that nuance but so does assuming solar makes no difference at all. The honest answer sits somewhere in the middle, and depends on numbers specific to your own system and your own home.
NEXT IN THIS SERIES: Zoning: Not Every Room Needs to Be Cold at 3pm
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