How Much CO₂ Does a 6.6 kW Home Solar System Actually Save? (Real Numbers)

Written by Bec Ramirez·Published 16 May 2026·7 min

Make us a preferred sourceTap the toggle on Google so Why Solar shows up more often in your Top Stories.

Share with a mate

Most homeowners thinking about solar know it is "good for the environment" in a hand-waving sort of way. That is roughly the level of detail in the average sales pitch too. "Reduce your carbon footprint." "Help the planet." "Equivalent to planting trees."

None of which is wrong. But none of which is specific enough to act on, either.

So here is the actual maths for a 6.6 kW system in Australia. Real numbers, with comparisons that mean something. The kind of breakdown you can read out at the dinner table and people will actually nod.

The two numbers you need

To work out CO₂ savings, you need two figures. How much electricity the system generates, and how dirty the grid electricity it replaces is.

For a well-installed, mostly-north-facing 6.6 kW system in Sydney, annual generation lands around 10,000 kWh. Brisbane homes generate slightly more (closer to 10,500 kWh) because the sun is better. Melbourne sits closer to 8,500 kWh. Hobart around 7,500 kWh. We will work the rest of the numbers on the Sydney figure to keep it concrete.

For grid emissions, the most recent National Greenhouse Account Factors put the National Electricity Market average at around 0.65 kg of CO₂ equivalent per kWh. That number drops every year as more coal retires and more wind and solar comes online, but it is not dropping fast. Coal still produces around half of NEM electricity in 2026.

Multiply the two: 10,000 kWh × 0.65 kg = 6,500 kg of CO₂ avoided per year. Or 6.5 tonnes.

Hold on to that figure. Now let us make it mean something.

What 6.5 tonnes of CO₂ a year actually looks like

Numbers like "6.5 tonnes" are basically meaningless to anyone who has not worked in climate research. Nobody walks around with a personal sense of how much a tonne of CO₂ is. So here are the comparisons that make it concrete.

Compared to flights

A return economy flight Sydney to Los Angeles produces about 3.0 to 3.5 tonnes of CO₂ per passenger (depending on aircraft, load factor, and methodology). So a 6.6 kW system avoids roughly the carbon footprint of two long-haul return flights per year. That is a meaningful comparison because most Australians know what flying overseas feels like. If you and your partner each took one international trip a year, your rooftop solar is more than cancelling out both of you.

Compared to driving

An average Australian petrol car driven 12,000 km per year produces around 2.4 tonnes of CO₂. So a 6.6 kW solar system offsets the emissions of roughly 2.7 average cars. If you have two cars in the driveway and rooftop solar, the system is paying off the emissions of both vehicles plus a bit more.

Compared to trees

A mature tree absorbs about 22 kg of CO₂ per year on average. So 6.5 tonnes is equivalent to having 295 mature trees on your property doing their thing. The difference is that the trees take 20 to 40 years to reach that absorption rate. The solar system hits its full rate within weeks of being switched on. It is like the difference between planting an orchard and walking into a working one.

Compared to other green choices

Australian beef carries an emissions weight of around 27 kg of CO₂ per kg of meat. So 6.5 tonnes is the carbon equivalent of avoiding about 240 kg of beef consumption per year. For comparison, the average Australian eats around 26 kg of beef per year. So rooftop solar produces a CO₂ saving equivalent to about 9 average Australians going vegetarian for a year.

(None of this is to say you should not also drive less, fly less, or eat less beef if that is what you want to do. But if you are picking single household actions ranked by CO₂ impact per dollar, rooftop solar punches above almost everything else available to a typical homeowner.)

The lifetime number

Panels installed today are warranted to produce at least 85 per cent of rated output at 25 years. Most quality panels keep generating useful electricity for 30 plus years. So the savings keep stacking long after the system has paid for itself financially.

Even allowing for declining grid emissions intensity over the next 25 years (as more coal retires and more renewables come online, each kWh of solar displaces a slightly smaller emissions baseline), the lifetime CO₂ avoided lands in the 150 to 160 tonne range for a 6.6 kW system in Sydney.

150 tonnes is genuinely a lot. That is roughly:

• 50 long-haul return flights to Europe
• 62 years of driving an average Australian car
• 30 to 40 average cars taken off the road for a full year
• The annual emissions of 9 average Australians for a year

From one rooftop. Without changing how anyone in the household lives.

The battery makes the swap dirtier-for-cleaner more efficient

One nuance worth knowing. The CO₂ saving above is calculated on grid-average emissions. But the grid is not the same dirty all day. Midday is the cleanest period (lots of rooftop solar and utility solar generating). Evening peak (5pm to 9pm) is the dirtiest (gas peakers and coal running hard to meet demand).

Without a battery, your solar mostly displaces midday electricity (the cleaner end of the day). With a battery, you can shift that generation to the evening peak, displacing the dirtier electricity. The CO₂ avoided per kWh of solar can be 20 to 40 per cent higher when discharged during peak periods.

So if maximum environmental impact matters to you (and it does to a growing number of homeowners), adding a battery to a solar system is not just a financial decision. It also genuinely makes each kWh of your solar do more environmental work. With the federal Cheaper Home Batteries rebate plus state schemes, the economics of adding a battery have also shifted dramatically in 2026.

Putting it on the dinner table

Back to the opening point. The reason most people cannot get excited about "reducing your carbon footprint" is that the unit is meaningless without comparison.

But "our roof cancels out our family's overseas trips and both cars every year" lands differently. So does "equivalent to having 295 mature trees on the block." So does "in 25 years this thing will avoid 155 tonnes of CO₂, which is more than my entire personal carbon footprint for a decade."

Those are the numbers worth knowing. Not because they will make you feel better (although they might). But because if you are weighing up whether to put solar on the roof, the environmental side of the ledger is not vague anymore. It is specific, large, and starts paying back from week one.

If you want to see what a system on your specific roof would generate (and therefore what your specific CO₂ saving would look like), check what rebates apply for your state as a starting point.

Written by

Bec Ramirez

Aussie Mum & Energy Expert

Helping families navigate the switch to solar with practical, real-world advice. Bec focuses on the financial side — rebates, bill savings, and financing options — so everyday Australians can see real value from going solar.

Learn more about Bec Ramirez