The savings in an EV live at home — not at the highway fast charger. Worked numbers against petrol, in plain language.
The one number you need
Forget kilowatts for a moment. The number that decides your running cost is kilowatt-hours per 100 km, and for most EVs sold in Australia it sits between 15 and 20 kWh/100 km in real driving.
Small hatchbacks and efficient sedans land near the bottom. Large SUVs, utes and anything driven hard on a highway land at the top or beyond. Cold weather, hills, roof racks and towing all push it up.
Take 17 kWh/100 km as a reasonable middle for the maths below, then adjust for your own car once you have a few months of data.
Four ways to buy those kilowatt-hours
Excess solar — effectively the value of the feed-in tariff you gave up, so a few cents per kWh in most of Australia. At 17 kWh/100 km that is roughly $0.50 to $1.20 per 100 km.
Off-peak or EV tariff — commonly somewhere around 8 to 20 c/kWh depending on retailer, state and plan. That works out to roughly $1.40 to $3.40 per 100 km.
Flat residential rate — commonly 25 to 40 c/kWh. Roughly $4.25 to $6.80 per 100 km.
Public DC fast charging — commonly 45 to 70 c/kWh and sometimes more. Roughly $7.65 to $11.90 per 100 km.
Rates vary by state, retailer and year, so treat these as the shape of the answer rather than a quote. Check your own bill for the actual c/kWh.
Against petrol
A petrol car using 8 L/100 km at $2.00 per litre costs about $16 per 100 km.
So home charging on an off-peak tariff is in the order of one fifth of that. Charging on your own surplus solar is closer to a tenth. Charging exclusively on public DC is roughly half of petrol — still cheaper, but nothing like the saving people expect.
That last line is the one worth internalising: the savings in an EV come overwhelmingly from charging at home. A driver who relies on public fast charging has bought a much smaller win than the brochure implied.
A realistic annual picture
Take 15,000 km a year at 17 kWh/100 km — about 2,550 kWh annually, which is roughly the consumption of a decent ducted air conditioner.
On a 15 c/kWh off-peak tariff that is about $380 a year. On a blend of surplus solar and off-peak, meaningfully less. On a 30 c/kWh flat rate, about $765. On public DC only, comfortably north of $1,400.
The same distance in that 8 L/100 km petrol car is about $2,400. The spread between the best and worst EV charging strategy is larger than most people's entire expected saving — which is the argument for getting the home setup right.
Start simple, upgrade later
You do not need the most expensive charger to capture most of the saving. Overnight off-peak charging on any certified unit already beats petrol by a wide margin.
If you add solar later, look for scheduling and optionally load-aware charging so surplus goes to the car instead of the grid.
The mistake to avoid is relying on public DC fast charging as your main source — that is where the brochure savings disappear.
Key takeaways
- Most EVs use 15–20 kWh/100 km in real driving; use your own data once you have it
- Off-peak home charging runs roughly $1.40–$3.40 per 100 km against about $16 for petrol at 8 L/100 km
- Public DC fast charging costs several times home charging — the savings live at home
- Any certified charger on an off-peak schedule captures most of the benefit; optimise later if you add solar