The basic maths
Charging an EV at home comes down to one simple calculation: the size of the charge (in kilowatt-hours) multiplied by the rate you pay per kilowatt-hour. If your car uses roughly 15–18 kWh to travel 100km, then every 100km of driving costs you that energy times your electricity rate.
The number that changes everything is the rate. On a standard flat usage rate you might pay in the high-20s to low-40s of cents per kWh. On an off-peak or dedicated EV rate overnight, that can drop dramatically. And with rooftop solar charging in the middle of the day, the marginal cost of the energy can be close to nothing. Same car, same distance: wildly different running cost depending on how and when you charge.
How to work out your own cost per 100km
- Find your car’s energy use per 100km (its efficiency, often shown in the car’s display or specs, commonly 15–18 kWh/100km).
- Identify the rate you would charge at: your flat usage rate, an off-peak rate, a dedicated EV plan rate, or effectively your solar feed-in rate if charging from surplus solar.
- Multiply energy per 100km by that rate to get your cost per 100km.
- Compare it with petrol: a comparable petrol car often costs several times more per 100km in fuel. Even at a flat electricity rate, home charging usually wins comfortably; on off-peak or solar it is not close.
- Scale it to your driving. Multiply by your annual distance (in hundreds of km) to see yearly charging cost.
Why timing is everything
Because home charging is a large, flexible load you can schedule, when you charge matters as much as the plan you are on. Charging overnight on an off-peak or EV tariff, or during the day off your own solar, can cut your running cost to a fraction of charging at the evening peak.
This is the opposite of most appliances, which run when they run. An EV can usually be told to charge at a set time via the car or charger app, so you can line it up with the cheapest window on your plan. That flexibility is precisely why the right tariff can save an EV household hundreds of dollars a year.
Solar and EVs: a natural pair
If you have rooftop solar and can charge during daylight, an EV becomes one of the best ways to use solar you would otherwise export at a low feed-in rate. Instead of selling a midday kilowatt-hour cheaply and buying petrol, you pour that energy straight into your car for the cost of the feed-in you gave up, often the cheapest fuel you will ever buy.
The trade-off is availability: many people are out with the car during the sunniest hours. If your routine allows daytime charging a few days a week, or you add a home battery to shift solar into the evening, the solar-plus-EV combination is hard to beat. EnergySorted values your feed-in on every plan, so you can see the true cost of charging from solar versus the grid on each option.
Watch the whole plan, not just the EV rate
A plan with a headline-cheap overnight EV rate can quietly charge more through higher daytime usage rates or a steeper daily supply charge. If most of your household load is outside the EV window, those other rates can wipe out the overnight saving. The only reliable way to compare is to cost the whole plan against your real usage, with the EV charging load included.
Because EnergySorted is independent and takes no retailer commissions, it ranks plans purely on what you would actually pay across all your usage (EV charging, everything else, and your solar feed-in) rather than on a single attractive rate. That is how you find the plan that is genuinely cheapest for an EV household, not just the one with the best-looking overnight number.