Cost per kilometre is the honest comparison. Purchase price matters, but the monthly difference is driven by efficiency, charging mix and fuel price.
Public charging can erase the advantage. A car charged mostly at home is cheap to run; one charged mostly at fast public chargers can approach petrol costs.
Solar changes the answer again. The calculator sizes an array for your daily driving and shows whether charging from your own roof beats buying grid electricity.
What the EV cost calculator answers
This is not a “which car is nicer” tool. It compares the running economics of an electric vehicle against a petrol or diesel car you already have in mind, then adds the solar question:
- Energy cost per kilometre versus fuel cost per kilometre.
- Savings per day, month and year, including maintenance differences.
- Payback on the price premium and the break-even distance.
- Eight-year total cost of ownership.
- Home, work and public charging shares and their blended rate.
- The solar array needed to cover your daily driving.
- CO₂ avoided, using average grid and petrol factors.
Every result is an estimate. Real costs depend on your tariff, driving style, weather, tyre wear, insurance, resale value and the reliability of public charging.
The core comparison
The calculator reduces both vehicles to a cost per kilometre, then scales that to your driving:
EV cost/km = EV energy × blended electricity rate ÷ daily km
Fuel cost/km = fuel price ÷ fuel economy (km/L)
Savings/km = fuel cost/km − EV cost/km
For a 60 kWh car with a 400 km range, 40 km/day uses about 6 kWh before losses. At 10% charging loss that is 6.6 kWh from the wall. If the blended rate is $0.164/kWh, the daily energy cost is about $1.08, or $0.027/km. A petrol car doing 8 km/L at $1.20/L costs $6.00/day, or $0.15/km. The EV saves about $4.92/day before maintenance.
Charging losses and charger power
Charging is not free of losses. Alternating current from the wall is converted to direct current in the car, and some energy is lost as heat. A 10% loss is a reasonable planning value; older cars and high-power charging can differ. The loss is applied on top of the energy the battery actually stores, which is why the wall energy is higher than the battery’s rated capacity suggests.
Charger power determines time, not cost:
20–80% time ≈ 60% of battery kWh ÷ charger kW ÷ efficiency
A 7.2 kW wallbox adds roughly 7 kWh per hour after losses, so a 60 kWh battery takes about 8–9 hours from empty. A 3.7 kW charger takes twice as long. The calculator reports both the full charge and the 20–80% window because the second is what most public charging stops actually deliver.
Payback and break-even distance
The purchase premium is the EV price minus the fuel car price. The annual saving is the per-kilometre saving times annual distance, plus the maintenance difference:
Payback = price premium ÷ annual savings
Break-even distance = price premium ÷ savings/km
With an $8,000 premium and $2,095/year of savings, payback is about 3.8 years. The break-even distance is about 65,000 km, or roughly 4.5 years at 40 km/day. If you drive 15,000 km/year, the same premium breaks even in a little over four years; if you drive 8,000 km/year, it takes much longer.
The solar question
If you already have solar, enter its kWp and the calculator shows how much of the car’s charging it can cover. If you are considering adding solar for the car, it sizes an array from your daily energy and the peak sun hours you enter:
Panels = solar kWp × 1000 ÷ panel wattage (rounded up)
At 6.6 kWh/day and 4.5 peak sun hours, the array is about 1.47 kWp, or three 550 W panels. That is a small addition compared with a whole-house system, and it may be the cheapest way to run the car if you have spare roof space and the charging happens during the day.
The timing is the catch. Solar produces at midday; most cars charge at night. Without a battery or daytime charging, the solar may export at a low credit while the car imports at the retail rate. The “solar saves vs grid” figure assumes the energy is used directly or credited at a useful rate, so check your tariff and charging schedule before treating it as free motoring.
A worked example
| Item | EV | Petrol car |
|---|---|---|
| Purchase price | $35,000 | $27,000 |
| Daily distance | 40 km | 40 km |
| Energy / fuel use | 6.6 kWh/day (with 10% loss) | 5 L/day at 8 km/L |
| Unit cost | $0.164/kWh blended | $1.20/L |
| Daily running cost | $1.08 | $6.00 |
| Cost per km | $0.027 | $0.150 |
| Maintenance / year | $400 | $700 |
| Annual saving | ≈ $1,795 fuel + $300 maintenance = $2,095 | |
| Payback on $8,000 premium | ≈ 3.8 years | |
| Break-even distance | ≈ 65,000 km | |
Solar for the daily commute: 6.6 ÷ 4.5 ≈ 1.47 kWp, rounded to three 550 W panels (1.65 kWp). CO₂ avoided is roughly 2.9 tonnes per year using average grid and petrol factors, but the exact figure depends on how the electricity is generated.
Where the model stops
Use it to compare a specific EV with a specific fuel car at your real driving distance and charging mix, then check the total with insurance and resale quotes. If the case only works with home charging you cannot install, or with a public rate that is about to change, it is not a robust case yet.
Frequently asked questions
Is an EV cheaper per kilometre than petrol?
Usually yes, especially with home charging. A typical EV uses 15–20 kWh/100 km, so at $0.15/kWh that is $2.25–3.00/100 km. A petrol car at 8 km/L and $1.20/L costs $15/100 km. Public fast charging at $0.40–0.60/kWh narrows the gap but rarely eliminates it. The calculator uses your own tariff and charging mix.
How long does it take to charge an EV?
It depends on battery size and charger power. A 60 kWh battery on a 7.2 kW wallbox takes about 8–9 hours from empty after losses; the 20–80% window takes roughly 5 hours. A 3.7 kW charger doubles that. A 50 kW public charger can add 20–80% in well under an hour, but the price per kWh is usually much higher.
How many solar panels do I need to charge an EV?
Start with daily energy. A car driven 40 km/day at 6 km/kWh needs about 6.7 kWh/day, or 6.6 kWh after 10% charging loss. At 4.5 peak sun hours, that is about 1.5 kWp, or three 550 W panels. A longer commute or a less efficient car needs proportionally more. The calculator sizes it from your own numbers.
Does the calculator include battery degradation?
It shows an estimate of battery life left after eight years based on your stated battery warranty cycles and daily charging energy. It does not replace the manufacturer’s warranty model. Real degradation depends on chemistry, climate, fast-charging frequency and how often the battery sits at very high or very low states of charge.
Why is the payback different from the dealer’s figure?
Dealers often compare the EV with a much more expensive fuel car, assume a high annual mileage, ignore the cost of a home charger and use a low electricity rate. The calculator lets you enter the actual fuel car price, your real driving distance and your blended charging rate. If the payback only works with assumptions you cannot reproduce, treat it as marketing rather than analysis.
Is EV charging from solar really free?
Only if the solar energy would otherwise be wasted or exported at a very low credit, and only if the car charges while the sun is shining. If you charge at night from the grid, the solar may have been exported at $0.05/kWh while you import at $0.15/kWh. A battery can shift the energy, but it adds cost and losses. The calculator reports the solar saving separately so you can see the assumption.