How much does charging an EV really cost, and do they save on emissions?

“You’re just burning coal instead of petrol.”

“Yeah, fuel costs are rising but so are electricity prices.”

These are just some of the arguments we’ve come across on social media from those who doubt that EVs can cost less to run and save on emissions.

And switching from a car with an internal combustion engine to one with a battery is a big learning curve. There’s shifting from fuelling up at the servo to plugging in at home, and planning to top up at public fast-chargers when out and about.

Doubts about costs, and energy sources, only add to the confusion.

Here’s a rundown on why charging an EV – even when the power comes from a coal-powered station – is better for the environment, and how to work out how much it will cost you to charge up.

Why are EVs more efficient at using energy?

New charts using data from the US-based fueleconomy.gov and shared by Yale Climate Connections highlight just how much better at using energy electric cars are than those with engines that burn petrol or diesel.

As little as 20% of fuel is used to actually drive a combustion engine car

As Yale Climate Connections explains, much of the energy consumed by internal combustion engines is lost via heat due to the multiple steps needed to spark the fuel, creating pressure to push the pistons to turn a crankshaft to ultimately drive the vehicle’s wheels.

As anyone who has ever opened the bonnet of a car after even a quick drive down to the shops and back would know, there’s a considerable amount of heat generated. So much heat is created that an oily rag accidentally left on the engine after a trip to the mechanics can combust, causing irreparable damage to the car (and believe me we’ve had firsthand experience of this!).

It’s estimated that some 68-72% of energy is lost this way by a combustion engine. More energy again – about 4-6% is used to power the water pump and fan belt used to help cool the engine down while you drive. Other transmission and drivetrain losses account for 3-5% of energy used, while 0-2% is lost using auxiliary components like lights, audio and so on.

This means that for every $2 a litre spent on fuel, only about 40 cents per litre is actually used to drive the car.

Electric vehicles on the other hand are far more efficient at using energy

There are far less moving parts in an EV, and the electricity used to power the car goes directly to a cylinder that creates a magnetic field, inside which is a rotor that gets pulled along by the spinning magnetic field and which then directly turns the axle (this is why electric motors sit on the axle instead of under the bonnet).

The system is not perfect but loses much less energy than a combustion engine. Data estimates only 18% of energy is lost by an electric motor, while an additional 3% is lost by the cooling system and steering, and some 0-4% by auxiliary systems.

There is approximately 10% energy lost in the charging process also. All up, around 31-35% energy is lost by an EV – but here’s the kicker: because EVs have regenerative braking they recover around 22% of the energy, with the added bonus of rarely needing new brake pads (and also not leaving as much brake dust in the air.)

What this means in terms of running costs we will get to below, but let’s just say for now that if you are charging at a public fast-charger and paying 60 cents per kilowatt-hour, about 54 cents are going towards actually driving the vehicle.

OK, so EVs are better at using energy; but with much of our electricity still generated by coal or gas, how can they still be considered better for the environment?

We’ve established that EVs are better than combustion engine cars at using energy, but is all electricity the same? The chart below spells out the difference in fuel use compared to electricity use depending on the source of that energy.

Put simply, coal-powered plants are far more inefficient than other sources at creating electricity. They lose around 67% of the power used to make the electricity, but powering an EV using coal-power still saves around 31% compared to just burning barrels of gas.

A gas-powered plant is a bit better than a coal-powered plant at using energy to create electricity, but not by much. 56% of the energy used is lost in inefficiencies. However, this would still halve the amount of power needed to drive an EV fleet. So, still a pretty significant win in terms of carbon emissions saved.

The last energy resource considered by Yale Climate Connections is hydropower, which it says loses just 10% of energy in electricity creation. This reduces energy needs of an automotive fleet by a whopping 75%.

The article in question doesn’t discuss other renewable resources such as wind and solar, although suffice to say that the transmission losses in rooftop solar would be next to minimal, meaning if a fleet could be charged directly from solar then energy needs would be close to 90% less. That said, battery storage would also likely be required so there could be minimal losses there.

What does this mean for the cost of charging an EV?

How much power is needed to run an EV depends on its efficiency. The bigger and heavier the vehicle, the more watt-hours a kilometre it will need to drive.

Knowing your energy consumption in an EV – unlike in a combustion engine car – is easy. Most EVs will display this in the car’s interface, usually in terms of kWh/100km or Wh/km.

How much this figure is depends on how you drive, and where you are driving. Stop/start in traffic in a flat area is going to use a lot less energy than a highway in the hills, for example.

Let’s say for argument’s sake you have a vehicle with a 60kWh battery and you’re using around 20kWh/100km on the highway. That will get you around 300km from 100% down to 0% (although you would be stopping at a charger before you reached 0%!).

Many public fast-chargers now cost around 60 cents per kilowatt-hour, although some may cost less if they are slower (eg 50kW chargers) and some may offer a discount if you are a member of a motoring club (eg Chargefox fast-chargers).

Very simply though, if you pay for 66kWh worth of energy, and lose 10% of that in charging, it will cost around $40 for a 300km drive. Compare that to $60 worth of petrol for a car that uses 10 litres/100km, paying $2 a litre.

If you’re charging at home you may be paying about half that ($18 for 60kWh at 30 cents per kWh) or even less if you have a cheaper time of use tariff, or nothing if you charge directly from rooftop solar (although you may be losing a feed-in tariff instead).

Here is a rundown on most of the charging networks currently in operation in Australia. If you spot any inaccuracies – please let us know at news@thedriven.io.