One of the most commonly asked questions from clients is ‘how much does it cost to charge an electric car’? We are told it’s a fifth of the price of fuel. Now we know we get cheaper road tax and running costs, but the exact charging cost is harder to pinpoint. Here’s how to work it out.

You need to consider pence per litre as pence per kilowatt hour (kWh) when working out electricity costs used to fill up your vehicle. A kWh is a standard measurement of energy that your energy supplier will use to bill you and refers to a person using 1,000 watts of electricity for 1 hour. For home charging your electricity bill will show this cost – on average it will be between 10-14 pence. To fill up, if you look at petrol being 128p per litre, electricity will be between 10-14 pence per kWh.

We now understand the cost of electricity, but we don’t know the size of the tank. If your petrol car has a 40 litre tank and petrol is £1.28, the cost to fill it up is £51.20. With an electric vehicle your tank size is now a measurement of capacity, representing how many kWh of energy it can store. The larger the capacity the bigger the tank. The largest battery size currently available is the Tesla model s 100d – the 100 representing amount of kWhs it can store.

The cost to charge for this vehicle at 10 pence per kWh would be £0.10 x 100 = £10.00.

The table below shows the costs for various vehicles assuming price per kWh is 10 pence.

Vehicle Battery Size kWh Cost Cost to Charge
Tesla model s 100d 100 0.10 £10.00
Nissan Leaf 30 0.10 £3.00
BMW i8 7 0.10 £0.70
Renault Zoe 22 0.10 £2.20
Mitsubishi Outlander 12 0.10 £1.20

From this information we can work out the pence per mile cost. If we take a Nissan Leaf 30kWh as an example, the real-life range is around 120 miles. Cost divided by distance will give us the cost per mile. 3/120 = £0.025 per mile. The same calculation can be used for all vehicles. We would advise that you use the real-life distance rather than the manufacturer’s figures as a guide per cost.

Should you change to an off peak tariff?

A lot of customers, after buying an electric car, believe they are better off with an off-peak tariff often referred to as Economy 7, the seven being the number of hours the electricity is cheaper for. The rate per kWh may drop to 6 pence in off-peak hours, but in peak hours it may be as high as 17 pence. End users need to be very disciplined with their energy use and most will have to use 40% of their energy off-peak in order to benefit. We would advise clients do the calculations to work out if they will be better off with an off peak tariff.