How to calculate costs of charging an electric vehicle

Here’s’s guide on how to work out the charging costs of an electric vehicle.

The lower running costs of an electric vehicle are one of the biggest attractions for motorists beset by rising fuel prices. Indeed, Carzone’s research showed that 51 per cent of Irish motorists are now considering switching to an electric car precisely because of rising fuel costs, despite never having considered making the switch before.

While the daily running cost of an EV is much cheaper than that of a petrol and diesel car, it’s not free. Though you might no longer be emptying your wallet at filling stations, you will notice an increase in the size of your electricity bills — but just how much of an increase?

Calculating electricity cost

The key metric to keep in mind when calculating charging costs is kilowatt hours (kWh). Battery capacity will be given in kilowatt hours, i.e. how much energy it can store. A Honda e has a 35.5kWh battery, for example, giving it an official range of up to 222km. A Volkswagen ID.4 with a 52kWh battery can go around 340km between charges, while the Mercedes EQS 450+, thanks to its massive 107.8kWh pack, can manage a substantial 729km, though it’ll need quite a bit more electricity to top up from empty than the Honda.

Kilowatt hours are also the unit by which suppliers usually charge for electricity, meaning that if you know your battery’s capacity and the cost per kWh of the electricity going in, it’s easy to calculate what it’ll cost to charge whether you’re at home or at a public charging point. The formula is:

Electricity required (kWh) x Electricity cost (cents/kWh) = cost to charge

The majority of Irish EV owners do most of their charging at home at rates much cheaper than those of public chargers. Most EV owners will charge their cars overnight and be able to avail of cheaper night-time tariffs offered by many electricity suppliers. Energia, for example, offers night rates of as low as €0.0822/kWh including VAT, for example, while Electric Ireland offers a price plan (effective from May 1) with standard night rates of €0.1544/kWh, though which may work out lower once various discounts are applied.

Let’s apply the formula to calculate the approximate cost of fully recharging a 62kWh Nissan Leaf from empty at Energia’s night rates:

62 x 0.0822 = €5.10

Most electric cars won’t match their quoted range figures in everyday driving (the Leaf’s is 385km) and a wide range of variables can reduce range significantly, but for anything approaching even 350km, €5.10 is really quite cheap compared to petrol or diesel. Given that many motorists may not be even covering 350km in a week, that works out at less than an extra €250 per year on an electricity bill.

Though the figure will obviously vary from provider to provider, the average daytime cost of electricity in Ireland is €0.24/kWh, meaning that by exclusively charging during the day, it’ll cost the average 62kWh Leaf owner around €15 per charge from empty to full.

To compare the running costs of the Leaf with one of Nissan’s closest petrol equivalents, the 1.0-litre Nissan Juke, to cover 350km, it would cost €37.67 at the current average rate of €1.82 per litre for petrol.

Public charging

Public chargers tend to be more expensive than charging at home, and depending on the provider or your subscription, prices can vary. Taking ESB ecars’ 22kW pay-as-you-go rate of €0.27/kWh and applying it to fully recharge the Nissan Leaf looks something like this:

62 x 0.27 = €16.74

Most drivers using public chargers though won’t be charging their car from empty to full, and a top-up from 20-80 per cent, for example, is more likely. In the Leaf, that would mean that 37.2kWh of electricity was required meaning a calculation at the same €0.27/kWh ESB rate of:

37.2 x 0.27 = €10.04

In real-world conditions those 37.2kWh are approximately equivalent to around 200km.

High speed (50kW+) chargers tend to cost more to use than slower ones with Ireland’s fastest being those from IONITY, which, at pay-as-you-go rates, can cost up to €0.73/kWh to use, though some car manufacturers will provide preferential rates at IONITY stations.

Other costs

Electricity prices aren’t the only cost component of home charging. The SEAI will provide a grant of up to €600 for the installation of home chargers, though typically homeowners will need to fork out an extra €400-€500 for the cost of installation and even more if other infrastructural work is required to get your home’s wiring up the required standard for EV charging.

How to calculate cost per kilometre?

With electric vehicles the measure of efficiency is kWh/100km in much the same way as petrol or diesel cars’ is miles per gallon or litres/100km. Like with internal combustion cars, energy consumption depends on a wide range of factors including driving style, road conditions and the load on the battery, though the trip computer will usually be able to give you your average kWh/100km figure.

The formula for calculating the cost per kilometre is:

(Cost of electricity x Energy consumption) ÷ 100

For simplicity’s sake, let’s take the Nissan Leaf’s figure of 18kWh/100km as an example, using Energia’s night rate of €0.0822/kWh for the cost of electricity. The equation will look like this:

(0.0822 x 18) ÷ 100 = €0.0147

Using those numbers as an example, the cost of running the Leaf will be just over 1c per kilometre.

Just using public charging at ESB ecars’ rate, the sum and cost per kilometre will be:

(0.27 x 18) ÷ 100 = €0.048

Compare those numbers with the figure for the Nissan Juke calculated using current petrol prices and its fuel economy figures and the fuel cost per kilometre is much higher.

(1.82 x 6.1) ÷ 100 = €0.111

Again, there are a huge number of variables at play, but if you know the cost of your electricity and the average energy consumption of your car, using the above formula, you’ll be able to calculate the cost per kilometre to run an electric vehicle.