Diesel vs electric: which is cheaper on a long journey?

If you’re thinking about making the switch to an electric car, there’s a lot to think about. The main consideration you’re likely to be pondering is whether or not an EV can go far enough on a charge, and whether or not it can actually achieve the manufacturer’s claimed range. You might also be wondering if running an EV is actually cheaper than an internal combustion engined car, and we’re going to answer all of these questions today.

To find out how accurate an EV’s claimed range figure is, we recently drove six of the latest electric cars up the motorway until they died. The test featured the Audi Q4 e-tron, the updated Kia EV6, the new Polestar 4, the new Porsche Macan, the new Ford Explorer and the Tesla Model Y.

The Polestar 4 went the furthest of the six cars, managing 333 miles before conking out just north of the Scottish border – equating to an impressive 90% of its claimed range. You can watch the video below for a full breakdown of everything that unfolded.

Interestingly though, we were also joined on this journey by our long-term Skoda Kodiaq camera car. It’s a 2.0-litre diesel with all-wheel drive, and this got us thinking: are EVs actually cheaper than old-school diesels for motorway mile munching?

To find out, we brimmed the Skoda’s tank at the start of the journey and reset the trip computer to find out how much it cost us to do the same distance.

On the drive up, the Skoda averaged just over 47mpg and had 205 miles of range remaining at the end. However, we still had to drive it and the Polestar all the way back to the start point, so a round trip of 666 miles.

Our Kodiaq needed filling up with diesel once on the trip, and after some maths we worked out that it used £92 worth of fuel to complete the whole journey. The Polestar needed charging twice, and it worked out to the exact same £92 in electricity to complete the same trip.

But that’s not the end of the story. The Polestar’s initial charge was done at a home charger, which is significantly cheaper than a public charge point. Assuming a rate of 26 pence per kWh, it would cost around £26 to fully charge it from 0-100%. If that initial charge was done at a public DC fast charger, it would cost closer to £80 based on an average price of 80 pence per kWh.

So if you didn’t have an EV charger at home, this journey would’ve cost you around £140 in electricity – making it around £50 more expensive than the diesel Kodiaq.

But what does all this mean? Well, if you have access to charging at home, doing a long journey like this will cost you around the same as an economical diesel car – however you’re likely to save money on your normal day-to-day driving if you don’t have to use public chargers.

It’s also worth noting that you can get much cheaper deals on home charging than 26 pence per kWh – with some suppliers offering prices as low as seven pence. This would bring the total cost of our journey down to £77.

So to sum up, if you have access to charging at home then an EV is likely to work out cheaper for you than a diesel, unless you regularly find yourself doing more than 600 miles a day. But if you’re relying on public chargers, sticking to an oil burner may be a better bet for regular cross-country slogs.

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