Is an Electric Car cheaper to run than a diesel?

Murray Callander
3 min readSep 23, 2022

TLDNR*: only if the average cost of your electricity is below 30p per kWh.

UPDATE: since I wrote this blog, the RAC have commented that the cost of charging an EV is now approaching that of petrol [link].

Making the decision to buy an Electric Car is a big decision. A question I get asked a lot is how much it costs to charge and so I thought I would make chart that might help people work it out for their circumstances.

Sorry if it’s a bit geeky! But I think it really useful to show that..

..it only makes sense to own an EV if you can charge at home. And then it only makes sense to own one of the bigger EVs if you can charge at a cheaper tariff at night.

If you want to know why, then stick with me…

The table shows the equivalent Miles Per Gallon (mpg) of an Electric Vehicle (EV) for different efficiencies** and electricity prices (based on a fuel price of £1.70 per litre).

The cells in green are the combination of charging cost and EV efficiency where it makes sense to own an EV. The cells in blue are where you are on par with a modern diesel, and the cells in white or grey are where an EV is more expensive.

The blue cells are the miles per gallon that you would get from a typical 2.0-litre modern diesel, which I am placing at between 40–60mpg ***.

Along the top is how efficient the EV is and, above these numbers, I have indicated the typical range of efficiency you would get with some common EVs.

The left hand column is the cost of the electricity per kilowatt-hour (kWh).

An EV gets the same (or worse) equivalent MPG as a modern diesel if you have to charge on the public networks (blue cells or below). It is only cost effective if you can charge at home, and the larger EVs are only cost effective at the cheaper night-time tariffs
Blue cells = similar cost to a moder diesel, Green cells = better value, Grey rows = cost of electricity on a motorway

So, for example, if you have an Audi eTron or a Tesla S, and you charge it at home on a standard tariff (now around 40p/kWh), you are getting the equivalent of 50mpg.

(Find 2.6 miles/kWh on the top and read down to the row level with £0.40 per kWh on the left).

This means there is no real advantage over a modern diesel — at least in terms of fuel.

However, if you can do most of your charging at a cheap night-time rate of around 10p per kWh, then you are getting more like 200mpg equivalent!

Alternatively, if you have to do most of your charging at motorway services, where the price varies between 50p-80p per kWh, then you are down in the 30s or even 20s for mpg (just as the RAC have recently commented).

The EVs with higher efficiencies like the Model 3, Kia eNero and Hyundai Iconiq, are better where Domestic tariffs are concerned, but even they are not much better than a modern diesel when it comes to charging on the motorway.

So, in conclusion, if you can keep the average cost of all your charging below 30p/kWh then an EV has a cost advantage when it comes to fuel prices.

— oOo —

*TLDNR = too long, did not read

**EV Efficiency is measured in Miles per kilowatt-hour (m/kWh). A typical kettle uses 3 kW of power. If you left it on for 1 hour it would use 3 kWh. If your EV gets 1 mile per kWH then you could drive 3 miles on the same amount of energy (that’s not very good by the way, a typical EV should be getting nearer 3 miles per kWh, so you 3 kWh would get you 9 miles).

***Comparisons with a standard diesel at the very low EV efficiencies are debatable because if you did the same drag racing or short trips in the winter with a diesel you wouldn’t get 40–60mpg! Also, the efficiency of the Lucid Air is based on figures from the internet of tests by others — you can’t buy them in the UK and I don’t know anyone that has one.

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Murray Callander

Co-Founder & CEO @eigenltd — How can we help industrial companies become more efficient? And how do we make sure we do a great job?