Petrol vs electricity: which is cheaper?

An electric car will cost you significantly more to buy than a petrol equivalent, but you’ll make some (or even all) of that extra investment back with lower running costs, right? Well, that’s the general assumption, but is it actually true – particularly if you’re using the UK’s public charging infrastructure? We decided to find out.

For a fair comparison, we rounded up two pairs of cars that are available in petrol and electric forms. The first was the electric Peugeot e-208 and the petrol-powered Peugeot 208 Puretech 130, with the other being the much pricier BMW i4 M50 and BMW 4 Series Gran Coupé M440i (the two cars are very similar, despite their different names).

The test

Our experiment started at Cobham services on the M25 motorway in Surrey, home to six Ionity rapid chargers. These can deliver up to 350kW of power at a cost of 69p per kilowatt hour (kWh) and are available to anyone. We chose to focus on these chargers because, although they’re among the priciest to use, they’re faster and more reliable than those of most other suppliers, plus there are usually more than one or two at each location, reducing the chances of having to queue up for access.

The first match-up was between the i4 and M440i. The former was plugged into an available charger and left until its battery was at 100%, while the latter was brimmed at the adjacent Shell petrol station. When both cars were full, we reset their trip computers, set the desired interior temperature to 21deg C and selected Comfort driving mode, before setting off in convoy for Skelton Lake services, near Leeds – another Ionity charging location.

For directions, the lead driver relied on a phone navigation app, connected to the car using Apple CarPlay. It was originally supposed to be a 208-mile journey, but shortly after leaving we were diverted off the M25 due to an accident ahead, adding just under 20 miles to the trip. Where possible, we drove at the speed limit and averaged 53.5mph.

When we arrived in Leeds, we plugged in the i4 and brimmed the M440i’s tank to find out how much the journey cost.

The following morning, we found ourselves back at the same services with the two Peugeots. We followed exactly the same process for charging the e-208 and fuelling the 208, adjusting the interior temperature and selecting Normal driving mode in both.

The return journey to Cobham was a smoother affair and there were no significant traffic problems. Nevertheless, it was clear from early on that the e-208 wouldn’t make the journey in one hit, with the mileage on its range indicator dropping far quicker than the miles we were actually racking up. So, we decided we’d have to make a pitstop near Milton Keynes for a quick top-up.

But even this initial 144-mile stint started to look optimistic when cruising at 70mph, so we dropped to 65mph in both cars and switched to their Eco modes. Shortly after doing this, we hit a long stretch of 60mph road works, so we actually made the Ionity site in Newport Pagnell without too much range anxiety.

After just under 20 minutes of charging and with the battery topped up to 70%, we set off for our final destination – at 70mph (when possible) and with Normal driving modes re-engaged. The average moving speed for the journey was 57mph. When we arrived at Cobham, we plugged in the e-208, brimmed the 208’s tank and then began to crunch some numbers.

How much did the journey cost?

The M440i used 26.19 litres of regular unleaded for the 228-mile journey from Cobham to Leeds, which averaged out to a very respectable 39.5mpg. We paid £1.989 per litre at the Texaco station at Skelton Lake (fuel prices were close to an all-time high when we did the test), so the total bill was £52.09.

Ionity’s prices haven’t gone up since the charging network switched from an initial flat rate of £8 per charge to the current price-per-kWh payment structure in 2020, even though wholesale electricity costs have gone through the roof since the start of 2022. Despite this, the bill for the i4 was an eyebrow-raising £57.73, due to that steep 69p/kWh tariff. The i4 used 83.68kWh of electricity to complete the trip at an average efficiency of 2.7 miles/kWh. Put simply, the electric BMW worked out £5.64 (11%) more expensive than the petrol equivalent.

But what about the 208s? These are much cheaper cars, and their owners might be even more concerned about running costs. Well, the petrol version drank a total of 15.96 litres of regular unleaded for the 208-mile journey from Leeds to Cobham. That’s an average of 59.2mpg and we were charged £1.999 per litre at the filling station, so the total bill came to £31.90.

The e-208 used a total of 59.37kWh for the trip (23.72kWh at the Newport Pagnell pitstop and 35.65kWh at the final destination). This worked out to a total cost of £40.97 at an average consumption of 3.5 miles/kWh. Again, the petrol version worked out cheaper, but this time but an even greater margin of £9.07, or 28%.

So, petrol cars are cheaper to run?

Not necessarily. Our experiment focused on the refuelling (and recharging) costs at motorway service stations – the type of usage more typical of drivers doing long journeys.

It’s also important to note that anyone who buys a new BMW electric car gets a 12-month subscription to BMW Charging, which means they initially pay only 26p/kWh to use Ionity chargers, with the full 69p/kWh rate only kicking in from the second year.

In addition,  Ionity isn’t the only public charging network. Instavolt, for example, charges 66p/kWh across all of its sites, while Gridserve charges between 39p and 50p/kWh, depending on the speed of the charging point. If you charge at home, you’ll pay considerably less again; the average residential cost for a kilowatt hour of electricity is currently around 28p, although prices vary wildly in these tumultuous times.

Unless you happen to live in an oil refinery, filling your car with petrol at home won’t be an option. However, prices are generally a lot cheaper if you fill up off the motorway network and, at the time of writing, the average price of a litre of regular unleaded across the country as a whole had dropped to roughly £1.75.

There are plenty of other considerations as well, of course. As we said at the beginning, electric cars are generally much more expensive to buy than their petrol equivalents, and their efficiency suffers in colder weather (our tests were carried on in balmy July). However, they’re much cheaper for company car drivers paying benefit-in-kind tax, and they often qualify for various other perks, including London Congestion Charge exemption.

In our wider tests, electric cars have also proved relatively more efficient than petrol and diesel cars in urban environments, because they can harvest some of the energy lost when slowing down to recharge their batteries.

Key numbers

Final verdict

When deciding whether an electric car is right for you, it’s important to consider how you would charge it. Even with energy bills going through the roof, an electric car should cost significantly less to run than any petrol alternative if you can charge it up at home overnight. However, as our test has shown, lower fuel bills are certainly not a given if you’re relying on the public network, due to the high prices of some companies.

Electricity cost comparison (based on efficiency in test)

*CCS or CHAdeMO up to 60kW **Based on 28p/kWh

Petrol cost comparison (based on efficiency in test)

*Confused.com petrol prices, 18 August 2022

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