• Greg Foot

Should you switch to an Electric Car?

Updated: Apr 21



Electric cars are said to be ‘cleaner’ and ‘cheaper’ to run, but with a higher purchase price than their petrol equivalent - and a greater environmental footprint of manufacture - should you switch your old petrol car for an Electric Vehicle (or ‘EV’)?


How many miles would you need to drive a new EV before your fuel savings off-set these initial costs - both financially and environmentally?


I’m Greg Foot and I’m the host of a new series of “Sliced Bread” on BBC Radio 4 and BBC Sounds - a show that scrutinises the adverts promising us the world. These ‘wonder-products’ claim to make us happier, healthier and greener, but are they really ‘the best thing since sliced bread’?


For the first episode of the new series Producer Julian asked whether he should replace his old petrol car with a new electric one? Or whether, as it’s still working well and only has 35k miles on the clock, should he keep driving the 2008 1.2l petrol car and “run it into the ground” before considering switching?


He asked me to investigate two angles to the question:


  1. The environmental angle: How many miles does he have to drive to make any real difference when it comes to his carbon emissions?

  2. The financial angle: How many miles does he need to drive before the money saved on petrol covers the increased cost of buying an EV?


I own an EV and I love driving it - it's nippy, it's quiet, and I feel like driving electric is something I can do to reduce my carbon footprint. But I have always wondered how 'green' it really is. I made a podcast with Which? last year that investigated exactly that, explaining how the environmental impact of making the batteries, and the need to generate the electricity to charge the EV, means that these ‘zero emission’ EVs sadly don’t leave zero footprint.


I recommend EVs to anyone who is considering their next car (and I've been involved in the brilliant Fully Charged Show on YouTube which does a great job of explaining and encouraging an electrified life) BUT I've also always wondered about the questions Julian asked: what are the break-even points when driving an EV really is the best option for the planet and your pocket?


The trouble was, no one, it seemed, had done the real-world tests needed to get the data to figure out some real-world answers. So that's what we did in the first episode of this returning series of Sliced Bread.



The Test


We spoke to Ollie Marriage, Top Gear’s Head of Testing, and Professor and Author of ‘How Bad Are Bananas?’, Mike Berners-Lee, and after their advice we hatched the following plan:


Mike advised us to pick a “sensible” “modest sized” car, something with as close to a “like for like" electric equivalent as we could, so we picked a petrol Vauxhall Corsa which has the ‘equivalent’ electric Corsa-e. We also picked it because the Corsa was the UK’s best selling car last year (2021) with close to 41 thousand registered.


We wanted to work out a real-world best estimate ‘miles per gallon’ for the petrol car and a real-world best estimate ‘miles per kilowatt hour’ for the electric car. To do that I wanted to drive a new Vauxhall Corsa and a new Corsa-e the same distance, in the same conditions, at as close as possible to the same speeds.


We used 10 loops around a track in Lichfield, starting & ending the test at the petrol station about a mile away. The total distance was 13 miles* for each test.


We worked out the petrol car’s ‘real world mpg’ by first filling the tank at the petrol station, setting the odometer to 0, then driving to the track, completing 10 laps, and driving back to the petrol station. We then filled the tank back up, recorded the amount of petrol used, the distance driven, and from that calculated a ‘real world mpg’ of 42.52.


We did the same with the electric car but instead of filling it up at the petrol station, we recorded how much charge was left in the 50 kWh battery. We recorded the amount of charge at the start of the drive, completed the same route, and returned to the petrol station to see how much charge was left. It used 6.25% of the battery, 3.13 kWh, giving a ‘real world miles per kWh’ of 4.16.


Using the above real-world test results, and many hours staring at a spreadsheet**, we calculated the best-estimate figures to answer Julian's questions. Our conclusions are below.


* I'm very aware this was just one test, with one set of vehicles, on one day, over a short distance. Sadly this was the best we could do within our production limitations. The statistician in me (albeit the one that hasn't seen the light of day since university) appreciates the considerable wiggle-room (error bars) in each number and hence in the final results. Hence why I'm referring here to 'real-world best estimates'. I would LOVE for someone more qualified than me - and for someone with more time / resources - to repeat the test (multiple times), over a longer distance, with other sets of EV & ICE vehicles. And also to factor in some of the aspects outlined below that we couldn't build into this simplified model. If you do please do get in touch with your figures & results - I'll add them to the bottom of this blog.


** You can download the spreadsheet we used to calculate our results below - please only consider (or share) the spreadsheet with this blog so that all the considerations around it can be read. It would be great if you could input your own data and share the results in the comments below (or on twitter @gregfoot). It would be even better if you could conduct your own test and update the real-world mpgs and real-world miles per kWh too!

Sliced Bread EV v ICE Test Data & Calculations
.xlsx
Download XLSX • 62KB



The environmental angle: How many miles do you have to drive to make any real difference when it comes to your carbon emissions?


To answer this question, we first needed the ‘embodied carbon footprint’ for each car - the carbon footprint for the manufacture of the vehicle, taking into account the full supply chain. As the time of researching the episode, only two makers, Volvo and Polestar, had publicly published that data for their vehicles so we asked Mike to work this out for us. His figures (6700 CO2e kg for the Petrol Corsa & 12000 CO2e kg for the Corsa-e) considered the full supply chain of manufacture.


We also wanted to work out the ‘carbon per mile’ for each car. To do that we used our real world mpg and miles per kWh figures alongside figures provided by Mike for unleaded petrol’s ‘carbon footprint per litre’ (3.56kg CO2e) - a figure that factors in every aspect of getting the oil from the ground, refining it and getting it to the pump - and also the ‘carbon footprint of UK Electricity per kWh’ based on the UK energy mix last year (0.25kg CO2e).


The test results and spreadsheet calculations gave the 'carbon per mile' of the petrol car (0.38) and the EV (0.06) that we needed to tackle this first question.


Which leads us to these first-pass best-estimate real-world results:


  • If you have a working petrol car and you switch it for a new EV then purchasing that new EV roughly doubles your annual carbon footprint.

  • Driving an EV isn’t “clean”. On the day of our test the UK Energy Mix said that fewer than 1 in 3 of the miles driven in the EV were powered by truly renewable energy. On that day nearly 40% of UK electricity was coming from fossil fuels. However, the carbon per mile calculation suggests that each mile driven in an EV is significantly cleaner than an equivalent mile driven in an equivalent petrol car by a factor of almost 6 times.

  • If you buy a new EV you would need to drive over 37,000 miles before the environmental savings you’re making using electric rather than petrol add up and start to ‘offset’ the carbon footprint of making the new EV in the first place.

  • With an average annual mileage in the UK of 7,000 miles you would need to drive for 5 years and 4 months before the environmental savings you’re making using electric rather than petrol add up and start to ‘offset’ the embodied carbon footprint of making the new EV in the first place.

  • However, if you choose to buy a new EV rather than a new petrol equivalent then you need to drive close to 17,000 miles in the new EV before the environmental savings you’re making using electric rather than petrol add up and start to ‘offset’ the additional embodied carbon footprint of making the new EV compared to the new petrol equivalent.

  • With an average annual mileage in the UK of 7,000 miles you would need to drive for just over 2 years before the environmental savings you’re making using electric rather than petrol add up and start to ‘offset’ the additional embodied carbon footprint of making the new EV compared to the new petrol equivalent.


TO NOTE WITH THESE FIGURES:


1. The above environmental impact calculations were made for an EV charged using electricity generated from the UK Energy Generation Mix as displayed on this Energy Dashboard on the day of the test.


2. If an EV owner charges their EV with electricity generated by their own solar panels, that would of course have a lower footprint and change the calculations.


3. It's also interesting to note that where you live in the UK can change the energy mix and therefore how 'green' the EV is per mile.


4. These calculations don't consider the future carbon intensity of electricity production.


5. The embodied carbon figures provided by Mike looked to factor in the full supply chain of each vehicle, but these results don't consider the end of life impact of the cars. We have also not factored in battery degradation / replacement.


This test was 'complicated' enough (read: took way way more time to plan, conduct and process than we had available for one episode of the series) so we were unable to dive into the above in the detail I'd want to build lines into the spreadsheet. Again, I would LOVE to see people recalculate the results using real-world figures for all these elements too.


6. We only considered NEW EVs & ICE cars in the episode and the calculations because that's what Julian specifically asked me to look into, but also because we're limited to a duration of 23'50" for the programme. I would have really liked to have discussed the impact Second Hand Cars and Car Shares would have on these calculations. I haven't done a deep dive on them but here are some quick thoughts:


If you don’t think you’ll drive a new EV far enough in it's lifetime to off-set the above environmental costs it's possible that you’d sell the EV when you're done with it and someone else would continue to offset that initial production.


That's a great thing about buying second hand. You're either continuing to off-set the embodied carbon cost of production, or that has already been off-set by the previous owner(s).


With Car Shares that embedded footprint is shared between multiple users.


Also there are of course also other options to get around for shorter trips with lower per mile footprints, such as e-bikes.




The financial angle: How many miles do you need to drive before the money saved on petrol covers the increased cost of buying an EV?


To work out the equivalent break-even points for this second question we needed to work out the ‘petrol cost per mile’ and ‘EV cost per mile’.


We recorded the cost of petrol on the day (£1.68 per L), and had a figure for electricity per kWh (£0.21) [see below], but the day after our test the chancellor cut fuel duty, and then a week later the new ofgem energy price cap kicked in. This meant we had to adapt our real world figures to be applicable beyond the 1st April (where a kWh of electricity rose to £0.28).


Again, I've added some important things to consider with these results below, but, here are our first-pass best-estimate real-world results:


  • For every mile you drive in an electric car you save just over 10p compared to a petrol equivalent

  • You need to drive close to 80,000 miles before your financial savings on electricity over fuel offset the initial extra upfront financial cost of a new electric vehicle (EV) compared to a new petrol or ‘ICE’ (Internal Combustion Engine) equivalent

  • With an average annual mileage in the UK of 7,000 miles you would need to drive for just over 11 years before your financial savings on electricity over petrol offset the initial extra upfront financial cost of buying an EV compared to a new petrol equivalent


TO NOTE WITH THESE FIGURES:


7. We only considered NEW EVs & ICE cars in the episode and the calculations because that's what Julian specifically asked me to look into, but also because we're limited to a duration of 23'50" for the programme. As mentioned in Vauxhall's reponse below there are other ways of buying a car - Personal Contract Purchase (PCP), Hire Purchase, Personal Lease, Personal loan etc - and they will of course hugely effect the calculations and results above. I would REALLY like to see someone crunch various scenarios for these so that we can see where the financial break-even points are.


8. The £/kWh figures above come from the UK Energy Price Cap - the cap on standard variable and default tariffs set by regulator Ofgem. Therefore the calculations essentially use the maximum £/kWh figure for charging at home, during the day. This figure would likely be higher if you charge an EV using a public on-street or destination charger. However, many EV drivers who charge at home (me included) charge their EV overnight when there is a surplus and the costs are significantly lower. This is an important point to consider when looking at the conclusions below. We needed to choose figures to use in our calculations and it was decided that the UK Energy Price Cap figure was the best to use for this first real-world calculation. I would love to see people recalculate these break even points for their average £/kWh (& for different models of EVs too).


9. We have not factored standing charges into our calculations (£0.45 per day after the UK Energy Price Cap rise) for a couple of reasons 1) The more miles you drive, the more the standing charge is shared out... We only did 13 miles in our test so including standing charge over those 13 miles adds much more to the cost per mile compared to cost per mile if we'd driven further. And 2) Even if you don't have an EV you still pay the standing charge if you're on mains electricity, which most people are. So most people will pay the standing charge across their normal electricity use regardless.


10. These calculations don't consider how future electricity costs may change.


11. It may also be worth saying that if you’re not going to drive the car for 11 years you’re probably going to sell it. EVs keep their value well, so you may get a good chunk of that financial difference back, and that may actually push you into financial savings overall. Hoping someone will do this calculation.


11. We have not factored in road tax or maintenance costs, including battery replacement. Again, I would LOVE to see people recalculate the results using real-world figures for all these elements too.



Vauxhall's Reply


We always give any products or brands we analyse in the episodes the opportunity to reply. Here is some of what Vauxhall said:

More than 90% of private Corsa customers do not purchase their vehicle outright, as implied by your calculations, and instead opt for a Personal Contract Purchase (PCP) arrangement. In this instance, it is the monthly cost that is the most relevant to consider – and not solely the On-The-Road price.


We were told Vauxhall has figures for the embodied carbon footprint of their cars but were unable to share them with us.



Send me your 'wonder-products' to investigate


This series I’m investigating YOUR suggestions… Is there a product that keeps promising you the world on TV, or in a podcast ad, or in a magazine?


Have you spotted an influencer hyping something on Instagram or TikTok and you want to know if it really delivers?


If so I’d love to hear from you - you can drop us an email to sliced.bread@bbc.co.uk or send it to me direct via the contact bit of this website, or on twitter or instagram where I’m @gregfoot



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