BMW i3 Fuel Cost Comparison

So, yay! My shiny new BMW i3 has been delivered, in all its "solar orange" glory. I've driven around excitedly, and smelled the new car smell, and done all the things that might be expected at such moments. However, despite all my excitement, I did eventually manage to calm down for long enough to wonder how much it was costing me to fuel. This is a much less explicit cost than that of petrol or diesel, as it takes the form of a non-itemised increase to my electricity bill.


This question led to the following spreadsheet, comparing the fuelling cost of my previous car (a diesel BMW 320d) with the i3.

So, the cost per mile to fuel the i3 is comfortably under half of that for the 320d. Call me ungrateful, but I found this a little disappointing as I had guesstimated it to be more like 20% of the cost.

Turns out, however, that calculating the true cost is not that simple.

Firstly, it's winter. The range of electric vehicles is impacted by the effects of the cold on their batteries. BMW have done various clever things on the i3 to try and mitigate this. For example, if you leave the i3 on charge and tell it in advance when you plan to leave your house, then it will use your domestic electricity supply to warm up the battery and the cabin, rather than using battery power after you drive off. This, and other optimisations, help quite a bit, but it remains the case that range is more limited in winter. This makes the i3 look more expensive than it would look if I were able to average the miles per kWh across all four seasons.

Secondly, there's a lot of free charging around, at least for now. I can plug my i3 into the Ecotricity chargers that can be found in an increasing number of motorway service stations, and charge my car with fantastic rapidity, and this doesn't, as yet, cost me a penny. An ever-increasing number of business establishments offer free charging to their customers. This means that when I do longer journeys, or travel to places with chargers, my fuel costs are subsidised. It's hard to see how this situation can go on indefinitely, but it certainly has the potential to save me money in the short to medium term.

Thirdly, Ecotricity give me a discount on my domestic electricity supply for having an electric vehicle. This amounts to £40 per year, and I have not taken it into account in the calculation above. It will further reduce the overall cost per mile. Using the above figures, I calculate that this £40 discount buys me about 79 miles per month – thank you very much, Ecotricity!

Fourthly, world oil prices have dropped recently, and with them diesel prices at the pumps. For most of the four years during which I drove the 320d, the cost of diesel was around £1.30 or even £1.40 per litre. At these prices, the cost per mile for the i3 is closer to a third of the diesel price than a half of it.

So I think that, on balance, I can overcome my initial disappointed reaction, and be pleased with the reduction in fuel costs per mile from the i3 when compared with the 320d.

It's great that I can have all this fun driving, and save money at the same time. In four years time, when the i3's lease expires and I'm looking around again, I'm sure the landscape will have changed. New cars will have 1,000 mile batteries in them rather than the 80-100 miles of the current crop of vehicles, and the cost models will be different again. Time will tell, I suppose.

In the mean time, I love the i3 - it is a great car to drive, and it feels like the future.

Update, 22nd Feb, 6:20pm

I shared this post on the BMW i3 UK Facebook group, which prompted some really useful and interesting feedback.

First off, I've been reminded about Economy 7, which is a split cost tariff offering very cheap overnight electricity rates, offset by more expensive daytime rates. If the car charging occurred almost exclusively overnight (so far it does), then this would bring the per-mile cost down to around 16% of the cost of the 320d.  Much more in line with what I was expecting.

Also, installation of solar roof panels can allow free charging at home too, especially in the summer.  It's not really an option for us at the moment, but I can see that it would be very satisfying to drive around on self generated fuel.

Update, 10th March, 5:00pm

The i3 now shows the average consumption over 1068 miles as being 4.0 miles per kWh, which brings the fuel cost per mile down slightly to around 3.9p/mile.

If I was really dedicated to reducing the cost per mile, I could switch providers away from Ecotricity, and pay as little as 3.2p/mile, but my energy would then come mostly from non-renewable sources which seems to rather defeat the object of the exercise.

However, if I were to remain with Ecotricity but switch to an Economy 7 meter, then the cost per mile would be reduced dramatically. The fuel cost would be down to 1.4p per mile, providing that I timed recharges so that they started at 2am. However, due to the additional cost of daytime and evening consumption under Economy 7, it may not be cost effective overall unless I can shift other consumption to the overnight slot.

I will be doing my own calculation to see whether this adds up or not. Watch this space.

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BMW i3 - Test Drive Notes

I've been test driving an electric car over the course of last weekend - the BMW i3.  It turns out that a lot of people are curious about electric vehicles, so I thought that it would be useful to write down some thoughts and impressions.

Short version - my next company car will be a "Solar Orange" i3.

Here are a few pictures of the demonstrator car that I've been testing.

The i3 feels big and airy inside, and can comfortably seat four adults although if you want to squeeze in another, they'll be sitting on cup holders in the middle of the back seat.  The boot (trunk) isn't huge, but is comfortably sufficient for most purposes, and the back seats fold down to provide a load of extra space.  Everything looks super modern, from the two screens that cover all of the instrumentation displays, to the blue piping around the steering wheel, and the iDrive menu on the car's computer has a lot more features and settings in it than the one in my current car.

Electric vehicles are generally rather more expensive to buy than their ICE (internal combustion engine) competitors, even though the government currently offers a £5000 incentive payment towards the cost in order to help drive adoption.  The running costs are much less, however, with fuel costs per mile coming in at something like 10-15% of the cost of petrol or diesel.  Servicing is cheaper too - electric motors are a lot simpler than traditional engines, and there's a lot less to wear out or go wrong.

Driving the i3

Driving the i3 is really very easy.  You get in, press the brake pedal and the On button to switch the car on.  Then, move into drive and off you go.

The most surprising thing about driving the i3 is just how fast it feels.  In fact, it has a 0-60mph time of 7.2 seconds. which means that it's much nippier than my current car.  The electric motor just delivers loads of torque whenever you put your foot down.  There are no gears, and no uneven delivery of power depending on engine revs, it just goes.  I live somewhere with a lot of hills, and the i3 just effortlessly sailed up and down them.

The second most surprising thing about driving the i3 is the regenerative braking that kicks in when you lift off the accelerator.  When you lift your foot, the car slows quickly, the brake lights come on, and the battery charges.  So if you want to coast, you'll find that you still have to press the accelerator pedal a little, and if you anticipate the road ahead, you will rarely have to use the brake pedal to stop the car.  I found that this encouraged me to look ahead, and try to stop the car using only the regenerative braking, a habit that will certainly increase the range.


The biggest and most obvious difference between traditional ICE cars and electric vehicles lies in the limited range of the latter.  My brief experience indicates that the i3 has a real-world range of something like 80-100 miles if driven sensibly.  This is a lot less than my current car, a diesel which can drive 600-700 miles on a tank.

Almost all of our family car journeys are well within this sort of distance, but even so it turns out that worrying about whether you'll have enough charge to make any given journey is common enough to actually have a name.  BMW have taken a number of steps in the design of the i3 to try and alleviate this "range anxiety".

First of all, the concept of range is deeply integrated into the navigation system.

Immediately upon looking at the map, it is obvious what the range will be on the current charge.  Click the picture to see the full image, although it does not do justice to the bright, clear, and sharp looking screens in the car.  It's not just a circle, so it is clearly taking into account more than just the distance as the crow flies.  Notably the range changes significantly and dynamically based on driving style, and so you can increase it quite a bit by driving more gently, and using the eco modes provided.

There are three driving modes, called "COMFORT", "ECO PRO", and "ECO PRO+".  COMFORT mode offers best driving performance and allows unrestricted use of the climate control and other battery consuming extras.  Conversely, in ECO PRO+ mode, the car limits the speed to 56mph, and severely reduces the level of climate control. ECO PRO (without the plus) mode does some of this, but also provides access to additional screens containing feedback on driving style, as shown in the picture.  The smooth road and the 5 star scores for Acceleration and Anticipation indicate that I was doing pretty well. Making economical driving into a kind of game is a very clever move on BMW's part, and it's probably going to be important to get good at this game, in order to get the most out of the i3.

In addition to being range-aware, the satnav knows all about the national network of charging points, and can display them along with their status (free or occupied).  The one shown in the picture was apparently available at the time when I took the picture, indicated by the green light on the list, and on the map icon.

The DC fast charge option, in my view an essential add-on, allows compatible public charging points to charge the car from empty to 80% in half an hour.  This makes it possible to make longer journeys with one or two 30 minute breaks in the middle.

Finally, BMW offer a "range extender" option, which is a small and quiet motorcycle engine that sits under the floor of the boot (trunk) and recharges the battery.  My demonstrator did not have this option, but apparently it adds another 80-100 miles onto the range and I am sure that it is very well executed.  To me, however, this feels much more mundane and ordinary - I don't want to be queueing up for petrol (gas) in my electric car.


We all loved the i3, although some family members are unconvinced by my selection of Solar Orange for the colour - hopefully they'll come around!  We're all looking forward to the new car arriving early next year; it feels like the future.