Originally published in CleanTechnica
The Question
This was a question about EV efficiency that I was asked recently, and apart from thinking that the Hyundai Ioniq must be fairly efficient, as it gets about 120 miles out of its 28 kWh battery, I was not able to answer. It is sometimes the case that it is only when somebody asks what is a fairly obvious question that one thinks — “heck, I’d never really thought about that.” In my case, I have the excuse that if looking at an EV to buy, I would be more concerned with range and price, rather than efficiency, but once the question was asked, I felt bugged by it and just had to come up with the answer.
The Answer
It required a lot of technical research on a wide range of cars to come up with an answer. The basic idea is that an EV is there to convert electrical energy into kinetic energy, or less technically, electricity in for miles of travel out. What we would need to establish for each car is the size of the battery (which roughly equates to the amount of electricity it takes to charge it) and the average real-world range achieved.
The size of the battery is not a perfect indicator because a battery cannot be allowed to drain completely, so all of the capacity cannot be used. The stated capacity is either not the full capacity or that stated capacity is not all available. Also, some electrical energy is lost in the internal charging system of the car, so the energy input might be slightly more than the battery capacity. However, it is not an unreasonable assumption that all these variations will be about the same for all EVs, so the stated battery capacity can be taken as a reasonable measure.
Range is harder to pin down. On a recent test drive with a 2018 Nissan Leaf, the range claimed by the Nissan dealer was 150 miles, the best range I achieved was 202 miles, and the overall range I achieved on a 175-mile journey was 185 miles per charge. See 175 Miles In The “150-Mile” 2018 Nissan LEAF (#CleanTechnica Review) for more on that drive.
Any car would give a similar spread of ranges, according to how they are driven. The most accurate test would be to meter the precise current consumption over a measured distance, but that would require a research program involving driving and measuring all of the different cars, which would be way beyond my resources. Even doing that, the efficiency varies according to how the car is driven: a car driven hard and fast in rally style will be a lot less efficient than the same car driven in sedate chauffeur style. The cars would all have to be driven the same way. See How EV Range Is Affected By Quick Acceleration.
The Data
Not being able to do a research project like that, I have to rely on the data I can find that is already existing. Battery capacity and an average range for each of a list of cars is the best I can come up with. The average range, divided by the battery capacity, to get the miles per kWh, seems the easiest way of calculating efficiency. The averages I have obtained are derived from range achieved in city driving and in highway driving, both in summer and winter, so that four separate range values for each car are used to get the average. Some cars, and possibly most cars, have different driving modes — for example, the Ioniq has “Sport” mode and the Nissan Leaf has B and D modes, both of which can be modified with the “eco” button for battery saving. The level of efficiency would be different in different modes, but the figures I have used appear to be for the standard mode and version, and so are all comparable. On that basis, having looked at a number of different highway-capable cars, they come out as follows in the chart below.
Highway-capable Road cars in order of Miles per kWh
Data Source – https://ev-database.uk/ (Where included there, otherwise various sources)
In Conclusion
I was right about the Hyundai Ioniq, which is impressive for a relative newcomer. I was also surprised that my own car, the Peugeot iOn, did so well. It is stated in most places to have a range of 90 miles, which is utter fantasy, and I know that 60 miles is about right — though, I get nearer to 70 miles on long journeys. I am sure the same kind of thing can be said for most of the cars, but I have used the most realistic averages I could.
Some of the cars are just differently badged versions of the same car, such as the Citreon C-Zero and Mitsubishi i-MiEV, which are the same as mine, and the Opel Ampera-e which is the European version of the Chevy Bolt. The Bolt does very well for efficiency, range, and performance.
I also notice the 8.4 seconds 0–60 mph time for the Nissan Leaf, which I can well believe, having driven it for the road test. The Teslas do well on range and performance, but are not particularly efficient, with the Model X at the bottom of the pile. The Tesla Model 3 comes out in company with the Nissan Leaf and Renault Zoe, and all do very well with efficiency just below the magic 4 miles per kWh. At close to 4.5 miles per kWh, the Ioniq is outstanding.
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