Q: I see figures being quoted for kWh/100km now for electric cars. What’s a good economy figure to look for in your average EV? – T O’Driscoll
A: This is a really good question, as it opens up a big part of EV driving on which many of us are only starting to pay attention. Until now, we’ve been focused on how much range an electric car has, but this is something of a blunt force figure.
For a start, range will be hugely variable according to driving style, location, topography, and weather conditions, so ultimately it’s not really all that helpful a measure. It gives you an idea of how flexible an electric car can be, but it’s not telling you the full story.
It’s far more useful to know a car’s kWh/100km figure, as just like litres per 100km, this tells you how much it’s going to cost you to do each journey.
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We had just got used to converting litres per 100km from miles per gallon (and sometimes back again, just to be sure), but now we have to get our heads around kWh/100km (kWh standing for kilowatt-hours, of course).
This is the battery equivalent of fuel consumption, and is a rating of how fast a given car will burn through its battery charge while driving. As with fuel consumption, there’s the official WLTP test that gives a car its equally official figure.
However, there’s a rub – as with fuel consumption, the official WLTP kWh/100km figure will be a best-case scenario, achieved in laboratory testing. Real-world driving is another thing. So, how do you know if your car is performing well?
So far, the best and most efficient EVs will generally return around 17-18kWh/100km in mixed driving, including some motorway miles – always the hardest yards for any EV. If you drive predominantly in town, you might see a little better, say 15kWh/100km.
One of the best EVs we’ve tested is the Hyundai Ioniq 6, which, thanks to its slippery body, managed to return an average of 16kWh/100km in mostly motorway driving.
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More recently, Peugeot’s tall but sleek E-3008 came close to matching that figure in real-world driving. If you’re getting down to mid-teens in kWh/100km, then you’re doing well.
Some manufacturers – Stellantis Group notably – are targeting averages as low as 12kWh/100km, which would be really impressive if it were achievable anywhere outside of the WLTP laboratory, but alas it isn’t really. Not yet, anyway.
If you want a handy rule of thumb, then we generally consider that 18-20kW/100km is about the equivalent of 40mpg, while 15-16kWh/100km is about the equivalent of 50mpg.
So what’s poor electric consumption? Anything over 20kWh/100km on average is generally considered to be fairly thirsty, while anything over 25kWh/100km is properly problematic on a longer journey. You’re starting to look at big bills from fast-charging if you’re trying to do anything other than a short journey in a car averaging over the 25kWh/100km.
One of the worst we’ve experienced was the Audi Q8 e-Tron quattro, which cost us more than €100 in fast-charging in just one week’s driving. Ouch.
How good will EVs become in terms of efficiency? Well, given that in the space of a couple of decades, we went from people being happy with about 35mpg on average, to considering anything less than 50mpg as unacceptably thirsty (ah, the good old days of diesel ...) there’s still plenty of potential for electric cars to improve.
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Consider Mercedes’ experimental EQXX electric prototype. That car, thanks to its impressively slippery bodywork, was driven in one go from the Mercedes factory in Stuttgart to the Silverstone race circuit in the UK – that’s a 1,200km drive – without stopping for a charge-up.
Impressively, the EQXX had enough charge left in its battery at that point for a couple of laps of the track afterwards, but even more impressively it managed to average just 8.7kWh/100km on that mammoth journey, and the Mercedes drivers weren’t trickling along at 30km/h in the slow lane – they were driving normally, but with a bit more care and attention than most of us would normally pay.
So, that’s with current technology turned up to the maximum, and while it might be some time before an EV that regularly averages sub-10kWh/100km in real-world conditions comes along, the tech from that EQXX has already influenced the design and engineering of the new all-electric Mercedes CLA, the one with the 790km range ...
Further improvements in battery technology – such as the oft-hailed arrival of solid-state batteries – may improve efficiency further, as will upgrades in the software and electronics that govern and monitor the condition of an EV’s battery as it is used and as it’s charged.
However, there may come a point when we have to make a decision on which is the better and more fruitful technological route: batteries that are more efficient when you use them; or batteries that can charge much faster, and the charging network to make the most of them? In some ways, the second option might actually be the better one, assuming that the cost of charging (currently appallingly expensive unless you’re doing all of your charging at home) can be brought under control, and ultra-fast charging hubs for 10-minute top-ups can be built in sufficient number.
However, given the glacial slowness of the roll-out of the infrastructure needed to make electric cars work properly, perhaps it’s the batteries we need to concentrate on for now, and concentrate on squeezing every last drop of efficiency from them.
