A potentially important Rubicon has been crossed in our transition to electric motoring – electric cars are now covering more kilometres each year than their petrol brethren. According to the RAC (Royal Automobile Club) in the UK, using data drawn from MOT odometer recordings, the average annual mileage for an electric car is now 15,217km.
That compares with 16,737km across all types, which is comparable to the figure seen for average annual mileages for cars in Ireland, according to the Central Statistics Office. The RAC's figures, taken from more than 500,000 cars, shows that diesel cars – perhaps unsurprisingly given their long-haul economy and popularity with company fleets – cover the most kilometres every year, with an average of 20,161km per year. Petrol-powered cars, by contrast, cover a mere 12,080km per year.
The electric car mileage figure is brought up, significantly, by Tesla. The drivers of Tesla Model S cars are covering, each year, an average of 19,987km – almost the same as their diesel equivalents. The next highest mileage recorded by electric drivers is that of Nissan Leaf owners, who are covering 13,291km each year. In third place comes the Renault Zoe, whose owners are racking up annual averages of 9,251km.
Tesla actually tops the overall mileage charts for three-year old vehicles. Its 20,095km average puts it in front of Mercedes-Benz on 19,516km. Volvo is in third place on an average of 18,674km each year.
Irish figures
In Ireland, the picture is rather less clear, as the CSO does not yet separate out electric cars by mileage, but according to the 2106 figures – the most recent available – cars powered by ‘other’ fuels (which includes electric, hybrid and plug-in hybrid) 14,422km each year, slightly more than their petrol equivalents, which covered 14.224km on average. Diesel cars covered 22,430km each year.
Of course, part of the equation is charging speeds. If you’re going to cover big annual mileages in an electric car, it helps – indeed it might be critical – to be able to charge your car rapidly from a public charging point. Tesla’s Supercharger network is among the fastest, able to charge the Model 3, for example, at speeds of up to 200kW.
As ever, though, it's not that simple. The power output of the charger is one thing, but the ability of the car and its battery to be able to draw down that power is quite another. Audi has just made a rather interesting claim – that its e-Tron quattro electric SUV is the fastest electric car you can buy when it comes to inhaling battery juice from a fast-charging point.
“Most charging processes of an electric car generally occur at home or at work. The time factor generally does not play a substantial role there. By contrast, every minute counts and fast charging is essential on a long-distance journey,” said an Audi spokesperson, presumably while swinging an extension cord in a coquettish manner.
“After a brief break, the car should be ready for the next stage again. Therefore, many customers orient themselves toward the maximum charging capacity of their electric car to assess the charging characteristics – but this value is of only limited use if it concerns quick refuelling of range at a fast-charging terminal. High charging speed over the entire charging process is essential for a short charging duration. In other words, a high charging capacity must be available for as long a period as possible. The e-Tron models with their continuous output impress with precisely this property.”
Basically, what that means is that Audi reckons its battery and charging control software are the best in the biz. Charging a battery is not like filling a bath from a tap. If you turn up the tap to full capacity, your bath fills more quickly, and for a given shape will do so pretty consistently. A battery, in general, can only be truly fast-charged up to a certain point – after that, the speed of charge has to be reduced, so as to avoid damaging the battery and weakening its performance. When connected to a 150kW fast-charger Audi claims that its e-Tron’s battery can keep gulping down a fast charge until it is 70 per cent full, and only then does the software throttle things back. Even then, Audi reckons that it can hit an 80 per cent charge (from flat) in just 30 minutes, and a full charge in just 45 minutes. The Germans reckon that’s about as fast as it’s going to get.
Fastned is a European company which is currently rolling out a planned 1,000 charging points across the continent. It has also done some independent testing of just how fast an electric car can draw down a charge, and how consistently it performs during that charge.
Charging characteristics
Once you start delving into this arcane little corner of vehicular performance, there are some really interesting comparisons to draw. Consider the Hyundai Kona Electric. It's one of Ireland's most popular electric cars, and with its 64kWh battery, has one of the best one-charge ranges around. Its charging characteristics are a little odd, though. When Fastned plugged one into a 175kW charger, its charging performance curve looked like a set of broad stairs – descending in chunks from 40 per cent charged, with a big dip at about 72 per cent charged. Having started with a charging speed of just shy of 80kW, by the time the charge was complete, that speed had dropped to 10kW. At the 80 per cent full mark, the charging speed was 25kW.
Fastned also reckons that Audi is being a little modest with the e-Tron’s charging performance claim. Hooked up to the same 175kW charger, it kept charging at around 150kW right up to almost 80 per cent full, before plummeting to 50kW as the battery level approached 100 per cent. (On a 50kW charger, which is mostly what you’ll find in Ireland, the e-Tron charged at the full 50kW for the entire charge.)
Tesla’s Model 3, one of the most popular electric cars in the world right now, doesn’t perform all that well in the same tests. Fastned hooked one up to a 300kW charger, and found that while it would charge initially at a very fast 180-200kW, the battery’s charging performance started to wane once it was about 40 per cent full. On the 175kW charger, the performance would drop off once it was past the 55 per cent full mark. On a 50kW charger, it kept charging at maximum speed until about 85 per cent, and then tailed off.
Audi reckons that its strong charging performance is down to a combination of battery design and the way that it is cooled when plugged in. Twenty-two litres of coolant circulates in a total of 40m of cooling lines around the battery. During direct-current charging with 150kW, cold coolant takes away the heat that occurs as a result of electrical internal resistance in the battery.
A newly-developed, thermally conductive adhesive joins the cooling unit to the battery housing. The gap filler forms the contact between the housing and the cell modules placed in it. This filler is a thermally conductive gel that fills the space to the housing beneath every cell module. The gel evenly transfers the waste heat produced by the cells to the coolant via the battery housing. The physical separation of elements and battery cells carrying cooling water also increases the overall system safety.
