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02 May 2018

EVs and Changing Behaviour



When we think of the bottlenecks surrounding the rate of adoption of electric vehicles, there are probably two things that first come to mind. One is the speed with which the cars can actually be designed, built and put on the road, and the other is the availability of electric charging points to fuel them. These are both important issues, closely linked, because there is no point in having the cars and no way to charge them, or in having the plug-in points and nothing to connect to them. There is another point, though, which probably gets less attention, since it’s a more difficult one for the layman - like me - to feel entirely comfortable with. This is the question of the rate at which the fuel can be put into the vehicle. It’s a little complicated because there are three variables: the amount of power available to put down the cable (or wireless) connection, the capacity of that cable and the maximum speed at which the battery can absorb it. Some will regard this as an existential question for electric vehicles - since if the physics and chemistry of metallic batteries and electric charging rates always guarantee that charging will take several hours, then it would seem the technology is a blind alley and we should be focussing our research elsewhere (hydrogen fuel cells, maybe) - whereas others will see it as more of an issue about how we use the vehicles compared with what we do now with fossil fuel power.

So, I’m not a scientist, my degrees are a long way from physics, engineering or chemistry; however, I can understand the basic principles here. When a liquid is moved from one storage to another via a pipe, the factors that dictate how fast it flows are pressure, the capacity of the pipe and the absorptive capacity of the receiving storage. It’s the same with electricity. The amount of power available is effectively the pressure, the cable is the pipe - with a maximum throughput capacity - and the battery is the receptacle - with a maximum rate of filling. In an ideal world, the properties of the materials involved would enable an electric charge to be transmitted as quickly as we can currently transfer a liquid - like petrol - into the car. Unfortunately, this is one of the ways that the world isn’t ideal; current technology cannot persuade the materials to act that quickly, so charging an electric car takes longer than filling a conventional one with petrol or diesel. Will that turn out to be the achilles heel that stops a universal acceptance of electric cars?

That’s the stance adopted by some - that research time and effort spent on electric vehicles is time effectively wasted that could be spent looking at other (and hydrogen is at the front of the queue) putative replacements for fossil fuel powered engines. I’m not sure about that, though, for two major reasons. 

The first is the simple onward march of technology; what was impossible yesterday has become normal by today, so is it not reasonable to expect tomorrow to move further forward? After all, think back to the battery life and recharging time of your first mobile phone, thirty-odd years ago. Then compare that with what you have in your pocket now. It’s not only the size that’s changed, it’s the life and time to recharge. 

Secondly, there is a degree of behavioural modification. Right now, at the top of the market, the longest range vehicles are capable - in the right conditions - of around 300 miles on a charge. That doesn’t compare terribly favourably with petrol or - particularly - diesel vehicles, and given that to put in a full charge takes considerably longer currently than to fill a petrol tank, that looks like a double whammy; shorter range and much slower refuelling. However, it’s not that simple. The curve that represents the rate of charge of a battery is not a straight line; the first 60 or 70 percent flows rapidly, and then the curve flattens out and the balance takes far longer. I’m sure the scientists can give an explanation of why current behaves like that: I can’t, but it’s a fact. So, as somebody recently pointed out to me, taking Germany, with less speed restrictions and a relatively larger charging network than in many other countries, as an example, drivers need to modify their behaviour to achieve maximum efficiency. Rather than try and husband the charge by driving slowly and gently, the technique surely is to drive as fast as one feels confident with and stop frequently to put in a short, quick charge. Since every motorway I travel on these days tells me constantly to take a break, or tiredness kills, or whatever is the preferred form of words, adjusting to that regime is surely killing two birds with one stone.

I don’t intend to be flippant here. To realise the potential of EVs (and automated driving, in the future) will require us to change our behaviour; understanding that is an important step. 

     

    

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