EV Road Trials — Different Levels of Range Under Different Conditions

Introduction

On 1 October this year, I published an article in CleanTechnica, in which I shared my experience of driving an EV. I explained the facts, and theory, behind getting the best range out of an electric vehicle. The title of the article was “Electric Car Range Tips, & How An Electric Car Works.” I originally intended to call it “EV Experience,” but the longer title was chosen for the sake of search engine optimisation.

Discussion below the Line

There was much interesting discussion below that article. One person insisted that a particular pattern of braking, using the brake pedal, optimised regenerative braking, where, in reality, the two are entirely unconnected. Regenerative braking is optimised by not using the brake pedal at all. He had made the age-old logical error of confusing correlation with cause. He had observed that regenerative braking is greatest when slowing from higher speeds, and then made the incorrect assumption that braking gently at the beginning would somehow result in more regenerative braking, which is not the case.

His braking technique was not the cause of higher regenerative braking, but just something occurring concurrently with it. Using the brakes, at all, is, simply, robbing your regenerative braking system of the opportunity to convert your motion back into electricity. The only way to maximise regenerative braking is to not use the brake pedal, at all. There is a certain truth in what he was saying, however — if you are going to rob yourself of regenerative braking by using the foot brake, doing this the least when initially slowing from higher speeds, where regenerative braking gains are at a maximum, would make some sense. Not using the brake at all would make even more sense.

Correlation Confused with Cause

That particular type of mistake is very common. It can be seen in both professional research conclusions, inadvertently, and propagandist news sites, deliberately. Whenever you see something cited as the cause of a particular outcome, it is always worth asking yourself, is it really the cause, or just correlation.

Any real-life examples might be controversial, so I will not quote any. A good illustration of the principal is an experiment where someone drops an egg onto the floor and shouts “splat” just before the egg hits the floor. Having done this a number of times, they come to the conclusion that shouting “splat” is essential for the egg to break. Well, we all know it is not, and this could simply be proved by dropping the egg without shouting “splat.” In the same way, whether we believe a certain pattern of using the brake pedal will optimise regenerative braking or not, the truth of the matter is just as easily proven by slowing down and not using the brake pedal at all.

The Discussion-Question This Article Answers

Another useful part of the discussion was someone asking me for precise figures in the difference, in range, between driving slower, driving faster, and driving behind a large vehicle to reduce air resistance. I had to confess that I couldn’t give him precise figures, as I had based my article just on my experience of driving an EV for a couple of years and noticing a definite difference in range in those three scenarios. I decided that, rather than leaving it open, I would perform some road trials to see exactly what the difference was.

Trial protocol

My electric car has an indicator for battery charge level, which mimics a fuel gauge. It shows bars that slowly disappear, one by one, as the level goes down. When the car gets to the last three, they start to flash on and off to tell me that I am nearly running out of energy, as if I did not already know. That would not be much use for giving precise figures for battery level and ranges.

Getting the Figures

I have noticed that when I charge up using Ecotricity fast-chargers on the motorway (freeway), the display on the charger includes a precise figure for state of charge, expressed as a percentage. What I decided to do was to drive from my home to a fast charger on the M1 motorway (not far from where I live), connect my car to the charger, and charge it to 80%. This is the point at which it automatically switches off in any case, so it was easy to get a precise starting point of 80%.

I took photographs of the charger display, and I then drove south on the motorway until I reached the next charging point, about 23 miles away. There, I connected the car to the charger again and photographed the display on the charger, showing the precise percentage of charge remaining at the beginning of that charge session. By comparing the two, I was able to provide a precise figure for the percentage of charge used in travelling the 23 miles.

Getting the Comparisons

I performed this operation on three separate occasions. The first time, I drove behind various large vehicles, including a bus, at speeds of between 60 and 65 mph. On the second occasion, I drove at speeds between 60 and 65 mph, in roughly the pattern of variation that I remembered, but avoiding travelling behind any other vehicle. On the third occasion, I drove at 70 mph, the maximum speed allowed on the motorway — again, without travelling behind any other vehicle. By doing this, I arrived at the precise figures that I had been asked for.

I also made images of the emails from Ecotricity, detailing a record of each particular charge event. Those emails provide independent corroboration of my statement that I did charge at those particular places on those particular days and times.

Before anyone starts to think how dedicated I must be to do all of this driving just to get figures for my readers, I did this on three separate days, when I had other reasons for driving along that stretch of the M1. The only extra trouble was in making the extra charging stop to charge up to the 80% first, and in photographing the displays. I was interested to find out for my own sake, too, just to make sure that I was not, unnecessarily, restricting my view of an otherwise panoramic motorway landscape to the back end of a bus. I also wanted to know just how much difference it would make to be driving at the maximum motorway speed, rather than slower, range-saving speeds.

Limitations

The Ideal World

I would be the first to admit that this is not a precise scientific study. To get something more precise, I would have needed to drive on a circular test track, all on the same day, where no wind and temperature differences could affect the figures, and where speeds would be very precise and constant and any shielding vehicle constantly present or not.

The Real World

Obviously, driving on the motorway on three different days, there might have been some small differences in wind direction and strength and in the air temperature, but not significantly so. Also, I would have been very lucky to have found a large vehicle to drive behind from the start, and to remain behind it constantly throughout. There was a short period with no vehicle in front, at the start, and as the first vehicle I found was driving rather slower than I required, I switched to another, after a few miles.

When trying to drive without any vehicles in front, but at the same average speed as before, and having due consideration for other drivers on the road, I was not always able to do so. As these defects reduce, rather than increase any differences, I am not too concerned about them. Finally, one last problem was that on the last occasion, the charger comms failed. As I did not get the usual emailed bill, you will have to take my word for it.

The Data

The Peugeot Ion has a 16 kWh battery, which is where the “16” comes from in the table below. The “Distance in Miles,” of 23 miles, is the 22.6 miles taken from the sat-nav and the car’s own trip counter, and then rounded up.

Date	Battery Capacity kWh	Start %	End %	Distance in Miles	Driving Style
12/10/2017	16	80	49	23	Shielded 60-65 mph
25/10/2017	16	80	41	23	Unshielded 60-65 mph
02/11/2017	16	80	36	23	Unshielded at 70 mph

The Results

Below, the “% Used” is simply 80% minus the “End %.” The “kWh Used” is calculated as the “% Used” of 16 kWh.  The “Miles per kWh” is the 23  miles, divided by the “kWh Used.” The “Calculated Range in Miles” is the range from 100% charge, assuming 16 kWh is available from the battery, and so is 16 multiplied by the “Miles per kWh”.

Date	% Used	Calculated kWh Used	Miles per kWh	Calculated Range in Miles	Driving Style
12/10/2017	31	4.96	4.64	74.19	Shielded 60-65 mph
25/10/2017	39	6.24	3.69	58.97	Unshielded 60-65 mph
02/11/2017	44	7.04	3.27	52.27	Unshielded at 70mph