EV range and driving styles

k6chris

Came across this range calculator on the Citroen website https://www.citroen.co.uk/about-citroen/electric-for-all/range-optimisation.html

It suggests that the range when driven 'calmly' at 50 mph is 198 miles, but drive 'normally' at 70 and you only get 129 miles?  I know my ICE car is slightly more fuel efficient at 50, but not sure the difference is that great?  Is this a normal profile for EVs, i.e. they better suit a calm and slower driver?  What is the cause?

Martin_the_Unjust

The faster you go the more factors like friction and airflow come into play.

i.e. you are expending a lot more fuel overcoming those at 70 than you are at 50.

YBR

I think that sounds worse reduction in range than my Nissan Leaf. 
Nominal range is 167miles, and I've managed close to that driving at 60mph (I did a130 mile journey, mainly motorways to test this).
Of course the range is less in the winter using heaters, lights etc full time (nominal 156 mile range).

My experience, and that of colleagues with hybrid company cars, is that we change how we drive to suit the vehicle.

The reason is simple physics: higher speed = higher losses in friction, air resistance and so on = more energy needed to attain and maintain that higher speed.

mgfvvc

I think it's more obvious in electric cars, because they have a higher efficiency than ICE cars.

In an ICE car only around 20% of the energy in the fuel goes into useful work. If you need a quarter more useful work to overcome air resistance at high speeds, that only translates to an extra 5% of your fuel (ignoring the possibility that rate of waste goes up as well).

In a BEV around 90% of the energy goes into useful work. If you need the same quarter more useful work, that translates to an extra 22.5% of your fuel.

MX5huggy

My experiments show that dynamic driving with a lower top speed, I accelerate and brake faster than my wife but generally stay within 10% of the speed limit uses more energy than my wife who is calmer and less heavy on the pedals but in danger of getting points more of the time. 

DrEskimo

Not all EVs are equal. As with ICE, some are more efficient than others.

The Citroen isn't a particularly efficient EV to begin with.

I did a 200miles journey recently in my Zoe and with the cruise set to 70mph I was very impressed to get a solid 150miles out of it, which is what I expected this time of year for general town driving.

facade

The primary factor is air resistance.  This depends on the speed squared. So if you go 40% faster, there is 96% more air resistance (1.4 x 1.4 = 1.96), nearly double!

Most of the energy used is overcoming the air resistance, so energy per mile will virtually double, halving the range.

On the other hand, if you drive at a steady 20mph on the flat, it will go an awful long way

ElefantEd

The drag is proportional to the square of the velocity, the power required (=energy/second) to overcome this is therefore proportional to the cube of the velocity.

If I'm ever a bit concerned about my range, dropping to 50mph from 60mph makes a noticeable difference.

Like facade, I've also found that in dire circumstances, 20mph gives you a long (but nerve-wrackingly drawn out) range. Especially on our first Leaf where the display stops giving the eact amount of remaining battery below 5% and just has increasingly strident warning signs!

Petriix

facade said:

The primary factor is air resistance.  This depends on the speed squared. So if you go 40% faster, there is 96% more air resistance (1.4 x 1.4 = 1.96), nearly double!

Most of the energy used is overcoming the air resistance, so energy per mile will virtually double, halving the range.

On the other hand, if you drive at a steady 20mph on the flat, it will go an awful long way

Almost this - I'm not sure you're accounting for the extra distance you'll cover in the same time when driving faster. AFAIK 70mph uses ~ 40% more energy than 50mph to cover the same distance. That's still a significant difference, but it's not double.

The other significant factor is temperature. Batteries are simply less efficient when they're cold. Compounded with running cabin heating, this also significantly reduces range.

Then of course there's weather. Headwinds and even crosswinds reduce your range and so does any water on the road - the energy required by the tyres to displace the water is significant.

Ultimately these factors combine so your worst case range will be around half of your optimal range. I can just about extend my MG5 to 280 miles in the summer, by sticking to 50mph. At 70mph in winter it might only get 150 miles.

[wipers, lights and stereo etc make basically zero difference]

Martin_the_Unjust

So basically what you EV owners appear to be saying is that you can only get the maximum miles out of your vehicle if you drive it in such a way that it would be a fail on a driving test?

ontheroad1970

Martin_the_Unjust said:

So basically what you EV owners appear to be saying is that you can only get the maximum miles out of your vehicle if you drive it in such a way that it would be a fail on a driving test?

Pretty much the same as an ICE in many ways.