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Discussion Starter · #1 ·
Hello fellow Zoeans,

Having just done a 1300 km round trip (over 4 days, hence only ~300km per day) in an R240, I decided to investigate if driving faster and charging more is better or driving slower and charging less (should have done this before the trip!). What I found is that driving faster than 55-60mph is counter-productive for trips that are longer than what one can do in one charge...

Overall consumption based on charging history is 16.9 kWh/100km, which translates to 3.7 mpkWh. The journey was from Italy to Germany up and down over the Brenner pass and back again, with temperatures in the -3 to 10°C range. Some snow, rain and wind.

See attached for the Excel file that I did for the purpose of checking my calcs. Also did this as I am trying to figure out how much we truly save if we were to upgrade the battery on the Zoe. The conclusion was that we would save 120 minutes each way, but what it truly does is that it makes the journey possible in 1 day (10 hours on the road) rather than borderline impossible (12 hours on the road). On the other hand, if we only do this once a year, then there is no reason to upgrade.

To use the file, insert your numbers in the yellow highlighted cells, enable the solver function on Excel and run the solver. Alternatively one can change the numbers manually.

I have assumed energy consumption is 17 kWh/100km at 100 km/hr and then just use a square function to extrapolate energy consumption at different speeds.

Comments (especially on the equations) welcome!
 

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That's a really useful spreadsheet. End of December, I'm going to make a 180 km/112 mi. trip. I wasn't sure whether I would need to charge or not. But with the sheet, I can simply lower my speed until the "number of charges" field drops to 1. Much appreciated.
 

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Discussion Starter · #3 ·
That's a really useful spreadsheet. End of December, I'm going to make a 180 km/112 mi. trip. I wasn't sure whether I would need to charge or not. But with the sheet, I can simply lower my speed until the "number of charges" field drops to 1. Much appreciated.
Thanks for the kind words. I hope that salt is taken with the numbers as your mileage may vary (ok, I will stop now).

The energy consumption figures are not modelled on anything other than an educated "guess" at 17 kWh/100km at 100 km/hr. So please use with caution and always have a backup charger handy!

Also note that I have not accounted for elevation change. On a lightly loaded car, I would expect (1800 kg × 100 m × 9.81 m/s2 / 3600 J/Wh / 1000 Wh/kWh) 0.5 kWh every 100m in positive elevation change. So for every +100m of elevation change between origin and destination, take off 3km of range. Based on 60% efficiency of regeneration, you could also increase your range estimate by 2 km for every negative 100m elevation change between origin and destination... Though if you are starting from the Netherlands it is pretty difficult to find negative elevation change? ;)

In fewer words: please use with caution!
 

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Noted, I'll use it with caution :)

My driving style is normally pretty speedy (130 km/h, 80 mph), so this month I'm going to keep an eye on the overview that the Zoe shows when you turn it off and probably adjust that 17 kWh/100km number.

As for negative elevation change, I could always drive the car off a **** ;)
 

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Discussion Starter · #5 ·
Hi All,

I came across this website which calculates the range of a car (100% - 0%). I then compared it to my recorded data and it looks like it might be a bit pessimistic (around 3%-5%). In the interests of further understanding how to drive for longer journeys, here is the website: Electric car range

I'm also uploading the speed-consumption data (some of which are really weird) that I have recorded so far. Maybe someone else is doing a similar experiment and has different numbers?
 

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Conclusion is - driving slower in a lower range EV car means less charging and then a faster overall journey time?
Exactly. Not sure how others do it, but when I make long trips (more than 200 km/125 mi), I usually drive 90-95 km/h / 56-59 mph). Not sure where the optimum sits, but really I don't want to drive any slower. It would be dangerous, IMHO.

DD
 

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Conclusion is - driving slower in a lower range EV car means less charging and then a faster overall journey time?

JJ
Yes but OP has an R240 so small battery and only 22kW charging.

I know you are getting Q90 so will be different, but generally in any EV if you can reduce number of stops it helps overall journey time. However, If a stop take 30 or 40 minutes doesn't make as much difference, especially if planned around a break, lunch, etc. That is our experience.
 
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Discussion Starter · #9 ·
The (maybe) interesting thing is that a 40 kWh battery with 22 kW charging rate reduces the trip time by (only) 17%, if the trip exceeds the range you have (say a 600 km journey) and assuming finding chargers is quick (say UK rest stops and not going 10km out of your way to get to a charger). That was one of the reasons I didn't go for the battery upgrade as most times long trips will be holidays and I will have time to stop.

However, even with 43 kW charging and a 40 kWh battery, the optimal speed changes from 90 km/h for the 22kW/22kWh scenario to 99 km/hr. However, once you reach 150 kW charging rates, then we are back to driving at 130 km/hr for shortest total drive times.

A quick search shows me that petrol is 9 kWh/litre and petrol pumps in the US are limited to 38 l/minute. If I say a normal pump does 20 l/minute, then a petrol pump is dispensing 11 MW so doesn't matter how inefficient your car is you can always drive at 150 km/hr (or 250 km/hr in case of Autobahn).
 

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In our experience it also depends if you have guaranteed destination charging or need plenty left to seek out as working charger!

In an ICE in Europe the main reason to drive slower is the cost of fuel! I have occasionally driven slower in one so I wouldn't need to get fuel, especially when on a motorway with ripoff prices!
 
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Conclusion is - driving slower in a lower range EV car means less charging and then a faster overall journey time?

JJ

In the R mode yes. In a Q model driving faster means warmer pack, meaning much reduced charge time on rapid.
 
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