EV Discussion thread

Exiled_Tyke

So not WLTP but a lot of our perceptions even beliefs come from what our cars are telling us.  Last year a drove my diesel A6 on a journey that miraculously turned out to be exactly 250 miles (as reported by the car and checked with googlemaps).  The car reported that I'd averaged 63 miles to the gallon.  I was chuffed with this. But I'd filled up at one end of the journey and again at the other end and got 20 litres in when I filled up.  So I make this just under 57 miles to the gallon.  Most of the time we don't question the numbers our cars report.  But I was disappointed how far out this was. Now may be it's just the inaccuracy of the measurements but on numerous other checks I found it was always over optimistic in its 'estimate'.  

EV owners have a far easier job keeping track of consumption/mileage and are likely to be far more aware of how their cars are performing. 

JKenH

Exiled_Tyke said:

So not WLTP but a lot of our perceptions even beliefs come from what our cars are telling us.  Last year a drove my diesel A6 on a journey that miraculously turned out to be exactly 250 miles (as reported by the car and checked with googlemaps).  The car reported that I'd averaged 63 miles to the gallon.  I was chuffed with this. But I'd filled up at one end of the journey and again at the other end and got 20 litres in when I filled up.  So I make this just under 57 miles to the gallon.  Most of the time we don't question the numbers our cars report.  But I was disappointed how far out this was. Now may be it's just the inaccuracy of the measurements but on numerous other checks I found it was always over optimistic in its 'estimate'.  

EV owners have a far easier job keeping track of consumption/mileage and are likely to be far more aware of how their cars are performing. 

How does your EV consumption as reported by the car compare to the fuel (electricity) taken from the plug to refill it at the end of a journey? 

Edit: I am fortunate that I have a Zappi which reports the amount of electricity supplied by the charger but of course not everyone has one of these so they might not be able to access an accurate figure. On Friday my son visited in his 40kWh leaf and the driving conditions were perfect (no HVAC, dry roads etc) and the car reported 5 miles/kWh (mpk). It is exactly 100 miles door to door and I popped out in the car for an 8mile round trip to the Coop in the next village so 108 miles covered in total. It took 26.4kWh to refill the battery so the true consumption was 4.1 mpk. That’s only 82% of the reported efficiency. 

thevilla

That assumes the Zappi is accurate.  Mine over reports grid import, especially at low power levels.  Its probably more accurate at 7kw but you can't simply assume it is correct.  I suppose the only true measurement is from the meter since that is its sole purpose.

JKenH

thevilla said:

That assumes the Zappi is accurate.  Mine over reports grid import, especially at low power levels.  Its probably more accurate at 7kw but you can't simply assume it is correct.  I suppose the only true measurement is from the meter since that is its sole purpose.

That’s a fair point. Mine also records more import.  In the first 6 months of this year the my energi app recorded was 2978 kWh compared to 2850 kWh recorded by my smart meter. (That’s 4.5% over reading compared to the smart meter).Grid import as recorded by the myenergi app is I believe measured by a clamp so might not be quite as accurate.

I don’t know exactly how the Zappi measures the electricity that flows through it but it does measure grid voltage and charging amps so presumably the charging watts recorded will be more accurate than the grid import measured by a clamp.

Edit: there was some discussion on this thread about what wattages the Zappi and smart meter recorded.
https://www.speakev.com/threads/how-accurate-is-zappi-power-draw-measurement.171473/

Martyn1981

Exiled_Tyke said:

So not WLTP but a lot of our perceptions even beliefs come from what our cars are telling us.  Last year a drove my diesel A6 on a journey that miraculously turned out to be exactly 250 miles (as reported by the car and checked with googlemaps).  The car reported that I'd averaged 63 miles to the gallon.  I was chuffed with this. But I'd filled up at one end of the journey and again at the other end and got 20 litres in when I filled up.  So I make this just under 57 miles to the gallon.  Most of the time we don't question the numbers our cars report.  But I was disappointed how far out this was. Now may be it's just the inaccuracy of the measurements but on numerous other checks I found it was always over optimistic in its 'estimate'.  

EV owners have a far easier job keeping track of consumption/mileage and are likely to be far more aware of how their cars are performing. 

True, and it doesn't help that there are so many different testing regimes for EV's, especially as news items from different regions will typically use the figures quoted there. From the NEDC (not even damn close) that the Chinese use, to the fairer, but still generous WLTP, to the roughly 12% tougher EPA figures the US uses, which actually seem to be pretty decent. But of course the EPA figures will require moderate driving, in moderate weather ..... just like the ICE ratings.

I think Grumpy's approach was pretty good - decide what mileage you'd really like to get, when needed, then select a BEV that can do that in harder conditions. Then decide what the hell, and get a long range Tesla. 

Magnitio

This spreadsheet from "Sunday driving" tests of EV's shows that many cars can exceed WLTP with some care:

https://docs.google.com/spreadsheets/d/1V6ucyFGKWuSQzvI8lMzvvWJHrBS82echMVJH37kwgjE/edit#gid=866693557

Martyn1981

Guilty secret (  ), but having read the figures that CW and Grumpy get, I am trying to do a bit less 'point and squirt', or to put it differently 'grow up', and get some better numbers. Nice to see 4+ miles/kWh on my trips this summer, but smaller %age of motorway miles tbf.

EricMears

JKenH said:

How does your EV consumption as reported by the car compare to the fuel (electricity) taken from the plug to refill it at the end of a journey? 

You shouldn't expect the car's report of power used to exactly match the metered input to charger.   There will always be conversion losses. Alas,  not always consistent losses.

Exiled_Tyke

EricMears said:

JKenH said:

How does your EV consumption as reported by the car compare to the fuel (electricity) taken from the plug to refill it at the end of a journey? 

You shouldn't expect the car's report of power used to exactly match the metered input to charger.   There will always be conversion losses. Alas,  not always consistent losses.

Like others have mentioned I just use Zappi for a rough enough idea or look at what I've imported overnight on my Octopus dashboard.   And OK it's not coming from the car but my previous point stands: It's far easier to calculate consumption rates and costs per mile than faffing about with litres to mpg etc.  And so I simply don't have to rely so much on what my car is telling me. Often I clock what Zappi tells me when I unplug on a morning and knowing what I drove the previous day (I can look it up if I've forgotten) I get the maths done before I get to the end of the road.  And of course when charging at only  9.5p a kWh it's far less crucial to be accurate than doing ICE calculations.  

Grumpy_chap

Martyn1981 said:

I think Grumpy's approach was pretty good - decide what mileage you'd really like to get, when needed, then select a BEV that can do that in harder conditions. Then decide what the hell, and get a long range Tesla. 

It's proving to have been a good choice - the car is fantastic. 
It would be nice to have better seats - the TESLA seats are what other manufacturers would market as "comfort seats" and what other manufacturers would market as "sports seats" would be far better.
I also find the cruise control annoying.  It works well on the primary routes but in local roads it fails to identify the difference between a stopped car in queued traffic (for which you need to slow) versus a traffic island or parked car (both of which you will navigate around).  It can also be overly sensitive to traffic coming in the opposite direction at times.

Martyn1981 said:

Guilty secret (  ), but having read the figures that CW and Grumpy get, I am trying to do a bit less 'point and squirt', or to put it differently 'grow up', and get some better numbers. Nice to see 4+ miles/kWh on my trips this summer, but smaller %age of motorway miles tbf.

I am doing my first charge tonight with my power monitor plug so will have a figure to give some assessment of the accuracy of the energy assessed by the car versus actual plug power draw.
I am doing a 140-mile round trip tomorrow so will be able to measure that as well.  It will be all mileage and no "vampire loss" energy as charging overnight today and will charge again when I return home tomorrow evening.

I am not sure that the reference to better miles / kWh and less motorway miles is necessarily true.  I seem to find some of the best energy consumption when doing a long motorway run which would match physics in so far as keeping a car rolling at a set speed needs less energy than getting a car rolling at that speed.  In short, local roads journeys, the in car energy shows really high consumption as there is a load of climate stuff, lots of getting rolling and stopping rolling, all inefficient events.