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Further edited to fix my horrendous unit error. 
Edited to add what I've got my EVSE limited to.
After tracking my car for a while, I've finally got what appears to be some semi-stable real-world energy consumption that includes losses from charging.
We've all looked at the miles/kWh figure on the vehicle info screens, but there are inevitable losses from resistance in the charging cable and heat generated in the batteries from charging them. Cooling those warmed up batteries also uses some energy. So, I wanted to figure out just how much electricity does this car actually use?
The short answer: my vehicle info screen shows a lifetime usage of 3.6 miles/kWh. However, if I measure electricity used by my EVSE unit and divide by miles driven, I get somewhere in the range of 3.3 to 3.4 miles/kWh. The end result is a loss of between 0.2 and 0.3 miles/kWh driven to what I'll call "EVSE and charging losses." So, I'm losing about 5.6-8.3% to charging inefficiencies.
I think it's important to note that I've got my EVSE set to a max of 32A, quite a bit slower than the car can take or even what the EVSE can do. That's in an effort to limit some of these losses as well as take care of the battery.
This is in moderate to very warm outside temperatures. Perhaps 25% of the miles were with lows in the 60F range, and highs near 75-80F. The balance is more of a summertime in the south, with lows in the 70-80F range with highs between 90 and 98F. I drive the majority of my miles in a semi-urban environment; 35-45MPH speed limits with 1-3 miles between lights and stop signs. Maybe 20% of my miles are highway at 65-70MPH in moderate traffic. I make liberal use of pre-cooling the cabin and running the AC while I'm in a store. I didn't buy an EV so I could walk out to a hot car. I keep my car's cabin set between 74 and 76F, with recirculate on. Yes, I have to select recirc on every time. I've found that on hot days over about 80F the car does better at cabin temp control if I also select "sync" on the HVAC screen to get air out of all of the vents...which is another three presses. I wish I could just have that stay how I want it, but that's a topic for another very long thread!
Here's how I did this, problems, etc.:
The big one is I have to guess at what the "rest of the house" is using when I'm charging the car. By waiting until after 8 or 9PM, my house is usually only drawing 1kWh/hour at that time, occasionally zero. They don't have anything more granular than 1 kWh increments unfortunately. I don't charge every night, so I do get some baseline info. Of course even that's not terribly accurate because of rounding. But, over enough time, I figure the rounding will smooth out and I'll get more accurate numbers. It's close enough.
Another issue is I really don't have a terribly large sample size. This is only over 500 miles or so and initial numbers were all over the map. I've waited for things to smooth out a bit; I'm now wobbling in a range from 3.27 to 3.43 miles/kWh.
I'm in the temperature sweet spot for EV usage. 70-90F is where EVs really shine for efficiency. However, I'm hopeful that this display of "EVSE losses" if you will translates smoothly to colder weather. Have to wait a while for that test.
Finally, I do wish I had a dedicated meter for my EVSE. Maybe someday, but I've spent so much on this car already I'm having a hard time justifying that expense. Perhaps those with smart EVSEs can chime in?
Edited to add what I've got my EVSE limited to.
After tracking my car for a while, I've finally got what appears to be some semi-stable real-world energy consumption that includes losses from charging.
We've all looked at the miles/kWh figure on the vehicle info screens, but there are inevitable losses from resistance in the charging cable and heat generated in the batteries from charging them. Cooling those warmed up batteries also uses some energy. So, I wanted to figure out just how much electricity does this car actually use?
The short answer: my vehicle info screen shows a lifetime usage of 3.6 miles/kWh. However, if I measure electricity used by my EVSE unit and divide by miles driven, I get somewhere in the range of 3.3 to 3.4 miles/kWh. The end result is a loss of between 0.2 and 0.3 miles/kWh driven to what I'll call "EVSE and charging losses." So, I'm losing about 5.6-8.3% to charging inefficiencies.
I think it's important to note that I've got my EVSE set to a max of 32A, quite a bit slower than the car can take or even what the EVSE can do. That's in an effort to limit some of these losses as well as take care of the battery.
This is in moderate to very warm outside temperatures. Perhaps 25% of the miles were with lows in the 60F range, and highs near 75-80F. The balance is more of a summertime in the south, with lows in the 70-80F range with highs between 90 and 98F. I drive the majority of my miles in a semi-urban environment; 35-45MPH speed limits with 1-3 miles between lights and stop signs. Maybe 20% of my miles are highway at 65-70MPH in moderate traffic. I make liberal use of pre-cooling the cabin and running the AC while I'm in a store. I didn't buy an EV so I could walk out to a hot car. I keep my car's cabin set between 74 and 76F, with recirculate on. Yes, I have to select recirc on every time. I've found that on hot days over about 80F the car does better at cabin temp control if I also select "sync" on the HVAC screen to get air out of all of the vents...which is another three presses. I wish I could just have that stay how I want it, but that's a topic for another very long thread!
Here's how I did this, problems, etc.:
- I've got a "dumb" EVSE, it's a Grizzl-E charger. Not the smart version, but I do have the upgraded cable.
- I don't have any way to directly meter what's going into the EVSE. I'm not too cheap to install a dedicated meter, I'm "value conscious."
- My electricity provider recently began allowing for hourly reporting of electricity usage by my house, which facilitated this little experiment. It's pretty simple: I only charge at home, I always plug in after 9PM when the house no longer has solar loading so the HVAC isn't running too much.
- So...check the miles on the car, and do some simple math. Easy-peasy!
The big one is I have to guess at what the "rest of the house" is using when I'm charging the car. By waiting until after 8 or 9PM, my house is usually only drawing 1kWh/hour at that time, occasionally zero. They don't have anything more granular than 1 kWh increments unfortunately. I don't charge every night, so I do get some baseline info. Of course even that's not terribly accurate because of rounding. But, over enough time, I figure the rounding will smooth out and I'll get more accurate numbers. It's close enough.
Another issue is I really don't have a terribly large sample size. This is only over 500 miles or so and initial numbers were all over the map. I've waited for things to smooth out a bit; I'm now wobbling in a range from 3.27 to 3.43 miles/kWh.
I'm in the temperature sweet spot for EV usage. 70-90F is where EVs really shine for efficiency. However, I'm hopeful that this display of "EVSE losses" if you will translates smoothly to colder weather. Have to wait a while for that test.
Finally, I do wish I had a dedicated meter for my EVSE. Maybe someday, but I've spent so much on this car already I'm having a hard time justifying that expense. Perhaps those with smart EVSEs can chime in?
