Feb 2018: Grid to Road Efficiency. (Spoiler: its about 80%!)

After a few complete months of driving, I've gathered some interesting numbers for consumption. In this case, we're looking at the conversion from the electrical grid to what the battery provides for the motor. The ultimate figure in terms of distance can be easily found on the odometer.

To measure the electricity from the grid, we use the data logging features of the JuiceBox that tallies up all the charging sessions. Here's our charging log for the month showing a total of 161.1kWh:

Circuit Electrique, the only public charging network we've used so far, provides energy consumption info as well (despite billing by time only).

From the above two sources, we have a total of 182kWh of energy provided to the car from the grid, not counting the energy consumed by the EVSE to facilitate the charge. I expect this ancillary value to be negligible considering the simple electronics involved... the public station might be a bit more power hungry but as you can see above, we don't use them much.
What might also be interesting is we charged a total of 14 times (not counting the small blips shown in the JuiceNet chart above, which is probably from pre-heat after a night of charging. this value actually *slightly* overstates our energy input, but we can ignore it for this rough analysis... :P). This is basically once every 2 days, on average. I expect things will be better once the weather gets warmer.

On the car end, Nissan Connect/CarWings contains detailed info under the confusingly named "electric rate simulation" menu. Here we can find the net power output measured from the battery. The actual number is the total energy consumed by the car, minus the amount recovered through regeneration, and measured 146kWh.

Putting the two together, we find an overall efficiency of about 80% from grid input to battery output. This source measures L2 efficiency to around 90%. However, this is what the battery gets on the INPUT, after PDM conversion and charging overhead only. It doesn't account for how much the battery gains from that input power, and as we know, we always lose some due to heat. Additionally, when charging the car to a full 100%, after about 80% or so the charge rate slows down to balance the cells, and in this situation, the relative efficiency will go down further as the charging overheads stay the same. So all in all, a not-surprising value. Finally, one more obvious assumption we make here is that the roll-over effects at the beginning/end of the month are negligible.

One conclusion worth considering at this point is if you're on level 1 charging exclusively, you would see an even more significant loss. Because electricity is still so much cheaper than gas, its likely not a huge deal unless you drive a lot so from a purely financial perspective, you might not actually need to install a level 2 at home. On the flip side, if you drive a lot, you probably want to have a L2 charger at home to gain the mileage back at a faster rate anyways.

Putting Some More Numbers Together

Some other interesting numbers to keep track of, which I will try to do on a more regular basis:

Efficiency: 80% Average temperature: -5C
Kilometers driven: 835km
Grid to road km/kWh: 4.58 km/kWh
Battery to road km/kWh: 5.72km/kWh
Charging days: 14 (once every 2.0 days)

I will try to compile these values every month, as soon as the data is available.