Tag Archives: Winter

Long trip planning, the Tesla way…or is it the EV way?

I found this article quite interesting for a few reasons (take some time to go read it…I’ll wait):

  • The current lack of Tesla Super Chargers on the east coast forces the driver to plan a bit more–like having a Focus Electric, or a Leaf (or any other <100 mile range BEV)
  • The driver comes to the conclusion at the end that is better to be more efficient than to rush (determining that driving slower and using less electricity actually saves time in the long run)
  • His reported “burn rate” for electricity is really not much higher than the FFE “burns” (300+ Wh/mile in the cold with the heater running, ~270 Wh/mile in milder conditions without heat from the article).

The ability to quick charge the Tesla does make for a much nicer experience when taking a long drive. In the above article he gets 190+ miles for 45 minutes of charge–short enough that a simple stop for dinner fills it up. I certainly hope that the next generation of EVs (FFE included) has a provision for fast charging (the J1772 Combo Plug option is already available on the Chevy Spark, and Ford has pledged to support it on future BEV and PHEV vehicles).


Another weather related observation

Here is an interesting thought/observation: If you keep your EV outside in the winter (as I do) you’ll often wake up to a bunch of snow piled up on the car. In my case, during weekday mornings, the car will heat itself up and melt off some of that snow–mostly the snow on the windows. Snow on the roof and hood typically will stay.

Here is the thing: If that snow is the slightest bit sticky and you don’t clear it off it will stay on the car. EVs don’t generate all the excess heat like an ICE vehicle does that would melt the snow off the hood (and most likely the roof as the heater will be run continuously throughout the commute). Since we’re driving with the heat off most of the time to extend the range as much as possible the cabin doesn’t stay warm during the commute and heat the roof.

The net affect of all this is that any snow on the car will stay there until its physically removed (scraped off, car wash, etc.). If left to accumulate that snow could have an overall negative impact on range–snow weighs a lot.
Snow on the car in the cold


Some numbers on the cold

Last night I took some data down on how much electricity the car used overnight while charging (should have done this in the summer months as well!).

To start with I recorded my power usage for the day (at least what the car thought it was using, this value corresponded with 59% of the battery remaining):
Trip meter display

These numbers are somewhat typical for my daily commute. Ironically this commute was on a rather cold day with just under 1/4″ of snowfall overnight. Preconditioning the car combined with everyone’s cautious driving caused me to only use 7.2kWh of electricity! These past few cold days I’ve been using closer to 8kWh of electricity for my 31 mile commute.

Right when I arrived home I grabbed my meter reading (the car’s EVSE has its own meter):
Meter reading 1

At the time I plugged it in the outside temperature was 35F and thus the car stated “Waiting to charge” with my normal start time of 1:00am. As the evening went on the temperature dropped–when it hit freezing the car switched from waiting until 1:00am to waiting to start at the current time–it was starting its warming/trickle charge cycle.
This morning I recorded the meter right before driving away (with no preconditioning, outside temp: 20F):
Meter reading 2

So overnight the car used a total of 10kWh to keep itself warm, and charge up to 100%. Thus 7.2kWh of that went into the battery along with some burned up in the charger due to the charging efficiency (according to the EPA charging efficiency is roughly 80%) which would be about 2kWh. This leaves about 1 kWh used overnight to keep the car warm. (I’m being purposely vague here because I don’t know the exact efficiency of my EVSE + car combination. Doing the math directly yields 1.36 kWh which is close enough to my 1 kWh value.)

The numbers above align rather nicely with the daily average power consumption reported by my electricity provider. The daily averages per month also seem to be reflecting the additional power usage as the temperatures drop:

  • September: 9.9 kWh/day
  • October: 10.1 kWh/day
  • November: 12.8 kWh/day

Around here the temperatures took a dive in November which is reflected in the numbers. There are other factors in those numbers as well: In September and early October we were driving around a bit more each day due to various school/sporting activities (which may be the reason that there is only a 0.2 difference between September and October).

At this point, with our early blast of arctic air, I’ve been very pleased with the performance of the FFE–I was expecting a much greater drop in total range as an affect of cold weather.

Update: Power required for a precondition. Prior to driving the car across town for Thanksgiving I had set it up to precondition to 85F. This was the perfect opportunity to measure how much that takes. Before the car started the meter looked like this:
Power meter
Just before leaving I grabbed a picture of the meter (when the car was done preconditioning):
Power meter
Thus the car used about 5kWh of electricity to warm itself up from the ambient 25F.