Tesla Power Use in Summer and Winter

This is part of a series that covers my experience with a Tesla Model Y.

When I look at my top destinations in the Tesla, I find that home is the top one (327) and my gym is second (102). That seems about right as I go to the gym 3-4 days a week and usually run some other errand then.

2022-06-07 08_51_39-Drive Stats - Grafana — Mozilla Firefox

When we got the Tesla and started to drive a bit, I found myself enamored with the Energy usage screen. It tracks the last 30 miles (configurable) and gives you a range estimate. Here is a typical screen for me:

20210922_161212

This shows the energy usage as I drive, with the most recent mile on the right and the oldest (30th) on the left. I see the amount of watt hours used at that time and then an average. There’s also a solid horizontal line for the rated range.

For this 30 miles, I averaged 218Wh/mile, which is pretty good. You can see there are some high spikes in the 500Wh/mi range and some low ones. The green areas are where I actually recovered some energy back. This was at the lowest point leaving my house and heading West to Parker, CO, which is about 800 feet lower in elevation. I actually am generating power with the regenerative braking thanks to gravity.

The Gym Run

I go to the gym regularly, often 3-4 times a week. It’s an easy drive, and I’ve played the energy video game for years, trying to use the minimum amount of gas (Prius) or power (Tesla) on my trip there. I found this to be fun, and I’ve beaten my high (or low) score a few times.

With the Tesla, it’s been an interesting metric to see how much power I used in the summer and winter. I grabbed a few screen shots in the fall when the weather was warm and then again in the winter. Here’s what I learned.

Summer(ish)

Here’s a summer graph. This trip was a 72F day, so not too summer-ish, but warm. A pleasant day. The drive stats are:

  • 11.8mi
  • ~2% battery used downhill
  • 21 minutes
  • 133 Wh/mi downhill
  • 1.6kWh

The return home is as little different as I went to the grocery, but I had:

  • 9.8mi
  • ~4% battery used
  • 342 Wh/mi
  • 3.3kWh

This is reflected in my graph for the downhill. The arrow is about where I start from home and the end is the gym. Lots of downhill, though not all. I was trying to be careful here and managed to get my 30mi average down to 184Wh/mi.

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This was pretty good to me, though admittedly I don’t have any point of reference as this is my first electric car. In terms of cost, this still is about US$0.69 for the drive. As a point of comparison, the X5 would cost about a gallon of gas. Around US$3.20 back then. The Prius would have been US$1.47.

Winter

A similar trip, slightly longer, so I must have varied the route a bit, but I see this:

  • 12.0mi
  • ~3% battery
  • 228Wh/mi
  • 2.7kWh
  • 33F

The return:

  • 10.2mi
  • ~5% battery
  • 360Wh/mi
  • 3.7kWh
  • 28F

The temperature dropped here, and as you might have guessed, I was using the seat and car heaters.

What is interesting here is the downhill show 133Wh/mi in summer and 2.7 in winter, a significant change. The uphill has less of a difference ( 3.3 v 3.7kWh). Gravity is a bigger issue, I’m guessing. Maybe some battery conditioning on the downhill as well, but that’s still a factor.

The cost in winter is more like US$0.90. While the BMW is still in the 20-21 range in winter, the Prius dropped from 47-48mpg to 42mpg, so it also showed a bigger battery effect in cold weather.

Conclusions

I don’t quite know what to make of this, other than expect range to shorten in the winter and plan for more charging. In general, since I mostly charge at home and my daily trips never get close to the range limit, this doesn’t change anything for me. We will use more power in winter, but since we don’t have time of day (or year) cost changes, and we have solar power to somewhat stabilize the cost of power, I don’t worry about this affecting my life.

We have learned to cut off Sentry mode and also to charge a little more in cold weather if the car is sitting outside and unplugged. It’s not a big deal, but it is something to think about if you have an electric car in a cold climate. A little more forward thinking is needed in this paradigm.

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