By Sherry Listgarten
Don't Miss Your Exit (and other lessons from an EV drive)Uploaded: Jul 14, 2019
Driving an EV to Tahoe? Don’t miss your exit! I learned this and other lessons from two round trips between Palo Alto and Tahoe City in a Chevy Bolt (1). Maybe you are thinking of getting an EV but are nervous about longer drives. Or maybe you have an EV and want to understand what impacts mileage. Or maybe you’d just like to understand a little more about EVs and what they show on their dashboards. Then this blog post is for you!
For EV newbies, a little terminology: A gas-powered car has a tank filled with gas. We fill up the car with gallons of gas, and we talk about efficiency in terms of “miles per gallon”. An electric car has a battery instead of a tank. So we fill up the car (charge the car) with kilowatt-hours (kWh) and we talk about efficiency in terms of “miles per kWh”. So the concepts are pretty similar, as shown in this table:
The Chevy Bolt has a relatively large battery (60 kWh) and an estimated range of around 240 miles. The dashboard has a gauge that shows how “full” the battery is, just like the gauge in a gas-powered car. You can see the gauge on the left emptying in this series of pictures from one of the drives.
The Bolt provides more detailed information about mileage and capacity than a traditional car if you choose the “enhanced” display (shown above). It gives an estimate of how many miles are left, with an upward green indicator if mileage is improving (left picture), or a downward yellow indicator if mileage is decreasing (middle picture). The number on the right of the dashboard shows real-time power consumption (e.g., 14 kW in the left picture). If you accelerate quickly, the number is much higher (e.g., 40 kW). Imagine knowing how much gas you are burning at any given moment in a gas-powered car!
So how did the drives go? Below is a summary of the four trips between Palo Alto (PA) and Tahoe City (TC).
Mileage was much better than I expected, even though I made little effort to drive efficiently. I had to charge the car once on each trip to Tahoe City, but not on the way back. The overall trip times were fine -- there wasn’t much traffic, and the charging stops took about 35 minutes. I was impressed. But I learned some things along the way...
Mileage varies a lot
The car takes a snapshot of its mileage every five miles. Here is a chart showing the variation on the drive to Tahoe.
Mileage varies from under 2 mi/kWh to 16 mi/kWh. So if the battery has 5 kWh left, you might go just another 10 miles or you might last 40. You can see the mileage dropping as the grade increases just after Auburn (around 150 miles). The Bolt’s battery neared empty right around the steepest part of the climb. Which brings me to my next point.
Don’t miss your exit
I used PlugShare to find exits with fast chargers, located every 10-20 miles on 80 past Auburn. The first trip up was pretty straight-forward. I stopped at Nyack Road with about 30 miles left, charged for 30 minutes while I walked the dog, then kept going. No problem. So I wasn’t paying as much attention the second trip up. I had used up more battery than the first trip, due to being routed through Livermore, but I knew I could make it to the same stop, which I remembered was in Emigrant Gap. Unfortunately, I was looking for the Emigrant Gap exit (no charger) instead of Nyack Road (charger). I drove past Nyack Road about the same time I realized that was my exit. My battery was nearly empty (less than 10 miles left), and exits are generally spaced far apart on this stretch of 80. I briefly panicked until I realized that, luckily, the actual Emigrant Gap exit wasn’t much farther. I got to that exit, turned around, and rolled into Nyack Road with just a few miles to spare.
The car gave a series of battery warnings, as shown here.
This is the first low-battery warning -- the gauge turned orange.
When the estimated miles left dropped farther, the dashboard spelled out a warning.
When the battery dropped even farther, it stopped showing miles remaining and limited acceleration, displaying “Propulsion Power is Reduced”. In my case, though, the car slowed down because I realized I just passed the exit with the charger and was wondering what to do...
At this point there was just one bar left on the battery gauge. The dash didn’t change, but I have sped up. I saw a sign indicating the next exit isn’t that far after all. I knew I could make it.
The battery gauge went completely blank a short while later. Even though I was confident I had enough battery, the dashboard was doing its best to unnerve me.
Finally, the radio display disappeared, indicating that the radio and other non-essentials were going to be disabled. The “infotainment” display went dark, and could only be re-enabled by pushing on a manual button.
The Chevy Bolt takes running out of battery very seriously!
The cost of charging an EV on the road is often opaque and can be high
While I feel like the Bolt has my back on a drive, I don’t have that warm and fuzzy feeling about the charging infrastructure.
When you pay at the pump for gas, you generally know what it is going to cost you. You are charged by the gallon, so all you really need to know is how many gallons you will pump.
Many commercial EV chargers don’t work that way. Instead of charging per kWh, they charge per time! Since some pumps are faster than others, and advertised rates are not always truthful, it can be hard to know what you will end up paying.
In the case of the Nyack Road station, they advertise 50 kW chargers. Here is a screenshot from the EVGo charging app.
A 50 kW charger should put 25 kWh of charge on an empty battery in 30 minutes. (4) But it only added 17.5 kWh. And this happened twice. This charger only has 35 kW of power. Luckily I didn’t have far to go so I didn’t need more than that.
The city of Palo Alto charges about 19 cents per kWh for electricity. This pump charges 86 cents per kWh! You can think of that in terms of gas prices. A gallon of gas might cost $4 and last 30 miles. That is 13 cents per mile. If an EV goes about 4 miles per kWh, then this station is charging 21 cents per mile, which is similar to $6.50 for a gallon of gas(!) In contrast, charging an EV at home would cost less than 5 cents per mile, similar to $1.50 for a gallon of gas.
I hope that pricing becomes more transparent over time. Some new regulations on public EV chargers are being considered, addressing this and some other issues (e.g., many do not accept a credit card).
Your mileage may vary
A number of factors affect mileage besides incline. The Bolt keeps track of four of them throughout the trip: driving technique, terrain, climate control, and outside temperature. Here is a picture of the dashboard at the end of the first (uphill) trip to Tahoe City. You can see that the uphill drive (“terrain”) and my insistence on driving at speed uphill (“technique”) contributed to a loss of over 25 miles from expected mileage.
In contrast, the downhill drive added about 30 miles of range. (I’m not sure why “technique” is favorable. Maybe there were just fewer opportunities for me to drive inefficiently, given so much downhill.)
It’s interesting to look at the second downhill trip as well. My technique was worse than the first downhill trip, leading to poorer mileage (4.5 mi/kWh instead of 4.7) despite the trip being identical. I think I was just going faster.
It’s fine to use the AC
As you can see from the pictures above, warm temperatures ("outside temperature") improve mileage. Running the AC ("climate settings") reduced the mileage, but not as much as the warmer temperatures helped. So I would not hesitate to use the car’s AC on a warm day. I can imagine, in contrast, that cold days are problematic. The battery would already be running less efficiently, and heating the car would exacerbate that. That is why Chevrolet advises turning on the heated seats and steering wheel on cold days, rather than using the more power-hungry forced-air heat.
Inflate your tires
For some reason, the mileage on this trip was much better than I expected. I have been averaging about 3.5 on a normal highway trip, and here I averaged 3.6 or 3.7 on an uphill, largely highway trip. The only thing I can attribute that to, besides the warmer temperatures, is tire pressure. The recommended pressure for this car is 38 psi, but my tires were 34-35 on previous trips. I don’t think tire pressure is supposed to make a particularly big difference -- a few percentage points in mileage -- but I figure it helped some. I also found a cute dashboard display.
Tire pressure went up during the trip, probably due to warmer tires:
And lots more
Here are a few other things I observed. You can also look at the raw data here if you are interested.
- It is fun to watch your “gas tank” fill up as you are driving. Because EVs recharge the battery when braking, and because the Bolt has an option of doing this even when you don’t explicitly brake, the battery seems to magically refill as you are driving on long downhill stretches. You can see the long downhill stretch in this chart, starting around mile 30 (Donner Summit) down to about mile 90 (Loomis).
- It is nice to get to a beautiful place like Tahoe and consider that you got there by driving on sunshine. I know that is an exaggeration; there was certainly some fossil fuel in the power mix, though I charge my battery midday. And of course there are lifecycle emissions of the car, asphalt on the roads, etc.... But it’s a nice thing to contemplate.
- A lot of thought seems to have gone into the various estimates that the dashboard shows. For example, the display of how many miles are left adjusts up and down depending on factors like how you are driving and the overall terrain. It seems to work pretty well. After driving over 60 miles towards home from Tahoe City, the estimated miles left had actually gone up from 221 to 228, due to much downhill terrain. Similarly, on a long uphill stretch after Auburn, the estimated mileage plummeted from 100 to 18 miles, though I’d driven less than 50 miles.
The efficiency estimates also seem pretty good. For example, the car estimated a 55 mile difference in range between the uphill and downhill drives. The actual energy consumption differed by about 14.8 kWh, which at 4 miles/kWh is 59 miles -- pretty close!
There is a lot of EV expertise in this area. I’m interested to hear your take on how they operate or what is changing, and your experience with longer trips. The worst story I heard was of a guy who drove his EV to see the eclipse and missed it because all the charging stations were full…
This post is dedicated to the memory of Laurie Naiman, this blog’s #1 fan and one of my parents’ oldest friends. Laurie was a big fan of the Weekly and a frequent participant in (and winner of) its photo contests. He was also an EV enthusiast and would have enjoyed this post more than most. My family will cherish the memory of his wit, warmth, and wisdom.
Notes and References
1. The Chevy Bolt has a pretty big battery (60 kWh) and can go a good distance (200+ miles) without a charge. This car also accommodates a fast (level 3) charger, which not all EVs do. The big battery and fast charger were essential for making this a fast and easy trip.
2. Yes, that is a big range of electricity prices! This post explains how prices (on the road) can get so high. Electricity prices at home are more like 15-20 cents per kWh.
3. The first trip (PA to TC via SF) had a short 3-mile, 10-minute or so detour near the start.
4. One problem with the Chevy Bolt’s fast charging is that it becomes much less fast once the battery is about 60-70% full. So you can only “fast charge” when it is relatively empty, and you cannot “fast charge” to a full charge.
5. Now that I think about it, “Don’t miss your exit” applies for any type of vehicle on 80 if you are going to run as low as I did on fuel. The issue wasn’t so much a lack of chargers as it was that I drove to near-empty, using the detailed vehicle information. I wouldn’t have done that in a gas car because the information wouldn’t have been available. But some people do. So the lesson is really “If you are going to run your car to near empty, don’t miss the re-fueling exit.” Which you probably already knew…
6. For those of you who don’t have an EV, you should know that in practice you just need to look at the battery gauge periodically, just like you’d look at a gas gauge. All this other information is available but not really necessary.
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