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Tuesday, May 20, 2014

Three Years of Nissan Leaf Driving Part 3 of 3

In part 1, I talked about all the fun I have had with this car. In part 2, you saw the measured and predicted range degradation. In this finale, we'll cover the capacity bars, range estimation, & the mysterious 3000 charging events.

Capacity Bars

The Nissan Leaf has a 12 bar meter to show you how much capacity the battery pack has left. These are shown on the right in the image below. As you can see, my car only has 11 of the 12 bars.

2011 Nissan Leaf - After three years of ownership
The capacity bars (right) are different from the "fuel gauge" bars (left). The bars on the left show you how full the batteries are currently. While the capacity bars on the right show you how healthy the batteries are compared to a new pack. As you saw in part 2, over time the range of a battery electric car slowly decreases.

As you can see in the image above, I have lost one of my capacity bars. This happen at the 2 year 11 month mark. Nissan has said that they expect the 12th bar to the one that "goes the fastest". Meaning that the degradation rate slows as the battery ages (given similar usage and environment). This matches the battery aging model's prediction. We shall see.

I started comparing notes with some of my fellow EV drivers. Several of us received our Leafs around the same time. The 12th bar seemed to started dropping at the 2 year mark for high mileage drivers here in Oregon. Now, as we approach the 3 year mark, the 12th bar is dropping away from many of the cars. Yet, there are still a few even some that are over 50,000 miles that still have all 12. This is what you would expect from a normal Gaussian distribution.

2011 Nissan Leaf on her 3rd birthday, fresh from a rain shower bath
One comparison example, my friend and fellow EV driver, Alan, picked up his Leaf near the same time I did and now we both have just over 26,000 miles. However, our driving and charging patterns are very different. I drive about 20 miles a day and have only taken the car on a few roadtrips. Alan only drives a few miles on most days but takes several treks from Corvallis to Portland and back monthly. He has quick charged 330 times and level 2 charged only 548 times. My car, on the other hand, has only quick charged 26 times and level 2 charged 3017 times. Yet within a month of each other we both dropped our 12th bar.

From my little sample set, three years seems to be near the mean of the 12th bar's life. It would be very interesting to have access to all of the battery information that Nissan has collected. What matters most to battery lifespan & degradation? Is it ambient temp, fast charging, miles driven, age, depth of discharge... All of these are relevant to some degree. A published correlation analysis would be very informative.

The 2014 Leaf no longer has the 80% charge (long battery life) option. Is this because Nissan saw that it had only a minor effect relative to other factors? Or was it simply to avoid the EPA rule changes that included this in the range estimation? Which factors matter most?

Guess-o-meter


Above you can new compared to three years old for my 2011 Leaf. I included these images earlier to show the capacity bars. The number in the lower left is the range estimation value. This is the car's estimation of how far you can drive given the current charge. These are far more optimistic than the EPA range estimate. These values are based on my recent driving. It is important to note that this is just an estimate. Many Leaf owners affectionately (or not) refer to this as the guess-o-meter(GOM). The value depends on how you have been driving recently. For example, if you were to drive from Timberline to Welches, OR (20 miles, nearly all downhill), the GOM would show an unrealistically high value. This estimate is based on your recent driving, not the drive that is likely coming up. Future driving condition predictions would be very difficult to get correct; whereas, past data is easy to collect and analyze, so the latter method used.

I prefer to use Leaf Spy's range estimate since it used a fixed efficiency value that can be adjusted as needed. If there is any concern that I may not make it to my destination, I can set the efficiency rate based on the route ahead that I plan on taking. This gives me a range based on my predicted future driving style rather than the drive I took yesterday.

3000 Charges

In part 1 of this series, we saw that I had over 3000 charging events. The final official count is 3017 Level 1 & Level 2 charges. Three years of ownership is only 1096 days. How could I have ~3000 charges in just ~1000 days? There are a few answers to that question. First, I only charge the car to 80% on most days. This means that if I have a lot of driving to do, then I take opportunities to charge midday. Around here, where there is a lot of infrastructure, there are plenty of opportunities to grab a few kilowatt-hours. Second, I have charging stations at work. I don't use them much anymore, but for the first year I had the car, when I had one of the few EV there, I usually charged both at home and at work.

The third reason I have so many charge events is that I joined (and used) all the charging networks in this region. New charging stations were being installed daily. It was a fun game to find them and plug in. It was like geocaching for EVs. As a practical benefit, whenever the car is plugged in, it automatically added the location to the car's map. There is a simple "Find Nearest Charging Station" option in the menu. As I found more stations, it seemed like I was never more than a few blocks from a charging station. The city I work in, Hillsboro, Oregon, has more charging stations than gas pumps. It was easy to drive around with confidence that I could 'fuel up' whenever I needed to.
Nissan Leaf Charging Station Map Display (Portland, OR)

Three Years 

There you have it, three years of EV driving. I have had a lot of fun. The car has performed perfectly. By not buying gasoline or oil changes, I have saved a lot of money. The only things I have replaced are the windshield wipers and cabin air filter. The tires are starting to show wear and I'll likely replace them at 30,000 miles.

The range is slowly decreasing as the batteries age, but there is still plenty of range for my needs. Three years from now, I may need to start charging to 100% or that might be the time to start shopping for an electric Infiniti or a Tesla BlueStar.


Next Story - A "Kodak Moment" for the Auto Industry