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Friday, December 11, 2015

Nissan Leaf Turns 5 - Incremental Improvements Add Up

The first Nissan Leaf was sold on December 11, 2010. The 2016 model year vehicles are currently available, making this the  sixth model year. Let's look at how the Leaf has evolved.

Looking back before we look forward

Chevy S10 Electric Vehicle
My first electric vehicle (EV) driving experience was in 2007. Lucky for me, there were still a few EVs around from the late 1990s. Thanks to Don't Crush (now Plug In America), not every EV from the turn of the millennium era suffered the same fate as the GM EV1. I found a Chevy S10 Electric pick-up. It was great. It had more than enough range for my commute, it went 70 MPH, and having a truck was pretty handy.

One day a couple other S10 EV drivers and I got together to swap stories. When we met, of course we started checking out each other's trucks. The other two were the 1997 models, while mine was the 1998. The differences were subtle, but very noticeable to an owner. The '98 added a rubber seal between the cab and the bed and there was a valance on the bumper. These were minor changes, but they looked like small efforts to improve the vehicle's aerodynamics.

Looking at even these minor improvements, we wondered what a 2007 electric Chevy truck would look like. Unfortunately, there was no 2007 model (or even a 1999 model year) since GM stopped making these trucks after these first two model years. That question has stuck with me. How would EVs improve year over year with continued iterations and technological advancements?

2011 launched a new generation of plug-in vehicles

With the reintroduction of EVs in 2011, we finally have a several model years of some plug-in cars to compare. Both the Chevy Volt and the Nissan Leaf came out in December of 2010 and the specs for the 2016 vehicles are available. This gives us of 5 years of cars and we can see how they have evolved from the 2011 model year to the 2016 vehicles.

EVolution of the Nissan Leaf

As we look at each year, I'll be focusing primarily on the range, drivetrain, and battery tech. New paint colors or backup cameras are nice, but not important in this context. The 1st year Nissan Leaf was EPA rated at 73 miles of range and it had an efficiency rating of 99 MPGe or (my preferred format) 2.94 miles per kWh.

The 2012 Leaf had the same EPA range and efficiency. This model year also added heated seats and a heated steering wheel. This allows the occupants to be warmed directly, rather than heating all the air in the car first. The high-voltage battery pack has more insulation and a warming system for extremely cold environments.

Nissan integrated electric powertrain
2013 brought the first redesign of the Leaf. Nissan integrated the motor, inverter, DC reducer, and power delivery module (PDM) into a smaller and lighter package. This reduced the volume of these components by 30% and their weight by 176 pounds. This increased the luggage space by more than 10%, improved the regenerative brake system, and reduced the amount of a rare earth element by 40%.

Nissan continued to improve the heating system by exchanging the immersion heater for a heat pump. The heating system has turned out to be very important in an EV. When a vehicle has the energy equivalent of less than one gallon of gas, it is important that anything that consumes this energy is highly efficient (just ask Mark Watney).

All of these changes resulted in a notable improvement in the driving efficiency. The EPA rating jumped from the 99 MPGe of the 2011/12 to 115 MPGe (3.45 miles/kWh). The EPA range, however, was only 75 miles. The reason the EPA rated range didn't increase a corresponding percentage is complicated. With a full charge, the 2013 Leaf earned an 84 mile EPA range. However, in 2013 the EPA changed the test. A new rule stated that if the vehicle offered an 80% charge (which the Leaf did to extend the battery life), then this would be tested too. With an 80% charge the Leaf only scored a 67 mile range. The final 75 mile range was the average of the 100% range and the 80% range (84 and 67).

In 2014, there were only minor physical changes. One notable software change was that the 80% charge option was removed. This meant that the EPA would now rate the Leaf's range only on its 100% charge. With this software change the Leaf scored a 84 mile range. Minor changes to the EPA test reduced the efficiency rating to 114 MPGe or 3.33 miles/kWh.

The 2015 model was again a small change. The range and efficiency remained the same as the 2014 vehicle at 84 miles and 3.33 miles/kWh. There was, however, one important battery improvement that does not show up in the EPA tests. The 2015 introduced the much anticipated “lizard” battery. This was an improvement to the Leaf's battery chemistry to make it more tolerant to extreme heat. Owners in places like Phoenix were experiencing advanced battery degradation due to heat. This was bad PR for Nissan and the new batteries were an important part of repairing the relationship with these early adopters that took a chance on the technology.

The 2016 Leaf was a big change from the 2015. This is the first year that Nissan offered two different battery size options. The 24 kWh battery is the same as the 2015 with an EPA-rated range of 84 miles. The new 30 kWh battery pack, provides an EPA rated range of 107 miles.

Here is a snippet from Nissan press release:
The new 30 kWh battery design adds capacity without increasing battery package size by improving the cell structure of the laminated lithium-ion battery cells. Improved electrode material with revised chemistry results in higher power density and enhanced battery durability upon charge and discharge.
It is also worth noting that the base price for the 24kWh Leaf dropped to $21,510. This is significantly cheaper than the $29,010 base price of the 2015 Leaf.
Correction, the base model MSRP was not reduced in 2016. Fueleconomy.gov has an incorrect price listed. Thanks to reader "aarond12" for the correction on the MyNissanLeaf forum.

Here's a table of the Leaf model years to-date:

Year Range (miles) Efficiency
2011 73 2.94 1st Year
2012 73 2.94 Added heated seats &
steering wheel
2013 75/84 3.45 Integrated elec. powertrain
2014 84 3.33 80% charge opt removed
2015 84 3.33 Heat tolerant "lizard"
84 3.33 New lower MSRP
107 3.33 1st battery capacity
increase for the Leaf

So, Nissan addressed cold weather areas by adding a better heating system that use less energy and they addressed hot weather regions by improving the battery chemistry. They also increased the battery capacity in 2016. Nissan will undoubtedly increase the range again when competitors such as the Chevy Bolt and the Tesla Model 3 come to market.

Nissan Leaf ratings from fueleconomy.gov

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