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Monday, May 16, 2016

Leaf Repurposed

When I purchased my Nissan Leaf in 2011, it was intended to be my commuter vehicle. I have a 21 mile round trip commute. This is perfect for a short range EV. The 73 mile EPA rated range of the 2011 Leaf gave me plenty of room to spare for errands, HVAC use and the battery degradation that I knew would come as the car aged.

That was the plan and for four and a half years, things went according to the plan. We took the Leaf on a few road trips to check out the West Coast Electric Highway, but for the most part, the Leaf was the commuter and errand mobile. I wanted to take care of the batteries in the Leaf. I was not leasing the car, I bought it and I wanted to make it last 10 years if I could.

To this end, I used the Long Battery Life setting in the car. This only charged it up to 80%. Also, I set the charge timer so that is started charging at 3AM. This had the car fully charged by 7AM and the batteries would not stay charged up for too long before my morning commute discharged them. Lithium Ion batteries are the least stressed in the middle third of their charging range and this method had them there about 16 hours each day.

For long trips we took the usually took the Prius. The Prius, however, was ended when an Uber driver in a Highlander ran a stop sign as he raced to pick up a fair. The Prius was totaled.

So now, the Leaf has taken on the job of the Prius and it's a very different usage pattern. The old pattern was:
   3AM Charge up to 80%
   8AM Drive to work (10 miles)
   5PM Drive home (10 miles)
   (maybe an errand - 7 miles)
   Repeat

The new pattern is:
   3AM Charge to 100%
   8AM Drive to school and back (23 miles)
   9AM Charge to 100%
   Noon Mid-day errands (10 miles)
   1PM Charge to 100%
   3PM Drive to school and back (23 miles)
   4PM Charge to 100%
   6PM Evening errands (piano, soccer, dinner ...) (6 miles)
   7PM charge until 8PM or 100%
   Repeat

As you can see the new pattern is much more demanding. There are many more charging events and the drive to school and back has a 700 ft hill climb. That is 4 times per day over that hill (hence the 100% charges). Summer is almost here and the school trips will end. Next year we're transferring schools, so the trip will be much easier both for the driver (less traffic) and for the batteries (no big hill). When the Leaf was new, this drive would not be a problem with an 80% charge, but now with the batteries ageing, 100% is needed to make sure the needed range is there.

The Leaf has also had to fill in on longer drives where we would have taken the Prius. Trips to Woodburn and Gresham have meant that we are stopping at DC fast chargers. This too has a wear and tear impact on the batteries.

I have been measuring the battery capacity of the vehicle since I found Leaf Spy in 2013. Here is the table of my car's actual degradation:


2011 Nissan Leaf Range Degradation
Year Range Loss Range
0 0 73
1 4.0 69
2 3.4 65.6
3 3.0 62.6
4 2.7 59.9
5 2.2 57.7

I didn't have Leaf Spy for the first 2 years, so that data is assumed based on the battery model that the known starting point and the measured values give us.

You can see from the table that there is a notable range loss each year. As the car ages, the loss is reducing, but the effects are still adding up.

For my fixed commute, there is still plenty of range. And my workplace has EV charging as well, this would allow me to use it even when it was down to ~20 miles of range. For a more spontaneous needs, however, at less than 60 miles, the range is not enough.

This is one reason that the 200 mile range cars are needed. With a longer range comes a larger battery pack and more cells. This means that each cell is individually worked less. When the motor needs 80 kWs of power, there are many more cells to distribute the demand across.

Due to circumstances that we had no control over, we have recently asked the Leaf to do more than we intended it to do when we bought it. It has handled this challenge extremely well, especially given the age of the batteries.