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Sunday, November 25, 2012

Nissan Leaf Range Issues


Cross-posted from Consumer Energy Report

A group of Nissan Leaf owners recently conducted a test in Arizona to see if high ambient summer temperatures in Arizona have  permanently reduced the capacity of their batteries to hold a charge.


 Does the Leaf go as far as advertised?

From Tony Williams, organizer of the group that tested the twelve Leafs:
“If you need the car to go that mythical 100 miles that Nissan advertises, first know that it never really went 100 miles for the typical US consumer.”
That conclusion, of course, depends entirely on your definition of myth and  “typical US consumer” (a term not used by Nissan on its U.S. website). Click here and then click on one of the colored boxes to see how far a Leaf will go for a variety of driving conditions.

The first question any Leaf owner gets is “How far will it go?” My standard answer is, “Around 100 miles if you’re tooling around town, and roughly 70-75 miles on the highway.” As that chart attests, the car is quite capable of going further than 100 miles especially if you minimize interstate highway speeds. The electric-only range estimates of the Chevy Volt plug-in hybrid are just as dependent on speed but because it automatically starts sucking gas when the charge is used up, the fact that it may not go as far as hoped on a charge is largely a moot point.

Jump on the nearest bicycle and try to make it go 40 miles an hour. The only thing stopping you (gearing permitting) is wind resistance, which increases exponentially with velocity. You would have no problem riding a bicycle 40 miles an hour on the moon where there is no wind resistance.
Interestingly enough, most conventional cars using internal combustion engines actually get better mileage on the freeway. It’s complicated, but in a nutshell, that’s because conventional cars are so inefficient in city driving scenarios (braking and engine acceleration losses) that those inefficiencies actually exceed wind resistance losses below a given speed.
 Analysis of the test results

I was putting together an analysis of their test data when I found a blog post by Mark Larson that beat me to the punch.

Click here to read his report AZ Leaf Capacity Kerfuffle: Much Ado About Nothing?


The above graph, published by Larson, summarizes the test results.


The table above, also created by Larson, summarizes the data in a different format.

This test would never pass muster in the world of science, where a hypothesis is proposed and tested using methods to minimize researcher bias. These guys were out to prove that the capacity of their batteries had been reduced by exposure to extreme heat beyond what the published specifications would predict. When any researcher sets out to prove he’s right, he will invariably manage to do so, at least until his research is peer reviewed or attempts are made to duplicate results. That is why the scientific method was invented.

There is a simple, relatively crude gauge, in the Leaf dashboard to warn owners when their battery won’t hold as much charge as it did when new. Nissan has suggested that some of these gauges may be out of calibration (possibly because of the extreme heat) and may be providing overly conservative estimates of battery life. Lo and behold, one of the cars in the test with a gauge indication of just 10 bars out of 12 went further than any other car.

The fact that more than one of the twelve cars tested by the Leaf owners had gauges that were not accurately indicating battery capacity suggests that a significant number of  Leafs may have gauges that exaggerate battery capacity loss.
In short, this paper failed its peer review. The test actually proved that:
  1.  Out-of-calibration gauges really are contributing to misperceptions.
  2.  All but two of the twelve cars thought to be damaged were actually performing within or just a few percentage points outside of the range band stated in a published Nissan technical bulletin (76 to 84 mile range when consuming energy at a rate of 4 miles/kWh at 70 degrees F ambient air temperature).
Again, from Williams, organizer of the group that tested the twelve Leafs:
“It was sheer stupidity to tell this group of owners that the batteries are ok…”
That conclusion, of course, depends entirely on your definition of OK, and stupidity. Larson’s analysis of the test results (which I concur with) didn’t jive with some Leaf owner’s misperceptions:
 “What I cannot see anywhere in these data is evidence that a Leaf is only achieving half its original range after one year, nor that another Leaf has lost 30% of its capacity in the same amount of time, nor that yet another is losing its capacity at 3 times the rate as anybody else, nor that a relatively new Leaf has lost 9% of its range in only one month.”
 Temperature impact on battery life and performance

Rightly or wrongly, Nissan never claimed that the batteries would perform per that specification no matter what and has warned from day one (in the owner’s manual and in a waiver signed at purchase) that exposing batteries to high ambient temperatures will likely permanently reduce their energy storage capacity faster than what would be expected for batteries not exposed to such temperatures.

Following is an excerpt from that disclaimer from the Williams analysis:


Nissan was anticipating that some cars would be driven in places like, say, Death Valley, or maybe Phoenix during record heat waves. It is likely that these car batteries were affected by heat.
 Click on the pink box in this link to get a feel for how much low temperatures can impact range.
The Leaf owner’s manual makes it clear that the rate of battery degradation will depend on how it is treated over its life.  From my owner’s manual:
The capacity of the Li-ion battery in your vehicle to hold a charge will, like all such batteries, decrease with time and usage. As the battery ages and capacity decreases, this will result in a decrease from the vehicle’s initial mileage range. This is normal, expected,and not indicative of any defect in your Li-ion battery. NISSAN estimates that battery capacity will be approximately 80% of original capacity after five years, although this is only an estimate, and this percentage may vary (and could be significantly lower) depending on individual vehicle and Li-ion battery usage.
Use of quick charge should be minimized in order to help prolong Li-ion battery life.

NISSAN recommends charging the Li-ion battery using the long life mode to help maximize the Li-ion battery useful life.

To prevent damage to the Li-ion battery do not expose a vehicle to ambient temperatures above 120 degrees F for over 24 hours.
If the outside temperature is −13 degrees F or less, the Li-ion battery may freeze and it cannot be charged or provide power to run the vehicle. Move the vehicle to a warm location.
 Passive battery cooling an engineering faux pas?

 Some pundits are questioning the wisdom of Nissan’s decision not to use an active battery cooling system.

Heat is an anticipated potential issue for a few dozen cars in very hot places. Certainly for 99% of the Leafs in the world, the passive system is perfectly adequate. Because there is no such thing as a free lunch, is it a good idea to saddle all cars with the weight, complexity, cost, and energy consumption penalties that come with an active cooling system (pumps, fans, tubes, hoses, radiators, coolant) just for a handful of cars (one or two percent of all Leafs sold in the world) in very hot places even when the owners signed a waiver?

It might be cheaper to buy back a few cars than stick all Leaf owners with that engineering trade off. The plug-in hybrid Volt recalled 8,000 vehicles for safety reasons. Recalls, retrofits and buybacks are common even with conventional cars.

 Nissan’s response

 At the time of my writing this article, Nissan had bought back two Leafs in the Arizona. They also took seven Leafs from owners complaining of reduced range back to their test facility for evaluation.
Nissan’s test results:
  • Nissan identified seven LEAF owners in the Phoenix area who had reported concerns with their vehicles. Nissan brought the cars to its Arizona test facility, removed the batteries for evaluation, measured capacity, and conducted voltage testing on individual battery cells.
  • The Nissan LEAFs inspected in Arizona are operating to specification and their battery capacity loss over time is consistent with their usage and operating environment. No battery defects were found.
  • A small number of Nissan LEAF owners in Arizona are experiencing a greater than average battery capacity loss due to their unique usage cycle, which includes operating mileages that are higher than average in a high-temperature environment over a short period of time.
  • In Arizona, we have approximately 450 LEAFs on the road. Based on actual vehicle data, we project the average vehicle in that market to have battery capacity of 76 percent after five years—or a few percentage points lower than the global estimate. Some vehicles in Arizona will be above this average, and some below. Factors that may account for this differential include extreme heat, high speed, high annual mileage and charging method and frequency of the Nissan LEAFs in the Phoenix market.
They may eventually have to offer consumers a hot climate cooling package for a few thousand extra, similar to the quick charge package I paid for (but have never used …that is now standard). Seattle residents would not need a cooling package.
Expectations and a Class Action Lawsuit

Williams, author of the independent Leaf owner study tells us:
I planned, and completed a promotional trip from Mexico to Canada, “BC2BC”, in June 2012 with my Nissan LEAF. However, my first car could not complete the trip as planned, due to its reduced range capability, so I leased my current LEAF, built in April 2012 and took delivery at the end of May. Now, with 7000 miles (11000 km), and only 3 months of actual use, this car could not complete the trip that it did in June. During the BC2BC trip, several times I arrived with 4%-5% capacity remaining, which means today, just a few months later, I would come up 4%-5% short. This car has never been exposed to the heat of Phoenix, although it was 104F (40C) in San Jose, California the one day that I was there.
He’s convinced that his new Leaf is also deficient even though it has never been exposed to “the heat of Phoenix.” What are the odds?

I strongly suspect that there’s nothing wrong with his car. I see the problem largely as a matter of expectations. Anyone who keeps careful track of car mileage (like my wife in her Prius) knows that it varies all over the place, usually for reasons unknown. Electric cars are no different in that respect. But, as common sense might suggest, because an electric car only has an 80 mile gas tank instead of a 300 mile one, and because you can’t quickly refill it, you should avoid the edges of its range envelope.

It just isn’t wise to ever purposely drive this generation of electric car to within 5% of its potential range estimate. In the sixteen months I’ve owned my Leaf I have done that exactly twice, and not on purpose (got lost). There are dozens of variables that you can’t control that impact range and with today’s slow rates of charge, you can’t count on filling up in a timely manner if you fall short.

Rule of thumb; if you can’t meet 95% of your annual driving needs within 75% of your car’s estimated range, don’t buy an electric car.

The entire concept of 120 and 240 volt public chargers (levels I and II respectively) seems like one of those “The Emperor has no clothes on” situations. It takes several hours to put a significant charge in a battery with these.  Why would anyone risk finding someone else already using that charger you were counting on (or finding that the charger is on the blink as is often the case), in order to get back home again?

I recently pulled in next to a Volt at a public charger at my local grocery store. I never bother to plug in because it isn’t worth a few cents of free electricity. I certainly don’t need that charge to get home. I asked the Volt owner why he bothered to plug in, which resulted in one of those awkward blank stares. The idea that maybe there was no good reason to plug in had not crossed his mind.

If I were offered more battery capacity for a fee, I’d decline. Because 99 percent of my driving missions are less than 50 miles, I already have more battery capacity than I need. I swap cars with a family member if I need to drive anywhere near the limit of my Leaf’s range. I have my car’s timer set to charge after 1:00 AM to 80% capacity to maximize battery life. I will on occasion charge it all the way up when I have a lot of driving to do the next day. If my daily commute took me to the edge of the Leaf’s range, I wouldn’t have bought it. Leaf owners who bought a Leaf needing to drive it to the edge of its range, quite simply, should have known better.

There are many people who bought Leafs who probably shouldn’t have and some of them are regretting it, as this recently filed class action lawsuit attests.

Having said all that, it will be interesting to see how Nissan now deals with what they already knew was coming–the fact that some owners would have faster than normal battery life degradation. Nissan may have underestimated how many people would experience early degradation because of where and how they are used, and just as importantly, how an American consumer would react to it.

2 comments:

  1. alain8:28 AM

    " I have my car’s timer set to charge after 1:00 AM to 80% capacity to maximize battery life. "

    What technical reason do you have to not charge it to 100% every time ?

    ReplyDelete
  2. Hi Alain,

    The owner's manual suggests it as a way of extending battery life if you don't need all of the mileage. In the winter I tend to charge it to 100% because the range is lower in cold weather.

    ReplyDelete

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