Real-World Nissan LEAF Fleet Data Reveals…

MAR 6 2015 BY MARK KANE 32

It's not necessarily the snow that diminishes range, but cold temps do.

Nissan LEAF

Tugce Yuksel and Jeremy Michalek form the Carnegie Mellon University recently published an article titled “Effects of Regional Temperature on Electric Vehicle Efficiency, Range, and Emissions in the United States.”

According to the summary on Green Car Congress, the effect of temperature is significant and varies depending on location. In general, energy consumption in Northern states will be higher.

The best environment for electric cars are moderateĀ temperatures.

When the temperatures are high, air conditioning (A/C) consumes part of the energy, thus lowering range and increasing Wh/mi.

In the cold, additional energy from the battery is needed for heat and the batteries themselves have lower efficiency, so the overall effect is even stronger.

Based on the real-world data for the fleet of Nissan LEAFs, the impact could be up to 40%. Results could be slightly different for other cars.

“Ambient temperature determines initial battery temperature and thermal management loading (if the vehicle is parked outside, the battery is not thermally preconditioned, and solar radiation is negligible) as well as battery temperature and thermal management load during use. Weather conditions, therefore, have a direct impact on battery efficiency. Ambient temperature also drives use of cabin air conditioning to either heat or cool the cabin at cold and hot days respectively. The net effect of these factors causes customers to report up to 40% decrease in their driving range on cold winter and/or hot summer days compared to the maximum range they achieve. The cold temperature effect is generally larger for two main reasons: electric cabin heating consumes more power compared to cooling, and batteries have poorer performance at low temperatures.”

“Air conditioning (A/C) use during hot days is an important factor affecting the fuel economy in all types of vehicles, since A/C is the largest auxiliary load in many vehicles. Cold temperatures, on the other hand, are particularly disadvantageous for BEVs, since vehicles with internal combustion engines can use engine waste heat for cabin heating, whereas in BEVs heat must be generated using limited onboard stored electrical energy. Reduced efficiency results in increased energy consumption and increased emissions from the electricity grid when BEVs charge. The net effect on emissions varies across the country due to source of electricity generation as well as the regional differences in marginal electricity grid mix.”

Nissan Leaf energy consumption per mile versus ambient temperature. The blue stars correspond to data points obtained by converting FleetCarma range data to energy consumption. The red curve is the polynomial fit. Credit: Yuksel and Michalek.

Nissan Leaf energy consumption per mile versus ambient temperature. The blue stars correspond to data points obtained by converting FleetCarma range data to energy consumption. The red curve is the polynomial fit. Credit: Yuksel and Michalek.

Authors assumed Nissan LEAF energy consumption versus ambient temperature using data collected by Canadian company FleetCarma (over 7,000 trips) reported as average driving range versus ambient temperature.

Then, they were able to estimate the regional effects of temperature on LEAF efficiency:

“To estimate the regional effects of temperature on electric vehicle efficiency, range and emissions, Yuksel and Michalek constructed models of vehicle energy consumption vs. temperature; US temporal and spatial temperature variation, vehicle driving and charging patterns; and US regional grid emission factors.

To establish the relationship between energy consumption and ambient temperature, the authors used publicly available data collected by Canadian company FleetCarma from Nissan Leaf users for more than 7,000 trips across North America, reported as average driving range versus ambient temperature. Thus, the CMU results are based on results experienced by real drivers in actual driving conditions instead of simulation models.

They used the Typical Meteorological Year (TMY) Database from the National Renewable Energy Laboratory (NREL) to obtain time- and location-dependent ambient temperature data, and the National Household Travel Survey (NHTS) 2009 dataset to obtain driving patterns. For grid emission factors, they used a recent analysis by Graff Zivin et al..”

Source: Green Car Congress

Categories: Nissan

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32 Comments on "Real-World Nissan LEAF Fleet Data Reveals…"

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Interesting study. It left out the effect of wet roads though. I found wet roads to be on the same level as running heat for reducing range in the LEAF.

It also looks like Down East Maine is either unpassable, or white hot on efficiency (not sure if that is good or bad).

I would agree. Back in the days when I had my hybrid Highlander, I would see mileage indications that showed the friction of the road surface was definitely in play. I always watched my mileage fall when I ventured into NY from PA. I got online and found out that NY had additives for its asphalt to aid in traction (due to the presumably colder and more slippery conditions?). So the safer road was definitely not as fuel efficient. The commentary on the additives was that when the road was WET (as discussed in this posting), the friction of road surface went up- so indeed the observations of wet roads reducing range is extremely plausible.

Disclosure: don’t have a Leaf

This looks understated, from what Leaf owners say. If the ~80 mile BEV becomes a ~60 mile BEV, in freeezing weather, than the 50 watt-hour difference in the heat map is closer to a 100 watt-hour difference.
(280Wh/(60/80range)=~373

Leaf owners, what say you?

“7,000 trips” isn’t descriptive enough. The guy taking this information, and applying it to shorter range use, could be in for a big surprise. Watt-hour use is a lot bigger over shorter trips, and a lot smaller over longer ones. That’s winter effects, in a nut shell. Bring the two ends together, and you are simply smoothing your results.

We had plenty of chances for cold weather BEV testing, last month. Purple=bragging rights:

https://cbsboston.files.wordpress.com/2015/02/feb.png?w=620&h=349&crop=1
“Departure from average temperatures in February 2015. Courtesy: Weatherbell.com”

This chart is talking about efficiency not range. Being in Houston, I can’t contribute much to the cold weather data. The once in awhile 30s temps would draw somewhere between 1.5 kW and 2.0 kW to maintain 68 degree temps inside the car on a 35 mile highway commute. I usually preheated on those days, so didn’t get hit to hard by that initial 6 kW warm up phase.

I would say that being in a hot climate with a 2011 LEAF, the biggest effect on range was Year 1 vs. Year 3.

Range is a mark of how efficient a car is, with its kwh. No?

Only if capacity is a fixed number, which is not a given with the 1st gen LEAF. Let’s hope the lizard pack improved that.

The answer to your question is that these numbers are year-round averages. It’s not freezing cold in the upper midwest year-round.

Actually, the plot looks just about right to my eyes.

Leaf owner say…battery not hold as much Kwh in cold weather. Difference in range not all due to watts per mile usage. My battery at -10F can lose almost 50% capacity.

You think the study would at least mention that range is also lost in colder climates for an ICE.

Future battery chemistry “may” reduce the loss of range in extreme weather conditions for the EV. As for the ICE, you will always suffer these losses unless you eliminate some of those moving parts and rewrite the second law of thermodynamics…

That’s because no one cares about the range loss on a car with a 300-mile gas tank. Similarly, once BEVs have comparable range, no one will care about BEV range any more.

except that the 300 bev will lose LESS than the ice one because now, 65% of the loss at 0F is due to the heating of the cabin. Since this is a constant factor, it will melt like snow under the sun with the increasing range of batteries.

No need to rewrite no law , even though science is always rewriting itself.
Just see how 65% of the loss with a Leaf will shrink to almost nothing in upcoming 300 – 500 – and more – batteries.

On the other hand the average ICE car will always loose about 20% efficiency in cold weather.

http://www.fleetcarma.com/cold-weather-fuel-efficiency/

I have a problem with taking a Nissan Leaf’s example and generalizing to all EVs. It has early generation batteries that are not liquid thermal managed. While the general shape of the graph is correct for all EVs, the amplitude at each end is different. The impact on the Leaf and other EVs that do not have liquid thermal management is far higher.

Data from what resulted from other users is somewhat useful, but I don’t like things like “40%”. 40% of what? Just give me kWh. In fact, I’d rather skip all the data collection from drivers and just tell me the engineering data on the car. How many kW does it use to heat the cabin, to heat the battery, to move the car? How much usable battery is there in ideal conditions, cold conditions, hot conditions. This is all data Nissan should have. There’s so many variables that could have effected the data they got from the real-world driving, I’d rather just have the engineering specs.

I have a 2012 Nissan leaf, and I find this study to be fairly accurate. I have gotten as little as 45 miles on a full charge in the winter and I’ve gotten as much as 75 miles per charge in the summer. I live in Baltimore Maryland.

It is usually in the Spring or Fall I get the best mileage. In the Summer when the air conditioning is not running I can get good mileage per charge also.

test

One map combining extreme winter temperature and elevation data only tells of ‘energy use’ in Dec-Feb timeframe.

What do the maps for Spring/Fall and Summer look like?

A better approach would be separate maps for:
1. elevation
2. seasons: Summer, Spring/Fall, & Winter
3. snow/ice coverage
4. rain: for each season
5. wind
6. road maintenance condition

Ideally the map would be online and interactive, allowing to (un)check season, weather and road conditions. šŸ˜‰

That would be a cool feature of Google Maps. You could put in your destination, and it would look at the weather & topography, and estimate kWhs required. If you put in a future date, it would take the data for the average temp that day, or look at the forecast data.

I sketched out a system to do exactly that as an overlay on Google Maps. Just looked at the dev time required and decided it wouldn’t be worth it.

Now if Tesla (or any other OEM) would open up their infotainment for 3rd party development, I would put some work into it.

If you look at Google maps bicycle tab, terrain is forcast.
Maybe crowd funding to develop app?

So if it is too hot or too cold, you don’t get good EV performance. California is lucky in that most the areas where people live, it is an ideal place for EVs. Temperate climate and yet great sun for solar PV to charge them up.

The SouthEast also looks like a great place for EVs. But sadly there are a lot of people ideologically opposed to such new-fangled green energy stuff around there.

question – did the study assume electric resistance heat or heat pump heat? It wouldn’t change the AC power draw, but heating power draw would be cut to 1/3 of resistance heat down to about 25 deg. F.

I’m surprised about how fast they assumed the power use rose with outside air temperature when in cooling mode. My experience with my Volt has been that electric heating at 40 deg. F kills AER a lot more than AC at 105 deg. F. My range doesn’t seem to change that much during the hot Redding CA summers from spring-fall AER. Winters are AER killers, though, even with the relatively mild winters we get here.

Also have to consider on days with below 0 temperatures a car thats been plugged in all night will still start. While an ICE may not.

I drive my leaf above that map. It goes down to -50 c with wind chill Jan/Feb and winter runs October to end March. I leave my car outside and preheat before driving. Just had my first year inspection on my 2014 leaf and it was 5 stars 82 miles on the service sheet with over 19000km on th Odo. Great car, winter range is easily half of summer driving. This discussion won’t mean much when nissan anounces the new battery capacity however if they partition the battery readout to allow say 5 – 8 kWh as dedicated for environmental heat or air conditioning in a 48 kWh pack it would help with winter range anxiety and you would really feel impressed when you don’t need to use it and your range increases. Just saying…your going to loose a little with the battery heater and winter tires / snowy roads. Only other point.. How about heated floor mats for a Canadian leaf edition. cheers

A lot of the comments above are confusing range with efficiency. The range on our LEAFs has dropped over time as the total battery capacity degrades. Efficiency, in terms of miles/kWh, is still the same.

We live in a very snowy winter climate, with pre-2013 LEAFs without the heat pump. In the summer they tend to average 4.0-4.5 miles/kWh. It’s never too hot here and the non-heat pump A/C is very efficient, so there is negligible A/C “tax” on the battery. In the winter the LEAF with snow tires averages 2.7-2.9 miles/kWh and the one with all season tires averages about 3.1-3.5 miles/kWh. Of course, the snow tire LEAF gets drive more often in heavy snow conditions, which is more taxing on the battery, so the difference is not all about the higher resistance tires.

So, the numbers in this study match our own experiences. Which makes sense, given that it is based on real-life data.

The “Real-World” part of the article tittle and content omits a few important facts related to the data used for this study.

1. Data is from Canadian 2011/2012 LEAFs as data published in Feb 2013, over a month before 2013 was released in US (6 months before 2013 was available in Canada. This mean data only consists of LEAFs with inefficient resistive heater.
http://insideevs.com/fleetcarma-explores-the-impact-of-temperature-on-range-of-nissan-leaf/
2. Canadian data was mapped onto US map. (the context of the data is no longer “real”, just an interpretive study ā€¦ next study map, Canadian sports overlaid on a US map)
3. US climatological temperature averages from the last 120 years is the base map. Compared to 2010-215 climatological data, totally different (not to mention the east-west extremes of 2015).
3. The study makes further poor assumptions in that average regional power plant CO2 emmissions relate directly to LEAF emissions.

While the topic is a good one, the data choices and data assumptions made mean the results are questionable. If anything, the study results represent a worst case, that can be improved upon.

Nice to see someone finally acknowledging this. I live in Wisconsin and I didn’t need to read a report to learn that my mileage is cut in half in winter. The manual states that the car will not work at -13 F. Well we got close (-10) but it did work. Looking forward to warmer temperatures. If there is any good reason for 200 mile range EV it’s the issue of reduced mileage in winter. I would really appreciate it if Nissan was more upfront about this. Nice to claim an 85 mile range but one that is dependent on temperature should be in a legal disclaimer.

I drove a Leaf in Wisconsin for the last 2 years and I usually average 4-4.5 miles per kWh. On really cold winter days it dips to 3.5mpkWh and on mild days it tops out at 5mpkWh.

The data looks sqewed towards Winter energy consumption. We don’t have mountains and use less air condidtioning in the summer than say Florida.

There are no Dealers selling the Leaf in Northern Wisconsin or Upper Michigan so it looks to me like they extrapolated a lot of the data for less populated areas.

I think the heat map colors might be a little unfortunate – if you look at 290(green) vs 320(very red) that is only a 30Wh per mile difference which is just a 10% difference. If you can live with 10% less range in the winter it doesn’t seem like much of a problem.