Thermal Effects on Energy Consumption and Range

Looking at energy consumption, right off the bat, we can see that cold weather has a significant impact on EC - nearly double in urban driving, 40% more in the highway cycle, and 25% on the US06. It’s worth noting here: the Leaf has an 80 kW electric motor, a 24 kWh battery, and a 5 kW resistive heating element.

When broken down further, into a base load case (driving cycle EC at 72F), the amount of extra energy needed to drive the cycle at 20F (listed as EC cold), and then the heater load required to maintain a cabin temperature of 72F, we can see that a significant portion of the additional energy consumption is down to the heater. As with most gasoline cars, driving in sub-freezing temperatures only makes the car about 10% less efficient before heater loads are considered. The mechanically-driven heating elements in conventional vehicles add another 5% or so in terms of mechanical efficiency loss, while obviously the electric heater in the EV is far more costly from an energy consumption standpoint even though it doesn’t increase mechanical losses at all.

(Note: graphs were created by ANL using the raw 10Hz data instead of the filtered 1Hz data available on D3. Available as part of APRF's AVTA Nissan Leaf testing analysis and summary, as presented by Dr. Henning Lohse-Busch. Full presentation available here.)

And while energy consumption is a big deal, range is the be-all, end-all concern for most consumers. With the heater on, that’s a decrease in range by anywhere from 20-50% depending on your drive cycle. That’s a lot. And you can just look at the APRF’s full charge tests at 20F and 72F to see what I mean: 

Think about that - this is a car that, at launch, Nissan claimed had a 100 mile range. My own real-world driving suggests 80-85 a decent estimate. EPA says that number is closer to 73. The APRF’s instrumented testing backs that up (74.1 mile range at 72F), but the same instrumented testing, in 20F weather? 46 miles. That’s it. 

Introduction and Technology Background How this Impacts the Model S & Final Thoughts
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  • relztes - Monday, February 18, 2013 - link

    How can it possibly be unfair to test the US model in the US? If they took it to Nunavut for a test at -30 F, I'd see your point, but there is nothing extreme about 20 F in at least half of the US. Reply
  • Kerdal - Monday, February 18, 2013 - link

    Trust me, they don't have to go as far as Nunavut to test at -30F (-35°C), it was -45°C (-50F) a few days ago over here (QC) haha

    Most cars wouldn't start, I wonder what kind of range an EV would get at those temperatures but that's probably why we don't have any over here.
    Reply
  • Alexvrb - Monday, February 18, 2013 - link

    Bingo. The Nissan Leaf is a POS. It sucks horribly in cold weather (anything below freezing point of water, apparentely). It also uses air cooling for the battery pack, so it suffers quite horribly in hot climates, especially long-term. The Leaf is an all-compromise car. The Model S is leaps and bounds better, though it's got a price tag to show it.

    The Volt and even more common hybrid designs are a better option at this point, if you don't have the cash for a Tesla Model S.
    Reply
  • Alexvrb - Monday, February 18, 2013 - link

    Err, and by better option I mean if you are only considering EVs, PHEVs, etc. There are lots of good options depending on how you're driving and what your needs are. For example small diesels or specially tuned small turbo gas motors for highway commutes. Reply
  • IKeelU - Monday, February 18, 2013 - link

    Thanks for this article. It's nice to hear an educated response to the controversy. Reply
  • ricardoduarte - Monday, February 18, 2013 - link

    Without having much to do with post, i have a few questions since the Vivek is electric car driver.
    I admit that i know little about EV's and I am a petrolhead, which loves everything about petrol cars, however i always wondered what would be like to compare the fuel expense with a petrol car (I am in uk and both are quite expensive at the moment).

    I wonder if you have any other cars (for longer journeys), or this is the household main car?
    - How many times do you charge your car per day?
    - Have u noticed any big advantage financially to the use of an electric car?
    - Do you avoid random driving because of fear of running out of charge, or that you might actually need the car later?

    Sorry for the questions, but i always wondered if drivers of electrical car feel restricted because of the battery recharge time, and if the financial advantages are big enough to compensate any anxiety that the presence of batteries might give.
    Reply
  • happycamperjack - Monday, February 18, 2013 - link

    The fundamental problem of pure EV car is simple, Limited Freedom. Since the introduction of car, it has been the symbol of freedom throughout ages. How many hollywood films have you watched that have cars driving into the sunset? Sure current EV might last you 200 miles or 300 miles and that's plenty for everyone, but that anxiety of running out of juice is always gonna be in the back of your mind. People don't want to wait to charge their car, that directly limited their freedom of movement. If they don't mind that, they probably wouldn't mind public transportation either. So what you end up is a product that's perfect for engineers who can plan ahead and optimize their schedule around it. For anyone else it's a product that's unproven, anxiety inducer, pricey, and just a chore to deal with.

    Plug in hybrids make a lot more sense. For city driving, the 30+ miles range is enough for most of the people during work days. For vacation or weekend getaways, that's where gasoline comes in. Knowing that you would not have to plan all the "charging" stops well ahead of time, makes life so much easier. Volt is a good start, but it's pretty ugly and feels cheap inside out when you compared to cars in the same price range, that's why it's not selling well. Fisker's reliability problems from multi sourcing parts(reminds me of F35) is scaring away potential buyers. The market is really waiting for a winning design. I really hope Tesla would consider adding at least a small gasoline motor to keep the electric motor running at perhaps 50% capacity when it's out of juice.
    Reply
  • IKeelU - Monday, February 18, 2013 - link

    The points you make about EVs could become less relevant over time. Namely:
    - Recharging stations will become more common, making the more limited range of an EV less of an issue, and eventually (hopefully) a non-issue. After all, limited gas stations didn't hamper the adoption of gas-fueled cars a century ago.
    - Recharging times will shorten as battery tech improves.
    - Battery charges will increase as battery tech improves.

    I agree about the hybrids. I rented a For C-Max for a week and mostly did city driving (except for the 30-mile drive to and from the airport), and the top-off before returning to the airport cost me about 8 bucks. I'm pretty much sold on renting hybrids from now on.
    Reply
  • happycamperjack - Monday, February 18, 2013 - link

    Thanks for the comment. As for now, there are more than 10x the gas stations than charging stations in US, and a lot of them are in california. Not to mention it takes 10 times longer (in charging stations, even longer without it) to charge a EV than a gasoline car. And if everyone's doing it, it's gonna overload the grid and force more "dirty" electricity production to keep it up. I think all this add up to an inconvenient solution for most of the population in US. Like I said, for more well organized people like engineers, this would not be as much of a problem. But why have a problem when you can have none? Our electric technology and the grid is not quite there yet.

    This situation reminds me a lot of Tablet PC. The concept was good, but technology(capacitive screen and battery) wasn't there to make it good enough to sell to the mass.
    Reply
  • melgross - Monday, February 18, 2013 - link

    Try 1,000 to 1, or more. But the point is that so far, these EVs, are very range limited, and people expect a $100,000 car to do better. So while these road tests aren't exactly fair, or done well, they do illustrate the point that they come nowhere near a gas fueled vehicle Reply

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