To what degree does temperature impact EV range?

Published on May 25, 2020 in Electric Vehicles by Charlotte Argue


Understand how temperature affects how far your EV can go on a full battery.

With another winter behind us and a summer on the horizon, now is a great time to reflect on the impact temperature has on electric vehicle (EV) range. Following an in-depth analysis of EV data – drawn from 4,200 connected EVs and 5.2 million trips – we are better able to understand the relationship between temperature and how far your EV can go on a full battery.

Here we reveal the optimal operating temperature, how much range you might expect to lose in the dead of winter (or the peak of summer), and key takeaways on what you can do to extend the daily range of your EVs.

We are pleased to unveil our new Temperature Tool for EV Range that helps give vehicle operators confidence in knowing the expected range for a variety of EV makes and models at a given temperature.

See also: Podcast: EV myths and management with Charlotte Argue

The reality of EV range

When deciding on an EV to buy, range is often the first spec that’s considered. But as EV drivers know, the officially listed range (or how far a car can drive on a single charge) is best taken as a guideline.

While a vehicle’s published range is based on standardized testing performed on a dynamometer in a test facility, EVs, like gas cars, perform differently in real-life conditions depending on terrain, passenger load, speed, driver behavior or outdoor temperature. These factors all impact the vehicle’s efficiency and therefore its range.

A vehicle’s “fuel” efficiency (where fuel in the case of an EV is watt-hour, Wh) can be described in two ways:

  • Fuel economy is how far a vehicle can go on a given amount of fuel (think miles per gallon); for EVs this is km/Wh (or miles/Wh).
  • Fuel consumption is how much fuel a vehicle needs to drive a given distance (think liters per 100km); for EVs this is Wh/km (or Wh/mile).

While both are a measure of efficiency, as you can see, one is the inverse of the other. Fuel economy prioritizes distance, whereas consumption highlights the amount of fuel needed to travel a given distance. Multiplying the fuel economy by the battery size (generally measured in kilowatt-hours, kWh) will give you the vehicle’s range.

The more energy a vehicle’s battery pack can store, the longer its range, but this is impacted by the vehicle’s design (weight, shape, size, etc.) which sets the parameters of how efficient the vehicle can be. For a bus to go as far as a 60kWh sedan, it would need a much bigger battery. However, external conditions can negatively or positively impact the vehicle’s fuel economy on any given trip. This is not unique to electric cars. Slamming on the accelerator between traffic lights or driving on a frigid day means worse efficiency regardless of how you fuel your car.

See also: Overcoming EV range anxiety with electric vehicles

Winter weather woes

The most notorious EV range-killer is cold weather. Since EVs first came to market, a frequent knock against them was that they didn’t work well in winter. While many Canadian and Norwegian EV drivers beg to differ, it is true that temperature is a culprit when it comes to range.

Day-to-day range is affected by temperature primarily due to auxiliary heating and cooling. Energy from the battery not only powers the vehicle, but also the auxiliary systems, most notably:

  1. Heating and cooling the vehicle cabin
  2. Heating and cooling the battery

People often assume range loss in cold temperatures is due to reduced battery performance.

While lithium-ion batteries are more sluggish in extreme temperatures (cold temperatures impact their ability to store and release energy), this has far less impact on range than auxiliary load. Additionally, automakers have designed battery thermal management systems to keep batteries within an optimal temperature range, further minimizing loss in battery performance (but costing us auxiliary load).

We set out to fully understand the impact temperature has on range, and whether all EV models were impacted equally. To find out, Geotab looked at anonymized data from 5.2 million trips taken by 4,200 EVs representing 102 different make/model/year combinations, and analyzed average vehicle trip efficiency by temperature.

Our analysis showed that:

  1. Most EVs follow a similar temperature range curve, regardless of make or model.
  2. While both cold and hot temperatures impact range, colder climates have a larger impact.
  3. 21.5 C (70 F) is the vehicle trip efficiency sweet-spot.

Unveiling the temperature range curve

Temperature-range-curve

Chart 1: Temperature range curve

Our data shows that most EVs follow the same efficiency curve by temperature, irrespective of their make, model or year. Note: early analysis shows there may be slight variations with a few models, and we’ll be investigating these further for future posts.

The above graph shows the range an EV will get (on average) compared to its rated range at any given temperature. At optimal temperatures, EVs are performing better than their rated range, peaking at 115% at 21.5 C or 70 F. So, most EV owners are exceeding the rated range of the vehicle in peak temperature conditions. As you turn up or down the temperature, however, the loss of range is apparent. At -15 C (5 F), EVs drop to 54% of their rated range, meaning a car that is rated for 250 miles (402 km) will only get on average 135 miles (217 km).

Cold gets a bad rap, but it turns out heat is also culpable.

Interestingly, if you look closely you’ll notice the range drops slightly faster (the slope is steeper) as you increase temperature. The real-world impact manifests less in hot temperatures, however, as Earth’s climate doesn’t often hit temperatures beyond 50 C (122 F), so we don’t know (nor hopefully need to care) what happens to our range after that point.

The cost of being comfortable

It’s no coincidence that across the board the most efficient trips were taken on days where the average outdoor temperature was 21-22 C (70-71 F). Interesting fact: this happens to be the temperature at which we humans like to keep our homes.

If you get into your car and the temperature outside is below 20 C, you are more likely to turn on the heat; above 22 C and you’ll probably switch on the AC. Getting the cabin temperature to a comfy house-like condition draws energy from the battery that could have otherwise been used to move the car.

Like humans, batteries also like to be comfortable and function best at moderate temperatures (although they’re a bit more cold-friendly and tolerate a wider temperature range). An EV’s on-board thermal management system is designed to draw energy to warm or cool the vehicle’s battery, as needed, to ensure it operates in that ideal range. Therefore, the car is working to heat/cool both the occupants and the batteries in cold or hot conditions.

Side note: A lithium-ion battery’s optimal temperature (for providing maximum capacity or least resistance) is slightly higher than the optimal temperature for prolonging its service life, but the vehicle’s thermal management systems are designed with both in mind. Interestingly, hot temperatures are worse for battery longevity than cold temperatures; check out our handy battery degradation post for more on this).

Let’s see how temperature is likely to impact your favorite EV’s range with our interactive tool.

Find out the range of your EV!

To use the Temperature Tool for EV Range, first select a vehicle model, year and battery size and then slide the temperature bar to see the impact on range.

The number indicated in blue is the average range that can be expected at the selected temperature for that vehicle. The red and green lines indicate the worst and best range distributions (10th and 90th percentiles).


Tool notes:

Maximum range
This comes from the range at optimal temperature conditions for the top 10% performers (green), and is not the vehicle’s rated range; in most cases it is about 150% higher. (The average range (blue) at optimal temperature is about 115% higher than the rated range).

Battery degradation
Battery size isn’t exactly a constant, as battery capacity decreases over time. To account for battery capacity loss by age, we applied the average annual loss of 2.3% for older model years. This accordingly reduces the maximum range for older vehicles. Without degradation applied, the result is what the range would have been when the vehicle was new. With degradation applied, it provides an estimate of what range would be expected now given average degradation rates.

Note: in the real world, degradation rates differ across makes and models. Check out our battery degradation tool to get the full details.

Excluding plug-in hybrid electric vehicles (PHEVs)
We only included fully electric vehicles for this tool. Although batteries of PHEVs will also be impacted by temperature, the all-electric range for PHEVs is a more complex concept, given both fuel types (e.g., electric and gasoline) are often used simultaneously.

The best and the worst performers

Real-world-range-vs-rated-range

Chart 2: Range curve with 10th and 90th percentiles shows the distribution of trip efficiency one might expect at any given temperature.

Our range curve is based on the average efficiency of all trips in our databases taken at a given temperature. Because these trips were made in the real world, they were exposed to a wide variety of external factors that can impact vehicle efficiency such as terrain, speed, driver habits, trip length and start-conditions (e.g., if the trip started in a climate-controlled garage).

This analysis does not attempt to isolate the relative impact of each factor on range – this is something we look forward to digging into in future posts. It is reasonable to assume that the most efficient trips (or best performers) at any given temperature will be due to a combination of external factors that influence vehicle efficiency.

Overall, the best performers (those in the 90th percentile) obtained 32% more range than the average, and had twice the range as those in the worst 10th percentile. This suggests there is some leeway with how far you can expect to drive on a single charge, which may be partially within your control.

While for the most part all vehicle models followed this temperature range curve, we expect as battery management systems improve, we may see it “flatten” for some models. For example, Tesla has recently begun delivery of their crossover, the Model Y which uniquely comes with a heat pump, a very efficient climate control method. We won’t be surprised if its temperature range curve is more flat, and await next winter to see the results.

Tips to extend your EV range on hot and cold days

As outlined, the major offender for causing range loss in cold and hot temperatures is auxiliary load. Therefore, minimizing auxiliary load will help extend those miles:

Take advantage of the amenities that come with your car – heat or cool the human, not the air. Be sure to use those heated seats and steering wheel. Heating the cabin air can draw 3000-5000 watts, and is much less efficient than heating your seat and steering wheel (around 75 watts) which transfers heat to your body via conduction. Using these increasingly common features can keep you comfortable without resorting to the cabin heater. However, in very cold temperatures, minimizing cabin heating can only take you so far, and you will still lose energy from your battery thermal management system.

Pre-condition your vehicle. Just like you would before exercise, warm up before a long trip! If it’s hot, cool down. Turning on your car’s heaters while it’s still plugged in will minimize the auxiliary load by warming (or cooling) your car before it starts its trip. Take advantage of the guilt-free pre-conditioning that EVs allow. If the option is available to you, park in a temperature-controlled garage to get a similar effect.

Keep your vehicle plugged in on extreme cold or hot days. In addition to the benefits of preconditioning before your trip, automakers recommend vehicles are plugged in during very hot or very cold days when the vehicle is not in use. (Note: this is not the same as actively charging, which is better to avoid in extreme conditions, particularly heat). Having a vehicle plugged in allows the internal system to maintain battery temperature controls, prolonging the life of your battery in the long run.

Don’t let the cold confound you

You will lose range – don’t be worried, be informed. As battery sizes have increased with new EV models, range loss has become less of an issue. Larger capacity means little impact on most daily trip needs, and charging infrastructure continues to expand for that occasional road trip. Knowing your daily distance needs will ensure you choose the right vehicle for you or for your fleet.

Check out other tips for driving electric vehicles in the winter.

Additional info for fleets

Vehicle telematics can help ensure fleet operators choose the right vehicles for the job. Geotab offers their customers a free EV Suitability Assessment that identifies which existing fleet vehicles are the best candidates for replacement by EVs. The analysis assumes the worst-case temperature, so fleet managers can be confident that their EVs will be range-capable in winter chills, summer heat waves, and everything in between.


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Disclaimer

Geotab's blog posts are intended to provide information and encourage discussion on topics of interest to the telematics community at large. Geotab is not providing technical, professional or legal advice through these blog posts. While every effort has been made to ensure the information in this blog post is timely and accurate, errors and omissions may occur, and the information presented here may become out-of-date with the passage of time.

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