Cold Weather Idling in an EV | How Long Will You Stay ...

Recent reports described people stranded for up to 19 hours on a Virginia highway in freezing weather during a winter storm. To stay warm, people ran their cars&#; engines, heating their cabin and protecting against hypothermia. The fuel gauge moves ever so slowly toward &#;empty,&#; with occupants assured of a reasonable number of hours of comfort before the situation becomes unsafe. And, while it&#;s possible to run out of fuel in a situation like this, it&#;s rare that traffic jams last long enough for fuel endurance to be of grave concern.

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As the adoption of electric vehicles expands, the variety of climates and geographies where they are driven increases accordingly. Gone are the days of EVs being exclusive to sunny California! Many are aware of the quantifiable limitations of an EV&#;s range in cold weather (if not, check out our report on the truth about winter EV range loss). But what about the safety and endurance of an EV in hazardous conditions like a white-out? What exactly happens when an EV gets stuck in a winter storm &#; and can it keep its occupants safely warm for as long as an internal combustion engine vehicle? 

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Idling Misconceptions

There are numerous misconceptions abound about how long you can &#;survive&#; a winter storm in a stranded EV, with most time estimates being drastically underestimated. But not to worry, we have battery science on our side!

First, here are a few points of reference about gasoline cars as they idle in cold weather:

1. Fuel combustion generates carbon monoxide, which may be deadly if the car is stuck in a snowbank, avalanche, or other air-restricted environment. 
2. Idling endurance is determined largely by how much gas is in the tank; refueling is possible if you carry spare gas or someone offers a spare canister, but carrying gas during treacherous driving conditions poses its own set of risks.
3. Depending on the car, you may be able to eke out 30+ hours of idling before you run a tank from full to empty.
4. Gas cars heat their cabins with waste heat generated from the engine&#;s moving parts, which is an incredibly inefficient process if the car doesn't need to move. 
   

The first concern about idling in cold weather is moot in an EV. There are no tailpipe emissions to worry about; an electric car&#;s heater can be safely run regardless of fresh air ventilation. 

The second point is largely a commonality between gas and electric cars. The amount of time you can sit in a car with the heat on is determined by how much fuel is in your tank or by the battery&#;s state of charge. However, unlike in the gas car, it is not common or practical to recharge an EV while stranded. However, mobile chargers and emergency batteries will grow in popularity as EVs become more common. 

For the third point, given the enormous range of fuel efficiency and tank sizes on gas cars, it&#;s hard to nail down an exact figure for how long one can idle in cold weather. We&#;re using 30 hours as a baseline, assuming a full tank of gas in an average ICE vehicle.

Lastly, while a gas vehicle does generate its cabin heat through a very inefficient process, the same is true for most electric vehicles. In a stationary EV, there is little waste heat, so cabin heat is generated by heating up resistive elements, drive stators, or through heated seats or steering wheels. This heat also costs energy, and figuring out exactly how much it uses determines how long an EV can keep occupants warm.

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By the Numbers

Let&#;s assume we have an average EV as per stats: around 250 miles of range powered by a battery with around 70 kilowatt-hours of capacity. There are five variables that affect how long you can heat an EV while sitting, in rough order from most important to least important:

1. Battery size: Assuming the EV above, a driver has plenty of energy at their disposal. With full charge, you have more electricity at your disposal than an average American household uses in two days (60kWh).

2. Battery state of charge (percentage remaining): Considering the same EV, assume you get stranded with 50% charge remaining. This leaves you with 35kWh of battery remaining - still a lot of electricity!

3. Heater draw: This is where things get fun, as EVs run a huge gamut in heater efficiency. Earlier EVs &#; and some modern ones like the Rivian &#; rely on resistive heating. This means heating coils draw additional electricity from the battery with the sole purpose of heating cabin air. This costs a lot of energy. Other EVs &#; and largely newer ones &#; use a heat pump to transfer heat from motor stators to the cabin. Transferring existing heat in the vehicle costs a lot less energy than generating new heat, even when idle, but supplementary heat may still be needed. Depending on the car &#; and the size of its cabin &#; a heater may average between 1kW and 5kW of electrical draw, with more energy needed to heat the cabin from cold than to maintain a warm interior. Fun fact: Tesla patented a method to transfer heat from motors even when the motor hasn't been moving. 

4. Outside temperature: The colder the outside air, the more heat is transferred away from a vehicle. Thus, more energy is required to heat a vehicle&#;s cabin. EVs use the least amount of energy for heating and cooling in the 55-75 degree Fahrenheit range. A vehicle idling in zero degree weather will require more electricity to heat the cabin than a vehicle idling in freezing, 32 degree weather.

5. Accessory draw (onboard electronics, sound system, etc.): Perhaps one of the least quantifiable variables here is the amount of energy required to run onboard computers and other accessories in a car. This can consume anywhere from 500 watts to more than a kilowatt, depending on the car.

How does this all play out practically? Let&#;s take for example an EV with a resistive heater, like the Volkswagen e-Golf. It is a small car with a small battery, and a small cabin to heat. Because of its resistive heating elements, all heat generated for the cabin costs the same regardless of whether or not the vehicle is moving. Drivers report approximately 1.5-2.5 kW of heater draw in outside temperatures from 35 to 15 degrees Fahrenheit. With 50% charge on a 32kWh battery, that translates to between 6.5-10.5 hours of heat on a 15-35 degree day; double that on a full charge. 

But what about a modern EV with a bigger battery and better heating options, such as heated seats?

Enter the Tesla Model 3. For , Tesla switched from resistive heating to a heat pump. Drivers report greatly improved efficiency when it comes to heating their cars. One user slept in his Model 3 and ran metrics on it overnight in sub-freezing weather, finding the battery consumed 1.36kW per hour, on average. For a Tesla with a 80kWh battery, this means you could sit in your Tesla nice and toasty for almost 59 hours on a full charge, or about 29 hours on a half charge. 

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Real-world EV Idling Test

In fact, while writing this post, I decided to run a quick test on my own Model 3. Although I am in California where the temperatures aren't as cold as the Northeast, I blasted the heat in my parked car for 30 minutes. I set the temperature to "hi," which is the only temperature setting above 81 degrees, and boy - was it warm in there! After running for half an hour, my battery percentage declined from 88% to 85%, indicating that I used 3% charge over 30 minutes to make my car uncomfortably warm. At this rate, 6% an hour, I would still get at least 12 hours of heat, and honestly, no one would want it to be that warm for that long!

To conclude, modern EVs with average battery packs offer cold weather heating endurance equaling or exceeding that of average gasoline cars, with the added benefit of not needing to worry about carbon monoxide poisoning. For some, this ability may come as an added luxury. For example, drivers report using their EVs for camping, readily using the heat all night without compromising too much range for the next leg of their trip.

Do you have a story to tell about using your EV in cold weather situations? We&#;d love to hear! Get in contact with us.

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