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:
- Fuel combustion generates carbon monoxide, which may be deadly if the car is stuck in a snowbank, avalanche, or other air-restricted environment.
- 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.
- Depending on the car, you may be able to eke out 30+ hours of idling before you run a tank from full to empty.
- 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:
- 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).
- 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!
- 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.
- 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.
- 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!
Starting the experiment at 88% battery capacity
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.
Electric cars have ushered in a new era of innovation, with brands regularly updating vehicles to feature all kinds of modern technology.
That includes lots of technology to improve the range of modern EVs, such as regenerative braking. That takes the kinetic energy that would be lost by a car slowing down and feed it back into the battery.
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One of the most notable bits of new technology helping to boost the range of an EV &#; particularly in winter &#; is a heat pump. Now an optional extra on many EVs, heat pumps retain heat from the batteries and use it to increase the range of an EV.
Here we explain how heat pumps work, how they benefit your electric car and how much they cost as an optional extra.
How does a heat pump work?
Motors, whether electric or combustion engine, produce heat when they're used. That's effectively wasted energy, so in an attempt to make the most of it combustion engine cars use a small amount of it to help run a car's heating and ventilation.
By comparison, EVs are just too efficient for their own good: while the motors and batteries do produce excess heat that can harm the range, there isn't enough to be used for the ventilation system. So EV drivers either go cold, or have to draw extra power from the battery to operate a fan heater. Not ideal.
That's where a heat pump comes in. It&#;s effectively a refrigerator but in reverse: its function is the opposite of the one found in your kitchen.
A household fridge contains refrigerant gas which becomes hot when compressed. Once compressed the gas is transported around a number of tubes to the condenser.
The condenser then radiates the heat out, thus cooling the refrigerant gas which then travels into a grid called the evaporator. Because the evaporator is larger than the condenser, the pressure drops and the liquid refrigerant is evaporated. The temperature then drops and the fridge is cooled.
An EV heat pump draws air in from outside, compresses it, then uses the heat from the condenser to raise the temperature in either the battery or the car's interior.
Reversible heat pumps can also warm, as well as cool, the battery. If cooling, any excess heat from the battery can be sent to the inside via the cabin heater.
Does it increase the range of an EV?
Adding a heat pump has many benefits, but most importantly is its ability to increase the range of your electric car, particularly during the winter months.
When an electric car is switched on in winter months, it takes longer for the battery to warm up which reduces efficiency. The lithium-ion batteries in an EV rely on chemical reactions to store and create electricity. Cold weather slows these reactions down resulting in the drop in performance and range.
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It is estimated that EVs range drops by around 10 per cent in winter, even before you account for using extra energy for cabin heating. Heat pumps can really help reduce that drop-off.
During our winter real-world range test &#; conducted in partnership with sister brand What Car? &#; the electric cars fitted with a heat pump fell short of their official range by an average of 25.4 per cent, while those without suffered a 33.6 per cent deficit.
Cars with heat pumps also proved more efficient, averaging 3.2 miles/kWh, compared with 2.9 miles/kWh for ones without.
In addition, heat pumps are often programmed to be remotely controlled by your smartphone, allowing EV owners to heat their car before they set off on a journey. And if you&#;re plugged into the mains electricity you won&#;t drain the battery either.
Do heat pumps come as standard?
Heat pumps becoming more popular, and some brand such as Tesla, Porsche and BMW offer EVs with such devices as standard. Some manufacturers offer a heat pump as an optional extra, and frustratingly they can be a pricey addition.
The Hyundai Ioniq 5, for example, offers a heat pump as an optional extra for £995. Skoda asks for £ for a heat pump for the Enyaq iV. It is worth noting that heat pumps are often included in the kit list for higher trim levels of many models.
Even if they are an expensive option, a heat pump is worth considering: they have extensive benefits, from improving efficiency, to increasing the range of your EV.
Whether you&#;re thinking of making the switch to an EV or about to order your new set of zero-emission wheels, we&#;d recommend adding a heat pump for peace of mind.
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