If you own an electric car and live in a cold winter climate, you will be aware of how the cold weather impacts your range. Some users report that the range of a Tesla Model 3 can decrease by almost 50% when temperatures plummeted down to -8 Celsius.
This does not just take place in permanently cold climates with an even more frigid winter like northern Sweden or northern Canada. It takes place to some extent in the majority of western civilisations, including the USA and the UK.
Many say that Tesla’s in specific were just designed and tested in California climates, where the weather is mild all year round, but it seems as though all electric cars seem to have this problem to some extent.
Let’s explore why this takes place, as well as some measures that you can take to improve the efficiency of your car in cold weather. That way, you should be able to travel further than just to work and back without worrying about range.
In short, winter temperatures impact both internal combustion engine (ICE) cars and electric cars. However, due to the inefficiencies of ICE cars, the wasted engine heat goes on to heat the cabin. In an electric car, the chemical reactions in the battery slow down in the winter, and the car works to maintain the temperature of the battery. There are many ways to increase the efficiency of your electric car in the winter, including preconditioning the battery, scraping excess snow off, and using seat heaters rather than cabin heaters.
Why does Electric Car Range Decrease in Colder Climates?
To be clear, cold weather does not just impact the range of electric cars, it will impact the range of any car. However, internal combustion engines are quite inefficient (usually up to about 40%), this means that they produce lots of excess heat which can be funnelled into the cabin. Furthermore, they have more range to start with, meaning the effects of cold weather are less noticeable.
It’s also worth noting that many internal combustion engine (ICE) cars cannot start when the temperatures drop significantly, whereas electric cars can.
Currently, Tesla uses the excess heat created from the motors of the vehicle to heat the battery or the cabin, though this requires the the car to be moving.
There are a number of factors leading to a decrease in electric vehicle efficiency in colder climates. Let’s start with the battery packs.
Battery Packs in Cold Weather
Lithium Ion Batteries (LIBs) have a comfortable operating temperature which usually lies between 15 and 35 Celsius. Once the temperature escapes these boundaries, LIBs can have reduced performance, as well as suffering from other unwanted effects like thermal runaway (where an increase in heat leads to an increase in heat from the battery, which leads to another increase in heat, and so on…).
The effects on batteries which are operating outside of their comfortable temperature zone can be split into two categories, low temperature effects and high temperature effects. We’ll focus on the low temperature effects.
At low temperatures the chemical reaction activity within the cell is slowed, as well as the charge transfer velocity decreasing. The resultant effect of these two is a decrease in ionic conductivity. Essentially, the chemical reactions in the battery happen slower so the battery cannot produce peaks of instant power so easily, and more energy is required to get the reactions started.
Low temperatures also mean that the batteries, if not properly managed, are unable to charge. Fortunately, electric cars have battery management systems which keep the battery temperature at a safe level to mitigate this. However, these systems use more power to heat in the winter, and to cool in the summer.
Many automakers have calculators on their websites which provide data on how the range of the vehicle will be impacted by different temperatures. Below is a graph with data that I compiled from Nissan’s website. I set the speed to 65 mph, turned eco mode on, and kept the heater or air conditioning on, whichever it thought was appropriate for the temperature.
As you can see, at -20 Celsius, the range of the Leaf is almost half of that at 20 Celsius. The range of the vehicle also starts to drop off as temperature increases past 20 Celsius.
As air cools down, it becomes more dense. Denser air means that the car will encounter more air particles at a given speed. Transferring more energy away to the kinetic stores of the air molecules, or wasted heat generated in the collisions.
At high speeds, air resistance is generally considered to be proportional to the square of velocity. So, if the velocity of a car goes from v to 2v, air resistance will go from f to 4f, quadrupling.
This is why electric car manufacturers try to make their vehicles so aerodynamic. If they had a similar design to some ICE cars, then their range would be significantly lower, just down to the energy density of the fuel type.
Likewise, if ICE cars were designed more efficiently, they would burn less fuel and the owners would save more money.
Keeping the Cabin Warm
As I previously mentioned, in an ICE car, much of the wasted energy from the inefficient engine is used to heat the cabin of the vehicle. However, batteries don’t quite work like that.
Tesla funnels the wasted heat from the motors into either the battery or the cabin, however that requires the car to be moving.
To heat the cabin otherwise, Tesla, as well as most other EV manufacturers opt with resistive heating systems. Put simply, electricity is passed through a resistor, which heats up, thus warming the cabin. This is also used in ICE cars to heat their cabins.
Resistive heating is 100% efficient, that is every joule of energy that is put in comes out as heat. How could we possibly get a more efficient heating system?
That’s where heat pumps come in. They’ve been an option on the Nissan Leaf for a while now, and Tesla is just starting to use them in their new Model Y. Impressively, heat pumps can be up to 300% efficient, meaning everything joule of energy put in returns 3 joules of heat. How do they do this?
Despite how cold the air outside the car may seem, it still has plenty of heat in it. In fact, it always has heat in unless it is at absolute zero, the lowest possible thermal energy state.
A heat pump works to transfer the heat from the air outside and put it into the air inside. This essentially makes the air outside colder and the air inside warmer. Of course, it requires energy to run, but is 3x more efficient than resistive heating.
Once EVs start adopting heat pumps in mass quantities, they will be much more efficient in winter.
How can you increase the Efficiency of your Electric Car in Winter?
1. Keep your car plugged in when not in use
As I stated earlier, the battery management system in electric cars is designed to keep the temperature of the battery at an optimal temperature for storage. Hence, it keeps it warm in winter.
If you leave your electric car without plugging it into the wall, the battery will drain and your range will be decreased. You might as well use as much mains electricity as you can before taking your car out on the road.
Tesla states that you can leave your car plugged in without fear of it overcharging. The onboard computer knows when your car is charged and doesn’t allow this to happen. The same applies for many other EV manufacturers.
2. Precondition the Cabin and Battery
Heating any vehicle, especially in climates where the temperature frequently drops well below zero, uses significant amounts of energy. Cleverly, Tesla allows you to preheat your cars cabin from the driver app so when you arrive to take your car out, it’s nice and toasty inside.
Make sure to do this when your car is plugged in to avoid losing range, heating the car requires quite a lot of energy as the heaters can draw a couple of kW.
This can also be done in the summer to cool down the car before taking it out. Once it has been set to the right temperature, maintaining that temperature uses less energy than starting from scratch.
If your car gives you an option to fully precondition your battery ready for use, use that feature whilst the car is still plugged in.
3. Try to Use Heated Seats rather than the Cabin Heater
Many cars (including Tesla’s) come standard with front (and sometimes rear) heated seats. Although these use resistive heating too, they are much more efficient than heating the whole cabin. This is because they are just heating a localised area, that being your body.
The excess heat that is not used to heat your body is then used to heat the cabin. You could combine this trick with preheating the cabin so the cabin remains reasonably warm whilst the occupants of the car are heated with the seat.
In addition to seat warmers, you could also enable your steering wheel heater.
4. Clear the Snow off your Car
If you store your car outside overnight in a snowstorm, make sure to clear the snow off the car in the morning. Not only does it save weight, reducing friction, making the car more efficient, but it also reduces the strain on the car’s heating system.
When snow piles up on top of the car, it takes heat away from the cabin faster than air typically does. Furthermore, it blocks the sunlight from heating the cabin.
In fact, if you aim to precondition your car in the morning, you should clear the snow off first. You’ll see the energy savings on your energy bill.
5. Reduce your Speed and Calm your Driving Style
Keeping your speed under 65mph can go a long way to increasing the range of your electric car. As I stated earlier, air resistance increases in proportion to the square of your velocity.
Keeping your speed at 40mph on slow roads rather than 80mph on the highway will dramatically increase your range.
Furthermore, aggressive acceleration goes a long way to draining your battery. If your car has an eco-mode, use it. Your car may feel a little more sluggish than usual, but it will save you precious miles.
Where possible, use regenerative braking. Not only does this feed more energy to your battery, but it also uses the motors to slow you down. In Tesla’s case, the extra heat generated here will go back into the cabin.