Cold vs Warm Weather in an Electric Vehicle
By: Electric Motoring W Dave Clark
Tags: Tesla, Electric Vehicles, Electric Car

Every electric vehicle (EV) suffers from range degradation in cold ambient conditions. Battery chemistry slows down when it gets cold resulting in less available energy for the car. If some of the battery’s energy is used to warm itself to a more efficient operating temperature, that too will reduce the state of charge and the car’s overall efficiency. The exact amount depends on how low the temperature is, and how much energy is needed to warm the batteries and the passenger cabin, which can be as much as 40% if you aren’t aware of the best practices to help deal with it.

However, EVs are not alone, gas-powered cars are also less efficient due to cold engine oil and increased idling when warming the car. This too will reduce fuel economy in freezing conditions by an average of 15–20%.

2018 Tesla Model 3 Average Efficiency by Temperature

Here is an example from my daily commute that shows the difference in efficiency from warm vs cold weather, using TeslaFi to log all of my Tesla Model 3 data. This is from June 24, 2020, and shows my morning commute to work at around 6 am. The average temp for the drive was 75 degrees (24c), the road conditions were dry and my average speed was 60 miles per hour. My efficiency over my 67-mile drive was nearly 89% and used 15.49kWh of battery. Comparing that to December 11, 2020, where the average temp for the same drive was 39 degrees (4c) with dry road conditions and the same average speed of 60 miles an hour. But, you will see the efficiency has dropped to 72% and consumed 20.44kWh of battery. This is about a 20% difference due to the temperature being 35 degrees (20c) cooler.

But, there are a few things EV drivers can do in winter to ensure you are getting the best possible efficiency:

Heating up your cabin and batteries BEFORE you unplug the car means you’ll have the best range possible because your car won’t need to use its own internal battery power to get up to temperature. Many electric vehicles have in-car settings that will ensure it reaches it set end-state charge percentage shortly before the desired departure time. This smart car technology is becoming more prevalent as EVs increase in number. This is also known as preconditioning. It is best practice to adjust nighttime scheduled charging to stop no more than 15–30 minutes before you typically leave each day is beneficial for better cold-weather efficiency.

Vehicle accessories such as heated steering wheels and seats, use less energy than heating the entire cabin. In addition, the warmth on your backside and fingers can minimize the amount of cabin heat needed to make you and your passengers feel comfortable. You can even bundle up with heavier coats and/or blankets if there are concerns when traveling to ensure you make it between charging stations.

Although it’ll make your car a little slower, driving in Eco mode will squeeze out a few extra miles. Tesla refers to this setting as “Chill” mode. Excessive acceleration and braking, and driving at high speeds all drain battery life.

By anticipating the need to brake and avoiding harsh braking, you will allow the regenerative braking system to work, recovering energy and storing it back into the battery. Keep in mind that in extreme cold, the regenerative braking system will be less effective because cold batteries can’t accept as much energy as warm batteries can.

Snow or ice on your vehicle adds extra weight and increases aerodynamic drag by changing your vehicle’s profile, and results in more energy being consumed. Since EVs don’t produce waste heat from the engine, snow on your hood may stay there if you don’t brush it off before you start your trip. There are also safety concerns while driving, as the snow and ice could fly off resulting in distraction and loss of visibility for you and the people behind you.

Keep the battery topped up by charging whenever and wherever you can just to ensure you are never too low. For the optimal health of the battery remember it is best to not charge above 90% or allow it to get below 20% regularly.

Most electric vehicle manufacturers acknowledge that the prevet use of electric resistance heating systems is less than efficient from a battery consumption perspective. These types of heating systems send electricity through a resistive heating element which helps warm up the cabin. This is similar to how heated seats or some electric space heaters operate.

To improve battery efficiency many manufacturers, like Tesla, are now equipping their cars with a heat pump. A heat pump transfers heat energy from a source of heat into a thermal reservoir. Basically, it works as an air conditioner, but in reverse. In ACs, the heat is trapped inside an area using a refrigerant and then thrown outside. In the case of a heat pump, it works the same way, but there is a reverse valve that moves the hot air back inside.

A heat pump can also produce 3kW of thermal energy for every 1kW of electric energy, thus resulting in an efficiency of 300-percent. Since the heat pump uses less energy in heating the cabin, better range is achieved.

Another challenge of the cold weather is when the roads become slick from snow or ice.

In a gas-powered car, you can select a lower gear to help reduce wheel spin in order to slow the vehicle instead of pressing on the brake pedal. In an EV there is no conventional gearbox to do this with, as you typically only have one gear, with the Porche Taycan being an exception.

The best practice to maximize traction for electric vehicle drivers is to utilize economy or low modes for regenerative braking instead of the standard-setting. This can help prevent the car from skidding because of a too aggressive brake setting that may cause traction issues.

EV’s also have a natural advantage with their low center of gravity created by battery packs located between the wheels and along the bottom of the frame of the car. This helps add to the overall driving stability in slick conditions.

Finally, the tread quality of your tires is critical for negotiating the roads in adverse weather conditions. A snow tire offers an extra deep tread that works well for driving on snow-covered roads by using a softer type of rubber to help provide better grip in slippery conditions. Most all-season tires offer a balance of tread and rubber composition and do work well for diving in dry, wet, and snow or ice conditions. However, if you live in a location that is frequently covered in snow throughout the winter, it is best to have winter tires. Also, be sure to monitor your tire inflation levels to get the best performance out of any tire and to prevent premature wear.