Electric Cars, Winter Driving, Range Anxiety, & You

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There has been a lot written lately about driving electric cars in winter. Some say EV drivers are in a panic trying to figure out what they can turn off to keep their batteries from running out of power. Most don’t know how much electricity various accessories consume, so Wired went out and found the answers.

The Basics

To get started, Wired turned to the Electric Vehicle Database, which summarizes the efficiency of virtually every EV made according to how many watt-hours it needs to travel one kilometer. The lowest is the Lightyear One at 104 Wh. The highest is the Mercedes EQV Long Range at 295 Wh. The average is 202 Wh/km, but Wired opted to to use an average of 180 Wh/km, as that is approximately what several Polestar, Porsche, and BMW EV models require.

Next, the magazine turned to Pete Bishop, chief technology officer of Silver Power Systems, an electric systems design company that specializes in EV battery analytics. Bishop created a spreadsheet detailing the power usage of more than 50 components and systems found in electric cars, making it possible to calculate the approximate range reduction in kilometers per hour driven for each system.

Cabin Heating & Cooling

Bishop’s calculations take into account a circulation fan, heating and cooling systems, heated front and rear windows, heated mirrors, heated seats, and a heated steering wheel. Cabin heating and cooling systems use the most power in this category, requiring up to 3 kW and 4 kW, respectively, and decreasing range by between 8.3 km and 11.1 km per hour of use. Tesla’s Camp Mode, which extends the climate functions, uses about 10 to 15% of a Model 3’s battery in eight hours.

Heated seats are a far more efficient way to warm a car’s occupants than heating the entire passenger compartment. They consume 50 Wh each, which translates into a decrease in range of just 560 meters per hour if two are turned on.

Battery Heating & Cooling

After powering the motor(s) that move electric cars forward, heating and cooling the battery pack is one of the biggest drains on their batteries, says Ashley Fly, a lecturer in vehicle electrification at Loughborough University in the UK. “The energy required depends on a lot of external factors, like temperature and sunlight. Heating and cooling power consumption could range from a few hundred watts when the ambient temperature is close to optimal, 1-2 kW when the environment is very hot or cold, or even up to 5+ kW if the vehicle is starting off very cold and the battery needs to be warmed up by a resistive heater.”

Why is battery temperature so important? When you have a cold battery, specific chemical reactions limit performance. The batteries commonly used in electric cars today do not handle the high current loads associated with charging and discharging well at low temperatures. In some cases, a phenomenon known as lithium plating can occur. It is similar to corrosion and will cause aging and degradation of battery performance.

Fly stresses that the best course of action is to always preheat an electric car while it is plugged into the charger. That way, grid electricity is used to heat the battery and cabin, instead of sapping energy from the car itself. Once up to a set temperature, an EV can keep itself warm using far less energy than when starting from cold. “Heating a Tesla Model 3 Long Range battery pack from zero to 20 degrees Celsius without a heat pump needs around 2.4 kWh of energy, or 3.4 percent of its claimed usable energy,” Fly says.

Ancillary Systems

If it’s cold out and you are stuck in traffic, does that mean you should shut off the stereo system or stop playing Donkey Kong on your touchscreen? Maybe, but the effects will be modest. Video game systems use up to 350 watts of power while a sound system tops out at about 100 watts. That means listening to Bohemian Rhapsody will cut your range by about half a kilometer for ever hour of listening. Unplugging devices from your car’s USB ports won’t help much, either. Each one of them lowers range by about 9 meters per hour of use.

The ABS, brake servo, power steering motor, and suspension compressor of many modern cars do use a small amount of electricity. All of them combined account for about 100 Wh of power consumption, leading to a loss of range of about half a kilometer per hour.

Exterior lighting consumes very little power, thanks to modern LEDs. Bishop’s calculations estimate the entire exterior lighting system typically accounts for 48.80 Wh of energy. For a vehicle with an energy consumption of 180 Wh/km, this reduces range by 270 meters per hour of driving.

Aerodynamic Drag & Speed

Rather than not using the entertainment features of your spiffy new EV to eke out a little more range, the best thing a driver can do is reduce speed a little. “At highway speed, by far the biggest [energy] loss is aerodynamic drag,” says Ashley Fly. “For a Tesla Model 3, which has a drag coefficient of 0.23 and 2.22 m² frontal area, 9.5 kW of power is required to overcome aerodynamic drag. If we also consider a few hundred watts for tire friction, an estimated 90 percent combined efficiency of the inverter and motor, and another few hundred watts for the essential onboard computers, we need 11 kW to cruise at 70 mph.”

Here’s the interesting part. Because drag increases geometrically — doubling your speed quadruples the amount of drag — driving a little bit slower saves more energy than you might imagine. Lowering your cruise control from 70 mph to 68 mph — a reduction of 2.6% — will reduce energy consumption by 8.4%.

Other Factors That Effect Range

Packing your electric car with 5 adults and a weekend’s worth of stuff will lower your range. “The number of passengers and luggage will change the energy required to bring the vehicle up to speed,” says Fly. “But it is not reflected in our simple 70 mph cruise example, except for a small change in tire friction.”

Tires can have a large impact on range, however. Ian Coke, chief technical officer of Pirelli North America, tells Wired that not using the correct tire can lead to a significant change in efficiency and therefore range. Tire maker ENSO is developing a tire specifically for electric cars which the company says could increase the range of a Renault Zoe by 11.5%. By contrast, the wrong tires can reduce range by 10% or more. If you own an EV, you may be wise to use the same tires your car came with when it’s time for new sneakers.

The Takeaway

Wired says ambient temperature is the single biggest factor in determining the range of an electric car. The best way to deal with cold temperatures is to plug into a charger and preheat the battery and passenger compartment before driving. It also advises planning your route and your charging stops before setting off. (Tesla’s navigation software already performs that function.)

“The good news,” it says, “is that in all likelihood turning off the heated seats isn’t going to make any meaningful difference to range and it’s a much more charge-friendly way of keeping warm in your EV than blasting the heater.”

Electric car drivers do need to readjust their thinking somewhat. Maybe they need to slow down a little or do some planning for their trips. Is that too much to ask for a sustainable planet?