Electric Vehicle Performance Found to Slide in Winter

We've all heard the saying that oil and water don't mix, but now it turns out that oil-free cars, namely EVs, and snow don't mix that well either. There have been many reports over the years that hybrids, like the Prius, don't do very well in the snow. The claims are hotly challenged by loyal Prius owners with the debate ranging from "this car is really junk in the snow," to "I have no issues with it in the snow," to "all Prius owners need in winter is a good set of winter tires."

Green Car Reports describes the issue in terms of how the traction control system operates.

The traction control sometimes works against the owner in icy conditions. The purpose of the system is to prevent wheel slip and loss of traction, but because electric motors provide maximum torque from 0 rpm, on slippery roads the wheels spin easily--whereupon the traction control promptly brakes the spinning wheel. The result, is halting acceleration with beeping from the skid alert.

Refinements in more recent models have improved the situation.

But alongside the debate about handling is the added question of fuel economy. Hybrids don't do as well in winter for reasons ranging from modified winter gasoline formulations, to increased stationary warm-up time, to increased heater usage, to reduced battery performance in cold weather.

A recent report in MIT Technology Review claims that the situation gets even worse when moving from hybrids to all-electrics. Both types of vehicles share the issue of battery capacity being reduced in cold weather. “Cold temperatures primarily affect how quickly the energy can be taken out of the battery or put back in—that is, how much power it can deliver for acceleration, and how quickly it can be recharged,” according to the article. Some manufacturers, like Nissan, put an electric heater beside the battery to maintain its internal temperature, but that's not without its cost. This heater will also drain the battery, reducing the car's effective range.

Then of course, there is the cabin heater. In “normal” internal combustion vehicles, excess heat is pulled from the engine and passed through a heat exchanger, providing essentially free heat to the cabin. In the case of an EV, there is no engine, and therefore an electric heater is often used to warm the cabin, which further drains the battery. Of course the electric motors do generate a small amount of heat, and in the case of the Tesla, this heat is used, in winter, to warm the battery.

The reduced rate at which the vehicle can be recharged also comes into play when the regenerative braking is deployed. Regenerative braking uses energy extracted from the vehicle's momentum to recharge the battery. This contributes to the vehicle's overall efficiency, reducing energy consumption by as much as 10 to 25 percent. But since the battery cannot recharge as quickly when it's cold, the regenerative braking will be less effective in winter as well.

The MIT article describes several measures that are being pursued to address the situation. Researchers at Canada's Dalhousie University are investigating ways to make battery chemistry less sensitive to temperature. In particular, they are looking at ways to improve the conductivity of the electrolyte. Decreasing electrode particle size can also help, though it could raise safety issues due to their high reactivity.

As for the heater issue, some cars already use electric seat heaters, which warm the passenger rather than the cabin, but they still require additional power. The Department of Energy is funding thermal storage research. One system that is being developed for Ford behaves like a heat pump -- that can be run in reverse for cooling, using water as the refrigerant. The system can be recharged using heat, which could potentially be derived from solar, or from the electricity provided when the car is charging. This could eliminate most of the “parasitic” losses associated with heating and cooling the car. Ford hopes to have it on the market in its Focus EV within two years.

So, before we pour too much cold water on the growing enthusiasm, or snow on the EV parade, particularly among those who live up North, we need to ask how serious these cold weather drawbacks actually are.

To put this into perspective, it might be worth considering the fact that the most popular country for EVs in the world is Norway, where the average winter temperature is -1 °F. Of course, generous government incentives certainly help to improve the popularity of the vehicles. The cars are not only exempt from high purchase and value-added tax rates, but their drivers also pay no road and ferry tolls or parking fees. They also cost less to insure, can be charged up using free electricity from thousands of points and are allowed to utilize bus lanes -- a major boon in crowded cities. Local governments also subsidize the installation of charging stations in homes. The perks are estimated to be worth more than $8,200 per car, per year. Yes, that's a lot of money, but if the performance was really that bad, do you think that the Tesla Model S would be the nation's best-selling car in September and December, while the Nissan Leaf was Norway's third best-selling car for the year?

Time will tell, and of course, as the EPA says, your mileage will vary.

Image courtesy of Nissan

RP Siegel, PE, is an inventor, consultant and author. He co-wrote the eco-thriller Vapor Trails, the first in a series covering the human side of various sustainability issues including energy, food, and water in an exciting and entertaining format. Now available on Kindle.

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