A Tesla Model S tested under varying winter conditions was found to use approximately 40-percent more energy according to a Tesla owner’s written report.
The information documented by Rob M., an engineer, is posted at Teslarati.com. Even though this website is geared towards Tesla owners and enthusiasts, reviews and articles appear balanced without expressing obvious bias in favor of the brand.
The author outlined his protocol as follows:
I recorded my Tesla’s rated range at the beginning of the day and once again at the end of the day. I logged the amount of kWhs consumed during my daily journey, the actual miles driven and the average temperature for that day. All of this was plotted into a data grid so that I can analyze the effects winter conditions would have on my battery range.
Results depended on temperature and level of snowy and icy conditions. Temperatures ranged from 8 degrees F to 35 degrees, and percentage of actual energy used versus rated ranged from 21-percent more used to an “outlier ” of 57 percent, with 40-percent being a rough average.
Rob methodically charted the number of miles driven and kilowatt-hours used, comparing the data with the rated miles used.
Before testing, Rob prepared for the New England winter by mounting Nokian Hakkapeliitta R2 winter tires on 19-inch aftermarket TST wheels. His Model S features the larger 85-kwh battery, which has EPA-rated range of 265 miles.
Rob pulled the 57-percent “outlier” from one data set, though, to more accurately calculate the average difference in expected versus actual power used.
The report that a Model S loses range in subzero temperatures is not a new discovery. What is significant with this information, however, is how high this range reduction was found to be in real world conditions. Previously, most estimates indicated that freezing weather will only lower an electric vehicle’s range by 25-percent.
For years, automakers have dealt with the impact from cold weather on lithium-ion batteries. Operating the heater and defroster, running winter tires with a higher rolling resistance and tire slippage on slick roads amplify this further by drawing extra energy from the battery.
Not only was this Model S found to be using more energy in cold weather, but its system limits on-the-road recharging as well. Similar to many hybrid systems, under normal conditions Tesla recaptures energy for the battery during regenerative braking (regen).
“When the Model S is cold it limits the ability to regen since the batteries need to be at an optimal temperature before it receives any additional charge,” said Rob.
For the Chevrolet Volt, engineers combat cold-weather energy draining by engaging ERDTT – Engine Running Due To Temperature. This runs the Volt’s supplementary gasoline engine to ensure enough power is available to run the defroster. But the all-electric Tesla doesn’t have this option.
Even with other sources stating that cold weather lowers the Model S range by only a quarter, Rob said drivers should anticipate on using an average of 40-percent more power. When the roads are icy or wet, increase this by another 25-percent.
“Expect to lose about 10 miles of real range for every 10 degree drop,” said Rob. “Plan your charging and driving accordingly – don’t cut it close.”
Charts and further details may be seen at Teslarati