Winter chills limit range of the Tesla Model S electric car

Consumer Reports News: February 15, 2013 03:08 PM

We've been enjoying the Tesla Model S as it goes through its break-in period, leading into formal testing. During this time, I've been keen to find out its real-world range, and recently confirmed that driving this electric car—like any other—can bring some range anxiety. Although winter highway driving may present a worst-case scenario, our Tesla actually delivered the range it projected.

It was a chilly 45° F when I pointed our fully charged Model S homeward for my informal experiment, a distance of 75 miles. With 240 miles on the car's range indicator, I figured there would be more than ample juice to cover the distance, plus some nighttime errands, the morning drop-off at school, and then my 75-mile return trip to the track. The Model S has an additional range predictor called "projected range" that estimated 188 miles remain. This secondary display is part of the energy graph, a function you can choose to view on the large iPad-like screen. The projected range takes into account ambient temperature and driving style, and it provides a more accurate estimate than the default display. Based on that estimate, too, the range appeared to be sufficient.

Although the car predicted its range fairly accurately, I barely made it back to the office the next day, running the last three miles on an indicated zero charge. Yes, I was a bit stressed, but the car did what it said it would. The entire trip totaled 176 miles. So, how did I run the battery all the way to empty?

Tesla-Model-S-176-miles-traveled-screen.jpgOur S has the larger 85-kWh battery, the one Tesla claims is good for 300 miles in optimum conditions. The EPA pegs the range at 265 miles. In our experience with other EVs we've tested, we've come mighty close to the EPA's estimate on range. In general, we heed Tesla's advice against charging for "max range" due to the adverse effect on battery life, as any other owner would, and charge in "standard" mode.

According to Tesla, the rated range indicator (front and center in the instrument panel) is based on the EPA's "rated" 265 mile range. When I got home with 80 miles on the trip odometer, I noticed that 100 miles got slashed from my "rated" range, showing 140 miles left. (See our alternative fuel guide and fuel economy guide.)

Anyhow, after a seven-hour overnight park (unplugged) and temperatures dropping below freezing, the "rated" range dropped to 65 miles. (Because we're tracking energy poured into the Tesla at our track, I resisted the temptation to top off at home, like a typical owner would.) The "projected" range was even scarier at 15 miles left after cold soaking at 30° F through the night.

But by now I've gained enough familiarity with our Tesla to assume the car would readjust once I started driving and things warmed up. (Owners would likely pre-condition the car before leaving, using household current to raise the battery temperature and heat the cabin.) Indeed, 30 miles into my trip, the car predicted 55 miles of range. Occasionally the "rated" and "projected" agreed. I considered stopping in Milford, CT, for a quick "supercharge" as I had a few days earlier, but changed my mind in the spirit of my experiment. I knew the distance to my office was 55 miles at that point, so I decided to risk taking one for the team to determine the Model S real-world range when it's cold outside and you drive the car as you would any other car, electric or not. Call me a gambler, but I kept cruising and crossed my fingers.

Thumbnail image for Tesla-Model-S-low-battery-screen.jpgAs the range indicator sank to 20 remaining miles on the way to work, I exited the freeway, hoping that the lower-speed rural road driving would allow more regenerative braking and would extend the range. I got a little "credit" by coasting and hovering on the brake pedal, which was soon expended on the hills that followed. With four miles left on the range gauge, I was seven miles away from our track. I shut off the climate control to preserve some range. (The anxiety alone was enough to keep me warm.) Soon enough, the range indicator became a red zero with the notification "charge now."

In the end, I made it with no need for a rescue, rolling on for three miles on empty. All in all, I covered 176 miles during a typical winter day in the Northeast and not too far off the 188-mile range initially projected.

Making sure this wasn't a fluke, I repeated the nearly identical round trip on another day with similar results, a bit less anxiety, and six miles left in the range.

To be clear, cold temperatures, need for cabin heat, and a high portion of freeway driving, which minimizes the opportunity for regenerative braking, are the most adverse conditions for any electric vehicle.

To its credit, the Model S delivered 176 miles from a full charge in cold weather--considerably more than any other EV on the planet. While it was in line with what the car predicted, it proved well short of the rated 240 miles the car promised when I started, let alone the 265 estimated by the EPA or the 300 touted by Tesla. So even for the impressive Model S, it turns out that range anxiety is not completely eliminated. Adapting to EVs needs and limitations is still relevant. But the Tesla has proven to have far less limitations than other EVs.

Any potential EV buyers in the Snow Belt should consider our experience; winter exacts a tough toll on range. As spring arrives, we'll keep you advised on how the thaw affects the range.

One additional takeaway: Perhaps it's the "projected range" that needs to display more prominently than the "rated range."

Read our complete road test of the top-scoring Tesla Model S.

Consumer Reports takes delivery of its own Tesla Model S
Tesla Model S - The electric car that shatters every myth
Inside the impressive Tesla Model S electric sedan
Tesla Model S electric sedan rated at 89 MPGe

Gabe Shenhar

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