Researchers: EV Drivers Respond to Range Anxiety in Distinct Ways

By · January 07, 2014

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The term “range anxiety” has become a common way to describe to an electric car owner’s worry about running out of charge and getting stranded on the roadside. What gets lost in the casual use of the term is that range anxiety is rare and highly subjective. Researchers at Technische Universität in Chemnitz, Germany, recently published a study that demonstrates the high degree to which an individual driver’s state-of-mind plays a greater role than an EV battery’s state-of-charge.

Thomas Franke and Josef F. Krems—the primary researchers of the study entitled, “Understanding Charging Behaviour of Electric Vehicle Users,” published in the journal Transportation Research in November 2013—identified charging styles. The charging patterns of behavior in some ways resemble driving styles.

As defined by the authors, it comes down to how EV owners prepare for, and respond to, times when an electric car’s available range is less than the driver’s perceived “comfortable” range. “EV users seem to be mostly free to choose how they manage their battery resources in everyday use,” they write.

In other words, there could be plenty of juice remaining to reach a destination, but an insufficient “safety buffer” that makes the driver uncomfortable. The question for the researchers is how users cope with that insecurity.

Choose Your Style

Researchers break the coping strategies into two main categories. Which one describes you?

  • Type-A users: The first group takes advantage of every charging opportunity to avoid dealing with safety margins altogether.
  • Type-B users: The second group bases decisions more on the necessity to charge, so that charging fill-ups occur no more than necessary.

The study was based on two studies of nearly 80 drivers of BMW’s converted Mini Cooper electric cars in and around Berlin, during a time when there were about 50 public charging stations. The Mini-E, a car used as a temporary platform for testing, has a range of about 100 miles. The field trial consisted of two consecutive six-month studies, with data collected from participants prior to receiving the EV, after three months of driving, and after returning the EV after about six months.

Most users (87%) agreed that charging was easy. Several users (57%) reported that handling the charging cable was cumbersome. Most users (78%) were not bothered by the longer time required for recharging relative to refueling a conventional vehicle. Users charged their vehicle, on average, about three times a week and typically drove 23 miles with the EV per day.

Why It Matters

Researchers believe the practical implications of their study relates to the use of cleaner energy resources, such as wind energy, for EV charging. “The more frequent and regular charging patterns should be promoted as they support the utilization of excess energy from wind,” they write. In essence, it would be hard to manage and modify how the grid is used, when charging actually occurs (after the car is plugged in) or the type of energy, if an EV is being infrequently charged.

Franke and Krems write that a charging strategy that might delay when the car is plugged in utilizes the battery resources less often, but still, it's less favorable for controlling the type of energy used. That’s okay during the first few months behind the wheel of an electric car, when a driver is still establishing a charging style, but drivers should be encouraged to plug in more frequently over time.

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