Electric cars are still such a novelty that little is known about their owners and how they use the vehicles. But recent research is beginning to unlock some of the mysteries.

Plug-in vehicles—those that run entirely on battery power or hybrids that combine electric and gasoline drives—represent less than 1% of total U.S. vehicle sales, but in the past three years their numbers have grown rapidly.

Sales nearly tripled in 2012 and are on track to nearly double this year, according to the Electric Drive Transportation Association, a trade group.

Since 2009, the EV Project—financed with grants from the U.S. Energy Department and operated by

Among the findings:

• Owners of electric cars drive less, possibly because they are using electric vehicles primarily for short trips, to work or the grocery.
• Or it may be that they fear running out of juice. A separate survey found that limited range caused many EV owners to avoid longer or discretionary trips—to the movie theater or to visit friends, for instance.
• The EV Project’s data also shows that buyers of plug-in vehicles are relatively more affluent than the average motorist.

That reflects the cost of the vehicles: General Motors gas-and-electric Chevrolet Volt costs around $40,000, while the all-electric Nissan Leaf sells for about $30,000.

Owners are also more likely to be “greener”—a large portion of electric-car buyers report having solar panels.

The results are important for the utilities that build, maintain and operate the power grid. EV Project data show that owners of electric vehicles tend to cluster in the same neighborhoods and plug in at similar times—usually in the evening.

This can increase the load on a single transformer significantly, and lead to the equipment aging more quickly, as well as to power outages.