A growing fleet of electric cars will need a comprehensive network of public charging stations, but those who build and maintain those stations have some choices to make.
They have to provide charging infrastructure that will be useful to the public, but is also financially sustainable.
Level 2 AC charging stations are relatively inexpensive and straightforward to install, but require cars to stay put for a fairly long time, usually at least a few hours.
DC fast-charging stations allow much quicker charges, but are more expensive and place greater demands on electricity infrastructure.
Now a survey of driver habits in one region with high electric-car adoption shows that DC fast-charging may be the better way to attract patronage.
Network operator NRG eVgo recently surveyed a handful of its stations in the San Francisco Bay Area, and found that drivers vastly preferred DC fast charging.
NRG eVgo electric-car charging station
It analyzed 10 of its Freedom Station sites--which offer both Level 2 AC and DC fast charging--sited at Whole Foods stores in the region.
When comparing the number of DC fast-charging sessions to Level 2 sessions, it found drivers preferred fast charging 12 to 1.
In September 2015, there were 6,900 DC fast-charging sessions at those stations, NRG eVgo said.
For drivers, the speed of DC fast charging is obviously a plus.
Stations can charge most electric-car battery packs to 80-percent capacity in around 30 minutes, compared to hours for Level 2 AC charging.
That means they can fit a fast-charging session in while running a quick errand, while Level 2 charging requires a greater time commitment.
Nissan Leaf at eVgo Freedom Station Daly City, California
But the extra time required for Level 2 charging means drivers linger longer at the businesses hosting stations, arguably letting them spend more money there.
That's often the only way they can make money off of electric-car charging, as many sites--both Level 2 and DC fast-charging--are currently free for customers to use.
Over time, advocates suggest, some businesses may simply decide that Level 2 charging is an amenity they can afford to provide for free.
That means Level 2 charging may become like WiFi service in hotels: free in some, where it becomes an expected amenity, but with a fee at others where the market supports it.
Over time, though, a sustainable business model will have to be developed for public DC fast charging.
Businesses will have to weigh the extra initial costs and operating expenses of providing DC fast charging against their potential to draw in new customers.
Expect more studies.