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How Americans Charge Their Plug-In Vehicles

Posted by Content Coordinator on Monday, October 5th, 2015


Executive Summary

Widespread adoption of PEVs has the potential to significantly reduce the United States transportation petroleum consumption and greenhouse gas (GHG) emissions. However, barriers to adoption remain. One of the most commonly cited barriers is the need for public charging infrastructure that would allow PEV drivers to recharge their vehicles. Questions include: how many and what kind of charging stations are needed and where and how often will PEV drivers choose to charge?

To answer these questions, the DOE launched the following five ARRA projects:

  • 1. The EV Project
  • 2. ChargePoint America Project
  • 3. Chrysler Ram PHEV Pickup – Vehicle Demonstration
  • 4. GM Chevrolet Volt – Vehicle Demonstration
  • 5. SCAQMD/EPRI/Via Motors PHEVs – Vehicle Demonstration.

The EV Project and the ChargePoint America Project, combined, form the largest PEV infrastructure demonstration in the world. Between January 1, 2011, and December 31, 2013, these combined projects installed 17,000 alternating current (AC) Level 2 electric vehicle supply equipment (EVSE) (i.e., 240-volt charging stations) for residential and commercial use and dual-port direct current (DC) fast chargers (DCFCs) in 22 regions across the United States. Over 7,800 privately owned Nissan Leafs™ and Chevrolet Volts and more than 400 Smart ForTwo electric drive vehicles in Car2Go car-sharing fleets were enrolled in The EV Project.

These projects were not just about installing charging infrastructure; the purpose was to study charging infrastructure use and develop lessons learned that can be applied to future deployments of PEVs and charging infrastructure. To accomplish this, INL partnered with the Blink Network, ChargePoint, General Motors (GM) and OnStar, Nissan North America, and Car2Go to collect and analyze data from the electric vehicle charging stations and the PEVs enrolled in these two projects.

Every PEV owner participating in The EV Project had an EVSE installed in their residence. In return, the PEV owners gave written consent for researchers to collect and analyze data from their home charging units and their PEVs. Data also were collected from publicly accessible charging stations installed at a wide variety of venues in and between metropolitan areas around the United States.

Data collected from vehicles and charging infrastructure over the 3-year project period captured use profiles for125 million miles of driving and 6 million charging events, providing the most comprehensive study of PEV and charging usage to-date.

Through partnerships with states, municipalities, electric utilities, local business owners, and numerous other stakeholders, The EV Project and ChargePoint America Project installed charging stations in 22 regions across the United States (Figure 3-1).

Figure 3-1. Areas where public charging infrastructure was installed and vehicles were enrolled in The EV Project and ChargePoint America Project.

What Have We Learned?

With gas stations seemingly on every block, it would be logical to expect that a similarly ubiquitous network of public charging stations would be needed to refuel, or rather, recharge PEVs. However, charging stations can be installed where gas stations cannot (i.e., at homes, workplaces, and destinations where PEVs spend a long time parked). The projects installed EVSE and DCFC stations (480 V) in a wide variety of locations, including homes, workplaces, stores, restaurants, gas stations, and many other venues, to allow researchers to observe where PEV drivers charge. The primary question about charging infrastructure placement was: would PEV drivers recharge around town at the nearest charging station, following the pattern they followed with the gas-powered cars they grew up with or would they adopt a new refueling paradigm and charge at the few places where they park their cars for the longest periods of time?

The answer is clear: despite installation of extensive public charging infrastructure, in most of the project areas, the vast majority of charging was done at home and work. About half The EV Project participants charged at home almost exclusively. Of those who charged away from home, the vast majority favored three or fewer away-from-home charging locations, with one or more of these locations being at work for some drivers.

This is not to say that public charging stations are not necessary or desirable. Some DCFCS, all of which were accessible to the public, experienced heavy use, which supported both intra and inter-city driving. Also, a relatively small number of public AC Level 2 EVSE sites saw consistently high use. This begs the question: what is it about the small number of highly used charging sites that led to their popularity?

There was some correlation between public charging location characteristics and utilization. Public AC Level 2 EVSE installed in locations where vehicles were typically parked for longer periods of time often were among those used most often. These locations included shopping malls, airports and commuter lots, and downtown parking lots or garages with easy access to a variety of venues. Also, not surprisingly, public charging station utilization was higher in regions with higher PEV sales. However, examples of highly utilized charging sites existed in almost every region and at venues that were not obviously appealing locations for charging. Conversely, many charging sites in seemingly ideal locations did not experience much use.

In the end, it was apparent that exact factors that determine what makes a public charging station popular are predominantly community-specific. More research is needed to pinpoint these local factors. Nevertheless, the projects demonstrated that a ubiquitous charging network is not needed to support PEV driving. Instead, charging infrastructure should be focused at home, workplaces, and in public “hot spots,” where demand for AC Level 2 EVSE or DCFC stations is high.

Naturally, there are exceptions to this rule. There may be reasons for an organization to install public charging stations, even if they are not used (e.g., attract a certain customer demographic, communicate a “green” image, or encourage PEV adoption). Additionally, DCFCs along travel corridors were found to effectively enable long-distance range extension for BEVs. These chargers were not typically used frequently; therefore, their value is hard to quantify from the perspective of the charger host, but when they were used, they provided a vital function to the BEV driver.

Regardless of motivation for installing public charging infrastructure, the project found that public charging stations were more expensive to install than residential and workplace units. Installation costs also varied widely by region and by venue. This further emphasizes the benefit of focusing the bulk of charging infrastructure at home, work, and strategic public charging locations.

The projects shed light on other facets of PEV use. It found that public and workplace charging infrastructure enabled drivers to increase their electric driving range, although most drivers did not charge away from home frequently. It was also discovered that drivers of the Chevrolet Volt (an extended-range electric vehicle [EREV]) tended to charge more frequently and to more fully deplete their vehicle’s battery than drivers of the Nissan Leaf (a BEV). This allowed the overall group of Volts studied to average nearly as many electric vehicle (EV) mode (EVM) miles traveled as the Leafs in the project. Finally, based on observed charging patterns, the project found that there were opportunities to use pricing structures and other policies to manage demand for PEV charging, both in terms of charging station throughput at charging hot spots and electricity demand on the electric grid during peak and off-peak periods.

Download full version (PDF): Plug-in Electric Vehicle and Infrastructure Analysis 

About the Idaho National Laboratory
INL is part of the U.S. Department of Energy’s complex of national laboratories. The laboratory performs work in each of the strategic goal areas of DOE: energy, national security, science and environment. INL is the nation’s leading center for nuclear energy research and development.

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