04.29.2014 - by Tom Saxton
How Do EV Drivers Choose To Charge Their Cars?

EV drivers have a choice in how they charge their cars. The major models all offer at least two choices: charge from an ordinary 120V household outlet (Level 1) or from a 240V charging station (Level 2).

Level 2 charging covers a wide range of charging speeds. A Chevy Volt can charge at 3.3 kilowatts (kW), about 10 miles of range per hour. The Nissan Leaf offers two charging configurations, 3.3 kW and 6.6 kW, yielding up to about 20 miles of range per hour. The Tesla Roadster can charge at 16.8 kW, about 60 miles of range per hour. The Tesla Model S offers two charging configurations, 10 kW or 20 kW, yielding up to 58 miles of range per hour.

Depending on the vehicles, an EV driver may have a wide range of choices in charging speed. For overnight charging at home, there may be no benefit to charging at a vehicle’s highest speed. For example, if your typical commute is 30 miles per day, then Level 1 charging from an ordinary outlet will fully charge your EV overnight whether it’s a Chevy Volt with a 40-mile electric range or a top-end Model S with a 300-mile range. Generally speaking, the cost of install charging increases with charge rate, so EV owners may well choose to use lower rate charging when it meets their needs and saves them money.

How do these trade-offs play out with actual EV owners?

Plug In America has been conducting surveys on various plug-in vehicles since 2012. We are now surveying owners of four models and have data for over 900 vehicles. Three of the vehicles offer choices in charging levels, the Tesla Roadster, Nissan Leaf and Tesla Model S. For each of these vehicles, owners are asked to specify how they most often charge. The 2002-2003 Toyota RAV4 EV uses a legacy charging technology that only offers one charging level, approximately 6.6 kW. Considering the three modern EV models, we have data for 842 vehicles.

To help understand the data, I broke the reported charging levels into four groups: Level 1 (120V charging, under 2 kW), Level 2 charging up to 7 kW, 7 to 10 kW, and 10 to 20 kW. Here’s how the responses add up by vehicle model.

The Nissan Leaf comes with a 120V charging cord, so no extra expense is required when an owner has access to an outlet where they park. About 12% of Leaf owners responding report Level 1 as their most common charging method.

The Tesla Roadster was sold with a 120V charge cord. Also available at additional cost were a mobile charge cord that could charge at various levels up to 9.6 kW and a charging station that would allow 16.8 kW charging. 9% of Roadster owners report using the 120V charge cord for their daily charging, not too different from the Leaf owners. This illustrates that charging needs aren’t determined by the vehicle’s battery size, but by the number of electric miles driven per day. The majority of Roadster owners, 72%, use Level 2 charging below 10 kW, leaving 20% that charge above 10 kW.

The Tesla Model S includes charge cords for both 120V charging and 240V charging up to 10 kW, so the only incremental cost to use Level 2 charging is just getting an outlet installed, the same type of outlet used by an electric range or oven. To charge above 10 kW, a Model S owner needs to purchase both an add-on option for the car to support up to 20 kW charging and also a Level 2 charging station. Only 4% of Model S survey participants report using 120V as their most common charging method. The large majority, 76%, take advantage of Level 2 charging up to 10 kW, with 20% opting to charge above 10 kW.

Both the Leaf and Model S have options for DC quick charging at rates up to 50 kW for the Leaf and up to 120 kW for the top-end Model S.

The table below shows the full data taken from the surveys.

ModelLevel 17kW or less7 kW to 10 kW10 kW to 20 kWTotal
Nissan Leaf53390n/an/a443
Tesla Roadster13386728146
Tesla Model S103415950253

Vehicles like the Chevy Volt that use a gasoline engine to augment a smaller electric range have smaller batteries that can be charged from empty to full overnight using a 120V outlet regardless of how far the vehicle is driven per day. Since these vehicles can be conveniently charged from a simple outlet using a charge cord included with the vehicle, there’s less incentive for owners to go to the extra expense of purchasing Level 2 charging equipment. Although I don’t have direct data for these owners, I would expect their use of Level 1 charging to be even higher than for the all-electric vehicles. It would be interesting to get data from owners.

Level 2 charging stations are coming down in price and generally offer a more convenient charging experience than the cords that come with the cars, so that may be a motivating factor for drivers even when 120V charging can meet their daily electric driving needs.

3 comments on “How Do EV Drivers Choose To Charge Their Cars?”
  1. Tom Saxton says:

    In my experience with several different vehicles, charging at Level 2 is more efficient than charging at Level 1. For our 2011 Nissan Leaf, it’s about 10% more efficient, and thus 10% less expensive, to charge at Level 2.

    The impact on the grid is more complex. The grid doesn’t want everyone starting their charge at the same time. It’s better to spread charging out over time. It’s better to set a charge timer so you start charging off peak. Since Level 2 takes less time, users generally have more flexibility in when they start charging.

    Eventually, I expect we’ll see utilities playing more of a role in when charging is done. You’ll configure your charging to complete by a hour before you’ll need it, then the utility will manage the time and rate at which your car charges, and give you a discount on the electricity because you’re helping the utility manage load.

    For now, I recommend:

    1. If Level 1 meets your charging needs, use Level 1. Plug in and charge whenever you like, don’t worry about scheduling if you need most of the night to get a full charge.

    2. If you need or want Level 2, use Level 2. If you can, schedule your charge to start off peak. If you can control your charge rate, use the lowest rate that will conveniently charge your vehicle. Even if your vehicle and charging equipment allow you to charge at 70A or more, limit your charging to 32A or less if you can.

  2. Jeanne LeVett says:

    Can you please comment on the differences in the electric costs for charging at Level 1 versus Level 2 versus Level 3.? It is my understanding that charging at Levels 2 and 3 is not only more costly, but creates a bigger drain on the grid. What are the impacts on individuals and utilities?

  3. Robert Winfield says:

    appx 12,000 miles Volt,about 9,600 electric. probably 98% L1 at work and home. rare use of L2 just to “show the flag” at EV stations (which cost ~$1/hr !!) or about $0.35/kW!!)
    takeaway after 14 months, need min 200 mile charge, supercharge capable, temp controlled battery

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