DOE takes real world look at electric car use

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Credit: Reuters

While the current use of electric cars is low, electric power companies say they are prepping for a 400% growth in annual sales of plug-in autos by 2023. With such growth in mind, understanding customer charging patterns can help utilities predict future grid changes that will be needed to handle larger vehicle charging loads.

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The utilities can get a small sampling of what’s coming from a U.S.

Department of Energy’s report issued this week by six utilities the agency tapped for a real world project. That project looked at electric car use and evaluated more than 270 public charging stations in parking lots and garages and more than 700 home charging units.

The six utilities involved in the project are Burbank Water and Power (BWP); Duke Energy (Duke); Indianapolis Power & Light Company (IPL); Madison Gas and Electric (MGE); Progress Energy (Progress, now part of Duke Energy as a result of a merger in 2012); and Sacramento Municipal Utility District (SMUD).

According to the DOE “specific project objectives varied, but the utilities evaluated the technical performance of the charging systems, the potential grid impacts of charging during peak periods, and the potential need for distribution system upgrades and capacity additions to meet expected electricity demand growth from rising adoption of plug-in electric vehicles.”

Some of the interesting facts from the study included:

  • The vast majority of in-home charging participants charged their vehicles overnight during off-peak periods.
  • Where offered, time-based rates were successful in encouraging greater off-peak charging.
  • Public charging station usage was low, but mostly took place during business hours and thus increased the overlap with typical peak periods.
  • Plug-in hybrid owners frequently used the(often free)public stations for short charging sessions to “top offtheir tanks.”
  • The length of charging sessions and the power required varies based on the vehicle model, charger type , and state of battery discharge.
  • The average power demand to charge most vehicles was 3-6 kilowatts, which is roughly equivalent to powering a small, residential air conditioning unit.
  • However, depending on the model, the load from one electric vehicle model can be as much as 19 kilowatts, which is more than the load for most large, single-family homes.
  • Faster chargers may require more expertise to installin homes and public stations.
  • Installing a 240-volt charging station, which typically charges 3-5 times as fast as a charger using a standard 120 –volt outlet, requires a licensed electrician and occasionally service upgrades.
  • Public charging station installation had high costs and required substantial coordination with equipment vendors, installers, and host organizations to address construction, safety, and code requirements.
  • Some utilities found residential interoperability problems in communication between smart meters and charging stations.
  • SMUD found that the two devices only connect ed successfully about 50% of the time during load reduction events.
  • Electric vehicle charging stations are available in 120-volt, 240-volt, and 480-volt models. Many different models are available with different power levels that determine the speed with which they recharge vehicle batteries. The most common type of charger is a portable 120-volt special charging cord, referred to as AC Level 1 charging, which typically provides 3-5 miles of range per hour of charge. Depending on the size of the battery, and the initial state of charge, this could take 8 to 20 hours to fully charge a depleted battery.
  • Some makes and models—particularly all-electric vehicles or those with larger battery packs—may take about 20 to 60hours to charge a fully depleted battery at 120 volts. While 120-volt charging is relatively slow, it can often be accomplished with little to no additional cost or installation work if an outlet is already available at home.

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