Electric vehicles: fact and fiction

By Nicole Pennington and Nicole Naassan

The smart grid is typically thought of a system designed to alleviate stress on the electric grid. The vast majority of smart grid technologies are produced with this concept in mind – with the exception of electric vehicles. These are touted as part of the smart infrastructure, yet they put a strain on the grid rather than lighten the load. But how much stress do these vehicles really put on the grid and are there ways to mediate this?

The amount of stress that electric vehicles will put on the grid has been grossly exaggerated.  In 2009, the U.S. census reported a total of 57,185 electric vehicles were registered in the United States. That accounts for 0.02% of the 246,283,000 vehicles registered nationwide.

There are many initiatives in place to accelerate the rate of adoption for electric vehicles.  The Electric Vehicle (EV) Project is one such mechanism for the DOE and President Obama to reach their goal of putting 1 million electric cars on the road by 2015. The EV Project has qualified 8,300 LEAF and Volt customers in 2010-2011 for participation. ECOtality is deploying approximately 14,000 chargers in 18 major cities and metropolitan areas located in six states and the District of Columbia – making it the largest electric vehicle project to date. Those states include California, Oregon, Washington, Arizona, Texas, Tennessee and Washington, D.C.

Even if all of these initiatives succeeded in putting a million electric vehicles on the road – only 0.3% of the population would have a registered electric vehicle. With the distribution of vehicles and the varying charge times, the impact on the electric grid is anticipated to be minimal. A study by EPRI with the National Personal Transportation Survey (NPTS) shows that even if people plug in their cars as soon as they arrive home, the load of vehicle charging is relatively well distributed. According to EPRI,

“Vehicle home arrival is correlated with peak load, so it is often assumed that vehicle charging could create a large coincident peak. Still, vehicles will not all be connected at the exact same time. Even during the peak hour of 5 to 6 PM, only about 12% of drivers arrive home during the hour… Even without smart charging the load of vehicle charging is relatively well distributed.”  “Since home arrival is coincident with other activities the load occurs on peak, but vehicle charging has a maximum of about 0.7 kilowatts per vehicle, and is relatively evenly distributed over about six hours.”

Much of the media hype is related to the anticipated strain on the grid due to the demand of electric vehicles. Based on multiple reports and findings from EPRI, it is expected that the load on the grid due to EV charging will be relatively well distributed (see Figure 1).  The figure below shows a load profile of an uncontrolled EV charging environment – where smart charging and other load shifting mechanisms are not applied.

Source: EPRI Transportation Electrification, A Technology Overview, July 2011, page 5-2

Data reported by DOE’s Idaho National Laboratory shows that battery electric vehicles (BEVs) in the EV Project are mainly charged overnight, during off-peak hours. Most residents are expected to use a Level 2 charging system rather than DC fast charging. According to the EV Project website:

·         Level 2 charging systems recharge EVs in 4-6 hours utilizing 220 volt power. Level 2 charging systems are typically used for overnight charging at home or at businesses that operate fleets of EVs.

·         DC fast charging allows vehicles to be recharged in minutes rather than hours. For the EV Project, DC fast chargers are being deployed in high-density areas of each of the launch markets and in major transportation corridors to allow EV users to commute between major cities.

Some commuters may also be able to use a Level 1 charge system. A Level 1 charge will recharge a vehicle in approximately 20 hours and uses 120V – which essentially is a standard house outlet. For the drivers with a long commute, this is not a probable option. However, if you have a short commute (40 miles round trip or half the battery) – you should be able to get a complete charge at night if you can plug in the vehicle for 10 hours or so.

For residential charging systems, the draw on the electrical system is minimal. A Level 1 charge is roughly equivalent to a 1,500 watt hair dryer. A Level 2 home charging station will require a new circuit, similar to the requirement for an air conditioner or an electric clothes dryer.