Plug-In Electric Vehicles Could Help the Grid: The Capacity Question

This is the first post in a three-part series that explores some potential impacts of electric vehicles on the electrical grid. Part 2 and Part 3.

One of the main concerns over the electrification of vehicles is their impact on the electrical grid. Will they lead to power outages due to the increased demand in certain areas? Will a marked increase in electricity demand raise prices for consumers who don’t own a plug-in hybrid electric vehicle (PHEV) or an all-electric vehicle (EV)? In a series of blog posts, we’ll take a look at a claim from some utilities that vehicle electrification could actually help improve the stability of the grid while keeping costs low through a process called frequency regulation.

In this post, we’ll try to answer the capacity question. In order to determine whether the grid has the capacity to handle the influx of Plug-in Electric Vehicles (PEVs or PHEVs/EVs), utilities must estimate at what time of day these vehicles will demand power from the grid and how many of them the grid can charge at a time without causing power disruptions.

Utilities expect that people would do most of their vehicle charging at night when electricity demand is low. Moreover, wind power production, which is growing rapidly in the United States, tends to be at its highest daily levels at night (when winds are heavier on average). This creates the potential, as both wind power and electric vehicle penetration increase, to charge these vehicles with carbon-free electricity from wind farms. However, since coal supplies almost 50 percent of electricity in the U.S., there are many places today where electric vehicles will depend on power from coal in order to operate. Since the greenhouse gas emissions (GHG) from vehicles charged from coal power are almost as high those of a conventional vehicle, comprehensive policy is necessary in order to maximize the environmental benefits of PEVs.

A study by the makers of the MINI E showed that reality matches these expectations. Participants in the study were switched to time-of-use electricity rates in order to encourage them to charge their vehicles at night when generation costs are lowest, which they did. The study concluded that people also like to top off the vehicles’ batteries while they are at work, which could pose a greater burden on electricity suppliers. As of today, many utilities do not offer time-of-use rates to their customers; however, the list of utilities that do support this rate structure continues to grow (see here and here).
Impact on Grid
Impact of one million Nissan Leafs or over three million Chevrolet Volts on the day with highest demand in 2009 within PJM’s territory. (SOURCE:

At a macro level, it is important to consider how much capacity is available on the grid for the EVs and PHEVs to use. For example, let’s consider the first mass-market PHEV, the Chevrolet Volt, and the first mass-market EV, the Nissan Leaf. Both vehicles will be available in the U.S. by the end of this year. The figure above shows the amount of electricity (or load) required to charge over three million Chevrolet Volts or one million Nissan Leafs out of the electricity supply. The data comes from PJM, a regional transmission organization (RTO) that coordinates the movement of wholesale electricity in the mid-Atlantic region and parts of the Midwest and serves over 51 million people.

This illustration provides some evidence that the grid can handle the load from PEVs, especially considering President Obama’s goal is to have one million PHEVs nationwide by 2015. The figure also illustrates PEVs might have a minimal impact on the grid if time-of-use pricing is put and place and utilities and vehicle owners could coordinate in order to concentrate electricity demand for charging vehicles during the typical late-night and early-morning demand trough.

The next post in this series will discuss a technical problem that could arise if there are too many people with electric vehicles in one particular area.

Nick Nigro is a Solutions Fellow