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Plugging In

Can the grid handle the coming electric vehicle load?

Fortnightly Magazine - June 2010

As electric vehicles become commonplace, will the grid be able to handle the extra load? Too many cars plugging in at once might cause disruptions and necessitate costly infrastructure upgrades. Handling the vehicle load in a smart way, however, will ensure a smooth transition to the plug-in future.

Plug-in electric vehicles (PEVs)—powered in part or fully by the electric grid—might offer an opportunity to shift much of the transport sector’s energy demands away from petroleum, reducing dependence on imported oil and improving the environment. If the electric grid can be decarbonized (still an open question), this shift will help to reduce overall carbon dioxide (CO 2) emissions as well. The potential has drawn much attention from a variety of quarters—including policymakers concerned about climate change and energy security, and vehicle manufacturers wanting to capitalize on a new market. Power system planners concerned about the possible effect of PEVs on the electric system also have begun exploring the issues.

Transportation as a whole uses an immense amount of energy—about two-thirds as much primary energy as consumed by the entire U.S. electric sector—and emits about a third of the nation’s CO 2. If a large share of the transport sector were to convert to electricity, it could become a huge new electric load that raises many questions, concerns and maybe opportunities for the power sector. If PEVs were to charge up during off-peak times so that they help fill the valleys in the daily load shape and improve the utilization of the existing grid infrastructure, they could be a valuable complement to the power grid. However, if PEVs are adopted in large numbers but do not coordinate with the grid ( e.g., charging at times that add to peak demand or create rapid load ramps)—they could be disruptive and might necessitate significant additional infrastructure and investment.

As PEVs penetrate the transportation industry, they present a range of possible impacts on the U.S. power system. 1 Because the relationships among PEV penetration, charging behavior, electric infrastructure requirements and environmental outcomes might not always be aligned, PEVs pose some interesting tradeoffs that policymakers and the power industry are just beginning to grapple with.

PEV Market Outlook

Although electric vehicles were developed in the early days of the automobile, the advantages of the internal combustion engine and petroleum fuels in terms of cost, performance and quick refueling relegated electric vehicles to the sidelines for the 20th century. The commercial introduction of hybrid electric vehicles (HEVs) about a decade ago offered a new way to capture some of the advantages of electric vehicles. HEVs don’t use electricity as a primary fuel; all their power originates with their internal combustion engine, with the battery and electric motor simply storing surplus energy and recovering it later. But they can improve fuel efficiency considerably, and their sales have grown rapidly, making up about 3 percent of U.S. light-duty