Plug-in vehicles generate new variables for power grids

By Daniel Sperling

The full version of this article was originally published in FierceSmartGrid October 1 2013

Numerous factors must be taken into account as electric vehicle use grows, including human behavior and an aging infrastructure. Detailed data on electrical vehicle usage, particularly charging patterns, will ultimately inform utilities on how to handle the impact on the power grid.

Vehicles are now on a trajectory to become more sustainable as hybrid and plug-in electric vehicles (EVs) become more common, but there are still a number of barriers to mass adoption. Automakers are struggling to make vehicles more affordable, consumer hesitance must be overcome, and utilities are grappling with the potential impact on power grids.

One of the biggest challenges for many municipalities is the old grid, which was not built with electric vehicles in mind, never mind air conditioners, flat screen TVs and computers. Most homeowners aren’t thinking about the burden they put on the grid; they’re more concerned about their monthly bill. Aging grids are already dealing with the additional strain of these many new appliances and devices; and, now they must accommodate EVs, which not only creates additional demand, but also a set of new complexities.

Approximately 50,000 EVs were sold in the United States last year; predictions vary wildly on how many more and when EVs will be on the road. According to researchers at the U.S. Department of Energy’s Pacific Northwest National Laboratory, the grid has enough excess capacity to support 150 million battery-powered vehicles.

But while the capacity exists to power these vehicles, the challenge for utilities is managing the distribution of power to specific neighborhoods to meet energy demands of home, workplace and public charging stations.

Disruptive Loads

Local transformers, particularly those in older inner city neighborhoods, were designed with relatively low electrical loads in mind. They convert electricity to the right voltage for use in people’s homes. But if there is significant uptake of EVs in a single neighborhood and a large number draw power from the grid at the same time, they could cause a localized outage depending on the age and condition of the infrastructure. At the very least, it will shorten the lifespan of transformers and require investments in larger ones.

The challenge for utilities is understanding which areas of the grid will be stressed due to expanding EV ownership in specific neighborhoods.

Taking Charge

Transformers are not the only equipment that must be kept in mind. EVs require charging stations, not only at single-family homes and multi-dwelling units, but also at public parking garages and commercial properties. Who will own and provide charging services outside the home? This is uncertain and of great concern, since more stations are needed to enhance the utility of the vehicles and to overcome range anxiety concerns of drivers and prospective buyers, but the revenue potential seems limited. The significant energy savings benefit for the driver is a huge business challenge for charging stations. A typical EV requires no more than a few dollars for a full charge.

And then there are the many regulatory complexities regarding who is allowed to sell electricity, how much they can charge, and how they relate to the many new policies and regulations affecting electricity use.  In addition to utilities, charging stations can be owned by governments, employers and retailers.

No matter who ends up owning the charging station, new rate plans will have to be developed and utilities will have to be involved with their installation to guarantee reliable and safe performance, since they will be connected to the power grid.

How Much and How Long?

Not all EVs are created equal – it can take from half an hour to a day or more to charge an EV. Charging times and how much power a car draws can vary wildly depending on battery capacity, state of charge, and the type of charging infrastructure. In addition, an EV sold today might draw electricity at a higher rate when they are charging compared to models that came out just a couple of years ago.

Changeable Weather

Not all neighborhoods are created equal; it’s not just the state and age of the infrastructure that varies, it’s the weather. Take the state of California, for example.  In San Francisco, where residents rarely use air conditioning due to cooler weather, the peak demand of a home is less than that of a home in a hotter part of the state.  A typical San Francisco home draws only two kilowatts of power during peak time. A new electric vehicle could easily draw more than six kilowatts and a fast charging vehicle could draw significantly more (but not in homes). Ultimately, different regions will have different distribution challenges and demand based on climate.

The Human Equation

User behavior will also have an impact on the grid: If every EV owner decides to charge their car as soon as they get home from work, utilities can expect a great deal of strain on the grid. Most of the extra capacity within the grid is available late at night and very early in the morning, which means getting users into the habit of charging their cars overnight, rather than during the day and early evening. Workplace and retail charging will be especially challenged.

Driven by Data

Ultimately, utilities need to understand user behavior, so they can cost-effectively upgrade the grid in a timely manner, and can develop rate plans that are most effective at shifting charging behavior. This includes understanding when and where people charge and what affect it has on the peak load of the grid and how it affects equipment. It will also be important to understand the “clustering” phenomenon that occurs when a significant number of EV owners live close to each other in a neighborhood.

This kind of data and understanding will influence many investment and planning decisions. It will influence the granting of permits to charging stations, upgrading transformers and other equipment, and detecting trouble spots.

The good news is some utilities have already gained considerable experience and invested considerable effort in addressing these challenges, which other utilities can learn from.  Southern California Edison, one of the largest utilities, recently released a whitepaper detailing the impact of the approximately 12,000 plug-in vehicles on its infrastructure. Overall, the effects on infrastructure costs and grid stability have been minimal so far. The small number of plug-in vehicles, even when clustered in certain neighborhoods, has not required any upgrading of the grid.


Dr. Daniel Sperling, an IEEE Transportation Electrification expert, is Professor of Civil Engineering and Environmental Science and Policy, and founding Director of the Institute of Transportation Studies at the University of California, Davis (ITS-Davis). Dr. Sperling is widely recognized for his ability to bring together practitioners, policy makers and strategists in industry, government and academia to develop new vehicle- and fuels-policy approaches that are models for the world, for example the UC-Davis Transportation Institute will be co-hosting a IEEE Distinguished Lecturer Series on Transportation Electrification: Policy and Technology Challenges & Opportunities at UC Davis on November 7, 2013.


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