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Study: 'Power Packets' Can Stablize Demand From Plug-In Cars

Toby Talbot
An electric charging station in Montpelier might be getting more traffic as the number of plug-in cars grows. A new study looks at how the grid might handle that demand.

People who care about the environment would like to envision a future in which cars are fully electric, with drivers plugging into an outlet to recharge and get going.

That is the reality now for some, as a number of car companies are selling plug-ins and plug-in hybrids. And while they still represent just a sliver of overall car sales, the percentage of people buying electric cars is growing fast. And Vermonters are a big part of that trend.

But as electric car sales increase, so will stress and demand on the electric grid, and concerns that too many people plugging in at once to charge their cars could crash it.

Jeff Frolik is an associate professor of Electrical Engineering at the University of Vermont, and he’s been studying that issue. Frolik spoke with VPR’s Mitch Wertlieb.

The problem is that too many people coming home from work and charging overnight could place stress on the grid.

“A person may need to charge their car for four hours overnight. Instead of plugging in right away and charging for the four hours, we break that time up into what we’re calling power packets. And the idea is that you charge for a little bit at a time, and through the course of the evening you will get all the charge you need,” Frolik explained.

The owner wouldn’t notice this break up in the charging over the evening, and when they wake up in the morning, their car would be fully charged.  If the owner needed the car charged up right away, there would be a choice between urgent and non-urgent charging.

“Anyone that’s utilizing our staggered method of charging would have some sort of price incentive to do so, and if someone needed the charge very quickly they would be basically paying the full rate,” Frolik said.

Electric cars will place a big demand on the grid, sometimes doubling a house’s monthly usage.

“That’s a lot, especially if you live in a small neighborhood, with aging infrastructure, it could put a stress on it.”

Frolik said many scientists have developed different ways to solve this same problem. But his study differs in that it’s a decentralized approach.

“A lot of approaches look at a very optimized scheme where every user is being provided a schedule for charging. But in order to create the schedule, a central agency, say the utility, needs to know when you’re going to leave in the morning, what time you’re arriving at night, how much charge is in your battery now, and basically use all this information to come up with an optimal schedule. That’s a lot of information that needs to be sent back and forth and maybe information that people don’t want to give. So our approach is very decentralized, very limited communications and really leverages a lot of techniques utilized for data communications,” Frolik explained.

“Think about drawing balls from a bucket, you’re drawing a ball out, that happens to be your car. You’re getting charged. You throw it back in there and someone else gets drawn out. The grid doesn’t know who’s charging at any point in time.”

The system still needs a lot of simulation work, and a pilot study on the system could begin as soon as this summer. It’s been published in IEEE Transactions on Smart Grid, a journal of the Institute of Electrical and Electronics Engineers. Frolik co-authored the study with professor Paul Hines and graduate student Pooya Rezaei.

Melody is the Contributing Editor for But Why: A Podcast For Curious Kids and the co-author of two But Why books with Jane Lindholm.
A graduate of NYU with a Master's Degree in journalism, Mitch has more than 20 years experience in radio news. He got his start as news director at NYU's college station, and moved on to a news director (and part-time DJ position) for commercial radio station WMVY on Martha's Vineyard. But public radio was where Mitch wanted to be and he eventually moved on to Boston where he worked for six years in a number of different capacities at member station a Senior Producer, Editor, and fill-in co-host of the nationally distributed Here and Now. Mitch has been a guest host of the national NPR sports program "Only A Game". He's also worked as an editor and producer for international news coverage with Monitor Radio in Boston.
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