What can electrifying your ride do to the grid?

Around 1 in 5 cars sold last year were electric vehicles (EVs). While they offer benefits—including zero tailpipe emissions, minimizing noise pollution, and reducing reliance on imported fossil fuels—they could also include drawbacks. EVs may strain the power grid.

In the Department of Electrical and Computer Engineering at Texas A&M University, Dr. Thomas Overbye, a professor and the Texas A&M Engineering Experiment Station Smart Grid Center director, and Dr. Jonathan Snodgrass, a senior research engineer, are working to understand the ramifications of the increased number of EVs on the power grid—and how to potentially use EVs to the grid’s advantage.

“If everyone got an electric vehicle, it would more or less double the usage of the grid, and that’s a big deal,” Snodgrass said. “So, the question is, how do we leverage the flexibility of residential charging? Because if EVs are flexible, they can actually be an asset to the grid, not just a liability.”

Flexible charging is used to maintain balance, Snodgrass added. For instance, right now, when a user plugs their car in for the night, the car starts charging immediately, which adds strain on the grid, since the grid usually has its highest load between 4–7 p.m. However, if we can use the “smarts” in an EV charger to allow the utility company to change when the vehicle charges, the EV can truly become a flexible load.

Known as a price-responsive load, the EV could charge for the first three hours, then stop and start again, depending on what the grid can handle. All of this would consider a user’s driving needs and ensure their car is charged before they leave the next morning.

“Suppose you get home at eight or nine at night after running your errands and picking up your kids,” he said. “When you plug in your car, you don’t necessarily care when it charges, you just care if it’s going to have enough juice to get you to work and school in the morning.”

Charging Levels

Typically, charging EV batteries can range from hours to days, depending on the charging speed. Level 1 uses a standard 120-volt house outlet and can take days to fully charge a car or truck. Level 2 uses a 240-volt supply, the kind that water heaters need, and can charge most electric vehicles overnight.

If a user wants to quickly charge their EV, they use Level 3 fast chargers, which are high-speed charging stations. A fast charger at 50 to 350 kilowatts has the same electricity demand as 25 to 50 houses and can charge a car in 30 to 60 minutes. Since these stations have their own converters, the car does not have to rely on its slower internal converter. However, it’s a big load on the grid.

Imagine several people pull up at the same time to a charging station and plug in their EVs to DC fast chargers. A megawatt of load would be added to the power grid almost immediately, and the frequency of the grid would fluctuate because the balance between electricity supply and demand is off. The grid prefers a load that changes predictably and smoothly.

“The power grid can handle multiple megawatt loads, switching in and out, but it puts pressure on the grid,” Snodgrass said. “It’s not designed for that. It’s like, can you drop a glass on the floor without it breaking? Yeah, totally. But it’s not designed to be dropped on the floor. It was designed to be placed down carefully and lifted up carefully.”

Partnerships

The research team is working with the Texas A&M Transportation Institute (TTI) and ElectroTempo, a leading software firm and a startup out of TTI.

“TTI is one of the best transportation centers in the world, and we have one of the best grid modeling groups in the country led by Professor Overbye, the group leader for energy and power in the electrical and computer engineering department. For a university, we have some of the best grid modeling and simulation capabilities in the world,” Snodgrass added.

ElectroTempo takes real transportation data (i.e., real miles traveled) and converts it to EV miles to determine a forecasted load. They pass the data to Overbye’s team, and they perform grid simulations to make predictions about the impact it would have on the grid if “x” percent of people switched to EVs.

With that information, they could inform utility companies if distribution, transmission lines or transformers need to be upgraded or if they could expect overload problems in certain areas. Some of those issues could be solved by shifting the EV load around or by replacing power lines or transformers before they become overloaded.

“In some cases, it may not be worth electrifying a certain area. For example, utilities should tell people who live in this neighborhood, if you really want electric vehicles, the first 10% of customers can electrify, no problem. After that, they will have to pay a surcharge because utilities will need to upgrade your line. It depends on how utility companies want to handle it,” Snodgrass said.