NEWS
Plugging In, Powering Up
Optimized vehicle-to-grid charging could make renewable energy more profitable, reshape how power plants are built, and slash emissions.
Written by Annemarie Mannion
LETTING ELECTRIC VEHICLES not just draw power from the grid—but also give some back—could deliver a double win for the planet and public health, new research from the University of Michigan and Carnegie Mellon University suggests.
“When you’re trying to understand how clean an electric vehicle is compared to a gasoline vehicle, one of the biggest components is what the emissions are when you charge an electric vehicle,” said Jeremy Michalek, professor of mechanical engineering and of engineering and public policy at Carnegie Mellon and senior co-author of the study, “Negative Electric Vehicle Emissions: Vehicle-to-Grid Can Incentivize Enough Wind and Solar Investment to Reverse EV Charging Emissions.”
“What we really wanted to understand is how the emissions consequences of charging an electric vehicle change when you account for the incentives that charging creates for building infrastructure and, in particular, when the charging is not just random, but when it is optimized for the vehicle to be charging at the cheapest times of the day,” he added.
In other words, the EVs sitting unused at times in Americans’ garages could be leveraged for supplying the electric grid while allowing consumers to access more affordable energy with less emissions, and influence the types and number of power plants that are constructed as the transition to EVs occurs, the study found.
Image: Matt Davenport/University of Michigan
“These new installations would decarbonize not only EVs, but other parts of the whole power system,” said Jiahui Chen, a lead author of the study and U-M doctoral student in environment and sustainability. “By adding EV flexible loads, you actually reduce emissions from the entire grid.”
That’s big news when you consider that the transportation and power sectors together account for more than half the greenhouse gas emissions in the United States.
Nature dictates when solar panels and wind turbines are working—of course, that’s when the sun is shining or the wind is blowing—and they generate nearly free energy without any greenhouse gas emissions. It’s an entirely different story when nature fails to cooperate, and the clean energy produced by these power plants goes to waste when supply exceeds demand.
What could change this calculation? Electric vehicles discharging to the power grid.
“These new installations would decarbonize not only EVs, but other parts of the whole power system. By adding EV flexible loads, you actually reduce emissions from the entire grid.”
—Jiahui Chen, a doctoral researcher in energy systems at the University of Michigan
“You can then store that excess power for later use,” said Parth Vaishnav, senior co-author of the study and U-M professor of environment and sustainability. “So that’s what makes building additional renewables, such as solar or wind plants, profitable.”
In addition to the benefits of smart charging EV, the study delved into vehicle-to-grid, or V2G, which would allow EV drivers to sell their stored clean energy to the grid when demand is high, instead of power plants needing to burn more fossil fuels to answer energy needs.
The study proposes that having many EV owners charging their vehicles at times when electricity is cheapest and then selling excess power back to the grid could have enormous implications.
Effect of PEV charging load on power generation. Changes in annual generation by fuel type for each PEV charging scenario when ignoring versus including induced wind and solar capacity investment. Image: Matt Davenport/University of Michigan
“It changes the composition of the electricity grid and it changes what plants actually get built,” Michalek said.
The authors acknowledge there are many additional questions that need to be pursued, including whether it would damage a vehicle’s battery to charge and discharge to the grid, how willing EV owners are to participate in such a program, and how it would impact the electric distribution network.
“If you incentivize everybody to charge at the same time, for example, when electricity is cheap or clean, that may be good from the point of view of the bulk power system, but it may stress the distribution system,” Vaishnav said.
Michalek and Vaishnav agree that one of the challenges of the study, which started in 2021, was to test their conclusions against a range of assumptions.
“What if the ratio of solar to wind was different than what you assume?” Michalek asked. “What if people built a lot more stationary storage [batteries] than you’re assuming? Accounting for all these things is deeply uncertain and challenging.”
“The other challenge is computational limits,” Vaishnav added. “We would love to find what is the exact optimal set of power plants to build under each electric vehicle scenario. We found that wasn’t really computationally feasible.”
To address this hurdle, the researchers ran a bunch of scenarios for different types of potential build-out of wind and solar plants, Vaishnav explained.
“And then we looked across those scenarios to see which were most profitable. Or, more specifically, we looked at the maximum amount of wind and solar that one could build before losing profit,” he said.
Vehicle to grid smart charging EVs and the potential to clean both the transportation and power sectors, “gives us hope,” Michalek added.
Annemarie Mannion is a technology writer in Chicago.
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