Vehicle-to-grid integration uses cars as batteries

Posted by Emma Woollacott

An engineer at the University of Michigan thinks our cars just have it too easy. Instead of sitting idle for hours in parking lots, they should be earning their keep by helping store power for the electricity grid.

"Cars sit most of the time," said Jeff Stein, a mechanical engineering professor at the University of Michigan. "What if it could work for you while it sits there? If you could use a car for something more than just getting to work or going on a family vacation, it would be a whole different way to think about a vehicle, and a whole different way to think about the power grid, too."

Stein's National Science Foundation-funded team is looking at plug-in hybrid electric vehicles (PHEVs) that not only use grid electricity to meet their power needs, but also store electricity from the wind or sun, or even feed it back into the grid, earning money for the owner.

The concept is called vehicle-to-grid (V2G) integration.

Stein and his colleagues envision a world where electric cars become "distributed" storage, doubling as mobile holding tanks for electricity.

"If we had lots of PHEVs all plugged into the grid, then what seems like an insignificant amount of energy storage becomes a large energy storage," he said.

Stein's team has already made some progress understanding battery health and life.

"We're exploring how an owner can charge it and utilize the battery in a way that is battery health-conscious to extend the useful life of the battery," Stein said. "That's especially important if we also think about charging vehicles at off-peak hours, and it's also important if we're talking about this shared opportunity for electric storage. What's good for the battery isn't necessarily good for the grid."

The team is also designing new generations of PHEV powertrains, grid systems and intelligent controllers for these powertrains and systems to maximize the benefit of V2G integration.