In 2008, University of Michigan researchers won a $2 million grant to make parked EVs feed power back to the grid. 18 years later, some firms have reached commercial offerings, turning some parked cars into grid-connected batteries

An electric car parked overnight may look completely inactive. Its battery, though, could become a useful piece of America's electricity system. That is the central idea behind vehicle-to-grid technology, which allows compatible electric vehicles to send electricity back toward the grid. Instead of treating every parked EV as a finished charging load, utilities could eventually treat groups of them as flexible energy storage.

The concept is not new, but the technology around it is changing. Researchers at the University of Michigan received a $2 million National Science Foundation grant in 2008 to study vehicle-to-grid integration. Their work examined how plug-in hybrid vehicles could connect transportation and electricity systems more closely.