A system under development by University of Delaware scientists could turn parked electric and plug-in hybrid cars into energy storage devices for the electricity grid. By using their batteries to release stored energy back into the grid during demand spikes, electric cars could help power plants operate more efficiently, reducing pollution. This currently unused storage capacity could be even more helpful in bringing more renewable energy sources online, as their electricity generation naturally varies.
This reminds us of Ford's plans to allow electric and hybrid cars to store energy for the benefit of the individual. They envision the electric storage capacity to allow owners to purchase electricity during off-peak hours when it's cheaper, and then rely on the car for power when it's expensive.