For 15 years, Willette Kempton, who directs the University of Delaware’s Center for Carbon-Free Power Integration, saw fleets of electric vehicles as valuable backup power on demand to utilities. Using electric vehicles for grid backup would reduce the need for costly new generating plants and help ensure a reliable supply of electricity. Instead of paying other utilities for backup power, a utility could pay an electric vehicle owner for backup electricity, an approach known as "vehicle to grid."
Kempton has calculated the amount of klowatts that could be available to the grid if the 146 million cars, SUV's and pickups in the U.S. provided their stored electricity to the grid. They could produce 10 times the power of all U.S. power plants combined. The car owner would enter information into a dash-mounted control panel, including when he needed to travel, and how far. A microprocessor in the control panel would calculate whether the car had power to spare.
The advanced batteries in electric vehicles can respond within seconds to a need for extra power. They are especially useful for frequency regulation that balances supply and demand which must be kept in balance at all times, something that's done 400 times a day. The value of such regulation could be worth $5,000 a year for a single car. With our current electricity system, most of the supply is constant while demand varies. As more wind and solar is used to provide our electricity, not only demand, but also the main sources of supply will vary making balancing the system more complicated. For more details, see the article: Vehicle to Grid: A New Spin on Car Payments.