At first glance, the Toyota Scion sitting in the University of Delaware parking lot looks like a normal boxy car.
But a second look shows it lacks a tailpipe and has an electrical outlet set into the grille below the hood. Inside, the Scion's identity as an electric car is revealed by the lack of a fuel gauge and by a dashboard display showing that it has used 54.3 kilowatt hours to drive 210 miles.
But this is no ordinary electric car because, in addition to recharging its battery when not being driven, it also gives power back to the grid.
Willett Kempton, who is leading the university's Vehicle to Grid (V2G) programme, believes electric car batteries will represent a vast, reliable source of energy for the grid in a future when the national power supply will increasingly rely on renewable but fluctuating sources like sun and wind.
"Because in future, electricity will come more and more from sources that fluctuate, we need some form of storage that can reliably supply the grid, and electric car batteries are the most cost-effective form of that," he said.
One typical electric car can put out more than 10 kilowatts, the average draw of 10 houses, according to university researchers, and the power is readily available, since cars are idle on average for 95 per cent of each day.
Since 1997 the V2G programme has been promoting the idea that electric or hybrid vehicles, if widely adopted, could give back to the grid during the many hours when they are not being driven.
With three converted Scions now in service and using V2G technology, and another four owned by the state of Delaware, the Centre for Carbon-free Power Integration is proving not only that the vehicles are contributing energy to the national grid but also that the owner gets paid for his or her contributions.
On a laptop in his office, Prof Kempton points to a display showing real-time data on the charging status of five V2G vehicles, including the power that each has put back into the grid, and the money that contribution has earned.
During March 1 to 25, one of the vehicles had earned €106.53 for the university from PJM, the local grid operator.
A key to the programme is a cable that can transmit power to or from the car, and which is connected in a campus parking lot from the radiator grille outlet to a socket that looks like a recreational vehicle hook-up.
In the ideal world of V2G, such hook-ups would be commonplace at highway rest stops or parking lots where electric-vehicle drivers can recharge. Overnight, a fully-charged battery can give back to the grid.
Auto Port Inc. of Wilmington installs the V2G technology in the Scions.
The power needs of both the battery and the grid at any moment are determined via an internet signal carried down the connector, allowing each end to communicate with the other, Prof Kempton said.
To help lay the groundwork for V2G in Delaware, the state passed a 2009 law - the first of its kind in the world - requiring utilities to compensate electric car owners for power sent back to the grid at the same rate they pay to charge the battery.
At a current cost of about €56,000 per Scion - including V2G conversion and the basic car - the vehicles are beyond the reach of most drivers. But Kempton argues that costs will fall as production increases. With all costs optimised, a V2G car should eventually sell for between €2,200 and €3,700 more than an equivalent gasoline model, he said. Prof. Kempton boosts his vision with a prediction that most US cars will be hybrid or pure electric in 30 years' time because of the rising cost of gasoline.
"There's not going to be enough oil, and China is going to buy it all," he said.