I know that some health clubs have rigged their treadmills so that exercisers produce energy to help run the gyms, and experiments show that smart sidewalks can turn pedestrians into a power source. So, it only makes sense that automobiles could be used to create, not just consume, energy. From the Futurist:

“A scheme envisioned at the Technology University of Delft would use fuel cells of parked electric vehicles to convert biogas or hydrogen into more electricity. And the owners would be paid for the energy their vehicles produce. 

Another project at the university is the Energy Wall, a motorway whose walls generate energy for roadside lighting and serve as a support for a people mover on top.”