May 3, 2014
This is not plausible. By attaching some kind of turbine to the vehicle, you are creating more drag. All the power you are able to generate from this turbine will be less than (or in the case of 100% efficiency, equal to) the amount of energy needed to overcome the drag.
May 15, 2014
I like your idea a lot, a friend of mine once had a similar idea: he wanted to attach wind turbines to a subway for power provision. But unfortunately, they were facing the same problem as stated in the comment above. They asked an expert who stated the same problem. Also, the following webpage describes why this is not feasible: http://transportevolved.com/2014/01/09/were-sorry-gizmodo-but-mini-wind-turbines-wont-power-your-electric-car-for-free/
Jun 10, 2014
I usually get irritated by any perpetual motion notion. However, in my mind I am not as sure this fits entirely in that category as the two previous commentators are. If the turbine is placed on top of the car I am in total agreement that, on a still day or a day when the tail wind is less than the speed of the car, the increase in drag would be greater that the energy produced by the turbine. But there are other possibilities that I am not so sure about. How about if there is a strong head wind? Would it not be possible that the energy generated would be greater than the drag? After all don't sailing ships sail into a head wind by tacking back and forth? I have even seen it suggested that turbines on the masts of a sailing ship would allow it to sail directly into the wind. Another possibility that I can imagine is that if the turbine is located directly in front of a vehicle with a poor aerodynamic design, such as a box truck traveling into the wind, that it might even reduce the drag and produce some energy as well.
Jun 11, 2014
The point that I don't want people to miss is that the drag is already there. The faster we drive, the more the drag. We are pushing the energy out of the way. This pushed energy is the drag. An efficient, low friction, turbine could be placed in flow through body ports and would not contribute to drag. Don't miss my point. Flow through body ports alone would reduce drag. Small turbines would send considerably more energy to the batteries. Lateral thought, people.