[heleneekman]

heleneekman asked the Naked Scientists:
   
Can the spinning wheels of an electrically powered car be used to drive a generator to help power the car?

What do you think?

[Kryptid]

If you were thinking about doing that in order to have a car with limitless endurance, then I'm afraid it won't work. Whenever one form of energy is changed into another form(mechanical energy into electrical energy, for example) there will be unrecoverable losses in the form of heat. It's the second law of thermodynamics.

Another problem would be drag. As a car moves forward, air pushes back on it and tries to slow it down. Energy is lost in that way too. Ultimately, even if you could build a 100% efficient electric generator in the wheels, it would still never be able to regain all of the electrical energy that the motor had converted into mechanical energy in the first place.

[RD]

Can the spinning wheels of an electrically powered car be used to drive a generator to help power the car?

A. Yes, when braking ...

The most common form of regenerative brake involves using an electric motor as an electric generator ... in battery electric and hybrid electric vehicles, the energy is stored in a battery or bank of capacitors for later use

http://en.wikipedia.org/wiki/Regenerative_braking
 

[CliffordK]

As mentioned, regenerative breaking is possible to recoup some of the energy in the momentum when one is stopping.  There may be issues of too high of a charge rate, as well as efficiency of battery charge/discharge cycles.

One can also add solar panels, although it is difficult to generate enough energy to power the car, or even a very large fraction thereof, except in special "concept" situations.

Like with wheel friction, you would also create friction if you tried to use wind generators creating a net loss of energy.

There is a unique faster than air, wind powered car.  But, its application is purely experimental, and would not be applicable to normal driving.
http://www.sofcoast.com/weblog/2010/06/signals-drumbeats-windpowered-car-settles-dwfttw-debate.html