text: there are two reason's you are off base.  The really physicsy reason is that the second Law of Thermodynamics forbids any 100% efficient engine (in your case, the whole car is the engine).  Without going into too much detail, this is because energy is always conserved in the Universe, and any engine loses energy to heat, at least by friction.\n\nThe more understandable reason is this: taking your pinwheel windmill generators as an example, the work that they provide (to charge up the battery) does not come from wind, it comes from the car moving, which comes from the car's engine.  Therefore, all the energy going into the battery is extra work the car has to do.  \n\nYou can, however, save some energy when you slow down the car, you can return some of its moving energy (kinetic) into a battery.