Quote:
Originally Posted by brennerator
When youre braking wouldnt the fans help conserve some energy. So in a city environment where one is constantly braking...
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First a bit of information about energy use in cars, at different speeds. There are three basic ways that typical cars use energy, all of the energy comes from the gasoline powered engine, but goes to different things.
The first is overcoming rolling resistance....it takes energy to overcome the tire's resisance to roll. This load is mostly proportional to the speed of the car, so the faster you drive, the more power it takes to keep the car moving. To get a feel for this, try (safely!) pushing a car, it will be easy to push it slowly, but it becomes harder to push the faster it goes.
The second is overcoming air resistance, this is aerodynamic drag.....it takes energy to move the air out of the way of the body of the car. This load is mostly proportional to the square of the speed of the car. That means that it is very small at low speeds, but very high at high speeds. To get a feel for this, see if a light breeze will push a car, and also see how it is different driving into a headwind at highway speed, vs. driving with a tailwind.
The third is accelerating the mass of the car. This energy is not wasted, unless you use the brakes to slow down (then your kinetic energy turns into heat energy, which is dissipated by the brakes). Hybrid cars get about the same mileage in town as they do on the highway, because they recover the kinetic energy, and store it in a battery for use in accelerating the car again.
I think that you are trying to recover a very small part of the energy that is being used to overcome aerodynamic drag. In city driving, there is not much energy lost to drag, most is lost to the brakes and overcoming rolling resistance. And still, the best way to reduce losses to air resistance, is to make the car "smoother" to reduce the coefficient of drag, and to reduce the frontal area (height and width).
If you don't understand any part of this, please ask more questions!