So basically, it is wrong to instantly dismiss any thought of running a car on hydrogen or HHO as people do, but you simply cannot do it in the way that many people attempt.
If you can aquire the hydrogen cheaply enough, produce it by other means at home, or recharge a battery at home then use it to generate hydrogen whilst driving then it is actually possible to make gains with it. It's just a question of whether you gain more than you lose
.
I've wondered about making a windmill that rises up out of the sunroof while the car is parked xD. Not sure where it would go inside the car though... fold up inside the roof maybe? :L