One of the most exciting technologies in electric cars is regenerative braking or KERS (Kinetic Energy Recovery System). As the name says: breaking fuels the batteries (some of the solutions don't even use the batteries but are totally mechanical-based, which make them even more 'pure' - there's a Porsche model using that).
In hybrid cars the energy could be recovered from the combustion engine heat, exhaust gases heat, etc. I suppose, in future, we'll be able to extract/recover some energy from almost everything (like radio or A/C) making the cars super efficient.
Interesting idea. I wonder what the efficiency gain of using the exhaust fumes with a generator would be vs. that of using it for a turbocharger (the main use of exhaust fume power currently in cars, lets the fuel burn more completely by pushing compressed air into the cylinder).
I wouldn't say that a turbocharger allows fuel to burn more completely, if that's what you meant. A turbocharger uses energy in the exhaust to spin a turbine, which is connected to an impeller, compressing air going into the engine. More air allows more fuel, and together you get a bigger bang in a smaller space - the engine behaves like it's larger than it is, burning more air and fuel then it would otherwise. A turbocharged car can still burn fuel inefficiently, and they often do run rich (injecting more fuel than will be burned) in order to avoid pre-ignition and to cool the cylinders.
A turbocharger may also be used to increase fuel efficiency without any attempt to increase power. It does this by recovering waste energy in the exhaust and feeding it back into the engine intake. By using this otherwise wasted energy to increase the mass of air, it becomes easier to ensure that all fuel is burned before being vented at the start of the exhaust stage. The increased temperature from the higher pressure gives a higher Carnot efficiency.
