Using a small engine to rotate a generator to put power to wheels seems like added losses in efficiency unless a transmission has an efficiency loss of 10% and I don't believe they do. So with that The engine energy loss is 74% as heat to radiator, 5% conversion loss at the generator, 4% loss at the motors so the total loss is 83% of energy in.

With the recent advancement of transonic combustion a highly efficient fuel injection system, a 4 cylinder engine will get over 60 mpg, and at highway speeds the engine even get more efficient to get close to 85 mpg. With the increase efficiency of 50% a normal engine with 30% efficiency now becomes over 60%. So with the new fuel injection (no plugs required) and the use of lithium ion or better yet more efficient lithium polymer batteries, the volt could even get better mileage and reliability.

Since Li-poly batteries have denser packaging without intercell spacing between cylindrical cells and the lack of metal casing, the energy density of Li-poly batteries is over 20% higher than that of a Li-ion battery. Li-poly batteries also weigh less the lithium ion batteries of same amp-hr capacity.

Juan, its a great idea, but it just isn't practical. the average amount of energy that gets to the Earth's surface is about 250 watts per meter squared (W/m^2). That is a fair bit, but then you consider the roof of the volt is maybe half a square meter, you're down to 125 W/m^2. Then you have to consider what most Solar cells efficiencies are, for most applications its about 20%. With that you are down to 25 watts, and that would be at peak, on average it would be much lower. And then you have to take into account whether or not it's cloudy, then you would be luck to get half that.

So to put it in other terms, that is about a 12 volt supply with 2 amps of power, maximum. The Volt uses a 380 volt battery and 8 KILO-watts of power. If the battery were to be charged by just the solar it would take roughly 320 hours, by comparison it take only roughly 5 hours to charge from a household outlet.

So that means even if they did put a solar roof on the volt the gains would be minimal, and could realistically power nothing more than a little fan.

Why not use solar power? on daylight the car is moving,, and it can charge the car.,,, while its parked,, it can charge the battery,

Monistat7 is right! If the rear wheels were to be used to regenerate electricity, while being at a constant speed or accelerating, the power they would recoup would be exactly equal to what the vehicle would have to supply. And thus resulting in poorer performance. I say only when at a constant speed or accelerating because when you are at those states you want the least amount of resistance, having a generator in the rear wheels adds a LOT of extra work to overcome, and complexity. But thats why it is a good idea when braking, because during braking you are getting rid of your extra speed, and momentum, through friction and thus through heat. This heat is just wasted to the outside normally, but by using regenerative braking you are able to capture what was otherwise just going to be wasted heat, back into usable energy!

It seems to me that since the rear wheels are doing nothing nothing else they should be utilized as generators to put electricity back into the batteries.

I do not know for sure, but my guess would be that using the rear wheels to gain energy would create extra mechanical drag. So by doing that it would be counterperductive. Pretty much you would be using extra energy to make energy and that would just cancel each other out. That is just my guess, I am no engineer.

The back wills of this car are rolling free,why not use them to power a high frequency generator allow it to charge a booster and compensating the main battery with it? REGARDS