Misho.

Fantastic idea there but unfortunately conservation of energy comes into play. If you want to hook a generator up to a cars wheels to make power then you will use more fuel aswell. However the Hybrid cars of today have a similar mechanism where when you brake the energy is converted to electricity, and when you are driving in the city i.e. at idle alot the power the engine generates is again converted to electricity.
Because hybrid cars work in this way, you will find that there is no difference in fuel consumption when cruising on highways.

Whilst solar energy is Great !!! unfortunately at this stage it is unviable.
Solar electricity costs 7-9 times more in Australia than coal power.
It has developed alot over time and there is massive research being done into it at the moment.
In about 10 years solar power MIGHT start being introduced.
However at this stage wind (which is only 3 times more expensive than coal power) and other alternatives are more viable.
Solar power technology will change significantly over the next decade or so and is too expensive to expensive to maintain at the moment.

The NSW state government in Australia is talking about nuclear power at the moment till solar technology is a good solution.
Nuclear power plants will never break even not to mention make a profit(Thats if the waste is disposed of properly), this shows how expensive solar power really is at the moment. But it is on the cards for the future