[RedDevil]

The power output of those is quite low, even in full sunlight. If you have it somewhere inside the car chances are that it will be in the shade or turned away from the sun most of the time. Even in fair weather you cannot expect more than one watt on average.

Then there is the weight of the panel. Probably less than a kilogram, but not really nothing. The panel will just generate a few Watt per kilo. In comparison, the ICE produces about 500 Watt per kilo or more.
Adding the panel will most likely raise your fuel consumption ever so slightly, and will definitely hurt performance a tiny bit.
It is the same problem as the exhaust heat recovery systems have; too heavy for the tiny amount of power they produce. In general they can barely make up for their cost in stationary, continuously operating installations. Logic forbids they could break the odds in a car, where weight is a penalty and operation is usually limited to a few hours a day or less.

The solar array could be used to charge your battery when the car is resting. Sadly, not in this setup.
The cigarette outlet will be switched off once you remove the key. Otherwise it could keep the battery charged, but not now.

As has been said before, it is best to put solar arrays on your house and charge your car batteries from the mains.