On their own the answer is no. There is not enough surface on the average vehicle to collect enough sun tower that vehicle for any period of time. In my opinion an electric car with a small gas or diesel motor that runs a generator that charges the on board batteries supplemented with solar cells on the roof is an ideal option. It should get well over 200 mpg and not be a strain on our over used electrical grid. 
we are stupid pushing electric cars when cities like Phoenix charge a fine if you turn your washer/dryer on before 7pm. You can have air conditioning or an electrical car, but not both! How many new generating plants are being built? None!