the funny thing is that the car would be more efficient if it were just using the solor energy.... hmmmmm how is that you say? Well when you convert the solor energy into hydrogen there is an energy loss in the process. This means that if the solor power was being put into a battery and used, the car would have more energy to use.
Today, natural gas reformation is the cheapest and most common way to produce hydrogen. Even with a 15% energy loss in natural gas reformation, hydrogen fuel cell vehicles are cleaner and more energy efficient than gasoline or gasoline-hybrid vehicles.