At the basic level, the process is pretty efficient. Depending on the type of hydrogen fuel cell, the efficiency ratio tends to average out around 60 percent of the total amount of energy being released by the process above. However, large-scale hydrogen fuel cells with molten carbonate or solid oxide for their electrolyte membrane can use both the heat and electricity produced for extra efficiency, getting as high as 85 percent. Meanwhile, portable fuel cells like the polymer electrolyte membranes (PEM) used in fuel cell cars get anywhere from 50 percent to 60 percent efficiency, according to the U.S. Department of Energy.
OK, but how does that compare to a regular car? Incredibly well. As cool as it is to run our cars on what basically amounts to controlled explosions and liquid dinosaurs, internal combustion engines are anything but efficient. Not counting time spent idling, energy loss along the driveline, air drag and friction, most gasoline engines lose around 62 percent of their fuel energy just to wasted heat.