This is the most popular type of fuel cell and has already found it’s way into many commercial applications. It is being used to supply energy in a wide variety of places such as hotels, schools, hospitals, office buildings, nursing homes, airport terminals, and utility power plants. Phosphoric acid fuel cells can also be put to use in large transportation vehicles, such as buses and locomotives. This type of fuel cell is very efficient, with an efficiency of over 40%. Meanwhile, the most efficient internal combustion engine is only 30% efficient. Furthermore, the phosphoric acid fuel cell is nearly 85% efficient if it participates in a cogeneration system. In such a system, the steam it produces is used to turn turbines to produce even more electricity. One can see why this fuel cell is such a popular type.