It is fair to assume that a lot of engineers at mobile and stationary original equipment manufacturers understand the technology of Proton Exchange Membrane (PEM) fuel cells. After all, fuel cells have been around since the mid-1800s (at least in concept) and over the years have been involved in some rather high-profile applications with the most notable arguably the US space program.But as the push toward cleaner and hydrogen-based becomes more pronounced, how do fuel cells work has taken a backseat to a much more prosaic queries, such as How will they fit in my vehicle or machine? How many do I need to use in my equipment? How long do they last? How are they serviced?As Diesel Progress editors have regularly heard these kind of questions, we have collated the most common queries and asked two leading professionals for their answers.Philippe Gorse (director of fuel cell technologies at mtu solutions in Germany) and Ryan Sookhoo (business development director for Cummins’ fuel cell business in Canada) were posed the questions.