How would this be determined? What variables affect the volume of water produced per watt/kilowatt? If a cell is loaded heavily, does it produce more/less/same amount of water per watt than if it is lightly loaded?
1. The PEM fuel cell works by migrating the protons through a membrane. So, for each H2O molecule, you get 2 electrons. Use molar weights to determine amount of water. Power E * I, where I is coulomb per second. Look up number of electrons per coul to calculate. 2. The efficiency. This is a function of voltage drops and unreacted fuel, see article. 3. Less.
