Question: But compression seems like a simple thing. Why are compression energy costs so high?|
Simply put, all of the hydrogen fed to the cell has to have been compressed for transport. The number I give is for a Fuel Cell efficiency of 35.5%. This is a system efficiency which includes parasitic power. So lots of hydrogen has to be compressed and transported to feed the Fuel Cell.
Theoretical compression energy can be calculated using standard engineering equations, for example those in "Perry" -Chemical Engineers Handbook, A compressor efficiency is used to compute actual requirement.