Hydrogen is a potential mitigation for the peak use vs peak production issue of renewables. Think of hydrogen tanks less like conventional fuel but batteries, with higher energy density by volume and simpler engineering and less resource intensivs to manufacture compared to lithium ion.

Also, if you have a lot of tracks, the resistive and inductive losses of overhead wiring can actually put your energy efficiency below batteries or even hydrogen. Also, maintaining overhead wires and associated poles and gantries can both be more expensive and consume more resources than batteries or hydrogen. It can double the infrastructure costs per distance of track. What is the most efficient or cost effecrive system all things considered depends on factors like how much track you have, how often the trains run and how much power they draw, and whether you can use any tricks like dynamic electrification that turn off when no train is passing by. Though this is more of a problem with long distance heavy rail that runs less frequently.