For discussion purposes, we can assume one of two Green methods are used to produce Hydrogen using Renewables produced electricity: 1.PEM Electrolysis; 2.Reversible Solid Oxide Fuel Cell (RSOFC)(High-Temperature Electrolysis (HTE) steam system).
1. Electrolysis is a well documented method using electricity to breakdown water into Hydrogen and oxygen. Proton Exchange Membrane (PEM) technology is a good choice for the electrolysis system. A typical PEM layout as shown with a photograph of Siemens Silyzer 300 unit for PEM electrolysis.
Future large scale applications of the Siemens Silyzer 300 units are Module Arrays with 24 modules rated at 17.5 MW, system efficiency ~75%, producing 340 kg/hr of Hydrogen (0.02kg/kWh).
A 10 MW ITM electrolyser facility was installed with 5 submodules rated at 2 MW each, stack efficiency 0.02kg/kWh.
2. RSOFC is an interesting method to use solid oxide fuel cells able to work in two directions: initially one direction to produce Hydrogen and subsequently the reverse direction to produce energy from the Hydrogen. The solid oxide fuel cells (SOFC) act as a High-Temperature Steam Electrolyser.