Evaluation of conceptual electrolysis-based energy storage systems using gas expanders

In this study, four energy storage systems (Power-to-Gas-to-Power) were analysed that allow electrolysis products to be fully utilized immediately after they are produced. For each option, the electrolysis process was supplied with electricity from a wind farm during the off-peak demand periods. In the first two variants, the produced hydrogen was directed to a natural gas pipeline, while the third and fourth options assumed the use of hydrogen for synthetic natural gas production. All four variants assumed the use of a gas expander powered by high-temperature exhaust gases generated during gas combustion. In the first two options, gas was supplied from a natural gas network, while synthetic natural gas produced during methanation was used in the other two options. A characteristic feature of all systems was the combustion of gaseous fuels within a ballast-free oxidant atmosphere without nitrogen, which is the fundamental component of air in conventional systems. The fifth variant was a reference for the systems equipped with gas expanders and assumed the use of fuel cells for power generation. To evaluate the individual variants, the energy storage efficiency was defined and determined, and the calculated overall efficiency ranged from 17.08 to 23.79%, which may be comparable to fuel cells.