The merger of adiabatic compressed air storage (A-CAES) and large scale solid-oxide electrolysis cells (SOEC) is proposed for the production of green hydrogen via excess power from wind and solar photovoltaic facilities.

In the system configured by researchers from the Korea Institute of Machinery and Materials, the A-CAES can store compression heat or compressed air in thermal energy storage (TES) and air storage reservoirs, respectively, and then release the heat and compressed air for power production. The SOECs use a solid oxide or ceramic electrolyte to produce hydrogen and syngas fuel from a mixture of water and carbon dioxide or oxygen from carbon dioxide, respectively. The combined cooling, heat and power system recovers heat from compression in a TES for subsequent use in the expansion process.

A motor, compressor and TES units are connected to both a turbine for power generation and the SOEC unit. Hot compressed air cooled in the TES unit is stored in large underground caverns. In the discharging process, the compressed air is released from the cavern and heated by the TES and is then conveyed to the expander for power generation or to the SOEC unit.

A parametric analysis outlined in Energy Reports shows that the total round-trip efficiency of the combined cooling, heat and power-A-CAES system was found to be 121.2% and its over-unity efficiencies were in the range of 100% to 120%. The round-trip efficiency of conventional power-only A-CAES systems is approximately 70%; the remaining 30% of the input energy is wasted as heat due to the irreversibility of the A-CAES processes.