Off-grid electrochemical nitrogen reduction to ammonia II: Energy storage utilizing process streams

Off-grid operation of electrochemical nitrogen reduction requires energy storage to power separation processes with limited flexibility during times with low electricity availability. In part II, we investigate the use of two side products for energy storage: hydrogen and low-temperature heat. Hydrogen can be compressed at high electricity availability, stored at high pressure, and reconverted to electricity during low availability. Low-temperature heat can be upgraded in a heat pump, stored at high temperature, and reconverted in a heat engine. Both storage technologies allow individual sizing of storage capacity and discharge power and can be tailored to the needs of the process. Depending on the renewable profile, production costs can be reduced by 5 % to 7 %, but remain considerably higher than those of the electrified Haber–Bosch. The considered ideas have the potential to be utilized in other power-to-chemical processes, but this needs to be analyzed in future work.