Reversible solid oxide cell systems for integration with natural gas pipeline and carbon capture infrastructure for grid energy management

Electrical energy storage (EES) is necessary to enable greater penetration of renewables and as a grid-balancing solution, but current EES technologies suffer from capacity or geological limitations and high cost. Reversible solid oxide cells (ReSOCs) are an electrochemical energy conversion technology that can produce both electricity from fuel (gas-to-power) and fuel from electricity (power-to-gas), depending on resource availability and demand. Leveraging in situ C-O-H chemistry and operating at intermediate temperature (600 degrees C) and elevated pressure (10-20 bar) enables these cells to be mildly exothermic, eliminating the need for external heat input or high over-potential (low-efficiency) operation during electrolysis mode. This operating strategy also results in higher methane production during electrolysis, facilitating easier integration with natural gas pipeline infrastructure over steam/hydrogen electrolytic processes. This study proposes a ReSOC system integrated with both natural gas pipeline and carbon capture and storage (CCS) infrastructure to render a flexible, grid energy management resource. In gas-to-power mode, the system takes natural gas from a pipeline to produce electricity. Un-utilized fuel is combusted with oxygen and expanded through a turbine to produce more power. The water in the exhaust is condensed, and the remaining carbon dioxide is compressed for tanker or pipeline transportation to a carbon sequestration site. In power-to-gas mode, carbon dioxide and water are co-electrolyzed in the stack to produce methane and hydrogen, which can be injected directly into a natural gas pipeline or further refined into a purer stream of methane. We explore system design concepts, performance, and cost of a 50 MWe ReSOC system. Results indicate that synthetic natural gas (92.0% methane) can be produced at $22.7/MMBTU with a lower heating value efficiency of 81%. Alternatively, a system that net meters produced syngas and operates in power producing mode 50% of the time can generate electricity at a levelized cost of 10.5(sic)/kWh with an efficiency of 69% (LHV), while producing exhaust that is 95.5% carbon dioxide at 40 bar. If the system operates disproportionally in gas-to-power mode the LCOE drops to near 6 cent/kWh. The economic outlook for mature ReSOC systems presented herein are found to be competitive with current energy storage technologies and natural gas peaker plants.