Performance analysis of a MW-scale reversible solid oxide cell energy storage system utilizing steam-hydrogen chemistry
Javad Hosseinpour, Omid Babaie Rizvandi, Robert J. Braun
Abstract
The future of renewable energy, including solar and wind, depends on scalable grid-energy storage. Solid oxide cells (SOCs) with bidirectional operation are advantageous for various applications, including time shifting and long-duration storage, without relying on rare earth elements. This study presents a system evaluation of a stand-alone 1 MW (8 MWh) capacity reversible SOC system using H 2 –H 2 O chemistry under pressurized conditions. A one-dimensional cell model is calibrated using test data from an anode-supported SOC platform. A process system design is proposed that accounts for all balance of plant components and maximizes the recovery of thermal energy in the cell-stack exhaust in both operating modes. As a standalone system, thermal integration with external energy conversion processes (e.g., nuclear energy, fuel synthesis, etc.) is not considered. The system performance sensitivity to a variation in design parameters, including current density, stack temperature and pressure, and recirculation ratios on both the air and fuel sides of the stack, is characterized through a parametric study. The system design parameters are adjusted to obtain an optimal system round-trip efficiency (RTE) that minimizes the levelized cost of storage (LCOS). The results show that by carefully selecting the system design and operational parameters, it is possible to achieve a system RTE approaching 50% with an LCOS of 13.5 ¢/kWh. It is demonstrated that increasing the operating current density of the electrolysis stack from endothermic regions to the thermoneutral operating condition only modestly enhances overall system efficiency. Moreover, higher stack operating pressure deteriorates stack performance in electrolysis mode by raising open-circuit voltage, nevertheless increases system RTE due to enhanced system performance in fuel cell mode. An optimal LCOS is obtained at a stack operating pressure near 15 bar and arises due to a trade-off between diminishing efficiency gains and capital expenditures (first costs) with increasing pressure. • A MW-scale reversible solid oxide cell system using H 2 –H 2 O chemistry is assessed. • Achieved 50% round-trip efficiency and minimized the storage cost to 13.5 ¢/kWh. • Stack pressure at 15 bar balances CAPEX and efficiency for lowest LCOS. • Increased stack pressure & temperature improve fuel cell mode but worsen electrolysis. • Higher current density in electrolysis mode offers minimal efficiency gains.