HIGH-EFFICIENT reversible solid oxide fuel cell coupled with waste steam for distributed electrical energy storage system

Abstract

Recently, the penetration of renewable energy into the power sector has dramatically increased; thus, electrical energy storage (EES) systems with long duration time, high capacity, and high energy density are essential. Reversible solid oxide fuel cell (RSOFC) systems have become a promising candidate for this important role. In this study, a new RSOFC system coupled with waste steam considering the compatibility between charge and discharge modes is proposed. A lumped model of RSOFC stack was integrated into EBSILON (R) Professional commercial software for system analysis. Parametric studies were conducted to examine the effects of fuel composition, waste steam temperature, and steam conversion ratio on three system round-trip efficiency types: reference system round-trip efficiency (eta(RT1)), electrical roundtrip efficiency (eta(RT2)), and exergy round-trip efficiency (eta(RT3)). Base case calculation shows that the system round-trip efficiencies eta(RT1), eta(RT2), and eta(RT3) are 37.9%, 53.8% and 49.6%, respectively. In the parametric analysis, as hydrogen volume concentration in the hydrogen-steam mixture in the SOEC mode was increased from 10% to 60%, eta(RT1) and eta(RT2) increased, reaching a maximum value of 54.2% and 38.7% at 30% and 40% of H-2 concentration, respectively. The exergy round-trip efficiency had the same trend as eta(RT2) and reaches maximum value of 50.1%. The waste steam temperature had a small effect on all round-trip efficiency types. The increase in steam conversion ratio relatively improved eta(RT1) and eta(RT)(3), but negligibly influences eta(RT2). The proposed system provided a solution for upgrading the EES system performance via integrating a RSOFC system with low exergy waste steam. The efficiencies eta(RT2) and eta(RT3) were much higher than n RD because of the use of waste steam. The exergy round-trip efficiency with consideration of waste steam exergy was a good indicator of system performance. (C) 2018 Elsevier Ltd. All rights reserved.