Degradation Analysis of a Commercial SOFC System

Abstract

Solid Oxide Fuel Cell (SOFC) technology offers several advantages such as fuel flexibility, high efficiency, and zero criteria pollutant emissions. SOFC systems have the potential to be cheaper and provide more reliable and cleaner electrical load-following characteristics compared with other technologies by dynamic operation and control. Cost and durability are major challenges associated with current SOFC technology. Durability of Solid Oxide Fuel Cell (SOFC) technology is a key aspect for its commercialization and long-lasting deployment in different applications. Dynamic operating conditions have considerable effects on the long-term performance and durability of SOFC systems.In this study, we evaluate the performance and degradation of a 1.5 kW (AC) commercial system under steady state and dynamic load cycling conditions for over 6000 hours. We monitored and evaluated the initial and degraded performance characteristics of the SOFC stack, while testing under constant 1.6 kW load, 85% fuel utilization, and at 760°C stack temperature for 4000 hours and under dynamic cycling load for more than 2000 hours. We conducted degradation tests based upon two load cycling profiles: i) accelerated daily cycles with load changing from 0.5 kW to 1.6 kW, with stack temperatures ranging between 720°C and 760°C, and fuel utilization between 55% and 85% for 42 cycles (~1000 hours), and ii) weekly cycling test with load changing from 0.5 kW to 1.6 kW with lower slope for 10 cycles (1600 hours). A machine learning model based upon experimental data is developed to correlate the degradation rate of the system to different features of dynamic profiles to be used in the prediction of degradation rate for a wide range of dynamic load profiles.Test results show that the degradation rate is 0.025% (2mV) per 1000 hours of operation under steady state operating conditions. As the system degrades under steady state conditions, fuel consumption increases 0.3% while the efficiency drops 0.3% per 1000 hours of operation. We observe that at beginning of life and during the first 1000 hours of operation, the degradation rate is roughly twice as high as that achieved under steady state operation (i.e., 4.8mV). Results show that the system also degrades twice as fast when forced to meet daily dynamic cycling loads. The degradation rate observed under highly dynamic daily load cycling conditions is 0.58% (4.7mV) per 1000 hours of operation over 42 daily cycles.