Solid oxide fuel cells (SOFCs) are a promising next-generation technology for power production from fossil fuels. Because they convert chemical energy into electricity electrochemically, they are generally more efficient than combustion-based power plants due to the thermodynamic limitations of combustion cycles, and accordingly, have lower carbon intensities [1]. However, one of the main drawbacks of SOFCs (and SOFC stacks) is that they can degrade over time in a variety of ways, including accruing damage to the anode, cathode, interconnects, and other cell or stack components. SOFCs are most commonly used in “constant power” mode, in which the fuel flow rate and current density are increased over time to counteract the degradation effects and yield a constant power output. However, higher flow rates cause the degradation rates to grow even faster, resulting in a lifetime potentially as short as 1.5 years [2].

Recent research has found that by operating in “constant voltage” mode, along with some other operating strategies, can result in SOFC lifetimes as long as 13-14 years [2]. However, the power produced decays over time, and in fact, the fuel utilization (the percentage of fuel oxidized in the anode) decays as well. This means that the anode exhaust has a large and unused heating value. The solution is to use this anode exhaust as a fuel for a gas turbine (GT), creating the SOFC/GT hybrid system [3]. The system is designed such that as the SOFC decays in power production while operating in constant voltage mode, the GT turbine increases in power production over time as the anode exhaust heating value increases. The efficiency of the GT changes during its life as well depending on the anode exhaust conditions. The net effect is that the total system power decays slowly over time, and is suitable for baseload grid-power generation in the long term. It is also more efficient than a standalone GT system.

In this work, we present an eco-technoeconomic (eTEA) analysis of the SOFC/GT concept with degradation considered. Dynamic Matlab Simulink models of the SOFC which considers degradation effects were coupled with Aspen Plus steady state models of the balance of plant in a pseudo-steady approach. This enables the simulation of the gradual degradation of the plant over a 14 year lifetime. This simulation was used to compute key performance indicators like levelized cost of electricity, greenhouse gas emissions, cost of CO2 avoided, efficiency, and dynamic performance curves for power, current, voltage, fuel utilization, etc. These are used in turn to quantify the tradeoffs between standalone SOFC, standalone GT, and SOFC/GT hybrid systems. They results show that SOFC/GT hybrids are a promising near-term approach because existing SOFC technology can be used directly while both avoiding short cell lifetimes and still getting near-baseload performance.

1. Adams TA II, Nease J, Tucker D, Barton PI. Energy conversion with solid oxide fuel cell systems: A review of concepts and outlooks for the short- and long-term. Ind Eng Chem Res, 52:93089–3111 (2013).
2. Tucker D, Harun NF, Abreu-Sepulveda M. SOFC lifetime assessment in gas turbine hybrid power systems,” J Fuel Cell Sci Technol, 11:051008-1 (2014).
3. Tucker D, VanOsdol J, Liese E, Lawson L, Zitney S, Gemmen R, Fort JC, Haynes C. Evaluation of methods for thermal management in a coal-based SOFC turbine hybrid through numerical simulation. J Fuel Cell Sci Technol, 9:041004 (2012).