Design and Eco-techno-economic Analyses of SOFC/Gas Turbine Hybrid Systems Accounting for Long-Term Degradation

Abstract

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. However, one of the major drawbacks of SOFCs is that they degrade over time, and the degradation rate varies with different operating conditions. When operated in constant power mode (the most common way of baseload power production), the degradation rate is fast such that the lifetime of the SOFC stack is around one tenth of that when in constant voltage mode (in which the power output from SOFC stack decreases). To achieve baseload power production and a long lifetime simultaneously, one potential solution is to integrate SOFC stack (operated in constant voltage mode) with a gas turbine (GT) in a SOFC/GT hybrid system. As the SOFC stack degrades, the power produced from GT increases over time by using the increasing heating value of the unspent fuel from the SOFC exhaust. We performed an eco-technoeconomic analysis (eTEA) of the SOFC/GT concept with degradation in comparison with the SOFC standalone system. The results of model simulations showed that, with certain operating conditions, the SOFC/GT hybrid system was around 36% more efficient than the SOFC standalone system, and also had about 18 times longer lifetime. On a 550 MW scale and 30-year-lifetime, SOFC/GT hybrid system can reduce the levelized cost of electricity (LCOE) by around 80 % as well as CO2 emission by around 27 %, compared to the SOFC standalone system. The 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.