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Highlights • The optimal power share between GT and SOFC in a hybrid system was analyzed. • SOFC voltage degradation and a mitigation strategy were considered. • Genetic algorithm was used to optimize the plant internal rate of return. • The proposed strategy to reduce degradation effect resulted in 50–50 optimal share. • Local analysis of degradation effects in the SOFC was performed. Abstract The coupling of a pressurized solid oxide fuel cell (SOFC) and a gas turbine has been proven to result in extremely high efficiency and reduced emissions. The presence of the gas turbine can improve system durability compared to a standalone SOFC, because the turbomachinery can supply additional power as the fuel cell degrades to meet the power request. Since performance degradation is an obstacles to SOFC systems commercialization, the optimization of the hybrid system to mitigate SOFC degradation effects is of great interest. In this work, an optimization approach was used to innovatively study the effect of gas turbine size on system durability for a 400 kW fuel cell stack. A larger turbine allowed a bigger reduction in SOFC power before replacing the stack, but increased the initial capital investment and decreased the initial turbine efficiency. Thus, the power ratio between SOFC and gas turbine significantly influenced system economic results. [ABSTRACT FROM AUTHOR]

The performance of a solid oxide fuel cell (SOFC) is subject to inherent uncertainty in operational and geometrical parameters, which can cause performance variability and affect system reliability. Operating conditions such as current demand, cell temperature and fuel utilization play an important role on the degradation mechanisms, which affect typical SOFCs. In previous work, a deterministic empirical degradation model of a SOFC was developed as a function of such operating conditions. By the nature of experimental data and regression fitting, this model was not deterministic. The aim of this work is to evaluate the impact of the uncertainties in the degradation model through a stochastic analysis. In particular, the Response Sensitivity Analysis (RSA), an approximate stochastic method based on Taylor series expansion, is applied to a standalone SOFC model and a fuel cell hybrid system model both subjected to cell degradation. The attention is principally focused on the impact on the fuel cell lifetime. To provide an indication of degradation effect and resulting lifetime uncertainty on economic performance, a cursory economic analysis is performed. [ABSTRACT FROM AUTHOR]

The hybridization of Solid Oxide Fuel Cell (SOFC) and gas turbine technologies provides an increase in system efficiency and economic performance. The latter aspect is significantly affected by fuel cell degradation, due to several mechanisms. However, hybrid systems allow different control strategies to minimize degradation effects on system performance and their impact on economic feasibility. A real-time distributed model of a SOFC was used to simulate fuel cell degradation in the cases of a standalone stack and a hybrid configuration, in the latter of which the numerical model is normally coupled with the hybrid system hardware components of the National Energy Technology Laboratory (NETL) hyper facility. The results showed how in a hybrid system it is possible, with an appropriate strategy, to maintain constant voltage even if the cell is degrading, reducing degradation rate during time. At constant power demand, fuel cell life could be significantly extended using the operating strategies allowed by coupling with a turbine (an order of magnitude longer than a standalone fuel cell), maintaining high system efficiency despite fuel cell degradation. [ABSTRACT FROM AUTHOR]

Fuel cell gas turbine hybrids present significant challenges in terms of system control because of the coupling of different time-scale phenomena. Hence, the importance of studying the integrated system dynamics is critical. With the aim of safe operability and efficiency optimization, the cold air bypass valve was considered an important actuator since it affects several key parameters and can be very effective in controlling compressor surge. Two different tests were conducted using a cyber-physical approach. The Hybrid Performance (HyPer) facility couples gas turbine equipment with a cyber physical solid oxide fuel cell in which the hardware is driven by a numerical fuel cell model operating in real time. The tests were performed moving the cold air valve from the nominal position of 40% with a step of 15% up and down, while the system was in open loop, i.e. no control on turbine speed or inlet temperature. The effect of the valve change on the system was analyzed and transfer functions were developed for several important variables such as cathode mass flow, total pressure drop and surge margin. Transfer functions can show the response time of different system variables, and are used to characterize the dynamic response of the integrated system. Opening the valve resulted in an immediate positive impact on pressure drop and surge margin. A valve change also significantly affected fuel cell temperature, demonstrating that the cold air bypass can be used for thermal management of the cell. [ABSTRACT FROM AUTHOR]