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Purpose: A reliability analysis of a solid oxide fuel cell (SOFC) system is presented for applications with strict constant power supply requirements, such as data centers. The purpose is to demonstrate the effect when moving from a module-level to a system-level in terms of reliability, also considering effects during start-up and degradation. Design/methodology/approach: In-house experimental data on a system-level are used to capture the behavior during start-up and normal operation, including drifts of the operation point due to degradation. The system is assumed to allow replacement of stacks during operation, but a minimum number of stacks in operation is needed to avoid complete shutdown. Experimental data are used in conjunction with a physics-based performance model to construct the failure probability function. A dynamic program then solves the optimization problem in terms of time and replacement requirements to minimize the total negative deviation from a given target reliability. Findings: Results show that multi-stack SOFC systems face challenges which are only revealed on a system- and not on a module-level. The main finding is that the reliability of multi-stack SOFC systems is not sufficient to serve as sole power source for critical applications such as data center. Practical implications: The principal methodology may be applicable to other modular systems which include multiple critical components (of the same kind). These systems comprise other electrochemical systems such as further fuel cell types. Originality/value: The novelty of this work is the combination of mathematical modeling to solve a real-world problem, rather than assuming idealized input which lead to more benign system conditions. Furthermore, the necessity to use a mathematical model, which captures sufficient physics of the SOFC system as well as stochasticity elements of its environment, is of critical importance. Some simplifications are, however, necessary because the use of a detailed model directly in the dynamic program would have led to a combinatorial explosion of the numerical solution space. [ABSTRACT FROM AUTHOR]

The start-up of a solid oxide fuel cell (SOFC) is investigated by means of numerical simulation with a view to material and operational constraints on a component and system level, as well as thermo-mechanical stresses. The applied multi-physics modeling approach couples thermal-, electrochemical, chemical-, and thermo-mechanical phenomena. In addition to constraints, emphasis is given to degrees of freedom with respect to manipulated and controlled variables of the system. Proper ramping during the start-up procedure keeps critical parameter values within a safe regime. Of particular interest are gradient in terms of temperature and chemical concentrations. Nevertheless, simulations show that thermo-mechanical stresses are relatively high during the initial start-up phase, the system is, thus, more susceptible to failure. The combination of multi-physics modeling in conjunction with practical control aspects for start-up of an SOFC, which is presented in this paper, is important for applications. [ABSTRACT FROM AUTHOR]

We use a detailed solid oxide fuel cell (SOFC) model for micro-grid applications to analyze the effect of failure and degradation on system performance. Design and operational constraints on a component- and system level are presented. A degrees of freedom analysis identifies controlled and manipulated system variables which are important for control. Experimental data are included to model complex degradation phenomena of the SOFC unit. Rather than using a constant value, a spatially distributed degradation rate as function of temperature and current density is used that allows to study trajectory-based performance deterioration. The SOFC unit is assumed to consist of multiple stacks. The failure scenario studied is the loss of one individual SOFC stack, e.g. due to breakage of sealing or a series of fuel cells. Simulations reveal that degradation leads to significant drifts from the design operating point. Moreover, failure of individual stacks may bring the still operating power generation unit into a regime where further failures and accelerated degradation is more likely. It is shown that system design, dimensioning, operation and control are strongly linked. Apart from specific quantitative results perhaps the main practical contribution are the collected constraints and the degrees of freedom analysis. • System analysis of SOFC-based plant combining design, control and reliability aspects. • System simulation of degradation effects and failure scenario. • Parameter-dependent degradation rates with ohmic and activation polarization loss contributions. • Collection of design and operational constraints on plant level. • Set of controlled and manipulated variables of system for control. [ABSTRACT FROM AUTHOR]