Solid oxide cell systems (SOCs) are increasingly being considered for electrical energy storage and as a means to boost the use of renewable energy and improve the grid flexibility by power-to-gas electrochemical conversion. The control of several variables (e.g., local temperature gradients and reactant utilization) is crucial when the stacks are used in dynamic operation with intermittent electrical power sources. In the present work, two 1D models of SOC stacks are established and used to investigate their dynamic behavior and to select and tune a suitable control strategy. Subsequently, safe operating ranges were determined to meet the thermal constraints of the stack by analysing not only the fuel cell (SOFC) and electrolyzer (SOEC) individual modes but also the switching between the two modes when the stack operates reversibly. The dynamic analysis shows that the control loops of our multi-input (reactant molar flow rates), multi-output (reactant utilization and maximum local temperature gradients) control system are strongly decoupled. Therefore, a proportional integral control strategy can be used to prevent dangerous stack operating conditions in dynamic operation. Finally, the controllers were tuned, and their transfer functions were reported. Convective heat transfer via air flow allows controlling the temperature of the solid structure of the cell/stack component, thus avoiding issues related to temperature variation during transient operation. Moreover, the reactant utilization controllers can avoid component fracture or degradation owing to fuel starvation under dynamic operation. The process can be approximated by two first order transfer functions. It can help in the design of more complex control systems in the future if necessary, with embedded process models, such as model predictive control. Results in the simulation environment are preparatory to the programming phase of an actual controller in real-world applications.

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Bi-directional solid oxide cell systems (Bi-SOC) are being increasingly considered as an electrical energy storage method and consequently as a means to boost the penetration of renewable energy (RE) and to improve the grid flexibility by power-to-gas electrochemical conversion. A major advantage of these systems is that the same SOC stack operates as both energy storage device (SOEC) and energy producing device (SOFC), based on the energy demand and production. SOEC and SOFC systems are now well-optimised as individual systems; this work studies the effect of using the bi-directionality of the SOC at a system level. Since the system performance is highly dependent on the cell-stack operating conditions, this study improves the stack parameters for both operation modes. Moreover, the year-round cumulative exergy method (CE) is introduced in the solid oxide cell (SOC) context for estimating the system exergy efficiencies. This method is an attempt to obtain more insightful exergy assessments since it takes into account the operational hours of the SOC system in both modes. The CE method therefore helps to predict more accurately the most efficient configuration and operating parameters based on the power production and consumption curves in a year. Variation of operating conditions, configurations and SOC parameters show a variation of Bi-SOC system year-round cumulative exergy efficiency from 33% to 73%. The obtained thermodynamic performance shows that the Bi-SOC when feasible can prove to be a highly efficient flexible power plant, as well as an energy storage system.

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Solid Oxide Cells systems (SOCs) are increasingly being considered as an electrical energy storage method and therefore as a means to boost the penetration of Renewable Energy and to improve the grid flexibility by power-to-gas electrochemical conversion. However, temperature and reactant utilization control become crucial if the systems are to be used in dynamic operation with intermittent electrical power sources. In the present work, two 1D models of SOC stacks are built and used to study the dynamic behaviour of such stacks, and to select and tune the best control systems. After having compared with literature the accuracy of the models, safe operating ranges are determined to respect the thermal constraints of the stack. The dynamic analysis points out that inputs (m_fuel, m_atr) and outputs (U, ΔT max) are strongly decoupled; therefore, proportionalintegral control strategy has a good potential to prevent dangerous operating conditions in dynamic operation. Finally, the controllers are tuned and their transfer functions are reported.
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Using catalytic supercritical water gasification (CSCWG) in generating energy from wet biomass is efficient and environmentally friendly. However, one of the main challenges in using CSCWG is the low syngas yield and low heating value. Syngas for power and for synthetic fuel production requires high-purity and a high heating value. In this work, a novel system is proposed which increases the CSCWG syngas heating value and yield and produce electricity using a reversible solid oxide cell (ReSOC). The plant can be used for syngas production, working in electrolyser mode powered by excess renewable electrical energy. Thermodynamic calculations indicate that the energy efficiency of the CSCWG-SOEC is in the order of 72%, in this mode the syngas yield increases around five times and is rich in hydrogen and methane, its composition allows operation within the carbon-free region of the C-H-O diagram.@en

A summary of research activities and on-going multiple projects at Delft University of Technology aimed at the development of Solid Oxide Fuel Cells (SOFCs) integrated waste to energy systems are presented in this paper. A wide range of studies ranging from pattern cell impedance analysis to integrated system development is also presented. Cleaning the gas to match constraints of SOFCs requires complex approaches. A brief discussion on the achievable system efficiencies with SOFC integrated waste to energy systems is presented and novel concepts such as gasifier-Reversible SOFC integrated power production cum energy storage systems are discussed. Additionally, an overview of a wide range of national, European and international projects that helped or currently helping us to carry out the above mentioned research activities are presented.@en

This paper describes the dynamic behaviour of a high temperature electrolysis system through a transient model. The system is based on solid oxide electrolysis cells (SOECs), coupled with a wind farm in a power-to-gas configuration. The model takes into account mass and energy balances for the SOEC stack as well as for the different balance of plant components. A 1D approach has been implemented to study the system behaviour along the flow direction. The model is able to capture the physical behaviour of the SOEC system under transient operation including shifts in thermal regimes (e.g. endothermic versus exothermic), consumption of reactants and hydrogen production. Dynamics of pressurized SOEC systems are reported. The model is used to evaluate the storage option of energy produced from a wind farm in Italy. The evaluation includes the incorporation of the model with daily curves of an Italian wind farm and power consumption of local users.@en