This work aims to analyse and compare the thermodynamic performance and size of two types of solid oxide fuel cell (SOFC)-based plants. The former is the conventional H₂-fed plant based on SOFC with an oxygen-ion conducting electrolyte (SOFC-O), and the latter is based on SOFC using a proton-conducting electrolyte (SOFC-H). Thermodynamic analysis reveals that in the SOFC-H system, due to H₂O formation at the cathode side, not only the anode concentration losses decreases, but also the partial pressure difference between H₂ and H₂O increases which leads to an increase in Nernst voltage compared to the SOFC-O system. Due to this, SOFC-H and SOFC-O based plants exhibit different performance in terms of the cell voltage, power, efficiency, stack outlet temperature and size of heat exchangers used for preheating the fuel and air. The results indicate, for current densities less than around 3,000 A/m², the energy and exergy efficiencies of SOFC-H-based system are more than those of the SOFC-O-based plant. This results in reduced area of heat exchangers per unit power used in the SOFC-H-based plant as compared with the SOFC-O-based plant. In addition, the sensitivity analysis demonstrates that using thin cells in the SOFC stack is favourable for the SOFC-H-based plant.

In this work, dynamic modelling of a system based on a reversible solid oxide cell (rSOC) is developed so that it can be integrated with the grid for power balancing. The focus of this work is on the dynamic operation of a system, which is investigated using representative profiles of wind electricity production. In addition, the effect and challenges of dynamic operation on the system and stack itself are studied. Detailed operation strategies are defined during the switching process from one operational mode to another and are implemented on the dynamic process model. Simulation results show that when the rSOC system is operated in solid oxide electrolysis (SOE) and solid oxide fuel cell (SOFC) modes alternatively, energy balancing can be implemented on a continuous basis. In this process, the results show that the rSOC system operates in a safe operating range and does not deviate from the pre-defined limits. This is due to the accurate strategies developed for the switching process. It is also observed from the simulation results that the switching time is significantly influenced by the initial power of the first and the final power of the later operational mode. The proposed model of rSOC was validated using experimental data, and good agreement with experimental data was demonstrated.

In this work, the dynamic modelling of a system based on reversible solid oxide cell (rSOC) is developed so that it can be integrated with the grid for power balancing. The focus is on the compatibility with profiles of wind electricity production. In addition, the effect and challenges of such a dynamic operation on the system and stack itself are studied. Detailed operation strategies are defined during the switching process from one operational mode to another and are implemented on the dynamic process model. Simulation results show that when the rSOC system is operated in solid oxide electrolysis cell (SOEC) and solid oxide fuel cell (SOFC) modes alternatively, energy balancing can be continuously implemented. In this process the results show that rSOC system operates in the safe operating range and does not deviate from the system limits. This is due to the accurate strategies developed for the switching process. It is also observed from simulation results that the switching time significantly is influenced by the initial power of one operational mode and the final power of another operational mode.

The power to gas concept is promising for the next generation of electrochemical energy storage and grid stabilization technologies. The fuel produced from electricity-driven fuel production can be an efficient energy carrier for excessive grid power. Here, a reversible solid oxide cell(s) system integrated with methane synthesis (ReSOC-MS) is proposed for the grid stabilization application at Mega Watts class. CH ₄ can be synthesized at grid surplus conditions and can be a transportation friendly energy carrier. A control strategy is proposed for this combined system, based on the grid state and H ₂ tank state of the system for the normal solid oxide fuel cell (SOFC) mode and solid oxide electrolysis cell (SOEC) mode. Simulation results of these two operational modes demonstrate that the ReSOC-MS can achieve 85.34% power to gas efficiency in SOEC mode and 46.95% gas to power efficiency in SOFC mode. Dynamic simulations of stepping grid state for 5000 s operation show that the power to gas efficiency can be higher than 70%, thereby successfully demonstrating the capability of grid-balancing and methane production.

The power to gas process concept is promising for the next generation of grid electricity storage and stabilization technologies. The electricity-driven fuel production can be chosen to be the efficient energy carrier for excessive grid power. Here, a reversible solid oxide cells system integrated with methane synthesis (ReSOC-MS) is proposed for the grid stabilization application at MW class. Besides H2, CH4 can be inclusively synthesized at grid surplus conditions as a transportation friendly energy carrier. A control strategy is proposed for this combined system, based on the grid state and H2 tank state of the system for the normal SOFC mode and SOEC mode operating. Simulation results of these two modes operating demonstrate that the ReSOC-MS can achieve an 85.34% power to gas efficiency at SOEC mode and 46.95% gas to power efficiency at SOFC mode.

This paper presents a mini-review in the field of energy storage using reversible solid oxide cells (rSOCs) for development of energy storage systems for the future. Such energy storage systems fall under the category of power-to-X-to power systems where excess electrical energy produced through renewables is stored in the form of chemicals and the same chemicals are used for conversion back to power. The main competitors of energy storage systems based on rSOC are pumped hydro storage, compressed air storage and batteries and it is envisioned that with better heat integration techniques, the round trip efficiency of rSOC systems can be improved to reach the target value of 80% as specified in the joint EASE-EERA report for European energy storage technology.

Solid Oxide Fuel Cells (SOFCs) have become the promising energy source for stationary and portable applications. The design of SOFCs including its structure and its operation are an important part to be properly optimized in order to achieve the best performance. The topic on optimization of SOFC has gained tremendous attention recently in line with the growing applications of fuel cell. This paper involves a literature survey of the application of SOFC in particular the optimization strategies. The strategies are reviewed in detail based on five features, which are the decision variable, objective analysis, constraint, method and tools. The future trends of research related to the optimization for SOFC are also discussed to provide better insight for future research work in this area.