Development of a reversible solidoxide cell test station

In a effort to curb climate change, more and more countries are adding solar and wind farms to their electrical grid. These solar and wind farms produce electrical energy based on environmental conditions, for example solar irradiation intensity or wind speed. As such these farms create fluctuations in the electrical grid and create a mismatch between energy supply and demand. To solve this problem the European Balance project proposes to use reversible solid oxide cell (ReSOC) systems. These systems can convert the excess energy produced by the solar and wind farms into an energy carrier when the supply of energy is bigger than the demand. At a later time this energy carrier can be reverted back to electrical energy when the energy demand is bigger than the supply. As these ReSOC systems are still in the development phase, experimental work is being carried out to develop these systems. For the Balance project the university of technology Delft (TuD) is tasked to determine the performance and the degradation, during constant operation and during cyclic operation, of a ReSOC system. To achieve these goals the university utilises a ReSOC test station. After use of the test station, the university found that the ReSOC systems showed high degradation and fractured within short use in the test station. As these results were not replicated by other balance partners, a cause for these results had to be found. In this work the test station was investigated to find the cause of the high degradation and breaking of the cells. After investigations of the voltage fluctuations and voltage spikes seen during electrolysis operation, it was found that water condensed in the fuel inlet duct. The liquid water droplets, formed as a result of condensation, caused the voltage fluctuations, high degradation and thermal gradients in the system that eventually fractured the cells. By redesigning the water injection system the fluctuations were reduced by 70% and the voltage spikes were completely removed. This indicates that the redesign solved the problem of water condensation in the fuel inlet duct. The resulting decrease in degradation rate of the ReSOC system extended the experimental duration up to a verified 1000 hours of continuous operation. The extended duration allowed the ReSOC system to complete 900% more cycles, within Balance protocol specification, whilst the current density was also increased by 60%. These improvements enable the test station to determine the objectives given by the Balance project. Whilst investigating the the high degradation, markings were found on the fuel electrode of the cells as well. A computational fluid dynamics (CFD) study confirmed that these markings indicated the fuel flow distribution. By converting the CFD data to current density and fuel utilisation data, it was shown that the overall performance of the ReSOC system was influenced negatively by the flow distribution plate. The results also showed that the ReSOC performance in the test station of the TuD can improve significantly if the fuel inlet flow is switched from a perpendicular to a tangential flow direction at the cell surface area. A redesigned flow distribution plate is therefore proposed that closely matches an ideal tangential flow distribution.Mechanical Engineerin