Experimental Analysis of a Hydrogen Power-To-Power System based on Solid Oxide Technology

In the present thesis, a Power-To-Power system has been experimentally analysed to perform the stack characterization in both SOFC and SOEC operation mode. The aim was to calculate the round-trip efficiency for the stack, defining a performance map able to identify the working zones with higher stack efficiency. In order to achieve such objective, experimental tests in FBK laboratory have been performed with two different strategies: in control voltage and in control current. In case of control voltage, for both the SOFC and SOEC, the stack voltage has been varied with a ramp and the correspondent current values have been observed. These tests have been performed at variable fuel utilization, keeping fixed the inlet fuel flow rate, while the current has varied. Five different stack temperatures have been analysed in SOFC and eight stack temperatures in SOEC. On the other hand, in case of control current the current has been varied with a ramp and the correspondent voltage values have been observed, even in this case for both SOFC and SOEC mode. These tests have been performed at constant fuel utilization. Therefore, the current has been varied in an automatic way following the imposed fuel inlet flow rate ramp, in order to keep constant the ratio between current and fuel flow rate. Three stack temperatures have been analysed in SOFC, while four stack temperatures in SOEC mode. The data acquired from these tests have allowed to build the i-V curves and consequently, through an elaboration phase, to calculate the stack efficiency values and ASR values of the stack, in both the SOFC and SOEC mode. Three different stack efficiencies have been calculated (the electrical, the empirical and the exergy efficiency) and their results have been discussed and compared, to understand which could be the most representative one to map the performance of the stack. Considering the stack efficiency in both the operation modes, the round-trip efficiency has been calculated, allowing to determine a performance mapping of the stack when operated in reversible operation. Finally, an analysis of the system in SOFC mode has been performed too, with the aim to investigate its performance and the working point of thermal self-sustainability. The system control volume includes the stack and the heat exchangers which heat-up the inlet fluids, exploiting the heat recovery of the outlet fluids from the stack.