Reversible wasserstoffbetriebene Festoxidzellensysteme

Frank, Matthias Helmut; Stolten, Detlef (Thesis advisor); Scherer, Viktor (Thesis advisor)

Jülich : Forschungszentrum Jülich GmbH, Zentralbibliothek, Verlag (2019, 2020)
Book, Dissertation / PhD Thesis

In: Schriften des Forschungszentrums Jülich. Reihe Energie & Umwelt = Energy & environment 475
Page(s)/Article-Nr.: 1 Online-Ressource (187 Seiten) : Illustrationen, Diagramme


Renewable energy sources such as wind and solar energy shall cover a large part of the electricity demand in the future. However, the natural fluctuation of these energy sources leads to a fluctuating electricity production, which is not always in accordance with demand. The storage of surplus electricity and the delayed reconversion in case of electricity demand represents a solution to counteracting this issue. Due to the large amount of energy, a chemical storage is particularly suitable for this purpose. To realize this solution, conversion of electrical into chemical energy with solid oxide cells by steam electrolysis can takes place first. The produced hydrogen is temporarily stored and will be reconverted at electricity demand with the same solid oxide cells by fuel cell operation. This offers an economic advantage over systems with two solid oxide cell stacks. Due to the pure hydrogen/steam operation, this reversible solid oxide cell system (rSOC-system) is environmentally friendly and thereby differs from the known rSOC-systems which are using carbonaceous energy sources. The main objective of this work is the research of a technically and economically efficient hydrogen-powered rSOC-system. First, the developments of the system design and of the operating strategies, which should ensure a safe and fast operating point change, have priority. In order to develop a highly efficient rSOC-system, the system components were investigated experimentally. Based on this, dynamic component models were created, which were validated with the help of the examination results. The ensuing system models are basing on the interconnection of the validated component models and allow investigations at system level. The final economic analysis represents the economic viability of the investigated rSOC-systems. This analysis takes different quantities, system sizes and system designs into account. The influence of varying electricity generation costs and operating hours is shown in a sensitivity analysis. First, an rSOC basic system was developed that only contains necessary components for operation. This system achieved an efficiency of 43.4% and is the starting point for the investigation of efficiency enhancing-measures. On the one hand, the efficiency could be increased to 45.5% via an internal heat recovery in electrolysis operation and, on the other hand, the parasitic system consumption could be significantly reduced with the integration of an off-gas recirculation. In addition, a condenser is included in the recirculation which mainly enables the recirculation of hydrogen and leads to an efficiency increase to 49.9%. The operating strategies developed for this final rSOC-system enables, inter alia, a system startup in two hours. The load change from full load to 50% partial load takes ten minutes in fuel cell operation and three minutes in electrolysis operation. Switching between these two operating modes is possible in less than five minutes. For the solid oxide cells critical operating areas were analyzed and avoided. The economic analysis showed that a 5 kW rSOC-system can be economical from 100 units upwards in comparison to mains supply. This system pays for itself after only seven years, resulting in electricity generation costs of € 0.232 / kWh (100 units) up to € 0.148 / kWh (100,000 units). rSOC-systems with higher power output (≥ 50 kW) pay for themselves later and at higher quantities because the competing electricity price by mains supply decreases with increasing purchase quantities.