Use of NaNiCl battery for mitigation of SOFC stack cycling in base-load telecommunication power system-a preliminary evaluation

Fuel cells are among the most promising technologies for clean power generation. Solid oxide fuel cells (SOFC) are characterized by high efficiency, fuel flexibility and a wide range of operating conditions. SOFC are the preferred fuel cell technology for micro-combined heat and power (micro-CHP) units, but they are prone to rapid performance degradation when exposed to thermal and electrical cycling. To overcome this issue, alternative methods are sought to assure high durability and long-lasting operation by mitigating the cycling. This can be achieved by limiting the number of cycles and maintaining stable operating conditions. One of the proposed solutions is to create a hybrid system combining an SOFC stack with a molten salt (NaNiCl) battery module. The NaNiCl battery is well known for its high energy density, high durability and zero electrochemical self-discharge. This hybrid system is a solution in which the fuel cell stack and the battery module are thermally and electrically integrated and operate as a part of a cogenerator. Since both modules operate at elevated temperature, heat generated in the stack can be partially used to maintain a sufficient operating temperature of the battery pack. The SOFC/battery hybrid enables high operational flexibility which is achieved by proper selection of the power ratios between the two components. In this configuration the battery pack can be used to stabilize operation of the fuel cell stack and to allow for load-following operation of the hybrid. To evaluate the operation of a SOFC/battery, the dynamic models of the battery and fuel cell stack were developed in Aspen Hysys 8.5. The simulator enables predictive modeling of various operating conditions corresponding to the different power demand profiles.