Concept and system design for a ZEBRA battery–intermediate temperature solid oxide fuel cell hybrid vehicle

This paper explores the combination of a sodium–nickel chloride (ZEBRA) battery and an intermediate temperature solid oxide fuel cell (IT-SOFC) to form a hybrid power system that is intended for automotive applications. A range of vehicle types, drive cycles and fuels are investigated and compared in terms of their suitability for the pairing of this particular fuel cell and battery technology. In order to avoid the problem of stop–start cycles and load transients on the SOFC, a nominally ‘always-on’ strategy is investigated for the fuel cell. Sizing of the system is performed for each vehicle/drive cycle by adopting the minimum fuel cell power and battery energy in order to preserve charge neutrality over a 24 h period, while accommodating the requisite vehicle performance characteristics. Weight and volume estimates are reported for the hybrid system and opportunities for efficiency improvement brought about by synergistic operation of the fuel cell and the battery are discussed.