The alkali metal thermoelectric converter (AMTEC) utilizing the sodium ion conducting β‐alumina is a device to convert heat energy to electric energy directly. It is characterized by high conversion efficiencies, high power densities, no moving parts and low maintenance requirements. Because of these merits, AMTEC is one of the most promising candidates for aerospace power systems, remote power stations and dispersed small‐scale power stations. In this paper, the experimental results of the series‐connected cells and the theoretical considerations about internal resistances have been reported. For the single cell, the open voltage of 1.37 V and the maximum power of 7.89 W and maximum power density of 0.40 W/cm2 at the sodium temperature of 1077 K have been obtained. For the two series‐connected cells, the open voltage of 2.60 V and the maximum power of 12.3 W at the sodium temperature of 1016 K have been obtained. This power was about 90 percent of the sum power of two cells. This power decrease is due to the resistance of the current‐collecting busbar. It is necessary to optimize the current‐collecting busbar considering the electrical resistance and heat conductance.
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