Abstract: An improved thermoelectric generator of the type having (1) enclosure means for a first reaction zone; (2) enclosure means for a second reaction zone; (3) a reaction zone separator which (a) separates and essentially completes enclosure of the two reaction zones and (b) comprises a cationically-conductive, solid electrolyte that is essentially impermeable to elemental alkali metal and compounds thereof and ionically conductive with respect to cations of the alkali metal; (4) alkali metal within the first reaction zone and in fluid communication with the solid electrolyte; (5) an electrode within the second reaction zone in electrical contact with the solid electrolyte and sufficiently porous to permit alkali metal vapor to pass therethrough; (6) conduction means for electron flow between the alkali metal within the first reaction zone and the electrode; (7) inlet means for introducing the alkali metal into the first reaction zone; and (8) temperature control means adapted to maintain a temperature in the firs