The alkali metal thermoelectric converter (AMTEC) is a regenerative concentration cell for direct conversion of heat to electrical energy. Optimization of the components in AMTECs has been gained wide interest to improve power output and cell efficiency. A lumped thermal-electrochemical model has been developed in this work based on some previous efforts by Tournier et al. (1997). The main contribution of the present model is to simplify the calculation of radiation heat exchange by rendering the BASE, the condenser and the cell walls as a system of three closed-surfaces. The net radiative heat loss from the BASE is determined using a network method of radiation. For model validation purposes, the lumped model is applied to a PX-3A type cell. Good agreements have been obtained between numerical results and experimental data on variations of voltage, current, power output and cell efficiency within a wide range of external loads. Based on the numerical results, the role and separate influence of each component are quantitatively analyzed, including temperature levels for hot and cold ends, BASE properties, electrode materials, heat reduction methods and conductor leads. Optimum parameters are suggested in the analyses. With the recent advances in BASE and electrode materials, an integrated optimization is made to the AMTEC aiming for extra-terrestrial application. In the new module, the surface area of electrodes is increased, new electrodes materials are used and thermal radiation losses are minimized. With stable parameters, the peak power of the cell has been over 8.0 W-e. The stable voltage is over 3.0 V when R-L > 1.2 Omega and the cell efficiency is over 20% when R-L is within 1.2-4.0 Omega.