The thermal energy storage and thermal-to-electric conversion components of a satellite power system were analyzed computationally. A phase- change material provided the energy storage while thermophotovoltaic cells converted the thermal energy to electrical. The phase-change mechanics were modeled and the associated system temperatures determined throughout the orbit. Using an equivalent circuit model for low-bandgap thermophotovoltaic diodes, those temperatures were then used to predict the maximum power output of the thermophotovoltaic cells. The system was modeled at five different altitudes. Two different thermophotovoltaic cells, gallium antimonide (GaSb) and gallium indium arsenide antimonide (GaInAsSb), were evaluated, and the system was analyzed when there were no voids in the phase-change material and when there were voids present. For all situations evaluated, the GaInAsSb cell produced significantly more power, but experienced greater variation in performance. The presence of voids in the phase-change material significantly lowered the power available during eclipse.