A solar thermal electrolytic reactor was developed for studying at a 10 kW scale how a solar reactor’s electrolytic cell design and operating variables influence the performance of a solar process for producing metals from their oxides. Current versus voltage maps as well as current versus time for specified voltages were obtained for the electrolysis of ZnO and MgO within the temperature range of 1200–1500 K and various electrolytic cell configurations. An example of a map is presented. The data from maps and steady-state runs were used to illustrate how we quantify the influence of the cell’s operating temperature and current density on process performance. We also illustrate how one design variable, the cell’s electrolyte, influences process performance.