We present a kinetic study performed in asolar-driven vacuum thermogravimeter(solar-TG), in which solid reactants are directly exposed to high-flux irradiationwhile their weight change is continuously monitored. The system allows testing under a total vacuum pressure as low as 10mbar. With this arrangement, the rate of thermochemical reactions can be examined under the same radiative heat transfer characteristics and heating rates typical of solar reactors. The solar-TG system is used to investigate metal oxides redox cycles for splitting H2O and CO2and forhigh-temperature heat storage. Operation ofthemetal oxide reduction under vacuum pressures is of special interest because it eliminates the need for purge gas, thus simplifying the process and avoiding energy penaltiesassociated withinert gas recycling.