Effective storage and release of low‐to‐moderate temperature thermal energy (e.g., solar thermal or geothermal) could be transformational for applications such as space heating/cooling, domestic hot water, or off‐grid cooking. Good candidates for thermal energy storage in this temperature range include latent heat storage (LHS) systems and thermochemical energy storage (TCES) systems using reversible salt‐hydrate dehydration reactions. Here, we propose that an energy‐storage system by use of magnesium nitrate hexahydrate can potentially improve upon independent TCES or LHS systems by utilizing both the thermochemical hydration reaction and the latent heat available through the solid–liquid phase change of one magnesium nitrate hydrate eutectic. This chemistry is investigated through thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC) analysis and shows a total energy density of approximately 1170±94 kJ kg−1 when dehydrating the material up to 145 °C. Reversible latent heat cycling at a eutectic melting temperature of 130 °C is shown by the DSC signal and estimated to be on the order of 115±9.2 kJ kg−1—a 10 % increase over the thermochemical energy storage alone. Although the latent energy release was found to decrease slightly over several cycles, the mass was found to stabilize near an asymptotic value corresponding to the published eutectic composition. These results suggest the concept of reactive phase‐change materials could be a promising solution to increasing the stored volumetric energy density.
In this study, a directly irradiated, milli-scale chemical reactor with a simple nickel catalyst was designed for dry reforming of methane for syngas. A milli-scale reactor was used to facilitate rapid heating, which is conducive to combating thermal transience caused by intermittent solar energy, as well as reducing startup times. Milli-scale reactors also allow for a distributed and modular process to produce chemicals on a more local scale. In this setup, the catalyst involved in the reaction is located directly in the focal area of the solar simulator, resulting in rapid heating. The effects of mean residence time and temperature on conversion and energy efficiency were tested. The process, which is intended to store thermal energy as chemical enthalpy, achieved 10% thermal-to-chemical energy conversion efficiency at a mean residence time of 0.028 s, temperature of 1000 °C, and molar feed ratio of 1:1 CO2:CH4. A significant portion of the thermal energy input into the reactor was directed toward sensible heating of the feed gas. Thus, this technology has potential to achieve solar-to-chemical efficiency with the integration of recuperative heat exchange.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.