A lunar regolith circulation system for high efficiency thermal energy storage

This study proposes a lunar thermal energy storage system that uses the low-gravity environment to circulate in-situ regolith and heat it directly with concentrated solar radiation. Conventional gas-heated lunar thermal energy storage systems use solar-heated gas to transfer heat to stationary beds of processed regolith. In contrast, the proposed system circulates in-situ collected regolith and heats it directly with concentrated solar radiation, thereby avoiding the need for regolith sintering to enhance thermal conductivity. The system is modeled using computational fluid dynamics coupled with a two-fluid model (CFD-TFM), support vector regression (SVR), and time-discretization methods. Multi-objective optimization is performed to balance heliostat area, final storage temperature, and heated-regolith inventory under different lunar conditions. The TOPSIS results reveal a clear trade-off among heliostat area, final temperature, and regolith inventory. At latitudes of 0°, −60°, and − 75°, the temperature-priority scenario heats 22.0–28.5 t of regolith to 1146.1–1162.3 K using heliostat areas of 50.3–142.4 m 2 , whereas the inventory-priority scenario heats approximately 100 t to 252.2–434.7 K using heliostat areas of 47.2–77.2 m 2 . At the lunar South Pole, the temperature-priority solution heats 290.4 t of regolith to 969.9 K using a heliostat area of 1631.5 m 2 , while the inventory-priority solution heats approximately 494 t to 278.7 K with a heliostat area of 427.2 m 2 . A subsequent Pareto optimization shows that the system can continuously deliver 13.1, 12.9, and 12.8 kW throughout the lunar night at latitudes of 0°, −60°, and − 75°, respectively, using heliostat areas of 79.57, 148.66, and 277.21 m 2 and approximately 64–66 t of regolith. At the lunar South Pole, the maximum continuous output over the 137.7-Earth-day lunar night is approximately 3.8 kW, requiring 1671.56 m 2 of heliostat area and 341.65 t of regolith. The proposed system provides a new approach to in-situ lunar-resource utilization and thermal-energy storage for future lunar exploration.