Modeling and analysis of PCM-encapsulated solar thermal energy storage system for space heating

In this study, a phase change material (PCM)-encapsulated packed-bed thermal energy storage (PB-TES) system is intended for Day-round space heating in the winter. Solar concentric collectors act for day-time heating and TES charging, while the stored energy can be used at night and intermediate time for space heating. A region-wise techno-economic analysis of PCM candidates is made to compare the costs and sizes of solar collectors and PB-TES. A spherical capsule filled with sodium nitrite (NaNO2) and sodium nitrate (NaNO3) is numerically investigated during the PCM charging at constant thermal input. After complete liquefication, the charging time for NaNO2 and NaNO3 capsules is 3280 and 4300 s, respectively, holding the maximum stored energy of 733.4 KJ/kg at 285 degrees C and 687.27 kJ/kg at 310.12 degrees C, respectively. In addition, the stored exergy is obtained 238.78 and 234.74 kJ/kg for NaNO2 and NaNO3, respectively; however, the average exergetic effectiveness for NaNO2 and NaNO3 are 0.54 and 0.46. Despite the lower energy storage capacity (kJ/kg) of NaNO3, the PB-TES volume is less with NaNO3 than with NaNO2 due to higher density. However, the average cost ($/tonne) of NaNO3 PCM is 50% higher than NaNO2. Subsequently, the thermal efficiency of the proposed system is estimated at 27.68% and 26.94% during day and night-time operations.