Performance of a coupled transpired solar collector-phase change material-based thermal energy storage system

The transpired solar collector (TSC) is a low-cost technology for heating ventilation air for mainly for use in industrial and agricultural applications. Storing the excess energy generated during daytime in phase change material (PCM) could improve the economics of using TSCs. Since energy generated for storage could be increased by using a two-stage TSC (with a glazing) vs. a one-stage TSC, first, the thermal performance of the two configurations were compared. Then, performance of the PCM-based thermal energy storage (TES) unit coupled to a TSC was evaluated. At a suction velocity of 0.023 m/s, the one-stage TSC produced a 2 °C higher temperature rise and 8% higher efficiency than the two-stage TSC. The one-stage TSC was coupled to a TES unit packed with 80 kg of salt-hydrate type PCM (specific energy of ∼185 kJ/kg). When evaluated at four airflow rates, the TES unit stored between 76 and 107% of its theoretical heat storage capacity and provided tempered air 4 °C warmer than ambient air during nighttime. While residual energy (for daytime heating) increased with airflow rate, energy charged or discharged was unaffected. Over a week, the TSC-TEC stored 34% of the total useful energy produced for nighttime use, with a potential to displace 1.35 kg of liquefied natural gas. Replacing the expensive metal TSC with a perforated plastic TSC and a simpler TES design would improve the economics of storing solar energy for use after sundown.