Optimizations of cascaded packed-bed thermal energy storage units for next-generation concentrating solar power

Packed-bed thermal energy storage (PBTES) is important for smoothing the intermittent solar energy in the next-generation concentrating solar power (CSP). To enhance its thermal performance, a three-layer PBTES was designed and optimized by developing a numerical model, considering a combined parameter of cyclic heat transfer rate (Pcy,i) and cyclic efficiency (ηcy,i) as optimization objective (rcy,i). After the optimization, an optimal PBTES that reaches the highest rcy,i of 90.12 % was obtained. Then, the simulation indicates that the optimal design can improve the rcy,i by 8.14 % and 36.11 % compared with a single-layer design and a three-equal-layer design, respectively. Furthermore, the influences of the mass flow rate (min) were analyzed, revealing the variation in min slightly affects the Pcy,i and ηcy,i of the optimal design, indicating present design is suitable for variable flow, as expected in the CSP. Additionally, the cyclic performance of the optimal design was evaluated, finding its Pcy,i and ηcy,i stabilize at 128,1533 kJ·s−1 and 99.74 %, respectively, after five charging-discharging cycles. Meanwhile, its outlet temperature also remains stable after multiple cycles. Finally, the unit cost of the optimal PBTES is lower than that of a single-layer design by 3.30 %. Results from current study can provide valuable insights to advance PBTES.