A pseudo-analytical model based on the enthalpy approach for the simulation of packed-bed rock thermal energy storage systems

Packed-bed rock thermal energy storage with solids for heat storage is a cost-effective solution. Approaches to model thermal storage systems range from simplified models based on analytical solutions to the partial differential equations representing the system, to more advanced models based on the finite volume method, or even complex models based on computational fluid dynamics. Previous works presenting simulation models for packed-bed rock energy storage systems address single-phase heat transfer fluids (either liquid or gaseous), with or without a solid packed-bed. Such systems represent what is currently commercially available. However, for applications where the heat transfer media is in the two-phase or vapour state, it may offer advantages to use a packed-bed rock thermal energy storage system with phase change of the heat transfer fluid. In this work, we present a novel simulation approach to model packed-bed rock thermal energy storage systems based on the enthalpy approach, unlike the typically used temperature based approach. This approach allows the modelling of the packed-bed rock storage with phase change of the heat transfer fluid, in addition to the modelling of the charging of a packed-bed rock storage system using a liquid or gaseous heat transfer fluid. The presented model is based on an analytical solution to the partial differential equations representing the system. The model is validated using experimental results, with a mean absolute percentage deviation of 0.7 % and 1.1 %, for the charging of the packed-bed rock thermal energy storage with liquid and gaseous heat transfer fluids, respectively.