Performance investigation of a 100-kWhth thermocline packed bed thermal energy storage system: Comparison between synthetic oil and vegetable oil

Abstract

Thermal energy storage has been considered as an important solution to extend the operation of a concentrated solar power plant by meeting the peak demand of power in the time period from sunset to night, or providing power during cloudy days. Discussed in this work is a thermocline thermal energy storage system with a solid filler material. For this reason, a one-dimensional single-phase model is developed and validated with experimental data to investigate the thermal behavior of such thermal energy storage. The described model is further applied to design a 100-kWhth thermocline thermal energy storage system with a packed bed of quartzite rocks and oil as the heat transfer fluid. A synthetic oil (Therminol VP-1) and a vegetable oil (rapeseed oil) are the two candidates to be used as the heat transfer fluid. Their thermal and economic performances are calculated and compared. The results show that rapeseed oil is more cost-effective than Therminol VP-1 offering a lower energy cost (€18.3/kWhth vs €92.925/kWhth for Therminol VP-1).