Investigation on transient performance of a large-scale packed-bed thermal energy storage

The packed-bed thermal energy storage technology has gained a significant market worldwide as it offers a huge potential for high-temperature air based storage with no adverse environmental impact. The present paper numerically investigates a high-temperature 175,000 m3 truncated conical shaped packed-bed thermal energy storage. One-dimensional, two-phase model is developed to simulate the transient behavior of the storage where the energy balance of both phases, the fluid and the solid, are based on modified equations of the Schumann model. The model developed is used to carry out a parametric study where it is subjected to different design and operating parameters such as storage shape, rock diameter, charge-discharge rate and insulation thickness. The storage performance is assessed through energy and exergy efficiencies taking energy stored and recovered into account. The model satisfactorily predicts the dynamic behavior of a large-scale packed-bed storage system within the range of parameters investigated. Results obtained denote that the truncated conical shaped storage with rock diameter of 3 cm, insulation thickness up to 0.6 m and charging-discharging rate of 553 kg/s leads to lower thermal losses estimated under 1% of the energy recovered during discharge. Furthermore, energy and exergy efficiencies of thermal cycles are found to exceed 98% for most of the selected parameters in the study. The model developed can assist in identifying more advance and cost-effective storage design solutions for a large-scale application.