Experimental study and analysis of a novel layered packed-bed for thermal energy storage applications: A proof of concept.

• Layered thermal store was both experimentally and numerically studied. • Layered control resulted in >60 % reduction on pressure drop. • Layered control resulted in uniform exit temperature for a longer period. • Layered store outperforms simple store as it reaches steady-state in 3rd cycle. • 1st and 2nd Law storage cycle efficiencies were analysed. This paper presents a study carried out as part of commissioning and testing of world's first grid-scale 150 kW e Pumped Heat Energy Storage (PHES) demonstration system. The system employs two novel layered packed-bed thermal stores. The present study experimentally investigates one of the stores designated as "hot thermal store", which has an energy storage density of 1072 MJ/m3 and stores heat at 500 °C and 12 bar. The layered store is an enhancement of a normal packed-bed store and offers a higher degree of thermal stratification. Experiments show that layering results in about 64 % reduction in pressure loss along with yielding considerably narrower thermocline. Round-trip efficiency, storage capacity and utilisation were calculated based on 1st Law analysis considering both simple and layered mode operation at nominal design conditions. Two cycle control scenarios were considered: time-based and temperature-based. In the time-based scenario, the store shows nearly similar performance in both modes. However, in temperature-based scenario, layered mode outperforms. During cyclic operation, layered mode outperforms as it reaches steady-state in merely 3rd cycle, without any loss in efficiency, capacity and utilisation; simple mode yields competitive efficiency but capacity and utilisation deteriorate after each successive cycle and steady-state is achieved in 20th cycle. 2nd Law analysis was additionally performed to gain insight into various losses and their impact on the performance. [ABSTRACT FROM AUTHOR]