Thermocline control through multi-tank thermal-energy storage systems. (1st January 2021)

• Record Type: Journal Article
• Authors: Roos, Philipp; Haselbacher, Andreas
• Is Part Of: Applied energy. Volume 281(2021)
• Publication Date: 2021-01-01
• Subjects: Thermal-energy storage -- Thermocline storage -- Thermocline control -- Multi-tank storage -- Compressed air energy storage -- Simulation; Power (Mechanics) -- Periodicals; Energy conservation -- Periodicals; Energy conversion -- Periodicals; 621.042
• DOI: 10.1016/j.apenergy.2020.115971
• Languages: English
• ISSNs: 0306-2619

Abstract

Abstract: Thermal-energy storage systems consisting of multiple tanks allow the implementation of thermocline-control methods, which can reduce the drop in the outflow temperature during discharging and increase the volumetric storage density and utilization factor. Multi-tank systems based on the extraction and mixing thermocline-control methods were assessed using simulations assuming fluvial rocks as storage material and compressed air as heat-transfer fluid. For adiabatic conditions, the simulations showed improved performance for all multi-tank systems, with diminishing improvements as the number of tanks increases. The mixing method performed better than the extraction method. The mixing method delivered an outflow temperature drop of 5.1% using two tanks whose total volume was 2.15 times smaller than that of the single-tank system. For diabatic conditions, more than three tanks were not beneficial. With two tanks, the mixing method attained a temperature drop of 5.8% with a volume that is 2.5 times smaller than that of the single-tank system. The exergy efficiency of the two-tank system was 91.3% compared to 98.1% of the single-tank system. The specific material costs of the two-tank system were 1.5 times lower than those of the single-tank system. Highlights: Multi-tank thermal-energy storage systems allow for thermocline control. Multi-tank systems with up to four tanks were assessed through simulations. Simulations considered both adiabatic and diabatic conditions. For same outflow temperature drop, two-tank system is 2.5 times smaller. In addition, specific material costs two-tank system are 1.5 times lower.