Analysis of a hybrid cascaded latent/sensible storage system for parabolic-trough solar thermal plants
1Energy and Power Engineering Division, School of Energy Environment and Agrifood, Cranfield University, Cranfield, Bedfordshire, MK43 0AL, UK
2Energy and Power Engineering Division, School of Energy Environment and Agrifood, Cranfield University, Cranfield, Bedfordshire, MK43 0AL, UK
J Ther Eng 2021; 7(3): 608-622 DOI: 10.18186/thermal.888469
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Abstract

The molten-salt two-tank system is the state-of-the-art thermal storage technology employed in the more mature parabolic-trough solar thermal power generation using synthetic oil as the heat-transfer fluid (HTF). This storage technology requires high storage-material inventory, making it very expensive. The use of latent-heat storage (LHS) system offers smaller storage size and material inventory. However, such a storage system faces two challenges: there are limited number of commercially-available phase-change materials (PCMs) are suitable in the operating temperature range; and these materials have very low thermal conductivities. The use of finned tubes, nevertheless, can overcome the later shortcoming. In this study, the analysis of a hybrid storage system, consisting of a three cascaded finned-tube LHS stages and a sensible concrete tube register stage, was carried out through modelling and simulation. A procedure for the design of the finned-tube cascaded LHS stages was developed. For a typical 50 MW parabolic-trough solar thermal power plant, the dimensions of a storage system with 6 hours of operation at full load were obtained. The three-stage cascaded LHS sub-system provides 45.5% of the total storage capacity of the entire system and has a volumetric specific capacity of 54% greater than that of the two-tank system. The volumetric specific capacity of the entire storage system is 9.3% greater than that of the two-tank system.