Critical diameter for a single-tank molten salt storage – Parametric study on structural tank design

Molten salt thermal energy storage (TES) is a cost-effective option for grid-connected storage in both concentrating solar power (CSP) plants and retrofitted thermal power plants in a multimegawatt scale. Current systems use two tanks (hot and cold), but future systems may use a single tank with a transient temperature profile (hot in the top and cold in the bottom) to reduce costs and space. However, the structural and mechanical design of large-scale molten salt single-tank storages at 560 °C has not been fully explored, and the impact of increasing the operating temperature to 620 °C is still uncertain. The challenge presented by a single tank is the existence of a temperature profile that results in a varying thermal expansion of the tank shell along its height. In the case of larger tanks, this discrepancy can reach a magnitude of centimeters, which in turn gives rise to bending moments. To the best of our knowledge, this study addresses the issue of bending stresses in large-sized high-temperature tanks with thermal stratification for the first time. The modelling approach is applied to single-tank CSP TES systems as a case study to evaluate the constraints imposed by tank size and wall thickness.