Design and feasibility of high temperature shell and tube latent heat thermal energy storage system for solar thermal power plants

A simple shell and tube heat exchanger provides a straightforward design for near-term integration of latent heat thermal energy storage (LHTES) systems in concentrated solar thermal-tower (CST-tower) plants, but currently there is no literature available for this configuration in the 286-565 °C temperature range. Therefore, the primary objective of this work is to evaluate the potential of this configuration for CST-tower plants. In addition, a proper design method of this storage configuration should simultaneously account for the effects of geometric parameters and the number of modules. The present work optimizes these parameters for market ready phase change materials (PCM) that are suitable in the aforementioned temperature range. This optimization consisted of fixing the PCM volume while varying the other geometric parameters (namely, L,  L/d,  R/ro) simultaneously over a wide range. The goal was to achieve the highest amount of total stored/delivered energy with a minimum heat transfer surface area. This analysis revealed that there was an optimum area between 36 and 63 m2 GJ−1 (or 0.12-0.22 m2 kWhth−1), depending on the PCM employed. This optimum surface area can be obtained with several combinations of geometric parameters, but only certain combinations were found to achieve the highest total stored/delivered energy. The charging and discharging efficiency for the selected PCMs was found to be ∼99% and 75-85%, respectively. Using the optimized designs, the cost of this shell and tube LHTES system was found to vary between 27 and 170 US$ kWhth−1, which indicates that with further development it may be competitive with conventional sensible storage systems (e.g. two-tank molten salts).