This work focuses on the design of a low cost utility scale thermal storage, consisted of vertically placed cylindrical phase change material capsules, for next-generation power plants. In this paper a simple model for the design of a storage unit is presented. This model includes both latent and sensible heat stored in phase change material. The exergetic efficiency and the operation time of the storage is considered as the design criterion in this model and the influence of various design parameters on the exergetic efficiency and operation time is investigated. Results show that under study conditions exergetic efficiency varies between 98.991% and 98.692% and operation time changes between 4h and 21h. Higher efficiency values obtained for lower number of capsules, lower heat transfer fluid flow rates and lower distance between capsules. Decreasing number of capsules and the distance between capsules also decreases the operation time. However, the decrease in the flow rate increases the operation time.