This work focuses on the design of latent heat storage unit for direct steam generation power plants. In this paper a simple model for the design of a storage unit is presented. This model includes phase change of water/steam and the sensible heat stored in phase change material. The effectiveness of the storage is considered as the design criterion in this model and the influence of various design parameters on the effectiveness is explained. Results show that: Length of storage has a major impact on the effectiveness. Flow rate of heat transfer fluid is important. Diameter of the tubes has an impact on the effectiveness. Distance between tubes does not have significant effect on effectiveness. (C) 2015 Elsevier Ltd. All rights reserved.