Solar domestic hot water (SDHW) systems are a cost effective and efficient way to pre-heat domestic water for hot water use in buildings. Currently used sensible energy storage systems (commonly using water as the storage medium) are simple and inexpensive, but require large amounts of storage material, and therefore are heavy and take up considerable space. Latent heat energy storage systems (LHESS) store the energy absorbed/released when a material goes through a phase transition: these materials are called phase change materials (PCMs). Because of the large quantities of energy that are stored during a phase change, latent heat energy storage is more dense than sensible energy storage, and can therefore reduce the weight and space requirements of the energy storage system. The main objective of this research is to study the heat transfer processes and phase change behavior of a PCM during consecutive charging and discharging of a LHESS. This leads to better understanding of the melting and solidification processes in order to optimize future LHESS design. In part 1 of this paper the design of a LHESS that can operate under both consecutive and simultaneous charging and discharging modes is introduced. Dodecanoic acid is used as the PCM, as it has been shown to be safe, relatively inexpensive, and has a melting temperature in a range suitable for use with SDHW. Experimental results of consecutively charging and discharging the system are presented and the effect of the heat transfer fluid flow rate is explored. It was found that during charging a faster flow rate leads to shorter melting times; however, during discharging, the flow rate does not affect the rate of solidification. (C) 2013 Elsevier Ltd. All rights reserved.