An experimental and a theoretical study has been conducted to determine the performance of phase-change energy storage materials for solar water-heating systems. Simulation techniques are used to determine the system performance over the entire heating season. Variations of the solar-supplied fraction of the load with storage mass and collector area for water-based systems with sensible and latent heat storage have been examined. The variation of the outlet fluid temperature with different values of NTU and the variation of the stored energy with time for a phase change material (CaCl2 . 6H(2)O) are also investigated.