Solar domestic hot water systems using latent heat energy storage medium: a review

Solar energy is a clean, abundant and easily accessible form of renewable energy. Its intermittent and dynamic nature makes thermal energy storage (TES) systems highly valuable for many applications. Latent heat storage (LHS) using phase change materials (PCMs) is particularly well suited for solar domestic hot water (SDHW) applications as it offers high storage density and heat transfer at near-constant temperature. This article reviews TES technologies for solar water heating systems with a particular focus on techniques for integrating PCM into these systems. These techniques include integrated PCM storage vessels, integrated PCM solar collectors, and integrated a PCM unit inside the solar hot water circuit. It is found that the integrated PCM storage vessel is the most widely applied technique in SDHW systems using PCMs. The latent heat storage unit configuration and heat transfer mechanisms are further reviewed. Furthermore, this review presents recent findings on the performance comparison between conventional SDHW systems and SDHW systems containing PCMs and the long term performance of SDHW system using PCMs are discussed. This review highlights the need for further research in several areas including performance evaluation of different integration techniques, numerical model for system optimization, and long-term performance of solar domestic hot water systems featuring PCMs.