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The study presents the experimental and analytical investigation, which was carried out to evaluate the charging/discharging performance of phase change material (PCM) in the thermal energy storage (TES) unit. The experiments performed under different operating modes of the heat storage system, changing the inlet temperature and the mass flow rate of the heat transfer fluid (HTF). The calculated amount of thermal energy based on the partial enthalpy distribution provided by the manufacturer’s datasheet compared to that obtained from the experiments. Based on the experimental results, a three-dimensional response surfaces formed and a regression models obtained, which allow predicting the PCM charging and discharging performance.

Increase in solar fraction has been noted as one of the main goals for wider application of domestic solar thermal systems. To increase solar fraction, higher energy density thermal storage availability is a key point. In this paper phase change materials have been analysed as part of a domestic solar thermal system. Sensitivity analysis of annual simulation in TRNSYS with climate data of Riga, Latvia is used. The paper also explores better methods for evaluating phase change material (PCM) performance based on temperature measurements in PCM. The results showed that the melting point of PCM and temperature set point of an auxiliary heater have the highest sensitivity of aspects analysed in the paper. It also reports that the coefficient of variation of energy in PCM correlates well with solar fraction and can be used as a parameter to evaluate PCM’s suitability for certain applications.