Investigation of a heat storage system consisting of basalt stones, water and a phase change material

•A special heat storage unit is designed to store solar energy in liquid, stones and phase change material.•Basalt stones, water and paraffin wax are used as heat storage materials.•The effect of direct solar radiation and the use of paraffin wax on heat storage is investigated.•A higher temperature can be reached when the heat storage unit receives direct solar radiation than the heat storage unit that does not receive it.•It is possible to benefit from the heat storage supported using PCM for a longer period. In this study, the storage of solar energy as thermal energy is experimentally examined. A special heat storage unit is designed to store solar energy in liquid, stones and phase change material. Water, basalt stones, paraffin and air were used as the liquid, stones, phase change material and heat transfer fluid, respectively. Unlike classical designs, a glass cover is used for the heat storage unit, which receives direct solar radiation from the southern facade. Thus, the effect of the direct contact of the solar radiation with the stones on the performance of the heat storage unit is investigated. In the heat storage unit, if the sun does not directly reach the stones, the maximum temperature of the stones that can be reached is 46.6 °C, whereas when the sun hits the stones directly, a maximum temperature of 56.8 °C can be achieved. It is suggested that an average of 50.3% of the energy requirement for heating from sunset to sunrise, depending on the weather conditions of the days of the experiments can be obtained using the solar energy heat storage unit designed in this study.