Controlling the melting and solidification points temperature of PCMs on the performance and economic return of the water-cooled photovoltaic thermal system

•The study focuses on examining different PCMs to be used in PVT systems.•Hybrid PCMs were produced from mixing Vaseline and paraffin.•Vaseline mixes with paraffin and reduces its melting point.•Lower melting point of the PCM corresponds to an increase in the heat flow rate.•Best cooling results were obtained when using the hybrid PCM. The use of phase change materials (PCMs) in photovoltaic-thermal systems (PVT) is essential for developing PV systems and raising their productivity. PCM is distinguished by its many variations and properties, the most important of which is the melting point. In this study, the driven question and focus was on investigating which is better for use in a PVT, PCM systems with a high or low melting point? Two types of PCM were used in the study: paraffin wax (melting point 45 °C), Vaseline -petroleum jelly (melting point of 25 °C), and hybrid PCM (mixtures of the two PCMs in proportions of 25%, 50% and 75%). The study was conducted indoors by simulating the harshest condition in Iraq's weather in summer. The results showed that the wax and the Vaseline mixed entirely with an apparent decrease in the product's melting point. In contrast, the rest of the thermophysical properties of the product were relatively affected. The use of paraffin, petroleum jelly and 50% paraffin + 50% Vaseline in the PVT system caused a decrease in the surface temperatures of the photovoltaic cell, which resulted in a more significant improvement in the performance of the system. The maximum electrical efficiency reached was 13.7%, while the maximum thermal efficiency was 39.0%. Reducing paraffin melting point leads to better performance of PVT systems, as the hybrid paraffin (50% wax + 50% Vaseline) have better productivity than pure paraffin wax due to its lower melting point.