Thermal properties of a new type of calcium chloride hexahydrate-magnesium chloride hexahydrate/expanded graphite composite phase change material and its application in photovoltaic heat dissipation

PV-PCM technology can not only achieve higher photoelectric conversion efficiency, but also has the advantages of energy saving, high efficiency, and economical applicability. In this paper, a new type of CaCl2·6H2O-MgCl2·6H2O composite PCM for PV-PCM was prepared by physical blending method using calcium chloride hexahydrate-magnesium chloride eutectic mixture as PCM and expanded graphite as carrier. The shape stability, thermal properties and thermal reliability of CaCl2·6H2O-MgCl2·6H2O eutectic materials under EG conditions were discussed. The change of temperature and output power of PV panel combined with PV-PCM was studied. The experimental results show that the CaCl2·6H2O-MgCl2·6H2O composite with 8 %EG has high phase change enthalpy (171.4 kJ/kg), suitable phase change temperature (27.1 °C), and negligible supercooling degree (0.11 °C) and excellent thermal conductivity (3.359 W/m·K). After 100 heating–cooling cycles, the modified composite phase change material still has excellent thermal reliability. Surface temperature of photovoltaic panels can be significantly reduced, and the average temperature of photovoltaic panels can be kept below 40 °C. The photovoltaic panel power can work for a long time (3.5–4 h) close to the rated power, keeping the photovoltaic panel power at a high and stable state, and producing 7.9% more power than using only photovoltaic panels to generate electricity.