Abstract: In order to understand the operation conditions of the phase-change energy storage solar vacuum heat collector, the operation of single vacuum tube and three vacuum tubes in series under different working conditions were experimentally studied. The experiments were mainly divided into two phases: endothermic and exothermic. The research results of the single vacuum tube operation show that the daily heat collection efficiency can reach30%~45% in the endothermic stage in sunny and cloudy conditions. The heat collection efficiency in cloudy conditions is very low, only about 6%. During the endothermic phase, due to the natural convection of the water in the U-shaped copper tube and the paraffin after liquefaction, the paraffin in the vacuum tube will have the temperature stratification phenomenon of high paraffin temperature at the top and low paraffin temperature at the bottom. During the exothermic phase, the amount of hot water provided in sunny conditions is the biggest, and the hot water temperature is also high. After calculation, it can provide 2.89 L of hot water at 50 ℃, 4.44L of hot water at 40 ℃ and 9.56 L of hot water at 30 ℃. The experimental results of the series operation show that the average paraffin temperature of each vacuum tube will be different during the heat absorption process. The closer to the water outlet of the series system, the higher the average temperature of the paraffin in the vacuum tube; the hot water temperature and hot water volume that can be provided by the series system are significantly increased.In a single-day experiment, 7.64 L hot water of 60 ℃ and 13.07 L hot water of 40 ℃ can be provided.

Key words: solar energy, phase change energy storage, vacuum tube, paraffin, heat collection efficiency