Photoelectricity and photothermal performance experiment on solar photovoltaic/loop-heat-pipe water heating system

Abstract: The aim of this paper was to present a dedicated experimental investigation of the thermal and electrical performance of a solar photovoltaic/loop-heat-pipe water heating system. The studied system was the combination of the loop heat pipe and the solar photovoltaic/thermal technology, which was assisted by the electric water heater to product hot water for residential buildings in cold zone. The proposed system could work in 2 operational modes, and the operational modes were mainly determined by the variation of solar radiation. When solar radiation was high, the system operated in the photovoltaic/loop-heat-pipe mode; when solar radiation was low or it was a rainy day, the electric water heater was turned on to heat water to match the preset value. The experimental platform for the solar photovoltaic/loop-heat-pipe water heating system was built and a series of experiments under real weather conditions were conducted. Based on test results, energy and exergy performance of the studied system under typical working condition was analyzed. And the typical working conditions include the transitional season condition, the summer condition and the winter condition. Besides, energy and exergy performance of the system on the specific 2 days was discussed and compared. What was more, the impact of the refrigerant charge quantity on the operating performance was analyzed. Therefore, main content of this paper was composed of energy and exergy performance analyses under typical working conditions and selected full days. The experimental results in the photovoltaic/loop-heat-pipe mode were analyzed in terms of the solar thermal efficiency, the photovoltaic efficiency, the overall energy efficiency and the overall exergy efficiency. For the solar thermal efficiency and overall energy efficiency, the experimental results were the highest in summer, and the daily average values were 62.1% and 68.1% respectively. For the photovoltaic efficiency and overall exergy efficiency, the experimental results were the highest in winter, and the daily average values of them were 13.7% and 10.9% respectively. The whole system performance considered the performance of 2 operational modes, and therefore the overall energy and exergy efficiency of the whole system were a litter higher than those of the mode of photovoltaic/loop-heat-pipe. In this paper, the experimental results of April 20th and December 9th were chosen to analyze full-day performance of this system, and the solar thermal efficiency and overall energy efficiency were higher on April 20th, while the photovoltaic efficiency and overall exergy efficiency of full-day performance were higher on December 9th. This paper also discussed the system performance with different refrigerant charge quantities in similar ambient environment. And the results showed that 30% refrigerant charge quantity was conducive to the improvement of solar thermal efficiency and overall energy efficiency of this system and 40% refrigerant charge quantity was conducive to the improvement of electrical efficiency and overall exergy efficiency of this system.