In order to improve the practicability of PV/T solar system, we proposed the theory and method on the application of diffuse-reflection concentrator in the PV/T solar system and analyzed the concentration characteristics of this proposed application. In addition, we designed experimental prototype of PV/T solar system and conducted test and analysis of the thermal and electrical characteristics of the PV/T solar system with or without a concentrator, respectively. The results showed that for the PV/T solar system with diffuse-reflection concentrator, the amount of incident irradiance was increased by an average of 26% during test period, and the 200-L water in the system was heated to 58°C, which was 12°C higher than that of PV/T solar system without diffuse-reflection concentrator; moreover, the max output power was increased by 11%. Therefore, it is a feasible way to improve the practicability of PT/V solar system by integrating a diffuse-reflection concentrator.
Summary
In this work, a heat storage vacuum tube solar collector intubated with heat storage tube is designed, which consists of solar vacuum tube, phase change material insert tube, and heat holding cover. The internal energy conversion, transmission, and storage theory are established based on the structure of the heat storage vacuum tube. The parallel and series‐parallel solar air collector system prototype consisting of nine heat storage solar vacuum tube solar collectors is designed and tested. The test results showed that the daily average conversion efficiency of the parallel and series‐parallel prototype reached 56.9% and 48.46%, respectively. Compared with nonheat storage prototype, the heat storage parallel and series‐parallel prototype had higher conversion efficiency by, respectively, 10.9% and 7.8%, longer effective heating time, and better heating stability and practicability. At the same time, the heat storage solar collector has compact structure, which is convenient to use.
SA-LA binary composite phase change material was prepared by mixing stearic acid (SA) and lauric acid (LA) in different mass fractions, and tested for thermal properties. The results indicate that composite PCM has a lowest peak melting point of 42.9°C, thus suitable for application in solar cell thermal control system. In addition, PV/PCM solar cell thermal control prototypes with different PCM thicknesses were designed and tested for thermal and electrical properties. The effects of different PCM volume on solar cell thermal control properties were studied, showing that compared with non-PCM systems, solar cell temperature in the PV/PCM system was reduced by more than 20°C, with output power increased by more than 11%. The research results provide experimental references for the preparation of SA-LA composite phase change materials and their application in thermal control of solar cells.
Abstract-According to the structural features of partially covered photovoltaic/thermal (PV/T) solar system, the theory model and optimum design method of the partially covered PV/T solar system is established. The effect of different design parameters on the performance of the partially covered PV/T solar system is analyzed by using the theory model. Meanwhile, the prototype of the partially covered PV/T solar system was designed, and the characteristics of the partially covered PV/T solar system are studied by experiment at Chuxiong City. Experimental results show that the glass cover is essential for improving the thermal efficiency of the PV/T solar system, which related to the transmittance and thickness of the glass cover. In addition, the thermal efficiency will decrease with increasing covering area of the PV modules on the PV/T solar collector. Under the condition of the covering area of 0.8m2 for the PV modules, the thermal efficiency and the output power of the prototype are 40.2% and 25.1W, respectively. Under the condition of covering area of 1.02m2 for the PV modules, the thermal efficiency and output power of the prototype are 36% and 33.6W, respectively. Thus, the partially covered PV/T solar system has batter practicality, and can meet the need of the ordinary rural families in lighting electricity and hot water.
Three composite phase change materials (PCM) with peak melting points of 42°C, 50°C and 58°C were prepared using different mass fractions of stearic acid (SA) and lauric acid (LA). A thermal control model structure of thermoelectric generation/PCM (TG/PCM) was designed using PCM, and analyzed for its internal thermal conversion, transmission and storage mechanisms. In addition, TG/PCM experimental prototypes with PCM melting points at 42°C, 50°C and 58°C were designed and tested for their temperature control properties and output power. The results showed that under PCM melting points of 42°C, 50°C and 58°C, temperature difference between the cold and hot end of the TG/PCM prototype thermoelectric battery was maintained above 8°C for 70 minutes, 45 minutes and 27 minutes, respectively. The total energy of system output power above 6mW was 73.9J, 52.4J and 18.9J.
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