| As the problems of environmental pollution and energy crisis become more and more prominent,many scholars at home and abroad pay more and more attention to solar energy because of its high efficiency,environmental protection and huge reserves.Photovoltaic/thermal comprehensive utilization technology(PV/T),as one of the important directions of solar energy applications,combines photovoltaic and photothermal,not only to achieve the diversity of energy output methods,but also to increase solar radiation Energy utilization.As the core component of solar radiant energy collection and conversion,the performance of solar collectors has the most direct impact on the utilization efficiency of solar energy.Flat-plate solar PV/T hot water/air collectors have been widely used because of their simple structure and high economy.Although the existing domestic and foreign research on flat-panel solar PV/T hot water/air collectors is to a certain extent,it is helpful to improve the comprehensive performance of PV/T collectors and reveal the photovoltaic and photothermal conversion of PV/T collector systems.The process has a better promotion effect.However,due to the limitations of the structure of each PV/T collector system and the cooling medium used,the existing flat-plate PV/T collectors still have certain shortcomings: for most tube-plate PV/T hot water collectors In other words,the temperature of the solar cell is still high in the working conditions with high solar radiation intensity such as noon in summer,which will have a negative impact on the power generation efficiency and service life of the solar cell;for most solar PV/T air collectors Heaters,their air-cooling systems are often idle or simply used as PV systems during non-heating seasons because there is no demand for hot air,resulting in a significant decrease in solar cell power generation efficiency and service life and an increase in building cooling load;Although PV/T collectors can provide heat and electricity at the same time,because the selected cooling medium is relatively single,the output mode of heat energy(hot air or hot water)is also relatively single.This results in users not being able to flexibly choose the operating mode of PV/T collectors according to their own needs for different types of heat.Therefore,in response to the above problems,this paper proposes a new type of tube-sheet solar PV/T collector structure,and conducts related research on the performance of the collector.This article first proposes a new type of solar PV/T collector structure.The solar PV/T collector is based on the tube-sheet hot water PV/T collector.The cooling air channel is set between the photovoltaic panel and the glass cover plate,so that water cooling,air cooling and cooling can be realized under different working conditions.Multiple operating conditions with simultaneous action of water cooling and air cooling provide buildings with hot air and domestic/heating hot water.Secondly,the thermal and photoelectric conversion process of the collector is theoretically analyzed,and a two-dimensional unsteady energy transfer mathematical model when water and air are running at the same time is established.The mathematical model established by the MATLAB program is compiled.The model is solved,and the accuracy of the mathematical model is verified through the experimental results in the relevant literature.Aiming at the operating characteristics of the collector again,an evaluation method for the new PV/T collector is proposed.Finally,on the basis of the established mathematical model,outdoor environmental parameters(solar radiation,ambient temperature,ambient wind speed),operating parameters(air flow in the flow channel,water flow,water inlet temperature),structure are discussed through the controlled variable method.The influence of important parameters such as the height of the air flow path,the length of the collector,the coverage rate of photovoltaic cells,etc.on the performance of the collector.Through exploring the influence of outdoor environmental parameters on the performance of the collector,it is found that:(1)Under other conditions unchanged,as the solar radiation intensity increases,the outlet temperature of the air and water of the collector increases,and the air,The rate of increase of the outlet temperature of the water remains basically unchanged.Compared with summer conditions,the solar radiation intensity has a greater impact on the light-to-heat conversion efficiency of PV/T collectors in winter conditions,but in summer conditions,the thermal efficiency of the collectors is significantly higher than in winter.In addition,the intensity of solar radiation is negatively correlated with the photoelectric conversion efficiency of the collector.(2)Under the working conditions studied,the air outlet temperature of the collector and the water outlet temperature decrease with the increase of the ambient wind speed,and the rate at which the outlet temperature of water and air decreases is getting lower and lower.As the ambient wind speed increases,the thermal efficiency of the collector continues to decrease,and the rate of decline becomes smaller and smaller,and the electrical efficiency increases slightly,with a maximum increase of 0.02%.It can be seen that the wind speed of the surrounding environment has little effect on the photoelectric conversion efficiency of PV/T collectors.By exploring the influence of operating parameters on the performance of the collector,it is found that:(1)With the increase of air flow and water flow,the outlet temperature of air and water of the collector is getting lower and lower,and the rate of decrease is related to the water flow and air flow.It is inversely proportional;when the water flow rate is greater than 0.04kg/s,the change of the air flow rate has a lower impact on the electrical efficiency,thermal efficiency and overall performance efficiency of the collector.(2)When the water flow rate is greater than0.07kg/s,increasing the water flow rate is of little significance for reducing the temperature of the photovoltaic heat sink.As the water inlet temperature increases,the thermal efficiency,electrical efficiency,and overall performance efficiency of the collector continue to decrease,and the overall performance efficiency decreases by about 10%.Through exploring the influence of structural parameters on the performance of the collector,it is found that:(1)Based on the analysis of comprehensive performance and efficiency,for the new collector,the recommended design value of the air flow channel height is 30-35mm;(2)With the solar cell coverage With the increase of the rate,the overall performance efficiency of the collector is getting bigger and bigger,but in this process,the thermal efficiency of the collector is continuously decreasing.Therefore,the choice of solar cell coverage rate needs to be determined by users according to their actual demand for heat and electric energy.(3)When the external environment where the collector is located is the average outdoor condition in winter in Taiyuan,as the length of the collector increases,the thermal efficiency,electrical efficiency,and overall performance efficiency of the collector gradually decrease,and the photovoltaic heat-absorbing panel The temperature distribution of the temperature difference is getting bigger and bigger,but the outlet temperature of water and air is getting higher and higher,the growth rate of the air outlet temperature is 2.7℃/m,and the growth rate of the water outlet temperature is about 4.5℃/m. |
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