Research On The Performance Of PV/T Air Collector Integrated With Amorphous Silicon And Crystalline Silicon Solar Cells

The Photovoltaic /thermal(PV/T)collector is a device that the solar photovoltaic cell laminates on the absorber plate of the traditional collector and produce electricity and collect heat at the same time.Compared with the separate photovoltaic system and solar heat collection system,the advantage of solar PV/T collector is that it can reduce the temperature of the cells,improve the cell′s service life and the efficiency of power generation,and also can recycle and use the excess heat to improve the comprehensive utilization efficiency of solar energy.The solar PV/T water heater integrated with crystalline silicon cells is a common solar energy comprehensive utilization technology,but its shutdown will prevent all the water in the pipeline from being discharged,and it is prone to freezing at night when the temperature is low in winter,which will cause the water pipe to rupture.In addition,the temperature is too high during the day,which easily leads to heat dissipation and reduces the thermal efficiency.At the same time,the temperature coefficient of the crystalline silicon cells is relatively high,and its electrical efficiency decreases significantly with the increase of the PV temperature;the crystalline silicon cells is laminated on an aluminum plate,and the thermal expansion coefficient of the crystalline silicon cells is much smaller than that of the aluminum plate.The large temperature difference between the two may cause uneven thermal shrinkage and large thermal stress,so that in the long-term operation process,the thermal stress will cause technical failures such as deformation,interruption and destruction.Related researchers have found that amorphous silicon cells can effectively replace the crystalline silicon cells.The reason is that the flexibility and negative power temperature coefficient of amorphous silicon cells is small(about-0.1%/°C),so under high temperature fluctuations,large thermal stress problems can be significantly resolved.Therefore,this article proposes an amorphous silicon solar PV/T air collector with straight fins welded on the back of the heat absorption plate and the integrated PV/T air collector of the crystalline silicon cells were studied.The amorphous silicon solar PV/T air collector can operate stably at medium and high temperatures and the solar PV/T air collector integrated with crystalline silicon cells can maintain high electrical efficiency at low temperatures.Then,the thermal,electrical and exergy performance of PV/T air collectors integrated with amorphous silicon and crystalline silicon solar cells are compared and analyzed experimentally and theoretically.The main work content is as follows:(1)Designed and built a comparison test bench for separate amorphous silicon cells,amorphous silicon solar PV/T air collector and traditional solar air collector,and explored the thermal,electrical and energy performance of single amorphous silicon cells,traditional solar air collector and amorphous silicon solar PV/T air collector under the circumstances of different air mass flow rates and different inlet temperatures by experimental comparisons.The results show that the average thermal efficiency of the amorphous silicon solar PV/T air collector is 45.70%,which is about 25.88% lower than the average thermal efficiency of the traditional solar air collector;when the air mass flow rate increases to 0.048 kg/s,The average electrical efficiency of amorphous silicon photovoltaic cells in amorphous silicon solar PV/T air collectors is higher than that of single amorphous silicon photovoltaic cells.Their average electrical efficiencies are 4.70% and 4.54% respectively,a difference of 0.16%;for every degree of increase in the collector inlet temperature,the thermal efficiency of the amorphous silicon solar PV/T air collector decreases by about 0.45%,the electrical efficiency decreases by about 0.042%,and the temperature difference between inlet and outlet decreases by0.24 °C.The maximum total exergy efficiency(12.22%)of the amorphous silicon solar PV/T air collector and the maximum thermal efficiency(8.71%)of the traditional solar air collector both appear when the inlet air temperature is 60 °C.(2)Designed and built a comparison experiment platform for PV/T air collectors integrated with crystalline silicon solar cells(monocrystalline silicon and polycrystalline silicon),and contrastive studied the thermal,electrical and energy performance of solar PV/T air collectors based on the monocrystalline silicon and polycrystalline silicon by experiments.At the same time,it is compared with the previous experimental results of amorphous silicon solar PV/T air collectors.The results show that with the same air mass flow rate,the outlet temperature of the PV/T air collector integrated with crystalline silicon solar cells will decrease slightly and the thermal efficiency will increase greatly;the collector inlet temperature will increase by one degree.The electrical efficiency of PV/T air collectors integrated with monocrystalline silicon and polycrystalline silicon is reduced by about 0.073% and0.052%,respectively,while the electrical efficiency of amorphous silicon solar PV/T air collectors is reduced by about 0.042%,so the efficiency of amorphous silicon cells is minimally affected by temperature.If the PV/T air collectors integrated with crystalline silicon cells are used in series for two or more stages,and their advantages will be reflected.(3)The energy balance equation of each layer of the solar PV/T air collector is established,and the average outlet temperature of each layer is calculated through simulation,then the thermal,electricity,and exergy efficiency are calculated under stable irradiation conditions.The correctness of the theoretical model is verified by comparison with experimental test results.The verification results show that the maximum relative errors of the experimental test values and theoretical calculation values of PV/T air collectors integrated with amorphous silicon,monocrystalline silicon and polycrystalline silicon solar cells are less than 7%,5%,and 5%,respectively.The theoretical model of the solar PV/T air collector is correct within the tolerance range.(4)Using the verified theoretical model,theoretically analyze the impact situation of thermal efficiency of PV/T air collectors integrated with amorphous silicon and crystalline silicon solar cells under different wind speeds,air mass flow rates,inclination angles and collector lengths.The results show that: the wind speed increases,the instantaneous thermal efficiency of solar PV/T air collectors decreases,and the total heat loss coefficient increases,that is,the smaller the wind speed,the greater the thermal efficiency;corresponding to the maximum thermal efficiency of the solar PV/T air collector The best air mass flow rate is 0.060 kg/s;the best inclination angle is related to the local latitude,so during the actual installation of the collector,it can be installed according to the local latitude,and its thermal performance is better;The thermal efficiency is the largest when the length of the collector at 3 mm.If the length is further increased,the loss along the way will increase,and the outlet temperature will increase more slowly than the heat-absorbing plate areas,which will cause the thermal efficiency to decrease.