| The PV/T system combines independent photovoltaic modules with heat collection modules to absorb heat from photovoltaic cells through air,water and other refrigerants to improve the output of photovoltaic cells.Its integrated photovoltaic-thermal design has the advantages of high efficiency,multi-function,low-cost and so on.However,influenced by geographical location and environmental factors,PV/T technology also has many deficiencies.For example,the water stored in the copper tube of the water-cooled PV/T collectors tends to freeze under the low temperature in winter,which can damage the pipes or collectors;For the non-heating season,the heating function of the air-cooled PV/T collectors is left unused.Therefore,excess temperature inside the PV/T collector can lead to a reduction in the system’s photovoltaic conversion efficiency,which can affect the life of the PV cells.Moreover,until now,PV/T system has only one form of cooling for PV modules,and less research has been involved in dual-cooled PV/T integrated modules that combine air and water duplex.Furthermore,the air-cooled PV/T that scholars mostly proposed is a single air duct structure,where the air cannot adequately exchange heat with the absorber plate,thus the temperature at the air outlet often fails to meet the usage requirements.In response to such problems,this paper proposes a novel air/water-cooled PV/T integrated module,in which the double-layer air flow channels are equipped with parallel finned construction to enhance the heat transfer coefficient between the air and the absorber plate.The module has three working modes: water cooling,air cooling or air-water composite cooling according to climatic conditions and user needs.In this way,it will improve the limitations of single working medium PV/T systems so as to meet seasonal heating demand and maximize solar energy utilization throughout the year.To this end,the research involved in this paper is as follows:1.A novel air/water-cooled PV/T integrated module are designed and constructed.According to the three operating modes of PV/T modules,namely air-cooled,water-cooled and air/water-cooled,two test platforms are built in this paper.The test platforms enable the experimental study of the electrical/thermal performance of PV/T modules in different operating modes and under variable flow conditions.2.The performance of PV/T module under air-cooled mode,water-cooled mode,air/water-cooled mode and variable flow condition is experimentally studied.At the same time,the first and second laws of thermodynamics are combined to analyze the electro-thermal characteristics and comprehensive performance of PV/T modules.The experimental results show that the photovoltaic/thermal conversion efficiency and the overall efficiency of the three cooling modes are improved as the mass flow rate of air and water increases.And the overall efficiency of modules in air-cooled,water-cooled and compound cooling mode is 76.05%,74.51% and 84.83%,respectively.In addition,the cooling effect of the module is better under the action of air-water duplex medium.Compared to a module without working medium,its heat-absorbing plate temperature can be reduced by 39.43 °C,which is markedly higher than the dropping scale of temperature under both the air-cooled and water-cooled mode respectively.3.ANSYS is used to construct a three-dimensional numerical model for the three operating modes of air-cooled,water-cooled and air/water-cooled of the modules.The flow and heat transfer characteristics and temperature cloud distribution of the module are obtained through numerical simulation,and the simulation results are compared with the experimental data.The comparison results show that the average relative errors of the air-cooled,water-cooled and air/water-cooled modes are 0.68%,0.75% and 3.27%respectively,and the accuracy of the model is verified.4.Based on the numerical models,the effects of flow rate,temperature,irradiation intensity and other parameters on the operation performance of PV/T module are simulated and analyzed.It is found that the overall efficiency of the PV/T module is improved by increasing the inlet mass flow rate,ambient temperature and solar irradiation intensity for three operating modes.By increasing the temperature of the inlet,the electrical and thermal efficiency and overall efficiency of the PV/T module tend to decrease.In addition,the electrothermal performance of the module can be effectively enhanced the heat transfer between the working medium and the PV/T module through finned structure with double air ducts under the air-cooled mode and compound cooling mode.This causes 9.51% and6.39% increase in the overall module efficiency compared to a single duct finless structure,respectively.And the study found that in the air/water-cooled mode,if only the air flow rate is increased,then the air thermal efficiency is increased and the water thermal efficiency decreases.If only the water flow rate is increased,then the water thermal efficiency is improved while the air thermal efficiency decreases.The total thermal efficiency and combined efficiency of the PV/T module tends to increase under both operating conditions.Figure [62] table [26] reference [76]... |
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