Thermoelectric Analysis And Radiative Cooling Of Double-Glass Photovoltaic Module

The temperature effect of photovoltaic modules has always been one of the most important problems in the field of solar power generation.With the increase of temperature,the power output of the modules decreases due to the increase of electron and hole recombination rate of solar cells.The service life of the modules will also be affected.Therefore,reducing the temperature of photovoltaic modules is the key to improve the efficiency and life of photovoltaic power generation.Among the cooling methods of photovoltaic modules,passive thermal management based on coating technology with spectral regulation has attracted a lot of attention in recent years.However,the application of this technology only appears on the upper surface of the module,and the research on the application of coating on the rear surface is almost zero.In this paper,the monofacial double glass module was taken as the research object.By means of the theoretical methods of thermoelectric coupling simulation and finite element simulation,the spectral regulation of surface,enhancing in-plane thermal conductivity and their coupling effect on the thermal management of module were investigated,which were also supplemented by experiments to study and verify.The main research contents and results are as follows:（1）The thermoelectric coupling model of double-glass module was constructed.Three spectrally regulated coatings including ideal sub-bandgap reflection（iSBG）,ideal mid-infrared emission（iMIR）and ideal sub-bandgap reflection+ideal mid-infrared emission（iSBG+iMIR）were applied on the modules and the thermal management effect of the coatings on the modules were evaluated under standard working condition.The cooling effect of iSBG is about twice that of iMIR.The cooling effect of iSBG+iMIR is the sum of iSBG and iMIR.In practice,in order to achieve the total reflection in the sub-bandgap wavelengths and full emission in the mid-infrared wavelengths,it is often at the expense of the transmittance of coating.Considering the“practical situation”,the coating transmissivity in the wavelength of 0.3～2.5μm decreased by 1%/2%/3%and theoretical calculation demonstrated that the mid-infrared emission coating on the rear surface of PV module has the best cooling effect.According to the simulation results,the TPX coating including SiO₂ particles were prepared and applied as the mid-infrared emissive coating on the rear surface of the module.The thermoelectric coupling model was used to calculate the optimal parameters of TPX/SiO2 coating:the particle size of 200 nm,volume fraction of 5 vol%and thickness of 60μm.The experiment results show that the cooling effect is 1℃by the optimal coating and the efficiency is improved by 0.21%in outdoor experiment.（2）In order to improve the in-plane thermal conduction of the modules,Al foil was inserted into the module as the heat-conduction layer.Finite element method was used to simulate the steady-state temperature field of the modules after enhancing the in-plane thermal conduction.The results show that the addition of Al foil can reduce the temperature of module by about 6℃.Two modules with Al foil layer were prepared,and outdoor experiments were conducted.The results showed that the addition of Al foil layer had cooling effect on modules.The average cooling effect of EAG and CAE module was 2.3℃and 1.5℃,respectively.Compared with standard module,the average in-plane temperature differences were reduced by 5.3℃and 5.1℃,respectively.（3）In order to explore the coupling cooling effect of spectrally regulated coating and enhancement of in-plane thermal conduction,finite element method was used to simulate the backsheet temperature field of standard module and EAG module with the coatings.The results show that compared with the standard module,the temperature of the EAG module with iSBG,iMIR and iSBG+iMIR coating on the front surface decreased by 9.874℃,7.802℃and 11.383℃,respectively,and the temperature of the EAG module with iMIR coating on the rear surface decreased by 7.982℃.EAG module also enhance the cooling effect of iMIR coatings.During the outdoor experiments of two days,the average temperatures of EAG module decreased by 5.7℃and 6.4℃,respectively,compared with the standard module.The average cooling effects of optimal TPX/SiO₂ coating on the standard module were 0.59℃and 1.1℃,respectively.The average cooling effects of the optimal TPX/SiO₂ coating on the EAG module were 0.91℃and 1.6℃,respectively.（4）Whether the experimental results above are still kept valid for the commercial double-glass module was evaluated.The finite element method verified by the experiment was used to simulate the double-glass model with the same size as the commercial module,and the temperature field of the rear surface of the standard commercial module and EAG commercial module with or without iMIR coating was simulated.The cooling effect of the rear iMIR coating on the standard commercial module and EAG commercial module are 2.919℃and 2.906℃,respectively.The cooling effect of the iMIR coating on the EAG commercial module is reduced by 0.013℃compared with that on the standard commercial module.The coupling cooling effect of the EAG and rear iMIR coating is 3.213℃.However,the temperature of the EAG commercial module is only 0.307℃lower than that of the standard commercial module.The coupling cooling method can still achieve a nice cooling effect on the commercial module,but the main contribution is from the radiative heat dissipation of the rear surface of module.The heat-conduction effect of Al foil on the commercial module is almost negligible.Due to the addition of thermal resistance,the Al foil layer will even inhibit the cooling effect of the rear iMIR coating.