Coupled Thermal-Electrical Model And Hot Spot Mechanism Analysis Of Large-Size Photovoltaic Modules

Photovoltaic(PV)power generation is in the stage of vigorous development at present,and PV modules are an important device of PV power generation system.With the development of PV module technology,increasing power and reducing cost have become an important direction of industry development.The size of silicon wafer from domestic and foreign manufacturers is getting larger and larger.The market share of large-size PV modules is higher and higher.But researches on large-size PV modules are less.In view of the above background,this paper aims to construct the thermoelectric coupling model of large-size PV modules,analyze the hot spot mechanism and output performance of large-size PV modules under shaded condition,analyze the shaded cell temperature change of large-size PV modules.Firstly,in order to simulate the electrothermal performance of PV modules under actual operating conditions.an electrical model and a thermal model of PV modules are introduced.And a coupled thermal-electrical model of PV model is proposed.The single diode model is used for the electrical model of the PV module.The data in the literature is used to compare and verify the electrical model.The maximum root mean square error(RMSE)of the simulated value of the single diode model and the measured value is 4.7%,which is better than the RMSE of the simulated value of a double diode model and the measured value of 5.9%.Through the measured temperature and power data on outdoor PV measurement platform,the accuracy of the thermal model and coupled model is verified.The verification results of thermal model show that the RMSE of the simulated temperature value of the thermal model and the measured value is no more than 4.3%.And the RMSE between the simulated value of Nominal Operating Cell Temperature(NOCT)model and Sandia model and measured value is no more than 6.7% and 6.2% respectively.The accuracy of the thermal model is higher.Under the three typical weather conditions of sunny,rainy and cloudy days in winter and summer,the RMSE of the simulated power results of the coupled model and the measured values is no more than 12.6%.The performance of coupled model is the best on sunny day in summer.The RMSE of simulation and measurement is 8.1%,which has good universality and accuracy.Secondly,the hot spot mechanism and output characteristics of large-size PV modules are explored.The causes of hot spot are analyzed.Based on the single diode model of PV cells,the mathematical model of PV cells under shading is deduced.The output power of large-size PV modules of 210-55 and 182-72 is simulated under the conditions of shading single cell,shading long side and shading short side.The results show the output power of the two modules will loss under shaded conditions.The power loss of PV modules under short side shaded condition is always more than that long side shaded condition.The loss rate of 210-55 PV module is 32.7%,which is better than33.3% of 182-72 PV module.Under the same shading ratio,the maximum difference of output power loss rate of 210-55 PV module under short side and long side shaded condition is 57%,and that of 182-72 PV module is 63.7%.The 210-55 PV mdoule has good output performance under shaded condition.In the actual operation of PV modules,short side shaded conditions should be avoided as far as possibleFinally,the temperature of different size PV module under the shaded condition of a single cell is simulated and analyzed.The hot spot temperature data of PV modules under the condition of 30%-90% shading of a single cell is collected,which is used for verification of simulated results.The results show that with the increase of shading ratio,the temperature of the shaded part of the cell increases and then decreases.The RMSE of the simulated temperature and the measured value is no more than 14.8%,and the error between the simulated maximum temperature of the shaded cell and the measured value is no more than 4.7℃.The model can simulate the highest temperature of the PV module under shaded condition.Under the high shading ratio,the temperature of the shaded cell of 210-55 PV module is the lowest.The shaded cell temperature of three different sizes modules is the highest when the shading ratio is 50%.The maximum shaded cell temperature of the 210-55 PV module is reduced by at least 7.2℃.The 210-55 PV module has good performance on hot spot resistance under shaded conditions.In case of shaded conditions,the temperature of the shaded cell will rise sharply.In order to avoid irreversible damage to the PV module,the structural design of the PV module can be optimized through the allocation of cell string and diode.