Analysis and model verification of surface heat transfer effects of non-concentrating photovoltaic-thermoelectric coupling system

Surface heat transfer has posed a great impact on the energy conservation in the non-concentrated photovoltaic-thermoelectric coupling systems. However, the one-dimensional heat transfer models were commonly used at present, particularly without considering the effects of natural convection and natural radiation heat transfer on the surface of the system. It is very necessary to introduce the contribution of the surface heat transfer in a photovoltaic cell, especially in the photovoltaic thermoelectric system with the a low surface energy flux density. In this study, a multi-physics model was established to consider the thermal radiation and convection on the surface of a non-concentrating photovoltaic-thermoelectric coupling system using an ANSYS simulation software. Three photovoltaic thermoelectric coupling systems were selected, including the non-focusing mode c-Si, CIGS, and GaAs. A systematic investigation was made on the influence of surface heat convection and thermal radiation heat transfer on the system energy during operation under different irradiance. Three photovoltaic cells with different cooling modes were selected to verify the model using the simulation and measurement data in the experiment. The result showed that the ambient temperature and the temperature of the photovoltaic cell were greatly contributed to the effect of surface convection and radiation heat transfer on the heat flux in the non-concentrated photovoltaic thermoelectric coupling system. Specifically, the convection and radiation on the surface of the system were had dissipated the heat, when the temperature of the photovoltaic cell was higher than the ambient temperature. By contrast, the surrounding environment raised the photovoltaic cell temperature through the convection and radiation below the ambient temperature. The closer the temperature of the photovoltaic cell was to the ambient temperature, the smaller the effect of convection and radiation heat transfer on the surface of the system was. In three photovoltaic cells, the heat flux of the photovoltaic backplane was reduced by up to 22.60% under different cooling modes, when considering the convection and radiation heat transfer on the surface of the system. There was the greatest impact of surface convection and radiation heat transfer on the accuracy of the system under the natural air-cooling heat dissipation mode, where the heat flux of the photovoltaic backplane was reduced by at least 9.21%. Furthermore, the surface convection and radiation heat transfer usually led to an increase of the heat flux of the photovoltaic backplane, increasing by 7.17% at most. Correspondingly, the water cooling presented the highest efficiency of power generation, followed by the forced air-cooling, and the natural air-cooling was the lowest. The CIGS photovoltaic thermoelectric coupling system in the water cooling mode presented the highest power generation efficiency of 21.09%. The temperature coefficient of a GaAs cell was the lowest, whereas, the power generation efficiency was the least due to the irradiance. By contrast, the GaAs photovoltaic-thermoelectric coupling system was had reduced the efficiency by up to 0.12% in the irradiance range of 600-1 400 W/m2. The test experiment demonstrated that the maximum absolute error of the improved model was -0.299 5%, and the maximum relative error was -3.032 0%. Anyway, the new model was much more suitable for the characteristic analysis of the photovoltaic thermoelectric coupling system in a non-concentration mode.