| It is extremely crucial to solve the growing scarcity of energy supply,so it has become inevitable to speed up the development of new energy sources.The connection of building energy efficiency and renewal energy is crucial to reduce building energy consumption,environmental pollution and carbon emissions.As the latest development direction of combining building energy saving and renewable energy,the advantages of photovoltaic building integration have led to its rapid development trend in the world,but in high temperature climate,the temperature of PV modules is considerably raised,leading to a substantial reduction of its electricity efficiency.Since the cooling effect of different installation structures of integrated PV on the roof is about the same in the high wind speed range,the main purpose of this study is to reduce the temperature of PV modules,and to provide theoretical,experimental and simulation studies on two typical installation structures of integrated PV on the roof:parallel structure（PV arrays installed parallel above the roof）and grid structure（PV arrays installed non-parallel above the roof）in the wind speed range of class 1 to class2.The main studies are as follows:（1）Theoretically studied the working principle and essential parameters of PV cell,analyzed the correlation between open circuit voltage,short circuit current and filling factor and PV module temperature,and found that: open circuit voltage and filling factor are adversely correlated with the temperature of PV module,while short circuit current is actively correlated with the temperature of PV module.Then,the general solar radiation irradiated on the inclined surface of the PV module was then calculated based on the parameters of direct solar normal radiation,direct radiation on the horizontal surface and solar incidence angle,and the calculation model of the general solar radiation on the inclined surface was established,and the heat transfer model of integrated PV on the roof is also constructed to analyze the heat transfer procedure of each part and provide the theoretical basis for following experimental research and simulation study.（2）An experimental bench with parallel structured single photovoltaic panels was built,and experimental contents and experimental steps were designed to conduct single panel studies.It was found that: the input temperature of the air channel is approximately the same as the environmental air temperature;the output current of the photovoltaic panel is positively correlated with the solar radiation intensity;the temperature trends of the longitudinal measurement points of the wood roof panels and the PV panels were the same,that is,the lowest temperature was measured at the import location,followed by the middle location and the highest temperature at the export location.Numerical modeling of parallel structural single panel using CFD（Computational Fluid Dynamics）program,and the deviation of the experimental data from the measured temperature values at the import and export points of the PV panel,roof and air channel was calculated to be within 10%,and the reliability of the model was experimentally validated.（3）Numerical simulations of parallel and grid structures are performed using the validated model and compared and analyzed.The results indicate that: with the rise in spacing,the average temperature of PV array increases first and then remains basically the same;the optimal spacing of air channels diminishes with the rise of wind speed;the larger the wind speed is,the lower the average temperature of PV array and roof;with the increase of roof inclination,the average temperature of PV array and roof tends to rise first and then drop at a slower pace.Along the direction of air flow in the channel,the temperature of each PV panel rises progressively in the parallel structure,but the temperature of the first panel rises sharply,while that of the third panel rises slowly and the temperature at the end drops marginally;in the grid structure,the temperature of each panel rises progressively when the spacing is relatively small;when the spacing is large,the temperature rises first and then drops.As the spacing or wind speed decreases,the cooling effect of the grid structure is more obvious than that of the parallel structure.A heat dissipation study using theoretical,experimental and simulation methodologies for two typical installation structures of integrated PV on the roof found that the easy-to-install grid structure has better cooling effect in the wind speed range of class 1 to class 2 with a smaller spacing,which is of great significance in reducing the air conditioning cooling load and reducing the probability of fire hazards caused by high roof temperature. |
PDF Full Text Request