| Energy crisis and environmental pollution are two serious social problems of the world, so the solar energy attracts more and more attention of community because of its sustainability safe, reliable, and wide distribution. There are many different kinds of way to utilize the solar energy in people’s life and production. However, at the present stage, only the solar thermal utilization and photovoltaic utilization have practical meaning, because their technology is relatively mature. The efficiency of solar thermal utilization can reach about55%, but only get the thermal energy with low grade energy. In another way, photovoltaic utilization can obtain high grade electrical energy; however, most of the long wave irradiation cannot be used, so the efficiency of photovoltaic utilization is relatively lower than the solar thermal utilization. Photovoltaic and thermal (PV/T) technology can carry the photovoltaic conversion and photothermal conversion at the same time, which could significantly improve the efficiency of solar energy utilization. The theoretical overall efficiency can reach60-80%in PV/T system. Therefore, the PV/T technology is an important development direction of the application of solar energy.The PV/T system includes solar thermal and photovoltaic conversion application operating at the same time, Therefore photothermal conversion and its system architecture design requirements will affect the photovoltaic conversion process, especially in the temperature distribution and the irradiation distribution of system. Moreover, due to the PV/T systems have a high temperature requirement of the working fluid, the temperature difference between the import and export is significant. Taking into account the good thermal conductivity between the photothermal structure and the photovoltaic component and the insulation measure of outer packing, the temperature of the working fluid can affect the photovoltaic component, causing the temperature of solar cells changing along the flow direction of the working fluid. On the other hand, the structural characteristics of PV/T systems will lead to the uneven irradiance distribution such as frame shadows. Since the temperature has a direct impact on the short circuit current and open circuit voltage of the solar cell, the photocurrent of the solar cell is nearly linear changed with the irradiation intensity battery, therefore, non-uniform temperature distribution and irradiation distribution cause the voltage and current diverse in different cells, thereby lead solar cell mismatching and reducing the photovoltaic conversion efficiency of the PV/T system.At present, few attentions have been paid to the non-uniform distribution of temperature and irradiation in the research of PVT systems. And the impact on the output performance of the system also lack of discussion. Moreover, it is common to use the model of photovoltaic system to simulate the photovoltaic performance of PV/T systems, but PV/T systems is affected by the heat exchange portion of the system in the photovoltaic conversion process. Therefore, it is necessary to discuss that whether the model of photovoltaic system can been used to simulate the photovoltaic performance of PV/T systems.Based on the above analysis, this paper will consider the non-uniform distribution of temperature and irradiation in the research of PVT systems, and carry an experiment to test the performance of PV/T system. Then a theoretical modeling will been present based on the experimental data to simulate and predict the photovoltaic performance of PV/T system. The results can be used for the design of PV/T system, and provide a theoretical basis to evaluate the performance of PV/T system. The content of this paper as following:(1) Based on the method of experimental test and numerical simulation, expanding the traditional model of the solar cell and to make it appropriate to apple in the simulation of the performance of the solar cell under non-uniform illumination. And the involved parameters can be easily obtained from cell suppliers. On this basis, considering the characteristics of plate PV/T systems, the distributed photovoltaic performance analysis model of PV/T system is established. In this model, each cell can be considered as a single node and assigned parameter independently. In addition, the experiment is conducted to verify the model, so that the model can be applied to simulate PV/T systems under non-uniform irradiation. The results can provide a theoretical basis and numerical models for the analysis of PV/T.(2) Considering the temperature distribution characteristics of the PV/T systems, namely the change of average temperature is relatively large and temperature range spatial differences is obvious, the temperature distribution of a typical PV/T systems due to the structural characteristics is analyzed; the mathematical model of a series circuit and a parallel circuit are established respectively. The photovoltaic performance parameters which affected by temperature factors at maximum power tracking mode and constant pressure operation mode are analyzed respectively. The kinds of solar cell include mono-crystalline silicon cells, poly-crystalline silicon cells, thin-film cells and triple-junction amorphous silicon solar cells.(3) Studying the phenomenon of frame shadow on plate PV/T system. The distribution of frame shadow in plate PV/T system is analyzed; simulating the photovoltaic performance of PV/T system is simulated by the distributed photovoltaic performance analysis model. On this basis, the electrical loss which caused by frame shadow is analyzed and the performances between a series circuit and a parallel circuit are compared.(4) The distribution of frame shadow in BIPV/T system is studied; the frame shadow distribution model of system is established; the distribution of frame shadow in different times and in different orientation are discussed in detail; the photovoltaic performance of BIPV/T system is simulated by the distributed photovoltaic performance analysis model. On this basis, according to the typical meteorological year data in Hefei, the annual average electrical output of BIPV/T system is estimated; annual energy loss caused by shadow on different azimuth angles are evaluated. The results can be used to evaluate the performance and annual loss of BIPV/T system. |
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