Research on Concentrating Photovoltaic Systems

Research on Concentrating Photovoltaic Systems


In recent years, as the price of international traditional fossil energy has risen and environmental problems have become increasingly prominent, renewable energy sources such as solar energy have attracted attention in all countries. The utilization technology of solar photovoltaic has also become a hot topic for researchers. The development of relevant markets as well as mature and efficient technologies are of great significance to the energy security of China and the world.
 
The utilization technologies of current solar energy mainly include photovoltaic power generation, solar thermal utilization, comprehensive utilization of solar photovoltaic and solar thermal. In recent years, researchers have devoted themselves to improving the conversion efficiency of photovoltaic cells by improving materials for solar cells. The energy conversion efficiency of ordinary solar cell modules has increased from 15% at the beginning to 20% now. Among them, GaAsII-V semiconductor materials have higher conversion efficiency. The conversion efficiency of single junction GaAs cells can reach up to 28%, and that of multi junction GaAs cells can reach up to 38%. The improvement of solar cell materials has brought about the improvement of photoelectric conversion efficiency, but there is still a large amount of solar energy that cannot be converted into usable electric energy and stored in the cell as heat. Therefore, researchers began to consider improving the utilization of solar energy from the perspective of concentrating photovoltaic system structure. In order to reduce the impact of heat accumulation on the photoelectric conversion efficiency of solar cells, a concentrated photovoltaic system with a good heat dissipation device has become a hot topic for the current research.
 
Solar photovoltaic utilization systems can be divided into non-concentrating and concentrating systems in terms of structure. Compared with non-concentrating systems (PV or PV/T), concentrating systems (CPV or CPV/T) use cheap concentrating and reflecting glass, parabolic and butterfly reflectors, and the sunlight is converged on a small area through a lens; it was projected onto solar panels to generate electricity. The use of concentrating systems can reduce the use of expensive solar cells, thereby reducing costs. At the same time, appropriately increasing the concentration ratio can increase the output power of photovoltaic modules, improve the photoelectric conversion efficiency, and meet the peak power of the cell. In addition, since the heating area of the concentrated system is small, the heat loss will be much less. With an efficient heat collection system, a high-grade heat source can be obtained. Even if this part of the heat is not used, the electricity generated by the CPV/T system has a certain price advantage compared with the electricity price of traditional thermal power plants. For urban individual users, the CPV/T system can effectively use roofs or slopes and improve the utilization rate of the building area. In addition, the concentrating system also has the advantages of low toxic material content, easy recycling, easy and rapid expansion of manufacturing, and nearby enhancement of the local manufacturing capacity.
 
Concentrated sunlight is projected on the solar panel, and high heat will be generated at the focal point. On the one hand, heat loss will occur, and on the other hand, the surface temperature of the photovoltaic cell will rise sharply. An increase in temperature will bring about two effects: First, the photoelectric conversion efficiency of photovoltaic cells decreases with increasing temperatures. Every time the temperature of the solar module decreases by 1 K, the output power increases by 0.2% to 0.5%. Second, long-term high temperatures will cause irreversible damage to photovoltaic cells, thereby reducing conversion efficiency and affecting the service life.
 
Therefore, people have gradually explored and studied a variety of different cooling and heat dissipation methods for concentrating photovoltaic systems in practice. The predecessors generally discussed and studied the different types of radiators and cooling media. We are going to discuss the heat dissipation from the two perspectives include battery combinations and concentrating multiples, which have better systematicness and integrality and are convenient for researchers to choose the corresponding cooling system.