In recent years, with the large-scale construction of photovoltaic power stations, there have been varying degrees of quality and safety hazards. Safety and quality have become the number one killer of long-term stable power generation of photovoltaic power stations.
Once there is a serious accident such as an aircraft explosion or even a fire, it will not only affect the power generation but also have a very bad impact on national property and even human life.
Therefore, safety and quality have become the primary consideration of photovoltaic power plants.
The safety problems faced by photovoltaic power plants partly come from solar panels. The problems of solar panels mainly come from the junction boxes and the hot spot effects.
Analysis of quality problems of the junction box
The humble junction box is the “culprit” causing the spontaneous combustion of many solar panels. At present, the junction box market is chaotic and disorderly.
Due to the rough interior and few contact points of the poor connector, the resistance is too high to ignite the junction box, and then burn the backplate of the solar panel, resulting in the fragmentation of the solar panel.
It is suggested that when purchasing junction boxes, solar panel enterprises should take quality rather than price as the best choice, and inspect key parts such as connectors to eliminate hidden dangers from the source.
Causes and solutions of hot spot problem
In practical applications, solar panels are generally composed of multiple solar cells in series or in parallel to obtain the desired voltage or current. In order to achieve high photoelectric conversion efficiency, each solar cell in the solar panel must have similar characteristics.
During use, one or a group of solar cells may not match, such as cracks, internal connection failure, or shading, resulting in disharmony between their characteristics and the whole.
Under certain conditions, the shielded solar panels in a series branch will be used as a load to consume the energy generated by other illuminated solar panels. The obscured solar panel will heat up at this time, which is the hot spot effect. This effect can seriously damage solar panels.
In addition to seriously affecting the service life of solar panels, the hot spot effect may also burn solar panels and even cause a fire.
Generally, it is considered that when the temperature of the solar panel under normal operation is 30 ℃ and the local temperature is 6.5 ℃ higher than the surrounding temperature, the solar panel can be considered as a hot spot area.
However, this is not absolute, because the hot spot detection will be affected by factors such as irradiance, solar panel output power, ambient temperature, solar panel working temperature, and the cause of hot spot formation. Therefore, it is best to judge the hot spot effect based on the data analysis on the thermal imager image.
Generally speaking, the electrical characteristics of the solar cells used in each solar panel should be basically the same, otherwise, the hot spot effect will happen in the solar cells with poor electrical performance or blocked (problematic solar cells).
Most of the shielding is caused by unreasonable design or untimely operation and maintenance, while the causes of problematic solar cells are various. The main causes are the self defects of solar cells caused by inferior silicon materials, edge short circuit, local short circuit of grid lines, insufficient or excessive sintering degree in the manufacturing of solar cells, which will cause hot spots.
In addition, the detection ring shall be strictly controlled In addition, when purchasing solar panels, it is best to know the source of solar cells and even silicon materials of the solar panels.
What’s more, during the manufacturing of solar panels, the solar cells of the same batch shall be selected as far as possible and pass the precise test to avoid different performance. At the same time, the phenomenon of artificial mixing of solar cells shall not occur. During welding, hidden cracks, false soldering, and foreign matters shall be checked.
