Solar cell modules are usually installed in areas with open areas and plenty of sunlight. In long-term use, it is inevitable that flying birds, dust, fallen leaves and other shelters will fall on them. These shelters will form shadows on the solar cell modules. If the row spacing is not suitable in a large-scale solar cell module square array, shadows can also be formed on each other. Due to the existence of partial shadows, the current and voltage of some single cells in the solar cell module have changed. As a result, the product of the local current and voltage of the solar cell modules increases, thereby generating a local temperature rise on these cell modules. The defects of some single cells in the solar cell module may also cause local heating of the module during operation. At this time, the shaded part of the series branch will be used as a load to consume the energy generated by other unshaded solar cells. , so the shaded part will heat up at this time, which is the hot spot effect.
1 How do component hot spots arise?
When one or a group of cells in the module is covered or damaged by cracks, the power generation of the cell will be affected, and the current will be lower than that of the surrounding normal power generating cells. When the operating current of the component exceeds the short-circuit current of the battery, the shaded battery will change from power generation to energy consumption, causing the local temperature of the component to rise. This effect can severely damage solar cells. Part of the energy produced by illuminated solar cells may be consumed by shaded cells. The hot spot effect may be just a piece of bird droppings.Also read:When will solid-state batteries be available
2 Main causes of component hot spots
①Battery defects: hidden cracks, broken grid, virtual welding, etc.;
②External factors: partial occlusion, dust accumulation, dirt, etc. on the surface of the module.
Battery defects can be controlled by various monitoring and quality management systems. At present, many first-tier component factories have introduced electroluminescent infrared monitoring systems in the production process to prevent defective cells from being used in components. However, the bumps during the transportation of the modules and the irregular operation and handling of the power station installation will also lead to the occurrence of cracks. Especially for the whole monocrystalline solar cell modules, the external factors caused by hot spots are difficult to eliminate.
3 What are the potential safety hazards of hot spots?
In addition to affecting the power generation of the module, the hot spot will also cause the local temperature of the module to rise sharply, posing a safety hazard. When the temperature of the components is too high, it can cause a fire. We observed during experimental testing that the hot spot temperature of some monocrystalline PERC cells is as high as 170 degrees. Therefore, when the power output of the entire battery module increases, the energy consumption accumulated by the hot spot battery will also increase, the temperature will rise higher, and the safety hazard will increase.Also read:How much do solar batteries cost
In order to prevent the solar cell from being damaged due to the hot spot effect, it is better to connect a bypass diode in parallel between the positive and negative poles of the solar cell module to prevent the energy generated by the lighting module from being consumed by the shaded module. When the hot spot effect is severe, the bypass diode may be broken down, causing the components to burn out.
4 Hot spot temperature rises with module power increase
After the hot spot test of the latest standard of IEC 61215 (2016), we found that the hot spot temperature is related to the power of the module. The higher the module power, the higher the hot spot test temperature, and the greater the risk of hot spot. The temperature at the hot spot of the 355W 72-piece monocrystalline PERC module can reach about 170°C.