Cracks, hot spots, and PID effects are three important factors that affect the performance of crystalline silicon photovoltaic modules. Today, let's learn about the reasons for cracks in batteries, how to identify them and how to prevent them.
1. What is "hidden crack"
Cracks are a relatively common defect of crystalline silicon photovoltaic modules. Generally speaking, they are some tiny cracks that are invisible to the naked eye. Due to the characteristics of its own crystal structure, crystalline silicon components are very prone to cracking.
In the process flow of crystalline silicon module production, many links may cause cell cracks. The root cause of cracks can be summarized as mechanical stress or thermal stress on the silicon wafer. Now in order to reduce the cost, crystalline silicon cells are becoming thinner and thinner, which reduces the ability of the cells to prevent mechanical damage and is more prone to cracks.
2. The impact of "hidden cracks" on component performance
The current generated by the battery sheet is mainly collected and exported by the main grid lines and thin grid lines perpendicular to each other on the surface. Therefore, when the cracks (mostly hidden cracks parallel to the main grid lines) cause the thin grid lines to break, the current will not be able to be effectively delivered to the busbar lines, which will lead to the failure of part or even the entire cell, and may also cause fragments, Hot spots, etc., while causing power attenuation of components.
The cracks perpendicular to the main grid lines hardly affect the thin grid lines, so the area of cell failure is almost zero.
However, thin-film solar cells, which are in rapid development, do not have the problem of cracks due to their material and structural characteristics. At the same time, its surface collects and transmits current through a layer of transparent conductive film. Even if the battery sheet has small flaws that cause the conductive film to rupture, it will not cause large-scale failure of the battery.
Studies have shown that if the failure area of a certain battery in a module is within 8%, it will have little effect on the power of the module, and 2/3 of the diagonal stripe cracks in the module will have no effect on the power of the module. Therefore, although cracks are a common problem in crystalline silicon batteries, there is no need to worry too much.
3. Methods to identify "hidden cracks"
EL (Electroluminescence, electroluminescence) is a kind of internal defect detection equipment of solar cells or components, and it is a simple and effective method for detecting hidden cracks. Utilizing the electroluminescent principle of crystalline silicon, the near-infrared images of the components are captured by a high-resolution infrared camera to obtain and determine the defects of the components. It has the advantages of high sensitivity, fast detection speed, and intuitive results.
4. Reasons for the formation of "hidden cracks"
External force: Cells will be subjected to external forces during welding, lamination, framing or handling, installation, construction, etc. When parameters are set improperly, equipment failures or improper operation will cause cracks.
High temperature: Cells that have not been preheated at low temperature, and then suddenly expand after being exposed to high temperature in a short period of time will cause cracks, such as excessively high welding temperature, unreasonable setting of lamination temperature and other parameters.
Raw materials: Defects of raw materials are also one of the main factors leading to cracks.
5. Key points to prevent cracks in photovoltaic modules
During the production process and subsequent storage, transportation, and installation, avoid improper external force intervention on the cells, and also pay attention to the temperature range of the storage environment.
During the welding process, the battery sheet should be kept warm in advance (hand welding), and the temperature of the soldering iron should meet the requirements.