Cracks, hot spots, and PID effects are three important factors that affect the performance of crystalline silicon photovoltaic modules. Today, I will take you to understand the causes of battery cracks, how to identify and prevent them.
1. What is "crack"
Cracks are a relatively common defect in crystalline silicon photovoltaic modules. In layman's terms, they are micro-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 costs, crystalline silicon cells are becoming thinner and thinner, which reduces the ability of cells to prevent mechanical damage and is more prone to cracks.
2. The impact of "cracking" on component performance
The current generated by the cell is mainly collected and derived by the busbars and thin gridlines whose surfaces are perpendicular to each other. Therefore, when cracks (mostly cracks parallel to the busbars) cause the thin gridlines to break, the current will not be effectively delivered to the busbars, resulting in partial or even failure of the cell, and may also cause debris, Hot spots, etc., at the same time cause the power attenuation of the components.
The cracks perpendicular to the busbars hardly affect the thin gridlines, so the area that causes the failure of the cell is almost zero.
The thin-film solar cell, which is developing rapidly, does not have the problem of cracking due to its material and structural characteristics. At the same time, the surface collects and transmits current through a layer of transparent conductive film. Even if the conductive film is broken due to small defects in the battery, it will not cause large-scale failure of the battery.
Studies have shown that if the failure area of a battery in a module is within 8%, it has little effect on the power of the module, and 2/3 of the diagonal stripe cracks in the module have no effect on the power of the module. Therefore, although cracking is a common problem of crystalline silicon cells, there is no need to worry too much.
3. Methods to identify "cracks"
EL (Electroluminescence, electroluminescence) is a kind of internal defect detection equipment of solar cells or components, which is a simple and effective method for detecting cracks. Using the electroluminescence principle of crystalline silicon, the near-infrared image of the component is captured by a high-resolution infrared camera to obtain and determine the defects of the component. It has the advantages of high sensitivity, fast detection speed, and intuitive results. The picture below is the test result of EL, which clearly shows various defects and cracks.
4. The reasons for the formation of "cracks"
External force: The battery will be subjected to external force during welding, lamination, framing or handling, installation, construction, etc., which will cause cracks when parameters are improperly set, equipment malfunctions or improper operation.
High temperature: The cell has not been preheated at low temperature, and then it will expand after being suddenly exposed to high temperature in a short period of time, which will cause cracks, such as excessive welding temperature, unreasonable setting of lamination temperature and other parameters.
Raw materials: Defects in raw materials are also one of the main factors leading to cracking.
5. The main points of preventing cracking of photovoltaic modules
In the production process and subsequent storage, transportation, and installation, avoid improper external force intervention on the battery cells, and also pay attention to the temperature change range of the storage environment.
During the welding process, the battery should be kept warm in advance (hand welding). The temperature of the soldering iron should meet the requirements.