Cracking, identification and prevention of photovoltaic modules

1. What is "hidden crack"?

Cracking is a relatively common defect in crystalline silicon photovoltaic modules. In general, it is a micro-crack that is invisible to the naked eye. The crystalline silicon component is very susceptible to cracking due to its own crystal structure.

In the process of producing crystalline silicon components, many aspects may cause the cell to crack. The root cause of cracking can be summarized as mechanical stress or thermal stress on the silicon wafer. Now in order to reduce the cost, the crystalline silicon cell is developing in a thinner and thinner direction, which reduces the ability of the cell to prevent mechanical damage and is more prone to cracking.

2. The impact of "cracking" on component performance

The structure of the crystalline silicon solar cell is as shown in the following figure, and the current generated by the cell is mainly collected and derived by the main gate line and the fine grid line whose surfaces are perpendicular to each other. Therefore, when a crack (mostly a crack parallel to the main gate line) causes the fine gate line to break, the current will not be efficiently transported to the main gate line, causing partial or even partial failure of the cell, possibly causing debris, Hot spots, etc., while causing power attenuation of the component.

The crack perpendicular to the main gate line hardly affects the fine gate line, so the area causing the cell failure is almost zero.

However, in the rapid development of thin film solar cells, due to its material and structural characteristics, there is no problem of cracking. At the same time, the surface collects and transmits current through a transparent conductive film. Even if the battery sheet has a small flaw, the conductive film is broken, which will not cause a large area failure of the battery.

Studies have shown that if the failure area of ​​a battery in a component is less than 8%, the power of the component is not affected, and the 2/3 diagonal stripe crack in the component has no effect on the power of the component. Therefore, although cracking is a common problem with crystalline silicon cells, there is no need to worry too much.

3. Identify the "crack" method

EL (Electroluminescence) is an internal defect detection device for solar cells or components. It 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 acquire and determine component defects. It has the advantages of high sensitivity, fast detection speed and intuitive image. The figure below shows the results of EL detection, clearly showing various defects and cracks.

4. Reasons for the formation of "hidden cracks"

External force: The battery piece will be subjected to external force during welding, lamination, frame or handling, installation, construction, etc. When the parameters are improperly set, equipment failure or improper operation will cause cracking.

High temperature: The battery sheet is not preheated at low temperature, and then it will cause cracking when it is suddenly exposed to high temperature in a short time. For example, the welding temperature is too high, and the lamination temperature is unreasonable.

Raw materials: Defects in raw materials are also one of the main factors leading to cracking.

5. Points to prevent cracking of PV modules

In the production process and subsequent storage, transportation, installation, the battery is not subject to improper external force intervention, but also pay attention to the storage environment temperature range.

In the welding process, the temperature of the battery should be preheated (hand soldered) to meet the requirements.