Analysis of Photovoltaic Module Welding Technology

Abstract: To achieve the power generation function of a solar module, it is necessary to connect the monolithic batteries together to make them a whole. The common connection method is welding. However, if the welding process is not controlled properly, hot spots, debris, etc. will be caused. In severe cases, the life of the components will be affected, and even the components will be burned. Therefore, most of the crystal silicon assembly workshops will set welding as a special process for monitoring at any time. This article gives a new welding process, which provides a guarantee for the manufacture of high-quality solar modules.

1 Introduction

In the manufacturing process of a solar cell module, the quality of the single-side and back-side welding of the cell sheet is very important. Since the design life of the solar module is about 25 years, and the components are usually installed outdoors, the temperature of the solder strip is changed to several tens of degrees Celsius per day. The base material of the tape is pure copper, and the coefficient of expansion of copper is about silicon (cell). Six times that, as long as there is a temperature change, both the ribbon and the battery are subjected to stress, so bad soldering can cause component failure.

At present, most domestic manufacturers mainly use manual welding methods, and manual welding causes many welding failures. In order to improve the quality of the finished solar modules, this paper gives an improved method to prevent the bad welding.

2. The battery is easy to appear bad phenomenon

Solar cell manual welding process is as follows:

The first single front welding. The tinned copper ribbon is soldered to the front (negative) main grid line of the cell sheet with a soldering iron at a certain temperature.

Then back welding of the cell is performed. On a special welding template (which can ensure the relative position of the cell), an electric soldering iron is used to solder the interconnection strip to the electrode on the back of the cell, so that the cells are serially connected together, and the positive and negative electrodes are welded out of the lead.

The use of manual welding has certain limitations, and it is easy to have bad welding phenomena. The main ones are as follows:

(1) Weld

The mechanism of the formation of the Weld Weld is the difference in the degree of formation of the Sn-Pb alloy with the silver electrode of the cell electrode. The factors affecting the formation of alloys are the temperature and the activity of the surface metal of tin, lead, and silver.

The reasons for the occurrence of false weld abnormalities in manual welding of production lines are as follows:

Whether the employees are concentrated or not, whether the welding time is too fast or not, and whether the welding method is different from other employees.

Whether the welding process fluctuates, focusing on observing whether the soldering iron temperature and the welding time meet the requirements.

Whether the battery slice is concentrated is mainly whether the battery silver paste is oxidized or yellowed. For example: yellow back electrode.

Whether the interconnect strips are immersed in compliance with the requirements, such as whether the flux on the interconnect strip is volatilized or not, and whether the interconnect strips are oxidized.

Interconnect/flux batch manufacturers are replaced.

(2) Slits

The mechanism of cell splinters is the impact of external forces, cell cracking or temperature shrinkage to generate stress.

The reason for the occurrence of abnormal splinters in the manual welding of the production line is as follows:

Observe the position of the sliver and the discovery process to see if the distribution of all sliver locations is regular.

Check whether the battery lot's batch (wafer manufacturer, line type, production date) is centralized.

Check to see if the interconnect strip is distorted.

Check if the splinters are caused by welding difficulties such as cold welding.

Check the welding temperature, welding method is normal.

Check if the starting and ending points are at the front.

(3) tin wire dross

The mechanism of tin slag production is the difference between the tin-lead and the battery electrode silver layer alloy. The factors affecting the alloy formation include the temperature and the surface metal activity of tin, lead, and silver.

The reason for the abnormality of tin wire dross in the manual welding of the production line is as follows:

Inspect employee welding practices, focusing on several factors such as speed, finishing, and straightness of pulling iron

Check the soldering iron temperature;

Check whether the cell electrode is oxidized;

Check the desktop cleanliness, iron cleaning sponge water content and so on.

3. Improve the welding process

In view of the bad phenomenon occurring during welding, this article has improved the single welding and string welding process to improve the quality of the finished product of the assembly.

3.1. Improved single solder process

The improved single solder process includes the following steps:

(1) When welding, the left hand takes the battery slice from the single welding zone, and the right hand takes the welding tape. The welding direction is uniformly welded from left to right and from top to bottom according to the busbar line. The three grid lines follow the first three thirds. Principles (The starting and ending points are the third fine grid line of the cell). During the welding process, the soldering station temperature and the soldering time should be taken care of, and there should be no phenomena such as whitening, soldering, soldering, and tin dross. 156 battery series single welding time is 3-5S, series welding time is 2-4S; 125 battery series single welding time 2-4S, string welding time 1-2S (for special silver paste special treatment).

(2) Hold the soldering iron handle at a 45 degree angle while welding.

(3) When welding, the welding pen and the arm must move in parallel. Do not rely on the wrist to drag the welding pen.

(4) After soldering each soldering tape with a single solder, check whether there is any defects such as tin, tin, and tin slag.

(5) Take the battery from the left side of the preheated table and place it in the area to be welded. After the welding is completed, it is required that the front of the battery be slanted, whether there is any false white, foreign matter of tin dross, or distortion of the ribbon.

(6) When the single welding is used to solder the battery, the ribbon cannot bend.

(7) Welded countertops should be kept clean and tidy, articles should be placed in designated areas as required, and bent soldering strips must not be used.

(8) The soldering station temperature is 350±3°C, the preheating station temperature is 50±3°C, and the soldering tip is switched to the tip of the 500-4DK.

(9) Ribbon material: Coating: Sn60/Pb40; Substrate: Cu ≥ 99.9%; Coating thickness: 0.05mm; Finished product thickness: 0.35mm; Width: 8mm; Elongation: ≥ 20%; tensile strength Strength: ≥145MPa; resistivity: <12mΩ/25°C.

3.2. Improved string welding process

The improved string welding process includes the following steps:

(1) Clean the string welding template before string welding to prevent the tin slag and tin wire from falling off the top crack cell (every assembly is cleaned once after welding).

(2)After series welding, clean the tin wire and tin slag on the battery string with a brush (clean every time after welding a string of battery strings). The cleaning brush can only clean the battery string and the preheating table. It is forbidden to clean the work table with a cleaning brush. . The cleaning brush is changed every 2 hours (contamination should be replaced in less than 2 hours).

(3) Take the battery from the area to be soldered and distribute it to the string welding template to prepare for welding.

Distribute the battery from left to right and then start welding from right to left. When distributing the battery, pay attention to that the battery does not rest on the template stopper; ensure that the welding string template before welding is clean and free from foreign matter.

(4) During the string welding process, pay attention to the following two requirements:

a. When soldering starts, solder joints are welded from the first twisted wire. After soldering is completed, check whether the solder strips are parallel and in the back of the battery.

b. The string welding operation should pay attention to the monolithic spacing of the battery pieces, and prevent the battery pieces from colliding with the template block and causing debris.

(5) The temperature of the string soldering station is 360±3°C and the preheating stage temperature is 60±3°C.

4. Results and discussion

In order to verify the feasibility of the improved single-weld process, welding was performed before and after the process of welding the same single wire, and the welding volume was counted for one week. The results showed that the output was 804 when the old process was used. The new process For the 939 block, the output increased by 14.4%.

The new process also greatly improves the welding quality. The improved single welding and string welding processes were used to weld the solar cells, and the number of cells in which the welds, splinters, and solder tin slag had occurred within one month was counted, and the number of cells exhibiting bad phenomena before the process improvement was compared. It can be seen from the figure that the new process significantly reduces the chances of the occurrence of false welds, splinters, and solder tin slag during the welding of the cell sheet.

One piece of the components welded under this process was randomly selected for the environmental aging test. According to the IEC 61215 design identification and finalization test methods 10.13, 10.12, and 10.11, the components had no abnormal appearance, and the wet insulation was qualified.

5. Summary

The use of new processes for welding reduces the chances of undesirable phenomena such as imaginary welding, splinters, and tin wire dross in the welding process, improves the quality and output of solar modules, and provides a guarantee for the manufacture of high-quality solar modules. It is worth promoting in the photovoltaic industry. . (Author: Wang Wei, Zheng Ji-Hong, Li Hao, Wang Shipeng, Haiyan Huang, Lu Chuan unit: Jiuquan Chint Solar Energy Technology Co., Ltd.)

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