Solar photovoltaic module power generation principle
For positive and negative charges, since the positive and negative charges are separated in the PN junction region, an external current field can be generated. The current flows from the bottom of the crystalline silicon solar cell through the load to the top of the cell. This is the "photovoltaic effect". When a load is connected between the top and bottom surfaces of the solar cell, current will flow through the load, and thus the solar cell will generate current; the more photons the solar cell absorbs, the greater the current generated. The energy of a photon is determined by its wavelength. Photons with energy below the base energy cannot produce free electrons, while a photon with energy above the base energy will only produce one free electron. The excess energy will cause the cell to heat up, and the resulting energy loss will reduce the efficiency of the solar cell.
Battery component manufacturing process
1. Battery testing
Due to the randomness of battery cell manufacturing conditions, the performance of the produced batteries varies. Therefore, in order to effectively combine batteries with consistent or similar performance, they should be classified according to their performance parameters. Battery testing involves classifying batteries by measuring their output parameters, such as current and voltage. This improves battery utilization and produces qualified battery modules.
2. Front welding
The busbar is soldered to the main grid line of the negative electrode on the front side of the battery. The busbar is a tin-plated copper strip, and the soldering machine we use can spot-weld the strip to the main grid line in a multi-point manner. The heat source for soldering is an infrared lamp that utilizes the thermal effect of infrared radiation. The length of the solder strip is approximately twice the side length of the battery. The excess solder strip is connected to the back electrode of the subsequent battery cell during back-side soldering.
3. Backside connection
Backside soldering involves connecting cells in series to form a module string. This process is manual. Cell positioning relies primarily on a template with grooves for placing the cells. The size of these grooves corresponds to the size of the cells, and their positions are pre-designed. Different templates are used for different module sizes. The operator uses a soldering iron and solder wire to solder the negative electrode of the front cell to the positive electrode of the back cell. This process is repeated sequentially, and leads are soldered to the positive and negative terminals of the module string.
4. Lamination installation
After the back-side connections are completed and pass inspection, the module strings, glass, and cut EVA, fiberglass, and backsheet are laid out in layers according to a specific plan, ready for lamination. A primer is applied to the glass beforehand to increase the adhesion between the glass and EVA. During installation, the relative positions of the battery strings and other materials such as glass are ensured, and the distance between the cells is adjusted to lay a solid foundation for lamination. Laying layers: from bottom to top: tempered glass, EVA, battery cells, EVA, fiberglass, backsheet.
5. Component lamination
The laid-out cells are placed in a laminator. Air is extracted from the module through vacuuming, and then the EVA is heated to melt, bonding the cells, glass, and backsheet together. Finally, the module is cooled and removed. The lamination process is a crucial step in module production; the lamination temperature and time depend on the properties of the EVA. When using fast-curing EVA, the lamination cycle time is approximately 25 minutes. The curing temperature is 150℃.
6. Trimming
During lamination, EVA melts and solidifies outwards due to pressure, forming burrs. Therefore, these burrs should be removed after lamination is completed.
7. Framing
Similar to framing a glass mirror, framing a glass assembly with an aluminum frame increases its strength, further seals the battery assembly, and extends its lifespan. The gaps between the frame and the glass assembly are filled with silicone resin. The frame members are connected using corner keys.
8. Welding junction boxes
A box is soldered to the lead wires on the back of the component to facilitate connection between the battery and other devices or batteries.
9. High-voltage test
High-voltage testing involves applying a certain voltage between the component frame and the electrode leads to test the component's withstand voltage and insulation strength, ensuring that the component is not damaged under harsh natural conditions such as lightning strikes.
10. Component Testing
The purpose of the test is to calibrate the battery's output power, test its output characteristics, and determine the quality level of the module. The main test is the Standard Test Condition (STC), which simulates sunlight. Typically, the test time for one solar panel is around 7-8 seconds.
