The diode in the junction box of the solar panel

The bypass diode in the junction box of the solar panel is generally connected to the two ends of several rows of cells connected in parallel and connected in parallel. When all the cells are fully illuminated and generate energy normally, the bypass diode is reverse biased, and current flows through each cell. When the current flowing through a battery slice decreases and the battery slice becomes reverse-biased, the bypass diode connected in parallel with it becomes forward-biased and conducts, and the current flows through the bypass diode, bypassing it and not working properly The battery slices to prevent damage to the battery. 

From the most ideal point of view, each cell should be connected to a bypass diode, but this is very uneconomical. In addition, the positions of the cells of the solar panel are relatively concentrated, and after the corresponding diodes are connected, sufficient heat dissipation conditions must be provided for these diodes.

Therefore, in actual use, a generally reasonable method is to use a bypass diode to provide protection for multiple interconnected battery groups. This can reduce the production cost of solar panels, but also adversely affect its performance.

In fact, if the output power of a cell in a string of cells drops. Then this string of cells, including those cells that work normally, will be isolated from the entire solar panel system due to the bypass diode. This will cause the output power of the entire solar panel to drop excessively due to the failure of a certain cell. 

At present, most commonly used diodes for solar panel junction boxes are 10SQ050, 10SQ045, 12SQ045, 10A10, MBR1545S, MBR1545CT, SB1050, etc. These diodes are low-power, ultra-high-speed semiconductor devices, and the most notable feature is the extremely short reverse recovery time (can As small as a few nanoseconds), the forward conduction threshold voltage and forward voltage drop are lower than PN junction diodes (about 0.2V lower). IEC 61215-2005 "Crystalline Silicon solar panels for Ground Use-Design Appraisal and Finalization" 10.18  Bypass Diode Thermal Performance Test and  DIN V VDE 0126-5:2008 "solar panel Junction Box" H1 Bypass Diode Thermal Performance Test. The specific operation steps of the bypass diode thermal performance test.


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