Applications

The junction box plays a very important role in solar cell modules. With the rapid development of the photovoltaic industry, more and more attention is turning to the junction box; Because it not only facilitates the transmission of electricity generated by solar cells to external circuits, but also serves as the "protector" of solar cell components.

A junction box is a cross disciplinary comprehensive design that combines electrical design, mechanical design, and materials science; When the junction box acts as a "bodyguard", it utilizes the performance of the diode itself to ensure that the solar cell module can still operate and reduce losses appropriately when other adverse factors such as shading and current mismatch occur.

Due to its inherent characteristics, more and more people in the field of solar energy are gradually paying attention to this "protector" of solar cell modules, accompanied by the development of the photovoltaic market.

The role of junction boxes in solar cell modules can be summarized into two points: a) connection and transmission functions, b) protection of modules; It is a comprehensive interdisciplinary design that combines electrical design, mechanical design, and materials science.

Solar cell modules undergo photoelectric conversion through solar cells, and the electricity generated by a single module must be transmitted to the charging and control system through a junction box; And the junction box is also the "link" of the entire solar array, connecting many components together to form a power generating whole, so the role of the junction box in solar energy applications cannot be ignored.

The junction box also has a more important function of protecting components; When the components in the array are obstructed by dark clouds, branches, bird droppings, and other obstacles, causing thermal spots, the diodes that bypass the components use their unidirectional conductivity to bypass the problematic battery or battery string, protecting the entire component and even the entire array, ensuring that it can be maintained in the necessary working state and reducing unnecessary losses.

The most ideal component would be to bypass a diode on each battery cell to ensure absolute safety of the component. However, from a cost and process perspective, the current approach is to bypass a diode on a string of battery cells, which is a simple and effective method.

According to the requirements of IEC6121510.18.3, the following is the process of testing the thermal performance of a component's bypass diode: first test the electrical performance of the component, determine Isc as 5.53A, and test the diode's tube voltage drop; After the preparation of the preliminary work is completed, place the components in a chamber with a temperature of 75 ℃± 5 ℃ for heating, and at the same time, apply a current equal to ± 2% of the short-circuit current under standard testing conditions; After 1 hour, test the surface temperature of each diode, and then use the formula to calculate the maximum junction temperature of the diode during testing.

After the diode junction temperature test, increase the component current to 1.25 times the short-circuit current under standard test conditions, while maintaining the component temperature at 75 ℃± 5 ℃ and passing the component current for 1 hour to verify that the diode can still operate.

Due to the importance of junction boxes for solar cell modules, as well as the widespread application of the photovoltaic market and customers, major junction box manufacturers are currently striving towards high-quality junction boxes, such as designing junction boxes with high rated current, high waterproofness, excellent heat dissipation, low body resistance, etc. These will inevitably appear in future junction box products with technological development.

On the other hand, traditional solar modules degrade over time (usually at a rate of 0.5% to 1.0% per year), which may be caused by mismatches between photovoltaic modules, accelerated degradation of module performance due to the heat dissipation of bypass diodes, and various environmental factors such as floating clouds, dirt, and debris; Greatly reducing the power generation of individual components and the entire system, people have made modifications inside the junction box to solve or minimize this problem, and the modified junction box is called "Smart Box", while the components that use this junction box are called "Smart Module".

Today, the main technologies used in solar panel are polycrystalline and mono crystalline silicon solar cells. When one solar cell of the panel is shaded while the others are illuminated, a hot spot could appear and leads to the shaded cell destruction. The bypass diode is an efficient solution to eliminate the “hot spot” and maintain the current delivery. The Schottky diode is a cost effective candidate.

SMC, as a professional power semiconductor manufacturer, can provide customers with bare Schottky diode chips or finished Schottky diodes of different current levels. Many models have been successfully applied to customers around the world.