1.0 Introduction
The junction box plays a very important role in the solar cell module because it can not only transmit the electricity generated by the solar cell to the external circuit, but also it is the "bodyguard" of the solar cell module. The junction box is a cross-domain integrated design that integrates electrical design, mechanical design, and materials science; when the junction box serves as a “bodyguard,†it uses the properties of the diode itself to make the solar cell components shading, current mismatch, and other unfavorable factors. When it happens, it can keep it working and reduce losses appropriately.
The junction box has such an important role. Once a failure occurs, it will have a great impact on the application system of the component and cause economic losses to the system operator. This article focuses on the impact of temperature on the junction box, in order to cause the junction box manufacturers and component manufacturers to pay attention.
2.0 Temperature Effect on the Junction Box
The main factors that increase the temperature inside the junction box are diode and ambient temperature. Diodes generate heat when they conduct, and they also generate heat due to the contact resistance of the diodes and the terminals. In addition, an increase in the ambient temperature will increase the internal temperature of the junction box.
2.1 Influence on the box
Junction box and box cover material is PPO. The box body, the lid and the sealing ring form a sealed space. As the temperature rises, the volume of air in the sealed space expands, the gas pressure increases, and the temperature increases, so that the mechanical strength of the box lid decreases, thereby making the wiring. The cassette body or the lid is deformed to achieve the same inside and outside air pressure in the box. In this way, the tightness of the junction box is greatly reduced, and the entry of water vapor and dust can damage the metal devices inside the box and cause the junction box to be scrapped.
2.2 Effect on the seal
The material of the seal ring is silicone rubber. High temperature will accelerate the aging of the seal ring, affect the sealing of the junction box, and reduce the level of waterproof and dustproof.
2.3 Effect on the diode
There is a reverse current inside the diode. When the temperature rises by 10°C, the reverse current will double, and the reverse current will reduce the current generated by the component and affect the power of the component.
3.0 preventive measures
Components that are susceptible to high temperatures in the junction box are the seals, the diodes, and the lid. Therefore, the junction box must have excellent heat dissipation, or special heat dissipation design to reduce the impact of temperature.
The common heat dissipation design is to increase the surface area of ​​the metal parts or install heat sinks. However, this does not completely solve the heat problem. If the heat sink is installed inside the terminal box, although the temperature of the diode is temporarily lowered, the temperature of the cavity of the terminal box will still rise, which will affect the service life of the rubber seal. If it is installed outside the box, it will affect the terminal box on the one hand. The overall tightness will also easily cause the heat sink to be corroded.
The feasible solution is to install special devices inside and outside the communication box, which has reached the role of balancing air pressure, reducing the temperature and pressure inside the box, and reducing the risk of damage to the junction box. (The author WeChat public account: Photovoltaic experience network)
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