How To Choose The Model And Specification Of The Junction Box

How To Choose The Model And Specification Of The Junction Box

The photovoltaic junction box serves as a pivotal connector within the solar cell module, primarily facilitating the exportation of electric energy generated by the solar cell module through cables. Given the unique application and substantial value of solar cells, photovoltaic junction boxes necessitate specialized design to align with the operational requirements of solar cell modules.

In the realm of photovoltaic power generation systems, an inappropriate selection of a photovoltaic junction box can lead to the burning of solar panels or even the collapse of the entire photovoltaic system. As the adage goes, “Avoid sacrificing the greater for the lesser.” So, how should one approach the selection of a junction box to ensure optimal functionality and system integrity?

1. Connection

The junction box serves as a pivotal connector, forming a bridge between solar modules and control devices like inverters. It draws out the current generated by the solar module and introduces it to electrical equipment through the terminal block and connector, minimizing power loss with low-resistance conductive materials and ensuring minimal contact resistance of the bus strip’s lead wire.

2. Protection

The junction box’s protective functions are threefold. Firstly, it prevents the hot spot effect and safeguards the cells and components through bypass diodes. Secondly, it employs specialized materials to ensure waterproofing and fire resistance. Lastly, it utilizes a unique heat dissipation design to lower the working temperature of the junction box and the bypass diode, reducing power loss due to leakage current.

3. Weather Resistance

Weather resistance is crucial for materials exposed to the elements, ensuring they withstand climatic tests, including damage from light, temperature fluctuations, wind, rain, and bacteria. The junction box’s exterior components— the body, cover, and connector (PC)— are crafted from robust weather-resistant materials like PPO (polyphenylene ether), a top engineering plastic known for its high rigidity, heat resistance, flame retardancy, strength, and superior electrical properties. PPO’s minimal dielectric constant and loss, unaffected by temperature and humidity, make it suitable for varying electric fields, with a deformation temperature above 190℃ and an embrittlement temperature of -170℃.

4. High Temperature and Humidity Resistance

Given the diverse and harsh working environments of components—ranging from tropical to high-altitude regions— the junction box must exhibit exceptional resistance to high and low temperatures, ensuring optimal performance in areas with significant daily temperature variations, like deserts.

5. UV Resistance

Ultraviolet rays can significantly damage plastic products, especially in plateau areas where the air is thin, and ultraviolet irradiance is exceptionally high. A junction box with UV resistance is crucial in such regions to maintain the longevity and functionality of solar modules.

6. Flame Retardancy

Flame retardancy is a crucial property, inherent or treated, that significantly delays the spread of flames. The flame retardant grade ascends from HB, V-2, V-1 to V-0, with HB being the lowest flame retardant rating in UL94 and CSA C22.2 No 0.17 standards. A higher grade ensures enhanced safety and durability of the junction box in varying environments.

7. Waterproof and Dustproof

Adherence to IEC62852 /UL6703 “Enclosure Protection Level (IP Code)” standards ensures the junction box’s resilience against water and dust, with an available level of IP65, safeguarding the components against environmental elements and prolonging operational life.

8. Heat Dissipation

Heat within the junction box primarily arises from diode conduction and ambient temperature increases. Effective heat dissipation or specialized thermal designs are imperative to protect sealing rings and diodes from accelerated aging and to maintain the optimal power output of the components. While heat sinks are a common solution, their placement and integration need careful consideration to avoid adverse impacts on the junction box and its sealing integrity.

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