The photovoltaic junction box is a connection device between the solar cell array composed of solar cell modules and the solar charging control device. Its main function is to connect and protect the solar photovoltaic modules, connect the power generated by the solar cells to external circuits, and conduct photovoltaic The current generated by the component.
The junction box has two functions: connection and protection. The connection function is to draw out the current generated by the photovoltaic modules and introduce it into the electrical equipment through cables and connectors. In order to reduce the loss of the junction box itself, the conductive material's own resistance and contact resistance are required to be as small as possible. The protection function consists of two parts. One is to protect the photovoltaic modules through bypass diodes and improve the power output of the photovoltaic modules under fault conditions such as shading. The other is to achieve the purpose of waterproofing and fireproofing and reducing the operating temperature of the junction box through special material sealing and heat dissipation design. , thereby protecting photovoltaic modules and reducing the loss of photovoltaic module output power caused by bypass diode leakage current.
As the power of battery components continues to grow, battery conversion efficiency also keeps increasing year by year, and the operating current in the photovoltaic system increases significantly. As an important connection and protection device between battery modules, the junction box is responsible for the power output and line protection of photovoltaic modules, so it needs to have a higher current carrying capacity.
The current carrying capacity is closely related to many indicators such as heat dissipation, conduction efficiency, reliability and endurance. Therefore, photovoltaic module junction box manufacturing companies need to maintain synchronized technological innovation to adapt to the rapid development of cell technology. Photovoltaic module junction boxes are moving towards higher current carrying capacity, better heat dissipation capacity, higher system stability, and lower energy consumption. Trends such as production costs develop.
Development stages of photovoltaic junction boxes
In recent years, as the performance of photovoltaic module products continues to improve, the market has increasingly higher requirements for the current carrying capacity, heat dissipation capacity, and system stability of junction box products. Junction box products have also gone through many iterations.
From the earliest sealing ring junction boxes with complicated processes to the glue-filled patch junction boxes with simplified processes, better sealing performance, smaller size, and higher degree of automation; from single junction boxes with more materials to the bonding area A split junction box that is smaller, saves materials and has better heat dissipation effect. Junction box products are constantly pursuing better performance at lower costs in market competition, and will continue to iterate in the future.
Classification and composition of photovoltaic junction boxes
1. Classification of photovoltaic junction boxes
Solar photovoltaic junction boxes are divided into crystalline silicon junction boxes, amorphous silicon junction boxes, and curtain wall junction boxes.
2. Composition of photovoltaic junction box
The solar photovoltaic junction box consists of three parts: box body, cable and connector.
Box body: including box bottom (including copper terminals or plastic terminals), box cover, and diode;
Cables: divided into commonly used cables such as 1.5MM2, 2.5MM2, 4MM2 and 6MM2;
Connector: divided into MC3 and MC4;
Diode models: 10A10, 10SQ050, 12SQ045, PV1545, PV1645, SR20200, etc.
There are two types of diode packages: R-6 SR 263;
3. Main features of solar cell module junction box:
(1) The shell is produced from imported high-grade raw materials and has extremely high anti-aging and ultraviolet resistance;
(2) Suitable for use under harsh environmental conditions during outdoor production, with effective use of more than 30 years;
(3) 2 to 6 terminal blocks can be built in as needed;
(4) All connection methods adopt quick-connect plug-in connection.
Production process flow of junction box
1. Material selection
The main materials of the junction box include steel plate, aluminum alloy, plastic, etc. These materials should comply with relevant national standards and requirements. When selecting materials, you need to consider the use environment of the product, such as anti-corrosion performance, high temperature resistance, etc., to select appropriate materials.
2. Processing technology
1. Processing of steel plates or aluminum alloy materials:
Steel plates or aluminum alloy materials require shearing, bending, stamping and other processing techniques to complete the required shape and structure.
2. Processing of plastic materials:
Plastic materials require injection molding or blow molding, embossing and other processing techniques to complete the required shape and structure.
After the processing is completed, surface deburring, grinding and other processing are required to ensure that the product surface is smooth and smooth.
3. Assembly
Assemble the processed components, including assembly, fixing, wiring, etc. After the assembly is completed, conduct an overall inspection to ensure that the product quality meets the requirements.
4. Detection
Inspect the electrical properties, mechanical properties, etc. of the product to ensure that the quality of the product is stable and reliable. This includes appearance inspection, electrical performance inspection, reliability testing, etc. Only after passing the inspection can it be packaged and shipped out of the factory.
During the production process, relevant production standards and requirements need to be strictly followed to ensure that the quality of the junction boxes produced meets customer needs. At the same time, it is necessary to strengthen the management of material composition, process flow and other links to improve product quality stability and meet market demand.
Analysis of common faults of junction box
1. Common faults of junction box
Common faults of the photovoltaic module junction box at the project site include: aging and deformation of the box body, false soldering in the junction box, breakdown failure of the bypass diode, burnt junction box, and separation of the junction box from the silicone.
2. Analysis of common fault principles of junction boxes
Failure principle 1: Component welding process quality issues
In the junction box, there is a weak solder at the connection between the diode pin and the copper conductor, and at the connection between the bus bar and the copper conductor. When the photovoltaic module is blocked by shadow or other problems cause the bypass diode to turn on, the soldered joint will heat up. When the soldered joint is When the heat accumulation exceeds the thermal deformation temperature of the junction box insulation material, the junction box will undergo aging and deformation. The longer the bypass diode is turned on, the greater the risk of deformation and aging of the junction box. When the temperature is greater than the upper limit of the diode junction temperature, the high temperature It will cause thermal breakdown of the bypass diode and even burn the junction box.
Failure principle 2: Component sealing process quality issues
There was contamination during the gluing process between the junction box and the photovoltaic module backplane, which caused the junction box to separate from the silicone later.
Fault Principle 3: Shadow occlusion, hidden cracks and other problems
Photovoltaic modules are exposed to conditions such as shadows, cracks, and local hot spots for a long time, which causes the bypass diode to be in continuous operation for a long time, causing the junction temperature of the bypass diode to rise. When the junction temperature accumulates to a certain level, the bypass The diode will fail due to thermal breakdown. If not handled in time, when the heat accumulation reaches the deformation temperature of the insulation material of the junction box, the junction box will deform and age. In serious cases, the junction box will burn out.
Failure principle 4: Lightning strike
When the photovoltaic module is struck by lightning, the bypass diode will be instantly broken down by high voltage. When the rain has passed and the sky has cleared, as the normal module current flows through the failed diode for a long time, the diode will generate heat. When the heat accumulates to a certain level, it will It may cause aging and deformation of the junction box, or even burn the junction box.
Summarize
Photovoltaic power stations must ensure stability throughout the entire life cycle, and system reliability with components as the core is the basis for ensuring customer return on investment and realizing customer value. As an important part of photovoltaic modules, the junction box will cause a reduction in the power generation of the photovoltaic power station when it fails. In serious cases, it may even cause a fire. At present, visual inspection, infrared thermal imaging technology, and I-V testing methods are often used in outdoor photovoltaic power stations to determine junction box faults. In recent years, with the development of intelligent technology, more convenient methods such as inverter intelligent I-V scanning and power station evaluation system software have become available. , further expanding the system side's method of detecting photovoltaic module junction box faults. After the current great leap forward in the size and current of photovoltaic modules, the risk of junction box reliability will increase significantly. We should consider choosing products with excellent quality, good reliability, and sound after-sales support that "integrate life cycle standards throughout product production and application." "Head brand components in every link to avoid hidden dangers caused by process quality problems such as false welding; during component transportation and installation, component maintenance must be done to reduce the occurrence of component cracks; during daily operation and maintenance, It is necessary to do a good job in lightning protection and troubleshooting of power stations. When problems such as shadows, hot spots, cracks, etc. are found in components, they must be dealt with promptly to avoid failure of the junction box.