Application case of photovoltaic combiner box for 46kW small and medium-sized factory rooftop photovoltaic system in Wenzhou, China

II. Customer Pain Points and Needs
(I) Customer Pain Points
High electricity bills: As the factory's electrical equipment increases, monthly electricity bills continue to rise, creating a significant long-term expense.
A commitment to environmental protection but lacks the means: The customer wants to contribute to environmental protection and reduce their carbon footprint, but lacks the knowledge to effectively implement this approach.
Concerns about the safety of the photovoltaic system: Fear of fires caused by short circuits.
Environmental adaptability: Wenzhou's climate is humid and rainy, so the combiner box must have excellent dust and water resistance (IP rating) and corrosion resistance to ensure long-term stable outdoor operation.
(II) Customer Needs
Reducing electricity bills and reducing dependence on the grid through photovoltaic power generation.
Install an environmentally friendly and efficient photovoltaic system to achieve green electricity consumption.
The photovoltaic system must be simple to operate, stable and reliable, and easy to maintain, minimizing future problems.

Solution Design: Customized 8-input, 2-output photovoltaic combiner box service
1. Calculate the required rated voltage and current of the combiner box
Input voltage per string: 42.3V * 10 = 423V. Input current per string: 13.83A
Output voltage per string: 423V. Output current per string: 55.32A

2-core configuration and electrical performance
Product model: LQX-C2/2DC1000V
Enclosure structure: Made of high-strength cold-rolled steel, it offers excellent weather resistance, corrosion resistance, and insulation properties, achieving an IP65 protection rating and is suitable for outdoor installation.
Input adapter: Equipped with a 20A DC1000V fuse, the maximum input current per circuit is 13.83A (designed for 1.25 times the string short-circuit current: 13.83A * 1.25 = 17.2875A). This fast-blow fuse has a breaking capacity of 33kA and provides overload and short-circuit protection. If a fault occurs in a PV string, the fuse will quickly open, preventing the fault from spreading and affecting other strings. T2 surge protector: Equipped with a 20kA/40kA 1000V DC DC lightning protection module, this multi-stage lightning protection design boasts a response time of ≤25ns. In the event of a lightning strike or surge, it rapidly discharges the surge current to the ground, protecting the combiner box and subsequent equipment from damage. The lightning protection module features a degradation indicator, facilitating timely replacement.

Output Configuration: A 63A 1000V DC thermal-magnetic circuit breaker with a 6kA sectionalizing capacity effectively switches the circuit while providing overload and short-circuit protection.

Circuit Topology: Each four-string PV module is connected to the combiner box's four input terminals, then fuses to the busbar, where it is then output to the inverter via a DC circuit breaker.
Insulation Design: The insulation distances between live components and the box body meet relevant standards, ensuring electrical safety. The box body is reliably grounded, with a ground resistance of ≤4Ω. Heat Dissipation Design: All circuits pass through hollow aluminum metal modules to reduce circuit heat generation.
Intelligent Monitoring: Utilizing Longchi's built-in RS485 communication module, current and voltage are collected in real time (with an accuracy of ±1%) and connected to the customer's inverter's cloud platform via RS485.
Anti-Reverse Current Design: Prevents reverse current flow from damaging the solar panels.
Installation and Optimization
Installation Location: Select a well-ventilated location on the rooftop near the PV panels and close to the inverter to minimize line losses. The installation height is convenient for maintenance personnel.
Wiring Specifications: Input and output cables utilize dedicated PV-specific DC cables, with secure connections and proper sealing to prevent rainwater ingress.
Optimization Measures: Clear markings are placed on the outside of the combiner box to indicate the PV panel strings corresponding to the input branches, facilitating future maintenance. The box's color coordinates with the roof's color to minimize aesthetic impact.

Project Highlights
Energy Efficiency: Utilizing high-efficiency PV panels and inverters, the system achieves high conversion efficiency, generates significant annual power, and effectively reduces household electricity bills. Safety and Reliability: The PV combiner box and other equipment are equipped with comprehensive protection features, and the brackets are securely installed, ensuring safe and stable system operation without damaging the building structure.
Easy Operation: The system operates automatically, requiring no manual intervention. Customers can easily monitor system status via a mobile app, simplifying maintenance.
Aesthetics and Harmony: The color and style of the PV panels and brackets complement the roof perfectly. The combiner box is compact and discreetly installed, creating a beautiful overall aesthetic.
Environmentally Friendly and Green: PV power generation replaces traditional thermal power, reducing carbon emissions and achieving green electricity consumption, meeting the customer's environmental needs.

V. Project Achievements
Economic Benefits: Upon commissioning, the project will generate an average annual power generation of approximately 43,000 kWh. Based on the local electricity price of 0.5 yuan/kWh, this will save approximately 21,500 yuan in electricity bills annually. The investment is expected to be recovered in approximately 11 years, and the system has a lifespan of up to 25 years, ensuring substantial future returns.
Improved Power Stability: The installation of energy storage equipment ensures basic power supply during power outages, improving the reliability of household electricity supply. Significant environmental benefits: It reduces carbon dioxide emissions by approximately 22 tons annually (calculated based on the 0.528kg of carbon dioxide emitted per kilowatt-hour of thermal power), contributing to environmental protection.
High customer satisfaction: The system operates stably, is easy to operate, and has an attractive appearance. It effectively addresses customer needs and satisfies them, resulting in high customer satisfaction with the project results.

Appendix: Key Equipment Parameters