In a photovoltaic (PV) power system, PV modules (commonly known as "solar panels") are the core components that convert light energy into electrical energy. The PV junction box, however, serves as the "bridge" connecting the internal circuit of PV modules to the external system. It not only undertakes the critical task of electrical energy transmission but also protects modules from fault damage, making it an "invisible guardian" for the stable and efficient operation of PV systems.

Core Functions of PV Junction Boxes：

Electrical Energy Transmission: Building a "Power Channel"

PV modules' internal solar cells (connected in series/parallel) generate DC power, which is collected via busbars into the junction box. The box then sends this power to inverters (for AC conversion) or storage devices via MC4-plugged cables. Poor conductivity here directly reduces power output.

Fault Protection: Resisting the "Hot Spot Risk"

During the operation of a PV system, modules may suffer from the "hot spot effect" due to dust accumulation, leaf shading, or cell aging. Shaded cells cannot generate electricity normally; instead, they become "loads" and are heated reversely by the current from other normal cells. Temperatures can exceed 100°C, which may burn the module or even cause fires. The bypass diodes (connected in parallel with each group of cells) built into the junction box are the "key weapon" against hot spots: when a group of cells is shaded, the bypass diode conducts due to reverse bias, providing a "bypass channel" for the current. This prevents the shaded cells from overheating while ensuring the normal power generation of other cells.

Mainstream Types

Split-type PV Junction Box

Structural Features: "Function-Split" Modular Design

Unlike the integrated type, the split-type junction box usually consists of three independent units:

Positive junction box (with MC4 plug, DC cable, and diode);

Negative junction box (same structure as the positive one, only with opposite polarity);

Middle diode junction box (only contains diodes and conductive terminals, no external cables).

These three units are fixed at different positions on the PV module and connected via internal busbars to form a complete circuit.

Advantages: Lower loop resistance (boosts output by 0.5%-1%), better heat dissipation (temp down 15-20°C), less cable use (30%+ reduction).

Applications: Large ground plants, high-power modules (shingled, TOPCon, HJT).

Integrated-Type PV Junction Box

Structural Features: "All-in-One" Integrated Design

The integrated junction box integrates all components-including conductive terminals, bypass diodes, cables, and seals-into a single housing. One PV module only needs one such junction box. The housing is usually made of flame-retardant plastic (e.g., PA66 + glass fiber), and the interior is filled with potting glue (e.g., silicone) for waterproofing, dustproofing, and heat conduction.

Advantages: Easy installation (one box per module), low cost, simple maintenance.

Applications: Distributed systems (rooftops), small ground plants, conventional modules.

General Product specification parameters

PV Junction Box Selection

To choose a PV junction box, the current size of the component is the main information , one is the working maximum current , one is the short circuit current. Of course, the maximum current that the components can output when short-circuit current, according to the short-circuit current calculation of the rated current of the junction box should be a relatively large safety factor, according to the maximum working current calculation of the junction box is a smaller safety factor.

Scientific way to selecte PV junction box should be according to the rule of cell voltage and cell current change with light intensity.You have to know what the peak light is in your area, then check the maximum current possible against the curve of the cell current with the intensity of the light, and then choose the rated current of the PV junction box.