In the photovoltaic power generation system, the grid-connecting cabinet and the convergence box are important components, but they have significant differences in function, structure and application scenarios.
 
First, the functional difference
Confluence box
Its primary function is to converge several DC powers of photovoltaic module strings. Generally, DC power generated by the photovoltaic module has lower current and voltage output; the convergence box will gather those scattered currents into one, improve the whole current output, and forward the signal for further transmission to the inverter and other equipment for processing.
Generally, it is equipped with anti-reverse current, over-current protection, and over-voltage protection to ensure the safe operation of PV module strings. For instance, once a PV module string has a fault or reverse current, the convergence box can cut off the current in that way in time to prevent the impact on the whole system.
Grid-connected cabinet
Its core function is to achieve the connection between the PV power generation system and the power grid, and grid integration. Synchronize the AC power converted by the inverter with the grid, and feed the power to the grid under certain conditions.
It contains more sophisticated protection and control functions such as over-voltage protection, under-voltage protection, over-frequency protection, under-frequency protection, and anti-islanding protection. In fact, these protection functions will enable the PV power generation system to safely and stably connect to the grid under different working conditions and also protect the grid against adverse effects of the PV power generation system.
 
Second, the structural difference
Confluence box
It usually consists of a box, fuse, circuit breaker, lightning protection, terminals, and other components. The box is generally made of metal with a certain level of protection to adapt to the outdoor installation environment.
Internal fuses and circuit breakers for overcurrent and short-circuit protection of each PV module string; Lightning arresters to prevent lightning overvoltage damages to the convergence box and PV modules; Terminal blocks to connect the PV string cables with the output cables. Cabinet Grid-connected
The structure is relatively complex, generally consists of cabinet, disconnect switch, circuit breaker, contactor, relay, instrumentation, protection devices and so on. The cabinet is also made of metal and has a high level of protection.
Disconnect switches are used to isolate the PV power generation system from the grid during maintenance or faults. Circuit breakers and contactors are used to control the on-off of electrical energy. Instrumentation is used to monitor the voltage, current, frequency and other parameters of the grid and the PV power system. Protection devices are configured according to different protection functions, such as over-voltage protection device, under-voltage protection device, over-frequency protection device and so on.
 
Third, the difference in application scenes.
Convergence box Mainly used at the front end of the photovoltaic power generation system, that is, between the photovoltaic module array and the inverter. Multiple convergence boxes can converge the currents from PV module strings in different areas and then deliver them to the inverter through cables.
It is suitable for all scales of PV power generation systems, from small distributed PV systems to large centralized PV power stations, all of which have to use the convergence box. Grid Connection Cabinet It is installed at the output end of the PV power generation system, near the connection point with the grid, and is a key interface device between the PV power system and the grid.
Mainly applied in occasions where connecting the PV power generation system to the grid is needed, for instance, commercial rooftop PV and ground-based centralized PV power plants. For the off-grid photovoltaic power generation systems, there is no requirement of grid-connecting cabinets.

To put it briefly, there are different functions borne by the grid-connecting cabinet and convergence box within the photovoltaic power generation system. Among these, it is primarily up to the convergence box to realize the DC convergence of the PV module string and primary protection, whereas the functions of grid-connected cabinets involve realizing a connection between the PV power generation system and the power grid and ensuring safety and security protection. Grasping their differences will promote better design, installation, and maintenance in order to obtain a stably running and efficient PV power generation system.