What is a photovoltaic combiner box and its function
2024-09-04
With the construction of more and more photovoltaic power stations, the use of photovoltaic combiner boxes has become popular. Many people don't know what a photovoltaic combiner box is, its function, how to choose a combiner box, etc.
The combiner box is a very important component in the entire photovoltaic system. It is responsible for collecting the photovoltaic current. However, this component is also where we think the failure rate is high, so I will share it as a special topic in the article.
The definition and composition of the photovoltaic combiner box
The combiner box is a wiring device that ensures the orderly connection and combiner function of photovoltaic modules in the photovoltaic power generation system. This device can ensure that the photovoltaic system is easy to cut off the circuit during maintenance and inspection, and reduce the scope of power outage when the photovoltaic system fails.
Composition of photovoltaic combiner box:
Box: The box is generally made of steel plate sprayed with plastic, stainless steel and other materials. It is strong and durable, easy to install, and has a protection level of IP 54 or above. It is waterproof and dustproof, meeting the requirements of long-term outdoor use.
DC circuit breaker
The power generated by solar panels is direct current. The DC circuit breaker is the output control device of the entire junction box, mainly used for the opening/closing of the line. Its working voltage is as high as DC1 500 V.
DC fuse
When current backflow occurs, the DC fuse quickly removes the faulty string from system operation without affecting other normally operating strings, and can safely protect the photovoltaic string and its conductors from the threat of reverse overload current.
Anti-reverse diode
The role of the diode in the junction box is different from that of the diode in the module junction box. The diode in the module junction box mainly provides a freewheeling channel when the battery cell is blocked, while the diode in the junction box mainly prevents the generation of circulating current between the strings.
Data acquisition module
In order to facilitate monitoring of the working status of the entire power station, a data acquisition module is generally added to the primary junction box. Using Hall current sensors and single-chip microcomputer technology, the current signal (analog quantity) of each photovoltaic array is sampled, converted into digital quantity through A/D conversion, and then converted into a standard RS-485 digital quantity signal output, so that users can grasp the working status of the entire power station in real time.
Protection unit Surge protector
The DC high-voltage surge protection unit is a lightning protection product dedicated to photovoltaic power generation systems. Since the photovoltaic combiner box is installed in an outdoor environment, we must consider lightning protection for the combiner box. To this end, we connected a photovoltaic DC-specific lightning surge protector (i.e., lightning arrester) in parallel to the DC output part of the combiner box. Once a lightning strike occurs, the surge protector will quickly discharge the excessive electrical energy to ensure stable output of electrical energy and protect the combiner box from lightning damage.
Combiner boxes can be divided into DC combiner boxes and AC combiner boxes according to the application scenario.
Since DC combiner boxes are more widely used, this article mainly discusses the working principle of DC combiner boxes.
The photovoltaic combiner box is actually a parallel circuit, which brings all the currents together and then transmits them to the next level.
In a parallel circuit, there will be current superposition and voltage loss. So, how should this loss be avoided? These are also some potential problems that should be paid attention to during the operation and maintenance of photovoltaic power stations.
First: the role of the photovoltaic DC combiner box.
The occurrence of combiner box safety accidents, such as fire, is either caused by the burning of components, the breaking of fuses, the burning of lightning protection devices, or the burning of terminal blocks, etc.
Therefore, we must pay special attention to how to improve the safety and reliability of photovoltaic combiner boxes.
The function of the combiner box is to combine and superimpose the current of all branches.
There are many types of combiner boxes, such as 6-into-1, 8-into-1, 16-into-1, 12-into-1, etc.
What does the 16-into-1 model of the combiner box mean? For example, if this combiner box is 16-into-1, it means that this combiner box has 16 inputs and 1 output, that is, 16 inputs and 1 output.
However, if the 8-input photovoltaic strings are combined, since they are connected in parallel, the string voltage of each string must also be selected to be consistent when connected to the combiner box, otherwise, there will be voltage loss.
Therefore, in the process of connecting the combiner box, paying attention to the system voltage of each photovoltaic string is a necessary means for us to improve the conversion efficiency of the combiner box.
For example: 15 kilowatt solar panel system, using 550W photovoltaic panels, a total of 15000W/550w=27.2PCS is required. Considering the consistency of each voltage, we can divide it into 4*7 series = 28PCS series, so that the voltage of each line is the same. So we can choose a 4-input 1-output or 4-input 2-output photovoltaic combiner box.
In short, the number of photovoltaic panels in each series is required to be the same. Finally, they are connected in parallel and enter the combiner box.
In addition to collecting current, the combiner box can also improve the efficiency of the entire system.
But how can we improve its efficiency in photovoltaic operation and maintenance?
The goal is to ensure the consistency of the voltage of each string and the current of each photovoltaic string. If these two consistencies are achieved, the conversion efficiency of the photovoltaic system can be increased by at least 3% to 5%.
The output of the combiner box finally enters the photovoltaic inverter.
Taking the 15 kilowatt solar panel
system as an example, we choose a 4-input 1-output combiner box with a total power of 15000W. Finally, it enters the inverter to be inverted into AC power with a specific voltage and current for grid connection or use for load electrical appliances.
Let's summarize the role of the photovoltaic DC combiner box.
The first function is:
In the photovoltaic power generation system, it is a wiring device that ensures the orderly connection and convergence function of photovoltaic components. This device can ensure that the photovoltaic system is easy to switch circuits during maintenance and inspection, and reduce the scope of power outages when the photovoltaic system fails.
The second function is:
In the solar photovoltaic power generation system, in order to reduce the connection between the solar photovoltaic cell array and the inverter, the user can connect a certain number of photovoltaic cells of the same specifications in series to form a photovoltaic string, and then connect several photovoltaic strings in parallel to the intelligent photovoltaic junction box. After the convergence in the intelligent photovoltaic junction box, the DC circuit breaker output is used in conjunction with the photovoltaic inverter to form a complete photovoltaic power generation system and achieve grid connection.
The third function is:
In order to improve the reliability and practicality of the system, photovoltaic-specific DC lightning protection modules, DC fuses and circuit breakers can be configured in the intelligent photovoltaic junction box, and working status indicator lights, lightning counters, etc. can be set to facilitate users to grasp the working conditions of photovoltaic cells in a timely and accurate manner, and ensure that the solar photovoltaic power generation system can achieve the maximum effect.
For large-scale photovoltaic grid-connected power generation systems, in order to reduce the connection lines between photovoltaic modules and inverters, facilitate maintenance, and improve reliability, it is generally necessary to add a device such as a DC combiner box between photovoltaic modules and inverters.
When using a photovoltaic combiner box, users can string a certain number of photovoltaic modules with the same specifications into a photovoltaic module string according to the range of the DC voltage input by the inverter, and then connect several strings to the DC combiner box of the photovoltaic array, and output through the lightning arrester and circuit breaker to facilitate the subsequent inverter connection.
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