What is Solar Combiner Box?

What is Solar Combiner Box?

Created by: Glen Zhu | Updated Date: May 14th, 2024

What is Solar Combiner Box?

The Solar combiner box in the photovoltaic power generation system is a wiring device that ensures orderly connection and convergence of photovoltaic modules. This device can ensure that the photovoltaic system is easy to disconnect during maintenance and inspection, and reduces the range of power outages when the photovoltaic system fails.

A solar combiner box refers to a user being able to connect a certain number of identical specification photovoltaic cells in series, forming individual photovoltaic strings, then connecting several such strings in parallel into a solar combiner box. After converging within the solar combiner box, it goes through controllers, DC distribution cabinets, PV inverters, AC distribution cabinets for coordinated use thus constituting a complete solar power generation system achieving grid-tied operation.

How Does a Solar Combiner Box Work? (Purpose and Function)

It collects and distributes the electrical energy emitted by solar panels.

The solar combiner box mainly includes parts such as the combiner, electronic components, relays, and fuses. The primary function of the solar combiner box is to centralize and parallel multiple solar panel currents to form a direct current convergence. Then through AC input, it transmits electrical energy to the power grid.

The specific working principle of solar combiner box is as follows:

  1. Multiple solar panels generate direct current.
  1. Direct current converges centrally and is filtered and controlled by electronic components.
  1. With the protection of relays and fuses, direct current is converted into alternating current output.
  1. The alternating current is transmitted to the power grid for distribution and utilization of electrical energy.

The solar combiner box also has various protective measures such as overcurrent protection, overvoltage protection, leakage protection etc., to ensure safe operation of the system. In practical applications, a combiner box usually needs to be networked with a station monitoring system in order to achieve real-time monitoring and remote control of system operating status.

Is a Solar Combiner Box DC or AC?

Answer: DC

A solar combiner box is mainly used to collect the direct current generated by photovoltaic modules and distribute it to subsequent inverters or other equipment.

In a photovoltaic power generation system, photovoltaic cell modules form a series through stringing, and then these series are connected to the photovoltaic combiner box via cables.

Inside the solar combiner box, the direct current is combined and distributed through controllers and DC distribution cabinets. It is finally converted into alternating current by a PV inverter for grid connection or supplying other AC loads.

Therefore, the electricity handled by the solar combiner box is direct current, not alternating current.

Solar Combiner Box Classification

Solar combiner boxes are divided into three types based on their functions.

  • The first type is the basic model, which does not have anti-reverse and monitoring functions;
  • the second type has an anti-reverse function but no monitoring function;
  • the third type has both anti-reverse and monitoring functions, making it the most comprehensive combiner box with the highest cost and price.

Components of a Solar Combiner Box

Box Body / Enclosure (used for solar combiner box)

The box body is usually made of materials such as steel plate spray plastic, stainless steel, engineering plastics etc., featuring an elegant appearance, robustness and durability. It’s easy to install with a protection level reaching IP54 or above for waterproofing and dustproofing to meet long-term outdoor use requirements.

DC Circuit Breaker (used for solar combiner box)

The DC circuit breaker serves as the output controller for the entire combiner box mainly used for line switching. Its working voltage can reach up to DC 1000 V. Since solar panels generate direct current electricity that can easily cause arcing when circuits are opened or closed, considerations should be given to its temperature coefficient at different altitudes during selection process. A photovoltaic-specific DC circuit breaker must be chosen.

DC Fuse (used for solar combiner box)

When reverse current occurs in components, photovoltaic-specific DC fuses can timely cut off faulty component strings with rated working voltages reaching up to DC 1000 V. Rated currents generally choose 15 A (silicon components). The fuse used by PV modules is specially designed for photoelectric systems (external dimensions: Φ10 mm × 38 mm), installed using special enclosed bases to prevent inter-string reverse current from burning out components.

DC Isolator Switch (used for solar combiner box)

The main function of the DC isolator switch is to isolate the power supply, ensuring that electrical equipment reaches a safe isolation state. The isolator switch, used in conjunction with circuit breakers or fuses, can perform switching operations as needed by system operation modes to change the system’s wiring method. The isolator switch does not have a dedicated arc extinguishing device, so it cannot be used to connect or disconnect load current and short-circuit current; it can only operate when the electrical line is disconnected.

Anti-Reverse Diode (used for solar combiner box)

In a combiner box, diodes serve different purposes than those in component junction boxes. Diodes in component junction boxes primarily provide continuous flow channels when battery cells are covered while diodes in combiner boxes mainly prevent loop currents between strings.

Data Acquisition Module (used for solar combiner box)

To facilitate monitoring of the entire power station’s working status, a data acquisition module is generally added to primary combiner boxes. Using Hall current sensors and microcontroller technology, it samples each photovoltaic array’s current signal (analog quantity), converts it into digital quantities through A/D conversion, then transforms them into standard RS-485 digital signals for output so users can grasp the whole power station’s working status in real time.

Protection Unit (used for solar combiner box)

The DC high-voltage surge protection unit is a lightning protection product specifically designed for photovoltaic power generation systems with overheating and overcurrent dual self-protection functions. It adopts modular design that allows live replacement and has degradation display windows; remote monitoring can be achieved using data acquisition modules.

Human-Machine Interface (used for solar combiner box)

The data collection unit comes with a human-machine interface where you can view the device’s real-time operating status and set local parameters via keyboard input.

Lightning Protection Design

Since solar combiner boxes are installed outdoors, we must consider providing them with lightning strike protection. For this reason, we have paralleled a PV-specific DC surge protector (i.e., lightning arrester) at the DC output part of our combiner box.

In case of a lightning strike, the surge protector will quickly discharge excessive electrical energy to ensure stable energy output and protect the combiner box from damage caused by lightning strikes. Combiner boxes equipped with anti-lightning components are referred to as PV anti-lightning combiner boxes.

Historical Updates

First Generation Solar Combiner Box

The first-generation solar combiner box only had convergence and lighting protection functions.

Second Generation Solar Combiner Box

From merely having convergence and lighting protection capabilities in previous versions, second-generation models could monitor every path’s voltage and current while also detecting temperature and humidity levels within their own enclosures.

Third Generation Solar Combiner Box

Sola combiner boxes have now evolved into their third generation. In addition to the advantages of previous generations, these models can also alert users when they fail, collect data and transmit it wirelessly.

Existing Problems

Various problems have arisen during application operation such as RS485 bus wiring issues with combiner monitoring units, address representation problems, wiring issues, waterproof terminal problems and polarity reversal issues among others.

Many solar combiner boxes can only monitor string currents but cannot automatically control situations where part of a battery panel is covered causing reverse current in battery components which could burn out fuses or even damage battery components under severe conditions. This issue restricts automatic control implementation in photovoltaic systems and must be resolved.

Latest Developments

A new solar photovoltaic string current monitoring system based on microcontroller control has been designed recently. By measuring string currents through Hall sensors and having microcontrollers read vector values of these currents, we can determine their magnitude and direction. Then by controlling output from solid-state relays (whose contacts are connected to combiner box buses and PV strings) via microcontrollers we can achieve inputting or cutting off PV strings.

In smart sola combiner boxes apart from general functions/performances of ordinary ones electronic switches are used retaining anti-reverse function while adding current switching control capabilities; temperature sensors are added inside them setting multiple monitoring points so that when abnormal temperatures occur the single-chip controller board sends out a signal timely disconnecting input current to protect the box from burning up.

Solar Combiner Box Installation Location and Environment

The solar combiner box should be located between the solar cell modules and the inverter. When it is in an optimal position within the array, it can limit power loss.

Long-term exposure to sunlight will increase the temperature of internal components, reducing their effectiveness and lifespan inside the solar combiner box. Therefore, installing a solar combiner box on a north-facing wall with shade helps limit its direct sun exposure.

The Size of solar combiner box does indeed matter. A larger casing allows for more air volume and surface area. This is very convenient for cooling internal components. Furthermore, by leaving more workspace during installation and maintenance processes, a larger casing makes onsite wiring easier.

What electrical parameters should be considered when selecting Solar Combiner Box?

For residential systems, choosing standardized solutions can save time and cost. Small residential systems (2-3 strings) may not need to use a solar combiner box.

For complex commercial or industrial power station projects, it is necessary to use a solar combiner box or customized photovoltaic combiner boxes.

Main technical parameters to consider when choosing a solar combiner box:

  1. Input Power Parameters

The input power of the solar combiner box is one of the key considerations in the selection process. This parameter refers to the maximum input power that the solar combiner box can withstand. When selecting, it is necessary to determine the input power parameters of the solar combiner box based on the total installed capacity and expected power generation of the photovoltaic station.

  1. Input Voltage Parameters

Input voltage parameters are another important consideration in selecting a solar combiner box. This parameter refers to the maximum input voltage that a solar combiner box can withstand.

  1. Number of Circuits

Determine number of input circuits, usually equal to string count;

Determine number of output circuits, this parameter mainly depends on system power and used inverters;

  1. Maximum Current

Determine rated peak value for PV strings, common currents are below 15A and 20A;

Choose appropriate circuit numbers and max current according to the quantity and specifications of solar panels.

  1. Lightning Protection

Photovoltaic (PV) Solar Combiner Boxes should have surge protection features to avoid impacts from thunderstorms on entire solar energy systems.

  1. Reverse Flow Protection

In on-grid systems, solar combiner boxes should have reverse flow protection features preventing current flowing back into grid causing harm.

  1. Overload Protection & Short Circuit Protection

To protect system from overload or short-circuit damage, choose solar combiner box with these functions.

  1. Communication Function

Modern solar energy systems often use remote monitoring which uploads operation data through main controller onto cloud for management/control purposes.

  1. Monitoring Function

Monitoring function is crucial for real-time tracking performance;

Typically includes DC voltage/current as well as switch status/temperature/humidity etc.

  1. Protection Level

Protection level is an important index in selecting a PV solar combiner box. This parameter evaluates the protective performance of the solar combiner box, including dustproof, waterproof and anti-corrosion aspects.

  1. Temperature Range & Working Environment

Consider working temperature range and conditions for solar combiner box;

choose one that meets requirements. For example, if it’s operating under high temperatures, select one with good heat dissipation performance and high-temperature working ability.

Based on different input voltages, the commonly used photovoltaic solar combiner boxes can be classified into the following three types:

  • 1500V DC Solar Combiner Box
  • 1000V DC Solar Combiner Box
  • 600V DC Solar Combiner Box

Classified by the number of circuits, commonly used photovoltaic solar combiner boxes include the following types:

  • 1 String Solar Combiner Box
  • 2 String Solar Combiner Box
  • 3 String Solar Combiner Box
  • 4 String Solar Combiner Box
  • 5 String Solar Combiner Box
  • 6 String Solar Combiner Box
  • 7 String Solar Combiner Box
  • 8 String Solar Combiner Box
  • 9 String Solar Combiner Box
  • 10 String Solar Combiner Box
  • 11 String Solar Combiner Box
  • 12 String Solar Combiner Box
  • 13 String Solar Combiner Box
  • 14 String Solar Combiner Box
  • 15 String Solar Combiner Box
  • 16 String Solar Combiner Box

Alternatively, classified by the number of input and output circuits, commonly used photovoltaic solar combiner boxes include the following types:

  • 1 input 1 output PV DC Solar Combiner Box
  • 2 input 1 output PV DC Solar Combiner Box
  • 2 input 2 output PV DC Solar Combiner Box
  • 3 input 1 output PV DC Solar Combiner Box
  • 3 input 3 output PV DC Solar Combiner Box
  • 4 input 1 output PV DC Solar Combiner Box
  • 4 input 2 output PV DC Solar Combiner Box
  • 5 input 1 output PV DC Solar Combiner Box
  • 5 input 2 output PV DC Solar Combiner Box
  • 6 input 1 output PV DC Solar Combiner Box
  • 6 input 2 output PV DC Solar Combiner Box
  • 12 input 1 output PV DC Solar Combiner Box
  • 16 input 1 output PV DC Solar Combiner Box

How to select solar combiner box for different PV application?

Regarding usage scenarios, photovoltaic solar combiner boxes are suitable for various types of photovoltaic power systems, such as off-grid photovoltaic stations, rooftop photovoltaic stations, ground-based photovoltaic power stations, distributed photovoltaic power systems, solar street lights and so on.

When choosing a suitable photovoltaic solar combiner box, it is necessary to select based on the actual application scenario and usage requirements.

For example in harsh environments, you need to choose a PV solar combiner box with higher lightning surge protection, overload protection and short circuit protection capabilities;

While in distributed PV power generation systems, you need to choose a PV solar combiner box with higher efficiency, smaller size and lower cost.

List some videos to help you select solar combiner box for different PV application

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Surge Protection Installation Guidelines for Solar Panel Applications

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