What is a Solar Combiner Box and Why Do You Need It

The solar combiner box is a common device in PV installations. It allows you to safely group the string outputs together. It also lets you do so without using too many wires. But is a solar combiner box necessary? Below, we take a look at what it means and crucial role it plays in a PV power system.

What is a Solar Combiner Box?

By definition, the solar combiner box is a type of enclosure that joins the wires coming from your solar modules—or strings—into one circuit. In other words, and just as its name implies, it combines the output of the panels into one input for the inverter or charge controller.

The box may also be known by several other names such as solar junction box, PV combiner box, or PV array combiner. Depending on your system and its components, the box can be an AC or DC type: here’s more about that.

Solar AC Combiner Box

This type of PV combiner is built to work with AC inputs, or incoming power that’s in the form of alternating current. It ensures the different voltages do not do combine out of phase, and that the power coming out is safe and smooth.

Solar DC Combiner Box

The solar DC combiner box is meant for use with DC power. It works like the AC type, but comes with features that make is suitable for the direct current application. As such, you can only use it if the power coming from your array has not been converted to AC.

How Does a Solar Combiner Box Work?

You solar string combiner box is an IP-rated enclosure that houses the necessary components needed to consolidate the separate inputs of your solar panels. The power coming from the panels enter the box via openings.

Inside the box, the inputs encounter protective devices that ensure overcurrent and overvoltage situations are taken care of. The power is then routed to a busbar. The bus combines the lines into one, before exiting from the box.

Just like the junction box of a conventional power system, a combiner box for solar power comes with a front access door and a way to mount it to a wall or other surface.

Solar Combiner Box Function

The function of a combiner box for solar panels is just as it sounds, which is to combine their outputs into one circuit. For that, it comes with various entry points for the individual strings, and a busbar that serves to join the circuits together. This is essentially what it does:

• It organizes your wires so they appear neat, professional, and easily identifiable.
• In large installations, these boxes help minimize costs by reducing the amount of labor and cabling required.
• In addition combining the array wires, the box also houses protective devices such as circuit breakers, surge protection devices or disconnects, array monitoring hardware.

PV Combiner Box Components

Inside a solar combiner box are components that help it to safely serve its function, which is consolidate individual string circuits into one. The main components that can be found in a typical box include circuit breakers, fuses, surge protection devices, disconnect switch, and a busbar.

1. DC Circuit Breaker

The circuit breakers help protect the circuits running into the combiner against electrical faults that excessive voltage may cause. Their number and rating depends on the size of your solar system.

2. Solar Fuse

As part of the protection measures, the circuits from your array terminate into a series of fuses for string protection. During a fault, these fuses will blow and cut off the affected circuit. Again, the types of fuses will depend on the size of your panels and strings.

3. Surge Protection Device

An SPD is also one of the most important PV combiner box components. It connects the circuits to ground, and offers protect against electrical surges that may possibly happen.

4. DC Disconnect Switch

This is a switch that you can use to quickly disconnect power whenever needed. The switch can isolate one part of the system, either during an emergency situation or for maintenance purposes.

5. Busbar

This is a mechanical conductor (strip or rail), and whose role is to combine the different circuits into one. It’s essentially located behind the mentioned components where all the wires route to it before reaching the main breaker.

Other components that may be included are: blocking diodes to prevent the back feeding of power, a wireless device to enable power disconnection from a remote location, and equipment that monitor the condition of the array.

Do You Need a Combiner Box for Solar Panels?

If your PV system is composed of more than 3 string connected together, you definitely it to safely group the cables and circuits. This is especially if the modules are connected in parallel and multiplying the amount of current to warrant its safe transmission to the inverter or charge controller.

If using fewer strings or a single string, you can safely combine and protect them at the inverter or charger level, even without the need to route them through a combining box. That being said, it’s crucial that you find the right type of solar array combiner box for your system. This is explained below.

How to Size Solar Combiner Box

When buying a combining box for your system, special attention should be given to the array size. That’s because each box is specially rated for a specific system size. Here’s what you need to know:

• Solar combiner box manufacturers often make boxes that can accommodate 3 strings or more.
• In order to size the box correctly, determine the number of strings in your system, and use that to find the minimum box size
• The box is also sized based on the string voltage and current levels
• You may also want to take into consideration any future upgrades.
• If you intend to add more strings later, consider finding a box that can accommodate additional breakers

Conclusion

The solar combiner box is a plug and play device that comes already pre-configured, which makes it easy to install and use. Available in a range of sizes, the box is also easy to customize for your system. That’s in addition to its many benefits that include protection equipment, cost reduction in terms of labor and cabling, and wire organization.