Not all small PV systems need a hộp kết hợp năng lượng mặt trời.
Whether a combiner box is needed depends on the number of PV strings, the number of available inverter inputs, whether string combining is required, and the configuration of DC-side protection.
What Is a “Small PV System”?
The term “small PV system” does not have a unified capacity limit.
For example, the U.S. NREL defines a small solar PV system as a generating installation, with a capacity of less than 1 megawatt (MW); however, in Australia, “small-scale” has a specific policy definition. In 2026, a proposed scheme in Australia would make solar PV systems, with a total installed capacity between 100 kilowatts (kW) and 1 megawatt (MW), eligible for Small-scale Technology Certificates (STCs).
In this article, “small PV system” refers to a residential or small commercial PV system with a small number of strings, rather than being defined by a fixed system capacity.
When Can a Small PV System Operate Without a Combiner Box?
Only One PV String
If the system has only one PV string and there are no other strings that need to be connected centrally, then there is usually no string combining requirement.
The connection can be made directly:
PV String → Downstream Equipment
However, if the system requires other functions at this location, such as centrally configured specific protection or isolation components, then whether a box is used needs to be determined based on the actual design.
Two PV Strings with Two Suitable Inputs
Two PV strings remain independent.
For example:
PV String 1 → Input 1
PV String 2 → Input 2
In this case, there is no external string combining requirement.
When Does a Small PV System Need a Combiner Box?
When multiple strings need to be connected centrally to a common output, the combiner box has a clear purpose.
The basic structure can be expressed as:
Multiple Strings → Combiner Box → Common Output
For example, a system has four strings that need to be connected centrally:
String 1
String 2
String 3
String 4
↓
Combiner Box
↓
Common Output
If the system also requires centrally installed protection or isolation components, the combiner box can also provide corresponding installation space based on the product configuration.
Even if the overall system size is not large, a combiner box is needed as long as there are multiple strings that need to be connected centrally.
Phần kết luận
For a system with only one circuit, or multiple separate circuits, there is no need to add a separate combiner box just for the sake of it.
When a small solar system has multiple circuits that need to be connected centrally, a combiner box is the appropriate solution.
Câu hỏi thường gặp
Q1: How many PV strings can one DC combiner box connect?
It depends on the number of inputs on the combiner box.
For example, a DC combiner box with 4 inputs can connect up to 4 PV strings, and a model with 8 inputs can connect up to 8 PV strings.
Q2: Can two PV strings share one input of a DC combiner box?
No.
One input typically corresponds to one independent PV string. It can only be one-to-one, not many-to-one.
Q3: Must a fuse be installed on every input of a DC combiner box?
Not necessarily.
Whether a fuse needs to be configured for each input circuit depends on the system’s protection design and the combiner box configuration. If the combiner box already has fuses configured in the input circuits, there is no need to add fuses again at the same location.
Q4: Does a combiner box always come with an SPD?
Not necessarily.
An SPD is an internal configuration of some combiner boxes, and not all combiner boxes come with an SPD as standard. The product configuration needs to be confirmed at the time of purchase.
Q5: Does a combiner box always come with an isolation switch?
Not necessarily.
Some combiner boxes integrate an isolation switch, while some products are mainly used for circuit combining. The product configuration needs to be confirmed at the time of purchase to determine whether the corresponding isolation function is provided.
Q6: Can a DC combiner box be installed between the PV array and the inverter?
Yes, this is a common connection method in PV systems:
Multiple PV Strings → DC Combiner Box → Inverter
The DC combiner box is responsible for centrally connecting multiple PV strings, and the inverter receives the combined DC output.
An AC combiner box is used for combining circuits on the AC side and is not used for combining PV strings.
Q7: Can a combiner box be installed outdoors?
Yes, but a product suitable for outdoor environments needs to be selected.
For outdoor installation, the enclosure protection rating and the product’s permitted operating environment should be confirmed.
