Solar Combiner Box -Collects all the Power!

Solar Combiner Box is one of the important equipments required for setting up a solar power plant be it a mega watt scale power plant or your own personal solar power plant.

What is a Combiner Box?

The combiner box is an electrical equipment which collects current from a set of solar panels. The current thus collected is then given at the inputs of the central or string solar inverter. The Inverter takes care of the rest after it receives input from the combiner boxes. Typically a large number of such boxes are required in utility scale projects.

Solar Combiner Box
Combiner Box By Shawn Schreiner

Why is a Solar Combiner Box needed?

I knew you will actually ask this question my friend, so here's the answer!

  • In large scale solar power plants, solar panels are present which do the job of generating electricity. But the current generated by every single panel is very less as compared to the input current required by any solar inverter.

  • Even if you decide to connect a single solar panel to the inverter, there will be significant loss of current as it reaches the inverter input due to the length of wiring involved. That particular current magnitude will not be sufficient for the inverter’s operation.

  • So a pv combiner box actually integrates the panels in a string which can be a series – parallel combination to provide substantial amounts of current to the inverter’s input.

Secondly combiner boxes reduce fair amount of wiring & labor costs, thereby making the plant look tidier. This helps in improving the plant uptime as exposed wiring would be subjected to harsh weather as well as rodents. These rodents may nibble at the wires eventually cutting them. I am puzzled as to why do rodents find it so enjoyable to chew at such wires. Maybe we should find a way to ask them!

A solar combiner box is also required whenever the utility plant’s management wants to monitor the status of the plant periodically. They offer higher resolution in fault analysis, which in turn reduces the time required for fault finding, as this is a very time consuming activity in large scale plants due to their vast area. You can actually point out a fault occurrence to a particular string among the plethora of solar panel strings in the entire plant. But this can be possible only if your combiner boxes have the current monitoring feature.

What Components are found in a combiner box?

A combiner box consists of gPV fuse links. The fuses are placed in finger safe fuse holders. Many times these fuse holders also provide indication of blown fuses, which can be replaced in a snap. The fuse ratings are calculated by multiplying the short circuit rating of the solar panel with 1.56 (156% of the panel’s short circuit current) and the product is rounded off to the next standard fuse size.

Surge arrestors are an optional component in solar combiner boxes of many manufacturers. They are basically used for providing effective protection of the combiner boxes from lightening storms. The grounding terminal can be effectively connected at site. Sizing for the grounding wire is calculated by multiplying the short circuit current rating of the solar panel with 1.25 (125% of the panel’s short circuit current) and the product is rounded off to the next wire size.

Types of combiner boxes

Combiner boxes are manufactured by almost all the major players in the solar industry. Pv combiner boxes with and without disconnector switch are most commonly implemented in large scale utility projects. They are also used in small scale power plants.

A Solar Combiner Box with string monitoring and without string monitoring are also available. After this you can have different types of boxes with their own unique selling points.

For a box equipped with String monitoring feature, current output from a pair of solar panels can be monitored. Any changes in the current levels can be monitored visually on a SCADA system.

The DC disconnector switch enables you to isolate a particular set of solar panels during maintenance works or during emergencies like short circuits in the field.

These boxes are available from minimum DC voltage of 600 V to a maximum DC Voltage of 1200V. Many manufacturers utilize metallic containers whereas fiber glass reinforced polycarbonate enclosures are put to use. These enclosures are subjected to harsh weather conditions as the product life needs to be minimum 20 to 25 years, so they must be of apex quality.

A Solar Combiner Box also needs to have protections like Short-circuit, Over current, Surge, Ground fault, etc. Commonly all or combinations of these protection schemes are found in models manufactured by various companies.

Last but Not the Least

Combiner Boxes continue to carry current even when disconnected, please take help of qualified personnel before you start installing or trouble shooting your combiner boxes.

Now that you know what is a pv combiner box, go ahead and use them in your solar power plant project.

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