The solar distribution box doesn’t always get the attention it deserves. Usually, pre-installed on the back of a solar module, installers pay little attention until they connect the panels.
The PV junction box has a simple but important role: to house all the electrical bits on a solar panel and protect it from the environment. The wires connect to the diodes on the inside, providing an easy way to join the panels together.
Although developers and solar owners don’t get to choose the types of solar distribution box (module companies settle those contracts during manufacturing), it’s still important to understand the role of this product, especially as it houses more smart technologies.
Basics Of The Solar Distribution Box
A solar distribution box has bypass diodes that keep power flowing in one direction and prevent it from feeding back into the panels. Frank Rosenkranz, solar product manager for EMEA, India, and the Americas for connector and junction box manufacturer TE Connectivity, described the solar DB as the most important part of a panel.
If part of a solar panel is shaded, that string will want to draw power, reversing the flow of electricity. Diodes inside the distribution box prevent that from occurring.
There are two different techniques of solar distribution box production: soldering/potting and clamping. With the solder and pot method, the sheets leading from the solar panel are soldered to the diodes in the solar power distribution box. The junction box must then be potted or filled with a type of adhesive material to allow for thermal heat transfer, hold the solder joint in place, and prevent it from failing. Once enough time has passed for the encapsulant material to cure sufficiently, the panel is ready to go.
With clamp production, a simple clamp mechanism attaches the foil to the cables. The prices for both methods are fairly equal when comparing the material and labor costs as a whole. The clamp box may be more expensive, but the labor required to weld and pot the other boxes is often more.
Although opinions differ on the best way to produce a solar distribution box, there has been little discussion of the primary role of this often ignored product until new technologies became involved in the industry.
Solar Distribution Box Evolution
As the modules have changed, the junction box has kept the same functionality. But now, with higher voltages and power outputs, junction boxes had to grow stronger for the solar system to maintain that power.
The general function of the junction box remains the same. What has changed is that the modules are getting more powerful? As power generation increases, the bypass diodes have to work more intensely. They absorb that power by releasing heat. You have to take care of that heat with the diodes.
Cold bypass switches are replacing traditional diodes in some junction boxes to mitigate excessive heat generated by taller module outputs. When shaded panels instinctively want to consume power, a traditional diode prevents that from happening, but heat is generated in the process. A cold bypass switch functions as an on/off switch and opens the circuit when the panels attempt to draw power, preventing heat buildup.
Bypass diodes are 1950s technology. As solar junction box components, they are robust and reliable, but that heat generation has always been a problem. Cold bypass switches solve the heat problem, but they are much more expensive than a 20-cent diode. And everyone wants solar panels to be as affordable as possible.
Types Of Solar Distribution Box
To get the most out of their investment, many system owners are turning to bifacial panels. Power is still fed through a junction box, even though power is produced at both the front and rear of the module. DB box makers have had to be more innovative with their designs.
On a bifacial panel, you want to place the junction boxes at the edge where you’re sure the back isn’t shadowed. When it’s on the edge, the junction box can no longer be a rectangle, it has to be small.
Most distributors offer three small junction boxes for bifacial modules, one for the left corner, one for the middle corner, and one for the right corner of the module, which function just like a larger rectangular box.
The rapid popularity of bifacial modules meant that solar DB board designs had to be updated on the fly. Other sudden upgrades to solar systems include rapid shutdown and various module-level features required by the National Electrical Code, and the junction box must keep up.
The industry is changing so fast that it’s hard to stick with one venue and hope it’s viable. How do you create a device that can handle PV temperatures and still work properly and last a long time? How do you make it so that you can change that technology if it fails or becomes obsolete? The solar distribution box now has to be able to be opened and closed.
Most microinverters and optimizers are added to the rear of the module in addition to the junction box. But a power optimizer can replace the solar distribution box on factory-assembled smart modules. The built-in power optimizer provides smart capabilities while performing the basic power functions of a junction box.
It has an advanced thermal design that allows for heat dissipation to maintain a lower cell temperature and avoid hot spots. We have specifically designed our built-in power optimizer to allow manufacturing flexibility so that module manufacturers can quickly adjust manufacturing based on demand.
Junction box manufacturers are also considering adding solar inverters to some of the types of solar junction boxes.
The next step will be that module that has the inverter in the standard junction box with an AC source going out. That makes the installation simpler and makes the panels more versatile. We hope this article has given you a better understanding of solar distribution box. To get a free consultation about installing a solar junction box, contact our solar equipment shop.