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How do solar junction boxes work? Answered

With solar systems, you often see a junction box that apparently is necessary equipment for a solar installation.

What is it?
It has diodes inside, right?
Why do you need it?


Websearch for "solar junction box" finds a few manufacturers, some of whom describe what the product is intended to do. No endorsement implied, but one such is


Diodes are often used with solar panels to keep the power flow going in one direction, and prevent power from feeding back into the panels in the dark...

.  Without seeing what you are talking about, it's difficult to say for sure. The j-box is probably just a good place to wire the sub-assemblies together and/or interface with the "outside world."
.  It's probably not 100% necessary, but does keep corrosion at the terminals to a minimum by excluding water.