In general, most household solar panel setups do not need a solar combiner box. Solar combiner boxes are required for those that have more than three solar panels in a system. It also makes fixing problems harder. Are Combiner Boxes Necessary for Solar Systems? People often ask, “are. The short answer: It depends on your solar system size and setup—but for most homeowners, yes, a combiner box for solar panels is a smart (and often necessary) investment. Built-in DC switches, SPDs, fuses, and multi-MPPT inputs already provide safe string merging and protection.