To properly size the combiner box, first calculate the maximum current for each string and then multiply by 1. Designing a high-efficiency solar power system begins with choosing the right inverter and PV combiner box. But with so many technical parameters, how can you be sure you're making the right decision? In this article, we walk you through a real-world case—144 solar panels of 555W each paired with a. Incorrect sizing or selection of a photovoltaic combiner box can lead to system inefficiencies, overheating risks, or even complete power failure. What Is a PV Combiner Box in Large-Scale Solar. to a single outpu ance cables by combining strings at the array locat ciency, reliability and safety in solar energy systems. String Voltage (Voc): Find the open-circuit voltage (Voc) for your solar modules.