
Modbus TCP
SunSpec Model 404 — String Combiner (Advanced)
SunSpec
Overview
SunSpec Model 404 is the Advanced String Combiner information model, published by the SunSpec Alliance for photovoltaic DC collection systems. The template reads the full combiner block over Modbus TCP: aggregate DC current, voltage, power, cumulative energy, amp-hours, DC performance ratio, and enclosure temperature, plus all per-string scale factor registers needed to decode individual input measurements. Event and vendor-event bitmask registers surface fault and warning states without requiring a separate alarm channel. Connecting any SunSpec Model 404 compliant combiner to the ModbusCloud Gateway gives installers and asset managers live and historical string-level production data in one portal.
Use cases
- Monitor total combiner DC power and cumulative energy daily to verify array production against expected yield.
- Track the DC performance ratio register to detect soiling, shading, or module degradation across seasons.
- Alert on non-zero values in the combiner event bitmask to catch fault conditions before they affect inverter output.





