SunSpec Model 120 — Nameplate

Installation

1. 1Enable Modbus TCP on the DER device through its web interface or commissioning tool, under the communication or Modbus section, and note the TCP port (typically 502) and unit ID.
2. 2Connect the DER device to the same Ethernet network as the ModbusCloud Gateway, confirming the device IP is reachable from the Gateway before proceeding.
3. 3In the ModbusCloud portal, add the Gateway, import the SunSpec Model 120 Nameplate template, and set the target IP address, port 502, and the unit ID assigned to the DER device.
4. 4Trigger a manual poll and verify that wrtg and vartg return non-zero values consistent with the device nameplate; confirm scale factors (wrtg_sf, vartg_sf) are applied correctly in the portal register table.

Things to watch for

01

Why do wrtg or vartg read zero or 65535?

A value of 65535 (0xFFFF) is the SunSpec not-implemented sentinel. This means the device does not populate that register for its DER type. For pure PV inverters, whrtg, ahrrtg, maxcharte, and maxdischarte are commonly not implemented and will return 65535. Treat these as absent, not as a communication fault.

02

My calculated wattage is orders of magnitude wrong. What is the cause?

SunSpec uses signed 16-bit scale factor registers (wrtg_sf, vartg_sf, etc.). The true value is the raw register multiplied by 10 raised to the power of the scale factor. A scale factor of -2 means divide the raw value by 100. If your integration ignores scale factors, all readings will be incorrectly scaled. Confirm your portal template applies each _sf register to its associated measurement.

03

The gateway connects but the dertyp register shows an unexpected value.

The DERTyp enumeration is vendor-defined within the SunSpec framework. A value of 4 typically indicates a PV inverter, while other values represent wind, storage, or hybrid types. If your device returns an unexpected value, consult the device Modbus documentation for its specific DERTyp mapping before assuming a communication error.

04

Register addresses in my poll tool do not match the template. Why?

SunSpec Model 120 uses relative block offsets, not absolute Modbus addresses. The actual register addresses depend on where the device places the model in its holding register map, which can start at base address 0, 40000, or 50000. The template uses offsets 0 to 26 relative to the model block start. Configure the correct base address in the ModbusCloud Gateway settings to align the template.

Registers (27)

27 read / 0 write

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