St-ems wattsonic (pv)
The Wattsonic is a residential and commercial hybrid PV inverter that converts DC power from rooftop solar arrays into AC power for on-site consumption or grid export. The St-ems wattsonic (pv) template connects to the inverter over Modbus TCP, reading the PV generation power register at address 11028. This single register gives your ModbusCloud portal a live watts figure for solar yield, which is the foundation for energy-balance dashboards and yield-verification workflows. Installers working with St-ems-badged Wattsonic Gen3 units can import this template with one click and start logging production immediately.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 1, read only
- Brand
- St-ems
- Compatible models
- wattsonic
- Last updated
Registers (1)
1 read, 0 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| power | W | Read |
Loading registers…
Send your device list
If a device is not in the library yet, we build the template for free as soon as we have the register data.
Use cases
- Monitor real-time PV generation power to verify that the Wattsonic array is producing at the expected level.
- Track daily and seasonal PV yield trends to detect soiling, shading, or module degradation over time.
- Alert on sustained zero-watt readings during daylight hours to identify inverter faults or tripped DC breakers.
- Compare PV generation against site consumption data to calculate self-sufficiency ratios across multiple periods.
- Report PV output to building owners or energy managers as part of a monthly performance summary.
Installation
Connect the Wattsonic inverter's LAN port to your local network and confirm it has a stable IP address; the inverter exposes Modbus TCP on port 502 with unit ID 255 by default.
Attach the ModbusCloud Gateway to the same LAN segment as the inverter, then power it on and confirm it appears online in the ModbusCloud portal.
In the ModbusCloud portal, add a new device, import the St-ems wattsonic (pv) template, and assign unit ID 255 together with the inverter's IP address and port 502.
Trigger a manual poll and check that the power register at address 11028 returns a plausible watt value during daylight; a value of zero at midday indicates a connection or unit-ID mismatch.
Things to watch for
Why does register 11028 always return zero at midday?
Confirm the inverter is generating power by checking its local display or app. If the inverter is active but the register reads zero, verify the unit ID is set to 255 and the TCP port is 502. Also check that no firewall rule on the local router is blocking Modbus traffic from the Gateway to the inverter.
The gateway connects but the power value looks far too large or negative.
Register 11028 is an int32 decoded from two consecutive 16-bit holding registers. Confirm the template decodes the register as int32 and not as two separate uint16 values. Incorrect decode type causes byte-order artefacts that produce wildly wrong or negative readings.
Polling fails with an illegal data address exception on function code 3.
The Wattsonic Gen3 firmware requires register addresses to be specified as the documented table value plus 1. The template already accounts for this, so do not manually adjust the address in the portal. If you are testing with an external Modbus tool, use address 11029, not 11028.
The inverter is offline at night and the portal shows read errors. Is this normal?
Yes. The Wattsonic communication module remains active, but some firmware versions stop responding to Modbus queries when PV input is absent. Schedule polling intervals to expect null or error responses after sunset. Configure the ModbusCloud alert thresholds to ignore read errors outside daylight hours to avoid false fault notifications.
Want to see how it works?
