Why does the power register return 0 during daylight hours?

The OpenEMS Modbus-API maps channels dynamically based on which components are exported. If the PV component is not included in the Modbus-API controller's component list, register 327 will return 0 or null. Open the OpenEMS UI, navigate to the Modbus-API controller configuration, and verify that the PV component ID is listed as an exported component.

Why do I get NaN or invalid float values on register 327?

Register 327 uses a 32-bit IEEE 754 float spanning two consecutive Modbus registers. Some polling tools interpret these as two separate 16-bit integers. Ensure your Modbus client (or ModbusCloud template) reads two registers starting at address 327 and decodes them as a single float32 in big-endian byte order, which is the OpenEMS default.

The gateway connects but register 367 reads stale or frozen values.

Register 367 holds a float64 energy counter across four consecutive registers. If the polling request spans fewer than four registers, the value will be incomplete or appear frozen. Confirm the Modbus read length covers all four registers (367 to 370 inclusive) and that function code 3 is used, matching the register's holding-register type.

Modbus connection is refused even though OpenEMS Edge is running.

The Modbus-TCP API controller must be explicitly activated in OpenEMS Edge. A running Edge instance does not expose Modbus by default. Check in the Apache Felix Web Console that a component of type 'Controller.Api.ModbusTcp.ReadOnly' or 'ReadWrite' is active, and confirm no firewall rule blocks TCP port 502 between the ModbusCloud Gateway and the Edge host.

Free Modbus template: OpenEMS Modbus-API (pv)

The OpenEMS Modbus-API is a software interface built into the OpenEMS Edge energy management platform, exposing internal channels to external systems over Modbus TCP. The PV variant of this template targets the photovoltaic production component of an OpenEMS installation. It reads two channels from the configured PV component: instantaneous production power at address 327 and cumulative produced energy at address 367. Both are floating-point values updated every cycle. Connecting ModbusCloud Gateway to the OpenEMS Edge TCP port gives installers a live view of solar yield and long-term production totals without modifying the EMS configuration.

Name	Address	Function	Type	Unit	Access
power Instantaneous PV production power, watts, float32.	327	FC04	float32	W	R
energy Cumulative PV energy produced, watt-hours, float64.	367	FC03	float64	Wh	R

OpenEMS Modbus-API (pv)

Overview

Use cases

Installation

Things to watch for

Registers (2)

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