Siemens Junelight Smart Battery (grid)
The Siemens Junelight Smart Battery is a modular residential lithium-ion storage system designed to pair with rooftop PV installations. This Modbus TCP template reads the grid-side power register, capturing the real-time power flow between the battery system and the public grid. Positive values indicate import; negative values indicate export. With the ModbusCloud Gateway connected to the same network as the Junelight, you can log grid power continuously, build historical trend charts, and trigger alerts, giving installers and building owners a clear picture of household energy autonomy.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 1, read only
- Brand
- Siemens
- 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…
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Use cases
- Monitor real-time grid power flow to verify the Junelight Smart Battery is charging and discharging as expected.
- Track grid import and export patterns over weeks to identify periods of excessive grid dependency.
- Alert on sustained grid import during daylight hours, indicating possible battery or PV underperformance.
- Compare logged grid power data before and after battery capacity expansions to confirm expected improvement.
- Report daily grid exchange totals to building owners for energy cost analysis and self-consumption audits.
Installation
Enable Modbus TCP access on the Siemens Junelight Smart Battery by contacting Siemens support or your installer to activate the Modbus interface, confirming port 502 is reachable on the local network.
Connect the ModbusCloud Gateway to the same LAN as the Junelight Smart Battery, ensuring no firewall rules block TCP port 502 between the Gateway and the battery's IP address.
In your ModbusCloud portal, add the Gateway, import the Siemens Junelight Smart Battery (grid) template, and set the unit ID to 1, which is the default Modbus slave ID reported by the Junelight.
Verify the integration by opening the live register view in the portal and confirming the power register at address 14 returns a plausible signed integer value reflecting current grid flow.
Things to watch for
Why does the power register always return zero or null?
The Junelight Modbus TCP interface must be explicitly activated by Siemens or your certified installer. If the interface has not been enabled, all register reads will fail silently or return zero. Confirm activation status with your Siemens service contact before troubleshooting further.
The Gateway connects to port 502 but reads time out. What is wrong?
Check that the Junelight and the ModbusCloud Gateway are on the same IP subnet and that no router or firewall is blocking port 502. Also verify the battery's IP address has not changed due to DHCP reassignment. Assigning a static IP to the Junelight resolves most persistent timeout issues.
Power values look correct in sign but are far too large or too small. Why?
The power register is a signed 32-bit integer spanning two consecutive 16-bit holding registers. If your client reads only one 16-bit word instead of two, the value will be incorrect. Confirm the ModbusCloud template is read as int32 across two registers starting at address 14.
Readings drop out periodically even though the network is stable. What causes this?
The Junelight's Modbus TCP server has a limited number of simultaneous connections. If another system, such as a home automation controller, already holds an open connection, the Gateway may be refused. Close unused connections or configure the other client to release connections between polls.
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