SunSpec Model 502 — Solar Module
SunSpec Model 502 is a standardized Modbus TCP information model for solar module monitoring, defined by the SunSpec Alliance for use across compliant PV devices regardless of manufacturer. This template reads per-module output and input electrical data: current, voltage, instantaneous power, and cumulative energy on both the input (inw, ina, inv, inwh) and output (outpw, outa, outv, outwh) sides, plus module temperature and operating timestamp. Status, standard event flags, and vendor event flags expose fault and alarm states. Three read-write control registers (ctl, ctlvend, ctlval) allow module-level commands. Importing this template into your ModbusCloud portal gives you structured, manufacturer-independent panel telemetry in one click.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 23, read and write
- Brand
- SunSpec
- Last updated
Registers (23)
23 read, 3 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| id | Read | ||||
| l | Read | ||||
| a_sf | Read | ||||
| v_sf | Read | ||||
| w_sf | Read | ||||
| wh_sf | Read | ||||
| stat | Read | ||||
| statvend | Read | ||||
| evt | Read | ||||
| evtvend | Read | ||||
| ctl | Read and write | ||||
| ctlvend | Read and write | ||||
| ctlval | Read and write | ||||
| tms | Secs | Read | |||
| outa | A | Read | |||
| outv | V | Read | |||
| outwh | Wh | Read | |||
| outpw | W | Read | |||
| tmp | °C | Read | |||
| ina | A | Read | |||
| inv | V | Read | |||
| inwh | Wh | Read | |||
| inw | W | Read |
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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 per-module output power and input power to detect underperforming panels across a PV array.
- Track cumulative input and output energy (inwh, outwh) to verify energy conversion efficiency over time.
- Alert on non-zero event flags (evt) to identify module faults or alarms before they escalate.
- Compare module temperature (tmp) against output power to correlate thermal derating with reduced yield.
- Verify operating status (stat) after grid events to confirm all modules have returned to normal operation.
Installation
Confirm that the target device implements SunSpec Model 502 and has Modbus TCP enabled, typically under the communication or Modbus section of its web interface or configuration tool.
Connect the device to the same LAN as the ModbusCloud Gateway, ensuring TCP port 502 is reachable from the Gateway's network segment and no firewall blocks it.
In the ModbusCloud portal, add a new device using the ModbusCloud Gateway, import the SunSpec Model 502 Solar Module template, and set the correct unit ID matching your device's Modbus slave address.
Spot-check connectivity by reading register offset 0 (id): a returned value of 502 confirms the correct model block is addressed and data is flowing.
Things to watch for
Register id returns a value other than 502. Why?
The model block base address may be wrong. SunSpec devices place models at dynamic offsets discovered by walking the device map from the SunSpec start address. Confirm the base address of Model 502 by scanning from the SunSpec identifier register rather than assuming a fixed offset.
Current and power readings look wrong by a factor of 10 or 100. What is the cause?
SunSpec uses signed integer scale factors. The raw outa, outpw, ina, and inw values must be multiplied by 10 raised to the power of a_sf or w_sf respectively. If your integration ignores these scale factor registers, all derived readings will be off by a power of ten.
The gateway connects but outwh and inwh show zero or no change. What should I check?
Energy accumulator registers (outwh, inwh) are uint32 and increment only while the module is producing power. Verify the module's stat register is in an active operating state and that the module is not in a fault condition indicated by the evt bitfield.
Is it safe to write to the ctl, ctlvend, and ctlval registers in normal monitoring?
No. These are read-write control registers that send commands to the module. Writing incorrect values to ctl or ctlval can alter module operating mode, interrupt production, or trigger protective shutdowns. Only write to these registers if you have verified the command sequence in the device's documentation and understand the consequences.
Knowledge base articles for this device
SunSpec Modbus: one register map for many inverters
SunSpec Modbus is the open register map SMA, Fronius, SolarEdge and Kostal share. The layout, int+SF vs float, the TCP port per brand and reading a mixed fleet.
Fronius Modbus: read a Symo GEN24 over Modbus TCP
Fronius Modbus explained: enable Modbus TCP on the Symo GEN24 on port 502, choose between int+SF and float, read the right SunSpec registers and scale them correctly. Practical guide for solar installers.
SMA Modbus: reading a Sunny Boy over Modbus TCP (installers)
SMA Modbus explained: enable the Modbus TCP server on port 502, choose between the SMA profile (unit ID 3) and SunSpec (unit ID 126), read the right registers, and handle the NaN values at night. Practical guide for installers.
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