SunSpec Model 220 — Secure AC Meter Selected Readings
SunSpec Model 220 is a standardized AC meter information model defined by the SunSpec Alliance, used by any SunSpec-compliant energy meter that supports cryptographically signed readings. The template reads instantaneous measurements, including current, phase voltage, grid frequency, real power, apparent power, reactive power, and power factor, each paired with its scale factor. It also captures four-quadrant cumulative energy totals (active, apparent, and reactive), plus tamper-evident security fields: a Unix timestamp, millisecond offset, sequence number, cryptographic algorithm identifier, and signature block count. This template enables verifiable, audit-ready energy monitoring over Modbus TCP.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 33, read only
- Brand
- SunSpec
- Last updated
Registers (33)
33 read, 0 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| id | Read | ||||
| l | Read | ||||
| a | A | Read | |||
| a_sf | Read | ||||
| phv | V | Read | |||
| v_sf | Read | ||||
| hz | Hz | Read | |||
| hz_sf | Read | ||||
| w | W | Read | |||
| w_sf | Read | ||||
| va | VA | Read | |||
| va_sf | Read | ||||
| var | var | Read | |||
| var_sf | Read | ||||
| pf | Pct | Read | |||
| pf_sf | Read | ||||
| totwhexp | Wh | Read | |||
| totwhimp | Wh | Read | |||
| totwh_sf | Read | ||||
| totvahexp | VAh | Read | |||
| totvahimp | VAh | Read | |||
| totvah_sf | Read | ||||
| totvarhimpq1 | varh | Read | |||
| totvarhimpq2 | varh | Read | |||
| totvarhexpq3 | varh | Read | |||
| totvarhexpq4 | varh | Read | |||
| totvarh_sf | Read | ||||
| evt | Read | ||||
| ts | Read | ||||
| ms | Read | ||||
| seq | Read | ||||
| alg | Read | ||||
| n | 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
- Verify grid frequency stays within tolerance using the hz register during commissioning.
- Track totwhexp and totwhimp over time to produce accurate import/export energy reports.
- Monitor the evt bitmask register to detect and alert on meter fault conditions in real time.
- Compare totvarhimpq1 and totvarhexpq3 quadrant energy values to audit reactive power flows.
- Use the ts and seq registers to confirm reading freshness and detect replayed or stale data.
Installation
Enable Modbus TCP on the meter under its communication or network settings, and note the assigned IP address and TCP port (default 502).
Connect the meter to the same LAN segment as the ModbusCloud Gateway, ensuring no firewall blocks port 502 between them.
In the ModbusCloud portal, add a new device, import the SunSpec Model 220 template, and assign the correct Modbus unit ID configured on the meter.
Verify the connection by spot-checking the w register for a live real power reading and confirming the ts register advances with each poll.
Things to watch for
Why do current or power readings appear to be off by a factor of ten?
SunSpec uses paired scale-factor registers. Read a_sf alongside a, then compute the real value as a * 10^a_sf. The same pattern applies to every measured quantity. If your client ignores scale factors, all readings will be systematically wrong.
The gateway connects but all registers return zero or NaN. What now?
Confirm the meter has Modbus TCP enabled and is actively measuring an energised circuit. Check that the Modbus unit ID in the portal matches the meter configuration. Some meters only expose SunSpec registers when the metered circuit carries live voltage.
Why does the ts register never change between polls?
The timestamp and seq registers are updated only when the meter generates a new signed snapshot. If the meter's signing interval is longer than your poll interval, ts will appear static. Check the meter's signing or logging period in its configuration interface.
What does the alg register value represent, and can I ignore it?
The alg register identifies the cryptographic algorithm the meter uses to sign the reading snapshot. It is informational for most monitoring setups, but if you are using the signature for compliance or billing verification, record it alongside the signature blocks and the ts value to reconstruct a verifiable audit trail.
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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