StecaGrid 3600 RS485 MQTT Service

The protocol

As far as I can tell its a s simple request and response protocol that Steca had implemented to talk to StecaGrid inverters (around 2013 time frame). Newer models seem to have a better XML API.

• A dynamic datagram structure is used, which starts with 0x02 and ends with 0x03.
• The second data word holds the overall length of the datagram.
• Following that the RS485 id of the recipient and of the sender are always present.
• The next byte (as well as the last word before 0x03) are obviously some CRC.
• The rest (payload) of the datagram depends on the topic and if its the request or response for it
• It typically has a header (requests start with 0x40, 0x64, 0x20, ... responses start with 0x41, 0x65, 0x21, ... respectively)
• The topics are represented in the fifth byte of the payload of both the request and the reponse. A few of the discovered topics are:
  • Grid voltage = L1 MeasurementValues ENS1 (measurement 1/2, value 1/4)
  • Grid power = AC Power (0x29)
  • Grid frequency = L1 MeasurementValues ENS1 (measurement 2/2, value 2/4)
  • Panel voltage (0x23)
  • Panel current (0x24)
  • Panel power (0x22)
  • Daily yield (0x3c)
  • Total yield = (0xf1)
  • Time (0x05)
• Data is respresented as Pascal-type strings (pre-fixed by their length as a 16-bit word), proprietary 3-byte floats (pre-fixed by a unit byte) in the payload. Pre-fixed length field are used here and there. Unit prefixes are:
  • V (0x05)
  • A (0x07)
  • Wh (0x09)
  • W (0x0B)
  • Hz (0x0D)
  • NUL (0x00) (some fields switch to this unit type when they fall to zero)

To Do

• CRC: without the CRC calculation no datagram can be synthesized.

Install

pip3 install pyserial pyyaml paho-mqtt

Cableing

Usage

usage: StecaGrid3600_mqtt.py [-h] [-v] [-c CONFIG]

Feed MQTT based on RS485 from StecaGrid3600

optional arguments:
  -h, --help            show this help message and exit
  -v, --verbose         Enable verbose output
  -c CONFIG, --config CONFIG
						Load config from (default config.yaml)

config.yaml

mqtt_broker_address: 'nas.ds18' # Set this to your mqtt broker address
mqtt_username: 'mqtt_user' # Uncomment and change this to your username if required
mqtt_password: 'xyzxyz'

# List the (OBIS) values that you want to send to the mqtt broker
values_of_interest:
  - CURRENT_ELECTRICITY_DELIVERY
  - ELECTRICITY_EXPORTED_TOTAL

client: serial
serial_device: /dev/ttyS0

topic: DS18/PV/StecaGrid_3600

Home Assistant sensor config

mqtt:
	sensor:
	  - name: "StecaGrid 3600 Total"
		unique_id: "StecaGrid_3600_Total"
		device_class: "energy"
		state_class: "total_increasing"
		unit_of_measurement: "Wh"
		state_topic: "DS18/PV/StecaGrid_3600/ELECTRICITY_EXPORTED_TOTAL"
	  - name: "StecaGrid 3600 Power"
		unique_id: "StecaGrid_3600_Power"
		device_class: "power"
		state_class: "measurement"
		unit_of_measurement: "W"
		state_topic: "DS18/PV/StecaGrid_3600/CURRENT_ELECTRICITY_DELIVERY"

evcc meter config

meters:
  - name: StecaGrid_3600
	type: custom
	power:
	  source: mqtt
	  topic: DS18/PV/StecaGrid_3600/CURRENT_ELECTRICITY_DELIVERY
	  timeout: 10s

Steca RS485 requests for replay approach

The following telegrams are requests to extend the replay beyond AC Power. Note, that they all address the inverter with the RS485 ID #1. You will have to change your Steca to that ID until we have figured out the CRC generation to synthesize a full new telegram for a different id. Contact me of you need a replay telegram for a differnt ID, and I might be able to record one for you from the SEM.

SG_NOMINAL_POWER = bytes.fromhex("02 01 00 10 01 7b b5 40 03 00 01 1d 72 30 95 03")
SG_PANEL_POWER   = bytes.fromhex("02 01 00 10 01 7b b5 40 03 00 01 22 77 12 ee 03")
SG_PANEL_VOLTAGE = bytes.fromhex("02 01 00 10 01 7b b5 40 03 00 01 23 78 78 e4 03")
SG_PANEL_CURRENT = bytes.fromhex("02 01 00 10 01 7b b5 40 03 00 01 24 79 a0 b6 03")
SG_VERSIONS      = bytes.fromhex("02 01 00 0c 01 7b c6 20 03 79 8c 03")
SG_SERIAL        = bytes.fromhex("02 01 00 10 01 7b b5 64 03 00 01 09 5e 85 6e 03")
SG_TIME          = bytes.fromhex("02 01 00 10 01 7b b5 64 03 00 01 05 5a 3a 44 03")
SG_DAILY_YIELD   = bytes.fromhex("02 01 00 10 01 7b b5 40 03 00 01 3c 91 e1 c9 03")
SG_TOTAL_YIELD   = bytes.fromhex("02 01 00 10 01 7b b5 64 03 00 01 f1 46 cc 79 03")
SG_AC_POWER      = bytes.fromhex("02 01 00 10 01 7b b5 40 03 00 01 29 7e 98 5b 03")

Based on versions

All of my tinkering is based on the following firmware versions.

python3 getStecaGridData.py -ve

StecaGrid 3600

HMI BFAPI       5.0.0   19.03.2013 14:38:59
HMI FBL         2.0.3   05.04.2013 11:46:20
HMI APP         15.0.0  26.07.2013 13:19:06
HMI PAR         0.0.1   26.07.2013 13:19:06
HMI OEM         0.0.1   11.06.2013 08:11:29
PU BFAPI        5.0.0   19.03.2013_14:38:42
PU FBL  1.0.1   19.12.2012_16:36:04
PU APP  4.0.0   03.05.2013_09:37:55
PU PAR  3.0.0   31.01.2013_13:47:24
ENS1 BFAPI      5.0.0   19.03.2013_14:38:51
ENS1 FBL        1.0.1   19.12.2012_16:34:47
ENS1 APP        39.0.0  11.07.2013_14:39:50
ENS1 PAR        0.0.14  11.07.2013_14:40:03
ENS2 BFAPI      5.0.0   19.03.2013_14:38:51
ENS2 FBL        1.0.1   19.12.2012_16:34:47
ENS2 APP        39.0.0  11.07.2013_14:39:50
ENS2 PAR        0.0.14  11.07.2013_14:40:03
HMI     PU      ENS2
Net11

Your milage may vary.