Solving Python SolarEdge PyModbus compatibility error after Debian upgrade

Written by Claudio Kuenzler - 0 comments

Published on January 11th 2026 - Listed in Linux Python Monitoring

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A while ago I started using the SolarEdge Modbus Python library to obtain statistics from my SolarEdge inverter. This library uses the  uses the pymodbus library in the background, to establish a TCP Modbus connection to the inverter.

This has worked fine for a very long time. Until today. Today I upgraded the relevant machine from Debian 11 (Bullseye) to 12 (Bookworm) - yes, I know, still one version away from stable again.

No data

Unfortunately I noticed this several hours later, when I had a look at my SolarEdge Grafana Dashboard:

As it turns out, the service used to run the Python script failed since the distribution upgrade. Manually running the Python script confirmed the error:

ck@debian:~$ /home/ck/solaredge_modbus/modified_influxdb.py --interval 60 --influx_host localhost --influx_db solaredge solaredgeinverter 1502
Traceback (most recent call last):
  File "/home/ck/solaredge_modbus/modified_influxdb.py", line 10, in <module>
    import solaredge_modbus
ModuleNotFoundError: No module named 'solaredge_modbus'

With the Debian upgrade, the Python version was upgraded from 3.9 to 3.11. Hence the previously installed Python modules (using pip3) were not installed.

Let's install the solaredge-modbus library again:

ck@debian:~$ pip3 install solaredge-modbus --break-system-packages
[...]
Installing collected packages: pyserial, pyserial-asyncio, pymodbus, solaredge-modbus
Successfully installed pymodbus-3.11.4 pyserial-3.5 pyserial-asyncio-0.6 solaredge-modbus-0.8.0

pymodbus compatibility issue

The module "solaredge_modbus" could now be loaded, but unfortunately another error showed up:

ck@debian:~$ /home/ck/solaredge_modbus/modified_influxdb.py --interval 60 --influx_host localhost --influx_db solaredge solaredgeinverter 1502
Traceback (most recent call last):
  File "/home/ck/solaredge_modbus/modified_influxdb.py", line 10, in <module>
    import solaredge_modbus
  File "/home/ck/.local/lib/python3.11/site-packages/solaredge_modbus/__init__.py", line 4, in <module>
    from pymodbus.constants import Endian
ImportError: cannot import name 'Endian' from 'pymodbus.constants' (/home/ck/.local/lib/python3.11/site-packages/pymodbus/constants.py)

This time there's an issue with the pymodbus library, which was installed by pip3 as a dependency.

After a bit of research, I stumbled across an open issue which mentions compatibility issues of the solaredge_modbus module with newer pymodbus versions:

There are some breaking updates on pymodbus that require updates to their users, including solaredge_modbus.
The requirements for this repository are pymodbus ~= 3.5.0 (see setup.cfg).

Herbi3 made a fork which states pymodbus >= 3.5.0 (see https://github.com/herbi3/solaredge_modbus), but it fails with pymodbus >= 3.9.0 . 

pip3 installed a recent version (3.11.4) of pymodbus:

ck@icinga2:~$ ls -la .local/lib/python3.11/site-packages/
total 32
drwxr-xr-x 11 ck ck 4096 Jan 11 14:39 pymodbus
drwxr-xr-x  3 ck ck 4096 Jan 11 14:39 pymodbus-3.11.4.dist-info
drwxr-xr-x  2 ck ck 4096 Jan 11 14:39 pyserial-3.5.dist-info
drwxr-xr-x  2 ck ck 4096 Jan 11 14:39 pyserial_asyncio-0.6.dist-info
drwxr-xr-x  6 ck ck 4096 Jan 11 14:39 serial
drwxr-xr-x  3 ck ck 4096 Jan 11 14:39 serial_asyncio
drwxr-xr-x  3 ck ck 4096 Jan 11 14:39 solaredge_modbus
drwxr-xr-x  2 ck ck 4096 Jan 11 14:39 solaredge_modbus-0.8.0.dist-info

Revert to older pymodbus version

This information turned out to be crucial; the script worked before. What version of pymodbus was used before? 

ck@debian:~$ ls -la .local/lib/python3.9/site-packages/
total 64
drwxr-xr-x 6 ck ck 4096 Apr 29  2024 dateutil
drwxr-xr-x 5 ck ck 4096 Apr 29  2024 influxdb
drwxr-xr-x 2 ck ck 4096 Apr 29  2024 influxdb-5.3.2.dist-info
drwxr-xr-x 3 ck ck 4096 Apr 29  2024 msgpack
drwxr-xr-x 2 ck ck 4096 Apr 29  2024 msgpack-1.0.8.dist-info
drwxr-xr-x 9 ck ck 4096 Apr 29  2024 pymodbus
drwxr-xr-x 2 ck ck 4096 Apr 29  2024 pymodbus-3.6.8.dist-info
drwxr-xr-x 2 ck ck 4096 Apr 29  2024 pyserial-3.5.dist-info
drwxr-xr-x 2 ck ck 4096 Apr 29  2024 pyserial_asyncio-0.6.dist-info
drwxr-xr-x 2 ck ck 4096 Apr 29  2024 python_dateutil-2.9.0.post0.dist-info
drwxr-xr-x 4 ck ck 4096 Apr 29  2024 pytz
drwxr-xr-x 2 ck ck 4096 Apr 29  2024 pytz-2024.1.dist-info
drwxr-xr-x 6 ck ck 4096 Apr 29  2024 serial
drwxr-xr-x 3 ck ck 4096 Apr 29  2024 serial_asyncio
drwxr-xr-x 3 ck ck 4096 Apr 29  2024 solaredge_modbus
drwxr-xr-x 2 ck ck 4096 Apr 29  2024 solaredge_modbus-0.8.0.dist-info

As it turns out, the script was working fine before under Debian 11 with Python 3.9 and pymodbus 3.6.8. 

Will it work if I use the same site-packages from 3.9 in 3.11? 

ck@debian:~$ rm -rf .local/lib/python3.11/site-packages/pymodbus*
ck@debian:~$ cp -Rp .local/lib/python3.9/site-packages/pymodbus* .local/lib/python3.11/site-packages/
ck@debian:~$ /home/ck/solaredge_modbus/modified_influxdb.py --interval 60 --influx_host localhost --influx_db solaredge solaredgeinverter 1502
Startup complete

It works again, hurray!

As an alternative to the manual package copy, the pymodbus pip3 package can be downgraded to the same version:

ck@debian:~$ pip3 install pymodbus==3.6.8 --break-system-packages
Defaulting to user installation because normal site-packages is not writeable
Requirement already satisfied: pymodbus==3.6.8 in ./.local/lib/python3.11/site-packages (3.6.8)

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