Modernizing Modbus in Home Assistant

[balloob]

Hey 👋

We are modernizing how Modbus works in Home Assistant. You can read more about it here: https://developers.home-assistant.io/blog/2026/07/05/modernizing-modbus/

Would love to see this integration adopt modbus-connection and make it's way to Home Assistant!

[WillCodeForCats]

Thanks, I will take a look and try it out.

[balloob]

For the inverters/models that cannot handle certain fields, I've been working on home-assistant-libs/modbus-connection#81 to make that work. You would then probe or ask user for their model to decide which fields to restrict.

[WillCodeForCats]

SolarEdge inverters are very inconsistent. I have two inverters: same model, installed together, serial numbers are almost sequential so they were manufactured at the same time, yet they don't respond to modbus requests the same way between the two of them. One of them will send exceptions for unknown registers and the other will ignore them. Beyond that SolarEdge has settings only visible to them where they can make define what's available on an inverter. So there's really no good way to predetermine what may or may not work other than to try it, and even if it does work at first I've had users report access to things quietly taken away from their inverter. They also reboot and reset themselves every 24 hours.

I already have a somewhat elaborate probing system with retries and backoffs, checking responses, internal flags, external options, and raising repair issues to deal with all of their inconsistencies in the most user friendly way as possible. It's just a matter of playing with it in a new abstraction layer. All of the potential "problem" registers, which are things not officially supported by SolarEdge, are disabled by default and have to be turned on in options after adding the hub.

I left the first attempt using modbus-connection running on a VM overnight and it's been working without any errors. I will clean it up a bit more, test writes, and start v4.0.0 pre-releases out of it.

[WillCodeForCats]

After the release of modbus-connection that adds the connect on demand I will make a 4.0.0-pre.0 pre-release.

[balloob]

I expect to do a new release of modbus-connection next week, need to get the release notes written up. Currently traveling.

[balloob]

modbus-connection 4.0.0a3 is out. Let me know if you run into any issues!

[WillCodeForCats]

Release v4.0.0-pre.0 using modbus-connection (with pymodbus backend) is now available. I've installed it on my personal HA setup.

[balloob]

Could you try out the tmodbus backend ? It is our preferred backend and the one that Home Assistant will use when we integrate connection sharing.

[WillCodeForCats]

Sure, I can try it. I chose pymodbus because I'm already familiar with it if something wasn't working right.

[balloob]

I noticed that you are not leveraging any of the device modelling including support for Sunspec field helpers provided by modbus-connection.

[WillCodeForCats]

Right now my plan is to get it working with as few changes as possible and then do more in sections.

I can see an old problem has resurfaced which causes entities to become unavailable when the inverter does its self reset and reboot cycle every 24 hours, so that's first up on my list to figure out a new workaround (that I have wait to test once a day).

[WillCodeForCats]

I've started adding some device modeling components one at a time as I learn about them while making sure they provide a one-to-one match to the direct reads it's replacing.

[WillCodeForCats]

I'm happy to report that as of Release v4.0.0-pre.11 all reads and writes are exclusively through modbus-connection components.

One thing to note about the component choices: I'm intentionally not using the SunSpec discovery and generation because SolarEdge inverters are only partially SunSpec: batteries and all of the writable controls are not under SunSpec. Rather than mixing the two, everything is a Component for the sake of uniformity.

[balloob]

Woohooo! That's great to hear.