H3-8.0E – Disabling Grid Export During Negative Electricity Prices

[Noel_V70]

Hi everyone,


I have a question that may soon become relevant for many solar users across Europe.

During periods of high solar production—typically around midday—electricity prices can turn negative. In these situations, we might actually have to pay to inject excess energy into the grid.

To avoid this, I’d like to throttle or completely disable grid export during such times, so that no surplus power is fed into the grid.

Is there any way to achieve this via the FOXESS app, API, or perhaps using Home Assistant?
For context, I’m using a FOXESS H3-8.0E inverter, but I currently don’t have access to the installer settings.

Would it be possible for someone to help me gain installer access—at least to explore the available options? I assume having installer-level permissions would reveal more configurable features than are visible to an end user (though that’s just an educated guess).

Just as an FYI: I’m an electronics engineer, so I’m quite comfortable with the electrical concepts involved.

I know the inverter can be powered off via the hardware button, but that’s neither a clean nor acceptable long-term and/or flexible solution. Ideally, I’d like to dynamically disable grid export when electricity prices go negative. (note: have Home Assistant running over a locally connected mod-bus-polling, (for some years).. etc etc )


Any insights, tips, or workarounds would be greatly appreciated!

Thanks in advance!

[Will]

Hello,

To answer your first question about installer level, sadly, normal end users are not allowed installer access. While fox don't police it to link your site to you as an installer would require you to be a fox professional installer.
Only other option would be to replace your datalogger with a brand new one and make sure you setup your agent, installer and end user profiles from scratch. If you want to go down this route I can help you once you have the new datalogger.

On the preventing negative solar export dynamically, this is a perfect use case for the DRM control, page 37 of the user manual.
With a simple home assistant-controlled smart relay like a shelly, you can short out the required pins on a old network cable to control the inverter. DRM5 mode looks like the right one for you telling the inverter to not generate power.
This combined with some battery and inverter automation via home assistant you should have exactly what you need.

[Noel_V70]

Wow, very nice / good answer — thanks a lot!


This definitely points me toward a usable solution.

It's great to know that it's possible to manage this by sending signals to the DRM connector.

However, I still keep wondering whether there's a software-based option for controlling it — perhaps via Modbus.

I currently have a physical Modbus connection active (since cloud access was too slow for my purposes). I built a galvanically isolated Modbus converter that's connected to my Home Assistant setup, and I use it to communicate with the inverter and retrieve data.

So, while the DRM connector is a valid and workable solution (and one I could implement), I’m still curious whether the same control might be possible through Modbus registers instead.

Best regards,
Noel

[Will]

You can control the inverters output using modbus registers, maybe a simple script to reduce the inverter output during the peak solar day.

Figuring out which modbus register, if one exists for the export control would be the perfect solution.

[Dave Foster]

Try reading the holding register 41012, this should be your export power limit on the H3 - if it reads correctly you can write to this register to throttle your export power.

[Will]

Nice one Dave

[Noel_V70]

Hi all,

Thanks for the responses so far. However, I ran into some issues over the weekend.

I haven't been able to identify any registers yet, and it appears that my inverter is running on quite an outdated firmware version.

Additionally, it seems that I cannot use DRM mode 5, as only DRM mode 0 is supported by the current firmware.

My next step will likely be to attempt a firmware upgrade for the inverter. A more recent version might provide better support—possibly unlocking more options related to DRM and improving the Modbus register readout.
( i did never upgrade invertor software... so will have to dig a little to find / correct versions for H3 i guess )

I'll need to look into how to perform this firmware upgrade, as it seems the inverter firmware is split into three separate components. This will be target 1 atm

Best Regards

[Will]

Hey,

I publish firmware versions here viewtopic.php?t=1927

You will need an agent-level account, normally reserved for installers to upgrade the firmware.
I recorded the process here:


If you're not an installer, simply email fox support and they'll do it for you.

[Noel_V70]

Hello,

I've been trying to get support for upgrading my inverter firmware by emailing service@fox-ess.com earlier (begin of the week) this week, since support@fox-ess.com was failing ( to accept an email ).

However, I haven’t received any response so far.

Can anyone confirm the correct email address to reach Fox ESS support? I'd like to give it another try, as I don’t have installer privileges ( seems the only way to get my inverter upgraded) .

Thanks in advance,
Noel

[Will]

That's the wrong email.
Email the address for your country from this page https://us.fox-ess.com/get-in-touch/
Ensure you include your inverter serial and datalogger serial in your request.