FoxESS Community - Owners & Installers Forum

Hi,

I have been advises by Dave here in the forum to set the Compensation Bias to 80W as the system is still pulling off the grid at night when there is a full battery.

Would anyone know how this can be set and where or does the installer have to do it as he has no idea where to look.

Thanks in advance

It is an installer option and not available via the menus (you must also have the latest firmware), contact your installer and ask them to set it for you, or if you have problems email Fox support with your inverter serial number and ask them to set it for you.

Thanks Dave, The installer doesn't know how to set it but they pushed my firmware update to Fox to do. Bit worrying? as they should be doing it right? I will ask FOX to set it. Is it possible to view what the BIAS is set to currently to make sure know when the correct value is set? Is it in the settings to view anywhere?

Keen to get it sorted, the system has generated over 1.6Mwh in last 3.5 weeks so its good to know the system will be set correctly and not drawing off the grid at night. If the 80W setting doesn't change much, is there anything else to set or check why the house is drawing off the grid at night when there is a 14KW battery to cover the house usage?

This is the example I'm looking at for why the house is using electricity at night. Doesn't seem right to me if I have a decent battery and minimal load at night. Always pulling from the grid. Top image is a typical DAY, the bottom one is the week view.

That looks pretty normal in Self use mode, no grid use during the day when the sun is up and the bias automatically shifts towards export, and overnight when the bias shifts the other way there is a small usage.

You would expect your installer to know how to do it, the larger installers that work closely with Fox would but for installers that use a variety of equipment it's probably a bit much to stay on top of every feature and this is quite a new feature.

Sadly there is no way of telling what it has been set to unless your are an installer, nothing in the settings or in the app - so once set the only obvious way to tell is the very small overnight grid use should reduce fairly close to zero.

Thanks Dave,

I'll follow up with the installer, failing that I'll ask FOX to do the change. Is 80W the recommend value then? I'm still very unclear why near 2kWh is used over night for a fridge and small derives on like internet and Wi-Fi router etc. I invested in a large battery to be able to have next to ZERO draw off the grid other than the sync with the grid at most. Why is 2kWh used I do not understand, thinking that the whole idea was to be as off grid as possible and reduce as much dependency from the grid as possible. If the bias is set to 80w, do you think this is the ideal value or is there any point in putting a higher or lower value here....what makes 80W the best value for the Bias - keen to learn more.

If you look at your first octopus graph of grid usage overnight, you are trying to find an average bias point that would overcome the hourly usage - in that graph if you draw a line across at 0.08kwh (80 watts) you would have the vast majority of the import peaks below that line.

You might want to start a little bit smaller at say 60 watts which would cover much of the import as you will probably never achieve absolute zero (but if you are getting Fox to do it for you best to start at 80 watts and monitor for a few weeks).

The reason for this is that with any grid tied inverter when larger appliances such as fridges turn on /off (particularly the larger American fridges) the load is instantly there and whilst it may only take several hundred watts the inverter has to firstly measure the load change and then balance the load from batteries, it takes the inverter a small amount of time (seconds) and in that small window of time the grid will be filling in until the load has balanced. Likewise when the load turns off the battery will be still supplying power and again for a few seconds that will be sent to export until the inverter adapts to the new balance - this is what creates the usage (and export) you see overnight.

When you set the bias to 80 watts the first 80 watts of any instant load will always be taken from battery making the grid demand much smaller, as I said there will always be some demand but if you can get it down to 0.5kWh in a day you will be doing well.

Just to add, as an alternative test that will help - change your workmode to Feed-in First overnight and then back to Self-Use in the morning, whilst that may seem a little counter intuitive feed-in first changes the bias slightly towards export and so your overnight usage should drop - perhaps as much as half of what you are seeing.

Thank you Dave,

That's a really good and clear explanation and really helps. I will leave it with the installer for now, if they don't reply end of the week I'll ask FOX to do this for me. 80w is a good number as you say, I'm generating around 55-65kWh per day for export as I use very little day to day. At most it was 6kWh given my low usage.

Will mentioned that the new firmware in his Jan 2025 video was initially for the K series, has it been rolled out to the H3 series yet?

I have just been told by my installer that the Compensation Bias option is not available for the H Series yet. Do we have any ideas on how often FOX role out updates from the K series to the H Series so this feature will be possible?

merango wrote: Wed May 07, 2025 11:29 am I have just been told by my installer that the Compensation Bias option is not available for the H Series yet. Do we have any ideas on how often FOX role out updates from the K series to the H Series so this feature will be possible?

It’s definitely on the KH, H3 and H1 (Gen 2), it’s possible it hasn’t yet made it to the H3 Pro but with that being at the premium end of the spectrum you would certainly expect it to - i’ll add this question to the next Fox update session and get confirmation.

Thank you Dave, very kind. If they do have a response, could you ask rough ETA for possible adoption for the H3 Pro. Keen to get that set and tested.

Thanks again.