This document describes an issue I had with a LuxPower LXP 3.6K inverter where timed forced discharge appeared to be configured correctly, but the inverter would not export battery power to the grid.
The issue was eventually traced to a hidden or unavailable LuxPower setting called Sell Power to Grid / Grid Sell Back / Feed-in Grid.
Once LuxPower support enabled Sell Power to Grid on my system, manual export started working and PredBat/Home Assistant control began to behave as expected.
The goal was to create an automated battery charging and exporting setup using Home Assistant and PredBat.
The intended behaviour was:
- Use Octopus Agile electricity prices to identify cheap import periods and expensive export periods.
- Charge the battery from the grid when electricity is cheap.
- Use solar PV generation during the day where available.
- Export stored battery energy back to the grid during high export value periods.
- Let PredBat calculate the best charge and discharge plan automatically.
- Let Home Assistant and the LuxPower Modbus integration apply those charge and discharge windows to the inverter.
In simple terms, the aim was:
Cheap grid import -> charge battery -> hold energy -> export during better value periods
The inverter was expected to support this through its timed charge and timed forced discharge settings.
The setup was using:
- LuxPower LXP 3.6K hybrid inverter
- Pylontech battery stack
- Solar PV connected to the LuxPower inverter
- Home Assistant
- LuxPower Modbus integration
- PredBat
- Octopus Agile tariff data
PredBat was being used as the decision engine.
Home Assistant and the LuxPower Modbus integration were being used to apply the required settings to the inverter.
The main symptoms were:
- Forced Discharge could be enabled in the LuxPower web interface.
- Forced Discharge time windows could be set successfully.
- Forced Discharge power rate and stop SOC could be configured.
- PredBat was writing discharge/export slots.
- Home Assistant showed the relevant Lux entities.
- The battery would not discharge to the grid during the scheduled window.
switch.lux_feed_in_gridin Home Assistant would briefly turn on, then revert back to off.- LuxPower web portal sometimes returned errors such as:
Failure: readParamFailed
Failure: setTimeRangeFailed
DATAFRAME_TIMEOUT
Initially this looked like it could have been a PredBat issue, Home Assistant YAML issue, Modbus issue, inverter timezone issue, or battery stack issue.
It was not.
In Home Assistant, the relevant entity was:
switch.lux_feed_in_grid
The entity appeared to map to the LuxPower setting for allowing export back to the grid.
When checking the LuxPower web interface using browser developer tools, I found a hidden page element with:
FUNC_FEED_IN_GRID_EN
The label was:
Grid Sell Back
The tooltip text was:
Enable to export power back to the grid. Disable for no export to the grid.
This was the missing setting.
The important point is that the normal LuxPower settings page showed the forced discharge controls, but did not visibly expose this Grid Sell Back / Feed-in Grid control to my account.
Forced Discharge controls when the inverter should discharge the battery.
Grid Sell Back / Feed-in Grid controls whether the inverter is allowed to export that power to the grid.
So the inverter can have all of these configured correctly:
Forced Discharge Enable = enabled
Forced Discharge Power Rate = 100%
Stop Discharge SOC = 15%
Forced Discharge time window = active
but still not export if this is disabled or unavailable:
Grid Sell Back / Feed-in Grid / Sell Power to Grid
In the LuxPower web interface, confirm that forced discharge is enabled and that the time window is active.
Typical settings:
Forced Discharge Enable = Enable
Forced Discharge Power Rate = 100%
Stop Discharge SOC = below current battery SOC
Start Time = current time or earlier
End Time = future time
In Home Assistant, check these entities if available:
switch.lux_forced_discharge
switch.lux_feed_in_grid
switch.lux_fast_zero_export
sensor.lux_battery_discharge_power
sensor.lux_grid_flow
sensor.lux_battery_soc
Expected state for export:
switch.lux_forced_discharge = on
switch.lux_feed_in_grid = on
switch.lux_fast_zero_export = off
battery discharge power > 0
grid export > 0
SOC falling
In my case, switch.lux_feed_in_grid would not stay on.
The Home Assistant logbook showed that I turned it on, but it later turned off without any automation or user being shown as the cause.
That suggested the inverter or LuxPower cloud was reading the setting back as disabled.
Using Chrome DevTools, I searched for hidden settings on the LuxPower Remote Set page.
This browser console command was useful:
Array.from(document.querySelectorAll('[functionparam]'))
.map(e => [e.getAttribute('functionparam'), e.innerText.trim()])
.filter(([p, t]) => /FEED|SELL|ZERO|EXPORT|GRID/i.test((p || '') + ' ' + (t || '')))This revealed:
FUNC_FEED_IN_GRID_EN
Grid Sell Back
The control existed in the page, but was not visibly available to my account.
The root cause was that Sell Power to Grid was not enabled on my LuxPower system/account/station/inverter.
This prevented battery export even though forced discharge settings were present and could be configured.
LuxPower support enabled the Sell Power to Grid option on my system.
After that, manual export started working.
I contacted LuxPower support and asked them to check whether my account, station and inverter had permission to enable:
Sell Power to Grid
Grid Sell Back
Feed-in Grid
After LuxPower support enabled the option, forced discharge/export began working.
The support response confirmed:
I have now enabled the Sell Power to Grid option on your system.
You can use something like this:
Hi LuxPower Support,
My inverter is an LXP 3.6K.
I am trying to use timed forced discharge / battery export.
The Forced Discharge settings can be enabled and the time windows can be set successfully, but the inverter does not discharge to the grid.
I understand that under Grid Sell Back, I should be able to see an option to "Enable to export power back to the grid. Disable for no export to the grid." However, I do not appear to have access to this option in the LuxPower web interface.
Can you please check whether my account, station and inverter have permission to enable Grid Sell Back / Feed-in Grid / Sell Power to Grid?
Please also confirm:
1. Whether Grid Sell Back is locked by installer permissions.
2. Whether Grid Sell Back Power / Feed-in Power is set above zero.
3. Whether Fast Zero Export is forcing export off.
4. Whether this setting can be changed by the end-user account.
5. Whether my inverter or dongle firmware needs updating for this setting to be available.
6. Whether battery forced discharge to grid is permitted on this inverter configuration.
The issue does not appear to be the forced discharge schedule. The issue appears to be that I do not have access to the Grid Sell Back / Feed-in Grid export setting.
Regards,
<your name>
I experienced regular timeout/read errors when using the LuxPower web interface.
Examples:
Failure: readParamFailed
Failure: setTimeRangeFailed
DATAFRAME_TIMEOUT
These appeared to be related to the LuxPower cloud/dongle communication path.
For reliable day-to-day automation, I prefer using Home Assistant with the LuxPower Modbus integration rather than relying on the LuxPower web interface.
The LuxPower Quick Discharge button can get out of sync with the actual inverter state.
In my case, the inverter was discharging, but the web button did not reflect the real state correctly.
Use Home Assistant / Modbus entities where possible.
I also noticed that the inverter timezone setting did not look correct for my setup, so I changed it to the London option shown in the LuxPower interface.
This may help if forced discharge windows appear to be shifted or not matching the intended time.
Check that Fast Zero Export is not blocking export:
switch.lux_fast_zero_export = off
If Fast Zero Export is active, the inverter may attempt to prevent export to the grid.
Once Sell Power to Grid was enabled, PredBat/Home Assistant could be tested again.
A clean test is:
- Stop manual LuxPower web changes.
- Let PredBat write the charge/discharge windows.
- Wait for a scheduled export period.
- Confirm:
battery discharge power > 0
grid export > 0
SOC falling
If your LuxPower inverter allows you to configure Forced Discharge but does not actually export battery power to the grid, do not assume PredBat, Home Assistant, Modbus, or the battery stack is at fault.
Check whether Sell Power to Grid / Grid Sell Back / Feed-in Grid is actually enabled on your LuxPower account/station/inverter.
In my case, that setting was hidden or not available in the normal web interface. LuxPower support had to enable it.
Once they did, manual battery export started working.
Later on in the day PredBat successfully managed to control the inverter as per it's calculated.
Big shoutout to LuxPower support, they were quick to respond and were very helpful and understanding.