The solar battery also powers some loads in the house via the inverter. The fridge, oil heating / hot water and some lighting is included in the loads. The inverter will automatically switch off when the state of charge drops below 40% and those loads will instead be powered by the grid until the state of charge reaches 100% again.
This is to ensure that there is always a good state of charge available for these loads in the event of a power failure.
The webserver always runs from the solar battery as this is not powered via the inverter.