The Solar Charging feature does not currently have access to any hardware integrations with your battery or inverter.
This means that we can't assess the house "base load" or your home battery's charge level, and our algorithm doesn't take them into account. Your car's battery will take precedence over other household loads, including your home battery.
In future, we plan to take into account the load on your home battery. Ultimately this will provide you with a choice of whether to draw on your home battery or not.
We ask all of our users for their battery and inverter information when they first turn on Solar Charging. We do this so that we can decide which hardware integrations to prioritise on our roadmap.