What you can do: When EcoFlow is empty and there is no more voltage at the output, you can ensure that it switches back to 230 volts by using a "mains priority circuit" or "changeover station" (please google). The unit is connected to the output. EcoFlow must be connected to Prio 1. If it has to be almost interruption-free, you have to switch to a more expensive unit (google). Caution: Use a device that is designed for 16 amperes. The whole process should be supervised by a specialist. The use of EcoFlow in the "home" as a UPS is not entirely unproblematic.

The EcoFlow Delta Pro (EU) can be manually connected to either the mains or the solar panel for charging. This works perfectly. However, so far I have no need for automatic switching, I do not know of such an automatic device. That would have to be the task of an additional control unit of which I am not aware. Perhaps the supplier can help with this, it would indeed be useful from my point of view.