Photovoltaic system, heat pump, household electricity, and 3 two-way meters

Hello everyone,

we have bought a house and the following setup is present there:

Photovoltaic system -> Inverter -> Meter ZE (photovoltaic generation) -> Household electricity -> Meter Z2 (household electricity) -> Heat pump -> Meter Z1 heat pump

ZE = Meter with feed-in with backflow preventer
Z1 = Meter for consumption and feed-in
Z2 = Submeter for consumption

All meters are two-way meters

Now I don’t understand the following:
Why are 3*two-way meters needed here or what is the purpose of this?
Unfortunately, I can’t find anything about this in the documents?

I know cascade wiring with 2 meters. I assume the ZE is not an official meter, but purely to satisfy the owner's curiosity about how much electricity was produced

They are all meters of the local network operator (and accordingly "sealed" - completely official). Might have to call the city utilities next week to see if they can shed some light on it.

Reads like measurement concept 8 with third meter (ZE), so that you don't have to calculate yourself.

Sounds reasonable. But why is the third meter then sealed (and chargeable?). Wouldn't a privately installed meter be sufficient?

Would be, but isn’t. In principle, you could also just calculate what he shows.