Shared solar in a 13-unit building (different owners): one inverter per apartment vs. centralized in

Q&A and troubleshooting
,
1

Hi all.
I’m fully renovating a residential building in Portugal with 13 individually owned apartments — 13 different owners, each with their own utility meter and their own electricity retailer. The roof has several orientations and I’ll be installing 34 × 715 W panels (~24.3 kWp). The renovation is still ongoing, so I have full freedom to run cables, reserve plant-room space, etc.
What I’m trying to achieve:

  1. All panel production consolidated into a single system (the different roof orientations shouldn’t penalize any particular apartment);
  2. Dynamic sharing: if at a given moment only 2 apartments are consuming, all production goes to them; if all 13 are consuming, it gets split. Whoever isn’t consuming releases their share to the others (or to a battery);
  3. Surplus is sold centrally (revenue goes to the owners’ association) — no individual apartment can sell energy on its own.
    I have two architectures on the table and would love input from anyone who has built something similar:
    Option A — centralized DC + one inverter per apartment
    Panels → central MPPT charge controllers → 48 V DC busbar stabilized by a battery bank (in the plant room) → 13 inverter/chargers (e.g. Victron MultiPlus-II 48/3000), one per apartment, installed downstream of each utility meter in zero-feed mode with a CT at each apartment’s entry, plus a central EMS (Modbus TCP) enforcing power quotas and metering the kWh delivered to each unit.
    My concerns: at 24 kW peak that’s ~460 A on the busbar at 48 V (serious cable cross-sections and DC protection), 13 separate grid registrations, getting a private DC network running through common areas certified, the permanent standby draw of 13 inverters (I estimate 1–2 MWh/year lost), and a cost in the range of €35–50k on top of the panels.
    Option B — centralized inverter and battery + virtual sharing (Portugal’s collective self-consumption scheme)
    A single 20–25 kW three-phase hybrid (GoodWe ET style) + central battery, connected to the building’s common services as a single production unit. Sharing is virtual: Portugal’s “autoconsumo coletivo” framework lets the DSO allocate production across the 13 meters in proportion to each unit’s actual consumption in every 15-minute interval — so nothing is physically rewired, the allocation is done in the billing. The owners’ association acts as the managing entity and sells the surplus under a single contract. Hardware cost is a fraction of option A, but you depend on the DSO’s metering/settlement pipeline and take on the admin (internal regulation, settling accounts between owners).
    My concrete questions:
  4. Has anyone run a scheme like B (virtual allocation proportional to consumption) in a condo building? How did licensing and the start-up phase go in practice?
  5. Has anyone seen or installed physical sharing (DC bus, or devices like Allume’s SolShare) in Europe? Is it ever worth it where virtual sharing frameworks exist?
  6. In option B, would you install the central battery from day one, or only after learning the building’s consumption profiles?
  7. How would you structure the internal rules and the surplus revenue with 13 distinct owners (revenue split, maintenance fund, owners moving in/out)?
  8. Ballpark turnkey costs for either option, and any installer recommendations with multi-unit experience?
    Thanks in advance to anyone willing to share experience.
4

@Miguelfful
Triggering the AI hard with your post there.

This is a large systen best actually directed toward your local distribution centre

Option A with a centralised EMS is great if you have a solid comms network.

Option B easier to meter out an energy meter in each apartment.
And one central system. Downside is people abuse what they do not see. (Decentralised systems such as option A means if one part goes down not everyone is affected)
I would have AC PV on the buildings and some DC for the system directly this will simplify the DC side and take the load off the system in the day.

This is very much a local regulator question.

5

Completely agree with lx here. For large system design, you need to speak to a local supplier, we don’t encourage design topics here beyond smaller DIY systems in that specific category.

Good rule for any system - keep it simple.

6

I will simply provide AC coupled PV power to the buildings shared spaces such a lighting, heating etc. and then sell any excess to contribute to lowering the building’s bills that will serve everyone equally. This is done at our apartment block. No storage. Specialised embedded network solutions already exist where owners can even auction off their share of unused electricity if they are e.g. away, but there can only be one supplier and also storage system for the complex. Just to add, search embedded networks and also legal implications as end-users who buy into such developments cannot select alternative suppliers.