You're right to be cautious. Sharing a single PV/BESS system across multiple individually metered units in a townhome building presents significant code challenges and potentially violates several sections of the NEC (National Electrical Code). Here's a breakdown of the issues and potential solutions

Why Sharing a PV/BESS is Problematic:
Article 230: Services (and generally, Service Equipment) This is likely where your concerns stem from. The NEC is very prescriptive about service conductors, service equipment, and who is allowed to control whose power. You're essentially creating a distributed power system behind the meters, which blurs the lines of responsibility and control. 230.2 Number of Services. The NEC generally limits the number of services allowed per building, primarily for safety and utility grid management. While not a direct violation in itself, sharing a BESS behind multiple meters could be seen as circumventing the intent of this rule. The argument would be that you're effectively creating a "shared service" even though each unit has its own utility connection. 230.40 Identification of Service Disconnecting Means. Each service disconnecting means must be clearly identified. Sharing a BESS output behind multiple meters complicates this, as it's not clear which unit has control or responsibility for disconnecting the source of power (the BESS) in an emergency. 705.12 Point of Connection. The NEC dictates where interconnected power sources (like solar and BESS) can connect to the electrical system. Connecting behind multiple service meters, creating a "shared" system, is typically not permitted under standard interpretations. Metering Issues and Utility Regulations. This is outside the NEC, but crucial. Utilities typically own and control the meters. Tampering with or altering the way power is measured and billed would likely violate your agreement with the utility. They want to accurately measure each unit's consumption from the grid, and your proposed setup would make that very difficult or impossible. Billing and Ownership Complications. Even if code-compliant, who owns the solar/BESS system? How are the benefits (cost savings, energy credits) allocated among the townhome owners? What happens when someone moves? This creates a complex legal and financial entanglement that could lead to disputes. Safety and Coordination. In the event of a fault or emergency, how is the shared BESS system safely disconnected from all the units? Who is responsible for maintaining the system and ensuring its safety?Why Separate Inverters Might Help (But is Still Complex)

The key here is ensuring each system remains independent and tied to each individual service after the meter.

Dedicated Inverter per Meter

If each unit has its own dedicated solar panels, BESS, and inverter system connected after its utility meter, it's less likely to run afoul of the NEC and utility regulations. This is because each unit's system is independent and doesn't affect the metering or service of other units. Each unit is individually consuming the power after its meter.

However, there are still potential challenges



Cost

This approach is generally more expensive because it requires multiple sets of equipment.

Space

Finding enough space for multiple inverters and batteries can be difficult.

Interconnection Agreements

Each unit would need its own interconnection agreement with the utility, which can be a lengthy and costly process.

Aggregate System Size

The utility might have limits on the total aggregate capacity of PV/BESS systems in a given area or on a single transformer.

Backup Power for Critical Loads Only

Each unit could have a battery and inverter dedicated only to critical loads such as refrigerators or medical equipment. This approach limits the scale of the BESS and the potential for shared energy.

What to Do Instead


Consult with a Licensed Electrical Engineer and a Solar/BESS Installer

This is the most important step. They can evaluate the specific situation, local codes, utility regulations, and the physical constraints of the building.2.

Contact the Local Utility

Discuss your plans with the utility before you invest any significant time or money. They can provide information about their interconnection policies, metering requirements, and any specific restrictions they might have.3.

Consider Individual Systems

The simplest and often most practical solution is for each townhome owner to install their own independent solar and/or BESS system on their unit (behind their own meter), if permitted. This avoids the complexities of shared systems.4.

Microgrids (Highly Complex)

In very specific cases, a carefully designed microgrid might be possible. This would involve a completely separate electrical system, dedicated metering, and a complex agreement with the utility. Microgrids are typically only feasible for very large projects.

In summary, sharing a BESS across multiple services is generally not code-compliant and could create significant problems. While separate inverters might* make a system more viable, it still requires careful consideration and consultation with experts to ensure compliance and feasibility. Flag for review