Sub-electricity meters as the basis for metering concepts in companies

Brief overview

A electricity submeter is the basis of every commercial measurement concept for PV systems and battery energy storage systems (BESS). It records the energy flow at a specific point within a property – in addition to the main meter at the grid connection point. Companies use it to separately visualize the consumption and generation of individual building areas, individual systems, or individual users and Own consumption, third-party consumption and Feed-in clearly distinguishable from each other.

What is a sub-meter for electricity?

A sub-meter is a measuring device that downstream main meter is installed within a property and records the energy flow at a defined metering point. This can be the consumption of a building section or major consumer, as well as the generation of a PV system or the charging/discharging power of a battery storage system. It does not replace the main meter, but rather complements it with an additional measurement plane.

For differentiation:

• Main metermeasures the total electricity consumption or total feed-in at the grid connection point. It forms the basis for billing with the grid operator and energy supplier and is always subject to mandatory calibration.
• Sub-meter: measures a subset of consumption or generation within the property, downstream of the main meter.
• Submeter: In practice, this term is often used interchangeably with “intermediate meter.” In some metering concepts, however, the term is defined more narrowly—to refer to meters used exclusively for internal cost control and that have no billing implications for third parties. There is no uniform definition; in each specific case, the meter’s function is always the decisive factor, not its name.

Legal framework: Calibration law and metrology

Whether an intermediate meter must comply with calibration regulations does not depend on its designation, but rather on its use. The Measurement and Calibration Act (MessEG) and the Measurement and Calibration Ordinance (MessEV) are the governing regulations.

Principle: A measuring instrument is subject to mandatory verification if it is used in commercial transactions to determine a fee that is billed to a third party.

For practice, this means two categories of cases:

• Relevant for billing (subject to verification): The submeter forms the basis for billing costs to a third party. This can be tenants within the scope of tenant electricity, a group company, or participants in an energy-sharing community. In these cases, the meter must comply with calibration law (MID-compliant or approved under national calibration law).
• For information purposes only (not subject to legal verification): The submeter is used exclusively for internal monitoring or controlling. This might be necessary, for example, to track the energy consumption of individual production lines as part of energy management without generating a bill for third parties. In this case, a non-calibrated meter is sufficient.

This distinction is particularly important for PV and BESS projects: A submeter that was initially intended only for internal monitoring can become subject to calibration laws as soon as it is later used as a billing basis for tenant electricity or energy sharing – the technical equipment should take this into account from the very beginning.

Relevance of intermediate electricity meters in PV & BESS operation

As soon as a PV system or a Battery storage comes into operation, the pure import meter or main meter at the grid connection point is no longer sufficient to track the flow of energy within the company. Submeters close this gap on multiple levels—both on the consumption and the generation side.

Separate tracking by building area (consumption)

For rented or multi-user properties – such as business parks, hall complexes with multiple tenants, or corporate locations with several companies – a submeter makes it visible how much electricity is attributable to which part of the building. This is a prerequisite for models such as the Tenant electricity model or the Communal building supply, in which PV electricity is shared proportionally among multiple users within a property.

Separate collection by major consumers (consumption)

Charging infrastructure for electric vehicles, heat pumps, or individual production plants, [they] can be recorded separately using dedicated sub-meters. This creates the data basis required to specifically allocate the self-consumption share from the PV system to individual major consumers – for example, for internal cost accounting or to make the effect of load shifting visible.

Separate tracking of generation (PV) and charging/discharging power (BESS)

Just as important as the consumption side is the generation side. A sub-meter for electricity at the inverter output records PV generation independently of the property's total consumption. Only in this way is it possible later to clearly distinguish between self-consumption, surplus feed-in, and grid power purchase. In the case of a battery energy storage system, the charging and discharging direction is added. A dedicated sub-meter at the BESS interface makes visible how much energy is flowing in which direction, and thus forms the basis for the correct allocation of quantities relevant to self-consumption, feed-in, and redispatch.

Separate recording by user

For multiple consumers within a property – tenants, group companies or participants in a Energy Sharing- merger pursuant to Section 42c of the German Energy Industry Act (EnWG) – user-specific consumption recording is mandatory as soon as the PV or BESS electricity is to be billed on a proportional basis. The submeter is the technical prerequisite here for legally compliant billing.

Just in case, the allocation logic: Who measures what, at which point, and in which direction. This creates overall transparency of consumption and generation as well as the basis for the measurement concept underlying the PV and BESS project.

The electricity submeter as a component in the metering concept

What is a metering concept?

A metering concept specifies at which points on a property specific amounts of energy are measured and how consumption, generation, self-supply, and grid withdrawal or feed-in are calculated based on those measurements. It serves as the technical and contractual basis for grid operators, energy suppliers, tax authorities (e.g., for electricity or sales tax exemptions), and third parties (Third-party quantity delimitation) be able to clearly trace the energy flow. Without a coherent measurement concept, neither self-consumption can be correctly delineated nor regulatory benefits reliably claimed.

The Interplay of Counting Levels

In a property with a PV system and BESS, several meters typically work together:

• Import meter (main meter): measures the electricity drawn from the public grid
• Feed-in meter: measures the amount of electricity that is fed back into the public grid
• Generation meter (submeter at the PV inverter): measures total PV generation, regardless of whether the electricity is consumed directly, stored, or fed into the grid
• BESS meter (submetering at the storage interface): measures charging and discharging power separated by direction
• Sub-meters for consumption: record the consumption of individual building areas, major consumers, or users within the property

The complete picture emerges from the joint consideration of the levels. The difference between generation, grid import, and grid feed-in yields self-consumption. The total self-consumption of the property can be calculated from the PV generation meter, import meter, and feed-in meter. Only the intermediate consumption meters break this self-consumption down further – to individual building areas, major consumers, or users.

Example measurement concept: PV + BESS with multiple loads

A typical scenario in practice: A commercial property with a rooftop PV system, a battery storage system, and three rental units.

This concept makes it clear that not every intermediate electricity meter in the system has the same legal significance. The BESS intermediate meter is used primarily for internal control and analysis, while the intermediate meters at the rental units are directly relevant to billing and are therefore subject to calibration requirements.

Technical Design of Intermediate Electricity Meters

Types

Today, intermediate electricity meters are predominantly digital measuring devices; mechanical Ferraris meters are rarely used in new installations. For billing-related applications, the devices must MID-compliant —that is, approved in accordance with the Measuring Instruments Directive (2014/32/EU) and bearing a valid conformity marking. For intermediate meters used solely for informational purposes, a standard, non-calibrated meter is sufficient; however, it should ideally offer the same interface technology as the meters that comply with metrology regulations—so that both types of meters can be analyzed within the same system.

Connection and Data Collection

For integration into an energy management system (EMS) or billing software, submeters require a digital interface:

• Modbus RTU/TCP Communication via RS-485 or Ethernet is the most widely used standard in commercial and industrial applications—it is robust, vendor-neutral, and natively supported by most EMS and storage controllers.
• S0 Interface (Pulse output) can be found in simpler meters, but only provides counting pulses without further measured values such as voltage or power factor.
• Smart Meter Gateway Capability: Meters that are intended to be connected to a smart meter gateway (SMGw) in the future require a compatible interface that meets the BSI’s technical specifications—this becomes relevant as soon as a submeter is also used for accounting purposes under the Metering Point Operations Act (MsbG).
• Radio/Wireless Connection (e.g., Wireless M-Bus) is a good option in situations where wiring would be structurally complex—such as when retrofitting submeters in existing rental units.

Integration into an energy management system

It is only through digital connectivity that intermediate electricity meters can deliver their full benefits for PV and BESS operations. The EMS reads the measurements from all intermediate meters in real time or at short intervals (typically 1–15 minutes) and uses them for two purposes:

• Control: The BESS submeter provides the EMS with actual values for charging and discharging power, which are used to calculate charging and discharging strategies (e.g., optimization of self-consumption, peak load shaving).
• Billing and ReportingIntermediate utility meters provide the data basis for tenant electricity billing, internal cost center reports, or documentation for grid operators and tax authorities.

Important for planning: The choice of interface should not be made in isolation for each meter. It should be based on the overall metering concept—subsequently changing the communication technology for meters that have already been installed involves additional effort.

Real-World Use Cases

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