Bi-directional meter for PV systems & battery storage

Brief overview

A Bidirectional meter measures separately how much electricity a system draws from the grid and how much it feeds in. This is a basic prerequisite for any PV system and any battery storage system with a grid connection. It is mandatory as soon as a system feeds electricity into the public grid and is used at PV systems with an installed capacity of 7 kW or more replaced or supplemented by an intelligent metering system (smart meter). The installation is carried out by the competent local or commercial metering point operator. For companies with a PV and BESS combination, the bidirectional meter directly ensures correct billing for feed-in, self-consumption, and grid consumption.

Definition & Function of a Bidirectional Meter

Unlike a traditional single-tariff meter, a bi-directional meter measures the flow of electricity in both directions. It counts the Purchasing from the public grid and the Grid feed-in. He records both values separately, usually via two separate registers (OBIS codes 1.8.0 for consumption, 2.8.0 for feed-in).

This separation is necessary because, with PV systems and battery storage, the energy flow no longer runs in only one direction.

• PV systems feed electricity into the grid when there is excess generation and draw power from the grid when there is no self-generation (e.g. at night).
• Battery storage depending on the operating mode, can both charge from the grid (grid power consumption) and temporarily store excess PV energy and feed it into the grid or use it for self-consumption as needed.

Older Ferraris meters with mechanical registers often simply ran backward when power was fed back into the grid. Although this was physically possible, it was an impermissible offsetting method in terms of measurement technology, since consumption and feed-in could no longer be tracked separately. As a result, Ferraris meters without a non-return ratchet have no longer been permitted for new PV systems since 2020. At the latest with the smart meter rollout, their grandfathered status will also cease to apply.

For companies with a PV system and battery storage, bidirectional metering is therefore not an option, but rather the fundamental technical prerequisite for being able to correctly account for feed-in tariffs, self-consumption, and grid power draw in the first place.

Legal framework

The legal basis for a bidirectional meter is not metrology law (MessEG/MessEV) in the narrower sense, but rather the Metering Point Operation Act. While MessEG/MessEV regulate the accuracy requirements for the measuring device itself – more on that in the article on electricity submeter –, the MsbG stipulates, who a measuring point like must equip.

Central is § 29 MsbG (Equipping of metering points with intelligent metering systems, control units and modern metering devices):

• Mandatory installation of an intelligent measuring system (iMSys) inter alia for generation systems with an installed capacity of more than 7 kW – regardless of the amount fed into the grid – as well as for final consumers with an annual electricity consumption of 6,000 kWh or more and for controllable consumer devices (this also includes a battery storage system).
• If there is no obligation for an iMSys, basic competent metering point operators must equip the metering point in accordance with Section 29 Paragraph 3 MsbG with at least a modern metering device equip – by the end of 2032 at the latest.
• For additional services (e.g., early installation at the customer's request), separate price caps apply in accordance with Section 35 of the German Metering Operation Act (MsbG). The general price caps for the installation and operation of intelligent metering systems themselves are governed by Section 30 MsbG in the version applicable since December 23, 2025; the Federal Network Agency may replace these statutory price caps with its own determinations pursuant to Section 33 MsbG.

In practice, they exceed commercial PV and BESSAlways project the 7 kW and consumption thresholds. As a result, the bi-directional meter is effectively always implemented as an iMSys as soon as a battery storage system or a PV system of relevant size is involved – a separate “simple” bi-directional meter without smart meter functionality is hardly ever used in a commercial context.

Demarcation from related meter types

In practice, the term “bi-directional meter” is often used synonymously with “smart meter.” However, this is imprecise and frequently leads to false expectations among companies regarding costs and functional scope. In reality, these are distinct, partially overlapping concepts.

Modern metering device (mME) vs. intelligent metering system (iMSys)

Both are digital meters that can measure bidirectionally – the difference lies in the Communication skills. The mME records consumption and feed-in values without transmitting them automatically. The iMSys (colloquially smart meter) adds a smart meter gateway to the measuring equipment, which encrypts and transmits the values to grid operators, suppliers, and, where applicable, direct sellers. With appropriate equipment, it is even capable of integrating a control device for flexible loads such as a battery storage system. A “simple” bi-directional meter without a gateway connection technically corresponds to the mME.

RLM meter (registered power measurement)

Above certain consumption or system sizes (final consumers with an annual consumption of 100,000 kWh or more), it is no longer just bidirectional, but registering measured with quarter-hourly load profile recording. These RLM meters are required for balance group settlement in the market process and are implemented in practice today as iMSys. We have covered the details on this in the article Smart meters in industry treated. For PV and BESS projects above the RLM threshold, two-way metering is mandatory anyway.

Sub-meter

While the bidirectional meter measures the interface to the public grid (consumption/feed-in at the grid connection point), a submeter records the internal distribution within of a property. These can be, for example, multiple tenants, parts of a building, or consumer groups. Both meter types complement each other in a PV/BESS metering concept, but serve different purposes. We have detailed the internal metering design in the article on the electricity submeter described.

Overview Table Meter Types

Installation, Rollout & Responsibility

Who is responsible for bi-directional meters?

Basically, the responsible metering point operators – usually the local distribution system operator – is responsible for the installation, operation, and maintenance of the smart meter. However, system operators have the legal right to instead use a competitive metering point operator to commission, provided that it meets the technical requirements of the MsbG (Metering Point Operation Act). For companies with multiple locations or more complex metering concepts (e.g., with parallel PV, BESS, and sub-meter structures), a switch may make sense if the competitive provider offers shorter installation times or better integration into the existing energy management system.

duty to tolerate

According to Section 3 (3a) of the German Metering Point Operation Act (MsbG), the meter replacement itself must be tolerated—neither the grid user nor the grid connection owner can object to the installation of a modern metering device (mME) or intelligent metering system (iMSys) once the legal requirements are met.

Installation of bidirectional meters in PV/BESS projects

After registering the systems in Market Participant Registry (MaStR) and a change to a bidirectional meter is routinely initiated with the responsible grid operator. In practice, it is advisable to check the meter cabinet for sufficient free meter spaces already during the planning phase. This applies in particular if the PV system and BESS are commissioned at different times or if a later expansion is foreseeable. If the meter replacement is delayed for an unreasonable period of time, a qualified third party can be commissioned with the installation under the conditions of the MsbG.

Costs for a bi-directional meter

The ongoing costs for installation and operation are subject to the statutory price caps pursuant to Section 30 of the German Metering Operation Act (MsbG) (or the stipulations of the Federal Network Agency pursuant to Section 33 MsbG, provided these replace the statutory caps). Pursuant to Section 35 MsbG, this also applies to additional services. For commercial systems with a mandatory iMSys requirement, the price caps are tiered according to system size. Consequently, a direct reimbursement of installation costs by the system operator is usually not required, as the replacement is covered by the regular grid usage fees.

Bi-directional meter in the metering concept for PV + BESS

The bi-directional meter is the starting point of every metering concept for PV systems with battery storage. It marks the grid connection point and thus the legally relevant boundary between the property and the public grid. Everything that happens within this boundary is mapped via submeters or the energy management system – everything that crosses the boundary runs through the bidirectional meter.

The assignment is crucial

Self-consumption rate: Only the grid power consumption measured by the bidirectional meter counts as “not self-consumed.” A faulty or insufficiently detailed metering point can distort the actual self-consumption rate. This has consequences for the economic viability calculation of the BESS.

Market premium / Direct marketing: For directly marketed PV systems, the amount fed into the grid measured by the bi-directional meter (or interval meter) is the basis for billing by the direct marketer. Inaccurate or delayed allocation leads to billing discrepancies.

Battery energy storage operating modes: Whether the storage system predominantly buffers excess PV power or is also charged from the grid (e.g., for peak shaving or balancing energy) can only be tracked if the bi-directional meter cleanly separates grid consumption from internal PV storage shifting. Without this separation, there is a risk of misaligned incentives in the operating strategy and, in the worst case, the loss of eligibility for subsidies.

Energy Management System (EMS) & Bidirectional Meter

In practice, the bidirectional meter provides the “official” reference value at the grid connection point, while the EMS controls in real time based on submeter and system data (charging decisions, feed-in limitation, peak shaving). Therefore, coordinating the two data sources is particularly important for the metering concept. Subsequent corrections are usually much more complex than proper planning prior to commissioning.

Frequently Asked Questions