Zero feed-in and feed-in limitation: what the meter does for it

A photovoltaic system without a control unit feeds everything that the house does not currently need into the grid. If this is not to happen, or only to a limited extent, or if the surplus is to charge a storage unit or an electric car, the inverter must know what is currently happening at the property’s connection point. This task is carried out by an energy meter. How this works and what you need for it is explained on this page.

• Zero-feed-in: The system does not feed any electricity into the public grid. The planning guide from the inverter manufacturer SMA describes it as follows: The inverter regulates the power generated so that only as much energy is produced as is currently being consumed.
• Grid feed-in limit: The system may provide grid feed-in, but only up to a specified value. This value is set in the inverter, usually by a specialist contractor.

In both cases, solar power remains unused if more is generated than the house requires and is permitted for grid feed-in. A storage unit or a wallbox can absorb this excess before the inverter cuts back. You should clarify with your grid operator or specialist contractor whether and to what extent your system needs to be limited.

The energy meter is located at the grid connection point – that is, where the electricity enters the house – and continuously measures whether electricity is currently being drawn or fed into the grid through grid feed-in. According to HTW Berlin, it is usually connected in series behind the grid operator’s meter and permanently installed in the sub-distribution board (Wallbox Inspection 2025). Its readings are usually transmitted to the inverter via an RS485 cable.

The inverter uses this value to control:

• Grid feed-in: It throttles the modules if more power is fed into the grid than is permitted.
• the storage unit: According to HTW Berlin, the system adjusts the battery’s charging power to the current surplus based on the power balance at the grid connection point (Electricity Storage Inspection 2025). If the battery charges more slowly than the surplus is available, the surplus is fed into the grid; if it charges faster, electricity is drawn from the grid.
• The Wallbox: According to HTW Berlin, even when charging with surplus solar power, measurement at the grid connection point is a fundamental requirement. Find out more under ‘Wallbox with surplus solar charging’.

Without a meter at the property connection point, the inverter only knows what the modules generate, not what the property consumes.

In everyday language, ‘smart meter’ refers to two different devices:

• The smart metering system: According to the Federal Network Agency, it consists of a modern metering device – i.e. a digital electricity meter – and a smart meter gateway as the communication unit. According to the BSI, the metering point operator is responsible for installation and operation; billing is carried out via this meter.
• The PV system’s energy meter: it performs additional measurements, forms part of the system and supplies the readings to the inverter, storage unit or wallbox. It does not replace the billing meter.

When an intelligent metering system is installed, see ‘Smart Meter for PV’: energy meters for inverters.

Communication between the meter and the inverter depends on the manufacturer. You should therefore select the meter specified by your inverter manufacturer for that model series. There are two types:

• Direct measurement: The current flows through the meter. According to the data sheet, the Fronius Smart Meter TS 65A-3 measures up to 3 × 65 A, whilst the Growatt TPM-E measures up to a maximum of 100 A.
• About current transformers: The meter measures via transformers which are fitted around the cables; this is suitable for high currents or when the cables are not to be disconnected. According to the data sheet, the Fronius Smart Meter TS 5kA-3 operates with transformers having an output current of 5 A, whilst the SunGrow DTSD1352 also operates exclusively with external transformers.

For some meters, the manufacturers explicitly mention zero feed-in: Growatt for the SPM-C with Growatt inverters, SAJ for the DTSU666 with SAJ inverters. The available meters are listed under ‘Smart Meters for PV: Energy Meters for Inverters’.

Some storage units for balcony power plants are also controlled by a meter. According to the data sheet, the Anker SOLIX Smart Meter is compatible with the Solarbank 2 Pro and Plus and connects via Wi-Fi, Bluetooth or an RS485 cable. It provides the storage unit with the reading at the property connection point, just as the main meter does for the inverter. Information on when it makes sense to use a storage unit with a balcony power plant can be found under ‘Balcony power plant with storage: when does it make sense?’.

The meter is installed in the meter cupboard or the sub-distribution board, usually on a DIN rail. Installation is carried out by a qualified electrical contractor, who coordinates the work on the meter cupboard with your network operator; ACTEC supplies the meter but does not install it. Information on how meters, inverters and storage systems are integrated into a system can be found under ‘Planning a PV system’.