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Glossary · Energy industry & energy transition

CLS channel

CLS channel smart meter gateway iMSys (intelligent metering system) control metering flexibility grid operation

The CLS channel is a secured communication path through the smart meter gateway. Through it, authorized external market participants can exchange data with controllable devices behind a grid connection. CLS stands for Controllable Local System. In the Technical Guideline TR-03109 of the German Federal Office for Information Security (BSI), a CLS is a device in the gateway's home network. This home network is called the Home Area Network (HAN). Examples of a CLS are a control box, a charging controller, the control system of a heat pump, the control of a battery storage system or an energy management system. The channel itself is neither a device nor a meter. It is a protected connection that the gateway establishes between such a device and an external party.

Technical structure

An intelligent metering system consists of a modern metering device and a smart meter gateway. The gateway is the certified communication unit and separates three network domains: The local metrological network (LMN) connects the meters. The home network (HAN) connects devices and end-customer displays. The wide area network (WAN) connects the gateway with the external market participants. In the home network, the gateway has two separate physical interfaces. HAN-CLS is used to connect controllable systems. HAN-CON provides access for connection users and service technicians.

For the connection between a CLS and an external party, the gateway provides a transparent proxy channel encrypted via TLS. According to the BSI's description, only the smart meter gateway administrator can configure this channel. Transparent means that the gateway forwards the payload data without interpreting it itself. Which commands or data are transmitted is determined by the application and the remote party. Put simply, the administrator opens a secured tunnel for a specific purpose between a specific device in the home and a specific authorized partner. This does not create an arbitrary internet connection.

The devices on the home side are also subject to security requirements. The sub-guideline TR-03109-5 describes minimum requirements for communication adapters used to connect CLS devices to the gateway's home network. TR-03109-6 governs the administration of the gateway. A dedicated public key infrastructure for smart metering issues the certificates with which the communication partners prove their identity to each other.

Distinction from meter, gateway and control box

The CLS channel is often confused with the gateway itself. The gateway is the communication unit; the CLS channel is a specific usage path through that unit. Nor is it equivalent to the electricity meter. The meter measures amounts of energy in kilowatt-hours. The CLS channel, by contrast, transmits control information and data from installations. It does not measure, it does not switch by itself, and it does not create flexibility. However, it is an important prerequisite for flexible installations to be securely integrated into grid and market processes.

In this architecture, a control box is typically itself a CLS device. It is attached to the HAN-CLS interface, receives control signals via the CLS channel and passes them on to the installation via relay contacts or a digital interface. Control box and CLS channel are therefore not opposites. The control box is the device at the end of the chain; the channel is the secured path to it. Whether a wallbox is actually throttled in the end depends on the on-site installation, the interface of the installation, the applicable rules and the authorizations of those involved.

The separation between measured values and control data is also important. The gateway itself processes billing-relevant measured values and sends them according to defined market processes. The CLS channel is intended for applications that go beyond pure metering, such as control commands, status messages, installation parameters or communication with an energy management system. Metering, billing and control serve different purposes and intervene to different degrees in the operation of a connection.

Significance for grid operation and § 14a EnWG

With heat pumps, private charging points and electricity storage systems, many high-power installations are being added to the low-voltage grid, and they often run at the same time. Distribution grids are not designed according to annual energy volume but according to peaks in load and feed-in. If many vehicles in one street charge at the same time in the early evening, a local grid bottleneck can arise even though the annual electricity volume appears uncritical. According to the Federal Network Agency's assessment, most of the low-voltage grids are currently not yet designed for a rapid ramp-up of such applications.

This is where § 14a EnWG comes in, together with the Federal Network Agency's determination BK6-22-300. The rules have applied since 1 January 2024 to newly commissioned controllable consumption devices with a grid connection capacity of more than 4.2 kW. These include:

  • private, i.e. not publicly accessible, charging facilities for electric cars,

  • heat pumps, including supplementary or emergency heating such as heating rods,

  • space cooling systems,

  • electricity storage systems, insofar as they draw electricity from the grid.

If an overload threatens, the grid operator may temporarily throttle the electricity consumption of these installations. With direct control, at least 4.2 kW per installation generally remains available. With control via an energy management system, the grid operator determines a joint minimum power using a simultaneity factor. The remaining household electricity is not affected, and feed-in, for example from photovoltaics, is not throttled. In return, operators receive a reduction in grid charges, and the grid operator may no longer refuse or delay the connection of such installations by citing possible grid overload. For existing installations with control already agreed, the previous conditions apply until the end of 2028. Night storage heaters remain permanently under the old rules.

This control requires a reliable technical chain, in practice usually consisting of an intelligent metering system and a control box or energy management system. In the smart meter architecture, the CLS channel is the intended secure path by which the control signal reaches the control box or the energy management system. Besides grid operators, suppliers, aggregators or direct marketers can also use the channel, for example for variable tariffs, storage management or pooling small installations into marketable flexibility. Their interests differ. The channel does not resolve such conflicts of objectives; it merely creates the technical framework for authorized communication.

Typical misunderstandings

An intelligent metering system does not mean that the grid operator can control all devices in the household. This requires a controllable installation with a suitable interface, a correctly integrated control device, a set-up channel and a legal basis. Under § 14a EnWG, moreover, only the throttling of certain consumption devices down to the minimum power is permitted, not a shutdown of the household.

The CLS channel is also not a universal real-time channel. Protection technology or frequency maintenance in the range of seconds impose different requirements than throttling a wallbox or transmitting operating data. Which response times are achievable depends on the application, the mobile or line connection and process specifications. Control also does not replace grid expansion. It can reduce peaks and spread investments over time or make them more targeted. With permanently strong electrification, lines and transformers must nevertheless be reinforced. The Federal Network Agency itself emphasizes that grids must be optimized, digitalized and expanded.

Conversely, control does not mean only restriction. An energy management system behind the gateway can also give priority to using its own solar power and storage discharge during throttling. Flexible tariffs or a better-used grid connection can also benefit households economically.

Roles and open practical questions

The CLS channel makes clear how many roles are involved in the digitalization of the electricity system. The metering point operator provides the intelligent metering system and, where applicable, the control box. The gateway administrator sets up the secured channels and manages certificates and profiles. The grid operator determines the need for control. Suppliers or service providers offer market-based applications. The installation operator must be able to trace who intervenes, when and for what reason. This protects against uncontrolled access and serves data protection, but also creates effort: devices must be compatible and certified, processes must work for millions of connections, and costs must be allocated. Whether the architecture holds up in everyday use depends on whether manufacturers supply suitable interfaces, installers set them up correctly and market processes run reliably.

Sources

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Edited by eCMS on 11.11.2026 17:31

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