Interoperability of Technologies Behind the Meter – Implementations of the S2 Standard – Jorrit Nutma, TNO & Nicolas Höning, Seita
Event Recap: LF Energy Summit Europe 2025
TL;DR
At LF Energy Summit Europe 2025, Jorrit Nutma of TNO and Nicolas Höning of Seita discussed how the S2 standard can improve interoperability between home energy management systems and flexible energy devices. The session explored why standardized interfaces are needed behind the meter, how S2 represents energy flexibility as an abstract concept, and what early implementation projects reveal about deploying interoperable residential energy management systems.
Why Behind-the-Meter Flexibility Needs Coordination
Nutma opened by framing energy management as the control of smart appliances so they can deviate from their baseline behavior in time and power. In residential settings, this includes devices such as heat pumps, EV chargers, PV inverters and home batteries.
He explained that household energy consumption is expected to increase significantly as mobility and heating become electrified. At the same time, grids may not have enough capacity to transport all of that additional electricity without better use of flexibility. Energy management can help households shift consumption, follow production and respond to incentives such as dynamic tariffs.
The presentation described several categories of home energy management systems already appearing in the market. Some are tied to specific appliances, some are provided by energy suppliers or aggregators, and others are independent energy managers that coordinate flexibility across multiple devices.
Nutma emphasized that today’s residential systems often manage only a limited number of flexible devices and use cases. As more devices become flexible, and as new use cases emerge, homes will need coordination mechanisms that can avoid conflicts between different control strategies.
Why Home Energy Management Systems Matter
The session used several examples to show why device-level optimization alone can create problems. If a heat pump and an EV charger both respond independently to a grid connection limit, they may reduce and increase consumption in ways that create oscillation. If a battery and EV charger both try to maximize self-consumption, they may react to changing household loads in ways that do not match the intended behavior.
Another example showed how multiple devices optimizing for low energy prices could overload a grid connection if they all increase consumption at the same time. In each case, the issue is not that the individual device logic is wrong, but that devices are not aware of each other or of the full household context.
Nutma argued that a home energy management system can address this by coordinating flexibility across all devices in the home. It can also act as a bridge between technologies behind the meter and signals from outside the home, such as dynamic prices or congestion management signals.
The key requirement is standardization. For a scalable system, the interfaces between home energy management systems and devices need to be standardized so that devices purchased today can support future use cases.
How the S2 Standard Represents Energy Flexibility
Nutma then introduced the S2 standard, which began more than 10 years ago as work on an energy flexibility interface. The approach is to treat energy flexibility as an abstract concept rather than relying on device-specific details such as battery cell voltages or heat buffer temperatures.
S2 does not assume what kind of device provides flexibility. A heat pump converting electricity into heat and a battery storing electricity can both be described in terms of energy storage or flexibility. The standard also avoids embedding specific use cases, such as price optimization or grid limit management, directly into the device protocol.
This separation of concerns is central to S2. Devices communicate their flexibility options to the energy manager, referred to in S2 terminology as the Customer Energy Manager, or CEM. The energy manager can then use external information, such as dynamic prices or DSO congestion signals, to decide how to use that flexibility.
Nutma also emphasized that the device remains in control. Devices are responsible for respecting safety limits and user comfort constraints. The energy manager can choose among the flexibility options offered by the device, but the device can ignore control signals if needed.
The S2 standard was approved by European standardization bodies in 2022 as EN 50491-12-2. Since then, work has continued on an open source communication layer specification, Python and Rust libraries, documentation and broader adoption.
Implementation Lessons From S2 Projects
Höning then shared implementation experience from ongoing projects where Seita worked on the energy management side of S2. He explained that S2 allows different deployment architectures, including cloud-to-cloud, local-to-cloud and fully local implementations.
In one project, Seita worked as the Customer Energy Manager party while other participants implemented the Resource Manager side. The project used a local implementation and included heat storage and a heat pump, with the energy management work connected to FlexMeasures. Höning described this as useful because the energy manager can communicate with the Resource Manager instead of needing to handle device-specific integrations directly.
He noted that this can reduce the time required to build integrations, especially compared with situations where developers need to work through device-specific protocols such as Modbus. However, he also emphasized that early pilots still require work before S2-capable resources become more broadly available.
A second project focused again on smart heating, this time involving a more established heat pump manufacturer. That project used a local-to-cloud architecture and included work on secure communication, WebSockets and handshake implementation.
Höning also described work on a tutorial showing how to create an S2-compatible home energy management system with FlexMeasures. He framed the current stage as a “chicken and egg” problem: broader adoption depends on both energy managers and device manufacturers implementing the standard.
Driving Adoption of the S2 Standard
Both speakers pointed to the importance of open source tooling and community development around S2. Nutma highlighted the open source communication layer specification on GitHub, documentation for developers, and libraries intended to make implementation easier for energy management systems and devices.
He also described ongoing work to establish an S2 Alliance. The goal is to create a governance body and community around the standard, organize events and meetups, support certification work, and help guide the S2 roadmap.
During the Q&A, the speakers discussed how S2 differs from other protocols. Nutma contrasted S2 with EEBus by explaining that S2 is not organized around specific use cases. Instead, it separates flexibility capabilities from the use cases the energy manager may want to optimize for, which he described as important for future readiness.
The discussion also touched on Matter and low-level device communication. Nutma explained that S2 semantics can be used to express energy flexibility, while another protocol may still handle communication closer to the device. Ideally, the Resource Manager is implemented by the device manufacturer, because the manufacturer has the most knowledge of the device’s capabilities and constraints.
The session closed with a call for broader collaboration around S2. The speakers emphasized that continued work will be needed from energy managers, OEMs, developers and the wider community to make behind-the-meter interoperability more scalable.
About LF Energy
LF Energy is an open source foundation within the Linux Foundation focused on advancing collaboration in digital energy infrastructure.
Learn more: https://lfenergy.org
Last updated: June 18, 2026
AI Disclosure
This post used artificial intelligence tools for research, structural assistance, or grammatical refinement. The final content was reviewed, edited, and validated by human contributors to LF Energy to ensure accuracy and alignment with our community standards. We remain committed to transparency in the use of generative technologies within the open source ecosystem.
